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  • Other Sources  (1,318)
  • Elsevier  (923)
  • AGU (American Geophysical Union)  (394)
  • American Meteorological Society
  • 2010-2014  (1,318)
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  • 101
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    Mineralogy and geochemistry of hydrothermal precipitates from Kairei hydrothermal field, Central Indian Ridge (2014)
    Elsevier
    In:  Marine Geology, 354 . pp. 69-80.
    Details
    Publication Date: 2017-06-23
    Description: The Kairei hydrothermal field was the first confirmed active submarine hydrothermal system on the Central Indian Ridge. It has been suggested to be related to mafic as well as ultramafic host rocks based on vent fluid composition and the presence of ultramafic rocks in its vicinity. In this study, detailed geochemical and mineralogical analyses have been carried out on the hydrothermal precipitates from the Kairei vent field in order to investigate the possible presence of indications for an ultramafic substrate at this vent site. The studied samples included fragments of sulfide chimneys, massive sulfides and talc-bearing and silicified breccias. Three mineralization stages were identified: (1) a high-temperature stage consisting largely of chalcopyrite, isocubanite, and pyrite; (2) a medium to low temperature stage characterized by the mineral assemblages of sphalerite and pyrite; and (3) a weathering stage characterized by secondary Cu-sulfides (bornite, digenite, covellite and idaite), Fe-oxihydroxides, Opal-A, and Cu-chloride (paratacamite and atacamite). The sulfide geochemistry is characterized by high concentrations of Cu and Zn (Cu + Zn up to 29.3 wt.%, n = 17) and Au (mean 5.28 ppm, n = 17), which is comparable to results from seafloor massive sulfides collected from ultramafic-hosted sites in the Atlantic Ocean, but differs from those of typical mafic-hosted deposits. The high concentrations of Cu and Au at the Kairei hydrothermal field could be an indication for the involvement of ultramafic rocks in the subseafloor. Ultramafic-hosted, Au-rich sulfide deposits may not be restricted to the Atlantic Ocean and may be common along all slow- and intermediate-spreading ridges.
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  • 102
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    Plume versus plate origin for the Shatsky Rise oceanic plateau (NW Pacific): Insights from Nd, Pb and Hf isotopes (2014)
    Elsevier
    In:  Lithos, 200-201 . pp. 49-63.
    Details
    Publication Date: 2017-09-12
    Description: Shatsky Rise, an early Cretaceous igneous oceanic plateau in the NWPacific, comprises characteristics that could be attributed to either formation by shallow, plate tectonic-controlled processes or to an origin by a mantle plume(head). The plateauwas drilled during Integrated Ocean Drilling Program(IODP) Expedition 324. Complementary to a recent trace element study (Sano et al., 2012) this work presents Nd, Pb and Hf isotope data of recovered lava samples cored from the three major volcanic edifices of the Shatsky Rise. Whereas lavas from the oldest edifice yield fairly uniform compositions, awider isotopic spread is found for lavas erupted on the younger parts of the plateau, suggesting that the Shatsky magma source became more heterogeneous with time. At least three isotopically distinct components can be identified in the magma source: 1) a volumetrically and spatially most common, moderately depleted component of similar composition to modern East Pacific Ridge basalt but with low 3He/4He, 2) an isotopically very depleted component which could represent local, early Cretaceous (entrained) depleted upper mantle, and 3) an isotopically enriched component, indicating the presence of (recycled) continental material in the magma source. The majority of analyzed Shatsky lavas, however, possess Nd–Hf–Pb isotope compositions consistent with a derivation from an early depleted, non-chondritic reservoir. By comparing these results with petrological and trace element data of mafic volcanic rock samples from all three massifs (Tamu, Ori, Shirshov), we discuss the origin of Shatsky Rise magmatism and evaluate the possible involvement of a mantle plume (head).
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  • 103
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    Strong responses of Southern Ocean phytoplankton communities to volcanic ash (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (8). pp. 2851-2857.
    Details
    Publication Date: 2021-04-23
    Description: Volcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty-one 1-2day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling.
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  • 104
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    Surface nitrification: a major uncertainty in marine N2O emissions (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (12). pp. 4247-4253.
    Details
    Publication Date: 2019-09-23
    Description: The ocean is responsible for up to a third of total global nitrous oxide (N2O) emissions, but uncertainties in emission rates of this potent greenhouse gas are high (〉100%). Here we use a marine biogeochemical model to assess six major uncertainties in estimates of N2O production, thereby providing guidance in how future studies may most effectively reduce uncertainties in current and future marine N2O emissions. Potential surface N2O production from nitrification causes the largest uncertainty in N2O emissions (estimated up to ~1.6 Tg N yr-1, or 48% of modeled values), followed by the unknown oxygen concentration at which N2O production switches to N2O consumption (0.8 Tg N yr-1, or 24% of modeled values). Other uncertainties are minor, cumulatively changing regional emissions by 〈15%. If production of N2O by surface nitrification could be ruled out in future studies, uncertainties in marine N2O emissions would be halved.
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  • 105
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    The impact of fluid advection on gas hydrate stability: Investigations at sites of methane seepage offshore Costa Rica (2014)
    Elsevier
    In:  Earth and Planetary Science Letters, 401 . pp. 95-109.
    Details
    Publication Date: 2017-03-13
    Description: Highlights • We map out the 3D extent of gas hydrate stability beneath two methane seep sites. • Focused fluid flow has sustained large-scale gas hydrate instability. • The two seeps likely have the same deep fluid source, despite shallow differences. • Fault networks influenced the initiation of advective flow through the hydrate system. • Ongoing flow towards the seeps is likely sustained by networks of hydrofractures. Abstract Fluid flow through marine sediments drives a wide range of processes, from gas hydrate formation and dissociation, to seafloor methane seepage including the development of chemosynthetic ecosystems, and ocean acidification. Here, we present new seismic data that reveal the 3D nature of focused fluid flow beneath two mound structures on the seafloor offshore Costa Rica. These mounds have formed as a result of ongoing seepage of methane-rich fluids. We show the spatial impact of advective heat flow on gas hydrate stability due to the channelled ascent of warm fluids towards the seafloor. The base of gas hydrate stability (BGHS) imaged in the seismic data constrains peak heat flow values to View the MathML source∼60 mWm−2 and View the MathML source∼70 mWm−2 beneath two separate seep sites known as Mound 11 and Mound 12, respectively. The initiation of pronounced fluid flow towards these structures was likely controlled by fault networks that acted as efficient pathways for warm fluids ascending from depth. Through the gas hydrate stability zone, fluid flow has been focused through vertical conduits that we suggest developed as migrating fluids generated their own secondary permeability by fracturing strata as they forced their way upwards towards the seafloor. We show that Mound 11 and Mound 12 (about 1 km apart on the seafloor) are sustained by independent fluid flow systems through the hydrate system, and that fluid flow rates across the BGHS are probably similar beneath both mounds. 2D seismic data suggest that these two flow systems might merge at approximately 1 km depth, i.e. much deeper than the BGHS. This study provides a new level of detail and understanding of how channelled, anomalously-high fluid flow towards the seafloor influences gas hydrate stability. Thus, gas hydrate systems have good potential for quantifying the upward flow of subduction system fluids to seafloor seep sites, since the fluids have to interact with and leave their mark on the hydrate system before reaching the seafloor.
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  • 106
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    Long-term effects of elevated CO2 and temperature on the Arctic calanoid copepods Calanus glacialis and C. hyperboreus (2014)
    Elsevier
    In:  Marine Pollution Bulletin, 80 (1-2). pp. 59-70.
    Details
    Publication Date: 2014-07-21
    Description: Highlights • First long-term experiments on effects of high pCO2 and temperature on Calanus spp. • CO2 concentration of 3000 μatm had no effect on the copepods performance. • Temperature of 10 °C induced sublethal stress in diapausing C. hyperboreus females. • Synergistic effects of temperature and CO2 on body carbon were found at 5 °C. Abstract The sensitivity of copepods to ocean acidification (OA) and warming may increase with time, however, studies 〉10 days and on synergistic effects are rare. We therefore incubated late copepodites and females of two dominant Arctic species, Calanus glacialis and Calanushyperboreus, at 0 °C at 390 and 3000 μatm pCO2 for several months in fall/winter 2010. Respiration rates, body mass and mortality in both species and life stages did not change with pCO2. To detect synergistic effects, in 2011 C. hyperboreus females were kept at different pCO2 and temperatures (0, 5, 10 °C). Incubation at 10 °C induced sublethal stress, which might have overruled effects of pCO2. At 5 °C and 3000 μatm, body carbon was significantly lowest indicating a synergistic effect. The copepods, thus, can tolerate pCO2 predicted for a future ocean, but in combination with increasing temperatures they could be sensitive to OA.
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  • 107
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    Peak Last Glacial weathering intensity on the North American continent recorded by the authigenic Hf isotope composition of North Atlantic deep-sea sediments (2014)
    Elsevier
    In:  Quaternary Science Reviews, 99 . pp. 97-111.
    Details
    Publication Date: 2019-09-23
    Description: We have retrieved radiogenic hafnium (Hf) isotope compositions (ɛHf) from authigenic Fe–Mn oxyhydroxides of deep northwest Atlantic sediments deposited over the past 26 ka to investigate the oceanic evidence of changes in dissolved weathering inputs from NE America during the last deglaciation. The extraction of seawater-derived Hf isotopic compositions from Fe–Mn oxyhydroxides is not a standard procedure. Comparisons between the Al/Hf ratios and Hf isotopic compositions of the chemically extracted authigenic phase on the one hand, and those of the corresponding detrital fractions on the other, provide evidence that the composition of past seawater has been reliably obtained for most sampled depths with our leaching procedures. This is endorsed most strongly by data for a sediment core from 4250 m water depth at the deeper Blake Ridge, for which consistent replicates were produced throughout. The Hf isotopic composition of the most recent sample in this core also closely matches that of nearby present day central North Atlantic seawater. Comparison with previously published seawater Nd and Pb isotope compositions obtained on the same cores shows that both Hf and Pb were released incongruently during incipient chemical weathering, but responded differently to the deglacial retreat of the Laurentide Ice Sheet. Hafnium was released more congruently during peak glacial conditions of the Last Glacial Maximum (LGM) and changed to typical incongruent interglacial ɛHf signatures either during or shortly after the LGM. This indicates that some zircon-derived Hf was released to seawater during the LGM. Conversely, there is no clear evidence for an increase in the influence of weathering of Lu-rich mineral phases during deglaciation, possibly since relatively unradiogenic Hf contributions from feldspar weathering were superimposed. While the authigenic Pb isotope signal in the same marine sediment samples traced peak chemical weathering rates on continental North America during the transition to the Holocene a similar incongruent excursion is notably absent in the Hf isotope record. The early change towards more radiogenic ɛHf in relation to the LGM may provide direct evidence for the transition from a cold-based to a warm-based Laurentide Ice Sheet on the Atlantic sector of North America.
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  • 108
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    The transition on North America from the warm humid Pliocene to the glaciated Quaternary traced by eolian dust deposition at a benchmark North Atlantic Ocean drill site (2014)
    Elsevier
    In:  Quaternary Science Reviews, 93 . pp. 125-141.
    Details
    Publication Date: 2016-09-15
    Description: We present Plio-Pleistocene records of sediment color, %CaCO3, foraminifer fragmentation, benthic carbon isotopes (δ13C) and radiogenic isotopes (Sr, Nd, Pb) of the terrigenous component from IODP Site U1313, a reoccupation of benchmark subtropical North Atlantic Ocean DSDP Site 607. We show that (inter)glacial cycles in sediment color and %CaCO3 pre-date major northern hemisphere glaciation and are unambiguously and consistently correlated to benthic oxygen isotopes back to 3.3 million years ago (Ma) and intermittently so probably back to the Miocene/Pliocene boundary. We show these lithological cycles to be driven by enhanced glacial fluxes of terrigenous material (eolian dust), not carbonate dissolution (the classic interpretation). Our radiogenic isotope data indicate a North American source for this dust (∼3.3–2.4 Ma) in keeping with the interpreted source of terrestrial plant wax-derived biomarkers deposited at Site U1313. Yet our data indicate a mid latitude provenance regardless of (inter)glacial state, a finding that is inconsistent with the biomarker-inferred importance of glaciogenic mechanisms of dust production and transport. Moreover, we find that the relation between the biomarker and lithogenic components of dust accumulation is distinctly non-linear. Both records show a jump in glacial rates of accumulation from Marine Isotope Stage, MIS, G6 (2.72 Ma) onwards but the amplitude of this signal is about 3–8 times greater for biomarkers than for dust and particularly extreme during MIS 100 (2.52 Ma). We conclude that North America shifted abruptly to a distinctly more arid glacial regime from MIS G6, but major shifts in glacial North American vegetation biomes and regional wind fields (exacerbated by the growth of a large Laurentide Ice Sheet during MIS 100) likely explain amplification of this signal in the biomarker records. Our findings are consistent with wetter-than-modern reconstructions of North American continental climate under the warm high CO2 conditions of the Early Pliocene but contrast with most model predictions for the response of the hydrological cycle to anthropogenic warming over the coming 50 years (poleward expansion of the subtropical dry zones).
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  • 109
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    Variability in under-ice export fluxes of biogenic matter in the Central Arctic Ocean (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (5). pp. 571-583.
    Details
    Publication Date: 2014-08-27
    Description: A critical question regarding the organic carbon cycle in the Arctic Ocean is whether the decline in ice extent and thickness and the associated increase in solar irradiance in the upper ocean will result in increased primary production and particulate organic carbon (POC) export. To assess spatial and temporal variability in POC export, under-ice export fluxes were measured with short-term sediment traps in the northern Laptev Sea in July-August-September 1995, north of the Fram Strait in July 1997, and in the Central Arctic in August–September 2012. Sediment traps were deployed at 2–5 m and 20–25 m under ice for periods ranging from 8.5 to 71 h. In addition to POC fluxes, total particulate matter, chlorophyll a, biogenic particulate silica, phytoplankton, and zooplankton fecal pellet fluxes were measured to evaluate the amount and composition of the material exported in the upper Arctic Ocean. Whereas elevated export fluxes observed on and near the Laptev Sea shelf were likely the combined result of high primary production, resuspension, and release of particulate matter from melting ice, low export fluxes above the central basins despite increased light availability during the record minimum ice extent of 2012 suggest that POC export was limited by nutrient supply during summer. These results suggest that the ongoing decline in ice cover affects export fluxes differently on Arctic shelves and over the deep Arctic Ocean and that POC export is likely to remain low above the central basins unless additional nutrients are supplied to surface waters.
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  • 110
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    Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2levels (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Biogeosciences, 119 (6). pp. 1216-1230.
    Details
    Publication Date: 2020-10-20
    Description: A large-scale multidisciplinary mesocosm experiment in an Arctic fjord (Kongsfjorden, Svalbard; 78°56.2′N) was used to study Arctic marine food webs and biogeochemical elements cycling at natural and elevated future carbon dioxide (CO2) levels. At the start of the experiment, marine-derived chromophoric dissolved organic matter (CDOM) dominated the CDOM pool. Thus, this experiment constituted a convenient case to study production of autochthonous CDOM, which is typically masked by high levels of CDOM of terrestrial origin in the Arctic Ocean proper. CDOM accumulated during the experiment in line with an increase in bacterial abundance; however, no response was observed to increased pCO2 levels. Changes in CDOM absorption spectral slopes indicate that bacteria were most likely responsible for the observed CDOM dynamics. Distinct absorption peaks (at ~ 330 and ~ 360 nm) were likely associated with mycosporine-like amino acids (MAAs). Due to the experimental setup, MAAs were produced in absence of ultraviolet exposure providing evidence for MAAs to be considered as multipurpose metabolites rather than simple photoprotective compounds. We showed that a small increase in CDOM during the experiment made it a major contributor to total absorption in a range of photosynthetically active radiation (PAR, 400–700 nm) and, therefore, is important for spectral light availability and may be important for photosynthesis and phytoplankton groups composition in a rapidly changing Arctic marine ecosystem.
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  • 111
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    The East Greenland Spill Jet as an important component of the Atlantic Meridional Overturning Circulation (2014)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 92 . pp. 75-84.
    Details
    Publication Date: 2019-07-10
    Description: Highlights: • Mooring observations show the East Greenland Spill Jet to be ubiquitous. • It is fed by classical DSOW in Denmark Strait, shelf water, and Irminger Sea water. • Its transport is similar to the classical DSOW plume. • It is the origin of a large fraction of the water in the Labrador Sea Water density range. Abstract: The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean׳s role in climate.
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  • 112
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    Thermogenic methane injection via bubble transport into the upper Arctic Ocean from the hydrate-charged Vestnesa Ridge, Svalbard (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (5). pp. 1945-1959.
    Details
    Publication Date: 2017-09-15
    Description: We use new gas-hydrate geochemistry analyses, echosounder data, and three-dimensional P-Cable seismic data to study a gas-hydrate and free-gas system in 1200 m water depth at the Vestnesa Ridge offshore NW Svalbard. Geochemical measurements of gas from hydrates collected at the ridge revealed a thermogenic source. The presence of thermogenic gas and temperatures of similar to 3.3 degrees C result in a shallow top of the hydrate stability zone (THSZ) at similar to 340 m below sea level (mbsl). Therefore, hydrate-skinned gas bubbles, which inhibit gas-dissolution processes, are thermodynamically stable to this shallow water depth. This was confirmed by hydroacoustic observations of flares in 2010 and 2012 reaching water depths between 210 and 480 mbsl. At the seafloor, bubbles are released from acoustically transparent zones in the seismic data, which we interpret as regions where free gas is migrating through the hydrate stability zone (HSZ). These intrusions result in vertical variations in the base of the HSZ (BHSZ) of up to similar to 150 m, possibly making the shallow hydrate reservoir more susceptible to warming. Such Arctic gas-hydrate and free-gas systems are important because of their potential role in climate change and in fueling marine life, but remain largely understudied due to limited data coverage in seasonally ice-covered Arctic environments.
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  • 113
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    Nd-isotope evidence for the distal provenance of the historical (c. 〈3000BP) lateritic surface cover underlying the Equatorial forest in Gabon (Western Africa) (2014)
    Elsevier
    In:  Aeolian Research, 15 . pp. 177-192.
    Details
    Publication Date: 2019-01-21
    Description: Highlights: • The first Nd isotopic data on the lateritic surface cover (Cover Horizon) of western Equatorial Africa. • Clearly different Nd isotopic signatures between the Cover Horizon and underlying basement. • A consistent model attributing the Cover Horizon to the settling of aeolian particles derived from the Namib desert. Abstract: Surficial formations in Gabon, as well as in other places of western Central Africa include a ubiquitous, homogeneous and 1–3 m-thick clayey to sandy lateritic surface cover known as the ‘Cover Horizon’. From 14C radiometric dating it has been concluded that the emplacement of this unit was correlative with a major environmental crisis which affected Central Africa c. 3000–2000 years ago. 10Be and Nd-isotopic analyses have been performed to provide new constraints on the age and origin of this layer. Six samples from two depth profiles investigated for 10Be exhibit an almost constant concentration consistent with a very recent deposition age. Nd-isotopic analyses performed on the silt to clay fraction of eleven samples from widely spaced locations over Gabon attest for mildly radiogenic signatures (εNd = −23 to −17) in ten of them, and a slightly radiogenic signature (εNd = −9) in one sample. TDM model ages range from 1.6 to 2.6 Ga, and a perfect discrimination is observed between the Nd-isotopic signature of the Cover Horizon and that of the underlying Congo Craton. This makes an aeolian origin as the most probable for the Cover Horizon. The average εNd (c. −20) is however rather unusual for aeolian sediments or aerosols. A possible source of particles is therefore tested by considering the present-day atmospheric flux over Gabon and adjacent regions. Combined atmospheric modeling and Nd-isotopes leads to the conclusion that the fine fraction of the Cover Horizon could have originated from the northern part of the Namib desert.
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  • 114
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    Contrasting conditions of rift and off-rift silicic magma origin on Iceland (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (16). pp. 5813-5820.
    Details
    Publication Date: 2017-04-10
    Description: Factors controlling the origin of silicic magmas on Iceland are poorly constrained. Here we present new data on H2O content, pressure, temperature, oxygen fugacity, and oxygen isotope composition of rhyolites from Askja, Öræfajökull, and Hekla volcanoes. All these parameters correlate with tectonic (rift and off-rift) setting of the volcanoes. Askja rift rhyolites originate through extensive assimilation of high-temperature hydrothermally altered crust (δ18O 〈 2‰) at shallow depths (≥1.8 km). These rhyolites are hot (935–1008°C), relatively dry (H2O 〈 2.7 wt%), and oxidized (QFM = +1.4). Cooler (874–902°C), wet (H2O = 4-6.3 wt%), and non-oxidized (~QFM to QFM-1) off-rift rhyolites (Öræfajökull, Hekla) originate through differentiation deeper in the crust (≥4 km) with almost no or little assimilation of high-T, altered crust, as reflected by slightly lower to normal δ18O values (5.2–6‰). Although off-rift rhyolites predominate during the Holocene, older silicic rocks on Iceland primarily formed in a rift setting possibly analogous to the oldest continental crust on Earth.
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  • 115
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    Crustal structure across the Møre margin, mid-Norway, from wide-angle seismic and gravity data (2014)
    Elsevier
    In:  Tectonophysics, 626 . pp. 21-40.
    Details
    Publication Date: 2018-01-05
    Description: The Møre Margin in the NE Atlantic represents a dominantly passive margin with an unusual abrupt transition from alpine morphology onshore to a deep sedimentary basin offshore. In order to study this transition in detail, three ocean bottom seismometer profiles with deep seismic reflection and refraction data were acquired in 2009; two dip-profiles which were extended by land stations, and one tie-profile parallel to the strike of the Møre–Trøndelag Fault Complex. The modeling of the wide-angle seismic data was performed with a combined inversion and forward modeling approach and validated with a 3D-density model. Modeling of the geophysical data indicates the presence of a 12–15 km thick accumulation of sedimentary rocks in the Møre Basin. The modeling of the strike profile located closer to land shows a decrease in crustal velocity from north to south. Near the coast we observe an intra-crustal reflector under the Trøndelag Platform, but not under the Slørebotn Sub-basin. Furthermore, two lower crustal high-velocity bodies are modeled, one located near the Møre Marginal High and one beneath the Slørebotn Sub-basin. While the outer lower crustal body is modeled with a density allowing an interpretation as magmatic underplating, the inner body has a density close to mantle density which might suggest an origin as an eclogized body, formed by metamorphosis of lower crustal gabbro during the Caledonian orogeny. The difference in velocity and extent of the lower crustal bodies seems to be controlled by the Jan Mayen Lineament, suggesting that the lineament represents a pre-Caledonian structural feature in the basement.
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  • 116
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    Sulfur budget and global climate impact of the AD 1835 eruption of Cosigüina volcano, Nicaragua (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (19). pp. 6667-6675.
    Details
    Publication Date: 2017-04-10
    Description: Large explosive volcanic eruptions can inject massive amounts of sulfuric gases into the Earth's atmosphere and, in so doing, affect global climate. The January 1835 eruption of Cosigüina volcano, Nicaragua, ranks among the Americas’ largest and most explosive historical eruptions, but whether it had effects on global climate remains ambiguous. New petrologic analyses of the Cosigüina deposits reveal that the eruption released enough sulfur to explain a prominent ca. AD 1835 sulfate anomaly in ice cores from both the Arctic and Antarctic. A compilation of temperature-sensitive tree-ring chronologies indicates appreciable cooling of the Earth's surface in response to the eruption, consistent with instrumental temperature records. We conclude that this eruption represents one of the most important sulfur-producing events of the last few centuries and had a sizable climate impact rivaling that of the 1991 eruption of Mount Pinatubo.
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  • 117
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    Texture development in naturally compacted and experimentally deformed silty clay sediments from the Nankai Trench and Forearc, Japan (2014)
    Elsevier
    In:  Tectonophysics, 636 . pp. 125-142.
    Details
    Publication Date: 2019-09-23
    Description: The petrophysical properties of fine-grained marine sediments to a large extent depend on the microstructure and crystallographic preferred orientations (CPOs). In this contribution we show that Rietveld-based synchrotron texture analysis is a new and valuable tool to quantify textures of water-saturated fine-grained phyllosilicate-rich sediments, and assess the effects of compaction and tectonic deformation. We studied the CPO of compositionally almost homogeneous silty clay drillcore samples from the Nankai Accretionary Prism slope and the incoming Philippine Sea plate, offshore SW Japan. Basal planes of phyllosilicates show bedding-parallel alignment increasing with drillhole depth, thus reflecting progressive burial and compaction. In some samples calcite and albite display a CPO due to crystallographically controlled non-isometric grain shapes, or nannofossil tests. Consolidated-undrained experimental deformation of a suite of thirteen samples from the prism slope shows that the CPOs of phyllosilicate and calcite basal planes develop normal to the experimental shortening axis. There is at least a qualitative relation between CPO intensity and strain magnitude. Scanning electron micrographs show concurrent evolution of preferred orientations of micropores and detrital illite flakes normal to axial shortening. This indicates that the microfabrics are sensitive strain gauges, and contribute to anisotropic physical properties along with the CPO.
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    Seaglider observations of equatorial Indian Ocean Rossby waves associated with the Madden-Julian Oscillation (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (6). pp. 3714-3731.
    Details
    Publication Date: 2018-02-26
    Description: During the CINDY–DYNAMO field campaign of September 2011–January 2012, a Seaglider was deployed at 80°E and completed 10 north-south sections between 3 and 4°S, measuring temperature, salinity, dissolved oxygen concentration, and chlorophyll fluorescence. These high-resolution subsurface observations provide insight into equatorial ocean Rossby wave activity forced by three Madden-Julian Oscillation (MJO) events during this time period. These Rossby waves generate variability in temperature O(1°C), salinity O(0.2 g kg−1), density O(0.2 kg m−3), and oxygen concentration O(10 μmol kg−1), associated with 10 m vertical displacements of the thermocline. The variability extends down to 1000 m, the greatest depth of the Seaglider observations, highlighting the importance of surface forcing for the deep equatorial ocean. The temperature variability observed by the Seaglider is greater than that simulated in the ECCO-JPL reanalysis, especially at depth. There is also marked variability in chlorophyll fluorescence at the surface and at the depth of the chlorophyll maximum. Upwelling from Rossby waves and local wind stress curl leads to an enhanced shoaling of the chlorophyll maximum by 10–25 m in response to the increased availability of nutrients and light. This influence of the MJO on primary production via equatorial ocean Rossby waves has not previously been recognized.
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    Western Pacific atmospheric nutrient deposition fluxes, their impact on surface ocean productivity (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (7). pp. 712-728.
    Details
    Publication Date: 2018-02-27
    Description: The atmospheric deposition of both macronutrients and micronutrients plays an important role in driving primary productivity, particularly in the low-latitude ocean. We report aerosol major ion measurements for five ship-based sampling campaigns in the western Pacific from similar to 25 degrees N to 20 degrees S and compare the results with those from Atlantic meridional transects (similar to 50 degrees N to 50 degrees S) with aerosols collected and analyzed in the same laboratory, allowing full incomparability. We discuss sources of the main nutrient species (nitrogen (N), phosphorus (P), and iron (Fe)) in the aerosols and their stoichiometry. Striking north-south gradients are evident over both basins with the Northern Hemisphere more impacted by terrestrial dust sources and anthropogenic emissions and the North Atlantic apparently more impacted than the North Pacific. We estimate the atmospheric supply rates of these nutrients and the potential impact of the atmospheric deposition on the tropical western Pacific. Our results suggest that the atmospheric deposition is P deficient relative to the needs of the resident phytoplankton. These findings suggest that atmospheric supply of N, Fe, and P increases primary productivity utilizing some of the residual excess phosphorus (P*) in the surface waters to compensate for aerosol P deficiency. Regional primary productivity is further enhanced via the stimulation of nitrogen fixation fuelled by the residual atmospheric iron and P*. Our stoichiometric calculations reveal that a P* of 0.1 mu mol L-1 can offset the P deficiency in atmospheric supply for many months. This study suggests that atmospheric deposition may sustain similar to 10% of primary production in both the western tropical Pacific.
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    Atlantic meridional overturning circulation and the prediction of North Atlantic sea surface temperature (2014)
    Elsevier
    In:  Earth and Planetary Science Letters, 406 . pp. 1-6.
    Details
    Publication Date: 2019-09-23
    Description: Highlights: • North Atlantic sea surface temperature exhibits high decadal predictability potential. • Model bias hinders exploiting the decadal predictability potential. • An innovative method was developed to overcome some of the bias problem. • North Atlantic sea surface temperature will stay anomalously warm until about 2030. Abstract: The Atlantic Meridional Overturning Circulation (AMOC), a major current system in the Atlantic Ocean, is thought to be an important driver of climate variability, both regionally and globally and on a large range of time scales from decadal to centennial and even longer. Measurements to monitor the AMOC strength have only started in 2004, which is too short to investigate its link to long-term climate variability. Here the surface heat flux-driven part of the AMOC during 1900–2010 is reconstructed from the history of the North Atlantic Oscillation, the most energetic mode of internal atmospheric variability in the Atlantic sector. The decadal variations of the AMOC obtained in that way are shown to precede the observed decadal variations in basin-wide North Atlantic sea surface temperature (SST), known as the Atlantic Multidecadal Oscillation (AMO) which strongly impacts societally important quantities such as Atlantic hurricane activity and Sahel rainfall. The future evolution of the AMO is forecast using the AMOC reconstructed up to 2010. The present warm phase of the AMO is predicted to continue until the end of the next decade, but with a negative tendency.
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    Effects of ocean acidification on the biogenic composition of the sea-surface microlayer: Results from a mesocosm study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (11). pp. 7911-7924.
    Details
    Publication Date: 2019-09-23
    Description: The sea-surface microlayer (SML) is the ocean's uppermost boundary to the atmosphere and in control of climate relevant processes like gas exchange and emission of marine primary organic aerosols (POA). The SML represents a complex surface film including organic components like polysaccharides, proteins, and marine gel particles, and harbors diverse microbial communities. Despite the potential relevance of the SML in ocean-atmosphere interactions, still little is known about its structural characteristics and sensitivity to a changing environment such as increased oceanic uptake of anthropogenic CO2. Here we report results of a large-scale mesocosm study, indicating that ocean acidification can affect the abundance and activity of microorganisms during phytoplankton blooms, resulting in changes in composition and dynamics of organic matter in the SML. Our results reveal a potential coupling between anthropogenic CO2 emissions and the biogenic properties of the SML, pointing to a hitherto disregarded feedback process between ocean and atmosphere under climate change.
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    Progress in physical oceanography of the Baltic Sea during the 2003-2014 period (2014)
    Elsevier
    In:  Progress in Oceanography, 128 . pp. 139-171.
    Details
    Publication Date: 2019-09-23
    Description: We review progress in Baltic Sea physical oceanography (including sea ice and atmosphere–land interactions) and Baltic Sea modelling, focusing on research related to BALTEX Phase II and other relevant work during the 2003–2014 period. The major advances achieved in this period are: • Meteorological databases are now available to the research community, partly as station data, with a growing number of freely available gridded datasets on decadal and centennial time scales. The free availability of meteorological datasets supports the development of more accurate forcing functions for Baltic Sea models. • In the last decade, oceanographic data have become much more accessible and new important measurement platforms, such as FerryBoxes and satellites, have provided better temporally and spatially resolved observations. • Our understanding of how large-scale atmospheric circulation affects the Baltic Sea climate, particularly in winter, has improved. Internal variability is strong illustrating the dominant stochastic behaviour of the atmosphere. • The heat and water cycles of the Baltic Sea are better understood. • The importance of surface waves in air–sea interaction is better understood, and Stokes drift and Langmuir circulation have been identified as likely playing an important role in surface water mixing in sea water. • We better understand sea ice dynamics and thermodynamics in the coastal zone where sea ice interaction between land and sea is crucial. • The Baltic Sea’s various straits and sills are of increasing interest in seeking to understand water exchange and mixing. • There has been increased research into the Baltic Sea coastal zone, particularly into upwelling, in the past decade. • Modelling of the Baltic Sea–North Sea system, including the development of coupled land–sea–atmosphere models, has improved. Despite marked progress in Baltic Sea research over the last decade, several gaps remain in our knowledge and understanding. The current understanding of salinity changes is limited, and future projections of salinity evolution are uncertain. In addition, modelling of the hydrological cycle in atmospheric climate models is severely biased. More detailed investigations of regional precipitation and evaporation patterns (including runoff), atmospheric variability, highly saline water inflows, exchange between sub-basins, circulation, and especially turbulent mixing are still needed. Furthermore, more highly resolved oceanographic models are necessary. In addition, models that incorporate more advanced carbon cycle and ecosystem descriptions and improved description of water–sediment interactions are needed. There is also a need for new climate projections and simulations with improved atmospheric and oceanographic coupled model systems. These and other research challenges are addressed by the recently formed Baltic Earth research programme, the successor of the BALTEX programme, which ended in 2013. Baltic Earth will treat anthropogenic changes and impacts together with their natural drivers. Baltic Earth will serve as a network for earth system sciences in the region, following in the BALTEX tradition but in a wider context.
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    Neoglacial change in deep water exchange and increase of sea-ice transport through eastern Fram Strait: evidence from radiogenic isotopes (2014)
    Elsevier
    In:  Quaternary Science Reviews, 92 . pp. 190-207.
    Details
    Publication Date: 2019-09-23
    Description: Sediment core MSM5/5-712 from the West Spitsbergen continental margin has been investigated at high resolution for its seawater-derived neodymium (Nd) and lead (Pb) isotope compositions stored in ferromanganese oxyhydroxide coatings of the sediment particles to reconstruct Holocene changes in the sources and mixing of bottom waters passing the site. The radiogenic isotope data are used in combination with a multitude of proxy indicators for the climatic and oceanographic development of the eastern Fram Strait during the past 8500 years. To calibrate the downcore data, seawater and core top samples from the area were analysed for their radiogenic isotope compositions. Core top leachates reveal relatively high (more radiogenic) Nd isotope compositions between εNd −9.7 and −9.1, which are higher than present-day seawater εNd in eastern Fram Strait (−12.6 to −10.5) and indicate that the seawater values have only been established very recently. The core top data agree well with the downcore signatures within the uppermost 40 cm of the sediment core (εNd −9.1 to −8.8) indicating a reduced inflow of waters from the Nordic Seas, concurrent with cool conditions and a south-eastward shift of the marginal ice zone after ca 2.8 cal ka BP (Late Holocene). High sea-ice abundances in eastern Fram Strait are coeval with the well-known Neoglacial trend in the northern North Atlantic region. In contrast, warmer conditions of the late Early to Mid-Holocene were accompanied by lower (less radiogenic) εNd signatures of the bottom waters indicating an increased admixture from the Nordic Seas (−10.6 to −10.1). A shift to significantly more radiogenic εNd signatures of the detrital material also occurred at 3 cal ka BP and was accompanied by a marked increase in supply of fine-grained ice-rafted material (IRF) from the Arctic Ocean to the core site. The most likely source areas for this radiogenic material are the shallow Arctic shelves, in particular the Kara Sea shelf. The evolution of the Pb isotope compositions of past seawater was dominated by local signatures characterized by high 208, 207, 206Pb/204Pb values during the warm Early and Mid-Holocene periods related to enhanced chemical weathering on Svalbard and high glacial and riverine input derived from young granitic (more radiogenic) material to the West Spitsbergen margin. At 3 cal ka BP both detrital and seawater Pb isotope data changed towards more Kara Sea-like signatures.
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    Influence of environmental gradients on C and N stable isotope ratios in coral reef biota of the Red Sea, Saudi Arabia (2014)
    Elsevier
    In:  Journal of Sea Research, 85 . pp. 379-394.
    Details
    Publication Date: 2017-07-19
    Description: The Red Sea features a natural environmental gradient characterized by increasing water temperature, nutrient and chlorophyll a concentrations from North to South. The aim of this study was to assess the relationships between ecohydrography, particulate organic matter (POM) and coral reef biota that are poorly understood by means of carbon (δ13C) and nitrogen (δ15N) stable isotopes. Herbivorous, planktivorous and carnivorous fishes, zooplankton, soft corals (Alcyonidae), and bivalves (Tridacna squamosa)were a priori defined as biota guilds. Environmental samples (nutrients, chlorophyll a), oceanographic data (salinity, temperature), POMand biotawere collected at eight coral reefs between 28°31′ N and 16°31′ N. Isotopic niches of guilds separated in δ13C and δ15N isotopic niche spaces and were significantly correlated with environmental factors at latitudinal scale. Dietary end member contributionswere estimated using the Bayesian isotope mixingmodel SIAR. POMand zooplankton 15N enrichment suggested influences by urban run-off in the industrialized central region of the Red Sea. Both δ15N and their relative trophic positions (RTPs) tend to increase southwards, but urban runoff offsets the natural environmental gradient in the central region of the Red Sea toward higher δ15N and RTPs. The present study reveals that consumer δ13C and δ15N in Red Sea coral reefs are influenced primarily by the latitudinal environmental gradient and localized urban runoff. This study illustrates the importance of ecohydrography when interpreting trophic relationships from stable isotopes in Red Sea coral reefs.
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    Evolution in an acidifying ocean (2014)
    Elsevier
    In:  Trends in Ecology and Evolution, 29 (2). pp. 117-125.
    Details
    Publication Date: 2019-01-24
    Description: Highlights: • We summarize tools for assessing evolutionary potential under ocean acidification. • We review studies of past adaptation, genetic variation, and experimental evolution. • We highlight progress and challenges and recommend future research directions. • Longer-term experiments that focus on fitness-related responses are recommended. Ocean acidification poses a global threat to biodiversity, yet species might have the capacity to adapt through evolutionary change. Here we summarize tools available to determine species’ capacity for evolutionary adaptation to future ocean change and review the progress made to date with respect to ocean acidification. We focus on two key approaches: measuring standing genetic variation within populations and experimental evolution. We highlight benefits and challenges of each approach and recommend future research directions for understanding the modulating role of evolution in a changing ocean.
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    Strategies for the sustainability of online open-access biodiversity databases (2014)
    Elsevier
    In:  Biological Conservation, 173 . pp. 155-165.
    Details
    Publication Date: 2019-09-23
    Description: Highlights: • Open-access online scholarly biodiversity databases are threatened by a lack of funding and institutional support. • Strategic approaches to aid sustainability are summarised. • Issues include database coverage, quality, uniqueness; clarity of Intellectual Property Rights, ownership and governance. • Long-term support from institutions and scientists is easier for high-quality, comprehensive, prestigious global databases. • Larger multi-partner governed databases are more sustainable; i.e. ‘bigger (multi-partner) databases are better’. Abstract: Scientists should ensure that high quality research information is readily available on the Internet so society is not dependant on less authoritative sources. Many scientific projects and initiatives publish information on species and biodiversity on the World Wide Web without users needing to pay for it. However, these resources often stagnate when project funding expired. Based on a large pool of experiences worldwide, this article discusses what measures will help such data resources develop beyond the project lifetime. Biodiversity data, just as data in many other disciplines, are often not generated automatically by machines or sensors. Data on for example species are based on human observations and interpretation. This requires continuous data curation to keep these up to date. Creators of online biodiversity databases should consider whether they have the resources to make their database of such value that other scientists and/or institutions would continue to finance its existence. To that end, it may be prudent to engage such partners in the development of the resource from an early stage. Managers of existing biodiversity databases should reflect on the factors being important for sustainability. These include the extent, scope, quality and uniqueness of database content; track record of development; support from scientists; support from institutions, and clarity of Intellectual Property Rights. Science funders should give special attention to the development of scholarly databases with expert-validated content. The science community has to appreciate the efforts of scientists in contributing to open-access databases, including by citing these resources in the Reference lists of publications that use them. Science culture must thus adapt its practices to support online databases as scholarly publications. To sustain such databases, we recommend they should (a) become integrated into larger collaborative databases or information systems with a consequently larger user community and pool of funding opportunities, and (b) be owned and curated by a science organisation, society, or institution with a suitable mandate. Good governance and proactive communication with contributors is important to maintain the team enthusiasm that launched the resource. Experience shows that ‘bigger is better’ in terms of database size because the resource will have more content, more potential and known uses and users of its content, more contributors, be more prestigious to contribute to, and have more funding options. Furthermore, most successful biodiversity databases are managed by a partnership of individuals and organisations.
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    Perceptions of sub-seabed carbon dioxide storage in Scotland and implications for policy: A qualitative study (2014)
    Elsevier
    In:  Marine Policy, 45 . pp. 9-15.
    Details
    Publication Date: 2013-12-17
    Description: The geological storage of carbon dioxide (CO2) offers notable potential, as part of larger carbon dioxide capture and storage (CCS) processes, to be a significant climate change mitigation technology. This paper challenges the argument often put forward that, due to the greater distances from centres of population, it will be ‘easier’ to garner public and stakeholder support for offshore CO2 storage than onshore. Based on the results of research interviews carried out with stakeholders and informed publics in Scotland, challenges for public and stakeholder acceptance of sub-seabed CO2 storage that may require further policy attention are identified. Whilst existing policy for sub-seabed CO2 storage is cognisant of the need for societal engagement, it may be the case that these regulations may need further reinforcement to ensure future developments are able to address social acceptability issues as fully as possible. The value of taking into account social as well as physical characteristics at the site selection phase, the need for mechanisms to take seriously stakeholder conceptions of uncertainty, and the importance of extending social engagement beyond risk communication are discussed.
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    Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean (2014)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 126 . pp. 321-337.
    Details
    Publication Date: 2017-06-19
    Description: More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4,000–6,000 years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chemical composition, structure, and biochemical formation and degradation mechanisms are still unresolved. We have compiled the most comprehensive molecular data set of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extracted marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50° N to 70° S). Molecular trends and radiocarbon dating of 34 DOM samples (comprising Δ14C values from -229 to -495‰) were combined to model an integrated degradation rate for bulk DOC resulting in a predicted age of 〉24 ka for the most persistent DOM fraction. First order kinetic degradation rates for 1,557 mass peaks indicate that numerous DOM molecules cycle on timescales much longer than the turnover of the bulk DOC pool (estimated residence times of 〉100 ka) and the range of validity of radiocarbon dating. Changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks. The combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 molecular formulae represented the most stable composition in the oceanic environment (“island of stability”). These most persistent compounds encompass only a narrow range of the elemental ratios H/C (average of 1.17 ± 0.13), and O/C (average of 0.52 ± 0.10) and molecular masses (360 ± 28 and 497 ± 51 Da). In the Weddell Sea DOC concentrations in the surface waters were low (46.3 ± 3.3 μM) while the organic radiocarbon was significantly more depleted than that of the East Atlantic, indicating average surface water DOM ages of 4,920 ± 180 a. These results are in accordance with a highly degraded DOM in the Weddell Sea surface water as also shown by the molecular degradation index IDEG obtained from FT-ICR MS data. Further, we identified 339 molecular formulae which probably contribute to an increased DOC concentration in the Southern Ocean and potentially reflect an accumulation or enhanced sequestration of refractory DOC in the Weddell Sea. These results will contribute to a better understanding of the persistent nature of marine DOM and its role as an oceanic carbon buffer in a changing climate.
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    β-Glucan supplemented diets increase poly(I:C)-induced gene expression of Mx, possibly via Tlr3-mediated recognition mechanism in common carp (Cyprinus carpio) (2014)
    Elsevier
    In:  Fish & Shellfish Immunology, 36 (2). pp. 494-502.
    Details
    Publication Date: 2015-01-09
    Description: Highlights: • mx expression was stable or slightly up-regulated in carp after β-glucan treatment. • Poly(I:C) markedly increased mx expression in samples from β-glucan fed fish. • Two sequences for carp tlr3 were retrieved (tlr3.1 and tlr3.2) and characterized. • β-Glucan-supplemented diets increased the transcript levels of both tlr3 genes. We have previously observed that in common carp (Cyprinus carpio), administration of β-glucan (MacroGard®) as feed additive leads to a lower expression of pro-inflammatory cytokines suggesting that this immunostimulant may be preventing an acute and potentially dangerous response to infection, particularly in the gut. However, in general, mechanisms to detect and eliminate pathogens must also be induced in order to achieve an efficient clearance of the infection. Protection against viral diseases acquired through β-glucan-supplemented feed has been extensively reported for several experimental models in fish but the underlining mechanisms are still unknown. Thus, in order to better characterize the antiviral action induced by β-glucans in fish, MacroGard® was administered daily to common carp in the form of supplemented commercial food pellets. Carp were fed for a period of 25 days prior to intra-peritoneal injection with polyinosinic:polycytidylic acid (poly(I:C)), a well-known double-stranded RNA mimic that triggers a type-I interferon (IFN) response. Subsequently, a set of immune related genes, including mx, were analysed by real-time PCR on liver, spleen, head kidney and mid gut tissues. Results obtained confirmed that treatment with β-glucan alone generally down-regulated the mRNA expression of selected cytokines when compared to untreated fish, while mx gene expression remained stable or was slightly up-regulated. Injection with poly(I:C) induced a similar down-regulated gene expression pattern for cytokines in samples from β-glucan fed fish. In contrast, poly(I:C) injection markedly increased mx gene expression in samples from β-glucan fed fish but hardly in samples from fish fed control feed. In an attempt to explain the high induction of mx, we studied Toll-like receptor 3 (TLR3) gene expression in these carp. TLR3 is a prototypical pattern recognition receptor considered important for the binding of viral double-stranded RNA and triggering of a type-I IFN response. Through genome data mining, two sequences for carp tlr3 were retrieved (tlr3.1 and tlr3.2) and characterized. Constitutive gene expression of both tlr3.1 and tlr3.2 was detected by real-time PCR in cDNA of all analysed carp organs. Strikingly, 25 days after β-glucan feeding, very high levels of tlr3.1 gene expression were observed in all analysed organs, with the exception of the liver. Our data suggest that β-glucan-mediated protection against viral diseases could be due to an increased Tlr3-mediated recognition of ligands, resulting in an increased antiviral activity of Mx.
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    Copepod assemblages in the northern South China Sea during inter-monsoon transition periods (2014)
    Elsevier
    In:  Journal of Sea Research, 86 . pp. 43-48.
    Details
    Publication Date: 2017-07-19
    Description: Highlights: • Spring and autumn copepod assemblages are depicted in the northeast South China Sea. • Copepod assemblages are partially driven by temperature in the SCS. • S. subtenuis and A. negligens are indicative of the South China Sea central gyre. • We provide a synoptic picture of the copepod community structure in the SCS We investigated the influence of permanent oceanographic features in structuring copepod assemblages in the northern South China Sea during the inter-monsoon transition periods, spring and autumn. A total of 25 families, 48 genera and 88 species, were recorded, as well as a decrease in species richness along with the seasonal temperature decrease. We show that copepod assemblages are influenced by quasi-permanent oceanographic conditions governing the Northeastern South China Sea, i.e. China Coastal Current and the Kuroshio Current intrusion. This study provides a synoptic picture of the seasonal changes in the community structure of copepods during spring and autumn in the northern South China Sea.
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    On the spatial and temporal distribution of near-inertial energy in the Southern Ocean (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (1). pp. 359-376.
    Details
    Publication Date: 2019-09-23
    Description: We use an eddying realistic primitive equation model of the Southern Ocean to examine the spatial and temporal distribution of near-inertial wind-power input (WPI) and near-inertial energy (NIE) in the Southern Ocean. We find that the modelled near-inertial WPI is almost proportional to inertial wind-stress variance (IWSV), while the modelled NIE is modulated by the inverse of the mixed-layer depth. We go on to assess recent decadal trends of near-inertial WPI from trends of IWSV based on reanalysis wind-stress. Averaged over the Southern Ocean, annual-mean IWSV is found to have increased by 16 percent over the years 1979 through 2011. Part of the increase of IWSV is found to be related to the positive trend of the Southern Annular Mode over the same period. Finally, we show that there are horizontal local maxima of NIE at depth that are almost exclusively associated with anticyclonic eddies.
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    Late Weichselian deglaciation and early Holocene development of a cold-water coral reef along the Lopphavet shelf (Northern Norway) recorded by benthic foraminifera and ostracoda (2014)
    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 99 . pp. 249-269.
    Details
    Publication Date: 2020-08-05
    Description: Cold-water coral (CWC) settlement in northern Norway is strongly related to the outlet-glaciers of the Fennoscandian Ice-sheet, and dating of known CWC structures show clearly post-glacial ages. Two gravity cores (POS391 559/2,277 cm long and POS391 559/3,282 cm long) were recovered on a CWC reef in the area of Lopphavet, northern Norway. Detailed investigations on lithology (sediment structures and composition), micropaleontology (foraminifera and ostracoda) and AMS 14C dating on the epibenthic foraminifera Discanomalina coronata were performed on the two cores. Phosphorus analyses were performed only on core POS391 559/3. Results indicate that the whole core POS391 559/2 is representative of a CWC reef environment. The base of the core is dated at 10,600±120 cal. yr BP, thus representing one of the oldest ages of a Norwegian coral reef. Core POS391 559/3 documents the passage from a proximal glacier environment characterized by fine silty sediments with intercalation of several dropstone layers to a CWC ecosystem. The transition from the glacial to the interglacial stage is dated as old as 10,725±205 cal. yr BP, whereas the base of the core is dated to an age of 15,300±550 cal. yr BP. Diversity of benthic foraminifera is higher within the CWC, especially in the intervals containing coral framework. Five clusters are identified based on the Bray–Curtis Similarity Term Analyses and the interpretation of data shows that they are related to different ecological settings, e.g., fluctuations of the sea-ice cover; influence of the warmer and more saline Atlantic water masses; transitional to a fully interglacial environment; well oxygenated, nutrient-rich and high current setting being conducive to CWC. Ostracod assemblages show that these crustaceans may be also used to characterize sedimentary facies on CWC reefs.
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  • 133
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    Controls on the seasonal variability of calcium carbonate saturation states in the Atlantic gateway to the Arctic Ocean (2014)
    Elsevier
    In:  Marine Chemistry, 158 . pp. 1-9.
    Details
    Publication Date: 2021-04-23
    Description: In addition to ocean acidification due to a gradual anthropogenic CO2 uptake, strong seasonal variations in the carbonate system occur in the Arctic Ocean as a result of physical and biological processes. Understanding this seasonal variability is critical for predicting the onset of calcium carbonate mineral (Ω) undersaturation with increasing atmospheric CO2 concentrations. However, these variations are currently poorly understood because of a lack of winter data due to the challenging field conditions in this season. Here we report observations over an annual cycle of the carbonate system of surface waters in the Atlantic gateway to the Arctic Ocean, covering the region between Svalbard and mainland Norway. Dissolved inorganic carbon (DIC) concentrations ranged from 2137–2148 μmol kg− 1 in winter to 1986–2094 μmol kg− 1 in summer, and total alkalinity (TA) concentrations between 2312–2341 μmol kg− 1 in winter and 2199–2317 μmol kg− 1 in summer. This resulted in an increase in TA:DIC ratios from 1.077–1.090 in winter to 1.106–1.112 in summer, mainly due to the biological uptake of CO2 during spring and summer. Similarly, a significant seasonal variability was observed in Ω (0.4–0.9), with lowest saturation states in winter (Ωaragonite ~ 1.8–2.1) and highest in spring and summer (Ωaragonite ≈ 2.4). Analysis of the biogeochemical and physical processes that impact aragonite saturation states (Ωar) showed biological production to be the most important factor driving seasonal variability in Ωar in this area, accounting for 45–70% of the difference between winter and summer values. Future changes in these processes may alter the seasonal cycle of the carbonate system in both amplitude and timing, and further observations are required to determine the progress of ocean acidification in the Atlantic waters entering the Arctic Ocean.
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  • 134
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    Crustal thinning in the northern Tyrrhenian Rift: Insights from multichannel and wide-angle seismic data across the basin (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 119 . pp. 1655-1677.
    Details
    Publication Date: 2018-02-27
    Description: Extension of the continental lithosphere leads to the formation of rift basins or rifted continental margins if breakup occurs. Seismic investigations have repeatedly shown that conjugate margins have asymmetric tectonic structures and different amount of extension and crustal thinning. Here we compare two coincident wide-angle and multichannel seismic profiles across the northern Tyrrhenian rift system sampling crust that underwent different stages of extension from north to south and from the flanks to the basin center. Tomographic inversion reveals that the crust has thinned homogeneously from ~24 km to ~17 km between the Corsica Margin and the Latium Margin implying a β factor of ~1.3–1.5. On the transect 80 km to the south, the crust thinned from ~24 km beneath Sardinia to a maximum of ~11 km in the eastern region near the Campania Margin (β factor of ~2.2). The increased crustal thinning is accompanied by a zone of reduced velocities in the upper crust that expands progressively toward the southeast. We interpret that the velocity reduction is related to rock fracturing caused by a higher degree of brittle faulting, as observed on multichannel seismic images. Locally, basalt flows are imaged intruding sediment in this zone, and heat flow values locally exceed 100 mW/m2. Velocities within the entire crust range 4.0–6.7 km/s, which are typical for continental rocks and indicate that significant rift-related magmatic underplating may not be present. The characteristics of the pre-tectonic, syn-tectonic and post-tectonic sedimentary units allow us to infer the spatial and temporal evolution of active rifting. In the western part of the southern transect, thick postrift sediments were deposited in half grabens that are bounded by large fault blocks. Fault spacing and block size diminish to the east as crustal thinning increases. Recent tectonic activity is expressed by faults cutting the seafloor in the east, near the mainland of Italy. The two transects show the evolution from the less extended rift in the north with a fairly symmetric conjugate structure to the asymmetric margins farther south. This structural evolution is consistent with W-E rift propagation and southward increasing extension rates.
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  • 135
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    Securing Blue Wealth: The Need for a Special Sustainable Development Goal for the Ocean and Coasts (2014)
    Elsevier
    In:  Marine Policy, 48 . pp. 184-191.
    Details
    Publication Date: 2019-09-23
    Description: The ocean regulates the global climate, provides humans with natural resources such as food, materials, important substances, and energy, and is essential for international trade and recreational and cultural activities. Together with human development and economic growth, free access to, and availability of, ocean resources and services have exerted strong pressure on marine systems, ranging from overfishing, increasing resource extraction, and alteration of coastal zones to various types of thoughtless pollution. Both economic theory and many case studies suggest that there is no “tragedy of the commons” but a “tragedy of open access”. With high likeliness, structures of open access are non-sustainable. International cooperation and effective governance are required to protect the marine environment and promote the sustainable use of marine resources in such a way that due account can be taken of the environmental values of current generations and the needs of future generations. For this purpose, developing and agreeing on one Sustainable Development Goal (SDG) specifically for the Ocean and Coasts could prove to be an essential element. The new SDGs will build upon the Millennium Development Goals (MDGs) and replace them by 2015. Ensuring environmental sustainability in a general sense is one of the eight MDGs but the ocean is not explicitly addressed. Furthermore, the creation of a comprehensive underlying set of ocean sustainability targets and effective indicators developed within a global Future Ocean Spatial Planning (FOSP) process would help in assessing the current status of marine systems, diagnosing ongoing trends, and providing information for inclusive, forward-looking, and sustainable ocean governance
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  • 136
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    Seasonal variability of methyl iodide in the Kiel Fjord (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (3). pp. 1609-1620.
    Details
    Publication Date: 2019-09-23
    Description: From October 2008 to November 2010, CH3I concentrations were measured in the Kiel Fjord together with potentially related biogeochemical and physical parameters. A repeating seasonal cycle of CH3I was observed with highest concentrations in summer (ca. 8.3 pmol L−1; June and July) and lowest concentrations in winter (ca. 1.5 pmol L−1; December to February). A strong positive correlation at zero lag between [CH3I] and solar radiation (R2 = 0.93) was observed, whereas correlations with other variables (SST, Chlorophyll a) were weaker, and they lagged CH3I by ca. 1 month. These results appear consistent with the hypothesis that SSR is the primary forcing of CH3I production in surface seawater, possibly through a photochemical pathway. A mass balance of the monthly averaged data was used to infer mean rates of daily net production (Pnet) and losses for CH3I over the year. The sea-to-air flux of CH3I in the Kiel Fjord averaged 3.1 nmol m−2 d−1, the mean chemical loss rate was 0.047 pmol L−1 d−1, and Pnet varied systematically from winter to summer (from 0 to 0.6 pmol L−1 d−1). Pnet was correlated at zero lag with SST, SSR, and Chla (R2 = 0.55, 0.67, and 0.73, respectively, p 〈〈 0.01). The lagged cross-correlation analysis indicated that SSR led Pnet by 1 month, whereas the strongest cross correlations with Chla were at lags of 0 to +1 month, and SST lagged Pnet by 1 month. The broad seasonal peak of Pnet makes it difficult to determine the key factor controlling CH3I net production using in situ concentration data alone.
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  • 137
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    Neodymium and hafnium boundary contributions to seawater along the West Antarctic continental margin (2014)
    Elsevier
    In:  Earth and Planetary Science Letters, 394 . pp. 99-110.
    Details
    Publication Date: 2017-03-06
    Description: Highlights: • Nd and Hf are released from sediments to the water column in the Amundsen Sea Embayment. • Seawater Nd and Hf isotope compositions show opposed trends close to the Marie Byrd Seamounts. • AABW is isotopically distinct in Nd between the Atlantic and the Pacific sectors. • Hf isotope variations occur between the sectors, but not with depth in each sector. Abstract: Neodymium and hafnium isotopes and elemental concentrations (Sm, Nd, Hf, Zr) have been measured in three water column profiles south of the Antarctic Circumpolar Current in, and to the east of the Ross Sea, in conjunction with five bottom water samples from the Amundsen Sea Embayment. Neodymium and hafnium both appear to be released from sediments in the Embayment. In the case of Nd, this is reflected in radiogenic isotope compositions (εNdεNd up to −5.4) and highly elevated concentrations (up to 41 pmol/kg). Hafnium isotopes, on the other hand, are only very slightly altered relative to the open ocean sites, and boundary release is most prominently indicated by elevated concentrations (〉1 pmol/kg versus ∼0.7 pmol/kg). There is also a local input of both Hf and Nd at the Marie Byrd Seamounts, which leads to Nd isotope compositions as radiogenic as −3.1, and hafnium shifted to less radiogenic compositions in local bottom water. A compilation of the new data with literature data reveals a consistent view of the influence of Antarctica on the Nd isotope composition in Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW). Sector specific Nd addition shifts AABW formed in the Atlantic sector to less radiogenic isotope compositions (average εNd=−9εNd=−9) relative to LCDW (average εNd=−8.4εNd=−8.4), whereas AABW in the Pacific sector is shifted to more radiogenic values (average εNd=−7εNd=−7). The evolution towards more radiogenic εNdεNd with depth in LCDW in the Pacific sector is likely to reflect admixture of AABW but, in addition, is also controlled by boundary exchange with the slope as observed at the Marie Byrd Seamounts. Hafnium isotopes are relatively homogeneous in the data set, ranging between εHf=+2εHf=+2 and +3.8 for most samples, excluding less radiogenic compositions in deep waters close to the Marie Byrd Seamounts. The Hf isotope composition in the Pacific sector is, however, slightly less radiogenic than in the Atlantic, corresponding to an average of +3 relative to an average of +3.8. This probably reflects unradiogenic Hf inputs from Antarctica to the Pacific sector, which are vertically homogenized by reversible scavenging. The Hf isotope heterogeneity in LCDW between both sectors is likely to indicate a shorter seawater residence time for Hf than for Nd, which is consistent with the dissolved – particulate phase partitioning of both elements.
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  • 138
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    Dissolved organic carbon and apparent oxygen utilization in the Atlantic Ocean (2014)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 85 . pp. 80-87.
    Details
    Publication Date: 2021-04-23
    Description: Highlights • Meridional pattern in surface DOC in Atlantic Ocean. • POC mineralization determines AOU in equatorial Atlantic. • DOC utilization determines AOU in Atlantic subtropical gyres. Abstract Dissolved organic carbon (DOC) distributions along two Atlantic Meridional Transects conducted in 2005 in the region between 47°N and 34°S showed clear latitudinal patterns. The DOC concentrations in the epipelagic zone (0–100 m) were the highest (70–90 µM) in tropical and subtropical waters with stable mixed layers, and lowest (50–55 µM) at the poleward extremities of the transects due to deep convective mixing supplying low DOC waters to the surface. A decrease in DOC occurred with depth, and lowest DOC concentrations (41–45 µM) in the 100–300 m depth range were observed in the equatorial region due to upwelling of low DOC waters. A strong relationship between DOC and AOU was observed in the σ–t 26–26.5 isopycnal layer which underlies the euphotic zone and outcrops at the poleward extremities of the North and South Atlantic Subtropical Gyres (NASG and SASG) in the region ventilating the thermocline waters. Our observations reveal significant north–south variability in the DOC–AOU relationship. The gradient of the relationship suggests that 52% of the AOU in the σ–t 26–26.5 density range was driven by DOC degradation in the NASG and 36% in the SASG, with the remainder due to the remineralisation of sinking particulate material. We assess possible causes for the greater contribution of DOC remineralisation in the NASG compared to the SASG.
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  • 139
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    Interplate seismicity at the CRISP drilling site: The 2002 Mw=6.4 Osa Earthquake at the southeastern end of the Middle America Trench (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (7). pp. 3035-3050.
    Details
    Publication Date: 2018-02-28
    Description: We investigate potential relations between variations in seafloor relief and age of the incoming plate and interplate seismicity. Westward from Osa Peninsula in Costa Rica, a major change in the character of the incoming Cocos Plate is displayed by abrupt lateral variations in seafloor depth and thermal structure. Here a Mw 6.4 thrust earthquake was followed by three aftershock clusters in June 2002. Initial relocations indicate that the main shock occurred fairly trenchward of most large earthquakes along the Middle America Trench off central Costa Rica. The earthquake sequence occurred while a temporary network of OBH and land stations ∼80 km to the northwest were deployed. By adding readings from permanent local stations, we obtain uncommon P wave coverage of a large subduction zone earthquake. We relocate this catalog using a nonlinear probabilistic approach within both, a 1-D and a 3-D P wave velocity models. The main shock occurred ∼25 km from the trench and probably along the plate interface at 5–10 km depth. We analyze teleseismic data to further constrain the rupture process of the main shock. The best depth estimates indicate that most of the seismic energy was radiated at shallow depth below the continental slope, supporting the nucleation of the Osa earthquake at ∼6 km depth. The location and depth coincide with the plate boundary imaged in prestack depth-migrated reflection lines shot near the nucleation area. Aftershocks propagated downdip to the area of a 1999 Mw 6.9 sequence and partially overlapped it. The results indicate that underthrusting of the young and buoyant Cocos Ridge has created conditions for interplate seismogenesis shallower and closer to the trench axis than elsewhere along the central Costa Rica margin.
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  • 140
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    Experimental investigation of Ca isotopic fractionation during abiotic gypsum precipitation (2014)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 129 . pp. 157-176.
    Details
    Publication Date: 2017-06-19
    Description: Experiments investigating Ca isotopic fractionation during gypsum precipitation were undertaken in order to elucidate the mechanisms and conditions that govern isotopic fractionation during mineral precipitation. Both stirred and unstirred free drift gypsum precipitation experiments were conducted at constant initial ionic strength (0.6 M) and variable initial saturation states (4.8–1.5) and Ca2+:SO42− ratios (3 and 0.33). Experimental durations varied between 0.5 and 190 h, while temperature (25.9–24.0 °C), pH (5.8–5.4) and ionic strength (0.6–0.5) were relatively constant. In all experiments, 20–80% of the initial dissolved Ca reservoir was precipitated. Isotopically light Ca preferentially partitioned into the precipitated gypsum; the effective isotopic fractionation factor (Δ44/40Cas–f = δ44/40Casolid − δ44/40Cafluid) of the experimental gypsum ranged from −2.25‰ to −0.82‰. The log weight-averaged, surface area normalized precipitation rates correlated with saturation state and varied between 4.6 and 2.0 μmol/m2/h. The crystal size and aspect ratios, determined by SEM images, BET surface area, and particle size measurements, co-varied with precipitation rate, such that fast growth produced small (10–20 μm), tabular crystals and slow growth produced larger (〉1000 μm), needle shaped crystals. Mass balance derived δ44Cas and Δ44Cas–f, calculated using the initial fluid δ44Ca and the mass fraction of Ca removed during precipitation (fCa) as constraints, suggest that the precipitate was not always sampled homogeneously due to the need to preserve the sample for SEM, surface area, and particle size analyses. The fractionation factor (αs–f), derived from Rayleigh model fits to the fluid and calculated bulk solid, ranged from 0.9985 to 0.9988 in stirred experiments and 0.9987 to 0.9992 in unstirred experiments. The αs–f demonstrated no clear dependence on either precipitation rate or initial saturation state in stirred reactors, but exhibited a positive dependence on rate in unstirred experiments. The differences in αs–f between stirred and unstirred reactors, as well as a general correlation between αs–f and crystal morphology, led us to hypothesize that growth on different crystal faces controls the isotopic composition of gypsum. We also explore the idea that speciation in solution explains the difference between experiments in which the only major difference was the Ca2+ to SO42− ratio in solution. The importance of understanding the environmental controls on the fractionation factor during mineral precipitation is highlighted in this study. The fractionation factor of gypsum precipitation near chemical equilibrium was found to be ∼0.9995, rather than 1, indicating that even at near equilibrium conditions, the δ44Ca of minerals are not likely to record the δ44Ca of the solution directly. However, the measurable isotopic fractionation associated with gypsum formation does suggest that a gypsum-based proxy may be useful in constraining Ca cycling in marginal environments over geologic time scales. Model examples are provided that demonstrate how such a proxy would operate.
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  • 141
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    How the chemotactic characteristics of bacteria can determine their population patterns (2014)
    Elsevier
    In:  Soil Biology & Biochemistry, 69 . pp. 346-358.
    Details
    Publication Date: 2019-06-27
    Description: Highlights • An individual-based model was developed and coupled to a pore-network model. • The bacterial distribution patterns were geostatistically analyzed. • The effects from bacterial chemotactic properties on bacterial distribution patterns were examined. • The additional influences from structural heterogeneities were examined. Abstract Spatial distribution of soil microorganisms is relevant for the functioning and performance of many ecosystem processes such as nutrient cycling or biodegradation of organic matters and contaminants. Beside the multitude of abiotic environmental factors controlling the distribution of microorganisms in soil systems, many microbial species exhibit chemotactic behavior by directing their movement along concentration gradients of nutrients or of chemoattractants produced by cells of their own kind. This chemotactic ability has been shown to promote the formation of complex distribution patterns even in the absence of environmental heterogeneities. Microbial population patterns in heterogeneous soil systems might be, hence, the result of the interplay between the heterogeneous environmental conditions and the microorganisms' intrinsic pattern formation capabilities. In this modeling study, we combined an individual-based modeling approach with a reactive pore-network model to investigate the formation of bacterial patterns in homogeneous and heterogeneous porous media. We investigated the influence of different bacterial chemotactic sensitivities (toward both substrate and bacteria) on bacterial distribution patterns. The emerging population patterns were classified with the support of a geostatistical approach, and the required conditions for the formation of any specific pattern were analyzed. Results showed that the chemotactic behavior of the bacteria leads to non-trivial population patterns even in the absence of environmental heterogeneities. The presence of structural pore scale heterogeneities had also an impact on bacterial distributions. For a range of chemotactic sensitivities, microorganisms tend to migrate preferably from larger pores toward smaller pores and the resulting distribution patterns thus resembled the heterogeneity of the pore space. The results clearly indicated that in a porous medium like soil the distribution of bacteria may not only be related to the external constraints but also to the chemotactic behavior of the bacterial cells.
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  • 142
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    Occurrence and fate of fatty acyl biomarkers in an ancient whale bone (Oligocene, El Cien Formation, Mexico) (2014)
    Elsevier
    In:  Organic Geochemistry, 68 . pp. 71-81.
    Details
    Publication Date: 2017-01-31
    Description: Highlights • Fatty acids preserved in an Oligocene whale bone were analysed. • The fatty acid content of the fossil was in the permil range vs. a recent whale vertebra. • Ca. 80% of the n-C16 and n-C18 alkyl moieties were extractable, ca. 20% being bound to kerogen. • Endogenous fatty acids were largely of microbial origin (sulfate reducers, actinobacteria). Abstract The taphonomic and diagenetic processes by which organic substances are preserved in animal remains are not completely known and the originality of putative metazoan biomolecules in fossil samples is a matter of scientific discussion. Here we report on biomarker information preserved in a fossil whale bone from an Oligocene phosphatic limestone (El Cien Fm., Mexico), with a focus on fatty acyl compounds. Extracts were quantitatively analysed using gas chromatography–mass spectrometry (GC–MS) and, to identify macromolecular-linked remains, demineralised extraction residues were subjected to catalytic hydropyrolysis (HyPy). To better recognise potential authentic (i.e. animal-derived) lipids, the data from the ancient bone were compared with those obtained from (i) the adjacent host sediment of the fossil and (ii) a recent whale (Phocoena phocoena) vertebra. In addition, the spatial distribution of organic and inorganic species was observed at the μm level by imaging MS (time-of-flight-secondary ion mass spectrometry, ToF-SIMS). Our results revealed a rather even distribution of hydrocarbon-, O- and N-containing ions in the trabecular network of the ancient bone. A different, more patchy arrangement of organic compounds was evident in the former marrow cavities that were partly cemented by clotted micrites of putative microbial origin. The concentration of fatty acids (FAs) in the ancient bone was in the permil range of the amount extracted from the recent whale vertebra. Endogenous compounds, including monoenoic n-C16 and n-C18 as well as branched FAs, were identified in the fossil bone by comparison with the host sediment. Ca. 80% of the prevalent n-C16 and n-C18 moieties in the ancient bone were extractable as FAs, whereas ca. 20% were covalently bound in the non-saponifiable kerogen fraction. Ample pyrite precipitates, distinctive 10-methyl branched FAs and microbial microborings (“tunneling”) indicate that sulfate reducers and collagen-degrading actinomycetes were central players in the microbial decomposition of the bone. Similarities with reported microbial FA patterns suggest that the FAs in the fossil bone were largely contributed by these microbial “last eaters”. The results highlight some of the degradation and preservation mechanisms during marine FA diagenesis in the “natural laboratory” of bones, and therefore the processes that lead to either degradation, preservation, or introduction of these widespread biomolecules in the fossils of ancient marine animals.
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  • 143
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    Is late Quaternary climate change governed by self-sustained oscillations in atmospheric CO2? (2014)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 132 . pp. 413-439.
    Details
    Publication Date: 2019-09-24
    Description: A simple earth system model is developed to simulate global carbon and phosphorus cycling over the late Quaternary. It is focused on the geological cycling of C and P via continental weathering, volcanic and metamorphic degassing, hydrothermal processes and burial at the seabed. A simple ocean model is embedded in this geological model where the global ocean is represented by surface water, thermocline and deep water boxes. Concentrations of dissolved phosphorus, dissolved inorganic carbon, and total alkalinity are calculated for each box. The partial pressure of CO2 in the atmosphere (pCO(2A)) is determined by exchange processes with the surface ocean and the continents. It serves as key prognostic model variable and is assumed to govern surface temperatures and global sea-level. The model is formulated as autonomous system, in which the governing equations have no explicit time-dependence. For certain parameter values, the model does not converge towards a steady-state but develops stable self-sustained oscillations. These free oscillations feature pCO(2A) minima and maxima consistent with the ice-core record when vertical mixing in the ocean is allowed to vary in response to pCO(2A)-controlled temperature change. A stable 100-kyr cycle with a rapid transition from glacial to interglacial conditions is obtained when additional non-linear equations are applied to calculate deep ocean mixing, iron fertilization and the depth of organic matter degradation as function of pCO(2A)-controlled surface temperature. The delta C-13 value of carbon in the ocean/atmosphere system calculated in these model runs is consistent with the benthic delta C-13 record. However, the simulated C-13 depletion in the glacial ocean is not driven by the decline in terrestrial carbon stocks but by sea-level change controlling the rates of organic carbon burial and weathering at continental margins. The pCO(2A)-and delta C-13 oscillations develop without any form of external Milankovitch forcing. They are induced and maintained by sea-level change generating persistent imbalances in the marine carbon and phosphorus budgets. Stable oscillations are also obtained when sea-level change is allowed to lag temperature with a realistic time scale for ice-sheet adjustment
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  • 144
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    Feeding common carp Cyprinus carpio with β-glucan supplemented diet stimulates C-reactive protein and complement immune acute phase responses following PAMPs injection (2014)
    Elsevier
    In:  Fish & Shellfish Immunology, 39 (2). pp. 285-295.
    Details
    Publication Date: 2017-01-05
    Description: Highlights: • Feeding 0.1% Macrogard® for 25 days increased CRP and complement responses in carp. • β-glucan affected gene expression in the liver, head kidney and mid-gut tissues. • Gene expression was more affected by LPS and poly(I:C) in the β-glucan fed fish. • Carp acute phase response to PAMPs injection was stimulated by β-glucan. Abstract: The effect of β-glucan as a feed additive on the serum and gene profile of C-reactive protein (CRP) and complement acute phase responses was ascertained in common carp Cyprinus carpio. In addition effects of subsequent intraperitoneal injections of pathogen-associated molecular patterns (PAMPs), i.e. LPS or poly(I:C), to mimic bacterial or viral infection respectively, were studied. Carp were first orally fed with β-glucan (MacroGard®) with a daily β-glucan intake of 6 mg per kg body weight or with control food for 25 days and then injected with PBS containing either LPS (4 mg/kg) or poly(I:C) (5 mg/kg) or PBS alone. Fish were sampled during the 25 days of the feeding period and up to 7 days post-PAMPs injections for serum and liver, head kidney and mid-gut tissues. Oral administration of β-glucan for 25 days significantly increased serum CRP levels and alternative complement activity (ACP). In addition, the subsequent LPS and poly(I:C) challenges significantly affected CRP and complement related gene expression profiles (crp1, crp2, c1r/s, bf/c2, c3 and masp2), with the greatest effects observed in the β-glucan fed fish. However, in fish fed β-glucan the PAMPs injections had less effects on CRP levels and complement activity in the serum than in control fed fish, suggesting that the 25 days of β-glucan immunostimulation was sufficient enough to reduce the effects of LPS and poly(I:C) injections. Results suggest that MacroGard® stimulated CRP and complement responses to PAMPs immunological challenges in common carp thus highlighting the beneficial β-glucan immunostimulant properties.
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  • 145
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    Variability in calcitic Mg/Ca and Sr/Ca ratios in clones of the benthic foraminifer Ammonia tepida (2014)
    Elsevier
    In:  Marine Micropaleontology, 107 . pp. 32-43.
    Details
    Publication Date: 2019-09-23
    Description: Biological activity introduces variability in element incorporation during calcification and thereby decreases the precision and accuracy when using foraminifera as geochemical proxies in paleoceanography. This so-called 'vital effect' consists of organismal and environmental components. Whereas organismal effects include uptake of ions from seawater and subsequent processing upon calcification, environmental effects include migration- and seasonality-induced differences. Triggering asexual reproduction and culturing juveniles of the benthic foraminifer Ammonia tepida under constant, controlled conditions allow environmental and genetic variability to be removed and the effect of cell-physiological controls on element incorporation to be quantified. Three groups of clones were cultured under constant conditions while determining their growth rates, size-normalized weights and single-chamber Mg/Ca and Sr/Ca using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Results show no detectable ontogenetic control on the incorporation of these elements in the species studied here. Despite constant culturing conditions, Mg/Ca varies by a factor of similar to 4 within an individual foraminifer while intra-individual Sr/Ca varies by only a factor of 1.6. Differences between clone groups were similar to the intra-clone group variability in element composition, suggesting that any genetic differences between the clone-groups studied here do not affect trace element partitioning. Instead, variability in Mg/Ca appears to be inherent to the process of bio-calcification itself. The variability in Mg/Ca between chambers shows that measurements of at least 6 different chambers are required to determine the mean Mg/Ca value for a cultured foraminiferal test with a precision of 〈= 10%
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  • 146
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    Seismic structure of the north-central Chilean convergent margin: Subduction erosion of a paleomagmatic arc (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (5). pp. 1523-1529.
    Details
    Publication Date: 2017-04-10
    Description: We study the erosive convergent margin of north-central Chile (at similar to 31 degrees S) by using high-resolution bathymetric, wide-angle refraction, and multichannel seismic reflection data to derive a detailed tomographic 2-D velocity-depth model. In the overriding plate, our velocity model shows that the lowermost crustal velocities beneath the upper continental slope are 6.0-6.5km/s, which are interpreted as the continental basement composed by characteristic metamorphic and igneous rocks of the Coastal Cordillera. Beneath the lower and middle continental slope, however, the presence of a zone of reduced velocities (3.5-5.0km/s) is interpreted as the outermost fore arc composed of volcanic rocks hydrofractured as a result of frontal and basal erosion. At the landward edge of the outermost fore arc, the bathymetric and seismic data provide evidence for the presence of a prominent trenchward dipping normal scarp (similar to 1km offset), which overlies a strong lateral velocity contrast from similar to 5.0 to similar to 6.0km/s. This pronounced velocity contrast propagates deep into the continental crust, and it resembles a major normal listric fault. We interpret this seismic discontinuity as the volcanic-continental basement contact of the submerged Coastal Cordillera characterized by a gravitational collapse of the outermost fore arc. Subduction erosion has, most likely, caused large-scale crustal thinning and long-term subsidence of the outermost fore arc.
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  • 147
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    Vertical export flux of metals in the Mediterranean Sea (2014)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 87 . pp. 14-23.
    Details
    Publication Date: 2016-11-02
    Description: We examined metal (Al, V. Cr, Mn, Fe, Ni, Cu, Zn, Cd and Pb) and particulate organic carbon (OC) concentrations of the marine vertical export flux at the DYFAMED time-series station in the Northwestern Mediterranean Sea. We present here the first data set of natural and anthropogenic metals from sediment trap moorings deployed at 1000 m-depth between 2003 and 2007 at the DYFAMED site. A highly significant correlation was observed between most metal concentrations, whatever the nature and emission source of the metal. Cu, Zn and Cd exhibit different behaviors, presumably due to their high solubility and complexation with organic ligands. The observed difference of atmospheric and marine fluxes in terms of temporal variability and elemental concentration suggests that dense water convection and primary production and not atmospheric deposition control the marine vertical export flux. This argument is strengthened by the fact that significant Saharan dust events did not result in concomitant marine vertical export fluxes nor did they generate significant changes in metal concentrations of trapped particles
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  • 148
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    The regional approach to the conservation and sustainable use of marine biodiversity in areas beyond national jurisdiction (2014)
    Elsevier
    In:  Marine Policy, 49 . pp. 109-117.
    Details
    Publication Date: 2017-09-12
    Description: Highlights: • Regional initiatives have recently developed in areas beyond national jurisdiction. • They advance the governance of these areas while the global discussions are on-going. • They however face many challenges, which should be tackled. • Global discussions and regional actions are two interconnected processes. Abstract: The development of regional initiatives for the protection of the environment is a cornerstone of international environmental policies. With regard to marine and coastal issues, this regionalisation has mainly been taking place through regional seas programmes and Regional Fisheries Management Organisations. Some regional initiatives and organisations have progressively extended their activities to areas beyond national jurisdiction. This paper aims at analysing these recent developments, highlighting their interests and challenges, and proposing options to strengthen the efficiency of regional actions in these areas. It also highlights the need to consider the global discussions on a possible new global agreement and the development of regional actions as two interconnected processes.
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  • 149
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    A sustainable development goal for the ocean and Coasts: Global ocean challenges benefit from regional initiatives supporting globally coordinated solutions (2014)
    Elsevier
    In:  Marine Policy, 49 . pp. 87-89.
    Details
    Publication Date: 2019-09-23
    Description: The ocean regulates the global climate, provides humans with natural resources such as food, materials, important substances, and energy, and is essential for international trade and recreational and cultural activities. Together with human development and economic growth, free access to, and availability of, ocean resources and services have exerted strong pressure on marine systems, ranging from overfishing, increasing resource extraction, and alteration of coastal zones to various types of thoughtless pollution. International cooperation and effective governance are required to protect the marine environment and promote the sustainable use of marine resources in such a way that due account can be taken of the environmental values of current generations and the needs of future generations. The high seas deserve particular attention since they suffer from a number of regulatory shortcomings due to the basic structures set out under international law. Against this backdrop, developing and agreeing on a focussed Sustainable Development Goal (SDG) specifically for the Ocean and Coasts could prove to be an essential element to provide guidance and a framework for regional implementation agreements.
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  • 150
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    Floating along buoyancy levels: Dispersal and survival of western Baltic fish eggs (2014)
    Elsevier
    In:  Progress in Oceanography, 122 . pp. 131-152.
    Details
    Publication Date: 2017-08-10
    Description: Highlights: • Belt Sea cod, plaice and flounder differentiate in their specific egg densities. • Ontogenetic egg density increase in stage IV cod eggs elevates modeled egg mortality. • Drift model indicates retention in western Baltic in cod and flatfish yolk sac larvae. • No eastward transport to Arkona Sea or Bornholm Sea until end of yolk sac stage. • Ambiguity in flounder egg density could reflect more complex population structure. Abstract: Vertical distribution is an important feature of pelagic fish eggs and yolk sac larvae impacting their survival and dispersal, especially in heterogeneous and highly variable estuarine environments like the Baltic Sea. Egg densities determining the vertical distribution pattern were experimentally ascertained for cod (Gadus morhua), plaice (Pleuronectes platessa) and flounder (Platichthys flesus) from the western Baltic Sea. Plaice eggs floated at lower mean (±standard deviation) density range (1.0136 ± 0.0007 g cm−3) compared to cod (1.0146 ± 0.0009 g cm−3) and flounder eggs (1.0160 ± 0.0015 g cm−3), which floated on the highest density level. In flounder egg diameter was significantly related to egg density and in cod a weak correlation could be found between egg dry weight and density. All other relationships between female size, egg size, egg dry weight and egg density were not significant for any of the species. Available egg density data for Baltic Sea cod, plaice and flounder are summarized considering ICES subdivisions and stock management units. A hydrodynamic drift modeling approach was applied releasing drifters in the Belt Sea continuously from December to May, covering the species’ spawning seasons. The model implemented experimentally derived egg density ranges and included ontogenetic egg density modifications for cod eggs, increasing egg density from a late egg development stage to first hatch. A drifter was removed from the model, i.e. considered dead, when its initially prescribed density value exceeded the density range available at the temporally resolved geographical positions along the drift trajectories. Highest survival occurred during releases in April and May but no cohorts survived if they were drifted east into the central Arkona Basin or the central Baltic Sea, irrespective of whether a major Baltic Inflow (1992/1993) or a stagnation-year (1987/1988) was simulated. The dispersal characteristics of the surviving yolk sac larvae of all three species reflected retention within the Belt Sea or northwards transport through the Great Belt into the Kattegat and partly into the Skagerrak. There was no successful transport to more eastern Baltic areas past a hypothetical line from the island of Moen (Denmark) to Kap Arkona on Rügen Island (Germany).
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  • 151
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    The influence of natural and anthropogenic factors on major stratospheric sudden warmings (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Atmospheres, 119 (13). pp. 8117-8136.
    Details
    Publication Date: 2019-06-28
    Description: Major stratospheric sudden warmings are prominent disturbances of the Northern Hemisphere polar winter stratosphere. Understanding the factors controlling major warmings is required, since the associated circulation changes can propagate down into the troposphere and affect the surface climate, suggesting enhanced prediction skill when these processes are accurately represented in models. In this study we investigate how different natural and anthropogenic factors, namely, the quasi-biennial oscillation (QBO), sea surface temperatures (SSTs), anthropogenic greenhouse gases, and ozone-depleting substances, influence the frequency, variability, and life cycle of major warmings. This is done using sensitivity experiments performed with the National Center for Atmospheric Research's Community Earth System Model (CESM). CESM is able to simulate the life cycle of major warmings realistically. The QBO strengthens the climatological stratospheric polar night jet (PNJ) and significantly reduces the frequency of major warmings through reduction of planetary wave propagation into the PNJ region. Variability in SSTs weakens the PNJ and significantly increases the major warming frequency due to enhanced wave forcing. Even extreme climate change conditions (RCP8.5 scenario) do not influence the total frequency but determine the prewarming phase of major warmings. The amplitude and duration of major warmings seem to be mainly determined by internal stratospheric variability. We also suggest that SST variability, two-way ocean/atmosphere coupling, and hence the memory of the ocean are needed to reproduce the observed tropospheric negative Northern Annular Mode pattern after major warmings.
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  • 152
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    Modeling the biogeochemical seasonal cycle in the Strait of Gibraltar (2014)
    Elsevier
    In:  Journal of Marine Systems, 139 . pp. 348-361.
    Details
    Publication Date: 2017-07-13
    Description: Highlights: • Strait processes trigger phytoplankton production and biomass in the Atlantic Inflow. • Strait processes may modify original phytoplankton succession in the Atlantic Inflow. • Model shows that nanoflag. may dominate during spring/autumn, picophytopl. in summer. • Strait processes lead in a constant supply of nutrients and biomass to Alboran Sea. Abstract: A physical-biological coupled model was used to estimate the effect of the physical processes at the Strait of Gibraltar over the biogeochemical features of the Atlantic Inflow (AI) towards the Mediterranean Sea. This work was focused on the seasonal variation of the biogeochemical patterns in the AI and the role of the Strait; including primary production and phytoplankton features. As the physical model is 1D (horizontal) and two-layer, different integration methods for the primary production in the Biogeochemical Fluxes Model (BFM) have been evaluated. An approach based on the integration of a production-irradiance function was the chosen method. Using this Plankton Functional Type model (BFM), a simplified phytoplankton seasonal cycle in the AI was simulated. Main results included a principal bloom in spring dominated by nanoflagellates, whereas minimum biomass (mostly picophytoplankton) was simulated during summer. Physical processes occurring in the Strait could trigger primary production and raise phytoplankton biomass (during spring and autumn), mainly due to two combined effects. First, in the Strait a strong interfacial mixing (causing nutrient supply to the upper layer) is produced, and, second, a shoaling of the surface Atlantic layer occurs eastward. Our results show that these phenomena caused an integrated production of 105 g C m− 2 year− 1 in the eastern side of the Strait, and would also modify the proportion of the different phytoplankton groups. Nanoflagellates were favored during spring/autumn while picophytoplankton is more abundant in summer. Finally, AI could represent a relevant source of nutrients and biomass to Alboran Sea, fertilizing the upper layer of this area with 4.95 megatons nitrate year− 1 (79.83 gigamol year− 1) and 0.44 megatons C year− 1. A main advantage of this coupled model is the capability of solving relevant high-resolution processes as the tidal forcing without expensive computing requirements, allowing to assess the effect of these phenomena on the biogeochemical patterns at longer time scales.
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  • 153
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    An Arctic perspective on dating Mid-Late Pleistocene environmental history (2014)
    Elsevier
    In:  Quaternary Science Reviews, 92 . pp. 9-31.
    Details
    Publication Date: 2016-09-16
    Description: To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required, not least for correlation to extra-Arctic records. In this paper we discuss, from an Arctic perspective, methods and correlation tools that are commonly used to date Arctic Pleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, with focus on factors that affect the possibility and quality of dating, and support this overview by examples of application of modern dating methods to Arctic terrestrial and marine sequences. Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided by radiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning. Recent advances in dating technology, calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material (i.e. foraminifera for C-14, and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolution of most dating methods. Consequently improving the accuracy and precision (analytical and geological uncertainty) of dating methods through technological advances and better understanding of processes are important tasks for the future. Another challenge is to better integrate marine and terrestrial records, which could be aided by targeting continental shelf and lake records, exploring proxies that occur in both settings, and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers.
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  • 154
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    Global patterns of phytoplankton nutrient and light colimitation inferred from an optimality-based model (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (7). pp. 648-661.
    Details
    Publication Date: 2019-09-23
    Description: The widely used concept of constant ”Redfield” phytoplankton stoichiometry is often applied for estimating which nutrient limits phytoplankton growth in the surface ocean. Culture experiments, in contrast, show strong relations between growth conditions and cellular stoichiometry with often substantial deviations from Redfield stoichiometry. Here we investigate to what extent both views agree by analyzing remote sensing and in situ data with an optimality-based model of nondiazotrophic phytoplankton growth in order to infer seasonally varying patterns of colimitation by light, nitrogen (N), and phosphorus (P) in the global ocean. Our combined model-data analysis suggests strong N and N-P colimitation in the tropical ocean, seasonal light, and N-P colimitation in the Northern Hemisphere, and strong light limitation only during winter in the Southern Ocean. The eastern equatorial Pacific appears as the only ocean area that is essentially not limited by N, P, or light. Even though our optimality-based approach specifically accounts for flexible stoichiometry, inferred patterns of N and P limitation are to some extent consistent with those obtained from an analysis of surface inorganic nutrients with respect to the Redfield N:P ratio. Iron is not part of our analysis, implying that we cannot accurately predict N cell quotas in high-nutrient, low-chlorophyll regions. Elsewhere, we do not expect a major effect of iron on the relative distribution of N, P, and light colimitation areas. The relative importance of N, P, and light in limiting phytoplankton growth diagnosed here by combining observations and an optimal growth model provides a useful constraint for models used to predict future marine biological production under changing environmental conditions.
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  • 155
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    Trace metal distribution in the Atlantis II Deep (Red Sea) sediments (2014)
    Elsevier
    In:  Chemical Geology, 386 . pp. 80-100.
    Details
    Publication Date: 2019-09-23
    Description: The Atlantis II Deep is one of the only locations on the modern seafloor where active formation of a brine pool-type stratiform ore deposit can be studied. The presence of the brine pool causes retention of the hydrothermally released metals within the brine covered area, resulting in the accumulation of 90 Mt of low-grade metalliferous sediment (2.06% Zn, 0.46% Cu, 41 g/t Ag, and 0.5 g/t Au; Guney et al., 1988). Almost all metals are derived from hydrothermal input, but some are also derived from seawater (e.g., Mo), pelagic phytoplankton (Ni) and detrital input (Cr). The hydrothermal fluid that is vented into the pool is rich in metals but relatively low in reduced sulfur compared to open ocean black smokers. Metals are deposited as sulfides from the cooling hydrothermal fluid but also by adsorption onto non-sulfidic “surface-active” particles (Si–Fe-OOH) in the brine pool. An unexpected increase in the Cu/Zn ratio of the sediments with distance from the vent source(s) may reflect pulses of higher-temperature venting and increased Cu fluxes to the brine pool, which are recorded as higher Cu/Zn ratios in the distal sediments or, alternatively, more efficient adsorption of Cu to Fe-OOH particles in the distal brine. During early diagenesis (a few thousand years) metals that are loosely bound to surface-active particles in the sediment apparently react with H2S to form sulfides. Proximal to the inferred vents, the ambient pore water is highly concentrated in trace metals such as Cd, Ag and Hg that are incorporated in diagenetic sulfides, including chalcopyrite and sphalerite. At greater distance from the vents, trace metals such as Mo, As, and Ga are taken up by framboidal pyrite. High concentrations of Au (up to 3 ppm) are found in both proximal and distal metalliferous sediments, indicating that both primary deposition with sulfides and adsorption by diagenetic pyrite are important depositional processes. Some of the inferred pathways for metal precipitation in the Atlantis II Deep sediments, especially adsorption onto surface-active particles and subsequent incorporation in sulfides during diagenesis, may have been important unrecognized processes for metal accumulation in ancient stratiform ore deposits thought to have formed in brine pools.
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  • 156
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    Quantifying tidally-driven benthic oxygen exchange across permeable sediments: An aquatic eddy correlation study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (10). pp. 6918-6932.
    Details
    Publication Date: 2018-02-26
    Description: Continental shelves are predominately (~70%) covered with permeable, sandy sediments. While identified as critical sites for intense oxygen, carbon, and nutrient turnover, constituent exchange across permeable sediments remains poorly quantified. The central North Sea largely consists of permeable sediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigate the benthic O2 exchange across the permeable North Sea sediments using a combination of in situ microprofiles, a benthic chamber, and aquatic eddy correlation. Tidal bottom currents drive the variable sediment O2 penetration depth (from ~3 to 8 mm) and the concurrent turbulence-driven 25-fold variation in the benthic sediment O2 uptake. The O2 flux and variability were reproduced using a simple 1-D model linking the benthic turbulence to the sediment pore water exchange. The high O2 flux variability results from deeper sediment O2 penetration depths and increased O2 storage during high velocities, which is then utilized during low-flow periods. The study reveals that the benthic hydrodynamics, sediment permeability, and pore water redox oscillations are all intimately linked and crucial parameters determining the oxygen availability. These parameters must all be considered when evaluating mineralization pathways of organic matter and nutrients in permeable sediments.
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  • 157
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    From the lavas to the gabbros: 1.25 km of geochemical characterization of upper oceanic crust at ODP/IODP Site 1256, eastern equatorial Pacific (2014)
    Elsevier
    In:  Lithos (210/211). pp. 289-312.
    Details
    Publication Date: 2020-10-20
    Description: Here we present trace element and Sr-Nd-Hf-Pb (double spike) isotopic data covering the entire igneous section of oceanic crust drilled at Ocean Drilling Program (ODP)/Integrated Ocean Drilling Program (IODP) Site 1256 on the Cocos Plate. The penetrated interval extends from the upper lavas through the sheeted dike complex to the gabbroic plutonic rocks, formed during superfast spreading at the mid-Miocene equatorial East Pacific Rise. The data are used to characterize the effects of chemical alteration, resulting from convection of seawater and hydrothermal fluids, on the trace element and isotopic composition of oceanic crust. Compared to normal mid-ocean-ridge basalt, the igneous basement of Site 1256 (Holes 1256C/D) is isotopically slightly enriched but shows only narrow downhole variations in Nd-Hf-Pb isotope ratios: 143Nd/144Nd = 0.513089 ± 0.000028 (2σ), 176Hf/177Hf = 0.283194 ± 0.000033 (2σ), 206Pb/204Pb = 18.61 ± 0.11 (2σ), 207Pb/204Pb = 15.521 ± 0.014 (2σ), 208Pb/204Pb = 38.24 ± 0.15 (2σ). We believe that this minor variability is mainly of primary (magmatic) origin. The Sr isotopic composition shows considerably larger variation and, as expected, serves as sensitive tracer of seawater influence, which is particularly pronounced in the lava-dike transition zone and the sheeted dikes. The seawater influence is most prominent in a highly metal sulfide-enriched breccia layer encountered in the transition zone with 87Sr/86Sr of ~ 0.706, indicating a maximum water-rock mixing ratio of ~ 12. However, compared to the igneous section drilled at Site 504 (Hole 504B), which formed at intermediate, i.e., slower spreading rates at the Galápagos Spreading Center and hosting a much thicker sulfide-rich stockwork zone, the average intensity of water-rock interaction is lower. This is expressed by lesser mobility of base metals, narrower variability of alteration-sensitive incompatible elements, and less radiogenic Sr isotopic compositions on average at Site 1256. The amount of metal sulfide precipitation seems to be positively correlated with the degree of hydrothermal overprint. The less intense alteration of the Site 1256 transition zone, compared to Site 504, most likely reflects the higher rate of spreading, eventually resulting in a shorter period of time of continuous exposure to hydrothermal convection at the ridge crest. The observed seafloor alteration, leading to modified radiogenic parent/daughter ratios in the Site 1256 rocks, is ultimately not sufficient to develop time-integrative high 206Pb/204Pb and moderate 87Sr/86Sr ratios, as being characteristic of the HIMU (high μ = high 238U/204Pb) mantle signature proposed to originate from hydrothermally altered, subducted oceanic crust. Therefore, additional modification during the subduction process must be taken into account.
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  • 158
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    Hydrothermal carbonate chimneys from a continental rift (Afar Rift): Mineralogy, geochemistry, and mode of formation (2014)
    Elsevier
    In:  Chemical Geology, 387 . pp. 87-100.
    Details
    Publication Date: 2019-09-23
    Description: Carbonate chimney-like deposits up to 60 m high are scattered or arranged in rows at the shores of a desiccating hypersaline and alkaline lake from a continental rift setting (Lake Abhé, Afar Rift, Djibouti). The chimneys formed sub-aqueously in the lake water body at a higher water level than observed today. Alternating calcite and low-Mg calcite + silica concentric layers compose the chimney structures. Mineralogical and geochemical investigations of the chimneys, lake water, and hot spring (hydrothermal) fluids suggest that the chimneys are a result of rapid carbonate precipitation during the mixing of hydrothermal fluids with lake water. In contrast to the hot spring fluid, lake water is enriched in HREE and possesses a pronounced positive Ce anomaly, features that are preserved in the carbonate chimney layers. Mixing calculations based on Sr-isotope and concentration data indicate a hydrothermal fluid contribution of ~ 45% in the chimney interior, which decreases to ~ 4% in the external chimney layer. Sr in the hydrothermal fluids is predominantly leached from the underlying volcanic rocks, whereas the lake's Sr budget is dominated by riverine input. Considering the fluid mixing ratios calculated by Sr-data, the measured C and O isotope compositions indicate that chimney carbonates precipitated at temperatures between 14 °C (internal part) and 22 °C (external part) with δ13C-carbonate mainly controlled by isotope equilibrium exchange of lake water with atmospheric CO2. The low-Mg calcite layers, including the outermost layer, have enhanced signals of lake water inheritance based on elevated concentrations of immobile elements, ΣREE, and Sr and Ca isotope compositions. Ca-isotope data reveal that internal chimney layers formed by non-equilibrium calcite precipitation with a predominantly hydrothermal Ca source. The external low-Mg calcite layer received Ca contributions from both hydrothermal fluid and lake water, with the latter being the dominant Ca source. Highly positive δ44/40Ca of lake water likely reflects non-equilibrium Ca-carbonate precipitation during lake water evaporation with resulting 44Ca enrichment of residual lake water. The strong degree of 44Ca enrichment may point towards multiple lake drying and Ca-reservoir depletion events. Coupled C–O–Ca-isotope data of the sampled carbonate chimney suggest late-stage (low-temperature) hydrothermal carbonate chimney formation during strongly evaporative lake conditions at the time of low-Mg calcite precipitation. U–Th age dating suggests that the chimneys formed no earlier than 0.82 kyr BP (0.28 ± 0.54).
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  • 159
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    Neodymium isotopes and concentrations in Caribbean seawater: Tracing water mass mixing and continental input in a semi-enclosed ocean basin (2014)
    Elsevier
    In:  Earth and Planetary Science Letters, 406 . pp. 174-186.
    Details
    Publication Date: 2018-06-08
    Description: We present the first full water column Nd isotope (εNd) and concentration data for Caribbean seawater, as well as for stations close to the Orinoco River mouth and in the Florida Straits. The surface inflow into the southeastern Caribbean via the Guyana Current is characterized by an εNdsignature of −10.9, which is a consequence of the mixing of relatively unradiogenic εNdsignatures (−13.6) supplied by the Orinoco River with contributions from the Amazon River (∼−10). Despite the proximity to land, sub-surface and intermediate waters within the Caribbean largely retain the εNdsignatures of their source water masses in the Atlantic. In contrast, the deep waters of the Caribbean show εNdsignatures at least 3 εNdunits more radiogenic than the inflowing Upper North Atlantic Deep Water (UNADW). A εNdshift from −13 to −9.7 can be explained by addition of radiogenic Nd to the deep Caribbean through weathering inputs from land. However, in order to balance such large shifts in εNdwith at the same time modest increases in Nd concentrations, Nd must also be removed from seawater within the basin. It is suggested that the long residence time of deep waters in the Caribbean allows significant interaction of seawater with sinking particles and seafloor sediments resulting in more radiogenic values. These findings have implications for the use of εNdas a proxy for paleocirculation in restricted basins, in which the residence times of the deep waters are long.
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  • 160
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    Seasonal spatial pattern and community structure of zooplankton in waters off the Baleares archipelago (Central Western Mediterranean) (2014)
    Elsevier
    In:  Journal of Marine Systems, 138 . pp. 82-94.
    Details
    Publication Date: 2017-07-13
    Description: We investigated the zooplankton community in two different areas of the Baleares Archipelago, Western Mediterranean, using data obtained in autumn (December 2009) and summer (July 2010). Micrometazooplankton and mesozooplankton samples were collected in the 0-200 m layer above the shelf (200 m) and the slope (900 m) of each area by a 53 mu m and a 200 mu m mesh size net respectively. The zooplankton biomass (expressed as dry weight) was higher in autumn than in summer (930 and 6.95 mg m(-3), respectively) with an important contribution of micrometazooplankters (29% and 41% of total biomass respectively). The latter fraction overwhelmed in the entire metazooplankton abundance, suggesting a non-negligible role as potential food for fish in the epipelagic waters of the Baleares archipelago. The abundance of micrometazooplankton was two-fold higher in December (3581 ind. m(-3)) than in July (1585 ind. m(-3)), represented mainly by small copepods and nauplii. Likewise, the mesozooplankton community showed smaller difference between months (554 and 390 ind. m(-3), in December and July). Micrometazooplankton abundance was higher in the northern area than in the southern area during autumn, probably linked to the presence of a front, while the opposite was found in summer. In both periods and areas copepods dominated, and within the highly diverse community ten species and their juveniles accounted for 70% of the community. In both areas, Clausocalanus (C pergens + paululus and C. arcuicornis), Paracalanus parvus, Oncaea media, Oithona plumifera and Acartia clausi were abundant in autumn, whereas Centropages typicus, Temora stylifera and Mecynocera clausi were mainly present in summer. ANOSIM analysis revealed significant differences in the mesozooplankton community composition between months while differences between areas were detected only in summer
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    A Late Glacial–Early Holocene multiproxy record from the eastern Fram Strait, Polar North Atlantic (2014)
    Elsevier
    In:  Marine Geology, 355 . pp. 15-26.
    Details
    Publication Date: 2017-06-23
    Description: The paleoceanographic development of the eastern Fram Strait during the transition from the cold Late Glacial and into the warm Early Holocene was elucidated via a multiproxy study of a marine sediment record retrieved at the western Svalbard slope. The multiproxy study includes analyses of planktic foraminiferal fauna, bulk sediment grain size and CaCO3 content in addition to Mg/Ca ratios and stable isotopes (delta C-13 and delta O-18) measured on the planktic foraminifer Neogloboquadrina pachyderma. Furthermore paleosubsurface water temperatures were reconstructed via Mg/Ca ratios (sSST(Mg/Ca)) and transfer functions (sSST(Transfer)) enabling comparison between the two proxies within a single record. The age model was constrained by four accelerator mass spectrometry (AMS) C-14 dates. From 14,000 to 10,300 cal yr B.P. N. pachyderma dominated the planktic fauna and cold polar sea surface conditions existed. The period was characterized by extensive sea ice cover, iceberg transport and low subsea surface temperatures (sSST(Transfer) similar to 2.1 degrees C; sSST(Mg/Ca) similar to 3.5 degrees C) resulting in restricted primary production. Atlantic Water inflow was reduced compared to the present-day and likely existed as a subsurface current. At ca. 10,300 cal yr B.P. Atlantic Water inflow increased and the Arctic Front retreated north-westward resulting in increased primary productivity, higher foraminiferal fluxes and a reduction in sea ice cover and iceberg transport. The fauna rapidly became dominated by the subpolar planktic foraminifer Turborotalita quinqueloba and summer sSST(Transfer) increased by similar to 3.5 degrees C. Concurrently, the sSST(Mg/Ca) recorded by N. pachyderma rose only similar to 0.5 degrees C. From ca. 10,300 to 8600 cal yr B.F. the average sSST(Mg/Ca) and sSST(Transfer) were similar to 4.0 degrees C and similar to 55 degrees C, respectively. The relatively modest change in sSST(Mg/Ca) compared to sSST(Transfer) can probably be tied to a change of the main habitat depth and/or shift in the calcification season for N. pachyderma during this period.
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  • 162
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    Rare earth elements as indicators of hydrothermal processes within the East Scotia subduction zone system (2014)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 140 . pp. 20-38.
    Details
    Publication Date: 2017-06-19
    Description: The East Scotia subduction zone, located in the Atlantic sector of the Southern Ocean, hosts a number of hydrothermal sites in both back-arc and island-arc settings. High temperature (〉348 °C) ‘black smoker’ vents have been sampled at three locations along segments E2 and E9 of the East Scotia back-arc spreading ridge, as well as ‘white smoker’ (〈212 °C) and diffuse (〈28 °C) hydrothermal fluids from within the caldera of the Kemp submarine volcano. The composition of the endmember fluids (Mg = 0 mmol/kg) is markedly different, with pH ranging from 〈1 to 3.4, [Cl−] from ∼90 to 536 mM, [H2S] from 6.7 to ∼200 mM and [F−] from 35 to ∼1000 μM. All of the vent sites are basalt- to basaltic andesite-hosted, providing an ideal opportunity for investigating the geochemical controls on rare earth element (REE) behaviour. Endmember hydrothermal fluids from E2 and E9 have total REE concentrations ranging from 7.3 to 123 nmol/kg, and chondrite-normalised distribution patterns are either light REE-enriched (LaCN/YbCN = 12.8–30.0) with a positive europium anomaly (EuCN/Eu∗CN = 3.45–59.5), or mid REE-enriched (LaCN/NdCN = 0.61) with a negative Eu anomaly (EuCN/Eu∗CN = 0.59). By contrast, fluids from the Kemp Caldera have almost flat REE patterns (LaCN/YbCN = 2.1–2.2; EuCN/Eu∗CN = 1.2–2.2). We demonstrate that the REE geochemistry of fluids from the East Scotia back-arc spreading ridge is variably influenced by ion exchange with host minerals, phase separation, competitive complexation with ligands, and anhydrite deposition, whereas fluids from the Kemp submarine volcano are also affected by the injection of magmatic volatiles which enhances the solubility of all the REEs. We also show that the REE patterns of anhydrite deposits from Kemp differ from those of the present-day fluids, potentially providing critical information about the nature of hydrothermal activity in the past, where access to hydrothermal fluids is precluded.
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  • 163
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    Sulfate reduction and methane oxidation activity below the sulfate-methane transition zone in Alaskan Beaufort Sea continental margin sediments: Implications for deep sulfur cycling (2014)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 144 . pp. 217-237.
    Details
    Publication Date: 2017-06-19
    Description: Two ∼6 m long sediment cores were collected along the ∼300 m isobath on the Alaskan Beaufort Sea continental margin. Both cores showed distinct sulfate-methane transition zones (SMTZ) at 105 and 120 cm below seafloor (cmbsf). Sulfate was not completely depleted below the SMTZ but remained between 30 and 500 μM. Sulfate reduction and anaerobic oxidation of methane (AOM) determined by radiotracer incubations were active throughout the methanogenic zone. Although a mass balance could not explain the source of sulfate below the SMTZ, geochemical profiles and correlation network analyses of biotic and abiotic data suggest a cryptic sulfur cycle involving iron, manganese and barite. Inhibition experiments with molybdate and 2-bromoethanesulfonate (BES) indicated decoupling of sulfate reduction and AOM and competition between sulfate reducers and methanogens for substrates. While correlation network analyses predicted coupling of AOM to iron reduction, the addition of manganese or iron did not stimulate AOM. Since none of the classical archaeal anaerobic methanotrophs (ANME) were abundant, the involvement of unknown or unconventional phylotypes in AOM is conceivable. The resistance of AOM activity to inhibitors implies deviation from conventional enzymatic pathways. This work suggests that the classical redox cascade of electron acceptor utilization based on Gibbs energy yields does not always hold in diffusion-dominated systems, and instead biotic processes may be more strongly coupled to mineralogy.
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  • 164
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    The proteome of Atlantic herring (Clupea harengus L.) larvae is resistant to elevated pCO2 (2014)
    Elsevier
    In:  Marine Pollution Bulletin, 86 (1-2). pp. 154-160.
    Details
    Publication Date: 2019-09-23
    Description: Elevated anthropogenic pCO2 can delay growth and impair otolith structure and function in the larvae of some fishes. These effects may concurrently alter the larva’s proteome expression pattern. To test this hypothesis, Atlantic herring larvae were exposed to ambient (370 μatm) and elevated (1800 μatm) pCO2 for one-month. The proteome structure of the larvae was examined using a 2-DE and mass spectrometry. The length of herring larvae was marginally less in the elevated pCO2 treatment compared to the control. The proteome structure was also different between the control and treatment, but only slightly: the expression of a small number of proteins was altered by a factor of less than 2-fold at elevated pCO2. This comparative proteome analysis suggests that the proteome of herring larvae is resilient to elevated pCO2. These observations suggest that herring larvae can cope with levels of CO2 projected for near future without significant proteome-wide changes.
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  • 165
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    On the isotope composition of reactive iron in marine sediments: Redox shuttle versus early diagenesis (2014)
    Elsevier
    In:  Chemical Geology, 389 . pp. 48-59.
    Details
    Publication Date: 2019-09-23
    Description: The isotope composition of reactive iron (Fe) in marine sediments and sedimentary rocks is a promising tool for identifying Fe sources and sinks across ocean basins. In addition to cross-basinal Fe redistribution, which can modify Fe isotope signatures, Fe minerals also undergo diagenetic redistribution during burial. The isotope fractionation associated with this redistribution does not affect the bulk isotope composition, but complicates the identification of mineral-specific isotope signatures. Here, we present new Fe isotope data for Peru margin sediments and revisit previously published data for sediments from the California margin to unravel the impact of early diagenesis on Fe isotope compositions of individual Fe pools. Sediments from oxic California margin sites are dominated by terrigenous Fe supply with Fe release from sediments having a negligible influence on the solid phase Fe isotope composition. The highly reactive Fe pool (sum of Fe bound to (oxyhydr)oxide, carbonate, monosulfide and pyrite) of these sediments has a light isotope composition relative to the bulk crust, which is consistent with earlier studies showing that continental weathering shifts the isotope composition of Fe (oxyhydr)oxides to lighter values. Ferruginous sedimentswithin the Peruvian oxygen minimumzone are depleted in Fe relative to the lithogenic background, which we attribute to extensive Fe release to the water column. The remaining highly reactive Fe pool has a heavier isotope composition compared to California margin sediments. This observation is in agreement with the general notion of an isotopically light benthic Fe efflux. Most of the reactive Fe delivered and retained in the sediment is transferred into authigenic mineral phases within the topmost 10 to 20 cm of the sediments. We observe a first-order relationship between the extent of pyritization of Fe monosulfide and the isotope composition of authigenic pyrite. With increasing pyritization, the isotope composition of authigenic pyrite approaches the isotope composition of the highly reactive Fe pool. We argue that the isotope composition of authigenic pyrite or other Fe minerals that may undergo pyritization may only be used to trace water column sources or sinks if the extent of pyritization is separately evaluated and either close to 100% or 0%. Alternatively, one may calculate the isotope composition of the highly reactive Fe pool, thereby avoiding isotope effects due to internal diagenetic redistribution. In depositional settings with high Fe but lowsulfide concentrations, source and sink signatures in the isotope composition of the highly reactive Fe pool may be compromised by sequestration of Fe within authigenic silicate minerals. Authigenic silicate minerals appear to be an important burial phase for reactive Fe below the Peruvian oxygen minimum zone.
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  • 166
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    Seismic stratigraphy of Lake Van, eastern Turkey (2014)
    Elsevier
    In:  Quaternary Science Reviews, 104 . pp. 63-84.
    Details
    Publication Date: 2019-09-24
    Description: More than 1500 km of multi-channel seismic reflection profiles combined with ICDP (International Continental Scientific Drilling Program) drilling data, provide important insights into the stratigraphic evolution of Lake Van, eastern Turkey. Three major basins (Tatvan, Northern and the Deveboynu basins) comprise the main lake basin and are separated by morphological highs (Ahlat ridge and Northern ridge). Moreover, NE–SW faults, parallel to the general tectonic lineament of the area, dominate the entire basin and are in charge of creating graben and half-graben structures. Well-developed prograding deltaic sequences on top of the basement were recognized by seismic stratigraphy analysis. Most likely, they formed during the initial flooding of Lake Van ∼600 ka. The Tatvan basin sediments are dominated by mass-flow deposits of various origins alternating with undisturbed lacustrine sediments including distinct tephra layers. Faulting along the Tatvan basin margins may have triggered margin-wide slope failures. Ahlat ridge started to form between ca 340 ka–290 ka. Since then, Ahlat ridge was sheltered from major mass-flows due to its elevation. Hence, slow lacustrine sedimentation has prevailed throughout lake history on Ahlat ridge, which was the location of the main drill site during the ICDP. Several lake level fluctuations are evident on the eastern slope area but the deep basins were permanently covered by water. A significant lake-level low stand (ca 600 ka BP) was found at ∼610 m below present lake level. The setting of the lake changed at about 30 ka. Tectonic activity appears to have waned significantly as the mass-transport deposition decreased across the Tatvan basin while normal undisturbed lacustrine sedimentation prevailed. A different setting is found in the Northern basin from ca 90 ka to Present, especially due to the strong influx of mostly volcaniclastic turbidites causing sedimentation rates to be about 3.5 times higher (drill Site 1), than at Site 2 (Ahlat ridge).
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  • 167
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    Magnesium retention on the soil exchange complex controlling Mg isotope variations in soils, soil solutions and vegetation in volcanic soils, Iceland (2014)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 125 . pp. 110-130.
    Details
    Publication Date: 2015-01-09
    Description: Understanding the biogeochemical cycle of magnesium (Mg) is not only crucial for terrestrial ecology, as this element is a key nutrient for plants, but also for quantifying chemical weathering fluxes of Mg and associated atmospheric CO2 consumption, requiring distinction of biotic from abiotic contributions to Mg fluxes exported to the hydrosphere. Here, Mg isotope compositions are reported for parent basalt, bulk soils, clay fractions, exchangeable Mg, seasonal soil solutions, and vegetation for five types of volcanic soils in Iceland in order to improve the understanding of sources and processes controlling Mg supply to vegetation and export to the hydrosphere. Bulk soils (δ26Mg = -0.40±0.11‰) are isotopically similar to the parent basalt (δ26Mg = -0.31‰), whereas clay fractions (δ26Mg = -0.62±0.12‰), exchangeable Mg (δ26Mg = -0.75 ± 0.14 ‰), and soil solutions (δ26Mg = -0.89 ± 0.16 ‰) are all isotopically lighter than the basalt. These compositions can be explained by a combination of mixing and isotope fractionation processes on the soil exchange complex. Successive adsorption-desorption of heavy Mg isotopes leads to the preferential loss of heavy Mg from the soil profile, leaving soils with light Mg isotope compositions relative to the parent basalt. Additionally, external contributions from sea spray and organic matter decomposition result in a mixture of Mg sources on the soil exchange complex. Vegetation preferentially takes up heavy Mg from the soil exchange complex (Δ26Mgplant-exch = +0.50±0.09‰), and changes in δ26Mg in vegetation reflect changes in bioavailable Mg sources in soils. This study highlights the major role of Mg retention on the soil exchange complex amongst the factors controlling Mg isotope variations in soils and soil solutions, and demonstrates that Mg isotopes provide a valuable tool for monitoring biotic and abiotic contributions of Mg that is bioavailable for plants and is exported to the hydrosphere.
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  • 168
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    The spatial-temporal patterns of Asian summer monsoon precipitation in response to Holocene insolation change: a model-data synthesis (2014)
    Elsevier
    In:  Quaternary Science Reviews, 85 . pp. 47-62.
    Details
    Publication Date: 2019-09-23
    Description: Highlights: • Slice and transient simulations of Holocene climate change were performed. • Spatial–temporal patterns of Holocene Asian summer precipitation are investigated. • A tripole pattern of summer precipitation can be seen over monsoonal Asia. • Insolation change is a key factor for Holocene Asian summer monsoon change. • Internal feedbacks are important to Holocene Asian summer precipitation changes. Abstract: Paleoclimate proxy records of precipitation/effective moisture show spatial–temporal inhomogeneous over Asian monsoon and monsoon marginal regions during the Holocene. To investigate the spatial differences and diverging temporal evolution over monsoonal Asia and monsoon marginal regions, we conduct a series of numerical experiments with an atmosphere–ocean–sea ice coupled climate model, the Kiel Climate Model (KCM), for the period of Holocene from 9.5 ka BP to present (0 ka BP). The simulations include two time-slice equilibrium experiments for early Holocene (9.5 ka BP) and present-day (0 ka BP), respectively and one transient simulation (HT) using a scheme for model acceleration regarding to the Earth's orbitally driven insolation forcing for the whole period of Holocene (from 9.5 to 0 ka BP). The simulated summer precipitation in the equilibrium experiments shows a tripole pattern over monsoonal Asia as depicted by the first modes of empirical orthogonal function (EOF1) of H0K and H9K. The transient simulation HT exhibits a wave train pattern in the summer precipitation across the Asian monsoon region associated with a gradually decreased trend in the strength of Asian summer monsoon, as a result of the response of Asian summer monsoon system to the Holocene orbitally-forced insolation change. Both the synthesis of multi-proxy records and model experiments confirm the regional dissimilarity of the Holocene optimum precipitation/effective moisture over the East Asian summer monsoon region, monsoon marginal region, and the westerly-dominated areas, suggesting the complex response of the regional climate systems to Holocene insolation change in association with the internal feedbacks within climate system, such as the air-sea interactions associated with the El Nino/Southern Oscillation (ENSO) and shift of the Intertropical Convergence Zone (ITCZ) in the evolution of Asian summer monsoon during the Holocene.
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  • 169
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    The regulatory loop between gut cholecystokinin and tryptic enzyme activity in sea bass (Dicentrarchus labrax) larvae is influenced by different feeding regimes and trigger substances (2014)
    Elsevier
    In:  Aquaculture, 420/421 . pp. 139-146.
    Details
    Publication Date: 2017-12-12
    Description: Improving the understanding of digestive physiology in first feeding larvae is a prerequisite for advancing diet formulations and feeding protocols. In marine fish larvae that lack a stomach at first-feeding trypsin represents the main proteolytic enzyme. CCK is one of the key regulators of digestive enzyme secretion in adult vertebrates and current knowledge suggests that it is also involved in early stages of teleosts, although this may vary between species. Here, we investigated the influence of Artemia and a commercial microdiet on the ontogenetic development of tryptic enzyme activity as an indicator for digestive capacity in first-feeding sea bass. In order to examine the regulation and feedback mechanisms in the digestive tract we followed the response of gut CCK and tryptic enzyme activity during a one-day observation depending on the feeding regime at 23 days post hatch. Larvae fed the microdiet showed a higher tryptic enzyme activity, probably as an adaptation to the higher content in complex protein in the diet. The plant protein phytohemagglutinin (PHA), added to the microdiet as a potential stimulator for the digestive system, did not induce elevated tryptic enzyme activity nor was it beneficial for growth. This was possibly due to adverse effects of too high doses. We observed an endogenous rhythm of CCK over the day, independent of the dietary treatment or short-term fasting. Higher tryptic enzyme activity in larvae fed Artemia during the day might indicate a better stimulation by live prey in the digestive tract or the superiority of a discontinuous feeding schedule in this group. We suggest that a reduction in tryptic enzyme activity after several feeding events indicates a limit in diurnal digestive capacity. Sea bass larvae are apparently able to adapt to the feeding schedule by synchronizing the tryptic enzyme activity like adult fish.
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  • 170
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    Beyond the Black Sea paradigm: The sedimentary fingerprint of an open-marine iron shuttle (2014)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 127 . pp. 368-380.
    Details
    Publication Date: 2019-09-23
    Description: We present iron (Fe) concentration and Fe isotope data for a sediment core transect across the Peru upwelling area, which hosts one of the ocean’s most pronounced oxygen minimum zones (OMZs). The lateral progression of total Fe to aluminum ratios (FeT/Al) across the continental margin indicates that sediments within the OMZ are depleted in Fe whereas sediments below the OMZ are enriched in Fe relative to the lithogenic background. Rates of Fe loss within the OMZ, as inferred from FeT/Al ratios and sedimentation rates, are in agreement with benthic flux data that were calculated from pore water concentration gradients. The mass of Fe lost from sediments within the OMZ is within the same order of magnitude as the mass of Fe accumulating below the OMZ. Taken together, our data are in agreement with a shuttle scenario where Fe is reductively remobilized from sediments within the OMZ, laterally transported within the anoxic water column and re-precipitated within the more oxic water below the OMZ. Sediments within the OMZ have increased 56Fe/54Fe isotope ratios relative to the lithogenic background, which is consistent with the general notion of benthic release of dissolved Fe with a relatively low 56Fe/54Fe isotope ratio. The Fe isotope ratios increase across the margin and the highest values coincide with the greatest Fe enrichment in sediments below the OMZ. The apparent mismatch in isotope composition between the Fe that is released within the OMZ and Fe that is re-precipitated below the OMZ implies that only a fraction of the sediment-derived Fe is retained near-shore whereas another fraction is transported further offshore. We suggest that a similar open-marine shuttle is likely to operate along many ocean margins. The observed sedimentary fingerprint of the open-marine Fe shuttle differs from a related transport mechanism in isolated euxinic basins (e.g., the Black Sea) where the laterally supplied, reactive Fe is quantitatively captured within the basin sediments. We suggest that our findings are useful to identify OMZ-type Fe cycling in the geological record.
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  • 171
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    Major role of the equatorial current system in setting oxygen levels in the eastern tropical Atlantic Ocean: a high-resolution model study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 . pp. 2033-2040.
    Details
    Publication Date: 2019-09-23
    Description: Understanding the causes of the observed expansion of tropical ocean's oxygen minimum zones (OMZs) is hampered by large biases in the representation of oxygen distribution in climate models, pointing to incorrectly represented mechanisms. Here we assess the oxygen budget in a global biogeochemical circulation model, focusing on the Atlantic Ocean. While a coarse (0.5°) configuration displays the common bias of too large and too intense OMZs, the oxygen concentration in an eddying (0.1°) configuration is higher and closer to observations. This improvement is traced to a stronger oxygen supply by a more realistic representation of the equatorial and off-equatorial undercurrents, outweighing the concurrent increase in oxygen consumption associated with the stronger nutrient supply. The sensitivity of the eastern tropical Atlantic oxygen budget to the equatorial current intensity suggests that temporal changes in the eastward oxygen transport from the well-oxygenated western boundary region might partly explain variations in the OMZs.
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  • 172
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    Syn-orogenic high-temperature crustal melting: Geochronological and Nd-Sr-Pb isotope constraints from basement-derived granites (Central Damara Orogen, Namibia) (2014)
    Elsevier
    In:  Lithos, 192/195 . pp. 21-38.
    Details
    Publication Date: 2017-09-13
    Description: Major and trace element and Nd, Sr and Pb isotope data from c. 550 Ma-old gray granites and c. 510 Ma-old red leucogranites of the high-grade central part of the Damara orogen (Namibia) indicate a dominantly deep crustal origin. Moderately peraluminous gray granites are isotopically evolved (initial epsilon(Nd): C. - 17) and were likely derived from meta-igneous sources with late Archean to Paleoproterozoic crustal residence ages. Based on a comparison with experimental results, the granites were derived by partial melting of a granodioritic biotite gneiss at c. 900-950 degrees C and less than 10 kbar. Slightly peraluminous red leucogranites are also isotopically evolved (initial epsilon(Nd): - 15 to - 18) but have undergone extensive crystal fractionation coupled with minor contamination of mid crustal meta-pelitic material. Major and trace element data do not support closed-system fractional crystallization processes for all samples, however, some chemical features underline the importance of crystal fractionation processes especially for the leucogranites. Isotope data do not support mixing of different crust-derived melts or assimilation of crustal rocks by a mafic magma on a large scale. For the gray granites, unradiogenic Pb isotope compositions with substantial variation in Pb-207/Pb-204 at almost constant (206)pb/(204)pb, strongly negative epsilon(Nd) values and moderately radiogenic Sr isotope compositions argue for an undepleted nature of the source. High Rb/Sr ratios of the red leucogranites permit a comparison with the gray granites but similar initial ENd values indicate that the source of these granites is not fundamentally different to the source of the gray granites. The most acceptable model for both granite types involves partial melting of meta-igneous basement rocks of Archean to Proterozoic age. The consistency of the chemical data with a crustal anatectic origin and the observation that the gray granites intruded before the first peak of high-grade regional metamorphism suggests that they intruded simultaneously with crustal thickening. The red leucogranites are interpreted to be a result of crustal melting during the main peak of regional metamorphism. The heating events that promoted melting of fertile deep-crustal rocks might have been caused by the inferred high heat productivity of heat-producing radioactive elements (Th, U, K) together with crustal thickening during the main periods of orogeny
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  • 173
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    The provenance of Cretaceous to Quaternary sediments in the Tarfaya basin, SW Morocco: Evidence from trace element geochemistry and radiogenic Nd–Sr isotopes (2014)
    Elsevier
    In:  Journal of African Earth Sciences, 90 . pp. 64-76.
    Details
    Publication Date: 2017-05-31
    Description: We present trace element compositions, rare earth elements (REEs) and radiogenic Nd–Sr isotope analyses of Cretaceous to recent sediments of the Tarfaya basin, SW Morocco, in order to identify tectonic setting, source rocks composition and sediments provenance. The results suggest that the sediments originate from heterogeneous source areas of the Reguibat Shield and the Mauritanides (West African Craton), as well as the western Anti-Atlas, which probably form the basement in this area. For interpreting the analyzed trace element results, we assume that elemental ratios such as La/Sc, Th/Sc, Cr/Th, Th/Co, La/Co and Eu/Eu∗ in the detrital silicate fraction of the sedimentary rocks behaved as a closed system during transport and cementation, which is justified by the consistency of all obtained results. The La/Y-Sc/Cr binary and La–Th–Sc ternary relationships suggest that the Tarfaya basin sediments were deposited in a passive margin setting. The trace element ratios of La/Sc, Th/Sc, Cr/Th and Th/Co indicate a felsic source. Moreover, chondrite-normalized REE patterns with light rare earth elements (LREE) enrichment, a flat heavy rare earth elements (HREE) and negative Eu anomalies can also be attributed to a felsic source for the Tarfaya basin sediments. The Nd isotope model ages (TDM = 2.0–2.2 Ga) of the Early Cretaceous sediments suggest that sediments were derived from the Eburnean terrain (Reguibat Shield). On the other hand, Late Cretaceous to Miocene–-Pliocene sediments show younger model ages (TDM = 1.8 Ga, on average) indicating an origin from both the Reguibat Shield and the western Anti-Atlas. In contrast, the southernmost studied Sebkha Aridal section (Oligocene to Miocene–Pliocene) yields older provenance ages (TDM = 2.5–2.6 Ga) indicating that these sediments were dominantly derived from the Archean terrain of the Reguibat Shield.
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  • 174
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    Intraseasonal variability of nearshore productivity in the Northern Humboldt Current System: The role of coastal trapped waves (2014)
    Elsevier
    In:  Continental Shelf Research, 73 . pp. 14-30.
    Details
    Publication Date: 2017-12-12
    Description: Highlights: • Strong intraseasonal variability of near shore plankton in Peru upwelling system. • Chlorophyll variability is driven by the intraseasonal coastally trapped waves. • Chlorophyll anomalies propagate poleward at speed of high order CTW mode. • Intraseasonal wind impacts mainly the northern shelf variability and at 20–30 days. Abstract The impact of intraseasonal coastal-trapped waves on the nearshore Peru ecosystem is investigated using observations and a regional eddy-resolving physical-ecosystem coupled model. Model results show that intraseasonal variability over the period 2000–2006 represents about one fourth of the total surface chlorophyll variance and one third of the carbon export variance on the Peruvian shelf. Evidence is presented that subsurface nutrient and chlorophyll intraseasonal variability are mainly forced by the coastally trapped waves triggered by intraseasonal equatorial Kelvin waves reaching the South American coast, and propagate poleward along the Peru shore at a speed close to that of high order coastal trapped waves modes. The currents associated with the coastal waves induce an input of nutrients that triggers a subsequent phytoplankton bloom and carbon export. The impact of the local wind-forced intraseasonal variability on the ecosystem is of a similar order of magnitude to that remotely forced in the northern part of the Peru shelf on [50–90] day time scales and dominates over the entire shelf on [20–30] day time scales.
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  • 175
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    Ecogeochemical fate of coarse organic particles in sediments of the Rhône River prodelta (2014)
    Elsevier
    In:  Estuarine, Coastal and Shelf Science, 141 . pp. 97-103.
    Details
    Publication Date: 2017-01-04
    Description: Coarse particulate organic matter (CPOM) represents a small portion of the inner shelf sediments but occurs across all river outlets. To consider the ecogeochemical fate of CPOM in such an environment, we examined both the infauna community and secondary evidence of geochemical reactions preserved in the surface sediments of the Rhône prodelta. ICP-AES, scanning electron microscopy and energy dispersive X-ray spectrometry of the CPOM showed that the fate of organic matter in this environment is driven by sulphate reduction and geochemical reactions resulting from the precipitation of sulfide due to the presence of large amounts of iron-bearing minerals. Leaf litter debris contained such high quantities of iron that after dry ashing the remaining material is easily attracted by a magnet. The observed geochemical trade-off was proposed as a mechanism that helps to maintain a bioturbating animal community that in turn contributes to the mineralization of organic matter within this suboxic environment. This study showed that the accumulation of refractory organic carbon in sediments was intimately associated with the sequestering of iron and sulphur by providing a nucleation point for mineral deposition and also that the extent of decomposition of the organic materials did not necessarily increase progressively from coarser to finer particles.
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  • 176
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    Seismic structure of the Central Tyrrhenian basin: Geophysical constraints on the nature of the main crustal domains (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 119 (1). pp. 52-70.
    Details
    Publication Date: 2018-02-27
    Description: In this work we investigate the crustal and tectonic structures of the Central Tyrrhenian back-arc basin combining refraction and wide-angle reflection seismic (WAS), gravity, and multichannel seismic (MCS) reflection data, acquired during the MEDOC (MEDiterráneo OCcidental)-2010 survey along a transect crossing the entire basin from Sardinia to Campania at 40°N. The results presented include a ~450 km long 2-D P wave velocity model, obtained by the traveltime inversion of the WAS data, a coincident density model, and a MCS poststack time-migrated profile. We interpret three basement domains with different petrological affinity along the transect based on the comparison of velocity and velocity-derived density models with existing compilations for continental crust, oceanic crust, and exhumed mantle. The first domain includes the continental crust of Sardinia and the conjugate Campania margin. In the Sardinia margin, extension has thinned the crust from ~20 km under the coastline to ~13 km ~60 km seaward. Similarly, the Campania margin is also affected by strong extensional deformation. The second domain, under the Cornaglia Terrace and its conjugate Campania Terrace, appears to be oceanic in nature. However, it shows differences with respect to the reference Atlantic oceanic crust and agrees with that generated in back-arc oceanic settings. The velocities-depth relationships and lack of Moho reflections in seismic records of the third domain (i.e., the Magnaghi and Vavilov basins) support a basement fundamentally made of mantle rocks. The large seamounts of the third domain (e.g., Vavilov) are underlain by 10–20 km wide, relatively low-velocity anomalies interpreted as magmatic bodies locally intruding the mantle.
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    The West Melilla cold water coral mounds, Eastern Alboran Sea: Morphological characterization and environmental context (2014)
    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 99 . pp. 316-326.
    Details
    Publication Date: 2015-07-24
    Description: A new mound field, the West Melilla mounds, interpreted as being cold-water coral mounds, has been recently unveiled along the upper slope of the Mediterranean Moroccan continental margin, a few kilometers west of the Cape Tres Forcas. This study is based on the integration of high-resolution geophysical data (swath bathymetry, parametric sub-bottom profiler), CTD casts, Acoustic Doppler Current Profiler (ADCP), ROV video and seafloor sampling, acquired during the TOPOMED GASSIS (2011) and MELCOR (2012) cruises. Up to 103 mounds organized in two main clusters have been recognized in a depth range of 299–590 m, displaying a high density of 5 mounds/km2. Mounds, 1–48 m high above the surrounding seafloor and on average 260 m wide, are actually buried by a 1–12 m thick fine-grained sediment blanket. Seismic data suggest that the West Melilla mounds grew throughout the Early Pleistocene–Holocene, settling on erosive unconformities and mass movement deposits. During the last glacial–interglacial transition, the West Melilla mounds may have suffered a drastic change of the local sedimentary regime during the late Holocene and, unable to stand increasing depositional rates, were progressively buried. At the present day, temperature and salinity values on the West Melilla mounds suggest a plausible oceanographic setting, suitable for live CWCs. Nonetheless, more data is required to groundtruth the West Melilla mounds and better constrain the interplay of sedimentary and oceanographic factors during the evolution of the West Melilla mounds.
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  • 178
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    Generation of magnesian, high-K alkali-calcic granites and granodiorites from amphibolitic continental crust in the Damara orogen, Namibia (2014)
    Elsevier
    In:  Lithos, 198/199 . pp. 217-233.
    Details
    Publication Date: 2017-09-13
    Description: The Pan-African Damara orogen of Namibia is characterized by large-scale granitoid intrusions. Two plutons in the Northern Central Zone (NCZ) of the Damara orogen within the Okombahe district have U–Pb zircon ages of 576.2 ± 5.7 Ma and 570.9 ± 4.9 Ma that predate the time of high grade regional metamorphism which occurred between 540 and 480Ma. The intrusive rocks are magnesian high-K alkali-calcic granodiorites to granites, are enriched in HFSE and REE, and have undergone only a limited degree of fractional crystallization, and do not contain xenoliths of local country rocks. Initial isotope compositions are unevolvedwith 87Sr/86Sr between 0.704 and 0.706 and initial εNd ranging from −1.9 to−3.9. Lead isotopes are radiogenic (206Pb/204Pb: 18.32 to 18.61, 207Pb/204Pb: 15.61 to 15.69 and 208Pb/204Pb: 37.87 to 39.29) with variable 207Pb/204Pb ratios at almost constant 206Pb/204Pb and 208Pb/204Pb ratios, suggesting a derivation from ancient sources with comparatively high U/Pb but low Th/Pb ratios. The limited variations in Sr, Nd and Pb isotopes were not caused by crustal contamination or magma mixing, but instead reflect source heterogeneities. Strontium and Nd isotope compositions suggest mafic lithologies similar to amphibolites from the Kalahari Craton basement as potential sources. A comparison with amphibolite melting experiments confirms the possible derivation of the granodiorites from an amphibolitic source. Calculated maximum zircon saturation temperatures at insignificant amounts of inherited zircon, indicate intrusion temperatures of up to 900 °C. Apatite saturation temperatures are higher, up to ca. 950 °C. Pressures of 5 to 10 kbar are determined through Qz-Ab-Or systematics and are interpreted as minimum pressures at the site of melting suggesting that the granodiorites/granites represent high temperature partial melts generated in the lower crust. Although there are some compositional similarities with granites generated in subduction zones, radiogenic Pb isotope ratios and high δ18O values suggest that reprocessed amphibolitic rocks are more likely sources.
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  • 179
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    Cretaceous fore-arc basalts from the Tonga arc: Geochemistry and implications for the tectonic history of the SW Pacific (2014)
    Elsevier
    In:  Tectonophysics, 630 . pp. 21-32.
    Details
    Publication Date: 2018-01-05
    Description: Highlights: • The geochemistry of a Cretaceous Tongan fore-arc basalt (FAB) suite is reported. • The Tonga FAB suite is very similar to the Poya Terrane basalts of New Caledonia. • Similar geochemistry to IBM FAB but not associated with subduction initiation • Possibly a remnant of the hypothesized back-arc East New Caledonia Basin Abstract: The Tonga fore-arc preserves a complex history of subduction initiation, back-arc basin formation and arc volcanism which has extended from the Cretaceous to the present. In this paper, we discuss the geochemistry of a Cretaceous basalt/dolerite/gabbro suite recovered in two dredges from the Tonga fore-arc at ~ 19°S. The geochemistry of the Tonga fore-arc suite is unlike that of the uniformly depleted MORB basalts of the subducting Pacific Plate and therefore is unlikely to be accreted from Pacific Cretaceous crust. The ~ 102 Ma age obtained for one Tongan fore-arc dolerite is contemporaneous with a major phase of Cretaceous subduction-related volcanism, recorded both in detrital zircon age populations and associated volcanics from New Caledonia and New Zealand. We believe that the Tonga fore-arc basalts are a remnant of a hypothesized, once extensive Cretaceous back-arc basin, called the East New Caledonia Basin, which we propose to have existed from ~ 102 to 50 Ma. The allochthonous Poya Terrane of New Caledonia is geochemically very similar to the Tonga fore-arc basalts and represents a younger (~ 84–55 Ma) remnant of the same basin. Subduction-related Cretaceous volcanics from the SW Pacific, representing both arc and back-arc settings, all appear to have similar Zr/Nb values, suggesting a common mantle component in their petrogenesis. The Tonga fore-arc basalts are also similar to fore-arc basalts recovered from the Izu-Bonin-Mariana fore-arc, but unlike these basalts they are not associated with subduction initiation.
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  • 180
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    P and S wave velocity measurements of water-rich sediments from the Nankai Trough, Japan (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 119 (2). pp. 787-805.
    Details
    Publication Date: 2018-02-27
    Description: Acoustic velocities were measured during triaxial deformation tests of silty clay and clayey silt core samples from the Nankai subduction zone (Integrated Ocean Drilling Program Expeditions 315, 316, and 333). We provide a new data set, continuously measured during pressure increase and subsequent axial deformation. A new data processing method was developed using seismic time series analysis. Compressional wave velocities (V-p) range between about 1450 and 2200 m/s, and shear wave velocities (V-s) range between about 150 and 800 m/s. V-p slightly increases with rising effective confining pressure and effective axial stress. Samples from the accretionary prism toe show the highest Vp, while fore-arc slope sediments show lower Vp. Samples from the incoming plate, slightly richer in clay minerals, have the lowest values for V-p. V-s increases with higher effective confining pressures and effective axial stress, irrespective of composition and tectonic setting. Shear and bulk moduli are between 0.2 and 1.3 GPa, and 3.85 and 8.41 GPa, respectively. Elastic moduli of samples from the accretionary prism toe and the footwall of the megasplay fault (1.50 and 3.98 GPa) are higher than those from the hanging wall and incoming plate (0.59 and 0.88 GPa). This allows differentiation between normal and overconsolidated sediments. The data show that in a tectonosedimentary environment of only subtle compositional differences, acoustic properties can be used to differentiate between stronger (accretionary prism toe) and weaker (fore-arc slope, incoming plate) sediments. Especially V-p/V-s ratios may be instrumental in detecting zones of low effective stress and thus high pore fluid pressure
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    The seawater neodymium and lead isotope record of the final stages of Central American Seaway closure (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Paleoceanography, 29 (7). pp. 715-729.
    Details
    Publication Date: 2019-09-23
    Description: Key Points: Seawater Nd and Pb isotope records for the Pliocene Caribbean and EEP Caribbean Nd isotope composition became more UNADW-like during the Pliocene Short term changes support link between CAS closure and strength of AMOC The shoaling and final closure of the Central American Seaway (CAS) resulted in a major change of the global ocean circulation and has been suggested as an essential driver for strengthening of Atlantic Meridional Overturning Circulation (AMOC). The exact timing of CAS closure is key to interpreting its importance. Here we present a reconstruction of deep and intermediate water Nd and Pb isotope compositions obtained from fossil fish teeth and the authigenic coatings of planktonic foraminifera in the eastern equatorial Pacific (ODP Site 1241) and the Caribbean (ODP Sites 998, 999 and 1000) covering the final stages of CAS closure between 5.6 and 2.2 Ma. The data for the Pacific site indicate no significant Atlantic/Caribbean influence over this entire period. The Caribbean sites show a continuous trend to less radiogenic Nd isotope compositions during the Pliocene, consistent with an enhancement of Upper North Atlantic Deep Water (UNADW) inflow and a strengthening of the AMOC. Superimposed onto this long-term trend, shorter-term changes of intermediate Caribbean Nd isotope signatures approached more UNADW-like values during intervals when published reconstructions of seawater salinity suggested complete closure of the CAS. The data imply that significant deep water exchange with the Pacific essentially stopped by 7 Ma and that shallow exchange, which still occurred at least periodically until approximately 2.5 Ma, may have been linked to the strength of the AMOC but did not have any direct effect on the intermediate and deep Caribbean Nd isotope signatures through mixing with Pacific waters.
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  • 182
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    Observations of Stratospheric Sudden Warmings in Earth Rotation Variations (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Atmospheres, 119 (16). pp. 9666-9678.
    Details
    Publication Date: 2018-02-06
    Description: Stratospheric sudden warmings (SSWs) are extreme events in the polar stratosphere that are both caused by and have effects on the tropospheric flow. This means that SSWs are associated with changes in the angular momentum of the atmosphere, both before and after their onset. Because these angular momentum changes are transferred to the solid Earth, they can be observed in the rate of the Earth's rotation and the wobble of its rotational pole. By comparing observed Earth rotation variations to reanalysis data, we find that an anomaly in the orientation of the Earth's rotational pole, up to 4 times as large as the annual polar wobble, typically precedes SSWs by 20-40 days. The polar motion signal is due to pressure anomalies that are typically seen before SSW events and represents a new type of observable that may aid in the prediction of SSWs. A decline in the length of day is also seen, on average, near the time of the SSW wind reversal and is found to be due to anomalous easterly winds generated in the tropical troposphere around this time, though the structure and timing of this signal seems to vary widely from event to event.
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  • 183
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    The SPARC Data Initiative: Comparison of upper troposphere/lower stratosphere ozone climatologies from limb-viewing instruments and the nadir-viewing Tropospheric Emission Spectrometer (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Atmospheres, 119 (11). pp. 6971-6990.
    Details
    Publication Date: 2018-02-06
    Description: We present the first comprehensive intercomparison of currently available satellite ozone climatologies in the upper troposphere/lower stratosphere (UTLS) (300-70hPa) as part of the Stratosphere-troposphere Processes and their Role in Climate (SPARC) Data Initiative. The Tropospheric Emission Spectrometer (TES) instrument is the only nadir-viewing instrument in this initiative, as well as the only instrument with a focus on tropospheric composition. We apply the TES observational operator to ozone climatologies from the more highly vertically resolved limb-viewing instruments. This minimizes the impact of differences in vertical resolution among the instruments and allows identification of systematic differences in the large-scale structure and variability of UTLS ozone. We find that the climatologies from most of the limb-viewing instruments show positive differences (ranging from 5 to 75%) with respect to TES in the tropical UTLS, and comparison to a zonal mean ozonesonde climatology indicates that these differences likely represent a positive bias for p100hPa. In the extratropics, there is good agreement among the climatologies regarding the timing and magnitude of the ozone seasonal cycle (differences in the peak-to-peak amplitude of 〈15%) when the TES observational operator is applied, as well as very consistent midlatitude interannual variability. The discrepancies in ozone temporal variability are larger in the tropics, with differences between the data sets of up to 55% in the seasonal cycle amplitude. However, the differences among the climatologies are everywhere much smaller than the range produced by current chemistry-climate models, indicating that the multiple-instrument ensemble is useful for quantitatively evaluating these models.
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  • 184
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    Variability in pteropod sedimentation and corresponding aragonite flux at the Arctic deep-sea long-term observatory HAUSGARTEN in the eastern Fram Strait from 2000 to 2009 (2014)
    Elsevier
    In:  Journal of Marine Systems, 132 . pp. 95-105.
    Details
    Publication Date: 2014-09-04
    Description: Pteropods are an important component of the zooplankton community and hence of the food web in the Fram Strait. They have a calcareous (aragonite) shell and are thus sensitive in particular to the effects of the increasing CO2 concentration in the atmosphere and the associated changes of pH and temperature in the ocean. In the eastern Fram Strait, two species of thecosome pteropods occur, the cold water-adapted Limacina helicina and the subarctic boreal species Limacina retroversa. Both species were regularly observed in year-round moored sediment traps at ~ 200–300 m depth in the deep-sea long-term observatory HAUSGARTEN (79°N, 4°E). The flux of all pteropods found in the trap samples varied from 〈 20 to ~ 870 specimen m− 2 d− 1 in the years 2000–2009, being lower during the period 2000–2006. At the beginning of the time series, pteropods were dominated by the cold-water-adapted L. helicina, whereas the subarctic boreal L. retroversa was only occasionally found in large quantities (〉 50 m− 2 d− 1). This picture completely changed after 2005/6 when L. retroversa became dominant and total pteropod numbers in the trap samples increased significantly. Concomitant to this shift in species composition, a warming event occurred in 2005/6 and persisted until the end of the study in 2009, despite a slight cooling in the upper water layer after 2007/8. Sedimentation of pteropods showed a strong seasonality, with elevated fluxes of L. helicina from August to November. Numbers of L. retroversa usually increased later, during September/October, with a maximum at the end of the season during December/January. In terms of carbonate export, aragonite shells of pteropods contributed with 11–77% to the annual total CaCO3 flux in Fram Strait. The highest share was found in the period 2007 to 2009, predominantly during sedimentation events at the end of the year. Results obtained by sediment traps occasionally installed on a benthic lander revealed that pteropods also arrive at the seafloor (~ 2550 m) almost simultaneous with their occurrence in the shallower traps. This indicates a rapid downward transport of calcareous shells, which provides food particles for the deep-sea benthos during winter when other production in the upper water column is shut down. The results of our study highlight the great importance of pteropods for the biological carbon pump as well as for the carbonate system in Fram Strait at present, and indicate modifications within the zooplankton community. The results further emphasize the importance of long-term investigation to disclose such changes.
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  • 185
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    High-resolution modeling of the Eastern Tropical Pacific oxygen minimum zone: Sensitivity to the tropical oceanic circulation (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (8). pp. 5515-5532.
    Details
    Publication Date: 2018-02-26
    Description: The connection between the equatorial mean circulation and the oxygen minimum zone (OMZ) in the Eastern Tropical Pacific is investigated through sensitivity experiments with a high-resolution coupled physical-biogeochemical model. A validation against in situ observations indicates a realistic simulation of the vertical and horizontal oxygen distribution by the model. Two sets of climatological open-boundary conditions for the physical variables, which differ slightly with respect to the intensity and vertical structure of the Equatorial Current System, are shown to lead to contrasting characteristics of the simulated OMZ dynamics. From a Lagrangian perspective, the mean differences near the coast originate to a large extent from the different transport of deoxygenated waters by the secondary Tsuchiya Jet (secondary Southern Subsurface Countercurrent, sSSCC). The O2 budget further indicates a large difference in the balance between tendency terms, with advection exhibiting the largest difference between both simulations, which is shown to result from both linear and nonlinear advection. At regional scale, we also find that the variability of the physical contribution to the rate of O2 change is one order of magnitude larger than the variability associated with the biogeochemical contribution, which originates from internal high-frequency variability. Overall our study illustrates the large sensitivity of the OMZ dynamics to the equatorial circulation.
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  • 186
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    Gas emissions from five volcanoes in northern Chile, and implications for the volatiles budget of the Central Volcanic Zone (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (14). pp. 4961-4969.
    Details
    Publication Date: 2017-04-10
    Description: This study performed the first assessment of the volcanic gas output from the Central Volcanic Zone (CVZ) of northern Chile. We present the fluxes and compositions of volcanic gases (H2O, CO2, H2, HCl, HF, and HBr) from five of the most actively degassing volcanoes in this region—Láscar, Lastarria, Putana, Ollagüe, and San Pedro—obtained during field campaigns in 2012 and 2013. The inferred gas plume compositions for Láscar and Lastarria (CO2/Stot = 0.9–2.2; Stot/HCl = 1.4–3.4) are similar to those obtained in the Southern Volcanic Zone of Chile, suggesting uniform magmatic gas fingerprint throughout the Chilean arc. Combining these compositions with our own UV spectroscopy measurements of the SO2 output (summing to ~1800 t d−1 for the CVZ), we calculate a cumulative CO2 output of 1743–1988 t d−1 and a total volatiles output of 〉20,200 t d−1.
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  • 187
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    The detection of iron protoporphyrin (heme b) in phytoplankton and marine particulate material by electrospray ionisation mass spectrometry – comparison with diode array detection (2014)
    Elsevier
    In:  Analytica Chimica Acta, 841 . pp. 33-43.
    Details
    Publication Date: 2021-04-23
    Description: A mass spectrometric (MS) method for the identification of iron protoporphyrin (IX) (FePTP, heme b) in marine particulate material and phytoplankton is described. Electrospray ionisation of FePTP produced the molecular Fe(III)PTP+ ion (m/z = 616) or the pseudomolecular [Fe(II)PTP + H]+ ion (m/z = 617), depending on the oxidation state of the central iron ion. Collision induced dissociation (CID) in the ion trap mass spectrometer resulted in a single detected product ion (m/z = 557) indicative of loss of ethanoic acid from a carboxylic acid side chain. Widening the isolation width to 616 ± 3 resulted in production of a mass spectrum demonstrating the distinctive isotopic ratio of the iron containing fragment, further increasing the specificity of the analysis. Selective reactant monitoring (SRM) of the fragment ion (m/z = 557) was applied to the detection of FePTP after chromatography of ammoniacal OGP extracts of marine samples. The detection limit for FePTP analysed by SRM after chromatography was 1.2 ± 0.5 fmol. For phytoplankton samples, reasonably good agreement was achieved between results obtained with SRM and those obtained by monitoring absorbance at λ = 400 nm using a diode array detector (DAD). Use of SRM for analysis of particulate material obtained from the high latitude North Atlantic allowed for the analysis of FePTP in the presence of a co-eluting compound that interfered with detection by DAD. Simultaneous collection of mass spectra from m/z = 300 to 1500 resulted in identification of the pseudomolecular ion for the interfering compound. The CID fragmentation pattern and UV–visible mass spectra indicated that the interfering compound was a previously unidentified chlorin type compound. Comparison of FePTP determined by SRM and DAD on samples where this compound could not be detected showed that results collected using the two methods correlated. The use of both MS and DAD results in a powerful tool for quantifying this important biogenic component of the particulate iron pool.
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  • 188
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    The importance of shallow hydrothermal island arc systems in ocean biogeochemistry (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (3). pp. 942-947.
    Details
    Publication Date: 2021-04-23
    Description: Hydrothermal venting often occurs at submarine volcanic calderas on island arc chains, typically at shallower depths than mid–ocean ridges. The effect of these systems on ocean biogeochemistry has been under-investigated to date. Here we show that hydrothermal effluent from an island arc caldera was rich in Fe(III) colloids (0.02–0.2 µm; 46% of total Fe), contributing to a fraction of hydrothermal Fe that was stable in ocean water. Iron(III) colloids from island arc calderas may be transferred into surrounding waters (generally 0–1500 m depth) by ocean currents, thereby potentially stimulating surface ocean primary productivity. Hydrothermal Fe oxyhydroxide particles (〉0.2 µm) were also pervasive in the studied caldera and contained high concentrations of oxyanions of phosphorus (P), vanadium (V), arsenic (As), and manganese (Mn). Hydrothermal island arcs may be responsible for 〉 50% of global hydrothermal P scavenging and 〉 40% V scavenging, despite representing 〈10% of global hydrothermal fluid flow.
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  • 189
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    The karst of the Vaucluse, an exceptional record for the Last Glacial Maximum (LGM) and the Late-glacial period palaeoenvironment of southeastern France (2014)
    Elsevier
    In:  Quaternary International, 339-340 . pp. 41-61.
    Details
    Publication Date: 2019-09-23
    Description: Investigations in four natural traps from southeastern France have provided new and extensive information on the palaeoenvironment from the Last Glacial Maximum (LGM; 21,000 to 15,075 cal BP), the Late-glacial period (15,075 to 11,490 cal BP) and the beginning of Holocene (11,490 to 2835 cal BP). Radiocarbon and U/Th dates provided precise chronological data. In the Coulet des Roches, an LGM and a near complete Late-glacial period sequence were identified. The infilling preserved skeletons of large mammals, revealing a new faunal assemblage for southeastern France. For the first time, two distinct southern expansions of Dicrostonyx torquatus have been identified, correlated firstly to the LGM and secondly to the Late-glacial period. Dicrostonyx torquatus was found to be associated with Microtus oeconemus during the Oldest Dryas (15,075 to 18,270 cal BP). Morphological adaptations to the cold climate were indicated by some mammals (Vulpes vulpes, Mustela nivalis, Mustela erminea, Equus caballus gallicus). Among the birds, Bubo scandiacus and Pyrrhocorax graculus were found to be abundant. Palynological data suggested a very open landscape as well as a cold and rather dry climate. Rangifer tarandus remains were recovered from the Oldest Dryas layers of Aven des Planes. During the Allerød, a wooded environment permitted the dispersal of Cervus elaphus, Sus scrofa, Tetrao urogallus as well as reptiles and amphibians. Holocene sequences existed in these two natural traps as in Aven Souche n° 1 and n° 2. At this time, a sparsely wooded landscape covered much of the area. Cervus elaphus and Tetrao urogallus were still present with Canis lupus, Lynx lynx and Felis silvestris. Areas of open landscape were occupied by Otis tarda. During the Bronze Age (2200 to 800 cal BC) and Iron Age (800 to 50 cal BC), Aven des Planes, Aven Souche n° 1 and n° 2 were used by humans and had a sepulchral destination.
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  • 190
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    Sequestration efficiency in the iron-limited North Atlantic: Implications for iron supply mode to fertilized blooms (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (13). pp. 4619-4627.
    Details
    Publication Date: 2021-04-23
    Description: Estimates of the amount of carbon sequestered in the ocean interior per unit iron (Fe) supplied, as quantified by the sequestration efficiency (Ceffx), vary widely. Such variability in Ceffx has frequently been attributed to estimate uncertainty rather than intrinsic variability. Here we derive new estimates of Ceffx for the subpolar North Atlantic, where Fe stressed conditions have recently been demonstrated. Derived values of Ceffx from across the region, including areas subject to atypical external Fe fertilization events during the year of sample collection (2010), ranged from 17 to 19 kmol C (mol Fe−1). Comparing these estimates with values from other systems, considered in the context of variable bloom durations in the different oceanographic settings, we suggest that apparent variability in Ceffx may be related to the mode of Fe delivery.
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  • 191
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    Impact of volcanism on the evolution of Lake Van (eastern Anatolia) III: Periodic (Nemrut) vs. episodic (Süphan) explosive eruptions and climate forcing reflected in a tephra gap between ca. 14ka and ca. 30ka (2014)
    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 285 . pp. 195-213.
    Details
    Publication Date: 2017-08-08
    Description: Fifteen Lateglacial to Holocene rhyolitic, dominantly primary tephra layers piston-cored and drilled (ICDP Paleovan drilling project) in western Lake Van (eastern Anatolia, Turkey) were precisely correlated to either of the two adjacent and active large volcanoes Nemrut and Süphan based on shard textures, mineralogy and mineral and glass compositions. The young peralkaline (comenditic to pantelleritic) primary rhyolitic Nemrut tephras are characterized by anorthoclase, hedenbergitic to augitic clinopyroxene, fayalitic olivine, minor quartz, and rare accessory chevkinite and zircon. Phenocrysts in subalkaline primary rhyolitic Süphan tephras are chiefly oligoclase-labradorite, with minor K-rich sanidine in some, biotite, amphibole, hypersthene, rare augitic clinopyroxene, relatively common allanite and rare zircon. Two contrasting explosive eruptive modes are distinguished from each other: episodic (Süphan) and periodic (Nemrut). The Lateglacial Süphan tephra swarm covers a short time interval of ca. 338 years between ca. 13,078 vy BP and 12,740 vy BP, eruptions having occurred statistically every ca. 42 years with especially short intervals between V-11 (reworked) and V-14. Causes for the strongly episodic Süphan explosive behavior might include seismic triggering of a volcano–magma system unable to erupt explosively without the benefit of external triggering, as reflected in pervasive faulting preceding the Süphan tephra swarm. Seismic triggering may have caused the rise of more mafic (“trachyandesitic”) parent magma, heating near-surface pockets of highly evolved magma – that might have formed silicic domes during this stage of volcano evolution – resulting in ascent and finally explosive fragmentation of magma essentially by external factors, probably significantly enhanced by magma–water/ice interaction. Explosive eruptions of the Nemrut volcano system, interpreted to be underlain by a large fractionating magma reservoir, follow a more periodic mode of (a) long-term relatively constant supply of parent magma, (b) evolution by low pressure crystal fractionation resulting in sporadic relatively low-volume eruption of trachytic and minor rhyolitic magmas, (c) evolution of a large magma reservoir to the point of highly explosive large-volume peralkaline rhyolitic Plinian eruptions at temporal intervals of ca. 20–40 ky, some accompanied by ignimbrites and inferred caldera collapse. A striking tephra gap between ca. 14 ka and ca. 30 ka, i.e. during glacial climate conditions, is postulated to be due to climate-forcing via lithosphere unloading following deglaciation.
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  • 192
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    Twentieth century sea surface temperature and salinity variations at Timor inferred from paired coral δ18O and Sr/Ca measurements (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (7). pp. 4593-4604.
    Details
    Publication Date: 2018-02-27
    Description: The Indonesian Throughflow (ITF), which represents the global ocean circulation connecting the Pacific Warm Pool to the Indian Ocean, strongly influences the Indo-Pacific climate. ITF monitoring since the late 1990s using mooring buoys have provided insights on seasonal and interannual time scales. However, the absence of longer records limits our perspective on its evolution over the past century. Here, we present sea surface temperature (SST) and salinity (SSS) proxy records from Timor Island located at the ITF exit passage via paired coral δ18O and Sr/Ca measurements spanning the period 1914–2004. These high-resolution proxy based climate data of the last century highlights improvements and cautions when interpreting paleoclimate records of the Indonesian region. If the seasonality of SST and SSS is not perfectly in phase, the application of coral Sr/Ca thermometry improves SST reconstructions compared to estimates based on coral δ18O only. Our records also underline the importance of ocean advection besides rainfall on local SSS in the region. Although the El Niño/Southern Oscillation (ENSO) causes larger anomalies relative to the Indian Ocean Dipole (IOD), Timor coral-based SST and SSS records robustly correlate with IOD on interannual time scales, whereas ENSO only modifies Timor SST. Similarly, Timor SST and SSS are strongly linked to Indian Ocean decadal-scale variations that appear to lead Timor oceanographic conditions by about 1.6–2 years. Our study sheds new light on the complex signatures of Indo-Pacific climate modes on SST and SSS dynamics of the ITF.
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  • 193
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    Magmatic development of the outer Vøring margin from seismic data (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 119 (9). pp. 6733-6755.
    Details
    Publication Date: 2018-02-27
    Description: The Vøring Plateau off mid-Norway is a volcanic passive margin, located north of the East Jan Mayen Fracture Zone (EJMFZ). Large volumes of magmatic rocks were emplaced during Early Eocene margin formation. In 2003, an ocean bottom seismometer survey was acquired over the margin. One profile crosses from the Vøring Plateau to the Vøring Spur, a bathymetric high north of the EJMFZ. The P wave data were ray traced into a 2-D crustal velocity model. The velocity structure of the Vøring Spur indicates up to 15 km igneous crustal thickness. Magmatic processes can be estimated by comparing seismic velocity (VP) with igneous thickness (H). This and two other profiles show a positive H-VP correlation at the Vøring Plateau, consistent with elevated mantle temperature at breakup. However, during the first 2 Ma magma production was augmented by a secondary process, possibly small-scale convection. From ∼51.5 Ma excess melting may be caused by elevated mantle temperature alone. Seismic stratigraphy around the Vøring Spur shows that it was created by at least two uplift events, with the main episode close to the Miocene/Pliocene boundary. Low H-VP correlation of the spur is consistent with renewed igneous growth by constant, moderate-degree mantle melting, not related to the breakup magmatism. The admittance function between bathymetry and free-air gravity shows that the high is near local isostatic equilibrium, precluding that compressional flexure at the EJMFZ uplifted the high. We find a proposed Eocene triple junction model for the margin to be inconsistent with observations.
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  • 194
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    The role of ocean gateways on cooling climate on long time scales (2014)
    Elsevier
    In:  Global and Planetary Change, 119 . pp. 1-22.
    Details
    Publication Date: 2018-02-20
    Description: We examine ocean changes in response to changes in paleogeography from the Cretaceous to present in an intermediate complexity model and in the fully coupled CCSM3 model. Greenhouse gas concentrations are kept constant to allow a focus on effects arising from changing continental configurations. We find consistent and significant geography-related Cenozoic cooling arising from the opening of Southern Ocean (SO) gateways. Both models show significant deep ocean cooling arising from tectonic evolution alone. Simulations employing continental configurations associated with greenhouse climates, namely the Turonian and the Eocene simulations, systematically exhibit warm deep ocean temperatures at elevated pCO2 close to 10 °C. In contrast, continental configurations associated with (later) icehouse climates are associated with cooler deep ocean temperatures at identical pCO2, arising from a progressive strengthening of the Antarctic Circumpolar Current. This suggests that a component of the Cenozoic benthic cooling trend recorded in oxygen isotopes could arise directly from changes in continental configuration, and so be partially decoupled from the Cenozoic greenhouse gas history. In this paper we will present our model results against the background of an extensive review of previous work on ocean gateways and additional modelling results from several other global climate models.
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  • 195
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    A Holocene palynological record from the northeastern Laptev Sea and its implications for palaeoenvironmental research (2014)
    Elsevier
    In:  Quaternary International, 348 . pp. 82-92.
    Details
    Publication Date: 2016-09-19
    Description: A 844 cm long core PS51/118-3 (77°53.54′ N; 132°11.92′ E) recovered from the upper slope (122 m water depth) of the Laptev Sea (Russian Arctic) has been studied for pollen, spores and aquatic palynomorphs, including freshwater green algae and cysts of marine dinoflagellates. The age model was established on the basis of radiocarbon dates obtained on marine bivalve mollusk shells. The available dates suggest that the analyzed sediment was accumulated during the last ca. 10.8 cal. ka and reveal two intervals with markedly different sedimentation rates, reflecting the sedimentary regime changes of the Laptev Sea shelf during postglacial sea-level rise. Very high sedimentation rates (ca. 4.7 mm per year) in the lower part of the core (120–866 cm) between ca. 9.2 and 10.8 cal. ka BP reflect lower-than-present sea levels, high erosion activity and much closer position of the palaeo-shoreline with the Lena and Yana river mouths to the core site. Dramatic decrease in sedimentation rates (ca. 0.1 mm per year) during the middle and late Holocene interval reflects high sea-level and decreased amount of suspended material transported to the outer shelf by rivers. Despite the location of the core site at the continental slope and far away from the modern coastline pollen, spores and fresh-water algae constitute a major part of the microfossils throughout the whole record, indicating great impact of the Lena and Yana rivers and possibly prevalent wind regime on the pollen and non-pollen-palynomorph (NPP) assemblages. Although a number of short-term (decadal to multi-century) oscillations deviate from the mean Holocene values, pollen taxa percentages and pollen-based numerical biome reconstructions do not show very clear trends. The latter is likely a result of the mixed environmental signal and complex pollen contribution of several large environmental regions and vegetation zones of Siberia drained by the Lena and Yana rivers. The greater pollen contribution of the forested regions to the PS51/118-3 record reflects higher pollen production of the boreal trees and shrubs over the low-productive Arctic vegetation. The intervals of the relative increase in the tundra biome scores in the PS51/118-3 record reflect decreased arboreal pollen production or/and increased landscape openness within the pollen source area and can be correlated (within the uncertainty of the age models) with the cold episodes observed in the Greenland ice and North Atlantic sediment records.
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  • 196
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    Mechanotransduction Pathways Linking the Extracellular Matrix to the Nucleus (2014)
    Elsevier
    In:  International Review of Cell and Molecular Biology, 310 . pp. 171-220.
    Details
    Publication Date: 2019-06-07
    Description: Cells contain several mechanosensing components that transduce mechanical signals into biochemical cascades. During cell–ECM adhesion, a complex network of molecules mechanically couples the extracellular matrix (ECM), cytoskeleton, and nucleoskeleton. The network comprises transmembrane receptor proteins and focal adhesions, which link the ECM and cytoskeleton. Additionally, recently identified protein complexes extend this linkage to the nucleus by linking the cytoskeleton and the nucleoskeleton. Despite numerous studies in this field, due to the complexity of this network, our knowledge of the mechanisms of cell–ECM adhesion at the molecular level remains remarkably incomplete. Herein, we present a review of the structures of key molecules involved in cell-ECM adhesion, along with an evaluation of their predicted roles in mechanical sensing. Additionally, specific binding events prompted by force-induced conformational changes of each molecule are discussed. Finally, we propose a model for the biomechanical events prominent in cell–ECM adhesion.
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    Fluvial response to sudden input of pyroclastic sediments during the 2008–2009 eruption of the Chaitén Volcano (Chile): The role of logjams (2014)
    Elsevier
    In:  Journal of South American Earth Sciences, 54 . pp. 140-157.
    Details
    Publication Date: 2019-05-24
    Description: The rhyolitic Plinian eruption of the Chilean Chaitén Volcano, initiated on May 2, 2008, suddenly introduced abundant pyroclastic sediments in the Blanco River catchment area, which experienced important modifications. Before May 2, the river was characterised by gravelly and moderate to low-sinuosity channels crossing a vegetated and locally urbanised (Chaitén City) floodplain. This river, limited by steep and densely forested highlands, was connected with the Pacific Ocean via a tidally-influenced delta plain. After heavy rains in May 11–20, the river discharge increased and triggered several responses including logjam formation and breakage, crevassing, avulsion (and channel abandonment), changes in the pattern and dimensions of channels, and construction of a new delta plain area. In this context, the goals of this contribution were: i) to document the sedimentological processes within a detailed geomorphic framework and ii) to understand the influence of logjams on fluvial dynamics. Upstream of the logjam zone, the deposits are mostly composed of ash and lapilli with abundant palaeovolcanic (epiclastic) sediments, which were produced by dilute currents and debris flows. Downstream of the logjam zone, deposits are composed by ash and lapilli, both pumice-rich and lacking important participation of older (epiclastic) sediments. The abandoned and filled palaeochannel, and the proximal part of crevasse splays experienced transient dilute flows with variable sediment concentration and, subordinately, hyperconcentrated flows. The distal sectors of crevasse splays mostly record settling from suspension. At the delta plain, tephra transported by the Blanco River was mixed with older sediments by tide and wave action (dilute flows). We conclude that immediately after eruption, both geomorphic and sedimentary processes of the river were mainly controlled by a combination of high availability of incoherent pyroclastic sediments on steep slopes, abundant rains, large logs that jammed the river and huge areas of devastated forest. Logjams played an important role in the river response to the volcanic eruption; they were responsible of the marked compositional change recorded upstream and downstream of the logjam zone and its breakage resulted in downstream flooding and avulsion. The likelihood of formation of logjams in rivers draining forested volcanic areas should be considered in the evaluation of volcanic hazards related to Plinian eruptions.
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  • 198
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    The Chemical Composition of Subducting Sediments (2014)
    Elsevier
    In:  In: Treatise on Geochemistry. , ed. by Keeling, R. F. Elsevier, Amsterdam, pp. 607-629. 2. ed.
    Details
    Publication Date: 2019-05-21
    Description: More than a decade since the estimation of global subducting sediment (GLOSS), an expanding inductively coupled plasma mass spectrometry dataset for trace elements motivates a new assessment of the bulk sediment flux into deep-sea trenches and an update, GLOSS-II. The specific focus here is on key elements in solid earth recycling that are now better constrained by new data: Li, Be, B, Nb, Ta, Pb, Th, and U. The abundances of these elements reflect, to first order, dilution of continental detritus by biogenic opal and carbonate and, second, various continental and marine processes, such as the extent of continental weathering (Li/K2O), hydrogenous versus hydrothermal oxides (Pb/Fe), biophosphate accumulation and exposure age on the seafloor (Th and U), and organic carbon burial (U). The Be/K2O ratio (0.86 ± 0.04) and Nb/Ta ratio (14 ± 1) of terrigenous marine sediments reflect average upper continental crust and indeed refine those estimates. Given these new systematics, along with newly published data, revised bulk sediment compositions are calculated for 16 of the 25 trenches included in GLOSS. Two major additional margins are newly assessed (New Zealand-Hikurangi and Chile). Many element budgets are substantially revised for individual trenches, particularly Rb, Cs, Nb, and Pb. A new global weighted average, GLOSS-II, is similar to GLOSS (within 10% relative abundance) for many elements, with more significant changes (up to 50%) in Rb, Cs, Rb/Sr, Nd/Hf, and U/Th. The updated trench estimates provide new insights into sediment recycling at subduction zones, particularly for Li, Be, and Nb. The mass flux of Li subducted into different trenches correlates strongly with the Li/Y ratio in adjacent volcanic arcs, pointing to a direct control on Li enrichment in arcs by subducted sediment. Such a control may be consistent with Li-isotope variations in some arcs, with little fractionation required in the slab or mantle. On the other hand, arcs do not reflect the common Be/K2O ratio of most sediments and show fractionation to higher and lower ratios. These fractionations may relate to the different thermal structure of different slabs and/or subducted sediment versus basalt contributions. Sediments vary significantly in their Nb anomaly (i.e., Nb depletion with respect to La and Th), and some arcs inherit the sedimentary Nb anomaly (e.g., South Sandwich) with no new fractionation in the subduction zone, while others (e.g., Marianas and Aleutians) likely require residual rutile in the slab. The Nb anomaly is thus a nearly ubiquitous feature in arcs that has a complex origin, dependent on at least three variables: the sedimentary Nb anomaly, the presence of rutile in the slab (likely driven by Fe2 +, Fe3 +, and/or Ti abundances in the sediments), and Nb/La variation in the mantle. Trench sediments and GLOSS-II should thus continue to be useful in elucidating processes occurring in subduction zones, the continents, and the mantle.
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    Tracers of Ocean Mixing (2014)
    Elsevier
    In:  In: Treatise on Geochemistry. , ed. by Holland, H. D. Elsevier, Amsterdam, pp. 235-257. 2. ed.
    Details
    Publication Date: 2019-02-05
    Description: Tracers can be used to make quantitative inferences about the physical processes of mixing and advection in the ocean. After describing the nature of mixing in the ocean, the theoretical framework of tracer distribution analysis is discussed, starting with the derivation of advection–diffusion equations and tracer age dating. Next follows a description of three commonly used approaches, namely, optimum multiparameter analysis, transit time distributions, and tracer contour inverse analysis. Finally, the author discusses example applications for both steady-state (natural) tracers and transient (anthropogenic) tracers, followed by an application of tracer age dating and tracer release experiments.
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  • 200
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    Microbial ecology: Finding structure in the rare biosphere (2014)
    Elsevier
    In:  Current Biology, 24 (8). R315-R317.
    Details
    Publication Date: 2019-03-05
    Description: Protists (unicellular eukaryotes) play important roles in marine ecosystems but are tremendously diverse and many remain uncharacterized. Deep-sequencing of a universal marker gene has helped resolve community composition patterns among rare and abundant protistan sequence groups in coastal European waters.
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