ALBERT

Description: Gorgonians are a key group of organisms in benthic marine communities with a wide bathymetric and geographical distribution. Although their presence on continental shelves and slopes has been known for more than 100 years, knowledge concerning the ecology of deep gorgonian species is still in a very preliminary stage. To overcome this situation, gorgonian assemblages located at 40–360 m depth were studied over a large geographical area on the continental shelf and upper slope of the Menorca Channel (Western Mediterranean Sea). A quantitative analysis of video transects recorded by a manned submersible and a remotely operated vehicle, were used to examine the diversity, distribution and demography of gorgonian species. Results showed high gorgonian diversity within this depth range (a total of nine species were observed) compared to Mediterranean coastal areas. Gorgonian assemblages on the continental shelf and upper slope were mostly monospecific (respectively 73% and 76% of occupied sampling units contained one single species), whereas shelf edge assemblages were highly multispecific (92% of occupied sampling units contained several species). This contrasts with the monospecificity of Mediterranean coastal gorgonian assemblages. Gorgonian populations on the continental shelf were mostly dominated by small colonies (88% of measured colonies) with few intermediate and large colonies (12% of measured colonies). In deeper areas small colonies were still dominant (60% of measured colonies), but intermediate and large colonies were much more abundant (40% of measured colonies). This suggests high recruitment rates on the continental shelf, but perturbations (trammel nets, long lines and strong storms) may limit the presence of intermediate and large colonies. Conversely, on the shelf edge and upper slope a more stable environment may allow colonies to reach larger dimensions. The identification and ecological characterization of these deep assemblages further extends the current knowledge about Mediterranean gorgonians, and is fundamental in improving the management and conservation of deep benthic ecosystems.

Description: This study reconstructs the history of multiple industrial and urban mercury (Hg) emissions recorded in the sediment archive of Lake Luitel (France) from AD similar to 1860 to AD 2011. For this purpose, we provide a well constrained short-lived radionuclides continuous age-depth relationship of the sediment sequence (mean accumulation rate of 5.18 +/- 0.28 mm.yr(-1)) with Hg accumulation rates (Hg AR), Hg isotopic composition and extensive historical data. Hg AR were stable around 45 mu g.m(-2).y(-1) from 1860 to WWI and rose to reach their maximum at the end of WWII (250 mu g m(-2) y(-1)) followed by a gradual decreased to reach about 90 mu g m(-2) y(-1) in the current period. Normalization to a terrigenous Hg proxy highlighted the dominance of atmospheric Hg inputs to the lake. The combination of Hg AR with isotopic signatures through the use of binary mixing (Delta Hg-199 vs 1/Hg AR) models and isotopic plots (and comparison to literature data) allowed us to identify the main industrial and urban historical inputs. The major outcome of this study is that the Hg mass independent fractionation (MIF) signature did not enable the identification of particular anthropogenic sources but reflected an integrated pool of industrial and urban emissions which tend to shift to less negative MIF values (mean: -0.15 +/- 0.04%) during their period of maximum emissions. Temporal MIF and Hg AR variations depict the rising Hg emissions from the industrial revolution (1860-1910) to the modern industrial and urban development period (1950-1980). Mass dependent fractionation (MDF) signatures enabled the identification of major contributors in relation to their relative intensities lying between two endmember pools: (i) the combustion activities (smelters, cement factories and urban heating) with more negative delta Hg-202 values, and (ii) the chemical and electrometallurgical activities (electrochemistry, chlor-alkali) with higher delta Hg-202 values. Unconformities of MIF and MDF signatures were observed during WWI, WWII and interwar period, and were attributed to drastic and rapid changes in regional industrial activities. Finally, recent laws regarding Hg emissions (1998-2011) prove their efficiency as Hg AR decreased with a return to more negative MIF and MDF signatures such as during the industrial revolution period. Our study highlights that the combination of Hg isotopic data with Hg AR in sediment archives is a useful tool for reconstructing the history of anthropogenic Hg emissions, and has the potential to identifiy their relative contributions.

Description: Polysialic acid (PSA) serves as a hydrophilic polymer and affords conjugated biologically active molecules a longer circulation time in vivo. Furthermore, PSA could potentially target tumor tissues and help achieve better curative effects. In this study, PSA was conjugated with octadecyl dimethyl betaine (BS18) to yield a PSA-BS18 conjugate. The PSA-BS18 modified liposomal epirubicin (EPI-SL), had a particle size of 133.63 ± 0.92 nm, a zeta potential of −26.23 ± 1.50 mV and an encapsulation efficiency (%EE) of 96.23 ± 1.16%. In vitro release studies showed that PSA-BS18 could delay EPI release from the modified liposomes. The MTT assay suggested that EPI-SL led to stronger cytotoxic activity than that exhibited by common and PEGylated liposomes. The pharmacokinetic study showed that EPI-SL prolonged the residence time of the EPI in the blood compared with that observed from common liposomes. Bio-distribution results obtained from tumor-bearing mice clearly demonstrated that PSA-BS18 increased the accumulation of modified liposomes in tumors compared with that of common liposomes. In the antitumor efficacy study, EPI-SL showed the best antitumor and life-prolonging effects among all of the tested formulations. These findings strongly indicate EPI-SL might have great potential as an effective approach for anticancer therapy.

Description: The interior of the Australian continent shows evidence for late Quaternary to Recent fault-controlled mantle 3He and CO2 degassing. A series of interconnected NW-striking sinistral faults, the Norwest fault zone (NFZ), in south-central Australia are associated with travertine mounds, the latter show a regular spacing of 50–70 km. U-series ages on 26 samples range from to (2σ errors) and suggest a clustering every ∼3–4 ka since ∼26 ka. Geochemical data demonstrate a remarkable mantle-to-groundwater connection. Isotopic data indicate that the groundwater is circulating to depths 〉3 km and interacting with Neoproterozoic/Cambrian basement and mantle volatiles. 3He/4He isotope ratios show that the He comes in part from the mantle. This demonstrates that the NFZ cuts through the entire crust and provides pathways for mantle degassing. Scaling relationships suggest that the series of sinistral faults that make up the NFZ are interconnected at depths and have a significant strike length of 60–70 km or more. The NFZ occurs where a major compositional boundary and a significant heat flow anomaly occurs, and a major step in lithospheric thickness has been mapped. We discuss a tectonic model in which recent stress field, heat flow and lithospheric structure in central Australia reactivated a set of steeply dipping Neoproterozoic faults, which may now be growing into a crustal/lithospheric-scale structure.

Description: Highlights • Synthesis of timescales of magmatic processes at spreading centres. • Compilation of drilled MORB glass compositions, chemical stratigraphy of the oceanic crust. • No chemical difference between MORB sampled from active ridges or by drilling. • Chemical variations on timescales 〈 1 ka reflect changes in melt recharge relative to fractionation. • Changes in the composition of melt entering crust occur over timescales of 10 to 100 ka. Abstract Oceanic crust is continuously created at mid-ocean ridges by decompression melting of the upper mantle as it upwells due to plate separation. Decades of research on active spreading ridges have led to a growing understanding of the complex magmatic, tectonic and hydrothermal processes linked to the formation of new oceanic igneous crust. However, less is known about the timescales of magmatic processes at mid-ocean ridges, including melting in and melt extraction from the mantle, fractional crystallisation, crustal assimilation and/or magma mixing. In this paper, we review the timescales of magmatic processes by integrating radiometric dating, chemical and petrological observations of mid-ocean ridge basalts (MORBs) and geophysical models. These different lines of evidence suggest that melt extraction and migration, and crystallisation and mixing processes occur over timescales of 1 to 10,000 a. High-resolution geochemical stratigraphic profiles of the oceanic crust using drill-core samples further show that at fast-spreading ridges, adjacent flow units may differ in age by only a few 100 a. We use existing chemical data and new major- and trace-element analyses of fresh MORB glasses from drill-cores in ancient Atlantic and Pacific crust, together with model stratigraphic ages to investigate how lava chemistry changes over 10 to 100 ka periods, the timescale of crustal accretion at spreading ridges which is recorded in the basalt stratigraphy in drilled sections through the oceanic crust. We show that drilled MORBs have compositions that are similar to those of young MORB glasses dredged from active spreading ridges (lavas that will eventually be preserved in the lowermost part of the extrusive section covered by younger flows), showing that the dredged samples are indeed representative of the bulk oceanic crust. Model stratigraphic ages calculated for individual flows in boreholes, together with the geochemical stratigraphy of the drilled sections, show that at fast-spreading ridges, magma compositions vary over 〈 100 to 1000 a, likely due to variations in the relative rates of crystallisation and melt recharge. However, on longer timescales of 10 to 100 ka, variations in the composition of the primitive melt feeding the ridge lead to chemical variations in the erupted lavas, likely as a function of thermal and/or chemical heterogeneity of the mantle source. The further understanding of these temporal variations in magma composition, especially at shorter timescales of less than a few centuries, is a promising area for future research.

Description: Highlights • A serpentinised peridotite basement is strongly supported by S-waves analysis • Depth dependent serpentinisation resembles to that observed at magma-poor margins. • Mantle exhumation was preceded by MOR-type magmatism and later intraplate volcanism. Summary The Tyrrhenian basin opened in the Neogene following the E–SE retreat of the Appenines–Calabrian subduction system and the subsequent back-arc extension of an orogenic crust. The resultant crustal structure includes a complex distribution of continental, back-arc magmatism, and mantle-exhumation domains. A clear example of this complex structure is found in the central and deepest part of the basin (i.e. Magnaghi–Vavilov sub-basin) where geophysical data supported that the bulk of the basement is composed of partially serpentinised peridotite representing exhumed mantle rocks, and intruded by basalts forming low ridges and volcanic edifices. However, those data sets cannot univocally demonstrate the widespread presence of serpentinised mantle rocks, let alone the percentage of serpentinisation. Here, we use S-wave arrivals and available geological information to further constrain the presence of mantle serpentinisation. Travel times of converted S-waves were used to derive the overall Vp/Vs and Poisson's ratio (σ), as well as S-wave velocity of the basement in the Magnaghi-Vavilov Basins. This analysis reveals Vp/Vs ≈ 1.9 (σ ≈ 0.3) that strongly supports a serpentinised peridotite forming the basement under the basins, rather than oceanic-type gabbro/diabase. P-wave velocity models is later used to quantify the amount of serpentinisation from fully serpentinised (up to 100%) at the top of the basement to 〈 10% at 5–7 km deep, with a depth distribution similar to continent–ocean Transition zones at magma-poor rifted margins. Seismic reflection profiles show normal faulting at either flank of the Magnaghi–Vavilov Basin that is potentially responsible for the onset of serpentinisation and later mantle exhumation. These results, together with basement sampling information in the area, suggests that the late stage of mantle exhumation was accompanied or soon followed by the emplacement of MOR-type basalts forming low ridges that preceded intraplate volcanism responsible for the formation of large volcanoes in the area.

Description: Dilution experiments were performed to estimate phytoplankton growth and microzooplankton grazing rates at two sites: freshwater (Nida) and brackish water (Smiltyne) in the Curonian Lagoon (SE Baltic Sea). Using the size-fractionation approach and dilution experiments, we found that the microzooplankton community was able to remove up to 78% of nanophytoplankton (2–20 μm) standing stock and 130% of the total daily primary production in the brackish waters of the lagoon, and up to 83% of standing stock and 76% of the primary production of picophytoplankton (0.2–2 μm) in the freshwater part. The observed differences were attributed to the changes in ciliate community size and trophic structure, with larger nano-filterers (30–60 μm) dominating the brackish water assemblages and pico-nano filterers (〈20 μm and 20–30 μm) prevailing in the freshwater part of the lagoon.

Description: Marine teleost fish sustain compensation of extracellular pH after exposure to hypercapnia by means of efficient ion and acid-base regulation. Elevated rates of ion and acid-base regulation under hypercapnia may be stimulated further by elevated temperature. Here, we characterized the regulation of transepithelial ion transporters (NKCC1, NBC1, SLC26A6, NHE1 and 2) and ATPases (Na(+)/K(+) ATPase and V-type H(+) ATPase) in gills of Atlantic cod (Gadus morhua) after 4 weeks of exposure to ambient and future PCO2 levels (550 μatm, 1200 μatm, 2200 μatm) at optimum (10 °C) and summer maximum temperature (18 °C), respectively. Gene expression of most branchial ion transporters revealed temperature- and dose-dependent responses to elevated PCO2. Transcriptional regulation resulted in stable protein expression at 10 °C, whereas expression of most transport proteins increased at medium PCO2 and 18 °C. mRNA and protein expression of distinct ion transport proteins were closely co-regulated, substantiating cellular functional relationships. Na(+)/K(+) ATPase capacities were PCO2 independent, but increased with acclimation temperature, whereas H(+) ATPase capacities were thermally compensated but decreased at medium PCO2 and 10 °C. When functional capacities of branchial ATPases were compared with mitochondrial F1Fo ATP-synthase strong correlations of F1Fo ATP-synthase and ATPase capacities generally indicate close coordination of branchial aerobic ATP demand and supply. Our data indicate physiological plasticity in the gills of cod to adjust to a warming, acidifying ocean within limits. In light of the interacting and non-linear, dose-dependent effects of both climate factors the role of these mechanisms in shaping resilience under climate change remains to be explored.

Description: The extent of the global human footprint [1] limits our understanding of what is natural in the marine environment. Remote, near-pristine areas provide some baseline expectations for biomass [2, 3] and suggest that predators dominate, producing an inverted biomass pyramid. The southern pass of Fakarava atoll—a biosphere reserve in French Polynesia—hosts an average of 600 reef sharks, two to three times the biomass per hectare documented for any other reef shark aggregations [4]. This huge biomass of predators makes the trophic pyramid inverted. Bioenergetics models indicate that the sharks require ~90 tons of fish per year, whereas the total fish production in the pass is ~17 tons per year. Energetic theory shows that such trophic structure is maintained through subsidies [5–9], and empirical evidence suggests that sharks must engage in wide-ranging foraging excursions to meet energy needs [9, 10]. We used underwater surveys and acoustic telemetry to assess shark residency in the pass and feeding behavior and used bioenergetics models to understand energy flow. Contrary to previous findings, our results highlight that sharks may overcome low local energy availability by feeding on fish spawning aggregations, which concentrate energy from other local trophic pyramids. Fish spawning aggregations are known to be targeted by sharks, but they were previously believed to play a minor role representing occasional opportunistic supplements. This research demonstrates that fish spawning aggregations can play a significant role in the maintenance of local inverted pyramids in pristine marine areas. Conservation of fish spawning aggregations can help conserve shark populations, especially if combined with shark fishing bans.

Description: Time-series studies of arctic marine ecosystems are rare. This is not surprising since polar regions are largely only accessible by means of expensive modern infrastructure and instrumentation. In 1999, the Alfred Wegener Institute, Helmholtz-Centre for Polar and Marine Research (AWI) established the LTER (Long-Term Ecological Research) observatory HAUSGARTEN crossing the Fram Strait at about 79° N. Multidisciplinary investigations covering all parts of the open-ocean ecosystem are carried out at a total of 21 permanent sampling sites in water depths ranging between 250 and 5500 m. From the outset, repeated sampling in the water column and at the deep seafloor during regular expeditions in summer months was complemented by continuous year-round sampling and sensing using autonomous instruments in anchored devices (i.e., moorings and free-falling systems). The central HAUSGARTEN station at 2500 m water depth in the eastern Fram Strait serves as an experimental area for unique biological in situ experiments at the seafloor, simulating various scenarios in changing environmental settings. Long-term ecological research at the HAUSGARTEN observatory revealed a number of interesting temporal trends in numerous biological variables from the pelagic system to the deep seafloor. Contrary to common intuition, the entire ecosystem responded exceptionally fast to environmental changes in the upper water column. Major variations were associated with a Warm-Water-Anomaly evident in surface waters in eastern parts of the Fram Strait between 2005 and 2008. However, even after 15 years of intense time-series work at HAUSGARTEN, we cannot yet predict with complete certainty whether these trends indicate lasting alterations due to anthropologically-induced global environmental changes of the system, or whether they reflect natural variability on multiyear time-scales, for example, in relation to decadal oscillatory atmospheric processes.

Description: Incirrate octopods (those without fins) are among the larger megafauna inhabiting the benthic environments of all oceans, commonly in water depths down to about 3,000 m. They are known to protect and brood their eggs until the juveniles hatch, but to date there is little published information on octopod deep-sea life cycles and distribution. For this study, three manganese-crust and nodule-abundant regions of the deep Pacific were examined by remote operated-vehicle and towed camera surveys carried out between 2011 and 2016. Here, we report that the depth range of incirrate octopods can now be extended to at least 4,290 m. Octopods (twenty-nine individuals from two distinct species) were observed on the deep Ka‘ena and Necker Ridges of the Hawaiian Archipelago, and in a nodule-abundant region of the Peru Basin. Two octopods were observed to be brooding clutches of eggs that were laid on stalks of dead sponges attached to nodules at depths exceeding 4,000 m. This is the first time such a specific mineral-biota association has been observed for incirrate octopods. Both broods consisted of approximately 30 large (2.0–2.7 cm) eggs. Given the low annual water temperature of 1.5oC, it is likely that egg development, and hence brooding, takes years [1] . Stalked-sponge fauna in the Peru Basin require the presence of manganese nodules as a substrate, and near total collapse of such sponge populations was observed following the experimental removal of nodules within the DISCOL (DISturbance and COLonisation) area of the Peru Basin [2] . Stalked fauna are also abundant on the hard substrates of the Hawaiian archipelago. The brooding behavior of the octopods we observed suggests that, like the sponges, they may also be susceptible to habitat loss following the removal of nodule fields and crusts by commercial exploitation.

Description: An understanding of how terrain features influence abundance of a particular species greatly aids in the development of accurate predictive habitat suitability models. In this study, we investigated the observed seafloor coverage of cold-water coral Lophelia pertusa in relation to seabed topography at the Sotbakken and Røst Reefs on the Norwegian margin. The primary terrain features at the study sites are a SW-NE stretching mound at Sotbakken Reef and SW-NE running ridges at Røst Reef, located at depths of ~300–400 m and ~250–320 m respectively. Ship-borne multibeam bathymetry data, JAGO dive video data and JAGO positioning data were used in this study. Terrain variables were calculated at scales of 30 m, 90 m and 170 m based on the bathymetry data. Additionally, we investigated the relationships between the terrain variables at multiple scales using the Unweighted Pair Group Method.

Description: Coral-associated bacteria play an increasingly recognized part in coral health. We investigated the effect of local anthropogenic impacts on coral microbial communities on reefs near Jeddah, the largest city on the Saudi Arabian coast of the central Red Sea. We analyzed the bacterial community structure of water and corals (Pocillopora verrucosa and Acropora hemprichii) at sites that were relatively unimpacted, exposed to sedimentation & local sewage, or in the discharge area of municipal wastewaters. Coral microbial communities were significantly different at impacted sites: in both corals the main symbiotic taxon decreased in abundance. In contrast, opportunistic bacterial families, such as e.g. Vibrionaceae and Rhodobacteraceae, were more abundant in corals at impacted sites. In conclusion, microbial community response revealed a measurable footprint of anthropogenic impacts to coral ecosystems close to Jeddah, even though the corals appeared visually healthy.

Description: Primary productivity in both the Arctic Ocean and the Gulf of Alaska (GOA) is nitrogen limited in the summer when light limitation is relieved, and stratification in the GOA inhibits nutrient fluxes from deep water sources. Concentrations of nutrients and trace metals in these regions are higher closer to shore, and thus rivers have been attributed as the primary coastal source of nutrients and trace metals. Here we evaluate the role of Submarine Groundwater Discharge (SGD), a previously unquantified source of nutrients and trace metals to the coastal Arctic Ocean and GOA. SGD is an especially enriched in nitrate relative to other nutrients, contributing 1.2 ± 0.4 mol NO3 day− 1 m− 1 of shoreline of the Arctic Ocean. In the GOA, both SGD-associated nitrate flux (4.3 ± 2.1 NO3 day− 1 m− 1 of shoreline) and silicate flux (13 ± 6 SiO4 day− 1 m− 1 of shoreline), are substantial when compared to other external nutrient sources. Conservative extrapolations indicate overall SGD supplies more nitrate (1.5–17.5 times) to the GOA than rivers.

Description: The isotopic composition of boron (δ11B) in marine carbonates is well established as a proxy for past ocean pH, however, its robust application to palaeo-environments relies on the generation of species-specific calibrations. Existing calibrations utilising the deep-sea coral (DSC) Desmophyllum dianthus highlight the potential application of this pervasive species to pH reconstructions of intermediate depth waters. Nevertheless, considerable uncertainty remains regarding the estimation of seawater pH from these bulk skeletal δ11B measurements, likely resulting from microstructural heterogeneities in δ11B of D. dianthus. To circumvent this problem, thus improving the reliability of the D. dianthus δ11B-pH calibration, we present a new δ11B calibration of micro-sampled fibrous aragonite from this species. Modern coral specimens recovered from the Atlantic, Pacific, and Southern Oceans, micro-sampled using microdrilling, micromilling, and laser cutting extraction, were analysed for trace element (B/Ca, Mg/Ca, Sr/Ca, and U/Ca) and boron isotopic composition. We find the best calibration against the δ11B of borate in local ambient seawater (a function of pH and taken from hydrographic data sets; pH range 7.57 to 8.05) utilises δ11B measurements of fibres with likely slow growth rates and minimal contamination from adjacent microstructures (identified by low Mg/Ca) for each coral specimen. This new calibration exhibits a stronger, and better-defined dependence on ambient seawater pH compared to bulk coral δ11B; δ11Bfibre = (0.93 ± 0.17) × δ11Bborate + (12.02 ± 2.63). We suggest that the majority of the variability in measured δ11B between replicate bands of fibrous aragonite from a D. dianthus specimen can be explained by small incorporation of non-fibrous aragonite and surface impurities during microsampling and growth rate effects. This study confirms the utility of D. dianthus as an archive of precise palaeo-pH (± 0.07 pH units), provided that suitable sampling strategies are applied.

Description: Highlights • New multiscale seismic data of the Carboneras Fault Zone (CFZ). • The tectonic architecture and depth geometry of the Carboneras Fault is examined. • We characterise fault segments and sub-segments to estimate their seismic potential. • The basement plays a key role in the actual configuration of the fault. • We explore CFZ terminations to know how strain is transferred to nearby structures. Abstract In the SE Iberian Margin, which hosts the convergent boundary between the European and African Plates, Quaternary faulting activity is dominated by a large left-lateral strike–slip system referred to as the Eastern Betic Shear Zone. This active fault system runs along more than 450 km and it is characterised by low to moderate magnitude shallow earthquakes, although large historical events have also occurred. The Carboneras Fault is the longest structure of the Eastern Betic Shear Zone, and its southern termination extends further into the Alboran Sea. Previously acquired high-resolution data (i.e. swath-bathymetry, TOBI sidescan sonar and sub-bottom profiler) show that the offshore Carboneras Fault is a NE–SW-trending upwarped zone of deformation with a length of 90 km long and a width of 0.5 to 2 km, which shows geomorphic features typically found in subaerial strike–slip faults, such as deflected drainage, pressure ridges and “en echelon” folds. However, the neotectonic, depth architecture, and Neogene evolution of Carboneras Fault offshore are still poorly known. In this work we present a multiscale seismic imaging of the Carboneras Fault (i.e. TOPAS, high-resolution multichannel-seismic reflection, and deep penetration multichannel-seismic reflection) carried out during three successive marine cruises, from 2006 to 2010. The new dataset allowed us to define a total of seven seismostratigraphic units (from Tortonian to Late Quaternary) above the basement, to characterise the tectonic architecture and structural segmentation of the Carboneras Fault, and to estimate its maximum seismic potential. We finally discuss the role of the basement in the present-day tectonic evolution of the Carboneras Fault, and explore the northern and southern terminations of the fault and how the strain is transferred to nearby structures.

Description: Highlights • New high-resolution bathymetry and MCS images of the Palomares margin are presented. • Main geomorphological and tectonic features along the margin are analyzed. • Bathymetry is mainly controlled by erosive and halokinesis processes. Abstract The Palomares continental margin is located in the southeastern part of Spain. The margin main structure was formed during Miocene times, and it is currently part of the wide deformation zone characterizing the region between the Iberian and African plates, where no well-defined plate boundary occurs. The convergence between these two plates is here accommodated by several structures, including the left lateral strike–slip Palomares Fault. The region is characterized by sparse, low to moderate magnitude (Mw 〈 5.2) shallow instrumental earthquakes, although large historical events have also occurred. To understand the recent tectonic history of the margin we analyze new high-resolution multibeam bathymetry data and re-processed three multichannel seismic reflection profiles crossing the main structures. The analysis of seafloor morphology and associated subsurface structure provides new insights of the active tectonic features of the area. In contrast to other segments of the southeastern Iberian margin, the Palomares margin contains numerous large and comparatively closely spaced canyons with heads that reach near the coast. The margin relief is also characterized by the presence of three prominent igneous submarine ridges that include the Aguilas, Abubacer and Maimonides highs. Erosive processes evidenced by a number of scars, slope failures, gullies and canyon incisions shape the present-day relief of the Palomares margin. Seismic images reveal the deep structure distinguishing between Miocene structures related to the formation of the margin and currently active features, some of which may reactivate inherited structures. The structure of the margin started with an extensional phase accompanied by volcanic accretion during the Serravallian, followed by a compressional pulse that started during the Latemost Tortonian. Nowadays, tectonic activity offshore is subdued and limited to few, minor faults, in comparison with the activity recorded onshore. The deep Algero-Balearic Basin is affected by surficial processes, associated to halokinesis of Messinian evaporites.

Description: Highlights • Complete 3D reconstruction system from images and videos. • Refractive Structure from Motion for flat port underwater cameras. • Eliminates systematic modeling error caused by using perspective camera model. Cameras can be considered measurement devices complementary to acoustic sensors when it comes to surveying marine environments. When calibrated and used correctly, these visual sensors are well-suited for automated detection, quantification, mapping, and monitoring applications and when aiming at high-accuracy 3D models or change detection. In underwater scenarios, cameras are often set up in pressure housings with a flat glass window, a flat port, which allows them to observe the environment. In this contribution, a geometric model for image formation is discussed that explicitly considers refraction at the interface under realistic assumptions like a slightly misaligned camera (w.r.t. the glass normal) and thick glass ports as common for deep sea applications. Then, starting from camera calibration, a complete, fully automated 3D reconstruction system is discussed that takes an image sequence and produces a 3D model. Newly derived refractive estimators for sparse two-view geometry, pose estimation, bundle adjustment, and dense depth estimation are discussed and evaluated in detail.

Description: Highlights • A multidisciplinary approach to unravel the energetics of hydrothermal explosions. • Pressure failure caused by a lake drainage triggered the hydrothermal explosions. • Bedrock nature controlled the explosion dynamics and the way energy was released. • Approx. 30% of the available thermal energy is converted into mechanical energy. • Released seismic energy as proxy to detect past (and future?) hydrothermal explosions. Hydrothermal explosions frequently occur in geothermal areas showing various mechanisms and energies of explosivity. Their deposits, though generally hardly recognised or badly preserved, provide important insights to quantify the dynamics and energy of these poorly understood explosive events. Furthermore the host rock lithology of the geothermal system adds a control on the efficiency in the energy release during an explosion. We present results from a detailed study of recent hydrothermal explosion deposits within an active geothermal area at Kverkfjöll, a central volcano at the northern edge of Vatnajökull. On August 15th 2013, a small jökulhlaup occurred when the Gengissig ice-dammed lake drained at Kverkfjöll. The lake level dropped by approximately 30 m, decreasing pressure on the lake bed and triggering several hydrothermal explosions on the 16th. Here, a multidisciplinary approach combining detailed field work, laboratory studies, and models of the energetics of explosions with information on duration and amplitudes of seismic signals, has been used to analyse the mechanisms and characteristics of these hydrothermal explosions. Field and laboratory studies were also carried out to help constrain the sedimentary sequence involved in the event. The explosions lasted for 40–50 s and involved the surficial part of an unconsolidated and hydrothermally altered glacio-lacustrine deposit composed of pyroclasts, lavas, scoriaceous fragments, and fine-grained welded or loosely consolidated aggregates, interbedded with clay-rich levels. Several small fans of ejecta were formed, reaching a distance of 1 km north of the lake and covering an area of approximately 0.3 km2, with a maximum thickness of 40 cm at the crater walls. The material (volume of approximately 104 m3) has been ejected by the expanding boiling fluid, generated by a pressure failure affecting the surficial geothermal reservoir. The maximum thermal, craterisation and ejection energies, calculated for the explosion areas, are on the order of 1011, 1010 and 109 J, respectively. Comparison of these with those estimated by the volume of the ejecta and the crater sizes, yields good agreement. We estimate that approximately 30% of the available thermal energy was converted into mechanical energy during this event. The residual energy was largely dissipated as heat, while only a small portion was converted into seismic energy. Estimation of the amount of freshly-fragmented clasts in the ejected material obtained from SEM morphological analyses, reveals that a low but significant energy consumption by fragmentation occurred. Decompression experiments were performed in the laboratory mimicking the conditions due to the drainage of the lake. Experimental results confirm that only a minor amount of energy is consumed by the creation of new surfaces in fragmentation, whereas most of the fresh fragments derive from the disaggregation of aggregates. Furthermore, ejection velocities of the particles (40–50 m/s), measured via high-speed videos, are consistent with those estimated from the field. The multidisciplinary approach used here to investigate hydrothermal explosions has proven to be a valuable tool which can provide robust constraints on energy release and partitioning for such small-size yet hazardous, steam-explosion events.

Description: Ocean acidification (OA) is increasing due to anthropogenic CO2 emissions and poses a threat to marine species and communities worldwide. To better project the effects of acidification on organisms’ health and persistence, an understanding is needed of the 1) mechanisms underlying developmental and physiological tolerance and 2) potential populations have for rapid evolutionary adaptation. This is especially challenging in nonmodel species where targeted assays of metabolism and stress physiology may not be available or economical for large-scale assessments of genetic constraints. We used mRNA sequencing and a quantitative genetics breeding design to study mechanisms underlying genetic variability and tolerance to decreased seawater pH (-0.4 pH units) in larvae of the sea urchin Strongylocentrotus droebachiensis. We used a gene ontology-based approach to integrate expression profiles into indirect measures of cellular and biochemical traits underlying variation in larval performance (i.e., growth rates). Molecular responses to OA were complex, involving changes to several functions such as growth rates, cell division, metabolism, and immune activities. Surprisingly, the magnitude of pH effects on molecular traits tended to be small relative to variation attributable to segregating functional genetic variation in this species. We discuss how the application of transcriptomics and quantitative genetics approaches across diverse species can enrich our understanding of the biological impacts of climate change.

Description: Acoustic imaging has revealed more than 7000 pockmarks on the seafloor above the Troll East gas field in the Norwegian North Sea. We present the first comprehensive study conducted on one of the World's largest pockmark fields complementing the acoustic data with extensive sampling, geochemical and petrographical studies. Specifically, we aimed at detecting possible active seepage still present over this vast area. The pockmarks are present as isolated structures, on average ~ 35 m wide and up to 100 m in size. In addition, smaller satellite pockmarks surround some of the pockmarks. In contrast to the muddy surroundings, parts of the investigated pockmarks contain laterally extensive carbonate deposits or meter sized carbonate blocks. These blocks provide shelter to abundant colonies of benthic megafauna. The carbonate blocks are comprised of micritic Mg-calcite and calcite, micritic aragonite, and botryoidal aragonite. Framboidal pyrite is also commonly present. Carbon isotopic values of the carbonates are 13C-depleted (δ13C as low as − 59.7‰) and with δ18O up to 4.5‰, indicating a methanogenic origin, possibly linked to gas hydrate dissociation. Pore water extracted from shallow cores from the centre and the flanks of the pockmarks show similar Cl and SO4 profiles as the reference cores outside the pockmarks, ruling out active methane seepage. This conclusion is also supported by seafloor video observations that did not reveal any evidence of visual fluid seepage, and by the absence of microbial mats and by the fact that the carbonate blocks are exposed on the seafloor and party oxidized on the surface. We conclude that methane seepage formed this extensive gas field following to gas hydrate dissociation.

Description: Microfossil data on the foraminifers and radiolarians in the sediment core KOMEX LV28-44-3, the Kamchatka slope in the eastern Sea of Okhotsk, exhibit the changes in the water oxygen conditions during the last 146 ky. The paleoenvironmental proxies are the radiolarian species Cycladophora davisiana as indicator of the upper intermediate water ventilation, and the benthic/planktonic foraminifers as indicators of the bioproductivity and bottom water oxygenation. In case of sediment core LV28-44-3, the bottom water represents the lower intermediate one, so that conclusions on paleoenvironments are applicable for the most range of the local intermediate water. The well-oxygenated intermediate and near-bottom waters existed in the area of study during the penultimate glaciation of MIS 6, Early Weichselian initiation of the last glaciation within MIS 5b–d, and last glacial stages of MIS 3–2. The intervals of the short low-O2 bottom events with suboxic conditions (dissolved O2 in water 0.3–1.2 ml/l) occur during the last interglacial MIS 5e (Eemian stage) 125 to 113 ka, and during the last deglaciation 17.5 to 6.5 ka. Eemian low-O2 bottom events are associated with the high bioproductivity of the subsurface water but poor ventilation on the upper intermediate depths. The low-O2 bottom events during the last deglaciation occurred at the high bioproductivity of the subsurface water and active ventilation on the upper intermediate depths.

Description: Highlights: • Cystoseira ericaefolia assemblages were studied along the Mediterranean-Atlantic transition (Alboran Sea). • The assemblages showed significant differences at local and regional scales. • Regional oceanographic features seemed to play an important role explaining regional differences. • No significant differences were found between assemblages under different pollution pressures. • The results support that the effects of pollution are more visible at landscape scales than at assemblage ones. Abstract: The Cystoseira ericaefolia group is conformed by three species: C. tamariscifolia, C. mediterranea and C. amentacea. These species are among the most important habitat forming species of the upper sublittoral rocky shores of the Mediterranean Sea and adjacent Atlantic coast. This species group is sensitive to human pressures and therefore is currently suffering important losses. This study aimed to assess the influence of anthropogenic pressures, oceanographic conditions and local spatial variability in assemblages dominated by C. ericaefolia in the Alboran Sea. The results showed the absence of significant effects of anthropogenic pressures or its interactions with environmental conditions in the Cystoseira assemblages. This fact was attributed to the high spatial variability, which is most probably masking the impact of anthropogenic pressures. The results also showed that most of the variability occurred on at local levels. A relevant spatial variability was observed at regional level, suggesting a key role of oceanographic features in these assemblages.

Description: Highlights • Shield-type volcanoes in young backarc rifts may be linked to arc segmentation. • Arc-transverse faults act as magma conduits for voluminous basaltic eruptions. • The Nifonea volcano hosts the first large lava lake described in a submarine backarc. • Effusive eruptions produced short-live hydrothermal venting and an “event plume”. The Coriolis Troughs of the New Hebrides subduction zone are among the youngest backarc rifts in the world. They reach depths of 〉3 km, despite their small size (〈100 km in length and only 25-45 km wide) and their proximity to the arc front (∼50 km). The narrow, deep graben morphology is characteristic of magma-deficient arc rifts in the early stages of backarc extension, where the rate of extension and subsidence exceeds the magmatic input. Unexpectedly, the youngest graben, the Vate Trough, contains a centrally-located 1000-m tall and 14-km wide shield volcano with a large, 5 × 8 km breached summit caldera. The Nifonea axial volcano has a volume of ∼126 km3, reflecting unusually high extrusion rates, given its young age (〈3 Ma), and the summit caldera hosts the remnants of a large lava lake, the first described from a submarine backarc setting. Extensive diffuse hydrothermal venting and several clusters of black smoker chimneys, with the highest recorded fluid temperatures (368 °C) in the SW Pacific, occur on the youngest lava flows. Comparison with similar axial volcanoes on the mid-ocean ridges suggests that the 46 ×106 m3 of sheet flows in the caldera could have been erupted in 〈30 hours. The focusing of voluminous basaltic eruptions into an otherwise magma-deficient backarc has been linked to strong left-lateral transtension caused by clockwise rotation and segmentation of the southern portion of the arc after collision with d'Entrecasteaux ridge. This study shows that the upper plate stresses can result in dramatic variability in magma supply and hydrothermal activity at the earliest stages of arc rifting and could explain the wide range of melt compositions, volcanic styles and mineral deposit types found in nascent backarc rifts.

Description: Highlights: • Migrating shoals are found on all ebb-tidal deltas of the West and East Frisian Wadden inlets. • There is a clear difference between the behavior of migrating shoals on ebb-tidal deltas seaward of inlets that are comprised of either a single or multiple channels. • For inlets that are comprised of a single channel the following relationships are found: A larger tidal prism correlates with (1) a longer period between successive shoals, and (2) a lower migration velocity. Abstract: Ebb-tidal deltas are bulges of sand that are located seaward of tidal inlets. Many of these deltas feature shoals that cyclically form and migrate towards the coast. The average period between successive shoals that attach to the coast varies among different inlets. In this study, a quantitative assessment of the cyclic behavior of shoals on the ebb-tidal deltas of the Wadden Sea is presented. Analysis of bathymetric data and Landsat satellite images revealed that at the majority of inlets along the Wadden Sea migrating shoals occur. The average period between succeeding shoals correlates to the tidal prism and has values ranging between 4 and 130 years. A larger tidal prism favors larger periods between successive shoal attachments. However, such a relationship was not found for wide inlets with multiple channels. There is a positive relationship between the frequency with which the shoals attach to the coast and their migration velocity, and a negative relationship between the migration velocity of the shoal and the tidal prism. Finally, the data were too sparse to assess whether the longshore sediment transport has a significant effect on the period between successive shoals that attach to the coasts downdrift of the observed tidal inlets.

Description: Highlights • Hydrothermalism in off-axis Tertiary Iceland crust is low-temperature (〈 100 °C). • Hydrothermalism is dike-controlled, unlike the fault-hosted venting in on-axis areas. • Inactive off-axis faults seal quickly due to fluids reacting with fine-grained gouge. • Cracks in country rock next to the dikes form major vertical off-axis permeability. • We predict locations of venting in off-axis regions (〉 2 Ma) of the Reykjanes Ridge. Abstract Hydrothermal activity along the Mid-Atlantic Ridge is predominantly high-temperature venting controlled by volcano-tectonic processes confined to the ridge axis and neotectonic zone, which extends ~ 20 km on each side of the axis (e.g. TAG or Logatchev 1). These vents cannot, however, account for all the heat which needs to be removed to cool the plate and a significant amount of heat is probably removed in the off-axis regions as well. These regions have previously not been systematically surveyed for hydrothermal activity due to a lack of predictive models for its nature, location or controlling structures. Here we use hot springs in the Tertiary Westfjords of Iceland as onshore analogs for hydrothermal activity along the off-axis Mid-Atlantic Ridge to better understand tectonic and volcanological controls on their occurrence, as well as the processes which support hydrothermal circulation. Our results show that even crust ≥ 10 Ma has abundant low-temperature hydrothermal activity. We show that 66% of hot springs investigated, and 100% of those for which a detailed geological setting could be determined, are associated with basaltic dikes cross-cutting the sub-horizontal lava sequence. This is in strong contrast to on-axis springs, which are known (both from underwater and on land) to be predominantly associated with faults. Absence of earthquakes in Westfjords suggests that the faults there are no longer active and possibly sealed by secondary minerals, suppressing fluid circulation. In such a situation, the jointed and fractures dike margins may provide the major pathways for fluid circulation. Extrapolating this idea to the off–axis regions of the Reykjanes Ridge, we suggest, based on bathymetric maps, potential sites for future exploration for off-axis hydrothermal systems.

Description: Highlights • Sub-basalt imaging improvement on the Vøring Margin • Definition of a new seismic facies unit: the Lower Series Flows • Significant organic carbon content within the melting crustal segment • Apectodinium augustum marker for the PETM is reworked into the Lower Series Flows • The Lower Series Flows, early Eocene in age, predate the Vøring Margin breakup Abstract Improvements in sub-basalt imaging combined with petrological and geochemical observations from the Ocean Drilling Program (ODP) Hole 642E core provide new constraints on the initial breakup processes at the Vøring Margin. New and reprocessed high quality seismic data allow us to identify a new seismic facies unit which we define as the Lower Series Flows. This facies unit is seismically characterized by wavy to continuous subparallel reflections with an internal disrupted and hummocky shape. Drilled lithologies, which we correlate to this facies unit, have been interpreted as subaqueous flows extruding and intruding into wet sediments. Locally, the top boundary of this facies unit is defined as a negative in polarity reflection, and referred as the K-Reflection. This reflection can be correlated with the spatial extent of pyroclastic deposits, emplaced during transitional shallow marine to subaerial volcanic activities during the rift to drift transition. The drilled Lower Series Flows consist of peraluminous, cordierite bearing peperitic basaltic andesitic to dacitic flows interbedded with thick volcano-sedimentary deposits and intruded sills. The peraluminous geochemistry combined with available C (from calcite which fills vesicles and fractures), Sr, Nd, and Pb isotopes data point towards upper crustal rock-mantle magma interactions with a significant contribution of organic carbon rich pelagic sedimentary material during crustal anatexis. From biostratigraphic analyses, Apectodinium augustum was found in the The Lower Series Flows. This species is a marker for the Paleocene – Eocene Thermal Maximum (PETM). However, the absence of very low carbon isotope values (from bulk organic matter), that characterize the PETM, imply that A.augustum was reworked into the early Eocene sediments of this facies unit which predate the breakup time of the Vøring Margin. Finally, a plausible conceptual emplacement model for the Lower Series Flows facies unit is proposed. This model comprises several stages: (1) the emplacement of subaqueous peperitic basaltic andesitic flows intruding and/or extruding wet sediments; (2) a subaerial to shallow marine volcanism and extrusion of dacitic flows; (3) a proto-breakup phase with intense shallow marine to subaerial explosive volcanism responsible for pyroclastic flow deposits which can be correlated with the seismic K-Reflection and (4) the main breakup stage with intense transitional tholeiitic MORB-type volcanism and large subsidence concomitant with the buildup of the Seaward Dipping Reflector wedge.

Description: Highlights • Plate boundary re-organization in the central Mediterranean Sea • Segmentation of the subduction complex along lithospheric transverse faults • STEP faults in the Ionian Sea • Pleistocene active faulting and Mt. Etna formation Abstract The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. While crustal shortening is taken up in the accretionary wedge, transtensive deformation accounts for margin segmentation along transverse lithospheric faults. One of these structures is the NNW-SSE transtensive fault system connecting the Alfeo seamount and the Etna volcano (Alfeo-Etna Fault, AEF). A second, NW-SE crustal discontinuity, the Ionian Fault (IF), separates two lobes of the CA subduction complex (Western and Eastern Lobes) and impinges on the Sicilian coasts south of the Messina Straits. Analysis of multichannel seismic reflection profiles shows that: 1) the IF and the AEF are transfer crustal tectonic features bounding a complex deformation zone, which produces the downthrown of the Western lobe along a set of transtensive fault strands; 2) during Pleistocene times, transtensive faulting reactivated structural boundaries inherited from the Mesozoic Tethyan domain which acted as thrust faults during the Messinian and Pliocene; 3) the IF and the AEF, and locally the Malta escarpment, accommodate a recent tectonic event coeval and possibly linked to the Mt. Etna formation. Regional geodynamic models show that, whereas AEF and IF are neighboring fault systems, their individual roles are different. Faulting primarily resulting from the ESE retreat of the Ionian slab is expressed in the northwestern part of the IF. The AEF, on the other hand, is part of the overall dextral shear deformation, resulting from differences in Africa-Eurasia motion between the western and eastern sectors of the Tyrrhenian margin of northern Sicily, and accommodating diverging motions in the adjacent compartments, which results in rifting processes within the Western Lobe of the Calabrian Arc accretionary wedge. As such, it is primarily associated with Africa-Eurasia relative motion.

Description: Highlights • Ba/Ca and δ18OSW records of Core SK 168 reveal distinct changes in SAM intensity. • SAM over the Irrawaddy strengthened beginning at ∼18 ka leading observed changes in the Arabian sea by ∼2–3 kyrs. • Peak monsoon strength during the mid-Holocene in the Andaman Sea consistent with model simulations. • Changes in upper ocean stratification indicate limited influence of NH insolation. Abstract The past variability of the South Asian Monsoon is mostly known from records of wind strength over the Arabian Sea while high-resolution paleorecords from regions of strong monsoon precipitation are still lacking. Here, we present records of past monsoon variability obtained from sediment core SK 168/GC-1, which was collected at the Alcock Seamount complex in the Andaman Sea. We utilize the ecological habitats of different planktic foraminiferal species to reconstruct freshwater-induced stratification based on paired Mg/Ca and δ18O analyses and to estimate seawater δ18O (δ18Osw). The difference between surface and thermocline temperatures (ΔT) and δ18Osw (Δδ18Osw) is used to investigate changes in upper ocean stratification. Additionally, Ba/Ca in G. sacculifer tests is used as a direct proxy for riverine runoff and sea surface salinity (SSS) changes related to monsoon precipitation on land. Our Δδ18Osw time series reveals that upper ocean salinity stratification did not change significantly throughout the last glacial suggesting little influence of NH insolation changes. The strongest increase in temperature gradients between the mixed layer and the thermocline is recorded for the mid-Holocene and indicate the presence of a significantly shallower thermocline. In line with previous work, the δ18Osw and Ba/Ca records demonstrate that monsoon climate during the LGM was characterized by a significantly weaker southwest monsoon circulation and strongly reduced runoff. Based on our data the South Asian Summer Monsoon (SAM) over the Irrawaddyy strengthened gradually after the LGM beginning at ∼18 ka. This is some 3 kyrs before an increase of the Ba/Ca record from the Arabian Sea and indicates that South Asian Monsoon climate dynamics are more complex than the simple N-S displacement of the ITCZ as generally described for other regions. Minimum δ18Osw values recorded during the mid-Holocene are in phase with Ba/Ca marking a stronger monsoon precipitation, which is consistent with model simulations.

Description: To understand how ocean acidification (OA) influences sediment microbial communities, naturally CO2-rich sites are increasingly being used as OA analogues. However, the characterization of these naturally CO2-rich sites is often limited to OA-related variables, neglecting additional environmental variables that may confound OA effects. Here, we used an extensive array of sediment and bottom water parameters to evaluate pH effects on sediment microbial communities at hydrothermal CO2seeps in Papua New Guinea. The geochemical composition of the sediment pore water showed variations in the hydrothermal signature at seep sites with comparable pH, allowing the identification of sites that may better represent future OA scenarios. At these sites, we detected a 60% shift in the microbial community composition compared with reference sites, mostly related to increases inChloroflexisequences. pH was among the factors significantly, yet not mainly, explaining changes in microbial community composition. pH variation may therefore often not be the primary cause of microbial changes when sampling is done along complex environmental gradients. Thus, we recommend an ecosystem approach when assessing OA effects on sediment microbial communities under natural conditions. This will enable a more reliable quantification of OA effects via a reduction of potential confounding effects

Description: Highlights: • We compare the simulated Arctic Ocean in 15 global ocean–sea ice models. • There is a large spread in temperature bias in the Arctic Ocean between the models. • Warm bias models have a strong temperature anomaly of inflow of Atlantic Water. • Dense outflows formed on Arctic shelves are not captured accurately in the models. In this paper we compare the simulated Arctic Ocean in 15 global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE-II). Most of these models are the ocean and sea-ice components of the coupled climate models used in the Coupled Model Intercomparison Project Phase 5 (CMIP5) experiments. We mainly focus on the hydrography of the Arctic interior, the state of Atlantic Water layer and heat and volume transports at the gateways of the Davis Strait, the Bering Strait, the Fram Strait and the Barents Sea Opening. We found that there is a large spread in temperature in the Arctic Ocean between the models, and generally large differences compared to the observed temperature at intermediate depths. Warm bias models have a strong temperature anomaly of inflow of the Atlantic Water entering the Arctic Ocean through the Fram Strait. Another process that is not represented accurately in the CORE-II models is the formation of cold and dense water, originating on the eastern shelves. In the cold bias models, excessive cold water forms in the Barents Sea and spreads into the Arctic Ocean through the St. Anna Through. There is a large spread in the simulated mean heat and volume transports through the Fram Strait and the Barents Sea Opening. The models agree more on the decadal variability, to a large degree dictated by the common atmospheric forcing. We conclude that the CORE-II model study helps us to understand the crucial biases in the Arctic Ocean. The current coarse resolution state-of-the-art ocean models need to be improved in accurate representation of the Atlantic Water inflow into the Arctic and density currents coming from the shelves.

Description: Highlights • Sulphidic event on the shelf resulted in a temporal imbalance of the benthic N cycle. • Bacterial NOx storage is a major source of oxidative power during euxinia. • Peruvian shelf and upper slope sediments are strong recycling sites of fixed N. Abstract Oxygen minimum zones (OMZ) are key regions for fixed nitrogen loss in both the sediments and the water column. During this study, the benthic contribution to N cycling was investigated at ten sites along a depth transect (74–989 m) across the Peruvian OMZ at 12 °S. O2 levels were below detection limit down to ~ 500 m. Benthic fluxes of N2, NO3–, NO2–, NH4+, H2S and O2 were measured using benthic landers. Flux measurements on the shelf were made under extreme geochemical conditions consisting of a lack of O2, NO3– and NO2– in the bottom water and elevated seafloor sulphide release. These particular conditions were associated with a large imbalance in the benthic nitrogen cycle. The sediments on the shelf were densely covered by filamentous sulphur bacteria Thioploca, and were identified as major recycling sites for DIN releasing high amounts of NH4+up to 21.2 mmol m−2 d−1 that were far in excess of NH4+release by ammonification. This difference was attributed to dissimilatory nitrate (or nitrite) reduction to ammonium (DNRA) that was partly being sustained by NO3– stored within the sulphur oxidizing bacteria. Sediments within the core of the OMZ (ca. 200 to 400 m) also displayed an excess flux of N of 3.5 mmol m−2 d−1 mainly as N2. Benthic nitrogen and sulphur cycling in the Peruvian OMZ appears to be particularly susceptible to bottom water fluctuations in O2, NO3−and NO2−, and may accelerate the onset of pelagic euxinia when NO3−and NO2−become depleted.

Description: Highlights • Mantle plumes have broadly distinctive depleted and enriched compositions. • The Earth's lower mantle has a non-chondritic composition. • The deep mantle has large planetary-scale geochemical heterogeneity. • New normalising factors presented for modelling mantle-derived igneous rocks. Abstract Determining the composition and geochemical diversity of Earth's deep mantle and subsequent ascending mantle plumes is vital so that we can better understand how the Earth's primitive mantle reservoirs initially formed and how they have evolved over the last 4.6 billion years. Further data on the composition of mantle plumes, which generate voluminous eruptions on the planet's surface, are also essential to fully understand the evolution of the Earth's hydrosphere and atmosphere with links to surface environmental changes that may have led to mass extinction events. Here we present new major and trace element and Sr–Nd–Pb–Hf isotope data on basalts from Curacao, part of the Caribbean large igneous province. From these and literature data, we calculate combined major and trace element compositions for the mantle plumes that generated the Caribbean and Ontong Java large igneous provinces and use mass balance to determine the composition of the Earth's lower mantle. Incompatible element and isotope results indicate that mantle plumes have broadly distinctive depleted and enriched compositions that, in addition to the numerous mantle reservoirs already proposed in the literature, represent large planetary-scale geochemical heterogeneity in the Earth's deep mantle that are similar to non-chondritic Bulk Silicate Earth compositions.

Description: Highlights • Stratigraphic framework over the Miocene-Pliocene boundary at IODP Site U1387. • Abrupt sedimentary changes over the Miocene-Pliocene boundary. • Clear hints for onset of Mediterranean Outflow after the Messinian Salinity Crisis. • Evidence of bottom water currents in contouritic sedimentation and elevated Zr/Al. • Quiet, hemipelagic sediment deposition during the Messinian in the Gulf of Cadiz. Abstract Integrated Ocean Drilling Program (IODP) Expedition 339 cored multiple sites in the Gulf of Cadiz in order to study contourite deposition resulting from Mediterranean Outflow water (MOW). One hole, U1387C, was cored to a depth of 865.6 meters below seafloor (mbsf) with the goal of recovering the Latest Miocene to Pliocene transition in order to evaluate the history of MOW immediately after the end of the Messinian Salinity Crisis. To understand this history, an accurate age model for the succession is needed, but is challenging to construct, because the Miocene-Pliocene boundary is not marked by a clear biostratigraphic event in the Atlantic and coring gaps occur within the recovered stratigraphic record. These limitations are overcome by combining a variety of chronostratigraphic datasets to construct an age-model that fits the currently available age indicators and demonstrates that coring in Hole U1387C did indeed recover the Miocene-Pliocene boundary at around 826 mbsf. This boundary is associated with a distinct and abrupt change in depositional environment. During the latest Messinian, hemipelagic sediments exhibiting precession-induced climate variability were deposited. These are overlain by Pliocene sediments deposited at a much higher sedimentation rate, with much higher and more variable XRF-scanning Zr/Al ratios than the underlying sediment, and that show evidence of winnowing, particle sorting and increasing grain size, which we interpret to be related to the increasing flow of MOW. Pliocene sedimentary cyclicity is clearly visible in both the benthic δ18O record and the Zr/Al data and is probably also precessionally controlled. Two contouritic bigradational sandy-beds are revealed above the third sedimentary cycle of the Pliocene. On the basis of these results, we conclude that sedimentation associated with weak Mediterranean-Atlantic exchange, began in the Gulf of Cadiz virtually at or shortly after the Miocene-Pliocene boundary.

Description: Connectivity of pelagic, early life stages via transport by ocean currents may affect survival chances of offspring, recruitment success, and mixing of stocks across management units. Based on drift model studies, transport patterns of particles representing exogenously feeding cod larvae in the transition area between North Sea and Baltic were investigated to (i) determine long-term trends and variability in advective transport of larvae from spawning grounds to juvenile nursery areas, (ii) estimate the degree of exchange between different management areas, and (iii) compare the results with spatial distributions of juvenile cod. The transport of particles showed considerable intra- and interannual variability, but also some general patterns of retention within and dispersion to different management areas. Good spatial overlap of particle end positions, representing potential juvenile settlement areas, with observed distributions of juveniles in bottom trawl surveys suggests that the drift simulations provide reasonable estimates of early life stage connectivity between cod populations in the investigated areas. High exchange rates of particles between management areas of up to ca. 70% suggest that cod populations in the investigated areas are demographically correlated. Results are discussed in relation to their relevance for stock structure, fish stock assessment, and management.

Description: Highlights • PetroMod is the 1st basin modelling software including methane hydrate simulation. • The Gas hydrate module includes physical, thermodynamic, and kinetic properties. • PetroMod simulates the evolution over time of the GHSZ. • PetroMod includes a kinetic for the organic matter degradation at low temperature. Abstract Within the German gas hydrate initiative SUGAR, a new 2-D/3-D module simulating the biogenic generation of methane from organic matter and the formation of gas hydrates has been developed and included in the petroleum systems modelling software package PetroMod®. Typically, PetroMod® simulates the thermogenic generation of multiple hydrocarbon components (oil and gas), their migration through geological strata, finally predicting oil and gas accumulations in suitable reservoir formations. We have extended PetroMod® to simulate gas hydrate accumulations in marine and permafrost environments by the implementation of algorithms describing (1) the physical, thermodynamic, and kinetic properties of gas hydrates; and (2) a kinetic continuum model for the microbially mediated, low temperature degradation of particulate organic carbon in sediments. Additionally, the temporal and spatial resolutions of PetroMod® were increased in order to simulate processes on time scales of hundreds of years and within decimetres of spatial extension. In order to validate the abilities of the new hydrate module, we present here results of a theoretical layer-cake model. The simulation runs predict the spatial distribution and evolution in time of the gas hydrate stability field, the generation and migration of thermogenic and biogenic methane gas, and its accumulation as gas hydrates.

Description: Shallow (elevated) portions of mid-ocean ridges with enriched geochemical compositions near hotspots document the interaction of hot geochemically enriched plume mantle with shallow depleted upper mantle. Whereas the spatial variations in geochemical composition of ocean crust along the ridge axis in areas where plume-ridge interaction is taking place have been studied globally, only restricted information exists concerning temporal variations in geochemistry of ocean crust formed through plume-ridge interaction. Here we present a detailed geochemical study of 0-1.5 Ma ocean crust sampled from the Western Galápagos Spreading Center (WGSC) axis to 50 km north of the axis, an area that is presently experiencing a high influx of mantle material from the Galápagos Hotspot. The tholeiitic to basaltic andesitic fresh glass and few bulk rock samples have incompatible element abundances and Sr-Nd-Pb isotopic compositions intermediate between depleted normal mid-ocean-ridge basalt (N-MORB) from 〉95.5°W along the WGSC and enriched lavas from the Galápagos Archipelago, displaying enriched (E-)MORB type compositions. Only limited and no systematic geochemical variations are observed with distance from the ridge axis for 〈1.0 Ma old WGSC crust, whereas 1.0-1.5 Ma old crust trends to more enriched isotopic compositions in 87Sr/86Sr, 143Nd/144Nd, 207Pb/204Pb and 208Pb/204Pb isotope ratios. On isotope correlation diagrams, the data set displays correlations between depleted MORB and two enriched components. Neither the geographically referenced geochemical domains of the Galápagos Archipelago nor the end members used for principle component analysis can successfully describe the observed mixing relations. Notably an off-axis volcanic cone at site DR63 has the appropriate composition to serve as the enriched component for the younger WGSC and could represent a portion of the northern part of the Galápagos plume not sampled south of the WGSC. Similar compositions to samples from volcanic cone DR63 have been found in the northern part of the 11-14 Ma Galápagos hotspot track offshore Costa Rica, indicating that this composition is derived from the northern portion of the Galápagos plume. The older WGSC requires involvement of an enriched mantle two (EMII) type source, not recognized thus far in the Galápagos system, and is interpreted to reflect entrained material either from small-scale heterogeneities within the upper mantle or from the mantle transition zone. Overall the source material for the 0-1.5 Ma WGSC ocean crust appears to represent mixing of depleted upper mantle with Northern Galápagos Plume material of relatively uniform composition in relatively constant proportions.

Description: Shatsky Rise in the Northwest Pacific is the best example so far of an oceanic plateau with two potential hotspot tracks emanating from it: the linear Papanin volcanic ridge and the seamounts comprising Ojin Rise. Arguably, these hotspot tracks also project toward the direction of Hess Rise, located ∼1200 km away, leading to speculations that the two plateaus are connected. Dredging was conducted on the massifs and seamounts around Shatsky Rise in an effort to understand the relationship between these plateaus and associated seamounts. Here, we present new 40Ar/39Ar ages and trace element and Nd, Pb, and Hf isotopic data for the recovered dredged rocks and new trace elements and isotopic data for a few drill core samples from Hess Rise. Chemically, the samples can be subdivided into plateau basalt-like tholeiites and trachytic to alkalic ocean-island basalt compositions, indicating at least two types of volcanic activity. Tholeiites from the northern Hess Rise (DSDP Site 464) and the trachytes from Toronto Ridge on Shatsky’s TAMU massif have isotopic compositions that overlap with those of the drilled Shatsky Rise plateau basalts, suggesting that both Rises formed from the same mantle source. In contrast, trachytes from the southern Hess Rise (DSDP Site 465A) have more radiogenic Pb isotopic ratios that are shifted toward a high time-integrated U/Pb (HIMU-type mantle) composition. The compositions of the dredged seamount samples show two trends relative to Shatsky Rise data: one toward lower 143Nd/144Nd but similar 206Pb/204Pb ratios, the other toward similar 143Nd/144Nd but more radiogenic 206Pb/204Pb ratios. These trends can be attributed to lower degrees of melting either from lower mantle material during hotspot-related transition to plume tail or from less refractory shallow mantle components tapped during intermittent deformation-related volcanism induced by local tectonic extension between and after the main volcanic-edifice building episodes on Shatsky Rise. The ocean-island-basalt-like chemistry and isotopic composition of the Shatsky and Hess rise seamounts contrast with those formed by purely deformation-related shallow mantle-derived volcanism, favoring the role of a long-lived mantle anomaly in their origin. Finally, new 40Ar/39Ar evidence indicates that Shatsky Rise edifices may have been formed in multiple-stages and over a longer duration than previously believed.

Description: Highlights • Six combined 231Pa/230Th and εNdεNd down-core profiles back to 25 ka are presented. • Increased influence of SCW and northward advection of deep waters during LGM/HS1. • Evidence for an active but shallower northern overturning cell during LGM/HS1. Abstract Reconstructing past modes of ocean circulation is an essential task in paleoclimatology and paleoceanography. To this end, we combine two sedimentary proxies, Nd isotopes (εNdεNd) and the 231Pa/230Th ratio, both of which are not directly involved in the global carbon cycle, but allow the reconstruction of water mass provenance and provide information about the past strength of overturning circulation, respectively. In this study, combined 231Pa/230Th and εNdεNd down-core profiles from six Atlantic Ocean sediment cores are presented. The data set is complemented by the two available combined data sets from the literature. From this we derive a comprehensive picture of spatial and temporal patterns and the dynamic changes of the Atlantic Meridional Overturning Circulation over the past ∼25 ka. Our results provide evidence for a consistent pattern of glacial/stadial advances of Southern Sourced Water along with a northward circulation mode for all cores in the deeper (〉3000 m) Atlantic. Results from shallower core sites support an active overturning cell of shoaled Northern Sourced Water during the LGM and the subsequent deglaciation. Furthermore, we report evidence for a short-lived period of intensified AMOC in the early Holocene.

Description: Highlights: • The stress response to salinity in subpopulations of the Baltic cod was examined. • Two different profiles of response to salinity were observed. • Changes in response profiles may be a functional adaptation to variable salinity. • Adaptation protects cod against stress during vertical and long-distance migrations. • Salinity is a barrier maintaining the genetic and physiological separations of cod. Abstract: Atlantic cod (Gadus morhua) occur in marine water of different salinities: from oceanic waters at salinity of 35 to Baltic Sea waters where the lowest level of salinity reaches 5–6. The stress response to different salinities in the eastern and western Baltic cod populations was examined. Two genes of Na +, K + -ATPase 1a (atp1a) and heat shock protein 70 (hsp70) expression, plasma cortisol and osmolality were used as markers of osmotic stress to characterize the reaction profiles of two populations of G. morhua from the western and eastern parts of the Baltic Sea. Atlantic cod were sampled in November 2012 from western Kiel Bight (KIEL, salinity of 18) and eastern Gdańsk Bay (GDA, salinity of 8). Live fish were transported to the Marine Station of the University of Gdańsk in Hel and were settled in tanks (3500 L). Cod were kept at 10 °C in recirculated water, which simulated the natural salinities of the geographic source region of the fish. Results showed that in the reduced and elevated salinity water of the KIEL group, we observed no change in expression of atp1a and slightly increased expression of hsp70. In the GDA group, there were no significant changes of hsp70 expression but the level of atp1a was significantly increased in both salinities. In both groups, concentration of cortisol increased after exposure to elevated salinity, while in fish exposed to reduced salinity, a significantly higher concentration of cortisol was observed after 72 h. The high expression of atp1a that observed in the eastern group (GDA) supports the thesis of a genetic background to the adaptation to variable salinity. This adaptation may protect this species against an osmotic stress caused by daily vertical migrations and long-distance migration to spawning areas. At the same life-time, salinity is a barrier maintaining the genetic and physiological separations between G. morhua stocks and affecting the structure of this fish subpopulation in the Baltic Sea.

Description: Highlights • First dataset of 236U in the AO. • 236U/238U and 129I/236U: as new dual tracer for water mass circulation. • 236U/238U and 129I/236U: a tool to distinguish sources of artificial radionuclides to AO. • 236U/238U and 129I/236U: a sensitive tool to study isolation ages of deep waters in AO. Abstract The first dataset of 236U/238U in the water column of the Arctic Ocean (AO) is presented and shows the widest range of ratios reported so far in the open ocean, from (5±55±5) to (3840±260)×10−12(3840±260)×10−12. Surface samples and depth profiles were collected during two GEOTRACES expeditions in 2011–2012 and analyzed for the concentrations of 236U and 129I, with the aim of investigating whether the combination of 236U/238U and 129I/236U can be used as a new oceanographic tool in the AO. Results show that the distributions of the 236U/238U and 129I/236U atomic ratios are consistent with the different water masses in the AO. High 236U/238U and 129I/236U ratios in the upper water column (〉2000×10−12〉2000×10−12 and 〉200, respectively) illustrate the penetration of Atlantic waters (AW) into the AO. Lower values were found in Pacific waters (PW) and deep waters of the AO. Rivers seem to represent a temporally and spatially-constrained third anthropogenic source of 236U but more data are needed to confirm this. In a simple mixing model, the combination of 236U/238U and 129I/236U reveals a high contribution (〉99%) of natural background waters (pre-nuclear era) in the deep and bottom waters of the Amerasian basin, indicating an apparent water mass renewal time of 〉1000 years. Despite the relatively high apparent age of the Amerasian Basin deep waters, this work shows the potential of using the dual-tracer approach as a new oceanographic tool in the Arctic Ocean.

Description: Hydrothermal vent deposits form on the seafloor as a result of cooling and mixing of hot hydrothermal fluids with cold seawater. Amongst the major sulfide and sulfate minerals that are preserved at vent sites, barite (BaSO4) is unique because it requires the direct mixing of Ba-rich hydrothermal fluid with sulfate-rich seawater in order for precipitation to occur. Because of its extremely low solubility, barite crystals preserve geochemical fingerprints associated with conditions of formation. Here, we present data from petrographic and geochemical analyses of hydrothermal barite from the Endeavour Segment of the Juan de Fuca Ridge, northeast Pacific Ocean, in order to determine the physical and chemical conditions under which barite precipitates within seafloor hydrothermal vent systems. Petrographic analyses of 22 barite-rich samples show a range of barite crystal morphologies: dendritic and acicular barite forms near the exterior vent walls, whereas larger bladed and tabular crystals occur within the interior of chimneys. A two component mixing model based on Sr concentrations and 87Sr/86Sr of both seawater and hydrothermal fluid, combined with 87Sr/86Sr data from whole rock and laser-ablation ICP-MS analyses of barite crystals indicate that barite precipitates from mixtures containing as low as 17% and as high as 88% hydrothermal fluid component, relative to seawater. Geochemical modelling of the relationship between aqueous species concentrations and degree of fluid mixing indicates that Ba2+ availability is the dominant control on mineral saturation. Observations combined with model results support that dendritic barite forms from fluids of less than 40% hydrothermal component and with a saturation index greater than ∼0.6, whereas more euhedral crystals form at lower levels of supersaturation associated with greater contributions of hydrothermal fluid. Fluid inclusions within barite indicate formation temperatures of between ∼120 °C and 240 °C during barite crystallization. The comparison of fluid inclusion formation temperatures to modelled mixing temperatures indicates that conductive cooling of the vent fluid accounts for 60–120 °C reduction in fluid temperature. Strontium zonation within individual barite crystals records fluctuations in the amount of conductive cooling within chimney walls that may result from cyclical oscillations in hydrothermal fluid flux. Barite chemistry and morphology can be used as a reliable indicator for past conditions of mineralization within both extinct seafloor hydrothermal deposits and ancient land-based volcanogenic massive sulfide deposits.

Description: Introductions of non-indigenous species (NIS) are considered a major threat to aquatic ecosystems worldwide. While it is valuable to know the distributions and ranges of NIS, predictive spatial models along different environmental gradients are more useful for management of these species. In this study we modelled how external drivers and local environmental conditions contribute to the spatial distribution of an invasive species using the distribution of the round goby Neogobius melanostomus in the Baltic Sea as an example. Using the collected distribution data, an updated map on the species distribution and its invasion progress in the Baltic Sea was produced. The current range of the round goby observations is extensive, covering all major sub-basins of the Baltic Sea. The most recent observations appeared in the northern regions (Northern Baltic Proper, the Gulf of Bothnia and the Gulf of Finland) and on the eastern and western coasts of southern Sweden. Modelling results show that the distribution of the round goby is primarily related to local abiotic hydrological conditions (wave exposure). Furthermore, the probability of round goby occurrence was very high in areas in close proximity to large cargo ports. This links patterns of the round goby distribution in the Baltic Sea to shipping traffic and suggests that human factors together with natural environmental conditions are responsible for the spread of NIS at a regional sea scale.

Description: The permanent presence of microplastics in the marine environment is considered a global threat to several marine animals. Heavy metals and microplastics are typically included in two different classes of pollutants but the interaction between these two stressors is poorly understood. During 14 days of experimental manipulation, we examined the adsorption of two heavy metals, copper (Cu) and zinc (Zn), leached from an antifouling paint to virgin polystyrene (PS) beads and aged polyvinyl chloride (PVC) fragments in seawater. We demonstrated that heavy metals were released from the antifouling paint to the water and both microplastic types adsorbed the two heavy metals. This adsorption kinetics was described using partition coefficients and mathematical models. Partition coefficients between pellets and water ranged between 650 and 850 for Cu on PS and PVC, respectively. The adsorption of Cu was significantly greater in PVC fragments than in PS, probably due to higher surface area and polarity of PVC. Concentrations of Cu and Zn increased significantly on PVC and PS over the course of the experiment with the exception of Zn on PS. As a result, we show a significant interaction between these types of microplastics and heavy metals, which can have implications for marine life and the environment. These results strongly support recent findings where plastics can play a key role as vectors for heavy metal ions in the marine system. Finally, our findings highlight the importance of monitoring marine litter and heavy metals, mainly associated with antifouling paints, particularly in the framework of the Marine Strategy Framework Directive (MSFD).

Description: Highlights: • We propose a new Phytoplankton Index for monitoring the ecological status of lakes. • We develop a community index integrating the response to anthropogenic pressure. • We link high frequency Secchi depth with low frequency phytoplankton monitoring. • We demonstrate the correlation of the index with land use on the watershed scale. • The index offers a cost-effective tool, practical for medium-qualified personnel. Abstract: We propose and test a new Phytoplankton Community Index (PhyCoI) for monitoring the ecological status of lakes and reservoirs. The design of our PhyCoI is based on the fact that phytoplankton biomass and community structure respond to changes in water quality (mainly eutrophication) and by themselves also influence water quality. In order to accommodate this double role of phytoplankton as indicator and impact, PhyCoI is based on phytoplankton community properties at different hierarchical levels combining both specific metrics (total biomass, taxonomic group biomass, cyanobacteria contribution, taxonomic group species richness) and new or modified sub-indices. It is calculated from the scores of the different metrics/sub-indices resulting in a final index value in the range from 0 to 5, to assess water quality on the basis of five ecological classes according to the Water Framework Directive (WFD). The test of PhyCoI was based on Carlson's Trophic State Index (TSISD) based on water transparency (Secchi depth) in 26 Greek lakes and reservoirs covering the entire spectrum from oligotrophic to hypertrophic. A highly significant relationship at p 〈 0.001 between the two variables was found, with the values of the PhyCoI declining with increasing TSISD. Furthermore, a significant relationship between the PhyCoI and land use types at the watershed of the studied freshwaters was found identifying permanent crops, pastures and shrubs and herbaceous vegetation associations as significant predictors of PhyCoI values. Because of the amount of labor involved in obtaining the PhyCoI we suggest to combine low frequency PhyCoI determinations with a high frequency Secchi depth measurements for practical monitoring purposes.

Description: The cold water palinurid Jasus lalandii (“West Coast rock lobster”) is a commercially important crustacean in South Africa and Namibia and inhabits the Benguela Current Eastern Boundary System. This habitat is characterised by strong upwelling events in summer and algal blooms with their subsequent decay in autumn. Upwelling can lead to acute hypercapnia whereas the algal decay is associated with acute hypercapnic hypoxia. Both types of hypercapnic events could become more frequent and severe in the future due to ongoing climate change. The aim of the present study was, however, to study the capability and mechanisms of response in J. lalandii to hypercapnia exclusively. Accordingly, the following research questions were formulated: 1) To what extent is haemocyanin oxygen-binding affinity of adult J. lalandii pH-sensitive? 2) Can adult male J. lalandii respond swiftly to drastic changes in pH? 3) What physiological mechanisms facilitate a potential response to a drastically declining pH, i.e. acute hypercapnia? These questions were answered by analysing 1) the pH sensitivity of the haemocyanin's oxygen binding properties and 2) in vivo changes in the acid–base balance of adult J. lalandii during acute exposure to hypercapnia (pH 7.4). Results showed the following: 1) Haemocyanin displays a strong Bohr shift (whole haemolymph: ΔlogP50/ΔpH = − 1.17; dialysed haemolymph: ΔlogP50/ΔpH = − 0.84) in response to lowering of pH. 2) Acute hypercapnia leads to a decline in extracellular pH within the initial 1.5 h of exposure. 3) Thereafter, active compensation becomes apparent as the bicarbonate levels start to increase, with complete compensation reached after 5 h of exposure (+ 2.3 mmol l− 1; + 48%). 3) This bicarbonate increase is reversed when returning lobsters to normocapnia (pH 7.9). 4) Levels of molecular modulators of haemocyanin oxygen affinity (Ca2 +, Mg2 + and l-lactate) do not change during acute exposure to hypercapnia.

Description: Highlights: • We analyzed the transcriptome of sticklebacks exposed to different parasite genotypes. • A clustering of complement genes could be observed in head kidney samples. • Genotype of final infection was not essential to immune response. • Adaptive immune responses most likely optimized for genotype-independent resistance. Adaptive immunity in vertebrates can confer increased resistance against invading pathogens upon re-infection. But how specific parasite genotypes affect the temporal transition from innate to adaptive immunity under continual exposure to parasites is poorly understood. Here, we investigated the effects of homologous and heterologous exposures of genetically distinct parasite lineages of the eye fluke Diplostomum pseudospathaceum on gene expression patterns of adaptive immunity in sticklebacks (Gasterosteus aculeatus). Observable differences in gene expression were largely attributable to final exposures while there was no transcription pattern characteristic for a general response to repeated infections with D. pseudospathaceum. None of the final exposure treatments was able to erase the distinct expression patterns resulting from a heterologous pre-exposed fish. Interestingly, heterologous final exposures showed similarities between different treatment groups subjected to homologous pre-exposure. The observed pattern was supported by parasite infection rates and suggests that host immunization was optimized towards an adaptive immune response that favored effectiveness against parasite diversity over specificity.

Description: The Azores islands in the central North-Atlantic originate from a regional melting anomaly, probably created by melting hot, unusually hydrous and geochemically enriched mantle. Here, we present Hf, Pb and Os isotopic data in geochemically well-characterised primitive lavas from the islands Flores and Corvo that are located west of the Mid-Atlantic Ridge (MAR), as well as submarine samples from a subsided island west of Flores and from Deep Sea Drilling Project (DSDP) holes drilled in the western part of the Azores platform and beyond. These are compared to existing data from the Azores islands east of the MAR. The geodynamic origin of the two islands west of the ridge axis and furthest from the inferred plume centre in the central part of the plateau is enigmatic. The new data constrain the source compositions of the Flores and Corvo lavas and show that the western and eastern Azores mantle is isotopically similar, with the exception of an enriched component found exclusively on eastern São Miguel. Trace element ratios involving high field strength elements (HFSE) are distinctly different in the western islands (e.g. twofold higher Nb/Zr) compared to any of the islands east of the MAR. A similar signature is observed in MAR basalts to the south of the Azores platform and inferred to originate from (auto-) metasomatic enrichment of the sub-ridge mantle (Gale et al., 2011, 2013). In a similar fashion, low degree melts from an enriched source component may metasomatise the ambient plume mantle underneath the western Azores islands. Melting such a modified plume mantle can explain the chemical differences between lavas from the western and eastern Azores islands without the need for additional plume components. Recent re-enrichment and intra melting column modification of the upwelling mantle can cause local to regional scale geochemical differences in mantle-derived melts.

Description: Highlights: • Wound activated prostaglandin production was quantified in Gracilaria vermiculophylla. • Specimens from non-native populations contained higher prostaglandin concentrations. • Prostaglandins and related compounds deter animal consumers. • Activated defense through Prostaglandins was selected during Gracilaria's invasion history. • As a consequence specimens from invasive populations are not safe for human consumption. Abstract: The capacity of the East Asian seaweed Gracilaria vermiculophylla (“Ogonori”) for production of prostaglandin E2 from arachidonic acid occasionally causes food poisoning after ingestion. During the last two decades the alga has been introduced to Europe and North America. Non-native populations have been shown to be generally less palatable to marine herbivores than native populations. We hypothesized that the difference in palatability among populations could be due to differences in the algal content of prostaglandins. We therefore compared the capacity for wound-activated production of prostaglandins and other eicosatetraenoid oxylipins among five native populations in East Asia and seven non-native populations in Europe and NW Mexico, using a targeted metabolomics approach. In two independent experiments non-native populations exhibited a significant tendency to produce more eicosatetraenoids than native populations after acclimation to identical conditions and subsequent artificial wounding. Fourteen out of 15 eicosatetraenoids that were detected in experiment I and all 19 eicosatetraenoids that were detected in experiment II reached higher mean concentrations in non-native than in native specimens. Wounding of non-native specimens resulted on average in 390% more 15-keto-PGE2, in 90% more PGE2, in 37% more PGA2 and in 96% more 7,8-di-hydroxy-eicosatetraenoic acid than wounding of native specimens. Not only PGE2, but also PGA2 and dihydroxylated eicosatetraenoic acid are known to deter various biological enemies of G. vermiculophylla that cause tissue or cell wounding, and in the present study the latter two compounds also repelled the mesograzer Littorina brevicula. Non-native populations of G. vermiculophylla are thus more defended against herbivory than native populations. This increased capacity for activated chemical defense may have contributed to their invasion success and at the same time it poses an elevated risk for human food safety.

Description: Highlights: • D_Ba is investigated along a high resolution and quasi-zonal transect in the MedSea. • The D_Ba content ranges from 38 to 85 nmol kg− 1 with local deep D_Ba maxima reaching up to 172 nmol kg− 1. • The water column is largely undersaturated with respect to barite (0.2 〈 SI 〈 0.6). • The D_Ba distribution is impacted by the large-scale Mediterranean circulation and biogeochemical processes. • Local changes in the D_Ba patterns may be the key to better constrain the C dynamics in the MedSea. Abstract: The dissolved barium (D_Ba) data set for the Mediterranean Sea is here expanded with data from a large-scale transect sampled in April 2011 (M84/3 cruise) at high resolution. A total of 833 seawater samples have been analyzed for D_Ba. Over the basin the D_Ba content ranges from 38 to 85 nmol kg− 1 with local deep D_Ba maxima reaching up to 172 nmol kg− 1. Deep D_Ba maxima are associated with near bottom waters influenced by benthic processes and brine waters. The water column is largely undersaturated with respect to barite (BaSO4, the main phase of particulate biogenic barium P_Ba), with water column barite saturation state ranging between 0.2 and 0.6 over the basin. This new D_Ba dataset shows that the general zonal distribution of D_Ba is impacted by the large-scale Mediterranean circulation, as evidenced by the Levantine Intermediate Water zonal and meridional progression as well as by the eastward flow of surface Atlantic Water. However biogeochemical processes are also at play, as suggested by an elevated D_Ba content of deep waters and by local lower D_Ba contents in intermediate waters. These features could be attributed to active cycling between the particulate and dissolved Ba phases. Since P_Ba barite has been recognized in previous studies as a proxy for particulate organic carbon remineralization at intermediate depths, the significance of local changes in the water column D_Ba patterns may be the key to better constrain the Ba and carbon dynamics in the Mediterranean Sea.

Description: Highlights • Holocene sea subsurface temperatures after Husum & Hald (2012) estimated from planktic foraminifer fauna in E Fram Strait. • Biomarkers and IP25-derived indices (including DIP25) indicate surface water variability. • Delayed onset of early Holocene conditions in subsurface (∼10.6 ka) compared to surface (∼11.7 ka) water conditions. • Warm Atlantic layer likely occupied uppermost 200 m in eastern Fram Strait between 10 and 9 ka. • Diverging late Holocene trends in surface and subsurface conditions linked to presence of strong pycnocline/stratification. Abstract Two high-resolution sediment cores from eastern Fram Strait have been investigated for sea subsurface and surface temperature variability during the Holocene (the past ca 12,000 years). The transfer function developed by Husum and Hald (2012) has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period. Additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions, and to conclude on the Holocene climate and oceanographic variability on the West Spitsbergen continental margin. Results consistently reveal warm sea surface to subsurface temperatures of up to 6 °C until ca 5 cal ka BP, with maximum seawater temperatures around 10 cal ka BP, likely related to maximum July insolation occurring at that time. Maximum Atlantic Water (AW) advection occurred at surface and subsurface between 10.6 and 8.5 cal ka BP based on both foraminiferal and dinocyst temperature reconstructions. Probably, a less-stratified, ice-free, nutrient-rich surface ocean with strong AW advection prevailed in the eastern Fram Strait between 10 and 9 cal ka BP. Weakened AW contribution is found after ca 5 cal ka BP when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka BP. Cold late Holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high δ18O values of the subpolar planktic foraminifer species Turborotalita quinqueloba. While IP25-associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea-ice increase since about 7 cal ka BP in surface waters, planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface AW influx since ca 3 cal ka BP. The observed decoupling of surface and subsurface waters during the later Holocene is most likely attributed to a strong pycnocline layer separating cold sea-ice fed surface waters from enhanced subsurface AW advection. This may be related to changes in North Atlantic subpolar versus subtropical gyre activity.

Description: Highlights: • Strong longitudinal variability occurs in the North Atlantic subtropical gyre. • Allochthonous supply of semilabile DOP may occur in the western oligotrophic gyre. • Semilabile DON supply does not provide a significant direct N source. Abstract: We combine modelled timescales of ocean circulation with satellite-retrieved and in situ biogeochemical observations collected in spring along 24.5°N in the subtropical North Atlantic. Longitudinal gradients in the distribution of dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) and in other biogeochemical parameters are associated with the longitudinal variability in physical forcing and in the eastward increase of the timescale of advective transport. The western (West of 70°W) and eastern (East of 30°W) margins of the subtropical gyre appear influenced by the productive regions of the Gulf Stream and upwelling zones off Africa, respectively. Within the oligotrophic zone between 70 and 31°W, at approximately 46°W there is a change in the nutrient-controlling factors from the western ultra- oligotrophic with barely any seasonal cycle to an eastern oligotrophic environment with a more intense mixed layer dynamics. The allochthonous supply of semilabile-DOP may be important in the western sector of the oligotrophic gyre (approx. 70–46°W) where, together with the combination of shallow mixed layers, almost permanent stratification and high water temperatures create a niche for the growth of diazotrophs, which we detect from space. Turnover estimates exceeding 3 yr suggest that even re- active fractions of DON are unlikely to be a significant N source. In the eastern sector of the oligotrophic gyre (46–31°W), transit timescales longer than 3 years suggest that the allochthonous supply of the semilabile DOP is negligible due to its exhaustion. Here, an intense mixed layer dynamics favours nu- trient supply from below the mixed layer. We speculate that longitudinal variability in physical forcing and gradients in the timescale of advection, combined with distinct turnover timescales of reactive fractions of DON and DOP, drive diverse phytoplankton assemblages and surface nitrogen fixation gra- dients across our region of investigation.

Description: Highlights • Geochemical evidence confirms exchange between sediments and the basaltic crust fluids. • O2 exchange between the sediment and the basaltic crust produces a fully oxic sediment column. • Transport-reaction modeling was performed to quantify the exchange of O2 and nutrients. Abstract The Clarion–Clipperton Fracture Zone (CCFZ) in the Pacific Ocean is characterized by organic carbon-starved sediments and meter-scale oxygen penetration into the sediment. Furthermore, numerous seamounts occur throughout its deep-sea plain, which may serve as conduits for low-temperature hydrothermal seawater circulation through the oceanic crust. Recent studies in deep-sea environments of the Pacific and Atlantic Oceans have suggested and presented evidence of dissolved constituent exchange between the seawater flowing in the basaltic crust and the pore water of the overlying sediments. Through high-resolution pore-water oxygen and nutrient measurements, we examined fluxes and geochemical interactions between the seamount basaltic basement and pore waters of the overlying sediments at three sites located on a radial transect from the foot of Teddy Bare, a small seamount in the CCFZ. At three sites, located 1000, 700 and 400 m away from the foot of the seamount, we found that oxygen concentrations initially decrease with sediment depth but start to increase at depths of 3 and 7 m toward the basaltic basement. Nitrate (View the MathML sourceNO3−) concentrations mirror the oxygen concentration profiles, as they increase with sediment depth but decrease towards the basement. These profiles suggest an upward diffusion of oxygen from seawater circulating within the seamount crust into the overlying basal sediments and a downward diffusion of View the MathML sourceNO32− from sediment pore water into the basaltic crust. At one site, we determined that the 87Sr/86Sr ratios of the bottom water and of the deep sediment near the basaltic crust are similar, further supporting diffusive exchange between basaltic crust fluids and sediment pore water. Transport-reaction modeling performed at two of the study sites revealed that (1) the diffusive flux of oxygen from the basaltic basement outpaces the oxygen consumption through organic matter oxidation and nitrification in the basal sediments and (2) the nutrient exchange between the sediment and the underlying basaltic crust occurs at orders-of-magnitude lower rates than between the upper sediment and the overlying bottom water. These results further show that the diffusion of oxygen from the seamount basaltic basement into the overlying pore waters affects the preservation of organic compounds and helps to maintain a completely oxygenated sedimentary column at all 3 sites near the seamount.

Description: Conflicting results have been reported for the stable Sr isotope fractionation, specifically with respect to the influence of temperature. In an experimental study we have investigated the stable Sr isotope systematics for inorganically precipitated and biogenic (coral) aragonite (natural and laboratory-cultured). Inorganic aragonite precipitation experiments were performed from natural seawater using the CO2 diffusion technique. The experiments were performed at different temperatures and different carbonate ion concentrations. 88Sr/86Sr of the inorganic aragonite precipitated in the experiments are 0.2‰ lighter than seawater, but showed no correlation to the water temperature or to CO32− concentration. Similar observations are made in different coral species (Cladocora caespitosa, Porites sp. and Acropora sp.), with identical fractionation from the bulk solution and no correlation to temperature or CO32− concentration. The lack of 88Sr/86Sr variability in corals at different environmental parameters and the similarity to the 88Sr/86Sr fractionation in inorganic aragonite may indicate a similar Sr incorporation mechanism in corals skeleton and inorganic aragonite, and therefore the previously proposed Rayleigh-based multi element model (Gaetani et al., 2011) cannot explain the process of Sr incorporation in the coral skeletal material. It is proposed that the relatively constant 88Sr/86Sr fractionation in aragonite can be used for paleo reconstruction of seawater 88Sr/86Sr composition. The seawater 88Sr/86Sr ratio reconstruction can be further used in calcite samples to reconstruct paleo precipitation rates.

Description: Highlights: • Signal detection theory (SDT) was used to assess the BQI (Benthos Quality Index) performance. • BQI (Benthos Quality Index) was found to respond acceptably to eutrophication parameters at the exposed coastal areas. • BQI (Benthos Quality Index) response was affected by estuarine water outflow. • SDT provide a method to assess the accuracy of indicators. • SDT can be helpful for management decisions when planning environment monitoring intensity. Abstract The European Marine Strategy Framework Directive requires EU Member States to prepare national strategies and manage their seas to achieve good environmental status (GES) by 2020. There are many multimetric indices proposed as indicators of the ecological quality of the benthic environment. Their functionality and utility are extensively discussed in the literature. Different frameworks are suggested for comparative assessments of indicators with no agreement on a standardized way of selecting the most appropriate one. In the current study, we apply signal detection theory (SDT) to evaluate the specificity and sensitivity of the Benthic Quality Index (BQI), its response to the eutrophication pressure, and its performance under the effects of estuarine water outflow. The BQI showed acceptable response to total nitrogen, total phosphorus and chlorophyll-a concentrations in the study area. Based on the results, we suggest using SDT for setting GES thresholds in a standardized way. This aids a robust assessment of the environmental status and supports differentiation between the quality classes.

Description: Highlights • The basement at the mid-Norwegian Møre Margin is dominantly felsic in composition. • A lower crustal body is interpreted as a mixture of continental blocks and eclogite. • The thickness of the outer lower crustal body is twice as thick on the East Greenland Margin. • The thinning during this first phase of post-Caledonian extension was highest for proto Norway. Abstract The inner part of the volcanic, passive Møre Margin, mid-Norway, expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust. Previous P-wave modeling of wide-angle seismic data revealed the presence of a high-velocity (7.7–8.0 km/s) body in the lower crust in this transitional region. These velocities are too high to be readily interpreted as Early Cenozoic intrusions, a model often invoked to explain lower crustal high-velocity bodies in the region. We present a Vp/Vs model, derived from the modeling of wide-angle seismic data, acquired by use of Ocean Bottom Seismograph horizontal components. The modeling suggests dominantly felsic composition of the crust. An average Vp/Vs value for the lower crustal body is modeled at 1.77, which is compatible with a mixture of continental blocks and Caledonian eclogites. The results are compiled with earlier results into a transect extending from onshore Norway to onshore Greenland. Back-stripping of the transect to Early Cenozoic indicates asymmetric conjugate magmatism related to the continental break-up. Further back-stripping to the time when most of the Caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25% higher for proto Norway than proto Greenland.

Description: Highlights: • The natural ecohydrographic gradient of the Red Sea translates into an isoscape. • The Red Sea isoscape features increasing zooplankton δ15 N values towards the South. • Isotopic baseline variations propagate through the pelagic food web. • Eddy-induced upwelling modifies the natural ecohydrographic North-South gradient. Abstract: Although zooplankton occupy key roles in aquatic biogeochemical cycles, little is known about the pelagic food web and trophodynamics of zooplankton in the Red Sea. Natural abundance stable isotope analysis (SIA) of carbon (δ13C) and N (δ15N) is one approach to elucidating pelagic food web structures and diet assimilation. Integrating the combined effects of ecological processes and hydrography, ecohydrographic features often translate into geographic patterns in δ13C and δ15N values at the base of food webs. This is due, for example, to divergent 15N abundances in source end-members (deep water sources: high δ15N, diazotrophs: low δ15N). Such patterns in the spatial distributions of stable isotope values were coined isoscapes. Empirical data of atmospheric, oceanographic, and biological processes, which drive the ecohydrographic gradients of the oligotrophic Red Sea, are under-explored and some rather anticipated than proven. Specifically, five processes underpin Red Sea gradients: (a) monsoon-related intrusions of nutrient-rich Indian Ocean water; (b) basin scale thermohaline circulation; (c) mesoscale eddy activity that causes up-welling of deep water nutrients into the upper layer; (d) the biological fixation of atmospheric nitrogen (N2) by diazotrophs; and (e) the deposition of dust and aerosol-derived N. This study assessed relationships between environmental samples (nutrients, chlorophyll a), oceanographic data (temperature, salinity, current velocity [ADCP]), particulate organic matter (POM), and net-phytoplankton, with the δ13C and δ15N values of zooplankton collected in spring 2012 from 16°28′ to 26°57′N along the central axis of the Red Sea. The δ15N of bulk POM and most zooplankton taxa increased from North (Duba) to South (Farasan). The potential contribution of deep water nutrient-fueled phytoplankton, POM, and diazotrophs varied among sites. Estimates suggested higher diazotroph contributions in the North, a greater contribution of POM in the South, and of small phytoplankton in the central Red Sea. Consistent variation across taxonomic and trophic groups at latitudinal scale, corresponding with patterns of nutrient stoichiometry and phytoplankton composition, indicates that the zooplankton ecology in the Red Sea is largely influenced by hydrographic features. It suggests that the primary ecohydrography of the Red Sea is driven not only by the thermohaline circulation, but also by mesoscale activities that transports nutrients to the upper water layers and interact with the general circulation pattern. Ecohydrographic features of the Red Sea, therefore, aid in explaining the observed configuration of its isoscape at the macroecological scale.

Description: Reflecting the natural biology of mass spawning fish aquaculture production of fish larvae is often hampered by high and unpredictable mortality rates. The present study aimed to enhance larval performance and immunity via the oral administration of an immunomodulator, β-glucan (MacroGard®) in turbot (Scophthalmus maximus). Rotifers (Brachionus plicatilis) were incubated with or without yeast β-1,3/1,6-glucan in form of MacroGard® at a concentration of 0.5 g/L. Rotifers were fed to first feeding turbot larvae once a day. From day 13 dph onwards all tanks were additionally fed untreated Artemia sp. nauplii (1 nauplius ml/L). Daily mortality was monitored and larvae were sampled at 11 and 24 dph for expression of 30 genes, microbiota analysis, trypsin activity and size measurements. Along with the feeding of β-glucan daily mortality was significantly reduced by ca. 15% and an alteration of the larval microbiota was observed. At 11 dph gene expression of trypsin and chymotrypsin was elevated in the MacroGard® fed fish, which resulted in heightened tryptic enzyme activity. No effect on genes encoding antioxidative proteins was observed, whilst the immune response was clearly modulated by β-glucan. At 11 dph complement component c3 was elevated whilst cytokines, antimicrobial peptides, toll like receptor 3 and heat shock protein 70 were not affected. At the later time point (24 dph) an anti-inflammatory effect in form of a down-regulation of hsp 70, tnf-α and il-1β was observed. We conclude that the administration of MacroGard® induced an immunomodulatory response and could be used as an effective measure to increase survival in rearing of turbot.

Description: Highlights: - Analysis of a combined new high-resolution 2D seismic and bathymetric data set offshore Mt Etna - Extensional domains are mapped at the shallow subsurface of the continental margin - Compressional structures are mapped at the toe of the continental margin - A coupled volcano edifice / continental margin instability is proposed Mount Etna is the largest active volcano in Europe. Instability of its eastern flank is well documented onshore, and continuously monitored by geodetic and InSAR measurements. Little is known, however, about the offshore extension of the eastern volcano flank, defining a serious shortcoming in stability models. In order to better constrain the active tectonics of the continental margin offshore the eastern flank of the volcano, we acquired a new high-resolution 2D reflection seismic dataset. The data provide new insights into the heterogeneous geology and tectonics at the continental margin offshore Mt Etna. The submarine realm is characterized by different blocks, which are controlled by local- and regional tectonics. A compressional regime is found at the toe of the continental margin, which is bound to a complex basin system. Both, the clear link between on- and offshore tectonic structures as well as the compressional regime at the easternmost flank edge, indicate a continental margin gravitational collapse as well as spreading to be present at Mt Etna. Moreover, we find evidence for the offshore southern boundary of the moving flank, which is identified as a right lateral oblique fault north of Catania Canyon. Our findings suggest a coupled volcano edifice / continental margin instability at Mt Etna, demonstrating first order linkage between on- and offshore tectonic processes.

Description: Highlights: • Inter-annual to decadal variability in AMOC from CORE-II simulations is presented. • AMOC variability shows three stages, with maximum transports in mid- to late-1990s. • North Atlantic temporal variability features are in good agreement among simulations. • Such agreements suggest variability is dictated by the atmospheric data sets. • Simulations differ in spatial structures of variability due to ocean dynamics. Simulated inter-annual to decadal variability and trends in the North Atlantic for the 1958–2007 period from twenty global ocean – sea-ice coupled models are presented. These simulations are performed as contributions to the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II). The study is Part II of our companion paper (Danabasoglu et al., 2014) which documented the mean states in the North Atlantic from the same models. A major focus of the present study is the representation of Atlantic meridional overturning circulation (AMOC) variability in the participating models. Relationships between AMOC variability and those of some other related variables, such as subpolar mixed layer depths, the North Atlantic Oscillation (NAO), and the Labrador Sea upper-ocean hydrographic properties, are also investigated. In general, AMOC variability shows three distinct stages. During the first stage that lasts until the mid- to late-1970s, AMOC is relatively steady, remaining lower than its long-term (1958–2007) mean. Thereafter, AMOC intensifies with maximum transports achieved in the mid- to late-1990s. This enhancement is then followed by a weakening trend until the end of our integration period. This sequence of low frequency AMOC variability is consistent with previous studies. Regarding strengthening of AMOC between about the mid-1970s and the mid-1990s, our results support a previously identified variability mechanism where AMOC intensification is connected to increased deep water formation in the subpolar North Atlantic, driven by NAO-related surface fluxes. The simulations tend to show general agreement in their temporal representations of, for example, AMOC, sea surface temperature (SST), and subpolar mixed layer depth variabilities. In particular, the observed variability of the North Atlantic SSTs is captured well by all models. These findings indicate that simulated variability and trends are primarily dictated by the atmospheric datasets which include the influence of ocean dynamics from nature superimposed onto anthropogenic effects. Despite these general agreements, there are many differences among the model solutions, particularly in the spatial structures of variability patterns. For example, the location of the maximum AMOC variability differs among the models between Northern and Southern Hemispheres.

Description: Several recent studies have highlighted the potential of combined 238U–230Th and 235U–231Pa systematics to constrain upwelling rates and the role of recycled mafic lithologies in mantle plume-derived basalts. Accordingly, we present measurements of the 231Pa concentrations from 26 mafic volcanic rocks from Iceland, including off-axis basalts from the Snaefellsnes Peninsula, to complement previously published 238U–230Th–226Ra data. 231Pa concentrations vary from 27 to 624 fg/g and (231Pa/235U) ratios from 1.12 to 2.11 with the exception of one anomalous sample from the Southeast Rift which has a 231Pa deficit with (231Pa/235U) = 0.86. An important new result is that basalts from the Southeast Rift and the Snaefellsnes Peninsula define a trend at relatively low (231Pa/235U) for a given (230Th/238U) ratio. Many of the remaining samples fall in or around the global field for ocean island basalts but those from the Mid-Iceland Belt and the Southwest Rift/Reykjanes Peninsula extend to higher (231Pa/235U) ratios at a given (230Th/238U), similar to mid-ocean ridge basalts. In principle, these lavas could result from melting of peridotite at lower pressures. However, there is no reason to suspect that the Mid-Iceland Belt and the Southwest Rift lavas reflect shallower melting than elsewhere in Iceland. In our preferred model, these lavas reflect melting of garnet peridotite whereas those from the Southeast Rift and the Snaefellsnes Peninsula contain a significant contribution (up to 20%) of melt from garnet pyroxenite. This is consistent with incompatible trace element and radiogenic isotope evidence for recycled oceanic crust in these lavas. There is increasing agreement that the displacement of ocean island basalts to lower (231Pa/235U) ratios at a given (230Th/238U), compared to mid-ocean ridge basalts, reflects the role of recycled mafic lithologies such as garnet pyroxenite as well as higher average pressures of melting. It now seems likely that this interpretation may have more general application to plume-affected MORB that exhibit the same U-series disequilibria characteristics.

Description: A new high-precision Ar-40/Ar-39 anorthoclase feldspar age of 176.7 +/- 0.5 Ma (2-sigma) reveals that small-volume alkaline basaltic magmatism occurred at the rifted SW margin of the Baltic Shield in Scania (southern Sweden), at a time of global plate reorganization associated with the inception of Pangea supercontinent break-up. Our combined elemental and Sr-Nd-Hf-Pb isotope dataset for representative basanite and nephelinite samples (〉8 wt.% MgO) from 16 subvolcanic necks of the 30 by 40 km large Jurassic volcanic field suggests magma derivation from a moderately depleted mantle source (Sr-87/(86)Sri = 0.7034-0.7048; epsilon Nd-i = +4.4 to +5.2; epsilon Hf-i = +4.7 to +8.1; Pb-206/(204)Pbi = 18.8-19.5). The mafic alkaline melts segregated from mixed peridotite-pyroxenite mantle with a potential temperature of similar to 1400 degrees C at 2.7-4.2 GPa (similar to 90-120 km depths), which places ultimate melt generation within the convecting upper mantle, provided that the lithosphere-asthenosphere boundary beneath the southern Baltic Shield margin was at 〈= 100 km depth during Mesozoic-Cenozoic rifting. Isotopic shifts and incompatible element enrichment relative to Depleted Mantle reflect involvement of at least 20% recycled oceanic lithosphere component (i.e., pyroxenite) with some minor continent-derived sediment during partial melting of well-stirred convecting upper mantle peridotite. Although pargasitic amphibole-rich metasomatized lithospheric mantle is excluded as the main source of the Jurassic magmas from Scania, hydrous ultramafic veins (i.e., hornblendite) may have caused subtle modifications to the compositions of passing sublithospheric melts. For example, modeling suggests that the more radiogenic Hf (epsilon Hf-i = +6.3 to +8.1) and Pb (Pb-206/Pb-204(i) = 18.9-19.5) isotopic compositions of the more sodic and H2O-rich nephelinites, compared with relatively homogenous basanites (epsilon Hf-i = +4.7 to +6.1; Pb-206/Pb-204(i) = 18.8-18.9), originate from minor interactions between rising asthenospheric melts and amphibole-rich metasomatic components. The metasomatic components were likely introduced to the lithospheric mantle beneath the southern Baltic Shield margin during extensive Permo-Carboniferous magmatic activity, a scenario that is supported by the geochemical and isotope compositions of ca. 286 Ma lamprophyres from Scania (Sr-87/(86)Sri = 0.7040-0.7054; epsilon Nd-i = +2.0 to +3.1; epsilon Hf-i = +6.1 to +9.0; Pb-206/(204)Pbi = 17.8-18.2). Strong variations in lithosphere thickness and thermal structure across the southern Baltic Shield margin may have caused transient small-scale mantle convection. This resulted in relatively fast and focused upwellings and lateral flow beneath the thinned lithosphere, where mafic alkaline magmas formed by low degrees of decompression melting of sublithospheric mantle. Such a geodynamic scenario would allow for enriched recycled components with low melting points to be preferentially sampled from the more depleted and refractory convecting upper mantle when channeled along a destabilizing craton edge. Similar to the 'lid effect' in oceanic island volcanic provinces, lithospheric architecture may exert strong control on the mantle melting regime, and thus offer a simple explanation for the geochemical resemblance of continental and oceanic intraplate mafic alkaline magmas of high Na/K affinity.

Description: Highlights • Review of sediment archives from the Peruvian margin since the LGM. • Focus on the evolutionary feature of the hiatus found in archives. • Modern analogue for current-dominated environments for paleo reconstructions. • New results for erosional potential of the non-linear internal waves (NLIWs). Abstract The Peruvian continental margin is characterized by the presence of one of the strongest and most distinct Oxygen Minimum Zones (OMZs) in today's oceans. Therefore, it has long been in the focus of oceanographic and geological investigations. Observations indicate that OMZs are expanding in relation with currently changing climate. To advance understanding of the temporal evolution of OMZs and climate change, complete paleoceanographic and palaeoclimatological reconstructions are needed. However, the development of paleoenvironmental scenarios for the period since the Last Glacial Maximum at this region was hampered by a ubiquitous hiatus and short-term interruptions of the stratigraphical record. In the present study, we combined the stratigraphical information from 31 sediment cores from the Peruvian margin located between 3 and 18°S and water depths of 90 to 1300 m within and below today's OMZ, in order to determine the extent of the hiatus and assess the responsible mechanisms. A widespread unconformity and related erosional features, omission surfaces and phosphorites, were observed in sediment cores from the area south of 7°S, depicting a prograding feature on the continental slope from south to north during the deglaciation. Combining recent oceanographic and sedimentological observations, it is inferred that, tide-topography interaction and resulting non-linear internal waves (NLIWs) shape the slope by erosion, carry sediments upslope or downslope and leave widespread phosphoritic lag sediments, while the Peru Chile Undercurrent (PCUC) transports the resuspended sediments southward causing non-deposition. This exceptional sedimentary regime makes the Peruvian margin a modern analogue for such environments. Overall, our compilation of downcore records showed that enhanced bottom currents due to tide-topography interaction were progressively evolving and affected a wider area with the onset of the last deglaciation. Elevated tidal amplitudes and variability of mid-depth water masses (i.e.; density changes) and hydrodynamics in relation with changing climate were potential reasons of this evolving feature of erosion and reworking. Additionally, erosion and non-deposition was observed widest and even was encountered on the continental shelf during the early Holocene, potentially indicating a strong phase of the PCUC mirroring today's El Niño-like conditions.

Description: Polar oceans are particularly vulnerable to ocean acidification due to their low temperatures and reduced buffering capacity, and are expected to experience extensive low pH conditions and reduced carbonate mineral saturations states (Ω) in the near future. However, the impact of anthropogenic CO2 on pH and Ω will vary regionally between and across the Arctic and Southern Oceans. Here we investigate the carbonate chemistry in the Atlantic sector of two polar oceans, the Nordic Seas and Barents Sea in the Arctic Ocean, and the Scotia and Weddell Seas in the Southern Ocean, to determine the physical and biogeochemical processes that control surface pH and Ω. High-resolution observations showed large gradients in surface pH (0.10 to 0.30) and aragonite saturation state (Ωar) (0.2 to 1.0) over small spatial scales, and these were particularly strong in sea-ice covered areas (up to 0.45 in pH and 2.0 in Ωar). In the Arctic, sea-ice melt facilitated bloom initiation in light-limited and iron replete (dFe〉0.2 nM) regions, such as the Fram Strait, resulting in high pH (8.45) and Ωar (3.0) along the sea-ice edge. In contrast, accumulation of dissolved inorganic carbon derived from organic carbon mineralisation under the ice resulted in low pH (8.05) and Ωar (1.1) in areas where thick ice persisted. In the Southern Ocean, sea-ice retreat resulted in bloom formation only where terrestrial inputs supplied sufficient iron (dFe〉0.2 nM), such as in the vicinity of the South Sandwich Islands where enhanced pH (8.3) and Ωar (2.3) were primarily due to biological production. In contrast, in the adjacent Weddell Sea, weak biological uptake of CO2 due to low iron concentrations (dFe〈0.2 nM) resulted in low pH (8.1) and Ωar (1.6). The large spatial variability in both polar oceans highlights the need for spatially resolved surface data of carbonate chemistry variables but also nutrients (including iron) in order to accurately elucidate the large gradients experienced by marine organisms and to understand their response to increased CO2 in the future.

Description: Highlights • UV-Visible spectrophotometry provided valuable AgNP aggregation information • Aggregation rate of polymer-AgNPs are influenced by ionic strength and organic matter • Fjord waters indicated strong stabilization of AgNP by natural organic matter This study provides quantitative information on the aggregation and dissolution behaviour of silver nanoparticles (AgNPs) upon discharge in fresh and sea waters, represented here as NaCl solutions of increasing ionic strength (up to 1. M) and natural fjord waters. Natural polysaccharides, sodium alginate (ALG) and gum Arabic (GA), were used as coatings to stabilize the AgNPs and the compounds acted as models to study AgNP aggregation kinetics. The DLVO theory was used to quantitatively describe the interactions between the AgNPs. The stability of AgNPs was established using UV-Visible spectrophotometry, including unique information collected during the first seconds of the aggregaton process. Alginate coating resulted in a moderate stabilization of AgNPs in terms of critical coagulation concentration (~. 82. mM NaCl) and a low dissolution of 〈. 10% total Ag in NaCl solutions up to 1. M. Gum Arabic coated AgNPs were more strongly stabilized, with ~. 7-30% size increase up to 77. mM NaCl, but only when the silver ion content initially present in solution was low (〈. 10% total Ag). The ALG and GA coated AgNPs showed a strongly enhanced stability in natural fjord waters (ca. 5. h required to reduce the area of the surface plasmon resonance band (SPRB) by two fold) compared with NaCl at an equivalent ionic strength (1-2. min period for a two fold SPRB reduction). This is ascribed to a stabilizing effect from dissolved organic matter present in natural fjord waters. Interestingly, for AgNP-GA solutions with 40% of total silver present as unreacted silver ions in the NP stock solution, fast aggregation kinetics were observed in NaCl solutions (SPRB area was reduced by ca. 50% within 40-150. min), with even more rapid removal in fjord waters, attributed to the high amount of silver-chloride charged species, that interact with the NP coating and/or organic matter and reduce the NPs stabilization.

Description: Highlights: • 18 southern European charcoal records document 16,000 years of fire regime changes. • Since the Neolithic, land uses have artificially maintained high fire frequencies. • Human-induced decreases in forest cover led to a reduction in the biomass burned. • Human-modified landscapes affected ecological processes more meaningly than expected. Abstract: Variability in fire regime at the continental scale has primarily been attributed to climate change, often overshadowing the widely potential impact of human activities. However, human ignition modifies the rhythm of fire episodes occurrence (fire frequency), whereas land use alters vegetation composition and fuel load, and thus the amount of biomass burned. It is unclear, however, whether and how humans have exercised a significant influence over fire regimes at continental and millennial scales. Based on sedimentary charcoal records, we use new alternative estimate of fire frequency and biomass burned for the last 16000 years (here after 16 ky) that we evaluate with outputs from climate, vegetation, land use and population models. We find that pronounced regional-scale land use changes in southern Europe at the beginning of the Neolithic (8–6 ky), during the Bronze Age (5–4 ky) and the medieval period (1 ky) caused a doubling of fire frequency compared to the Holocene average (the last 11.5 ky). Despite anthropogenic influences, southern European biomass burned decreased from 7 ky, which is in line both with changes in orbital parameters leading climate cooling and also reductions in biomass availability because of land use. Our study underscores the role of elevation-dependent parameters, and particularly biomass and land management, as major drivers of fire regime variability. Results attest a determinant anthropogenic driving-force on fire regime and a decrease in fire-carbon emissions since 7 ky in Southern Europe.

Description: A detailed Holocene tephrostratigraphic framework has been developed for two predominately varved lake sediment sequences from NE Germany (Lake Tiefer See) and central N Poland (Lake Czechowskie). A total of thirteen tephras and cryptotephras of Icelandic provenance were detected and chemically fingerprinted in order to define correlatives and to integrate known tephra ages into the sediment chronologies. Out of these, three cryptotephras (Askja-AD1875, Askja-S and H€asseldalen) were identified in both records, thus allowing a detailed synchronization of developing high-resolution palaeoenvironmental proxy data. The early Holocene Saksunarvatn Ash layer and the middle Holocene Lairg-B and Hekla-4 cryptotephras in Lake Tiefer See are further important anchor points for the comparison with other high-resolution palaeoclimate records in Central and Northern Europe. Tentative correlations of cryptotephras have been made with a historical basaltic Grimsv€otn eruption (~AD890 e AD856) and three late Holocene rhyolitic eruptions, including the 2.1 ka Glen Garry and two unknown high-silicic cryptotephras of probably Icelandic provenance (~1.9 cal ka BP).

Description: Highlights: • Arctic sea ice extent and solid freshwater in 14 CORE-II models are inter-compared. • The models better represent the variability than the mean state. • The September ice extent trend is reasonably represented by the model ensemble mean. • The descending trend of ice thickness is underestimated compared to observations. • The models underestimate the reduction in solid freshwater content in recent years. Abstract: The Arctic Ocean simulated in fourteen global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE II) is analyzed. The focus is on the Arctic sea ice extent, the solid freshwater (FW) sources and solid freshwater content (FWC). Available observations are used for model evaluation. The variability of sea ice extent and solid FW budget is more consistently reproduced than their mean state in the models. The descending trend of September sea ice extent is well simulated in terms of the model ensemble mean. Models overestimating sea ice thickness tend to underestimate the descending trend of September sea ice extent. The models underestimate the observed sea ice thinning trend by a factor of two. When averaged on decadal time scales, the variation of Arctic solid FWC is contributed by those of both sea ice production and sea ice transport, which are out of phase in time. The solid FWC decreased in the recent decades, caused mainly by the reduction in sea ice thickness. The models did not simulate the acceleration of sea ice thickness decline, leading to an underestimation of solid FWC trend after 2000. The common model behavior, including the tendency to underestimate the trend of sea ice thickness and March sea ice extent, remains to be improved.

Description: Highlights: • Arctic liquid freshwater budget simulated in 14 CORE-II models is studied. • The models better represent the temporal variability than the mean state. • Multi-model mean (MMM) FW fluxes compare well with observations. • MMM FWC shows an upward trend in the recent years, with an underestimated rate. • FW flux interannual variability is more consistent where volume flux determines it. Abstract: The Arctic Ocean simulated in 14 global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE-II) is analyzed in this study. The focus is on the Arctic liquid freshwater (FW) sources and freshwater content (FWC). The models agree on the interannual variability of liquid FW transport at the gateways where the ocean volume transport determines the FW transport variability. The variation of liquid FWC is induced by both the surface FW flux (associated with sea ice production) and lateral liquid FW transport, which are in phase when averaged on decadal time scales. The liquid FWC shows an increase starting from the mid-1990s, caused by the reduction of both sea ice formation and liquid FW export, with the former being more significant in most of the models. The mean state of the FW budget is less consistently simulated than the temporal variability. The model ensemble means of liquid FW transport through the Arctic gateways compare well with observations. On average, the models have too high mean FWC, weaker upward trends of FWC in the recent decade than the observation, and low consistency in the temporal variation of FWC spatial distribution, which needs to be further explored for the purpose of model development.

Description: Highlights • Polypropylene and biodegradable plastic bags were incubated in marine sediments. • Bacterial colonization was highest on biodegradable plastic bags. • None of the two bag types showed signs of degradation after 98 days. • Marine sediments probably represent a long-term sink for both types of litter. Abstract To date, the longevity of plastic litter at the sea floor is poorly constrained. The present study compares colonization and biodegradation of plastic bags by aerobic and anaerobic benthic microbes in temperate fine-grained organic-rich marine sediments. Samples of polyethylene and biodegradable plastic carrier bags were incubated in natural oxic and anoxic sediments from Eckernförde Bay (Western Baltic Sea) for 98 days. Analyses included (1) microbial colonization rates on the bags, (2) examination of the surface structure, wettability, and chemistry, and (3) mass loss of the samples during incubation. On average, biodegradable plastic bags were colonized five times higher by aerobic and eight times higher by anaerobic microbes than polyethylene bags. Both types of bags showed no sign of biodegradation during this study. Therefore, marine sediment in temperate coastal zones may represent a long-term sink for plastic litter and also supposedly compostable material.

Description: Highlights • We present a Ba isotope data set of seawater, river waters and biogenic particles. • Ba isotope signatures of upper ocean waters are heavier than river and deep waters. • Adsorption of lighter Ba isotopes on biogenic particles induces the fractionation. • Ba isotopes trace land–sea interactions and ocean mixing processes. • Decoupling of Ba from major nutrients confirms Ba to be a biointermediate element. Abstract The distribution of barium (Ba) concentrations in seawater resembles that of nutrients and Ba has been widely used as a proxy of paleoproductivity. However, the exact mechanisms controlling the nutrient-like behavior, and thus the fundamentals of Ba chemistry in the ocean, have not been fully resolved. Here we present a set of full water column dissolved Ba (DBa) isotope (δ137BaDBa) profiles from the South China Sea and the East China Sea that receives large freshwater inputs from the Changjiang (Yangtze River). We find pronounced and systematic horizontal and depth dependent δ137BaDBa gradients. Beyond the river influence characterized by generally light signatures (0.0 to +0.3‰+0.3‰), the δ137BaDBa values in the upper water column are significantly higher (+0.9‰+0.9‰) than those in the deep waters (+0.5‰+0.5‰). Moreover, δ137BaDBa signatures are essentially constant in the entire upper 100 m, in which dissolved silicon isotopes are fractionated during diatom growth resulting in the heaviest isotopic compositions in the very surface waters. Combined with the decoupling of DBa concentrations and δ137BaDBa from the concentrations of nitrate and phosphate this implies that the apparent nutrient-like fractionation of Ba isotopes in seawater is primarily induced by preferential adsorption of the lighter isotopes onto biogenic particles rather than by biological utilization. The subsurface δ137BaDBa distribution is dominated by water mass mixing. The application of stable Ba isotopes as a proxy for nutrient cycling should therefore be considered with caution and both biological and physical processes need to be considered. Clearly, however, Ba isotopes show great potential as a new tracer for land–sea interactions and ocean mixing processes.

Description: Highlights: • We provide comprehensive discussion of carbon cycle forcings in interglacials. • We compare transient simulations of climate-carbon cycle models through Holocene and Eemian interglacials. • We synthesyze role of forcings in previous and current study in one summary figure. Abstract: Changes in temperature and carbon dioxide during glacial cycles recorded in Antarctic ice cores are tightly coupled. However, this relationship does not hold for interglacials. While climate cooled towards the end of both the last (Eemian) and present (Holocene) interglacials, CO2 remained stable during the Eemian while rising in the Holocene. We identify and review twelve biogeochemical mechanisms of terrestrial (vegetation dynamics and CO2 fertilization, land use, wildfire, accumulation of peat, changes in permafrost carbon, subaerial volcanic outgassing) and marine origin (changes in sea surface temperature, carbonate compensation to deglaciation and terrestrial biosphere regrowth, shallow-water carbonate sedimentation, changes in the soft tissue pump, and methane hydrates), which potentially may have contributed to the CO2 dynamics during interglacials but which remain not well quantified. We use three Earth System Models (ESMs) of intermediate complexity to compare effects of selected mechanisms on the interglacial CO2 and δ13CO2 changes, focusing on those with substantial potential impacts: namely carbonate sedimentation in shallow waters, peat growth, and (in the case of the Holocene) human land use. A set of specified carbon cycle forcings could qualitatively explain atmospheric CO2 dynamics from 8 ka BP to the pre-industrial. However, when applied to Eemian boundary conditions from 126 to 115 ka BP, the same set of forcings led to disagreement with the observed direction of CO2 changes after 122 ka BP. This failure to simulate late-Eemian CO2 dynamics could be a result of the imposed forcings such as prescribed CaCO3 accumulation and/or an incorrect response of simulated terrestrial carbon to the surface cooling at the end of the interglacial. These experiments also reveal that key natural processes of interglacial CO2 dynamics – shallow water CaCO3 accumulation, peat and permafrost carbon dynamics - are not well represented in the current ESMs. Global-scale modeling of these long-term carbon cycle components started only in the last decade, and uncertainty in parameterization of these mechanisms is a main limitation in the successful modeling of interglacial CO2 dynamics.

Description: In this study we combine for the first time silicon (Si) isotope compositions of small mixed diatom species (δ30SibSiO2) and of large handpicked mono-generic (i.e. genus = Coscinodiscus) diatom samples (δ30SiCoscino) with diatom assemblages extracted from marine sediments in the Peruvian upwelling region in order to constrain present and past silicate utilisation. The extension of a previous core-top data set from the Peruvian shelf demonstrates that δ30SiCoscino values record near-complete Si utilisation, as these are similar to the isotopic composition of the subsurface source waters feeding the upwelling. In contrast, the δ30SibSiO2 of small mixed diatom species increase southward along the shelf as well as towards the shore. We attribute highest δ30SibSiO2 values partly to transient iron limitation but primarily to the gradual increase of Si isotope fractionation within the seasonal diatom succession, which are mainly recorded by small diatom species during intense bloom events. In contrast, lower δ30SibSiO2 values are related to initial Si isotope utilisation during periods of weak upwelling, when low Si(OH)4 concentrations do not permit intense blooms and small diatom species record substantially lower δ30Si signatures. As such, we propose that the intensity of the upwelling can be deduced from the offset between δ30SibSiO2 and δ30SiCoscino (Δ30Sicoscino–bSiO2), which is low for strong upwelling conditions and high for prevailing weak upwelling. We apply the information extracted from surface sediments to generate a record of the present-day main upwelling region covering the past 17,700 years and find that this location has also been characterized by a persistent offset (Δ30Sicoscino–bSiO2). By comparison with the diatom assemblages we show that the coastal upwelling system changed markedly between weak and strong upwelling conditions. In addition, our model calculations to quantify species-specific Si isotope fractionation effects based on the diatom assemblages indicate an overall minor influence that cannot explain the high amplitude in the measured δ30SibSiO2 record.

Description: The upper oceanic crust is produced by magmatism at mid-ocean ridges, a process thought to be characterized by cyclic bouts of intense magmatic activity, separated by periods when faulting accommodates most or even all of the plate motion. It is not known whether there is a distinct periodicity to such magmatic–tectonic cycles. Here we present high-resolution sidescan sonar data from the neovolcanic zone of the North Kolbeinsey Ridge, a shallow slow-spreading ridge where high glacial and steady post-glacial sedimentation rates allow relative flow ages to be determined with a resolution of around 2 kyrusing backscatter amplitude as a proxy for sediment thickness and hence age. We identify 18 lava flow fields covering 40% of the area surveyed. A group of 7 flowfields showing the highest (and similar) backscatter intensity are scattered along 75 km of axial valley surveyed, suggesting that at least this length of the segment was magmatically active within a 1.2 kyrtime window. Based on conservative age estimates for all datable flows and estimated eruption volumes, the post-glacial volcanic activity imaged is insufficient to maintain crustal thickness, implying that episode(s) of enhanced activity must have preceded the volcanism we image.

Description: Recent research from the Shatsky Rise in the western Pacific Ocean provides new insights on the formation and evolution of this oceanic plateau as well as tests of mantle models to explain anomalous large igneous province (LIP) volcanism. Recent Shatsky Rise studies cored the igneous pile (Integrated Ocean Drilling Program Expedition 324), imaged the interior with seismic refraction and multichannel seismic reflection data, and mapped magnetic anomalies adjacent to the plateau to provide new constraints on its tectonic history. Coring data show that Tamu Massif, the largest edifice within Shatsky Rise, is characterized by massive sheet flows, similar to flows caused by voluminous eruptions in continental flood basalts. Core data also indicate that the massive eruptions waned as the plateau evolved and smaller edifices were built. Seismic data show intrabasement reflectors within Tamu Massif that indicate volcanism from its center, indicating that this is an enormous shield volcano with abnormally low flank slopes and thick crust (~ 30 km). Paleomagnetic data record minimal geomagnetic field variations, consistent with the inference of massive, rapid volcanism. Altogether, the physical picture indicates that Shatsky Rise was built by massive, rapid eruptions that formed enormous volcanoes. Geochronologic data support the previously inferred age progression, with the volcanic massifs formed along the trace of a triple junction starting from Tamu Massif and becoming progressively younger to the northeast. These data weaken support for rapid emplacement because they show that the last eruptions atop Tamu Massif encompassed several million years between the final massive flows as well as a long hiatus of ~ 15 Myr until late stage eruptions that formed a summit ridge. They may also indicate that the last eruptions on Tamu and Ori massifs occurred while the triple junction was hundreds of kilometers distant. Furthermore, magnetic anomaly data indicate that the plate boundary reorganization associated with Shatsky Rise formation occurred several million years prior to the first Tamu Massif eruptions, suggesting plate boundary control of Shatsky Rise initiation. Geochemical and isotopic data show that Shatsky Rise rocks are variably enriched, with the majority of lavas being similar to mid-ocean ridge basalts (MORB). However, the data indicate deeper (〉 30 km) and higher partial degree of melting (15–23%) as compared with normal MORB. Melting models indicate that the magma experienced a mantle temperature anomaly, albeit only a small one (~ 50 °C). Some lava compositions suggest the involvement of recycled subducted slab material. Recent investigations of Shatsky Rise initially envisaged a competition between two end-member models: the thermal plume head and the fertile mantle melting beneath plate extension (aka, plate model). Both hypotheses find support from new data and interpretations, but both do not fit some data. As a result, neither model can be supported without reservation. Noting that most basaltic oceanic plateaus have formed at triple junctions or divergent plate boundaries, we suggest that this dichotomy is artificial. Oceanic plateau volcanism is anomalous and focused at spreading ridges for reasons that are still poorly understood, mainly owing to uncertainties about mantle convection and geochemical reservoirs. Shatsky Rise investigations have vastly improved our understanding of the formation of this oceanic plateau, but highlight that important work remains to understand the underlying nature of this volcanism.

Description: Acknowledged as among the worst invasive marine species, Mnemiopsis leidyi has spread through European Seas since the mid-1980's. Here we report a bimonthly survey conducted in 2010-11 in three lagoons (Bages-Sigean, Thau and Berre) and at two adjacent coastal stations (Sète and SOMLIT-Marseille) along the French Mediterranean coast. M. leidyi was present only in Berre and Bages-Sigean with maximum abundances observed in late summer. M. leidyi adults were present year round in Berre with the largest organisms (~6 cm) observed in April. In Bages-Sigean, they occurred in sufficient abundance to be recorded by fishermen between August and November. Multiple linear regressions highlighted that abundance in both lagoons was mainly influenced by direct effects of salinity and chlorophyll-a, and temperature to a lesser extent. While M. leidyi has not yet been recorded in Thau, the lagoon is continually monitored to detect the potential establishment of M. leidyi.

Description: Detectible δ30Si variations in present-day chemical silica deposits have stimulated the application of silicon isotopes to infer environmental conditions from ancient equivalents. Interpretations of δ30Si signatures remain problematic in view of potential post-depositional changes, of which magnitudes and underlying mechanisms are largely unknown. A critical issue in the interpretation of isotope data from cherts concerns the extent to which early-diagenetic processes modify original δ30Si signatures. Here, we report δ30Si variations in opal-A, opal-A/CT and opal-CT from fossil sinter deposits in an active discharge apron in the Geysir geothermal field, Iceland. Opal-A samples show an average δ30Si of − 0.7 ± 0.2‰, while opal-CT samples are isotopically lighter with an average δ30Si of − 2.0 ± 0.4‰, implying a sizable shift of approximately 1.3‰ between the different phases. This shift can be explained by repetitive dissolution/re-precipitation processes, diffusive transport or temperature differences during phase transitions. On average, the fossil opal-A tends to be less negative in δ30Si than amorphous silica that recently precipitated from the hydrothermal water. The difference can be attributed to primary variability in isotopic fractionation that accompanies precipitation out of spring water at the surface, or to a post-depositional release of surface 28Si at the onset of diagenetic formation. Our results corroborate the perception that original silicon isotope signatures of silica, acquired during chemical precipitation from a saturated solution, may not be preserved in the geological record, and that post-depositional changes must be taken into account when interpreting data from ancient chert deposits.

Description: Highlights • Coseismic displacement documented and measured in a submarine fault following a 2004 Mw 6.3 event. • Coseismic deformation of hanging wall with cracking and fissuring of seafloor sediments. • High-resolution mapping, photomosaicing, and 3D video-derived terrain models to constrain earthquake rupture at seafloor. Abstract Properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard. Submarine faults can trigger tsunamis, whose characteristics are defined by the geometry of seafloor displacement, studied primarily through indirect observations (e.g., seismic event parameters, seismic profiles, shipboard bathymetry, coring) rather than direct ones. Using deep-sea vehicles, we identify for the first time a marker of coseismic slip on a submarine fault plane along the Roseau Fault (Lesser Antilles), and measure its vertical displacement of ∼0.9 m in situ. We also map recent fissuring and faulting of sediments on the hangingwall, along ∼3 km of rupture in close proximity to the fault's base, and document the reactivation of erosion and sedimentation within and downslope of the scarp. These deformation structures were caused by the 2004 Mw 6.3 Les Saintes earthquake, which triggered a subsequent tsunami. Their characterization informs estimates of earthquake recurrence on this fault and provides new constraints on the geometry of fault rupture, which is both shorter and displays locally larger coseismic displacements than available model predictions that lack field constraints. This methodology of detailed field observations coupled with near-bottom geophysical surveying can be readily applied to numerous submarine fault systems, and should prove useful in evaluating seismic and tsunamigenic hazard in all geodynamic contexts.

Description: We studied the response of the heterotrophic flagellate (HF) community to the combined impact of warming and ocean acidification in a mesocosm experiment with a plankton community from the western Baltic Sea. We performed a quantitative analysis of the response at the level of total biomass and size classes and a semi-quantitative one at the level of individual taxa. Total biomass of HF was significantly lower under higher temperatures while there was no significant effect of CO2. The mean biomass of the picoflagellates did not respond to temperature while the three nanoflagellate size classes (class limits 3, 5, 8, 15 μm) responded negatively to warming while not responding to CO2. The taxon-level results indicate that heterotrophic flagellates do not form a homogenous trophic guild, as often assumed in pelagic food web studies. Instead, the heterotrophic flagellates formed a “food web within the food web”. There was a pronounced succession of flagellates leading from a dominance of bacterivores and colloidal matter feeders before the phytoplankton bloom to omnivorous feeders preying upon phytoplankton and heterotrophic flagellates during and after the bloom. This complex intraguild predation patterns probably dampened the response to experimental treatments.

Description: Highlights • Empirical approach was used to study effects of seabird guano on marine phytoplankton. • Seabird guano enhances phytoplankton productivity in different water masses. • Nutrient run-off from seabird colonies is a significant nutrient source. Abstract Six incubation experiments were carried out to investigate the phytoplankton biomass response to seabird guano-enrichment under different nutrient regimes. Study locations included Antarctic waters of the Ross Sea and sub-Antarctic waters offshore of the Otago Peninsula, both being characterized by iron limitation of phytoplankton productivity in summer, the Sub-Tropical Frontal Zone offshore of the Snares Islands, which is generally micronutrient-replete, and the island wake waters of the Snares Islands, which have a high nutrient supply from land. In all of the experiments the increase of phytoplankton biomass was higher in the treatments with guano addition compared to the controls. Guano additions were compared to Fe and macronutrients treatments (both added in quantities similar to those in the guano treatment) to shed light on which constituent(s) of guano are responsible for the observed increases in phytoplankton biomass. Macronutrients increased the phytoplankton biomass in the Sub-Tropical Frontal Zone, however, the response was less prominent than in the Guano treatment, suggesting synergetic effects of nutrients in seabird guano on phytoplankton production. It was also found that the pattern of response varied between the water masses with 6–10 days lag phase in the Sub-Antarctic water mass and no lag phase in Sub-Tropical Frontal Zone. The calculations presented here suggest that micro- and macronutrients delivered from seabird colonies on some of the sub-Antarctic islands may provide a significant amount of limiting nutrients to the nutrient budget of the surrounding coastal waters, potentially sufficient to sustain a local phytoplankton bloom. Findings of the present study indicate that biological recycling of nutrients by seabirds likely supports marine primary production and enhances productivity of associated food webs in the vicinity of islands.

Description: Shell growth of oysters requires calcium uptake from the environment and transport to the area of shell formation. A shell regeneration assay in combination with radiolabelled calcium was used to investigate uptake and distribution of calcium to different tissues and hemolymph fractions in Pacific oysters, Crassostrea gigas (Bivalvia, Ostreoida). Oysters were notched at the shell margin and subsequently sampled for hemolymph and grading of shell regeneration during a two week experimental period. Half of the oysters were additionally exposed to (45)Ca and sampled for hemolymph and tissues. Total plasma calcium concentrations increased in notched oysters compared to controls on 1, 2 and 7days after notching. A decrease in plasma calcium levels was apparent on day 4, for both total and ionic calcium. The shell regeneration assay in the notched oysters resulted in a visible deposition of CaCO3 onto the regenerate from day 7 onwards. This was coinciding with an increased uptake of total calcium on days 11 and 14 as well as free, i.e. ionic and ligand-bound calcium, on day 14. At day 1, notching also increased calcium uptake into the mantle tissues, in areas above the notch and near the hinge. During the experiment, both the total hemocyte count and the number of granulocytes increased in notched compared to control oysters. The present study suggests that induced shell damage results in a dynamic regulation of the calcium uptake from the environment and the distribution of calcium within the body, starting directly after notching. Increases in both total calcium concentrations and uptake rates coincided with the visible depositions of CaCO3 on the regenerate shell. C. gigas was found to transport calcium mainly in the ionic form in the hemolymph, with only minor parts being bound to proteins or smaller ligands. Hemolymph measurement also revealed that C. gigas is able to regulate the extracellular concentrations of calcium and potassium. The changes in plasma calcium concentrations and speciation, concomitant with increases in granulocytes indicate that multiple calcium transport processes are activated after induced shell damage.

Description: The seawater radiogenic neodymium (143Nd/144Nd) isotope signature is an invaluable tool for the reconstruction of past deep water provenance. Sedimentary foraminifera or fish teeth are among the most reliable archives known for Nd isotope based reconstructions of past seawater. As the distribution and preservation of these archives are limited, the extraction of hydrogenetic ferromanganese oxyhydroxides from bulk sediments provide an easily applicable alternative. This method, however, implies the risk of generating artefacts due to the possible release of non-seawater derived Nd during the extraction procedure. Here we revisit and further investigate the reliability of the extraction of seawater derived Nd isotope signatures via leaching of bulk deep sea sediments with two commonly used buffered acetic acid and acid-reductive mix solutions. Repeated application of such stepwise leaching procedures to different non-decarbonated sediments from distinct settings across the deep Atlantic Ocean shows pronounced elemental and Nd isotope trends during the leaching process in the laboratory. Our results show that seawater Nd isotope compositions are extracted together with carbonates and manganese oxides only at the beginning of the leaching series. During chemical extraction, the carbonates effectively work as a buffer preventing acid-induced mobilisation of Fe oxides and volcanogenic material. Once this buffer is consumed, potentially present volcanogenic phases are considerably attacked, leading to shifts in the extracted Nd isotope signal of up to + 12 epsilon units. Such volcanogenic phases are a significant source of contaminant Nd reflected by markedly elevated Al/Nd signatures. We consequently propose a revised weak leaching protocol for carbonate bearing deep sea sediments, which is simple to use, provides excellent agreement with data obtained from uncleaned foraminifera, and can be easily screened for contamination.

Description: A new chlorinated quinolone, ageloline A, was isolated from the broth culture of Streptomyces sp. SBT345 that was cultivated from the Mediterranean sponge Agelas oroides. The structure of this compound was determined by spectroscopic analysis including 1D and 2D NMR as well as HR-ESI-MS experiments. Ageloline A exhibited antioxidant potential using cell-free and cell-based assays and was further able to reduce oxidative stress and genomic damage induced by the oxidative stress inducer 4-nitroquinoline-1-oxide (NQO). Moreover, ageloline A inhibited the formation and growth of Chlamydia trachomatis inclusion in a dose-dependent manner with an IC50 value of 9.54 ± 0.36 μM. Interestingly, experimental data showed that the antichlamydial activity of ageloline A might be related to its antioxidant potential. These results demonstrate that sponge-associated actinomycetes are rich sources for natural products with new pharmacological activities and relevance to drug discovery

Description: Dissolved silicon isotope compositions have been analysed for the first time in pore waters (δ30SiPW) of three short sediment cores from the Peruvian margin upwelling region with distinctly different biogenic opal content in order to investigate silicon isotope fractionation behaviour during early diagenetic turnover of biogenic opal in marine sediments. The δ30SiPW varies between +1.1‰ and +1.9‰ with the highest values occurring in the uppermost part close to the sediment–water interface. These values are of the same order or higher than the δ30Si of the biogenic opal extracted from the same sediments (+0.3‰ to +1.2‰) and of the overlying bottom waters (+1.1‰ to +1.5‰). Together with dissolved silicic acid concentrations well below biogenic opal saturation, our collective observations are consistent with the formation of authigenic alumino-silicates from the dissolving biogenic opal. Using a numerical transport-reaction model we find that approximately 24% of the dissolving biogenic opal is re-precipitated in the sediments in the form of these authigenic phases at a relatively low precipitation rate of 56 μmol Si cm−2 yr−1. The fractionation factor between the precipitates and the pore waters is estimated at −2.0‰. Dissolved and solid cation concentrations further indicate that off Peru, where biogenic opal concentrations in the sediments are high, the availability of reactive terrigenous material is the limiting factor for the formation of authigenic alumino-silicate phases.

Description: The Gulf of Cadiz and the passive continental margin of southern Iberia to the west of the Strait of Gibraltar locally accommodate the presently ongoing convergence between Africa and Eurasia by widespread, rather diffusive, seismic activity. Seismicity of the northern Gulf of Cadiz was derived from an amphibious seismological network, including 24 temporary marine offshore stations, besides the permanent networks in Portugal, Spain, and Morocco. During the 6 month of the offshore network operation, in total 86 local earthquakes were located at six or more offshore stations with the majority of earthquakes occurring to the southwest of Iberia and along the Algarve continental margin off southern Iberia. The distribution of events along the Algarve margin mimics features reported for the Atlantic passive continental margins of both South and North America. Focal mechanisms at the Portimão Bank support that seismically active areas are associated with compression. Similar stress patterns are reported for the east coast of South and North America. However, while earthquakes along the American east coast occur at crustal levels, earthquakes in the northern Gulf of Cadiz occur both in the lower crust and upper mantle, with the majority of events rupturing within the mantle, including a number of well-located earthquakes beneath crust forming the continent-ocean transition zone. The large number of earthquakes in the mantle might be caused by the unique geological setting, where deformation occurs in cool lithosphere of Mesozoic age. We suggest that seismicity along the Algarve margin is caused by re-activation of pre-existing margin-parallel faults rather than corresponding to newly formed structures related to a new developing plate boundary.

Description: Highlights: • In situ observations can provide valuable information on feeding behavior in deep-sea organisms. • Gonatus spp. in Monterey Bay consume mesopelagic fishes, congeners and their own species. • Sympatric species of the Gonatidae show differences in prey choice. • Cannibalism is a significant component of the diet of Gonatus spp. in Monterey Bay. Abstract: In situ observations are rarely applied in food web studies of deep-sea organisms. Using deep-sea observations obtained by remotely operated vehicles in the Monterey Submarine Canyon, we examined the prey choices of more than 100 individual squids of the genus Gonatus. Off the California coast, these squids are abundant, semelparous (one reproductive cycle) oceanic predators but their diet has remained virtually unknown. Gonatus onyx and Gonatus berryi were observed to feed on mesopelagic fishes (in particular the myctophid Stenobrachius leucopsarus) as often as on squids but inter-specific differences in feeding were apparent. Gonatids were the most common squid prey and while cannibalism occurred in both species it was particularly high in Gonatus onyx (42% of all prey items). Typically, the size of prey was similar to the size of the predator but the squids were also seen to take much larger prey. Postjuvenile gonatids are opportunistic predators that consume nektonic members of the meso-and bathypelagic communities, including their own species. Such voracious feeding is likely necessary to support the high energetic demands associated with the single reproductive event; and for females the long brooding period during which they must depend on stored resources.

Description: Heinrich events are intervals of rapid iceberg-sourced freshwater release to the high latitude North Atlantic Ocean that punctuate late Pleistocene glacials. Delivery of fresh water to the main North Atlantic sites of deep water formation during Heinrich events may result in major disruption to the Atlantic Meridional Overturning Circulation (AMOC), however, the simple concept of an AMOC shutdown in response to each freshwater input has recently been shown to be overly simplistic. Here we present a new multi-proxy dataset spanning the last 41,000 years that resolves four Heinrich events at a classic mid-depth North Atlantic drill site, employing four independent geochemical tracers of water mass properties: boron/calcium, carbon and oxygen isotopes in foraminiferal calcite and neodymium isotopes in multiple substrates. We also report rare earth element distributions to investigate the fidelity by which neodymium isotopes record changes in water mass distribution in the northeast North Atlantic. Our data reveal distinct geochemical signatures for each Heinrich event, suggesting that the sites of fresh water delivery and/or rates of input played at least as important a role as the stage of the glacial cycle in which the fresh water was released. At no time during the last 41 kyr was the mid-depth northeast North Atlantic dominantly ventilated by southern-sourced water. Instead, we document persistent ventilation by Glacial North Atlantic Intermediate Water (GNAIW), albeit with variable properties signifying changes in supply from multiple contributing northern sources.

Description: Highlights • Marine Image Annotation Software (MIAS) are used to assist annotation of underwater imagery. • We compare 23 MIAS assisting human annotation including some that include automated annotation. • MIAS can run in real time (50%), allow posterior annotation (95%), and interact with databases and data flows (44%). • MIAS differ in data input/output and display, customization, image analysis and re-annotation. • We provide important considerations when selecting UIAS, and outline future trends. Abstract Given the need to describe, analyze and index large quantities of marine imagery data for exploration and monitoring activities, a range of specialized image annotation tools have been developed worldwide. Image annotation - the process of transposing objects or events represented in a video or still image to the semantic level, may involve human interactions and computer-assisted solutions. Marine image annotation software (MIAS) have enabled over 500 publications to date. We review the functioning, application trends and developments, by comparing general and advanced features of 23 different tools utilized in underwater image analysis. MIAS requiring human input are basically a graphical user interface, with a video player or image browser that recognizes a specific time code or image code, allowing to log events in a time-stamped (and/or geo-referenced) manner. MIAS differ from similar software by the capability of integrating data associated to video collection, the most simple being the position coordinates of the video recording platform. MIAS have three main characteristics: annotating events in real time, in posteriorly to annotation and interact with a database. These range from simple annotation interfaces, to full onboard data management systems, with a variety of toolboxes. Advanced packages allow to input and display of data from multiple sensors or multiple annotators via intranet or internet. Posterior human-mediated annotation often include tools for data display and image analysis, e.g. length, area, image segmentation, point count; and in a few cases the possibility of browsing and editing previous dive logs or to analyze annotation data. The interaction with a database allows the automatic integration of annotations from different surveys, repeated annotation and collaborative annotation of shared datasets, browsing and querying of data. Progress in the field of automated annotation is mostly in post processing, for stable platforms or still images. Integration into available MIAS is currently limited to semi-automated processes of pixel recognition through computer-vision modules that compile expert-based knowledge. Important topics aiding the choice of a specific software are outlined, the ideal software is discussed and future trends are presented.

Description: Highlights • Kuroshio Current proxy was established by statistical analyses on grain size spectrum. • Sr–Nd isotope analyses on Kuroshio grain size spectrum reveals source of Taiwan. • Synchronous shift in ENSO and the North Pacific Gyre is subject to the insolation. • Earth System Modeling results confirm our proxies-indicated Kuroshio Current strength. Abstract The Kuroshio Current (KC) is the northward branch of the North Pacific subtropical gyre (NPG) and exerts influence on the exchange of physical, chemical, and biological properties of downstream regions in the Pacific Ocean. Resolving long-term changes in the flow of the KC water masses is, therefore, crucial for advancing our understanding of the Pacific's role in global ocean and climate variability. Here, we reconstruct changes in KC dynamics over the past 20 ka based on grain-size spectra, clay mineral, and Sr–Nd isotope constraints of sediments from the northern Okinawa Trough. Combined with published sediment records surrounding the NPG, we suggest that the KC remained in the Okinawa Trough throughout the Last Glacial Maximum. Together with Earth-System-Model simulations, our results additionally indicate that KC intensified considerably during the early Holocene (EH). The synchronous establishment of the KC “water barrier” and the modern circulation pattern during the EH highstand shaped the sediment transport patterns. This is ascribed to the precession-induced increase in the occurrence of La Niña-like state and the strength of the East Asian summer monsoon. The synchronicity of the shifts in the intensity of the KC, Kuroshio extension, and El Niño/La Niña-Southern Oscillation (ENSO) variability may further indicate that the western branch of the NPG has been subject to basin-scale changes in wind stress curl over the North Pacific in response to low-latitude insolation. Superimposed on this long-term trend are high-amplitude, large century, and millennial-scale variations during last 5 ka, which are ascribed to the advent of modern ENSO when the equatorial oceans experienced stronger insolation during the boreal winter.

Description: The contributions of autonomous underwater gliders as an observing platform in the in-situ global ocean observing system (GOOS) are investigated. The assessment is done in two ways: First, the existing in-situ observing platforms contributing to GOOS (floats, surface drifters, moorings, research/commercial ships) are characterized in terms of their current capabilities in sampling key physical and bio-geochemical oceanic processes. Next the gliders’ capabilities are evaluated in the context of key applications. This includes an evaluation of 140 references presented in the peer-reviewed literature. It is found that GOOS has adequate coverage of sampling in the open ocean for several physical processes. There is a lack of data in the present GOOS in the transition regions between the open ocean and shelf seas. However, most of the documented scientific glider applications operate in this region, suggesting that a sustained glider component in the GOOS could fill that gap. Glider data are included for routine product generation (e.g. alerts, maps). Other noteworthy process-oriented applications where gliders are important survey tools include local sampling of the (sub)mesoscale, sampling in shallow coastal areas, measurements in hazardous environments, and operational monitoring. In most cases, the glider studies address investigations and monitoring of processes across multiple disciplines, making use of the ease to implement a wide range of sensors to gliders. The maturity of glider operations, the wide range of applications that map onto growing GOOS regional needs, and the maturity of glider data flow all justify the formal implementation of gliders into the GOOS. Remaining challenges include the execution of coordinated multinational missions in a sustained mode as well as considering capacity-building aspects in glider operations as well as glider data use.

Description: Highlights: • Asian green mussels were exposed to different concentrations of PVC particles. • Exposure to different microplastics concentrations was maintained for 3 months. • Microplastics exposure impaired the mussels' physiological performance. • Microplastics exposure increased mussel mortality. • The size of the induced effect was dosis dependent. Abstract: Marine bivalves are known to ingest microplastics, but information on the consequences for their physiological performance is limited. To investigate a potential exposure pathway that has not yet been addressed, we mimicked the resuspension of microplastics from the sediment in a laboratory exposure experiment. For this, we exposed the Asian green mussel Perna viridis to 4 concentrations (0 mg/l, 21.6 mg/l, 216 mg/l, 2160 mg/l) of suspended polyvinylchloride (PVC) particles (1–50 μm) for two 2-hour-time-periods per day. After 44 days, mussel filtration and respiration rates as well as byssus production were found to be a negative function of particle concentration. Furthermore, within 91 days of exposure, mussel survival declined with increasing PVC abundance. These negative effects presumably go back to prolonged periods of valve closure as a reaction to particle presence. We suggest that microplastics constitute a new seston component that exerts a stress comparable to natural suspended solids.

Description: Highlights • Iron content in krill muscle rises with the amount of ingested lithogenic particles • Krill feces have ∼5-fold higher proportions of labile iron than intact diatoms • Lithogenic iron mobilized by krill can enter the dissolved pool via multiple pathways • The prevailing foodweb structure plays an important role in ocean iron fertilization Iron is an essential nutrient for phytoplankton, but low concentrations limit primary production and associated atmospheric carbon drawdown in large parts of the world's oceans [1, 2]. Lithogenic particles deriving from aeolian dust deposition, glacial runoff, or river discharges can form an important source if the attached iron becomes dissolved and therefore bioavailable [3–5]. Acidic digestion by zooplankton is a potential mechanism for iron mobilization [6], but evidence is lacking. Here we show that Antarctic krill sampled near glacial outlets at the island of South Georgia (Southern Ocean) ingest large amounts of lithogenic particles and contain 3-fold higher iron concentrations in their muscle than specimens from offshore, which confirms mineral dissolution in their guts. About 90% of the lithogenic and biogenic iron ingested by krill is passed into their fecal pellets, which contain ∼5-fold higher proportions of labile (reactive) iron than intact diatoms. The mobilized iron can be released in dissolved form directly from krill or via multiple pathways involving microbes, other zooplankton, and krill predators. This can deliver substantial amounts of bioavailable iron and contribute to the fertilization of coastal waters and the ocean beyond. In line with our findings, phytoplankton blooms downstream of South Georgia are more intensive and longer lasting during years with high krill abundance on-shelf. Thus, krill crop phytoplankton but boost new production via their nutrient supply. Understanding and quantifying iron mobilization by zooplankton is essential to predict ocean productivity in a warming climate where lithogenic iron inputs from deserts, glaciers, and rivers are increasing [7–10].

Description: We investigated the evolution of the Pb isotopic composition of bulk sediments on the Cocos Plate in sedimentary successions of Deep Sea Drilling Project (DSDP) Site 495 and Ocean Drilling Program (ODP) Site 1256 over the past 23 million years of depositional history. Our study addresses the relationship of the sediment Pb isotope record to plate tectonics, weathering inputs, and paleoceanography. It is the first effort to characterize the Pb isotopic evolution of eastern equatorial Pacific sedimentation covering the entire tectonic pathway of the Cocos Plate from its formation at the East Pacific Rise to its arrival at the Central American subduction zone. The Sites 495 and 1256 bulk sediment Pb isotope records are fully consistent over time despite distinct differences between the type of sediment deposited at both locations. A systematic and continuous trend from ∼23 to ∼6–4 Ma toward more radiogenic Pb isotopic compositions, e.g., 206Pb/204Pb ratios increase from 18.29 to 18.81, reflects a decrease in the contribution of hydrothermal particles from the East Pacific Rise and an increase in the predominantly eolian contribution of mixed weathering products from the continental arcs of the Northern and south Central Andes as well as from southern Mexico. Surprisingly, both the Pb isotopic composition of the detrital fraction and that of past seawater indicate that inputs from nearby Central America and the Galápagos Archipelago did not significantly contribute to the sediments of our core locations but were overwhelmed by other sediment sources. A systematic change to less radiogenic Pb isotope ratios in sediments younger than ∼4–3 Ma, reaching present-day 206Pb/204Pb values near 18.70, reflects a reduction of the continental input from the South Central Volcanic Zone of the Andean Arc and increased contributions from southern Mexican igneous complexes. This isotopic trend reversal took place as a consequence of changes in atmospheric circulation, when the studied sites crossed the Intertropical Convergence Zone due to tectonic drift and concurrent climate cooling. Eolian transport has played a major role in the supply of detrital material over the entire Neogene and Quaternary. The delivery of hydrothermal Pb originating from the East Pacific Rise to the easternmost tropical Pacific has been a persistent feature that is attributed to a remarkably stable central and eastern Pacific deep-water flow pattern over millions of years. Thus, deep ocean circulation did not change significantly as a consequence of either (1) the Early Miocene closure of the deep gateway between the Caribbean and eastern Central Pacific or (2) the Late Pliocene complete closure of the Central American Seaway.