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  • Other Sources  (149)
  • Elsevier  (149)
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  • 2005-2009  (149)
  • 1990-1994
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  • 2005  (149)
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  • 2005-2009  (149)
  • 1990-1994
  • 1980-1984
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  • 1
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    Relating fault mechanics to fault zone structure (2005)
    Elsevier
    In:  Advances in Geophysics, ed.: Renata Dmowska, Warszawa, Elsevier, vol. 47, no. 7, pp. 65-111, pp. L21303, (ISBN: 0-12-018847-3)
    Details
    Publication Date: 2005
    Keywords: Fault zone ; Rock mechanics ; Friction ; Fracture ; Physical properties of rocks ; geometry
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Crustal deformation in the southcentral Alaska subduction zone (2005)
    Elsevier
    In:  Advances in Geophysics, ed.: Renata Dmowska, Heidelberg, Elsevier, vol. 47, no. 8, pp. 1-64, pp. 1516, (ISBN: 0-12-018847-3)
    Details
    Publication Date: 2005
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Subduction zone ; USA
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Acoustic and Elastic Wave Fields in Geophysics, III (2005)
    Elsevier
    In:  Amsterdam, 652 pp., Elsevier, vol. 39, no. XVI:, pp. 227-235, (0-444-51955-6)
    Details
    Publication Date: 2005
    Keywords: Seismics (controlled source seismology) ; Applied geophysics ; Wave propagation ; plane ; spherical ; and ; cylindrical ; Waves ; in ; isotropic ; and ; transversely ; isotropic ; solids, ; liquid-solid ; models, ; and ; media ; with ; cylindrical ; inclusions ; (boreholes) ; Textbook of geophysics
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Surface carbohydrate composition of a tapeworm in its consecutive intermediate hosts: Individual variation and fitness consequences (2005)
    Elsevier
    In:  International Journal for Parasitology, 35 (14). pp. 1499-1507.
    Details
    Publication Date: 2020-07-28
    Description: Carbohydrates on parasite surfaces have been shown to play an important role in host–parasite coevolution, mediating host non-self recognition and parasite camouflage. Parasites that switch hosts can change their surface molecules to remain undetected by the diverse immune systems of their different hosts. However, the question of individual variation in surface sugar composition and its relation to infectivity, virulence, immune evasion and growth of a parasite in its different hosts is as yet largely unexplored. We studied such fitness consequences of variation in surface sugars in a sympatric host–parasite system consisting of the cestode Schistocephalus solidus and its intermediate hosts, a copepod and the three-spined stickleback. Using lectins to analyse the sugar composition, we show that the tapeworm changes its surface according to the invertebrate or vertebrate host. Importantly, sugar composition seems to be genetically variable, as shown by differences among tapeworm sibships. These differences are related to variation in parasite fitness in its second intermediate host, i.e. infectivity and growth. Surface sugar composition may thus be a proximate correlate of the evolutionarily relevant variability in infectivity and virulence of parasites in different hosts.
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  • 5
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    Paleomagnetic modeling of seamounts near the Hawaiian–Emperor bend (2005)
    Elsevier
    In:  Tectonophysics, 405 (1-4). pp. 121-140.
    Details
    Publication Date: 2019-04-29
    Description: The Hawaiian–Emperor Seamount chain records the motion of the Pacific Plate relative to the Hawaiian mantle hotspot for ~80 m.y. A notable feature of the chain is the pronounced bend at its middle. This bend had been widely credited to a change in plate motion, but recent research suggests a change in hotspot motion as an alternative. Existing paleomagnetic data from the Emperor Chain suggest that the hotspot moved south during the Late Cretaceous and Early Tertiary, but reached its current latitude by the age of the bend. Thus, data from area of the bend are important for understanding changes in plume latitude. In this study, we analyze the magnetic anomalies of five seamounts (Annei, Daikakuji-W, Daikakuji- E, Abbott, and Colahan) in the region of the bend. These particular seamounts were chosen because they have been recently surveyed to collect multibeam bathymetry and magnetic data positioned with GPS navigation. Inversions of the magnetic and bathymetric data were performed to determine the mean magnetization of each seamount and from these results, paleomagnetic poles and paleolatitudes were calculated. Three of the five seamounts have reversed magnetic polarities (two are normal) and four contain a small volume of magnetic polarity opposite to the main body, consistent with formation during the Early Cenozoic, a time of geomagnetic field reversals. Although magnetization inhomogene ties can degrade the accuracy of paleomagnetic poles calculated from such models, the seamounts give results consistent with one another and with other Pacific paleomagnetic data of approximately the same age. Seamount paleolatitudes range from 13.7 to 23.7, with an average of 19.4F7.4 (2j). These values are indistinguishable from the present-day paleolatitude of the Hawaiian hotspot. Together with other paleomagnetic and geologic evidence, these data imply that the Hawaiian hotspot has moved little in latitude during the past ~45 m.y.
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  • 6
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    Recent seismic activity (1994–2002) of the Santorini volcano using data from local seismological network (2005)
    Elsevier
    In:  Developments in Volcanology, 7 . pp. 185-203.
    Details
    Publication Date: 2020-07-30
    Description: The South Aegean Active Volcanic Arc consists of a chain of five volcanic centers, the most active of which is the Santorini Volcano. A local radio-linked seismological network is installed on the island consisting of five permanent and four temporary stations. The temporary stations have been in operation periodically during the period 1994–1996 and two of them were installed on adjacent islands. All stations are equipped with vertical-component short period seismometers. During the period 1994–2002 a significant number of earthquakes has been recorded, with local (duration) magnitudes, MD, up to 5.0 and focal depths varying between 0 km and 35 km. Two clusters of epicenters have been located in the broader area of the Santorini Volcano. The first cluster is located in the caldera of the volcano and is associated with the volcanic process in the Kameni Island. The second (larger) cluster is located near the northern edge of the Santorini Island at the Kolumbo Reef and is connected with the volcanic process at this reef. These clusters can be appropriately associated with the two main tectonic features (faults) in the area under study. The first one (N60°E direction) corresponds to the continuation of the Amorgos fault in the area, while the secondary tectonic line (EW direction) is probably related with the southern edge of a submarine graben, which is located between the islands Amorgos and Santorini. Using the data set of the best-located earthquakes, recorded during the period 1994–2002, an attempt has been made to derive an appropriate equivalent 1 –D earth model for the area under study, in order to improve the accuracy of the determined hypocenters, as well as to obtain a preliminary knowledge of the volcano structure.
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  • 7
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    Major and trace element composition of the depleted MORB mantle (DMM) (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 231 (1-2). pp. 53-72.
    Details
    Publication Date: 2017-05-02
    Description: We derive an estimate for the chemical composition of the depleted MORB mantle (DMM), the source reservoir to mid-ocean ridge basalts (MORBs), which represents at least 30% the mass of the whole silicate Earth. A database for the chemical and physical properties of abyssal peridotites has become robust and complete enough to truly access a reference DMM. Using trace element depletion trends from the abyssal peridotites, it is possible to construct a large part of DMM’s trace element pattern. Splicing this information with isotopic constraints (Sr–Nd–Pb–Hf) and canonical ratios (Ce/Pb, Nb/Ta, Nb/U, Ba/Rb, H2O/Ce, CO2/Nb and Cl/K), we can extend abundance estimates to all the incompatible elements including volatile content. The resulting trace element pattern for average DMM constrains parental MORB to be generated by 6% aggregated fractional melting, consistent with recent models for hydrous melting of the mantle [P.D. Asimow, J.E. Dixon, C.H. Langmuir, A hydrous melting and fractionation model for mid-ocean ridge basalts: application to the Mid-Atlantic Ridge near the Azores, Geochem. Geophys. Geosyst. 5 (2004) 10.1029/2003GC000568]. We show that DMM is roughly balanced by the continental crust and better balanced upon inclusion of ocean island basalt source and oceanic crust components. Compared to the primitive mantle, DMM has been depleted by 2–3% melt extraction and has only 15% the radiogenic heat production.
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  • 8
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    Lipid geochemistry of methane-seep-related Black Sea carbonates (2005)
    Elsevier
    In:  Palaeogeography Palaeoclimatology Palaeoecology, 227 (1-3). pp. 31-47.
    Details
    Publication Date: 2017-06-30
    Description: Carbonates recovered from anoxic waters between 235 and 1555 m depth in the northwestern Black Sea were analyzed for lipid biomarkers and stable carbon isotopic compositions. In addition, a methane-seep-related microbial mat and a sample of surface sediment recovered from a non-seep site were studied for comparison. High concentrations of strongly 13C-depleted lipids attributed to bacteria and archaea mediating the anaerobic oxidation of methane (AOM) were found in all samples except for the sediment. Differences of the dominant AOM-performing communities between the carbonates indicated by specific lipid patterns appear to be caused by the respective biogeochemical settings. High proportions of ANME-2 consortia are found at sites of assumingly high partial pressures of methane while ANME-1 associations dominate at locations of moderate methane supply. In the sedimentary concretion, a complex mixture of biomarkers for terrestrial and planktonic organisms was found. Different molecular structures along with strong variations in the stable carbon isotopic compositions (δ13C = − 20.2‰ to − 94.3‰) allow for an estimation of the proportions of tetraether-bound biphytanes derived from planktonic Crenarchaeota and methanotrophic Euryarchaeota. Our data imply that the shape of AOM-derived carbonate precipitates in Black Sea environments is crucially influenced by the respective methane supply. Active AOM-driven chimney-like bioherms, similar to those previously observed on the Ukrainian shelf, might also develop in the deep euxinic zone at 1555 m water depths.
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  • 9
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    Calcium isotope fractionation in calcite and aragonite (2005)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 69 (18). pp. 4485-4494.
    Details
    Publication Date: 2017-09-08
    Description: Calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite. Precipitation temperatures ranged from 0 to 28°C. Calcium isotope fractionation shows a temperature dependence in accordance with previous observations: 1000 · ln(αcc) = −1.4 + 0.021 · T (°C) for calcite and 1000 · ln(αar) = −1.9 + 0.017 · T (°C) for aragonite. Within uncertainty the temperature slopes are identical for the two polymorphs. However, at all temperatures calcium isotopes are more fractionated in aragonite than in calcite. The offset in δ44/40Ca is about 0.6‰. The underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals, or to different Ca reaction behavior at the solid-liquid interface. Recently, the observed temperature dependence of the Ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting (Lemarchand et al., 2004). We show that this mechanism can in principle also be applied to CaCO3 precipitation in natural environments in normal marine settings. Following this model, Ca isotope fractionation in marine Ca carbonates is primarily controlled by precipitation rates. On the other hand the larger Ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates. The rate control model of Ca isotope fractionation predicts a strong dependence of the Ca isotopic composition of carbonates on ambient CO32− concentration. While this model is in general accordance with our observations in marine carbonates, cultured specimens of the planktic foraminifer Orbulina universa show no dependence of Ca-isotope fractionation on the ambient CO32− concentration. The latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water.
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  • 10
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    Holocene environmental history recorded in Lake Lyadhej-To sediments, Polar Urals, Russia (2005)
    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 223 (3-4). pp. 181-203.
    Details
    Publication Date: 2015-01-22
    Description: An 1180-cm long core recovered from Lake Lyadhej-To (68°15′ N, 65°45′ E, 150 m a.s.l.) at the NW rim of the Polar Urals Mountains reflects the Holocene environmental history from ca. 11,000 cal. yr BP. Pollen assemblages from the diamicton (ca. 11,000–10,700 cal. yr BP) are dominated by Pre-Quaternary spores and redeposited Pinaceae pollen, pointing to a high terrestrial input. Turbid and nutrient-poor conditions existed in the lake ca. 10,700–10,550 cal. yr BP. The chironomid-inferred reconstructions suggest that mean July temperature increased rapidly from 10.0 to 11.8 °C during this period. Sparse, treeless vegetation dominated on the disturbed and denuded soils in the catchment area. A distinct dominance of planktonic diatoms ca. 10,500–8800 cal. yr BP points to the lowest lake-ice coverage, the longest growing season and the highest bioproductivity during the lake history. Birch forest with some shrub alder grew around the lake reflecting the warmest climate conditions during the Holocene. Mean July temperature was likely 11–13 °C and annual precipitation—400–500 mm. The period ca. 8800–5500 cal. yr BP is characterized by a gradual deterioration of environmental conditions in the lake and lake catchment. The pollen- and chironomid-inferred temperatures reflect a warm period (ca. 6500–6000 cal. BP) with a mean July temperature at least 1–2 °C higher than today. Birch forests disappeared from the lake vicinity after 6000 cal. yr BP. The vegetation in the Lyadhej-To region became similar to the modern one. Shrub (Betula nana, Salix) and herb tundra have dominated the lake catchment since ca. 5500 cal. yr BP. All proxies suggest rather harsh environmental conditions. Diatom assemblages reflect relatively short growing seasons and a longer persistence of lake-ice ca. 5500–2500 cal. yr BP. Pollen-based climate reconstructions suggest significant cooling between ca. 5500 and 3500 cal. yr BP with a mean July temperature 8–10 °C and annual precipitation—300–400 mm. The bioproductivity in the lake remained low after 2500 cal. yr BP, but biogeochemical proxies reflect a higher terrestrial influx. Changes in the diatom content may indicate warmer water temperatures and a reduced ice cover on the lake. However, chironomid-based reconstructions reflect a period with minimal temperatures during the lake history.
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  • 11
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    Oxygen isotope fractionation during synthesis of CaMg-carbonate and implications for sedimentary dolomite formation (2005)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 69 . pp. 4665-4674.
    Details
    Publication Date: 2017-08-09
    Description: Hydrous CaMg-carbonate was synthesized at temperatures of 40 degrees, 60 degrees and 80 degrees C in the laboratory. This material has very similar mineralogical characteristics to natural disordered dolomite from the Coorong region in South Australia. Besides the dolomite variable amounts of amorphous carbonate are present in all samples. The oxygen isotope compositions of synthesized bulk carbonate samples (e.g., amorphous carbonate plus dolomite) plot significantly lower than the Northrop and Clayton (1966) dolomite-water equilibrium. Fractionated degassing of the samples, however, revealed relatively low oxygen isotope values for fast-reacting (using 100% H3PO4) amorphous carbonate. In contrast, slow-reacting dolomite has more positive oxygen isotope values, and calculated carbonate-water oxygen isotope fractionation values are close to strongest known dolomite-water oxygen isotope fractionation published earlier on. Variations of reaction/stabilization temperatures during synthesis gave evidence for dolomite formation from hypersaline solutions by a dissolution/reprecipitation process. It is likely that amorphous carbonate has been a problem in defining the dolomite-water fractionation in the past. Moreover, dolomite-associated amorphous carbonate contents probably led to incorrect speculations about lower oxygen isotope fractionation in a so-called protodolomite-water system. Copyright (c) 2005 Elsevier Ltd.
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  • 12
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    Sedimentology in the 21st century - a tribute to Wolfgang Schlager: editorial (2005)
    Elsevier
    In:  Sedimentary Geology, 175 . pp. 3-8.
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    Publication Date: 2018-07-19
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  • 13
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    Polyphase faulting during the development of the west Galicia rifted margin (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 237 (3-4). pp. 561-576.
    Details
    Publication Date: 2016-12-21
    Description: Rifted margins are commonly characterised by an extension discrepancy: the amount of extension measurable from the observed faulting is far less than that required to explain the crustal thinning. It is shown here that polyphase faulting may provide a simple explanation for this paradox, but can be very hard to recognise on seismic sections. However at the west Galicia rifted margin (the Galicia Interior Basin between the Galicia Bank and the mainland, and the deep Galicia margin to the west of the Galicia Bank), a combination of high quality depth images, seismic velocity information and stratigraphic control through ODP drilling and submersible sampling, provide complementary evidence for polyphase faulting. Berriasian–Hauterivian rifting in the Galicia Interior Basin occurred along two sets of faults: the first unroofed deep crustal rocks, evidenced by high seismic velocities close to top basement; the second cut and dismembered these early faults. Further rifting (up until the Aptian) then focussed west of the Galicia Bank, where two further phases of faulting can be inferred from the diachronous nature of seismostratigraphic units tilted within fault blocks. Removal of the latest phase of faulting aligns discontinuous reflections within the fault blocks into an anastomosing network of earlier faults; restoration along these brings the crust back to its early Hauterivian state, similar to the present structure of the Interior Basin.
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  • 14
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    History of freshwater runoff across the Laptev Sea (Arctic) during the last deglaciation (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 187-207.
    Details
    Publication Date: 2017-09-13
    Description: Sediment core PS2458 from the Laptev Sea continental margin (983-m water depth) stems from a position close to the paleoriver mouth of Lena and Yana rivers. It was dated by AMS-14C and analyzed in high resolution for oxygen isotopes of planktic foraminifers. Except the uppermost 100 cm and possibly the lowermost meter of the 8-m-long core, the sediments were deposited during the last deglaciation (14.5–8.0 cal-ka). According to 210Pb data, the uppermost 100 cm represents only the last 200 years. Planktic foraminifers are present throughout the dated deglacial interval, with the exception of a short time after ca. 13 cal-ka. Taking into account the global “ice volume effect” on the oxygen isotopic composition of the foraminifers, the isotopic record is considered to reflect salinity changes which were influenced by variable freshwater runoff and a growing marine influence during the postglacial transgression of the Laptev Sea shelf. The most conspicuous feature in the isotopic record is an outstanding peak dated to ca. 13 cal-ka. It is proposed that it represents a rapid outburst of large amounts of freshwater, possibly from an ice-dammed lake in the hinterland. Possible correlations to the onset of the cool Younger Dryas event in the northern hemisphere are discussed.
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  • 15
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    Removal and bioaccumulation of anthropogenic, halogenated transient tracers in an anoxic fjord (2005)
    Elsevier
    In:  Marine Chemistry, 94 (1-4). pp. 27-41.
    Details
    Publication Date: 2017-08-22
    Description: The persistence of the anthropogenic halogenated tracers, CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2FCClF2), carbon tetrachloride (CCl4) and methyl chloroform (CH3CCl3) in oxygen-depleted waters was investigated in the anoxic fjord Framvaren in southern Norway. A model for the ventilation of the water in the fjord was created based on tritium and CFC-12 profiles. The results suggest that CFC-12 is stable in this environment, although still affected by particulate scavenging, while the other four halocarbon species shows signs of significant removal in the oxic/anoxic interface. The first-order removal coefficients were calculated to be 0.35, 0.19, 1.23 and 0.31 year−1 for CFC-11, CFC-113, CCl4 and CH3CCl3, respectively. Significant downward flux of halogenated tracers by sinking organic matter is suggested by the model; the tracers are subsequently released to the water column by the remineralisation of the particles. This process acts as a sink of halogenated tracers in the surface waters, whereas it is a source for the deep waters. Our results points to bioaccumulation factors (BF) for the CFC tracers in the order of 4.4–5.4 (log BF), which is 100–600 times those previously reported. This might be of significance to near-shore, semi-enclosed, basins with a high flux of organic matter, but would still have little importance in open ocean basins.
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  • 16
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    Objective analyses of hydrographic data for referencing profiling float salinities in highly variable environments (2005)
    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 52 (3-4). pp. 651-664.
    Details
    Publication Date: 2020-08-05
    Description: The development of a broad-scale array of about 3000 autonomous profiling floats, known as Argo, has been underway since 2000. This array will deliver up to 100,000 vertical profiles of temperature, salinity and other parameters from the surface to depths up to 2000 m. While floats are expected to give good measurements of temperature and pressure, salinity measurements sometimes show significant sensor drift with time or offsets. Unless a float is recovered before the battery fails, recalibrations cannot be performed and a remote calibration method is required. Such a quality control system has been set up for the North Atlantic to identify and correct salinity sensor drifts by using historical hydrographic data. An objective mapping method is used that takes the spatial and temporal variations in water mass properties into account. These scales aim to represent the hydrographic structure of the North Atlantic, which follow the large-scale contours of the potential vorticity. The float measurements of each profile are compared to the mapped salinities in potential conductivity space by weighted least-squares, giving one correction for each profile. It is assumed that any conductivity offset changes slowly over time, so that a linear fit of the profile based corrections over the float time series is done. The result is a set of calibrated salinity data with corresponding uncertainties.
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  • 17
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    The first sorbicillinoid alkaloids, the antileucemic sorbillactones A and B, from a sponge derived Penicillium chrysogenum strain (2005)
    Elsevier
    In:  Tetrahedron (61). pp. 7252-7265.
    Details
    Publication Date: 2019-01-24
    Description: The saltwater culture of a Penicillium chrysogenum strain isolated from the Mediterranean sponge Ircinia fasciculata yielded three new sorbicillin-derived compounds (1-3), whose structures were elucidated mainly by 2D NMR and mass spectrometry. Among them, sorbicillactones A (1) and B (2) are the first sorbicillinoid natural products that contain nitrogen. Compound 1 is anti-HIV active and it exhibits a strong cytotoxic activity against L5178y leukemic cells, combined with a relatively low toxicity to cervical carcinoma HeLa S3 cells and pheochromocytoma PC 12 cells. The absolute configurations of I and 2 were elucidated by quantum chemical calculation of circular dichroism (CD) spectra. Another compound isolated, sorbivinetone (3), might be an artifact derived from sorbicillinol (4) by Diels-Alder reaction with ethyl vinyl ether. Furthermore, the known sorbicillinoid fungal metabolites oxosorbicillinol (5), sorbicillin (6), and bisvertinolone (7) were identified, as well as the alkaloids meleagrine and roquefortine C. The biosynthetic origin of sorbicillactone A (1) from acetate, alanine, and methionine was investigated by feeding experiments with C-13-labeled precursors
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  • 18
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    Differing controls over the Cenozoic Pb and Nd isotope evolution of deepwater in the central North Pacific Ocean (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 232 . pp. 345-361.
    Details
    Publication Date: 2016-12-21
    Description: Dissolved Pb and Nd isotope ratios of seawater, as recorded by chemical marine precipitates such as hydrogenetic ferromanganese crusts, have been used as paleoenvironmental proxy tracers. For the North Pacific, however, all ferromanganese crusts studied so far have either been subject to phosphatization or hydrothermal influence in their old part, or only the young parts have been analyzed. Thus, the Pb and Nd isotope compositions of North Pacific deep waters prior to ∼20 Ma are not well constrained. We present new results for three ferromanganese crusts, one of which (CJ01) shows no phosphatization and is located far away from the EPR. Its age is inferred to be ∼75 Ma and thus provides for the first time an opportunity to trace the Nd and Pb isotope evolution of central North Pacific seawater back to the latest Cretaceous. The three crusts, no matter whether phosphatized or not, display very similar Pb and Nd isotope trends with age, suggesting no modification of the Pb and Nd isotope distribution by post-depositional phosphatization. Our data suggest that dissolved Pb in deep waters of the central North Pacific over the Cenozoic and latest Cretaceous has mainly been derived from eolian dust and only to a minor extent from weathering of island arcs. For Pb these trends broadly resemble the Pb isotope evolution of the eolian silicate dust fraction of core LL44-GPC3 in the central North Pacific. We suggest that the isotope evolution of dissolved Pb in central North Pacific seawater has been mainly controlled by Pb released from eolian dust from North America prior to 50 Ma and after 40 Ma from Asia. In contrast, the Nd isotope time series of the crusts are by no means similar to the Nd isotope evolution of the silicate dust fraction in core GPC3, suggesting a decoupling from the Pb and negligible contributions from dust to the dissolved Nd in the central North Pacific deep water. The rise of Nd isotope ratios of Pacific seawater during the Cenozoic has most likely been caused by the increasing volcanic activity and erosion of the volcanic arcs around the Pacific.
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  • 19
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    Growth and erosion of a cold-water coral covered carbonate mound in the Northeast Atlantic during the Late Pleistocene and Holocene (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 233 . pp. 33-44.
    Details
    Publication Date: 2016-12-21
    Description: The first detailed stratigraphic record from a deep-water carbonate mound in the Northeast Atlantic based on absolute datings (U/Th and AMS 14C) and stable oxygen isotope records reveals that its top sediment sequences are condensed by numerous hiatuses. According to stable isotope data, mainly sediments with an intermediate signal are preserved on the mound, while almost all fully glacial and interglacial sediments have either not been deposited or have been eroded later. The resulting hiatuses reduce the Late Pleistocene sediment accumulation at Propeller Mound to amounts smaller than the background sedimentation. The hiatuses most likely result due to the sweeping of the mound in turn with the re-establishment of vigour interglacial circulation patterns after sluggish current regimes during glacials. Thus, within the discussion if internal, fluid-driven or external environmentally driven processes control the evolution of such carbonate mounds, our findings for Propeller Mound clearly point to environmental forcing as the dominant mechanism shaping deep-water carbonate mounds in the NE Atlantic during the Late Pleistocene and Holocene
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  • 20
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    Intercalibration of benthic flux chambers II. Hydrodynamic characterization and flux comparisons of 14 different designs (2005)
    Elsevier
    In:  Marine Chemistry (94). pp. 147-173.
    Details
    Publication Date: 2017-08-22
    Description: We have compared 14 different sediment incubation chambers, most of them were used on bottom landers. Measurements of mixing time, pressure gradients at the bottom and Diffusive Boundary Layer thickness (DBL) were used to describe the hydrodynamic properties of the chambers and sediment–water solute fluxes of silicate (34 replicates) and oxygen (23 replicates) during three subsequently repeated incubation experiments on a homogenized, macrofauna-free sediment. The silicate fluxes ranged from 0.24 to 1.01 mmol m−2 day−1 and the oxygen fluxes from 9.3 to 22.6 mmol m−2 day−1. There was no statistically significant correlation between measured fluxes and the chamber design or between measured fluxes and hydrodynamic settings suggesting that type of chamber was not important in these flux measurements. For verification of sediment homogeneity, 61 samples of meiofauna were taken and identified to major taxa. In addition, 13 sediment cores were collected, sectioned into 5–10-mm slices and separated into pore water and solid phase. The pore water profiles of dissolved silicate were used to calculate diffusive fluxes of silicate. These fluxes ranged from 0.63 to 0.87 mmol m−2 day−1. All of the collected sediment parameters indicated that the sediment homogenization process had been satisfactorily accomplished. Hydrodynamic variations inside and between chambers are a reflection of the chamber design and the stirring device. In general, pump stirrers with diffusers give a more even distribution of bottom currents and DBL thicknesses than paddle wheel-type stirrers. Most chambers display no or low static differential pressures when the water is mixed at rates of normal use. Consequently, there is a low risk of creating stirrer induced pressure effects on the measured fluxes. Centrally placed stirrers are preferable to off-center placed stirrers which are more difficult to map and do not seem to give any hydrodynamic advantages. A vertically rotating stirrer gives about five times lower static differential pressures at the same stirring speed as the same stirrer mounted horizontally. If the aim is to simulate or mimic resuspension at high flow velocities, it cannot be satisfactorily done in a chamber using a horizontal (standing) rotating impeller (as is the case for most chambers in use) due to the creation of unnatural conditions, i.e. large static differential pressures and pre-mature resuspension at certain locations in the chamber.
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  • 21
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    Plume-ridge interaction studied at the Galápagos spreading center: Evidence from 226Ra-230Th-238U and 231Pa-235U isotopic disequilibria (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 234 (1-2). pp. 165-187.
    Details
    Publication Date: 2016-12-21
    Description: New 238U–230Th–226Ra and 231Pa–235U disequilibria data measured by TIMS are presented for ridge-centered MORB glasses dredged during the R/V Sonne 158 cruise at the Galápagos or Cocos-Nazca Spreading Center (GSC) between 86.0°W and 92.3°W. The application of U-series isotopes to the GSC region, situated a few hundred kilometres to the north of the Galápagos hotspot, allows assessment of fundamental questions related to the dynamics of plume–ridge interaction. These include (1) the relationship between long-lived source variations, U-series disequilibria and extent of differentiation, (2) partial melting during solid upwelling, and (3) the nature and rates of plume–ridge mass transfer. The along axis U-series disequilibria variation show gradational patterns that locally are correlated with geochemical and isotopic parameters such as La/Sm, Tb/Yb, 206Pb/204Pb and 143Nd/144Nd as well as major element compositions. The correlation of (230Th)/(238U) with radiogenic isotopes and Tb/Yb provides constraints on the plume source influence on the melting process, reflecting an increase in the amount of melting at depth in the presence of garnet or aluminous clinopyroxene. Moreover, the correlation between U-series signatures, radiogenic isotopes, incompatible element abundance and MgO content indicates a causative relationship between the melting of plume source materials and how these lavas differentiate at shallow depths. We speculate that this involves loss of alkalis from ascending melts to shallow peridotite and crustal gabbro, resulting in increased olivine fractionation from the magmas. The U-series data place stringent constraints on the timing of plume–ridge mass transfer and thus distinguish whether mass transfer occurs by movement of melts or solid mantle. Within the likely conditions proposed by the model of (Braun and Sohn [EPSL 213 (2003): 417–430] and with knowledge of (231Pa)/(235U) and (230Th)/(238U) observed in Galápagos Islands lavas [A. Saal, personal communication], we show that all 226Ra excess will be lost and the initial 231Pa and 230Th excesses will be largely decayed. Therefore, we conclude that the plume influence on the GSC lavas results from a solid mantle flow process instead of through migration of plume-derived melts to the ridge.
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  • 22
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    Northern ice discharges and Antarctic warming: could ocean eddies provide the link? (2005)
    Elsevier
    In:  Quaternary Science Reviews, 24 (16-17). pp. 1809-1820.
    Details
    Publication Date: 2016-09-16
    Description: A mechanism is advanced for explaining the Antarctic warm events from 90 to 30ka BP which involves meltwater-induced changes in the salinity gradient across the Antarctic Circumpolar Current (ACC) and consequent changes in the poleward heat transport by ocean eddies. Based on simple linear scale analysis, the mechanism is shown to yield warming in the Antarctic interior of roughly the magnitude seen in Antarctic ice-core records (∼2 °C) in response to ice discharges into the North Atlantic. Consistent with observations, the mechanism produces gradual Antarctic warming and cooling, as dictated by the time required for salinity anomalies to build up and dissipate across the ACC. The mechanism also allows the onset of warming or cooling to be tied to changes in Atlantic overturning, which is relevant here, not for influencing ocean heat transport directly, but for influencing the routing of meltwater from the North Atlantic into the Southern Ocean. The ideas presented here highlight the possibility that eddy processes in the ocean may play a first-order role in aspects of climate variability on millennial time scales.
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  • 23
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    Reply to comment on "Gas hydrate growth, methane transport, and chloride enrichment at the southern sumnit of Hydrate Ridge, Cascadias margin off Oregon" (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 239 . pp. 168-175.
    Details
    Publication Date: 2016-12-21
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  • 24
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    Is the initiation of glaciation on Antarctica related to a change in the structure of the ocean? (2005)
    Elsevier
    In:  Global and Planetary Change, 45 (1-3). pp. 23-33.
    Details
    Publication Date: 2017-07-24
    Description: Today, the ocean is characterized by pools of warm tropical–subtropical water bounded poleward and at depth by cold water. In the tropics and subtropics, the warm waters are floored at depth by the thermocline–pycnocline, which crops out on the ocean surface between the subtropical and polar frontal systems that form the poleward boundary. It is along and between the frontal systems that the thermocline waters enter the ocean interior. These frontal systems form beneath the maxima of the zonal component of the westerly winds. Today, the location of the westerly winds is stabilized by the persistent high-pressure systems at the polar regions produced by the ice cover of the Antarctic and sea-ice cover of the Arctic. The paleobiogeographic distribution of plankton fossils indicates that, prior to the Oligocene, the subtropical and polar frontal systems were not persistent features. Recent climate model experiments show that without perennial ice cover in the polar regions a seasonal alternation between high and low atmospheric pressure systems can occur. These seasonal alternations would force major changes in the location and strength of the westerly winds, preventing the development of the well-defined frontal systems that characterize the Earth today. Without the subtropical and polar frontal systems, the thermocline would be less well developed and the pycnocline could be dominated by salinity differences. Evidence from ocean drilling suggests that the glaciation of East Antarctica began at the Eocene–Oligocene boundary, but took time to spread over the entire continent. The presence of calcareous nannoplankton in the Arctic basin prior to the Oligocene and their absence thereafter suggests that the ice cover of the Arctic Ocean also developed at the Eocene–Oligocene boundary. Both events appear to be related to the development of the modern oceanic structure, but it remains uncertain whether the ocean changed in response to the development of ice covered polar regions or vice versa.
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  • 25
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    Induction of defences and within-plant variation on palatability in two brown algae from the northern-central coast of Chile: effects of mesograzers and UV radiation (2005)
    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 325 . pp. 214-227.
    Details
    Publication Date: 2018-06-29
    Description: Macroalgae possess different defense mechanisms in response to herbivory. Some species produce anti-herbivore secondary metabolites, but production of these substances can be costly. Therefore, algae may produce defensive metabolites only in response to herbivory (inducible defense) or defend particular parts of the alga differentially (within-alga variation). In the present study, we examined whether two species of brown algae from the SE-Pacific show evidence of inducible chemical defense (non-polar compounds) or within-alga variation of defense, which we estimated in form of palatability of differently treated algae to amphipod grazers (with live algae and agar-based food containing non-polar algal extracts). In Glossophora kunthii (C. Agardh) J. Agardh, we observed an increase in palatability after algae were acclimated for 12 days without grazers. Subsequent addition of grazers for 12 days then resulted in a reduction of palatability indicating the existence of inducible defense. After removal of grazers for 12 days, these induced effects again disappeared. The reaction of G. kunthii was triggered even by the mere presence of grazers, which suggests that this alga can respond to waterborne cues by reducing palatability. Effects were only found for agar-based food containing non-polar extracts, but not for live algae, suggesting that some parts of the algae are undefended. Our second experiment on within-alga variation confirmed that only apical (growth region) and basal parts (near the holdfast region) of G. kunthii are defended against herbivores. For the second species, Macrocystis integrifolia Bory, the first experiment revealed no induction of defense, while the second experiment on within-alga variation showed that amphipods avoided basal parts and in particular stipes of M. integrifolia but only in live algae. Although both studied algal species differed substantially in their defensive strategies, their reaction was independent of the presence or absence of UV radiation. Thus, it appears that UV effects play only a minor role in anti-herbivore defense, which is in accordance with most previous studies.
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  • 26
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    Fields of multi-kilometer scale sub-circular depressions in the Carnegie Ridge sedimentary blanket: Effect of underwater carbonate dissolution? (2005)
    Elsevier
    In:  Marine Geology, 216 (4). pp. 205-219.
    Details
    Publication Date: 2017-08-03
    Description: Offshore Ecuador, the Carnegie Ridge is a volcanic ridge with a carbonate sediment drape. During the SALIERI Cruise, multibeam bathymetry was collected across Carnegie Ridge with the Simrad EM120 of the R/V SONNE. The most conspicuous features discovered on the Carnegie Ridge are fields of circular closed depressions widely distributed along the mid-slope of the northern and southern flanks of the ridge between 1500 and 2600 m water depth. These circular depressions are 1–4 km wide and typically 100–400 m deep. Most are flat floored and some are so densely packed that they form a honeycomb pattern. The depressions were carved into the ridge sedimentary blanket, which consists of carbonate sediment and has been dated from upper Miocene to upper Pleistocene. Several hypotheses including pockmark origin, sediment creeping, paleo-topography of the volcanic basement, effects of subbottom currents, and both marine and subaerial karstic origins are discussed. We believe that underwater dissolution process merits the most serious consideration regarding the origin of the closed depression.
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  • 27
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    Long-term annual water balance analysis of the Lena River (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 84-95.
    Details
    Publication Date: 2020-12-01
    Description: Historical data analyses show that the Lena River and its major tributaries experienced an extended low water period over 1936–1957 and high water periods over 1974–1983 and 1988–2001. Higher than normal river discharge and annual precipitation is particularly pronounced since the late 1960s due to large-scale changes in atmospheric circulation patterns. The trend in runoff observed in the Lena River basin increased by 10% from 1936 to 2001 due to extended wet periods during the second part of last century. The trend is weakened for the Vilui River basin since it experiences reservoir regulation, which causes additional water losses through reservoir filling and increased evaporation. Runoff regulation strongly affects the winter runoff regime of both the Vilui River and the lower reaches of the Lena River causing an increased winter discharge at the Lena river outlet station of approximately 33%.
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  • 28
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    The turbidity maximum zone of the Yenisei River (Siberia) and its impact on organic and inorganic proxies (2005)
    Elsevier
    In:  Estuarine, Coastal and Shelf Science, 65 (1-2). pp. 61-73.
    Details
    Publication Date: 2015-01-30
    Description: A general overview of the processes taking place in the summer mixing zone of the fresh Yenisei River water with the marine waters of the Kara Sea is given in this study, with special emphasis on the interaction between bulk (total suspended matter), inorganic (Fe, Mn) and organic (suspended organic carbon, suspended nitrogen) proxies. Within the mixing zone, a zone of enhanced turbidity (maximum turbidity zone) was observed comparable to studies in other rivers. Flocculation of particles due to changes in salinity and hydrography cause this maximum turbidity zone, and resuspension additionally enhances the turbidity in the near-bottom layers. Organic matter behaves conservatively in the mixing zone in terms of its percentage of suspended matter. It, however, undergoes degradation as revealed by amino acid data. Inorganic, redox- and salinity-sensitive, proxies (Mn, Fe) behave non-conservatively. Dissolved iron is removed at low salinities (〈2) due to precipitation of iron oxyhydroxides and adsorption of manganese on suspended particles, enhancing the Mn/Al ratio of the suspended matter in the same zone. At higher salinities within the mixing zone, Fe/Al and Mn/Al ratios of the suspended particles are depleted due to resuspension of sediment with lower Fe/Al and Mn/Al ratios. Dissolved manganese concentrations are significantly higher in the near-bottom layers of the mixing zone due to release from the anoxic sediment. All things considered, the Yenisei River mixing zone shows patterns similar to other world's rivers.
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  • 29
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    Humus accumulation and microbial activities in calcari-epigleyic fluvisols under grassland and forest diked in for 30 years (2005)
    Elsevier
    In:  Soil Biology & Biochemistry, 37 (11). pp. 2163-2166.
    Details
    Publication Date: 2020-01-01
    Description: The accumulation and transformation of organic matter during soil development is rarely investigated although such processes are relevant when discussing about carbon sequestration in soil. Here, we investigated soils under grassland and forest close to the North Sea that began its genesis under terrestrial conditions 30 years ago after dikes were closed. Organic C contents of up to 99 mg g−1 soil were found until 6 cm soil depth. The humus consisted mainly of the fraction lighter than 1.6 g cm−3 which refers to poorly degraded organic carbon. High microbial respiratory activity was determined with values between 1.57 and 1.17 μg CO2–C g−1 soil h−1 at 22 °C and 40 to 70% water-holding capacity for the grassland and forest topsoils, respectively. The microbial C to organic C ratio showed values up to 20 mg Cmic g−1 Corg. Although up to 2.69 kg C m−2 were estimated to be sequestered during 30 years, the microbial indicators showed intensive colonisation and high transformation rates under both forest and grassland which were higher than those determined in agricultural and forest topsoils in Northern Germany.
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  • 30
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    A 12-year study of the seasonal and interannual dynamics of mesozooplankton in the Laptev Sea: Significance of salinity regime and life cycle patterns (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 141-164.
    Details
    Publication Date: 2016-02-12
    Description: Over a 12-year period (1989–2000) the spatial and temporal distribution of zooplankton in the Laptev Sea (Arctic Siberia) has been investigated. A total number of 111 taxa from 10 phyla were found. Sixteen species are reported from this region for the first time. The distribution and abundance of zooplankton on the Laptev Sea shelf is dependent on the main direction of river water spread, which varies between years. While the western and northeastern Laptev Sea shelf is dominated by a marine–neritic fauna, the central part is inhabited by a transitional brackish–marine assemblage. A brackish–neritic community characterizes the eastern and southeastern regions, where lowest salinities usually prevail. Closer to estuaries the summer zooplankton consists of both freshwater and brackish-water species, whereas in winter brackish-water species are dominant. Average zooplankton abundance varies seasonally and interannually, particularly in the southeastern Laptev Sea. The amplitude of these variations mainly depends on the state of the populations of the most common Copepoda species, the intensity of their reproduction, and their success in overwintering. Two seasonal abundance maxima were found, at the end of winter and at the end of summer. During the period of highest reproduction in summer the abundance may be 50 times greater than during overwintering. The average population abundance can vary by the factor of 2 in summer and in winter from year to year.
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  • 31
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    Palaeobotanical evidence for warm summers in the East Siberian Arctic during the last cold stage (2005)
    Elsevier
    In:  Quaternary Research, 63 (3). pp. 283-300.
    Details
    Publication Date: 2015-02-12
    Description: Plant macrofossils from the “Mamontovy Khayata” permafrost sequence (71°60′N, 129°25′E) on the Bykovsky Peninsula reflect climate and plant biodiversity in west Beringia during the last cold stage. 70 AMS and 20 conventional 14C dates suggest sediment accumulation between about 60,000 and 7500 14C yr B.P. The plant remains prove that during the last cold-stage arctic species (Minuartia arctica, Draba spp., Kobresia myosuroides) coexisted with aquatic (Potamogeton vaginatus, Callitriche hermaphroditica), littoral (Ranunculus reptans, Rumex maritimus), meadow (Hordeum brevisubulatum, Puccinellia tenuiflora) and steppe taxa (Alyssum obovatum, Silene repens, Koeleria cristata, Linum perenne). The reconstructed vegetation composition is similar to modern vegetation mosaics in central and northeast Yakutian relict steppe areas. Thus, productive meadow and steppe communities played an important role in the Siberian Arctic vegetation during the late Pleistocene and could have served as food resource for large populations of herbivores. The floristic composition reflects an extremely continental, arid climate with winters colder and summers distinctly warmer than at present. Holocene macrofossil assemblages indicate a successive paludification possibly connected with marine transgression, increased oceanic influence and atmospheric humidity. Although some steppe taxa were still present in the early Holocene, they disappeared completely before ∼2900 14C yr B.P.
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  • 32
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    The pattern and process of mammoth evolution in Eurasia (2005)
    Elsevier
    In:  Quaternary International, 126-128 . pp. 49-64.
    Details
    Publication Date: 2015-11-04
    Description: Mammoth evolution in Eurasia represents one of the best-studied examples of evolutionary pattern and process in the terrestrial fossil record. A pervasive belief in the gradual transformation of chronospecies in Europe is giving way to a more complex model incorporating geographical variation across the whole of northern Eurasia. This in turn casts doubt on biostratigraphic deductions which assume gradual transformation of molar morphology, simultaneous across the species’ range. The earliest European elephantids, Mammuthus rumanus, occur in the interval 3.5–2.5 Ma, and are distinctly more primitive than the better-known M. meridionalis. The species ‘M. gromovi’, identified in the interval c. 2.6–2.2 Ma, appears to be a junior synonym of M. meridionalis. M. meridionalis dispersed widely and, in the interval 2.0–1.5 Ma, gave rise to M. trogontherii in eastern Asia, probably in China, spreading to NE Siberia by 1.2 Ma. Between that date and c. 600 ka, flow of genes and/or individuals westwards produced an interaction with European M. meridionalis which led to a network of populations in time and space and the eventual supplanting of that species by M. trogontherii. This conclusion is based principally on the earlier appearance of M. trogontherii morphology in eastern Asia, supplemented by complex morphological patterns in Europe during the time of transition. Subsequently, M. trogontherii did not undergo a gradual transformation into M. primigenius (woolly mammoth) in Europe, but remained in stasis (apart from size reduction) until 200 ka. In NE Siberia, however, M. trogontherii began a transformation into primitive M. primigenius morphology as early as 700 ka, and that species continued its evolution in the same region through the Middle and Late Pleistocene. The incursion of M. primigenius into Europe appears to have occurred soon after 200 ka, and its ‘replacement’ of M. trogontherii there probably included some introgression from the latter species.
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  • 33
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    Arctic Siberian shelf environments (2005)
    Elsevier
    In:  Global and Planetary Change - Special Issue, 48 (1-3). Elsevier, Amsterdam, pp. 1-8, 252 pp.
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    Publication Date: 2015-03-31
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  • 34
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    Long-term open-water season stream temperature variations and changes over Lena River Basin in Siberia (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 96-111.
    Details
    Publication Date: 2015-03-03
    Description: This study systematically analyzes long-term (1950-1992) stream temperature records for the major sub-basins within the Lena River watershed in order to describe water temperature regimes over the various parts of the Lena watershed and document significant stream temperature changes induced by reservoir regulation, and by natural variations/changes. The results show that the open water season can be divided into three consecutive stages---"increasing temperature stage" in the early open water season, "stable temperature stage" in the mid-warm season, and "decreasing temperature stage" in the late open water season. Temperature conditions are similar over the Aldan and Upper Lena regions. However, stream temperatures at the Lena basin outlet are up to 8 °C lower than those over the southern sub-basins. This suggests that the latitudinal difference in climatic variables, such as air temperature, might be the major control on stream temperature regime. Results also demonstrate that the reservoir regulation has a strong influence on the regional water temperature regime and change in the regulated sub-basin. Reservoir regulation has increased (decreased) the downstream water temperatures in the Vilui valley during the early (mid) open water season. Trend analyses show consistent warming trends across the entire Lena River basin in the early open water season. This may indicate a response to earlier snowmelt over the Lena River watershed. Trend results also demonstrate that the Aldan tributary, without much human impact, experiences warming (cooling) trends in the first (second) half of the open water season, leading to a stream temperature regime shift toward early open water season. The upper Lena River has warming (cooling) trends in the early (mid-late) open water season. Over the regulated Vilui tributary, however, stream temperatures have significantly increased in the early and late parts of the warm season due to combined effects of natural changes and reservoir regulation. Over the Lena basin as a whole, strong positive correlations have been found between the basin mean monthly air and water temperatures during the warm season. Increasing water temperatures were observed during the early and mid-June. Because of stream temperature increase in this peak flow period, the Lena River heat flux has gone up by 23% in June. This may have considerable impact on the thermal conditions of the Laptev Sea in the early summer season.
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  • 35
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    Long time series of deep water particle flux in three biogeochemical provinces of the northeast Atlantic (2005)
    Elsevier
    In:  Journal of Marine Systems, 56 (3-4). pp. 391-415.
    Details
    Publication Date: 2015-09-22
    Description: Long-term observations of the deep ocean particle flux from three sites in the northeast Atlantic (33 degrees N, 22 degrees W; 47 degrees N, 20 degrees W; 54 degrees N, 20 degrees W) provide the basis for comparison and characterization of the biogeochemical provinces in terms of sedimentation pattern. Deep ocean particle flux data (2000 in) for fluxes of total mass and the flux composition are presented and compared to published sediment trap data from this area to consider regional-scale variations in the quantity and composition of settling material. The observations show that in the northeast Atlantic gradient of decreasing mass flux from North to South, exists consistent with known changes of biological productivity in surface waters. This gradient is associated with similar trends in opal and particulate organic carbon, whereas calcium carbonate shows trend in the opposite direction. The changes in the composition of the settling material found along the transect are indicating that the calcium carbonate flux is critical in removing organic matter from the upper ocean to the deeper sink. Its role declines from the subtropical ocean (60-80% of the particle flux) towards North (〈 40%) reflecting the decreasing importance of coccolithophorid/foraminiferal blooms for particle flux from the subtropical to the subpolar North Atlantic. In contrast, the role of biogenic silica (opal) in regard to the ballasting effect increases towards North. The northern sites have much higher percentage of biogenic silica than the sites in the South, because of the deep winter mixing and the seasonality of phytoplankton dominated by diatom blooms during spring and summer. The comparison of the seasonal pattern of particle flux with the seasonal pattern of surface chlorophyll a concentrations from SeaWiFS together with the similarity of the pattern observed in calcium carbonate and opal leads to the conclusion that the particle flux at two positions (33 degrees N, 22 degrees W; 47 degrees N, 20 degrees W) is fast and directly coupled to the phytoplankton dynamics in the overlying euphotic zone.
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  • 36
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    New insights into the Weichselian environment and climate of the East Siberian Arctic, derived from fossil insects, plants, and mammals (2005)
    Elsevier
    In:  Quaternary Science Reviews, 24 (5-6). pp. 533-569.
    Details
    Publication Date: 2015-03-24
    Description: Multidisciplinary study of a key section on the Laptev Sea Coast (Bykovsky Peninsula, east Lena Delta) in 1998–2001 provides the most complete record of Middle and Late Weichselian environments in the East Siberian Arctic. The 40-m high Mamontovy Khayata cliff is a typical Ice Complex section built of icy silts with a network of large syngenetic polygonal ice wedges, and is richly fossiliferous. In combination with pollen, plant macrofossil and mammal fossils, a sequence of ca 70 insect samples provides a new interpretation of the environment and climate of the area between ca 50 and 12 ka. The large number of radiocarbon dates from the section, together with an extensive 14C database on mammal bones, allows chronological correlation of the various proxies. The Bykovsky record shows how climate change, and the Last Glacial Maximum in particular, affected terrestrial organisms such as insects and large grazing mammals. Both during the presumed “Karginsky Interstadial” (MIS 3) and the Sartanian Glacial (MIS 2), the vegetation remained a mosaic arctic grassland with relatively high diversity of grasses and herbs and dominance of xeric habitats: the tundra-steppe type. This biome was supported by a constantly very continental climate, caused by low sea level and enormous extension of shelf land. Variations within the broad pattern were caused mainly by fluctuations in summer temperature, related to global trends but overprinted by the effect of continentality. No major changes in humidity were observed nor were advances of modern-type forest or forest-tundra recorded, suggesting a major revision of the “Karginsky Interstadial” paradigm. The changing subtypes of the tundra-steppe environment were persistently favourable for mammalian grazers, which inhabited the shelf lowlands throughout the studied period. Mammal population numbers were lowered during the LGM, especially toward its end, and then flourished in a short, but impressive peak in the latest Weichselian, just before the collapse of the tundra-steppe biome. Throughout MIS 3 and MIS 2, the climate remained very favourable for the aggradation of permafrost. No events of regional permafrost degradation were observed in the continuous Bykovsky sequence until the very end of the Pleistocene.
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  • 37
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    Holocene environmental history of the Gotland Basin (Baltic Sea) - a micropalaeontological model (2005)
    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 220 (3-4). pp. 227-241.
    Details
    Publication Date: 2020-08-07
    Description: Organic microfossils of a well-dated sediment core from Gotland Basin were analysed and used for the ecological interpretation of the Holocene history of this area. To avoid confusion with corrected and uncorrected 14C ages, only calendar years BP are used. In the lowermost part organic microfossils are rare, but few marine dinoflagellate cysts between 11 300 and 11 000 years BP indicate the marine Yoldia Phase. At 9800 years BP a significant environmental change is indicated by the rapid increase of freshwater dinoflagellates and pine pollen. At the end of the freshwater stage an enormous abundance increase of cladoceran remains indicates an eutrophication event between 7600 and 7400 years BP. First permanent brackish water conditions of the surface water were established at 7400 years BP and the increasing salinity reached its maximum between 6700 and 6400 years BP. Further changes in the brackish surface water ecosystem of the Gotland Basin can be found at 5500, 4400, 3000, 1000, and 800 years BP, which are thought to be mainly climatically induced.
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  • 38
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    A short note on the cephalopods sampled in the Angola Basin during the DIVA I-expedition (2005)
    Elsevier
    In:  Organisms Diversity & Evolution, 5 (1). pp. 227-230.
    Details
    Publication Date: 2017-01-31
    Description: Five cephalopods, all belonging to different species, were identified from deep-sea trawl samples conducted during the DIVA 1-expedition of RV “Meteor” in the Angola Basin in July 2000. These were the teuthoid squids Bathyteuthis abyssicola, Brachioteuthis riisei, Mastigoteuthis atlantica, Galiteuthis armata, and the finned deep-sea octopus Grimpoteuthis wuelkeri. The present study contributes information on size, morphometry, biology and distribution of the species form this unique cephalopod collection.
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  • 39
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    Early to middle Holocene changes in Laptev Sea water masses deduced from diatom and aquatic palynomorph assemblages (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 208-222.
    Details
    Publication Date: 2017-09-13
    Description: On the basis of diatom and aquatic palynomorph assemblages in sediment cores obtained from the eastern Laptev Sea shelf, major phases of environmental change associated with the last postglacial global sea-level rise can be recognized for the time since 11.3 calendar years BP (cal. ka). Until 11 cal. ka, the outer Laptev Sea shelf (≥ 51 m paleodepth) was inundated and paleoenvironmental conditions were characterized by increased precipitation of river-loaded matter, primarily diatom plankton, in a river-proximal environment where reconstructed surface water salinities, using freshwater diatoms as proxy, remained below 9. The time interval 10.7–9.2 cal. ka was marked by a predominance of the dinoflagellate cyst Operculodinium centrocarpum as well as by the appearance of relatively warm-water indicative species in the outer Laptev Sea, probably due to enhanced influence of Atlantic Water at the continental margin. Because a continuously rising sea level resulted in an increasing distance between the investigated site and the southward retreating coastline, surface-water salinities on the outer shelf approached modern values of about 15–16 around 8.6 cal. ka. On the inner Laptev Sea shelf, modern-like environmental conditions were reached about 1 to 1.5 ky later, around 7.4 cal. ka, emphasizing the overwhelming influence of the global transgression on the Holocene evolution of Arctic shelf water masses.
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  • 40
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    A study of the chemistry of pore fluids and authigenic carbonates in methane seep environments: Kodiak Trench, Hydrate Ridge, Monterey Bay, and Eel River Basin (2005)
    Elsevier
    In:  Chemical Geology, 220 (3-4). pp. 329-345.
    Details
    Publication Date: 2017-12-07
    Description: Analyses of the chemical and isotopic composition of carbonates rocks recovered from methane seepage areas of the Kodiak Trench, Hydrate Ridge, Monterey Bay Clam Flats, and the Eel River Basin, coupled with the studies of the chemistry of the pore fluids, have shown that these carbonates have grown within the sediment column. Geochemical profiles of pore fluids show that, in deep water seeps (Kodiak Trench—4450 m; Monterey Bay—1000 m; Hydrate Ridge—650 m), δ13C (DIC) values are low (isotopically light), whereas in the Eel River area (∼ 350–500 m), δ13C (DIC) values are much higher (isotopically heavier). In all cases, the δ13C values indicate that processes of methane oxidation, associated with sulfate reduction, are dominant in the shallow sediments. Data on the isotopic composition of authigenic carbonates found at sites in Kodiak Trench, Eel River Basin South, and Eel River Basin North indicate a variable composition and origin in different geochemical environments. Some of the authigenic carbonates from the study sites show a trend in their δ13C values similar to those of the pore fluids obtained in their vicinity, suggesting formation at relatively shallow depths, but others indicate formation at greater sediment depths. The latter usually consist of high magnesium calcite or dolomite, which, from their high values of δ13C (up to 23‰;) and δ18O (up to 7.5‰), suggest formation in the deeper horizons of the sediments, in the zone of methanogenesis. These observations are in agreement with observations by other workers at Hydrate Ridge, in Monterey Bay, and in the Eel River Basin.
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  • 41
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    Methane hydrate accumulation in "Mound 11" mud volcano, Costa Rica forearc. (2005)
    Elsevier
    In:  Marine Geology, 216 . pp. 83-100.
    Details
    Publication Date: 2017-08-03
    Description: Shallow gas hydrate accumulation in mud volcanoes in the Costa Rica forearc was postulated before, but is now proven by a find in surface sediments at the southwestern slope of the recently discovered Mound 11, a mud volcano located 30 km arcward from the trench, on the continental slope off Costa Rica at 1000 m water depth. The gas hydrate content of the recovered core was up to 60% and consisted mainly of methane hydrate. The δ13C (−45.2‰ to −43.3‰ PDB) and δD (−125‰ to −143‰ SMOW) values of methane from sampled hydrates indicate a deep (thermogenic) source of fossil methane generated by degradation of organic matter within the subducted slab. Near surface faults and deeply cutting faults, identified in multichannel seismic reflection profiles, provide pathways for fluid migration through the ∼6 km thick margin wedge into the ∼1 km of overlying terrigenous sediments. Mound 11 overlies a bottom simulating reflection at 340 m bsf and transport of sediment and methane-rich fluids from greater depth through the gas hydrate stability zone is suggested. The upper core segment (0–150 cm bsf) is composed of mud breccia and fluid channels, which indicates mud expulsion from Mound 11. Anaerobic methane oxidation is indicated by sulfate and methane depletion, hydrogen sulfide formation and an increase of alkalinity in the interface between the upper sediment unit and the lower laminated sediment unit where the gas hydrate is interbedded. The seawater-like sulfate and chloride concentrations and the concave up chloride profile measured in pore water of the upper core unit may rather reflect seawater influx than fluid outflow at this sampling site. The inflow is possibly driven by (episodic) mud and fluid discharge in the center of the mud mound creating shallow convective circulation cells.
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  • 42
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    Seasonal variability of trace metals in the Lena River and the southeastern Laptev Sea: impact of the spring freshet (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 112-125.
    Details
    Publication Date: 2017-09-13
    Description: The distribution of dissolved and particulate trace metals (Fe, Mn, Cu, Ni, Zn, and Pb) was studied for the first time during the spring high flow period of the Lena River (Arctic Siberia). The results show that concentrations of dissolved metals in the river Lena during the spring high flow in June 1996 (spring freshet) were significantly higher than those reported for the rest of the year. For example the measured average concentration of dissolved Fe (6349 ± 2122 nM) during the high flow is approximately 7 times higher than previously published concentrations measured during the summer months. Dissolved Fe concentrations in the freshwater (salinity 〈 1) are positively correlated with the amount of suspended particulate matter (SPM) (p 〈 0.01), but negatively correlated with the Fe concentrations in SPM (p 〈 0.01). The data showed that the aluminium-normalized concentrations of particulate Fe, Mn, Pb, Ni, and Zn in the freshwater are negatively correlated with SPM. This suggests that the mobilization of metals from suspended particulate matter is the driving force for the observed high concentrations of dissolved Fe, Mn, Zn and Pb in the water of the Lena River during the spring freshet. During the high flow period in June about 35% of the total annual flow of the river Lena flows into the Laptev Sea. Previously published metal budgets for the river Lena that did not incorporate data from the spring high flow period, therefore, underestimate the fluxes of dissolved trace metals from the Siberian rivers to the Arctic Ocean. For instance, the estimated input of dissolved Fe in June 1996 is approximately 4.5 times higher than the average annual dissolved Fe input calculated on the basis of summer data. The results of this study demonstrate that the previous evaluations of the trace metal flux of the Lena river–which are based on data obtained from August to October–may underestimate the total riverine input of dissolved trace metals to the Arctic Ocean.
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  • 43
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    On the temporal increase of anthropogenic CO2 in the subpolar North Atlantic (2005)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 . pp. 681-698.
    Details
    Publication Date: 2016-11-01
    Description: The subpolar North Atlantic (NA) plays a key role in the oceanic uptake of anthropogenic CO2. The availability of a historical high quality data set from the Transient Tracers in the Ocean North Atlantic Study (TTO-NAS) in 1981, together with data from recent studies in 1997 and 1999, makes it possible to assess the temporal increase of anthropogenic CO2 (View the MathML sourceCTant) in the region. We introduce an extension of a previous published empirical approach for estimating temporal increases of View the MathML sourceCTant, which is known as multiple linear regression approach (MLR). The method is based on a multiple linear-regression model employing hydrographic and chemical parameters. The accuracy of the extended MLR calculation (eMLR) proposed here is estimated to be ±3 μmol/kg for a parameterization based on potential temperature, total alkalinity, silicate, and phosphate. Calculated increases of View the MathML sourceCTant (View the MathML sourceΔCTant(PO4)) for the time period 1981–1997 are 1–20 μmol/kg at depths greater than 100 m. The distribution corresponds well to silicate and CFC-12 distributions. Open ocean profiles show a relative minimum between 300 and 1000 m, which is not apparent in profiles of the total View the MathML sourceCTant concentration. The View the MathML sourceΔCTant(PO4) inventory calculation for the northern NA region (40–65°N) yields a change in anthropogenic CO2 storage of 4.2 (±1) pg C over the 16-yr time period 1981–1997. This is equivalent to a mean annual View the MathML sourceCTant increase of 0.27 (±0.06) pg C/yr or more than 10% of the global ocean uptake for this period.
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  • 44
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    The Nd isotope signature of Holocene Baltic Mn/Fe precipitates as monitore of climate change during the little Ice-Age (2005)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 69 (9). pp. 2253-2263.
    Details
    Publication Date: 2017-09-08
    Description: Neodymium (Nd) isotope profiles were analyzed on two Baltic Mn/Fe precipitates (99/2 and TL1) from shallow water (20 m) of the Mecklenburg Bay. The age range of these Mn/Fe precipitates determined by 226Raex/Ba dating reaches from recent growth back to ∼4300 and 1000 yr BP, respectively. Over this time range, the Nd isotope composition varies from εNd (0) = −13.1 to −17.5 in the selected Baltic precipitates indicating substantial changes in the Nd isotope composition of the Baltic Sea. The lowest εNd values were recorded during the time interval of the Little Ice Age (LIA, AD ∼1350 to 1850). These minimum values indicate either an increase of the input of less radiogenic Nd from Scandinavian Archean-Proterozoic sources (εNd about −22) to the Baltic Sea or a decrease of the input of more radiogenic Nd from continental European sources (εNd about −12) and/or North Sea water (εNd about −10). Variations of both, erosive continental input and North Sea inflow may indicate a direct response of the Nd isotope signal in the Baltic Sea to climate changes during the LIA and be related to cyclic shifts in the atmospheric circulation triggered by the North Atlantic Oscillation (NAO). Another aspect that possibly influenced the input of trace elements and Nd isotopes into the Baltic Sea is the population development in the circum Baltic area during the LIA. The lowest εNd values also correspond to the medieval demographic crises that led to a significant decrease of agricultural activity and farmland. The reduction of soil erosion and enhanced regrowth of natural vegetation may have changed the amount and proportions of dissolved and suspended particulate matter transported into the Baltic Sea by rivers which in turn may have resulted in a change of the Nd isotope composition of Baltic Sea water.
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  • 45
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    Seasonal variations in arctic sediment dynamics - evidence from one-year records in the Laptev Sea (Siberian Arctic) (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 126-140.
    Details
    Publication Date: 2019-09-23
    Description: Sediment dynamics on the Laptev Sea shelf (Siberian Arctic), which is ice-covered for about 9 months a year, were studied for a I-year period. Two oceanographic bottom-mooring stations equipped with an Acoustic Doppler Current Profiler (ADCP) and a Conductivity Temperature Depth meter (CTD) were deployed on the eastern Laptev Sea shelf between August 1998 and September 1999. Thus, for the first time information on current, suspended particulate matter (SPM), and bottom temperature variations were provided throughout one seasonal cycle for a Siberian shelf sea. The data set indicates that during and shortly after the river-ice breakup (June-early July) sediment transport is dominated by riverine input and transport onto the eastern Laptev Sea shelf within the surface layer beneath the fast ice. Under ice-free conditions (mid-July to September), SPM is mainly trapped on the eastern Laptev Sea shelf SPM discharged by the Lena River is transported within the surface layer to the mid-shelf where it sinks through the water column into the bottom nepheloid layer only to be carried back onto the inner shelf again together with newly resuspended bottom material. On the inner shelf the material is partly transported back into the surface layer by turbid mixing and carried out onto the mid-shelf again. During freeze-up (October), SPM in the surface layer on the inner shelf is incorporated into newly formed ice and transported with the ice over the continental margin into the deep Arctic Ocean. Beneath the ice cover (November to June-July) SPM slowly sinks and sediment transport is of minor importance on the inner shelf. However, beneath the polynya, bottom material is resuspended during storm events and transported onto the inner shelf where it temporarily settles. The study suggests a quasi-estuarine sediment circulation on the eastern Laptev Sea shelf, especially during ice-free conditions, and sediment export dominated by ice rather than bottom transport
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  • 46
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    A global survey of perfluorinated acids in the oceans (2005)
    Elsevier
    In:  Marine Pollution Bulletin, 51 . pp. 658-668.
    Details
    Publication Date: 2017-10-05
    Description: Perfluorinated acids and their salts have emerged as an important class of global environmental contaminants. Biological monitoring surveys conducted using tissues of marine organisms reported the occurrence of perfluorooctanesulfonate (PFOS) and related perfluorinated compounds in biota from various seas and oceans, including the Arctic and the Antarctic Oceans. Occurrence of perfluorinated compounds in remote marine locations is of concern and indicates the need for studies to trace sources and pathways of these compounds to the oceans. Determination of sub-parts-per-trillion (ng/L) or parts-per-quadrillion (pg/L) concentrations of aqueous media has been impeded by relatively high background levels arising from procedural or instrumental blanks. Our research group has developed a reliable and highly sensitive analytical method by which to monitor perfluorinated compounds in oceanic waters. The method developed is capable of detecting PFOS, perfluorohexanesulfonate (PFHS), perfluorobutanesulfonate (PFBS), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), and perfluorooctanesulfonamide (PFOSA) at a few pg/L in oceanic waters. The method was applied to seawater samples collected during several international research cruises undertaken during 2002–2004 in the central to eastern Pacific Ocean (19 locations), South China Sea and Sulu Seas (five), north and mid Atlantic Ocean (12), and the Labrador Sea (20). An additional 50 samples of coastal seawater from several Asian countries (Japan, China, Korea) were analyzed. PFOA was found at levels ranging from several thousands of pg/L in water samples collected from coastal areas in Japan to a few tens of pg/L in the central Pacific Ocean. PFOA was the major contaminant detected in oceanic waters, followed by PFOS. Further studies are being conducted to elucidate the distribution and fate of perfluorinated acids in oceans.
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  • 47
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    Quantitative assessment of chemical and mineralogical changes due to progressive low-temperature alteration of East Pacific Rise basalts from 0 to 9 Ma (2005)
    Elsevier
    In:  Chemical Geology, 218 (3-4). pp. 281-313.
    Details
    Publication Date: 2017-12-07
    Description: Many studies have focused on low-temperature alteration of the oceanic crust, nevertheless little is known about the initial processes of low-temperature alteration and their influence on the mineralogical and chemical composition of the oceanic crust once it leaves the spreading axis. The lack of such studies is primarily related to the difficulty of recovering samples representative of this initial alteration style. Such information is nevertheless important not only for crust–ocean mass-balances but also to characterize an important input to the subduction zones. We have studied dredged basalts from the eastern flank of the East Pacific Rise at 14°15′S, concentrating on the products of a single spreading segment in a corridor perpendicular to the spreading axis and covering a range of crustal ages from 0 to 9 Ma. Electron microprobe, X-ray fluorescence, X-ray diffraction and ICP-MS analyses have been carried out to examine the mineralogical and chemical changes in the basalts which make up the surface of the upper crust caused by low-temperature alteration. Fresh rocks were sampled at the ridge axis; off-axis basalts show features of progressive alteration. Celadonite is the main alteration component in 0.12–4.6 Ma old rocks, whereas phillipsite is more abundant in rocks older than 4.6 Ma. Changing compositions of secondary minerals, progressive sealing of fractures and the occurrence of more alteration rinds on older rocks show evidence for a slight change in redox conditions, from an oxidizing, water-dominated to a more reducing, rock-dominated environment with time. Iron oxyhydroxide and celadonite are the first alteration products, partly replaced or covered by saponite under more reducing conditions. The Fe necessary for the formation of these minerals is furnished by the dissolution of glass and the breakdown of olivine. Phillipsite is present in fractures and veins in rocks older than 1 Ma. Analyses also indicate an illite–smectite mixed layered mineral which is believed to be an intermediate between saponite and celadonite and small amounts of a chlorite/smectite mixed layered mineral. All samples are characterized by the lack of minerals formed by hydrothermal processes. We conclude that the alteration took place under seawater-dominated conditions at low temperature. A comparison of trace element analyses from altered whole rock samples and their appendant fresh glass chips provides a record of element mobility during alteration. Off-axis basalts show significant uptakes of Rb, Cs and Ba which are supplied by seawater and incorporated in or on secondary minerals. An enrichment of U is also apparent and appears to be especially strong when alteration conditions are oxidative. K2O is also gained in all altered off-axis basalts, believed to be linked to the formation of celadonite. However, the volume of rock being altered is so small relative to the volume of the oceans that this scavenging has no noticeable effect on the composition of the oceans. The composition of the oceanic crust, on the other hand, is affected significantly.
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  • 48
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    Water mass processes on Arctic shelves as revealed from δ18O of H2O (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1/3). pp. 165-174.
    Details
    Publication Date: 2019-09-23
    Description: The water masses of the Arctic Ocean shelf regions are significantly influenced by river water and sea-ice processes. Since river water is highly depleted in δ18O relative to marine waters as well as to sea-ice, the δ18O composition and salinity of a water sample can be used to separate the different water sources. In this paper the freshwater distribution on the Kara, Laptev and the Beaufort shelves are discussed based on δ18O and salinity data. Depending on the average depth the observed fields of salinity and δ18O values are different for each region. But comparing the overall δ18O and salinity correlations reveals a remarkable similarity for these three Arctic shelf regions. On all discussed Arctic shelves bottom water masses are formed by sea-ice processes. And remnants of these bottom water masses are found on all shelves during summer at a similar salinity of about 30.
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  • 49
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    Occurrence of kaolinite and mixed-layer kaolinite/smectite in hydrothermal sediments of Grimsey Graben, Tjornes Fracture Zone (north of Iceland) (2005)
    Elsevier
    In:  Marine Geology, 215 (3-4). pp. 159-170.
    Details
    Publication Date: 2017-08-08
    Description: The sediments at a site situated among high-temperature vents in the Grimsey Graben (Tjornes Fracture Zone, north of Iceland) exhibit features of strong hydrothermal alteration: (1) almost total dissolution of the volcaniclastic material composing the background sediment; (2) sulfate and sulfide precipitation; (3) kaolinitisation. Smectite, precipitated in the shallowest sediment, is gradually replaced downward by mixed-layer kaolinite/smectite and pure, well-crystallised kaolinite. The kaolinite/smectite is interstratified with up to 10% swelling smectitic layers. According to the oxygen isotope composition kaolinite/smectite mixed-layer mineral most likely formed at temperatures near 160 degrees C. The vertical sequence kaolinite -〉 kaolinite/smectite -〉 smectite as well as the distinct zonation across the kaolinitic veins (almost pure kaolinite in the central zone and kaolinite/smectite along the rim) suggest hydrothermal transformation of initially formed smectite -〉 kaolinite/smectite -〉 kaolinite. Most probably this conversion occurred in an evolving (from alkaline to slightly acidic) hydrothermal environment. (c) 2004 Elsevier B.V. All rights reserved.
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  • 50
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    Ocean bottom seismometer investigations in the Ormen Lange area offshore mid-Norway provide evidence for shallow gas layers in subsurface sediments (2005)
    Elsevier
    In:  Marine and Petroleum Geology, 22 (1-2). pp. 287-297.
    Details
    Publication Date: 2017-07-21
    Description: A multi-component Ocean Bottom Seismometer (OBS) survey in the Ormen Lange area of the Storegga Slide constrained the existence of free gas and possibly gas hydrates in the shallow subsurface. The three investigated areas (A, B, C) lie in close vicinity to the slide scar above one of the largest deep-water gas reservoirs on the mid-Norwegian margin. Generally, P-wave and S-wave velocities are high compared to average velocities at a given burial depth due to an exposure of deeper sediments as a consequence of sediment mass movement by the Storegga slide. Indications for the presence of gas within the sediments exist for two of the three investigated areas. The gas accumulates beneath less permeable layers of glacigenic debris flow deposits. Average gas concentration of pore space in both areas is 0.9% (area A) and 0.15% (area B). The geophysical data do not allow a conclusive answer about the occurrence of gas hydrates. Their presence might be masked by high-velocity debris flow deposits, which occur in the subsurface. Nevertheless, gas hydrate concentrations of pore space have been estimated to about 9% in area A and 7% in area B.
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  • 51
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    Mutvei's solution: an ideal agent for resolving microgrowth structures of biogenic carbonates (2005)
    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 228 . pp. 149-166.
    Details
    Publication Date: 2020-08-07
    Description: Accretionary hard parts of many organisms provide excellent archives of past climate and environmental conditions or life history traits. Variable growth rates function as environmental and physiological proxies, and growth increments as calendars. Recognition of growth structures is thus a prime necessity for sclerochronological studies. Here we present a new, handy, easy-to-use and time-efficient technique that resolves annual and sub-annual growth structures in skeletons of a wide range of different organisms. Mutvei's solution simultaneously etches biogenic carbonates and calcium phosphates, fixates the soluble and insoluble organic matrices and fibers, and stains mucopolysaccharides. It produces a filigreed three-dimensional relief of etch-resistant ridges (growth lines) and etched depressions (growth increments) and stains skeletal growth structures in shadings of blue. Growth lines stand out as crisp, darker-blue stained lines. Reflected optical light microscopy (axial and oblique illumination) and scanning electron microscopy can be used to analyze the microgrowth structures. We demonstrate the use of the technique on hard tissues of various marine and freshwater bivalves, a coral, a sclerosponge, a barnacle, gastropods, a cephalopod, a fish otolith and a whale's ear bone. This technique may be of interest for paleoclimatologists, geochemists and biologists. It can significantly expand the use of biogenic hard parts as environmental and physiological indicators because it reveals microgrowth structures of biogenic skeletons that potentially form on a periodic basis and thus function as calendars.
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  • 52
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    Seasonal variability of deep currents in the equatorial Atlantic: A model study. (2005)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 (1). pp. 99-121.
    Details
    Publication Date: 2016-11-01
    Description: A suite of high-resolution models of the Atlantic Ocean circulation is used to study the deep seasonal current variability in the equatorial regime, with a particular emphasis on its manifestation in the variability of the interhemispheric transports near the western boundary. The basic experiment has a resolution of 1/3∘1/3∘ horizontally and 45 vertical levels, and is subject to a monthly mean atmospheric forcing based on ECMWF flux fields. Sensitivity experiments explore the effects of higher horizontal resolution (1/12∘1/12∘), and alternative mixing parameterizations. The model behavior near the equator confirms previous suggestions based on solutions of the WOCE Community Modelling Effort (“CME”) and the “DYNAMO” model intercomparison project, of the presence of a system of vigorous seasonal current oscillations, spanning the whole water column and nearly the whole zonal extent of the basin. The patterns of the primarily zonal current anomalies are fairly robust across the range of model cases investigated, i.e., show relatively little sensitivity to horizontal resolution/mixing, or to the different choices of vertical discretization and vertical mixing as in the DYNAMO cases. The amplitude of the seasonal variation exceeds 10 cm/s in the surface layer, and decreases to about 5 cm/s near 1000 m and 2–3 cm/s in the deep ocean in both the basic 1/3∘1/3∘- and the 1/12∘1/12∘-cases, thereby leading to seasonally reversing current signatures at all depths below the EUC. A particular aspect of the seasonal current variability concerns its manifestation in the southward transport of North Atlantic Deep Water (NADW) by the Deep Western Boundary Current (DWBC). The temporal characteristics of the DWBC variability are in agreement with moored current meter observations at 44∘W44∘W, with simulated DWBC transports varying between a maximum of more than 30 Sv in January/February, and almost vanishing transport in September. However, in contrast to the annual-mean deep water transport which is confined to the DWBC and tight, O(100) km-recirculation cells, the seasonal cycle of transport is not trapped near the boundary: the simulations show that the zonal current variations of the equatorial wave guide, near the western boundary give rise to a broad system of seasonal recirculation cells of the DWBC. Calculations of the amplitude of the seasonal variability in the deep water transport near the equator are therefore strongly dependent of the spatial extent of the cross-section considered; in particular, for being approximately representative of low-frequency variations in the net, zonally-integrated meridional transport of deep water in the equatorial regime, transport sections would need to extend over nearly the whole western basin.
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  • 53
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    Methane and methane carbon isotopes in the Northeast Atlantic including the Mid-Atlantic Ridge (50°N) (2005)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 (6). pp. 1043-1070.
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    Publication Date: 2019-09-23
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  • 54
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    Revisiting the rare earth elements in foraminiferal tests (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 239 . pp. 79-97.
    Details
    Publication Date: 2017-01-19
    Description: Are the rare earth elements (REEs) in foraminifera a valuable proxy for use in paleoceanographic and climate change studies? In order to investigate this, we attempted a comprehensive study of REEs in planktonic and benthic foraminifera. Several different cleaning protocols were tested. Although the hydroxylamine used to clean all foraminifera in this study removes an unidentified source of REE contamination, it seems to remobilize metal oxides that are otherwise unaffected in flow-through dissolution. The calculated REE distribution coefficients, KD(REE)s, are between 100 and 500 for both planktonic and benthic foraminifera. These KDs are high compared to other elements in biogenic calcite but can be explained through a general model of element incorporation during foraminiferal calcification. From data taken from eight core tops in the southeast Pacific, we conclude that the REEs in planktonic foraminifera are, indeed, useful as a proxy for upper ocean water mass and mixed layer biogenic productivity. Alternatively, the REEs in benthic foraminifera are useful as a proxy for carbon flux to the sea floor. These proxies should be robust down core unless the sediments have undergone anoxic diagenesis, which stabilizes Fe carbonate thus overprinting the primary REE signature. However, it is clear from REE distributions in foraminiferal tests if anoxic conditions have occurred.
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  • 55
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    Accelerated simulation of passive tracers in ocean circulation models (2005)
    Elsevier
    In:  Ocean Modelling, 9 (1). pp. 51-69.
    Details
    Publication Date: 2017-02-13
    Description: A novel strategy is proposed for the efficient simulation of geochemical tracers in ocean models. The method captures the tracer advection and diffusion in a general circulation model (GCM) without any alteration (or even knowledge) of the GCM code. In comparison with offline tracer models, the proposed method is considerably more efficient and automatically includes all parameterizations of unresolved processes present in the most sophisticated GCMs. A comparison with a global configuration of the MIT GCM shows that the scheme can capture the complex three-dimensional transport of a state-of-the-art GCM. A key advantage of the proposed technique is the ability to directly compute steady-state solutions, a facility particularly well-suited to tracers such as natural radiocarbon. This capability is applied to develop a novel algorithm for accelerating the dynamical adjustment of ocean models.
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  • 56
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    The East Greenland Current studied with CFCs and released sulphur hexafluoride (2005)
    Elsevier
    In:  Journal of Marine Systems, 55 (1-2). pp. 77-95.
    Details
    Publication Date: 2017-07-12
    Description: The distribution and evolution of water masses along the East Greenland Current (EGC) from south of the Fram Strait to the Denmark Strait were investigated using chlorofluorocarbons (CFCs) and the released tracer sulphur hexafluoride (SF6) together with hydrographic data. Water masses contributing to the Denmark Strait overflow, and to some extent also contributions to the Iceland–Scotland overflow, are discussed from observations in 1999. Special emphasis is put on the advection and mixing of Greenland Sea Arctic Intermediate Water (GSAIW), which could be effectively traced thanks to the release of sulphur hexafluoride in the Greenland Sea Gyre in 1996. By means of the dispersion of the tracer, Greenland Sea Arctic Intermediate Water was followed down to the Denmark Strait Sill as well as close to the Faroe–Shetland Channel. The results indicate that this water mass can contribute to both overflows within 3 years from leaving the Greenland Sea. The transformation of Greenland Sea Arctic Intermediate Water was dominated by water from the Arctic Ocean, especially by isopycnal mixing with upper Polar Deep Water (uPDW) but, to a less extent, also by Canadian Basin Deep Water. A mixture of Greenland Sea Arctic Intermediate Water and upper Polar Deep Water was lifted 500 m on its way through southwestern Iceland Sea, to a depth shallow enough to let it reach the sill of the Denmark Strait from where it can be incorporated in the densest layer of the overflow. The observations show contributions to the Denmark Strait overflow from both the East Greenland Current and the Iceland Sea.
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  • 57
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    Changes in sedimentation patterns of the Nordic seas region across the mid-Pleistocene (2005)
    Elsevier
    In:  Marine Geology, 215 . pp. 107-122.
    Details
    Publication Date: 2017-08-03
    Description: Sediment core data from a site in the central Nordic seas suggest that during the mid-Pleistocene revolution (MPR) this region has experienced a systematic change in its overall oceanographic and climatic conditions. First distinct changes occur around 1 Ma and reveal the beginning of a shift in climate periodicity from stronger 41-ka cycles towards a dominant 100-ka cyclicity. Most pronounced are the changes at the study region between about 700 and 420 ka, when parallel to the evolution of large 100-ka cycles a distinct decrease in the input of magnetic particles is observed. Also, for this interval an intensification of glacial conditions is indicated by a marked increase in the accumulation rates of ice-rafted debris (IRD) during marine isotope stages 16 and 12. The observed mid-Pleistocene changes were likely due to a gradual shift from a more zonal behavior of the coupled ocean–atmosphere system at high northern latitudes prior to the MPR to more meridionality thereafter, a shift that affected both the patterns of ocean circulation and ice drift in the Nordic seas region. Accordingly, the subsequent MPR-related changes of these two climate parameters should be responsible for the decrease in the concentration of magnetic particles at the study site after 700 ka. With the mid-Pleistocene strengthening of the Nordic heat pump the mode of deep-water production and the flow of bottom currents changed at high northern latitudes, which led to an increased export of magnetic particles from basaltic source regions around Greenland and Iceland into the subpolar North Atlantic. Consequently, less magnetic material was deposited in the Nordic seas than before the MPR when water mass exchange between the Nordic seas and the North Atlantic was more restricted. In addition, the large Late-Pleistocene expansions of glacial ice caps on the eastern margin of the Nordic seas led to a major change in the composition of IRD material in the study area, with more material originating from the Scandinavian and Barents Sea shelf regions, which ultimately caused a dilution of the magnetic signal.
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  • 58
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    An overview of Calanus helgolandicus ecology in European waters (2005)
    Elsevier
    In:  Progress in Oceanography, 65 . pp. 1-53.
    Details
    Publication Date: 2016-10-05
    Description: We review current knowledge and understanding of the biology and ecology of the calanoid copepod Calanus helgolandicus in European waters, as well as provide a collaborative synthesis of data from 18 laboratories and 26 sampling stations in areas distributed from the northern North Sea to the Aegean and Levantine Seas. This network of zooplankton time-series stations has enabled us to collect and synthesise seasonal and multi-annual data on abundance, body size, fecundity, hatching success and vertical distribution of C. helgolandicus. An aim was to enable comparison with its congener Calanus finmarchicus, which has been studied intensively as a key component of European and north east Atlantic marine ecosystems. C. finmarchicus is known to over-winter at depth, whereas the life-cycle of C. helgolandicus is less well understood. Overwintering populations of C. helgolandicus have been observed off the Atlantic coast between 400 and 800 m, while in the Mediterranean there is evidence of significant deep-water populations at depths as great as 4200 m. The biogeographical distribution of C. helgolandicus in European coastal waters covers a wide range of habitats, from open ocean to coastal environments, and its contribution to mesozooplankton biomass ranges from 6% to 93%. Highest abundances were recorded in the Adriatic and off the west coast of Spain. C. helgolandicus is generally found in 9–20 °C water, with maximum abundances from 13–17 °C. In contrast, C. finmarchicus is found in cooler water between 0 and 15 °C, with peak abundances from 0 to 9 °C. As water has warmed in the North Atlantic over recent decades, the range of C. helgolandicus and its abundance on the fringes of its expanding range have increased. This review will facilitate development of population models of C. helgolandicus. This will not only help answer remaining questions but will improve our ability to forecast future changes, in response to a warming climate, in the abundance and distribution of this important species.
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    Arctic Siberian shelf environments : an introduction (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 1-8.
    Details
    Publication Date: 2017-09-13
    Description: 1. Why study the Arctic? 2. The Siberian shelf seas as sensitive “environmental recorder” 3. Outlook
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  • 60
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    Biogeochemical ocean-atmosphere transfers in the Arabian Sea (2005)
    Elsevier
    In:  Progress in Oceanography, 65 . pp. 116-144.
    Details
    Publication Date: 2016-10-05
    Description: Transfers of some important biogenic atmospheric constituents, carbon dioxide (CO2), methane (CH4), molecular nitrogen (N2), nitrous oxide (N2O), nitrate View the MathML source(NO3-), ammonia (NH3), methylamines (MAs) and dimethylsulphide (DMS), across the air–sea interface are investigated using published data generated mostly during the Arabian Sea Process Study (1992–1997) of the Joint Global Ocean Flux Study (JGOFS). The most important contribution of the region to biogeochemical fluxes is through the production of N2 and N2O facilitated by an acute, mid-water deficiency of dissolved oxygen (O2); emissions of these gases to the atmosphere from the Arabian Sea are globally significant. For the other constituents, especially CO2, even though the surface concentrations and atmospheric fluxes exhibit extremely large variations both in space and time, arising from the unique physical forcing and associated biogeochemical environment, the overall significance in terms of their global fluxes is not much because of the relatively small area of the Arabian Sea. Distribution and air–sea exchanges of some of these constituents are likely to be greatly influenced by alterations of the subsurface O2 field forced by human-induced eutrophication and/or modifications to the regional hydrography.
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    In situ benthic fluxes from an intermittently active mud volcano at the Costa Rica convergent margin (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 235 . pp. 79-95.
    Details
    Publication Date: 2019-09-23
    Description: Along the erosive convergent margin off Costa Rica a large number of mound-shaped structures exist built by mud diapirism or mud volcanism. One of these, Mound 12, an intermittently active mud volcano, currently emits large amounts of aqueous dissolved species and water. Chemosynthetic vent communities, authigenic carbonates, and methane plumes in the water column are manifestations of that activity. Benthic flux measurements were obtained by a video-guided Benthic Chamber Lander (BCL) deployed at a vent site located in the most active part of Mound 12. The lander was equipped with 4 independent chambers covering adjacent areas of the seafloor. Benthic fluxes were recorded by repeated sampling of the enclosed bottom waters while the underlying surface sediments were recovered with the lander after a deployment time of one day. One of the chambers was placed directly in the centre of an active vent marked by the occurrence of a bacterial mat while the other chambers were located at the fringe of the same vent system at a lateral distance of only 40 cm. A transport-reaction model was developed and applied to describe the concentration profiles in the pore water of the recovered surface sediments and the temporal evolution of the enclosed bottom water. Repeated model runs revealed that the best fit to the pore water and benthic chamber data is obtained with a flow velocity of 10 cm yr− 1 at the centre of the vent. The flux rates to the bottom water are strongly modified by the benthic turnover (benthic filter). The methane flux from below at the bacterial mat site is as high as 1032 μmol cm− 2 yr− 1, out of which 588 μmol cm− 2 yr− 1 is oxidised in the surface sediments by microbial consortia using sulphate as terminal electron acceptor and 440 μmol cm− 2 yr− 1 are seeping into the overlaying bottom water. Sulphide is transported to the surface by ascending fluids (238 μmol cm− 2 yr− 1) and is formed within the surface sediment by the anaerobic oxidation of methane (AOM, 588 μmol cm− 2 yr− 1). However, sulphide is not released into the bottom water but completely oxidized by oxygen and nitrate at the sediment/water interface. The oxygen and nitrate fluxes into the sediment are high (781 and 700 μmol cm− 2 yr− 1, respectively) and are mainly driven by the microbial oxidation of sulphide. Benthic fluxes were much lower in the other chambers placed in the fringe of the vent system. Thus, methane and oxygen fluxes of only 28 and 89 μmol cm− 2 yr− 1, respectively were recorded in one of these chambers. Our study shows that the aerobic oxidation of methane is much less efficient than the anaerobic oxidation of methane so that methane which is not oxidized within the sediment by AOM is almost completely released into the bottom water. Hence, anaerobic rather than aerobic methane oxidation plays the major role in the regulation of benthic methane fluxes. Moreover, we demonstrate that methane and oxygen fluxes at cold vent sites may vary up to 3 orders of magnitude over a lateral distance of only 40 cm indicating an extreme focussing of fluid flow and methane release at the seafloor.
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    Spatial and temporal distribution of Fe(II) and H2O2 during EisenEx, an open ocean mescoscale iron enrichment (2005)
    Elsevier
    In:  Marine Chemistry, 95 . pp. 65-88.
    Details
    Publication Date: 2019-07-03
    Description: Measurements of Fe(II) and H2O2 were carried out in the Atlantic sector of the Southern Ocean during EisenEx, an iron enrichment experiment. Iron was added on three separate occasions, approximately every 8 days, as a ferrous sulfate (FeSO4) solution. Vertical profiles of Fe(II) showed maxima consistent with the plume of the iron infusion. While H2O2 profiles revealed a corresponding minima showing the effect of oxidation of Fe(II) by H2O2, observations showed detectable Fe(II) concentrations existed for up to 8 days after an iron infusion. H2O2 concentrations increased at the depth of the chlorophyll maximum when iron concentrations returned to pre-infusion concentrations (〈80 pM) possibly due to biological production related to iron reductase activity. In this work, Fe(II) and dissolved iron were used as tracers themselves for subsequent iron infusions when no further SF6 was added. EisenEx was subject to periods of weak and strong mixing. Slow mixing after the second infusion allowed significant concentrations of Fe(II) and Fe to exist for several days. During this time, dissolved and total iron in the infusion plume behaved almost conservatively as it was trapped between a relict mixed layer and a new rain-induced mixed layer. Using dissolved iron, a value for the vertical diffusion coefficient Kz = 6.7±0.7 cm2 s−1 was obtained for this 2-day period. During a subsequent surface survey of the iron-enriched patch, elevated levels of Fe(II) were found in surface waters presumably from Fe(II) dissolved in the rainwater that was falling at this time. Model results suggest that the reaction between uncomplexed Fe(III) and O2− was a significant source of Fe(II) during EisenEx and helped to maintain high levels of Fe(II) in the water column. This phenomenon may occur in iron enrichment experiments when two conditions are met: (i) When Fe is added to a system already saturated with regard to organic complexation and (ii) when mixing processes are slow, thereby reducing the dispersion of iron into under-saturated waters.
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    Estimating recent growth in the cuttlefish Sepia officinalis: are nucleic acid-based indicators for growth and condition the method of choice? (2005)
    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 317 (1). pp. 37-51.
    Details
    Publication Date: 2020-06-26
    Description: A laboratory calibration study was undertaken with juvenile Sepia officinalis (80–85 g initial wet weight) to investigate the effects of different food rations and different starving intervals on RNA/dry weight (DW) ratios and RNA/DNA ratios in cephalopod mantle muscle at two different temperatures. The digestive gland index was also used as an additional indicator of recent growth. High food rations and low temperature went along with high RNA/DW ratios and high RNA/DNA ratios. Starving resulted in a linear decline in growth performance and a concomitant decrease in RNA/DW and RNA/DNA ratio, with RNA/DNA ratios representing the growth data better. RNA/DNA ratios decreased faster at higher temperatures. A fluorimetric assay for nucleic acid analysis was optimized for cephalopod mantle tissues and yielded reproducible RNA/DNA ratios with a relative variance below 10%. Thus, it may be possible to use this estimator of recently encountered feeding regime for the evaluation of mortality rates of early teuthid paralarvae to eventually support stock management. Also, log relative digestive gland weight showed a strong relationship with starving time, but, surprisingly, not with temperature. Data from the two temperatures analyzed could be combined to form a common regression line of relative digestive gland index with starving time. This indicator for recent growth might be especially suitable for large specimens with a well-developed digestive gland.
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  • 64
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    Climate records from a bivalved Methuselah (Arctica islandica, Mollusca; Iceland) (2005)
    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 228 . pp. 130-148.
    Details
    Publication Date: 2020-08-07
    Description: We measured annual shell growth rates of a 374-year-old (radiometrically confirmed) bivalve mollusk specimen of Arctica islandica (Linnaeus). This bivalve represents the oldest ever reported individual animal. In addition, we analyzed 1051 individual powder samples from ontogenetic years two to 40 (= 80% of the entire shell height) for isotope analyses. Oxygen and carbon isotopes exhibit clear intra-annual cycles. The highest measured carbon isotope values (on average + 2.73‰) occurred during summer, i.e., during maximum primary productivity. The δ18Oaragonite-derived temperature time-series cover the period of AD 1496–1533. Temperatures calculated from oxygen isotopes ranged from 4.5 to 9.3 °C and exhibit a mean value of 6.2 °C. The latter coincides well with the 1854–2003 mean value of 6.81 °C for sea-surface temperature between February and September (= growing season of A. islandica). Neither oxygen nor carbon isotopes exhibit age-related, unidirectional trends. However, δ13Caragonite and δ18Oaragonite values fluctuated at decadal periods of four, six and eight to nine years (NAO-type periods) as well as 12–14 years which may represent teleconnections to cycles in the tropical Atlantic. Annual shell growth is positively correlated to intra-annual δ18Oaragonite minima, i.e., warm summer temperatures (R2 = 0.34), and to intra-annual δ13Caragonite minima (higher food supply; R2 = 0.42). Using a linear multiregression model, 65% of the variation in annual shell growth can be explained by summer temperature and food supply. The formation of extremely narrow annual increments coincides with major volcanic eruptions (e.g., Tambora 1815). A period of extremely variable growth occurred during the culmination of the Little Ice Age in Iceland between ca. AD 1550 and 1620. Shell growth during AD 1765–1780, however, was characterized by very little year-to-year variability, probably as the result of extremely mild climate near the end of the Little Ice Age. This study demonstrates that shells of A. islandica provide subseasonal to multidecadal, precisely dated multi-proxies of environmental variables from marine, mid to high latitudes. Such data can be used to validate and complement climate models and further assess human impact on climate and ecosystems.
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    Impact of flaw polynyas on the hydrography of the Laptev Sea (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 9-27.
    Details
    Publication Date: 2019-09-23
    Description: Based on hydrological data from 1979 to 1999 the average long-term salinity of the flaw polynya in the Eastern Laptev Sea is estimated. A new method to evaluate ice production based on hydrological rather than sea-ice observations is proposed. Average annual ice production in the polynya ranges between 3 and 4 m. The probability of convective mixing penetrating down to the seafloor is highest in the regions of the flaw polynya, but does not exceed 20% in the Eastern and 70% in the Western Laptev Sea. Conductivity-temperature-depth (CTD) measurements and observations of currents carried out in April-May 1999 allowed us to investigate the surface circulation along the margins of the Laptev Sea flaw polynya. The convective nature of the surface currents, with velocities measured as high as 62 cm/s, is discussed. Currents are most likely part of circulation cells, which arise as a result of brine rejection due to intensive ice formation in the polynya. It is shown that the spatial alignment of sea ice crystals in the marginal part of the polynya is most likely a consequence of the quasi-stationary cellular circulation
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    Diagenetic processes within and below the zone of anaerobic oxidation of methane in sediments of the western Argentine Basin - focusing on iron diagenesis (2005)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 69 (16). pp. 4117-4126.
    Details
    Publication Date: 2017-09-08
    Description: Geochemical and rock magnetic investigations of sediments from three sites on the continental margin off Argentina and Uruguay were carried out to study diagenetic alteration of iron minerals driven by anaerobic oxidation of methane (AOM). The western Argentine Basin represents a suitable sedimentary environment to study nonsteady-state processes because it is characterized by highly dynamic depositional conditions. Mineralogic and bulk solid phase data document that the sediment mainly consists of terrigenous material with high contents of iron minerals. As a typical feature of these deposits, distinct minima in magnetic susceptibility (κ) are observed. Pore water data reveal that these minima in susceptibility coincide with the current depth of the sulfate/methane transition (SMT) where HS− is generated by the process of AOM. The released HS− reacts with the abundant iron (oxyhydr)oxides resulting in the precipitation of iron sulfides accompanied by a nearly complete loss of magnetic susceptibility. Modeling of geochemical data suggest that the magnetic record in this area is highly influenced by a drastic change in mean sedimentation rate (SR) which occurred during the Pleistocene/Holocene transition. We assume that the strong decrease in mean SR encountered during this glacial/interglacial transition induced a fixation of the SMT at a specific depth. The stagnation has obviously enhanced diagenetic dissolution of iron (oxyhydr)oxides within a distinct sediment interval. This assumption was further substantiated by numerical modeling in which the mean SR was decreased from 100 cm kyr−1 during glacial times to 5 cm kyr−1 in the Holocene and the methane flux from below was fixed to a constant value. To obtain the observed geochemical and magnetic patterns, the SMT must remain at a fixed position for ∼9000 yrs. This calculated value closely correlates to the timing of the Pleistocene/Holocene transition. The results of the model show additionally that a constant high mean SR would cause a concave-up profile of pore water sulfate under steady state conditions.
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    Elliptical calderas in active tectonic settings: an experimental approach (2005)
    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 144 (1-4). pp. 119-136.
    Details
    Publication Date: 2017-09-15
    Description: Caldera volcanoes form due to collapse of a magma chamber roof into the underlying magma chamber. Many field, theoretical and experimental studies have postulated that calderas are delimited by reverse ring faults and are surrounded by peripheral concentric normal faults. In the simplest theoretical scenario, circular magma chambers produce circular calderas. Many calderas, however, are elliptical in shape, particularly those in extensional and compressive tectonic settings. Several factors may explain elliptical calderas. The first is the presence of an elliptical magma chamber, established by, for instance, preferential intrusion along pre-existing basement structures or differential spalling of the magma chamber walls. The second is the overlap (nesting) of several discrete calderas to form a single, larger elliptical structure. The third is asymmetric subsidence. The fourth is variable pre-collapse topography. A fifth possible factor is distortion of the caldera faults by the regional stress field during caldera formation. A sixth factor is the post-collapse distortion of the caldera structure due to continued regional deformation. To better understand relationships between caldera surface expression, reservoir geometry and regional tectonic stresses, we conducted scaled analogue experiments. These experiments examined the impact of regional stress and associated structures on calderas formed during evacuation of reservoirs (circular rubber balloons) of known dimensions and depths. The results show that, in principle, calderas produced in compression/extension experiments are elongated parallel to the direction of minimum horizontal compressive stress, despite the chamber beneath being circular in plan view. As a consequence, model ring fault orientation varied from steeply dipping where striking perpendicular to the minimum horizontal regional compressive stress, to shallower dips where striking parallel to the minimum horizontal regional compressive stress. This leads us to suggest that the influence of a regional stress field on caldera fault orientation during and/or after caldera formation may be significant in the development of elliptical calderas. In addition, such variation of caldera ring fault dip from steep to relatively shallow could influence location and behaviour of ring fissure eruptions.
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    Phytoplankton distribution in the Agulhas system from a coupled physical-biological model (2005)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 (7). pp. 1300-1318.
    Details
    Publication Date: 2016-11-01
    Description: The greater Agulhas Current system has several components with high mesoscale turbulence. The phytoplankton distribution in the southwest Indian Ocean reflects this activity. We have used a regional eddy-permitting, coupled physical–biological model to study the physical–biological interactions and to address the main processes responsible for phytoplankton distribution in three different biogeochemical provinces: the southwest Subtropical Indian Gyre (SWSIG), the subtropical convergence zone (SCZ) and the subantarctic waters (SAW) south of South Africa. The biological model with four compartments (Nitrate–Phytoplankton–Zooplankton–Detritus) adequately reproduces the observed field of chlorophyll a. The phase of the strong modelled seasonality in the SWSIG is opposite to that of the SCZ that forms the southern boundary of the subtropical gyre. Phytoplankton concentrations are governed by the source-minus-sink terms, which are one order of magnitude greater than the dynamical diffusion and advection terms. North of 35°S, in the SWSIG, phytoplankton growth is limited by nutrients supply throughout the year. However, deeper stratification, enhanced cross-frontal transport and higher detritus remineralization explain the simulated higher concentrations of phytoplankton found in winter in the SWSIG. The region between 35° and 40°S constitutes a transition zone between the SCZ and the oligotrophic subtropical province. Horizontal advection is the main process bringing nutrients for phytoplankton growth. The front at 34°S represents a dynamical barrier to an extension further to the north of this advection of nutrients. Within the SCZ, primary production is high during spring and summer. This high productivity depletes the nutrient standing stock built up during winter time. In winter, nutrients supply in the convergence zone is indeed large, but the deep mixing removes phytoplankton from the euphotic zone and inhibits photosynthesis, yielding lower surface chlorophyll a concentrations. Waters south of the Subantarctic Front have a summer biomass close to that of frontal waters and higher than for subtropical waters. However, these simulated concentrations are slightly higher than the observed ones suggesting that limitation by iron and/or silica may play a role
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    On losing and recovering fisheries and marine science data (2005)
    Elsevier
    In:  Marine Policy, 29 . pp. 69-73.
    Details
    Publication Date: 2017-10-10
    Description: Large sums are spent annually collecting and, increasingly, electronically encoding field data, making them widely accessible. Earlier data were recorded on paper, and archived at a few institutions, which eventually discard them. Data recovery and distribution is a valuable contribution to science, as it counters the ‘shifting baseline’ syndrome and ensures long-term returns on funds society invested in data gathering. Data recovery need not be expensive. We present the data recovery from the Guinean Trawling Survey, conducted in the early 1960s off West Africa, which cost 0.2% of initial survey costs. Research and graduate training institutions, as well as funding agencies should make digital data globally available as part of their deliverables.
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    Calculation of the stability and solubility of methane hydrate in seawater (2005)
    Elsevier
    In:  Chemical Geology, 219 . pp. 37-25.
    Details
    Publication Date: 2019-09-23
    Description: Thermodynamic equations of stability and solubility of methane hydrate were developed using the method of Pitzer [Pitzer, K.S. (1991). Ionic interaction approach: Theory and data correlation. In: K.S. Pitzer (Editor), 2nd Edition, Activity Coefficients in Electrolyte Solutions. CRC Press, Roca Raton Ann Arbor Boston London, pp. 75–153.]. Dissociation pressures are calculated for different temperature and salinity conditions ranging from 273 to 293 K and 0–70 (salinity). The solubility of methane and methane hydrate in seawater is calculated for the same temperature and salinity ranges and for hydrostatic pressures (Pdis) up to 50 MPa. Since the composition of major pore water ions may change due to a variety of geochemical processes (i.e. anaerobic oxidation of organic matter or/and methane) affecting the activity of water, additional stability and solubility calculations are presented by substituting the equivalent amount of sulfate by hydrogen carbonate ions. Based on this rigorous thermodynamic analysis, the calculation of dissociation pressures has been approximated by empirical algorithms that are functions of temperature and salinity (chlorinity for pore water). Similar algorithms are presented for the calculation of methane concentrations in seawater and pore water equilibrated with methane hydrate as functions of salinity (chlorinity for pore water), temperature and hydrostatic pressure. In contrast to earlier approaches, the provided methods allow the calculation of these properties by easily applicable functions considering a continuous variation of the control parameters over a wide range of conditions that are met in the deep marine environment.
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  • 71
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    A conceptual model for block-and-ash flow basal avalanche transport and deposition, based on deposit architecture of 1998 and 1994 Merapi flows (2005)
    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 139 (1-2). pp. 117-134.
    Details
    Publication Date: 2018-05-30
    Description: The 1998 block-and-ash flow (BAF) deposits on the western flanks of Merapi were described both immediately following emplacement, and after one and two wet seasons of erosion. This afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches. The deposits of the basal avalanches from individual BAF events were classified into three major and two minor facies in channelised reaches, primarily resulting from effects of channel confinement and slope. Termination reaches were classified into three facies, related to preevent topography. The deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics. The transport model we propose for these basal avalanches involves unsteady flow conditions, generated by pulses of collapse as the source, and/or by development of kinetic waves during the granular flow. The coarsest clasts along with low-density material migrated to the wave/pulse fronts within these flows. Whereas, in bulk flow, grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top, with this tendency being greatest on higher slopes (=greater kinetic energy) and with greater flow confinement (maximising particle collisions). Deposition begins as the flow reaches near its full extent. An initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure, such that an upper higher energy part of the flow is still able to move downstream over the frozen base. Later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment. Hence, the overall flow freezes from its front to its tail. At termination reaches in unconfined areas, the overflowing upper part of flow gradually deposits from its base upward, resulting in a slightly tapering sheet formed deposit, marked by a front made up of wood fragments and large boulders. On sudden slope breaks in termination areas, piling up of sediment occurs in flat reaches, producing whaleback type forms as the flows rapidly lost competence. One implication of this model is that each kinetic wave or flow-pulse crest developed within the basal avalanche represents a portion of greater flow depth (or stage height). Hence, development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards.
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  • 72
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    Annual cycle and interannual variability of the mid-depth tropical Atlantic Ocean (2005)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 (2). pp. 199-219.
    Details
    Publication Date: 2016-11-01
    Description: Several shipboard sections acquired in the western equatorial Atlantic along 35∘W35∘W allow for the first time to analyze the annual cycle of the density and velocity field in the upper 2000 m within this region. The amplitude of the annual harmonic of the velocity field shows several distinct maxima at the equator. Strong amplitudes up to View the MathML source15cms-1 are found in the depth range of the equatorial intermediate current (EIC) between 400 and 1000 m depth that are slightly shifted northward with respect to the equator. The meridional structure of the annual harmonics as well as upward phase propagation is consistent with downward propagating odd meridional mode Rossby waves. The observations are compared with a regional numerical model with very high vertical resolution. Good agreement is found between the simulated and observed structure and the amplitude of the annual harmonics. The model results suggest the presence of equatorial beams composed of wind-generated Kelvin and Rossby beams (causing seasonality in the near surface layer) as well as Rossby beams generated by the reflection of Kelvin beams at the eastern boundary (causing seasonality in the depth range of the EIC at the 35∘W35∘W section). The annual cycle of the sea surface height (SSH) observed by TOPEX/Poseidon altimetry indicates an east–west seesaw pattern that corresponds to the fast response (about 30 days lag) of the zonal SSH gradient to the annual cycle of the zonal wind field at the equator due to the propagation of lowest baroclinic mode equatorial waves. The increase of the easterly winds in the western equatorial Atlantic associated with El Nino in the beginning of 1997 led almost instantaneously to an adjustment of the zonal SSH gradient with elevated (depressed) SSH in the western (eastern) basin. In contrast, the velocity field at intermediate depths lags the zonal wind forcing by several months up to a year as the model simulation reveals.
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  • 73
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    Last postglacial environmental evolution of the Laptev Sea shelf as reflected in molluscan, ostracodal and foraminiferal faunas (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 223-251.
    Details
    Publication Date: 2018-02-20
    Description: Temporal and spatial variations in the species composition of modern and Holocene assemblages of molluscs, ostracods, and foraminifers from the Laptev Sea shelf (Arctic Siberia) have been investigated to reconstruct palaeoenvironmental changes during the last postglacial times and associated sea-level rise. Analysis of coretop sediment samples allowed to distinguish four modern assemblages. The specific habitat preferences of these species groups, such as water depth and salinity, were then used to interpret past environmental changes on the basis of two radiocarbon-dated sediment cores from the eastern middle shelf region, i.e., obtained from the Yana (51 m water depth) and Lena (45 m water depth) palaeovalleys. Despite the water depth difference of the two core sites, all downcore data document uniform fossil evidence for a gradual transformation of the Laptev Sea shelf from a terrestrial to a marine environment due to the southward transgressing sea. Three major phases have been recognized. These reflect: (1) a nearshore brackish-water environment of the initial stage of inundation (11.3–11.1 in the Yana and 11.2–10.8 cal. ka in the Lena palaeovalley); (2) a shallow inner-shelf, fluvially affected environment (11.1–10.3 and 10.8–8.2 cal. ka); (3) a modern-like marine environment which eventually became established since 10.8 and 8.2 cal. ka, depending on the specific water depth of each core site.
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  • 74
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    Osmium isotope stratigraphy of marine ferromanganese crusts (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 238 . pp. 42-48.
    Details
    Publication Date: 2017-07-28
    Description: Ferromanganese crusts provide records of long term change in ocean circulation and continental weathering. However, calibrating their age prior to 10 Ma has been entirely based on empirical growth rate models using Co concentrations, which have inherently large uncertainties and fail to detect hiatuses and erosional events. We present a new method for dating these crusts by measuring their osmium (Os) isotope record and matching it to the well-known marine Os isotope evolution of the past 80 Ma. The well-characterised crust CD29-2 from the central Pacific, was believed to define a record of paleooceanographic change from 50 Ma. Previous growth rate estimates based on the Co method are consistent with the new Os isotope stratigraphy but the dating was grossly inaccurate due to long hiatuses that are now detectable. The new chronology shows that it in fact started growing prior to 70 Ma in the late Cretaceous and stopped growing or was eroded between 13.5 and 47 Ma. With this new technique it is now possible to exploit the full potential of the oceanographic and climatic records stored in Fe–Mn crusts.
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  • 75
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    Stability and predictability of a virtual plankton ecosystem created with an individual-based model (2005)
    Elsevier
    In:  Progress in Oceanography, 67 (1-2). pp. 43-83.
    Details
    Publication Date: 2016-10-05
    Description: This paper establishes the predictability of a one-dimensional virtual plankton ecosystem created by Lagrangian Ensemble integration of an individual-based model. It is based on numerical experiments for a scenario, in which the surface fluxes have stationary annual cycles, and the annual surface heat budget is in balance, i.e. solar heating equals cooling to the atmosphere. Under these conditions, the virtual ecosystem also followed a stationary annual cycle. We investigate the stability of this ecosystem by studying the statistics of multi-year simulations of the ecosystem in a virtual mesocosm moored off the Azores. The integrations were initialised by a first guess at the state of the ecosystem at the end of the cooling season, when the mixed layer was approaching the annual maximum depth. The virtual ecosystem quickly adjusted to a stable attractor, in which the inter-annual variation was only a few percent of the multi-year mean. This inter-annual variation was due to random displacement of individual plankters by turbulence in the mixed layer. The inter-annual variance is nearly, but not exactly ergodic; the deviation is due to inheritance of zooplankton weight through lineages. The virtual ecosystem is independent of initial conditions: that is the proof of stability. The legacy of initialisation error decays within three years. The form of the attractor depends on three factors: the specification of the ecosystem model, the resource level (nutrients), and the annual cycle of external forcing. Sensitivity studies spanning the full range of model parameters and resource levels demonstrate that the virtual ecosystem is globally stable. In extreme cases the zooplankton becomes extinct during the simulation; the attractor adjusts gracefully to this new regime, without the emergence of vacillation or a strange attractor that would signal instability. At high resource levels, some of the zooplankton produce two generations per year (as was observed by Marshall and Orr [Marshall, S. M., and Orr, A. P. (1955). The biology of a marine copepod. Edinburgh: Oliver and Boyd. 188 pp.]; again the attractor adjusts gracefully to the new regime. Ocean circulation does not disrupt the stability of the virtual ecosystem. This is demonstrated by a numerical experiment in which the virtual ecosystem drifts with the mean circulation on a five-year cycle, following a track in the Sargasso Sea that penetrates deep into the zones of annual heating and cooling. The legacy of initialisation error decays within three cycles of the external forcing. Thereafter the ecosystem lies on a five-year geographically/lagrangian attractor. The stability of virtual ecosystems offers useful predictability with a good sign-to-noise ratio. (c) 2005 Elsevier Ltd. All rights reserved.
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  • 76
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    The climate during the Maunder Minimum: a simulation with the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) (2005)
    Elsevier
    In:  Journal of Atmospheric and Solar-Terrestrial Physics, 67 (1-2). pp. 55-69.
    Details
    Publication Date: 2016-11-24
    Description: A model simulation of the climate during Maunder Minimum (MM) (1645–1715) was performed using the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM). A multi-year equilibrium integration with prescribed solar insolation, atmospheric composition and sea surface temperatures (SSTs) for MM conditions was compared with a present-day (PD) simulation. We find that during MM the stratosphere was significantly warmer (up to 3 K) than during PD, and dynamically more disturbed in winter. The warming is due to the dominant effect of the lower atmospheric CO2 concentration during MM, which leads to a reduced emission of long-wave radiation, and compensates the cooling due to the reduced solar irradiance. The troposphere was about 1–1.5 K cooler in the annual mean during MM. The global mean surface air temperature decreased by 0.86 K. Northern hemisphere winters were on average characterized by cooler and drier weather over the northern parts of the continents, with an increase in precipitation in the southern parts. These climate anomalies are shown to be related to a shift in the North Atlantic Oscillation (NAO) towards a predominantly low phase during MM. The simulated climate anomalies are in very good agreement with reconstructions from proxy-data. Changes in the dynamical coupling between the troposphere and stratosphere were found in the MM simulation, indicating the importance of the stratosphere for climate change.
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  • 77
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    Gas hydrate dissociation and seafloor collapse in the wake of the Storegga Slide, Norway (2005)
    Elsevier
    In:  In: Onshore-offshore relationships on the North Atlantic Margin. , ed. by Wandås, B. T. G., Eide, E., Gradstein, F. and Nystuen, J. P. Norwegian Petroleum Society (NPF) Special Publication, 12 . Elsevier, Amsterdam, pp. 285-292. ISBN 978-0444518491
    Details
    Publication Date: 2018-01-10
    Type: Book chapter , NonPeerReviewed
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    Radionuclide Fluxes in the Arabian Sea: The role of particle composition (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 230 (3-4). pp. 319-337.
    Details
    Publication Date: 2016-12-20
    Description: We investigated the influence of the composition of the vertical particle flux on the removal of particle reactive natural radionuclides (Th-230 and Pa-231) from the water column to the sediments. Radionuclide concentrations determined in sediment traps moored in the western, central and eastern Arabian Sea were related to the major components (carbonate, particulate organic matter (POC), opal, lithogenic material) of the particle flux. These data were combined with sediment trap data previously published from the Southern Ocean, Equatorial Pacific and North Atlantic [Z. Chase, R.F. Anderson, M.Q. Fleisher, P.W. Kubik, The influence of particle composition and particle flux on scavenging of Th, Pa and Be in the ocean, Earth Planet. Sci. Lett. 204 (2002) 215-229; J.C. Scholten, F. Fietzke, S. Vogler, M. Rutgers van der Loeff, A. Mangini, W Koeve, J. Waniek. P. Stoffers, A. Antia, J. Kass, Trapping efficiencies of sediment traps from the deep eastern North Atlantic: The Th-230 calibration, Deep Sea Research 1148 (2001) 2383-2408]. The correlations observed between the particle-dissolved distribution coefficients (K-d) of Th-230 and Pa-231 and the concentrations of the particle types depend on the sediment trap data set used. This result suggests that scavenging affinities of the nuclides differ between oceanic regions. Several factors (K-d values, reactive surface areas of particles, inter-correlations in closed data set) can, however, influence the observed relationships and thus hamper the interpretation of these correlation coefficients as a measure of relative scavenging affinities of the nuclides to the particle types investigated. The mean fractionation factor (F(Pa/Th)=K-d(Pa)/(K)d(Th)) from the Equatorial Pacific (F=0.11+/-0.03) is similar to that from the North Atlantic (F(Pa/Th)=0.077+/-0.026), and both are lower than the factors from the Arabian Sea (F(Pa/Th)=0.35+/-0.12) and from the Southern Ocean (F(Pa/Th) 0.87+/-0.4). For opal concentrations exceeding similar to60%, an increase in the fractionation factors is observed causing a higher mean fractionation factor for the Southern Ocean trap data set. For the other areas investigated, differences in the mean fractionation factors cannot be related to the particles types considered. In the Arabian Sea, seasonally variable Pa-231(ex)/Th-230(ex) ratios observed in the sediment traps as well as differences of the ratios between recently deposited phytodetritus (fluff) and normal surface sediments indicate seasonal changes in scavenging processes which the generally accepted reversible scavenging models do not envisage. We assume that variable sinking rates of particles, and/or particles not considered in this study (e.g. colloids, manganese oxides, transparent exopolymer particles) may play an important but as yet unexplored role in deep-water scavenging processes. (C) 2004 Elsevier B.V. All rights reserved.
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  • 79
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    Pathways and variability of the Antarctic Intermediate Water in the western equatorial Pacific Ocean. (2005)
    Elsevier
    In:  Progress in Oceanography, 67 . pp. 245-281.
    Details
    Publication Date: 2016-10-05
    Description: In the western equatorial Pacific the low-salinity core of Antarctic Intermediate Water (AAIW) is found at about 800 m depth between potential density levels σθ = 27.2 and 27.3. The pathways of AAIW and the degradation of its core are studied, from the Bismarck Sea to the Caroline Basins and into the zonal equatorial current system. Both historical and new observational data, and results from numerical circulation model runs are used. The observations include hydrographic stations from German and Japanese research vessels, and Eulerian and Lagrangian current measurements. The model is the JAMSTEC high-resolution numerical model based on the Modular Ocean Model (MOM 2). The general agreement between results from the observations and from the model enables us to diagnose properties and to provide new information on the AAIW. The analysis confirms the paramount influence of topography on the spreading of the AAIW tongue north of New Guinea. Two cores of AAIW are found in the eastern Bismarck Sea. One core originates from Vitiaz Strait and one from St. George’s Channel, probably arriving on a cyclonic pathway. They merge in the western Bismarck Sea without much change in their total salt content, and the uniform core then increases considerably in salt content when subjected to mixing in the Caroline Basins. Hydrographic and moored current observations as well as model results show a distinct annual signal in salinity and velocity in the AAIW core off New Guinea. It appears to be related to the monsoonal change that is typically found in the near-surface waters in the region. Lagrangian data are used to investigate the structure of the deep New Guinea Coastal Undercurrent, the related cross-equatorial flow and eddy-structure, and the embedment in the zonal equatorial current system. Results from 17 neutrally buoyant RAFOS floats, ballasted to drift in the AAIW core layer, are compared with a numerical tracking experiment. In the model 73 particles are released at five-day intervals from Station J (2.5°N, 142°E), simulating currents at a moored time series station north of New Guinea. Observed and model track patterns are fairly consistent in space and season. Floats cross the equator preferably north of Cenderawasih Bay, with a maximum range in eddy-motion in this region north of New Guinea. The northward route at 135°E is also reflected in a low-salinity tongue reaching up to 3°N. At that longitude the floats seem to ignore the zonally aligned equatorial undercurrents. Farther to the east (139 145°E), however, the float observations are consistent with low-latitude bands of intermediate currents.
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  • 80
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    Formation of Denmark Strait overflow water and its hydro-chemical composition (2005)
    Elsevier
    In:  Journal of Marine Systems, 57 (3-4). pp. 264-265.
    Details
    Publication Date: 2017-07-12
    Description: The dense overflow across the Denmark Strait is investigated with hydrographic and hydro-chemical data and the water mass composition of the Denmark Strait Overflow Water (DSOW) is determined by multivariate analysis. Hydrographical properties, the transient tracers CFC-11 and CFC-12, oxygen and nutrients are utilized for the water mass definitions. Distribution and characteristics of water masses north of Denmark Strait are described, the important water masses at the sill and the variability on weekly time-scales are discussed, and the entrainment and mixing of water into the overflow plume in the northern Irminger Basin is calculated. The analysis indicates that water masses both from the Nordic Seas and the Arctic Ocean are important for the formation of DSOW. It is found that water masses transported with the East Greenland Current make up about 75% of the overflow at the sill. The overflow at, and shortly south of, the sill is inhomogeneous with a low-salinity component dominated by Polar Intermediate Water. The high-salinity component of the overflow is mainly of Arctic origin. The water mass composition, and the short-term variability for 7 repeats of sections close to the sill are described, and these illustrate that the overflow is in fact a composite of a number of water masses with different formation and transport histories. This indicate that the overflow is a robust feature, but that it responds to variations in the circulation or atmospheric forcing that influences the formation of intermediate and deep water masses within the Arctic Mediterranean and the North Atlantic. At a section about 400 km south of the sill the overflow is well mixed and modified by entrainment of, mainly, Iceland–Scotland Overflow Water and Labrador Sea Water, together constituting 30% of the overflow plume. The entrainment of Middle Irminger Water dominates shortly downstream of the sill, before the overflow plume reaches too deep but the entrainment seems to be intermittent in time.
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  • 81
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    The bimodal composition of carbonatites: Reality or misconception? (2005)
    Elsevier
    In:  Lithos, 85 (1-4). pp. 129-139.
    Details
    Publication Date: 2016-05-24
    Description: The concept of compositional bimodality in carbonatites has become widely accepted and has been used to impose restrictions on the composition of carbonatite magmas. We agree that mineralogical bimodality exists in carbonatites (most are either calcitic or dolomitic/ankeritic), but we argue that there is no compositional bimodality. The idea of bimodality is based on the interpretation of a variety of element distribution diagrams which were compiled only from chemical analyses in which SiO2 is 〈 10 wt.%. All others were rejected. Even with such a restricted data set the case for compositional bimodality is extremely weak, but the inclusion of analyses with higher SiO2 content destroys it completely. Yet these more siliceous compositions must be included, for many carbonatites contain substantial amounts of Fe–Mg silicates which are an essential part of the magmatic mineralogy of the rocks. They account for much of the Mg in carbonatites that are otherwise calcitic. Many such carbonatites contain well in excess of 10 wt.% SiO2. Supporters of the bimodality concept argue that liquids having compositions between calcite and dolomite can precipitate neither calcite nor dolomite because the minimum on the solid solution loops in the system calcite–dolomite permits only a carbonate of intermediate composition. Therefore, it is argued, liquids of such intermediate composition cannot be parental to calcitic and dolomitic carbonatites; their parent magmas must be calcitic and dolomitic. This deduction is incorrect. It is well established that dolomitic liquids have calcite as the liquidus phase over substantial temperature intervals, and that this is followed by dolomite precipitation. Mixed calcite–dolomite carbonatites are explicable in this way. Therefore, dolomitic liquids can be parental to calcitic carbonatites. However, dolomitic carbonatites cannot crystallize from a calcitic liquid. We suggest that intermediate composition carbonatite magmas are probably common. Bimodality in carbonatites is solely mineralogical, not compositional.
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    The importance of Trichodesmium in the global nitrogen cycle (2005)
    Elsevier
    In:  Journal of Sea Research, 53 . pp. 53-67.
    Details
    Publication Date: 2019-09-23
    Description: Nitrogen fixation is one of the important biochemical pathways that play a role in controlling the oceanic nitrogen inventory. Here we review nitrogen fixation in the ocean, with a particular emphasis on Trichodesmium, one of the dominant marine diazotrophs. Distribution data for diazotrophs are scarce, except in specific regions where Trichodesmium is known to bloom. Although some regions are clearly under-sampled, Trichodesmium can generally be found in tropical regions where temperature is at least 20 °C, except in the North Atlantic, where drift to higher latitudes is possible via the Gulf Stream. Likewise, biomass estimates are problematic because of the colony-forming habit of this organism. Trichodesmium grows slowly with reported maximum growth rates of approximately 0.14 d-1. Studies of the photosynthetic physiology indicate that Trichodesmium can tolerate high light intensity with Ik and Ic values of ∼300 and ∼140 μmole photons m−2 s−1, respectively. Review of the elemental composition of Trichodesmium indicates that the C:N molar ratio of 6.3:1 does not depart significantly from the predicted Redfield stoichiometry of 6.6:1. Overall, measured N:P ratios from the field and the laboratory were around 50, a significant departure from the Redfield stoichiometry of 16:1. Whether this indicates phosphorus limitation is not clear at present. The iron requirements of diazotrophs in general and of Trichodesmium in particular have been the subject of debate, but some recent laboratory studies have converged on Fe:C (μmole:mole) of approximately 50 at 70% of the maximum growth rates (μmax) to 250 at μmax for this species. There is a noticeable lack of information on growth rate as a function of phosphorus and fixed nitrogen sources. Although Trichodesmium is a non-heterocystous cyanobacterium, carbon and nitrogen fixation co-occur during the light period, indicating that light energy is required for both of these processes. This is likely to be achieved through cellular differentiation of the trichomes and a tight control of the temporal expression of many biochemical pathways. A summary table presents a set of values for the initial parameterisation of parameters relevant to the incorporation of nitrogen fixation in biological and biogeochemical models.
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  • 83
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    Oxygen isotope evidence for slab melting in modern and ancient subduction zones (2005)
    Elsevier
    In:  Earth and Planetary Science Letters, 235 (3/4). pp. 480-496.
    Details
    Publication Date: 2019-09-23
    Description: We measured oxygen isotope compositions of 34 adakites, high-Mg andesites, and lavas suspected to contain abundant slab and sediment melts from the Western and Central Aleutians, the Andes, Panama, Fiji, Kamchatka, Setouchi (Japan), and the Cascades. This suite covers much of the diversity of arc lavas previously hypothesized to contain abundant ‘slab’ melts. Measured and calculated values of δ18O for olivine phenocrysts in these samples vary between 4.88‰ and 6.78‰, corresponding to calculated melt values of 6.36‰ to 8.17‰. Values of δ18O for these samples are correlated with other geochemical parameters having petrogenetic significance, including Sr/Y, La/Yb, 87Sr/86Sr, and 143Nd/144Nd. Archetypical adakites from Adak Island (Central Aleutian) and Cook Island (Andean Austral zone), previously interpreted to be nearly pure melts of basaltic and gabbroic rocks in subducting slabs, have values of δ18O slightly higher than those of normal mid-ocean-ridge basalts, and in oxygen isotope equilibrium with typical mantle peridotite (i.e., their subtle 18O enrichment reflects their Si-rich compositions and low liquidus temperatures, not 18O-rich sources). Other primitive adakites from Panama and Fiji show only subtle sub-per mil enrichments in the source. This finding appears to rule out the hypothesis that end-member adakites are unmodified partial melts of basaltic rocks and/or sediments in the top (upper 1–2 km) of the subducted slab, which typically have δ18O values of ca. 9–20‰, and also appears to rule out them being partial melts of hydrothermally altered gabbros from the slab interior, which typically have δ18O values of ca. 2–5‰. One explanation of this result is that adakites are mixtures of partial melts from several different parts of the slab, so that higher- and lower-δ18O components average out to have no net difference from average mantle. Alternatively, adakites might be initially generated with more extreme δ18O values, but undergo isotopic exchange with the mantle wedge before eruption. Finally, adakites might not be slab melts at all, and instead come from differentation and/or partial melting processes near the base of the arc crust in the over-riding plate. High-Mg andesites and Setouchi lavas are commonly higher in δ18O than equilibrium with the mantle, consistent with their containing variable amounts of partial melts of subducted sediments (as we conclude for Setouchi lavas), slab-derived aqueous fluid (as we conclude for the Cascades) and/or crustal contaminants from the over-riding plate (as we conclude for Kamchatka).
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  • 84
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    Seasonal variability in the Deep Western Boundary Current around the eastern tip of Brazil (2005)
    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 52 . pp. 1414-1428.
    Details
    Publication Date: 2020-08-05
    Description: The spreading of recently ventilated North Atlantic Deep Water (NADW) from the formation region to the equatorial Atlantic occurs mainly in the Deep Western Boundary Current (DWBC). When crossing the equator between 44°W and 35°W, the DWBC is split in two velocity cores through a chain of seamounts around the Atoll das Rocas at 3.5°S. Further eastward the DWBC contributes to the zonally oriented equatorial current system. The circulation of the NADW in the crucial region around the eastern tip of Brazil is examined using 8 CTD and Chlorofluorocarbon (CFC) sections along 35°W and along 5°S, respectively, taken mainly in spring and fall in the years 1990–2002. As expected from the short direct flow path between the two sections, the CFC concentrations in the upper NADW (1400–2200 m) were similar at 35°W and 5°S during boreal autumn. In spring, however, a significant downstream CFC decrease was observed. If one attributes the decrease solely to the older age of water further downstream, the CFC concentration age difference between 35°W and 5°S in May 2002 would be 3–5 years. We interpret the aging to be caused by an eastward detour of the flow with the deep equatorial circulation before reaching 5°S in spring. Another conspicuous anomaly was found in the middle NADW (2200–3400 m) with downstream decreasing salinities in boreal spring, but not in autumn. This variability might also be caused by differences in the deep equatorial circulation, but in contrast to the uNADW, one cannot exclude enhanced mixing with water of South Atlantic origin in spring to be the cause of that variability. No seasonal difference was observed in the hydrography or the CFC concentrations for the lower NADW. The weaker CFC decrease along the equator compared with that in the DWBC downstream of 35°W, and the topographic features along the downstream path, point to a predominantly eastward flow of the deep lNADW core. The lNADW CFC core is no longer observed at 11°S. Repeated observations of CFCs in the DWBC highlight the diverse variability affecting the components of NADW.
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  • 85
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    Linkage of Arctic atmospheric circulation and Siberian shelf hydrography: a proxy validation using δ18O records of bivalve shells (2005)
    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 175-186.
    Details
    Publication Date: 2017-09-13
    Description: High resolution oxygen isotope profiles of aragonitic bivalve shells (Astarte borealis) collected alive in different years are used to trace hydrographical changes on the Laptev Sea shelf, which are mainly forced by changes in riverine freshwater discharge and arctic atmospheric circulation patterns. By merging individual isotope profiles, a high resolution time series of relative changes in bivalve δ18O is obtained for the eastern Laptev Sea for the period 1969 to 1998. The resulting pattern in the δ18O time series reflects seasonal bottom-water salinity changes in the Laptev Sea, which is dominated by the peak input of freshwater discharged by the Lena River onto the Laptev Sea shelf during summer. The relative changes in summer bottom-water salinity, deduced from the δ18O values in the bivalves and the discharge anomaly of the Lena River, show a significant negative correlation. It is therefore suggested that the annual and subdecadal variations of the riverine freshwater and its influence on the shelf hydrography are imprinted in the bivalve shells. Moreover, we note that extreme summer precipitation anomalies in the Lena River catchment area affect the river discharge characteristics, events which are detectable in the δ18O time series. This all implies that δ18O records of bivalve shells have the potential to build long-term records of atmospheric-forced changes in arctic circulation.
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  • 86
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    Meddies and decadal changes at the Azores Front from 1980 to 2000 (2005)
    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 52 (3-4). pp. 583-604.
    Details
    Publication Date: 2020-08-05
    Description: Twenty years of time series observations from the deep-sea mooring KIEL276 are used to obtain information on the frequency and propagation of meddies (Mediterranean Water eddies), on long-term changes in flow properties, and on a possible relation to the North Atlantic Oscillation. The mooring was set at the nominal position 33°N, 22°W at a water depth of more than 5200 m in the northern Canary Basin. It is located near the southern boundary of the Azores Current (AC), which is part of the North Atlantic subtropical gyre, and also in the large-scale Mediterranean Water (MW) tongue originating from the Strait of Gibraltar. The amplitudes of time-varying vertical quasi-geostrophic modes and the correlation of current and temperature changes at levels in the MW and the North Atlantic Central Water above are used to identify meddies. A total of 10 meddies passed the mooring during the period 1980–2000. Half of the events can be related to earlier observations. Directional changes in meddy-related velocities are used to estimate speeds and directions of meddy propagation. Directions of propagation are very homogeneous, with all the 10 meddies observed propagating with a southward velocity component within a sector of 90°, and typical speeds are 2–3 cm/s. Meddy occurrence was uneven in time, with six meddies found during the first four years and only four meddies during the remaining 16 years. Decadal changes show the annual-mean and the fluctuating kinetic energy levels at the site changing from lower values in the 1980s to high values in the 1990s. This change appears to be correlated with variations in the North Atlantic Oscillation (NAO) index, with a delay in oceanic response of about 3 years. A conceptual model of AC meanders is used to identify meander signals in the upper-layer time series. The AC axis appears to be closer to the site during the 1990s than during the preceding decade and indicates a southward or southwestward displacement of the AC with increasingly positive values of the NAO index. Meddy frequency is lower when the AC gets closer from the north. A reduction in meddy occurrence in the region just south of the AC is possibly caused by the shear-induced blocking of some meddies crossing the front from the north.
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  • 87
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    Picophytoplankton - a comparative study of their biochemical composition and photosynthetic properties (2005)
    Elsevier
    In:  Journal of Sea Research, 53 . pp. 7-24.
    Details
    Publication Date: 2017-07-18
    Description: Picophytoplankton are a small or major component of the phytoplankton community and present in all oceanic systems, from pole to pole. They dominate in the low chlorophyll biomass areas, such as the (sub)tropical regions, but also contribute considerably (up to 20%) in the high chlorophyll biomass areas. The ecosystems of occurrence contrast significantly in physical and chemical settings. This includes a strongly mixed upper water column replete in nutrients as well as a strongly thermally stratified euphotic zone depleted in nutrients at the surface with a steep inverse light and nutrient gradient. These changes impose a strong impact on the composition of the picophytoplankton community but also on the biochemical and physiological properties of the species present. In particular, the pigmentation and cellular carbon, nitrogen and phosphorus quota and requirement will differ from a stratified compared to a well-mixed water column. As a result no characteristic values for the parameters required for this specific algal group in a global phytoplankton carbon model (the SWAMCO model,Lancelot et al. (2000), Deep-Sea Res. I, 47, 1621) can be given. In the present paper an inventory is made of the biochemical, physiological and photosynthetic parameters of two species of cyanobacteria (Prochlorococcus and Synechococcus) and the pico-size class fraction of the eukaryote phytoplankton component. Other groups of phytoplankton, such as diatoms, Trichodesmium, Phaeocystis and coccolithophorids, will be discussed in separate papers in this issue. This inventory is a mixture of laboratory experiments using well-defined algal populations as well as data derived from field surveys including a mixture of species. Where possible, the relevance of the parameters will be discussed in relation to the nature of the physico-chemical conditions of the area of occurrence.
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  • 88
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    Radiochemical methods for uranium determination (2005)
    Elsevier
    In:  In: Encyclopedia of Analytical Science. , ed. by Worsfold, P. J., Townsend, A. and Poole, C. F. Elsevier, pp. 44-49. 2. ISBN 978-0-12-369397-6
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    Publication Date: 2014-02-05
    Type: Book chapter , NonPeerReviewed
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  • 89
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    Cathodic Stripping Voltammetry (2005)
    Elsevier
    In:  In: Encyclopedia of Analytical Science. , ed. by Worsfold, P. J., Townsend, A. and Poole, C. F. Elsevier, pp. 203-212. 2. ISBN 978-0-12-369397-6
    Details
    Publication Date: 2014-02-05
    Description: Cathodic stripping voltammetry (CSV) is an analytical technique used for the analysis of low levels of analytes (principally trace metals and sulfur containing organic compounds) in aqueous solutions, and is based on the measurement of a reductive current response as a function of a potential scan towards more negative potentials. The technique is highly sensitive (limits of detection of 10− 10–10− 12 mol l− 1) because of the application of a preconcentrations step prior to the stripping step. During the preconcentration the analyte is collected on the surface of the working electrode (typically a mercury drop), often in the presence of an added electro-active ligand. The CSV technique has been used for automated measurements of trace metals in marine waters, but a key strength of CSV is in its use in trace metal speciation measurements in natural waters, in particular dissolved iron in marine waters.
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  • 90
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    Leishmanicidal cycloartane-type triterpene glycosides from Astragalus oleifolius (2005)
    Elsevier
    In:  Phytochemistry, 66 (10). pp. 1168-1173.
    Details
    Publication Date: 2020-06-11
    Description: Two new cycloartane-type glycosides oleifoliosides A (1) and B (2) were isolated from the lower stem parts of Astragalus oleifolius. Their structures were identified as 3-O-[β-xylopyranosyl-(1 → 2)-α-arabinopyranosyl]-6-O–β-xylopyranosyl-3β,6α,16β,24(S),25-pentahydroxycycloartane and 3-O-[β-xylopyranosyl-(1 → 2)-α-arabinopyranosyl]-6-O–β-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxycycloartane, respectively, by means of spectroscopic methods (IR, 1D and 2D NMR, ESI-MS). Three known cycloartane glycosides cyclocanthoside E (3), astragaloside II (4) and astragaloside IV (5) were also isolated and characterized. All five compounds were evaluated for in vitro trypanocidal, leishmanicidal and antiplasmodial activities as well as their cytotoxic potential on primary mammalian (L6) cells. Except for the compound 5, all compounds showed notable growth inhibitory activity against Leishmania donovani with IC50 values ranging from 13.2 to 21.3 μg/ml. Only weak activity against Trypanosoma brucei rhodesiense was observed with the known compounds astragaloside II (4, IC50 66.6 μg/ml) and cyclocanthoside E (3, IC50 85.2 μg/ml), while all compounds were inactive against Trypanosoma cruzi and Plasmodium falciparum. None of the compounds were toxic to mammalian cells (IC50’s 〉 90 μg/ml). This is the first report of leishmanicidal and trypanocidal activity of cycloartane-type triterpene glycosides.
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  • 91
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    Anti-protozoal and plasmodial FabI enzyme inhibiting metabolites of Scrophularia lepidota roots (2005)
    Elsevier
    In:  Phytochemistry, 66 (3). pp. 355-362.
    Details
    Publication Date: 2014-08-20
    Description: The ethanolic root extract of Scrophularia lepidota, an endemic plant of the Turkish flora, has been investigated for its anti-protozoal and inhibitory effect towards plasmodial enoyl-ACP reductase (FabI), a key enzyme of fatty acid biosynthesis in Plasmodium falciparum. Chromatographic separation of the extract yielded 10 iridoids (1–10), two of which are new, and a known phenylethanoid glycoside (11). The structures of the new compounds were determined as 3,4-dihydro-methylcatalpol (8) and 6-O-[4″-O-trans-(3,4-dimethoxycinnamoyl)-α-l-rhamnopyranosyl]aucubin (scrolepidoside, 9) by spectroscopic means. The remaining metabolites were characterized as catalpol (1), 6-O-methylcatalpol (2), aucubin (3), 6-O-α-l-rhamnopyranosyl-aucubin (sinuatol, 4), 6-O-β-d-xylopyranosylaucubin (5), ajugol (6), ajugoside (7), an iridoid-related aglycone (10) and angoroside C (11). Nine isolates were active against Leishmania donovani, with the new compound 9 being most potent (IC50 6.1 μg/ml). Except for 4, all pure compounds revealed some trypanocidal potential against Trypanosoma brucei rhodesiense (IC50 values 29.3–73.0 μg/ml). Only compound 10 showed moderate anti-plasmodial (IC50 40.6 μg/ml) and FabI enzyme inhibitory activity (IC50 100 μg/ml). 10 is the second natural product inhibiting the fatty acid biosynthesis of Plasmodium falciparum.
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  • 92
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    Onset of recent rapid sea-level rise in the western Atlantic Ocean (2005)
    Elsevier
    In:  Quaternary Science Reviews, 24 (18-19). pp. 2083-2100.
    Details
    Publication Date: 2014-02-04
    Description: A high-resolution record of sea-level change spanning the past 1000 years is derived from foraminiferal and chronological analyses of a 2 m thick salt-marsh peat sequence at Chezzetcook, Nova Scotia, Canada. Former mean tide level positions are reconstructed with a precision of ±0.055 m using a transfer function derived from distributions of modern salt-marsh foraminifera. Our age model for the core section older than 300 years is based on 19 AMS 14C ages and takes into account the individual probability distributions of calibrated radiocarbon ages. The past 300 years is dated by pollen and the isotopes 206Pb, 207Pb, 210Pb, 137Cs and 241Am. Between AD 1000 and AD 1800, relative sea level rose at a mean rate of 17 cm per century. Apparent pre-industrial rises of sea level dated at AD 1500-1550 and AD 1700-1800 cannot be clearly distinguished when radiocarbon age errors are taken into account. Furthermore, they may be an artefact of fluctuations in atmospheric 14C production. In the 19th century sea level rose at a mean rate of 1.6 mm/yr. Between AD 1900 and AD 1920, sea-level rise accelerated to the modern mean rate of 3.2 mm/yr. This acceleration corresponds in time with global temperature rise and may therefore be associated with recent global warming. © 2005 Elsevier Ltd. All rights reserved.
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  • 93
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    Pressure dependence and anisotropy of P-wave velocities in ultrahigh-pressure metamorphic rocks from the Dabie–Sulu orogenic belt (China): Implications for seismic properties of subducted slabs and origin of mantle reflections (2005)
    Elsevier
    In:  Tectonophysics, 398 (1-2). pp. 67-99.
    Details
    Publication Date: 2020-10-21
    Description: The compressional wave velocities (Vp), pressure derivatives (Vp′) and anisotropy (A) of three types of eclogites and country rocks from the Dabie–Sulu ultrahigh-pressure (UHP) metamorphic belt, China, have been measured under confining pressures up to 800 MPa. Type-1 eclogites, which are coarse-grained and subjected to almost no retrograde metamorphism, experienced recovery-accommodated dislocation creep at peak metamorphic conditions (in the diamond stability field). Type-2 eclogites are fine-grained reworked Type-1 materials that experienced recrystallization-accommodated dislocation creep under quartz/coesite boundary conditions during the early stage of exhumation. Type-3 eclogites are retrogressed samples that were overprinted by significant amphibolite facies metamorphism during a late stage of exhumation within the crust. Type-1 eclogites are richer in Al2O3 and MgO but poorer in SiO2 and Na2O than Type-2 and Type-3 eclogites. Anisotropy of Type-1 and Type-2 eclogites is generally low (〈4%) because volumetrically important garnet is elastically quasi-isotropic, while Type-3 eclogites can exhibit high anisotropy (〉10%) due to the presence of strongly anisotropic retrograde minerals such as amphibole, plagioclase and mica. The transition of the pressure dependence of velocity from the poroelastic to elastic regimes occurs at a critical pressure (Pc), which depends mainly on the density and distribution of microcracks and in turn on the exhumation history of rocks. The Vp–pressure relationship can be expressed by Vp=a(lnP)2+blnP+c (P≤Pc) and Vp=V0+DP (P≥Pc), where P is the confining pressure, a and b are constants describing the closure of microcracks below Pc, c is the velocity when P is equal to one (MPa), V0 is the projected velocity of a crack-free sample at room pressure, and D is the intrinsic pressure derivative above Pc. When data are curve-fit, pressure derivatives and anisotropy as functions of pressure are determined. The average Vp of the eclogites in the linear regime is 8.42+1.41×10−4P for Type-1, 7.80+1.58×10−4P for Type-2, and 7.33+2.04×10−4P for Type-3, where Vp is in km/s and P in MPa. The decrease in V0 and increase in D from Type-1 to Type-3 eclogites are attributed to a decrease in garnet content and an increase in retrograde minerals. The NE–SW trending, NW-dipping, slab-like high Vp anomaly (8.72 km/s at a depth of 71 km) which extends from the Moho to at least 110 km beneath the Dabie–Sulu region, can be interpreted as the remnant of a subducted slab which is dominated by Type-1 eclogites and has frozen in the upper mantle since about 200–220 Ma. Such relic crustal materials, subducted and preserved as eclogite layers intercalated with felsic gneiss, garnet–jadeite quartzite, marble and serpentinized peridotite, could be responsible for regionally observed seismic reflectors in the upper mantle.
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  • 94
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    Sea-level change in the Mediterranean Sea since the LGM: model predictions for tectonically stable areas (2005)
    Elsevier
    In:  Quaternary Science Reviews, 24 (18-19). pp. 1969-1988.
    Details
    Publication Date: 2021-05-10
    Description: Sea-level change in the Mediterranean Sea during glacial cycles is determined by the temporally variable eustatic change and by the spatially variable glacio-hydro-isostatic response of the earth and ocean to the growth and decay of ice sheets. Superimposed upon this are the relative changes from any vertical tectonic movement of the land. For sites that are either tectonically stable or where the magnitude of tectonic uplift is known, comparisons of observed change with predictions of the glacio-hydro-eustatic signals provide constraints on the earth–ice parameters used. The resulting predictive models can then be used to interpolate sea-level change and shoreline migration between the spatially and temporally limited observational data set. Whether such parameters reflect the true properties of the mantle and ice sheets depends on whether an effective separation has been achieved from the inversion of the observational data set. This paper explores this issue and demonstrates that observations from certain regions in the Mediterranean are particularly important in effecting the separation. This is supported by a trial analysis of a small observation data set from sites that exhibit some of the desirable features of an ideal data set. Basin-wide predictions of sea-level change, palaeo-water depth and shoreline locations based on these analyses are presented for selected epochs.
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  • 95
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    The red flying squid (Ommastrephes bartramii): A review of recent research and the fishery in Japan (2005)
    Elsevier
    In:  Fisheries Research, 76 (1). pp. 39-55.
    Details
    Publication Date: 2021-08-03
    Description: We review the biology, ecology, fisheries, and resource status of the red flying squid (Ommastrephes bartramii) in the North Pacific focusing on recent literature published in Japan. The North Pacific population of O. bartramii comprises two seasonal cohorts (fall and winter–spring) and four stocks: (1) central stock of the fall cohort, (2) east stock of the fall cohort, (3) west stock of the winter–spring cohort, and (4) central-east stock of the winter–spring cohort. The population makes an annual round-trip migration between its subtropical spawning grounds where the sea surface temperature ranges from 21 to 25 °C and its northern feeding grounds near the Subarctic Boundary. O. bartramii matures at 7–10 months and has an estimated 1-year life span. Near the Subarctic Frontal Zone, adult squid commonly occupy 0–40 m depths at night and 150–350 m depths during the day. They prey primarily on fishes, squids and crustaceans. Predators include marine mammals and swordfish (Xiphias gladius). The North Pacific population of O. bartramii was targeted by an international driftnet fishery during 1978–1992, and annual catches reached more than 350,000 t during the 1980s. It is now targeted by jigging vessels from Japan, China, South Korea and Taiwan. Annual catches in the Japanese jigging fishery ranged from 49,000 to 71,000 t during the mid-1990s, but dropped to below 25,000 t in 2000 and 2001.
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  • 96
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    Environmental associations of shortfin squid Illex argentinus (Cephalopoda: Ommastrephidae) in the Northern Patagonian Shelf (2005)
    Elsevier
    In:  Fisheries Research, 76 (3). pp. 401-416.
    Details
    Publication Date: 2021-07-28
    Description: We identified environmental associations (depth, bottom temperature and bottom salinity) of the shortfin squid Illex argentinus in the Northern Patagonian Shelf. Data are from 15 research bottom trawl surveys conducted in the Argentine–Uruguayan Common Fishing Zone (AUCFZ) between 1985 and 1998. Squid distribution in the surveyed area showed significant associations (p 〈 0.05) mostly with depth and bottom temperature. Bathymetric associations of squid detected in March–April, May–June and July–August cruises revealed a preference of squid for deep depths (80–280 m, intermediate and external shelf) and cool bottom temperatures (4–10 °C, subantarctic water) within the survey area. In contrast, the results observed during November–December cruises showed a preference of squid for shallower depths (70–90 m) and warmer bottom temperatures. The majority of two-way environmental analyses showed significant associations, suggesting the existence of a strong correlation between the environmental factors used in our analyses. The identification of significant associations between squid distribution and bottom temperature seem to be related to the presence of strong thermal gradients within the study area. This could be supporting the existence of an association between I. argentinus with the Brazil–Malvinas confluence front and also with the shelf break front.
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  • 97
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    Evolution of the Rhône delta plain in the Holocene (2005)
    Elsevier
    In:  Marine Geology, 222-223 . pp. 235-265.
    Details
    Publication Date: 2021-01-08
    Description: The delta plain of the Rhone shows many sandy beach ridges cropping out at the surface. We propose here a radiocarbon chronology for the accumulation of the sedimentary bodies and an interpretation of the morphology of the mouth lobes that they form. Morphologies of the lobes depend on four principal factors: (1) the variation of the relative sea level, which constitutes the morphogenic base level, (2) the fluvial input (volume of water discharge and sedimentary input, number and position of the mouths), (3) marine dynamics (volume and direction of the longshore drift, dominant wave direction) (4) the accommodation space created by the rise of relative sea level, along with the paleobathymetry onto which the lobe will prograde immediately in front of the delta and at sea. Our conclusions are: the main Holocene paleo-delta lobes of Ulmet and Saint Ferréol were contemporaneous, being deposited from 4000 to 2000 yr BP. However, the fluvial style of their downstream channel (meandering for Ulmet channel and linear for Saint-Ferréol) and the lobe morphologies of both channels are contrasted: rounded in the case of Ulmet and elongated for Saint-Ferréol. The role of the accommodation space is confirmed by two recent drillholes traversing the entire Holocene succession, which reveal a prior stage of sedimentary filling in the case of the Saint-Ferréol lobe, thus limiting the accommodation space and favouring a rapid and pointed progradation of this lobe. The decoupling between hydrological activity and progradation of lobe indicates the complexity of mechanisms in the large catchment basin of Rhône. However, the high rate of progradation of Saint-Ferréol lobe after 2900 BP is probably a consequence of the increase of human activity after this date. The variation of relative sea level remains an important factor controlling the evolution of the Rhone delta after 6000 BP. The local (?) stabilization of the relative sea level between 4585 BP and 3520 BP played an important role in the triggering of coastal progradation (Saint-Ferréol lobe, eastern margin Rhône delta).
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  • 98
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    Upper ocean momentum balances in the western equatorial Pacific on the intraseasonal time scale (2005)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 (5). pp. 749-765.
    Details
    Publication Date: 2021-03-23
    Description: Surface meteorology, upper ocean current, and hydrographic measurements, collected along a repeated survey pattern and from a central mooring in the western equatorial Pacific during late 1992 to early 1993, were used to analyse upper ocean momentum balances on the intraseasonal time scale. Wind stresses derived from meteorological measurements were compared with numerical weather prediction products. Advection terms in the momentum equations were estimated by planar fits to the current and hydrographic data. Pressure gradient terms were derived from planar fits to the dynamic heights calculated from the hydrographic data, referenced by balancing the momentum equation in a selected layer below the mixed layer. Under prevailing westerly winds, westward pressure gradient forcings of 2 x 10 -7 ms -2 were set up in the western equatorial Pacific, countering the surface wind, while the total advection tended to accelerate the eastward momentum in the surface layer. During both calm wind and westerly wind burst periods, zonal turbulent momentum fluxes estimated from the ocean budgets were comparable with those estimated from microstructure dissipation rate measurements and with zonal wind stresses, so that the zonal momentum could be balanced within error bars. The meridional momentum balances were noisier, which might be due to the fact that the short meridional length scale of the equatorial inertial-gravity waves could contaminate the dynamic signals in the mixed temporal/spatial sampling data, so that the meridional gradient estimates from the planar fits could be biased.
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  • 99
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    The effects of sand extraction on the macrobenthos of a relict sands area (northern Adriatic Sea): results 12 months post-extraction (2005)
    Elsevier
    In:  Marine Pollution Bulletin, 50 (7). pp. 768-777.
    Details
    Publication Date: 2021-06-25
    Description: Sands for the nourishment of beaches along the Emilia-Romagna coast (northern Adriatic Sea) were dredged from an offshore area characterised by relict sands formed during the last Adriatic post-glacial transgression. The short-term effects of the sand extraction on macrozoobenthic communities were investigated before, during and 1, 6 and 12 months after dredging at three impacted stations and seven control stations. Sand extraction activities did not significantly influence the granulometry and %TOC in the sediment but caused almost complete defaunation at dredging stations. Yet, just 12 months after the extraction, the recolonisation of communities at the impacted stations was at an advanced stage. Unlike other studies on the effects of extraction of marine sand, no significant settlement of opportunistic species was observed. The limited impact of the sand extraction operation on the physical characteristics of the sediment and hydrological-sedimentary characteristics in the relict sand area should aid its rapid recovery and the restoration of the original community in a short period of time (2–4 years after dredging).
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  • 100
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    Fluorescence imaging application: effect of leaf age on seagrass photokinetics (2005)
    Elsevier
    In:  Aquatic Botany, 81 (1). pp. 69-84.
    Details
    Publication Date: 2021-07-19
    Description: We used the Imaging-PAM fluorometer to map spatial variability of photosynthesis in three seagrass species, Halophila ovalis, Zostera capricorni and Posidonia australis. Photosynthesis was described by relative photosynthetic rate (PS/50), effective quantum yield (ΦPSII), non-photochemical quenching (NPQ and qN), electron transport rate (ETR) and leaf absorptivity. Photosynthetic patterns were linked to leaf age and light climate but patterns were not consistent across species. Longitudinal heterogeneity in photosynthesis was apparent along the leaves of all three species while lateral spatial heterogeneity was found only across Z. capricorni and H. ovalis leaves. Age of leaf tissue, determined by longitudinal location on the leaf, strongly influenced photosynthetic activity of Z. capricorni and P. australis. A comparison of H. ovalis leaves of differing maturity demonstrated the influence of leaf age on photosynthetic activity, yet a comparison of Z. capricorni leaves of differing maturity showed no leaf-age effects. Variations in stress-induced changes across a seagrass leaf can be used to identify areas or particular regions of the leaf, which are more susceptible to photodamage. Clear evidence of substantial within-leaf heterogeneity in photosynthetic activity (i.e., a two-fold variation in half saturation constant along a leaf of P. australis) has serious implications for use of small sections of leaf for photosynthetic incubations (such as O2 or single-point chlorophyll a fluorescence measurements).
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