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  • Elsevier  (208,192)
  • Springer  (194,604)
  • 2010-2014  (237,310)
  • 1980-1984  (165,486)
  • 2014  (237,310)
  • 1983  (86,941)
  • 1980  (78,545)
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  • 1
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    The Phanerozoic δ88/86Sr Record of Seawater: New Constraints on Past Changes in Oceanic Carbonate Fluxes (2014)
    Elsevier
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    Publication Date: 2024-03-23
    Description: The isotopic composition of Phanerozoic marine sediments provides important information about changes in seawater chemistry. In particular, the radiogenic strontium isotope (87Sr/86Sr) system is a powerful tool for constraining plate tectonic processes and their influence on atmospheric CO2 concentrations. However, the 87Sr/86Sr isotope ratio of seawater is not sensitive to temporal changes in the marine strontium (Sr) output flux, which is primarily controlled by the burial of calcium carbonate (CaCO3) at the ocean floor. The Sr budget of the Phanerozoic ocean, including the associated changes in the amount of CaCO3 burial, is therefore only poorly constrained. Here, we present the first stable isotope record of Sr for Phanerozoic skeletal carbonates, and by inference for Phanerozoic seawater (δ88/86Srsw), which we find to be sensitive to imbalances in the Sr input and output fluxes. This δ88/86Srsw record varies from ∼0.25‰ to ∼0.60‰ (vs. SRM987) with a mean of ∼0.37‰. The fractionation factor between modern seawater and skeletal calcite Δ88/86Srcc-sw, based on the analysis of 13 modern brachiopods (mean δ88/86Sr of 0.176±0.016‰, 2 standard deviations (s.d.)), is -0.21‰ and was found to be independent of species, water temperature, and habitat location. Overall, the Phanerozoic δ88/86Srsw record is positively correlated with the Ca isotope record (δ44/40Casw), but not with the radiogenic Sr isotope record ((87Sr/86Sr)sw). A new numerical modeling approach, which considers both δ88/86Srsw and (87Sr/86Sr)sw, yields improved estimates for Phanerozoic fluxes and concentrations for seawater Sr. The oceanic net carbonate flux of Sr (F(Sr)carb) varied between an output of -4.7x1010mol/Myr and an input of +2.3x1010mol/Myr with a mean of -1.6x1010mol/Myr. On time scales in excess of 100Myrs the F(Sr)carb is proposed to have been controlled by the relative importance of calcium carbonate precipitates during the “aragonite” and “calcite” sea episodes. On time scales less than 20Myrs the F(Sr)carb seems to be controlled by variable combinations of carbonate burial rate, shelf carbonate weathering and recrystallization, ocean acidification, and ocean anoxia. In particular, the Permian/Triassic transition is marked by a prominent positive δ88/86Srsw-peak that reflects a significantly enhanced burial flux of Sr and carbonate, likely driven by bacterial sulfate reduction (BSR) and the related alkalinity production in deeper anoxic waters. We also argue that the residence time of Sr in the Phanerozoic ocean ranged from ∼1Myrs to ∼20Myrs.
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  • 2
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    Environmental boundary conditions of cold-water coral mound growth over the last 3 Million years in the Porcupine Seabight, Northeast Atlantic (2014)
    Elsevier
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    Publication Date: 2024-03-22
    Description: IODP Expedition 307 made it for the first time possible to investigate the entire body of a cold-water coral carbonate mound. Here we provide new insights into the long-term history of Challenger Mound on the European continental margin off Ireland. This study is based on age determinations (230Th/U, 87Sr/86Sr) and geochemical signals (Mg/Li and Ba/Ca) measured in the scleractinian cold-water coral Lophelia pertusa from IODP Site 1317 in the Porcupine Seabight. The paleoceanographic reconstructions reveal that coral growth in the Porcupine Seabight was restricted to specific oceanographic conditions such as enhanced export of primary production and Bottom-Water Temperatures (BWT) between ∼8–10 °C, related to the water mass stratification of the Mediterranean Outflow Water (MOW) and Eastern North Atlantic Water (ENAW). The geochemical signals from the coral skeletons can be explained by the close interaction between cold-water coral growth, sea-surface productivity and the surrounding water masses - the boundary layer between MOW and ENAW. Enhanced sea-surface productivity and the build-up of a stable water mass stratification between ENAW and MOW caused enhanced nutrient supply at intermediate water depths and facilitated a steady mound growth between∼3.0 - 2.1 Ma. With the decrease in sea-surface productivity and related reduced export productivity the food supply was insufficient for rapid coral mound growth between∼1.7 - 1 Ma. During the late Pleistocene (over the last∼0.5 Myr) mound growth was restricted to interglacial periods. During glacials the water mass boundary between ENAW/MOW probably was below the mound summit and hence food supply was not sufficient for corals to grow.
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  • 3
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    Semidiurnal tides in the Laptev Sea Shelf zone in the summer season (2014)
    Elsevier
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    Publication Date: 2024-01-01
    Description: Tidal processes play an important role in the dynamics of shelf circulation in the Laptev Sea. The Unstructured Grid Finite Volume Coastal Ocean Model (FVCOM) is used to simulate the tidal dynamics in the Lena Delta region of the Laptev Sea in ice-free barotropic case. The grid element size ranges from 400 m to 5 km. The major semidiurnal tidal waves M2M2 and S2S2 are investigated with the M2M2 being the most important in generating large sea level amplitudes and currents over shallow areas. A correction to the tidal elevation at the open boundary is proposed, which minimizes the discrepancy between the model prediction and observations. The observations include both recent mooring data and the standard set of tide gauge measurements used in previous studies. The comparison of results to known tidal solutions is carried out. The paper also discusses the residual circulation and energy fluxes and assesses the impact of additional bathymetric information. Highlights • Our simulations reproduce the semidiurnal tidal waves M2M2 and S2S2 in the Laptev Sea region. • We develop special procedure for the construction of optimal open boundary conditions for tidal elevation for M2M2 and S2S2 constituents. • The simulated tidal maps show an improved agreement with observations. • We analyze barotropic currents, residual circulation and evolution of energy fluxes in the region. • We consider the energy balance for the M2M2 and S2S2 waves and the sensitivity to the bathymetry.
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  • 4
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    Clay minerals as indicators of late Quaternary sedimentation constraints in the Mendeleev Rise, Amerasian Basin, Arctic Ocean (2014)
    Springer
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    Publication Date: 2024-01-01
    Description: The results of study of six cores taken from different morphostructural zones in the Mendeleev Ridge area are discussed. Average contents of minerals of the illite group, chlorite, kaolinite, and smectite are about 60, 21, 12, and 5%, respectively. It was found that fluctuations of minerals along the section correlate with variations in sedimentation constraints in the Late Quaternary. Peaks of kaolinite usually coincide with increased contents of the sand fraction, probably, due to its delivery by icebergs. In contrast, illite shows good correlation with the pelite fraction, testifying to its transport mainly by ices and currents. Minerals of the chlorite and smectite groups in the studied cores are less informative.
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  • 5
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    Late Quaternary evolution of sediment provenances in the Central Arctic Ocean : mineral assemblage, trace element composition and Nd and Pb isotope fingerprints of detrital fraction from the Northern Mendeleev Ridge (2014)
    Elsevier
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    Publication Date: 2024-01-01
    Description: Mineral assemblage, trace element content and Nd and Pb isotope signatures were analysed on the fine fraction (〈20 μm) of sedimentary records from the Northern Mendeleev Ridge in the Central Arctic Ocean. Our aim was to identify the detrital particle provenance and to interpret the changes over the past ∼250 ka in the relative contribution of the different source-areas in relation to paleoenvironmental conditions. The clay mineral assemblage and the Nd and Pb isotope signatures depict systematic changes over the Late Quaternary. The bulk mineralogy exhibits increases in the relative contribution of carbonate minerals vs. silicates in interglacial/deglacial intervals. In glacial intervals, the mineral assemblage of the 〈20 μm fraction is characterised by an enrichment in kaolinite, counterbalanced by a decrease in illite. The Nd and Pb isotope signatures of 〈20 μm fraction are interpreted using a three end-member mixing model, involving crustal supplies from North America and Canada, from the Siberian margin and some from volcanic material. A compilation of geochemical signatures of geological terraines surrounding the Arctic Ocean allowed each end-member to be assigned a representative signature, averaging the signal of the eroded terraines. The Suspended Particulate Matter (SPM) of the MacKenzie River represents an average signature of the sedimentary supplies delivered from the North American platform and Canadian margin. The SPM of the Lena River reflects the mean sedimentary signature of the Siberian platform. The Okhotsh-Chukotka province from the Eastern border of Siberia is identified as the most probable volcanic source. Late Quaternary evolution of the estimated relative contribution of the three end-members confirms that the sediment provenances in the Central Arctic Ocean remain close to the current conditions during past interglacials/deglacials MIS1–3, MIS5/TII and MIS7/TIII. In contrast, glacial conditions (MIS4 and MIS6) record minimum supplies from the American margin, associated with increased volcanic contribution, to the Mendeleev Ridge core location suggesting a different sea-ice circulation associated with a low sea-level and reduced shelf area. Highlights • Nd and Pb isotope signatures of fine detrital sediment fraction are tracer of sources. • Glacial and interglacials are characterised by systematic changes in sediment sources. • The volcanic Okhotsh-Chukotka province has major contribution during glacials.
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  • 6
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    Bathymetric variations in vertical distribution patterns of meiofauna in the surface sediments of the deep Arctic ocean (HAUSGARTEN, Fram strait) (2014)
    Elsevier
    Details
    Publication Date: 2024-01-01
    Description: Deep-sea benthic communities and their structural and functional characteristics are regulated by surface water processes. Our study focused on the impact of changes in water depth and food supplies on small-sized metazoan bottom-fauna (meiobenthos) along a bathymetric transect (1200–5500 m) in the western Fram Strait. The samples were collected every summer season from 2005 to 2009 within the scope of the HAUSGARTEN monitoring program. In comparison to other polar regions, the large inflow of organic matter to the sea floor translates into relatively high meiofaunal densities in this region. Densities along the bathymetric gradient range from approximately 2400 ind. 10 cm-2 at 1200 m to approximately 300 ind. 10 cm-2 at 4000 m. Differences in meiofaunal distribution among sediment layers (i.e., vertical profile) were stronger than among stations (i.e., bathymetric gradient). At all the stations meiofaunal densities and number of taxa were the highest in the surface sediment layer (0–1 cm), and these decreased with increasing sediment depth (down to 4–5 cm). However, the shape of the decreasing pattern differed significantly among stations. Meiofaunal densities and taxonomic richness decreased gradually with increasing sediment depth at the shallower stations with higher food availability. At deeper stations, where the availability of organic matter is generally lower, meiofaunal densities decreased sharply to minor proportions at sediment depths already at 2–3 cm. Nematodes were the most abundant organisms (60–98%) in all the sediment layers. The environmental factors best correlated to the vertical patterns of the meiofaunal community were sediment-bound chloroplastic pigments that indicate phytodetrital matter. Highlights • Small-scale heterogeneity is the main source of variation in meiofauna community. • Trophic conditions influence vertical patterns of meiofauna distribution. • Meiofauna abundance and biomass decrease with increasing water depth.
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  • 7
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    Appraisal of TEX86 and TEXL86 thermometries in subpolar and polar regions (2014)
    Elsevier
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    Publication Date: 2024-01-01
    Description: TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) is a sea surface temperature (SST) proxy based on the distribution of archaeal isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs). In this study, we appraise the applicability of TEX86 and View the MathML sourceTEX86L in subpolar and polar regions using surface sediments. We present TEX86 and View the MathML sourceTEX86L data from 160 surface sediment samples collected in the Arctic, the Southern Ocean and the North Pacific. Most of the SST estimates derived from both TEX86 and View the MathML sourceTEX86L are anomalously high in the Arctic, especially in the vicinity of Siberian river mouths and the sea ice margin, plausibly due to additional archaeal contributions linked to terrigenous input. We found unusual GDGT distributions at five sites in the North Pacific. High GDGT-0/crenarchaeol and GDGT-2/crenarchaeol ratios at these sites suggest a substantial contribution of methanogenic and/or methanotrophic archaea to the sedimentary GDGT pool here. Apart from these anomalous findings, TEX86 and View the MathML sourceTEX86L values in the surface sediments from the Southern Ocean and the North Pacific do usually vary with overlaying SSTs. In these regions, the sedimentary TEX86-SST relationship is similar to the global calibration, and the derived temperature estimates agree well with overlaying annual mean SSTs at the sites. However, there is a systematic offset between the regional View the MathML sourceTEX86L-SST relationships and the global calibration. At these sites, temperature estimates based on the global View the MathML sourceTEX86L calibration are closer to summer SSTs than annual mean SSTs. This finding suggests that in these subpolar settings a regional View the MathML sourceTEX86L calibration may be a more suitable equation for temperature reconstruction than the global calibration.
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  • 8
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    Geochemical and physical constraints for the occurrence of living cold-water corals (2014)
    Elsevier
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    Publication Date: 2023-11-08
    Description: Cold-water coral communities cover a wide range of possible habitats in terms of latitude, ocean basins, and depth, with ongoing studies continually expanding occurrences in various regions of the global ocean. A range of factors determines the formation of cold-water coral reefs, such as physical, hydrochemical, and biological (e.g. food supply) factors. Recently, more and more modeling studies have emerged using a variety of mathematical approaches have emerged including environmental niche factor analysis (ENFA) and predictive habitat suitability models. However, only few studies have attempted to characterize the underlying suite of hydro-biogeochemical and physical constraints of cold-water coral reefs and to differentiate between pristine reef growth vs. sites with reduced or no coral occurrences. This study concentrates on new data and a compilation of existing data sets on the physical and chemical properties in the NE Atlantic and the Mediterranean. It explores the influence of ambient bottom waters and its characteristics on living cold-water reefs and mounds formed by Lophelia pertusa. Several questions are addressed: (1) what are the physical and geochemical boundary conditions of living cold-water corals? (2) Do these geochemical parameters correlate with proposed physical prerequisites? (3) Is there a general difference in the signature of living and dead coral sites?
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  • 9
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    Oxygen variance and meridional oxygen supply in the Tropical North East Atlantic oxygen minimum zone (2014)
    Springer
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    Publication Date: 2023-11-08
    Description: The distribution of the mean oceanic oxygen concentration results from a balance between ventilation and consumption. In the eastern tropical Pacific and Atlantic, this balance creates extended oxygen minimum zones (OMZ) at intermediate depth. Here, we analyze hydrographic and velocity data from shipboard and moored observations, which were taken along the 23°W meridian cutting through the Tropical North East Atlantic (TNEA) OMZ, to study the distribution and generation of oxygen variability. By applying the extended Osborn–Cox model, the respective role of mesoscale stirring and diapycnal mixing in producing enhanced oxygen variability, found at the southern and upper boundary of the OMZ, is quantified. From the well-ventilated equatorial region toward the OMZ core a northward eddy-driven oxygen flux is observed whose divergence corresponds to an oxygen supply of about 2.4 μmol kg−1 year−1 at the OMZ core depth. Above the OMZ core, mesoscale eddies act to redistribute low- and high-oxygen waters associated with westward and eastward currents, respectively. Here, absolute values of the local oxygen supply 〉10 μmol kg−1 year−1 are found, likely balanced by mean zonal advection. Combining our results with recent studies, a refined oxygen budget for the TNEA OMZ is derived. Eddy-driven meridional oxygen supply contributes more than 50 % of the supply required to balance the estimated oxygen consumption. The oxygen tendency in the OMZ, as given by the multidecadal oxygen decline, is maximum slightly above the OMZ core and represents a substantial imbalance of the oxygen budget reaching about 20 % of the magnitude of the eddy-driven oxygen supply.
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  • 10
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    Post-glacial time series of explosive eruptions and associated changes in the magma plumbing system of Lonquimay Volcano, South Central Chile (2014)
    Springer
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    Publication Date: 2023-11-08
    Description: The Lonquimay volcanic complex (LVC) in the high Southern Andes comprises a stratocone and NE-trending flank-cone alignments. Numerous effusive and explosive volcanic eruptions characterize its post-glacial magmatic activity. Our tephrostratigraphic record, pre-dating the four historically documented eruptions, comprises 22 dated pyroclastic deposits that are used to constrain repose time distribution and eruption probability of the LVC magmatic system. Statistical examination of the stratigraphy-based eruption time series yields probabilities of 20–50 % for at least one explosive (VEI ≥ 3) eruption within the next 100 years as of 2011. The tephra deposits are subdivided into three petrographic groups: a felsic group (Lonquimay colored-pumice tephra, LCPT), an intermediate population (Lonquimay gray pumice tephra, LGPT), and a mafic member (Lonquimay dark scoria tephra, LDST). The distribution of these petrographic groups through the LVC tephrostratigraphy is linked to the observed changes in repose times. LDST-deposits as well as deposits compositionally zoned from LCPT to LGPT dominate the lower part of the stratigraphy for which recurrence times are short (RTmean = 417 ± 169a). Deposits younger than 6,000 b2k (years before 2000 AD) have dominantly LCPT and minor LDST compositions, no longer contain LGPT, and repose times are significantly longer (RTmean = 1,350 ± 310a). We interpret the change in eruption regime to result from a rearrangement in the magma storage and plumbing system. Thermobarometric calculations based on cpx–liquid equilibria and amphibole compositions reveal three distinct magma storage levels: the mafic LDST derive from mid crustal storage (P mean = 476 ± 95 MPa, T mean = 1,073 ± 24 °C), felsic LCPT mainly erupted from upper-crustal level (P mean = 86 ± 49 MPa, T mean = 936 ± 24 °C), whereas LGPT samples yield intermediate storage depths (P mean = 239 ± 100 MPa, T mean = 1,013 ± 17 °C). Magma contributions from this intermediate reservoir are restricted to 〉6,000 b2k when the Lonquimay plumbing system was in a regime of short repose times; disappearance of the intermediate reservoir coincides with the change to longer repose times between eruptions.
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