ALBERT

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.

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.

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.

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.

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.

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.

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?

Description: Preprocessing software, which converts large instrumental data sets into a manageable format for data analysis, is crucial for the discovery of chemical signatures in metabolomics, chemical forensics, and other signature-focused disciplines. Here, four freely available and published preprocessing tools known as MetAlign, MZmine, SpectConnect, and XCMS were evaluated for impurity profiling using nominal mass GC/MS data and accurate mass LC/MS data. Both data sets were previously collected from the analysis of replicate samples from multiple stocks of a nerve-agent precursor and method blanks. Parameters were optimized for each of the four tools for the untargeted detection, matching, and cataloging of chromatographic peaks from impurities present in the stock samples. The peak table generated by each preprocessing tool was analyzed to determine the number of impurity components detected in all replicate samples per stock and absent in the method blanks. A cumulative set of impurity components was then generated using all available peak tables and used as a reference to calculate the percent of component detections for each tool, in which 100% indicated the detection of every known component present in a stock. For the nominal mass GC/MS data, MetAlign had the most component detections followed by MZmine, SpectConnect, and XCMS with detection percentages of 83, 60, 47, and 41%, respectively. For the accurate mass LC/MS data, the order was MetAlign, XCMS, and MZmine with detection percentages of 80, 45, and 35%, respectively. SpectConnect did not function for the accurate mass LC/MS data. Larger detection percentages were obtained by combining the top performer with at least one of the other tools such as 96% by combining MetAlign with MZmine for the GC/MS data and 93% by combining MetAlign with XCMS for the LC/MS data. In terms of quantitative performance, the reported peak intensities from each tool had averaged absolute biases (relative to peak intensities obtained using instrument software) of 41, 4.4, 1.3 and 1.3% for SpectConnect, MetAlign, XCMS, and MZmine, respectively, for the GC/MS data. For the LC/MS data, the averaged absolute biases were 22, 4.5, and 3.1% for MetAlign, MZmine, and XCMS, respectively. In summary, MetAlign performed the best in terms of the number of component detections; however, more than one preprocessing tool should be considered to avoid missing impurities or other trace components as potential chemical signatures.

Description: Numerous calcium carbonate veins were recovered from the igneous basement of the Early Cretaceous Shatsky Rise during Integrated Ocean Drilling Program (IODP) Expedition 324. The chemical (Sr/Ca, Mg/Ca) and isotopic (87Sr/86Sr, 143Nd/144Nd, !18O, !13C) compositions of these veins were determined to constrain the timing of vein formation. A dominant control by seawater chemistry on calcite composition is evident for most vein samples with variable contributions fromthe basaltic basement. Slightly elevated precipitation temperatures (as inferred from oxygen isotope ratios), indicative of hydrothermal vein formation, are only observed at Site U1350 in the central part of Shatsky Rise. The highest 87Sr/86Sr ratios (least basement influence) of vein samples at each drill site range from 0.70726 to 0.70755 and are believed to reflect the contemporaneous seawater composition during the time of calcite precipitation. In principle, age information can be deduced by correlating these ratios with the global seawater Sr isotope evolution. Since the Sr isotopic composition of seawater has fluctuated three times between the early and mid Cretaceous, no unambiguous precipitation ages can be constrained by this method and vein precipitation could have occurred at any time between ~80 and 140 Ma. However, based on combined chemical and isotopic data and correlations of vein compositionwith formation depth and inferred temperature, we argue for a rather early precipitation of the veins shortly after basement formation at each respective drill site.