Composition of organic matter from water, suspended matter, and bottom sediments of Nha Trang Bay, South China Sea

This research has been carried out in the Nha Trang Bay (Southern Vietnam, South China Sea) at a section from the estuary of the Cai River to the marine part of the bay, as well as in the area of coral reefs. River- and sea waters, suspended matter, and bottom sediments are studies. Data on dissolved organic carbon and total nitrogen in water are obtained. Organic carbon concentration is estimated in suspended matter; organic carbon and molecular and group compositions of n-alkanes are determined in bottom sediments. Molecular and group compositions of n-alkanes in bottom sediments of the landfill made it possible to identify three types of organic matter (OM): marine, mixed, and mainly of terrigenous origin. All these types of OM are closely related to specificity of sedimentation and hydrodynamics of waters in this area.

Changes in bottom water corrosiveness and carbonate ion concentrations in the sub-Antarctic Atlantic during the last glacial period

The glacial climate system transitioned rapidly between cold (stadial) and warm (interstadial) conditions in the Northern Hemisphere. This variability, referred to as Dansgaard-Oeschger variability, is widely believed to arise from perturbations of the Atlantic Meridional Overturning Circulation. Evidence for such changes during the longer Heinrich stadials has been identified, but direct evidence for overturning circulation changes during Dansgaard-Oeschger events has proven elusive. Here we reconstruct bottom water [CO3]2- variability from B/Ca ratios of benthic foraminifera and indicators of sedimentary dissolution, and use these reconstructions to infer the flow of northern-sourced deep water to the deep central sub-Antarctic Atlantic Ocean. We find that nearly every Dansgaard-Oeschger interstadial is accompanied by a rapid incursion of North Atlantic Deep Water into the deep South Atlantic. Based on these results and transient climate model simulations, we conclude that North Atlantic stadial-interstadial climate variability was associated with significant Atlantic overturning circulation changes that were rapidly transmitted across the Atlantic. However, by demonstrating the persistent role of Atlantic overturning circulation changes in past abrupt climate variability, our reconstructions of carbonate chemistry further indicate that the carbon cycle response to abrupt climate change was not a simple function of North Atlantic overturning.

(Table 2) Distribution of alkenone unsaturation index UK37 of the eastern North Atlantic

This paper reports the concentrations and within-class distributions of long-chain alkenones and alkyl alkenoates in the surface waters (0-50 m) of the eastern North Atlantic, and correlates their abundance and distribution with those of source organisms and with water temperature and other environmental variables. We collected these samples of >0.8 µm particulate material from the euphotic zone along the JGOFS 20°W longitude transect, from 61°N to 24°N, during seven cruises of the UK-JGOFS Biogeochemical Ocean Flux Study (BOFS) in 1989-1991; the biogeographical range of our 53 samples extends from the cold (<10°C), nutrient-rich and highly productive subarctic waters of the Iceland Basin to the warm (>25°C) oligotrophic subtropical waters off Africa. Surface water concentrations of total alkenone and alkenoates ranged from <50 ng/l in oligotrophic waters below 40°N to 2000-4500 ng/l in high latitude E. huxleyi blooms, and were well correlated with E. huxleyi cell densities, supporting the assumption that E. huxleyi is the predominant source of these compounds in the present day North Atlantic. The within-class distribution of the C37 and C38 alkenones and C36 alkenoates varied strongly as a function of temperature, and was largely unaffected by nutrient concentration, bloom status and other surface water properties. The biosynthetic response of the source organisms to growth temperature differed between the cold (<16°C) waters above 47°N and the warmer waters to the south. In cold (<16°C) waters above 47°N, the relative amounts of alkenoates and C38 alkenones synthesized was a strong function of growth temperature, while the unsaturation ratio of the alkenones (C37 and C38) was uncorrelated with temperature. Conversely, in warm (>16°C) waters below 47°N, the relative proportions of alkenoates and alkenones synthesized remained constant with increasing temperature while the unsaturation ratios of the C37 and C38 methyl alkenones (Uk37 and Uk38Me, respectively) increased linearly. The fitted regressions of Uk37 and Uk38Me versus temperature for waters >16°C were both highly significant (r**2 > 0.96) and had identical slopes (0.057) that were 50% higher than the slope (0.034) of the temperature calibration of Uk37 reported by Prahl and Wakeham (1987; doi:10.1038/330367a0) over the same temperature range. These observations suggest either a physiological adjustment in biochemical response to growth temperature above a 16-17°C threshold and/or variation between different E. huxleyi strains and/or related species inhabiting the cold and warm water regions of the eastern North Atlantic. Using our North Atlantic data set, we have produced multivariate temperature calibrations incorporating all major features of the alkenone and alkenoate data set. Predicted temperatures using multivariate calibrations are largely unbiased, with a standard error of approximately ±1°C over the entire data range. In contrast, simpler calibration models cannot adequately incorporate regional diversity and nonlinear trends with temperature. Our results indicate that calibrations based upon single variables, such as Uk37, can be strongly biased by unknown systematic errors arising from natural variability in the biosynthetic response of the source organisms to growth temperature. Multivariate temperature calibration can be expected to give more precise estimates of Integrated Production Temperatures (IPT) in the sedimentary record over a wider range of paleoenvironmental conditions, when derived using a calibration data set incorporating a similar range of natural variability in biosynthetic response.

Concentrations of aliphatic hydrocarbons and hexachlorocyclohexane isomers in under-ice water, snow, and sea ice from the Greenland Sea

Data on concentrations of aliphatic hydrocarbons and isomers of hexachlorocyclohexane in specimens of various natural environments (water, snow, and ice) of the Greenland Sea obtained during field studies on the ice breaker Otto Shmidt are presented. Analyses were carried out with gas chromatographs using capillary and packed columns. Concentrations of aliphatic and chlorinated hydrocarbons were higher in snow and ice specimens than in sea water and were also higher in less saline water beneath ice. It is concluded that pollutants in this ocean area are at the background level.

Organic geochemistry of water and bottom sediments during a seasonal flood in 2006 in the North Dvina River estuary

Heavy contaminant load released into the Northern Dvina River during flooding increased the concentrations of aliphatic (AHC) and polcyclic aromatic (PAH) hydrocarbons in water and bottom sediments. The composition of hydrocarbons was different from that of the summer low flow season. The concentrations of dissolved and particulate AHC ranged from 12 to 106 and from 192 to 599 µg/l, respectively, and bottom sediments contained from 26.2 to 329 µg/g AHC and 4 to 1785 ng/g PAH. As the transformation of AHC occurred at low spring temperatures, the alkane composition was shown to be dominated by terrigenous compounds, whereas more stable PAH showed elevated contents of petrogenic and pyrogenic compounds. It was also shown that the Northern Dvina-Dvina Bay geochemical barrier prevents contaminant input into the White Sea, i.e., acts as a marginal filter.

Foraminiferal abundance, carbonat concentration and dissolution index of sediment core W9903B-51GC

In order to investigate the paleoceanographic record of dissolution of calcium carbonate (CaCO3) in the central equatorial Pacific Ocean, we have studied the relationship between three indices of foraminiferal dissolution and the concentration and accumulation of CaCO3, opal, and Corg in Core WEC8803B-GC51 (1.3°N, 133.6°W; 4410 m). This core spans the past 413 kyr of deposition and moved in and out of the lysoclinal transition zone during glacial-interglacial cycles of CaCO3 production and dissolution. The record of dissolution intensity provided by foraminiferal fragmentation, the proportion of benthic foraminifera, and the foraminiferal dissolution index consistently indicates that the past corrosion of pelagic CaCO3 in the central equatorial Pacific does not vary with the observed sedimentary concentration of CaCO3. Although there is a weak low-frequency variation (~100 kyr) in dissolution intensity, it is unrelated to sedimentary CaCO3 concentration. There are many shorter-lived episodes where high CaCO3 concentration is coincident with poor foraminiferal preservation, and where, conversely, low CaCO3 concentration is coincident with superb foraminiferal preservation. Spectral analyses indicate that dissolution maxima consistently lagged glacial maxima (manifest by the SPECMAP delta18O stack) in the 100-kyr orbital band. Additionally, there is no relationship between dissolution and the accumulation of biogenic opal or Corg or between dissolution and the burial ratio of Corg/CINorg (calculated from Corg and CaCO3). Because previous studies of this core strongly suggest that surface water productivity varied closely with CaCO3 accumulation, both the mechanistic decoupling of carbonate dissolution from CaCO3 concentration (and from biogenic accumulation) and the substantial phase shift between dissolution and global glacial periodicity effectively obscure any simple link between export production, CaCO3 concentration, and dissolution of sedimentary CaCO3.

Fractional abundance and indices for brGDGTs and crenarchaeol in dust samples, surface water samples and surface sediment samples

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids produced by soil bacteria and occur in near coastal marine sediments as a result of soil organic matter input. Their abundance relative to marine-derived crenarchaeol, quantified in the BIT index, generally decreases offshore. However, in distal marine sediments, low relative amounts of brGDGTs can often still be observed. Sedimentary in situ production as well as dust input have been suggested as potential, though as yet not well constrained, sources. In this study brGDGT distributions in dust were examined and compared with those in distal marine sediments. Dust was sampled along the equatorial West African coast and brGDGTs were detected in most of the samples, albeit in low abundance. Their degree of methylation and cyclisation, expressed in the MBT' (methylation index of branched tetraethers) and DC (degree of cyclisation) indices, respectively, were comparable with those for African soils, their presumed source. Comparison of DC index values for brGDGTS in global soils, Congo deep-sea river fan sediments and dust with those of distal marine sediments clearly showed, however, that distal marine sediments had significantly higher values. This distinctive distribution is suggestive of sedimentary in situ production as a source of brGDGTs in marine sediments, rather than dust input. The presence of in situ produced brGDGTs in marine sediments means that caution should be exercised when applying the MBT'-CBT palaeothermometer to sediments with low BIT index values, i.e. < 0.1, based on our dataset.

Compression and expansion index and void ratio of samples from Lomonosov Ridge and Yermak Plateau

With the coupled use of multibeam swath bathymetry, high-resolution subbottom profiling and sediment coring from icebreakers in the Arctic Ocean, there is a growing awareness of the prevalence of Quaternary ice-grounding events on many of the topographic highs found in present water depths of <1000 m. In some regions, such as the Lomonosov Ridge and Yermak Plateau, overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin. However, there exists no comprehensive analysis of the geotechnical properties of these sediments, or how their inferred stress state may be related to different glacigenic processes or types of ice-loading. Here we combine geophysical, stratigraphic and geotechnical measurements from the Lomonosov Ridge and Yermak Plateau and discuss the glacial geological implications of overconsolidated sediments. The degree of overconsolidation, determined from measurements of porosity and shear strength, is shown to result from consolidation and/or deformation below grounded ice and, with the exception of a single region on the Lomonosov Ridge, cannot be explained by erosion of overlying sediments. We demonstrate that the amount and depth of porosity loss associated with a middle Quaternary (~ 790-950 thousand years ago - ka) grounding on the Yermak Plateau is compatible with sediment consolidation under an ice sheet or ice rise. Conversely, geotechnical properties of sediments from beneath late Quaternary ice-groundings in both regions, independently dated to Marine Isotope Stage (MIS) 6, indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf.