Composition of organic matter in bottom sediments from the Antarctic sector of the Atlantic Ocean

We identify geochemical features of sedimentary organic matter in various morphostructural zones of the Antarctic sector of the Atlantic. We present background geochemical organic parameters for shelf and deep-sea sediments from the Weddell and Scotia Seas and the Bransfield Strait. Geochemical organic parameters are good indicators of environmental and facial variations in sediments and could be used for environmental monitoring of the World Ocean.

Fe-Mn crusts from the Atlantic Ocean

Mineral and chemical compositions of a set of crust samples collected from the North, Central and South Atlantic were examined by means of analytical electron microscopy and ICP-MS, chemical, and microchemical elemental analysis. Vernadite, asbolane, and goethite are dominant mineral phases of the crusts, ferrihydrite is minor, hematite and feroxyhyte are rare. The samples show wide variability in major and trace element contents; however, their characteristic geochemical signatures indicate hydrogenous origin. A comparison between compositions of oceanic hydrogenous and hydrothermal crusts and metalliferous hydrothermal sediments from different ocean areas suggests that the geochemical approach may be insufficient in some cases and fail to identify hydrothermal input in ferromanganese crusts of mixed composition.

(Table 2) Chemical composition of Fe-Mn nodules and volcanic glass in sediments of the Atlantic Ocean

Distribution pattern of titanium in Quaternary sediments of the Atlantic Ocean are examined on the base of 750 Ti and Fe determinations, and several dozen of complete chemical analyses. Analyses of surface sediment samples and sediment cores up to 6 m long were made. Stratigraphic levels from Middle Pleistocene to Holocene were identified from planktonic foraminifera. Distributions of Ti in recent and Pleistocene deposits were mapped. High titanium contents were found in sediments containing products of basalt vulcanism and in iron-manganese nodules. To determine origin of titanium concentrations in sediments, Ti/Fe ratios were calculated. Maximal values of this ratio were found in areas of basaltic volcanism and of intensive terrigenous sedimentation.

Benthic organic carbon flux and oxygen penetration depth in the Southern Ocean

For the investigation of organic carbon fluxes reaching the seafloor, oxygen microprofiles were measured at 145 sites in different sub-regions of the Southern Ocean. At eleven sites, an in situ oxygen microprofiler was deployed for the measurement of oxygen profiles and the calculation of organic carbon fluxes. At four sites, both in situ and ex situ data were determined for high latitudes. Based on this dataset as well as on previous published data, a relationship was established for the estimation of fluxes derived by ex situ measured O2 profiles. The fluxes of labile organic matter range from 0.5 to 37.1 mgC m**2/day. The high values determined by in situ measurements were observed in the Polar Front region (water depth of more than 4290 m) and are comparable to organic matter fluxes observed for high-productivity, upwelling areas like off West Africa. The oxygen penetration depth, which reflects the long-term organic matter flux to the sediment, was correlated with assemblages of key diatom species. In the Scotia Sea (~3000 m water depth), oxygen penetration depths of less than 15 cm were observed, indicating high benthic organic carbon fluxes. In contrast, the oxic zone extends down to several decimeters in abyssal sediments of the Weddell Sea and the southeastern South Atlantic. The regional pattern of organic carbon fluxes derived from micro-sensor data suggest that episodic and seasonal sedimentation pulses are important for the carbon supply to the seafloor of the deep Southern Ocean.

(Table 2) Uranium concentrations and isotopic ratios in surface waters of the Atlantic Ocean in April 1977

Uranium concentrations and isotope ratios were measured in thirteen surface-water samples collected across the entire Atlantic Ocean. The mean isotope ratio was 1.15+/-0.01, and the mean concentration 3.1+/-0.2 µg/l.