Mineralogy of northern Indian Ocean surface sediments and of suspended sediments of Indian rivers (Table 2 and 5)

The solid phases from surface sediments, atmospheric dusts, and rivers of the Indian Ocean environment have been analyzed for their clay minerals and quartz. Such data have been used to delimit the transport paths and sources of the detrital minerals in the oceanic deposits. Diagnostic in distinguishing fluvial and eolian inputs to the northern Indian Ocean is a combination of the clay mineral assemblages and of their geographic distributions. River borne solids are the primary components of the Bay of Bengal deposits. The eastern part receives its continental input through the Ganges-Brahmaputra river system, while drainage of the Indian Peninsula by rivers introduces solids to the western part. The former materials are characterized by high illite and chlorite in the clay mineral assemblages; the latter by montmorillonite. The winds over the Bay bear distinctive dust burdens based upon their directions. However, their contributions to the sediments are insignificant. The eastern sector of the Arabian Sea receives major contributions of continental debris from the rivers and the high montmorillonite levels clearly indicate a source in the Indian Peninsula. The rest of the Sea appears to receive most of its land-derived materials from the north, perhaps the desert regions of northern India and West Pakistan, and they are wind-borne. These materials are also transported to the equatorial regions of the Indian Ocean. A gradient in attapulgite, just north of the equator, may indicate an eolian contribution to the Arabian Sea from the African continent. The halogenated hydrocarbon pesticides were assayed in the southwest monsoon winds and enter the Bay of Bengal at levels of a half ton per month, an amount comparable to those introduced by other wind and river systems to the marine environment.

(Table 1) Granulometry of sediments obtained during research cruises of Tender Ems and Hermann Wattenberg in Kiel Bay, Baltic Sea

Sediment cores, mainly push-box samples, from a channel system of the Kiel Bay are described. The channel system, of glacial and fluviatile origin, is important for the distribution of heavy, salt-rich water entering from the North Sea through the Great Belt, Sediment erosion and transport in the channels is due entirely to currents, because the bottom lies too deep for wave action. The sediments of these channels proude information about current velocities and their frequencies. Grain-size, minor sediment structures and thickness of the sediments vary remarkably. Nevertheless, for those parts of the channels where stronger currents occur, some typical features can be shown. These include: small thickness of the marine sediments, erosional effects upon the underlying sediments, and poor sorting of the sediments, whereby fine and coarse fractions are mixed very intensively. Besides strong currents which effect the bottom configuration and deposits in the Fehmarn Belt, there must exist longer periods of low current action upon the bottom, although current measurements show that current velocities higher than 50 cm/sec at some meters above the bottom occur frequently during the year. In the channel to the west of the southern mouth of Great Belt, coarse sediments were found only in elongate, deep throughs within the channels. This is believed to be due to an acceleration of the entering tongues of heavy water as they flow downslope into the throughs. Minor structures of two sediment cores were made visible by X-ray photographs. These showed that the mixing of sand and clayey material is due partly to bottom organisms and that the mud, which appears 'homogeneous' to the bare eye, is built up of fine wavy laminae which are also partly destroyed by boring animals. At another location in the channel system, there was found a thin finegrained layer of marine sediment resting upon peat. Palynological dating of the peat shows that very little older sediment could have been eroded. The current velocities, therefore, must be too low for the movement of coarse material and erosion, but too high to allow the Sedimentation of a lot of fine-grained material.

Distribution of opal and quartz in surface sediments from the subtropical southeastern Pacific (Table 1)

The distribution patterns of opal and quartz on the ocean floor of the subtropical southeastern Pacific have been defined by analyzing 59 surface-sediment samples. The opal distribution resembles that of primary productivity in the surface waters, except along the Peruvian and northern Chilean coasts, where dilution reduces opal values. The distribution pattern of quartz represents both eolian and fluvial transport. Quartz distribution extends out as a tongue in the same direction and position as the prevailing southeast trade winds. Along the South American coast, high quartz concentrations are found in patches near shore and decrease rapidly seaward.

Biogenic components, major, trace and rare earth elements of equatorial Pacific Ocean surface sediments (Table 1)

We have analyzed the major, trace, and rare earth element composition of surface sediments collected from a transect across the Equator at 135°W longitude in the Pacific Ocean. Comparing the behavior of this suite of elements to the CaCO3, opal, and Corg fluxes (which record sharp maxima at the Equator, previously documented at the same sampling stations) enables us to assess the relative significance of the various pathways by which trace elements are transported to the equatorial Pacific seafloor. The 1. (1) high biogenic source at the Equator, associated with equatorial divergence of surface water and upwelling of nutrient-rich water, and 2. (2) high aluminosilicate flux at 4°N, associated with increased terrigenous input from elevated rainfall at the Intertropical Convergence Zone (ITCZ) of the tradewinds, are the two most important fluxes with which elemental transport is affiliated. The biogenic flux at the Equator transports Ca and Sr structurally bound to carbonate tests and Mn primarily as an adsorbed component. Trace elements such as Cr, As, Pb, and the REEs are also influenced by the biogenic flux at the Equator, although this affiliation is not regionally dominant. Normative calculations suggest that extremely large fluxes of Ba and P at the Equator are carried by only small proportions of barite and apatite phases. The high terrigenous flux at the ITCZ has a profound effect on chemical transport to the seafloor, with elemental fluxes increasing tremendously and in parallel with Ti. Normative calculations, however, indicate that these fluxes are far in excess of what can be supplied by lattice-bound terrigenous phases. The accumulation of Ba is greater than is affiliated with biogenic transport at the Equator, while the P flux at the ITCZ is only 10% less than at the Equator. This challenges the common view that Ba and P are essentially exclusively associated with biogenic fluxes. Many other elements (including Mn, Pb, As, and REEs) also record greater accumulation beneath the ITCZ than at the Equator. Thus, adsorptive scavenging by terrigenous paniculate matter, or phases intimately associated with them, appears to be an extremely important process regulating elemental transport to the equatorial Pacific seafloor. These findings emphasize the role of vertical transport to the sediment, and provide additional constraints on the paleochemical use of trace elements to track biogenic and terrigenous fluxes.

Clay mineral analysis of sediments from the Amundsen Sea

The Amundsen Sea embayment is a probable site for the initiation of a future collapse of the West Antarctic Ice Sheet. This paper contributes to a better understanding of the transport pathways of subglacial sediments into this embayment at present and during the last glacial period. It discusses the clay mineral composition of sediment samples taken from the seafloor surface and marine cores in order to decipher spatial and temporal changes in the sediment provenance. The most striking feature in the presentday clay mineral distribution is the high concentration of kaolinite, which is mainly supplied by the Thwaites Glacier system and indicates the presence of hitherto unknown kaolinite-bearing sedimentary strata in the hinterland, probably in the Byrd Subglacial Basin. The main illite input is via the Pine Island Glacier. Smectite originates from the erosion of volcanic rocks in Ellsworth Land and western Marie Byrd Land. The clay mineral assemblages in diamictons deposited during the last glacial period are distinctly different from those in corresponding surface sediments. This relationship indicates that glacial sediment sources were different from modern ones, which could reflect changes in the catchment areas of the glaciers and ice streams.

Mineralogy of sea-floor surface sediments, Sonne cruise SO202/1 to the North Pacific and Bering Sea

During expedition 202 of research vessel SONNE in 2009, 39 sea-floor surface sediments were sampled over a wide area across the North Pacific and the Bering Sea, which are well suited as reference archives of modern environmental processes. In this study, we used the samples to infer the documentation of land-ocean linkages of terrigenous sediment supply. We followed an integrated approach of grain-size analysis, bulk mineralogy, and clay mineralogy in combination with statistical data evaluation (end-member modelling of grain-size data, fuzzy-cluster analysis of mineralogical data), in order to identify the significant sources and modes of sediment transport in an overregional context. We also compiled literature data on clay mineralogy and updated those with the new data. Today, two processes of terrigenous sediment supply prevail in the study area: far-distant aeolian sediment supply to the pelagic North Pacific as well as hemipelagic sediment dispersal from nearby land sources by ocean currents along the continental margins and island arcs of the study area. The aeolian particles show the finest grain sizes (clay and fine silt), while the hemipelagic sediments have high abundances of sortable silt, particles >10 microns.

(Table 1) Sr, Nd and Os isotopic composition from marine sediments of the Bengal Fan

Sr, Nd, and Os isotopic data are presented for sediments from diverse locations in the Bay of Bengal. These data allow the samples to be divided into three groups, related to their sedimentary contexts. The first group, mainly composed of sediments from the shelf off Bangladesh and the currently active fan, has Sr and Nd characteristics consistent with a dominantly Himalayan source. Their 187Os/188Os ratios (~1.2-1.5) show that the average detrital material delivered by the Ganga-Brahmaputra (G-B) river system is not unusually radiogenic. A large difference in 187Os/188Os ratio exists between these Bengal Fan sediments and Ganga bedloads (187Os/188Os ~2.5, Pierson-Wickmann et al. (2000, doi:10.1016/S0012-821X(00)00003-0)). This difference mainly reflects addition of a less radiogenic Brahmaputra component, though mineralogical sorting and loss of radiogenic Os during transport may also play some role. The second sample group contains sediments from elsewhere in the Bay, particularly those located on the continental slope. They display Os isotopic compositions (0.99-1.11) similar to that of present seawater and higher Os and Re concentrations. These characteristics suggest the presence of a large hydrogenous contribution, consistent with the lower sedimentation rate of these samples. Sr and Nd ratios indicate that a significant fraction of these sediments is derived from erosion of non-Himalayan sources, such as the Indo-Burman range. These observations could be explained by the deflection of sediments from the G-B river system by westward currents in the head of the Bay. The third group contains only one sample, but shows that in addition to a Himalayan source, sediment discharge from Sri Lanka may influence the detrital component in the distal part of the fan. The similarity between the isotopic compositions of the group I R/V Sonne samples and those of Ocean Drilling Program Leg 116 (France-Lanord et al., 1993; Reisberg et al., 1997, doi:10.1016/S0012-821X(00)00003-0) suggests that the material eroding in the Himalayas has been roughly constant since the Miocene. The high Os isotopic ratios of leachates of both Sonne group I and Miocene Leg 116 sediments imply that much of the leachable highly radiogenic Os component was conserved during transport through the estuary or interaction with seawater. In constrast, samples with lower, but still relatively high, sedimentation rates (Sonne groups II and III and Pliocene Leg 116) seem to have significantly adsorbed or exchanged Os and Re with seawater. This suggests that in some cases the Os isotopic ratios of leachates of detrital sediments can be used to constrain the ancient marine Os record, or conversely, to date unfossiliferous sediments.

Strontium and neodymium concentrations and isotopic compositions of Arctic marine sediments

Sr and Nd isotopic compositions of Arctic marine sediments characterize changes of sediment source regions and trace shelf-ocean particle pathways during glacial-interglacial transitions in the eastern Arctic Ocean. In the 140-ka sedimentary record of a marine core from Yermak Plateau, north of Svalbard, 87Sr/86Sr ratios and epsion-Nd values vary between 0.717 and 0.740 and 39.3 and 314.9, respectively. Sr and Nd isotopic composition both change characteristically during glacial-interglacial cycles and are correlated with the extension of the Svalbard/Barents Sea ice sheet (SBIS). The downcore variation in Sr and Nd isotopic composition indicates climatically induced changes in sediment provenance from two isotopically distinct end-members: (1) Eurasian shelf sediments as a distal source; and (2) Svalbard bedrock as a proximal source that coincide with a change in transport mechanism from sea ice to glacial ice. During glacier advance from Svalbard and intensified glacial bedrock erosion, epsion-Nd values decrease gradually to a minimum value of 314.9 due to increased input of crystalline Svalbard bedrock material. During glacial maxima, the SBIS covered the entire Barents Sea shelf and supplied increasing amounts of Eurasian shelf material to the Arctic Ocean as ice rafted detritus (IRD). Epsion-Nd values in glacial sediments reach maximum values that are comparable to the average value of modern Eurasian shelf and sea ice sediments (epsion-Nd = 310.3). This confirms ice rafting as a major sediment transport mechanism for Eurasian shelf sediments into the Arctic Ocean and trace a sediment origin from the Kara Sea/Laptev Sea shelf area. After the decay of the shelf-based SBIS, the glacial shelf sediment spikes during glacial terminations I (epsion-Nd = 310.6) and II (epsion-Nd = 310.1) epsion-Nd values rapidly decrease to values of 312.5 typical for interglacial averages. The downcore Sr isotopic composition is anticorrelated to the Nd isotopic composition, but may be also influenced by grain-size effects. In contrast, the Nd isotopic composition in clay- to silt-size fractions of one bulk sediment sample is similar to within 0.3-0.8 epsion-Nd units and seems to be a grain-size independent provenance tracer.

Compilation of organic carbon distribution and sedimentology in the surface sediments on the continental margin offshore southwestern Africa

In this study we demonstrate the relevance of lateral particle transport in nepheloid layers for organic carbon (OC) accumulation and burial across high-productive continental margins. We present geochemical data from surface sediments and suspended particles in the bottom nepheloid layer (BNL) from the most productive coastal upwelling area of the modern ocean, the Benguela upwelling system offshore southwest Africa. Interpretation of depositional patterns and comparison of downslope trends in OC content, organic matter composition, and 14C age between suspended particles and surface sediments indicate that lateral particle transport is the primary mechanism controlling supply and burial of OC. We propose that effective seaward particle transport primarily along the BNL is a key process that promotes and maintains local high sedimentation rates, ultimately causing high preservation of OC in a depocenter on the upper slope offshore Namibia. As lateral transport efficiently displaces areas of enhanced OC burial from maximum production at highly productive continental margins, vertical particle flux models do not sufficiently explain the relationship between primary production and shallow-marine OC burial. On geologic time scales, the widest distribution and strongest intensity of lateral particle transport is expected during periods of rapid sea-level change. At times in the geologic past, widespread downslope lateral transport of OC thus may have been a primary driver of enhanced OC burial at deeper continental slopes and abyssal basins.

Bacteriohopanepolyol biomarkers of sediments from the Congo fan

The transport and deposition of terrestrially derived organic matter (TOM) into the ocean is an important but poorly constrained aspect of the modern global carbon cycle. A preliminary study of Late Quaternary sediments from the Congo deep sea fan (ODP leg 175, site 1075, 2 km water depth) and four surface samples from associated cores has confirmed the presence of proposed soil-specific bacteriohopanepolyol biomarkers (BHPs) including adenosylhopane, in samples to a depth of 89 m. Concentrations of soil marker BHPs are high in the upper sediment section (to 49 m) and the closest related surface sample (4913), supporting the case for these molecular markers as novel proxies for soil organic carbon (SOC) supply via riverine transport and subsequent burial. Distinct peaks for the markers at about 21, 34 and 60 m below surface level tentatively imply that the rate of TOM discharge from tropical Africa significantly increased at these times, possibly associated with periods of reduced soil stability in the Congo catchment.

Magnetic susceptibility and ice-rafted debris in surface sediments of the Nordic Sea

Magnetic susceptibility and ice-rafted debris of surface sediments in the Nordic Seas were investigated to reconstruct source areas and recent transport pathways of magnetic minerals. From the distribution of magnetic susceptibility and ice-rafted debris and published data on petrographic tracers for iceberg drift, we reconstructed a counter-clockwise iceberg drift pattern during cooler phases in the Holocene, which is similar to conceptual and numerical models for Weichselian iceberg drift. The release of basaltic debris at Scoresby Sund played a significant role for the magnetic signature of stadial/interstadial events during isotope stage 3 recorded in sediment cores of the Nordic Seas.