ALBERT

Description: Organic geochemical and visual kerogen analyses were carried out on approximately 50 samples from Leg 81 (Rockall Plateau, North Atlantic). The sediments are from four sites (Sites 552-555), Pleistocene to Paleocene in age, and represent significantly different depositional environments and sources of organic matter. The Pleistocene glacial-interglacial cycles show differences in sedimentary organic matter based on Rock-Eval pyrolysis, organic phosphorus, and pyrolysis/mass-spectrometry analyses. Glacial samples contain more organic carbon, with a larger proportion of reworked organic matter. This probably reflects increased erosion of continental and shelf areas as a result of low sea level stands. Inter glacial samples contain a larger proportion of marine organic matter as determined by organic phosphorus and pyrolysis analyses. This immature, highly oxidized marine organic matter may be associated with the skeletal organic matrix of calcareous organisms. In addition, Rock-Eval data indicate no significant inorganic-carbonate contribution to the S3 pyrolysis peak. The Pliocene-Miocene sediments consist of pelagic, biogenic carbonates. The organic matter is similar to that of the Pleistocene interglacial periods; a mixture of oxidized marine organic matter and reworked, terrestrial detritus. The Paleocene-Oligocene organic matter reflects variations in source and depositional factors associated with the isolation of Rockall from Greenland. Paleocene sediments contain primarily terrestrial organic matter with evidence of in situ thermal stress resulting from interbedded lava flows. Late Paleocene and early Eocene organic matter suggests a highly oxidized marine environment, with major periods of deposition of terrestrially derived organic matter. These fluctuations in organic-matter type are probably the result of episodic shallowing and deepening of Rockall Basins. The final stage of Eocene/Oligocene sedimentation records the accelerating subsidence of Rockall and its isolation from terrestrial sources (Rockall and Greenland). This is shown by the increasingly marine character of the organic matter. The petroleum potential of sediments containing more than 0.5% organic carbon is poor because of their thermal immaturity and their highly oxidized and terrestrial organic-matter composition.

Description: Significantly older 14C ages by 2500-7900 years are found for sedimentary total organic carbon (TOC) when compared to ages of codeposited surface-dwelling foraminifera in the southern Okinawa Trough. This age discrepancy increases with rising sea level since the Last Glacial Maximum. A progressive shift in TOC d13C toward more negative values with rising sea level reflects an increasing fractional contribution of terrestrial organics (soil organics, plant debris, and/or fossil organics) to the buried organic pool. Organic matter previously stored on the East China Sea shelf during sea level lowstand and riverine material from Taiwan may be the sources that cause the d13CTOC to shift to more terrestrial values. During the Holocene when sea level is above -40 m, d13CTOC values stabilize within a narrow range (-22.3 to -22.8 per mil) while age discrepancies continue to increase and less chemically weathered sediments are deposited. The increase in age discrepancy between TOC and foraminifera in the Holocene may be due to a wetter climate that drove higher rates of physical weathering on Taiwan and greater transport rates of fossil organic C-bearing lithogenic sediment to the ocean. The climate impact on the relative delivery of fossil and nonfossil TOC in depositional settings influenced by fluvial sources should be considered in interpretations of sedimentary C isotope records.

Description: This data product contains dissolved silicon concentrations and isotopic composition, major ion concentrations and discharge for streams in Potter Peninsula, King George Island and Commonwealth Stream, McMurdo Dry Valleys, Antarctica.