Organic chemistry of Neogene sediments from ODP Leg 113

Stable carbon and nitrogen isotopic compositions as well as organic carbon and total nitrogen contents of cored material are reported for the Weddell Sea, Ocean Drilling Program (ODP) Sites 689 and 690 (Maud Rise), Site 693 (continental margin), and Site 694 (abyssal plain). Results from both high resolution sampling (up to six samples per section) and low resolution (one sample per section) are documented. In general, these results indicate large changes in the types and amounts of carbon and nitrogen preserved in the sediments of the Weddell Sea region during the past 25 m.y., with an especially important and dramatic event coinciding with the western Antarctic ice-sheet becoming a semi-permanent or permanent feature about 5 Ma.
The overall results may be correlated with the onset of major ice-sheets on West Antarctica, stabilization of the icesheet in the Pliocene and the intensified recycling of organic carbon and total nitrogen, which is possibly the result of increased ice cover. Evidence is also presented for either low production of organic carbon or the presence of a water column, in the eastern Weddell Sea during the early and middle Neogene, which was highly corrosive to organic matter. This condition, together with slow sediment accumulation rates, inhibited the preservation of carbon in the sediments.