Witte, U. GEOMAR Research Center, uwitte@geomar.de

The steep chemical gradients characterizing shallow water sediments are usually less pronounced in well oxygenated deep-sea sediments. During a 3-years study of biogeochemical processes in the abyssal Arabian Sea (3200 - 4500 m), however, striking regional differences in sediment biochemistry as well as macro- and megafaunal community structure have been encountered: in the western Arabian Sea (WAST) chemical gradients are steep: oxygen penetration depth is < 10 mm and nitrate is not available below 3-4 cm. Macrofauna is dominated by ostracods and 3-5 times as abundant as at other stations, extending down to 20 cm sediment depth despite the lack of oxygen. Megafauna, however, is rare and bioturbative activity as inferred from 234 Th and 210 Pb measurements as well as sediment bioroughness is much lower at WAST than at the other stations. In the southern Arabian Sea (SAST) oxygen penetration depth is high and macrofaunal colonisation is restricted to the upper sediment centimeter. Large infaunal organisms occur frequently and Chl a-profiles indicate non-local mixing. The northern and central Arabian Sea depict intermediate conditions. The western Arabian Sea is strongly influenced by the monsoons and stable upwelling filaments extend from the coast of Oman into the open ocean, which is mirrored by very high rates of vertical particle flux (Haake et al 1993). The data set thus provides an excellent opportunity to highlight the mutual relationship between sediment chemistry and benthic community organisation in the deep-sea as well as their relation to vertical food input and bottom-near transport- and exchange processes in the BBL.
Day: Thursday, Feb. 4
Time: 09:00 - 09:15am
Location: Hilton of Santa Fe
Code: SS30FR0900S