PARTICLE FLUXES, BENTHIC PROCESSES AND THE PALEOENVIRONMENTAL RECORD IN THE NORTHERN WEDDELL SEA

At the northern edge of the Weddell Gyre, Antarctica, fine-grained sed iments accumulate beneath eastward-flowing Weddell Sea Bottom Water. W e report on sediment trap material and core tops from four sites, with relevant water-column data. In this cold, low-productivity oceanograp hic setting it is the processes in the benthic nepheloid layer (resusp ension, transport, winnowing of fines) and in the upper few cm of sedi ment (bioturbation, dissolution of biogenic silica and carbonate, degr adation of organic matter) that dominate the palaeoenvironmental recor d. Biogenic productivity is low and seasonal because of sea-ice cover; terrigenous sediment is supplied by resuspension of Weddell Sea slope and rise sediments and by ice-rafting. The benthic nepheloid layer is up to 150 m thick, with particulate matter concentrations of up to 0. 51 mg/l. Sediment traps moored for 2 years 827 m above the seabed coll ected mainly biogenic opal with well-preserved and diverse diatoms and radiolarians. Traps 21 m above the seabed recorded additional high fl uxes of terrigenous silt and clay. Core tops are terrigenous with very little organic matter or opal except at the northernmost site and a v ery restricted diatom assemblage. Core tops consist of silty clay or s andy silty clay, depending on current regime; the proportion of fine s and is related to the annual frequency of high ( > 15 cm/sec) current speeds at each site. AMS C-14 dates on organic carbon in sediment trap s are 965+/-50 and 1895+/-55 radiocarbon years, reflecting the high re servoir age of Southern Ocean surface waters. Core top ages of particu late organic carbon are 10500 and 13000 calendar years B.P. These high ages are related to the glacial-age source of resuspended slope and r ise sediments. Cores from this area contain a textural record of Wedde ll Sea Bottom Water flow, but only fragmentary data on palaeo-surface conditions. (C) 1998 Published by Elsevier Science Ltd.