Sediment accumulation rates and carbon fluxes to bottom sediments at the Western Bransfield Strait (Antarctica)

Mean sediment and carbon accumulation rates in the western Bransfield Strait, during the last ca. 100 years, were determined at three sites by using Pb-210 as a radiotracer of sedimentation processes. Pb-210 profiles showed moderate mixing in the upper 8.5-12 cm, which was attributed to bioturbation. Sediment accumulation rates calculated assuming no mixing below the surface mixed layer (SML) were found to be relatively high (between 0.03 and 0.09 gcm- 2 -1), in good agreement with previously reported data based on both Pb-210 and C-14 dating in surrounding areas. These results, together with the calculated excess Pb-210 fluxes to the bottom sediments and the Pb-210 and Po-210 distributions in the water column, indicated the presence of a large net advective flux of material in the area, highlighting the importance of glacial related sedimentation processes in this semi-enclosed sea. Carbon in bottom sediments was mainly organic, and its content was moderately low (0.65-1.25%), being slightly higher within the SML, reflecting the presence of inhabiting organisms, However, organic carbon (OC) accumulation fluxes (3.1-6.7 gC m(-2) yr(-1)) were considerable, due to the high sediment accumulation rates. Pb-210 dated profiles allowed us to estimate the amount of carbon exported from the water column and buried in the bottom sediment, which represents about 3-7% of the mean annual primary production in the euphotic layer of the Bransfield Strait. The burial efficiency of OC in the sediment was estimated to be approximately 60 80%. (C) 2001 Published by Elsevier Science Ltd.