Sedimentation of biogenic constituents during the last century in western Bransfield and Gerlache Straits, Antarctica: a relation to currents, primary production, and sea floor relief

Abstract

As part of the FRUELA experiment, 11 sediment cores were recovered from the Bellingshausen Sea, the western Bransfield and Gerlache Straits (Antarctic Peninsula) to determine the spatial distribution of organic carbon (OC), biogenic silica (BSi), and nitrogen (N) in the sediment under regions of known irregular primary production rates (PPRs). OC, BSi, and N contents ranged from 0.3% to 1.2%, from 5.7% to 20.4%, and from 0.03% to 0.17%, respectively. Apparent mean sediment accumulation rates (SARs) varied between 0.25 and 3.11 mm year −1 (220 and 1750 g m −2 year −1). Central Gerlache and western Bransfield Straits (the Orleans Canyon) had the highest biogenic constituents contents and sediment accumulation rates, whereas the northern coast off Snow Island (Bellingshausen Sea) showed the lowest values. Central Gerlache Strait, with the highest primary production rates in the study area, was the only region where the OC and BSi contents in the sediment corresponded to the photosynthetic activity in the euphotic zone above it. At the extremes of Gerlache Strait as in western Bransfield Strait, sediment focusing by currents enhanced by depressions in the sea floor contributed to develop regions with high biogenic constituent concentrations, whereas at the Bellingshausen Sea and western Gerlache Strait, winnowing by currents may drift away the biogenic material exported from the euphotic zone. Apparently, bottom relief and currents rather than solely depth determined the modern distribution and accumulation rates of biogenic particulate matter in the study area. Paleoceanographic interpretations of the sedimentary record from Antarctic marginal seas, such as Gerlache and Bransfield Straits, should consider that focusing due to lateral transport and sea floor morphology and the preferential degradation of OC relative to BSi may increase to an important degree the biogenic contents in the sediment, especially the opal. OC and BSi accumulation in Antarctic marginal seas could be as important as the broad continental shelves despite large spatial differences.