Bioaccumulation record and paleoclimatic significance in the Western Bransfield Strait.: The last 2000 years

Two gravity cores, A-3 and A-6, from the western basin of the Bransfield Strait, Antarctica, were recovered during the BIO Hesperides expedition FRUELA 96. Both cores consist mainly of hemipelagic and laminated muds with black layers rich in sand-sized volcanic ash. Geochemical analyses (TOC and opal), radiometric dating techniques (AMS C-14 and Pb-210), and micropaleontological analyses (diatoms) were performed on both cores. AMS analyses on TOC yielded 14 C ages older than expected: 3960 +/- 50 yr BP for the core top of A-3, and 3410 +/- 50 yr BP for A-6. Pb-210 analyses revealed that core top age for both gravity cores could be estimated to be about 100 +/- 15 yr BP The results of diatom analyses were related to the sequence of neoglacial events that have occurred over the last two millennia. The abundance patterns of Chaetoceros RS, the biogenic silica content, and the abundance of diatom valves agree with the high productivity values previously reported for the Bransfield Strait waters. The significant recent reduction in resting spores of the diatom Chaetoceros suggests as a reduction in surface productivity. Trend differences between Chaetoceros resting-spore abundance and TOC contents are explained in terms of organic matter preservation, Diatom communities from the Bransfield Strait did not play an important role in the global CO2 cycle during cold periods. Bio- and geochemical changes have an overprinted high-frequency cyclicity at about 200 300 yr, which might be related to the 200-yr solar cycle, (C) 2001 Elsevier Science Ltd. All rights reserved.