Abstract
Geochemical analysis, micropalaeontological analysis and radiometric dating techniques were performed on four gravity cores, G-1, G-2, A-3 and A-6, recovered during the BIO Hesperides expeditions GEBRA-93 and FRUELA-96 from the Bransfield Strait (Antarctica). Moreover, in order to improve the sedimentation rate control we tentatively relate abundance variations in the sea-ice taxa group (SITG) to air temperature estimations based on Deuterium contents in Vostok ice-core. The results of diatom analyses were related to the sequence of neoglacial events that have occurred over the last three millennia. For these periods, a restricted communication between the Weddell, Bransfield and Bellingshausen seas has been proposed. The abundance patterns of diatom valves, resting spores (RS) of the diatom Chaetoceros and opal content agree with the high productivity values previously reported for the area. The significant reduction Chaetoceros RS towards the present is interpreted as a reduction in surface productivity. Trend differences between Chaetoceros RS 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 CO 2 cycle during cold periods. Bio- and geochemical changes have overprinted high frequency cyclicity at about 200-300 yr, which might be related to the 200-yr solar cycle.
Highlights
The Holocene has been a period of rapid climate change in which climate records have been obtained from both hemispheres (Domack and Mayewski, 1999)
In order to improve the sedimentation rate control in all cores we tentatively relate abundance variations in the sea-ice taxa group (SITG) directly related to climatic changes and sea-ice distribution, as widely discussed by Armand et al (2005), to air temperature estimations based on Deuterium contents in Vostok ice-core (Petit et al, 2000)
High numbers of diatom valves per gram of dry sediment were observed in both cores, ranging from 2×107 to 14.7×108 (Fig. 3)
Summary
The Holocene has been a period of rapid climate change in which climate records have been obtained from both hemispheres (Domack and Mayewski, 1999). Previous studies have shown that the general trend for the last three thousand years has been a reduction in primary productivity towards the present (Bárcena et al, 1998, 2002; Domack, 2001) Overprinted on this trend is a high-frequency oscillation in diatom abundance, which correlates with an approximately 250 year cyclicity, recognised in magnetic susceptibility, organic carbon, nitrogen and siliceous microfossil data (Leventer et al, 1996; Bárcena et al, 1998, 2002; Domack, 2001). These changes in primary productivity over time are mainly controlled by seaice conditions and surface water stability and stratification. Since over the years vertical fluxes are restricted to a short period, i.e. the austral summer (Wefer et al, 1988), palaeoclimatic evolution may help to study and better understand the biogenic cycles involved
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