Investigating the stable isotopic composition of Globocassidulina biora as a potential tracer of (paleo)environmental conditions near the Antarctic Peninsula

Abstract

We measured the stable isotopic composition of Globocassidulina biora from 17 surface sediments in Admiralty Bay, King George Island, taken during four consecutive austral summers (2002/2003–2006) spanning 44–80 m water depth. This species is widespread in relatively shallow, nearshore environments, and we test its applicability to paleoclimatic reconstructions. Results indicate that the majority of the δ18O values in the surface sediment samples fall within a narrow range between 3.8 and 3.4 per mil in good agreement with the δ18O of equilibrium calcite. Averaged over the four sampling seasons, the absolute differences between G. biora δ18O values and equilibrium calcite is 0.02 per mil. Similar to the δ18O of equilibrium calcite and modern water mass parameters, there are no spatial, or water depth, differences in G. biora δ18O values across the study sites. These observations suggest that this species would be a suitable tracer for paleoenvironmental conditions. However, maximum G. biora δ18O values of ~4.9 per mil in down-core Holocene samples from this region are higher than maximum surface sediment δ18O values of 3.88 per mil. Values >4.5 per mil cannot be reconciled with water temperature and δ18O of seawater in the Antarctic Circumpolar region suggesting that other effects, such as perhaps linked to pore water pH, might be dominating the signal at times. The lack of a high δ18O analogue in the surface sediment calibration data suggests caution when using G. biora for paleoceanographic and paleoclimatic reconstructions.