Palaeomagnetic and biostratigraphic dating of marine sediments from the Scotia Sea, Antarctica: First identification of the Laschamp excursion in the Southern Ocean

Abstract

Establishing accurate chronologies for Late Quaternary Antarctic marine sediments is often a challenge due to variable radiocarbon reservoir effects, the presence of coarse-grained glacial material and a lack of carbonate preservation. Without accurate age control the scope for precise comparison of palaeoenvironmental records is severely limited. In order to address this, we combined diatom abundance stratigraphy, magnetic and radiocarbon methods to build an accurate chronology for two late glacial marine sedimentary sequences, from cores TPC063 and TPC286 from the Scotia Sea, SW Atlantic. Palaeomagnetic data provide the first evidence for the Laschamp geomagnetic excursion (∼41 cal ka B.P.) in Antarctic marine sediments and a relative palaeointensity curve that is tuned to the independently dated SAPIS relative palaeointensity reference stack. Together, these key findings provide an accurate age model between 43.7 cal ka B.P. and 25.3 cal ka B.P. The age model was further extended to 17.3 cal ka B.P. through identification of the diatom Eucampia antarctica 2Ea 1 abundance stratigraphy datum. Radiocarbon dating did not provide dates that were in stratigraphic order, and magnetic susceptibility only identified glacial interglacial transitions in one core. We demonstrate that combining geomagnetic and diatom abundance data can enable generation of high-resolution geochronologies for glacial sediments from the Scotia Sea, and offers the potential for more widespread comparison and correlation of Antarctic and Southern Ocean palaeoenvironmental records.