Deglacial and Holocene sea-ice and climate dynamics in the Bransfield Strait, northern Antarctic Peninsula

The reconstruction of past sea-ice distribution in the Southern Ocean is crucial for an improved understanding of ice-ocean-atmosphere feedbacks and the evaluation of Earth system and Antarctic ice sheet models. The Antarctic Peninsula (AP) has been experiencing a warming since the start of regular monitoring of the atmospheric temperature in the 1950s. The associated decrease in sea-ice cover contrasts the trend of growing sea-ice extent in East Antarctica. To reveal the long-term sea-ice history at the northern Antarctic Peninsula (NAP) under changing climate conditions, we examined a marine sediment core from the eastern basin of the Bransfield Strait covering the last Deglacial and the Holocene. For sea-ice reconstructions, we focused on the specific sea-ice biomarker lipid IPSO25, a highly branched isoprenoid (HBI), and sea-ice diatoms, whereas a phytoplankton-derived HBI triene (C-25:3) and warmer open-ocean diatom assemblages reflect predominantly ice-free conditions. We further reconstruct ocean temperatures using glycerol dialkyl glycerol tetraethers (GDGTs) and diatom assemblages and compare our sea-ice and temperature records with published marine sediment and ice core data. A maximum ice cover is observed during the Antarctic Cold Reversal 13 800-13 000 years before present (13.8-13 ka), while seasonally ice-free conditions permitting (summer) phytoplankton productivity are reconstructed for the late Deglacial and the Early Holocene from 13 to 8.3 ka. An overall decreasing sea-ice trend throughout the Middle Holocene coincides with summer ocean warming and increasing phytoplankton productivity. The Late Holocene is characterized by highly variable winter sea-ice concentrations and a sustained decline in the duration and/or concentration of spring sea ice. Overall diverging trends in GDGT-based TEX(86)(L )and RI-OH' subsurface ocean temperatures (SOTs) are found to be linked to opposing spring and summer insolation trends, respectively.

Automated summary

The reconstruction of past sea-ice distribution in the Southern Ocean is crucial for understanding ice-ocean-atmosphere interactions and assessing Earth system and Antarctic ice sheet models. This study focused on the northern Antarctic Peninsula (NAP) and utilized marine sediment cores to reveal the long-term sea-ice history. Sea-ice biomarkers and diatom assemblages were used for reconstructions, while ocean temperatures were reconstructed using glycerol dialkyl glycerol tetraethers (GDGTs). The findings show varying sea-ice trends throughout different periods, with a maximum ice cover during the Antarctic Cold Reversal and decreasing ice cover during the Middle Holocene.