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

Abstract

Abstract. 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 (C25:3) 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 TEX86L and RI-OH' subsurface ocean temperatures (SOTs) are found to be linked to opposing spring and summer insolation trends, respectively.

Phaeocystisblooms caused carbon drawdown during the Antarctic Cold Reversal from sedimentary ancient DNA

“…This shift between communities and the time point of change is supported by a Latent Dirichlet allocation (LDA) and a Bayesian change-point model (Supplementary Figure 1). The increase in temperature from ice-core data (29), the decline in sea-ice biomarkers (11), and the decrease in abundance of sea ice-associated taxa are congruent with the onset of a warm period beginning with the termination of the ACR (Fig. 2).…”

“…Biogenic opal concentration in sediments is the most commonly used paleoproductivity and carbon export proxy (10). Studies have found a decline or stable low concentration of biogenic opal during the ACR (11), which is inconsistent with the assumption that diatom blooms in the Southern Ocean were of critical importance in the ACR CO 2 plateau (8). High Ba/Fe ratios may indicate organic carbon drawdown in the Southern Ocean (12) as barite (BaSO 4 ) can precipitate during phytoplankton blooms, which is linked to carbon precipitation (13), but records covering the ACR are lacking.…”

“…The ACR was a period of strong cooling in the Southern Hemisphere during deglacial warming, which is reflected in the EPICA Dome C ice core (29). Biomarker-based sea-ice reconstruction, the higher occurrence of sea-ice diatoms in the fossil record of core PS97/072-1 (11), and the estimated winter-summer sea-ice difference based on model results (Fig. 1) confirm a spatial and temporal increase in sea-ice cover during the ACR (Fig.…”

“…The core was recovered from a water depth of 1992.9 m and the total usable length was 1012 cm (51). The sediment of the core is described as a silty diatomaceous clay and the age model as well as microfossils, TOC, biogenic opal, and the biomarker data have been published by Vorrath et al (2023) (11).…”

“…The black arrow indicates the Antarctic Cold Reversal and the red arrow marks the halted deglacial CO 2 rise. Following is the P B IPSO 25 sea-ice biomarker graph over the last 14,000 years derived from the PS97/72-01 core (11). Next are the dominant primary producer taxa derived from shotgun metagenomics of sedaDNA over the last 14,000 years.…”