Sea ice changes in the southwest Pacific sector of the Southern Ocean during the last 140 000 years

• Published in: Climate of the Past
• Main Authors: Jones, J, Kohfeld, KE, Bostock, H, Crosta, X, Liston, M, Dunbar, G, Chase, Z, Leventer, A, Anderson, H, Jacobsen, G
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2022
• Subjects: Earth Sciences; Physical geography and environmental geoscience; Palaeoclimatology; Antarctic; Pacific; Southern Ocean; Antarc*; Sea ice
• Online Access: https://doi.org/10.5194/cp-18-465-2022; http://ecite.utas.edu.au/150276

Sea ice expansion in the Southern Ocean is believed to have contributed toglacialinterglacial atmospheric CO 2 variability by inhibiting airsea gas exchange and influencing the ocean's meridional overturning circulation. However, limited data on past sea ice coverage over the last 140 ka (a complete glacial cycle) have hindered our ability to link sea ice expansion to oceanic processes that affect atmospheric CO 2 concentration. Assessments of past sea ice coverage using diatom assemblages have primarily focused on the Last Glacial Maximum ( ∼21 ka) to Holocene, with few quantitative reconstructions extending to the onset of glacial TerminationII ( ∼135 ka). Here we provide new estimates of winter sea ice concentrations (WSIC) and summer sea surface temperatures (SSST) for a full glacialinterglacial cycle from the southwestern Pacific sector of the Southern Ocean using the modern analog technique (MAT) onfossil diatom assemblages from deep-sea core TAN1302-96. We examine how thetiming of changes in sea ice coverage relates to ocean circulation changesand previously proposed mechanisms of early glacial CO 2 drawdown. Wethen place SSST estimates within the context of regional SSST records tobetter understand how these surface temperature changes may be influencingoceanic CO 2 uptake. We find that winter sea ice was absent over thecore site during the early glacial period until MIS4 ( ∼65 ka), suggesting that sea ice may not have been a major contributor to earlyglacial CO 2 drawdown. Sea ice expansion throughout theglacialinterglacial cycle, however, appears to coincide with observedregional reductions in Antarctic Intermediate Water production andsubduction, suggesting that sea ice may have influenced intermediate oceancirculation changes. We observe an early glacial (MIS5d) weakening ofmeridional SST gradients between 42 and 59 ∘ S throughoutthe region, which may have contributed to early reductions in atmosphericCO 2 concentrations through its impact on airsea gas exchange.