PP029-0012
Sea Ice Changes in the Southwest Pacific Sector of the Southern Ocean During the Last 140,000 Years

Friday, 11 December 2020
Poster
Jacob Jones1, Karen Elizabeth Kohfeld2, Helen Bostock3, Xavier Crosta4, Melanie Liston5, Gavin B Dunbar5, Zanna Chase6 and Amy Leventer7, (1)Simon Fraser University, School of Resource and Environmental Management, Burnaby, BC, Canada, (2)Simon Fraser University, School of Resource and Environmental Management and School of Environmental Science, Burnaby, BC, Canada, (3)University of Queensland, School of Earth and Environmental Sciences, Brisbane, Australia, (4)Université de Bordeaux, Environnements et Paléoenvironnements Océaniques et Continentaux, Bordeaux, France, (5)Victoria University of Wellington, Antarctic Research Centre, Wellington, New Zealand, (6)University of Tasmania, Institute for Marine and Antarctic Studies, Hobart, TAS, Australia, (7)Colgate University, Geology, Hamilton, NY, United States
Abstract:
Sea ice expansion in the Southern Ocean has been hypothesized to have played a key role in early atmospheric CO2 drawdown during the last full glacial-interglacial climate cycle (130,000 years to present) through its roles in inhibiting air-sea gas exchange and influencing the ocean’s meridional overturning circulation. However, limited data have hindered our ability to link sea ice expansion to atmospheric CO2 concentration changes throughout the glacial cycle. Assessments of past sea ice concentrations using diatoms have primarily focused on the Last Glacial Maximum, with few published quantitative reconstructions extending to the onset of glacial Termination II (approximately 140,000 years ago). Here we provide new estimates of summer sea surface temperatures (sSST) and winter sea ice concentrations (wSIC) from the southwest Pacific sector of the Southern Ocean using fossil diatom assemblages from deep-sea core TAN1302-96 (59°5.3’S, 157°2.59’E, water depth 3099 m). We find that winter sea ice was consolidated over the core site during the penultimate glaciation, Marine Isotope Stage (MIS) 6 (from at least 140,000 to 134,000 years BP), but underwent a rapid retreat, coinciding with sSST increases, moving into the Last Interglacial Period (MIS 5e, 128,000 years BP). After 113,000 years BP, sSSTs continued to decline, but winter sea ice remained absent until MIS 4 (65,000 years BP), where it was sporadically present but unconsolidated (37% wSIC). WSIC and sSSTs reached their maximum (minimum) values during the Last Glacial Maximum (24,500 years BP) and quickly approached modern values during the early Holocene. These results broadly agree with nearby cores E27-23 and SO136-111 and provide a full glacial-interglacial history of sSSTs and wSIC south of the Polar Front in the southwest Pacific. These records suggest that the southwestern Pacific sector was free of sea ice during glacial inception (~116,000 years BP), and therefore the impact of sea ice on atmospheric CO2 drawdown was limited prior to MIS 4 (65,000 years BP).
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