C055-0006
ESTIMATING PALEOTEMPERATURES IN THE AMUNDSEN SEA FOR THE LAST 620,000 YEARS THROUGH DIATOM MORPHOMETRICS (IODP EXPEDITION 379)

Tuesday, 15 December 2020
Poster
Joseph Mastro, Northern Illinois University, DeKalb, IL, United States, Reed P Scherer, Northern Illinois Univ, De Kalb, IL, United States and IODP Expedition 379 Scientists, Integrated Ocean Drilling Program, College Station, United States
Abstract:
As global climate continues to rapidly change over the coming decades, West Antarctica will be a significant point of interest due to its susceptibility to marine ice sheet collapse. Past collapses during Pleistocene interglacials have been hypothesized but remain largely unproven. Drill core samples collected from the Amundsen Sea continental rise during IODP Expedition 379 allow for analysis of a more continuous record of Pleistocene glacial-interglacial cycles. Here we report paleotemperature estimates from the Amundsen Sea spanning the last 620 kyr.

Two distinct morphotypes of the pelagic diatom Fragilariopsis kerguelensis have been shown to reliably reflect summer sea surface temperatures (SST). Using the method pioneered by Kloster et al. (2018) we have analyzed 1,600 diatom specimens in 78 distinct samples down-core in U1533, establishing a paleotemperature record utilizing the imaging software SHERPA (SHapE Recognition, Processing, and Analysis) which establishes shape (rectangularity) and total valve area of each specimen.

The morphotype endmembers include a rounded-tip “High Rectangularity” form, reflecting cold waters, and a pointed tip “Low Rectangularity” form characteristic of warmer waters. Our results show distinct down-core changes in dominant rectangularity, from which we calculate SST, based on a modification of the Glemser and Kloster (2019) equation.

We find that the warmest interglacials of the post Mid-Pleistocene Transition period were MIS 15, 13 and 11. Our temperature reconstructions confirm previous suggestions that glacial MIS 14 was characterized by rather interglacial environmental conditions on the Antarctic margin (Hillenbrand et al. 2009, Konfirst et al. 2012), indicating an extended interval of warmth spanning MIS 15 to MIS 13. MIS-5e was not significantly warmer than today.

Tracking these changes in SST throughout glacial to interglacial transitions can help constrain ice sheet/ocean models that seek to forecast West Antarctic Ice Sheet behavior in the coming centuries under different warming scenarios.

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