Abstract
International Ocean Discovery Program (IODP) Expedition 374 sailed to the Ross Sea in 2018 to reconstruct paleoenvironments, track the history of key water masses, and assess model simulations that show warm-water incursions from the Southern Ocean led to the loss of marine-based Antarctic ice sheets during past interglacials. IODP Site U1523 (water depth 828m) is located at the continental shelf break, northeast of Pennell Bank on the southeastern flank of Iselin Bank, where it lies beneath the Antarctic Slope Current (ASC). This site is sensitive to warm-water incursions from the Ross Sea Gyre and modified Circumpolar Deep Water (mCDW) today and during times of past warming climate. Multiple incursions of subpolar or temperate planktic foraminifera taxa occurred at Site U1523 after 3.8Ma and prior to ~1.82Ma. Many of these warm-water taxa incursions likely represent interglacials of the latest Early Pliocene and Early Pleistocene, including Marine Isotope Stage (MIS) Gi7 to Gi3 (~3.72-3.65Ma), and Early Pleistocene MIS 91 or 90 (~2.34-2.32Ma) and MIS 77-67 (~2.03-1.83Ma) and suggest warmer-than-present conditions and less ice cover in the Ross Sea. However, a moderately resolved age model based on four key events prohibits us from precisely correlating with Marine Isotope Stages established by the LR04 Stack; therefore, these correlations are best estimates. Diatom-rich intervals during the latest Pliocene at Site U1523 include evidence of anomalously warm conditions based on the presence of subtropical and temperate planktic foraminiferal species in what likely correlates with interglacial MIS G17 (~2.95Ma), and a second interval that likely correlates with MIS KM3 (~3.16Ma) of the mid-Piacenzian Warm Period. Collectively, these multiple incursions of warmer-water planktic foraminifera provide evidence for polar amplification during super-interglacials of the Pliocene and Early Pleistocene. Higher abundances of planktic and benthic foraminifera during the Mid- to Late Pleistocene associated with interglacials of the MIS 37-31 interval (~1.23-1.07Ma), MIS 25 (~0.95Ma), MIS 15 (~0.60Ma), and MIS 6-5e transition (~0.133-0.126Ma) also indicate a reduced ice shelf and relatively warm conditions, including multiple warmer interglacials during the Mid-Pleistocene Transition (MPT). A decrease in sedimentation rate after ~1.78Ma is followed by a major change in benthic foraminiferal biofacies marked by a decrease in Globocassidulina subglobosa and a decrease in mud (<63μm) after ~1.5Ma. Subsequent dominance of Trifarina earlandi biofacies beginning during MIS 15 (~600ka) indicate progressive strengthening of the Antarctic Slope Current along the shelf edge of the Ross Sea during the mid to Late Pleistocene. A sharp increase in foraminiferal fragmentation after the MPT (~900ka) and variable abundances of T. earlandi indicate higher productivity, a stronger but variable ASC during interglacials, and/or corrosive waters, suggesting changes in water masses entering (mCDW) and exiting (High Salinity Shelf Water or Dense Shelf Water) the Ross Sea since the MPT.
Original language | English |
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Pages (from-to) | 211-238 |
Number of pages | 28 |
Journal | Journal of Micropalaeontology |
Volume | 43 |
Issue number | 2 |
DOIs | |
Publication status | Published - 11 Jul 2024 |
Bibliographical note
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Funding
We thank the scientists and crew of IODP Expedition 374 to the Ross Sea in 2018. This research used data and samples provided by the International Ocean Discovery Program (IODP), which is sponsored by the US National Science Foundation (NSF) and participating countries. This paper evolved from a Master's thesis presented by Julia L. Seidenstein in May 2020 and supported with funding from the University of Massachusetts graduate program in Geology and the U.S. Science Support Program. Thanks to Mike Jercinovic for assistance with the UMass Department of Geosciences Electron Microprobe/SEM Facility for use of the Carl Zeiss EVO50 variable pressure scanning electron microscope to take images of microfossil specimens for the plates. We acknowledge the very helpful and constructive reviews of Anieke Brombacher, Scott Ishman, and an anonymous referee. Thank you to Isla S. Casta\u00F1eda, Robert M. DeConto, Marci Robinson, and Harry Dowsett for helpful comments on earlier versions of the manuscript. Thanks to Anne Jennings for discussions about Arctic foraminifera preservation and to Ellen Thomas for guidance on the statistics of low specimen counts. A special thank you to Denise Kulhanek for handling this paper as special editor and to our UMass Micropaleo lab mates Samantha Bombard, Serena Dameron, and Erin Kim for their input, feedback, and support. This research has been supported by NSF OCE 14-50528 to RML (grant no. 19747558). We thank the scientists and crew of IODP Expedition 374 to the Ross Sea in 2018. This research used data and samples provided by the International Ocean Discovery Program (IODP), which is sponsored by the US National Science Foundation (NSF) and participating countries. This paper evolved from a Master's thesis presented by Julia L. Seidenstein in May 2020 and supported with funding from the University of Massachusetts graduate program in Geology and the U.S. Science Support Program. Thanks to Mike Jercinovic for assistance with the UMass Department of Geosciences Electron Microprobe/SEM Facility for use of the Carl Zeiss EVO50 variable pressure scanning electron microscope to take images of microfossil specimens for the plates. We acknowledge the very helpful and constructive reviews of Anieke Brombacher, Scott Ishman, and an anonymous referee. Thank you to Isla S. Casta\u00F1eda, Robert M. DeConto, Marci Robinson, and Harry Dowsett for helpful comments on earlier versions of the manuscript. Thanks to Anne Jennings for discussions about Arctic foraminifera preservation and to Ellen Thomas for guidance on the statistics of low specimen counts. A special thank you to Denise Kulhanek for handling this paper as special editor and to our UMass Micropaleo lab mates Samantha Bombard, Serena Dameron, and Erin Kim for their input, feedback, and support. This research has been supported by NSF OCE 14-50528 to RML (grant no. 19747558).
Funders | Funder number |
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International Ocean Discovery Program | |
University of Massachusetts | |
National Science Foundation | OCE 14-50528, 19747558 |
Harry Dowsett | 19747558 |