4 High latitude paleoceanographic discoveries from Scientific Ocean Drilling (IODP, ODP, DSDP)

Scientific Ocean Drilling has retrieved thousands of meters of sediment cores from the high latitude oceans.  This session provides the opportunity to present the results of work to understand Cenozoic climate and oceanographic changes.

Sunday, 22 March 2026
8:00 AM - 12:00 PM
CCC, Room 27

Filling a Critical Gap in the Ross Sea Record of the Miocene Climatic Optimum and Middle Miocene Climate Transition

Paper number: 4-9
Program: Technical Sessions
Time: 10:40 AM – 11:00 AM

Authors

Abstract

Foraminifera provide invaluable insight into paleoceanographic, depositional, and climatic conditions of the Ross Sea embayment during the Early to Middle Miocene. This study investigates the foraminifera from Deep Sea Drilling Project (DSDP) Site 273 and International Ocean Discovery Program (IODP) Site U1521 during the Miocene Climatic Optimum (MCO; 16.9 to 14.7 Ma), Middle Miocene Climate Transition (MMCT; 14.7 to 13.8 Ma), and the Mi3 glaciation (~13.8 Ma). DSDP Site 273 (distal western Ross Sea) and IODP Site U1521 (central Ross Sea) capture intervals of the MCO and MMCT that either overlap or are missing from ANDRILL Site 2A (proximal western Ross Sea).

Based on our age model, DSDP Site 273 captures the latter half of the MCO through the MMCT and Mi3 glaciation (expansion of the East Antarctic Ice Sheet), filling a critical gap in the Ross Sea record of the Early to Middle Miocene. This is the ice sheet advance event(s) that created Ross Sea Unconformity 4 (RSU4) truncated the AND-2A and U1521 records but did not erode Site 273. During the MCO, the benthic biofacies are dominated by Uvigerina, suggesting active bottom currents on the continental shelf. The benthic biofacies prior to the MCO (~18.6 to 18 Ma) and during the MMCT, are dominated by Globocassidulina subglobosa and Nonionella spp., suggesting a sub-ice shelf environment. In addition to the benthic biofacies, we note five occurrences of warm planktic species.

In contrast, the MCO and MMCT record at Site U1521 is sparse due to unconformities, but it partially overlaps with AND-2A. The foraminiferal record shows shifts in abundances between Uvigerina and G. subglobosa as well as numerous sporadic occurrences of warm planktic specimens. The MCO interval at U1521 coincides with peak warmth events recognized at AND-2A including PW-3 and PW-4.

Together, the foraminiferal records from Site 273 and Site U1521 suggest that the Ross Sea was a dynamic environment during the MCO and MMCT. The abundance of Uvigerina and G. subglobosa suggest changes in current activity and proto-Circumpolar Deep Water incursions. Also, sporadic occurrences of temperate planktic foraminifera indicate the import of warm water, and the relatively consistent presence of neritic Elphidium, providing ideal conditions to facilitate ice sheet growth prior to the MCO, and during the MMCT and Mi3.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2

doi: 10.1130/abs/2026NE-411404

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