97 New Perspectives on Beringian Paleoecology, Paleoclimate, and Paleoceanography

This session will showcase the use of new sedimentary records and analytical techniques to augment reconstructions of Beringian and North Pacific Gateway paleoclimate and paleoecology and elucidate the role of terrestrial and marine linkages.

Monday, 20 October 2025
8:00 AM - 12:00 PM
HBGCC, 303C

Preliminary Ecological Reconstructions of the Bering Land Bridge Submergence from Sediment Core Analysis in Norton Sound, Alaska

Paper number: 97-8
Program: Technical Sessions
Time: 10:00 AM – 10:15 AM

Authors

Abstract

During the peak of the Last Glacial Maximum (~20,000 years ago), lowered sea levels exposed the Bering Sea shelf, forming a vast subcontinent called the Bering Land Bridge (BLB) that connected present-day Russia and North America. As global temperatures rose between ~19,000 and ~11,500 years ago, the BLB gradually flooded, transforming freshwater and terrestrial environments into marine environments. Despite its significance as a migration corridor and potential ecological refuge, many aspects of the BLB’s environmental history remain unresolved. However, in 2023, a team of researchers on the R/V Sikuliaq collected sediment cores from 36 sites across the Bering Sea shelf to investigate pre- and post-submergence environments across the BLB. Here, we present preliminary results from one site (16GC), a 2.8-meter gravity core collected ~30 km offshore of Nome, Alaska, at a depth of 31 meters. Visual observations and grain size analysis reveal a basal freshwater unit of fine silt overlain by a marine unit of fine- and medium-grained sand occurring abruptly (within ~1 cm) at a depth of 64 cm. Radiocarbon dates from plant fragments yield a basal freshwater age of 13,000 cal BP and place the transition to marine conditions at approximately 11,400 cal BP. We target freshwater and transitional environments with 1-cm-interval diatom analysis to provide a detailed understanding of the transgression and investigate change at high temporal resolution. Diatoms, a group of photosynthetic, microscopic algae that dominate aquatic environments, provide a sensitive indicator of water salinity and habitat type and allow us to resolve the timing and nature of environmental change on the BLB. Our preliminary results demonstrate that although the abrupt lithologic transition is measured at 64-cm-depth, a more graduate transition took place over 14 cm, during which a freshwater lake diatom assemblage shifts to a brackish tidal river or low marsh assemblage at ~70 cm. This assemblage exists through the transition at 64 cm with taxa indicative of full marine conditions appearing at 56 cm. Our diatom results coincide well with gradual changes in loss-on-ignition and stable isotope (bulk δ¹³C and δ¹⁵N) results from the same horizons. The methods used here provide a detailed reconstruction of past environmental change during submergence of the BLB and will inform interpretations of regional changes across the subcontinent.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413949

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