Abstract & Bio.

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Date: Tues., February 10, 2026

Program: Bridge Over Troubled Tundra: Tracking Ancient Vegetation on the Bering Land Bridge

Speaker: Josh Barna Department of Geosciences, University of Alaska Fairbanks
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Abstract:

During the last glacial period, the Bering Land Bridge (BLB) functioned as a key dispersal corridor between Eurasia and North America. Understanding the environmental conditions on the emergent land bridge is critical for interpreting patterns of faunal migration and ecological filtering. In August 2023, the R/V Sikuliaq recovered 91 sediment cores from 36 sites across the Bering Sea shelf, including core 99VC (“Basinito”), a 5.31 m vibracore collected in 74 m of water from a site in the southeastern Bering Sea (58° 16’ 3.4” N, 169° 37’ 12.3” W). Bulk sediment carbon (δ¹³C) and nitrogen (δ¹⁵N) values suggest gradual marine inundation at this site between ~202 and 96 cm from the top of the core. Radiocarbon dating of terrestrial plant macrofossils constrains the freshwater portion of this core to ~20–13.5 ka cal B.P. (between ~531 and 96 cm). Pollen analysis reveals assemblages dominated by herbaceous taxa (Cyperaceae and Poaceae, with lesser amounts of Asteraceae, Caryophyllaceae, Amaranthaceae, and Ranunculaceae), and a few woody taxa (primarily Salix and minor amounts of Betula). Rare but well preserved bisaccate pollen grains suggest some isolated stands of Picea nearby. These data indicate that open, arid steppe prevailed at this location on the BLB during the Late Pleistocene, possibly interspersed with pockets of shrub tundra. For comparison, a longer core (7.55 m) from the “Deep Blue Sea” site (71JC), located approximately 360 km NNW of 99VC, contains assemblages with higher percentages of pollen from woody taxa, including Alnus, Betula, Picea, and Salix. Pollen analysis indicates the presence of trees, shrubs, and herbs, suggesting the BLB was somewhat mesic at this site. Bulk δ¹³C and δ¹⁵N values shift markedly at a depth of ~475 cm, coinciding with a radiocarbon age of 16.5 ka cal B.P., suggesting rapid marine inundation or erosion. In contrast, the younger and more southerly 99VC core preserves no such abrupt transition, underscoring regional variation in both vegetation and the character of the transgression. Together, these records point to spatial heterogeneity across the BLB during the Last Glacial Maximum and deglaciation. The abundance of herbaceous taxa in the southeast relative to the interior of the land bridge is supported by preliminary sedaDNA results and may reflect conditions less favorable to woody plant refugia, with potential implications for migrating megafauna.

Speaker Bio:  

Josh Barna is a PhD student at UAF studying palynology and paleoclimatology. Originally from California, he attended school at Utah State University in Logan, Utah. He is currently living in Fairbanks in a shack in the middle of the woods without running water with his patient wife and two cats while working toward his degree.

In-Person or Virtual Meeting Online

TIME: Doors open 11 am, announcements 11:15 am, talk 11:30 am - 12:30 pm

LOCATION for In-Person: BP Energy Center, Spruce/Willow Room, 1014 Energy Court, Anchorage

LOCATION for Online: Your home or office.

COST: Free. Bring your lunch to the lecture or your computer.
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Meeting ID: 234 091 280 033 72
Passcode: Xv2Cc3ac

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