CLIMATIC AND ECOLOGIC CHANGES DURING THE WOOLLY MAMMOTH EXTINCTION AT ST. PAUL ISLAND IN THE CENTRAL BERING SEA

St. Paul Island is located in the south central Bering Sea and was home to a local population of woolly mammoths until approximately 5.5 ka. The sediment record from the island’s Lake Hill offers a valuable opportunity to characterize the paleoclimate of the Bering Strait region and to assess the role of climate in the local extinction of woolly mammoths. Here, we use a suite of biomarkers from Lake Hill to document changes in temperature, precipitation, and aquatic and terrestrial ecology from 18 ka to present.

Based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) and leaf wax ²H/¹H ratios, we find that both winter and summer temperatures have been increasing over the past 18 kyr. Notably, the Holocene warming signal contrasts with records from interior Alaska where winters warmed but summer temperatures decreased significantly over the past 11 kyrs. The positive trend in summer temperatures in the Bering Sea suggests a high sensitivity to greenhouse gas forcing over the Holocene, or may be linked to seasonal carry-over effects from the decline in winter sea ice.

There is no abrupt change in winter or summer temperatures at 5.5 ka to explain the woolly mammoth extinction event, although gradual warming may have been a stressor on the mammoth population. Other biomarkers of ecological change show significant abrupt changes prior to, and just following, the mammoth extinction. At ~6 ka, the ratio of isoprenoid GDGT-0 to crenarchaeol increases dramatically, indicating increasingly anoxic conditions in Lake Hill; declining water quality of this drinking water source may have further stressed the mammal population. Closely following the extinction event, we observe an abrupt change in leaf wax n-alkane distributions reflecting a rapid response of the vegetation community to the release of grazing and trampling pressures from the mammoths. We discuss key relationships between climate, extinction, and ecological change in a sensitive island ecosystem.