Diatoms as Indicators of Climate Change on St. Lawrence Island, Alaska

Abstract

The Alaskan and Bering Sea region has warmed twice as fast as the rest of the United States over the past 60 years. St. Lawrence Island, Alaska, the most northern large island in the Bering Sea, has had some recent monitoring of climate; however, these data are of fairly short duration and thus long-term environmental change is relatively unknown. To develop a more complete assessment of anthropogenic climate change in the region, I applied paleolimnological techniques to assess changes over the past ~150 years in diatom assemblages and primary production estimates for two sites located on St. Lawrence Island. Sediment cores were obtained from Reindeer Pond and Atuk Lake in July of 2012. Examining these two different waterbodies provides the opportunity to assess the ecological variability in the region and compare how a lake and a pond differ in their response to warming. Diatom assemblages in both Atuk Lake and Reindeer Pond showed a response to anthropogenic climate change beginning in the late 19th and early 20th century. Shifts towards more diverse assemblages of benthic diatoms at both sites suggest greater benthic habitat availability, which is most likely due to the increased growing season allowing for the development of greater substrate complexity. The diatom change is accompanied by a corresponding increase in sedimentary chlorophyll-a, a change likely driven by a longer-ice free season allowing for increased phytoplankton and periphyton production. Cluster analyses on the diatom assemblages also detected a primary split around the 1970s for the Atuk Lake profile, which is consistent with a known period of marked warming in the Bering Sea region. This study provides important ecological information and a longer-term perspective on recent climate changes for this under-studied region and for the vulnerable subsistence communities that live in the on St. Lawrence Island, Alaska.