Diatoms as Indicators of Climate Change on St. Lawrence Island, Alaska
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Date
2015-04-28
Authors
Rampone, Janae
Keyword
diatoms , indicators , St. Lawrence Island , Alaska , climate change , sediment
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.