Freshening of the Alaska Coastal Current recorded by coralline algal Ba/Ca ratios

Chan, Phoebe, Halfar, Jochen, Williams, Branwen, Hetzinger, Steffen, Steneck, Robert, Zack, Thomas and Jacob, Dorrit E. (2011) Freshening of the Alaska Coastal Current recorded by coralline algal Ba/Ca ratios Journal of Geophysical Research: Biogeosciences, 116 (G1). G01032. DOI 10.1029/2010JG001548.

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Arctic Ocean freshening can exert a controlling influence on global climate, triggering
strong feedbacks on ocean‐atmospheric processes and affecting the global cycling of the
world’s oceans. Glacier‐fed ocean currents such as the Alaska Coastal Current are
important sources of freshwater for the Bering Sea shelf, and may also influence the Arctic
Ocean freshwater budget. Instrumental data indicate a multiyear freshening episode of
the Alaska Coastal Current in the early 21st century. It is uncertain whether this freshening
is part of natural multidecadal climate variability or a unique feature of anthropogenically
induced warming. In order to answer this, a better understanding of past variations in
the Alaska Coastal Current is needed. However, continuous long‐term high‐resolution
observations of the Alaska Coastal Current have only been available for the last 2 decades.
In this study, specimens of the long‐lived crustose coralline alga Clathromorphum
nereostratum were collected within the pathway of the Alaska Coastal Current and utilized
as archives of past temperature and salinity. Results indicate that coralline algal Mg/Ca
ratios provide a 60 year record of sea surface temperatures and track changes of the Pacific
Decadal Oscillation, a pattern of decadal‐to‐multidecadal ocean‐atmosphere climate
variability centered over the North Pacific. Algal Ba/Ca ratios (used as indicators of coastal
freshwater runoff) are inversely correlated to instrumentally measured Alaska Coastal
Current salinity and record the period of freshening from 2001 to 2006. Similar multiyear
freshening events are not evident in the earlier portion of the 60 year Ba/Ca record.
This suggests that the 21st century freshening of the Alaska Coastal Current is a unique
feature related to increasing glacial melt and precipitation on mainland Alaska.

Document Type: Article
Keywords: Biogeochemistry; Alaska Coastal Current, coralline algae, Ba/Ca ratios, Arctic Ocean freshening, Aleutian Islands
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
DOI etc.: 10.1029/2010JG001548
ISSN: 2169-8953
Date Deposited: 18 May 2011 10:07
Last Modified: 06 Feb 2018 14:05

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