Algal Growth Rings Tell a Story of Unprecedented Change in the Alaska Coastal
| Marilyn Sigman, Alaska SeaGrant/MAP
Tags: Climate Change, Red Algae, Gulf of Alaska, Bering Sea, Changing Ocean Current Patterns, Alaska Marine Ecosystems
University of Toronto graduate student Phoebe Chan won an award at the Alaska Marine Science Symposium for one of the best student presentations for the story told to her by the growth rings laid down by coralline red algae. Like trees, the algae grow a ring of new material every year by calcifying new tissue. Just as the width of tree rings are good indicators of wet or dry years, the ratios of calcium to barium in each algal ring is an indicator of salinity conditions at the time it was formed because freshwater runoff is high in barium.
Chan collected specimens and analyzed the growth rings in the species Clathromorphum nereostratum, one that is widespread and long-lived, from the Aleutian Island of Akun along the border of Unimak Pass – the main pathway for Alaska Coastal Current to flow from the Gulf of Alaska into the Bering Sea. The Alaska Coastal Current (ACC) is a narrow counterclockwise current that hugs Alaska’s Coast and is generally somewhat brackish as it collects all of the freshwater runoff from slopes of Alaska’s Coastal Range as it flows around the Gulf.
By analyzing the ratio of barium to calcium in each annual ring using a mass spectrometer, Chan was able to show that the ACC has freshened considerably in recent years and to an extent unprecedented in the last 65 years, possibly as a result of accelerated glacial melting. Analyses to extend the record farther back in time are on-going.
Coralline Red Algae as Recorders of Past Temperature and Salinity Variability of the Alaska Coastal Current
Phoebe Chan, University of Toronto; Jochen Halfar, University of Toronto; Steffen Hetzinger, University of Toronto; Robert Steneck, University of Maine; Thomas Zack, University of Mainz; Barbara Kunz, University of Mainz; Johannes Gutenberg University of Mainz; Dorrit Jacob, Johannes Gutenberg University of Mainz