NOAA/WDS Paleoclimatology - Aleutian Islands 225 Year Coralline Algae Growth Increment Data

STUDY NOTES: 225 year growth chronology of the coralline alga Clathromorphum nereostratum, derived from 29 samples collected off the Aleutian Islands, Alaska. C. nereostratum is a long-lived, shallow-marine crustose coralline algae. The 225 yr growth-increment width composite chronology was derived from 29 digitally imaged thick sections of coralline algae ranging from 15 to 185 yr in ontogenetic age, collected live along a 1500 km longitudinal transect spanning the entire Aleutian Islands. The composite chronology was constructed by normalizing time series to unit variance and averaging of the individual records.
ABSTRACT SUPPLIED BY ORIGINATOR: Bering Sea climate and ecosystem dynamics have recently undergone major changes that have affected seasonal sea ice distribution and marine life, including commercially important salmon fisheries. Unfortunately, long-term Bering Sea dynamics are poorly understood, largely because of an absence of high-resolution marine proxy archives. Here we present the first record compiled from annual growth-increment widths of long-lived coralline algae collected in shallow-water habitats spanning the entire Aleutian Islands. While algal growth in the Aleutians exhibits a variable relationship with regional temperatures, it is strongly driven by changes in solar radiation reaching the seafloor. Therefore, it provides an exceptional archive of long-term light dynamics, which in the Bering Sea is attributed to changes in strength of the Aleutian Low (AL), the dominant climate pattern of the subarctic North Pacific. The AL is positively related to Bering Sea cloudiness and wind strength, which in turn fosters upper-ocean mixing. Mixing raises surface-water nutrient concentrations and stimulates plankton production, which is positively linked to Alaskan salmon abundance. Enhanced clouds and plankton production increase shading on the shallow seafloor and reduce algal growth. Light-driven algal growth rates track proxy-derived salmon abundance from 1782 onward, but are poorly related to temperature-dominated Pacific Decadal Oscillation (PDO) variability prior to the twentieth century. The algal record suggests that the present-day relationship of AL and PDO varied historically and that salmon stocks have been more closely related to AL strength via its effect on plankton abundance rather than PDO-related temperatures.