Bivalves as indicators of environmental variation in the Arctic
|Serripes groenlandicus with foot extended and visible growth bands (alternating dark and light bands on shell) (http://www.sfos.uaf.edu/research/arcdiv/seabottom/bivalves/serripes-groenlandicus.html)|
|A thin section of a bivalve shell with sequential laser ablation spots for trace element analysis on an Inductively Coupled Plasma Mass Spectrometer (ICPMS) (http://www.futura-sciences.com)|
William Ambrose Jr. (Bates College), Michael Carroll (Akvaplan-niva), Michael Greenacre (Pompeu Fabra Univ.), Simon R. Thorrold (WHOI)
Identifying patterns and drivers of natural variability in populations is necessary to gauge potential
effects of climatic change and the expected increases in commercial activities in the Arctic on communities and ecosystems. We analyzed growth rates and shell geochemistry of Arctic bivalves over almost 70 years between 1882 and 1968. This period encompassed different phases of large-scale climatic oscillations with accompanying variations in local physical variables (temperature, atmospheric pressure, precipitation, sea ice cover), allowing us to analyze the linkage between growth rate, climatic oscillations, and their local physical and biological manifestations. The datasets were calibrated via annually-deposited growth lines, and growth, stable isotope (δ18O, δ13C), and trace elemental (Mg, Sr, Ba, Mn) patterns were linked to environmental variations on weekly to decadal scales. Standardized growth indices revealed an oscillatory growth pattern with a multi-year periodicity, which was inversely related to the North Atlantic Oscillation Index (NAO), and positively related to local river discharge. Up to 60% of the annual variability in Ba/Ca could be explained by variations in river discharge at the site closest to the rivers, but the relationship disappeared at a more distant location. Patterns of δ18O, δ13C, and Sr/Ca together provide evidence that bivalve growth ceases at elevated temperatures during the fall and recommences at the coldest temperatures in the early spring, with the implication that food, rather than temperature, is the primary driver of bivalve growth. The multi-proxy approach of combining the annually integrated information from the growth results and higher resolution geochemical results yielded a robust interpretation of biophysical coupling in the region over temporal and spatial scales. Our results suggest that bivalves, as sentinels of climate change on multi-decadal scales, are sensitive to environmental variations associated with large-scale changes in climate, but that the effects will be determined by changes in environmental parameters regulating marine production and food availability on a local scale. We thus demonstrate that sclerochronological proxies can be useful retrospective analytical tools for establishing a baseline of ecosystem variability in assessing potential combined impacts of climatic change and increasing commercial activities on Arctic communities.