A HIGH RESOLUTION d180 RECORD OF GROWTH BANDING IN ADAMUSSIUM COLBECKI: A PROXY FOR RECONSTRUCTION OF COASTAL SALINITIES AND CONTINENTAL TEMPERATURES ON ANNUAL TO CENTURY TIME SCALES

In 1986, a specimen of Adamussium colbecki from Explorers Cove was measured, tagged and released, and later recovered in 1998. Based on an analysis of growth rates determined from this and other specimens, shells of this taxon have the potential for environmental reconstruction on a seasonal scale, with records for individuals extending for over one century of growth. In this study, we have sampled growth banding at high spatial resolution (<100 µm intervals) utilizing a computerized micromilling system to calibrate the d¹⁸0 record contained in shell carbonate to environmental variation of the coastal setting of Antarctica. 

For this specimen, variation in shell d¹⁸0 across a 35mm traverse ranges from +4.5 to +2.7‰ and exhibits a high frequency of change at a sub-annual time scale. Given that present day shelf waters (~15m to >25m) exhibit only minor seasonal and inter-annual temperature variation, ranging from –1.7°C to –1.9°C, this environment is effectively isothermal.  Thus, observed shifts in shell d¹⁸0 reflect primary changes in coastal water salinity (and d¹⁸0water) in response to variable contributions of glacial meltwater. Assuming a d¹⁸0 value of -30‰ for these glacial waters, this provides an extremely sensitive proxy for paleosalinity with a –0.9 ‰ d¹⁸0 change in shell carbonate corresponding to each 1ppt decrease in salinity.  Paleosalinities reconstructed from shell d¹⁸0 for the last 80 years range from 35ppt to a low of 33ppt, with a marked shift in the mid-1950’s.

To investigate the cause for such salinity variation, the shell d¹⁸0 for the last 20mm of growth was correlated to measurements of maximum annual air temperature at McMurdo Station from 1956 to 1988.  This comparison demonstrates the potential to utilize the d¹⁸0 marine record preserved in the shell of A colbecki to reconstruct the history of Holocene warming and cooling in the adjacent terrestrial system, on annual, decadal, and century time scales throughout the Holocene.