科研之友
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摘要
Shells of intertidal bivalve mollusks contain sub-seasonally to inter-annually resolved records of temperature and salinity variations in coastal settings. Such data are essential to understand changing land-sea interactions through time, specifically atmospheric (precipitation rate, glacial meltwater, river discharge) and oceanographic circulation patterns; however, independent temperature and salinity proxies are currently not available. We established a model for reconstructing daily water temperatures with an average standard error of similar to 1.3 degrees C based on variations in the width of lunar daily growth increments of Saxidomus gigantea from southwestern Alaska, United States. Temperature explains 70% of the variability in shell growth. When used in conjunction with stable oxygen isotope data, this approach can also be used to identify changes in past seawater salinity. This study provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). In combination with delta(18)O(shell) values, increment-derived temperatures were used to estimate salinity changes with an average error of 1.4 +/- 1.1 PSU. Our model was calibrated and tested with modern shells and then applied to archaeological specimens. As derived from the model, the time interval of 988-1447 cal yr BP was characterized by similar to 1-2 degrees C colder and much drier (2-5 PSU) summers. During that time, the ACC was likely flowing much more slowly than at present. In contrast, between 599-1014 cal yr BP, the Aleutian low may have been stronger, which resulted in a 3 degrees C temperature decrease during summers and 1-2 PSU fresher conditions than today; the ACC was probably flowing more quickly at that time. The shell growth temperature model can be used to estimate seasonal to interannual salinity and temperature changes in freshwater-influenced environments through time.
- 出版日期2011-6
