Geochemistry of Slow-Growing Corals: Reconstructing Sea Surface Temperature, Salinity and the North Atlantic Oscillation

Nathalie Goodkin, Ph.D., 2007
Konrad Hughen, William Curry, Advisors

Basaltic ocean A 225-year old coral from the south-shore of Bermuda (64°W, 32°N) provides a record of decadal-to-centennial scale climate variability. The high accretion rates, longevity, and skeletal growth bands found in coral skeletons make them an ideal resource for well-dated, seasonal climate reconstructions. Coral skeletons incorporate strontium (Sr) and calcium (Ca) in relative proportions inversely to the sea surface temperature (SST) in which the skeleton is secreted. d18O of the coral skeleton changes based on both temperature and the d18O of sea water (dOw), and dOw is proportional to sea surface salinity (SSS). Sr/Ca was used to reconstruct winter-time and mean-annual SST, employing the first growth-corrected Sr/Ca-SST model. SSTs are ~1.5°C colder during the end of the Little Ice Age than today. SSS is fresher during that time. Winter-time SSTs at Bermuda are correlated to phases of the North Atlantic Oscillation (NAO). Using winter Sr/Ca as a proxy for temperature, we show strong coherence to the NAO at multi-decadal and inter-annual frequencies. These coral records show changes in variance in the NAO during the late 20th century, but limited changes in the mean phase of the NAO, implying that climate change may be pushing the NAO to extremes but not to a new mean position.