Geochemistry of Slow-Growing Corals: Reconstructing Sea Surface Temperature, Salinity and the North Atlantic Oscillation
WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
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A 225-year old coral from the south-shore of Bermuda 64CW, 32CN 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. Deltaexp 18O of the coral skeleton changes based on both temperature and the 8exp 18O of sea water DeltaOw, and 80 is proportional to sea surface salinity SSS. SrCa was used to reconstruct winter-time and mean-annual SST, employing the first growth-corrected SrCa-SST model. SSTs are l.5C 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 SrCa 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.
- Physical Chemistry
- Hydrology, Limnology and Potamology