Coral extension rates in the NW Indian Ocean I: reconstruction of 20th century SST variability and monsoon current strength |
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| Authors: | David Storz Eberhard Gischler |
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| Institution: | (1) Institut f?r Geowissenschaften, Goethe-Universit?t, 60438 Frankfurt am Main, Germany |
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| Abstract: | To date, only a few coral proxy studies have investigated coral growth as an indicator of climate variability. This study
presents the first extension-rate record (Porites lutea) from the Maldives (NW Indian Ocean), inferred from skeletal δ18O chronology for the lagoon of Rasdhoo Atoll (4°N/73°W) in the central area of the Maldives, influenced by the Indian monsoon.
The record spans 90 years over the period 1917–2007. The mean annual extension over this period was 9.9 mm/year, and an increase
of annual extension rates until 1990 by 3 mm/year can be explained by a rise of 0.7°C in sea surface temperature (SST) in
this region. After 1990, the extension rates do no continue increasing, possibly due to ecological stress caused by progressive
ocean warming and acidification. The correlation between annual extension rates and SSTs is thus significant and strong in
the lower part of the record until 1955 (r = +0.69, p < 0.0001), but weaker thereafter (r = +0.44, p < 0.001). The extension rates yield a distinct interannual variability of 3–4 years, caused by interannual SST fluctuations
driven by the El Ni?o-Southern Oscillation. A variability of 8–9 years is likely driven by SST variations endemic to the Indian
Ocean. Spectral peaks between 18–19 years and 6–7 years cannot be explained by SST fluctuations, but by variations in the
strength of the SW monsoon currents. It is suggested that during phases of stronger monsoon activity, the coral sacrificed
coral extension in favor of a denser, more robust skeleton. The geomorphology of the atoll may strengthen the potential of
this new coral archive to track climate variability. |
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