Coral extension rates in the NW Indian Ocean II: reconstruction of 20th century Indian monsoon strength and rainfall over India |
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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, coral proxy studies have proved largely unsuccessful in reconstructing temporal variability of the Indian monsoon
system in the NW Indian Ocean. In a recent publication in this journal, Storz and Gischler demonstrated that extension rates
in corals can be used to fill this gap. Those authors found a link between decadal and interannual variations of the SW monsoon
current velocities and Porites lutea extension rates in the lagoon of Rasdhoo Atoll (4°N/73°W) in the central Maldives for the period 1917–2007. This sister paper
shows that this extension-rate record can be used to reconstruct decadal variations of summer monsoon rainfall over peninsular
India and adjacent areas. The amount of monsoon rainfall and current velocities during summer are both affected by the strength
of the Indian monsoon system. Assessments of coral extension rates and the mean May–September All India Monsoon Rainfall index,
a measure of monsoon strength over the Indian subcontinent, revealed a significant spectral coherence within periods of 18–19
and 6–7 years. Almost 92% of variance is shared between both time series in the former band, and 85% in the latter. A correlation
between the 5-year running mean extension rate and rainfall records from the Western Ghats (grid of 73–76°E/13–15°N) is significant
especially for 1958–2006 (r = −0.82, p < 0.05). These findings imply that coral growth characteristics can serve as a new marine archive to reconstruct past variations
of the Indian monsoon system on interannual to decadal timescales. |
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