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South A sian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the A ndaman S ea

Abstract The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial‐interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd,...

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Bibliographic Details
Published in:Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2015-02, Vol.16 (2), p.505-521
Main Authors: Ali, Sajid, Hathorne, Ed C., Frank, Martin, Gebregiorgis, Daniel, Stattegger, Karl, Stumpf, Roland, Kutterolf, Steffen, Johnson, Joel E., Giosan, Liviu
Format: Article
Language:English
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Summary:Abstract The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial‐interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay‐size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval εNd values changed little, generally oscillating between −7.3 and −5.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo‐Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite + chlorite) ratios (up to 14), as well as low 87 Sr/ 86 Sr ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite‐poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short‐term northern Atlantic climate variability on millennial time scales. Key Points: Source of clay to Andaman Sea relatively constant for last 60 kyr Chemical weathering and South Asian monsoon stronger during the Holocene South Asian monsoon variability occurred on millennial timescales
ISSN:1525-2027
1525-2027
DOI:10.1002/2014GC005586