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| Titel |
Indian Summer Monsoon dynamics during Termination II and MIS 5e |
| VerfasserIn |
Matthias Magiera, Andrea M. Erhardt, Adam Hartland, Ola Kwiecien, Hai Cheng, Adrian Immenhauser, Alexandra Turchyn, Sebastian F. M. Breitenbach |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141705
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| Publikation (Nr.) |
 EGU/EGU2017-5241.pdf |
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| Zusammenfassung |
| The interpretation of speleothem oxygen isotope ratios (δ18O) as proxy for Indian Summer
Monsoon (ISM) dynamics is ambiguous, due to multiple influencing factors. Here we
combine δ18O and calcium isotope δ44Ca analyses with elemental data to delineate regional
shifts in moisture source, local rainfall amount, and changes in ISM intensity and length
during Termination II and MIS 5e. Oxygen isotope ratios reflect a mixed signal of moisture
source dynamics and rainfall amount; δ44Ca and Mg/Ca ratios are interpreted as proxies for
local effective moisture and prior calcite precipitation (PCP) in the epikarst. The age of
stalagmite MAW-3 from Mawmluh Cave, NE India, is constraint by six U-series dates. 108
samples, obtained at 0.4 mm resolution from the 70 mm long speleothem sample, have been
analysed for δ18O, δ44Ca and Mg/Ca. Oxygen isotope ratios were measured on a
ThermoFisher Scientific MAT 253 at Ruhr-University Bochum. Elemental ratios were
measured on a quadrupole ICP-MS at Waikato University. Calcium isotope ratios
were analyzed on a ThermoFisher Scientific Triton at University of Cambridge.
MAW-3 grew from 136 kyrs BP to 96 kyrs BP, covering Termination II and MIS
5e. Oxygen isotope values are high (ca. +0.91 ‰) during Termination II, reach a
minimum during MIS 5e (-3.5 ‰), and rise again to -0.2 ‰ at the end of MIS
5e. Calcium isotope ratios range from -0.32 ‰ to -0.70 ‰ and show a positive
correlation (R2= 0.7) with δ18O. High δ18O values during Termination II reflect
reduced atmospheric circulation and/or a proximal moisture source (Bay of Bengal),
implying lowered ISM intensity. A positive correlation of δ18O with δ44Ca suggests
concurrent changes of moisture source location and local rainfall amount, with a
proximal moisture source and reduced effective rainfall during periods of weak ISM.
Elevated Mg/Ca ratios at such intervals corroborate PCP occurrence, which reflects dry
conditions. The beginning of MIS 5e (ca. 132 kyrs BP) is marked by a rapid change to
lower δ18O and δ44Ca, suggesting increased local infiltration with increasing ISM
rainfall, and a concurrent change to a more distal moisture source. The MAW-3
multi-proxy record compares well with reconstructions from China and northern
India, the latter being more depleted, due to Rayleigh fractionation. We suggest that
multi-proxy analyses of δ18O, δ44Ca and Mg/Ca greatly help to delineate regional
circulation pattern and local effective moisture dynamics in monsoonal settings. |
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