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Strong influence of water vapor source dynamics on stable isotopes in precipitation observed in Southern Meghalaya, NE India

Breitenbacha, Sebastian F.M. and Adkins, Jess F. and Meyer, Hanno and Marwan, Norbert and Kumar, Kanikicharla Krishna and Haug, Gerald H. (2010) Strong influence of water vapor source dynamics on stable isotopes in precipitation observed in Southern Meghalaya, NE India. Earth and Planetary Science Letters, 292 (1-2). pp. 212-220. ISSN 0012-821X.

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To calibrate δ^(18)O time-series from speleothems in the eastern Indian summer monsoon (ISM) region of India, and to understand the moisture regime over the northern Bay of Bengal (BoB) we analyze the δ^(18)O and δD of rainwater, collected in 2007 and 2008 near Cherrapunji, India. δD values range from + 18.5‰ to − 144.4‰, while δ^(18)O varies between + 0.8‰ and − 18.8‰. The Local Meteoric Water Line (LMWL) is found to be indistinguishable from the Global Meteoric Water Line (GMWL). Late ISM (September–October) rainfall exhibits lowest δ^(18)O and δD values, with little relationship to the local precipitation amount. There is a trend to lighter isotope values over the course of the ISM, but it does not correlate with the patterns of temperature and rainfall amount. δ^(18)O and δD time-series have to be interpreted with caution in terms of the ‘amount effect’ in this subtropical region. We find that the temporal trend in δ18O reflects increasing transport distance during the ISM, isotopic changes in the northern BoB surface waters during late ISM, and vapor re-equilibration with rain droplets. Using an isotope box model for surface ocean waters, we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern BoB. Temporal variations in this source can contribute up to 25% of the observed changes in stable isotopes of precipitation in NE India. To delineate other moisture sources, we use backward trajectory computations and find a strong correlation between source region and isotopic composition. Palaeoclimatic stable isotope time-series from northeast Indian speleothems likely reflect changes in moisture source and transport pathway, as well as the isotopic composition of the BoB surface water, all of which in turn reflect ISM strength. Stalagmite records from the region can therefore be interpreted as integrated measures of the ISM strength.

Item Type:Article
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Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2010 Elsevier. Received 4 July 2009; revised 22 January 2010; accepted 25 January 2010. Available online 13 February 2010. We gratefully acknowledge the co-funding of the PhD work of Sebastian Breitenbach by the DeutscheForschungsgemeinschaft (DFG) and the Davidow Fund at Caltech. Norbert Marwan was supported by the DFG Graduate School GK 1364 “Shaping Earth's Surface in a Variable Environment”. JFA and lab work at Caltech were supported by NSF grant OCE-0318445. We thank Denis P. Rayen (Laitkynsew, India), Brian Kharpran Daly (Shillong, India), Pawel Prokop (Krakow, Poland), Thomas Arbenz (Matzendorf, Switzerland) and Rolf Siegenthaler (Gümligen, Switzerland) for sampling and logistical support.
Funding AgencyGrant Number
DeutscheForschungsgemeinschaft (DFG)GK 1364
Davidow Fund at CaltechUNSPECIFIED
Subject Keywords:India; Bay of Bengal; Indian Summer Monsoon; LMWL; precipitation; stable isotopes
Issue or Number:1-2
Record Number:CaltechAUTHORS:20100513-091934538
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18282
Deposited By: Tony Diaz
Deposited On:19 May 2010 19:50
Last Modified:24 Feb 2020 10:30

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