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Transformation of ENSO-related rainwater to dripwater δ^(18)O variability by vadose water mixing

Moerman, Jessica W. and Cobb, Kim M. and Partin, Judson W. and Meckler, A. Nele and Carolin, Stacy A. and Adkins, Jess F. and Lejau, Syria and Malang, Jenny and Clark, Brian and Tuen, Andrew A. (2014) Transformation of ENSO-related rainwater to dripwater δ^(18)O variability by vadose water mixing. Geophysical Research Letters, 41 (22). pp. 7907-7915. ISSN 0094-8276.

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Speleothem oxygen isotopes (δ^(18)O) are often used to reconstruct past rainfall δ^(18)O variability, and thereby hydroclimate changes, in many regions of the world. However, poor constraints on the karst hydrological processes that transform rainfall signals into cave dripwater add significant uncertainty to interpretations of speleothem-based reconstructions. Here we present several 6.5 year, biweekly dripwater δ^(18)O time series from northern Borneo and compare them to local rainfall δ^(18)O variability. We demonstrate that vadose water mixing is the primary rainfall-to-dripwater transformation process at our site, where dripwater δ^(18)O reflects amount-weighted rainfall δ^(18)O integrated over the previous 3–10 months. We document large interannual dripwater δ^(18)O variability related to the El Niño–Southern Oscillation (ENSO), with amplitudes inversely correlated to dripwater residence times. According to a simple stalagmite forward model, asymmetrical ENSO extremes produce significant offsets in stalagmite δ^(18)O time series given different dripwater residence times. Our study highlights the utility of generating multiyear, paired time series of rainfall and dripwater δ^(18)O to aid interpretations of stalagmite δ^(18)O reconstructions.

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Adkins, Jess F.0000-0002-3174-5190
Alternate Title:Transformation of ENSO-related rainwater to dripwater δ18O variability by vadose water mixing
Additional Information:© 2014 American Geophysical Union. Received 27 August 2014; accepted 24 October 2014; accepted article online 29 October 2014; published online 25 November 2014. The authors wish to thank the Gunung Mulu National Park staff, Eleanor Middlemas, Danja Mewes, Sang Chen, and Niko Sluzki for their assistance during fieldwork and the Mulu Meteorological Station staff for overseeing the collection of the daily rainfall samples. We also gratefully acknowledge the Mulu Caves Project for providing invaluable information about the Mulu karst system and an anonymous reviewer for comments that greatly improved the manuscript. Permits for this work were granted by the Malaysian Economic Planning Unit, the Sarawak State Planning Unit, and the Sarawak Forestry Department. This work was supported by NSF grant 0645291 to K.M.C., and J.W.M. was funded by a NSF Graduate Research Fellowship. Observational data sets of Mulu rainfall and dripwater isotopes used in this study can be found in the supporting information. M. Bayani Cardenas thanks one anonymous reviewer for his/her assistance in evaluating this paper.
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NSF Graduate Research FellowshipUNSPECIFIED
Issue or Number:22
Record Number:CaltechAUTHORS:20150122-083840589
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Official Citation:Moerman, J. W., K. M. Cobb, J. W. Partin, A. N. Meckler, S. A. Carolin, J. F. Adkins, S. Lejau, J. Malang, B. Clark, and A. A. Tuen (2014), Transformation of ENSO-related rainwater to dripwater δ18O variability by vadose water mixing, Geophys. Res. Lett., 41, 7907–7915, doi:10.1002/2014GL061696.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:53978
Deposited By: Jason Perez
Deposited On:22 Jan 2015 20:58
Last Modified:24 Feb 2020 10:30

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