Regional-scale climate influences on temporal variations of rainwater and cave dripwater oxygen isotopes in northern Borneo
Abstract
This study investigates the relationship between large-scale climate variability, rainfall oxygen isotopic composition (δ^(18)O), and cave dripwater δ^(18)O at Gunung Mulu and Gunung Buda National Parks in northern Borneo (4°N, 115°E) on intraseasonal to interannual timescales. A 3-yr timeseries of rainfall δ^(18)O contains prominent seasonal and interannual variability. The seasonal cycle in rainfall δ^(18)O is defined by lighter values of − 10‰ during late boreal summer and heavier values of − 4‰ during late boreal winter, and is poorly correlated to local precipitation, which displays very weak seasonality. Seasonally-varying moisture trajectories likely play a key role in the observed seasonal cycle of rainfall δ^(18)O, driving enhanced fractionation during boreal summer and less fractionation during boreal winter. Dripwater δ^(18)O timeseries display 2‰ seasonal cycles that follow the rainfall δ^(18)O seasonal cycles, with a mean δ^(18)O value equivalent to the mean δ^(18)O of rainfall. Large surveys of cave dripwaters conducted during three fieldtrips to Gunung Mulu/Buda reveal a system-wide response to rainfall δ^(18)O seasonality that supports a relatively short (less than 6months) response time for most drips. During the weak 2005/2006 La Niña event, sustained positive precipitation anomalies are associated with rainfall δ^(18)O values that are 4 to 5‰ lighter than previous years' values, consistent with the tropical "amount effect" observed in both models and data. Dripwater δ^(18)O values are 1 to 2‰ lighter during the weak La Niña event. The importance of the "amount effect" in driving intraseasonal rainfall δ^(18)O anomalies at our site is supported by an 8‰ increase in rainfall δ^(18)O that occurred over the course of two weeks in response to a pronounced decrease in regional convective activity. Dripwater discharge rates underwent a ten-fold decrease during the extended dry period, but dripwater δ^(18)O values remained constant. This study supports the interpretation of stalagmite δ^(18)O records from Gunung Mulu/Buda as paleo-precipitation records that are sensitive to the location and strength of deep convection in the West Pacific Warm Pool.
Additional Information
© 2007 Elsevier B.V. Received 23 February 2007; received in revised form 22 August 2007; accepted 22 August 2007. Available online 31 August 2007. Editor: M.L. Delaney. The authors are indebted to Jenny Malang and the staff of Gunung Mulu National Park for fieldtrip and sampling assistance, Johnny Baei Hassan for expert caving guidance, and Prof. Andrew Tuen (UNIMAS) for permitting assistance. Joel Despain, George Prest, Shane Fryer, Jed Mosenfelder, and Brad Hacker provided assistance during the 2003 fieldtrip. Permits for this work were granted by the Malaysian Economic Planning Unit, the Sarawak Forestry Department, and the Sarawak State Planning Unit. Mulu airport rainfall was provided by the Sarawak Department of Irrigation and Drainage. The research was funded by NSF grant ATM-0318445, and by a Comer Abrupt Climate Change Fellowship.Additional details
- Eprint ID
- 33603
- Resolver ID
- CaltechAUTHORS:20120828-100751466
- ATM-0318445
- NSF
- Comer Abrupt Climate Change Fellowship
- Created
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2012-08-28Created from EPrint's datestamp field
- Updated
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2021-11-09Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences