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Sarawak, Malaysia

Partin J.W.,Georgia Institute of Technology | Partin J.W.,University of Texas at Austin | Cobb K.M.,Georgia Institute of Technology | Cobb K.M.,University of Texas at Austin | And 3 more authors.
Geochemistry, Geophysics, Geosystems | Year: 2013

We investigate stalagmite trace metal ratios and carbon isotopic composition (δ13C) as potential paleoclimate proxies by comparing cave dripwaters, stalagmites, and bedrock composition from Gunung Mulu and Gunung Buda National Parks in northern Borneo, a tropical rainforest karst site. Three year long, biweekly time series of dripwater Mg/Ca, Sr/Ca, and δ13C from several drips at our site are not correlated with rainfall variability, indicative of a relatively weak relationship between hydroclimate and dripwater geochemistry at our site. However, combining all of the dripwater geochemical data gathered over four field trips to our site (N > 300 samples), we find that drips with highly variable Mg[Sr]/Ca have relatively invariable δ18O values close to the mean. We hypothesize that increased residence times translate into reduced variance in dripwater δ18O through mixing in the epikarst as well as increased Mg[Sr]/Ca values through increased calcite precipitation in the epikarst. Mg/Ca, Sr/Ca, and δ13C time series from three overlapping stalagmites that grew over the last 27 kyrs are characterized by strong centennial-scale variations, and bear little resemblance to previously published, well-reproduced δ18O time series from the same stalagmites. The only shared signal among the three stalagmites' geochemical time series is a relative decrease of 1‰ in δ13C from the Last Glacial Maximum to the Holocene, consistent with a transition from savannah (C4) to rainforest (C3) conditions documented in nearby records. Taken together, our study indicates that stalagmite Mg[Sr]/Ca ratios are poor indicators of hydroclimate conditions at our site, while stalagmite δ13C exhibits some reproducible signals on glacial-interglacial timescales. © 2013. American Geophysical Union. All Rights Reserved. Source


Moerman J.W.,Georgia Institute of Technology | Cobb K.M.,Georgia Institute of Technology | Adkins J.F.,California Institute of Technology | Sodemann H.,ETH Zurich | And 2 more authors.
Earth and Planetary Science Letters | Year: 2013

The relationship between climate variability and rainfall oxygen isotopic (δ18O) variability is poorly constrained, especially in the tropics, where many key paleoclimate records rely on past rainfall isotopes as proxies for hydroclimate. Here we present a daily-resolved, 5-yr-long timeseries of rainfall δ18O from Gunung Mulu National Park, located in northern Borneo (4°N, 114°E) in the heart of the West Pacific Warm Pool, and compare it to local and regional climatic variables. Daily rainfall δ18O values range from +0.7‰ to -18.5‰ and exhibit a weak but significant inverse relationship with daily local precipitation amount (R=-0.19, p<0.05), consistent with the tropical amount effect. Day-to-day δ18O variability at Mulu is best correlated to regional precipitation amount averaged over the preceding week (R=-0.64, p<0.01). The inverse relationship between Mulu rainfall δ18O and local (regional) precipitation amount increases with increased temporal averaging, reaching R=-0.56 (R=-0.72) on monthly timescales. Large, negative, multi-day rainfall δ18O anomalies of up to 16‰ occur every 30-90 days and are closely associated with wet phases of the intraseasonal Madden-Julian Oscillation. A weak, semi-annual seasonal cycle in rainfall δ18O of 2-3‰ bears little resemblance to seasonal precipitation variability, pointing to a complex sequence of moisture sources and/or trajectories over the course of the year. Interannual rainfall δ18O variations of 6-8‰ are significantly correlated with indices of the El Niño Southern Oscillation, with increased rainfall δ18O during relatively dry El Niño conditions, and vice versa during La Nina events. We find that Mulu rainfall δ18O outperforms Mulu precipitation amount as a tracer of basin-scale climate variability, highlighting the time- and space-integrative nature of rainfall δ18O. Taken together, our results suggest that rainfall δ18O variability at Mulu is significantly influenced by the strength of regional convective activity. As such, our study provides further empirical support for the interpretation of δ18O-based paleo-reconstructions from northern Borneo stalagmites as robust indicators of regional-scale hydroclimate variability, where higher δ18O reflects regional drying. © 2013 Elsevier B.V. Source


News Article | January 8, 2016
Site: http://motherboard.vice.com/

Every day at dusk, an estimated three million bats emerge from the mouth of one of the world’s largest caves to hunt. In order to make themselves a more elusive target for birds of prey, they gather in an eerie formation akin to a tornado, or a ribbon of campfire smoke. This video of the act, taken by François Chauvin, a visitor to Borneo’s Gunung Mulu National Park, is probably the most goth thing you’ll see today. Gunung Mulu National Park in Malaysia is a UNESCO World Heritage Site and a stunning example of tropical karst topography. A karst landscape is formed when the bedrock is predominantly composed of something easily soluble, like limestone. Over time, water erodes the rock, forming sinkholes, cenotes, jagged limestone formations, and caves. It’s not stated which of Gunung Mulu’s gigantic caves is home to these bats, but it was most likely Deer Cave, which is one of the largest cave passages on the planet. And though at least thirty different species of bats call Deer Cave home, it’s known specifically for its massive colony of Wrinkle-lipped bats, which are not one of the cuter species, unfortunately. (For cuteness, check out Honduran white bats, which have cuddle parties under giant leaves.) Wrinkle-lipped bats are tiny little guys, their bodies measuring only about three inches long, but apparently they still produce plenty of guano. Because of its massive and varied bat population, Deer Cave is a great place for bat enthusiasts to study. In 2008, Prince Albert of Monaco visited Gunung Mulu and gifted the park an infrared camera system so visitors could watch the bats hanging out. It looks like the live stream is no longer up, but the website still has a lot of information and more cool videos of the bats doing their thing.


Carolin S.A.,Georgia Institute of Technology | Cobb K.M.,Georgia Institute of Technology | Lynch-Stieglitz J.,Georgia Institute of Technology | Moerman J.W.,Georgia Institute of Technology | And 6 more authors.
Earth and Planetary Science Letters | Year: 2016

Over the past decades, tropical stalagmite δO18 records have provided valuable insight on glacial and interglacial hydrological variability and its relationship to a variety of natural climate forcings. The transition out of the penultimate glaciation (MIS 6) represents an important target for tropical hydroclimate reconstructions, yet relatively few such reconstructions resolve this transition. Particularly, comparisons between Termination 1 and 2 provide critical insight on the extent and influence of proposed climate mechanisms determined from paleorecords and model experiments spanning the recent deglaciation. Here we present a new compilation of western tropical Pacific hydrology spanning 0-160 ky BP, constructed from eleven different U/Th-dated stalagmite δO18 records from Gunung Mulu National Park in northern Borneo. The reconstruction exhibits significant precessional power in phase with boreal fall insolation strength over the 0-160 ky BP period, identifying precessional insolation forcing as the dominant driver of hydroclimate variability in northern Borneo on orbital timescales. A comparison with a network of paleoclimate records from the circum-Pacific suggests the insolation sensitivity may arise from changes in the Walker circulation system. Distinct millennial-scale increases in stalagmite δO18, indicative of reduced regional convection, occur within glacial terminations and may reflect a response to shifts in inter-hemispheric temperature gradients. Our results imply that hydroclimate in this region is sensitive to external forcing, with a response dominated by large-scale temperature gradients. © 2016 Elsevier B.V. Source

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