Lithostratigraphic analyses of a sub-annually laminated core from Ranu Lamongan, a maar lake on the island of Java, document considerable changes in the lake's chemistry and water balance over the past ca. 800 calendar years. Composition of the dark (clastics) and light (diatoms and/or calcium carbonate minerals) couplets suggests that these laminations form in response to seasonal changes in rainfall and water-column overturn in the lake. Calcium carbonate is not continuous in the core, and when it occurs it varies, sometimes abruptly, in carbonate phase and elemental composition (low Mg-calcite Mg-calcite, and aragonite). A significant correlation between Mg/Ca changes and δ18O variations in authigenic calcium carbonate suggest the basin is highly sensitive to hydrologic variation. Lithologic data suggest calcium carbonate precipitates and thus records hydrologic conditions during the dry season - a season in which rainfall anomalies are highly correlated with the phase of ENSO. Our carbonate-based record of Mg/Ca shows variability in evaporative concentration on a quasi-seasonal frequency for the past ca. 800 years. Our record shows two multi-decadal periods of drought - ca. 1275-1325 and ca. 1450-1650 CE - the latter of which was especially strong and/or prolonged. Our record also shows a possible change in drought frequency at around 1650 CE, in which periods of calcium carbonate precipitation and Mg/Ca change shifted from multi-decadal to interannual variability. Given the strong correlations between modern-day drought in East Java and ENSO variability, our drought record may indicate a regime shift in the behavior of the ENSO system about 350 years ago. Finally, comparisons between our record and others suggest that variation in ENSO on centennial and sub-centennial scales is not strongly associated with changes in the global mean climate state.
Bibliographical noteFunding Information:
First and foremost we thank Ed Cushing for providing the opportunity to work in Indonesia, as well as coring equipment and funding for some radiocarbon dates. We also thank the Indonesian government and local officials in East Java for allowing this research. Universitas Gadjah Mada, Yogyakarta, Java provided lab space while we were in Indonesia. Agus Pudjoarinto organized lab space, field trips, housing, and permits. Purnomo, Asteria Wudihastituti, Fatoni Burhanudin, Tjut Sugandawati Djohan, Wawan, and Bambang helped with coring. We thank Mark Joern, Jenni-fer Schmitz, and the Limnological Research Center for laboratory assistance. R. D’Arrigo, M. Riedinger-Whitmore, J.H. Schampel, S. Hotchkiss, G. Schuurman, and an anonymous reviewer provided valuable comments on this manuscript. This research was supported by NSF RTG: Pa-leorecords of Global Change and the Dayton-Wilkie Natural History Fund. We also thank Kerry Kelts for input at the beginning of this project.
Copyright 2008 Elsevier B.V., All rights reserved.
- Calcium carbonate
- Ranu Lamongan
- Stable isotopes
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