A ca. 800-Year Lithologic Record of Drought from Sub-annually Laminated Lake Sediment, East Java |
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Authors: | Shelley D Crausbay James M Russell Douglas W Schnurrenberger |
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Institution: | (1) Department of Botany, University of Wisconsin, 430 Lincoln Dr, Madison, WI 53706, USA;(2) Department of Geological Sciences, Brown University, Providence, RI 02912, USA;(3) DOSECC, Salt Lake City, UT 84108, USA;(4) Limnological Research Center, University of Minnesota, Minneapolis, MN 55455, USA |
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Abstract: | 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. |
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Keywords: | Calcium carbonate ENSO Indo-Pacific Laminations Ranu Lamongan Stable isotopes |
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