The paucity of long-term climate records from mainland SE Asia is a persistent limitation that inhibits comprehensive understanding of regional climate variability in this monsoon-dominated region. Hence, the ~30 kyr sediment record from Ia M’He, a crater lake in the Central Highlands of Vietnam, provides invaluable evidence of past precipitation in its δ2Hwax (fatty acid methyl esters) and other proxy (biomarkers, C/N, etc.) data. Dry conditions prevailed during the last glaciation as indicated by exceptionally slow, and possibly episodic, sedimentation of clay with very limited organic matter preservation. Persistent sub-aerial exposure of the lake floor is substantiated by the prominence of biomarkers indicative of microbially degraded organic matter (OM) and lack of diatoms. During the early Holocene, the δ2Hwax values, high C/N ratios, and lack of diatoms suggest continued dry conditions, albeit wetter than during the glacial period. These data contrast with other regional climate interpretations that report heightened moisture availability associated with peak monsoon rains linked to maximum summer insolation. Around 6.5 ka BP, the initiation of weak diatom preservation, decreased C/N ratios and δ2Hwax values all indicate a deepening of the lake and year-round water from an increase in effective moisture. By the late Holocene (~3 ka BP) diatoms are common, which is consistent with C/N ratios that reflect algal sources of OM and the concurrent minimum in δ2Hwax values. Biomarker distributions reflect better preserved OM from terrestrial vegetation, algae, and aquatic macrophytes. This change coincides with the onset of modern El Niño/Southern Oscillation (ENSO) conditions but does not conform with interpretations of decreased monsoon rainfall in response to waning summer insolation.
|Commitee:||Hagedorn, Benjamin, Buonora, Paul T.|
|School:||California State University, Long Beach|
|School Location:||United States -- California|
|Source:||MAI 82/4(E), Masters Abstracts International|
|Subjects:||Paleoclimate Science, Geochemistry, Limnology|
|Keywords:||Hydrogen isotopes, Mainland Southeast Asia, Paleolimnology, Vietnam|
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