HOLOCENE RECONSTRUCTIONS OF PRECIPITATION PATTERNS AND EXTREME COASTAL FLOODING FROM THE WESTERN PACIFIC

Lake Kaiike and Lake Namakoike are two deep (10-20 m) coastal lakes located on the remote island of Kamikoshiki in southwestern Japan. Extensive research has focused on the current meromictic and microbial processes of Lake Kaiike as a modern analogue to Cretaceous Ocean Anoxic Events; however, very little work has been done to address how the sediments of both Kaiike and Namakoike may have recorded past climate change in the region. The island of Kamikoshiki is located near the most northern extent of the Asian monsoon and is frequently affected by intense typhoon strikes. How past variability in both of these climactic phenomena have affected sedimentation within these lakes has been unclear; however, there is tremendous potential for developing well preserved regional paleo-reconstructions using sediments from these sites.

Here we present results from field work performed on the lakes of Kamikoshiki in August of 2006. Sub-bottom sonar surveys identify numerous reflectors which can be mapped throughout both lagoons. Sediments collected from coring sites reveal over 5 meters (~5000 yrs) of highly organic, finely laminated sediment episodically punctuated with less organic, de-laminated units. The depths of delaminated sediments correlate well with identified sub-bottom sonar reflectors. X-ray fluorescence (XRF) scans of these cores reveal that Ca and Sr concentrations and sediment densities significantly increase within de-laminated units, supporting the interpretation that these deposits are the result of episodic breaches to the barrier beach system during past periods of extreme overwash activity. Oscillations in Ti concentrations are similar to both modern instrumental records of regional precipitation, as well as previously developed paleo-reconstructions for the Asian monsoon. These results suggest that in addition to recording past periods of extreme coastal flooding, the lacustrian systems of Kamikoshiki also may contain a high-resolution record of past fluctuations in precipitation to the region related in part to mid-to-late Holocene shifts in the strength and location of the Asian monsoon.