Holocene hydrologic fluctuations on the southern coast of Korea and their link to ENSO activity.

To maintain a stable freshwater supply for sustainable economic activity in coastal areas in light of anticipated global climate change, it is important to understand the controlling factors and variability of past hydrologic behavior. In this study, we tested the grain size variability recorded in coastal sediments from Yeosu, on the southern coast of Korea, as an indicator of freshwater input change. We found a ca. 7 m sedimentary sequence (Stage 2) between lower fluvial to coastal marsh (Stage 1) and upper coastal marsh (Stage 3) deposits, which we infer was deposited in the inner bay at a water depth between ca. 10 and 2 m, over the time periods between 1.2 and 7.7 cal kyr BP. The variability in grain sizes corresponded to the low-resolution local freshwater input index in the Beolgyo area, providing a more detailed precipitation fluctuation record. The long-term variations in grain size was similar to that of the Asian summer monsoon fluctuation during the middle to late Holocene. Significant fluctuation at multicentennial time scales superimposed on the long-term variation clearly indicated intensified freshwater input periods (e.g., at 2.5, 3.0, 5.2, 6.3, and 7.7 cal kyr BP). These hydrologic changes in the study area appear to be linked to past El Niño-Southern Oscillation (ENSO) activity, such that intensified freshwater input occurred during stronger ENSO activity. Among these climatic shifts, severe rainfall events characterized by sand layers (e.g., at 7.7 and 2.5 cal kyr BP) can be used as isochronous sedimentary layers on the southern coast of Korea. [ABSTRACT FROM AUTHOR]