Sea-water paleotemperature and growth rate estimation using a rhodolith near Udo, Jeju Island: a preliminary study for paleoenvironmental reconstruction = 고환경 복원에 대한 예비 연구 결과

다국어 초록 (Multilingual Abstract)

Texture and high resolution trace element data of a rhodolith (UD-RAN-01) was investigated to delineate paleoenviroment. It was collected from shallow marine environment between Udo (U Island) and Seongsan, which is located in the northeastern part of Jeju Island. The rhodolith is mostly made up of coralline red algae with living ones on the surface and a minor contribution by bryozoans, serpulid worm tubes and boring bivalves. Conceptacles filled with shallow marine cements are commonly observed within red algae. Clear difference of cell size between summer and winter in the rhodolith can be observed. Cell size is larger during summer due to faster growth rate. Cell size variations together with seasonal cyclicity indicate that annual growth rate is about 0.25 mm/year. Based on cell counting and counting of annual growth laminae, it is estimated that the analyzed rhodolith had grown for about 100 years. Mg, Sr, Ba, U compositions were analyzed to delineate paleoenvironmental changes during the growth of the rhodolith. It is estimated that summer paleotemperature estimated from Mg contents was more or less similar to the present-day temperature whereas estimated winter paleotemperature was significantly lower by ca. 9℃. It is likely that microsampling of the rhodolith during winter intervals was not precise enough to show real seasonal value due to smaller cell size and narrower spacing of winter growth intervals. However, it cannot be ruled out that paleowinter temperature was higher. Higher resolution analysis will aid to better understand paleotemperature estimation and paleoceanographic changes in the study area.