Paleoenvironmental Change in the Holocene Sediments of Lake Maruwan Ooike on the Rundvagshetta, Soya Coast, Antarctica-The history of the Regression of the Ice Sheet and Uplift of Soya Coast-

Holocene marine sediments including the marine molluscan fossils are distributed on the ice-free area of Soya Coast, Antarctica. These sediments are exposed around the freshwater Lake Maruwan Ooike on the Rundvagshetta area. Therefore, we can easily estimate the period of marine environment in the history of this lake. To clarify the paleoenvironmental change in Lake Maruwan Ooike, we carried out the coring used by 2m hand-pushing piston corer. We were able to get the good core. Coring site is located at the north part of lake, which the water depth is 9.8m. Core of 187cm is recovered at this site. The purpose of this study is to clarify the paleoenvironmental change of Lake Maruwan Ooike, and to discuss about the history of the regression of the ice sheet and uplift of Soya Coast. Sediment core (Mw-4 core) is divided to 4 sedimentary unit based on sediment facies. Unit I (0-60cm) consist of laminated silt with cyanobacteria and moss. Unit II (60-68cm) consist of laminated cyanobacterial deposits. In this unit, total organic carbon content (10-15%) is higher than other unit. Unit III (68-150cm) is massive diatomaceous mud including marine benthic foraminifer. Unit IV (150-187cm) is laminated diatomaceous mud. The 14C AMS dating performed using by the organic carbon in sediment at 6 horizon. Calculating from the sedimentation rate and the 14C AMS dating, the boundary age between Unit I and II is estimated with 2900 yr.B.P., and II and III is estimated with 3650 yr.B.P. Unit III and IV show marine environment from the occurrence of benthic foraminifera, Trochammina antarctica and so on. Unit II is estimated the salt lake condition from cyanobacterial flora and high total sulfur content. Unit I is the fresh water lake condition with cyanobacteria and moss flora. Inflow of melt water of ice sheet started from the upper part of unit II, and two-layer structure is formed to salt lake during this unit. The age of change from marine to fresh water environment is estimated about 2900 yr.B.P., then the relative sea level is 8m of recent altitude. This result is harmonious with the record of Holocene marine sediments on the ice-free area of Soya Coast.