Holocene paleolimnological changes of Lake Oyako-ike in the Soya Kaigan of East Antarctica

Abstract

We studied Holocene paleolimnological changes as a part of studies of global change in Lake Oyako-ike in the Soya Kaigan of Lützow-Holm Bay region in East Antarctica, inferred from organic components and microscopic observation of microalgae and cyanobacteria in a sediment core (Ok4C-01, core length 135 cm), along with sedimentary facies and accelerator mass spectrometry (AMS) 14C dating. The Ok4C-01 core was composed mainly of silt and fine sand containing laminae between 135 and 65.5 cm, overlain by cyanobacterial mud between 65.5 and 0 cm. The mean sedimentation rate and crustal uplift rate were estimated to be 0.69 mm/y and 2.2 mm/y, respectively. The crustal uplift rate of Lake Oyako-ike basin is similar to those of present uplift rates but is somewhat greater than those estimated in the Lambert Glacier region, East Antarctica. The low biological production with diatoms in coastal marine environments (135–74.75 cm, ca. 2170–1300 cal BP) changes into green sulfur bacteria in stratified saline lake environments (74.75–60.95 cm, ca.1300–1100 cal BP), and then high biological production with cyanobacteria and green algae in freshwater environments (60.95–0 cm, ca.1100–220 cal BP). The ongoing retreat of glaciers and ongoing isostatic uplift during the mid-Holocene Hypsithermal (4000–2000 years ago) and thereafter are the main reasons for this isolation, whereas eustatic sea level change is believed to have played only a minor role.