Pollen records and stable isotope ratios of benthic foraminifera from sediment cores of the Sea of Okhotsk

In two cores with oxygen isotope stratigraphy from the southern Okhotsk Sea, marine pollen and siliceous microfauna record concurrent late glacial through Holocene variations in regional terrestrial and marine environments. Glacial vegetation around the southern Okhotsk basin, which resembles the present tundra/steppe of the northwest coast of this marginal sea, yields to spruce-dominated boreal forests during the glacial/interglacial transition. Temperate forest components, such as oak, peak during the mid-Holocene. Decreasing oak accompanied by increasing spruce reflects the effect of global cooling on local vegetation during the last 4 kyr. Although the radiolarian fauna in the Okhotsk Sea samples is similar to that present in the northwest Pacific, the dominant species in both regions differ. Concentrations of radiolarians are low in latest glacial samples, with higher concentrations occurring above and below this interval. Cycladophora davisiana, the dominant radiolarian species in the majority of Holocene Okhotsk Sea sediments, is present at lower percentages in late glacial samples from our two sites. Thus, this species' Holocene/latest Pleistocene abundance pattern in Sea of Okhotsk sediments is the reverse of that recorded in high-latitude open ocean sites. The combined marine pollen and radiolarian records indicate changes in the Sea of Okhotsk's physical oceanographic conditions and surrounding vegetation during the late glacial which were associated with this region's response to global climate change.