High-resolution variations of the Okhotsk Sea environment during the present and last interglaciations: comparison of foraminiferal and geochemical data (core MD01-2415)

Recent studies indicate that oxygen minimum zone (OMZ) was weakened during the last glaciation and strengthened during the Termination I and Holocene not only along the eastern but western margins of the North Pacific Ocean, including the Okhotsk Sea [1, 2]. Benthic foraminiferal (BF) assemblages along with the sedimentary concentrations of the redox-sensitive trace elements are widely used to reconstruct past variations of OMZ in the Ocean. Our study focuses on two key interglacial intervals: the Termination (T) I – marine isotope stage (MIS) 1 (the last 16 ka) and TII – MIS 5e (116-134 ka) of core MD01-2415. The core MD01-2415 was collected on the northern slope of the Okhotsk Sea at water depth 822 m during WEPAMA 2001 cruise of the R/V Marion Dufresne [3]. We were able to obtain high-resolution BF and geochemical data (e.g., the accumulation rates and percentages of the dominant BF species; contents of total organic carbon, СаСО3 and some trace elements Al, Ca, Mg, Mn) which allow for paleoreconstructions with temporal resolution of ~300-600 kyr. The preliminary analysis of available data points to the existence of more intense OMZ during the TI and TII than in the subsequent interglaciations, as well as in the TI than TII. We compare the resulting paleoreconstructions with variations of the solar insolation at 60°N and the global sea level. Our preliminary hypothesis is that lower sea level before the TI (-110 m at 16 ka) than before the TII (from -60 to 100 m at 134 ka) along with slower rate of the sea level rising in the TI than in the TII [4] were among the main controlling factors responsible for larger amount of terrestrial organic matter and nutrients transported from the submerged shelves into the Okhotsk Sea in the TI. It suggests more enhanced marine and export productivity, more intense oxygen consumption via the organic matter decay and, as a result, stronger OMZ in the TI (maximum in the Preboreal) than in the TII