Glacial terminations and the Last Interglacial in the Okhotsk Sea; Their implication to global climatic changes

Abstract

Paleoclimate data from the Okhotsk Sea (OS) over Terminations II and I (TII, TI), and the Last and Present Interglacial (LIG, PIG) periods were compiled in order to examine Northern Hemisphere climate and sea level changes. Based on records of four AMS 14C-dated OS cores over TI-PIG, it is argued that the OS productivity/climate, IRD (ice-rafted debris), and benthic foraminiferal oxygen isotope (δ18Obf) proxies provide representative and in-phase evidence of the Northern Hemisphere climate and continental ice sheet changes consistent with the LR 04 δ18Obf curve. Chronologies for two central OS cores over TII-LIG-cooling event 23 (C23) were constructed by correlating OS productivity proxies with well-dated δ18O records of Chinese speleothems because OS environment is modulated by East Asian Monsoon; and, as well as correlating measured magnetic paleointensity excursions with those in the dated PISO-1500 paleointensity stack. Results show several OS climatic and environment states, including TII coeval with Asian Weak Monsoon Interval (WMI) II since 136ka, LIG with a sharp two-step transition (130.2–129ka) and demise at С25 (116.5ka), and last glaciation with coolings at C24 (111ka) and C23. The OS productivity and IRD records demonstrate certain climate amelioration in the middle of WMI-II, and two insignificant cooling events inside the LIG marked by C27 (126ka) and C26 (120.6ka). OS δ18Obf records of both cores demonstrate a gradual trend of lighter values since around 131.5kaBP, continuing from the onset of LIG (129ka) to minimum values at 126kaBP (C27), then nearly constant values until 121.5ka, followed by a slight increase up to 120.6ka (C26), and a subsequent strong increase up to 116.5ka (C25). The magnitude of OS δ18Obf oscillations is 1.35‰, which is less than those in the N. Atlantic. It may therefore be suggested that this OS index probably tracks changes in continental ice sheet volume and sea level.