Evidence of sea ice-driven terrigenous detritus accumulation and deep ventilation changes in the southern Okhotsk Sea during the last 180 ka

Abstract

Sediment core OS03-1 retrieved from the Akademia Nauk Rise in Southern Okhotsk Sea was analyzed for the contents of rare earth elements (REEs) and combined with carbon isotope (δ13C) time series of benthic foraminifera to infer changes in terrigenous accumulation and bottom water ventilation on glacial–interglacial timescales in the study area. The age model of OS03-1 was constructed by a combination of foraminifer δ18O stratigraphy and 14C AMS dating, revealing that the 380cm long core provides a window on climate change in the southern Okhotsk Sea since ∼180ka. A grain size-controlled-REE content shows strong glacial–interglacial changes. The Cerium and Europium anomalies vary from 0.89 to 1.32 and from 1.14 to 1.37, respectively. The (La/Yb)N values range between 0.55 to 0.92. Both results suggest a significant contribution of volcanic debris in the core sediments. In addition, the relationships between Sm vs. Nd suggest main contribution origin from the Amur River and sea ice during warm intervals and from the sea ice during cold intervals, indicating that the sea ice played an important role in transporting terrigenous materials to the study site in the southern Okhotsk Sea. During the last 180ka, the mass accumulation rates (MAR) of ∑REEs are relatively higher during glacials and lower during interglacials with a peak accumulation during the early deglacial period. We infer that an intensified Mongolia High is responsible for the first-order accumulation pattern of ∑REEs in the southern Okhotsk Sea by mediating the dynamic changes in sea ice extent. Furthermore, six δ13C minima are associated with intensified Asian monsoon (AM) precipitation and maximum MARs of ∑REEs, indicating that the dominance of barrier layer effects by high fresh water input through sea ice melting. The maximum MAR of ∑REEs during the Marine Isotope Stage (MIS) 5c coincides with the minimum of benthic foraminiferal δ13C, indicating a major interruption of ventilation in the bottom water in the Okhotsk Sea. The major low ventilation event in the deep water of the Okhotsk Sea appears to be dampened by a cooling condition and a major blooming of surface productivity preceded the event.