Sea Ice Expansions And Provenance Changes On The Northern Okhotsk Sea Shelf Since The Last Glacial Maximum

As the second largest marginal sea in the northwest Pacific Ocean,the Okhotsk Sea is not only a crucial location for energy and water vapor exchange between the North Pacific and the East Asian Continent but also affected by the low and high latitude climate,including polar climate and East Asian summer monsoon,where is a typical climate sensitive area.In the Okhotsk Sea,the silicate weathering in the source area and sea ice play important roles in the sediment generation and transport,respectively,which are frontier research issues.Based on grain size end-member analysis of the core LV87-54-1,this paper has reconstructed the evolution history and controlling factors of sea ice on the northern Okhotsk Sea shelf since the Last Glacial Maximum.Based on clay minerals and bulk sediment geochemistry,we have discussed the source variation of terrigenous material under the influence of sea ice in the study area,and reconstructed silicate weathering history of sediment source area and explore its response to temperature and precipitation variability.The results of grain size end-member analysis study indicate the Okhotsk Sea has not been covered by perennial sea ice,but covered mainly by mobile seasonal sea ice since the Last Glacial Maximum.And sea ice variation was controlled by the local autumn insolation(September to November),the Arctic Oscillation and the East Asian Summer monsoon.The sea ice activity was intense during the Last Glacial Maximum and Heinrich Stadial 1.The negative Arctic Oscillation and the climate cooling at the middle and high latitudes of the Northern hemisphere were the main controlling mechanism for sea ice expansion during glacial periods.And weakened runoff from the Heilongjiang caused by decreased East Asian Summer monsoon would allow more sea ice formation in the Okhotsk Sea.Sea ice formation decreased at the onset of the B?lling-Aller?d warm period,and then decreased sharply after a slight peak during the Younger Dryas Event.Sea ice end-member levels remained low stably since the Holocene due to: increased local autumn insolation,positive Arctic Oscillation and enhanced East Asian Summer monsoon suppressed subsequent sea ice formation.Sediment rare earth element evidences indicate that the sediments in the Okhotsk Sea have two main sources: the Kamchatka Peninsula and Okhotsk-Chukchi volcanic belt,which could be divided into three phases.(1)During 22.8-11.4 ka,relatively prevalent sea ice induced a dominant Okhotsk-Chukotka volcanic belt sediment input.(2)After 11.4 ka,sea ice reduced,resulting in a significant reduction of sediment input from the Okhotsk-Chukotka volcanic belt.Together with rising sea level and strong West Kamchatka Current resulted in relatively strong northward sediment input from Kamchatka peninsula to the northern Okhotsk Sea.Sea ice and current are the main transportation forces of the terrigenous material inputted to the northern Okhotsk Sea shelf.The sediment source of core LV87-54-1 was relatively stable during 22.8-11.4 ka,which is suitable for reconstructing the silicate weathering history of the source area.The clay minerals and element geochemistry show that the silicate weathering intensity of sediment source region is characterized by a gradual weakening trend during 22.8-20.4 ka,which corresponds well to temperature cooling in the Northern Hemisphere and the variability of East Asia summer precipitation at low latitudes indicating that the silicate weathering processes in the Okhotsk Sea sediment source area respond significantly to both temperature and precipitation variability.From 20.4 to 11.4 ka,rapid sea-level rise resulted in reworking of old weathered sediments and/or the rapid away of the station from the coastline caused relatively reduced input of fresh terrestrial sediments to the northern Okhotsk Sea.The effect of together these processes on the silicate weathering process offset the East Asian Summer monsoon.These resulted in continuous enhancements in sediments chemical weathering state during 20.4-11.4 ka.