Rapid Changes In Sedimentary Environment On The Northern Slope Of The Bering Sea During The Early Holocene

It has been an important research topic in oceanography and climatology to understand the evolution of marine environment in the context of anathroprogenic warming.In the geological past,the Earth had experienced several warming periods（including the early Holocene）,which provided natural analogs for future climate.The global climate experienced rapid warming during the early Holocene,accompanied by ice sheet melting and rapidly sea level rised,which had significantly impacted sedimentary processes and marine environment in high-latitude marginal seas,included the Bering Sea.The Bering Sea consisted of a broad continental shelf,adjacented to the North American continent,and received material supplies from the Yukon River and Anadyr River.There were still significant gaps in our understanding of how the Bering Sea responds to the early Holocene climate.In this study,the LV63-19-3 core with a length of 5.5 m from the northern land slope of the Bering Sea was used to analyze for grain size,elemental geochemistry,paleoproductivity and stable isotope of carbon and nitrogen in combination with the sedimentary age model.We focused on the scientific question of the response of characteristics and driving mechanisms of the sedimentary environment to warming climate in the northern slope of Bering Sea during the early Holocene,to reveal the source and transport mechanism of the terrestrial clastic fraction in the study area during the early to middle Holocene（～11.7-5.5 ka）,to elucidate the marine——terrestrial organic matter content and burial fluxes changes in study area during the early Holocene,and preliminarily explored the response of terrestrial sediments accumulation、paleoproductivity and organic matter sources、sediment redox-environments in study area to climate warming during the early Holocene.The results of the sedimentation showed that the line sedimentation rate on the northern slope of Bering Sea was as high as～392.9 cm/kyr during 11.5～11 ka,and decreased rapidly to～16.8 cm/kyr after～9.7 ka.At～11～10.7 ka,a dark laminated sediment layer about of 40 cm thick was found.In the period of high sedimentation rate,the average grain size of sediments was finer,and increased gradually after 9 ka.Both major and minor element concentrations indicated that the lithological properties of terrigenous clastic sediments were mainly felsic sediments with a small amount of pyroclastic contributions.Stable isotope of carbon and nitrogen results showed that the terrestrial organic matter content and burial were higher and the marine organic matter content was lower at 11.5～10.7 ka,while the terrestrial organic matter content and burial decreased and the marine organic matter content increased after 10.7 ka.The results of redox-sensitive element showed that the values of authigenic Mo_xsand U_xsincreased at 11～10.7 ka,indicating the degree of anoxia in the middle and deep water column of the study area.The period of high line sedimentation rate on the northern slope of the Bering Sea corresponded to the meltwater pulse（MWP）-1B event（～11.4-11.1 ka）,the increased burial flux of terrestrial material was the result of enhancing river transport dynamics and the Meltwater Pulse event in this period.The resuspended detrital material in the submerged Bering shelf was transported by ocean currents to the study area under the action of tides and waves during the（MWP）-1B,and the input of organic and detrital material from terrestrial sources decreased after 9 ka.The formation of laminated sediments layer may be related to the enhanced seasonal sea ice activity and marine primary productivity on the northern Bering Sea land slope during 11-10.7 ka.The increased in seasonal sea ice activity inhibited the oxygen supply from the atmosphere to surface water and subsequent transport to the bottom water,while the persistent high productivity in summer and autumn further exacerbated the bottom water oxygen depletion in the Bering Sea,both of which together triggered the formation of laminated sediment layer.We suggested that the rapid shift in early Holocene sedimentary environment on the northern Bering Sea continental slope was the result of a combination of sea level,Meltwater Pulse event,seasonal sea ice activity and marine primary productivity,which was actually controlled by high-latitude solar insolation,north American ice sheet melting,and global climate.