The Water Exchange In Bering Strait And Its Effects On Arctic Sea Ice

The Bering Strait is located in the north of the Bering Sea and south of the Chukchi Sea,the only ocean gateway between the Pacific and Arctic.The water exchange in the Bering Strait can influence the significant changes in the atmosphere-sea-ice system of Arctic.The water exchange in the Bering Strait plays an important role in the process of sea ice melting and freezing.To study the water exchange in the Bering Strait and its effects on Arctic sea ice will improve understanding of the process of the water exchange in the Bering Strait,and so do the research of Arctic sea ice and global climate change.First of all,based on the finite-volume coastal ocean numerical model(FVCOM),a high resolution hydrodynamic model was established to study the tides and tidal energetics in the Bering Strait and its adjacent sea areas.The model results were in good agreement with tide gauge and current data.The model could well simulate the hydrodynamic.The co-tidal charts and the tidal current ellipses of major constituent are drawn and discussed using calculated results.It is shown that the M2 constituent is dominant in the Bering Sea Shelf,the Bering Sea and Chukchi Sea.However,the K1 constituent is dominant in the Norton Sound.The M2 constituent tidal current velocity is larger in the southeast Bering Sea shelf and Anadyr Bay.The maximum tidal current velocity for the K1 constituent appears in Norton Sound.Based on model outputs,to analyze tidal energy flux and dissipation,the results show that the tidal energy flux is small,the total energy dissipation of the major constituents in the research area is about 751 MW,the M2 tidal energy dissipation accounts for 52%,the K1 tidal energy dissipation accounts for 38%.When the tide enters the Bering sea shelf,most of the M2 constituent is dissipated in the south of the St.Lawrence Island,most of the K1 constituent mainly is dissipated in Norton Sound.In addition,we estimated the volume and heat flux through the eastern channel of the Bering Strait.We divided the eastern channel into two regions,Area 1 and Area 2.The multiple linear regression models about the velocity in area 1 and area 2 were built using the sea surface level anomaly slope and NECP 330°and 340° wind components and correlations were examined as well.The results imply that the velocity is mainly affected by ?SLA,and affected by NECP 330°and 340° wind components.This confirmed the previous finding.Based on the velocity multiple linear regression models,the volume transport through the eastern channel of the Bering Strait during the ice-free seasons between 1999 and 2013 was estimated.The results imply that the annual averaged volume transport increased from 2004.Volume transport in Area 1 dominates total transport at eastern channel,but the area 2 volume transport is faster than increase in area 1.As velocity was estimated previously,bottom water temperature were estimated by the similar multiple regression model.The results imply that the velocity is affected by SST and NECP 330°and 340° wind components.We assumed a simple 2-layer structure of temperature,which can be represented by SST and bottom water temperature.Based on the bottom temperature multiple linear regression models and SST,the heat flux through the eastern channel of the Bering Strait during the ice-free seasons between 1999 and 2013 was estimated.The results imply that the heat flux showed increasing trend.Averaged heat fluxes between 2004 and 2008 and between 2009 and 2013 are about 1.9 times and 2.3 times larger than those between 1999-2003.On the one hand,the warmer water coming from Bering Sea is responsible for the heat flux increased.on the orther hand,the volume transport increased is also responsible for that.Finally,we nanlyzed the characteristics of sea ice extent in the Bering Strait and its abjacent sea areas between 1999 and 2015 using the data of daily and monthly sea ice concentration from National Snow an Ice Data Centre based on SMMR and SSM/I.The results imply that there has been a fundamental shift in sea ice over the past several decades.Bering sea and Chukchi sea belong to two completely different ocean respectively.They have different sea ice trends,the extreme trend of sea ice extent occur in the Chukchi sea.For the Northern Bering Sea,statistically significant decreased trends(p< 0.10)are found only during the summer and fall season.In contrast,trends in sea ice cover in the Chukchi Sea have been far more dramatic and statistically significant for all months except January and April.During February,and March,slight increases in ice cover in the Chukchi Sea have been observed.For May through December,however,all trends show significant declines.The changes in sea ice extent have obvious seasonal characterics.The Northern Bering Sea sea ice extent maximum appeared in March,the minimum occurred between June and October.The Chukchi Sea ice extent extremum occurred in Decemeber to May the following year,and the extreme change significantly except the winter,the sea ice extent decreased significantly.The trends in sea ice extent have been spatially heterogeneous,with significant declines in the Chukchi Sea,slight declines in the Bering Strait region,yet increases in the northern Bering Sea south of St.Lawrence Island.The declines in the annual persistence of seasonal sea ice extent in the Chukchi Sea and Bering Strait region are due to both earlier sea ice breakup and later sea ice formation.