Study On Ocean Warming And Marine Heatwave Events In The Arctic Region

This paper uses COBE reanalysis dataset to calculate the sea surface temperature(SST)trend in the Arctic Ocean from 1960 to 2020 and discovers the “Arctic SST amplification” phenomenon.On this basis,we analyze the dominant season,the leading depths,and the main factors of the SST amplification in two different key regions,which we named the Arctic Pacific key region(AP)and the Arctic Atlantic key region(AA).Secondly,a database of marine heatwaves(MHWs)in the Arctic was constructed by using the OISST high-resolution data.The spatial and temporal patterns of MHW in the past 30 years are investigated by using the newly defined intensity composite index(ICI),and we find out the close relationship between severe events and first-year ice(FYI)areas.This relation has been discussed from the three perspectives of marine,atmosphere,and sea ice.In addition,this paper analyzes the process of a strong MHW event that occurred in the AP from June to December in 2007 and finds that this severe MHW is facilitated by a combination of the Pacific Water inflow driven by the surface wind field and the sea ice melting process.Finally,this paper picks out four models in CMIP6 that have a better performance in simulating the SST in the Arctic to simulate the long-term trend of the future Arctic ocean temperature under the SSP1-2.6 and SSP5-8.5 scenarios,and to describe the development of MHWs in the future ice-free summer.Conclusions of this paper will be stated briefly blow.SST in the 60°N-80°N latitude zone has increased significantly,that is,2 times greater than the global average.The warming characteristics between the AA(60°W-60°E,60°N-80°N)and AP(60°E-120°W,60°N-80°N)are significantly different.SST amplification mainly happened during summer in the AP region,with a shallow warming depth,seasonally changed affected sea area,and high enlargement factor.In comparison,the amplified area in the AA region is stable for each month,the intensity is maintained at more than twice,and the warming trend extends vertically to 500 m below the ocean surface.For the major impact factors of SST warming,the AP region is mainly driven by the atmospheric circulation which performs as a dipole of sea level pressure anomaly(SLPa)over the Beaufort Sea and the East Siberia Sea,while the AA region is mainly affected by the 0-300 m ocean heat content(OHC)along the Atlantic Water conveyor belt.The interannual change of the Arctic Oscillation(AO)determines the trend of the ocean heat content,thus affecting the rate of SST warming in the AA region.Results show that there is a significant annual growth in MHW frequency,duration,and intensity in 1988-2017.The increase in the ICI mainly occurs in area south of 80°N in summer after 2000.Particularly,severe MHW events mainly occur in the area where sea ice concentration ranges between 0.1 and 0.5 with ice thickness ranges between 0to 1m,which present the same pattern to the distribution of FYI.Due to the low density of sea ice in the FYI region,the surface seawater can be directly heated by shortwave radiation.At the same time,strong stratification in the FYI area impedes the deep mixing and downward transmission of energy from solar radiation,resulting in an anomalously high sea surface temperature in the FYI area.Besides,the downwelling shortwave radiation has increased significantly in the FYI area,and a large amount of solar shortwave radiation is absorbed by the seawater,which leads to the warmer SST and lesser sea ice extent,providing vast expanse for the generation of MHW events.The severe MHW event that occurred in 2007 was mainly affected by the atmospheric circulation,and its development is accompanied by the formation of the dipole pattern of Beaufort High and Iceland Low.The wind direction over the Bering Strait,which is driven by the Beaufort circulation,determines the strength of Pacific Water and influences the freeze-thaw process through dynamic processes.At the same time,the occurrence of MHW further heated the lower atmosphere,causing a positive feedback process between air and sea ice,jointly promoting the development of this strong event.In the next 80 years,SST in the Arctic region will continue to warm up,and the SST amplification will still exist,with about 5 degrees northward moving of maximum latitude zone.The amplification phenomenon under the SSP1-2.6 scenario is more significant than that under the SSP5-8.5 scenario.The ice-free summer begins to appear around 2060,after which the Arctic SST warming rate increased sharply.As the multiyear ice(MYI)edge gradually shrinks toward the Arctic Archipelago,MHWs will gradually erode the central sea,especially when the Arctic is occupied by FYI in the SSP5-8.5 scenario,MHWs will increase all across the Arctic.