Analysis Of Arctic Sea Ice Volume Change And Its Influencing Factors Based On The Fusion Of Remote Sensing And Model Data

Arctic sea ice is an important part of the global climate system.Sea ice changes affect global sea level,ocean circulation patterns,atmospheric dynamics and so on.Sea ice volume(SIV)is directly related to the energy balance and sensitive indicator of climate change.Due to the limitation of SIT data,there is lack of a long-term record of SIV change analysis.The research applies multi-source SIT data to establish the 1979-2018SIT dataset by data assessment,comparison,regression analysis and fusion.The spatiotemporal variability of SIV during the past 40 years is investigated using the SIT and SIA data.The factors influencing SIV change include dynamics(deformation and export)and thermodynamics(melting and freezing).It is needed to evaluate which factor has a greater impact on SIV change and whether the main factors affecting SIV change at different periods are same.Based on the sea ice drift data,sea ice deformation and export flux in 1979-2018 are estimated;the passive microwave bright temperature data can be utilized to analyzed melt and freeze onset.The influence of four factors on SIV change in the different periods are discussed.The main results are descripted as follows:(1)Based on multi-source data,the spatiotemporal variability of SIT is analyzed.Based on CS-2 data,there are three SIT products from the Alfred Wegender Institute(AWI),National snow and ice data center(NSIDC),and European Space Agency(ESA).Compared with Operation Ice Bridge(OIB)observation data,NSIDC CS-2 SIT is the closest to the OIB SIT,with ESA SIT exhibiting the highest bias.There are obvious seasonal differences between AWI(ESA)and NSIDC.The comparative results indicate that the factors resulting in the differences between the SIT products are mainly from freeboard retrieval methods and sea ice density.Based on the regression analysis,data fusion and the Pan-Arctic Ice-Ocean Modeling and Assimilation System model(PIOMAS),we extend the coverage region of the Envisat SIT(81.5°N)data to 88°.Based on NSIDC CS-2 SIT,the consistency of PIOMAS,Envi-PIO and CS-2 is analyzed to obtain a continuous and wide coverage SIT data from 1979 to 2018.The spatiotemporal variability of SIT over the three periods is analyzed based on the different data sources:PIOMAS period(from January 1979 to April 2002),Envisat period(from October 2002 to April 2010),CS-2 period(from October 2010 to December 2018).Because the altimeter observations are affected by the melt pond in summer,the research of SIT and SIV area mainly from October to next April,defined as the sea ice growth season.The SIT in the first two periods decreased significantly in each month.The declining rate in the Envisat period is larger than that in PIOMAS period,with the largest in December(5.9×10^-2 m/yr).There are significantly positive trends for October and November in the CS-2 period.Spatially,in the PIOMAS and Envisat periods,there are negative trends for almost study region with significant levels higher than 95%.The larger declining rates are mainly located to the north of Greenland and the Canadian Arctic Archipelago(CAA)where sea ice is rather thick.The positive trend in the CS-2 period is also located there.(2)The spatiotemporal variability of SIV over the past four decades are analyzed.The SIV trends for each month are similar to that of SIT.The declining rate in the Envisat period is largest and more than 200 km³/yr except for November-December.The declining rate during the PIOMAS period is larger than 100 km³/yr and smaller than 200 km³/yr.During the CS-2 period,the variability trend of SIV is insignificantly positive.Spatially,the regions with the largest variability trends occur in the Central Arctic,Chukchi Sea,East Siberian Sea and Barents Sea in the PIOMAS and Envisat periods;in the CS-2 period,the increasing rate in the northern region of Greenland and the CAA is rather large.Based on the Empirical Orthogonal Function(EOF)analysis,the SIT change has greater influence on SIV change compared with SIA.The older the sea ice age is,the greater SIT is.The annual declining rate of MYI area in 1984-2018reaches-6.5×10⁴ km²/yr.The decreasing rate of above fifth-year ice is the greatest and reaches-8.2×10⁴ km²/yr.The declining of MYI area result in the heavy decreasing of SIV during the Envisat period.(3)Sea ice deformation,export and their effects on SIV change.In the past 40 years,the sea ice drift rate has gradually increased.There is a significant negative correlation between sea ice thickness and drift.The sea ice deformation rate gradually increases in the past 40 years and is seasonal.In summer,the deformation rate is small and large in winter and spring.Large convergence mainly occurs in the north of the CAA and is quantified based on Ice convergence index(ICI).The proportion of ICI>0 in the CS-2period is 65%.It indicates that convergence frequently occur in this period which brings about the increase of SIV in the north of the CAA.The Fram Strait is the main channel for sea ice export in the Arctic Ocean.The annual SIA export through the Fram Strait significantly increased in 1979-2018.For 2007 and 2012,larger anomalies for SIA export show that sea ice export has contributed to the low 2007 and 2012 SIA minimum.There is no significant variability trend in SIV export and proportions of SIV export to monthly mean SIV which indicates that the SIV export is not the main factor for SIV change during the sea ice growth period.Based on linear regression analysis and SIA export,SIV export in May-September is calculated.The SIV export in May-September is significantly correlated with the MYI area(R=-0.39).Sea ice is dominated by MYI in summer.It indicates that SIV flux contribute to the change of MYI especially in the Envisat period.(4)Melt and freeze onset and its effect on SIV change.The EMO/CMO(early melt onset/continuous melt onset)is gradually advanced and the variability rate is-0.15/-0.23 days/year in 1979-2018;The EFO/CFO(early freeze onset/continuous freeze onset)is gradually delayed and the variability rate is 0.71/0.61 days/year;the length of the inner(outer)melt length gradually extend and the variability rate is 0.93(0.75)days/year.The largest variability for melt and freeze onset occurs in the Barents Sea,followed by Kara Sea,Chukchi Sea and Beaufort Sea,which is consistent with the spatial distribution of the larger variation of SIT and SIV in the past 40 years.The melt length in the PIOMAS and Envisat periods have changed significantly and varied insignificantly for the CS-2 period.The variability of the melt length in the Envisat period is larger than that in the PIOMAS period.The correlations between EMO(CMO)and SIV(R<0.8;R<0.4)are smaller than those between EFO(CFO)and SIV(R>0.8).Sea ice variability during the melting periods mainly results from melt and export.90%of sea ice variability results from melting.There is obviously significant negative correlation between TD(Sea surface temperature–surface atmospheric temperature,SST-SAT)and the melt length.The larger difference between SST and SAT is,the more favorable the heat release is.Further,it promotes sea ice formation.In summary,SIT and SIV changes are analyzed in the three(PIOMAS,Envisat,CS-2)periods.In the different periods,the SIT and SIV changes vary and decrease firstly,then decrease heavily,finally change less.Based on the variabilities of sea ice deformation,export,melt and freeze,SIT and SIV changes in different periods are reasonably explained.The results provide data and decision-making support in dynamics and thermodynamics for the sea ice change predictions by model in the future.