Retrieval of snow depth on Antarctic sea ice from the FY-3D MWRI data

The snow depth on sea ice is an extremely critical part of the cryosphere.Monitoring and understanding changes of snow depth on Antarctic sea ice is beneficial for research on sea ice and global climate change.The Microwave Radiation Imager(MWRI)sensor aboard the Chinese FengYun-3D(FY-3D)satellite has great potential for obtaining information of the spatial and temporal distribution of snow depth on the sea ice.By comparing in-situ snow depth measurements during the 35th Chinese Antarctic Research Expedition(CHINARE-35),we took advantage of the combination of multiple gradient ratio(GR(36V,10V)and GR(36V,18V))derived from the measured brightness temperature of FY-3D MWRI to estimate the snow depth.This method could simultaneously introduce the advantages of high and low GR in the snow depth retrieval model and perform well in both deep and shallow snow layers.Based on this,we constructed a novel model to retrieve the FY-3D MWRI snow depth on Antarctic sea ice.The new model validated by the ship-based observational snow depth data from CHINARE-35 and the snow depth measured by snow buoys from the Alfred Wegener Institute(AWI)suggest that the model proposed in this study performs better than traditional models,with root mean square deviations(RMSDs)of 8.59 cm and 7.71 cm,respectively.A comparison with the snow depth measured from Operation IceBridge(OIB)project indicates that FY-3D MWRI snow depth was more accurate than the released snow depth product from the U.S.National Snow and Ice Data Center(NSIDC)and the National Tibetan Plateau Data Center(NTPDC).The spatial distribution of the snow depth from FY-3D MWRI agrees basically with that from ICESat-2;this demonstrates its reliability for estimating Antarctic snow depth,and thus has great potential for understanding snow depth variations on Antarctic sea ice in the context of global climate change.

Temporal and spatial variation characteristics of Antarctic sea ice and the causes of its record decline during 2015–2016: a review

Satellite observations over the past four decades have shown that the long-term trend of Antarctic sea ice extent(SIE)is opposite to the trend of sea ice extent in the Arctic.Arctic sea ice extent continues to decline while Antarctic SIE is generally on the rise except for a dramatic decline in 2015–2016.Based on the 40-year climatology from 1981 to 2020,Antarctic SIE anomaly in December 2016 is–2.1×10^(6) km^(2),reaching the minimum since 1979.There are many studies on the cause of this record decline.This present review summarizes the spatial and temporal characters of Antarctic sea ice and recaps major findings on the causes of record decline in 2015–2016 from the perspective of direct thermodynamic and dynamic process of atmosphere and ocean as well as the modulation of climate modes.Finally,the challenges and key scientific problems to be solved in the future of Antarctic sea ice research are presented.

Antarctic sea ice and ENSO event

The characteristic low-frequency oscillation of the sea surface temperature anomaly (SSTA) of ENSO related regions, Nino 1 + 2, Nino 3, Nino 4 and Nino West, and the Southern Oscillation index (SOI) is analyzed with the method of maximum entropy spectrum. Antarctic sea ice is divided into 4 regions, i. e. East Antarctic is Region Ⅰ (0°-120° E), the region dominated by Ross Sea ice is Region Ⅱ (120° E-120° W), the region dominated by Ross Sea ice is Region Ⅲ (120° W-0°), and the whole Antarctic sea ice area is Region Ⅳ. Also, the month-to-month correlation series of the sea ice with ENSO from contemporary to 5-years lag is calculated. The optimum correlation period is selected from the series. The characteristics and the rules obtained are as follows.1. There are a common 4-years main period of the SSTA of Ninos 1 + 2,3 and 4, a rather strong 4-years secondary period and a quasi-8-years main period of that of Nino West. There are also 1. 5 and 2 to 3-years secondary periods of that of all 4 Nino regions.2. As another indicator of El Nino, the SOI represents the feature of the atmosphere in low latitude area, having a quasi-5-years main period; it also has secondary periods, 1, 1. 5 and 2 to 3 years, among them, the 2 to 3-years one is prominent.3. There is a close relationship between Antarctic sea ice and ENSO event. In the long-range correlation from contemporary up to 60 months of the SSTA in Ninos 1 + 2,3 and 4 and Antarctic sea ice area index, or the time series of 16 correlation coefficients made of each one of the 4 sea ice regions with that of the 4 Nino regions, there is a prominent common characteristic that all correlations are negative from contemporary to 34-months lag of the SSTA of the 4 Nino regions behind Antarctic sea ice, the optimum correlation periods with the confidences equal to or more than 5 % , 1 % lagging in 13-19, 24-34 month are the most. The correlations of sea ice in Regions Ⅱ , Ⅲ and W with the SSTA of Ninos 3 and 4 are the strongest. The correlation of the sea ice in Region Ⅰ with Nino West in 4 - 5-years lag becomes a very strong positive one. The correlations of the sea ice in Regions Ⅱ and Ⅲ with Ninos 1 + 2, 3 and 4 become strong positive ones during the quasi-4-years lag. The variation of the correlation series of the SOI and the 4 sea ice regions is the opposite of that of the 4 Nino regions. The correlations with the sea ice in Regions Ⅱ , Ⅲ and Ⅳ are strong, with the strong positive correlations of 6, 10 and 24-months lag being the optimum correlation periods. And the strong negative correlation period is 40-months lag.4. The characteristic variation of the correlation time series reflects the low-frequency oscillation feature of Antarctic sea ice and ENSO. In the periodic variation, the correlation becomes the strongest when the ice and ENSO are inresonance. Specifically,the Antarctic sea ice influences ENSO most in an earlier period of its own variation. Moreover, it is also related with the period of variation of ENSO itself, i. e. the correlation of sea ice and ENSO gets the best in a period lag of ENSO its own variation.

Anomalous change of the Antarctic sea ice and global sea level change

In this paper, the long-term variation trend of the Antarctic sea ice in 1973～1994 and the inter-decade variation rule of the global sea level are analyzed. It is found that the sea ice area in the Antarctic in the 1980s was significantly less than in the 1970s and the average global sea level height value in the 1980s was also significantly higher than in the 1970s. Connecting variation of both and analyzing their physical mechanism, it indicates that the accumulated sea ice anomaly value in the 1980s less than in the 1970s means a global climate warming, the sea water temperature and air temperature were obviously higher in the 1980s it introduced the long-term accumulated sea ice decreased greatly; a higher sea water temperature introduced sea water volume expanding, and more icebergs transporting from the ice cover in the Antarctic continent to ocean in the warmer year. As a result induced by these multi-causes, the global sea level raised significantly in the 1980s. The global average sea level value in the 1980s, was 22 mm higher than in the 1970s. The sea level raising(SLR) was distributed unevenly. It is especially true in the Pacific Ocean with two expensive we level raising regions in the Northeast Pacific and Southeast Pacific as well as a raising region near the Bering Sea; and with two descent regions in the Northwest and Southwest Pacific. It is considered that this kind of uneven SLR distribution closely relates to the sustained decreasing of the Antarctic sea ice. The higher sea water tem This study was supported both by the National Natural Science Foundation of China under contrast Nod 49376252 and by the National '85' Plan 'Key Project 903': 7th Popect.perature in the south ocean introduces a rather warmer water temperature of the Peru Cold Current which is a northward branch of the South Oceanic Current along the South American continent, then it is easier to the occurrence of El Nino event. When El Nino event occurs, the prevailed tropical easterlies over the Pacific weaken and the westerlies intensify. Normally, the sea level is higher in the west and low in the east. A lot of sea water is transported from west to east caused by gravity and wind dynamics in this situation. The uneven distribution of raising in the eastern Pacific and descending in the western Pacific was introduced.

The variation features of the Antarctic sea ice (Ⅱ)

In this paper, on the basis of the Antarctic sea ice data from 1972 to 1989 issued by the America JointIce Center, the distribution features of the Antarctic sea ice is analyzed, the net sea ice area indexes are calculated,and the long-range variation periods of the sea ice area index are analyzed with the maximum entropy spectrum, finally the distribution pattern of the Antarctic sea ice and its variation features are obtained.According to its spatial distribution feature, the Antarctic Sea ice is divided into three large regions. Region Ⅰ(0°～120°E) is a zonal area which includes the Prydz Bay area, and sea ice area extending from the Weddell Sea,Region Ⅱ (120°E～120°W) mainly includes the Ross Sea area, and Region Ⅲ (120°W～0°) mainly the WeddellSea area. Of all the regions, the ice area in Region Ⅲ is the largest, and that in Region Ⅰ is the smallest.In the Antarctic,the seasonal changes of the sea ice are very obvious, during summer, in February, there isleast sea ice in the Southern Ocean, the net sea ice area (not include the area of open water) is about 3 190 000 km2,during winter, in September, there is most sea ice in the Southern Ocean, the area index is about 16 840 000 km2,nearly 5. 3 times of that in February. The seasonal change of sea ice is one month lag of the changes of the air temperature, but almost synchronous with that of SST.Of all the three regions divided above, there are some points both common and uncommon in their sea icechange cycles, the common features are that there exist one and a half years, one year and ten-months secondaryperiods in all three regions, but their main periods are not the same, they are about 5, 11 and 6 a in Regions Ⅰ,Ⅱ,and Ⅲrespectively. The main periods of the sea ice change in Regions Ⅰand Ⅱ are very close because the ice areaextended eastward from the Weddell Sea ice area of Region Ⅲ is one of the main components of the Region Ⅰ. It isalso worth pointing out that in Region Ⅱ, southward extension of the Pacific Ocean, there exist not only a 11-yerasmain period but also a 2-yeras secondary period, which does not exist in the other two regions.

Microseism Variations in Response to Antarctic Seasonal Changes in Sea Ice Extent

The temporal and spatial distributions of Antarctic sea ice play important roles in both the generation mechanisms and the signal characteristics of microseisms. This link paves the way for seismological investigations of Antarctic sea ice. Here we present an overview of the current state of seismological research about microseisms on Antarctic sea ice. We first briefly review satellite remote-sensing observations of Antarctic sea ice over the past 50 years. We then systematically expound upon the generation mechanisms and source distribution of microseisms in relation to seismic noise investigations of sea ice, and the characteristics of Antarctic microseisms and relationship with sea ice variations are further analyzed. We also analyze the continuous data recorded at seismic station BEAR in West Antarctica from 2011 to 2018 and compare the microseism observations with the corresponding satellite remotesensing observations of Antarctic sea ice. Our results show that:(1) the microseisms from the coastal regions of West Antarctica exhibit clear seasonal variations,SFM with maximum intensities every April-May and minimum intensities around every October-November;while DFM intensities peak every February-March,and reach the minimum around every October. Comparatively,the strong seasonal periodicity of Antarctic sea ice in better agreement with the observed DFM;and(2) microseism decay is not synchronous with sea ice expansion since the microseism intensity is also linked to the source location,source intensity(e. g.,ocean storms,ocean wave field),and other factors. Finally, we discuss the effect of Southern Annular Mode on Antarctic sea ice and microseisms,as well as the current limitations and potential of employing seismological investigations to elucidate Antarctic sea ice variations and climate change.

Spatial-temporal characters of Antarctic sea ice variation

Using sea ice concentration dataset covering the period of 1968-2002 obtained from the Hadley Center of UK, this paper investigates characters of Antarctic sea ice variations .The finding demonstrates that the change of mean sea-ice extent is almost consistent with that of sea-ice area, so sea-ice extent can be chosen to go on this research. The maximum and the minimum of Antarctic sea ice appear in September and February respectively. The maximum and the maximal variation of sea ice appear in Weddell Sea and Ross Sea, while the minimum and the minimal variation of sea-ice appear in Antarctic Peninsula. In recent 35 years, as a whole, Antarctic sea ice decreased distinctly. Moreover, there are 5 subdivision characteristic regions considering their different variations. Hereinto, the sea-ice extent of Weddell Sea and Ross Sea regions extends and area increases, while the sea-ice extent of the other three regions contracts and area decreases. They are all of obvious 2-4 years and 5-7 years significant oscillation periods. It is of significance for further understanding the sea-ice-air interaction in Antarctica region and discussing the relationship between sea-ice variation and atmospheric circulation.

Impact of the El Nino on the Variability of the Antarctic Sea Ice Extent

In this paper, the spreading way in the southern hemisphere that anomalous warm water piled in tropical eastern Pacific is analysed and then impact of El Nino on the variability of the Antarctic sea ice extent is investigated by using a dataset from 1970 to 2002. The analysis result show that in El Nino event the anomalous warm water piled in tropical eastern Pacific is poleward propagation yet the westward propagation along southern equator current hasn't been discovered . The poleward propagation time of the anomalous warm water is about 1 year or so. El Nino event has a close relationship with the sea ice extent in the Amundsen sea , Bellingshausen sea and Antarctic peninsula .After El Nino appears , there is a lag of two years that the sea ice in the Amundsen sea , Bellingshausea sea, especially in the Antarctic peninsula decreases obviously. The processes that El Nino has influence with Antarctic sea ice extent is the warm water piled in tropical eastern Pacific poleward propagation along off the coast of southern America and cause the anomalous temperature raise in near pole and then lead the sea ice in Amundsen sea , Bellingshausen sea and Antarctic peninsula to decrease where the obvious decrease of the sea ice since 80' decade has close relation to the frequently appearance of El Nino .

Definition of Arctic and Antarctic Sea Ice Variation Index

It is well known that varying of the sea ice not only in the Antarctic but also in the Arctic has an active influence on the globe atmosphere and ocean. In order to understand the sea ice variation in detail, for the first time, an objective index of the Arctic and Antarctic sea ice variation is defined by projecting the monthly sea ice concentration anomalies poleward of 20°N or 20°S onto the EOF (empirical orthogonal function)-1 spatial pattern. Comparing with some work in former studies of polar sea ice, the index has the potential for clarifying the variability of sea ice in northern and southern high latitudes.

The signature analysis of summer Antarctic sea-ice distribution by ship-based sea-ice observation

Based on the Chinese 19th National Antarctic Research Expedition,we carried out ship-based Antarctic sea-ice observa-tion on icebreaker Xue Long using Antarctic sea-ice process and climate (ASPeCt) criteria during austral summer.Sea-ice distribution data were obtained along nearly 6,500 km of the ship’s track.The measurement parameters included sea-ice thickness,sea-ice concentration,snow thickness,and floe size.Analysis showed the presence of the large spatial varia-tions of the observed sea-ice characteristics.Sea-ice concentration varied between 0 and 80 percent and reached its peak value in Weddell Sea because of the specific dynamical process affecting in summer sea-ice melting.There are large areas of open water along the study section.Sea ice and the upper snow thickness of the section varied between 10 cm and 210 cm and 2 cm and 80 cm,respectively,and each reaches its peak values near Amery ice shelf.The floe size varied from less than 10 cm and the maximum of more than 2,000 km along the section.

Albedo of Coastal Landfast Sea Ice in Prydz Bay,Antarctica:Observations and Parameterization

The snow/sea-ice albedo was measured over coastal landfast sea ice in Prydz Bay, East Antarctica（off Zhongshan Station）during the austral spring and summer of 2010 and 2011. The variation of the observed albedo was a combination of a gradual seasonal transition from spring to summer and abrupt changes resulting from synoptic events, including snowfall, blowing snow, and overcast skies. The measured albedo ranged from 0.94 over thick fresh snow to 0.36 over melting sea ice. It was found that snow thickness was the most important factor influencing the albedo variation, while synoptic events and overcast skies could increase the albedo by about 0.18 and 0.06, respectively. The in-situ measured albedo and related physical parameters（e.g., snow thickness, ice thickness, surface temperature, and air temperature） were then used to evaluate four different snow/ice albedo parameterizations used in a variety of climate models. The parameterized albedos showed substantial discrepancies compared to the observed albedo, particularly during the summer melt period, even though more complex parameterizations yielded more realistic variations than simple ones. A modified parameterization was developed,which further considered synoptic events, cloud cover, and the local landfast sea-ice surface characteristics. The resulting parameterized albedo showed very good agreement with the observed albedo.

ANTARCTIC SEA ICE AND THE POLAR VORTEX INDEX:TEMPORAL AND SPATIAL CHARACTERISTICS AND THEIR RELATIONSHIP

The cluster analysis method has been used to divide the Antarctic sea ice variation field into 5 sectors.Then,for each of these sectors,the corresponding indexes of vortex area and vortex intensity on the 500 hPa level have been calcu- lated.These data were used to analyse the temporal and spatial characteristics of both Antarctic sea ice and the vortex index variations and their relationship.Our results show that substantial differences are presented in the climatic pattern and interannual variations of the sea ice data and vortex index in different sectors.The maximum sea ice extent varia- tions appear in sector 1 and sector 4.Oscillation periods of 2—2.5 and 5—7 years exist in the variations of sea ice extent and vortex index in most sectors.A positive trend is only found in sector 1 sea ice extent while the other sectors show negative trends.The average extent of the Antarctic sea ice as a whole has retreated at a rate of 1.6 latitudes per 100 years.The vortex areas for all sectors have decreased.Nevertheless,the vortex intensities in 3 sectors have increased.The relationship between sea ice and vortex characters in each sector is obvious,but a little complex.Sectors 1 and 5,which are located in the Southeast Pacific and South Atlantic,are the most sensitive areas in terms of sea ice/atmosphere interaction.

Characteristics of change in the Antarctic sea ice area and its relation to SST in the tropical Pacific

In this paper, the characteristics of change in the Antarctic sea ice area are analysed by using the observed data from 1973 1986. The analysed results show that the monthly and annual change of the Antarctic sea ice area is obvious, the biggest change value is in 160°E 120°W and 60°W 100°E, the smallest value is in 110°E 160°E and 120°W 60°W. The relation between the Antarctic sea ice area and the Sea Surface Temperature(SST) in tropical Pacific is close, and the relation between the Antarctic sea ice area in each longitude belt and SST in tropical Pacific shows a clear difference. It is obvious that the Antarctic sea ice areas in 0° 90°E and 100°E 110°W have a different feedbacking relation with SST in the tropical Pacific. The notable relationship occurs in the 3 4 and 41 45 months, that quite tallies with the occurrence of El Nino.

Upper limits for chlorophyll a changes with brine volume in sea ice during the austral spring in the Weddell Sea,Antarctica

During the winter and spring of 2006, we investigated the sea ice physics and marine biology in the northwest Weddell Sea, Antarctica aboard R/V Polarstern. We determined the texture of each ice core and 71 ice crystal thin sections from 27 ice cores. We analyzed 393 ice cores, their temperatures, 348 block density and salinity samples,and 311 chlorophyll a（Chl a） and phaeophytin samples along the cruise route during the investigation. Based on the vertical distributions of 302 groups of data for the ice porosity and Chl a content in the ice at the same position, we obtained new evidence that ice physical parameters influence the Chl a content in ice. We collected snow and ice thickness data, and established the effects of the snow and ice thickness on the Chl a blooms under the ice, as well as the relationships between the activity of ice algae cells and the brine volume in ice according to the principle of environmental control of the ecological balance. We determined the upper limits for Chl a in the brine volume of granular and columnar ice in the Antarctica, thereby demonstrating the effects of ice crystals on brine drainage, and the contributions of the physical properties of sea ice to Chl a blooms near the ice bottom and on the ice-water interface in the austral spring. Moreover, we found that the physical properties of sea ice affect ice algae and they are key control elements that modulate marine phytoplankton blooms in the ice-covered waters around Antarctica.

MATHEMATICAL STATISTICS OF HEAVY MINERALS AND THEIR REE AND TRACE ELEMENTS IN THE NORTHWESTERN SEA AREA OF ANTARCTIC PENINSULA

Based on the analysis and mathematical statistics of quantitative data on both the heavy minerals and their REE (La, Ce, Nd, Sm, Eu, Tb, Yb, Lu), trace (Zr, Hf, Th, Ta, U, Rb, Sr, Zn, Co, Ni, Cr, As, Sc) and major (Fe) elements in the surface sediments in the northwestern sea area of Antarctic Peninsula, the authors find that the heavy minerals as the carriers of REE and trace elements should not be overlooked.Q-mode factor analysis of the heavy minerals provides a 3-factor model of the heavy mineral assemblages in the study area, which is mainly controlled by the origin of materials and sea currents. The common factor P1, composed mainly of pyroxene and metal minerals, and common factor P2, composed of hornblende, epidote and accessory minerals, represent two heavy mineral assemblages which are different from each other in both lithological characters and origin of materials. And common factor P3 probably results from mixing of two end members of the above-mentioned assemblages. R-mode group analysis of the heavy minerals indicates that there are two heavy mineral groups in the sea area, which are different from each other in both genesis and origin of materials. With the help of R-mode analysis, 22 elements are divided into 3 groups and 9 subgroups. These element assemblages show that they are genetically related and that they are different in geochemical behaviors during diagenesis and mineral-forming process. In addition, the relationship between the heavy mineral assemblages and the element subgroups is also discussed.

A note on crustal structure between Antarctic Peninsula and East Antarctic craton across the shelf of southern Weddell Sea

Analysis of gravity data based on the Airy isostasy, magnetic depth estimates and few seismic refraction data taken together indicates a thinning of the crust between the Antarctic Peninsula and the East Antarctic craton below the Filchner and Ronne ice shelves.

Impacts of Ice-Ocean Stress on the Subpolar Southern Ocean:Role of the Ocean Surface Current

The mechanical influences involved in the interaction between the Antarctic sea ice and ocean surface current(OSC)on the subpolar Southern Ocean have been systematically investigated for the first time by conducting two simulations that include and exclude the OSC in the calculation of the ice-ocean stress(IOS), using an eddy-permitting coupled ocean-sea ice global model. By comparing the results of these two experiments, significant increases of 5%, 27%, and 24%, were found in the subpolar Southern Ocean when excluding the OSC in the IOS calculation for the ocean surface stress,upwelling, and downwelling, respectively. Excluding the OSC in the IOS calculation also visibly strengthens the total mechanical energy input to the OSC by about 16%, and increases the eddy kinetic energy and mean kinetic energy by about38% and 12%, respectively. Moreover, the response of the meridional overturning circulation in the Southern Ocean yields respective increases of about 16% and 15% for the upper and lower branches;and the subpolar gyres are also found to considerably intensify, by about 12%, 11%, and 11% in the Weddell Gyre, the Ross Gyre, and the Australian-Antarctic Gyre, respectively. The strengthened ocean circulations and Ekman pumping result in a warmer sea surface temperature(SST), and hence an incremental surface heat loss. The increased sea ice drift and warm SST lead to an expansion of the sea ice area and a reduction of sea ice volume. These results emphasize the importance of OSCs in the air-sea-ice interactions on the global ocean circulations and the mass balance of Antarctic ice shelves, and this component may become more significant as the rapid change of Antarctic sea ice.

The relationship between polar sea ice and the precipitation and temperature over China revealed by using SVD method

The relationship between polar sea ice anomalies and the precipitation and temperature anomalies over China is investigated by performing singular value decomposition (SVD) analyses. The first three coupling modes have been studied. Analyses show that there exist key areas of polar sea ice which are highly related with the precipitation and temperature anomalies over China. Different spatial anomaly patterns of these areas of polar sea ice are followed by different spatial anomaly patterns of the precipitation and temperature over China.

Purification and characterization of cold-active endo-1,4-β-glucanase produced by Pseudoalteromonas sp. AN545 from Antarctica

A bacterium hydrolyzing carboxymethylcellulose, isolated from Antarctic sea ice, was identified as Pseudoalteromonas sp. based on 16S rDNA gene sequences and named as Pseudoalteromonas sp. AN545. The extracellular endo-1,4-β-glucanase AN-1 was purified successively by ammonium sulfate precipitation, DEAE-Sepharose ion exchange chromatography and Sephadex G-75 gel filtration chromatography. The molecular mass of AN-1 was estimated to be 47.5 kDa utilizing SDS-PAGE and gel chromatography analysis. AN-1 could hydrolyze caboxymethylcellulose, avicel and β-glucan, but not cellobiose, xylan and p-Nitrophenyl-β-D-glucopyranoside. The optimal temperature and pH for the β-glucanase activity of AN-1 were determined to be at 30℃ and pH 6.0, respectively. AN-1 was stable at acidic solutions of pH 5.0-6.5 and temperatures below 30℃ for 1 h. Moreover, the specific activity was enhanced by Ca2＋ and Mg2., and inhibited by Cu2＋. The kinetic parameters Michaelis constant （Km） and maximum velocity （Vmax） of AN-1 were 3.96 mg/mL and 6.06×10-2 mg/（min.mL）, respectively.

Synoptic mode of Antarctic summer sea ice superimposed on interannual and decadal variability

In contrast to decreased Arctic sea ice extent,Antarctic sea ice extent shows a somewhat increased trend.There is a large interannual variability of Antarctic sea ice,especially in the Pacific sector of the Southern Ocean.The change and variability of Antarctic sea ice in synoptic timescales in the recent decades remain unclear.We identify synoptic modes of variability of Antarctic summer sea ice by applying the Self Organizing Map(SOM)technique to daily sea ice concentration data for the period 1979–2018.Nearly 40%of the variability is characterized by opposite changes between sea ice cover in the Bellingshausen,Amundsen and western Ross Seas and in the rest of the Antarctic seas,and another 30%by meridional asymmetry in the Weddell,Amundsen,and Ross Seas.Most of these spatial patterns may be explained by the dynamics and thermodynamic processes associated with anomalous atmospheric circulations related to the Southern Annular Mode(SAM)with a structure of strong zonal asymmetry.The interannual variability of the sea ice modes appears to have little connection to SAM,and only a weak relation to ENSO.The annual frequencies of SOM node occurrences also show a great decadal variability.Node 9 appears mainly prior to 1990;while node 1 occurs mainly after 1990.The decadal variability of nodes 1 and 9 is associated with the asymmetrical SAM,which results from two wavetrains excited over northern Australia and the southeastern Indian Ocean.These results further highlight the importance of understanding the role of southern mid-to-high latitude atmospheric intrinsic variability in predicting Antarctic summer sea ice variations from synoptic to decadal timescales.