The sudden ocean warming and its potential influences on earlyfrozen landfast ice in the Prydz Bay, East Antarctica

The ocean conditions beneath the ice cover play a key role in understanding the sea ice mass balance in the polar regions.An integrated high-frequency ice-ocean observation system,including Acoustic Doppler Velocimeter,Conductivity-Temperature-Depth Sensor,and Sea Ice Mass Balance Array(SIMBA),was deployed in the landfast ice region close to the Chinese Zhongshan Station in Antarctica.A sudden ocean warming of 0.14℃(p<0.01)was observed beneath early-frozen landfast ice,from(−1.60±0.03)℃during April 16-19 to(−1.46±0.07)℃during April 20-23,2021,which is the only significant warming event in the nearly 8-month records.The sudden ocean warming brought a double rise in oceanic heat flux,from(21.7±11.1)W/m^(2) during April 16-19 to(44.8±21.3)W/m^(2) during April 20-23,2021,which shifted the original growth phase at the ice bottom,leading to a 2 cm melting,as shown from SIMBA and borehole observations.Simultaneously,the slowdown of ice bottom freezing decreased salt rejection,and the daily trend of observed ocean salinity changed from+0.02 d^(-1) during April 16-19,2021 to+0.003 d^(-1) during April 20-23,2021.The potential reasons are increased air temperature due to the transit cyclones and the weakened vertical ocean mixing due to the tide phase transformation from semi-diurnal to diurnal.The high-frequency observations within the ice-ocean boundary layer enhance the comprehensive investigation of the ocean’s influence on ice evolution at a daily scale.

An improved algorithm for retrieving thin sea ice thickness in the Arctic Ocean from SMOS and SMAP L-band radiometer data

The aim of this study was to develop an improved thin sea ice thickness(SIT)retrieval algorithm in the Arctic Ocean from the Soil Moisture Ocean Salinity and Soil Moisture Active Passive L-band radiometer data.This SIT retrieval algorithm was trained using the simulated SIT from the cumulative freezing degree days model during the freeze-up period over five carefully selected regions in the Beaufort,Chukchi,East Siberian,Laptev and Kara seas and utilized the microwave polarization ratio(PR)at incidence angle of 40°.The improvements of the proposed retrieval algorithm include the correction for the sea ice concentration impact,reliable reference SIT data over different representative regions of the Arctic Ocean and the utilization of microwave polarization ratio that is independent of ice temperature.The relationship between the SIT and PR was found to be almost stable across the five selected regions.The SIT retrievals were then compared to other two existing algorithms(i.e.,UH_SIT from the University of Hamburg and UB_SIT from the University of Bremen)and validated against independent SIT data obtained from moored upward looking sonars(ULS)and airborne electromagnetic(EM)induction sensors.The results suggest that the proposed algorithm could achieve comparable accuracies to UH_SIT and UB_SIT with root mean square error(RMSE)being about 0.20 m when validating using ULS SIT data and outperformed the UH_SIT and UB_SIT with RMSE being about 0.21 m when validatng using EM SIT data.The proposed algorithm can be used for thin sea ice thickness(<1.0 m)estimation in the Arctic Ocean and requires less auxiliary data in the SIT retrieval procedure which makes its implementation more practical.

Parameterization, sensitivity, and uncertainty of 1-D thermodynamic thin-ice thickness retrieval

Retrieval of Thin-Ice Thickness(TIT)using thermodynamic modeling is sensitive to the parameterization of the independent variables(coded in the model)and the uncertainty of the measured input variables.This article examines the deviation of the classical model’s TIT output when using different parameterization schemes and the sensitivity of the output to the ice thickness.Moreover,it estimates the uncertainty of the output in response to the uncertainties of the input variables.The parameterized independent variables include atmospheric longwave emissivity,air density,specific heat of air,latent heat of ice,conductivity of ice,snow depth,and snow conductivity.Measured input parameters include air temperature,ice surface temperature,and wind speed.Among the independent variables,the results show that the highest deviation is caused by adjusting the parameterization of snow conductivity and depth,followed ice conductivity.The sensitivity of the output TIT to ice thickness is highest when using parameterization of ice conductivity,atmospheric emissivity,and snow conductivity and depth.The retrieved TIT obtained using each parameterization scheme is validated using in situ measurements and satellite-retrieved data.From in situ measurements,the uncertainties of the measured air temperature and surface temperature are found to be high.The resulting uncertainties of TIT are evaluated using perturbations of the input data selected based on the probability distribution of the measurement error.The results show that the overall uncertainty of TIT to air temperature,surface temperature,and wind speed uncertainty is around 0.09 m,0.049 m,and−0.005 m,respectively.

Spatial and temporal evolution of landfast ice near Zhongshan Station, East Antarctica, over an annual cycle in 2011/2012

Annual observations of first-year ice(FYI) and second-year ice(SYI) near Zhongshan Station, East Antarctica,were conducted for the first time from December 2011 to December 2012. Melt ponds appeared from early December 2011. Landfast ice partly broke in late January, 2012 after a strong cyclone. Open water was refrozen to form new ice cover in mid-February, and then FYI and SYI co-existed in March with a growth rate of 0.8 cm/d for FYI and a melting rate of 2.7 cm/d for SYI. This difference was due to the oceanic heat flux and the thickness of ice,with weaker heat flux through thicker ice. From May onward, FYI and SYI showed a similar growth by 0.5 cm/d.Their maximum thickness reached 160.5 cm and 167.0 cm, respectively, in late October. Drillings showed variations of FYI thickness to be generally less than 1.0 cm, but variations were up to 33.0 cm for SYI in March,suggesting that the SYI bottom was particularly uneven. Snow distribution was strongly affected by wind and surface roughness, leading to large thickness differences in the different sites. Snow and ice thickness in Nella Fjord had a similar "east thicker, west thinner" spatial distribution. Easterly prevailing wind and local topography led to this snow pattern. Superimposed ice induced by snow cover melting in summer thickened multi-year ice,causing it to be thicker than the snow-free SYI. The estimated monthly oceanic heat flux was ～30.0 W/m2 in March–May, reducing to ～10.0 W/m2 during July–October, and increasing to ～15.0 W/m2 in November. The seasonal change and mean value of 15.6 W/m2 was similar to the findings of previous research. The results can be used to further our understanding of landfast ice for climate change study and Chinese Antarctic Expedition services.

Specific Relationship between the Surface Air Temperature and the Area of the Terra Nova Bay Polynya,Antarctica

Antarctic polynyas play an important role in regional atmosphere?ice?ocean interactions and are considered to help generate the global deep ocean conveyer belt.Polynyas therefore have a potential impact on the Earth’s climate in terms of the production of sea ice and high-salinity shelf water.In this study,we investigated the relationship between the area of the Terra Nova Bay polynya and the air temperature as well as the eastward and northward wind based on the ERA5 and ERAInterim reanalysis datasets and observations from automatic weather stations during the polar night.We examined the correlation between each factor and the polynya area under different temperature conditions.Previous studies have focused more on the effect of winds on the polynya,but the relationship between air temperature and the polynya area has not been fully investigated.Our study shows,eliminating the influence of winds,lower air temperature has a stronger positive correlation with the polynya area.The results show that the relationship between the polynya area and air temperature is more likely to be interactively influenced.As temperature drops,the relationship of the polynya area with air temperature becomes closer with increasing correlation coefficients.In the low temperature conditions,the correlation coefficients of the polynya area with air temperature are above 0.5,larger than that with the wind speed.

The first 10 m resolution thermokarst lake and pond dataset for the Lena Basin in the 2020 thawing season

Climate warming rates in the Arctic are far greater than the global average,exerting stronger impacts on permafrost degradation and thermokarst landform development.Thermokarst lakes and ponds(TLPs),which are widely distributed in the Lena Basin in the Russian Arctic,play a vital role in altering local ecosystem.However,the detailed distribution of TLPs in the Lena Basin still remains poorly known.In this study,we built the first 10 m resolution TLP dataset for the Lena Basin in the 2020 thawing season by utilizing 4902 Sentinel-2 images.A robust mapping workflow was developed and implemented in the Google Earth Engine(GEE)platform.The accu-racy assessment demonstrates a satisfactory accuracy(93.63%),and our results exhibit a better consistency with real TLPs than global water body products.A total of 380,477 TLPs(~0.53%of the total surface area of the Lena Basin)were identified,showing an uneven distribution in the five sub-basins.The TLPs were found to be mainly located within plain areas,with an active layer thickness in the range of 80-100 cm.The higher ground ice content and mean annual ground temperature were favorable for TLP development.This dataset will be valuable for investigating the complex interac-tion between TLPs and permafrost.It will also serve as a baseline product for better incorporating thermokarst processes into perma-frostclimate models.

2022年1月汤加火山海啸引发南极冰舌前缘崩解

On 15 January 2022,the Hunga Tonga-Hunga Ha’apai volcano(20.54°S 175.39°W),a submarine volcano located about 65 km north of Tonga’s main island in the South Pacific,violently erupted with a powerful explosion[1].The volcanic explosivity index(VEI)was estimated to be 6 indicating that the eruption was among the largest volcanic activity ever observed with modern geophysical instrumentation[2].The explosion ejected an enormous ash plume to record-breaking heights of~55 km[3]and caused atmospheric waves that propagated across the globe in less than 24 h[4].

中国首个格陵兰冰盖自动气象站

The Greenland ice sheet(GrIS)is the second largest ice sheet in the world,but it is the largest contributor to sea level rise[1]as global warming continues.If its mass was lost completely,global mean sea level would rise by about 7.2 m[2].Over the recent three decades,mass loss of the GrIS driven by oceanic and atmospheric warming has been significantly increased[3].

Stable classi?cation with limited sample: transferring a 30-m resolution sample set collected in 2015 to mapping 10-m resolution global land cover in 2017

As the world strives to reduce the impact of population growth, urbanization, agricultural expansion, and climate change on food security, energy and water shortage, resource over-exploration, biodiversity loss, environmental pollution, and ultimately human health, timely and higher resolution land cover information is urgently needed to achieve the sustainable development goals of the United Nations.

北极冰区通航能力变化研究进展

北极海冰的快速消融使得北极航道的通航潜力不断增加,深入认识海冰快速消融背景下北极各航道通航能力变化规律,对北极地区保护与航道开发至关重要.本文系统回顾了北极冰区航行风险评估模型的发展过程和北极航道通航能力变化研究现状.北极冰区航行风险评估模型从早期静态的"区域/日期"航行安全控制机制,到近期国际海事组织融合各国管理经验推出的精细且具广泛适用性的POLARIS系统,取得了很大进展.未来应同时考虑发展融合实时冰情、海况及船况的综合风险评估模型和高时空分辨率的海冰遥感观测能力,以支撑冰区航行风险的快速、准确量化.现有研究对北极航道通航能力的整体认识仍然不足,体现在航道通航能力的历史变化研究仍停留在对沿线海冰范围等参量变化分析的间接认识水平,鲜有针对航道通航能力关键特征的分析;基于气候模式资料的北极航道通航未来潜力预测整体保守且差异较大;北极航道开通潜在经济、生态环境与政治风险与效益评估仍然存在争议.融合多源历史数据构建航道通航关键特征的提取与分析方案,有望系统揭示北极航道通航能力的历史变化规律;利用长时序遥感观测数据对模式资料进行修正,进一步对航道通航潜力进行预测可一定程度提高预测的可靠性;而评估北极航道开通的潜在综合效益与风险,有助于科学制订北极地区的保护与开发策略.

基于遥感观测的2010～2017年秋季北极东北航道通航能力时空变化

北极地区海冰的快速消融使得连接亚洲和欧洲的重要海上通道——北极东北航道的通航潜力不断增加.准确掌握海冰快速消融背景下东北航道通航能力的变化特征对航道开发具有重要价值.由于高质量海冰观测数据缺乏,现有研究多基于模式模拟数据对不同升温情景下航道未来的潜在变化进行分析,针对北极航道通航能力现状的研究并未有效开展.本研究利用美国冰雪数据中心发布的逐日海冰密集度数据和经过重建处理、质量得到有效提升的逐日SMOS海冰厚度数据,基于加拿大北极冰区航行系统(AIRSS)的通航可行性模型(ATAM)对北极地区2010～2017年通航季后期普通商船的航行风险进行了逐日量化制图,并对东北航道8年间通航能力的时空变化进行了分析.研究发现,虽然北极东北航道的通航能力已经显著提升,普通商船的通航结束期自2010年以来(除去2013年)平均已达第297±4天(10月24日左右),但过去8年间东北航道上普通商船的通航能力并没有显著增加趋势,且存在很大不确定性.北极东北航道通航结束期主要受东西伯利亚海、新西伯利亚群岛附近海域和北地群岛附近海域3个区域冰情的影响较大, 3个海域附近较早冻结的薄冰往往是导致整个航道通航结束的关键.鉴于北极东北航道通航能力变化的复杂性,高质量、准实时的海冰观测数据对于航道通航风险的准确量化十分必要.

The spatiotemporal patterns of sea ice in the Bohai Sea during the winter seasons of 2000–2016

In this study,sea ice thickness(SIT)and sea ice extent(SIE)in the Bohai Sea from 2000 to 2016 were investigated.A surface heat balance equation was applied to calculate SIT using ice surface temperatures estimated from the Moderate Resolution Imaging Spectroradiometer(MODIS)data with input from air temperature and wind speed from reanalyzing weather data.No trend was found in SIT during 2000–2016.The mean SIT and SIE during this period were 5.58±0.86 cm and 23×10^(3)±8×10^(3)km^(2),respectively.The largest SIT and SIE periods were observed during the second half of January and the first half of February,respectively.The Spearman correlation coefficient between mean ice thickness and average air temperature from 21 automatic weather stations around the Bohai Sea was–0.94(P<.005),and the coefficient between median ice extent and negative accumulated temperature was–0.503(P<.001).The rate of increase in air temperature around the Bohai Sea is 0.271℃per decade in winter for 1979–2016(P<.05),which is much lower than that in northern polar area(0.648℃per decade).This rate has not resulted in a decreasing trend in SIT and SIE for the past 16 years in the Bohai Sea.

A new image mosaic of Greenland using Landsat-8 OLI images

Greenland is the world’s largest island and over three-quarter of the entire land area is covered by the Greenland Ice Sheet(GrIS),which is the only permanent ice sheet besides Antarctica.Due to the global warming,GrIS is undergoing rapid changes[1,2],which has caused some environmental risks for the life of local people of Greenland.Greenland mass balance has been studied for several decades and we understand some its mass balance mechanism[3].However,the mechanism of GrIS changes is still unclear due to the lack of research data for Greenland.A satellite image mosaic is an important type of research data for Greenland studies.It can record the changes of land surface features with a relatively fine spatial resolution and support a variety of scientific researches in Greenland,such as supraglacial streams,rivers and lakes monitoring,mass balance estimation and land cover classification[4–6].The first Landsat Image Mosaic of Greenland(LIMG-GIMP)was released in 2014 by the Greenland Ice Mapping Project[7].The satellite images used to develop LIMG-GIMP were acquired between 1999 and 2002,which cannot represent recent GrIS status.Therefore,a new mosaic constructed by recent data is needed to monitor these changes of GrIS for future studies of Greenland.

Fingerprint of COVID-19 in Arctic sea ice changes

Arctic sea ice plays an essential role in regional and global climate by dynamic processes and feedbacks associated with its high reflectivity, thermal insulation especially in presence of snow cover, and brine rejection [1]. Both observations and model simulations show that Arctic sea ice extent has dramatically declined and thinned in the past few decades [2] in response to global warming and cumulative anthropogenic greenhouse gas(GHG)emissions [3,4].

Fine-resolution mapping of the circumpolar Arctic Man-made impervious areas(CAMI)using sentinels,OpenStreetMap and ArcticDEM

Man-made impervious areas map is of great demand in environmen-tal and urbanization studies since impervious areas are considered as a key indication of urbanization,especially for circumpolar Arctic.However,to date,finer resolution and spatially continuous imper-vious areas information remains scarce in the Arctic.In this study,we developed an accurate and complete circumpolar Arctic Man-made impervious areas(CAMI)map at a resolution of 10 m by combining Sentinel-1 C-band Synthetic Aperture Radar,Sentinel-2 multispectral images,OpenStreetMap,and ArcticDEM via Google Earth Engine platform.A random forest classifier model was trained and used to generate corresponding impervious areas map for the year 2020.The evaluation results suggested that CAMI was the most accurate with an overall accuracy of 86.36%and kappa coefficient of 70.73%as against the three existing impervious areas products.Based on the generated map and OpenStreetMap,we estimated that total imper-vious areas area in the Arctic has achieved 807.80 km2,of which roads,industrial and resident land were three major land use types,accounting for 54.08%,17.85%and 10.34%,respectively.The CAMI map will support for new application and provide advanced insight into the infrastructure vulnerability evaluation and environmental sustainability in the Arctic.

Ocean contributes to the melting of the Jakobshavn Glacier front

The Jakobshavn Glacier(JG)in Greenland is one of the most active glaciers in the world.It was close to balance before 1997 but this was followed by a sudden transition to rapid thinning.The reason for the change remains unclear.In this study,The NASA Pre-IceBridge ice thickness data are collected to monitor the melting of JG front.The surface elevation decreased by around 90 m from 1995 to 2002 on the floating front.A distributed energy balance model is developed to estimate the energy balance of JG front in the past 30 years(1986-2016).The results indicate that multi-year average energy fluxes absorbed by the floating front of JG from the ocean were about 500 Wm^-2 from 1986 to 2016.This is approximately two times of the energy fluxes from atmosphere during the same period.The energy fluxes from the ocean increased from 200 to 600 Wm^-2during the period from 1990 to 1998 while energy fluxes from the atmosphere remained stable at about 250 Wm^-2.These results demonstrate that ocean contributes more to the melting of the JG front,and suggest that bottom surface melting must have a profound influence on marine-terminating glacier dynamics.

Light from space illuminating the polar silk road

The rapid decline of Arctic sea ice has been reminding us the significant impacts caused by global warming.However,the other side of the coin is that this opens a window to utilize the Arctic sea routes in the summer seasons,bringing remarkable economic benefits for ocean transportation between Asia and Europe.However,commercial vessels with low ice classes must tackle substantial environmental challenges in the Arctic sea routes,particularly those caused by variable sea ice,even in the melting seasons.Therefore,the science-based support for shipping safety in the Arctic sea routes is being given more prominence.Emerging satellite remote sensing technology plays a critical role in environmental monitoring in the Arctic.This paper reviews state-of-the-art satellite observations on monitoring sea ice and potential applications on supporting shipping activities in the Arctic Ocean.Moreover,we introduced a recently developed system based on satellite observations to support the safe transportation of Chinese cargo vessels in the Arctic northern sea route,demonstrating the efforts by both the science and business communities to promote the development of the polar silk road.