The variation in basal channels and basal melt rates of Pine Island Ice Shelf

In recent years,there has been a significant acceleration in the thinning,calving and retreat of the Pine Island Ice Shelf(PIIS).The basal channels,results of enhanced basal melting,have the potential to significantly impact the stability of the PIIS.In this study,we used a variety of remote sensing data,including Landsat,REMA DEM,ICESat-1 and ICESat-2 satellite altimetry observations,and Ice Bridge airborne measurements,to study the spatiotemporal changes in the basal channels from 2003 to 2020 and basal melt rate from 2010 to 2017 of the PIIS under the Eulerian framework.We found that the basal channels are highly developed in the PIIS,with a total length exceeding 450 km.Most of the basal channels are ocean-sourced or groundingline-sourced basal channels,caused by the rapid melting under the ice shelf or near the groundingline.A raised seabed prevented warm water intrusion into the eastern branch of the PIIS,resulting in a lower basal melt rate in that area.In contrast,a deepsea trough facilitates warm seawater into the mainstream and the western branch of the PIIS,resulting in a higher basal melt rate in the main-stream,and the surface elevation changes above the basal channels of the mainstream and western branch are more significant.The El Ni?o event in 2015–2016 possibly slowed down the basal melting of the PIIS by modulating wind field,surface sea temperature and depth seawater temperature.Ocean and atmospheric changes were driven by El Ni?o,which can further explain and confirm the changes in the basal melting of the PIIS.

The Processes-Based Attributes of Four Major Surface Melting Events over the Antarctic Ross Ice Shelf

The Ross-Amundsen sector is experiencing an accelerating warming trend and a more intensive advective influx of marine air streams.As a result,massive surface melting events of the ice shelf are occurring more frequently,which puts the West Antarctica Ice Sheet at greater risk of degradation.This study shows the connection between surface melting and the prominent intrusion of warm and humid air flows from lower latitudes.By applying the Climate Feedback-Response Analysis Method(CFRAM),the temporal surge of the downward longwave(LW)fluxes over the surface of the Ross Ice Shelf(RIS)and adjacent regions are identified for four historically massive RIS surface melting events.The melting events are decomposed to identify which physical mechanisms are the main contributors.We found that intrusions of warm and humid airflow from lower latitudes are conducive to warm air temperature and water vapor anomalies,as well as cloud development.These changes exert a combined impact on the abnormal enhancement of the downward LW surface radiative fluxes,significantly contributing to surface warming and the resultant massive melting of ice.

Predicting impacts of climate change on the biogeographic patterns of representative species richness in Prydz Bay-Amery Ice Shelf

The research on the biological ecology of the Prydz Bay-Amery Ice Shelf in East Antarctica is inadequate under the increasing threat from climate change,especially for Antarctic fish and krill.The Dynamic Bioclimatic Envelope Model(DBEM)has been widely used in predicting the variation of species distribution and abundance in ocean and land under climate change;it can quantify the spatiotemporal changes of multi population under different climate emission scenarios by identifying the environmental preferences of species.The species richness and geographical pattern of six Antarctic representative species around Prydz Bay-Amery ice shelf were studied under RCP 8.5 and RCP 2.6 emission scenarios from 1970 to 2060 using Geophysical Fluid Dynamics Laboratory(GFDL),Institut Pierre Simon Laplace(IPSL),and Max Planck Institute(MPI)earth system models.The results showed that the species richness decreased as a whole,and the latitude gradient moved to the pole.The reason is that ocean warming,sea ice melting,and human activities accelerate the distribution changes of species biogeographical pattern,and the habitat range of krill,silverfish,and other organisms is gradually limited,which further leads to the change of species composition and the decrease of biomass.It is obvious that priority should be given to Prydz Bay-Amery ice shelf in the planning of Marine Protected Areas(MPAs)in East Antarctica.

The morphological changes of basal channels based on multisource remote sensing data at the Pine Island Ice Shelf

The basal channel is a detailed morphological feature of the ice shelf caused by uneven basal melting.This kind of specifically morphology is widely distributed in polar ice shelves.It is an important research object of sea-ice interaction and plays a vital role in studying the relationship between the ice sheet/ice shelf and global warming.In this paper,high-resolution remote sensing image and ice penetration data were combined to extract the basal channel of the Pine Island Ice Shelf.The depth variation of Pine Island Ice Shelf in the recent 20 years was analyzed and discussed by using ICESat-1,ICESat-2,and IceBridge data.Combined with relevant marine meteorological elements(sea surface temperature,surface melting days,circumpolar deep water and wind)to analyze the basal channel changes,the redistribution of ocean heat is considered to be the most important factor affecting the evolution and development of the basal channel.

Spatial distribution of Ice Shelf Water in front of the Amery Ice Shelf,Antarctica in summer

As a unique low-temperature water mass in Antarctic coastal region, the Ice Shelf Water (ISW) is an important component for the formation of the Antarctic Bottom Water (AABW). In this paper, we present a criterion for ISW identification based on freezing point at the sea surface, and we study spatial distribution of ISW in front of the Amery Ice Shelf (AIS) and its flow path in Prydz Bay by analyzing hydrographic data from Australian cruises in 2001 and 2002, as well as Chinese cruises in 2003, 2005, 2006, and 2008, all being made in the austral summer. The relatively cold and fresh ISW occurred as several discrete water blocks with cold cores in front of the AIS, within the depth range of 100?600 m, under the seasonal thermocline. ISW had obvious temporal and spatial variations and the spatial distribution pattern changed greatly after 2005. Most of ISW was concentrated west of 73°E during 2001 to 2003 and 2006, but it was widespread to east in 2005 and 2008. In all observation years, a small amount of cold ISW always occurs at the west end of the AIS front section, where the coldest ISW in the whole section also occurred in 2001, 2003 and 2006. Considering general cyclonic circulation pattern under the AIS, the ISW flowing out from west end of the AIS front might have experienced the longest cooling period under ice shelf, so it would have the lowest temperature. Analysis of data from meridian sections in Prydz Bay in 2003 implied that ISW in the west could spread north to the continental break along the east flank of the Fram Bank near 70.5°E, mix with the upwelling Circumpolar Deep Water and possibly contribute to the formation of AABW.

Monitoring the Amery Ice Shelf front during 2004-2012 using ENVISAT ASAR data

The Amery Ice Shelf is the largest ice shelf in East Antarctica. It drains continental ice from an area of more than one million square kilometres through a section of coastline that represents approximately 2% of the total circumference of the Antarctic continent. In this study, we used a time series of ENVISAT ASAR images from 2004-2012 and flow lines derived from surface velocity data to monitor the changes in 12 tributaries of the Amery Ice Shelf front. The results show that the Amery Ice Shelf has been expanding and that the rates of expansion differ across the shelf. The highest average annual rate of advance from 2004-2012 was 3.36 m＇d-1 and the lowest rate was 1.65 m.d-1. The rates in 2009 and 2010 were generally lower than those in other years. There was a low correlation between the rate of expansion and the atmospheric temperature recorded at a nearby research station, however the mechanism of the relationship was complex. This study shows that the expansion of the Amery Ice Shelf is slowing down, reflecting a changing trend in climate and ice conditions in East Antarctica.

Marine hydrographic spatial-variability and its cause at the northern margin of the Amery Ice Shelf

Conductivity, temperature and depth（CTD） data collected along a zonal hydrographic section from the northern margin of the Amery Ice Shelf on 25-27 February 2008 by the 24th Chinese National Antarctic Research Expedition （CHINARE） cruise in the 2007/2008 austral summer are analyzed to study thermohaline structures. Analysis reveals warm subsurface water in a limited area around the east end of the northern margin, where the temperature, salinity and density have east-west gradients in the surface layer of the hydrographic section. The localization of the warm subsurface water and the causes of the CTD gradients in the ＇surface layer are discussed. In addition, the results from these CTD data analyses are compared with those from the 22nd CHINARE cruise in the 2005/2006 austral summer. This comparison revealed that the thermoclines and haloclines had deepened and their strengths weakened in the 2007/2008 austral summer. The difference between the two data sets and the cause for it can be reasonably explained and attributed to the change in ocean-ice-atmosphere interactions at the northern margin of the Amery Ice Shell

Determination of grounding line on the Amery Ice Shelf using Sentinel-1 radar interferometry data

Delineation of the grounding line(GL) is necessary for calculating the mass balance of Antarctica, but GL measurements for most of the continent remain at a relatively coarse level. We used Sentinel-1 constellation data to map the GL of the Amery Ice Shelf(AIS) using double-differential synthetic aperture radar interferometry. The ice thickness anomaly deduced from hydrostatic equilibrium and existing Antarctic GL products is compared with our result. With this new and very accurate GL, we detected new ice rises in the north of the AIS. Our new measurement shows no major change of the AIS GL, particularly in the southernmost part.

Velocity of Surface Ice Flow on Amery Ice Shelf Determined with PPP

The main activities in the joint expedition between CHINARE and ANARE on Amery ice shelf are introduced. Five day continuous GPS observation data collected on the site which locates at the frontal part of Amery ice shelf was processed with precise point positioning (PPP) technology based on precise products from IGS. Velocity of the surface ice flow on Amery can be derived from the PPP solution. Preliminary result shows that the surface ice flow velocity of the site is 2.25 meters per day, the motion direction is northeastward. Semidiurnal oceanic tide and diurnal oceanic tide signal of that site can be recovered from the height variation series of PPP solution. These above solutions can be used to the consequent mass balance calculation.

Chinese GF-1 and GF-3 satellites observed the giant iceberg calving off the Larsen C Ice Shelf

A massive iceberg, named A-68 by National Ice Center （NIC） officially, calved away from the Larsen C Ice Shelf in Antarctica on luly 12, 2017. The iceberg A-68 is about 5 800 km2, weighs more than a trillion tons and it is one of the biggest ever recorded icebergs. Chinese satellites Gaofen-1 （GF-1） and Gaofen-3 （GF-3） data was used to monitoring the propagation of the rift and the iceberg by National Satellite Ocean Application Service （NSOAS）.

Temporal and spatial changes of the basal channel of the Getz Ice Shelf in Antarctica derived from multi-source data

Basal melting is an important factor affecting the stability of the ice shelf.The basal channel is formed from uneven melting,which also has an important impact on the stability of the ice shelf.Therefore,it has important scientific value to study the basal channel changes.This study combined datasets of Mosaics of Antarctica,Reference Elevation Model of Antarctica(REMA) and Operation Ice Bridge to study the temporal and spatial changes of basal channels at the Getz Ice Shelf in Antarctica.The relationships between the cross-sectional area and width of basal channel and those of its corresponding surface depression were statistically analyzed.Then,the changes of the basal channels of Getz Ice Shelf were derived from the ICESat observations and REMA digital elevation models(DEMs).After a detailed analysis of the factors affecting the basal channel changes,we found that the basal channels of Getz Ice Shelf were mainly concentrated in the eastern of the ice shelf,and most of them belonged to the ocean-sourced basal channel.From 2009 to 2016,the total length of the basal channel has increased by approximately 60 km.Affected by the warm Circumpolar Deep Water(CDW),significant changes in the basal channel occurred in the middle reaches of the Getz Ice Shelf.The change of the basal channels at the edge of the Getz Ice Shelf is significantly weaker than that in its middle and upper reaches.Especially in 2005–2012,the eastward wind on the ocean wind field and the westward wind around the continental shelf caused the invasion and upwelling of CDW.Meanwhile,the continuous warming of deep seawater also caused the deepening of the basal channel.During from 2012 to 2020,the fluctuations of the basal channels seem to be caused by the changes in temperature of CDW.

Evaluation of the Antarctic Mesoscale Prediction System Based on Snow Accumulation Observations over the Ross Ice Shelf

Recent snow height measurements(2008–15) from nine automatic weather stations(AWSs) on the Ross Ice Shelf are used to examine the synoptic and seasonal variability in snow accumulation,and also to evaluate the performance of the Antarctic Mesoscale Prediction System(AMPS) for precipitation. The number of snow accumulation events varies from one station to another between 2008 and 2015,thus demonstrating geographic dependence. The interannual variability in snow accumulation is too high to determine its seasonality based on the current AWS observations with limited time coverage.Comparison between the AMPS and AWS snow height measurements show that approximately 28% of the AWS events are reproduced by AMPS. Furthermore,there are significant correlations between AMPS and AWS coincident event sizes at five stations(p < 0.05). This finding suggests that AMPS has a certain ability to represent actual precipitation events.

Amery ice shelf DEM and its marine ice distribution

The Amery Ice Shelf is the largest ice shelf in East Antarctica. A new DEM was generated for this ice shelf, using kriging to interpolate the data from ICE- Sat altimetry and the AIS-DEM. The ice thickness distribution map is converted from the new DEM, assuming hydrostatic equilibrium. The Amery Ice Shelf marine ice, up to 230 m thick, is concentrated in the northwest of the ice shelf. The volume of the marine ice is 2.38 × 10^3 km^3 and accounts for about 5.6% of the shelf volume.

Hydrological character and sea-current structure in the front of Amery Ice Shelf

Hydrological character and Sea-current profiles structure are studied and analyzed in sea-area of the front of Amery Ice Shelf, Prydz Bay with LADCP, CTD data. These LADCP, CTD data were acquired during the 19th Chinese Antarctic Scientific Expedition. Results of this study agree with that, there exist four different kinds of water masses in the area of the front of Amery Ice Shelf in the summer of Antarctica. Current distribution presents a semi-circumfluence which flows in at the east and flows out in the west. Moreover, clockwise and anti - clockwise vortices were found in upper layer and mid-layer in the Prydz Bay. Western areas of these anticlockwise vortices are positions of inflows from Prydz Bay to Amery Ice Shelf. The source of these inflows is the coastal westward current originated in the east of Prydz Bay. All these characteristics come down to the pattern of circumfluence, ice melt rate under Ice Shelf, scale of Ice Shelf water production and form of water exchanges between area of Ice Shelf and area of Prydz Bay.

The tidal signals extraction from GPS data on the Amery Ice Shelf, Antarctica

Tidal motion is the source of short-term vertical motion that an ice shelf experiences, and hence has a significant impact on ice shelves. During the 2003/2004 Austral summer season, five days of GPS measurements were carried out on the front of the Amery Ice Shelf （AIS）, East Antarctica, by the 20th Chinese National Antarctica Research Expedition （CHINARE）. The GPS data was processed using GAMIT/GLOBK software with 2-hour static data segment and the vertical precision is less than 0.18 m. To verify our results for the vertical component, we compare the ice shelf GPS tidal signal with a tidal result derived from tide gauge measurements at China＇s Zhongshan Station on Antarctica. Comparison of the GPS results with the tide gauge were in good agreement in amplitude at the few cm level, which indicates that the tide under the front of Amery Ice Shelf is irregular semidiurnal tide, the maximal tidal differences is approximately 2 m. GPS data can be used to validate the ocean tide model around the Antarctic area and such studies are important to improve our knowledge of the Antarctic ice shelf mass balance and dynamical models of ice sheet/ocean interaction.

Distribution of modified Circumpolar Deep Water and its threat in Vincennes Bay,East Antarctica

The Antarctic Bottom Water formation site Vincennes Bay,East Antarctica is experiencing a substantial intrusion of modified Circumpolar Deep Water(mCDW),which may inhibit the formation of Dense Shelf Water(DSW)and drive basal melting of the ice shelves.Based on hydrographic data obtained from March to November in 2012,we evaluated the spatial spread of mCDW over the continental shelf region of Vincennes Bay and the associated temporal evolution of water properties,as well as the sea ice formation effect on water column in the coastal polynya.Results show that two branches of mCDW occupied the deep layers of the continental shelf,distinguished by the potential density(smaller than 27.8 kg/m^(3) or not)when potential temperatureθ=0.5°C in theθ-salinity space.The warmer and less dense branch observed on the east plateau,accessed the eastern ice shelves in the coastal polynya to drive basal melting of ice shelves.In contrast,the other colder and denser branch in the mid-depression reached the western Underwood Ice Shelf.DSW formation was detectable in the coastal polynya during September-November,proving the occurrence of deep convection.Surface heat loss and brine rejection during the intensive sea ice formation contributed to the destratification of the water column in the coastal polynya.It was estimated that at least 1.11±0.79 TW heat carried by mCDW into the inner part of the polynya.

Slurry ice as an alternative cooling medium for fish harvesting and transportation:Study of the effect on seabass flesh quality and shelf life

The objective of the study was to investigate the efficiency of slurry ice during harvesting and transportation of European sea bass(Dicentrarchus labrax)to retain flesh quality and extend shelf life,compared with conventional flake ice.Fish was slaughtered and transported in different mixtures of slurry ice and conventional flake ice(C:slaughtered and transported in 100%flake ice-Control samples,SC:slaughtered in 100%slurry ice and transported in 100%flake ice,S50:slaughtered and transported in 50%slurry ice-50%flake ice,S100:slaughtered and transported in 100%slurry ice)and subsequently stored under controlled isothermal conditions at 0℃for shelf life modelling and flesh quality evaluation(proteolytic enzymes).The replacement of conventional flake ice with slurry ice as a slaughtering method led to improved quality stability during subsequent refrigerated storage and shelf life extension,in terms of microbial growth,flesh quality and sensory degradation of fish.Based on microbial growth,the shelf life of C samples was found to be 19 days,whereas the shelf life of S50/S100 and SC was 21 and 25 days,respectively,showing that the replacement of flake ice with slurry ice resulted in 2–6 days shelf life extension of whole sea bass stored at 0℃.The use of slurry ice at slaughter and flake ice in transportation was accompanied by low activities and late peaks of all four enzymes that is expected to lead to delayed proteolytic degradation and extended freshness.

Retrieving the grounding lines of the Riiser-Larsen Ice Shelf using Sentinel-1 SAR images

Accurately locating and studying grounding lines is essential for predicting the response of glaciers to climate change.However,it is challenging tofind grounding lines since they are subglacial features.In this study,Sentinel-1 synthetic aperture radar(SAR)data were utilized to derive the grounding lines of the Riiser-Larsen Ice Shelf.A new method with inspiration drawn from multi-temporal baseline InSAR techniques is proposed.It takes advantage of the temporal consistency of the vertical displacement gradients and identifies grounding zones pixel-by-pixel on a stack of double differential interferograms,thereby providing grounding line proxies.As it fully exploits coherent signals in both spatial and temporal domains,the maximum possible number of grounding zone pixels can be obtained.Moreover,due to the introduction of the concept of the temporal consistency,the method can cope with short term grounding linefluctuations to some extent and may mitigate the influences of atmospheric disturbances and residual ice displacements.The resulting grounding lines are compared with the MEaSUREs Antarctic grounding line product.The comparison confirms the effectiveness of the proposed method and corroborates that the Riiser-Larsen Ice Shelf should have not undergone significant changes over the past few decades.

Status and trends in the stability of the three largest ice shelves in Antarctica

The Ross,Filchner-Ronne,and Amery ice shelves are the three largest ice shelves in Antarctica,playing a crucial role in supporting the Antarctic ice sheet.However,current studies on the stability of the three largest ice shelves primarily focus on singular or limited factors,lacking a comprehensive assessment of multiple parameters.To systematically and in-depth study the stability and trend of the three largest ice shelves,we comprehensively collected and analyzed key parameters,including elevation changes,basal melting,surface meltwater,major rifts propagation rate,suture zones,ice front area change rate,grounding lines,ice velocity,and mass balance.Additionally,we selected the collapsed Larsen B Ice Shelf(LBIS),the rapidly changing and structurally weakened Pine Island Ice Shelf(PIIS),and the accelerating Totten Ice Shelf(TIS)as reference ice shelves.By comparing and analyzing the key parameters between these reference ice shelves and the three largest ice shelves,we find the status and trends in the stability of the latter.Our findings reveal that most key parameters of the three largest ice shelves present relatively minor variations compared to those of the reference ice shelves.Specifically,50%of the parameters are smaller than those of the accelerating TIS,88%are smaller than those of the rapidly changing PIIS,and all parameters are smaller than those of the collapsed LBIS.Furthermore,after analyzing parameters that are not smaller than those of the TIS,it is observed that they remain in a stable state.Hence,the three largest ice shelves are currently undergoing natural changes that do not threaten their stability in the short term.Nevertheless,the evolution of the ice shelves under global climate change remains uncertain,making long-term observation and monitoring essential to assess their impact on sea level rise.

A precise monitoring of snow surface height in the region of Lambert Glacier basin-Amery Ice Shelf,East Antarctica

The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB69 (70°50'S, 77°04'E, 1850 m a.s.l.). east side of Lambert Glacier basin (LGB), and 4 year record at G3 (70°53'S, 69°52'E, 84 m a.s.l.), Amery Ice Shelf (AIS). The measurements were made with ultrasonic sensors mounted on automatic weather stations installed at two sites. The snow accumulation at LGB69 is approximately 70 cm. Throughout the winter, between April and September, there was little change in surface snow height (SSH) at the two sites. The negative SSH change is due to densification at LGB69, and is due to both ablation and densification at G3. The strongest accumulation at two sites occurred during the period between October and March (accounting for 101.6% at LGB69), with four episodic increasing events occurring during 2002 for LGB69, and eight events during 1999-2002 for G3 (2 to 3 events per year). At LGB69, these episodic events coincided with obvious humidity 'pulses' and decreases of incoming solar radiation as recorded by the AWS. Observations of the total cloud amount at Davis station, 160 km NNE of LGB69, showed good correlation with major accumulation events recorded at LGB69. There was an obvious anti-correlation between the lowest cloud height at Davis and the daily accumulation rate at LGB69. Although there was no correlation over the total year between wind speed and accumulation at LGB69, large individual accumulation events are associated with episodes of strong wind (>7 m/s), we estimate drift snow may contribute to total SSH up to 35%. Strong accumulation events at LGB69 are associated with major storms in the region and inland transport of moist air masses from the coast.