ISSN 1028334X, Doklady Earth Sciences, 2011, Vol. 438, Part 1, pp. 686689. Pleiades Publishing, Ltd., 2011.Original Russian Text V.M. Kotlyakov, M.Yu. Moskalevskiy, L.N. Vasilev, 2011, published in Doklady Akademii Nauk, 2011, Vol. 438, No. 2, pp. 263266.
Knowledge of the evolution and conditions of theAntarctic Ice Sheet plays an important role in theproblem of global changes. The level of the WorldOcean depends on its condition and the processes proceeding in different parts of the ice sheet. The Antarctic Ice Sheet plays an important role in the formationof the Earths climate and reflects climate changesassociated with continuous interaction between theice sheet with the ocean and the atmosphere. AntarcticIce Sheet has a sectional area of over 12 million km2 andcontains ~25 million km3 of ice; it is only comparable tothe vast ice sheets of the past in terms of the size.
After 50 years of instrumental observations of thesheet, we can imagine how similar shields reacted tothe ambient conditions, which were possibly differentin different parts of the sheet. Thus, while vast EastAntarctica remains stable, quite noticeable changesare observed in West Antarctica.
The principal indicator of the condition of the Antarctic Ice Sheet is its mass balance. The present daystatus of this mass balance and its changes in the pastare estimated ambiguously. For instance, there is nocommon view on the values of ice sheet snow accumulation and the grounded ice discharge, which are theprincipal components of the mass balance of Antarctica. We will show how this mass balance changedbased on estimates of the grounded ice discharge andthe data on snow accumulation within the main icecatchment basins. First of all, we determined theboundaries and sectional areas of the ice catchmentbasins in West and East Antarctica. Such an approachallowed systematizing a considerable amount of infor
mation contained in different literature references thathad sometimes been excluded from analysis.
There are 13 main ice catchment basins in EastAntarctica: the eastern part of the Weddell Basin,StancombWills, Jutulstraumen, Shirase, Rayner,Lambert, Denman and Scott, Totten, Power andFrost, Mertz and Ninnis, David, Mulock, and Byrd;there are four such ice catchment basins in West Antarctica: Pine Island, Thwaites, Ross, and the westernpart of the Weddell Basin (see figure). We combinedsome of these basins in order to compare the data onthe present day and earlier accumulation, since thefirst reliable data on snow accumulation were generated for vaster basins. Our investigation did notinclude ice catchment basins in the Antarctic Peninsula, the western part of Ellsworth Land, the northeastern end of Mary Byrd Land (Smith, Kohler, andLand), the central part of Queen Maud Land, andsome others. Unfortunately, there is no reliable information on snow accumulation and the grounded icedischarge for these basins. The total sectional area of theexamined basins is 7435.7 ths. km2, and the size of theglacierized area in Antarctica is 11 965.7 ths. km2.
The first data on snow accumulation on the Antarctic Ice Sheet were generated during the preparationfor and in the course of the International GeophysicalYear (IGY) (19571959) from numerous snow measurements. A significant result of the IGY was a snowaccumulation map of Antarctica . However, theboundaries of the principal ice catchment basins werenot yet shown on that map. Based on the data on snowaccumulation and the information on the position ofice divides generated in the 1960s and 1970s, a map ofsnow accumulation distribution was created for the icecatchment basins . We used the data of that map tocompare them with estimates of further changes insnow accumulation on the Antarctic Ice Sheet. These
Changes in the Mass Balanceof the Antarctic Ice Sheet over 50 Years
Academician V. M. Kotlyakov, M. Yu. Moskalevskiy, and L. N. VasilevReceived January 25, 2011
AbstractThe mass balance of the Antarctic Ice Sheet has been calculated based on instrumental estimatesof the grounded ice discharge and snow accumulation data. The boundaries and sectional areas of the mainice catchment basins in West and East Antarctica have been determined, and the data on the grounded icedischarge and snow accumulation in these basins have been systematized. The intensity of accumulation andablation processes in Antarctica has noticeably increased over the last 50 years. The mass balance of the icesheet in East Antarctica has been and remains positive, while in West Antarctica it was positive in the middleof the last century and has become negative by now. The mass balance of the entire Antarctic Ice Sheet hasbeen and remains positive, while the mass growth has noticeably decreased over the last 50 years.
Institute of Geography, Russian Academy of Sciences, Staromonetnyi per. 29, Moscow, 119017 Russia
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estimates were based on the measurement data underthe Global Precipitation Climatology Project(GPCP). Analysis allowed estimating annual snowaccumulations for the continental part of the Antarctic Ice Sheet as a whole . Our estimates (see table)were obtained based on systematic precipitation measurements on a 1 1 grid; these estimates are well inline with the data of direct and remote measurementsof snow accumulation during the last decade and theaccumulation calculations based on the models .According to these data, snow accumulations in themajority of the ice catchment basins in Antarcticahave increased over the last 50 years.
In order to estimate the grounded ice discharge, weused the position of the grounding line, i.e., the pointof concentration through which ice masses are discharged from ice catchment basins into the oceanalong the main discharge channels (outlet glaciers andglacial streams). The position of the grounding line forthe majority of the discharge channels was determinedduring the IGY and some later projects (19601970s)by repeated ground based geodetic measurements; itwas determined more accurately using aerial photo
graphs, and later on, using optical satellite imagery. Wecollected and systematized these measurement datacontained in the literature  and the databases of theinternational projects on ice creep rate  and icethickness  measurements. Based on this, estimatesof the grounded ice discharge at the middle of the lastcentury were obtained.
Novel radar technologies, e.g., interferometry,radio echo sounding, and altimetry, started beingapplied at the end of the last century. Successful airborne radio echo sounding over a considerable part ofAntarctica  controlled by the data of groundbasedradio echo sounding and seismic sounding accumulated in the BEDMAP database allowed obtainingquite reliable values of the ice thickness and usingthem in estimates of the grounded ice discharge in thevicinity of the grounding line for the discharge channels of individual ice catchment basins. The latest estimates of ice creep rates for outlet glaciers in the vicinity of the grounding line were obtained based on thedata of satellite geodesy and processing of amplitudeand inferometric components of space radar images. Systematization and analysis of these and previous
Changes in the mass balance of the examined ice catchment basin of the Antarctic Ice Sheet over the last 50 years. The figures inthe rectangles are the values of the changes in km3; + or denote the change tendency. The color denotes the present day statusof the mass balance: black is negative, and white, positive. The examined ice catchment basins are the following: (1) Shirase,(2) Rayner, (3) Lambert, (4) Denman and Scott, (5) Totten, (6) Power and Frost, (7) Mertz and Ninnis, (8) David, (9) Malloch,(10) Byrd, (11) Ross, (12) Thwaites, (13) Pine Island, (14) Western part of the Weddell Basin, (15) Eastern part of the WeddellBasin, (16) StancombWills, (17) Jutulstraumen.
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data on the thickness and movement rates of the icesheet in the vicinity of the grounding line allowed estimating the grounded ice discharge of Antarctic IceSheet for the second half of the 20th century (seetable). As is obvious, the grounded ice discharge in themajority of the examined basins has increased over thelast 50 years.
It can be stated that the intensity of accumulationand ablation processes in Antarctica has noticeablyincreased over the last 50 years. An increase in bothmass growth and the discharge component wasobserved.
Based on the data on snow accumulation and thegrounded ice discharge in Antarctica generatedrecently and those obtained in the middle of the lastcentury, we estimated changes in the mass balance ofthe Antarctic Ice Sheet over the last 50 years (see figure). In East Antarctica, an increase in the massgrowth is observed in the majority of the ice catchmentbasins. The David and Jutulstraumen basins and theeastern part of the Weddell Basin are an exception; inthese basins, while the mass balance is positive, the
mass growth decreases. Such a decrease was particularly strong in the eastern part of the Weddell icecatchment basin. Only one ice catchment basin (StancombWills) has a negative mass balance. In general,the mass balance of the ice sheet in East Antarctica hasbeen and remains positive