ilnnals of Glaciologl' 23 1996
(Q International Glaciological Societl,
Ice-sheet flow features and rheological parameters derived
frorn precise altirnetric topography F. RÉrrv, Ul'IR39lGRG,S fC:À'ES" C.À'R,l/. 1B ai,. E. Btlin, Touktuse Ciule.r 31055, Frarrce
C. Rrrz, Laboratoit'e de Glaciologit t,t Gioflg'siqut fu I'Enuironnement.3Bl02 Saiti-l,Iartin-d'IIàret Cedcr, lù.ance
L.
Br 1 (.rmall opan cirrles) or < I (large olten circlas). n, and
k
rn'e
identical: thi.ç
.çusse.çt.ç
that the
y
large-scale
signal (F'ig.2a) i.t reLated to Bç1 aariatians, and tlrut n and k retrieaal is not affected \ this signal.
Rlng' and olher.ç: Irt'-.çhtet
the
Antarctic ice sheet deduced from inversion ol'ERS-1 altimeter c1:rta, n,e can determine the icc-llou. clirection, the ba1:rnce velocitl. arrcl the bas:rl shear strcss. '-fhe Vialoi' (1958) eqLration and Lliboutry's (198 1) assLrmption f.icld :r relation linking thc thrcc lbllou.ing geoplrr'sicirl palamctcrs: (VlH)(p*2) (u'here p incluclcs icecolumn charactcristics ancl tempel'atLrre plofile), shear'
r
and basal temperature 7\,. I1'one assumes tl-rat the .B11 only r,art'u'ith onc oI thesc tlrrce geophvsical paramctcrs. this rclation a1lol,s ns to map the behaviour anomalies ol each gcophl'sical paramcter. Severai medir-rn-r-scale anomalies aflect the shcar-stress map. The n-redium-scale anomerlies are mosth. erplained
rhcological parameters ri, Ç ancl
br, thc longituclinal stress, u'hich can bc clr-rc either to slidir-rg or bcdrock preser)ce and u'hicl'r sho\\,s ellècts on i1 100-200km scale. This loneituclinal stless must then be
in the ice-flou, moclelling. A strong lalge-sc:r1e anomalr,is observed in (VlU)(p*2): it seems to be mostll, due to a vat'iatit-rtt in 811 but it celtainlt, is partiail,v allectcd b1, the poor knou'ledge of tlie seothermai flux and b1' the lalge-scale taken into accolurt
longituclinal strcss sisnal. Final11,, onc can shou. tl'rat the Glen exponent increases t'om 1 lbl temperature belou' 10"C to 3-4 for
liighcr temperatLlres. Thc bchaviour of thc Alr'henius rclation u,ith rcspcct to tempcrature sLrggests that the (Q:7Ohlmol 1) clo not clepencl valtrcs of 811 ancl "f Q on tcmpcrature.
The above results obtaincd u,itl'r thc hclp of the llrst global and accuratc surlàcc topographl' o1' Antarctica prove thc po\\'er of tl'rc approacli. ,'\ ncxt step shoulcl be the direct assimilation of :iltimetric data into icc-flou' models.
ACKNOWLEDGEMENTS zrrc gratefr-rl
to Dr P. Duval, ol the Laboratoire de
Glaciologie et Géophl,sique de l'Environnerrent, :rncl to
Dr P. \/inccnt liom the Centre National
c1'Étucles
for helpful discussions and commcnts. Àlso, Dr R. C. Â. Hindmarsli of'the British .\rrtalt lit Sunei. lor lri. t,rrnment.. Spatialcs,
\\,e arc grateful to
lla;i; ol lct
Drervr\'. D.J. 1983.'I'he surlirce ol the,\ntarctic itc sheet..Il Drelrl', D..1.. td. -lnttrttitn: glatialagiml and gtoplo:inlJolro. Canrl;rirlge. Scott Polar Rcsearch lnstitute. Sheet 2. Hamler-. T. C.. I. N. Smith ancl \. \\'. Younu. I9[]5r. \Iass-balartce iurcl ice-flou-larr pirralnetcrs frir I'last ,\nt:Lrctic:r. ,J. (;larial.. 3l(1091. 33 1 339. Honrer. D. R. ancl.].
\\'. GIen. 1978. Thc crccl;
:rr:tivatiotr crrtrqics olicc.
.J. (ilotial..21l85). +29 +++.
Hrrtrer. K. 1l)B'3. Tluotrtirtl gkriolaXt; malerial .;titntc Ltf itt antl lfu nLthrnit.t of glatitr.; orul irc -çhetts. Dorclrcr:ht. r:tc.. D. Ileiclel Publishing Co./ Tokro. 'fcrra Publishirrg Co. Hur l;rechts. P. 1990. -\ 3-L) nodel Ibr the .\ntarctic ice sheet: a serrsitivitv stutlv on the qlatial int.rqlacixl contlast. (.litnlt D-tu..
5(21,79 92. Huvbrethts. l'. ancl.]. Oerlernans. 1988. Ii'olutiorr of thc llast;\nt:irctic ice shee t: a numerical stuclt ol thcrrno-rnechrrnical l'esl)onse P:itterns rritfr changilg- climate. :lnn. Gl«iol.. ll. 52 59. Lliboutrr'. L. 98 1 . A critical revierl of anah ticirl a1;1;roxirratc sohrtions lbr steiLclr- state \-.locities alcl ternperatur-es in colcl ice-sheets. ,f. Gltt:tlurlil. Cil«ialgtol.. l5(2). 1979. 135 l'lB. 1
Llil;orrtrr'.
L.,\. I987. l'rrt :loit'
and glatiol agt. Dorrirt--cht.
f'loa'of salid;: batit; of nr,dtling in !ttid)nanri; \i jholi' Publishers.
ctc., \Iartinns
Lliboutn. L. anrl P. Duval. 1flU5. \'arious isotropic:rtrcl auisotropic ict-'s f'ouncl irr qlaciers arrrl polar ice caps and thoir corresponclinu rlreologics.,lnnaltt (|nlintirur. 31,2'1. 207 2'2+. \IcIntrre. \. 1'. 1983. 'I'he Lopoeraplir- :rncl florr o['thc lntiLrctic ice shcet. lPh. D. thesis, Universin' ol Ciarnbrirlg^e.) \[or]ancl. L. \\'. 1981. 'I hermomcchlLnical l;alartcts ol icc shcct Ilorrs. G to
p h-rs. -1
; l
roph l
;. I' l u i d
D.t
n.. 29. 237'266.
\I. S. B. I983. Delirrrn:rtiorr rrithin polar icc shcets: an atralrsis ol the Br rd Station :rncl C:rmp Clenturv bore hole-tiltinq mcasurenrcnts. (,oltl fug.,ÿi. 7 tthnol.. 8i2), 165 179. Patersorr. \\'.S.B. 199+. 7-1rc l:ltr.;it.; oJ'glatitts. Thinl trlition. Orlortl. r'rt.. l):rterson,
Illsevier Science Ltcl.
Pirniclta. I'. and P. Duval.
19f17.
Rate controlling processes in the creep
ol'polur glacier ite. J. Plt-t;. (Paris),48,
Clalloq.
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(Supplémeut aLr 3.) Rarlok. U.. D. Jcnsscn anrl B. \Iclnnes. i987. Or tlrc surgilg lottntial al' lnlu itt strtan.t. -lntarrtir surgtt a tltar and frLseù dantrr.) Boulder. ClO. Universitr of Cblorarlo. Clooper:rtive Institute lbr Rt'search in Erx'ironrncntal Scierrccs; llelbourne. Universitr- ol \Icll;ourrte. ]Icit--orolosr Dcpartrncnt. (US 1)e1;:Lrtment ol ErICrg\ Rcport DOD/IrR/60197-H l.) Rer:h. \.. S.J. Johrrscn and D. Dahl-.Jensen. 1985. Dating tltc Dle 3 rlcep ice corc lrv flou' rnorlcl calculatious. ft Lang-.l'ur'. C. C.. Jr. H. Or:sclrger and \\'. Dansgaarrl. d.s. Orunltnd itt corr: gcoltlq'sits. tLorlunisln. nnd lfu tniiranmtal. \\'ashing,-ton. DC), Atnerican Geoph;sical Lrrrion, 56 65. (Geophlsical llonograph 33.) Renrr'. F. ancl .|. F. \linstcr. 1993. Precise altimeuic tt4rog-.r:r1;lrl in it cslreet llorv stuclies. .'lzr. Glatiol..17. 19:r 200. Renl . ['.. P. \lazzeua. S. Hourr'. C. Brossier ancl .f . F. \Iinster. 1989.
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AIIev. R. Il. 1992. Flou -larr ht'potheses lbr ice-sheet rrorlcling. ./. Glarial.. 38(1'291. 24:l 256. llri-.st-'t. L. ancl lf . Rémr'. 1996. .\ntnrctic topographv arrrl kilornetre-scalt: rorrslrrress clerivecl liom ERS-l altimetr .:. -lnn. Glatial..23 (see paper
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