ABSTRACT. In the coas tal mou n tain cha in of south ern Victoria Land a pproxi ma tely 4,000 km.' of glacierc ut valleys a nd dividing ra nges are a lmos t completely ice-free, while the surrounding areas are full y glacierized .In the ice-free Wright Va lley a nd Victoria Valley system s evidence of fo ur glaciations is recognized . T he earliest two glac ia tions were the m os t extensive; glaciers flowed eastwards from the ice plateau through the coastal ranges and cut broad valleys extending to M c Murdo Sound and the R oss Sea . The mo raines of these glaciations are thin and highly weather ed. The third glaciation was less extensive, consisting of advances by smaller glac iers derived from the inland ice plateau, the Wilson Piedmont Glacier and ncve fi elds in the dividing ranges. The surfaces of moraines of this glac ia tion are now partly covered by saline lakes, evaporite d eposits and ex tensive areas of d esert pavements strewn with ventifacts. The fourth and youngest g laciation comprised small advances by remnants of the plateau-fed valley glaciers . Thick boulder moraines of this glaciation overlie earlier deposits.During ea ch glac iati on the greates t volume of ice was d eri ved from the inland ice plateau. The vo lume of ice entering the vall eys was d ep enden t on the diffe re nce in altitude b etween the plateau surface and subglacial rock thresholds a t the valley heads. Decrea se in the surface level of the inland ice plateau caused the rock thresho lds to increasingly hinder th e eastward fl ow of plateau ice until prac ti cally n o ice could fl ow d own into th e va lleys, thereb y terminating the glac iatio n. Such a condition exists at the present time. RESUME. Dans la chaine de m ontagnes co tieres du Sud d e la T erre de Victoria il existe environ 4000 km' de vallt'es d' erosion glaciaire e t des c haines de separation, presque entierement libres de glace, tandis que les regions environnantes sont complctem ent englacees.Dans les systemes d es vallees d e Wrigh t et de V ic to ria , libres de glace, o n a pu prouver le p assage pilr qua tre glac iations. L es deux premier es glaciations eta ie nt les plus etendues; les gl ac iers s'ecoulaient du plateau glaciaire, vers l'es t, a travers les chaines co tieres et decoupaient de larges vallees s'etend a nt jusqu 'au Detroit de M cMurdo e t la M er de R oss. L es m oraines de ces glacia tions sont minces e t tres erodees. La troisieme g laciati on etait m oins etendue et consistait en l'avan ce d e p etits glaciers venant du plateau glacia ire de l'interieur, d u glacier d e Wilson Piedmon t e t des zones de neve situees dans les chaines de separation . L es regions morainiques d e ce tte glac iation sont main tenant pa rtiellem e nt recouvertes d e lacs sal ins, de depo ts d 'evaporation e t de grandes e tend ues desertiques parsemees de caill oux erodes pa r le vent. La qua triem e e t derniere glaciation comporta it de faibl es ava nces des vestiges d e glaciers de vall ee s'eco ulant du plateau. D'epaisses moraines de caill oux prov...
On the Ross Ice Shelf near Scott Base the annual surface snow accumulation is about 18 g.cm.−2. The increase of firn density with depth is greater than normal, due to horizontal compaction. Where the bottom of the ice shelf has a density less than 0.8 g.cm.−3 the shelf becomes brine-soaked by vertical infiltration. The bottom of the shelf is melting, at about 44 g.cm.−2 yr.−1 where the bottom is impermeable ice and 73 g.cm.−2 yr.−1 where the bottom is permeable firn. Surface velocities at 40 points within 30 km. of Scott Base vary between 4 and 840 m.yr.−1. From the pattern of velocities, ice thicknesses and surface features, a transition zone is delineated, separating the Ross Ice Shelf from the “McMurdo Ice Shelf”.
The increased interest in past climatic changes, as revealed by studies of long ice cores from polar ice sheets, has stressed the need for a better understanding of the development of the stratigraphic record preserved in these cores. This paper presents some results of surface investigations at Dome C (74°30'S, 123°10'E), East Antarctica, carried out in austral summers 1978-79 and 1979-80. An explanation is presented of the snow stratigraphy, in terms of depositional and post-depositional processes, that is supported by detailed accumulation measurements at stakes and by snow-pit studies. Temporal and areal variability of snow accumulation are investigated to determine how representative the results interpreted from a single core might be for the Dome C region. Finally, the reliability of several stratigraphic methods for defining annual layers is assessed. Snow-pit studies show that major depositional features are preserved with depth. Visible annual strata at Dome C are composed of thin, hard crusts overlying thicker layers of soft to medium-hard snow. Low density depth-hoar layers, when they occur, are usually found below the thin, hard crusts. Depth profiles of gross 8-radioactivity and of microparticles concentration exhibit annual cyclicity which, together with the detailed visible stratigraphy, can be used to assign dates to the layers.
The concentration of microparticles in the 2 164 m long ice core from “Byrd” station Antarctica, varies cyclically. Highest concentrations of 0.65 μm diameter microparticles occur where oxygen-isotope studies show lowest paleotemperatures. The age of the bottom ice estimated from microparticle-concentration variations, assuming an annual cycle, is 27 000 years, much less than from oxygen-isotope studies.
On the Ross Ice Shelf near Scott Base the annual surface snow accumulation is about 18 g.cm.−2. The increase of firn density with depth is greater than normal, due to horizontal compaction. Where the bottom of the ice shelf has a density less than 0.8 g.cm.−3the shelf becomes brine-soaked by vertical infiltration. The bottom of the shelf is melting, at about 44 g.cm.−2yr.−1where the bottom is impermeable ice and 73 g.cm.−2yr.−1where the bottom is permeable firn. Surface velocities at 40 points within 30 km. of Scott Base vary between 4 and 840 m.yr.−1. From the pattern of velocities, ice thicknesses and surface features, a transition zone is delineated, separating the Ross Ice Shelf from the “McMurdo Ice Shelf”.
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