Former Ice Shelves in the Canadian High Arctic

Abstract

ABSTRACT. Moraines depos ited by the outermos t ice ad vance across Judge Daly Promontory, northeas tern Elles m e re I sland , reRect thin , topographically controlled ice lobes extending to sea-level. The termini of two ice lobes were in vestiga ted a nd both produced ice shelves where they Rowed into isostatically depressed e mbayme nts along wes te rn K ennedy Channel. M orphological evide nce for these ice shelves occurs at the e ntrance to these valleys whe re steeply descending la teral moraines become a bruptly horizontal for 2 km. In addition, both the h o rizontal moraines a nd associated pro-glacial terraces are fossiliferous downva lley from the a pparent grounding line. Based o n the differences in elevation between the h orizonta l moraines a nd the valley bottoms, the two ice shelves had es timated thicknesses of c. 110 a nd 150 m . A proglacial outwash terrace at 175 m a .s.l. is conside red to re present the a pproximate rel a tive sea-level during the formation a nd break-up of the ice shelves. This rela tive sea-level is consistent with the water depths required to Roa t the calcula ted ice thicknesses in b o th valleys. Associated with these ice margins are finite HC dates Of28 000-30000 B.P. a nd a mino-acid age es timates of > 35000 B.P. The importa nce and likelihood of additional past ice shelves in the Ca nadia n High Arcti c is discussed. R EsuME. Ancims glaciers dans le Grand N ord Canadien. D es moraines deposees par l' avance extreme de la gl ace a trave rs le Judge Da ly Promontory, au Nord-Est d e 1' lle d'Elles m e re, sont I'indi ce d e lobes de glace peu epa is contro les par la topog raphie et s'etendantjusqu' au niveau d e la m er. On a exa mine les extremites de deux lobes d e glace et tous d e ux ont engendre d es platformes de glace lo rsqu'elles fl ottaient d a ns d es baies rendues plus profo ndes pa r I' isostas ie le long de K ennedy Cha nnel occide nta l. Des preuves m o rphologiques de l'existence d e ces platformes subsistent a l'entree d e ces vallt!es lorsque les moraines la te rales jusque la en pente prononcee d eviennent brusquement horizon ta les sur 2 km. De plus, les morain es ho~izontales et les terrasses pro-glacia ires associees sont fossiliferes a l'aval d e la ligne d e rivage apparente. En se basant sur la difference d' a ltitude entre les mora ines horizon ta les e t les fonds d e la vallee, les deux glaciers avaient des epaisseurs es timees a ltO et 150 m . U ne terrasse pro-glaciaire alluvial e a 175 m au-dessus du niveau de la mer est conside ree comme representa nt le niveau rela tif a pproximatif d e la mer penda nt la fo rma tion et la dispa rition d es glaciers. Ce niveau d e la mer est coh e re nt a vec les epaisseurs d 'eau requises pour permettre que Rotte l'e paisseur de glace calculee dans les deux vall ees. A ces form a tions periglacia ires sont associees des da tations a u carbone 14 de 28000 a 30 000 ans ava nt le present e t d es a mino-acides ages d e 35 000 ans.L ' importa nce e t la vrai sembl a n ce d e l'existence d e glaciers sup...

Geomorphology and style of plateau icefield deglaciation in fjord terrains: the example of Troms‐Finnmark, north Norway

“…4a) that are interpreted as ice-shelf moraines on account of their bouldery surfaces and horizontal nature, lack of extensive Continued wave-washing evidence and a terrace altitude at least 20 m above the local marine limit, characteristics that they share with ice-shelf moraines elsewhere (e.g. England et al, 1978;Sugden and Clapperton, 1981;Hodgson and Vincent, 1984). Small cross-valley moraine ridges occur along Storvatnet, but not beyond the 50 m terrace, the internal structure of one revealing interbedded stratified diamictons, rippled sands and laminated muds with dropstones and occasional gravel lenses (Fig.…”

“…sea-levels required to float the ice shelves in outer Langfjorden and supports an early deglaciation of the fjords. As ice shelves occur only at non-temperate glacier margins, and their growth is encouraged by extensive sea-ice (England et al, 1978;Lemmen et al, 1988), the ice-shelf moraines constitute evidence for cold conditions and support a post-14 ka or possibly Older Dryas age (Andersen, 1979).…”

Holocene Sea-Ice Variations and Paleoenvironmental Change, Northernmost Ellesmere Island, N.W.T., Canada

“…A unique aspect of northern Ellesmere Island is that it presently supports the only landfast sea-ice ice shelves in the Northern Hemisphere (as distinguished from floating, glacier-ice ice shelves, England et al, 1978). If multi-year, landfast sea ice survives long enough to develop >2 m of freeboard it is termed an ice shelf.…”

Structure and sedimentology of George VI Ice Shelf, Antarctic Peninsula: implications for ice-sheet dynamics and landform development

“…This paper provides a detailed description of an ice-shelf moraine for the first time, and this can be used as a basis for locating such features in the geological record. Such features have already been identified in the Canadian Arctic (England et al 1978(England et al , 2009Hodgson & Vincent 1984) and northern Norway (Evans et al 2002), but there is no reason to suppose that they are not more widespread. The key identifiers are near-horizontal benches underlain by poorly sorted sediment, together with a scatter of local and fartravelled ice-transported boulders on the surface.…”