New Light on the Mode of Uplift of the Fish and Fossiliferous Moraines of the Mcmurdo Ice Shelf, Antarctica

Abstract

ABSTR ACT. The M cMurd o I ce Shelf a nd assoc iated faun a l rem a ins were exa mined in th e vicinity of th e easternmost D a iley Isla nd. Stra tig ra phi c, petrographi c, a nd chemical compos ition studi es of cores from two holes drilled through th e ice sh elf show th a t at th ese loca tions th e sh elf is composed onl y of fr esh-wa ter ice. Althoug h cores from the d eep e r h ole possessed typi call y glacial tex tures th ro ughout, m u ch of th e ice from this part of the M cMurdo I ce Shelf may have bee n fo rmed from th e freez ing of a layer of fres h wa ter found sandwich ed b e tween shelf b o tto m and th e und erl y ing sea-water . T he existen ce of fresh wa te r under the ice shelf ca n m ost proba bl y be a ttributed to dra inage o f surface melt wa te r during the ab la tio n season. Ther e wa s no eviden ce to indi cate that this pan of th e M c Murdo I ce S helf is b e in g nourished by th e g rowth of sea ice onto its lower surface. Th e fis h rema ins fo u nd o n the ice surface were confin ed to a n a r row zone along the tide c rack and a re beli eved to have been left in t hi s vicinity by d eep di v in g seals. Th e marine in vertebra te rema in s on top of the ice are associa ted with m o ra ina l m a teria l a nd a re b el ieved to have b een incorporated into th e ice at the time of fo rma ti on of th e mora ines. R ESU ME . .NollveLle Iwniere sllr le mode de remolltee de poissoll et morailles dJossiles £lit M cM llrdo Ice Shelf, Alltarctiqlle.Le M cMurd o I ce Shelf et Ies re liquats associes de fa un e ont ete exa min es d a ns le voisin age d e l' il e la plus it l'est d es Dailey I sla nds. D es etu des stra tigraphiques , pet rog raphiqu es e t d e compositio n c himi q ue d e ca rottes provena nt d e d eux forages it trave rs le ice shel f m o nu'e nt q ue, it ces sta tio ns, le ice shelf es t co mpose uni quemen t d e g lace d ouce. Bi en q u e les ca rOttes du b as du trou de fo rage p ossed ent tout a u lo n g d es tex tures glacia ires typiques, la plus g ra nd e pa ni e de la g lace d e cette pa rtie du M cMurdo I ce S he lf a pu se form er pa r le gel d ' une strate d'eau d o u ce sa isie entre le bas d u shelf et I'eau d e m e r sous-j acent e. L 'ex istence d 'ea u douce sous le ice shelf peut le plus proba blement e lre a ltribuee a u dra inage d e l'ea u d e fu sio n superfi ciell e penda nt la saison d 'abla li on . 11 n 'y avail a UCLln e ev ide nce en faveur d' un e cro issance pa r g lace d e mer SLlr la surface infer ieure de cett e par ti e d u M cMLlrdo I ce S h elf. Les rel iqua ts d e p o isson trou ves sur la surface de la glace etai ent confines it une zon e c tro ite le long d es c reva sses de ma ree e t I'on p ense q u' il s y ont e te a ba ndonn es par d es phoques chassa nt it g ra nd e profond eLlr. L es rc1 iqua ts d ' in ve rt e bres m a rins a u sommet d e la glace sont associes a vec du mat eri el mo ra ini q ue, et 1'0n pense qu ' ils ont ete in co rpo res it la glace lors d e la fo rma tion d es lTIora in es. Z USAMM EN FASSUNG . .Neues L i...

Marine ice recycling at the southern McMurdo Ice Shelf, Antarctica

“…1) (Clifford, 2005). The presence of marine ice was also detected in previous studies on ice composition (Kellogg and others, 1991a; Fitzsimons and others, 2012) and inferred from the presence of marine macrofossils at the ice-shelf surface (Debenham, 1919; Gow and others, 1965; Swithinbank, 1970; Kellogg and others, 1990, 1991b; Fitzsimons and others, 2012). Two of these shells were radiocarbon-dated to 1230 ± 50 and 2850 ± 30 radiocarbon years BP (Kellogg and others, 1990; Denton and Marchant, 2000) using an Antarctic reservoir correction of 1300 years (Berkman and Forman, 1996).…”

“…This meltwater then rises along the gradient of the ice shelf due to its buoyancy to shallower waters, where it becomes supercooled due to a change in the pressure-dependent freezing point and frazil ice crystals nucleate (Galton-Fenzi and others, 2012). Double diffusion-induced supercooling could occur close to the grounding line of shallower ice shelves, where surface meltwater can percolate through sediment (Souchez and others, 1998) or drain through tide cracks (Gow and others, 1965; Gow and Epstein, 1972) to the ice/water interface. Heat diffuses faster than salt from relatively warmer meltwater to colder sea water (Martin and Kauffman, 1974).…”

Debris characteristics and ice-shelf dynamics in the ablation region of the McMurdo Ice Shelf, Antarctica

“…This is in contrast to the dominance of surface inputs and outputs found in a typical glacial mass-balance system. The δ 18 O data collected on the ice surface in the ablation area of the ice shelf indicate that the ice here is of marine origin (Kellogg and others, 1990), whilst near the northern edge of the ice shelf, ice cores show the shelf to be composed of fresh-water ice, formed from surface meltwater refreezing at the base of the ice shelf after it has drained down tide cracks (Gow and others, 1965).…”

“…The combination of sea water and sediment freezing onto the base of the ice shelf and high surface ablation causes a net upward migration of ice and debris, allowing debris to become concentrated on the ice surface (Debenham, 1961, 1965). Subsequent work on the ice shelf’s marine biota and sediments includes that of Swithinbank and others (1961), Speden (1962), Gow and others (1965), Kellogg and others (1977, 1990), Brady (1978), Hayward and Taylor (1984), Kellogg and Kellogg (1987), Hart (1990) and Wilson (2000).…”

Basement Ige, Ward Hunt Ice Shelf, Ellesmere Island, Canada

“…If the ice shelf maintains a nearly constant thickness, curling up at its edges and, over the past several hundred years, accumulating firn and lake ice in the area between Ward Hunt and ElIesmere Islands, bottom melting is also a necessity under this median part of the ice shelf (Lyons and Ragle, 1962, p. 93-94). Similarly, accretion of ice under some parts of the McMurdo and Ross Ice Shelves of the Antarctic, and ablation under others, has recently been demonstrated by Gow and others ( 1965) and by Swithinbank (1970).…”