Glaciological and Oceanographic Calculations of the Mass Balance and Oxygen Isotope Ratio of a Melting Ice Shelf

Abstract

ABSTRACT. Glaciological es tim a tes of the ice supply to George VI Ice Shelf a re obtained by integrating th e accumu la tion over the ca tchment. The basal melt (or possible shelf thic kening) rates for the ice shelf are calcul ated by ba lancing the acc umulatio n with calving and melting. We calcula te a n average equilibrium melt rate for the ice shelf of2 m a -'. If the ice shelf is in mass balance it alone provid es 53 km 3 a -1 melt fro m its base compared to a total for Antarctica of on ly 320 km'a -' .The mean oxygen isotope com positio n of recent accumul ation on the catchment is det ermined by using accumulation and isotope data, supplemented by temperature measurements and a close empirical relationship between iso tope rati o and temperature . The catchment has a mea n isotope ratio of -20.8%0 relative to SMOW.O ceanog raphi c wo rk has previo usly shown that the sea-water under the ice shelf at th e north of Geo rge VI So und is Warm Deep Water modifi ed by melting ice. Th e melting ice has an isotope ratio of -20.3%0 . The good agreement in isotope rati os suggest tha t th e melting ice is from th e catchment and beca use th e basal ice of George VI Ice Shelf re p resents acc umulation over lh e last few millenni a the implica tion is that there has been no systemati c change in the isotope compositi on of th e accumu latio n during thi s peri od . This implies no sec ular c hange in eith er th e eleva ti on o r the climatic tempe raLUre of thi s part of th e ice sheet. R ESUME. Calculs glaciologigues el oceanographiques du bilall de masse el du pourcenlage de l'isolope de I'oxygene pour

Calving fluxes and basal melt rates of Antarctic ice shelves

“…Different atmospheric forcings explain most of the large discrepancies between different model simulations 17,18,22 (H. Hellmer, personal communication). However, our results for the BMB agree well with previous estimates using a similar methodology 14,23 (Supplementary Discussion 4).…”

Transport and Water Masses of the Antarctic Slope Front System in The Eastern Weddell Sea

“…Meltwater from the underside of glaciers will represent 8 18 0 values of the precipitation where the glacier originated, inland from the coast. The isotopic composition of precipitation varies with air temperature, so different glaciers around the continent of Antarctica could contribute meltwaters with different isotopic signals [Potter et al, 1984]. In addition, there is likely to be some influence from surface runoff from glaciers which will mix with waters near the front of the ice shelves.…”

“…While a hydrographic section of 8 18 0 will therefore closely resemble salinity, the value of 8 18 0 as a tracer in polar regions occurs where there are deviations from the usual 5 18 0-salinity relationship. Coastal precipitation around Antarctica exhibits 5 18 0 values between -13 %o and -20 %o [Bromwich and Weaver, 1983;Jeffries et al 1994], while Antarctic glacial ice is considerably lighter (-20 to -45 %o in Jacobs et al, [1985]), because it originates inland where the precipitation is further depleted in 18 0 [Morgan, 1982;Potter et al, 1984]. Therefore the influence of glacial ice melt is revealed as a particularly low 6 18 0 for the salinity of the water mass.…”

Circulation and melting beneath George VI Ice Shelf, Antarctica

“…It reaches a maximum thickness of around 500 m about 70 km from the southern ice front, where a ridge of thick ice extends across the sound (near 70°W). The vast majority (96–97%) of the flow into the ice shelf comes from Palmer Land while surface accumulation also makes a significant contribution (∼20%) to its mass budget [ Potter et al , 1984]. The northern ice front, which faces Marguerite Bay, appears to be near the geographical limit of ice shelf viability and has undergone a gradual retreat in recent decades [ Lucchitta and Rosanova , 1998], a timeframe over which much of the nearby Wordie Ice Shelf disintegrated [ Doake and Vaughan , 1991].…”

“…Ponding of meltwater occurs at the surface in summer, but only a small quantity (0.4 ± 0.2 km 3 ) appears to drain each year via moulins and tide cracks to the underlying ocean [ Reynolds , 1981]. This is less than 1% of the annual mass input to the ice shelf [ Potter et al , 1984]. Although summer melting has almost certainly increased since these estimates were made, drainage of meltwater probably remains an insignificant part of the overall mass budget.…”