Physical, chemical and isotopic investigations of Ward Hunt Ice Shelf and Milne Ice Shelf, Ellesmere Island, NWT
Abstract
The object of the research was to investigate the growth and structure of Ward Hunt and Milne Ice Shelves which have recently produced ice islands. The work involved ice core drilling and collection of snow and fiord water samples. These have been the subject of conductivity (SEC)-salinity, 180, tritium, ice density and ice texture analysis. Accorct;ng to these parameters, ten ice types have been identified (Tables 5.12A and 5.12B) and each is found in or adjacent to the ice shelves and plays a role in their growth and structure (Fig. 5.40). Ward Hunt Ice Shelf is largely composed of three types of basement ice, which are the product of a sequence of processes which transform first-year sea ice to very old multiyear sea ice, in the absence of 18 O depleted meltwater. Milne Ice Shelf is largely composed of glacier tongues which flowed into and coalesced in Milne Fjord. The ice tongues and the basement ice acted as stable platforms for further ice shelf thickening through snow and ice accumulation. The latter involved percolation and refreezing of meltwater, with attending isotopic homogenization and enrichment from snow o values of -31 .0 0 loo to ice o values of -29.2 0 loo. During periods of negative surface mass balance, meltwater accumulates in meltwater lakes in the summer and refreezes to trough ice (o 18 o, -24.0 °100) in the winter. The ice shelves act as dams creating stratified conditions of freshwater (runoff) overlying seawater (Arctic surface water and/or Atlantic water) in Disraeli Fjord and inner Milne Fjord. The freshwater just above the halocline is supercooled; frazil ice forms and floats to the surface and accretes as a freshwater fjord ice with a o1 8 O value of -26.0 0 loo. During a climatic amelioration ea. 250012000 BP to ea. 1600 BP, an extensive freshwater flow beneath Ward Hunt Ice Shelf led to the accretion of a freshwater, 18 O depleted ice (-25.5 0 loo), which originated with frazil ice growth, and is now sandwiched between basement ice layers. The conductivity and o18o value of this ice indicates that frazil ice growth and accretion at the bottom of the ice shelves does not lead to "brackish" basement ice growth as suggested by Lyons et al. (1971). The re-entrant (or multiyear) sea ice that has grown at the front of Milne Ice Shelf is the closest analogy to "brackish" ice. In this ice, salinity ranges from zero to 2.84 °100, and o18 o ranges from -23.8 0 loo to -4.2 0 loo. This variation, which is manifested as seasonal and 10 year fluctuations of salinity and 18 0, arises from similar variation in the water beneath the ice. Each summer, 180 depleted meltwater dilutes the underlying seawater. At the end of the summer a low salinity-low 180 ice freezes first and is followed by higher salinity-higher 180 winter ice. The annual and 10 year stratification leads to an interfingering of fresh, brackish and saline ice which resembles "brackish ice". Re-entrant ice is influenced by 18 O depleted meltwater, but basement ice is not. The ice shelves have experienced two periods of expansion and two periods of wastage. Re-entrant ice, which precedes basement ice growth, is forming during the present period of ice wastage. If the climate deteriorates, re-entrant ice might be succeeded by basement ice growth and further ice shelf expansion and thickening.
Description
Bibliography: p. 291-310.
Keywords
Citation
Jeffries, M. O. (1985). Physical, chemical and isotopic investigations of Ward Hunt Ice Shelf and Milne Ice Shelf, Ellesmere Island, NWT (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/16743