Chemical Fractionation of Brine in the McMurdo Ice Shelf, Antarctica

• Main Authors: Cragin, James H, Gow, Anthony J, Kovacs, Austin
• Other Authors: COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
• Format: Text
• Language: English
• Published: 1983
• Subjects: Physical Chemistry; Physical and Dynamic Oceanography; Snow; Ice and Permafrost; *ANTARCTIC REGIONS; *BRINES; *FRACTIONATION; *SEA ICE; CATIONS; CHEMICAL ANALYSIS; CHEMICAL COMPOSITION; CHEMICAL PRECIPITATION; CORE SAMPLING; ICE PENETRATION; PHYSICAL PROPERTIES; SALINITY; SODIUM SULFATES; SULFATES; THERMAL PROPERTIES; *MCMUNOO ICE SHELF; ICE SHELF FIRM; AST24; PE61102A; Antarctic; Austral; McMurdo Ice Shelf; Antarc*; Antarctica; Ice; Ice Shelf; permafrost; Sea ice
• Online Access: http://www.dtic.mil/docs/citations/ADA127821; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA127821

During the austral summers of 1976-77 and 1978-79, several ice cores were taken from the McMurdo Ice Shelf brine zone to investigate its thermal, physical and chemical properties. This brine zone consists of a series of superimposed brine layers (waves) that originate at the seaward edge of the ice shelf and migrate at various rates, depending upon their age and position in the ice shelf. The brine in these layers becomes increasingly concentrated as the waves migrate inland through the permeable ice shelf firn. Chemical analyses of brine samples from the youngest (uppermost) brine wave show that it contains sea salts in normal seawater proportions. Further inland, deeper and older brine layers, though slightly highly saline (S200%), are severely depleted in (S04)2- /Na+ ratio being an order of magnitude less than that of normal seawater. Analyses of Na+, K+, Ca2+, Mg2+, (So4)2- and C1-, together with solubility and temperature considerations, show that the sulfate depletion is due to selective precipitation of mirabilite, Na2S041OH2O. The location of the inland boundry of brine penetration is closely related to the depth at which the brine encounters the firn/ice transition. However, a small but measurable migration of brine is still occurring in otherwise impermeable ice; this is attributed to eutectic dissolution of the ice by concentrated brine as it moves into deeper and warmer parts of the McMurdo Ice Shelf.