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Ice-ocean interactions in Milne Fiord

University of British Columbia

Widespread break up of ice shelves, glacier tongues, and the loss of ice-dammed epishelf lakes on the northern coast of Ellesmere Island has motivated a need to understand fjord dynamics, yet the oceanography of fjords here is not well studied. Here, we present ocean profiling and mooring data collected from 2011 to 2015 in Milne Fiord, the last ice shelf-epishelf lake-glacier tongue fjord in the Arctic. The data reveal that seasonal and interannual variations of fjord water properties and circulation are strongly impacted by the presence of the Milne Ice Shelf. The ice shelf forms a floating dam that traps surface runoff resulting in strong stratification and an elevated fjord heat content. Water exchange below the ice shelf is restricted to a narrow basal channel, prolonging the export of fjord-modified water, including subglacial runoff, by several months. In contrast, intermediate waters that penetrate to the Milne Glacier grounding line are freely exchanged and respond to offshore variations, with implications for submarine melting. Unexpectedly, the depth of the halocline between the epishelf lake and seawater, often used to infer the thickness of the ice shelf, varied by several meters each year. This variability resulted from rapid inflow of surface runoff during summer followed by slow drainage under the ice shelf over winter, which is well modelled as hydraulically-controlled flow through a channel. A mixing event also abruptly changed the depth of the halocline by 1.5 m in less than 24 hours, indicating caution must be used when inferring ice shelf mass balance from halocline depth. Submarine melt rates, estimated by two independent approaches, are strongly dependent on the vertical distribution of heat in the fjord. Spatial variation of ice thickness resulted in a heterogeneous distribution of melt. The highest estimated melt rate (4 m/a) occurred where the glacier was in contact with warm AtlanticWater at the grounding line, and enhanced near-surface melting is driven by the elevated heat content of the upper water column. Estimated melt rates are limited by weak currents ( 1 cm/s) in the fjord imposed by the presence of the ice shelf.

Text

2016-09-02

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/59051

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/