Structure and variability of the circulation at tidal to intra-seasonal time scales near the 79 North Glacier


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luisa.von.albedyll [ at ] awi.de

Abstract

Greenland's largest floating ice tongue at the Nioghalvfjerdsfjorden Glacier (79 North Glacier) is thinning, most likely triggered by enhanced submarine melting. The strength of the cavity circulation beneath the floating ice tongue is essentially responsible for the ocean heat flux to the glacier ice and variability in the circulation may have consequences on the basal melt rate. Analyzing four moored records (summers 2016-2017) from the 79 North Glacier calving front, this study characterizes the variability of the cavity circulation and the relative importance of its local and regional drivers. The focus lies on the variability in the currents in Dijmphna Sund, the most relevant export pathway for glacially modifed waters out of the glacial cavity. Variability is split into three groups. (1) Half of the variance of the time series is concentrated at sub-daily to daily time scales (T = 0.25 - 2 days) and is associated with barotropic tides. (2) Periods of 2-30 days comprise one third of the variance. At those time scales, currents in Dijmphna Sund are weakly linked to sea ice conditions close to the coast and enhanced wind speeds. (3) In periods larger than 30 days, 1/6 of the variance is found. Low-pass filtered Empirical Orthogonal Functions reveal a strong link between the export of glacially modified waters through Dijmphna Sund and the inflow into the glacial cavity. This intra-annual variability of the cavity circulation was also observed by a mooring on the continental shelf 170km south of the 79 North Glacier. The time series from the calving front and the one from the continental shelf are significantly correlated (R = 0.65) and shifted by a time difference of 27 - 29 hours. The time delay fits well to travel times of baroclinic waves. This suggests that large-scale wave activity may be the main driver of the intra-annual variability of the cavity circulation.



Item Type
Thesis (Master)
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Not peer-reviewed
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Published
Eprint ID
48970
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Albedyll, L. v. (2018): Structure and variability of the circulation at tidal to intra-seasonal time scales near the 79 North Glacier Master thesis,


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