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Dissertation/Thesis Abstract

Geostrophic ocean currents, freshwater fluxes, hydrography, and salinity field in nares strait between the Canadian Arctic Archipelago and NW Greenland
by Rabe, Berit, Ph.D., University of Delaware, 2010, 186; 3423414
Abstract (Summary)

This dissertation focuses on ocean currents, geostrophic volume and freshwater fluxes, hydrography, and salinity fields in Nares Strait, one of the major straits in the Canadian Arctic Archipelago (CAA) to the NW of Greenland. Nares Strait connects the Arctic to the North Atlantic Ocean, facilitating an exchange of freshwater between both oceans. The freshwater budget of the Arctic Ocean plays an important role in the global climate system. Observations of freshwater flux through the CAA have been sparse, seasonally biased, and on short time scales in the past. Between 2003 and 2006 oceanographic instruments deployed near 80.5°N measured conductivity, temperature, pressure, and velocity at high temporal and spatial resolution across the 38 km wide and 400 m deep Nares Strait.

The focus of my research is on the analysis of the novel CT data set in combination with local wind, along-channel pressure differences, and ADCP data. Two different methodologies were developed to evaluate data from the innovative CT moorings that avoid ice and continuously sample the water column due to the mooring motion at tidal time scales. Nares Strait is ice-covered throughout the year with ice drifting in late summer, fall, and early winter, and ice being land-fast the remainder of the year.

Geostrophic volume and freshwater fluxes vary between the two ice states showing more variability during mobile ice conditions. Geostrophic freshwater flux (three-year mean of 20 ± 3 mSv, Sv = 106 m 3 s-1, no trend observed) is modulated by the ice cover and reveals 20% higher fluxes during mobile ice conditions than during land-fast ice conditions with maximum differences between individual ice seasons of 40%. A 40% increase occurs when extrapolating to the surface to account for freshwater in the unsampled surface layer. Enhanced freshwater fluxes during mobile ice conditions can have implications in the future when ice conditions change towards a more ice-free state due to no ice bridge forming in Smith Sound. The geostrophic volume flux (three-year mean of 0.47 ± 0.05 Sv) increases over the three-year period by 15 ± 4%. The domain for fluxes is 55% of the total area above 200 m, including a level of known motion at 200 m.

Forcing of the geostrophic freshwater flux through Nares Strait is a combination between local wind and along-channel pressure difference forcing during mobile ice conditions. During land-fast ice conditions only the along-channel pressure difference is forcing the geostrophic freshwater flux due to the decoupling from the atmosphere through the ice cover.

The three-year mean geostrophic velocity has a surface-intensified southward flow against the western side of the strait and a secondary core flowing southward in the middle of the strait. Distinguishing between the two different ice states, I find the surface-intensified core of up to 0.28 m s-1 in the middle of the strait during mobile ice conditions. A sub-surface core of about 0.25 m s-1 exists on the western side of the strait during land-fast ice conditions, intensifying over the three-year study period.

When comparing geostrophic velocity to ADCP velocity a large discrepancy exists during all seasons within five km of the western coast. This discrepancy can possibly be associated with the lateral or vertical boundary layer. Geostrophic velocity resembles free-slip conditions; ADCP velocity resembles no-slip conditions. In the eastern part of the strait velocities compare well.

Different water masses occupy the strait with fresh, cold water in the top layers on the western side and warm, salty water of Atlantic origin at depth on the eastern side of the strait. Salinity variations of about two psu in time and space reflect a variable freshwater outflow from the Arctic Ocean. One particularly strong pulse occurred at the end of July 2005. For several days, steeply sloping isohalines indicated strong geostrophic flow down the middle of the strait coinciding with an amplified ice export from the Arctic due to strong southward winds.

Indexing (document details)
Advisor: Muenchow, Andreas
Commitee: Falkner, Kelly K., Huq, Pablo, Samelson, Roger
School: University of Delaware
Department: Marine Studies
School Location: United States -- Delaware
Source: DAI-B 71/11, Dissertation Abstracts International
Subjects: Physical oceanography
Keywords: Freshwater fluxes, Hydrography, Nares strait, Ocean currents, Salinity field, Water masses
Publication Number: 3423414
ISBN: 978-1-124-24200-2
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