| 1. |
- Ha, H.K., et al.
(författare)
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Circulation and modification of warm deep water on the central Amundsen Shelf
- 2014
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Ingår i: Journal of Physical Oceanography. - 0022-3670. ; 44:5, s. 1493-1501
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Tidskriftsartikel (refereegranskat)abstract
- The circulation pathways and subsurface cooling and freshening of warm deep water on the central Amundsen Sea shelf are deduced from hydrographic transects and four subsurface moorings. The Amundsen Sea continental shelf is intersected by Dotson Trough (DT) leading from the outer shelf to the deep basins on the inner shelf. During the measurement period, warm deep water was observed to flow southward on the eastern side of DT in approximate geostrophic balance. A northward outflow from the shelf was also observed along the bottom in the western side of DT. Estimates of the flow rate suggest that up to one third of the inflowing warm deep water leaves the shelf area below the thermocline in this deep outflow. The deep current was 1.2°C colder and 0.3 psu fresher than the inflow, but still warm, salty and dense compared to the overlying water mass. The temperature and salinity properties suggest that the cooling and freshening process is induced by subsurface melting of glacial ice, likely from basal melting of Dotson and Getz ice shelves. New heat budgets are presented, with a southward oceanic heat transport of 3.3 TW on the eastern side of the DT, a northward oceanic heat transport of 0.5-1.6 TW on the western side, and an ocean-to-glacier heat flux of 0.9-2.53 TW, equivalent to melting glacial ice at the rate of 83- 237 km3yr-1 . Recent satellite-based estimates of basal melt rates for the glaciers suggest comparable values, 145 km3yr-1 (Getz) and 45 km3yr-1 35 (Dotson) (Rignot et al. 2013).
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| 2. |
- Kalén, Ola, 1971, et al.
(författare)
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Is the oceanic heat flux on the central Amundsen Sea shelf caused by barotropic or baroclinic currents?
- 2016
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Ingår i: Deep-sea research. Part II, Topical studies in oceanography. - : Elsevier BV. - 0967-0645. ; 123, s. 7-15
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Tidskriftsartikel (refereegranskat)abstract
- The glaciers that drain the West Antarctic Ice Sheet into the Amundsen Sea are accelerating and experiencing increased basal melt of the floating ice shelves. Warm and salty deep water has been observed to flow southward in deep troughs leading from the shelf break to the inner shelf area where the glaciers terminate. It has been suggested that the melting induced by this warm water is responsible for the acceleration of the glaciers. Here we investigate the structure of the currents and associated heat flow on the shelf using in-situ observations from 2008 to 2014 from Dotson Trough, the main channel in the western part of the Amundsen Sea shelf, and output from a numerical model. The model is generally able to reproduce the observed velocities and temperatures in the trough, albeit with a thicker warm bottom layer. In the absence of measurements of sea surface height we define the barotropic component of the flow as the vertical average of the velocity. It is shown that the flow is dominated by warm barotropic inflows on the eastern side and colder and fresher barotropic outflows on the western side. The transport of heat appears to be primarily induced by this clockwise barotropic circulation in the trough, contrary to earlier studies emphasizing a bottom-intensified baroclinic inflow as the main contributor.
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| 3. |
- Kalén, Ola, 1971
(författare)
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Ocean circulation in the Amundsen Sea, West Antarctica
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increase of mass loss from the Antarctic Ice Sheet is a significant contribution to global sea level rise. The most rapid changes are occurring in the Amundsen Sea area, where the thinning of the floating glaciers is assumed to be driven by the ocean. Relatively warm and salty deep water is forced upon the continental shelf and then flows southward in deep glacially scoured channels crossing the shelf. The warm waters contain enough heat to melt the glacial ice as they reach the base of the glaciers. The circulation of water masses on the Amundsen Sea shelf is sensitive to atmospheric forcing, while the regional atmospheric conditions are highly variable. A better understanding of this ice-ocean-atmosphere system is central to our ability to assess global sea level rise, which is occurring today and is projected to increase in the future. The temporal variability, heat content, pathways and vertical structure of the ocean currents in primarily the Dotson-Getz trough, the main western pathway for warm deep waters on the Amundsen Sea continental shelf, were investigated in this study. The major data source for these analyses was in-situ subsurface moorings giving time series of temperature, salinity and current velocity. Other material includes shipborne measurements, numerical model output and a variety of satellite and reanalysis data. The main findings from this work are the following. In the bottom layer on the eastern side of the trough, there is a continuous inflow of warm deep water with a temperature of several degrees C above the local freezing point. The currents transporting the heat have a strong a depth independent part. Flow variability is substantial on daily and sub-daily timescales and inflows are correlated with regional eastward winds. The warm inflows interact with the base of the ice shelves and a part of this flow leaves the channel on the western side as cooled and freshened water mass. The assessed melt rates induced by this clockwise circulation agree with satellite based estimates. The bathymetry databases for this region contain large errors, which has implications for model studies and transport calculations.
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| 4. |
- Stigebrandt, Anders, 1942, et al.
(författare)
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Improving oxygen conditions in the deeper parts of Bornholm Sea by pumped injection of winter water
- 2013
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 42:5, s. 587-595
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Tidskriftsartikel (refereegranskat)abstract
- Vertical diffusivity and oxygen consumption in the basin water, the water below the sill level at about 59 m depth, have been estimated by applying budget methods to monitoring data from hydrographical stations BY4 and BY5 for periods without water renewal. From the vertical diffusivity, the mean rate of work against the buoyancy forces below 65 m depth is estimated to about 0.10 mW m−2. This is slightly higher than published values for East Gotland Sea. The horizontally averaged vertical diffusivity κ can be approximated by the expression κ = a 0 N −1 where N is the buoyancy frequency and a 0 ≈ 1.25 × 10−7 m2 s−2, which is similar to values for a 0 used for depths below the halocline in Baltic proper circulation models for long-term simulations. The contemporary mean rate of oxygen consumption in the basin water is about 75 g O2 m−2 year−1, which corresponds to an oxidation of 28 g C m−2 year−1. The oxygen consumption in the Bornholm Basin doubled from the 1970s to the 2000s, which qualitatively explains the observed increasing frequency and vertical extent of anoxia and hypoxia in the basin water in records from the end of the 1950s to present time. A horizontally averaged vertical advection–diffusion model of the basin water is used to calculate the effects on stratification and oxygen concentration by a forced pump-driven vertical convection. It is shown that the residence time of the basin water may be reduced by pumping down and mixing the so-called winter water into the deepwater. With the present rate of oxygen consumption, a pumped flux of about 25 km3 year−1 would be sufficient to keep the oxygen concentration in the deepwater above 2 mL O2 L−1.
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| 5. |
- Wåhlin, Anna, 1970, et al.
(författare)
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Subinertial Oscillations on the Amundsen Sea Shelf, Antarctica
- 2016
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Ingår i: Journal of Physical Oceanography. - 0022-3670. ; 46:9, s. 2573-2582
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Tidskriftsartikel (refereegranskat)abstract
- Mooring data from the western flank of Dotson Trough, Amundsen Sea shelf region, show the presence of barotropic oscillations with a period of 40-80 hours. The oscillations are visible in velocity, temperature, salinity and pressure, and are comparable to tides in magnitude. The period of the oscillations corresponds to topographic Rossby waves of low group velocity and wavelength about 40 km, i.e. the half-width of the channel. It is suggested that these resonant topographic Rossby waves cause the observed peak in the wave spectra. The observations show that sparse CTD data from this region should be treated with caution and need to be complemented with moorings or yo-yo stations in order to give a representative picture for the hydrography.
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| 6. |
- Wåhlin, Anna, 1970, et al.
(författare)
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Variability of Warm Deep Water Inflow in a Submarine Trough on the Amundsen Sea Shelf
- 2013
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Ingår i: Journal of Physical Oceanography. - 0022-3670 .- 1520-0485. ; 43:10, s. 2054-2070
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Tidskriftsartikel (refereegranskat)abstract
- The ice shelves in the Amundsen Sea are thinning rapidly, and the main reason for their decline appears to be warm ocean currents circulating below the ice shelves and melting these from below. Ocean currents transportwarm densewater ontothe shelf,channeledby bathymetric troughs leadingto the deep inner basins. A hydrographic mooring equipped with an upward-looking ADCP has been placed in one of these troughs on the central Amundsen shelf. The two years (2010/11) of mooring data are here used to characterize the inflow of warm deep water to the deep shelf basins. During both years, the warm layer thickness and temperature peaked in austral fall. The along-trough velocity is dominated by strong fluctuations that do not vary in the vertical. These fluctuations are correlated with the local wind, with eastward wind over the shelf and shelf break giving flow toward the ice shelves. In addition, there is a persistent flow of dense lower Circumpolar Deep Water (CDW) toward the ice shelves in the bottom layer. This bottom-intensified flow appears to be driven by buoyancy forces rather than the shelfbreak wind. The years of 2010 and 2011 were characterized by a comparatively stationary Amundsen Sea low, and hence there were no strong eastward winds during winter that could drive an upwelling of warm water along the shelf break. Regardless of this, there was a persistent flow of lower CDW in the bottom layer during the two years. The average heat transport toward the ice shelves in the trough was estimated from the mooring data to be 0.95 TW.
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