Structure and transport of Atlantic Water north of Svalbard from observations in summer and fall 2018


 <p>The transport of warm Atlantic waters north of Svalbard is one of the major heat and salt sources to the Arctic Ocean. The circulation pathway and the associated heat transport influence the variability in the Arctic sea ice extent and the onset of freezing. We present observations obtained from research cruises and autonomous underwater glider missions in summer and fall 2018 to describe the hydrographic structure, volume transport rates and circulation patterns of the warm boundary current between 12E and 24E north of Svalbard.</p><p>A composite section is constructed along a representative, average bathymetry across the shelf break, using all available observations in order to obtain the hydrographic structure and the absolute geostrophic transport of the boundary current. The Atlantic water volume transport reaches a maximum of 3.0 &#177; 0.2 Sv in October, with an intraseasonal variability of 1 Sv. During summer and late fall, we observed Atlantic water flowing eastward (a counter current), in the outer part of the section away from the shelf break, in the Sofia Deep. The intensity of the Atlantic water counter current and the Atlantic water boundary current are very sensitive to the wind stress curl: we observed a near doubling of the volume transport in less than a week.</p><p>The composite section also reveals a bottom-intensified current flowing parallel to the boundary current, between the 1500 m and 2000 m isobaths. A composite of all historical data collected in the region, constructed identical to our observations, support the presence of the bottom intensified current.</p>



Why is it important?
The transport of warm Atlantic Waters (AW) north of Svalbard is one of the major heat and salt sources to the Arctic Ocean.The circulation pathway and the associated heat transport influence the variability in the Arctic sea ice extent, the onset of freezing, and marine ecosystems.

Research gaps:
The fraction of AW that enters the Arctic Ocean is not accurately known.
The observed along-path cooling rate of AW is larger than that indicated by vertical heat fluxes.It is not clear which processes can sustain such along-path cooling rates.

A
counter current in the Sofia Deep transports Atlantic Water westward Red arrows show the AW circulation in the study region.Black dashed arrows show possible anticyclonic circulation in the Sofia Deep.Small black arrows mark the possible generation site for eddies.
circulation patterns north of Svalbard, from high resolution observations summer and fall 2018.2 EGU20 -OS1.11-Eivind H. Kolås -Structure and transport of Atlantic Water north of Svalbard from observations in summer and fall 2018 Abstract ID: 18793 Methods • We present hydrographic observational data from two research cruises, one Seaglider mission and two Argo floats, summer and fall 2018.• Atmospheric forcing was extracted from the Norwegian Reanalysis Archive (NORA10).•Composite sections are constructed along a representative, average bathymetry across the shelf break, using all available observations.The composite sections enable us to compare data collected across different platforms and different locations • All current measurement are de-tided using the inverse tidal model AOTIM-2018. 3 Abstract ID: 18793 EGU20 -OS1.11-Eivind H. Kolås -Structure and transport of Atlantic Water north of Svalbard from observations in summer and fall 2018 Station map with CTD sections B to E (blue: June/July, green: September, red: Seaglider Oct-Nov).CTD stations used for composites are marked with circles.Black isobaths are at 800 m and 1500 m.Grey lines are isobaths from 200 m to 1400 m depth at every 200 meters, and 2000 m to 6000 m at every 500 meters.Results • AW boundary current with average transport of 2.6±0.2Sv, and associated heat transport of 35 TW • From summer to fall the average AW transport into the Arctic increased from 2.0±0.1 Sv to 3.0±0.2Sv, with a maximum in October.• North the AW boundary current we observed a return flow containing a separate patch of AW, overlaying an eastward .11-Eivind H. Kolås -Structure and transport of Atlantic Water north of Svalbard from observations in summer and fall 2018 a) Average composite sections for Θ, S A and u g , based on cruise data and Seaglider data.b) Summer anomalies for Θ, S A and u g (mean subtracted from individual season).c) Shows fall anomalies, and d) shows late fall anomalies.White dashed line indicates the location of the 800 m isobath.Blue line envelops the Atlantic Water with U g > 0. Blue dashed line envelopes the bottom-intensified current.Black line in the Θ plot is the 3.3°C isotherm.Red line in the S A plot is the 35.08 g kg −1 isohaline.Black lines in the u g plot are isopycnals..11-Eivind H. Kolås -Structure and transport of Atlantic Water north of Svalbard from observations in summer and fall 2018 a) Green arrows show 0-1000 m mean currents, bin-averaged over 3km by 3km horizontal bins, from Acoustic Doppler current profilers and Seaglider depth-averaged currents.Red arrows show drift trajectories from Argos.b) Objective interpolation of average currents in (a).Thick black lines show predefined sections.Black contours show the