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Hydrographical Properties of Storfjorden Polynya

Analyzing the hydrographical properties of Storfjorden Polynya focusing on water mass exchange and isopycnal mixing, observed through CTD stations and sections at the sill. Insights from the Bergen Ocean Model simulations further enhance understanding of the BSW downflow and overflow dynamics. Key findings highlight the impact of wind direction on brine year quality and the changing source water of the BSW.

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Hydrographical Properties of Storfjorden Polynya

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  1. Hydrographical Properties of the Storfjorden Polynya Ragnheid Skogseth1, Lars H. Smedsrud2 and Frank Nilsen1,3 1The University Centre in Svalbard 2Bjerknes Centre for Climate Research 3Geophysical Institute, University of Bergen

  2. CTD Stations in Storfjorden April 2004 and 2006

  3. TS-Diagram • 2004: poor brine year S < 34.8 • 2006: average brine year S ~ 35.2 • Super-cooled saline water in the polynya when freezing • Exchange of watermass in polynya with changing wind directions • Isopycnal mixing with warmer inflowing water over the sill • Mixing between warmer less saline inflowing water and cold saline brine water in the overflow at the sill

  4. Wind Direction and Air temperature, Edgeøya

  5. CTD Profile April 1 2006, Kapp Lee in Storfjorden

  6. CTD Profile April 4 2006, Kapp Lee in Storfjorden

  7. CTD Sections at the Sill

  8. CTD Sections at the Sill

  9. Downflow of Brine-enriched Shelf Water • 2004: Downflow of denser water from shallow area to the deep basins inside Storfjorden

  10. Downflow of Brine-enriched Shelf Water • 2004: Downflow of denser water from shallow area to the deep basins inside Storfjorden

  11. Downflow of Brine-enriched Shelf Water • 2006: Downflow of dense BSW from shallow area to the deep basins inside Storfjorden following trenches along the path

  12. Downflow of Brine-enriched Shelf Water • 2006: Downflow of dense BSW from shallow area to the deep basins inside Storfjorden following trenches along the path

  13. Downflow of Brine-enriched Shelf Water • 2006: Observed section (along depth contour) of downflow of dense BSW from shallow area to the deep basins inside Storfjorden • Densest BSW towards the steepest path

  14. Downflow of Brine-enriched Shelf Water • 2006: Observed section (along depth contour) of downflow of dense BSW from shallow area to the deep basins inside Storfjorden • Densest BSW towards the steepest path

  15. Downflow of Brine-enriched Shelf Water • 2006: No observed section (along depth contour) of downflow of BSW from shallow to deep area off Storfjorden-banken outside the sill • North-south density gradient across the sill latitude

  16. Downflow of Brine-enriched Shelf Water • 2006: No observed section (along depth contour) of downflow of BSW from shallow to deep area off Storfjorden-banken outside the sill • North-south density gradient across the sill latitude

  17. Bergen Ocean Model (BOM) • January 1 – May 1 1999 • Wind forcing derived from MM5 in mean polynya area and along West Spitsbergen • Salt and heat flux in mean polynya area derived from polynya model in winter 1999 • Salt flux: 2.05  10-5 psu m/s (893  109 kg in 120 days) • Heat flux: 4.71  10-5 C m/s (193 W/m2) • Mean polynya area: 3.0  109 m2 (812 grid points in selected area)

  18. Downflow of BSW estimated with BOM • Day 8: Downflow of BSW starts from shallow to deep basins inside Storfjorden at designated areas • No modelled downflow of BSW from shallow to deep area off Storfjorden-banken outside the sill

  19. Downflow of BSW estimated with BOM • Day 29: Deep basins inside Storfjorden are filled up to sill level with BSW due to the downflow from the shallow polynya area • Overflow of BSW begins at the sill

  20. Downflow of BSW estimated with BOM • Day 56: Inner Storfjorden is filled with BSW up to the ridge level • Overflow starts across the ridge in addition to the overflow across the sill • The BSW plume reaches the shelf break

  21. Conclusions • Winter 2004 poor brine year with S < 34.8 • Winter 2006 average brine year with S ~ 35.2 in the BSW overflow • Source water of BSW changes with wind direction • Inflow of warmer water at the sill during the overflow • Downflow of BSW from the shallow areas in the polynya is only observed inside Storfjorden and not off Storfjordenbanken south of the sill • Observations and BOM simulations indicate that the downflow of BSW inside Storfjorden occurs at topographically favoured areas • BOM simulations show that overflow occurs both across the sill and the submarine ridge when Storfjorden is filled with BSW up to ridge level

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