Opening and closing of the Storfjorden polynya

1. Opening and closing of the Storfjorden polynya Frank Nilsen1,2, Ragnheid Skogseth1, Katja Weigel1 1.The University Centre in Svalbard (UNIS), Longyearbyen, Norway 2.Geophysical Institute, University of Bergen, Bergen, Norway

2. Coastal Polynya Storfjorden is estimated to supply 5-10% of the newly formed dense waters of the Arctic Ocean Skogseth (2003), PhD thesis

3. The Barents Sea and Storfjorden

4. Storfjorden • Is approximately 190 km long and 190 m deep at its maximum depth. • A 120 m deep sill at about 77°N in the south. • The basin covers an area of about 13·103 km2 with a volume of 8.5·1011 m3. Skogseth et al. (2005), CSR

5. Storfjorden Polynya Skogseth (2003), PhD thesis

6. Maximum Salinity observed in the deepest part of Storfjorden Skogseth & Fer (2005), AGU Anderson et al. (2004), JGR

7. Polynya Area and SAR • We utilize the polynya width model formulated by Haarpaintner et al. (2001) and Skogseth et al. (2004). • The model calculates the area of open water and thin ice defined as the polynya area, and the area of fast and pack ice. • The model consist of two algorithms: polynya width algorithm and an open water width algorithm. • The polynya width algorithm needs two empirical factors as input: the opening (OF) and closing (CF) factors.

8. Empirical Tuning

9. Wind Stress Curl field (DJFM, 1970-2004) From the Hindcast data base (met.no) with a 75 km resolution

10. Sea Ice Drift

11. DJFMA wind stress

12. OF and CF correlated with the winter mean wind stress curl

13. DJFMA wind stress

14. Mechanical and thermodynamical sea ice growth 1+ O(1) + O(0) = OF 1- O(1) + O(10) = CF

15. Result Summary

16. Winters with low Iw More positive curl  Divergence

17. Winters with high Iw More negative curl  Convergence

18. Reproduced OF as a function of the curl at 75.4°N, 25.1°E

19. Total ice production (normalized)

20. Conclusions • Physical explanations for the empirical OF and CF are found. • CF is dominated by thermodynamical ice growth through consolidation of frazil ice, but mechanical ice growth determine the interannual variations. • OF’s deviations from the free drift solution is determined by divergence and convergence in the compact ice cover outside Storfjorden. • Annual variations in OF and CF are directly linked to the wind stress curl field and an empirical relations is found from the hindcast data base (met.no) time series. • The polynya model gives a more realistic sea ice production when the model is run with time varying OF and CF.

21. The Barents Sea Ice Index Iw The integrated winter ice covered area south of 76ºN in a zone between 25ºE and 45ºE. Ådlandsvik & Loeng (1990), Polar Res.

22. Correlation between the curl (DJFM) and Iw (1970-2003)