1 / 37

Water mass transformation in the Iceland Sea

Water mass transformation in the Iceland Sea. Kjetil Våge Kent Moore Steingrímur Jónsson H éðinn Valdimarsson. Irminger Sea, R/V Knorr , October 2008. Water mass transformation in the Iceland Sea - the Denmark Strait Overflow Water. Denmark Strait Largest overflow plume

kaden-briggs
Download Presentation

Water mass transformation in the Iceland Sea

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Water mass transformation in the Iceland Sea Kjetil Våge Kent Moore Steingrímur Jónsson HéðinnValdimarsson Irminger Sea, R/V Knorr, October 2008

  2. Water mass transformation in the Iceland Sea - the Denmark Strait Overflow Water Denmark Strait • Largest overflow plume • Source of densest water to the lower limb of the AMOC Iceland Sea • Wintertime convection • First definitive scenario for the source of DSOW (Swift et al., 1980)

  3. Water mass transformation in the Iceland Sea - overturning circulation schemes • Formed in the Iceland Sea (Swift et al., 1980) • Transformation within boundary current loop (Mauritzen, 1996)

  4. Water mass transformation in the Iceland Sea - the North Icelandic Jet – another source of overflow water? from Jónsson and Valdimarsson (2004)

  5. Water mass transformation in the Iceland Sea - overturning circulation schemes • Formed in the Iceland Sea (Swift et al., 1980) • Transformation within boundary current loop (Mauritzen, 1996) • Transformation within interior loop (Våge et al., 2011)

  6. Water mass transformation in the Iceland Sea - climatological winter total turbulent heat flux Winter (DJFM) climatological mean total turbulent heat flux from ERA-Interim from Moore et al. (2012)

  7. Water mass transformation in the Iceland Sea - circulation in the Iceland Sea Surface circulation • Cyclonic circulation in the central Iceland Sea • Typical wintertime mixed layer depths about 150-200 m • Surface densities exceeding 27.8 kg\m3 common in winter from Jónsson (2007)

  8. Water mass transformation in the Iceland Sea - historical hydrographic measurements in the Iceland Sea Collection of historical hydrographic measurements (1980 - present) • Determination of mixed-layer depth and properties • visual inspection of all profiles • automated detection routinesemployed • manually determined when those failed • → robust data set

  9. Water mass transformation in the Iceland Sea - February-April mixed-layer depths Map of mixed-layer depths

  10. Water mass transformation in the Iceland Sea - February-April mixed-layer depths Map of mixed-layer depths Contours of dynamic height

  11. Water mass transformation in the Iceland Sea - February-April mixed-layer densities Map of mixed-layer potential densities

  12. Water mass transformation in the Iceland Sea - convection in the north-central Iceland Sea Profiles located within the north-central Iceland Sea

  13. Water mass transformation in the Iceland Sea - the annual cycle Mixed-layer depths

  14. Water mass transformation in the Iceland Sea - the annual cycle Mixed-layer depths Mixed-layer potential densities

  15. Water mass transformation in the Iceland Sea - convective activity in the north-central Iceland Sea Potential density in the central Iceland Sea (time vs. depth)

  16. Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet Potential density in the central Iceland Sea (time vs. depth) σθ > 28.03 kg/m3 Transport of σθ > 28.03 kg/m3 in the NIJ: 0.6 ± 0.1 Sv

  17. Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet Mixed-layer depths Mixed-layer potential densities

  18. Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet Mixed layers denser than σθ= 28.03 kg/m3 5 profiles from 2013 • Important caveats • sparse data set • huge spatial and temporal variability

  19. Water mass transformation in the Iceland Sea - convective activity as recorded by Argo float winter 2008 Temporal evolution of potential vorticity along Argo float trajectory

  20. Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet Profiles at the outer end of the Langanes section Langanes 6 Langanes repeat hydrographic section

  21. Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet Depth of the 28.03 kg/m3isopycnal at Langanes6

  22. Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet Depth of the 28.03 kg/m3isopycnal at Langanes6 Difference: ~60 m → Reduced production of dense water? • → Different circulation regime?

  23. Water mass transformation in the Iceland Sea - atmospheric forcing Decrease in the total turbulent heat flux, discontinuity around 1995

  24. Water mass transformation in the Iceland Sea - atmospheric forcing Decrease in the total turbulent heat flux, discontinuity around 1995 Decrease in the wind stress curl, discontinuity around 1995

  25. Water mass transformation in the Iceland Sea - change in wintertime atmospheric circulation 1980-1995 Difference between the periods 1980-1995 and 1996-2013 • Increased pressure • Reduced northerly winds • Anti-cyclonic circulation anomaly 1996-2013

  26. Water mass transformation in the Iceland Sea - change in wintertime atmospheric circulation 1980-1995 Difference between the periods 1980-1995 and 1996-2013 • Increased pressure • Reduced northerly winds • Anti-cyclonic circulation anomaly 1996-2013 Difference between the periods

  27. Water mass transformation in the Iceland Sea - frequency of high heat flux events Frequency of high heat flux events • Decreasing occurrence of heat flux events exceeding the 90th percentile value • Consistent with a weakening of the northerly winds

  28. Water mass transformation in the Iceland Sea - composite means of high heat flux events 1980-1989 Nature of high heat flux events • Retreat of sea ice • Northward shift of the highest fluxes • Narrowing of marginal ice zone • Reduced number of events (75 during first period, 65 during last) 2004-2013

  29. Water mass transformation in the Iceland Sea - ramifications of reduced forcing November profiles from the Iceland Sea – initial conditions from Moore et al. (2014)

  30. Water mass transformation in the Iceland Sea - ramifications of reduced forcing Ramifications of reduced forcing • Gradual reduction in depth and density of convection • If this continues, it may weaken the overturning loop that feeds the NIJ and reduce the supply of the densest water to the AMOC 1D mixed-layer model in the Iceland Sea from Moore et al. (2014)

  31. Water mass transformation in the Iceland Sea The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.eu

  32. Water mass transformation in the Iceland Sea - NAO and ILD indices North Atlantic Oscillation (NAO) index Icelandic Lofoten Dipole (ILD) index

  33. Water mass transformation in the Iceland Sea - ramifications of reduced forcing Model-data comparisons suggest that the 1D mixed-layer model is reasonable from Moore et al. (2014)

  34. Water mass transformation in the Iceland Sea - Summertime stratification Difference in potential density between 10 and 250 m

  35. Water mass transformation in the Iceland Sea - June-August mixed-layer densities Map of mixed-layer potential densities

  36. Water mass transformation in the Iceland Sea - the Arctic domain Arctic domain • Local modification leads to formation of Arctic Intermediate Water • Contributes to overflows east and west of Iceland Polar inflow Atlantic inflow Surface salinity, from Swift and Aagaard (1981)

  37. The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.eu

More Related