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Abrupt Change in Greenland Sea Deep Water Formation

Explore hydrographic and tracer data revealing abrupt change in deep water formation around 1980 in the Greenland Sea. Learn about evolution of deep and intermediate waters, connections to outflow waters, and implications for the Atlantic THC.

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Abrupt Change in Greenland Sea Deep Water Formation

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  1. Abrupt Change in Deep Water Formation in the Greenland Sea: Results from Hydrographic and Tracer Time Series P. Schlosser, J. Karstensen, D. Wallace, J. Bullister, and J. Blindheim CU/L-DEO, IfM Kiel, NOAA PMEL, IMR Bergen SEARCH Open Science mtg., October 03 search_osm_10_03

  2. Outline • Background • Early hydrography tracer observations • Tracer and hydrographic data from the 1990s • Evolution of deep waters • Evolution of intermediate waters • Connection to outflow waters • Summary search_osm_10_03

  3. Greenland Sea in the context of Atlantic THC Levitus salinity map AMAP search_osm_10_03

  4. Greenland Sea in the context of Nordic seas Red: warm, salty Atlantic Water; Blue: cold, fresh Arctic outflow Black: deep circulation Inflow (Sv): NA: ca. 8 Sv; Bering Strait: ca. 1 Sv Outflow (Sv): Near surface: ca. 3 Sv; Overflows: ca. 6 Sv search_osm_10_03

  5. Mean surface conditions search_osm_10_03

  6. Sections across the central Greenland Sea (75N; 6/99) • Cyclonic circulation • Doming of isopycnals • Polar/Arctic front • Relatively homogeneous • deep water search_osm_10_03

  7. Evolution of tracer concentrations in surface waters search_osm_10_03

  8. Early Hydrography/tracer time series Boenisch et al., 1997 search_osm_10_03

  9. Evolution of T/S and tracer properties 2000 m to bottom 200 to 2000 m 2000 m to bottom Boenisch et al., 1997 search_osm_10_03

  10. Surveys during the 1990s 10 cruises 1991 to 2000 Cruises: Johan Hjort; IMR Norway, Johan Blindheim search_osm_10_03

  11. Hydrography/tracer time series during the 1990s search_osm_10_03

  12. Evolution of deep water T/S properties search_osm_10_03

  13. Evolution of deep water tracer properties search_osm_10_03

  14. Imprints from deep convection Background stratification versus features in convective cells. Conv. cells are characterized by temp. max. at the bottom of the feature. search_osm_10_03

  15. Evolution of tracer inventories Tracer inventories indicate formation of intermediate waters in 1994, 1999, and possibly 1992. search_osm_10_03

  16. Evolution of T and S anomalies search_osm_10_03

  17. Convection and tracer profiles During convection: Re-distribution of tracers No net mass transport After convection: Mass transport by eddies and meridional circulation Greenland Sea Sea ice may be important search_osm_10_03

  18. Properties on overflow water isopycnals search_osm_10_03

  19. Heat fluxes required to restore 1970’s conditions search_osm_10_03

  20. Summary • Change in deep water formation rates • Abrupt change in DWF rate occurred around 1980 • Reduction in DWF rate: ca. 80%; more or less constant since 1980 • Greenland Sea gyre still on trend away from properties known from instrumental records. ‘Recovery’ needs significant forcing. • Deep waters • Quasi-linear trends in T (10 mK yr-1) and S (1 ppm yr-1) • Advection of water from Arctic Ocean • Little influence of atmosphere (isolated from atm. Forcing on short time scales) • Intermediate waters • Variability in formation • Warmer and fresher (sea ice plays little role) • Events: 94/95 and 99/00 (possibly 92/93) • Transport: 0.1 to 0.2 Sv (0.5 during conv. events)

  21. Hydrography/tracer time series during the 1990s search_osm_10_03

  22. Background stratification versus features in convective cells. Conv. cells are characterized by temp. max. and its depth. search_osm_10_03

  23. GS variability Regional Local search_osm_10_03

  24. GS variability Regional Local search_osm_10_03

  25. Factors controlling GSDW Arctic outflow (quasi constant) Deep convection (sporadic) Connection to surface temperature? search_osm_10_03

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