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SEARCH Open Science mtg., October 03

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. Outline. Background

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SEARCH Open Science mtg., October 03

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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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