ATLANTIC WATER MASSES

1. ATLANTIC WATER MASSES NADW AABW AAIW Itay Halevy

2. OVERVIEW • Definition of water masses. • Motivation. • Classification of water masses. • Atlantic water masses and their properties.

4. WATER MASSES • Water mass mixing is a way of explaining T and S profiles in the ocean. • Any T-S profile displays properties that are a result of a mixture of discrete end member waters. • Assumption - T and S are conservative properties - i.e. there is no diffusive exchange with the surroundings and change in water properties is through mixing alone. • Water masses have a “core depth” where their typical characteristics are located. • Vertical mixing creates a range of depths, above and below the core, influenced by the water mass.

5. WATER MASSES CONT. • Low velocities: • Typically < 1 cm/sec • Up to as much as 15 cm/sec • Replenishment of nutrients to surface.

6. WATER MASSES CONT. • Waters classified by their DEPTH • their DENSITY • their TEMPERATURE & SALINITY Note: Density has higher dependence on T than on S.

7. SO WHY DO WE CARE? Differential solar influx  Pole-Equator temperature gradient Differential evaporation and precipitation  Requires meridional heat and salinity transport  Facilitated by Atmosphere & Ocean  Circulation characteristics influence climate

8. WHY THE ATLANTIC? Major role in T and S transport: Other oceans form much less deep water. • Pacific less saline due to lower SSTs. • Pacific also doesn’t reach as far north. • Indian too warm. • North Atlantic is high-lat and saline enough.

9. CLASSIFICATION OF WATER MASSES • Divided into SURFACE, INTERMEDIATE, DEEP. Surface water • Warm and saline. • Lower density - dependence of  on T, S. • Nutrient depletion - biotic productivity. • Oxygen abundance - mixing.

10. CLASSIFICATION OF WATER MASSES Intermediate water • T & S vary greatly. • Combination gives relatively high , typically 1027 to 1027.6 kg/m3.

11. CLASSIFICATION OF WATER MASSES Antarctic Intermediate Water - AAIW • T = 3°C • S = 34.25 •  = 1027.30 kg/m3 • Core depth ~ 1000 m • Source region: Southern Pacific, Indian and Atlantic Oceans near the Polar Front. • Spreads as far as 20°N in all ocean basins.

12. CLASSIFICATION OF WATER MASSES Deep water • T = -1 to 3°C • S = 34.5 to 35.0 •  = 1027.7 to 1028.0 kg/m3 • Nutrient enrichment. • Relative oxygen depletion.

13. CLASSIFICATION OF WATER MASSES Antarctic Bottom Water (AABW) • T = -1°C • S = 34.65 •  = 1027.87 kg/m3 • Core depth ~ 4000 m • Source region: Wendell Sea, Ross Sea. • Mean production rate: 20 Sv/yr

15. CLASSIFICATION OF WATER MASSES North Atlantic Deep Water (NADW) • T = 3°C • S = 34.93 •  = 1027.83 kg/m3 • Core depth ~ 2500 m • Source region: Imringer Sea, Nordic Sea, Labrador Sea. • Mean production rate: 15 Sv/yr

17. SUMMARY • Warm saline water cools and sinks in the Northern Atlantic Ocean (NADW). • Some of this water upwells near the ACC. • Some then flows south is cooled further and sinks to the ocean bottom (AABW). • Some flows north and sinks beneath warm, low latitude water (AAIW).

19. REFERENCES • www.ocean.washington.edu/ courses/oc513/ • www.iku.sintef.no • faculty.washington.edu/pdquay/OC210/ • www.ldeo.columbia.edu/dees/ ees/climate/lectures/o_atm.html • www.ldeo.columbia.edu/edu/dees/ees/climate/slides • www.deas.harvard.edu/climate/eli/Courses/2005fall_a/

20. QUESTIONS ???

21. THANKS