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ATLANTIC WATER MASSES

ATLANTIC WATER MASSES. NADW AABW AAIW Itay Halevy. OVERVIEW. Definition of water masses. Motivation. Classification of water masses. Atlantic water masses and their properties. WATER MASSES. Water mass mixing is a way of explaining T and S profiles in the ocean.

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ATLANTIC WATER MASSES

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  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.

  3. 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.

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

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

  6. 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

  7. 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.

  8. 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.

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

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. 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).

  15. 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/

  16. QUESTIONS ???

  17. THANKS

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