11/27/2007ESM 203: Ocean processes and circulation1ESM 203: ESM 203: Ocean Processes and Ocean Processes and CirculationJeff Dozier & Thomas DunneFall 2007What is sea water?ySea water is 96½% pure wateryRemaining 3½% is other materials◦Dissolved salts gases and organic substances as well as Dissolved salts, gases and organic substances, as well as particlesyPhysical properties are mainly related to the pure water, along with the dissolved saltsyWater mass characteristics◦Salinity temperature nutrients oxygen2Salinity, temperature, nutrients, oxygenyKey property (for circulation) is sea water density◦Variability in vertical – inhibit or enhance mixing◦Variability in horizontal – drive currentsSea water densityyA function salinity, pressure, and temperature◦Ranges from about 1020 to 1040 kg m–3yOceanographers use the sigma Tdescriptionsigma-T()(),f,,01000ranges from 20 to 40σ==−tS TS T P3TemperatureyTemperature generally decreases with depth in the oceanyChanges in temperature generally regulate changes in density◦except where ice is formed (which increases salinity)yRule of thumb:433kg m0.2 degi.e. 1 kg mfor 5 Cρρ−−Δ≈ −ΔΔ≈ +Δ= −DTT
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11/27/2007ESM 203: Ocean processes and circulation2Temperature in the Equatorial Pacific5Equatorial Pacific - WOCE150WTemperature in the Southern Ocean660S - WOCE150WSalinityyOcean waters are salty"lt "yThe “salts” (Cl–, SO4–2, Na+, K+, etc) are in approximately constant proportions◦Residence time is hugemass "salts"Salinitymass sea water≈7◦To practically estimate salinity, we measure just one ion, Cl–SalinityySalinity varies from 32 to 37 psu (practical salinity units ~ parts per thousand)units, ~ parts per thousand)◦Good water mass tracer◦Lower/higher values are unusual (river input, high evaporation, sea ice formation)yRule of thumb:83kg m1 psuSρ−Δ≈ +Δ