Summary from last class Importance of large scale ocean circulation climate biogeochemistry marine resources Characteristic Types of Ocean Circulation Patterns of circulation can be generalized for different regions Suggests that dynamical processes are the same Wind driven Buoyancy driven Coastal Scales spit on a basketball Sea Water Properties Water mass characteristics Salinity temperature nutrients oxygen Key property is seawater density Changes in vertical inhibit mixing Changes in horizontal drive currents See Lecture 3 of Tomzcak s web course gyre umeoce maine edu physicalocean Tomczak IntroOc lecture03 html What is Seawater Seawater is 96 5 pure water About 3 5 is other materials dissolved salts gases organic substances as well as particles Physical properties are mainly determined by pure water A Water Molecule Water is a non polar molecule Weak hydrogen bonding Consequences of Water s Hydrogen Bonding Water forms a lattice or aggregation of many molecules polywater Consequences of Water s Hydrogen Bonding High specific heat break the lattice High latent heat for phase changes Great solvent Consequences of Water s Hydrogen Bonding Ice crystals take up more space than liquid water Ice Floats rare for liquids Maximum density is water at 4C Critical for freshwater systems More about ice Seasonal turnover in lakes As lakes cool they reach temperature of maximum density 4C overturn Later ice forms at the surface sheltering the interior from winter conditions This allows fish over winter under the ice More on Hydrogen Bonding Back to Oceans Density of seawater is controlled by temperature salinity dissolved salt content pressure related to depth Equation of state f S T p kg m 3 S T p 0 range from 1020 to 1030 kg m 3 Temperature Temperature generally decreases with depth in the ocean Except where ice is formed temperature changes primarily regulate density Rule of thumb 1 kg m 3 for T 5 C Temperature Equatorial Pacific WOCE150W Temperature 60S WOCE150W Pacific Temperature eWOCE gallery www ewoce org Salinity Ocean waters are salty Salinity mass salts mass seawater The salts Cl SO4 2 Na K etc are in approximate constant proportion Law of salinity residence time is huge Measure one ion Cl estimate salinity Salinity Salinity is measured electrically now Units are practical salinity units psu Often bottles are used Salinity Salinity varies from 32 to 37 psu Atlantic is saltier than the Pacific Why Good water mass tracer Lower higher values are unusual riverine huge evaporation etc Typical T S Profiles Features Mixed layer Thermocline Halocline Pacific Salinities eWOCE gallery www ewoce org Atlantic Salinity Ocean Distribution of S Mean ocean 4 C S 34 8 psu Pressure Pressure is due to the weight of sea water lying above a depth hydrostatic Pressure varies from 0 to 5000 db p 0 is atmospheric pressure Note 1 db pressure 1 m depth Potential Temperature Hydrostatic pressure will heat a water parcel as descends within the ocean Adiabatic lapse rate is 0 0001 C m A surface parcel T 0 S 35 will heat 0 3C if moved to 3000 m depth Defines potential temperature or Potential Temperatu re Global SST World Ocean Atlas 1994 Annual Change in SST Annual Change in SST January July Net Air Sea Heat Fluxes Red Heat In Blue Heat Out Interannual SST Changes March 1998 relative to average March Global Salinity World Ocean Atlas 1994 Global Salinity Global Salinity AirSea Fluxes Global Salinity Why is the Atlantic so salty 1 Sverdrup 106 m3 s 1 Seawater Density Equation of state f S T p kg m 3 S T p 0 range from 1020 to 1040 kg m 3 Shorthand sigma t t S T 0 1000 t S T ranges from 20 to 40 Similarly sigma theta S 0 1000 Seawater Density Density of seawater is controlled by Temperature salinity pressure f S T p Rule of Thumb IF S 1 psu T 5C 1 kg m 3 OR OR p 100 db T S Diagram full Valu es o f t range Max density Freezing T S Diagram typical range Density Calculator http www phys ocean dal ca kelley seawater WaterProperties html http gyre umeoce maine edu physicalocean Tomczak Utilities index html Review Fundamental seawater properties Salinity temperature pressure Density is the important variable in situ density S T p Sigma t S T 0 1000 Sigma S 0 1000 Review Rules of thumb 1 kg m 3 T 5C S 1 psu or p 100 db Global surface T S driven largely by air sea exchanges Dense water sinks now we re talking dynamics