Notes

Outline

Lecture 7: The Ocean In Motion Basic Structures Surface Ocean Circulation Deep Ocean Circulation

Basic Ocean Structures  Upper Ocean (~100 m)     Shallow, warm upper layer where light is abundant and where most marine life can be found.  Deep Ocean    Cold, dark, deep ocean where plenty supplies of nutrients and carbon exist.

Vertical Structure of Ocean

Basic Ocean Current Systems

Two Circulation Systems

Thermohaline Circulation

Thermohaline Circulation  Thermo    è temperature    Haline    è salinity

Two Processes to Increase Salinity in High Latitudes  Evaporation: Extremely cold, dry winter air enhances evaporation from the relatively warm ocean è increase salinity in the ocean.  Formation of Sea Ice: When sea ice forms, salts are left in the ocean è increase salinity

Two Regions of Deep Water Formation

Thermohaline Conveyor Belt

It Takes ~1000 Years for Deep Ocean Waters to Travel Around…  If we date a water parcel from the time that it leaves the surface and sink into the deep ocean è Then the youngest water is in the deep north Atlantic, and the oldest water is in the deep northern Pacific, where its age is estimated to be 1000 year.

The Most Nutritious Waters are…     the waters in the deep northern Pacific.  The concentration of nutrients is at a minimum in the deep northern Atlantic because the water there has just arrived from the nutrient-depleted surface layers.  On its subsequent journey, the water is then steadily enriched by sinking organic materials and reaches it maximum concentration at the deep northern Pacific.

The Most Unpolluted Waters are..    the waters in the deep northern Pacific.  The man-released CFC and the chemical tritium and C14, which were released through atmospheric atomic bomb test in the 1950s and 1960s, entered the deep ocean in the northern Atlantic and are still moving southward slowly.  Those pollutions just cross the equator in the Atlantic è They have not reached the deep northern Pacific yet!!

Global Warming and Thermohaline Circulation  If the warming is slow     The salinity is high enough to still  produce a thermohaline circulation The circulation will transfer the heat to deep ocean The warming in the atmosphere will be deferred.  If the warming is fast      Surface ocean becomes so warm (low water density) No more thermohalione circulation The rate of global warming in the atmosphere will increase.

Four Possible Thermohaline Circulations

Thermohaline Conveyor Belt

Six Great Current Circuits in the World Ocean

Characteristics of the Gyres Currents are in geostropic balance Each gyre includes 4 current components:       two boundary currents: western and eastern       two transverse currents: easteward and westward Western boundary current (jet stream of ocean)        the fast, deep, and narrow current moves warm water polarward  (transport ~50 Sv or greater) Eastern boundary current       the slow, shallow, and broad current moves cold water equatorward (transport ~ 10-15 Sv) Trade wind-driven current        the moderately shallow and broad westward current (transport ~ 30 Sv) Westerly-driven current        the wider and slower (than the trade wind-driven current) eastward current

Major Current Names Western Boundary Current      Gulf Stream (in the North Atlantic)        Kuroshio Current (in the North Pacific)        Brazil Current (in the South Atlantic)        Eastern Australian Current (in the South Pacific)        Agulhas Current (in the Indian Ocean) Eastern Boundary Current       Canary Current (in the North Atlantic)        California Current (in the North Pacific)        Benguela Current (in the South Atlantic)        Peru Current (in the South Pacific)       Western Australian Current (in the Indian Ocean)

Winds and Surface Currents

Surface Wind And Surface Current

Ekman Transport

Ocean Surface Is Not Level

Boundary Currents

Gulf Stream

Costal Upwelling/Downwelling