MAR 110 LECTURE #10 The Oceanic Conveyor Belt Oceanic Thermohaline Circulation

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1 1 MAR 110 LECTURE #10 The Oceanic Conveyor Belt Oceanic Thermohaline Circulation Ocean Climate Temperature Zones The pattern of approximately parallel oceanic surface isotherms (lines of constant temperature) reflects the equator to pole solar heating contrasts. (?)

2 2 Surface Ocean Heat Transport The latitudinal deviations in the isotherms reflect the effects of ocean surface currents, which consist of clockwise gyres with particularly intense currents along the western boundaries in northern hemisphere ocean basins (counterclockwise in the southern hemisphere ocean basins). The arrows show the effect on the surface temperature field by both the Gulf Stream and the Brazil Currents, which transport warm water from the equatorial region towards the poles. (??) Wind-Driven Surface Ocean Currents The juxtaposition of the zonal winds trades, westerlies and easteries produces gyre circulations with intensified western boundary currents in the major ocean basins the North & South Atlantic, North Pacific, and Indian Ocean basins. (LEiO)

3 3 The World s Oceans A Bartholomew projection of the geography of the oceans. Nearly three-fourths (72%) of the Earth s surface is covered by oceans

4 4 The Oceanic Conveyor Belt Moves Heat Poleward The oceanic conveyor belt consists of (1) sinking in the North Atlantic polar region - as the ocean gives up its heat to the atmosphere- (2) deep southward transport of the colder water to the Southern Ocean around Antarctica, (3) distribution to the Indian and Pacific Ocean basins (4) upwelling primarily along the equator, and (5) surface flow returning to the North Atlantic via a series of intensified western boundary currents caused by the surface winds (CCaMA) The Oceanic Conveyor Belt - ON The oceanic conveyor belt consists of (1) sinking in the North Atlantic polar region - as the ocean gives up its heat to the atmosphere- (2) deep southward transport of the colder water to the Southern Ocean around Antarctica, (3) distribution to the Indian and Pacific Ocean basins (4) upwelling primarily along the equator, and (5) surface flow returning to the North Atlantic via a series of intensified western boundary currents caused by the surface winds. (CCaMA)

5 5 The Oceanic Conveyor Belt - OFF In this configuration the oceanic conveyor belt the sinking component disappears because fresh water and ice inhibit sinking in the polar North Atlantic. Only the wind-driven warm surface flow remains. (CCaMA) Ocean Surface Temperature Distribution - NH Winter (??)

6 6 Salinity Salinity is the term used to reflect the saltiness of the water. Salts (and other constituents of ocean water) are derived from erosion of continental land masses slowly being carried into the ocean with river water. Eventually these salts became concentrated in the ocean and are now in a steady state (loss of salts to sedimentation and other processes equals the input of salt from river discharges). Many factors may affect the local salinity value in the ocean, including evaporation, precipitation, river input, and mixing between two water masses. Salinity is measured in units of parts per thousand (ppt).

7 7 Ocean Density Sensitivity to Temperature (T) & Salinity (S) The density of the ocean varies with respect to both temperature (negative relationship) and salinity (positive relationship).

8 8 Ocean Surface Salinity Distribution Graph of evaporation and surface salinity as a function of latitude (top). Map of surface salinity distribution over the globe (bottom). Note that regions with increased evaporation also have higher levels of salinity. (??,??) Ocean Temperature & Salinity & Density Profiles The changes of temperature, salinity, and density with increasing depth. The clines are regions where the particular property in question (temperature, salinity, or density) changes rapidly with depth. (ItO)

9 An Atlantic Ocean Density section (??) MAR 110: Lecture 10 Outline Oceanic Conveyor Belt 9

10 10 Global Ocean Thermohaline Circulation A rough schematic cross section of circulation between the poles. Cold water at the poles becomes dense as it cools and sinks to a depth dependant on the density with the coldest and densest water sinking the deepest. As the water warms it becomes less dense and rises. (??)

11 11 A Two Layered Atlantic Ocean Cold water at the poles becomes dense as it cools and sinks to a depth dependant on the density with the coldest and densest water sinking the deepest. A surface layer of warm, less dense water exists nearer the equator, separated from the deeper and colder water by the pycnocline, an area where the density changes rapidly with depth. (ItO)

12 12 Atlantic Ocean-Deep Western Boundary Current (DWBC) The DWBC is a current that originates in the Norwegian Sea as very cold and dense water that travels along the deep sea bed towards the south. (??) Gulf Stream & the Deep Western Boundary Current off of Cape Hatteras (BG)

13 13 The Oceanic Conveyor Belt Moves Heat Poleward The oceanic conveyor belt consists of (1) sinking in the North Atlantic polar region - as the ocean gives up its heat to the atmosphere- (2) deep southward transport of the colder water to the Southern Ocean around Antarctica, (3) distribution to the Indian and Pacific Ocean basins (4) upwelling primarily along the equator, and (5) surface flow returning to the North Atlantic via a series of intensified western boundary currents caused by the surface winds. (CCaMA)