10 October 2008 MAR 110 – Fall 2008 1MAR 110 LECTURE #15 The Oceanic Conveyor Belt “Oceanic Thermohaline Circulation” Figure 15.1 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 oceans10 October 2008 MAR 110 – Fall 2008 2 Figure 15.3 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) Figure 15.2 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)10 October 2008 MAR 110 – Fall 2008 3 Figure 15.4 Ocean Climate Temperature Zones The pattern of approximately parallel oceanic surface isotherms (lines of constant temperature) reflects the equator to pole solar heating contrasts. (?) Figure 15.3 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)10 October 2008 MAR 110 – Fall 2008 4 Figure 15.5 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).10 October 2008 MAR 110 – Fall 2008 5 TemperatureTemperature(T) (T) SalinitySalinity(S)(S)Density Density ( gm/cm3)( gm/cm3)Density Density ( gm/cm3)( gm/cm3)30 30 ((ooC) C) --TT0 0 ((ooC) C) --3535(o/oo) (o/oo) --SS32 32 ((o/ooo/oo))--1.023 1.0281.023 1.0281.026 1.0281.026 1.028 The Sensitivity of Ocean Density Changes The Sensitivity of Ocean Density Changes TemperatureTemperature(T) (T) SalinitySalinity(S)(S)0.00015 0.00015 gm per gm per ooCC0.00078 0.00078 gm per gm per oo/oo/oo∆∆TT= = --3030ooC => C => ∆∆DD~ +~ +0.005 0.005 ∆∆SS= += +3 3 oo/oo/oo=> => ∆∆DD~ +~ +0.002 0.002 Figure 15.6 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).10 October 2008 MAR 110 – Fall 2008 6 Figure 15.7 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. (??, ??) Figure 15.8 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)10 October 2008 MAR 110 – Fall 2008 7 Figure 15.9 Ocean Surface Temperature Distribution - NH Winter (??) Contouring Ocean Density Contouring Ocean Density lines of constant densitylines of constant density--isopycnalsisopycnalspycnoclinepycnocline“region of “region of rapidly rapidly changing changing density”density” Figure 15.10 An Atlantic Ocean Density section (??)10 October 2008 MAR 110 – Fall 2008 8 Surface OceanSurface OceanDensity Density --1.0240 gm/cm1.0240 gm/cm33to 1.028 gm/cmto 1.028 gm/cm33Density AnomalyDensity Anomaly-->>24 to 2824 to 28The Ocean has a Two Layer StructureThe Ocean has a Two Layer StructurePYCNOCLINE PYCNOCLINE ÆÆFigure 15.11 (??) --A North/South Meridional Section A North/South Meridional Section --Figure 15.12 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. (??)10 October 2008 MAR 110 – Fall 2008 9 Figure 15.13 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)10 October 2008 MAR 110 – Fall 2008 10 The DWBCThe DWBC“hugs the “hugs the continental continental slope all the slope all the way to the tip way to the tip of South of South America” America” Figure 15.15 Gulf Stream & the Deep Western Boundary Current off of Cape Hatteras (BG) Figure 15.14 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. (??)10 October 2008 MAR 110 – Fall 2008 11 Figure 15.2 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