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Lecture 7: the Ocean in Motion Basic Ocean Structures Warm up by Sunlight!

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Lecture 7: the Ocean in Motion Basic Ocean Structures Warm up by Sunlight! Lecture 7: The Ocean In Motion Basic Ocean Structures Warm up by sunlight! !Basic Structures ! Upper Ocean (~100 m) !Surface Ocean Circulation Shallow, warm upper layer where light is abundant and where most marine life can be found. !Deep Ocean Circulation ! Deep Ocean Cold, dark, deep ocean where plenty supplies of nutrients and carbon exist. ESS11 ESS11 Prof. Jin-Yi Yu No sunlight! Prof. Jin-Yi Yu Basic Ocean Current Systems Vertical Structure of Ocean Upper Ocean surface Mixed Layer: T and S well mixed by winds circulation Temperature Thermocline: large gradient of T and S Salinity Deep Ocean: T and S independent of height cold salty Deep Ocean high nutrient level deep ocean circulation (from Climate System Modeling) ESS11 ESS11 Prof. Jin-Yi Yu (from “Is The Temperature Rising?”) Prof. Jin-Yi Yu 1 Two Circulation Systems Thermohaline Circulation Youngest Waters Oldest Waters density-driven wind-driven circulation (Figure from The Earth System) circulation ESS11 (Figure from Oceanography by Tom Garrison) ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Thermohaline Circulation Two Processes to Increase Salinity in High Latitudes ! Thermo " temperature ! Evaporation: Extremely cold, dry winter ! Haline " salinity air enhances evaporation from the relatively warm ocean " increase salinity in the ocean. Density-Driven Circulation ! Formation of Sea Ice: When sea ice forms, Cold and salty waters go down salts are left in the ocean " increase Warm and fresh waters go up salinity ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 2 Two Regions of Deep Water Formation Thermohaline Conveyor Belt ! Antarctic Bottom Water Salinity = 34.65‰ Temperature = -0.5°C Density = 1.0279 g/cm3 Formed at Weddell Sea Related to ice formation During Winter ! North Atlantic Deep Water Due to winter cooling and evaporation. (Figure from Oceanography by Tom Garrison) (Figure from Climate System Modeling) ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu It Takes ~1000 Years for Deep The Most Nutritious Waters are… Ocean Waters to Travel Around… the waters in the deep northern Pacific. ! The concentration of nutrients is at a minimum in ! If we date a water parcel from the time that it the deep northern Atlantic because the water there leaves the surface and sink into the deep ocean has just arrived from the nutrient-depleted surface layers. " Then the youngest water is in the deep north ! On its subsequent journey, the water is then Atlantic, and the oldest water is in the deep steadily enriched by sinking organic materials and northern Pacific, where its age is estimated to be reaches it maximum concentration at the deep 1000 year. northern Pacific. ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 3 The Most Unpolluted Waters are.. Global Warming and Thermohaline Circulation the waters in the deep northern Pacific. ! If the warming is slow The salinity is high enough to still produce a thermohaline ! The man-released CFC and the chemical tritium circulation and C14, which were released through atmospheric "The circulation will transfer the heat to deep ocean atomic bomb test in the 1950s and 1960s, entered "The warming in the atmosphere will be deferred. the deep ocean in the northern Atlantic and are still moving southward slowly. ! If the warming is fast ! Those pollutions just cross the equator in the Surface ocean becomes so warm (low water density) Atlantic " They have not reached the deep "No more thermohalione circulation northern Pacific yet!! "The rate of global warming in the atmosphere will increase. ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Four Possible Thermohaline Circulations Thermohaline Conveyor Belt ! Typical speed for deep ocean current: 0.03-0.06 km/hour. ! Antarctic Bottom Water takes some 250- 1000 years to travel to North Atlantic and Pacific. (Figure from Oceanography by Tom Garrison) (from “Is The Temperature Rising?”) ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 4 Six Great Current Circuits in the World Ocean Characteristics of the Gyres ! 5 of them are geostrophic gyres: (Figure from Oceanography by Tom Garrison) ! Currents are in geostropic balance North Pacific Gyre ! Each gyre includes 4 current components: two boundary currents: western and eastern South Pacific Gyre two transverse currents: easteward and westward North Atlantic Gyre Western boundary current (jet stream of ocean) South Atlantic Gyre the fast, deep, and narrow current moves warm water polarward (transport ~50 Sv or greater) Indian Ocean Gyre Eastern boundary current the slow, shallow, and broad current moves cold ! The 6th and the largest current: water equatorward (transport ~ 10-15 Sv) Trade wind-driven current Antarctic Circumpolr Current the moderately shallow and broad westward (also called West Wind Drift) current (transport ~ 30 Sv) Westerly-driven current the wider and slower (than the trade wind-driven (Figure from Oceanography by Tom Garrison) Volume transport unit: current) eastward current 1 sv = 1 Sverdrup = 1 million m3/sec ESS11 ESS11 Prof. Jin-Yi Yu (the Amazon river has a transport of ~0.17 Sv) Prof. Jin-Yi Yu Major Current Names Winds and Surface Currents ! Western Boundary Current ! Trade Wind-Driven Current Gulf Stream (in the North Atlantic) North Equatorial Current Polar Cell Kuroshio Current (in the North Pacific) South Equatorial Current Brazil Current (in the South Atlantic) Ferrel Cell Eastern Australian Current (in the South Pacific) Agulhas Current (in the Indian Ocean) Hadley Cell ! Eastern Boundary Current ! Westerly-Driven Current Canary Current (in the North Atlantic) North Atlantic Current (in the North Atlantic) California Current (in the North Pacific) North Pacific Current (in the North Pacific) Benguela Current (in the South Atlantic) Peru Current (in the South Pacific) Western Australian Current (in the Indian Ocean) (Figure from The Earth System) ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 5 Surface Wind And Surface Current Ekman Transport (Figure from The Earth System) (Figure from Oceanography by Tom Garrison) ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Ocean Surface Is Not Level Boundary Currents NASA-TOPEX Observations of Sea-Level Hight (from Oceanography by Tom Garrison) (Figure from Oceanography by Tom Garrison) ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 6 ocean weather / ocean eddy Gulf Stream Costal Upwelling/Downwelling A river of current Jet stream in the ocean ! A result of Ekman transport and mass # Speed = 2 m/sec # Depth = 450 m continuity. # Width = 70 Km # Color: clear and blue (Figure from Oceanography by Tom Garrison) (Figure from Oceanography by Tom Garrison) ESS11 ESS11 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 7.
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