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Gyre Currents Western Boundary Currents Introduction to Oceanography Lecture 18, Current 2 Midterm 2: Nov. 20 (Monday) Review Session & Video Screenings TBA Image from Sverdrup, Johnson, and Fleming, Sverdrup H.U., Johnson M.W., Fleming R.H. The Oceans.. their physics, chemistry, and general biology (1942), http://oceanworld.tamu.edu/resources/ocng_textbook/chapter11/Images/Fig11-7.htm Surface Ocean Currents. Video by Chris Henze, NASA Ames, Public Domain Gyre Currents Western Boundary Currents Cold, cold Northern Canada Temperate Northern Gulf Stream Europe British National Centre for Ocean Forecasting, Public Domain(?), http://www.nerc- essc.ac.uk/ncof/merse a/css- gif/Mapwithrectangle.g Gene Paull, UT Brownsville, Public Domain(?), if http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif Redhttp://www.itrd.gov/pubs/blue96/images/temp.atlantic.gif -- Warm surface waterBlue -- Cold surface water North Atlantic Gyre Boundary Currents Coriolis “Geostrophic” Response 100 50 Sea Surface 0 Height (cm) 0 500 1000 1500 2000 2500 Centers of gyre “hills”: Sargasso Sea, W. Pacific, Madagascar, etc. Animation from the Naval Research Laboratory, Public Domain, Distance (km) http://www7320.nrlssc.navy.mil/modas2d/anims/gbl/httot_gbl_12mon.fli 1 Gulf Stream time-lapse Surface Temp. Current flow rate in the Gulf Stream, in units of 106 m3/sec (roughly: millions of tons/sec) 106 m3/sec = 60 Mississippi Rivers! Image from Sverdrup, Johnson, and Fleming, Sverdrup H.U., Johnson M.W., Fleming R.H. The Oceans.. their physics, chemistry, and general biology (1942), http://oceanworld.tamu.edu/resources/ocng_textbook/chapter11/Images/Fig11-7.htm U. Miami /CIMAS, Public Domain. http://oceancurrents.rsmas.miami.edu/atlantic/img_rrsl/sst-composit.avi Western Boundary Currents Eastern Boundary Currents • Fastest, deepest gyre currents • Shallow, broad, slow currents – Equatorial currents are deflected to high latitudes by – Return flow to low latitudes continents – Transport warm water to high latitudes – Transport cold water to the equator • Gulf Stream (N. Atlantic); Kuroshio Current (N. Pacific); – Roughly 1/10 the speed of WBCs Brazil Current (S. Atlantic); Agulhas Current (Indian); • Canary Current (N. Atlantic); California East Australian Current (S. Pacific) Current (N. Pacific); Benguela Current • Gulf Stream is king of them all! (S. Atlantic); West Australian Current 2 m/s ≈ 200 km/day (Indian); Peru Current (S. Pacific) 55x106 m3/sec = 55 Sverdrups transported > 3000 Mississippi Rivers! Important non-gyre currents: Boundary Currents Equatorial Counter Currents Current Width (km) Depth (km) Flow Rate (km/day) • Right between the two Equatorial currents • No Coriolis at equator: only wind stress vs. Western < 100 km 1-2 km ~ 100 pressure Boundary km/day • Response of water to constantly being pushed / piled up on the west side of the Eastern > 1000 km < 0.5 km ~ 10 basin (up to 50 cm high) Boundary km/day • Tends to flow back towards East. 2 QUESTIONS? Upwelling of Deep Water British National Centre for Ocean Forecasting, Public Domain(?), http://www.nerc- essc.ac.uk/ncof/merse a/css- Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes- gif/Mapwithrectangle.g oceanicas.gif Red -- Warm surface water Blue -- Cold surface water if Equatorial Pacific Upwelling Sites & Causes of Upwelling • Equatorial Divergence: Opposite Coriolis bending on each side of the equator causes pull surface water away. Cold deep water rises to UPWELLING replace it. CORIOLIS N. Equ. Current Chris Henze, NASA Ames, Public Domain, Equator UPWELLING http://people.nas.n asa.gov/~chenze/E CCO/93- S. Equ. Current 02.T_1.raw.mpg CORIOLIS Figures, UCLA Blue-Yellow - Cold water Red-Magenta - Warm water Coastal Upwelling Coastal upwelling, California • Coastal Upwellings: Ekman transport away from shoreline forces upwellings CORIOLIS UPWELLING NOAA image, Public Domain, Figures, UCLA http://oceanexplorer.noaa.gov/explorations/02quest/background/upwelling/media/Fig1_cartoon.html 3 Upwelling and Downwelling Flows • Antarctic Divergence: –Two causes: Dense sinking waters (vertical mixing) and Ekman transport (upwelling) away from Antarctic Circumpolar Current –Results in intense upwelling around Antarctica –Very high biological Chlorophyll a productivity Concentration NASA image, Public Domain, http://earthobservatory.nasa.gov/Study/Polynyas/ Liusen Xie, UBC Climate Prediction Group, http://www.ocgy.ubc.ca/projects/clim.pred/Upwell/annualL.jpg Deep Currents in the Ocean QUESTIONS? • Two Types – Surface Currents • Mixed layer (0-300 m), most surface currents here • Pycnocline (to 1000m) – Sub-surface (deep) Currents • Deep water American Meteorological Society, http://oceanmotion.org/images/oc Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes- ean-vertical- oceanicas.gif structure_clip_image002.jpg Where does deep water come from? Deep Water Formation Labrador Sea Deep currents – sinking of dense water near the poles Weddell Sea Figure from Matthew England, Climate Change Research Centre (CCRC) University of New South Wales, Adapted from figure by Helen Hill(?), MIT, http://puddle.mit.edu/~helen/ http://web.maths.unsw.edu.au/~matthew/southern_ocean_variability.htm 4 Water Mass Classifications Water Mass Classifications Intermediate Waters: Water between cold, deep polar water and surface • Deep Waters: Example: Mediterranean outflow: Warm and highly saline at ~1000 m – North Atlantic Deep Water (NADW) Med. outflow figure by G. P. King, http://www.eng.warwick.ac.uk/staff/gpk/Teaching- • Vertical mixing & incorporation of salty N. undergrad/es427/rice.glacier.edu-oceans/GLACIER%20Oceans-%20-- %20Densitydriven.htm Atlantic waters near Greenland Sea-surface salinity map by Rosarinagazos, Creative Commons A S-A 3.0, • Bottom Waters: http://commons.wikimedia.org/wiki/File:Wiki_plot_04.png – Antarctic Bottom Water (AABW) • Forms dominantly in Weddell Sea in regions of active sea ice formation (polynyas) • Cold, saline sinking water • Densest water mass in the oceans Strait of Gibraltar % • • • • • • • • • Atlantic Deep Circulation Pacific UCAR/NOAA/NASA, Public Domain, http://www.meted.uca r.edu/tropical/met_top ics/media/graphics/m oc_atlantic_salinity.jp g MIW – Mediterranean Intermediate Water Antarctic Intermediate Water MIW North Atlantic Deep Water 0 0 0 0 0 0 Antarctic Bottom Water UCAR/NOAA/NASA figure, Public Domain, http://www.meted.ucar.edu/oceans/currents/media/graphics/pacific_s alinity_section.jpg Hannes Grobe, Wikimedia Commons, Creative Commons A S-A 2.5, Global deep water ‘conveyor’ http://upload.wikimedia.org/wikipedia/commons/2/2c/Antarctic_bottom_water_hg.png Robert Simmon/Robert Rohde, NASA/Wikimedia, Public Domain, http://en.wikipedia.org/wiki/File:Thermohaline_Circulation_2.png QUESTIONS? 5.
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