Lecture 15: Upwelling, Downwelling, and Density Currents
Lecture 15: Upwelling, Downwelling, and Density Currents 212
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This 2 page Class Notes was uploaded by Megan Dengler on Thursday October 13, 2016. The Class Notes belongs to 212 at University of Arizona taught by Dr. Richardson in Fall. Since its upload, it has received 5 views. For similar materials see Geosciences in Geoscience at University of Arizona.
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Date Created: 10/13/16
October 13, 2016 Lecture 15 Upwelling, Downwelling, & Density Currents - Things to Remember o Surf Zone: where waves interact with the shore o When waves come ashore They slow down The wavelength decreases They stand up on the bottom They eventually break o When waves hit the shore at an angle, we get Longshore currents (the water) Longshore transport (the sand) o Longshore transport acts to straighten curved coasts o Longshore transport is generally toward the equator o Effects of dams and seawalls on beaches - Biggest current on Earth: Antarctic Circumpolar Current o Carries 178 million cubic meters of water per second (Gulf Stream is 40, all the rivers in the world are 1) - Wind-driven transport in the ocean: o 1. Subtropical and Subpolar Gyre currents (the biggest currents) o 2. Longshore transport (moves a lot of sand, but not much water) o 3. Coastal upwelling/downwelling (drawing) Related to fisheries o 4. Equatorial upwelling o 5. Southern Ocean Upwelling - Offshore wind (Coastal Currents) o Coastal upwelling: Winds blow off the coast, so water has to upwell to “fill the hole” Cold Water High nutrients High productivity Good for fisheries o 100 meters - Onshore Wind o Coastal Downwelling: Onshore wind goes down to bottom against coast to keep water level Warm water (goes down to bottom) Low nutrients Low productivity Poor fishing - CO2, O2, and Nutrients vs Depth o Upwelling delivers the byproducts of bacteria back to the surface and feeds it to the plants (recycling) - CLICKER QUESTION: The ocean is productive wherever: upwelling brings nutrients to the surface - Equatorial upwelling o Water upwells to the surface at the equator and disperses out from equator o From 200m o Cold o Lots of productivity - Southern Ocean Upwelling o Left hand rule in southern hemisphere o Strongest winds on earth = huge upwelling o From 2000m (2km) - Global Ocean Circulation o Southern Ocean is massively mixed o Productivity isn’t higher than it is because of the lack of sunlight So much mixing in the water block sunlight “light limitation” – organisms can’t swim back to the top if they get caught below the massive waves Sun isn’t present for a lot of the year - Downwelling o Density depends on both temperature and salinity Warm water is less dense Saltier water is more dense o TANK EXPERIMENT Warm water rises Low salinity water rises Cold water sinks Salty water sinks
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