Unit 10 Notes - Ocean Currents Surface currents Affect surface water within and above the pycnocline (top ________ of ocean water) Driven by major wind _______ of the world Deep currents Affect deep water below pycnocline (bottom ________ of ocean water) Driven by ___________ differences Larger and slower than surface currents Measuring surface currents Direct methods Float meters (intentional and inadvertent) Propeller meters Indirect methods Pressure gradients, satellites, and Doppler flow meters Surface currents closely follow global wind belt patterns Trade winds at 0-30º blow surface currents to the ___________ Prevailing westerlies at 30-60º blow currents to the __________ Wind-driven surface currents (see figure) Current gyres Gyres are large ________-moving loops of water Subtropical gyres Five main gyres (one in each ocean basin): North Pacific South Pacific North Atlantic South Atlantic Indian Generally _________ currents in each gyre Centered at about _________north or south latitude Subpolar gyres Smaller and fewer than subtropical gyres Generally ___________currents in each gyre Centered at about _________north or south latitude Rotate in the opposite direction of adjoining subtropical gyres Ekman spiral describes the speed and direction of flow of surface waters at various depths Factors: Wind and Coriolis effect Ekman transport is the overall water movement due to Ekman spiral Ideal transport is 90º from the wind Transport direction (right or left) depends on the hemisphere Geostrophic flow and western intensification Geostrophic flow causes a _______ to form in subtropical gyres The center of the gyre is shifted to the west because of Earth’s rotation Western boundary currents are _______________ Western intensification of subtropical gyres The western boundary currents of all subtropical gyres are: Fast Narrow Deep Western boundary currents are also ___________ Eastern boundary currents of subtropical gyres have opposite characteristics Currents and climate Warm current warms air high water vapor ___________ coastal climate Cool current cools air low water vapor __________ coastal climate Upwelling and downwelling Vertical movement of water Upwelling = movement of deep water to surface Hoists _________, nutrient-rich water to surface Produces high productivities and abundant marine life Downwelling = movement of surface water down Moves __________, nutrient-depleted surface water down Not associated with high productivities or abundant marine life Coastal upwelling and downwelling Ekman transport moves surface water away from shore, producing ____________ Ekman transport moves surface water towards shore, producing _______________ Equatorial Upwelling Tradewinds blow equatorial waters north and south Upwelling from the deep replaces water moving north and south Antarctic surface circulation Surface currents circle Antarctica moving to the east Driven by prevailing westerlies The Gulf Stream and sea surface temperatures The Gulf Stream is a warm, western intensified current Meanders as it moves into the North Atlantic Creates warm and cold core rings (___________) The Sargasso Sea: What is it? ____________________________________ North Pacific Garbage Patch: What is it? ______________________________ Other surface currents Longshore currents Run _________ along coastlines Responsible for formation of barrier islands and transport of sand along beaches Rip currents Occur when coastal waves or currents ____________ Dangerous for swimmers because they flow off the beach towards the open ocean El Niño-Southern Oscillation (___________) El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around ____________ La Niña = opposite of El Niño Southern Oscillation = change in ____________ pressure over Pacific Ocean accompanying El Niño ENSO describes a combined oceanic-atmospheric disturbance El Niño recurrence interval Typical recurrence interval for El Niños = 2-12 years Pacific has alternated between El Niño and La Niña events since 1950 Effects of severe El Niños: Describe_______________________________________ Deep currents Begin in the subpolar North Atlantic when high density (cold salty) surface water ____________ Factors affecting density of surface water: Temperature (most important factor) Salinity Deep currents are also known as thermohaline circulation Deep ocean characteristics Conditions of the deep ocean: Cold Still Dark Essentially no _______________ Sparse life Extremely high pressure Identification of deep currents Deep currents are identified by measuring temperature (T) and salinity (S), from which density can be determined Global conveyer-belt It takes _______________ years for water to make a complete circuit. The Conveyor Belt and CO2 At the ocean surface, CO2 is dissolved by water and photosynthetic plankton convert it to ________ and carbonate (shells) CO2 in the water is also circulated on the conveyor belt into the deep oceans where it is sequestered In effect, the oceans and conveyor belt current acts as a carbon “sink”, removing it from the atmosphere .