Chapter 3 Chemical and Physical Features of the Oceans Why study this? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Part Two: Ocean Circulation Perpetual Ocean Video Currents move and mix ocean waters Transport/Move around:

Surface Circulation ___________ drives strongest ocean currents occur in surface layer Wind and surface currents: Driven by: Influenced by:

Coriolis Effect Because Earth is rotating, anything that moves over the surface tends to turn a little rather than in a straight line Deflects large-scale motions like winds and currents N. Hemis: S. Hemis:

Coriolis Effect Simulation

Winds driven by heat energy from sun. Wind Patterns Winds driven by heat energy from sun. 3 types of winds: 1) Trade Winds 2) Westerlies 3)Polar Easterlies Global Wind Patterns

Wind Patterns: Trade Winds

The trade winds, meet at the Intertropical Convergence Zone (also called the doldrums) between 5 degrees North and 5 degrees South latitude, where the winds are calm.

Wind Patterns: Westerlies At middle latitudes

Wind Patterns: Polar Easterlies Polar easterlies at high latitudes

The wind fields are pictured here as they would look if whole Earth covered in water. In actuality, modified by the influence of continents.

Surface Currents Winds push the sea surface creating currents Surface current moves off 45° b/c Coriolis Top layer pushes on layer below & again Coriolis Effect come into play: Second layer moves slightly to right and slower and is repeated down the water column Process =

Surface Currents-Ekman Transport lower waters move progressively at greater angles from wind effect of wind decrease with depth 100 m no wind is felt affected layer = Ekman layer Taken as a whole, the Ekman layer moves at 90⁰ from wind =Ekman Transport upper part of water column moves perpendicular to wind direction -- right N. Hemisphere & left in S. Hemisphere

Equatorial Currents and Gyres Trade winds move toward equator The equatorial currents created by trade winds, move parallel to equator because of Coriolis Effect All currents combine into huge gyres = huge circular systems

Major Surface Currents West side of gyres carry: Cold current flows **Remember , water has a high heat capacity*** Affects organisms:

Major Surface Currents Currents shown are AVERAGE patterns over large distances and a long time span. Currents shift with Currents affected by the Remember: Surface currents!

The role of surface currents in transporting heat is reflected in the sea surface temperatures, seen below.

Thermohaline Circulation and the Great Ocean Conveyor Ocean water stratified Cold water more dense on the bottom Warmer water less dense on top Three layers Surface/mixed layer Intermediate layer Deep and bottom layers So those were surface currrents, not onto deeper waters.

The Three-layered Ocean Surface layer or mixed layer 100 to 200m thick Mixed by wind, waves and currents Intermediate layer depth of 1000 to 1500m Main thermocline in open ocean A zone of transition between warm surface water and cold water below Rarely breaks down Deep or bottom layers Below 1500 m Uniformly cold, typically less than 4°C Stable Surface = mixed Int = thermocline Deep = stable

As temp approaches zero, density ________________. LOW stability HIGH stability Cold water is denser. As temp approaches zero, density ________________. Deep oceans are stable Density and Temperature are correlated

Stability and Overturn Water column with less dense water on top and dense water on bottom with no mixing is stable. How stable? depends on the difference in densities between layers If density difference is large, lots of energy needed to mix layers, high stability. If density difference is small not much energy is needed to mix the water, low stability

Stability depends on the difference in densities between layers LOW stability HIGH stability Water column with less dense water on top and dense water on bottom with no mixing is stable. Stability depends on the difference in densities between layers If density difference is large, lots of energy needed to mix layers, high stability. If density difference is small not much energy is needed to mix the water, low stability

Downwelling Occurs when top layers become more dense, sink The sinking water displaces the deeper water, bringing it the top Call the sinking water = water mass What shape is the temperature profile when downwelling is happening? Straight line What shape do you expect the density to be? A straight line This tends to happen in certain places in the ocean, Northern Atlantic.

Water Mass & Thermohaline Circulation Sinking water mass now has a “fingerprint” When it sinks, keeps characteristics it had at surface This “fingerprint” allows oceanographers to follow the movement of the water mass, its CIRCULATION. Because this form of circulation is driven by density changes, (determined by temperature and salinity) the circulation is called thermohaline circulation Thermo = temp Haline =salt

The Great Ocean Conveyor Water mass sinks, spreads through Atlantic and other ocean basins. Eventually rises somewhere else, returns to Atlantic Sinks again, cycle repeats Cycle called The Great Ocean Conveyor Takes 4,000 years to mix ocean The Great Ocean Conveyor: Regulates climate Alterations in circulation hypothesized to have produced rapid climate changes (ie ice ages) Bring dissolved oxygen to deep sea

The Great Ocean Conveyor A few locations where water masses sink all the way to the bottom 1) North Atlantic, south of Greenland 2) South Atlantic, north of Antarctica

The Great Ocean Conveyor Regulates climate Alterations in circulation hypothesized to have produced rapid climate changes (ie ice ages) Bring dissolved oxygen to deep sea