Ocean Surface Circulation How do currents form? How do they circulate?

Currents Ocean currents – masses of ocean water that flow from one place to another. Surface currents – movements of water that flow horizontally in the upper part of the ocean’s surface.

Cause of surface currents What do you think creates surface currents now that you know what they are? If you guessed the wind you are right!! Surface currents develop from friction between the ocean and the wind that blows across its surface.

Ekman Spiral Copy this diagram into your notes including all labels.

Ekman Transport Wind blowing on the surface of the ocean has the greatest effect on the surface. However, for the lower layers of the ocean to move they must be pushed by the friction between the layers of water above. Consequently, the lower layer moves slower than the layer above. With each successive layer down in the water column the speed is reduce. This leads to the spiral affect seen in the previous diagram. The net movement of water is 90 o to the right of the wind direction (in the northern hemisphere).

Coriolis Effect (Force) Recall from learning about global winds how the Coriolis effect deflected the winds. What effect if any does this phenomenon have on ocean currents? Discuss with table and fill in blanks. In the Northern Hemisphere currents are deflected to the ______. In the Southern Hemisphere they are deflected to the ______.

Coriolis Myth One of the biggest misconceptions associated with the Coriolis effect is that it causes the rotation of water down the drain of a sink or toilet. The water itself is simply moving too fast down the drain to allow for the Coriolis effect to have any significant impact. So water will not swirl down a drain in the opposite direct in Australia compared to here.

Continental Deflection Since the Earth’s surface is not fully covered by water, currents cannot move freely around the world. So when surface currents meet continents, they deflect, or change direction Predict what will happen with each labeled area.

Gyres (gyros = a circle) Huge circular moving current systems that dominate the surfaces of the oceans. Five main gyres –North Pacific –South Pacific –North Atlantic –South Atlantic –Indian Ocean (draw diagram In notebook)

Identify cold surface current and warm surface currents. On the next slide use the map of surface currents and the knowledge you have gained from the previous slides to determine which ones are cold currents and which are warm currents. In your notebook create a 2 column table and list all those you think are cold and all those you think are warm. There are 25 different currents You may work together at your table.

Ocean Characteristics Salinity – the total amount of solid material dissolved in water –the ratio of the mass of dissolved substances to the mass of the water sample. –Is expressed in parts per thousand; 35 parts per thousand or 3.5 parts per hundred or 3.5% –Most is NaCl, sodium chloride….also contains the salts MgCl, MgS, KCl, KS, CaCl, CaS

Sources of Salt Chemical Weathering of rock on land; – reach the ocean through runoff from rivers and streams. Earth’s Interior releases large quantities of water vapor and other gases through volcanic eruptions; –these eruptions contain certain elements that are found in abundance in the oceans.

Affects on Salinity Addition of fresh water decreases salinity: –Precipitation –Runoff –melting icebergs/glaciers –melting sea ice Removal of fresh water increases salinity: –evaporation –formation of sea ice

Ocean Temperature The surface temp –varies with the amount of solar radiation received –latitude dependant Under the surface temps –tend to decrease with depth in middle latitudes to about 1000meters –remain constant at high latitudes Thermocline –the layer of ocean water where there is a rapid change of temp with depth. –creates a vertical barrier to many types of marine life

Density What is it? –Mass /volume or how much of something is contained in a certain volume What affects it? –Salinity increase causes_____ in density decrease causes ______ in density –Temperature increase causes ______ in density decrease causes _____ in density

Deep Ocean Circulation Density currents –vertical currents of ocean water that result from density differences in water masses. Most begin in high latitudes at the surface –very cold dense water _____(rises, sinks) Evaporation at middle latitudes high –Mediterranean evaporation exceeds precipitation/runoff

North Atlantic

Conveyor Belt/Upwelling A simple representation of the way warm surface water flows towards the poles, sinks as it’s temp drops and salinity increases and then moves back toward the equator where it upwells and begins the process again. Upwelling – the rising of cold water from deeper layers to replace warmer surface water.

Oceans Effect on Climate Warm water currents that move into higher latitudes transfer heat. –Ex. Gulf Stream affects weather in ________ Cold water currents moving toward the equator help moderate temps of adjacent land. –Ex. California current flows from Alaska to bring ________ temperatures to California.

Upwelling Brings cool water to surface off coast of land; –cool water cools down adjacent land Also brings nutrients –such as nitrates and phosphates to surface –promotes growth of plankton –which feeds fish and other marine organisms.

El Nino Every 3 to 5 years the tradewinds weaken –this shifts the warm waters eastward –stops upwelling along the coast of South America; fishing industry devastated –causes drought in Australia and flooding in South America

El Nino An El Niño’s effect on weather can be complex, and in some cases didn’t behave as predicted. In drought-ravaged California, for example, meteorologists thought the ocean temperature phenomenon probably would bring above-average rain to the southern part of the state in January, with a lesser chance of precipitation in the north. Instead, the opposite happened — southern California stayed pretty much bone dry with just three days of rainfall, while northern California got the coveted rain and snow in the mountains.

La Niña During La Nina the trades winds strengthen more than normal.

La Niña 2016?? Expected La Niña impacts during April-June 2011 include suppressed convection over the west-central tropical Pacific Ocean, and enhanced convection over Indonesia. Potential impacts in the United States include an enhanced chance for below-average precipitation across much of the South, while above-average precipitation is favored for the northern Plains. An increased chance of below-average temperatures is predicted across the northern tier of the country (excluding New England). A higher possibility of above-average temperatures is favored for much of the southern half of the contiguous U.S.

Climate Project Research 1.What wind belt or latitude is your location nearest? How does that affect your general wind direction? 2.Is your location close to a warm or cold ocean current? If so how does that affect your climate? 3.How is your location affected by El Nino or La Nina conditions?