Oceans in Motion The ocean is constantly in motion Driven by: –Winds –Currents –Coriolis Effect

WINDS ARE NAMED FROM WHICH THEY BLOWWINDS ARE NAMED FROM WHICH THEY BLOW CURRENTS ARE NAMED BY THE DIRECTION THEY FLOWCURRENTS ARE NAMED BY THE DIRECTION THEY FLOW

What causes ocean currents? Winds produce a stress on the ocean and cause it to move –Wind-Driven Circulation Density differences created by the exchange of heat and moisture with the atmosphere cause movement –Thermohaline Circulation

How does the Ocean Circulate? Similar to a two story building… There is an upstairs and downstairs What goes on in each floor is separated by the floor or ceiling Connections between the two floors occurs only at limited locations Where elevators or stairways are found

Mixing In the ocean’s two stories, there is the surface and deep ocean. The floor that separates them is called the pycnocline –Effectively restricts direct mixing across this level Connections between the two parts of the ocean are only in limited regions

Cyclones and Hurricanes Doldrums – convergence of trade winds fuel tropical cyclones and hurricanes

OCEAN CIRCULATION Ocean water circulates in currents Surface currents are caused by wind = 10% of water movement The other 90% is driven by gravity dense water sinks, less dense rises

Surface Mix Layer Deep Water Layer 4000m m 0m Upwelling Downwelling wind sunlight Density driven

When several containers of children's bathtub toys spilled over a ship's side and were released into the Pacific Ocean, who would've thought a concerted research project to study the ocean's currents would be the result? January 10, 1992….

In January 1992, a container ship near the International Date Line, headed to Tacoma, Washington from Hong Kong, lost 12 containers during severe storm conditions. One of these containers held a shipment of 29,000 bathtub toys. Ten months later, the first of these plastic toys began to wash up onto the coast of Alaska. Driven by the wind and ocean currents, these toys continue to wash ashore during the next several years and some even drifted into the Atlantic Ocean.

60,000 Nike shoes wash ashore from ship spill

Scientists use these spills to help study ocean circulation This could help with oil spills and predicting in which direction the oil will travel Learn about pathway of currents and how they are changing and what affects them.

A Bad Break in Pool How do the winds make the ocean move?

Not the worst one ever, just a bad one A Bad Break in Pool cue hits at bad angle cue moving too slowly billiard balls poorly racked up

A “Bad Break” in the Ocean Air molecules hit water molecules at bad angle, AND: H 2 O’s irregularly spaced hydrogen bonded together imagine golf ball hitting billiard balls that are poorly racked N2N2 O2O2

Transfer of Kinetic Energy from Air to Ocean N2N2 O2O2 BILLIONS of air molecules hit the ocean every second The upper ~100 m of the ocean moves in response to winds BUT: the water does not move in EXACTLY the same direction as wind

Sverdrup et al., Introduction to the World’s Oceans, 8th edition, McGraw Hill, Fig. 9.1 Ekman Transport Wind bombards the surface ocean Water starts to move Coriolis deflection alters its path What happens UNDER the surface?

Remember that the Earth is rotating clockwise – to the east. Remember that the Earth is rotating clockwise – to the east. Objects traveling in Northern hemisphere are deflected to right (clockwise) Objects traveling in Northern hemisphere are deflected to right (clockwise) Southern hemisphere are deflected to left (counterclockwise) Southern hemisphere are deflected to left (counterclockwise)

The Coriolis Effect 1. The Earth’s rotation affects linear movement – it is deflected, the path is not linear, rather it is curvilinear 2. The effect is too subtle to notice over short distances, but things which travel over long distances such as airplanes, winds, and water currents display the Coriolis effect.

Ekman “Spiral” surface layer (1) drags on the water underneath (2) layer 2 starts to move. It moves more slowly than layer 1 due to friction. (smaller yellow arrow) Coriolis deflection alters path of layer 2.

Ekman “Spiral” layer 2 drags on the water underneath (layer 3) layer 3 moves more slowly Coriolis deflection alters path of layer 3.

Ekman “Spiral” The result? A spiral pattern. AVERAGE MOTION of the upper ~100m of the ocean is 90˚ to the wind.

Building the currents STEP 1: Ekman Transport Winds drive E-W currents Zones of convergence and divergence Continents get in the way EXCEPT around Antarctica (stormiest ocean on Earth) Pattern of circulating GYRES.

Sverdrup et al., Introduction to the World’s Oceans, 8th edition, McGraw Hill, Fig. 9.4 Geostrophic Flow Sargasso Sea - a mound of water in the Atlantic Ocean Coriolis deflection is piling up water. Gravity is pulling it down. The pile is ALWAYS THERE. These forces must be EQUAL.

Sargasso Sea “Sea of Weeds”

Sargasso Sea Home to Many…

Gyres Circuit of mid-latitude currents around the perimeter of an ocean basin. Example: the Gulf Stream, the North Atlantic Current, the Canary Current, & the North Equatorial Current make up the North Atlantic Gyre

Five major gyres and the Antarctic circumpolar current

Gyre Formation Warm Cool CLOCKWISE COUNTER CLOCKWISE

North Atlantic Gyre Notice how the winds are helping the currents. This also shows the effects of the Eikman spiral

What happens when you push in on a plastic container of water?

The container moves first, and water moves a fraction of a second later.

Water sloshes up again the left-hand side, creating a pile

Sverdrup et al., Introduction to the World’s Oceans, 8th edition, McGraw Hill, Fig. xxx Earth’s rotation As Earth rotates the continents smack into the oceans Asia, Australia hit the Pacific Ocean The Americas hit the Atlantic Ocean

Continents crash into the mound of water. The mound is asymmetrical. This leads to Western Intensification – water piles up on the coast West East North America A West to East Cross Section of the mound of water 1m Only ~ 1m high, but that’s enough to create BIG differences in the currents.

Western Intensification West East North America A West to East Cross Section of the mound of water Gravity is trying to pull this down and out to flatten the ocean. The flow is constricted on the WEST side and spread out on the EAST Think about constricting flow out of a garden hose by covering half the opening with your thumb. The constricted flow moves FASTER.

Western Intensification West East North America Think about constricting flow out of a garden hose by covering half the opening with your thumb. The constricted flow moves FASTER. WHY? SAME AMOUNT of water forced to move through smaller opening Canary Current (Flowing OUT of screen) diffuse, slow Gulf Stream (Flowing into screen) Narrow and fast

Western vs. Eastern Currents Western Currents Eastern Currents Gulf Stream, Kuroshio, Gulf Stream, Kuroshio, East Australia Currents East Australia Currents warm water moving from warm water moving from equator to pole equator to pole narrow: < 100 km wide narrow: < 100 km wide deep: down to 2 km deep: down to 2 km “fast:” 100s of km/day “fast:” 100s of km/day sharp boundaries defined by sharp boundaries defined by water temperature water temperature California, Canary, Peru California, Canary, Peru Currents Currents cold water moving from cold water moving from pole to equator pole to equator wide: ~ 1000 km wide wide: ~ 1000 km wide shallow: < 500 m shallow: < 500 m “slow:” 10s of km/day “slow:” 10s of km/day diffuse boundaries diffuse boundaries

Sverdrup et al., Introduction to the World’s Oceans, 8th edition, McGraw Hill, Fig Coupled Surface and Deep water Circulation

Convergence: water masses collide and sink  downwelling Divergence: Surface waters move APART. Deep water rises up to fill the gap  upwelling Back to Upwelling & Downwelling Upwelling brings NUTRIENTS (from DECAYED organic matter) back up to the surface. Sverdrup et al., Introduction to the World’s Oceans, 8th edition, McGraw Hill, Fig. 9.3

Area where trade winds converge Meteorlogical equator = Thermal equator Moves north & south of the Earth’s equator ITCZ =Inter-Tropical Convergence Zone

Sverdrup et al., Introduction to the World’s Oceans, 8th edition, McGraw Hill, Fig Major Zones of Convergence and Divergence