geo 103 test #3

What is Ekman transport\

-A decrease in current speed, coupled with continuous Coriolis deflection with increasing depth an apparent spiral of moving water called the Ekman spiral. Adding all vectors (magnitude and direction) of the Ekman spiral yields a net current direction that is ~90 degrees to the prevailing wind. This composite current is the Ekman transport and it controls the motion of the surface ocean.

What are geostrophic currents?

-A geostrophic current is an oceanic flow in which the pressure gradient force is balanced by the Coriolis effect. -Gravity acts on the water to pull it back from these hills or into these valleys. This continuous tug-of-war between opposing forces results in a partial balance or equilibrium that keeps water moving around these domes and valleys. -This geostrophic flow is represented by most surface currents in the ocean.

Deep & intermediate waters

-Deep waters from only in the Atlantic today. -North Atlantic Deep Water (NADW) forms in the northern North Atlantic (Greenland-Norwegian Sea) -Antarctic Bottom Water (AABW) forms in the souther South Atlantic (weddell Sea of Antarctica) -Deep waters of the Indian & Pacific oceans are a mix of NADW and AABW called Circumpolar Water (or "Common Water") -Other waters also form in the mid- to high latitudes and sink to intermediate depths. These intermediates waters are less dense and are produced in smaller volume than deep waters. Antarctic Intermediate Water (AAIW) forms at the Antarctic Convergence (polar front), then sinks and flows north into the South Atlantic, Caribbean Sea, Gulf of Mexico, and North Atlantic Similar intermediate waters also form in the north and south pacific. Mediterranean Intermediate Water (MIW) is a warm, salty water mass produced in the Mediterranean Sea due to high evaporation rates in the subtropics. MIW is among the densest waters formed in the ocean today. However it doesnt sink to become deep or bottom water because the relatively small volume of water that spills into the North Atlantic mixes with other water masses to dilute its originally dense character.

Western boundary currents vs Eastern boundary currents And What causes westward intensification

-Earth's rotation from west to east, assisted by the typically strong trade winds in the tropics, causes the water in the ocean to "pile-up" towards the western sides of the ocean basins. -As the Earth rotates from west to east, the water in the ocean starts to slosh toward the western sides of the basins and therefore, the ocean surface stands slightly higher on the western sides of the ocean basins. In this way, the dome of water created by convergence in the subtropics is not located in the center of the ocean basin, but it is instead displaced toward the western side - This offset dome causes water flowing on the western side of the dome to flow faster than the eastern side. This is called westward intensification. The surface currents are forced through a narrower passage between the continents and the crest of the dome causing them to flow faster. -The flow is wide and much weaker on the eastern side of the gyre (Canary Current in the N. Atlantic or the California Current in the N. Pacific) where it transports cool water towards the equator. -Strong western boundary currents mark the western sides of the subtropical gyres (Gulf Stream in the N. Atlantic or the Kuroshio Current in the N. Pacific)

What are the subtropical gyres?

-Gyres are the large horizontal wind-driven current systems that circulate around the subtle domes and depression on the ocean surface -The subtropical gyres represent large circulation cells around the hills created by convergence in the subtropics. -The subtropical gyre in the North Atlantic starts when the trade winds blow out of the northeast towards the Equator and initiate the westward-flowing North Equatorial Current. When this current encounters the Caribbean Islands and North America, the Coriolis Effect deflects the current to the right (North) as the Gulf Stream. This eventually becomes the North Atlantic current that flows toward Europe, and is deflected to the right (South) as the Canary Curent. -Subtropical gyres transport warm water waters toward the pole along the western sides of the ocean basins and cool waters toward the equator along the eastern sides. Subtropical gyres are prominent features of circulation in the North and South Atlantic, North and South Pacific, and the Indian Ocean

Thermohaline Circulation

-Intense winter cooling and sea-ice formation in polar seas during the several months of darkness that prevails in high latitudes results in the formation of cold, dense waters. These waters sink to the sea floor, since the absence of a pycnocline (density barrier) in the polar regions allows free interchange between surface and deep water. These dense waters move toward the equator beneath the pycnocline as "deep" or "bottom" waters and icy cold waters fill the entire world ocean below the pycnocline. This process is thermohaline circulation, which is the denisty-driven circulation in the deep ocean. -Thermohaline circulation also includes the production of deep and intermediate water masses. Both temperature and salinity are important in the production of deep and intermediate water masses. • Thermo (temperature) - haline (salt) • Thermohaline circulation is the density driven circulation of the ocean below the pycnocline

Wind-driven circulation

-The energy derived from the prevailing winds sets the uppermost water column in motion. This movement of the upper masses is the wind-driven circulation, and the motion is in a direction to the right of the prevailing winds in the Northern Hemisphere and to the left of the prevailing winds in the Southern Hemisphere. -Wind-driven circulation affects only the upper ocean to a depth of about 150 meters because of the pycnocline (or permanent thermocline) provides a stable density barrier between the less dense (warmer) near-surface waters and the more dense (very cold) deep waters.

<<< 3 >>> (recall) Permanent thermocline

-The interval through which temperature decreases rapidly with increasing water depth. The thermocline extends from the base of the mixed layer, at a depth of about 50-100 meters to approx 900-1000m -An effective barrier that prevents the mixing of cold, deep water with the surface mixed layer. -A well developed permanent thermocline exists in the low latitudes and into the mid-latitudes because of the strength of solar energy, although the temperature gradient weakens with increasing latitude -A permanent thermocline does not exist in polar regions because surface waters are very cold and deep waters are very cold. Therefore, there is little temperature contrast/gradient between polar surface and deep waters

(recall) Pycnocline

-The vertical interval in the ocean where density increases rapidly with depth -The pycnocline is very well developed in the tropics, but almost absent in the polar ocean.

(recall) permanent thermocline and pycnocline

-The world ocean is well stratified (layered) in the low to mid-latitudes due to solar heating of surface waters and the formation of a permanent thermocline. The thermocline separates warm (less dense) surface waters from icy cold (much more dense) deep waters. -The pycnocline represents this density barrier between the surface and deep waters. Insufficient solar heating in the high latitudes (polar) inhibits the formation of a permanent thermocline and pycnocline.

<<< 1 >>> How the prevailing winds move

-These are distinct global zones of weather development and migration -These zones compromise belts that stretch around the globe between specific latitudes, like the tropical zone(0-23.5 lat), temperate zone (23.5-66.5) or polar zone(66.5-90). These zones are each characterized by distinct prevailing winds -Storm tracks move from east to west in the tropics and near the poles, and from west to east across the broad temperate belt of the mid-latitudes -Unequal heating of the earth and its rotation on its axis give rise to the various wind belts around the globe. (prevailing winds)

<<< 2 >>> UPWELLING What special conditions cause coastal upwelling? and Where does divergence of surface water masses occur and why? and Why does upwelling result in high biological productivity?

-Upwelling: The general process by which cold, nutrient-rich deep-ocean waters rise to the surface. It is directly caused by prevailing winds. -The upward movement of water results from the displacement of surface waters by the prevailing winds and resultant Ekman transport that creates a divergence of surface waters. This transport of cool waters are toward the equator along the eastern sides. -Coastal upwelling occurs when prevailing winds blow roughly parallel to the shore and Ekman transport pushes surface waters away from the coast. In addition, since the western coastline of continents face the sluggish and broad Eastern Boundary Currents, winds blowing offshore can more easily drive the currents farther out to sea. Deeper, nutrient-rich waters come up to replace displaced surface waters. -This results in high biological productivity by primary producers (plankton) which in turn supports a greater abundance of fish and other marine life.

Water Masses

A water mass is a body of water that can be identified by its physical and chemical characteristics (temperature, salinity, density, dissolved gases, and dissolved nutrients)

Deep water masses & the Coriolis Effect

Deep water masses, like surface currents, are influenced by the Coriolis Effect resulting in strong western boundary currents. As deep waters flow toward the equator beneath the pycnocline they hug the lower continental slopes and rises on the western sides of the ocean basins.

Wave Base

Maximum depth at which a water wave causes significant water motion

<<< 4 >>> The Global Conveyor

The global conveyor describes the complete circuit of global ocean circulation involving horizontal flow of surface and deep waters, and the vertical flow of downwelling and upwelling. Waters of thermocline and surface mixed layer move under the influence of wind-driven circulation; waters below the permanent thermocline (and pycnocline) move by density-driven thermohaline circulation. Surface waters move independently of bottom, deep, and intermediate waters because of the pycnocline, which acts like a density barrier to separate surface and deeper water masses. Downwelling and upwelling are the processes that link the surface and deep ocean. Surface waters cool and sink in the Atlantic and spread to fill all the ocean basins of the world with cold deep waters. Coastal upwelling at the margins of the ocean, around the continent of Antarctica and in the equatorial Pacific return waters to the surface. Surface currents then return these waters back to the Atlantic. There is a net export of deep water out of the Atlantic and net import of surface water into the Atlantic.

Wind-driven circulation influenced by the Coriolis Effect

The prevailing wind moves water at the ocean surface, and this ocean current is deflected at an angle to the wind as determined by the Coriolis Effect. Water flowing at greater depths is also deflected, so that the net transport (Ekman Transport) of water is at right angles to the prevailing wind

Upwelling and Downwelling

The wind-driven surface currents of the world ocean, including the gyres, represent the horizontal flow of water masses. Upwelling and Downwelling are the processes that describe this vertical movement of water masses in the world ocean

<<< 5 >>> Waves

Waves represent the transmission of energy, not mass, along the interface between fluids of differing density; for example, between the surface of the ocean and the atmosphere. The waves may may move forward, but the water within those waves actually doesn't travel very far. The water molecules stay in the same place and orbit in circles as the waves pass by. The velocity of particles in orbital waves decreases with depth (no mass transport so waves are not affected by the Coriolis Effect)

Intermediate, Deep, & Bottom Water Masses (and their characteristics)

• water becomes more dense by lowering the temperature or by adding salt: - winter cooling - evaporation (water becomes saltier causing it to sink) - seasonal sea-ice formation (a salty brine is created, which sinks) • downwelling is the sinking of dense waters • parcels of water sink to their level of neutral buoyancy below the solar-warmed surface waters thereby producing intermediate, deep, & bottom water masses