Marine Ecology ch. 9

contour current

A bottom current made up of denser water that flows around (rather than over) seabed projections.

La Nina

A cooling of the ocean surface off the western coast of South America, occurring periodically every 4 to 12 years and affecting Pacific and other weather patterns.

Which of the following is not a western boundary current?

California Current

The southward-flowing current that intercepts water outflowing from the Mediterranean Sea and then flows past the west-African coast is called ____.

Canary Current

Who is the first person on record to have sailed solo around the world?

Capt. Joshua Slocum

The most dense and most prevalent body of water, found in every ocean is the ____. It is characterized by a salinity of 34.65 0/00, a temperature of -0.5°C (30°F), and a density of 1.0279 grams per cubic centimeter.

Central Water?

north atlantic deep water

Cold, dense water formed in the Arctic that flows onto the floor of the North Atlantic ocean.

Eastern Boundary Currents

Cold, shallow, broad (boundaries not well defined) -canary current -benguela current -california current -west australian current -peru current

In addition to being affected by land masses, the motion of ocean surface currents mirrors the major atmospheric circulation gyres. Therefore, the northern and southern equatorial currents of both the Atlantic and Pacific Oceanic gyres, along with the intervening equatorial counter-current ____.

Converge north of the equator

The Pacific Equatorial Undercurrent is known as the ____.

Cromwell Current

Countercurrents

Currents flowing on surface in opposite direction to main currents

Due to the combined effect of wind friction, Coriolis Effect, Ekman Transport, land mass, and the pressure gradient, ocean currents tend to ____.

Flow along the periphery (outside) of ocean basins

West Wind Drift (Antarctic Circumpolar Current)

Flows endlessly eastward around Antarctica ; driven by powerful, nearly ceaseless westerly winds ; greatest of all surface ocean currents ; never deflected by a continent

what is meant by "westward intensfication?" Why are western boundary currents so fast and deep?

For example in the northern hemisphere, the coriolis effect which increases as water moves farther from the equator, eastward moving water on the north side of a gyre is turned sooner and strongly toward the equator than westward flowing water at the equator is turned toward the pole. The peak of the hill described in figure 9.7 is not in the center of the ocean basin but closer to its western edge. If an equal volume of water flows around the gyre, the current on the eastern boundary is spread out and slow, and the current on the western boundary is concentrated in rapid

temperature-salinity (T-S) diagram

Identifies deep water masses based on temperature, salinity, and resulting density -many combinations of temperature and salinity can yield the same density and the density of water tends to increase with depth

Downwelling

the downward movement of fluid, especially in the sea, the atmosphere, or deep in the earth. supplies the deeper ocean with dissolved gases

El Nino

(oceanography) a warm ocean current that flows along the equator from the date line and south off the coast of Ecuador during the winter

According to the theory of Ekman Transport, ocean surface currents in the southern hemisphere will ____.

- Be deflected left - have a net deflection in a direction 90 degrees to surface flow

Eastern boundary currents are ___.

- Cold - Slow - Shallow

Thermohaline circulation instead of wind friction drives the mid- to deep ocean currents. This type of circulation is powered by ____.

- Uneven Solar input - Changes in water density that causes it to rise or fall through the water column

Western boundary currents tend to be ____.

- Warm - Fast - Deep

surface currents flow around the periphery of ocean basins: NOTES

-The fact of Ekman spiraling and the Coriolis effect causes the water within a gyre to move in a circular pattern -A body of water can be thought of as a set of layers. The top layer is driving forward by the wind, and each layer below is moved by friction. Each succeeding layer moves within a slower speed into an angle to the lawyer immediately above it - to the right in the northern hemisphere, to the left in the southern hemisphere - until water motion becomes negligible. though the direction of movement varies for each layer in the stack, the theoretical net flow of water in the northern hemisphere is 90° to the right of the prevailing wind force

boundary currents have different characteristics: NOTES

-general surface circulation of the north atlantic -numbers indicate flow rates in sverdrups (1 sv= 1 million cubic meters of water per second). -the unit used to express volume in transport in ocean currents is the sv named in horror of harald sverdrup, one of this century's pioneering oceanographers

Water masses may be identified by their characteristic properties of:

-surface water: a depth of 200 meters (600 ft); central water: bottom of the main thermocline;(varies with latitude);intermediate water: about 1,500 meters (5,000 ft); deep water: water below intermediate water but not in contact with the bottom to a depth of 4,000 meters (13,000 ft); bottom water: water in contact with the seafloor -near surface: warmer and less saline - precipitation may exceeded evaporation; intermediate depth: intermediate in density

convergence zone

-the water masses butt against one another and the heavier water can slide beneath the lighter water

surface currents are driven by the winds: NOTES

-the westerlies and the trade winds are two of the winds that drive the ocean's surface currents. -about 10% of the water in the world ocean is involved in surface currents, water flowing horizontally in the uppermost 400 m of the oceans surface, driven mainly by wind friction. -most of earths surface wind energy is concentrated in the easterlies and westerlies -due to the forces of gravity, the Coriolis effect, solar energy and solar wins, water often moves in a circular pattern called a gyre

One sverdrup equals ____ cubic meters/second.

10 to the 6th power

what percentage of the world ocean is involved in wind driven surface currents?

10%

undercurrent

A current flowing beneath a surface current, usually in the opposite direction. -discovered by townsend cromwell -pacific equatorial undercurrent/cromwell current flows eastward beneath the north equatorial current -volumes sometimes approach the volume of the current above them

surface currents

A horizontal movement of ocean water that is caused by wind and that occurs at or near the ocean's surface. -move water above the pycnocline, the zone of rapid density change with depth -primary force is wind

Gyre

A large-scale pattern of water circulation that moves clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere -gyros: "a circle"

float method

A method of current study that depends on the movement of a drift bottle or other free-floating object.

flow method

A method of current study that measures the current as it flows past a fixed object.

acoustical tomography

A technique for studying ocean structure that depends on pulses of low-frequency sound to sense differences in water temperature, salinity, and movement beneath the surface. -tomos: "to cut or slice"; graph: "to write"

sverdrup (sv)

A unit of volume transport named in honor of oceanographer Harald U. Sverdrup: 1 million cubic meters of water flowing past a fixed point each second. -gulf stream: 55 sv ; 300 times the flow of amazon river

what are water masses? what determines their relative position in the ocean?

A water mass has distinct temperature and salinity characteristics. The relative positions of water masses depend on their densities. Water masses don't often mix easily when they meet due to their differing densities; instead, they usually flow above or beneath each other.

How is La Nina different from El Nino?

After an ENSO event, normal circulation sometimes returns with surprising vigor, producing strong currents, powerful upwelling, and chilly and stormy conditions along the South American coast. These contrasting colder than normal events are given a contrasting name: la Niña

According to the temperature-salinity (T-S) profile graph, a mass of water of a certain density and having a unique temperature and salinity can ____.

Be mixed with a water mass having the same density(but a different temperature and salinity) to make a single water mass having a totally different density

ENSO is an acronym for a repeating meteorological and oceanographic event that can severely disrupt normal conditions. The ENSO-driven change in tropical Pacific surface trade winds causes ____.

Build up of seawater in the western Pacific downwelling in the east, and generally warmer sea surface water temperatures overall

Western current intensification is not affected by ___.

Deep-trench bathymetry

transverse currents

Currents that flow from east to west and west to east, linking the eastern and western boundary currents -westerly winds drive the east ward transverse currents of the mid-latitudes -the westward flow of the transverse currents near the equator proceeds unimpeded for great distances, but the eastward flow of transverse currents are middle and high latitudes in the northern ocean basin is interrupted by continents and island arcs

Oceanographers name currents and large bodies of water according to their relative vertical position in the water column. Which one of the following is the water mass that resides below 1,500 meters (5000 feet) to a depth of about 4,000 meters (13,000 feet)?

Deep Water

ENSO

El Nino Southern Oscillation, trade winds weaken & warm surface water moves toward South America. Diminished fisheries off South America, drought in western Pacific, increased precipitation in southwestern North America, fewer Atlantic hurricanes.

Looking at the track of high-latitude ocean currents (close to the poles) on a typical Mercatur projection map would show these currents ____.

Extending much deeper below the surface that the Hadley or Ferrel cell currents

Caballing

Mixing of two water masses of identical densities but different temperatures and salinities, such that the resulting mixture is denser than its components.

thermohaline circulation

Movement of ocean water caused by density difference brought about by variations in temperature and salinity. As ocean water freezes at the poles it concentrates salt, and the colder, denser water sinks. -therme:"heat" ; halos: "salt"

westward intensification

circulating surface waters will form fast, narrow and deep currents on the west side of a gyre and slow wide and shallow currents on the east side of a gyre

Of the world ocean's 6 great current circuits, how many are not peripheral gyres that tend to make large rotational geostrophic gyres, or boundary currents?

One

About 10% of the water in the world ocean makes up all of the surface currents. Most surface currents move water above the ____, the zone of maximum density change per unit depth.

Pynocline

Two distinct water masses with the ____ density, but ____ temperature and salinities will combine at a convergence to produce a new water mass of greater density. This mixing-and-sinking process is called caballing.

Same/Different

Transverse Currents

Tend to cross the lines of latitude

Which one of the following is a not an eastern boundary current? a. The East Australian Current b. The Canary Current c. The Benguela Current d. The California Current

The East Australian Current

Which one of the following western boundary currents carries the most volume? a. The Gulf Stream b. The Kuroshio Currents c. The Brazil Currents d. The Agulhas Currents

The Gulf Stream

Where are distinct water masses formed?

The characteristics of each water mass are usually determined by the conditions of heating, cooling, evaporation, and dilution that occurred at the ocean surface when the mass was formed.

Compare the length of time required for completion of a circuit of surface circulation with that needed for thermohaline circulation.

The circulation time of the most deepwater is about 200 to 300 years. In contrast, a bit of surface water in the north Atlantic gyre may take only a little more than a year to complete a circuit

Antarctic Bottom Water

The densest ocean water, formed primarily in Antarctica's Weddell Sea during Southern Hemisphere winters. -salinity (34.65%); temperature (-0.5 degrees celsius ~ 30 degrees fahrenheit); density (1.0279 gm/cm3)

Although nutrients in surface water are sometimes depleted by the rapid growth of organisms, deep water is often rich in nutrients. When ____, which makes deep water rise toward surface, occurs, biological productivity increase.

Upwelling

coastal upwelling

Upwelling adjacent to a coast, usually induced by wind. -in the northern hemisphere, coastal upwelling can be caused by winds from the north blowing along the west coast of a continent. water moved offshore by Ekman transport is replaced by cold, deep, nutrient laden water.

Southern Oscillation

the atmospheric pressure conditions corresponding to the periodic warming of El Nino and cooling of La Nina.

what happens in convergence zones? how is caballing associated with convergence zones?

Water masses butt against one another in convergence zones. In some cases, two distinct water masses with the same density but with different temperatures and salinities will combine at a convergence to produce a new water mass of greater density. This mixing-and-sinking process is called caballing.

The North Pacific trade winds set ocean surface water (<400 meters deep) in motion. Towards which general direction does this current flow?

West

What is a gyre? How many large gyres exist in the world ocean? Where are they located?

a gyre is a circuit of wind driven current flow around the periphery of an ocean basin. there are six major gyres located at the north and south pacific, north and south atlantic, indian ocean, and west wind drift(antarctic circumpolar current)

How is upwelling linked to biological productivity?

although nutrients in surface water are sometimes depleted by the rapid growth of organisms, deep water is often rich in nutrients. when that water rises toward the sunlit surface, biological productivity increases.

how can chlorofluorocarbons (CFCs) be used as such tracers? Would CFC-based methods be equally suitable for analysis of surface currents and thermohaline circulation?

because they dissolve easily in water, chlorofluorocarbons can be used as current tracers. totally artificial chemical first produced in the 1930s for use as refrigerants, aerosol propellants and blowing agents for foam, chlorofluorocarbons spread to the ocean like a dye, following oceanic circulation. The speed of thermohaline currents has been measured by careful analysis of their CFC content

equatorial upwelling

divergence of currents at equator generates upwelling and high productivity. -the south equatorial current, especially in the pacific, straddles the geographical equator. water north of the equator veers to the right (northward) and water south of the equator veers to the left (southward). surface water therefore diverges, causing upwelling. most of the upwelled water comes from the area above the equatorial undercurrent at depths of 100 meters or less.

written question: draw and explain western boundary currents vs eastern boundary currents ~ give specific examples

draw: figure 9.13 (bottom one) explain: western boundary currents are generally narrow, fast, deep currents that move warm water poleward in each of the gyres. in contrast, eastward boundary currents carry cold water towards the equator and are shallow and broad. both boundary currents have 5 large currents. The gulf stream, a western boundary current is distinct and marked by abrupt changes in water temperature, speed, and direction. Some other examples of western boundary currents are the japan current, brazil current, agulhas current, eastern australian current. Other currents of the eastern boundary currents are the benguela current, california current, west australian current, and the peru current. To express the volume of transport in these ocean currents is in sverdrups which determines the general surface circulation.

written question: draw and explain surface currents

draw: figure 9.8 explain: surface currents affect the upper 10% of the ocean, mostly the pycnocline. some are characterized as rapid and riverlike, with well-defined boundaries on the eastern and western side, other currents are slow and diffuse. The largest are organized into gyres, or huge circuits. A combination of surface winds, heat from the sun, the coriolis effect, and gravity circulate the ocean surface clockwise in the northern hemisphere and counterclockwise in the southern hemisphere cause the gyre to move in a circular pattern. Warm ocean surface currents are displayed in red, whereas cold ocean surface currents are displayed in blue. Air is chilled as it approaches the west and warmed as it approaches the east.

what two general methods are used to study ocean currents?

float and flow method

surface currents affect weather and climate: NOTES

general summer air circulation patterns of the east and west coasts of the united states. warm ocean currents are shown in red (east); cold currents are blue(west). air is chilled as it approaches the west coast and warmed as it approaches the east coast

Geostrophic Gyres

gyres in balance between the pressure gradient and the Coriolis effect -geos: "earth"; strophe: "turning" -independent of one another -north/south atlantic gyre, north/south pacific gyre, indian ocean, [antarctic circumpolar current/west wind drift]

how does wind blowing over a surface current influence the climate downwind?

if a continent is downwind of a mass of warm water, the atmosphere will transfer some heat. for example, mild climates of edinburgh, dublin, and london are due to eastward moving air only recently in contact with warm north atlantic current

What is the Southern Oscillation? how is this related to el nino?

in the southern oscillation, winds across the tropical pacific reverse direction and blow west to east - the trade winds weaken or reverse. reversed winds lead to reversed currents (el nino). the phenomena of the southern oscillation and el nino are coupled, so the terms are combined to form ENSO.

how might weather in the western united states be affected by the el nino?

it can double rain fall amounts and erode the coast much more quickly

eddies

looping meanders connect to form turbulent rings and trap warm and cold water in their centers and separate from the main flow

Eddy Formation

meanders form at the western boundary, and can pinch off and become isolated cells -western boundary of the gulf stream is usually distinct, marked by abrupt changes in water temperature, speed, and direction

traditional methods of studying currents are being replaced with high tech devices. how do some of these work?

modern research on currents is being carried out by devices that the measure current speed by sensing the electromagnetic force generated by sea water as it moves in earths magnetic field, Doppler current profilers that project beams of sonic pulses into the water each second, autonomous gliders like the Slocum's and other promising technologies

western boundary currents

narrow, deep, fast currents found at the western boundaries of ocean basins -gulf stream -japan current -brazil current -agulhas current -eastern australian current

Langmuir circulation

operates within the surface layer and does not lift nutrients trapped within or below the pycnocline -irving langmuir

what causes the two major types of ocean currents?

surface currents are wind driven movements of water at or near the ocean surface and thermohaline currents are the slow, deep density driven currents that affect the vast bulk of seawater beneath the pycnocline

Ekman spiral

surface winds drive surface currents, and each layer of water drags the layer below, but the Coriolis Force changes each layer's direction slightly to make a spiral effect -water flows in the opposite direction from the surface current

How can wind-driven horizontal movement of water induce vertical movement in surface water?

the friction of wind blowing from the north along the ocean surface causes the water next to the west coast of a continent to begin moving. The Coriolis effect deflects the water to the right in the northern hemisphere and the resultant Ekman transport moves it off shore. Deepwater then rises and moves vertically to replace the Seaward moving surface water

thermohaline flow and surface flow: NOTES

the global pattern of deep circulation resembles a vast conveyor belt that carries surface water to the depths and back again. begin with the formation of north atlantic deep water north of iceland. this water mass flows south through the atlantic and then flows over (and mixes with) deep water formed near antarctica. the combined mass circumnavigated antarctica and moves north into the indian and pacific ocean basins. diffuse upwelling in all of the ocean returns some water to the surface. water in the conveyor warms and mixes upward to the north atlantic by surface circulation.

Ekman transport

the net motion of the water down to about 100 meters, after allowance for the summed effects of woman spiral. the direction of ekman transport is 90 degrees to the right of the wind direction in the northern hemisphere and 90 degrees to the left in the southern hemisphere

Upwelling

the upward movement of ocean water toward the surface as a result of diverging currents. brings cold, nutrient rich water towards the surface

What drives the vertical movement of ocean water? What is the general pattern of thermohaline circulation?

this slow circulation of water at great depths is driven by density differences rather than by wind energy. The whole ocean is involved in slow Thermohaline circulation, a process responsible for the large scale vertical movement of ocean water in the circulation of the global ocean as a whole

How is the Coriolis effect involved in equatorial upwelling?

through the coriolis effect is weak near the equator (and absent), water moving in the currents on either side of the equator is deflected slightly poleward and replaced by deeper water in which equatorial upwelling occurs westward

which way does wind typically blow over the tropical pacific? how does this flow change during el nino?

trade winds blow from the normally high pressure area over eastern pacific (near central and south america) to the normally stable low pressure area over western pacific (north of australia). these pressure areas change places at irregular intervals and air flow reverse direction

what are some effects of ocean currents?

transfer heat from tropical to polar regions, influence weather and climate, distribute nutrients and scatter organisms

Why do peruvian fisheries decine dramatically in el nino years?

upwelling within the nutrient laden Peru current is responsible for the great biological productivity of the ocean off the coast of Peru and Chile. Although upwelling may continue during an ENSO event, the source of the upwelled water is nutrient depleted water in the thickened surface layer approaching from the west. When the Peru current slows and it's upwelled water nutrients, fish and seabirds dependent on the abundant life it contains die or migrate elsewhere

wind-induced vertical circulation

vertical movement induced by wind-driven horizontal movement of water

Gulf Stream

warm ocean current that moves warm tropical water northward along eastern North America -largest of western boundary currents -moves at an avg. speed of 2 meters/sec (5 mi/hr) to a depth of 450 meters (1,500 ft) -move more than 160 km (100 mi) in a day -average width is 70 km (43 mi)

what is the relationship between surface currents and the climate downward?

warm water flows to higher latitudes, transfers heat to the air and cools, moves back to low latitudes, and absorbs heat again; then the cycle repeats. The greatest amount of heat transfer occurs at mid latitude's, where about 10 million billion calories and heat is transferred each second.

why does seawater in most surface currents flow around the periphery of ocean basins?

water flow in a gyre is dynamically balanced between downhill urge of the pressure gradient and uphill tendency of coriolis deflection

how does thermohaline circulation force the thermocline toward the oceans surface?

water sinks relatively rapidly in a small area where the ocean is very cold, but it rises much more gradually across a very large area in the warmer temperate and tropical zones. The continual diffuse upWelling of Deep water maintains the existence of the permanent thermocline found everywhere at low and mid latitudes

compare and contrast western and eastern boundary currents

western boundary currents tend to be hot, fast, and deep. eastern boundary currents tend to be shallow, cool, and slow.

name a western boundary current and an eastern boundary current

western: gulf stream - along the western boundary of the north atlantic eastern: california current - along the eastern boundary of the north pacific