EVPP 110
Instructor: Dr. Largen

Oceans

• Global Environments
• distribution of biomes results from interaction of physical geography and two key physical factors
• solar radiation
• global circulation patterns
• oceanic
• atmospheric

• Global Environments
• interdependent relationship between the ocean and the atmosphere
• has profound ramifications over the earth
• because the same physical processes determine the operation of both systems
• changes that occur in the ocean lead to long-term shifts in the general circulation of the atmosphere
• observing key features and processes in the oceans can lead to the prediction of atmospheric phenomena

• Global Environments
• the atmosphere and ocean together act like a global heat engine
• continually redistributing heat that reaches the earth from the sun

• Solar radiation
• warms the earth’s surface and drives the circulation of the oceans and the atmosphere
• is emitted by the sun, in the form of radiant energy, at same average rate in all directions
• is received on the earth’s surface in varying amounts, depending on
• distance between earth’s surface and sun
• duration of daylight (exposure to sun’s rays)
• varies with season and latitude
• angle at which sun’s rays impinge on surface

• Solar radiation
• variations in the amount of solar radiation reaching the earth’s surface
• leads to uneven heating of the atmosphere and the oceans
• which in turn drives the interrelated patterns of circulation of the oceans and the atmosphere

• The Oceans
• The Atmosphere
• composition and structure
• water vapor and its effects
• circulation
• special focus topics
• air quality
• acid deposition
• Global climate change

• The Oceans
• circulation
• El Nino
• tides

• Historical perspective
• most early knowledge of ocean currents came from ship captains and explorers
• Pliny (~AD 50) described strong currents flowing into Mediterranean thru Strait of Gibraltar
• Arabs (around 9th century) were aware of reversing currents of Arabian Sea & timed trading voyages to Africa to take advantage of the currents
• Benjamin Franklin (in 18th century) developed crude chart of the Gulf Stream current

• Historical perspective
• Matthew Fontaine Maury
• a lieutenant in US Navy
• first person to use large amounts of ocean data in a systematic study of surface currents
• from 1841 - 1853 he worked to compile data accumulated in thousands of old log books
• publishing the first pilot charts and sailing directions for all the world oceans

• Historical perspective
• Matthew Fontaine Maury
• additionally, he
• laid the foundation for the establishment of the US Weather Bureau
• did most of the work in determining the location for the first transatlantic cable
• was instrumental in the establishment of the US Naval Academy

• Circulation patterns of oceans
• two types of circulation exist in the oceans
• surface circulation
• horizontal movement of water
• driven by force of winds at water surface
• thermohaline circulation
• vertical movement of water
• driven by density differences resulting from variations in water
• temperature
• salinity

• Circulation patterns of oceans
• are affected by four main factors
• wind acting on the ocean surface
• wind itself is produced by uneven heating resulting from solar radiation
• containment of the oceans within boundaries set by land masses
• due to interference from land masses, no currents run all the way around the world except in the Antarctic region
• earth’s rotation
• water density

• mechanics of ocean circulation patterns
• the effect of wind
• blowing over the surface of the ocean exerts a push on the water
• due to the friction forces that are stronger in the water than in the air
• the speed of the water is only a fraction of that of the wind
• response time of ocean currents to changes in atmospheric circulation is many months

• mechanics of ocean circulation patterns
• the effect of wind
• if earth was covered entirely with water,
• the winds would form well-defined belts and ocean currents would also move in distinct belts under the influence of prevailing winds

• mechanics of ocean circulation patterns
• the effect of continents
• the presence of landmasses, continents, modifies the idealized oceanic circulation patters
• since an ocean current cannot easily leave its basin
• generalized circulation patterns in ocean basins tend to consist of closed loops called gyres

• mechanics of ocean circulation patterns
• the effect of the earth’s rotation
• due to the rotation of the earth, objects moving in a straight line along its surface are deflected, as if a sidewise force were acting on it
• this is called the Coriolis effect
• which always acts sidewise on objects moving horizontally on the earth

• mechanics of ocean circulation patterns
• the effect of the earth’s rotation
• because the earth spins to the east, the Coriolis effect causes a deflection
• to the right of the direction of motion in the Northern Hemisphere
• to the left of the direction of motion in the Southern Hemisphere

• mechanics of ocean circulation patterns
• the effect water density
• density increases with
• increases in salinity
• increases in pressure
• decreases in temperature
• thermohaline circulation

• mechanics of ocean circulation patterns
• the effect water density
• thermohaline circulation
• primarily a convection flow
• cold, dense waters from polar latitudes sink and move towards the tropics
• replaced by warmer surface waters that originated in the tropics

• Ocean surface circulation is dominated by two huge surface gyres which
• move around the subtropical zones of high pressure between 30° N & 30° S latitudes
• Northern Hemisphere gyre
• circulates in clockwise direction
• prevailing winds blow W to E due to earth’s eastward rotation are deflected to the right
• Southern Hemisphere gyre

• Ocean surface circulation is dominated by two huge surface gyres which
• move around the subtropical zones of high pressure between 30° N & 30° S latitudes
• Northern Hemisphere gyre
• Southern Hemisphere gyre
• circulates in counterclockwise direction
• prevailing winds blow west to east due to earth’s eastward rotation are deflected to the left

• Principle oceanic surface currents
• have tendency to
• form loops of circulation marked by
• strong currents on the perimeters
• relatively little movement internally
• move warm water poleward and cold water toward tropics
• thus helping to equalize distribution of heat

• Principle oceanic surface currents
• western boundary currents
• eastern boundary currents
• equatorial currents
• polar circulation

• Principle oceanic surface currents
• western boundary currents
• general northward current of warm equatorial water flowing at the west edge of each ocean basin
• tend to be narrow, swift, deep flows with well-defined boundaries

• Principle oceanic surface currents
• western boundary currents
• strong in Northern Hemisphere
• the Gulf Stream in the Atlantic Ocean
• the Kuroshio or Japanese Current in the Pacific Ocean
• weaker in the Southern Hemisphere
• the Brazil Current in the Atlantic Ocean
• the West Australia Current in the Pacific Ocean

• Principle oceanic surface currents
• western boundary currents, examples
• the Gulf Stream
• warm northward current in north Atlantic Ocean
• runs from Cape Hatteras to near the Grand Banks of Newfoundland
• reaches Europe near the southern British Isles
• as a result, western Europe is warmer and more temperate than eastern North American at similar latitudes

• Principle oceanic surface currents
• western boundary currents, examples
• the Kuroshio Current
• warm northward current in northen Pacific Ocean
• runs along Japan northeast towards Alaska
• as a result, Alaska has a more temperate climate than would be expected based on its latitude

• Principle oceanic surface currents
• eastern boundary currents
• occur along eastern sides of oceans
• tends to be broad, weak, shallow flows with poorly-defined boundaries
• the force of the wind and the Coriolis effect combine at western continental seacoast and cause warm surface water to move away from the coast and out to sea
• deep cold water then moves upward to replace the water that blows seaward
• producing a process called upwelling

• Principle oceanic surface currents
• eastern boundary currents, examples
• in Northern Hemisphere
• the Canary Current in the Atlantic Ocean
• the California Current in the Pacific Ocean
• in the Southern Hemisphere
• the Benguela Current in the Atlantic Ocean
• the Peru (Humboldt) Current in the Pacific Ocean

• Principle oceanic surface currents
• eastern boundary currents
• significance of upwelling
• brings deep, cool, nutrient-rich water to the surface
• water is rich in nutrients because of the the numerous creatures that die in surface waters and then sink
• the Peru (Humboldt) Current is an example

• Principle oceanic surface currents
• eastern boundary currents
• significance of upwelling
• the Peru (Humboldt) Current
• flows northward along western coast of South America
• a large amount of upwelling is normally associated with this current

• Principle oceanic surface currents
• eastern boundary currents
• significance of upwelling
• the Peru (Humboldt) Current
• upwelling provides nutrients for enough phytoplankton to support the largest anchovy population in the world
• the anchovy fishery is one of the largest industries in Peruvian economy

• Principle oceanic currents
• equatorial currents
• are confined mostly to the surface
• warm, well-mixed surface layer and a sharp thermocline that separates warm surface water from cold water below
• except at the equator where mixing across the thermocline occurs

• Principle oceanic currents
• equatorial currents
• North Equatorial Current
• westward-flowing
• southern-most portion of Northern Hemisphere gyre
• Equatorial Countercurrent
• eastward-flowing
• separates the North and South Equatorial Currents
• South Equatorial Current
• westward-flowing
• northern-most portion of the Southern Hemisphere gyre

• Principle oceanic currents
• polar circulation
• circulation N & S polar regions is different
• north polar region
• Arctic Ocean is covered by pack ice
• circulation is characterized by sluggish counterclockwise drift
• deep cold water from the Arctic Ocean is kept from mixing freely with that in the Atlantic and Pacific Oceans by shallow sills between continental blocks

• Principle oceanic currents
• polar circulation
• south polar region
• water flows freely between the Atlantic and Pacific Oceans
• Antarctic Circumpolar Current
• largest current in the world
• circles Antarctica
• extends all the way to the bottom
• flows eastward

• El Nino
• name originally coined in late 1800s by Peruvian fishermen as the name for a seasonal shift in the current pattern off the coast of Ecuador and Peru
• that occurred around Chrsitmas time
• thus El Nino (Spanish for "Christ child)
• would replace the cold, nutrient rich water in which they usually fished with less productive, warm southward flowing water
• slightly reducing the fish population and giving the fishermen some time off

• El Nino
• now the name refers to a catastrophic version of that original annual event
• part of a phenomenon known as El Nino-Southern Oscillation (ENSO)
• a continual but irregular cycle of shifts in ocean and atmospheric conditions that affect the globe

• El Nino-Southern Oscillation (ENSO)
• normally, the Pacific Ocean is fanned by constantly blowing east-to-west trade winds
• which push away from the coast the warm surface water along western coasts of Peru, Chile, Ecuador
• allowing cold, nutrient-rich water from depths to well up (upwelling) into the place of the warm water that has been pushed away

• El Nino-Southern Oscillation (ENSO)
• warm water that was pushed away from the coast "piles" up in western portion f the Pacific Ocean
• resulting in the waters of the western Pacific Ocean being several degrees warmer and about one meter higher than the waters in the eastern portion of the Pacific

• El Nino-Southern Oscillation (ENSO)
• if east-to-west trade winds slacken briefly
• warm water begins to slosh back across the Pacific Ocean from west to east
• ocean & atmosphere can conspire to ensure that it keeps happening
• the warmer the eastern ocean gets, the warmer and lighter the air above it becomes

• El Nino-Southern Oscillation (ENSO)
• the warmer the eastern ocean gets, the warmer and lighter the air above it becomes
• and, hence, the more similar to the air on the western side (of the ocean)
• reducing difference in pressure across ocean
• since a pressure difference is what makes the wind blow, a lack thereof causes the easterly trade winds to weaken
• the continued reduction in winds allows warm water to continue its eastward advance

• El Nino-Southern Oscillation (ENSO)
• end result is to shift the weather systems of the western Pacific Ocean about 6000km eastward
• tropical rainstorms that usually drench Indonesia and the Philippines are caused when seawater abutting these islands cause the air above it to rise, cool and condense into clouds
• when the warm water moves east, so do the clouds, leaving previously rainy Indonesia and the Philippines in drought

• El Nino-Southern Oscillation (ENSO)
• ecological effects during an El Nino
• in the waters of Peru and northern Chile
• commercial fish stocks virtually disappear
• the commercially valuable anchovy fisheries of Peru were essentially destroyed by the 1972 El Nino
• plankton dropped to 1/20th of their normal abundance

• El Nino-Southern Oscillation (ENSO)
• ecological effects during an El Nino
• weather effects are propagated across world’s weather systems
• violent winter storms, accompanied by flooding, lash the coast of California
• colder and wetter winters occur in Florida and along Gulf Coast
• American midwest and the Mid-east experience heavier than usual rains

• El Nino-Southern Oscillation (ENSO)
• although effects of El Nino are clear, what triggers them is not
• models suggest that the type of climate change that triggers El Nino is chaotic
• wind and ocean currents return again and again to the same condition but never in a regular pattern
• small nudges can send them off in many different directions

• El Nino-Southern Oscillation (ENSO)
• in the news, Washington Post, "Science Notebook, El Nino: The Sequel", 1/14/02
• El Nino may appear this spring after a 5 year absence
• prediction based on detection of warming over tropical Pacific Ocean
• its return would likely cause
• drier-than-normal fall in Pacific Northwest
• wetter-than-normal winter in Gulf Coast and maybe California
• warmer-than-normal in Great Plains

• El Nino-Southern Oscillation (ENSO)
• noteworthy El Ninos
• 1982 - 1983: 2100 deaths, $13 billion in damages
• Austraila, already in midst of worst drought in a century, suffered losses that cost billions
• wildfires, catastrophic agricultural & livestock losses
• drought in sub-Saharan Africa
• countries that were normally food-exporting had to turn to international community for help
• southern Ecuador and northern Peru
• app. 100 inches of rain fell in 6 month period

• El Nino-Southern Oscillation (ENSO)
• noteworthy El Ninos
• 1997 - 1998:
• California lashed by storms for months
• 1400 homes damaged or destroyed
• Florida ravaged by series of tornadoes, killing 39
• Panama Canal officials had to restrict shipping due to low water levels
• Indonesia suffered forest and peat fires producing smoke that affected southeast Asia

• Tides
• another type of movement of ocean waters
• normally raise and lower the water level of a coast, and as a result, are significant
• geomorphically
• changes in water level expose different parts of coast to erosive action of waves
• biologically
• organisms living in areas subject to changes in water level must have adaptations to deal with alternating periods of submersion and exposure

• Tides
• definition
• a periodic rise and fall of the Earth’s oceans
• caused by
• gravitational effects of the sun & moon on oceans
• produce "bulges" of water
• magnitude of these "bulges" is determined by the varying and complex interactions resulting from the relative positions of the earth, moon and sun

• Tides
• role of the sun and moon
• sun’s gravitational pull on earth is less than 1/2 that of the moon, its significance on tides
• is secondary to influence of moon
• is strongest sun aligns with moon and during equinoxes
• moon’s gravitational pull on earth is ~ 2X that of the sun
• it is primarily responsible for tides
• because moon’s distance from earth varies, so does its attractive forces

• Tides
• characteristics
• frequency
• some areas have 2 high tides each day, some have only 1
• average interval between successive high tides is app. 12.5 hours
• time of day
• changes each day
• height
• typically 1 - 2 meters above average sea level
• varies with the relative positions of the earth, moon & sun
• influenced by local coastal topography