1. Ocean Currents

2. Why is Ocean Circulation Important?
Transport ~ 20% of latitudinal heat
Equator to poles
Transport nutrients and organisms
Influences weather and climate
Influences commerce
4 th century BC ,Pytheas of Massalia, a Greek ship captain, explored eastern Atlantic
Okeanos (Greek for “Great River”) because he found the ocean flowing south (Canary Current) and thought it was a river too wide to cross.

3. Non-rotating Earth Convection cell model
Non rotating model- when the density of air is lower than normal, the atms pressure drops--- low pressure zone
When the density of air is higher than normal, the pressure increases--- high pressure zone

4. Add rotation and add landmasses
unequal heating and cooling of the Earth

5. Physical properties of the atmosphere: Density
Warm, low density air rises
Cool, high density air sinks
Creates circular- moving loop of air (convection cell)

6. Physical properties of the atmosphere: Water vapor
Cool air cannot hold much water vapor, so is typically dry
Warm air can hold more water vapor, so is typically moist
Water vapor decreases the density of air

7. Physical properties of the atmosphere: Pressure
A column of cool, dense air causes high pressure at the surface, which will lead to sinking air
A column of warm, less dense air causes low pressure at the surface, which will lead to rising air

8. High pressure, dry climate
90o
High pressure, dry climate
60o
Low pressure, wet climate
High pressure, dry climate
30o
ITCZ intertropical convergence zone= doldrums
Low pressure, wet climate 0o
30o
60o
90o

9. The Coriolis effect The Coriolis effect
Is a result of Earth’s rotation
Causes moving objects to follow curved paths:
In Northern Hemisphere, curvature is to right
In Southern Hemisphere, curvature is to left
Changes with latitude:
No Coriolis effect at Equator
Maximum Coriolis effect at poles
Coriolis Effect: Coriolis effect is an inertial force described by the 19th-century French engineer-mathematician Gustave-Gaspard Coriolis in Coriolis showed that, if the ordinary Newtonian laws of motion of bodies are to be used in a rotating frame of reference, an inertial force--acting to the right of the direction of body motion for counterclockwise rotation of the reference frame or to the left for clockwise rotation--must be included in the equations of motion.
The effect of the Coriolis force is an apparent deflection of the path of an object that moves within a rotating coordinate system. The object does not actually deviate from its path, but it appears to do so because of the motion of the coordinate system.

10. The Coriolis effect on Earth
As Earth rotates, different latitudes travel at different speeds
The change in speed with latitude causes the Coriolis effect

11. North Pole Buffalo moves 783 mph Quito moves 1036 mph 15o N South Pole
equator
Quito
Buffalo
equator
79oW
Quito
South Pole

12. Idealized winds generated by pressure gradient and Coriolis Force.
Horse Latitudes Around 30°N we see a region of subsiding (sinking) air.  Sinking air is typically dry and free of substantial precipitation. Many of the major desert regions of the northern hemisphere are found near 30° latitude.  E.g., Sahara, Middle East, SW United States.
Doldrums Located near the equator, the doldrums are where the trade winds meet and where the pressure gradient decreases creating very little winds.  That's why sailors find it difficult to cross the equator and why weather systems in the one hemisphere rarely cross into the other hemisphere.  The doldrums are also called the intertropical convergence zone (ITCZ).
Idealized winds generated by pressure gradient and Coriolis Force. 
Actual wind patterns owing to land mass distribution..

13. Ocean Currents Surface Currents
The upper 400 meters of the ocean (10%).
Deep Water Currents
Thermal currents (90%)

14. Surface Currents
Forces
Solar Heating (temp, density)
Winds
Coriolis

15. Wind-driven surface currents

16. Wind-Driven and Density-Driven Currents
Wind-driven currents occur in the uppermost 100 m or less
Density differences causes by salinity and temperature produce very slow flows in deeper waters.

17. Sailors have know about ocean currents for centuries
Sailors have know that “rivers” flow in the seas since ancient times. They used them to shorten voyages, or were delayed by trying to stem them.
If navigators do not correct to deflection by currents, they may be far away from where they think they are and meet disaster.

18. Ben Franklin and the Gulf Stream

19. Matthew Fontaine Maury
The first systematic study of currents was done by Maury based on logbooks in the US Navy’s Depot of Charts and Instruments.
His charts and “Physical Geography of the Sea” assisted navigators worldwide.

20. Winds and surface water
Wind blowing over the ocean can move it due to frictional drag.
Waves create necessary roughness for wind to couple with water.
One “rule of thumb” holds that wind blowing for 12 hrs at 100 cm per sec will produce a 2 cm per sec current (about 2% of the wind speed)

21. Top-down drag Wind acts only on the surface water layer.
This layer will also drag the underlying water, but with less force.
Consequently, there is a diminution of speed downward.
Direction of movement is also influenced by the Coriolis Effect and Ekman Spiral

22. Ekman spiral
Ekman spiral describes the speed and direction of flow of surface waters at various depths
Factors:
Wind
Coriolis effect

23. Ekman transport
Ekman transport is the overall water movement due to Ekman spiral
Ideal transport is 90º from the wind
Transport direction depends on the hemisphere

24. Ekman Transport
Water flow in the Northern hemisphere- 90o to the right of the wind direction
Depth is important

25. Currents in the “Real” Ocean
Currents rarely behave exactly as predicted by these theoretical explanations due to factors such as
Depth—shallow water does not permit full development of the Ekman spiral
Density—deeper currents moving in different directions influence the overlying surface movement

26. Geostrophic Flow
Surface currents generally mirror average planetary atmospheric circulation patterns

27. Current Gyres Gyres are large circular-moving loops of water
Five main gyres (one in each ocean basin):
North Pacific
South Pacific
North Atlantic
South Atlantic
Indian
Generally 4 currents in each gyre
Centered about 30o north or south latitude

28. Geostrophic flow and western intensification
Geostrophic flow causes a hill to form in subtropical gyres
The center of the gyre is shifted to the west because of Earth’s rotation
Western boundary currents are intensified
Figure 7-7

29. Western intensification of subtropical gyres
The western boundary currents of all subtropical gyres are:
Fast
Narrow
Deep
Western boundary currents are also warm
Eastern boundary currents of subtropical gyres have opposite characteristics

30. Boundary Currents in the Northern Hemisphere
Type of Current General Features Speed Special Features
Western boundary Currents warm swift sharp boundary
Gulf Stream, Kuroshio narrow w/coastal circulation,
deep little coastal upwelling
Eastern Boundary Currents cold slow diffuse boundaries
California, Canary broad separating from coastal
shallow currents, coastal
upwelling common

31. Geostrophic flow- caused by Coriolis deflection and Ekman transport

32. Pacific Ocean surface currents

33. “Hills and Valleys” in the Ocean
A balance between the Ekman transport and Coriolis effect produces “hills” in the center of the gyres and “valleys” elsewhere
Gravitational effects from sea floor features also produce variations in sea surface topography

34. What do Nike shoes, rubber ducks, and hockey gloves have to do with currents?

35. Lost at Sea
It began Jan. 10, 1992, when a container ship, en route from Hong Kong to Tacoma, ran into a hurricane near the international dateline. The waves were so powerful that they broke some of the steel cables holding the huge containers, releasing 12 of them over the side. One that was lost held 28,800 Friendly Floatee bathtub toys, made in China for The First Years Inc. of Avon, Mass. They were red beavers, green frogs, blue turtles and, of course, yellow ducks.
We might expect that elaborate wrapping around the toys would have dragged them straight to the bottom. But they managed to escape five levels of packing, from the heavy steel containers (violent waves opened the door latches) to the plastic and paper boxes (water pulped the cardboard) before finally floating free.
It took 10 months for the first 10 Floatees to reach shore near Sitka, Alaska, having been swept along by the Subpolar Gyre, the ocean current in the Bering Sea. By then they had covered about 3,200 km and two oceanographers in Seattle, Ebbesmeyer and James Ingraham, were tracking their progress. (Ebbesmeyer and Ingraham were already studying 61,000 Nike running shoes that had fallen in the ocean two years earlier.)
A few months later another 20 toys reached Alaska. By August 1993, 400 more had been found along the shores of the Gulf of Alaska. Ingraham logged them in his OSCUR (Ocean Surface Currents Simulation), a program that calculates the course of wind and currents. Other toys, after following a circuitous route to Washington state, began arriving there in 1996.
The oceanographers predicted that some toys would drift north, get locked in Arctic ice, then eventually be released. In a few years they could move across the Pole to the Atlantic. Then where would they go? Eventually they arrived in Maine, Iceland, Newfoundland, the U.K. and Germany.
The last of the survivors continued to float, Ebbesmeyer says, “bleached and battered but still recognizable after 16 years.” Well, the manufacturer said they were designed to survive 52 dishwasher cycles.
Ebbesmeyer approaches this narrative with a cheerful buoyancy: “These high-seas drifters offer a new way of looking at the seas. Call it ‘flotsametrics.’ It’s led me to a world of beauty, order and peril I could not have imagined even after decades as a working oceanographer.” He loves his status as flotsam headquarters for data sent back by the world’s 1,000 or so dedicated beachcombers.
It’s a joyful story of discoveries he tells in his book. But he brings the reader back to Earth, and starts us thinking again about BP, when he describes the seabed slowly filling with bits of plastic that poison the fish and eventually the humans who eat them. Thousands of containers fall into the sea every year, creating an oceanic junkyard.
And the junk never disappears. These days beachcombers keep coming across flotsam antiques, like a plastic ball decorated with 40-year-old cartoon characters or Japanese glass buoys for fishing nets that haven’t been used in half a century. These relics are fascinating bits of the past, but when it comes to the fate of the oceans, perhaps beachcombers have stumbled upon the melancholy truth.
Read more:
January shipwrecked in the Pacific Ocean, off the coast of China
November half had drifted north to the Bering Sea and Alaska; the other half went south to Indonesia and Australia
1995 to spent five years in the Arctic ice floes, slowly working their way through the glaciers
the duckies bobbed over the place where the Titanic had sunk
they were predicted to begin washing up onshore in New England, but only one was spotted in Maine
a couple duckies and frogs were found on the beaches of Scotland and southwest England.

36. Duckie Progress
January shipwrecked in the Pacific Ocean, off the coast of China
November half had drifted north to the Bering Sea and Alaska; the other half went south to Indonesia and Australia
1995 to spent five years in the Arctic ice floes, slowly working their way through the glaciers the duckies bobbed over the place where the Titanic had sunk
they were predicted to begin washing up onshore in New England, but only one was spotted in Maine
a couple duckies and frogs were found on the beaches of Scotland and southwest England.

37. A team of volunteers and experts from the National Oceanic and Atmospheric Administration (NOAA) Hazardous Materials
Division has released drift cards off Barber’s Point as part of a two-year study of the movement of surface currents off the Hawaiian Islands.
The purpose of the study is to learn where floating pollutants might go
if released from the south shore of O‘ahu. Made out of light wood and covered with non-toxic paint, the
4x6-inch cards are designed to biodegrade within a few months. NOAA is asking the public to help by reporting the date and location of
the cards when they float ashore. Instructions and contact information
are printed on the cards. Watabayashi said the study will help determine where future research
should be directed. “The results will be used by academia, private industry, government, conservation groups, and others for
various purposes. City managers, for instance, might use the information
to aid in wastewater management decisions. Biologists might use it to characterize larval transport patterns which help identify habitat areas,” Watabayashi
said. The data also may be used to verify trajectory models and track derelict fishing gear.
The study is a collaborative
effort of the NOAA National Weather Service, NOAA Coral Reef Conservation Program, the Clean Island Council Spill Response
Cooperative, Chevron, Tesoro, and the U.S. Coast Guard.
Barber’s Point

38. North Pacific Subtropical Gyre
“Great Pacific Garbage Patch”
Estimate: 46,000 pieces of floating garbage/mi2.

39. North Pacific Subtropical Gyre
What are the “garbage patches”?
The “garbage patch,” as referred to in the media, is an area of marine debris concentration in the North Pacific Ocean.  The name “garbage patch” has led many to believe that this area is a large and continuous patch of easily visible marine debris items such as bottles and other litter—akin to a literal blanket of trash that should be visible with satellite or aerial photographs.  This is simply not true. While litter items can be found in this area, along with other debris such as derelict fishing nets, much of the debris mentioned in the media these days refers to small bits of floatable plastic debris.  These plastic pieces are quite small and not immediately evident to the naked eye.  For more information on this type of debris visit our page on plastics.
What’s in a name? - The name “garbage patch” is a misnomer. There is no island of trash forming in the middle of the ocean nor a blanket of trash that can be seen with satellite or aerial photographs. This is likely because much of the debris found here is small bits of floating plastic not easily seen from a boat.
(top)
Where are the “garbage patches”?
Eastern Pacific garbage patch - Concentrations of marine debris have been noted in an area midway between Hawai‘i and California within the North Pacific Subtropical High, an area between Hawaii and California. Due to limited marine debris samples collected in the Pacific it is still difficult to predict its exact content, size, and location.  However, marine debris has been quantified in higher concentrations in the calm center of this high-pressure zone compared to areas outside this zone. It should be noted that the North Pacific Subtropical High is not a stationary area, but one that moves and changes. This area is defined by the NOAA National Weather Service as "a semi-permanent, subtropical area of high pressure in the North Pacific Ocean. It is strongest in the Northern Hemispheric summer and is displaced towards the equator during the winter when the Aleutian Low becomes more dominant. Comparable systems are the Azores High and the Bermuda High." The High is not a stationary area, but one that rotates, moves, and changes.
Western Pacific garbage patch - There is a small "recirculation gyre" south of the Kuroshio current, off the coast of Japan that may concentrate floating marine debris; the so-called western garbage patch. The exact forces that cause this clockwise rotation are still being researched; however it may be caused by winds and ocean eddies (clockwise or counter-clockwise rotating waters). Research is ongoing by academia such as the University of Hawaii and Massachusetts Institute of Technology, to further understand the true nature of and forces behind these recirculation gyres.
Are the Pacific “garbage patches” the only areas where marine debris concentrates?
The “patches” are not the only open ocean areas where marine debris is concentrated. Another important area is the North Pacific is the Subtropical Convergence Zone (STCZ). This area, located north of the Hawaiian archipelago, has a high abundance of marine life, is a known area of marine debris concentration, and is one of the mechanisms for accumulation of debris in the Hawaiian Islands (Pichel et al., 2007).
Oceanographic features similar to the North Pacific Subtropical High and STCZ exist in other oceans of the world. Little research to date has been conducted on marine debris in these areas. Because of this no one can say for sure how large these areas are, especially since they move and change, sometimes daily, and no accurate estimate exists of how much debris is out there.
Regardless of the exact size, mass, and location of these areas of concentration, man-made litter and debris do not belong in our oceans or waterways.
See below and our page on Marine Debris Movement for more information.
North Pacific Subtropical Convergence Zone (STCZ)
The STCZ is located along the southern edge of an area known as the North Pacific Transition Zone (click here for detailed information on the Transition Zone).  NOAA has focused on the STCZ because it is an area of high productivity, pelagic species feeding and migration, and documented marine debris concentration – and one of the reasons for marine debris accumulation in Hawaii (see below) (Kubota, 1994; Pichel et al., 2007). This area does not have distinct boundaries and varies in location and intensity of convergence throughout the year. This zone moves seasonally between 30° and 42° N latitude (approximately 800 miles), extending farther south (28°N) during periods of El Niño (Donohue and Foley, 2007). It is less well defined and located more northerly during the summer months, when convergence tends to be weaker, and is sharper and located farther south during winter months, when convergence is stronger. North Pacific Subtropical Convergence Zone as a mechanism for accumulation of marine debris in Hawaii: The Hawaiian Archipelago, extending from the southernmost island of Hawaii 1,500 miles northwest to Kure Atoll, is among the longest and most remote island chains in the world. In Hawaii, marine debris continues to present a hazard to marine habitat, safe navigation, and wildlife, including the endangered Hawaiian monk seal (Monachus schauinslandi) and various species of sea turtles, seabirds, and whales. It is the location of this archipelago, between 18° and 28° N latitude, which makes it prone to the accumulation of marine debris.  One of the reasons marine debris accumulates in these islands is the movement of debris within the North Pacific Subtropical Convergence Zone (STCZ). The STCZ concentrates debris and moves seasonally between 30° and 42° N latitude, dipping farther south (28°N) during periods of El Niño. This accumulation due to the STCZ is evidenced by an increase in the quantity of floating marine debris deposited on beaches during El Niño periods (Morishige et al., 2007).  Additionally, a correlation has been noted between increased entanglements of endangered Hawaiian monk seals in marine debris and periods of El Niño (Donohue and Foley, 2007).
What is the difference between the "gyre" and the “garbage patches”? Or are they the same thing?
A gyre is a large-scale circular feature made up of ocean currents that spiral around a central point, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Worldwide, there are five major subtropical oceanic gyres: the North and South Pacific Subtropical Gyres, the North and South Atlantic Subtropical Gyres, and the Indian Ocean Subtropical Gyre. The North Pacific Subtropical Gyre is the one most notable because of its tendency to collect debris. It is made up of four large, clockwise-rotating currents – North Pacific, California, North Equatorial, and Kuroshio. It is very difficult to measure the exact size of a gyre because it is a fluid system, but the North Pacific Subtropical Gyre is roughly estimated to be approximately 7 to 9 million square miles—not a small area!  This, of course, is a ballpark estimate. This is equivalent to approximately three times the area of the continental United States (3 million square miles).
While a gyre may aggregate debris on a very large scale, debris patches, as seen by those sailing the North Pacific, are actually the result of various smaller-scale oceanographic features such as oceanic eddies and frontal meanders (think of meanders as the deviation from a straight line. As energy (wind/currents) hit the front there are undulations and "curvature" which are described as frontal meanders (movements to the north and south along the front)).
How big are the “garbage patches”?
The reported size and mass of these "patches" have differed from media article to article. Due to the limited sample size, as well as a tendency for observing ships to explore only areas thought to concentrate debris, there is really no accurate estimate on the size or mass of the “garbage patch” or any other concentrations of marine debris in the open ocean. Additionally, many oceanographic features do not have distinct boundaries or a permanent extent, and thus the amount of marine debris (both number and weight) in this zone would be very difficult to measure accurately. The “patchiness” of debris in this expansive area would make a statistically sound survey quite labor-intensive and likely expensive.
Again, regardless of the exact size, mass, and location of the “garbage patch,” manmade debris does not belong in our oceans and waterways.
What is the main debris type found in these patches?
Plastics. Likely because of the abundance of plastics and the fact that some common types of plastic float.
Can you see the “garbage patches” with satellite photos?
NO. Relative to the expanse of the North Pacific Ocean, sightings of large concentrations of debris, especially of large debris items are not very common. A majority of the debris observed in the “garbage patch” is small plastic pieces. Small debris pieces are difficult to see due to their size, and many of these pieces may be suspended below the surface of the water, which would make them even harder to see, even with the human eye. For these reasons, the debris, or “patch” of debris is not visible with existing satellite technology. 
Is debris cleanup feasible in the “garbage patches” and other areas of our oceans?
The answer to this is not as simple as you may think. It is certainly not cost-effective to skim the surface of the entire ocean. Even a cleanup focusing on “garbage patches” would be a tremendous challenge. Keep in mind these points:
Concentration areas move and change throughout the year
These areas are typically very large (see below)
The marine debris is not distributed evenly within these areas
Modes of transport and cleanup will likely require fuel of some sort
Most of the marine debris found in these areas is small bits of plastic
This all adds up to a bigger challenge than even sifting beach sand to remove bits of marine debris. In some areas where marine debris concentrates, so does marine life (as in the STCZ). This makes simple skimming the debris risky—more harm than good may be caused. Remember that much of our ocean life is in the microscopic size range. For example, straining ocean waters for plastics (e.g., microplastics) would capture the plankton that are the base of the marine food web and responsible for 50% of the photosynthesis on Earth… roughly equivalent to all land plants! 
Also, keep in mind that our oceans are immense areas! The Pacific Ocean is the largest ocean on the planet covering nearly 30% of Earth’s surface area (~96 million square miles, or ~15 times the size of the continental US). Surveying less than 1% of the North Pacific Ocean, a 3-degree swath between 30° and 35°N and 150° to 180°W, requires covering approximately 1 x 106 km2. If you traveled at 11 knots (20 km/hour), and surveyed during daylight hours (approximately 10 hours a day) the area within 100m off of each side of your ship (Mio et al., 1990), it would take 68 ships one year to cover that area! Now, add to that the fact that these areas of debris concentration have no distinct boundaries, move throughout the year, and are affected by seasons, climate, El Nino, etc.
Is there a “garbage patch” in the Atlantic Ocean? 
There has been research conducted and published on marine debris in the Atlantic, mainly on ingestion in Atlantic species of sea turtles and seabirds or on nearshore trawls for plastic particles. There have also been anecdotal reports and some studies of debris concentrations such as Sea Education Association's work in the western North Atlantic and Caribbean Sea (Law et al., 2010). Still, compared to the North Pacific Ocean, there is a paucity of published literature on marine debris in the high-seas Atlantic Ocean. 
135° to 155°W and 35° to 42°N

40. North Pacific Subtropical Gyre
Great Pacific Garbage Patch- Good Morning America

41. Eddy
A circular movement of water formed along the edge of a permanent current
In an average year, rings are formed
km in diameter
Speed 1 m/sec
Warm core ring
Rotates clockwise
Found on the landward side of the current
Cold core ring (cyclonic eddy)
Rotates counterclockwise
Forms on the ocean side of the current

42. Sargasso Sea

44. Upwelling and downwelling
Vertical movement of water ()
Upwelling = movement of deep water to surface
Hoists cold, nutrient-rich water to surface
Produces high productivities and abundant marine life
Downwelling = movement of surface water down
Moves warm, nutrient-depleted surface water down
Not associated with high productivities or abundant marine life

45. upwelling
downwelling

46. Langmuir Circulation

47. Satellite Observations
TOPEX/Poseidon, Jason 1, and other satellites have observed patterns of change over the past few years
Animation of seasonal and climatically-influence shifts available at

48. El Niño-Southern Oscillation (ENSO)
El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime
Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño
ENSO describes a combined oceanic-atmospheric disturbance

49. Oceanic and atmospheric phenomenon in the Pacific Ocean
El Niño
Oceanic and atmospheric phenomenon in the Pacific Ocean
Occurs during December
2 to 7 year cycle
Sea Surface Temperature
Atmospheric Winds
Upwelling

50. Normal conditions in the Pacific Ocean

51. El Niño conditions (ENSO warm phase)

52. La Niña conditions (ENSO cool phase; opposite of El Niño)

53. Non El Niño
El Niño
1997

54. Non El Niño
upwelling
El Niño
thermocline

55. El Niño events over the last 55 years
El Niño warmings (red) and La Niña coolings (blue) since Source: NOAA Climate Diagnostics Center

56. World Wide Effects of El Niño Weather patterns Marine Life
Economic resources
Floods
El Niño Sea-Level Rise Wreaks Havoc in California's San Francisco Bay Region (31-Jan-2000)
1998 California Floods (11-Mar-1998)
The Spring Runoff Pulse from the Sierra Nevada (14-Jan-1998)
Effects of El Niño on Streamflow, Lake Level, and Landslide Potential (16-Dec-1997)
Climate and Floods in the Southwestern U.S. (10-Jul-1997)
Real-time flows on rivers and streams
More USGS information on Floods
Landslides
Recent landslide events--News and Information (updates regularly)
Landslide publications and reports (14-Oct-2003)
USGS Circular 1244 (26-Sep-2003) "National Landslide Hazards Mitigation Strategy—A Framework for Loss Reduction"
USGS Landslide Hazards web site
More USGS information on Landslides
Information on Landslides during the El Niño:
Map Showing Locations of Damaging Landslides in Alameda County, California, Resulting From El Niño Rainstorms (10-Jan-2000)
El Niño and 1998 California Landslides (20-Mar-1998)
Geologic mapping and El Niño: Landslide and debris-flow susceptibility maps, including southern California, Mojave Desert, and San Francisco Bay Area (02-Feb-1998)
Landslide Recognition and Safety Guidelines (29-Jan-1998)
USGS Producing Landslide Hazard Maps for Emergency Services in San Francisco Bay Area (16-Dec-1997)
Potential San Francisco Bay Landslides During El Niño (16-Dec-1997)
El Niño and the National Landslide Hazard Outlook for (16-Dec-1997)
Coastal hazards
El Niño Sea-Level Rise Wreaks Havoc (31-Jan-2000) in California's San Francisco Bay Region
Coastal Erosion Along the U.S. West Coast During El Niño (12-August-99)
Coastal Erosion From El Niño Winter Storms (31-Aug-1998) with before and after air photos from Southern Washington, Northern Oregon, Central California, and Southern California
El Niño Coastal Erosion, San Mateo County, California (6-May-1998)
El Niño Coastal Monitoring Program (31-Mar-1998) with before and after photos of Santa Cruz County, California beach erosion.
Hydroclimatology of San Francisco Bay Freshwater Inflows and Salinity, with weather and salinity movies (14-Jan-1998)
El Niño Effects on Sea-Level Near San Francisco Bay (16-Dec-1997)
Coastal Impacts of an El Niño Season (3-Nov-1997)
More USGS information on Coastal hazards
Climate
Long-term climate variation in the Mojave Desert (15-Jan-1998)
Effects of El Niño on Streamflow, Lake Level, and Landslide Potential (revised 16-Dec-1997)
El Nino Animation

57. Effects of severe El Niños

58. Surface and Deep-Sea Current Interactions
Unifying concept: “Global Ocean Conveyor Belt”

59. Heat Transport by Currents
Surface currents play significant roles in transport heat energy from equatorial waters towards the poles
May serve as “heat sources” to cooler overlying air, “heat sinks” from warmer
Evaporation and condensation participate in latent heat exchanges

60. Matter Transport and Surface Currents
Currents also involved with gas exchanges, especially O2 and CO2
Nutrient exchanges important within surface waters (including outflow from continents) and deeper waters (upwelling and downwelling)
Pollution dispersal
Impact on fisheries and other resources

61. Thermohaline Circulation
Global ocean circulation that is driven by differences in the density of the sea water which is controlled by temperature and salinity.

62. Thermohaline Circulation
                                                                                                                                                        
The global ocean circulation system, often called the Ocean Conveyor, transports heat throughout the planet. White sections represent warm surface currents. Purple sections represent deep cold currents. (Illustration by Jayne Doucette, WHOI Graphic Services).
White sections represent warm surface currents.
Purple sections represent deep cold currents

63. Thermohaline Circulation
Wind and the rotation of the Earth are important in determining the flow of surface currents and local areas of upwelling and downwelling, but the true driving force of deep water movement is thermohaline circulation. 
Sometimes called the ocean conveyer belt, this mechanism is responsible for bringing the oxygen that sustains life to the deepest reaches of the sea, and in moving warmer waters from the tropics towards the poles. Movement of this conveyer belt depends on sinking of cold water in certain polar regions, thereby triggering the global thermohaline circulation. 

64. What effect does global warming play in thermohaline circulation?
1.What is the Thermohaline Circulation
The thermohaline circulation is a global ocean circulation. It is driven by differences in the density of the sea water which is controlled by temperature (thermal) and salinity (haline). In the North Atlantic it transports warm and salty water to the North. There the water is cooled and sinks into the deep ocean. This newly formed deep water is subsequently exported southward. This slow (~0.1 m/s), but giant circulation has a flow equal to about 100 Amazon Rivers. Together with the Gulfstream it contributes (2/3 and 1/3) to the comparatively warm sea surface temperature along the coast of western Europe and to the relative mild European winters. Once the water are in the deep, they remain from the atmosphere for up to 1000 years. Broecker, W., Chaotic Climate, Scientific American, November, 62-68, Has the thermohaline circulation changed in the past ?
There is evidence for rapid climate change events lasting 1000 years or so during the last glacial. It is believed that the North European winter temperature was lowered by as much as 10 degrees during such climatic transitions. The last such cold event is known as the Younger Dryas. It occurred during the transition from the last glacial into the present holocene (~11000 years ago). The idea is that the melt water of dying continental ice masses was released into the North Atlantic where it substantially reduced the density of the ocean surface water and thereby shut down the deep water formation. This scenario is supported by both paleoclimatological evidence as well as model studies. Rahmstorf, S., Bifurcation of the Atlantic thermohaline circulation in response to changes in the hydrological cycle, Nature, 378, , Stocker, T. F., and D. G. Wright, Rapid transitions of the ocean's deep circulation induced by changes in surface water fluxes , Nature, 351, , 1991, (Abstract). 3.Can the thermohaline circulation change due to global warming ?
Whether or not the thermohaline circulation will be affected by human induced global warming is strongly dependent on the future temperature distribution and fresh water supply over the North Atlantic region. Most models predict an increase in precipitation in high latitudes and a region of minimum warming over the North Atlantic using a scenario of doubling CO2 within the next 70 years. Most models also predict a decrease in the strength of the thermohaline circulation. However, the exact reduction varies from 30% to only 10%. The details and the long-term effects (more then 100 years) of these changes have so far only been explored by very few studies. One of these studies was done at the University of Bern using a zonally averaged climate model (Stocker and Schmittner, 1997). It shows that the thermohaline circulation not only reduces, but may shut-down completely under “strong“ global warming with a fourfold increase of CO2 concentration within the next 140 years. This illustrates that global warming can affect the climate system in a very non-linear fashion.

65. Thermohaline Circulation1 2 3 4
CO2 fossil fuel combustion
Atmospheric and ocean temp
Subtropical evaporation
High latitude precipitation & runoff
North Atlantic
regional cooling
Step 1: Higher carbon dioxide (CO2) emissions increase atmospheric CO2 concentrations.
The burning of fossil fuels (coal, oil and natural gas) and land-use changes have already created a large increase in the concentration of CO2 in the atmosphere. CO2 concentrations have increased by about 35 per cent since the start of the industrial revolution to the current level of 379 parts per million by volume (ppmv) (CDIAC 2004). Concentrations are projected to rise much more if emissions are not sharply reduced (IPCC 2001).
Step 2: This increases global temperatures.
CO2 and other greenhouse gases in the Earth's atmosphere cause an increase in the air temperature near the surface of the Earth. Global average surface air temperature has already risen by 0.6° C over the past 100 years (IPCC 2001). It is projected to rise by another 1.4 to 5.8° C over the next 100 years, according to the range of climate models evaluated by the Intergovernmental Panel on Climate Change (IPCC 2001).
Step 3: Ocean evaporation and surface salinity increase in subtropical latitudes.
The atmospheric warming increases the evaporation of water from the surface of the subtropical oceans, increasing their salinity. A 5-10 per cent increase in evaporation has already been observed in the subtropical Atlantic Ocean over the past 40 years, equivalent to 5-10 cm of surface ocean water each year (Curry and others 1997). Figure 5 shows the resulting increase in surface water salinity in the subtropical Atlantic as calculated and interpolated from direct measurements of salinity. Similar trends in salinity have been observed in the Pacific and Indian Oceans (Wong and others 1999).
Step 4: Precipitation, runoff and glacial melt increase in northern high latitudes, adding excess freshwater to the ocean surface layers in these regions.
The increased moisture evaporated from the subtropical oceans condenses in the atmosphere at higher latitudes, leading to increased precipitation. There has in fact been an increase in precipitation of 6-12 per cent in the northern high latitudes over the last century (IPCC 2001), resulting in increased freshwater runoff from rivers in Russia. The most dramatic increases have occurred in recent decades (Peterson and others 2002) (Figure 6). Increased melting from the Greenland Ice Sheet and other arctic glaciers has also added more freshwater to the Arctic Ocean over the past 40 years (Dyurgerov and Carter 2004). By comparison, the construction of dams and the melting of permafrost have had minor impacts on the long-term pattern of change in river discharge (McClelland and others 2004).
Deep water formation & thermohaline circulation
Nordic seas salinity & deep convection
Potential feedback
of increased
tropical salinity 6 5
Global climate
interconnections

66. Inquiry What is a convection cell?
Which direction do currents get deflected in the Southern Hemisphere?
What depth should the water be for an Ekman spiral to occur?
How are surface currents created?
What is a gyre?
How can an El Nino impact upwelling?
Coriolis Effect is strongest near the _____?