Lecture 4- ENSO and upwelling

Question 1

Why is there a band of high productivity along the equator?

Answer 1

-region of upwelling

Question 2

How does the wind affect the current?

Answer 2

-surface current will be defelcted like wind but less, as we get deeper in the ocean the effect is smaller= then happens sort of a spiral as you go further down -this is because of the rotation of the Earth, the water on surface is deflected then then the layer underneath and so on and on and at about 100-150m the direction of the water is opposite to the wind but as you add up all the vectors then the net flow is 90 degrees to the right in the Northern Hemisphere and to the left in Southern Hemisphere

Question 3

What is the Sargasso sea and how does it arise?

Answer 3

-the Sargasso Sea is defined only by ocean currents. -the surface currents will trap water in the sargasso sea -as it’s deflected to the right -that is where all teh rubbish go( sea weed too) -created by the Gulf stream, Atlantic Current, Canary current and North Equatorial Current= they force this mass of water into an area= circulates, pushes it in there and it bulges upwards (Ekman transport forms dome)= creates a dome this water has to go somewhere and it pushes down(which sinks compressing the layers beneath forcing those layers to spread= thermocline is pushed deeper)= so the water bulges down as well= example of downwelling -the water bulging up creates a pressure gradient force that is balanced by the Coriolis effect (that is why it stays in one place) as the currents are circulating -there is seaweed and rubbish trapped in there

Question 4

What is the relationship between winds and surface currents? (N.H.)

Answer 4

-north hemisphere pic. -wind is pushing= the current is pushing it to the right but it is not exactly in the same direction -direction of the water is 90degrees to the right of the wind (that is the net flow is 90 degrees, at the point where the wind hits it’s only about 30-45degrees)

Question 5

How does the wind affect the current?

Answer 5

-surface current will be defelcted like wind but less, as we get deeper in the ocean the effect is smaller= then happens sort of a spiral as you go further down

Question 6

What is the Sargasso sea and how does it arise?

Answer 6

-the Sargasso Sea is defined only by ocean currents. -the surface currents will trap water in the sargasso sea -as it’s deflected to the right -that is where all teh rubbish go( sea weed too) -created by the Gulf stream, Atlantic Current, Canary current and North Equatorial Current= the force this mass of water into an area= circulates, pushes it in there and it bulges upwards= creates a dome this water has to go somewhere and it pushes down= so the water bulges down as well= example of downwelling -the water bulging up creates a pressure gradient force that is balanced by the Coriolis effect (that is why it stays in one place) as the currents are circulating -there is seaweed and rubbish trapped in there

Question 7

What is the Sargasso sea named after?

Answer 7

-the seaweed it traps= Sargassum seaweed

Question 8

How does the wind cause vertical movement of water?

Answer 8

-Water converges in a location, then has to dome up from the surface and/or (easier) move down into the ocean -locations where surface water spreads apart are regions of upwelling=where the water is spreading apart, the water from deeper down has to come to the surface, this will be colder water = upwelling regions are colder

Question 9

What is in the middle of each gyrus?

Answer 9

-downwelling region -low productivity, no nutrients (warm water), thermocline pushed deeper by the downwelling

Question 10

Why is there a band of upwelling along the equator?

Answer 10

-along the eqautor the wind is deflected to the left and right as it is right on the equator, forcing the water apart= upwelling, forces cold water up = high productivity -the southeast trade wind hits the equator and is deflected both to the left and right

Question 11

Where are the regions of the strongest upwelling?

Answer 11

-along the equator -also some coastal but those are more seasonal (e.g. east coast of Brazil in July, Middle East in July)

Question 12

What is the relationship between upwelling and productivity in the seas?

Answer 12

-correlation between upwelling and productivity -not perfect as more factors involved, especially the waters around land get nutrients from the land= more productive

Question 13

What sort of water has more nutrients?

Answer 13

-cold, deep water usually has lot of nutrients -in the equatorial Pacific regions siliceous oozes at depth

Question 14

How does coastal upwelling happen in the Northern Hemisphere?

Answer 14

-coast, wind from north (eckman transport= 90degrees to the right of the wind= water is being pulled away from the coast by the Eckman transport - as there is a coast, this cannot be replaced by water coming from other surface, has to be replaced by the water deeper down= upwelling -wind from south- would be downwelling as the Eckman drift is being pushed to the coast -that is when the coast is the western coastline

Question 15

How does coastal upwelling work in the Southern hemisphere?

Answer 15

-the other way around -southern wind in southern hemisphere, eastern coastline= will have upwelling as the Eckman is then away from coast -norhern wind is then downwelling as it will be deflected away from the coast

Question 16

What happens in regions of coastal upwelling?

Answer 16

-lot of chlorophyl as a result= more nutrient full water

Question 17

What are the two big regions of upwelling?

Answer 17

along the west coast of the US and west coast of S. America

Question 18

What effect does the ENSO (El Nino Southern Oscillation) have on sea temperatures?

Answer 18

-during El Nino waters in the eastern equatorial Pacific are much warmer than normal= higher air surface pressure -During La Nina, waters in this region are cooler than normal-lower air surface pressure

Question 19

What is ENSO?

Answer 19

-refers to variations in the temperature of the surface of the tropical eastern Pacific Ocean (El Niño and La Niña) and in air surface pressure in the tropical western Pacific -The two variations are coupled: the warm oceanic phase, El Niño, accompanies high air surface pressure in the western Pacific, while the cold phase, La Niña, accompanies low air surface pressure in the western Pacific -The extremes of this climate pattern’s oscillations cause extreme weather (floods, draught)

Question 20

Why is El Nino called that?

Answer 20

-means the boy in Spanish, refers to the Christ child, as El Nino occurs around christmas (usually)

Question 21

What is the definition of El Nino?

Answer 21

• defined by prolonged warming in the Pacific Ocean sea surface temperatures when compared with the average value. The accepted definition is a warming of at least 0.5°C (0.9°F) averaged over the east-central tropical Pacific Ocean. Typically, this anomaly happens at irregular intervals of two to seven years, and lasts nine months to two years.The average period length is five years -La Nina is the same just cooling

Question 22

What are the signs of El Nino?

Answer 22

1.Rise in surface pressure over the Indian Ocean, Indonesia, and Australia 2.Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean 3.Trade winds in the south Pacific weaken or head east 4.Warm air rises near Peru, causing rain in the northern Peruvian deserts 5.Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific. El Niño’s warm rush of nutrient-poor water heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current. When El Niño conditions last for many months, extensive ocean warming and the reduction in easterly trade winds limits upwelling of cold nutrient-rich deep water, and its economic impact to local fishing for an international market can be serious

Question 23

How does El Nino affect thermocline position?

Answer 23

normal conditions= thermocline shallow so upwelling easy -El Nino conditions= thermocline deep, much less upwelling

Question 24

What is the situation with upwelling during El Nina?

Answer 24

-upwelling stronger because there are strong east winds, lot of equatorial upwelling, shallow thermocline -winds are the determinants of this, the winds keep the warm water from getting close to the coast

Question 25

What is the situation with upwelling during El Nino?

Answer 25

-weak winds, no equatorial upwelling deep thermocline makes it even harder for upwelling to occur

Question 26

What is the effect of ENSO on Peruvian fisheries?

Answer 26

-the thermocline much deeper in El Nino conditions, the nutrients sink deeper and the fish follow or move elsewhere= fewer fish to catch

Question 27

How do you predict El Nino occurrence?

Answer 27

-SOI-SOuthern Oscillation Index- measures difference in atmospheric pressure between east and west pacific -la Nina= wet period -at present in between the two phases -2 to 7 years between the phases, very irregular

Question 28

What is the thermohaline circulation and why is it important?

Answer 28

-Warm water blown by the wind from the equatorial regions towards the poles and becoming saltier, cools as it goes towards the poles= then there it sinks due to the salt and water temp= more density -then driven on the ocean depth by the water that piles up behind it (at the poles) and this cold water travels towards the equator, upwells in the southern ocean.. -total time it takes for one unit of water to make it through this conveyor belt is 1000-1500 years -why is it important? 1.energy= in form of heat, moves it form the tropics to the poles= controlling the amount of sea ice, regulates the climate! Keeps areas warmer or cooler 2.nutrients- at great depths the water becomes enriched with many nutrients such as phosphates, nitrates, silicates and dissolved CO2, upwelling

Question 29

What did that idiot say in the lecture about thermohaline circulation?

Answer 29

-polar regions-lot of cooling at teh surface, surface water cool so it will freeze and the salt starts to sink (as teh freshwater locked up in teh ice) the salt tarvels to the equatorial regions and then goes up and returns to the polar region -dominated by the Gulf stream and Kuroshio -time required for all this to happen can be decades -possibly the reason for variation of climate in north atlantic -NORTH atlantic this is where this is the strongest this cycele

Question 30

Can thermohaline circulation be responsible for big changes in the climate?

Answer 30

• has been blamed for large differences in climate, quite big ones as well -when lot of ice melts, then get lot of freshwater= that is less dens than the salt water, so teh salt water is not produced there and the thermohaline circ. is stopped -this probably happened a few thousand years ago

Question 31

What about the oceans and climate change?

Answer 31

-Possible slowdown (or even breakdown) of the Atlantic thermohaline circulation –Mechanism is melting ice from Greenland putting layer of fresh water at surface, thus suppressing downwelling required in this high-­‐latitude region to keep this circulation going – Would interfere with Gulf Stream current –Would require a lot of melting, though - Future poleward shift of belts will move Antarctic circumpolar current further south – Change in nutrient distribution? -CO2 cycling through the oceans: biogeochemical processes

Question 32

What is ENSO caused by?

Answer 32

irregular variations in equatorial winds

Question 33

What does the Coriolis force do?

Answer 33

-deflects air and water movement to the right in the Northern Hemisphere, left in the Southern Hemisphere -responsible for direction of trade winds: instead of blowing from the south in the Southern Hemisphere, they blow from the southeast (instead of going straight they are deflected)