upwelling
what happens as distance from equator increase
progressively more mature communities
Antarctic Divergence
1. 2 major wind-driven currents: a. East Wind Drift travels anti-clockwise around Antarctica b. West Wind Drift travels clockwise around Antarctica 2. both currents diverted to left due to Coriolis Force (as in Southern Hemisphere) 3. results in divergence of the currents and upwelling of nutrient-rich water
productivity of southern ocean: summer
no light limitation and huge peak in production
where are major upwelling regions
1. some coastal areas 2. the Equator and 3. the Southern Ocean
causes of equatorial upwelling
1. westward current called South Equatorial Current 2. Coriolis Force causes current to be deflected to right in northern hemisphere and to left in southern hemisphere 3. divergence of water occurs on Equator, with replacement of water by upwelling
why does large scale upwelling occur
1. wind- driven currents 2. the Coriolis Force 3. the replacement of displaced water by nutrient-rich deep water
the antarctic divergence
2 major wind-driven currents: East Wind Drift travels anti-clockwise around Antarctica West Wind Drift travels clockwise around Antarctica both currents diverted to left due to Coriolis Force (as in Southern Hemisphere) results in divergence of the currents and upwelling of nutrient-rich water
how many areas of coastal upwelling are there
5 major regions (with 4 on western coasts) but lots of other smaller regions do exist haha
coastal upwelling
5 major regions, w ith 4 on w estern coasts numerous, smaller coastal upwelling regions also exist
what are biological consequences of coastal upwelling
Very high production e.g. annual production of: 26 m illion tons of sardines in West African system s >12 m illion tons of anchovies off Peru >5 million tons of anchovy & hake off California total of more than half of world's fish catch from coastal upwelling regions!
upwelling
any upwards movement of water most significant upwelling events are generated by wind-induced stress at the sea surface often carries nutrient-laden water to surface where it enhances primary production
how does upwelling enhance primary production
by carrying nutrient loaded water to surface
what is the displaced water replaced by
cold nutrient rich water at the coast
what happens then
current travels at right angels to the coast and then moves offshore
where is the highest productivity
east
what are biological consequences of equatorial upwelling
high primary production close to Equator progressively more mature communities as distance from Equator increases highest productivity in east
productivity of southern ocean: winter
ice causes light limitation and low production
productivity in southern ocean
in winter, ice causes light limitation and low production in summer, no light limitation and huge peak in production 100 x more productive than Arctic waters - why?
summary of upwelling
large-scale upwelling occurs as a result of wind- driven currents, the Coriolis Force and the replacement of displaced water by nutrient-rich deep water major upwelling regions include some coastal areas, the Equator and the Southern Ocean all of these regions are characterised by high levels of primary production and are among the most productive regions in the oceans
Pulses of Upwelled Water across Continental She
low production during cold, upwelling periods high production during warm, stratified periods
Case example: Canary Current System, Northwest Africa
strong wind increases rate of equatorward current (>30 cm s-1) generates a 2-layer circulation system with: a) off-shore movement at surface b) on-shore movement at depth circulation causes upwelling of cold, nutrient-rich water close to shore and its subsequent movement away from coast
east wind drift
travels anti-clockwise around Antarctica
west wind drift
travels clockwise around Antarctica
what direction does current go in southern hemisphere
turns left
what direction does current go in northern hemisphere
turns right
what is solution with coastal upwelling
upwelling followed by periods of calm & stratification promote primary production
what is problem with coastal upwelling
upwelling provides nutrients, especially nitrate & ammonia, but mixing carries phytoplankton out of euphotic zone
How does upwelling stimulate production?
upwelling provides nutrients, especially nitrate & ammonia, but mixing carries phytoplankton out of euphotic zone Solution upwelling followed by periods of calm & stratification promote primary production NB: gentler, constant Peruvian System is an exception
what causes equatorial upwelling
westward current called the South Equatorial Current (5oS to 5oN) Coriolis Force causes current to be deflected to right in northern hemisphere and to left in southern hemisphere divergence of water occurs on Equator, with replacement of water by upwelling
causes of coastal upwelling
wind drives surface current in same direction
what causes coastal upwelling
wind drives surface current in same direction current turns right in northern hemisphere/left in southern hemisphere due to Coriolis Force current eventually travels at right angles to coast and moves offshore displaced water replaced by cold, nutrient-rich water at coast (i.e. coastal upwelling)
what are most significant upwelling events caused by
wind induced stress at sea surface