Upwelling water - 16 Flashcards
What are the three main settings where upwelling occurs?
- Polar upwelling
- Equitorial upwelling
- Coastal upwelling
Where and why does polar upwelling occur?
Occurs in the Southern Ocean due to the interaction of density driven thermohaline currents and wind driven surface currents south of the Antarctic Convergence (50ºS)
Why does equatorial upwelling occur?
Ekman transport driven divergence in surface currents
Why does coastal upwelling occur?
Interaction of coastal surface wind circulation with Ekman transport
What is the Antarctic Circumpolar Current?
The largest ocean current, sometimes called the West Wind Drift, that flows clockwise around Antarctica. It is circumpolar due to lack of landmasses which keeps warm water away from the Antarctic continent
When is Antarctic sea ice at its maximum and minimum?
Minimum in February-March and Maximum August-September
What blooms are associated with Antarctic sea ice retreat?
- Ice algae dominates first phase
- Strong diatom bloom follows
- Phytoplankton bloom occurs near the Antarctic convergence
What dominates phytoplankton blooms in the open ocean compared to closer to the continent?
Dominated by diatoms and grazed by copepods in open ocean … grazed by krill closer to the continent
What is the average rate of upwelling?
5-10 metres a day (changed due to strength and distance of wind however)
What nutrients are deep waters rich in?
Nitrate, Phosphate and Silicic acid
What % of global marine productivity do phytoplankton contribute?
50%
What is the ocean food?
Phytoplankton … Zooplankton … Predatory zooplankton … filter feeders … predatory fish … marine birds and mammals
What are the 5 main coastal currents associated with upwelling?
- Canary current (NW Africa)
- Benguela current (S Africa)
- California current (California and Oregon)
- Humboldt current (Peru and Chile)
- Somali current (Somalia and Oman)
How much higher are sea surface temperatures (SST) in the western pacific dural normal conditions?
8ºC warmer
How much greater is the average sea level in the western pacific during normal conditions?
50cm
What effect does piling up of warm water in the western pacific have on ocean layers?
Creates a 150 metre deep warm layer in the west that pushes the thermocline down while it rises in the east to around only 30 metres deep
What is air pressure like during a positive ENSO phase?
Air pressure at Darwin, Australia is greater than air pressure at Tahiti
Why is upwelling decreased during El Niño?
Water piles up off South America, pushing the thermocline deeper and preventing upwelling
What are sea surface temperatures like during a positive ENSO phase?
Waters in the eastern pacific are warmer than normal, creating a shift in prevailing rainfall
What are conditions like during the cool phase of El Niño?
Lower than normal sea surface temperatures in the eastern pacific, causing increased upwelling and a shift farther to the west of prevailing rain patterns
How much do sea surface temperatures change during ENSO?
Plus or minus 3ºC
How much greater is sea level during La Niña?
60cm higher when winds are at full strength
What happens to thermocline during La Niña?
Thermocline tilts are nearly reaches the surface in the eastern pacific
Where is the ITCZ best established?
5º North
Why is the southern ITCZ weaker?
Widespread low sea surface temperature off South America due to the Humboldt current
