BIO3021 Lecture Notes - Lecture 10: Walker Circulation, Primary Production, Upwelling
25 May 2018
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Lecture 10 – Primary Production in Oceans: carbon pools and fluxes; climate
change and primary productions
• Net increase of CO2 in atmosphere → effects land use change
• Lots of carbon locked up in deep ocean
• Largest primary producers in ocean: phytoplankton
o Upwelling areas: 300
o Coastal zone: 100
o Open ocean: 50
o Achieved through bioCo2 pump
o Phytoplankton that are not consumed or decomposed fall through
water column to ocean floor → enter carbon cycle
o Inorganic CO2 can be locked in deep ocean
• Algae in marine systems are responsible for half (50%) of global primary
productivity
o Turnover rate is much higher in marine systems than terrestrial
▪ Effects rate of flow through food chains of marine system
(much faster)
• Ocean plays large role as a major sink for at least 40% of anthropogenic CO2
emissions since the Industrial Revolution
Long Term and short term changes in Climate
• Always been shifts
• Past: shifts have taken over long periods of time → allows organisms to adapt
to changed environment
• However, regulate changes in climate have major impacts on oceanic and
terrestrial processes
• E.g. El Nino Souther Oscillation (ENSO: El Nino), opposite is La Nina
o Every 3-5 years, Pacific Basin subjected to major shifts to oceanic
circulation – tightly coupled to atmospheric events (walker circulation)
o Consequence of changes to Walker circulation, oscillation occurs in
pressure difference across Pacific (b/w Tahiti and Darwin) → Southern
Oscillation (SO)
o Every 3-5 years, Magnitude of SO changes from positive (normal
conditions) to negative (El Nino)
o Change in pressure leads to reduction in strength of Trade Winds
across Pacific
▪ Leads to decrease in equatorial upwelling all across Pacific and
consequent increased sea temperatures
o Eastward movement of water suppresses upwelling events along west
coast of South America – consequences for phytoplankton and marine
food chains
▪ Nutrients can no longer come up to surface → phytoplankton
population don’t develop
o Strong trade wings (from E → W) along with equatorial currents,
brings upwelling
▪ El Nino Event: pressure over eastern and western pacific flip
flops → causes trade winds to diminish → eastward movement
of warm water along equator (W→E)
• Surface waters of central and eastern pacific warm
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