Transcript 03. Projected changes to the ocean

Projected changes to the
tropical Pacific Ocean
Based on.....
Outline
• Projected temperatures and currents:
surface and vertical structure
• Implications for oceanic nutrients
• Ocean acidification
• Sea-level rise
Sea surface temperature
Warm pool
Sea surface temperature
Change in SST °C (2000-2100)
• 2100: 29.9°C (+2.5°C)
Vertical structure and stratification
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Warm, mixed-layer
Thermocline depth
Cold, deep ocean
Vertical structure and stratification
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Warm, mixed-layer
Thermocline depth
Cold, deep ocean
Vertical structure and stratification
• Most warming
occurs at surface
• Leads to increase
in stratification
Projected changes in vertical currents
Less downwelling
Less downwelling
Less UPWELLING
Less downwelling
Implications for nutrients
Warm, mixed-layer
• Thermocline acts as a
barrier
Cold, deep ocean
Low nutrient
• Limits the supply of
nutrients
High nutrient
Implications for nutrients
Warm, mixed-layer
Cold, deep ocean
Low nutrient
•Increased stratification
makes it harder to bring
nutrients upwards
High nutrient
Why is this important?
• Nutrients support the
food web for tuna
Projected changes in major currents
Eddies
Nutrient supply by eddies
• Eddies temporarily lift
nutrient-rich waters
• Eddy activity is related
to current strength
Eddies and nutrients
Convergence zone
Importance of ENSO for fisheries
Skipjack tuna catch
Source: Lehodey et al. (1997)
Ocean acidification
Projected acidification
Saturation >4 = healthy
conditions
Saturation falls below 3.3,
causing problems for corals
Saturation decreases to 2.4
Sea-level rise
Projection
2035
2050
2100
IPCC
8 cm
18-38 cm
23-51 cm
20-30 cm
70-110 cm
90-140 cm
Semi-empirical
Summary
• Increases in sea surface temperature
• Stronger stratification
• Nutrient supply reduced due to increase in
stratification, with effects on tuna food web
• Slowdown of equatorial currents and upwelling
• Aragonite drops below critical levels
• Sea level rise, > 1 m cannot be ruled out