Transcript 3. Projected changes to the ocean

Projected changes to the
tropical Pacific Ocean
Based on Chapters 3 & 4
Outline
• Projected temperatures and currents:
surface and vertical structure
• Implications for oceanic nutrients
• Acidification
• Food web for tuna
• Influence of temperature on tuna
Sea surface temperature
Change in SST °C (2000-2100)
• 2000: 27.4°C
• 2035: 28.1°C (+0.7°C)
• 2100: 29.9°C (+2.5°C)
Ocean is heat sink!
Vertical structure and stratification
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Warm, mixed-layer
Thermocline depth
Cold, deep ocean
Vertical structure and stratification
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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
Image: Marc Taquet, FADIO, IRD/IFREMER
Projected changes in major currents
Eddies
Nutrient supply by eddies
• Eddies temporarily
lift the nutrient-rich
waters
• Eddy activity is
related to current
strengths
Eddies and nutrients
Convergence zone
Similarities with ENSO
Skipjack tuna catch
Source: Lehodey et al. (1997)
Ocean acidification
Projected acidification
Saturation >4 healthy
conditions
Saturation falls below 3.3
causing problems for
some 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