Projected changes to the tropical Pacific Ocean

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Projected changes to the tropical Pacific Ocean
Solomon Islands Government
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Based on.....
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Outline

• Projected temperatures and currents surface and
  vertical structure
• Implications for oceanic nutrients
• Ocean acidification
• Sea-level rise

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Sea surface temperature
Change in SST C (2000-2100)

• 2000 27.4C
• 2035 28.1C (0.7C)
• 2100 29.9C (2.5C)

The ocean is a heat sink!
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Vertical structure and stratification

Warm, mixed-layer

Thermocline depth

Cold, deep ocean
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Vertical structure and stratification

Warm, mixed-layer

Thermocline depth

Cold, deep ocean
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Vertical structure and stratification

• Most warming occurs at surface
• Leads to increase in stratification

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Projected changes in vertical currents
Less downwelling
Less downwelling
Less UPWELLING
Less downwelling
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Implications for nutrients
Warm, mixed-layer

• Thermocline acts as a barrier
• Limits the supply of nutrients

Cold, deep ocean
Low nutrient
High nutrient
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Implications for nutrients
Warm, mixed-layer
Cold, deep ocean
Low nutrient

• Increased stratification makes it harder to bring
  nutrients upwards

High nutrient
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Why is this important?

• Nutrients support the food web for tuna

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Projected changes in major currents
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Eddies
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Nutrient supply by eddies

• Eddies temporarily lift nutrient-rich waters
• Eddy activity is related to current strength

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Eddies and nutrients
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Convergence zone
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Importance of ENSO for fisheries

• Skipjack tuna catch

Source Lehodey et al. (1997)
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Ocean acidification
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Projected acidification

• Saturation gt4 healthy conditions
• Saturation falls below 3.3, causing problems for
  corals
• Saturation decreases to 2.4

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Sea-level rise
Projection 2035 2050 2100
IPCC 8 cm 18-38 cm 23-51 cm
Semi-empirical 20-30 cm 70-110 cm 90-140 cm
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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, gt 1 m cannot be ruled out