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

Change in SST °C (2000-2100)

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

Sea surface temperature

The ocean is a heat sink!

Thermocline depth

Vertical structure and stratification

Warm, mixed-layer

Cold, deep ocean

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Thermocline depth

Vertical structure and stratification

Warm, mixed-layer

Cold, deep ocean

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• Most warming occurs at surface

• Leads to increase in stratification

Vertical structure and stratification

Projected changes in vertical currents

Less downwelling

Less UPWELLING

Less downwelling

Less downwelling

Implications for nutrients

• Thermocline acts as a barrier

• Limits the supply of nutrients

Warm, mixed-layer

Cold, deep ocean

Low nutrient

High nutrient

Implications for nutrients

•Increased stratification makes it harder to bring nutrients upwards

Warm, mixed-layer

Cold, deep ocean

Low nutrient

High nutrient

Why is this important?

• Nutrients support the food web for tuna

Projected changes in major currents

Eddies

Nutrient supply by eddies

• Eddies can 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

Semi-empirical 20-30 cm 70-110 cm 90-140 cm

Summary

• Increases in sea surface temperature

• Stronger stratification

• Nutrient reduced due to increase in stratification

• Slowdown of equatorial currents and upwelling

• Aragonite drops below critical levels

• Sea level rise, > 1 m cannot be ruled out