Projected changes to the tropical Pacific Ocean Based

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 Change in SST °C (2000 -2100) • 2000: 27. 4°C • 2035: 28. 1°C (+0. 7°C) • 2100: 29. 9°C (+2. 5°C) The ocean is a heat sink!

Vertical structure and stratification } } } Warm, mixed-layer Thermocline depth Cold, deep ocean

Vertical structure and stratification } } } 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 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 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)

Year 13 20 12 20 11 20 10 20 09 20 08 20 07 20 06 20 05 20 04 20 03 20 02 20 01 20 Catch Per Unit Effort (kg/100 hooks) CPUE for Southern Cooks (all species) 2001 -2013 3000 2500 2000 1500 1000 500 0

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 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