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 • Acidification
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 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 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
Sea-level rise
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
- Slides: 22