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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.
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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 } Warm, mixed-layer } Thermocline depth } Cold, deepocean
Vertical structure and stratification • Most warmingoccurs 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 • Limits the supply of nutrients Cold, deepocean Lownutrient High nutrient
Implications for nutrients Warm, mixed-layer Cold, deepocean Lownutrient Increased stratification makes it harder to bring nutrients upwards High nutrient
Why is this important? Nutrients support the food web for tuna
Nutrient supply by eddies • Eddies temporarily lift the nutrient-rich waters • Eddy activity is related to current strengths
Similarities with ENSO • Skipjack tuna catch Source: Lehodey et al. (1997)
Projected acidification • Saturation >4 healthy conditions • Saturation falls below 3.3 causing problems for some corals • Saturation decreases to 2.4
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