Predicting Impact of Climate Change on Global Ocean Physics and Biology

Climate model predictions of this century generally show increased ocean temperatures, increased vertical stratification, and a poleward shift of the physical regimes that are associated with different ocean biomes, including a shrinking of seasonally ice covered regions. The general direction of the predicted physical changes is consistent between the five different models we considered for this study, giving a 6.1 ± 4.0% reduction in primary production for the last 20 years of this century in the band between 45°S and 45°N, compared with a 5.8 ± 0.6% response in a single model where the range in responses is due to internal variations resulting from an ensemble of six simulations with different initial conditions.  The five different models give a 7.1 ± 5.6% increase in primary production in the regions poleward of 60° in both hemisphere, compared to 6.9 ± 2.3% in the six member ensemble with a single model.  The decrease in tropical and subtropical productivity is due principally to reduced upward nutrient supply, while the increase in the subpolar and polar regions is due principally to an extension of the growing season as deep wintertime mixing events terminate earlier in the year.