Stronger North Pacific Circulation and Transition Zone

The climate variability and change of the North Pacific Transition Zone (NPTZ) exerts a strong control on marine populations that are sensitive to the strong productivity gradients between the polar and subpolar recirculation gyres. Previous studies have already noted that western boundary currents, such as the KOE, are likely shifting poleward and intensifying as a result of climate warming, however, it remains unclear if these changes in the mean are also followed by a change in the variability – which may have even more important impacts on marine populations.Given the reliance of marine ecosystem and fisheries on the interannual and decadal variability of the NPTZ, the goal of this study is to explore how the NPTZ variance responds to a warmer climate predicted by the Community Earth System Model Large Ensemble (CESM-LENS). First, a covariance analysis has been done in order to analyze the correlation between the SSH and the chlorophyll from satellite data. This prediction has been put in comparison with an ensemble of climate models from the Coupled Model Intercomparing Project (CMIP5) under the Representative Concentration Pathways RCP8.5. In this last case 23 models have been considered in order to avoid fluctuations. From the model analysis it has been found that the SSH variance will have an increasing trend. Also, because of the shifting in Westerlies the Kuroshio current will move poleward. To analyze the impact of these findings, a correlation between Kuroshio and an external mode (ENSO) has been considered. There are then two impacts, the first one regards the SLP fields that drives the Kuroshio, the second one instead is the feedback that correlates the SSH Kuroshio to the SLP and then to SST anomalies in the tropics.