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Diel vertical migrations in the ocean play a key role in predator-prey dynamics and the functioning of the biological carbon pump. However, changes in ocean conditions including warming and deoxygenation threaten to significantly perturb vertical migration patterns over the twenty-first century. Specifically, vertical migrations over regions of critically low oxygen, known as oxygen minimum zones (OMZs), are likely to be most sensitive to changes in temperature and oxygen. In this study, we apply a simplified prognostic ecosystem model (APECOSM-1D) to changing conditions in the Pacific Ocean OMZ as simulated by 13 Earth System Models from the Coupled Model Intercomparison Project Phase 6 (CMIP6). We find that modeled fish migration depths at a given location in the region may deepen or shoal by over 100 m by the end of the century; however, there are large uncertainties across the CMIP6 ensemble for the geographic pattern of migration depth changes. To reconcile this, we adopt a water mass based approach which aggregates changes into regions defined by their vertical oxygen minimum value. In this framework, we find that fish migration depths over the lowest oxygen core of the OMZ remain stable due to compensating changes in temperature and oxygen. Meanwhile, away from the OMZ core, ocean warming and deoxygenation together drive shallower migration depths in projected conditions. 

A decades-long affair Decadal climate variability and change affects nearly every aspect of our world, including weather, agriculture, ecosystems, and the economy. Predicting its expression is thus of critical importance on multiple fronts. Poweret al. review what is known about tropical Pacific decadal climate variability and change, the degree to which it can be simulated and predicted, and how we might improve our understanding of it. More accurate projections will require longer and more detailed instrumental and paleoclimate records, improved climate models, and better data assimilation methods. —HJS 

The El Niño–Southern Oscillation (ENSO), which originates in the Pacific, is the strongest and most well-known mode of tropical climate variability. Its reach is global, and it can force climate variations of the tropical Atlantic and Indian Oceans by perturbing the global atmospheric circulation. Less appreciated is how the tropical Atlantic and Indian Oceans affect the Pacific. Especially noteworthy is the multidecadal Atlantic warming that began in the late 1990s, because recent research suggests that it has influenced Indo-Pacific climate, the character of the ENSO cycle, and the hiatus in global surface warming. Discovery of these pantropical interactions provides a pathway forward for improving predictions of climate variability in the current climate and for refining projections of future climate under different anthropogenic forcing scenarios.