Climatic Controls on Metabolic Constraints in the Ocean

Abstract. Observations and models indicate that climate warming is associated with the loss of dissolved oxygen from the ocean. Dissolved oxygen is a fundamental requirement for heterotrophic marine organisms (except marine mammals) and, since the basal metabolism of ectotherms increases with temperature, warming increases organisms’ oxygen demand. Therefore, warming and deoxygenation pose a compound threat to marine ecosystems. In this study, we leverage an ecophysiological framework and compilation of empirical trait data quantifying the temperature sensitivity and oxygen requirements of metabolic rates for a range of marine species (“ecotypes”). Using the Community Earth System Model Large Ensemble, we investigate how natural climate variability and anthropogenic forcing impact the ability of marine environments to support aerobic metabolisms on interannual to multi-decadal timescales. Warming and deoxygenation projected over the next several decades will yield a reduction in the volume of viable ocean habitat. We find that fluctuations in temperature and oxygen associated with natural variability are distinct from those associated with anthropogenic forcing in the upper ocean. Further, the joint temperature-oxygen anthropogenic signals emerges sooner than independently from natural variability. Our results demonstrate that anthropogenic perturbations underway in the ocean will strongly exceed those associated with the natural system; in many regions, organisms will be pushed closer to or beyond their physiological limits, leaving the ecosystem more vulnerable to extreme temperature-oxygen events.