Recent mass loss from ice sheets and ice shelves is now persistent and prolonged enough that it impacts downstream oceanographic conditions. To demonstrate this, we use an ensemble of coupled GISS-E2.1-G simulations forced with historical estimates of anomalous freshwater, in addition to other climate forcings, from 1990 through 2019. In this ensemble there are detectable differences in zonal-mean sea surface temperatures (SST) and sea ice in the Southern Ocean, and in regional sea level around Antarctica and in the western North Atlantic. These impacts mostly improve the model’s representation of historical changes, including reversing the forced trends in Southern Ocean surface temperature and Antarctic sea ice. The changes in SST may have implications for estimates of the SST pattern effect on climate sensitivity and for cloud feedbacks. We conclude that the changes are sufficiently large that these drivers should be included in all-forcing historical simulations in coupled model intercomparisons.

Global ocean oxygen loss - deoxygenation - is projected to persist in the future. Previous generations of Earth system models (ESMs) have, however, failed to provide a consistent picture of how deoxygenation will influence oxygen minimum zones (OMZs; O2<= 80 μmol/kg), in particular the largest OMZ in the tropical Pacific Ocean. The expansion of the Pacific OMZ would threaten marine ecosystems and ecosystem services such as fisheries and could amplify climate change by emitting greenhouse gases. Here, we use the latest generation of ESMs (CMIP6) and a density framework that isolates oxygen changes in the thermocline and intermediate waters. We show that the Pacific OMZ expands by the end of the century in response to high anthropogenic emissions (multi-ESM median expansion of 2.4 * 10^15 m^3m, about 4% of the observed OMZ volume). The expansion is driven by a reduction of the shallow overturning circulation in the thermocline and a robust weakening of the oxygen supply to the upper OMZ in all ESMs. The magnitude of this expansion is, however, uncertain due to the less constrained balance between physical and biological changes in the lower OMZ. Despite uncertainties in the biological response, our results suggest that models with more complex biogeochemistry project weaker changes in the lower OMZ, and therefore stronger overall OMZ expansion. The fact that the OMZ largely expands in the upper ocean maximizes its ecological, economic, and climatic impacts (release of greenhouse gases).

The Pangeo project recently introduced large parts of the CMIP6 data archive into the cloud. This enables, for the first time, centralized, reproducible science of state-of-the-art climate simulations without the need to own large storage or a supercomputer as a user. The data itself however, still presents significant challenges for analysis, one of which is applying operations across many models. Two of the major hurdles are different naming/metadata between modeling centers and complex grid layouts, particularly for the ocean components of climate models. Common workflows in the past often included interpolating/remapping desired variables and creating new files, creating organizational burden, and increasing storage requirements. We will demonstrate two Pangeo tools which enable seamless calculation of common operations like vector calculus operators (grad, curl, div) and weighted averages/integrals across a wide range of CMIP6 models directly on the data stored in the cloud. cmip6_preprocessing provides numerous tools to unify naming conventions and parse grid information and metrics (like cell area). This information is used by xgcm to enable finite volume analysis on the native model grids. The combination of both tools facilitates fast analysis while ensuring a reproducible and accurate workflow.