North Atlantic water mass transformation in OMIP simulations

Simulations in the Ocean Model Intercomparison Project (OMIP) are all driven by the same atmospheric forcing, yet have a variety of responses. Our goal is to evaluate biases in OMIP simulations using surface-forced water mass transformation. Water mass transformation is a process-oriented diagnostic that connects buoyancy forcing to the meridional overturning circulation (MOC). It thus allows for the attribution of individual surface processes to circulation. We compute surface-forced water mass transformation in the subpolar North Atlantic of OMIP simulations. To evaluate biases, we use a set of observation-based water mass transformation benchmarks. Our observation-based water mass transformation benchmarks were created for the purpose of ocean model comparison and use the same atmospheric forcing used to force the OMIP models. Our analysis focuses on how well OMIP water mass transformation fits within the range of our observational benchmarks. A regional decomposition of water mass transformation in the subpolar North Atlantic is used to identify where ocean model biases in WMT occur and the processes leading to those biases. These results will inform our concurrent examination of AMOC in OMIP simulations.