Abstract
A barrier layer (BL) is the layer from the ocean’s isopycnal mixed layer bottom to the top of the thermocline, where density stratification is controlled by salinity. Here, we analyze BL thickness (BLT) in E3SMv1 and two other coupled earth system models. Compared to observation-based climatology, models reproduce the global distribution with semi-permanent BLs in some parts of the tropical oceans and seasonally-occurring BLs in higher latitudes. However, model BLs are generally too shallow in tropical regions and too deep in higher latitudes.
Comparison of E3SM coupled and forced ocean only runs suggest that the atmosphere model contributes significantly to BL biases. In the tropics, the main linkage to atmosphere model biases is through the effect of precipitation minus evaporation (P-E) on mixed layer depth (MLD). In higher latitudes, both (P-E) and wind stress affect MLD, but BLT biases are dominated by errors in the thermocline depth. These BLT biases in E3SM, in turn, affect entrainment of cold water from below the thermocline, especially in the tropics.