The Polar Transition from Alpha to Beta Regions Set by a Surface Buoyancy Flux Inversion

Abstract The stratification is primarily controlled by temperature in subtropical regions (alpha ocean) and salinity subpolar (beta ocean). Between these two lies a transition zone, often characterized deep mixed layers winter responsible for the ventilation of intermediate or layers. While primary interest, no consensus on what controls its position exists yet. Among potential candidates, we find wind distribution, air–sea fluxes, nonlinear cabbeling effect. Using an ocean general circulation model idealized basin configuration, sensitivity analysis performed testing different equations state. More precisely, thermal expansion coefficient (TEC) dependence explored, changing impact heat fluxes buoyancy series experiments. polar zone found to be located at where sign surface flux reverses become positive, region, while are likely secondary importance. This inversion becomes possible because TEC reducing low temperature, enhancing return relative freshwater forcing high latitudes. When made artificially larger required produce positive increases moves poleward. These experimets demonstrate important role competing setting zone. competition influenced spatial variations linked meridional temperature.