Objective determination of global ocean surface mixed layer depth

Abstract

Upper oceans are characterized by the existence of vertically quasi-uniform layer of temperature (T, isothermal layer) and density (ρ, mixed layer). The thickness of the mixed layer determines the heat content and mechanical inertia of the layer that directly interacts with the atmosphere. Objective and accurate determination of the mixed layer depth is crucial in ocean dynamics and climate change. This paper describes recently developed optimal linear fitting, maximum angle, and relative gradient methods to determine mixed layer depth from profile data. Profiles from the Global Temperature and Salinity Profile Program (GTSPP) during 1990–2010 are used to demonstrate the capability of these objective methods and to build up global mixed (isothermal) layer depth datasets. Application of the data in climate study is also discussed.