Global Distribution of the Oceanic Bottom Mixed Layer Thickness*

With the increasing observations in the abyssal ocean, the bottom ocean has received unprecedented attention. The bottom mixed layer (BML) is the only pathway for communication between the ocean interior and underlying, where interrelated physical, geochemical, and biological processes actively take place. In this study, over $30,000$ full-depth conductivity-temperature-depth (CTD) profiles archived during the past 30 years by the World Ocean Circulation Experiment (WOCE) Program were used to obtain the first approximation of the global distribution of the oceanic BML thickness $H_{BML}$ by applying an integrated method. We found that $H_{BML}$ had inhomogeneous distributions in different ocean basins and appeared thicker around mid-ocean ridges. In particular, the median $H_{BML}$ values were $40$, $42$, and $64$ m in the Atlantic, Indian, and Pacific Oceans respectively, and $47$ m globally. In the abyssal ocean, $H_{BML}$ became thicker in the deeper ocean ($D$), according to a statistical fitting result of an exponential function of $H_{BML} = 26.34+0.85e^{(D/1271.8)}$.