WHOI PO

Title: A theory for the stratification of the middepth ocean

Abstract: The middepth ocean, spanning from 1 to 3 kilometers in depth, ischaracterized by a remarkably exponential stratification profile. Traditionalconceptual models for this region attempt to reconcile dynamics from theSouthern Ocean with those from northern basins to predict the stratificationand overturning circulation from external parameters. However, these models donot capture both the robust exponential stratification seen in observations andthe shape of the overturning revealed by state estimates. We extend the idea ofmatching channel dynamics in the Southern Ocean with basin dynamics in theIndo-Pacific in two key ways: first by allowing for a variable diapycnaldiffusivity in the basin as implied by observations and theory, and second byusing scale analysis to reduce the matching problem to a single ordinarydifferential equation for the stratification. Analysis of this equation yieldsexplicit formulas for the leading-order structure of the basin stratificationand overturning in terms of external parameters. These predictions compare wellwith the results of idealized three-dimensional numerical simulations and areused to answer the question of why the middepth ocean is exponentiallystratified.