John Marshall

Cecil and Ida Green Professor of Oceanography, MIT

Role of eddies in ocean circulation

A central theme running through my research career has been an inquiry into the nature and role of the geostrophic eddy scale in the large-scale ocean circulation. Do eddies matter, or are they just a wrinkle on classical laminar theories of ocean circulation? The problem is much more challenging than the meteorological analogue because of the paucity of direct observations, the enormity of the challenge of modeling a fluid that is hundreds of eddy scales wide, and the inappropriateness – except in the southern ocean (see below and [74]) – of the zonal average.

My work has contributed to

  • understanding the nature of geostrophic waves and instabilities in the ocean [117], [129]
  • the interpretation of eddy fluxes and, in particular, the nature of their rotational components [2], [3], [4]
  • elucidating the role of eddies in setting ocean stratification and their orchestration of mixing, particularly in the southern ocean [66], [70]
  • the quantification and interpretation of eddy transfer coefficients, central to the parameterization of eddies in ocean climate models [39], [99], [114], [115], [116], [118]
  • the application of ‘residual-mean theory’ to ocean circulation, exposing the nature of the dynamical balances in the Antarctic Circumpolar Current (ACC) [74], [85], [93], [94], [98]

My interest in ocean eddies and the way they mediate lateral processes in the ocean mixed layer led to the CLIMODE field experiment, in collaboration with Terry Joyce of Woods Hole Oceanographic Institution and many others [111]. This project addressed the key diabatic role of eddy fluxes directed laterally across outcropping isopycnals in regions of intense jets such as the Gulf Stream and the ACC. This work challenges the stubbornly 1-dimensional paradigm of ocean mixed layers, which emphasizes vertical fluxes driven by air-sea interaction and entrainment from below.