31 May 2022
31 May 2022

Turbulent kinetic energy dissipation rate and associated fluxes in the western tropical Atlantic estimated from ocean glider observations

Peter M. F. Sheehan, Gillian M. Damerell, Philip J. Leadbitter, Karen J. Heywood, and Rob A. Hall Peter M. F. Sheehan et al.
  • Centre for Ocean and Atmospheric Sciences, School of Environmental Science, University of East Anglia, Norwich, NR4 7TJ, United Kingdom

Abstract. Ocean gliders enable us to collect the high-resolution microstructure observations necessary to calculate the dissipation rate of turbulent kinetic energy, ε, on timescales of weeks to months: far longer than is normally possible using traditional ship-based platforms. Slocum gliders have previously been used to this end; here, we report the first detailed estimates of ε calculated using the Batchelor spectrum method on observations collected by a FP07 fast thermistor mounted on a Seaglider. We use these same fast thermistor observations to calculate ε following the Thorpe scale method and find very good agreement between the two methods. The Thorpe scale method yields larger values of ε, but the average difference, which is less than an order of magnitude, is smaller than reported elsewhere. The spatio-temporal distribution of ε is comparable for both methods. Maximum values of ε (10−7 W kg−1) are observed in the surface mixed layer; values of approximately 10−9 W kg−1 are observed between approximately 200 and 500 m depth. These two layers are separated by a 100 m thick layer of low ε (10−10 W kg−1), which is co-located with a high-salinity layer of Subtropical Underwater and a peak in the strength of stratification. We calculate the turbulent heat and salt fluxes associated with the observed turbulence. Between 200 and 500 m, ε induces downward fluxes of both properties that, if typical of the annual average, would have a very small influence on the heat and salt content of the overlying salinity-maximum layer. We compare these turbulent fluxes with estimates of double-diffusive fluxes, having objectively identified those regions of the water column where double diffusion is likely to occur. We find that the double-diffusive fluxes of both heat and salt are larger than the corresponding mechanical fluxes.

Peter M. F. Sheehan et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-361', Anonymous Referee #1, 30 Jun 2022
  • RC2: 'Comment on egusphere-2022-361', Anonymous Referee #2, 01 Jul 2022

Peter M. F. Sheehan et al.

Peter M. F. Sheehan et al.


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Short summary
We calculate the rate of turbulent kinetic energy dissipation, i.e. the mixing driven by small-scale ocean turbulent, in the western tropical Atlantic Ocean via two methods. We find good agreement between the results of both. A region of elevated mixing is found between 200 and 500 m, and we calculate the associate heat and salt fluxes. We find that double-diffusive mixing in salt fingers, a common feature of the tropical oceans, drives larger heat and salt fluxes than the turbulent mixing.