B.D.M. and S.K.V. gratefully acknowledge the support of the Office of Naval Research under Grants N00014-12-1-0279, N00014-12-1-0282, and N00014-12-1-0938 (Program Manager: Dr. Terri Paluszkiewicz). S.K.V. also acknowledges support of the National Science Foundation under Grant OCE-1151838. L.S.L. acknowledges support for BBTRE by the National Science Foundation by Contract OCE94-15589 and NATRE and IWISE by the Office of Naval Research by Contracts N00014-92-1323 and N00014-10-10315. J.N.M. was supported through Grant 1256620 from the National Science Foundation and the Office of Naval Research (IWISE Project). The authors also wish to thank A. Scotti for discussions on the subject and the three anonymous reviewers for their constructive criticisms.
Temperature versus Density Sorting
Our analysis uses potential temperature as a surrogate for potential density in the Thorpe-scale calculations out of concerns over the noise and reliability of salinity measurements. To check on the sensitivity of our analysis to salinity-compensated temperature inversions, the analysis was rerun for all datasets using potential density (with indirectly estimated salinity for the IWISE data; see below) and plotted here in Fig. A1. The data generally shift to higher values of LT/LO—most likely due to added salinity noise. However, the general trend of increasing LT/LO with increasing
Two additional tests were performed on the IWISE data that have been most prominently featured in this work. To circumvent problematic issues with VMP conductivity measurements, the first of these tests uses indirect salinity values derived from temperature measurements of the VMP and a fit to the T–S relationship provided by nearby and quasi-simultaneous CTD casts. The largest temperature-sorted Thorpe-scale value LT,θ is then compared to the largest density-sorted value LT,σ on a profile-by-profile basis in Fig. A2 for all casts of the VMP. The correlation is quite good and does not discourage the use of potential temperature as a surrogate for density.
The second, and perhaps more convincing, test focuses solely on the CTD measurements and thus avoids problems associated with indirectly estimating salinity. Inferred values of dissipation using temperature and density sorting are shown in Fig. A3 for the locations and time period corresponding to the VMP measurements of Fig. 15. The two methods give consistent results for all but the third cast in which a single density inversion biases ϵT,σ high. It is also worth noting that the inferred energy consumed (≈400 kJ m−2) is in close agreement with the inferred value based on VMP measurements (Fig. 15c).
Comparison of N Estimates
We use the method of Smyth et al. (2001) to calculate N because it gives a bulk density gradient that is relatively insensitive to patch boundaries. In Fig. B1, estimates of N determined from the bulk method are compared to those obtained from an average gradient that uses the highest and lowest
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Our reference to convectively driven turbulence is restricted to that which follows collapse of an overturn in an otherwise stably stratified flow and not that due to a surface buoyancy flux.