Measuring the Dissipation Rate of Turbulent Kinetic Energy in Strongly Stratified, Low-Energy Environments: A Case Study From the Arctic Ocean

We compare estimates of the turbulent dissipation rate, epsilon, obtained independently from coincident measurements of shear and temperature microstructure in the southeastern Beaufort Sea, a strongly stratified, low-energy environment. The measurements were collected over 10days in 2015 by an ocean glider equipped with microstructure instrumentation; they yield 28,575 shear-derived and 21,577 temperature-derived epsilon estimates. We find agreement within a factor of 2 from the two types of estimates when epsilon exceeds 3 x 10(-11)W/kg, a threshold we identify as the noise floor of the shear-derived estimates. However, the temperature-derived estimates suggest that the dissipation rate is lower than this threshold in 58% of our observations. Further, the noise floor of the shear measurements artificially skews the statistical distribution of epsilon below 10(-10)W/kg, that is, in 70% of our observations. The shear measurements overestimate portions of the geometric mean vertical profile of epsilon by more than an order of magnitude and underestimate the overall variability of epsilon by at least 2 orders of magnitude. We further discuss uncertainties that arise in both temperature- and shear-derived epsilon estimates in strongly stratified, weakly turbulent conditions, and we demonstrate how turbulence spectra are systematically modified by stratification under these conditions. Using evidence from the temperature-gradient spectral shapes and from the observed epsilon distributions, we suggest that the temperature-derived dissipation rates are reliable to values as small as 2 x 10(-12)W/kg, making them preferable for characterizing the turbulent dissipation rates in the weakly turbulent environment of this study.