Comparison of objective descriptions of the thermocline

Paul C. Fiedler

Limnol. Oceanogr. Methods 8:313-325 (2010) | DOI: 10.4319/lom.2010.8.313

ABSTRACT: Temperature-depth profiles, including the thermocline, are typically described or characterized by mixed layer depth, thermocline depth, and thermocline strength. Objective methods of estimating these parameters are compared with empirical determinations for 200 CTD profiles collected in the eastern and central tropical Pacific, the subtropical North Pacific, and the California Current. The objective methods are (1) maximum slope by difference, (2) maximum slope by regression, (3) four-segment profile model, (4) inflection point, and (5) variable representative isotherm. Mixed layer depth is well estimated by the temperature criterion of (SST-0.8°C) independent of the estimation of thermocline parameters. Thermocline depth and strength are well estimated by the variable representative isotherm method. However, thermocline strength measured as the slope of the temperature-depth profile does not provide a good measure of stratification of the water column. Therefore, it is recommended that the thermocline strength estimate for a profile be supplemented by an estimate of the standard deviation of temperature in the near-surface layer including the thermocline.