Figure 2. Relative thermal resistance to mixing (RTRM) estimated from average temperature (July, August, September) at 0 and 50 m from 1948 – 2002.

Although vertical temperature profiles did not contain sufficient depth resolution for discerning thermocline depth or calculating a stratification index, temperature and density differences (calculated on each sampling date and averaged) implied increasing stratification across the time series, as represented by relative resistance to thermal mixing. RTRM is based on the difference in estimated water density at 0 m and 50 m temperatures, relative to the standard water density difference at 4° C and 5° C. The RTRM line was fitted with linear least-squares regression (R² = 0.135, p = 0.003).