HYDROGEN-PEROXIDE - A NATURAL TRACER OF STRATIFICATION AND MIXING PROCESSES IN SUB-ARCTIC LAKES

Distribution patterns of photochemically produced hydrogen peroxide (H 2O2) were studied in two lakes in the subarctic region near Hudson Bay . Both lakes were small and shallow (maximum depth of 2 m) with contra sting levers of DOC (4.6 and 9.3 mg C/l). Finescale temperature measur ements were conducted through the water column at each sampling period . The distribution patterns of H2O2 in both lakes were generally simil ar to mixing patterns inferred from temperature profiles but H2O2 prof iling was a more sensitive indicator of diurnal stratification. H2O2 l evers reached 600 nM during the formation of near-surface thermoclines . H2O2 concentrations were minimal and evenly distributed during perio ds of wind-induced mixing. Brunt-Vaisala buoyancy frequency (N-2) valu es were determined from finestructure temperature profiles at each sam pling and were significantly correlated with normalized H2O2 concentra tion gradient values (Lake Kayouk r=0.790, p<0.001; Lake Guinness r=0. 680, p = 0.003). This study demonstrates the potential applicability o f H2O2 in combination with finescale temperature measurements in deter mining mixing patterns in lakes. A quantitative approach towards estim ating vertical eddy diffusivities from H2O2 gradients is suggested.