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Small ice-covered lakes are stratified by temperature and solutes. Using time series measurements and profiles of temperature, specific conductance (SC), and dissolved oxygen obtained during spring 2014 and 2015, we identified the physical processes occurring under the ice and at ice-off in two ~2 ha, 10 m deep arctic lakes. The lakes are distinguished from other freshwater, ice-covered lakes by solutes initially stabilizing the density stratification when temperature decreased in the lower water column and, with one exception, stabilizing it during warming. With ice-cover 1 m thick, wind-forced internal waves occurred, with 2nd vertical mode waves prevalent where stratification was weak. Snowmelt induced near-surface chemical stratification such that diurnal thermoclines formed with stable temperature stratification in a ~4 m thick layer. Horizontal exchange was mediated by internal waves and gravity currents induced by greater heating near shore and as incoming snowmelt displaced water in shallow regions. Towards ice-off, the gravity currents reduced temperature stratification between the snowmelt induced near-surface pycnocline and the bottom pycnocline but slight increases in specific conductance precluded radiatively driven convection. Snowmelt retention was greater with rapid spring heating. The lakes did not mix by ice-off. With moderate winds, Wedderburn numbers decreased below 3 at ice-off, and the near-surface pycnocline upwelled and then deepened due to internal wave induced mixing. The concomitant downward mixing of heat caused a rapid onset of thermal stratification and, that, combined with incomplete mixing under the ice, led to persistence of near-bottom depletion in oxygen, and increased density and dissolved solutes. 

Seasonally flooded forests along tropical rivers cover extensive areas, yet the processes driving air‐water exchanges of radiatively active gases are uncertain. To quantify the controls on gas transfer velocities, we combined measurements of water‐column temperature, meteorology in the forest and adjacent open water, turbulence with an acoustic Doppler velocimeter, gas concentrations, and fluxes with floating chambers. Under cooling, measured turbulence, quantified as the rate of dissipation of turbulent kinetic energy (ε), was similar to buoyancy flux computed from the surface energy budget, indicating convection dominated turbulence production. Under heating, turbulence was suppressed unless winds in the adjacent open water exceeded 1 m/s. Gas transfer velocities obtained from chamber measurements ranged from 1 to 5 cm/hr and were similar to or slightly less than predicted using a turbulence‐based surface renewal model computed with measured ε and ε predicted from wind and cooling.