Turbulence in a small arctic pond

Small ponds, numerous throughout the Arctic, are often supersaturated with climate-forcing trace gases. Improving estimates of emissions requires quantifying (1) their mixing dynamics and (2) near-surface turbulence which would enable emissions. To this end, we instrumented an arctic pond (510 m(2), 1 m deep) with a meteorological station, a thermistor array, and a vertically oriented acoustic Doppler velocimeter. We contrasted measured turbulence, as the rate of dissipation of turbulent kinetic energy, epsilon, with values predicted from Monin-Obukhov similarity theory (MOST) based on wind shear as u(*w), the water friction velocity, and buoyancy flux, beta, under cooling. Stratification varied over diel cycles; the thermocline upwelled as winds changed allowing ventilation of near-bottom water. Near-surface temperature stratification was up to 7 degrees C per meter. With respect to predictions from MOST: (1) With positive beta under heating and strong near-surface stratification, turbulence was suppressed; (2) under heating with moderate stratification and under cooling with light to moderate winds, measured epsilon was in agreement with MOST; (3) under cooling with no wind and when surface currents had ceased, as occurred 20% of the time, turbulence was measurable and predicted from beta. Near-surface turbulence was enhanced under cooling and light winds relative to that under a neutral atmosphere due to higher values of drag coefficients under unstable atmospheres. Small ponds are dynamic systems with wind-induced thermocline tilting enabling vertical exchanges. Near-surface turbulence, similar to that in larger systems, can be computed from surface meteorology enabling accurate estimates of gas transfer coefficients and emissions.