Thermal Overturning Circulation in an Arctic Pond

In a 1.2-m-deep arctic permafrost pond, early-summer bottom-water renewal was dominated by thermal overturning circulation, rather than wind-driven overturning or vertical turbulent mixing. Three high-resolution current profilers measured turbulent dissipation rates. Three dense temperature logger arrays measured stratification. A turbulent surface mixed layer grew thicker with nightly cooling and thinner with daily warming. However, both day and night, turbulence was inhibited in a stratified layer that separated the surface mixed layer from the deeper pond. Nightly cooling, likely intensified in shallow regions of the pond, generated 10-cm-thick cold layers, which flowed down the sloping bed to renew bottom waters. A heat balance suggests sufficient flow to replace most bottom water each night. Groundwater flows were too slow to influence this circulation, but likely advected significant heat into sediments near the pond's western end. Bottom water renewal may influence greenhouse gas emissions and heat transport in the evolving permafrost landscape.