Thermal conditions and lake metabolism in the ice-covered North Aral Sea

Rapid desiccation of the Aral Sea, the former 4th largest lake worldwide, attracts continuous attention of researchers as an example of fast anthropogenically driven change of a large aquatic ecosystem on unprecedentedly large spatial scales. As a countermeasure preventing further desiccation, a dam was constructed in 2005 separating the northern part of the Aral Sea from the rest of the basin. The effort led to stabilization of the North Aral volume and salinity and was widely recognized as an exceptional success in large-scale water management and restoration. The “restarted” ecosystem developed within several years to a highly productive large lake. Owing to the cold arid climate, the lake is covered by ice for several months in winter while gaining significantly higher amount of solar radiation than temperate and polar ice-covered lakes. We present new results revealing characteristic features of large low-latitude brackish lake dynamics under ice cover: strong internal basin-scale waves with long periods, heating of the water column by solar light penetrating the ice cover, and arresting of vertical convective mixing by freshening of upper waters during the ice melt. The under-ice dissolved oxygen content was analyzed in terms of whole-lake metabolism and demonstrated primary production taking place during the entire ice-covered period with a strong intensification in spring months after the snow melt increased the photosynthetically active radiation level under ice.