Author(s): K. Graves; B. E. Laval; A. L. Forrest; G. Kirillin
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Abstract: Recent field observations and numerical modelling challenge the commonly held view that fluid motion under lake-ice is insignificant. This growing body of evidence indicates that under-ice circulation is an important mechanism for lateral and vertical transport of heat and pollutants in ice-covered lakes. Using direct measurements of temperature, conductivity and water column velocities in an ice-covered arctic lake, further field observations of circulation on a basin-wide scale over the entire lake depth are presented. These observations were made during a 2013 field research campaign in Lake Kilpisjärvi, Finland (approximately 69 ° N, 21 ° E). During the field observation period the entire water column was colder than the temperature of maximum density. Orthogonal density profiles of temperature show an approximately 500m wide upwelled density anomaly beneath the ice-cover. This anomaly consisted of warm, upwelled bottom water. Repeated temperature profiles, collected over a two-day period, show that the density anomaly persisted for the observation period of three days. Acoustic Doppler Current Profiler measurements of water column velocity show anti-cyclonic circulation around the density anomaly. The observed density profile and velocity measurements are shown to be consistent with a cyclogeostrophic force balance. These measurements show basin-wide circulation beneath ice-cover. These results contribute to the knowledge of winter hydrodynamics in lakes and the growing body of observation of lateral and vertical transport under-ice.
Year: 2014