Thermal Structure and Oxygen Depletion in Ice-covered Lakes

Arctic lakes are ice-covered for 9 months or more of the year yet mean temperatures and thermal structure and oxygen dynamics can vary considerably within one lake and between lakes of different morphometries. Here we use time series data obtained year round for over ~15 years for temperature and at least 4 years for specific conductance and oxygen to assess controls on variability in 5 lakes on the North Slope of Alaska ranging in size from 1 to 150 ha. Mean temperatures in winter primarily depended on mean summer temperatures in the lakes a few ha in size whereas heat loss in fall was a larger control on the lakes greater than 10 ha.  Patterns of fall cooling determined the dates of ice on, with the smaller lakes freezing two to ten days earlier than the larger lake.  When ice on followed winds of 5 m s^-1, initial thermal stratification was less than 1^oC. When stratification was greater, internal waves persisted for a few days.  Mean winter temperatures were independent of initial stratification.  Oxygen depletion varied with lake morphometry with higher loss rates in smaller lakes with their larger ratio of sediment area to volume. The transfer of heat and solutes was moderated by gravity currents, penetrative convection induced when light penetrated through the ice which also contributed to heating, and internal wave motions. Antecedent conditions and within lake hydrodynamics shaped the thermal and density structure which in turn influences biogeochemistry and organism habitat.

Primary Presenter: Sally MacIntyre, University of California - Santa Barbara (sally@eri.ucsb.edu)

Authors:

Sally MacIntyre, Marine Science Institute, University of California, Santa Barbara, CA., USA  (sally@eri.ucsb.edu)

Robert Schwefel, Leibniz Institute for Freshwater Biology, Berlin, Germany  (Robert.schwefel@igb-berlin.de)

Alicia Cortes, 5Department of Civil and Environmental Engineering, University of California at Davis, Davis, California  (alicortes@ucdavis.edu)