Simulated heat storage in a perennially ice‐covered high Arctic lake: Sensitivity to climate change

Abstract

[1] Perennially ice-covered, meromictic lakes occur along the northern coast of Ellesmere Island in the Canadian high Arctic and have distinctive conductivity and temperature profiles. They are salinity stratified and have deep thermal maxima that persist throughout the year at temperatures up to 60°C above the winter minimum in the overlying atmosphere. Heat transfer in one of these lakes (Lake A, latitude 83.0°N, longitude 75.4°W) was simulated using a high spatial resolution model based on a one-dimensional heat diffusion and radiative transfer equation, which was solved through numerical integration. Boundary conditions were forced using climate data from an automated weather station installed next to the lake. There was a good fit between simulated and observed water column temperatures, including the midwater temperature maximum of 8.5°C, after 63 years of heating (RMSE = 0.10°C). This suggests that Lake A became ice-free in the 1940s, a known period of intense warming of the circumpolar Arctic. The model was sensitive to forcing by photosynthetically active radiation (PAR, 400-700 nm), in addition to optically related parameters such as surface reflectance, snow and ice cover, and the PAR diffuse attenuation coefficient. The unusual thermal structure is affected by stratified layers of pigmented microbial communities, which enhance the absorption of solar radiation. Simulation of ice-free summers revealed that the lake's thermal profile would lose its characteristic shape over several decades and that ongoing climate change could reduce the thermal maximum from 8.5°to 4°C within 50 years.

High Arctic lakes as sentinel ecosystems: Cascading regime shifts in climate, ice cover, and mixing

“…At this point, it may be necessary to examine the deeper portions of water temperature profiles to evaluate the changes in lake heat content. Vincent et al (2008) showed how longterm seasonal ice loss will modify the Lake A water-column temperature profile. The resulting heat loss in this scenario was projected to reduce the temperature of the deep-water thermal maximum, while increasing its depth.…”

“…Lakes A and B have unglacierized catchment areas of 37 km 2 (Van Hove et al 2006) and approximately 5 km 2 , respectively. A perennial ice cover prevents windinduced mixing in all these lakes, while steep salinity gradients (with the exception of Lake C3) prevent convection in their water columns (Ludlam 1996;Vincent et al 2008). Consequently, the lakes have developed deep thermal maxima over many decades of solar heating .…”

Prediction of Ice‐Free Conditions for a Perennially Ice‐Covered Antarctic Lake

“…Heat within the water column is conducted upward through the ice cover and removed via sublimation of the ice (McKay et al, ). The high heat capacity of the water column, in conjunction with high deep water salinity in chemically stratified lakes, allows for the development of thermal maxima at depth (Obryk, Doran, Hicks, et al, ; Vincent et al, ). Deep (~>20 m) perennially ice‐covered lakes are often highly stratified, with dense and deep hypersaline waters (Chinn, ; Spigel et al, ; Spigel & Priscu, ).…”

Effects of Changes in Arctic Lake and River Ice

“…For some lakes, the loss of ice can result in the loss of vertical habitat structure and cooling (Vincent et al 2008a). A further evaluation of potential future changes in water temperature and thermal lake structure across the Northern Hemisphere was conducted by Dibike et al (2011).…”

“…A small number of Arctic lakes are permanently ice-covered (e.g., Vincent et al 2008a) and their summer melt-out is typically restricted to a narrow moat. This greatly limits the wind-induced mixing and the presence of some biota.…”