How Well Do We Know Lake Superior as an Indicator of Climate Change?
Posted on: January 14, 2019
Ye et al. (2018) used a Finite Volume Community Ocean Model (FVCOM) to model lake temperature while accounting for 3D variations in topography. (Source: Ye et al. 2018)

Recent Study Models Parameters Influencing Lake Superior Temperatures

As the climate changes and we look to our environment for clues about the nature of those changes, it becomes important to understand what we measure and just how much it can tell us. With this in mind, researchers from Michigan Technology University’s Great Lakes Research Center and Department of Civil and Environmental Engineering in Houghton, Michigan, and the National Oceanic and Atmospheric Association’s (NOAA) Great Lakes Environmental Research Laboratory in Ann Arbor, Michigan, provide some interesting insights into how water mixing in lake superior impacts near-surface temperatures and ice formation.


Changes in lake stratification (top: a,b) and temperature gradient (bottom: c,d) were visible between a modelled case where mixing was strong (left) and a modelled case where mixing was weaker (right). (Source: Ye et al. 2018)

The Trouble with Measuring Lake Superior Heat Content

As the authors state, the Laurentian Great Lakes are of great interest to researchers because they are potential indicators for climate change. Most studies using Lake Superior as a climate change indicator try to determine how much the lake temperature is increasing by inferring total heat content from lake surface temperatures, collected from the lakes extensive array of offshore buoys; however, it turns out that lake surface temperatures may not be accurately portraying the lake’s total heat content. Through the use of 3D hydrodynamic modelling of Lake Superior, Ye and others (2018) found that changes in lake surface temperature may not reflect the overall heat content of the lake because vertical mixing can have a major effect on how much the lake surface temperature changes relative to total heat content.


To read the full research article click here: Impact of Water Mixing and Ice Formation on the Warming of Lake Superior: A Model-guided Mechanism Study by Xinyu Ye, Eric J. Anderson, Philip Y. Chu, Chenfu Huang and Pengfei Xue (2018)


In the modelled case where mixing was weaker (right) lake ice coverage increased much more rapidly during the freezing period. (Source: Ye et al. 2018)

Mixing-up Surface Temperature and Total Heat Content

Ye and others (2018) focused on how vertical mixing influences lake stratification and consequently how efficiently energy is transferred between warmer and colder layers in the water column. The study ran two cases to examine vertical mixing, one where mixing was strong and another where it was weaker. When mixing was weaker, heat transfer was not as efficient during the lake stratification period in Fall, and resulted in a lower lake surface temperature than the strong mixing case where more total heat was lost. Interestingly, the model showed that ice formation was quicker and more extensive in the weak mixing case, where the lake was overall warmer, because of this lower lake surface temperature. Ye and others (2018) also looked at Ice Albedo (the effect of reduced absorption of the suns radiation due to the reflectivity of ice and snow) and determined that due to the ice’s seasonal nature, albedo was a minor contributor to lake heat and ice formation with only a minor impact in the ice melting period when the albedo affect is stronger.


In modelled cases focusing on Ice Albedo as a parameter for Lake Superior ice coverage, very little impact was made on ice formation and only minor impact was visible during ice melting. When Ice Albedo was set higher, melting took longer (left) (Source: Ye et al. 2018).

This study suggests that lake heat content measured from greater depths would result in a better indication of lake warming caused by climate change. The authors also show that 3D modelling can be a valuable tool to understand how different parameters contribute to the changes observed in a dynamic environment like Lake Superior.


 Reference


Ye, Xinyu, et al. “Impact of Water Mixing and Ice Formation on the Warming of Lake Superior: A Model‐guided Mechanism Study.” Limnology and Oceanography (2018).


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