Friday, 1 February 2013

What do we know about the temperature of lake water?

See the ice pushing up on the shoreline!
I became curious, watching the men try to rescue their fishing huts on Big Rideau.

Due to the density-temperature relationships lake water temperatures tend to stratify and separate into distinct layers.

Understanding Lake Ecology
Density Stratification
In the spring, immediately after ice-out in temperate climates, the water column is cold and nearly isothermal with depth. The intense sunlight of spring is absorbed in the water column, which also heats up as the average  daily temperature of the air increases.

Living beside a small lake, as we did from 2006 - 2010, and cottaging there
for 50 years, I began to get curious about lakes.

We had much Lake Effect Snow, and rain.

The Great Lakes don't freeze over as do smaller bodies of water. Lakes stay at a pretty constant at 4˚ C. on the bottom during winter.
Here you can see the meltwater on the top.
Once the ice warms up, it will sink, melt, and disappear.
It settles in layers by temperature.

Summer lake water varies in temperature
as the wind mixes it up.
The wind mixes the layers, whether there is ice there or not. I once heard a truck cross the ice, they were racing up and down. You could hear the lake water underneath sloshing on the shorelines. It made me curious!

You can see the ice on the top of the lakes. Underneath a demon lurks in the constant temperatures deep below the surface (4 C.).



Lake Effect Snow
The prevailing winds pick up the moisture from the open Great Lakes water, and dump it all over those of us to the east of Georgian Bay. The same is true of those parts south and east of the Great Lakes. You can check out the surface temperatures there.

Lake Effect Snow radar



Lake Effect Snow on its way

 Yesterday, according to NOAA's Great Lakes Research Lab, the mean surface temp of L. Huron is 3.3°C and  less than 5°C towards the centre. Here is my video of snow squalls, which illustrates the snow as it blows across the continent.
water on the web
WOTW
The Great Lakes
HOMES= a nemonic device I taught my students;
Huron, Ontario, Michigan, Erie, Superior.

Our Great Lakes have a monomictic mixing regime.  That is they mix fully once per year and are mixed winter and spring.

Lake Maximum Depth and Area 
Lake Huron
228m
14.8 x 106 acres (6.0 x 106 ha)
Lake Ontario
244m
4.9 x 106 acres (2.0 x 106 ha)
Lake Michigan
281m
14.4 x 106 acres (5.8 x 106 ha)
Lake Erie
70m
6.4 x 106 acres (2.6 x 106 ha)
Lake Superior
300m
20.3 x 106 acres (8.2 x106 ha)

Water differs from most other compounds because it is less dense as a solid than as a liquid. Consequently, ice floats, while water at temperatures just above freezing sinks. As most compounds change from a liquid to a solid, the molecules become more tightly packed and is more denser as a solid than as a liquid. Water, in contrast, is most dense at 4°C and becomes less dense at both higher and lower temperatures. 


Puddles in the ditch from Jennifer Jilks on Vimeo.
Doing some research on lake water, I noticed that our ditch puddle was simulating the lakes. The wind blows on the ice surface, which succumbs to the pressure, and ebbs and flows like a tidewater.

Spring
In lakes of the upper Midwest and at higher elevations, the water near a lake’s bottom will usually be at 4°C just before the lake´s ice cover melts in the spring. Water above that layer will be cooler, approaching 0°C just under the ice. 

1 comment:

Red said...

All interesting science that most people never think about. With huge trucks on ice roads they have to really slow down as the approach a lake shore. They are pushing lake water ahead of them. If you're on the ice as a truck goes by the cracking of ice can really freak you out.