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WEATHER U: Seasonal flip causes a flap

Warren Hoeg watched as these ducklings set out to explore a whole new world at Sullivan's Pond in Dartmouth, N.S. last week. I wonder if they noticed when the spring turnover occurred?
Warren Hoeg watched as these ducklings set out to explore a whole new world at Sullivan's Pond in Dartmouth, N.S. last week. I wonder if they noticed when the spring turnover occurred? - Contributed

I have mentioned this before, but it bears repeating: I love to get mail.  

Earlier this week, I sat down to this intriguing tale from Christina Brown: 

“Hi, Cindy.  Saturday, June 20th, three of us were sitting in our car, high on the cliff in the provincial park in Herring Cove, N.S. It seemed to be a usual ‘after supper’ drive with the usual sea. This cliff gave us a good view of the cove.  

All of a sudden there was the ever so slightest blip along the shore just below us (I sensed a blip of white), then poof, the surface of half of the water on our side of the cove - which was between us and the other side of the cove shore - turned a beautiful, smooth white. The edge looked as if it had been carved with a very sharp knife while the water on the other side (the side away from us) was navy coloured. This happened all at once. There was not a sign of a ripple or wave. There was no noise. 

Thinking I should take a picture, I turned to take my camera out of my bag and when I turned back, poof, the white was all gone.  None of us has ever seen anything like it. Any idea what it may have been? This was exciting to see, but what was it?” 

I have heard of this before and I recall a similar story, oddly enough, also in the Herring Cove area.  

I’ve never seen it, but I believe Christina and her friends witnessed “a spring turnover.” Spring turnover occurs as the weather warms up and the top layer of the water warms too. During the wintertime, the warmest water is at the bottom, which is where all of the pond life lives during the winter.  

Ice is less dense than water and therefore floats to the top. As the ice melts, the surface temperature will rise and eventually equal the warmer water at the bottom. When the temperature (density) of the surface water equals the bottom water, very little wind energy is needed to mix the water. This is called turnover. 

Imagine a bottle of salad dressing containing vegetable oil and vinegar. The oil is lighter (more buoyant) than the vinegar, which is mostly water. When you shake it you are supplying the energy to overcome the buoyant force, so the two fluids can be uniformly mixed. However, if allowed to stand undisturbed, the more buoyant (less dense) oil will float to the top and a two-layer system will develop. 

During spring turnover, the clarity of the water decreases because mixing brings up nutrient-rich water from the bottom and causes the surface water to look cloudy or milky. 

Christina mentioned a divide, where the water on the outer side of the cove was dark and clear. Away from the shore, the surface water had likely not warmed up as quickly and it wasn’t quite time for the flip. 

Thank you for sharing this rarely observed event.  



Cindy Day is the chief meteorologist for SaltWire Network

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