I know some of you may be thinking it’s a little early to discuss “ice out”. But, with March already cruising by, it may be the perfect time to take a look at our recent years in Northern New England and see just how “early” it is.
“Ice Out” is an annual event that draws a lot of attention from year-round residents and many folks who spend various times during the winter on the lakes. The term “ice out” wasn’t actually coined until 1951. It has several definitions, and with many friendly bets and contests out there dealing with it, it’s important to settle on a definitive definition. Ice out refers to the annual thawing of winter ice on a body of water. Most people accept ice out to refer to the time when the ice disappears from the surface of a body of water. Lake Winnipesaukee defines ice out when the MS Mount Washington can make it to every one of its ports (Center Harbor, Wolfeboro, Alton, Weirs Beach, and Meredith). The term “ice out” is not a scientific undertaking and can change from person to person and lake to lake, so, for our purposes, we will define “ice out” as the moment when all the ice is gone from a body of water.
Ice melting on Great East Lake – courtesy Wlavallee via panoramio.com
The bigger the lake, the more likely there is a long running data set of when ice out dates were. That being said, I’d be willing to wager that there is one person on every lake in New England that has been recording ice out dates for decades, if not longer. The United Stated Geological Survey (USGS) has a record of 29 New England lake ice out dates that stretch back anywhere from 1930 to present to Sebago Lake in Maine that has a record from 1807 to present. As I mentioned earlier, this is not an exact science. Dates ranging back into the 1800’s are from many individual records. Despite not being scientific, it gives us dates to look at and see if there are any trends to longer or shorter ice coverage seasons.
Although Lake Winnipesaukee is not in our watersheds, it is right next door and has an extensive data set for ice out. We can use this to show a few charts that have average ice out dates and the trend of ice out dates since 1887 when ice out was first recorded.
The chart above shows the trend of ice out dates for Lake Winnipesaukee for the last 125 years. Looking at this chart you can see that the average ice out date has been getting closer to March over that time and actually set a record last year for earliest ice out date in recorded history on March 23, beating the March 24 date set in 2010.
This chart shows a distribution of ice out dates in Lake Winnipesaukee for the last 125 years. This amazed me as it is a near perfect example of a bell curve. April 20 has been the most common ice out date over the last 125 years with frequent ice out dates a week before and after. The chances of ice out being more than a week on either side of April 20 begins to get pretty slim based on this chart.
Great East Lake
We were able to find a comprehensive data set for Great East Lake that stretched back to 1958. The chart below shows the ice out dates (in Julian days, continuous count days from January 1) from 1958 to 2011. Although a few dates were missing, the data shows a few neat trends. Overall, the trend of ice out has been getting earlier. The ice out date began getting earlier in the 1970’s right through the mid-1980’s. From the mid-1980’s on, the dates bounce between slightly higher than average to earlier than average. The average ice out date for the 53 year history is April 14 (Julian day 104).
We also created the below chart (bell curve) illustrating the number of recorded years the ice out happened on a given date. Normally, like the Lake Winnipesaukee chart, we would see a concentration of dates around the average and less as we get away from the average. The Great East Lake chart does not show this trend. This indicates that the Great East Lake ice out date is highly variable depending on the season.
While ice out is a fun annual event that effectively marks the beginning of spring for many people and instills excitement in the upcoming summer, ice out also marks a point in a lake when things begin to change again. In New England, our lakes undergo a series of changes with the seasons. We all know we can swim in lakes in the summer and that they are ice covered in the winter, but what is going on in the depths of our lakes during those seasons?
Mid-latitude lakes are different than many other lakes around the world. We have four distinct seasons and our lakes change during each of those seasons. In summer, most of our lakes are stratified into three distinct sections based on temperature and water density. We swim in the epilimnion where the water stays warm and mixed by the wind, usually the top 5-8 meters (16-26 feet). Below this the water undergoes a rapid temperature change in just a few feet of water that marks the thermocline and metalimnion. Below this is the hypolimnion where the water remains cold and in late summer can be depleted in oxygen due to no mixing.
In the fall, the lake cools and the bottom water and top water mix as they inevitably become the same temperature. By late fall, the temperature of the water is 4°C (water is most dense at this temperature). The entire water column needs to reach this temperature before a body of water can freeze. As winter rolls in, the very top of the lake freezes and the remaining water stays at around 4°C. When water cools below 4°C, it actually becomes less dense due to the crystal structure of water, thus allowing ice to float. Water is one five known compounds and elements on Earth to behave this way.
That brings us to our current time of year. The ice will begin melting with our warmer days and angle of the sun. Once the ice melts and ice out occurs, a lake will again return to that late fall state where the entire water column is 4°C. As the days lengthen and the weather warms, the lake will mix and stratify into the warm top and cold bottom layers.
While the lake undergoes these temperature fluxes, the biology of the lake needs to adapt as well. During the summer, many of you will know where your fish species hide. You will find the warm water fishery abundant in the top few meters and have to work harder for the cold water species, like trout, who hide out in the deepest sections of the lake. During the spring and fall, these cold water fisheries are more abundant as they can use the entire water column for refuge and food.
Many amphibians, like frogs, will swim to the bottom of lakes and ponds and bury themselves in the mud for a long winter nap. A neat aspect of frogs is that despite their lungs, they can actually absorb oxygen through their skin from the mud to breath through the winter.
There is always a human component to lakes. This time of year, one of the biggest influences we have on the lakes is everything that is left behind on the snow and ice. From snowmobile parts and gas to trash and dog poop. When the ice melts, lakes have to deal with a massive pollution pulse before they kick start into spring and summer. It is important for us to remember that despite the frozen wonderland we love in the winter, we need to treat it like the lake that it is underneath.