01/25/2011

Sub Zero in Lamoine

On Monday January 24, the Acadia Maine coast experienced the coldest temperatures so far this winter, right on schedule. We reached -8°F just before dawn. Fortunately the ground and roofs are covered by a one-foot blanket of snow and the thermal mass of the ground is not that cold due to the mildness of the winter so far. Still, the cats are refusing to go outside. They ask, but as soon as they get their human to open the door they sit there and fail to budge. All that fur and nowhere to go. And they call themselves Maine Coon Cats!

One of the reasons I can shrug off this cold snap is the fact that the ocean is not even starting to skin over with a layer of ice. February is right around the corner and the sun will be getting noticeably stronger, so we need a lot of cold weather to produce a sea ice layer. As long as it stays liquid, it serves as a thermal sink, keeping the immediate coast several degrees warmer than further inland.

The ocean freezes at -2°C or 28.4°F. This is a little misleading, since the freezing temperature depends on the salinity of the water, and this is always in flux. It also fails to account for the wind and tide stirring up the surface. In practical terms, the sea water has to have been chilled throughout to a temperature near 28.4°F in order for the top layer to begin freezing when exposed to cooler air temps. Right now our local buoys are reporting water temperatures close to 40°F, so freezing seems unlikely. Before freezing starts in earnest, shallow water close to shore skins over and that hasn’t even happened yet.

An odd thing happens when sea water freezes: it expels the salt. This happens because the crystalline structure of ice has no room for the salt ions. The salt is pushed into super-concentrated brine pockets in the ice or sinks below the ice layer. Sailors trapped on the ice knew this, they just melted the sea ice for drinking water. Anything mixed in water will behave the same way. One way to concentrate beer or wine is to freeze it. The high-alcohol product is then poured off the ice or filtered out. This is how Eisbok is made in Germany.

Thick, persistent layers of sea ice form in one of every 7-10 years here in Lamoine. These are the years locals remember and they tell tales of people moving houses out to the islands or deer migrations. Some islands have high deer populations and that’s how it happens. The effect of freeze-up on the local weather is dramatic, since the thermal sink of the liquid water is gone. Suddenly when the ice forms, our temperatures on the coast plummet and the usual annual bottom of -10°F becomes -20°F or less. In these years the lobsters are slow to arrive in shallower waters and may only molt once late in the summer. Lobster fishers waste a lot of time hauling and baiting empty traps. All this because the ocean cools off more than usual. But it won’t happen this year. There’s no sea ice! Not yet anyway.