07/12/2010

Maine’s Big Tide; Tide Cycles and Temperature

Tides around here are big. I mean really big at ten to eleven feet. We have cold cold water, and it turns out that combination of clarity of water, temperature and movement of tides make a productive sea life zone. This piece will explore the big reasons to look at tides and a future piece will discuss the plants & animals that live between the tides.

The tides pull large amounts of water in and off the shore. This cycle helps create great places for small creatures to grow. It also stirs up the sediments, and oxygen, making a pretty productive food supply for small animals to feed upon. We also have lots of marshy, muddy areas along the coast, which is also good for production of plants, animals and babies. Here at SeaCats’ Rest our shore gets about 250 feet larger at low tide. Because we have a gradual shoreline, the sea moves quite a bit. Our clam flats (found in muddy zones) are exposed at low tide. We have part rocks, part mud on our shore, so it’s not easy to dig clams, but they are there.

In addition to the tide cycle, some tides get lower and higher than normal. They are called spring tides, and have nothing to do with the season. They cause the flooding of coastal marshes beyond the normal boundaries: extreme high tide as well as extreme low tide. Extreme low tide is a great time for observing sea animals you normally don’t see.

Tides are created by the moon, sun and gravity. The semidiurnal range (twice daily cycle) varies in a two-week cycle.

Around the new and full moon when the Sun, Moon and Earth form a line, the tidal force from the Sun reinforces that of the moon and you get a maximum tide pull. This is what causes the spring tide (not after the season, but just the word “springs” as in jump, burst forth, rise forward). About every year and one-half there is a special tide called a Proxigean Spring tide. It occurs when the moon is both unusually close to the earth and in the New Moon Phase.

The eccentricity of the orbit of the moon in this illustration is greatly exaggerated.

Neap tides are extremely weak tides, where the gravitational forces are at their weakest point.

Geography also plays a role in how large the tides are. Just 2 hours up the coast they are the largest in the world in the bay of Fundy – 55 feet. This is caused by the shape of the bay. Here is an interesting map of larger tidal areas around the world that I found at wikipedia.

I was very surprised to find that the large tides were not unique to Maine or to northern areas. I had assumed in my experience of going to the tropics where I saw little tides, that the tides just got bigger the further north you went. While that is true in North America, if you look at Central America you will see an entirely different story. Tides range and the extremes are sure mysterious and depend a lot on the particular shape of the shore/water interface.

The weather of places is tied with their geography as well as ocean currents and ocean temperature. Places like England and Ireland, which are more northern than Maine have a different winter climate because of the warmer water that surrounds them. We here in Maine have a unique climate too because our ocean water is cooler than most areas of the east coast. That’s why we don’t get hurricanes up here – it’s too cold. The cold water slows them down and they cannot spin as fast, and they die out. On the map above purple is coldest, yellow the hottest zones.