On my summer trip to Maine we spent all of our time on the coat, enjoying the ocean, the rocky shoreline, and the tidepools. Among the state’s many wonders, I was awed by how great the tidal ranges were there; the difference between high and low tide was on average between 8-12 feet, and even higher in the more northern parts of Maine. I grew up on the east coast, experiencing tide ranges of only 2-3 feet on the Maryland shore. Which made me wonder, why is the tidal range so much greater in some places? I reasoned, incorrectly, that the range of tide increased with latitude.
A bit of research revealed that the tidal range experienced in any one location has nothing to do with latitude or longitude, but is instead affected by several other factors. To start, tidal range is affected by the shape and geometry of a coastline. Coastlines with more curves (inlets, bays, peninsulas, etc.), such as that of Maine, will have a greater tidal swing than coastlines that are straighter and less varied.
In addition, in the northern hemisphere, the continents are closer together in the higher latitudes, thus constricting the ocean and creating higher tidal ranges – the water has to go somewhere! However, in the southern hemisphere, the continents are not as close together in the higher latitudes and therefore this region does not experience the same tidal range as their northern counterpart.
Finally, continental shelves affect the tides. In places where the continental shelf just off the coast is shallow and wide, the greater the tidal range. And conversely, in places where there is no continental shelf and the water offshore is deeper, the less tidal range there will be, as in Hawaii – something I’ve also wondered about!
For even more information about tides, watch this video with Neil deGrasse Tyson!