Today and yesterday we had a king tide—a term popularly used to describe the highest tides of the year. When I first got into open water swimming last winter, I read all the books I could get my hands on: swimming memoirs, cold water swimming treatise, histories of swimming, wild swimming guides, and books about ocean tides.
This was one of my favorites:
There was so much I didn’t know about the tides, but the coolest thing I learned was that no one totally understands them. For all the science and research, there is still an element of mystery to it all. Planetary motion is predictable to a certain extent, but it’s also not. There is poetry and magic to the tides and I love that. No wonder they figure so heavily in religion, mythology, lore and art.
But I also loved learning about what is known about tides. While I had a vague sense that the moons controlled the tide, I didn’t know that the tide is affected by the gravitational pull of both the moon and the sun, though the moon’s influence is significantly greater. When the moon and sun are at opposite sides of the earth, there are less dramatic tides because the sun’s gravitational pull, albeit weaker, is acting in opposition to the moon’s. In contrast, tides are more extreme during a full or new moon because the earth, moon, and sun are roughly aligned (a phenomenon known as syzygy–when three or more celestial bodies line up) and the sun and moon are pulling from the same direction. These (mostly) twice monthly tides are known as spring tides. Conversely, when the moon is quarter full and opposite the sun, we get a neap tide, where there is the least dramatic difference between low and high.
At the same time, the planetary orbits are elliptical—more oval shaped than circle—and so sometimes the moon, sun, and earth are closer to each other and sometimes they are further away. When the moon is closest to the earth (in perigee) the tidal force can be 22% greater than average. If the moon is in perigee AND it’s a full or new moon, we get an extra dramatic tide (a full moon in perigee is what we call a supermoon). These extra dramatic tides happen about four times a year (twice during the new moon and twice during the full moon).
But the earth is also orbiting like a squashed circle and so sometimes it’s closer to the sun (in perihelion). Since the earth’s orbit around the sun is much slower than the moon’s around the earth (a year versus a month), this is less frequent (in fact, it only happens once a year around January 2nd). I’m sure I’m oversimplifying all of this. Charts and diagrams and mathematical equations abound to properly predict and explain the precise geometry of the planets and their gravitational influence on the tides. Geography plays a big role, time, centrifugal force, weather patterns, seismic shifts, and all sorts of other things I don’t understands. But the gist, as far as I can tell, is this: If everything is aligned; a new or full moon, the moon in perigee and the earth in perihelion, we get extra extra dramatic tides.
Which brings us to now: January 2nd was a new moon, the earth was in perihelion and the moon in perigee and, thus, we had a king tide yesterday and today. There is a cool organization called the King Tide Project collecting data on king tides to help understand what will come with climate change and ocean rise (the idea being that the king tides now will be the moderate tides of the future and we need to plan for that).
The Bulb at king tide
As for me and my swim, I’m back home so I trekked down to my favorite local swim spot, the Albany Bulb. I had a busy morning and missed my chance to swim with any of the usual bulb crew, so I set out on a solo swim. I’m not used to swimming alone and I didn’t know what to expect from the king tide—I’ve never seen it so full!—so I stuck close to the shore and did laps back and forth. It was gloriously cold and invigorating as well as distressingly filled with flotsam and jetsam.