It's Summer. Some Stuff You Should Know About the Ocean

It's June 20th, the official start of summer and the longest day of the year. For many of us, this conjures up thoughts about beaches and the ocean. Some people are scared of the sea. This may not help soothe your fears, but it's interesting anyhow. 

1. The Ocean Temperature is All About the Wind - Cold Water Upwelling 

Last week, the ocean temperature on Fire Island [1] finally reached a swimmable temperature. I'm guessing it was nearly 70 degrees. It felt great. Yet, the week before, if you stuck your toes in, they immediately disconnected from the rest of your central nervous system. Maybe 60 degrees. Wouldn't jump in there if I were on fire. So, what happened? What didn't happen was that the ocean warmed up in one week due to the sun. It could just as easily be 60 again next week. So, what is going on?

The answer is the wind, the primary driver of ocean temperature on the East Coast beaches. The wind direction can change the water temperature by 10 degrees in a few hours. It results from something called cold water upwelling, which is nicely illustrated by the figure. When the wind blows onshore (off the ocean) in a "disk" of warm, clear surface water, it forces the deeper, colder water away from the beach. The result is blue-green tropical-looking water. But when there is a strong offshore wind, the opposite occurs. The surface water is pushed away from the beach, and a phenomenon called cold water upwelling forces deeper water, which is darker and cloudier (algae prefer cold water), to the surface. The effect can be pretty dramatic.

Because of this effect, experienced ocean goers can usually tell whether the ocean will be warm or cold before they ever reach the beach, simply by noting the direction and strength of the wind. And when they get there, the color of the water is a dead giveaway. Dark or brown means cold. Blue-green means warm. You have probably seen something like this before:

 (Left) Cold, (Right) warm. Same spot, same beach, different day with a different wind direction. 

Rule of thumb: It is usually a good swimming day if you can smell the ocean before you get to it [2].

Little-known fact: Many beaches are hotter in the morning than in the afternoon because of the sea breeze. Why?

During the day, the sun heats the land faster than the sea. As the land warms, the air above it heats up and rises, creating low pressure. Cooler, denser air from the sea moves in to replace the rising warm air, creating a sea breeze. This breeze typically develops in the late morning to early afternoon and can extend several miles inland, providing a cooling effect

2. The purple and black sand is not dirty

I can't even estimate the number of times that I have heard people look at the dark sand found on many beaches and comment how awful it is and how we've polluted the ocean with oil. But they are entirely wrong. Here's what is really going on:

Purple and white, and black sand. Photo credit: Fire Island National Seashore

The dark sand is a mixture of three minerals — quartz, garnet, and magnetite- clearly visible under a microscope. If you take a magnet to a handful of the stuff, all the black gets picked up, leaving behind the purple and white. It works like this guy you may have played with as a kid.

Photo credit: Wikipedia

3. Blue is a great color, but not so much in the ocean

Although they are usually found in southern waters, Portuguese Man-of-War can be carried by winds and the Gulf Stream far up the East Coast of the Atlantic. I HATE them. (And have experienced the sting. It is pure agony.)

Portuguese Man-of-War. A hideous lifeform. Photo: Flickr

There are precisely two redeeming qualities of Portuguese Man-of-War:

1. They are very easy to spot because of a bright blue balloon-like air sac that floats atop the water.
2. I lied. There isn't anything else good about them.

You do NOT want to experience this sting. It is excruciating. So, if you see something blue floating at you, I recommend that you:

1. Scream
2. Turn around and run the other way
3. When you get there, keep going

Here is something else blue that you would do well to avoid. A bluefish:

A cranky-looking bluefish. Photo credit: Wikimedia Commons

Looks harmless enough, right? Nope:

These bad boys are not only in a perpetually lousy mood, but they have teeth to back it up. They have been known to bite through fishing hooks, so the following observations from The Outdoor Life website's "10 Fish You Need to Handle With Care" aren't that surprising:

• "If they had a taste for human flesh, no one would go swimming." (My personal favorite)
• "Mangled fingers cut to the bone will be your souvenir for a careless hook extraction."
• "True or not, bluefish seem to bite with purpose."

 So, have a lovely, safe summer. Enjoy the beach, but never turn your back on the ocean. Otherwise, it won't end well. Check out YouTube for people getting demolished by waves. Not as much fun as you'd think. This one is up for a Darwin Award: 

Notes:

(1) Fire Island National Seashore, a 32-mile barrier island, is part of a 120-mile group of beaches stretching from Coney Island to Montauk.  It is one of only a handful of developed US islands with no cars or roads.

(2) An offshore wind in the summer is a double whammy. The ocean is freezing, the normal sea breeze "loses" the fight with the offshore wind, and the beach is hot. A hot beach plus icy water isn't a great combination. Worse still, biting flies live in the dunes. When the wind is blowing from that direction, forget it – you're gonna be a meal.