What is Plankton?

One night, we’re reading a book about whales. It was the prize in a kid’s meal from Chik-Fil-A, and chock full of pictures of whales and dolphins, and he loved it. So we get to the page about the Blue Whale, and he asks what it eats. “Plankton,” I tell him.

He thinks about that for a moment. “What’s plankton?”

I think about that for a moment. “Little tiny plants,” I say. “And tiny shrimp.”

“Ew,” he says, wrinkling his nose.

So there you have it. Whales eat gross stuff.



It turns out that I was wrong. Plankton is not a type of creature, but a lifestyle – it’s defined as “the aggregate of passively floating, drifting, or somewhat motile organisms occurring in a body of water, primarily comprising microscopic algae and protozoa.” This is contrasted with nekton, which is “the aggregate of actively swimming aquatic organisms in a body of water, able to move independently of water currents.” The word comes from the German word Plankton from the Greek word plankton, meaning “wandering, drifting”. That words derives from the proto-Indo-European word *plak-, “to strike, hit”.

There are two different ways to divide plankton:  either by the kingdom the plankton falls into (phytoplankton, zooplankton, and bacterioplankton), or by whether or not the organisms are permanently plankton (holoplankton or meroplankton).


Phytoplankton, also known as microalgae, is “little tiny plants”.  They’re chlorophyll-containing organisms that float in the upper reaches of the ocean where sunlight can penetrate – generally the euphotic region, which is about 200 meters deep.  For the most part, phytoplankton is found along the coasts, in the upper northern and southern latitudes, and along the equator.

There are two magor groups of phytoplankton, dinoflagellates and diatoms.  According to NOAA, “Dinoflagellates use a whip-like tail, or flagella, to move through the water and their bodies are covered with complex shells. Diatoms also have shells, but they are made of a different substance and their structure is rigid and made of interlocking parts. Diatoms do not rely on flagella to move through the water and instead rely on ocean currents to travel through the water.”


Zooplankton include the “tiny shrimp”, just like I told my son.  However, there is a whole lot more to them than “tiny shrimp”.  They include shrimp, worms, water fleas, isopods, tunicates, the larval form of larger organisms, and any other sort of poorly-swimming oceanic ocean life.  This includes jellyfish.

Zooplankton are further classified by size:

Size categories include:  picoplankton that measure less than 2 micrometers, nanoplankton measure between 2-20 micrometers, microplankton measure between 20-200 micrometers, mesoplankton measure between 0.2-20 millimeters, macroplankton measure between 20-200 millimeters, and the megaplankton, which measure over 200 millimeters (almost 8 inches).


Many sources classify bacteroplankton as part of zooplankton, but others classify them as seperate because bacteria are in one of two kingdoms (Archaebacteria or Eubacteria) that is entirely separate from Animalia.  In brief, bacteroplankton are ocean-living bacteria, and there are a lot of them.  Estimates are that the ocean contains 3.1 x 1028 of them, which is a number I won’t type out because it is long and tedious to do so.

Holoplankton and Meroplankton

These two classifications merely describe whether the planktonic organism remains planktonic throughout its entire lifecycle.  Holoplankton are larval organisms, eventually maturing into nektonic creatures, while meroplankton are organisms that remain planktonic throughout their entire lifecycle.

So, next time you go… have fun at the beach.

How Long Is The Ohio (and other questions)?

We had cause to drive into Indiana yesterday, a trip that took us across the Ohio border into northern Kentucky, and then across the Kentucky border into Indiana. And in the area we live, both of those borders are the Ohio River.

My son loves this river – my wife and/or I probably cross the river with him in the car two or three times a week. When he first learned to talk, he called it “my river”, and would excitedly point it out every time he saw it. He’s speculated on whether or not sharks and whales are in the river, insisted it’s actually the ocean, and told me that there are pirates in the river.

Today, though, he was startled to realize we’d crossed it twice while driving in a straight line (well, for “driving on a beltway” values of “driving in a straight line”).  So, from the back seat, he asks “how long is the Ohio?”

Well, I have no idea. So, let’s find out. And maybe answer a few of his other questions while I’m at it.

How long is the Ohio River?


According to the Ohio River Foundation, the Ohio River is 981 miles long.  It begins in Pittsburgh, Pennsylvania at the meeting of the Allegheny and the Monongahela Rivers, and flows until it reaches the Mississippi River in Cairo, Illinois.  Ohio River Facts tells us that the average depth is 24 feet, although it hits a depth of 132 feet near Louisville, Kentucky, and it’s widest point is about one mile (at Smithland Dam)  Wikipedia adds that it is considered to be the main stream of the entire Mississippi river system

Are there sharks in the Ohio? Whales?

No.  Sharks and whales generally reside in salt water and generally would be unable to travel the thousand miles along the Mississippi that would be necessary to reach the Ohio River.  The Falls of the Ohio State Park does list the types of fish found in the river, though.  In brief, they are:

  • Bass
  • Bowfin
  • Carp
  • Catfish
  • Codfish
  • Darters
  • Drum
  • Eels
  • Gar
  • Minnows (and “Minnow-like” fish)
  • Lampreys
  • Mooneyes
  • Paddlefish
  • Perch
  • Pike
  • Walleyes
  • Sculpin
  • Shad
  • Sturgeon
  • Sunfish

Some oceanic fish do make it up the Mississippi to the Ohio, though.  These include the Coho Salmon, Atlantic Rainbow Smelt, and the Sea Trout.  There’s also at least one documented case of a South American fish called a red pacu being caught in the Ohio – most likely something from an aquarium that was dumped in the river.

Still, crazy things happen.  Remember how I said that “sharks and whales generally reside in salt water and generally would be unable to travel the thousand miles along the Mississippi”?  Well, in 2014, a dead bull shark was found near Manchester, Ohio.  It was small, only about 2 feet 9 inches (0.8382 meters) long, but there it was.  Sadly, I couldn’t find any follow-up information about how it got there.  They are freshwater tolerant, though, so it’s not unreasonable that it could have swum all the way.  The same isn’t true for the spiny dogfish shark found in Illinois in 2010, though, which was most likely caught by a fisherman in the Gulf of Mexico and then dumped.

I couldn’t find any confirmed sightings of dolphins or whales, though.


Are there pirates on the Ohio River?

Yes.  Or, at least, there were.  The town of Cave-In-Rock, Illinois was home to a few different bands of river pirates in the 18th century.  Most preyed on flatboats that became stuck on rocks, but at least one gang posed as river pilots.  They would take on the job of steering the boats through the tricky waters of the area, and then maroon them at Cave-In-Rock where they could be robbed and killed.

There were others, as well.  Cave-In-Rock wasn’t the only source of pirates on the Mississippi and Ohio, after all.

Is the Ohio River the ocean?

No.  Clearly not.

What If The Oceans Froze?

My son has a fascination with ice. He loves it in drinks (something he gets from me, more than from his mother), and he loves to look at it. We play games with it, like the time I put an ice cube in a bowl for him so he could watch it melt. Or the time we left a cup of water outside to see it freeze. I think he likes the idea that water can turn into a solid, and the fact that it’s cold is just a bonus bit of entertainment.

So we’re driving to church one Sunday, and looking at the snow that’s covered everything – one of the few days this winter where we’ve actually had snow – and he asks me “what if the oceans froze?”

Well, that sounds like an apocalyptic scenario if I’ve ever heard one. “Froze solid?” I reply?

“Yes! So we could ice skate on them!”

Bear in mind that my son has never gone ice skating. So I have no idea where that came from. But the question is interesting. And, sadly, nowhere near as much fun as he’d hope.

When Does Salt Water Freeze?

To start with, ocean water has a much lower freezing point than freshwater. In “Can the ocean freeze?“, NOAA informs us that seawater freezes at 28.4 degrees Fahrenheit (which is -2 degrees Celsius), because of the salt. They also tell us that the average temperature of all ocean water is about 38.3 degrees Fahrenheit (3.5 degrees celsius). So, in theory, to freeze the oceans we’d simply need to reduce the average ocean temperature by 9.9 degrees Fahrenheit (5.5 degrees Celsius).

How cold would it have to get?

Interestingly, the simple truth is that all you’d have to do to freeze the ocean is get the air below the freezing point of the ocean. Then, eventually, you’d manage it. That would require bringing the average equatorial temperature down to that level, and the best figure I could find for that average temperature is 77 degrees f (25 degrees C). That’s a 38.7 degree F (21.5 degree C) difference. This would bring average global temperatures down to 22.3 degrees F (-5.5 degrees C), so things would be terribly cold. To put it in perspective, polar climates have an average temperature of 50 degrees F (10 degrees C).

Killing Frost

A killing frost is a temperature that will kill a plant entirely – not just damage the extremities. Corn and soybeans will die below 28 degrees F. Wheat is a little hardier, depending on the growth stage, but will pretty much die at 24 degrees F (-4 degrees C). So if it got cold enough to freeze the oceans, we’d be living in a permanent killer frost.  Which is another way of saying that we’d be in huge trouble.

Snowball Earth

Interestingly, this may have happened before. There is something called the Snowball Earth hypothesis, that says the Earth may have been frozen like this some 650 million years ago. Equatorial temperatures would have been around what present day Antarctic temperatures are like now – which means an average range of -67.18 degrees F (-55.1 degrees C) in Vostok to 22.46 degrees F (-5.3 degrees C) in the Antarctic Peninsula. There’s a whole lot of disagreement about this theory, though, so take it with a grain of salt until and unless more information comes along.

Ice And Snow

It’s winter, and it finally snowed in these parts, and these two facts have combined to make my son quite happy. Every day after I pick him up from his preschool, he asks if we can go walk in the snow – something that turns into us hiking across snow-covered fields and throwing snowballs at each other, and which ends with us having to leave snow-caked shoes in the hallway and hanging snow-covered coats and gloves (and sometimes pants) in the bathroom to dry.

“Why does it snow?” he asked yesterday, after we were back inside and bundled up under some lovely fleece blankets.

Uhm… I haven’t the slightest idea. I mean, I know it must be related to the concept of rain. Both rain and snow are precipitation, after all. But I don’t really know why snowflakes form instead of, say, sleet. Which makes this a great question! And a great question to combine with another one he asked, which came up while he was drinking some water: “why is ice made out of water?”

So let’s find out.

What is “Freezing”?

To understand freezing, we’ll need to take a quick look at matter. For help with this, we’ll turn to LiveScience.com and Matter: Definition & the Five States of Matter. They define matter as “anything that has mass and takes up space). The state of matter is the form the matter takes, with the most common states being solids, liquids, gasses, and plasma. (The article lists Bose-Einstein condensate as the fifth state; Wikipedia lists twenty-one different states). Matter can also be said to be in a phase, which is “a region of space (a thermodynamic system) throughout which all physical properties of a material are essentially uniform”.

Using ice as an example, an ice cube is water in the solid state in a phase the size of the cube. Ice cubes in a glass of water then represent a system which has water in two states (solid and liquid) and two phases (the liquid volume, and the volume of the ice cubes).

With that in mind, we’ll turn to Purdue University and Freezing:

When a liquid is cooled, the average energy of the molecules decreases.

At some point, the amount of heat removed is great enough that the attractive forces between molecules draw the molecules close together, and the liquid freezes to a solid.

The temperature of a freezing liquid remains constant, even when more heat is removed.

The freezing point of a liquid or the melting point of a solid is the temperature at which the solid and liquid phases are in equilibrium.

The rate of freezing of the liquid is equal to the rate of melting of the solid and the quantities of solid and liquid remain constant.

What happens when water freezes?

When water freezes, it undergoes a phase change from liquid to solid. Energy is removed from the water molecules, slowing them down and making them become more dense. However, it hits maximum density at 4 degrees Celsius (39.2 degrees Fahrenheit) – below that temperature, water starts getting less dense.


As water begins to freeze, the molecules crystallize into open hexagonal structures.
This hexagonal structure contains more space than liquid water, making it less dense. So, by the time it has fully hardened into a solid, it floats on top of the liquid water.

How do snowflakes form?

Snowflakes start off just like rain – as water droplets forming around pollen or dust. The distinctive shapes arise because of crystalline hexagonal structure I mentioned above. A single water crystal will have six sides, and this causes the crystals to build up into a symmetrical pattern as they grow in size. The specifics of the shape are determined by the temperature and the atmospheric conditions:

Ultimately, it is the temperature at which a crystal forms — and to a lesser extent the humidity of the air — that determines the basic shape of the ice crystal. Thus, we see long needle-like crystals at 23 degrees F and very flat plate-like crystals at 5 degrees F.

The intricate shape of a single arm of the snowflake is determined by the atmospheric conditions experienced by entire ice crystal as it falls. A crystal might begin to grow arms in one manner, and then minutes or even seconds later, slight changes in the surrounding temperature or humidity causes the crystal to grow in another way. Although the six-sided shape is always maintained, the ice crystal (and its six arms) may branch off in new directions. Because each arm experiences the same atmospheric conditions, the arms look identical.

Sleet, Hail, and Frozen Rain

All of this made me wonder, though. If snow is literally created by the same process that creates rain, where to the other types of “winter weather” come from? That is, sleet, and hail, and frozen rain. Fortunately, NOAA has the answer.

Snow generally begins life in the “dendritic growth zone” (aka the “snow growth zone”), a layer in the atmosphere with temperatures between 10.4 and 0.4 degrees Fahrenheit (-12 to 18 degrees Celsius), and cannot form if the atmospheric temperature rises above 32 degrees Fahrenheit (0 degrees Celsius). Additionally, the relative humidity of the atmosphere must be at 70% or greater. Note, however, that the dendritic growth zone is not a formal layer of the atmosphere (hence the term “zone” instead of “layer”) – it can form at different altitudes, depending on the weather.

At some point – one which is determined by the size of the snowflake and the weather conditions – the snowflake falls. It may partially melt as it falls, but as long as it passes through no more than “a very shallow melting layer” (no more than 1,500 feet thick) that is no more than 33.8 degrees Fahrenheit (1 degree Celsius) and then refreezes. In fact, partially melted and refrozen snowflakes help produce the wet snow that is so beloved of people who build snowmen and pack snowballs.

Sleet starts life as snow, and goes through a similar process to the creation of wet snow. However, it hits a melting layer that is less than 2,000 feet thick and has a temperature between 33.8 and 37.4 degrees Fahrenheit (1 to 3 degrees Celsius). All of which is a fancy way of saying that sleet is partially melted snow.

Freezing rain also starts life as snow. However, it hits a melting layer with a temperature above 37.4 degrees Fahrenheit (3 degrees Celsius). This makes it melt completely. The exterior cools below freezing as it falls, but it doesn’t fall long enough to turn into sleet before it hits the surface. But, since the exterior is at the freezing point of water (or extremely close), it freezes on contact with the surface.

Hail is as unrelated to snow as anything that starts out life as “ice crystals in the upper atmosphere” can be. It israin that gets blown up into extremely cold layers of the atmosphere and freezes. Then it falls when the wind won’t hold it up, only to (possibly) get blown upwards again and have more layers of ice freze around it. This can continue until the updrafts that keep throwing it upwards are no longer able to do so.

What’s A Whirlpool?

It’s bath night for my son, and we’re nearly finished. The last step is our ritual of unstopping the drain and letting him play until all of the water runs out. This is generally a time of frantic activity as he tries to pack in as much play as possible. This night, he really pays attention to the way that his toys are caught by the current and begin spinning above the drain. He grabs one, pulls it away, and watches as it drifts back and starts spinning again.

“It’s like a whirlpool,” I observe.

“Yeah!” he agrees. And then, without missing a beat, adds “What’s a whirlpool?”

Uhm… uh… You know, I don’t actually know what a whirlpool is. Not really. Oh, sure I know what they look like – I have, ever since I watched 20,000 Leagues Under the Sea. But I don’t actually know what they are. All I can say is that I’m pretty sure they’re not places where water is draining out of the ocean through cracks in the sea floor.

Pretty sure.

Wikipedia defines a whirlpool as “a body of swirling water produced by the meeting of opposing currents”. The article goes on to note that powerful whirlpools are often known as maelstroms, and that any whirlpool with a downdraft is properly known as a vortex. Also, “the most powerful whirlpools are created in narrow, shallow straits with fast flowing water.”

The Times of India provides a paragraph-long explanation that, while generally agreeing, goes into more detail:

A whiirlpool is a large, swirling body of water produced by ocean tides. When flowing water hits any kind of barrier, it twists away and spins around rapidly with great force. This creates a whirlpool. Whirlpools can occur in a small area where a piece of land juts out into a river, causing the water to swirl around. They can also occur in the middle of the ocean when one current meets an opposing current, as when an incoming tide hits the ebb current of the last tide. Strong winds can also whip up the water into whirlpools.

Basically – for whatever value ‘basically’ has when dealing with a complex problem in physics – a vortex is a mass of fluid rotating on an axis and flowing towards the center. The speed of rotation is fastest at the center, and slows down as you move away thanks to the conservation of angular momentum. Whirlpools are an expression of vortexes in water, just like hurricanes and tornadoes are expressions of vortexes in the air. But what actually causes them? Well, here’s my layman’s understanding of the process.

You start with a moving mass of fluid (which can be water or air, because both are considered fluids for this purpose), which is better known as a current (in the water) or wind (in the air). The moving mass is not a single solid object, and so it will deflect if it hits an obstacle – whether solid object or another moving mass. If the deflecting obstacle is moving as well, or if the deflecting object is curved, it will cause the deflected mass to pick up a little spin. This spin is then exaggerated by the fact that the rest of the moving mass is still coming, forcing it to spin more. Thanks to the conservation of angular momentum, this forces the spinning section to pick up speed as the curve becomes tighter. A vortex is formed.

So, are whirlpools dangerous? The answer is an unequivocal it depends. Like all currents, their danger depends on how powerful they are and how experienced you are. You should always respect them and take them seriously, but you don’t need to fear them. Most of them.

Well, go ahead and fear that one. It’s the Saltstraumen Maelstrom, off the coast of Norway, and has the strongest tidal currents in the world – up 20 knots (about 23 mph, or 37 kph).  It can kill you.