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Babbel is a top language learning app that is intuitive and helps you learn by creating real life conversations. There are a lot of, like, weirdly specific  mysteries in the world that a small  subset of people care very much about.

Like, anthropologists really  want to know why we have chins. Astronomers want to know how the moon formed. And, for a long time,  oceanographers have wanted to know: how do the layers of the ocean mix together?

If it didn't happen, the ocean would be  like a layer cake, which would be bad. Many nutrients would just settle  at the bottom, while the oxygen produced via photosynthesis  would all stay at the top. But the do mix, and that's good.

But how does it happen? The energy that is put in by the winds  and tides is less than what’s required   for the amount of mixing that we see,  and yet… the ocean layers do mix. So what else is bringing the mixing energy?

Well, turns out, it might be anchovy sex. [♪INTRO♪] If you want to support this channel,   the Bizarre Beasts pin club is open  for subscriptions for the whole month! Sign up by July 20th and the first pin you get will be the anchovy pin and it is one of the best pins we have ever made! Look at this pin!

It's so good! And stick around at the end of the  video for some bonus anchovy facts. In the early 1900s, Swedish oceanographer  Johan Sandström noted that simple convection in water  cannot stir things up unless the  heat source is below the colder water.

And because the sun is, last time  we checked, above the ocean,   this mostly rules out convection as a  means for churning up the briny depths. But the exchange of water between way down deep  and the surface has been observed for many years. By the mid-20th century, technology  allowed scientists to more directly measure   water movement near the  seafloor,    but there were still a lot of unanswered questions about what was  driving these processes on a global scale.

Then, in 1966, an American physical oceanographer  named Walter Munk rose to the challenge,   and he attempted to calculate which candidates for  the motion of the ocean could explain the mixing. He extrapolated from a specific  sample area of the Pacific Ocean,   and produced several generalized energy equations  for the entire ocean, finding that the turbulence from wind, waves, and tides fell short of explaining the full scope of mixing. To fill that gap, Munk proposed that  the total energy available in marine   organisms was just about equal to  the energy deficit in his model.

That is, the energy expended by animals swimming through the ocean water might be enough to balance out the equation   and explain how the ocean layers mix the way we observe,   it may even be pretty comparable to  the energy of tides and storms. Years later, Munk would insist  that this concept of so-called   “biomixing” was intended  at least partly as a joke. After all, he did make a special point of  stressing that in addition to swimming,   animals also often eat at one depth and then  poop at a different depth,    and that this, too, would meaningfully contribute to the process.

But whether Munk’s initial biomixing  theory was sincere or not, the temptation of its simplicity, animals move through the water,  water moves around animals, got many scientists thinking in the decades since. For example, perhaps, krill could be the answer. There sure are a lot of them, and they  have a habit of moving considerable   vertical distances every day in a process  called diel vertical migration, or DVM.

Twice a day, these little critters swim tens  of thousands of times their body length,   eating and respiring as they go. And although initial studies supported krill as  a biomixing contender, others concluded that,   in spite of their impressive DVM distances,  their effect on mixing is probably minimal. Because they’re so small, the mechanical  energy of their swimming mostly dissipates   as heat energy before ever actually  moving a significant amount of water.

But could larger animals make a big enough splash? Using size and speed data  for a variety of species,   some researchers found promising  possibilities… at least on paper. But direct measurements took the  wind out of those theoretical sails   by yielding similar results to those of the krill: the energy of moving fish was lost as  heat before it could move much water.

So, experts still were not convinced about  the broader plausibility of biomixing. Was it just a rare fluke? Was it possible at all?

Well, this brings us back to the heroes of this story: a whole bunch of anchovies. The European anchovy, Engraulis encrasicolus,   is a nine-to-fourteen centimeter fish found  off the coast of Europe and western Africa. These anchovies travel in  large schools, they eat plankton,   and are an important food source for  bigger fish, seabirds, and marine mammals.

They gather together to spawn in warmer  months, and they tend to do so closer to shore. And, aside from their ability to tolerate  a wide range of salinities and comfortably   survive in brackish water, they  seem like a pretty ordinary fish. But this anchovy species also  engages in diel vertical migration...

In July of 2018, a research crew off the coast of Spain was studying ocean turbulence as a  possible cause for harmful algal blooms. They measured disturbances in the water  continuously for two straight weeks,   and found that each night, something  was causing as much of a ruckus as a major storm,   only to calm back down again by day. But the weather was perfectly fair throughout  the entire study – not a storm in sight.

The team also had a sounding instrument  that could detect the presence of fish,   but they mostly ignored this at first, since  they weren’t actually looking for fish. Then, after repeated nights of unexplained  commotion, the researchers noticed that there was   a strong correlation between the timing of these  events and the presence of fish on their sensors. And sure enough, plankton nets the following  morning pulled in oodles of anchovy eggs.

The nets cast in the morning yielded  eggs that were slightly further along  their 60ish-hour development,  while nets at night pulled in brand new eggs – the anchovies were actively spawning  each and every night of the two-week study. And these unexpected findings were perfectly in line with the known habits of the area’s anchovies. Previous reports of large anchovy  aggregations included peaks in   the middle of the night, and  maximums in July and August.

The fish were just doing what they always did,   and what they always did happened to  include mixing up the water column. The simple act of reproducing turned out to be  important for far more than just the anchovies participating,    and biomixing was finally, at least  in this localized instance, an observable fact. Cooler still, we have since learned that the impact  of biomixing may be more than just mechanical: chemical changes caused by organisms  moving through the water can have   lingering effects well after  the physical motion is over.

In addition to the anchovy,  species like squid, copepods, and jellies, sea creatures known for  both undergoing DVM and forming large aggregations,  are nowadays attracting  attention as possible biomixers, too. The right combination of behavior  and density may just hold the key. And given the major role that ocean mixing plays  in moderating the Earth’s climate,    it is becoming even more crucial for us to better understand  intricate interactions like biomixing.

If biomixing is actually a significant  aspect of ocean layer turnover,   then major disruptions to the ocean’s biosphere, for example, through overfishing, could have  unexpected climate consequences. From lighthearted speculation,  to empirically supported theory,   biomixing is a pretty nifty example of  the complexity and connectedness of our planet’s ecosystems,  and it’s led to a whole  lot of cool research since its joke origins. Munk would go on to refine his calculations  of the energy required for ocean mixing,   and would continue incorporating that very  same sense of humor into his work.

His initial silly suggestion led  to serious research,   and now the importance of biomixing is starting to become  more appreciated,    in no small part thanks to the unassuming European anchovy and its uniquely vigorous spawning practices. It all just goes to show that even  the behavior of small beasts can be   bizarre enough to affect something  as big as the physics of the ocean. Signing up for the pin club  at BizarreBeastsShow.com   helps keep the channel going and helps us keep exploring weird cool topics like this one.

If you want the anchovy pin to be your

first pin, you can sign up by July 20th. We’ve got some incredible artists lined up for the rest of the year, so don’t miss out! And now here are some bonus facts… Turns out Walter Munk isn’t the only scientist  to have a sense of humor about biomixing.

The anchovy study that inspired  this episode earned its authors   the Ig Nobel prize in physics for 2023! The Ig Nobel prizes honor, in their own words, “achievements that make people laugh, then think.” Some previous Ig Nobel winners have studied  what happens when scorpions lose their anuses along with their tails  and what happens when  you put a dead salmon in an MRI machine. If you want to know more  about either of those studies,   you can check out these  two videos over on SciShow.

Or, if paleontology is more your thing,  we wanted to be sure to introduce you to   the earliest representatives of the group that  modern anchovies belong to, which had saber-teeth. Well, to be more precise, they had a saber-tooth  – a single, large, slightly off-center fang. One of the species comes from just over 54  million years ago and it was found in Belgium, and the other dates to between about 48  and 41 million years ago in Pakistan.

If, like an anchovy, you like to travel far and wide, but, unlike an anchovy, you don't want to mix things up as you go you'll probably want to learn new languages along the way. And thanks to our sponsor Babbel, learning a new language has never been easier. Babbel is scientifically proven by researchers at Yale University, Michigan State University, and other major institutions, to help you star speaking a new language in just three weeks.

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