Introduction

The Ocean Cleanup, brainchild of Dutch inventor Boyan Slat, was in the news again this past week after announcing that in addition to the fact that their system is unable to collect plastic as intended, it suffered a mechanical failure. “Wilson” is currently being towed to Hawaii, where it will undergo repairs and upgrades, presumably to be towed back out to the garbage patch for a second trial.

I am not a mechanical engineer, so I don’t intend to comment on the details of their mechanical failure. I am, however, a sea-going oceanographer. Which means that I am used to the sorts of situations with scientific research equipment that was so succinctly paraphrased by Dr. Miriam Goldstein:

Designing for physics

But beyond the engineering, there are the questions of what the *physics* are that TOC are relying on for their system to be successful. Some of you may recall that the original design was to moor (i.e. *anchor*) their device in 6000m (20000 feet) of water, and let existing ocean currents sweep garbage into the U-shaped structure. Thankfully, they realized the challenges associated with deep-ocean moorings, and abandoned that idea.

The latest design iteration (misleadingly called “System 001”, as though they haven’t built and tested any other previous to it), is to have a freely-drifting system, avoiding the use of anchors. TOC claim that under the influence of current, wind, and waves, their design will drift *faster* than the plastic — causing it to accumulate in the U, making for easy pickup. They summarize the concept with a little explainer video on their website, with a representative screen shot below:

Based on a quick Twitter rant that I had after thinking about all this for a few minutes (see here), I wanted to explain out the various points that have either a) been missed by TOC design team, or b) deliberately excluded from their rosy assessment of how they expect their system to actually collect garbage. What follows is a “first stab” at a physical oceanographic assessment of the basic idea behind “System001”, and what TOC would need to address to convince the community (i.e. scientists, conservationists, etc) that their system is actually worth the millions of dollars going into development and testing.

The premise

As outlined in the video, the premise of System001 as a garbage collection system is that through the combined action of wind, waves, and currents, the U-shaped boom will travel faster through the water than the floating plastic, thereby collecting and concentrating it for eventual removal. This appears to be based on the idea that while both the boom and the plastic will drift with the current, because the boom protrudes from the water (like a sail), it will actually move faster than the surface water by catching wind.

There are some issues with this premise. Or, at least, there are some real aspects of oceanography that have either been ignored or missed in thinking that such a system will behave in the predictable way described by TOC. I’ll try and outline them here.

Stokes drift

Any of you who may have had an introduction to ocean waves may have heard that during the passage of a wave, the water particles move in little circles (often called wave orbital motion). While not a bad “first-order” description, it turns out that for real ocean waves there is also some drift in the direction of wave propagation. This drift is named after Gabriel Stokes, who first described it mathematically in 1847 (see wikipedia article here).

The amount of drift depends nonlinearly on both the amplitude and the wavelength of the wave. For example, for a 0.5m amplitude wave with a wavelength of 10m and period of 10s (something like typical ocean swell), the drift velocity is about 10 cm/s right at the surface.

Of course, the Stokes’ solution describes the motion of the water parcels being moved by the wave. For those water parcels to then have an effect on anything in the water, one would need to consider the various components of force/impulse/momentum (i.e. our buddy Sir Isaac Newton). Needless to say, it seems obvious that a smallish piece of neutrally buoyant plastic will respond to the Stokes drift much more readily than a 600m long floating cylinder with a large mass (and therefore large inertia).

This alone could be enough to quash the idea of a passive propagating collection system. Mr Slat?

Ekman currents

While we’re talking about long-dead European fluid mechanics pioneers, any study of the effect of winds and currents wouldn’t be complete without a foray into the theories proposed by Swedish oceanographer Vagn Walfrid Ekman in 1905. What Ekman found was that when the wind blew over the surface of the ocean, the resulting current (forced by friction between the air and the water) didn’t actually move in the same direction as the wind. The reason for this is because of the so-called “Coriolis effect”, whereby objects moving on the surface of the Earth experience an “acceleration” orthogonal to their direction of motion that appears to make them follow a curved path (for those who want to go down the rabbit hole, the Coriolis acceleration is essentially a “fix” for the fact that the surface of the Earth is non-inertial reference frame, and therefore doesn’t satisfy the conditions for Newton’s laws to apply without modification).

Anyway — the consequence is that in an ideal ocean, with a steady wind blowing over the surface, the surface currents actually move at an angle of 45 degrees to the wind direction! Whether it’s to the left or right of the wind depends on which hemisphere you are in — I’ll leave it as an exercise to determine which is which. And what’s cooler, is that the surface current then acts like a frictional layer to the water just below it, causing it to move at an angle, and so on, with the effect being that the wind-forced flow actually makes a SPIRAL that gets smaller with depth. This is known as the Ekman spiral.

The actual depth that the spiral penetrates to depends on a mysterious ocean parameter called Az, which describes the vertical mixing of momentum between the layers — kind of like the friction between them. What is clear though, is that a small particle of plastic floating close to the surface and a 3m deep floating structure will likely not experience the same wind-forced current, and therefore won’t move in the same direction. Hmmm … that’s going to make it hard to pick up pieces of plastic.

What is a “Gyre” anyway?

The final point I wanted to make in this article (I have more, which I’ll summarize at the end for a possible future article), is to try and give a sense of what currents in the ocean (including in the “gyre” or in the region often referred to as the “Great Pacific Garbage Patch”) actually look like. The conception that there is a great swirling current 1000’s of km across is true only when the currents are averaged for a very long time. At any given instant, however, the ocean current field is a mess of flows at various space and time scales. An appropriate term for describing typical ocean flow fields is “turbulent”, as in an oft-viewed video made by NASA from satellite ocean current data.

To illustrate this, I took some screenshots of current conditions from the wonderful atmosphere/ocean visualization tool at earth.nullschool.net showing: ocean currents, surface waves, and wind.

These images illustrate the potential problem with TOC idea, by highlighting the fact that the wind, wave, and current fields of the ocean (including even in the “quiet” garbage patch) are highly variable spatially and temporally, and are almost never aligned at the same period in time. What’s more, is that the currents and waves at a given time and location are not always a result of the wind at that location. Eddies in the ocean are generated through all kinds of different processes, and can propagate across ocean basins before finally dissipating.

Similarly, surface waves have been measured to cross oceans (i.e. the famous “Waves across the Pacific” study pioneered by the transformative oceanographer Walter Munk).

Other issues

Following the “rule of three”, I tried to hit what I consider to be the biggest concerns with TOC system design and principle, from my perspective as a physical oceanographer. However, there are other issues that should be addressed, if the system as designed is really believed by the TOC team to be capable of doing what they say. And really, it seems like a crazy waste of time on behalf of everyone involved to have spent this much time on something if they aren’t sure it will even work theoretically … not to mention the money spent thus far. So, part of me *has* to believe that all the dozens of people involved care deeply about making something that might actually work, and they have studied and considered all the effects and potential issues I (and others) have raised.

Anyway, the other issues are:

• What is the actual response of the system to a rapid change in wind/wave direction? Wind can change direction pretty quickly, especially compared to ocean currents. What’s to prevent a bunch of accumulated plastic getting blown out the open end of the U after a 180 degree shift in wind but before the system can re-orient?
• What about wave reflection from the boom structure itself? It is a well-known fact that objects (even floating ones) can reflect and “scatter” waves (scattering is when the reflected waves have a shorter wavelength than the original ones), and it seems like this could create a wave field in the U that might actually causes drift *out* of the system.
• The idea that all wildlife can just “swim under” the skirt (because it’s impermeable) is not supported by anything that I consider to be rigorous fluid mechanics, aside from the fact that much of what actually lives in the open ocean are non-motile or “planktonic” species. There are a lot of communities in the open ocean that float and drift at the surface, and I see no way that if the System collects floating plastic as it is designed that it won’t just sweep up all those species too. The latest EIA brushed off the effect of the System on planktonic organisms by stating that they “are ubiquitous in the world’s oceans and any deaths that occur as a result of the plastic extraction process will not have any population level effects”. But that doesn’t take into account that the stated mission is to deploy 60 such systems, which are estimated to clean the garbage patch of surface material at a rate of 50% reduction every 5 years. It stands to reason that they would also clean the Pacific of its planktonic communities by the same amount.

The post The (ocean) physics of The Ocean Cleanup’s System 001 first appeared on Deep Sea News.

Using computer art magic, Armand Dijcks has turned the still photographs of Ray Collins into wonderful kinetic images of waves. Turn on full screen. Press play. Be soothed. Calm out.

The post Morning Zen: The infinite waves of Ray Collins first appeared on Deep Sea News.

#Landsat8 saw fine, bright filaments on shallow, super salty #Garabogazkol yesterday.
Bands of foam perhaps? This tweeter does not know. pic.twitter.com/ugSzIS5IGB

— NASA Ocean (@NASAOcean) April 5, 2017

This is the point in class where I raise my hand, jump up and down in my seat, and yell “ME! ME! I KNOW THE ANSWER!” Yes, the filaments contain foam. They also contain flotsam, jetsam, and all sorts of other floaty sea bits. But lines of buoyant sea stuff isn’t the only story. The lines have a greater tale to tell about about the water underneath them.

If you have two people run into each other, they hurt. If you have two surface currents run into each other, they dive. This is what is happening along each of these lines. Waters meet up, have no where to go, then get pushed downward. Unfortunately for the floaty bits, they are just too floaty to descend and accumulate at the surface where the water converges. Come to think of it, this process might also be forming the dust bunnies under my bed. But I digress….

There are all sorts of dynamic ocean processes that forces water to downwell and form these foamy filaments. Traveling waves can overtake slower water and push it downward. Rotating, wind-driven Langmuir cells can push water together in long sets of lines that are parallel to the wind. Lighter water overrides denser water at fronts between different water masses forming lines at there interface. ALL OF THIS COULD BE HAPPENING IN THIS LAGOON ADJACENT TO THE CASPIAN SEA RIGHT NOW!

But foamy streaks aren’t just for satellite imagery. You can see them in your very own local ocean or lake! Plus you get the added bonus of seeing all the other non-foam they contain like seaweed, algae, driftwood, sea ice and all the sea life clumps of floaty stuff attract. Like a college student who has maybe had one too many, go forth and streak ocean, go forth.

The post If you love geophysical fluid dynamics, then you will love these foamy streaks in a lagoon first appeared on Deep Sea News.

Although I was hoping this robotic fleet was deployed for total ocean domination, their true goal was to pretend that they were plankton. Which means they have to act like a plankton. Some plankton are able to move around a little bit, but most of the time are just pushed about by water. For these robots to mimic the movements of plankton, the trick here was to make these Lagrangian floats follow a particular patch of water that is being pushed about by currents and waves. By deploying 16 robots, then you can see how these forces create the plankton patches that have been seen in the ocean.

Which is exactly what this tiny swarm did! And, be still my physical oceanographer heart, the robotic plankton patchiness was caused by internal waves. When the group was in the wave crest, they spread apart! When the group was in the wave through, they clumped together! Exactly as an internal wave should command them.

Let’s not forget the awesome tech that made this happen. Being able to follow a water blob isn’t easy. The robot needs to continually monitor its external surroundings and adjust its buoyancy to stay at a constant depth. And tracking the position of anything underwater? You need to do it with sound. Here they used an array of five sound sources around the swarm that talked to it with special acoustical pings. But to keep the robots small, they couldn’t answer back. They just listened and recorded a sequential round of pings from the sources, which was downloaded later. The location is then determined from the difference in time between when the five pings were transmitted and when they were received. This is some elegant signal processing people.

I only have one suggestion, you hand all the robots over to me and I call them Martini’s Tini Ocean Robot Navy. I shall appear tall, they shall remain small and together we shall drift over all.

REFERENCE

Jules S. Jaffe, Peter J. S. Franks, Paul L. D. Roberts, Diba Mirza, Curt Schurgers, Ryan Kastner & Adrien Boch. A swarm of autonomous miniature underwater robot drifters for exploring submesoscale ocean dynamics.Nat. Commun., 8. 14189 (2017) doi:10.1038/ncomms14189

The post Am I a Robot or am I a Plankter? first appeared on Deep Sea News.

-Space Oddity (Bowie)

A few weeks ago I took a visit to one of my favorite places in Los Angeles, The Huntington Library. Usually, I go because I am obsessed with the immaculate gardens and the 260 copies of “The Origin of the Species” in different editions and languages that the library houses. But this past visit had me excited for a different reason entirely.

As I came into the front entrance, I beheld “The Orbit Pavilion.” And without any background at all, I was like what in the heck is that big shiny thing??

Answer: One of the more interesting pieces of science communication I have seen in a while.

Created by Visual Specialists Dan Goods and David Delgado from the Jet Propulsion Laboratory in Pasadena, California, The Orbit Pavilion is a Natiloid metal enclosure, with an inner lattice structure comprised of speakers.

For 19 Earth Science satellites, composer Shane Myrbeck created a unique sound track based on the data of their mission.  As the satellites orbit the earth in real time, their noises are broadcast through the speaker systems transmitting back to earth the crashing of a wave, a tree branch moving, a frog croaking. Each, an auditory representation of drought, hurricanes, ocean currents, and more. For the International Space Station, a sound track of human voices to represent the only current satellite with a human presence on board.

I found the experience uniquely visceral and an interesting medium to make the seemingly intangible satellites into something more real.

Double upside…I had Bowie stuck in my head the rest of the day…”Commencing countdown engines onnnnn…”

The post Can you hear me, Major Tom? first appeared on Deep Sea News.

The drone they are talking about here is the underwater version, otherwise known as a glider. Gliders are vehicles that carry a suite of oceanographic sensors that measure ocean properties. This could include a CTD to estimate physical properties such as temperature, salinity, depth and sound speed or oxygen, chlorophyll fluorescence and backscatter sensors to measure biological properties. Oceanographers love these things because they are autonomous, meaning they can drive themselves with only a little help from humans on shore (although they sometimes do need to wake up at ungodly hours to help redirect them). Plus, they are much cheaper than using a ship.

From the vague and conflicting description on news reports, I haven’t been able to figure out exactly what kind of “ocean glider” was seized by the Chinese. It is either this Seaglider

or this Slocum Glider:

Operationally, both of these gliders work pretty much the same. They are buoyancy-driven, which means they have a bladder that fills up with either oil or seawater allowing it to sink or float. The wings force the glider forward as it is diving and dive pitch and speed is adjusted by internally shifiting weight inside the body (usually the heavy battery pack). The Seaglider also uses changes in the location of the battery pack to roll itself and steer, while the Slocum Glider steers with an adorable little rudder. What differs is the range and the scientific payloads these gliders can carry. Generally Seagliders go deeper but carry less stuff, while Slocum’s cruise the shallow seas and can be more heavily loaded.

It’s pretty well known that the US has economic and security interests in the region around the South China Sea where the drone was seized. These ocean gliders have been used here before, the Office of Naval Research regularly supports oceanographic research in the region. The question to ask is not why the glider was taken, as it was unclassified and a small asset, rather why was it taken now? As of the writing of this article, the answer to this question is still unclear. However, the US and China have struck a deal and apparently the US is getting its glider back unharmed, which is good news for once ocean robot who took an unexpected detour.

The post Ocean robot seized, causes international incident first appeared on Deep Sea News.

On the second day of Christmas NASA Earth Science gave to me:
Two working jet engines,
and advance warning of Hurricane Activity.

On the third day of Christmas NASA Earth Science gave to me:
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the fourth day of Christmas NASA Earth Science gave to me:
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the fifth day of Christmas NASA Earth Science gave to me
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the sixth day of Christmas NASA Earth Science gave to me
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the seventh day of Christmas NASA Earth Science gave to me
seven seas to sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the eight day of Christmas NASA Earth Science gave to me
eight less viruses to die from,
seven seas to sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the ninth day of Christmas NASA Earth Science gave to me
nine giant zucchinis,
eight less viruses to die from,
seven seas to safely sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the tenth day of Christmas NASA Earth Science gave to me
ten cups of water,
nine giant zucchinis,
eight less viruses to die from,
seven seas to safely sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the eleventh day of Christmas NASA Earth Science gave to me
eleventh hour rescues,
ten cups of water,
nine giant zucchinis,
eight less viruses to die from,
seven seas to safely sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the twelfth day of Christmas NASA Earth Science gave to me
twelve hundred degree cooling,
eleventh hour rescues,
ten cups of water,
nine giant zucchinis,
eight less viruses to die from,
seven seas to safely sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

THE END.

We’ve reached the end of this song, but we have also may have reached the end of NASA Earth Science too. In case you haven’t heard, NASA Earth Science may be on the chopping block. Yeah NASA Earth Science studies change, but it also figures out how we can safely live and move about this complicated environmental system that exists on our planet. Our way of life has been ridiculously improved by pointing the science lens inward from space as well as outward. If we lose NASA earth science, we lose all the verses in this song. If these are products that make your life better and safer, then support NASA Earth Science by sharing all the good things it does for you.

Thanks! *steps off tiny soapbox*

The post The Twelve Days of Christmas – NASA Earth Science Edition first appeared on Deep Sea News.

Love it or hate it, Pokémon Go is undeniably a phenomenon. Although we here at DSN previously warned of the perils of Poké hunting in the ocean, some Pokémon trainers have not heeded our warning. According to scientists at UCSB, some rather enthusiastic players spotted what they thought was a Pokéball floating in the ocean near Isla Vista, California. So of COURSE they swam out and got it.

Turns out this red and white ball attached to a wad of kelp contained no Pokémon. Instead it contained a GPS unit used to track kelp drift along the California coast. OOPS.

Fortunately the group that deployed the buoy plastered their name and contact info all over it and the Pokéless Poké players were able to return the drifter. But seriously Poképeople, no Pokéballs have been released into the ocean. These are scientific instruments with a job to do, so please don’t catch ’em all.

SOURCE:
First Record of Pokémon GO Disrupting Science

UCSB Kelp Study

The post Pokémon GO players, please don’t take drifters from the ocean. THEY ARE NOT POKÉBALLS. first appeared on Deep Sea News.

To any one who, for the first time, sees a great stretch of sandy shore covered with innumerable ridges and furrows, as if combed with a giant comb, a dozen questions must immediately present themselves. How do these ripples form? Are they made and wiped out with every tide, or do they take a long time to grow, and last for many tides? What is the relation between the ripple and the waves to which they owe their existence?

LADY FLUID DYNAMICIST ALERT! LADY FLUID DYNAMICIST ALERT! Let’s just say I was absolutely thrilled to open Google this morning and discover that today’s Doodle was of Hertha Marks Ayrton, a pioneering scientist, engineer and fluid dynamicist. Her list of accomplishments are long. She explained light bulb popping and hissing by experimenting with electric arcs and patented a device for dividing lines into equal parts. Although she was the first woman to be nominated but not elected to the Royal Society of London (due to some dubious issue with her being married), she did become the first female admitted to the Institution of Electrical Engineers (IEE) in 1901. She was also the first female to win the Hughes Medal in 1906. Only one other woman has won the same award, 102 years later in 2008!

But what really captivated me was her paper “The origin and growth of the ripple-mark.” It is beautifully written with a sense of wonder that is sorely lacking from scientific papers these days.

The solution of the problem cost me several weeks of observation and experiment, yet it was absurdly simply when it came to me. It was that a single ripple, existing alone, in otherwise smooth sand, initiates a ripple on either side of it, that each of these ripples produces another on its farther side-these in turn originate on their farther sides, and so on, till the whole sand is ripple-marked.

I love the nod to the difficulties and frustrations inherent in the scientific process, and her ultimate reverence of scientific discovery. She then goes on to show how initial ripples are formed, their growth and the various parameters affecting their size and orientation in a series of tank experiments. The illustrations accompanying the manuscript are also delightful.

Vortices that brush the bottom, removing particles to form hollows and depositing particles downstream to form bumps leading to ripples.

Ripple creation by oscillatory flows like tides (This handwritten font must have inspired Edward Gorey!)

Ripples were not Ayrton’s only foray into fluid dynamics. She also did experiments that showed theories on residual motion in stationary waves, pressure changes by vortices formed by water flowing over obstacles, and the relation of skin friction to vortice coupling were correct!  Not to mention the invention of the Ayrton Fan, which removed poisonous gas from WWI trenches by creating eddies. All in all, she was a pretty remarkable woman and her Google Doodle homage is well-deserved.

References:

http://cwp.library.ucla.edu/articles/ayrton/ayrtonbio.html

http://www.theiet.org/resources/library/archives/biographies/ayrtonh.cfm

Ayrton, Hertha. 1908. “On the Non-periodic or Residual Motion of Water Moving in Stationary Waves”.Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 80 (538). The Royal Society: 252–60. http://www.jstor.org/stable/92896.

Ayrton, Hertha. “The origin and growth of ripple-mark.” Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 84, no. 571 (1910): 285-310.

Ayrton, Hertha. 1915. “Local Differences of Pressure Near an Obstacle in Oscillating Water”. Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 91 (631). The Royal Society: 405–10. http://www.jstor.org/stable/93511.

Ayrton, H.. 1926. “Primary and Secondary Vortices in Oscillating Fluids: Their Connection with Skin Friction”. Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 113 (763). The Royal Society: 44–45. http://www.jstor.org/stable/94582.

Ayrton, Hertha. 1919. “On a New Method of Driving Off Poisonous Gases”. Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 96 (676). The Royal Society: 249–56. http://www.jstor.org/stable/93844.

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The post A little science, a little soccer. All while adrift on the ice. first appeared on Deep Sea News.