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.

This ocean expedition, lead by RSMAS scientist Lisa Beal and going on for the last three years, also has a pretty slick website.  For tech nerds like me, you can check out the instrumentation used to measure the Agulhas Current.

Full disclosure and shameless plug:  I know Lisa Beal (she’s awesome IRL) through a mentoring program for female Physical Oceanographers, MPOWIR. If you are just a female physical oceanography graduate student, postdoc or early career scientist you should definitely check the program out. It has helped me and many other PO ladies to navigate the twists and turns we have faced in our scientific life and career.

h/t to @marinexplore for the link to the movie

The post “Why should men have all the fun?” The seafaring ladies of physical oceanography first appeared on Deep Sea News.

We’re still working out the kinks…and trust us, these new things can get pretty kinky (#TWSS). Bear with us as we build up our visual smorgasbord, and be sure to check out our initial smattering of pinboards:

• Invertebrate Love – All invertebrate pictures, all the time
• Giant Squid – This board needs no explanation
• Habitats of the Deep – Showcasing what the deep sea actually looks like; it ain’t all mud plains!
• Gadgets & Gear – Because “every now and then you just need to stare at some cold hard steel”
• Waves + Fluds = Physics, baby! – All the physical oceanography goodness you ever wanted
• Let’s get it on – Come on, what would DSN be without a Pinterest board on marine sex?
• Fish, sharks, and marine mammals – Well someone needs to grow a backbone around here.
• Marine research bucket list – A personal board for us Deeplings, to showcase our most wished-for research questions and field sites
• The ocean…from SPAAAACE! – Satellite images of the ocean are so awesome that they need their own board.
• Drink up me harties – A board about beer and other tipples we drink while blogging
• Conservation & Conversation – Upcoming events, breaking news, viral content

The post Announcing the DSN Pinterest empire! first appeared on Deep Sea News.

It’s not Wednesday, but I am going to post this anyway!

Neil Banas is an oceanographer at the University of Washington*.  He also make incredible INTERACTIVE visualizations of biophysical processes.  There are so many he just gets an entire post.

Check out this schematic of a nutrient-phytoplankton-zoology model.  Even better, click on pic and you can play with all the models!  Adjust how much nitrogen, light, vertical mixing, etc. your sea beasties get to determine whether they survive or perish!! By adjusting these parameters, you can change how much nutrients N go into the system, how many phytoplankton P and zooplankton Z there are,  and finally how much detritus D is produced by these critters dying.  The models are controlled by a set of mathematical rules and connections, which are broken down into their most basic form here.

Like coastal circulation? Want to see where water goes? Then he has flowWeaver. Designed for output from a regional model of Puget Sound and coastal Washington, the simple GUI is a beautiful thing.

And finally, the funnest model of all to play with, the Okubo swarming model. Make your zooplankton attack the white attractor!  Give ’em coffee jitters with excitation. Make them hungover and sluggish by adjusting the damping.

Who knew zooplankton were so much fun?

* Disclaimer: Neil and I went to grad school together, which is how I know about his work.  His defense was one of the most beautiful presentations I have ever seen.

The post Visualization Vednesdays: Art and science first appeared on Deep Sea News.

We’re very excited to introduce another guest post from Kim Martini here at DSN (read previous posts here).  Kim is a physical oceanographer working at the University of Alaska, Fairbanks and as the post reveals below is interested in deep-ocean waves.  You can find her on Twitter at @rejectedbanana.  Make sure to comment below and welcome her to DSN.

As oceanographers, we have a pretty good idea of how much mixing there should be in the ocean. But the problem is, we don’t actually know where it is. Sounds kinda crazy right?

We measure turbulence to figure out how water is mixed in the ocean. Ocean mixing is important because not only does it exchange water between the deep and shallow seas, but it will also transport small particles that are in water. This includes nutrients, sediments, and even sea beasties!

What makes mixing so hard to find is the fact that turbulence tends to be `patchy.’ Turbulence isn’t uniform across the ocean and doesn’t always occur at the same place or time everyday. Most of deep ocean, far away from the coasts, has really low levels of turbulence. Therefore, there must be places where there are really high levels of turbulence. We have found some of these high mixing regions, but still haven’t found enough to close global mixing budgets. This includes places like the Southern Ocean where wild winds whip the sea but also trashes ships, spots where currents flow over bathymetric bumps such as seamounts and ridges, and regions where waves break such as deep canyons and rugged continental slopes.

But all is not lost my friends, we will find the mixing! We know the winds and the tides pump energy into the ocean to mix it. And we know something about the pathways and processes that cause this energy to eventually degrade into turbulence. There is even some evidence that the daily migrations of plankton and swimming of sea life can mix the oceans. With this information we can go out and continue our search for the missing mixing.

So next time you meet a scientist that studies ocean turbulence, don’t forgot to tell them Happy Hunting!

The post Searching for microscale turbulence at the macroscale first appeared on Deep Sea News.

The post The Largest Waves in the Sea Aren’t at the Beach first appeared on Deep Sea News.

Via @nparmalee

The post Must-watch video on rip currents first appeared on Deep Sea News.

Debris from the 2011 Japanese tsunami is headed towards Hawaii and the North American west coast. For those concerned, several new sources of information are now available on the web:

Explainers: NOAA has a new video and podcast explaining how the debris is moving across the ocean, and what you can do to help. (Click through – it can’t embed). Ocean Conservancy also has a really nice explainer webpage. Though this isn’t new, the NOAA Marine Debris program also has a tsunami FAQ page.

NOAA visualization of debris track: Here is a visualization of the possible debris track from the NOAA Environmental Visualization Laboratory. (Again, you must click through, sorry.) It is based off 5 years of historical weather patterns, and is an approximation of a path the debris may take. For another look at possible debris paths, see my post on how scientists tracked tsunami debris to 700 miles off Midway Island.

Webinar: Japanese Tsunami Marine Debris: Anticipating and Mitigating Its Impacts on the Northwestern Hawaiian Islands. This webinar took place last Monday, and a video is now available for those who couldn’t catch it live. You can also see my tweets at @seaplexscience. If you are interested in more events of this type, sign up for the MarineDebris.Info listserv.

National Geographic story on tourists paying to go on an expedition to hunt for the debris field with the NGOs Algalita Marine Research Foundation and 5 Gyres.

Transpacific Tsunami Debris Presentation by Dr. Curtis Ebbesmeyer and Jim Ingraham. Dr. Ebbesmeyer is the physical oceanographer famed for tracking rubber duckies and Nike sneakers across the world’s oceans, and Jim Ingraham is a retired NOAA oceanographer who developed the Ocean Surface CURrent Simulator (OSCURS) model. (The OSCURS model is the basis for the debris path models linked to above.) The presentation was given at Peninsula College (Port Angeles, WA) on December, 13th 2011 and sponsored by Peninsula College, Coastal Watershed Institute and the Olympic Peninsula Chapter of Surfrider Foundation.

The post Japanese tsunami debris link roundup first appeared on Deep Sea News.

T

The tsunami debris map above is a mathematical model, but it has a basis in the real world – it’s based on the paths taken by thousands of freely drifting buoys. The Global Drifter Program (GDP) currently tracks 1,037 of these buoys throughout the world’s oceans, and explains their design like this:

The modern drifter is a high-tech version of the “message in a bottle”. It consists of a surface buoy and a subsurface drogue (sea anchor), attached by a long, thin tether. The buoy measures temperature and other properties, and has a transmitter to send the data to passing satellites. The drogue dominates the total area of the instrument and is centered at a depth of 15 meters beneath the sea surface.

The drifters are easily deployed off any ship – you just toss them overboard (I’ve done this! It’s fun!) – which makes them a relatively inexpensive way of getting a lot of information about how the ocean’s surface moves and changes. All this information can be incorporated into mathematical models of how drifting objects move through the ocean, making these models more accurate. Drs. Maximenko and Hafner used this data to create the Surface CUrrents from a Diagnostic model (SCUD), which incorporates real-time satellite data and drifter tracks to predict how tsunami debris will move across the Pacific.

However, a drifting buoy with a 45-foot sea anchor is going to move pretty differently than tsunami debris that contains everything from cars to boats to the contents of people’s houses. That’s why it’s very important to test these models in the real world. Fortunately, the STS Pallada, a Russian sail training vessel going from Hawaii to Vladivostok, had Maximenko & Hafner’s debris maps and kept a eye out for tsunami debris. (The nonprofit organizations Algalita & 5 Gyres are also mounting an expedition to find the tsunami debris, scheduled to depart in May 2012).

Here’s what the crew of the Pallada found. From the UH press release (PDF):

“Yesterday, i.e. on September 22, in position 31 042,21 N and 174 045,21 E [about 700 miles northwest of Midway], we picked up on board the Japanese fishing boat. Radioactivity level – normal, we’ve measured it with the Geiger counter,” writes Natalia Borodina, Information and Education Mate of the Pallada. “At the approaches to the mentioned position (maybe 10 – 15 minutes before) we also sighted a TV set, fridge and a couple of other home appliances.”

Later, on September 27: “We keep sighting every day things like wooden boards, plastic bottles, buoys from fishing nets (small and big ones), an object resembling wash basin, drums, boots, other wastes. All these objects are floating by the ship.”

The debris is exactly where Maximenko & Hafner’s SCUD model predicted it would be! This means that we have a reasonably accurate method for predicting where the debris will go, and when it will make landfall. People on the US West Coast states are very concerned – here’s a recent article from Oregon Beach Connection worrying about the debris’ arrival in 2013 – but we are actually fairly well protected by the southbound California Current. It’s the the Hawaiian Islands that are going to bear the brunt of the impact. Hawaii gets nailed twice – first on the eastward journey, then again once the debris gets swept south in California Current (off the US West Coast), into the North Equatorial Current underneath the trade winds, and west to Hawaii. This is terrible for Hawaii’s fragile ecosystem, which already has a huge marine debris problem, but at least we know it’s coming and can prepare.

If you are concerned about marine debris and want to get involved, the most important thing is to get baseline data now, before the tsunami debris arrives. The easiest way to do this is to download the Marine Debris Tracker app (for Android and iPhone) and start recording what you find and where you find it. If you want your data to be scientific, the NOAA Marine Debris program has a Shoreline Survey Field Guide that they’ll send you – just email MDsightings@gmail.com.

The accuracy of Maximenko & Hafner’s SCUD model is a product of 50 years of government investment in basic science. All aspects of the model required huge investment in seemingly obscure measurements, such as watching buoys drift around in the ocean and developing satellites that measure wind and sea surface height. (Incidentally, the US satellite that measured wind went offline in 2009 and has not been replaced.)  Can’t you imagine a politician making fun of scientists using “high-tech messages in a bottle”? But the SCUD model is just another reason that it’s never a waste of resources to understand how the world works. Because we’ve made these investments, we have the information we need to reduce some of the consequences of the tsunami’s unpredictable destruction.

The post How scientists found debris from the Japanese tsunami 700 miles off Midway first appeared on Deep Sea News.

Twenty-eight percent of the men earning physical oceanography doctorates at key U.S. institutions from 1980 to 2009 obtained tenure-track positions, while the number of female physical oceanographers obtaining such positions dropped sharply from 23 percent for the period before 1995 to only 8 percent since then, according to LuAnne Thompson, University of Washington professor of oceanography. She’s lead author of correspondence about the findings in Nature Geosciences online.

Today’s tenure-track faculty numbers just don’t reflect that women earned nearly 30 percent of all doctorates in physical oceanography throughout the early 2000s, Thompson says.

“People have been saying to just wait, the gender disparity will resolve itself, but it doesn’t appear to be doing so,” she said.

Looking at the author’s handy pie chart (below), it appears that more women are going into the “research staff and instructors” category. This means they’re funded off grants. These positions are soft-money only, and for a fixed term. This can be more flexible – there’s often none of the obligations that come with a full-time faculty position such as teaching or service – but are also more uncertain. More women are also going into the private sector, perhaps because physical oceanographers have highly marketable computer programming and math skills.

The authors of the study suggest two reasons for this huge drop in tenure-track women: the lack of affirmative action and the fact that women may be making “different lifestyle choices.” To which I say, duh. These are not independent variables.

As has been amply pointed out in many other discussions about women in science, women face many interacting challenges on the tenure track, from the two-body problem (women are far more likely to be partnered with other scientists), to the perception that women are given an unfair advantage, to unconcious bias. Adding to the system-wide challenges, oceanography has even more restrictive travel requirements than other disciplines. Along with the usual week-long academic conferences and visits, many (if not most) oceanographers go to sea for a weeks or months at a time. You’re not allowed to go to sea when pregnant, and I can’t imagine that very many women would want to do so while their children were nursing, even if they did have the spousal support to be completely absent. (Though I have heard tales of some awesome ladies pumping breast milk & freezing it while at sea…but that’s super hardcore and shouldn’t be de rigueur.)

Adding to the physical difficulties, the social challenges should not be underestimated. I know many men who have spent considerable time at sea with young children at home. This is socially acceptable – heck, there’s an entire musical tradition based on leaving one’s family behind on the shore. I don’t know any women who have done so.

Leaving aside ship time and babies, I couldn’t help but hear a very snarky tone in the UW press release about this:

Thompson says she encounters more graduate students these days, both male and female, whose preferences about where to live, for example, override their desire to advance in their careers.

Sorry I don’t want to destroy my marriage for my career, UW! The whole system is still set up for professors with trailing spouses. More men than women have this kind of flexibility – certainly I am expecting geography to be a huge limiting factor in my own career search.

I’d love to hear from some physical oceanographers on this. I am not really familiar with that whole world. What do you think are the reasons behind this decline?

The post Gender gap doubles in physical oceanography first appeared on Deep Sea News.