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Diving Deeper: Marine Debris Movement

Episode 45 (March 28, 2013)

HOST: Welcome to Diving Deeper where we explore the ocean topics that are important to you. I'm your host Kate Nielsen.

Today we will talk about how marine debris moves in our environment, what causes it to move, and if we can predict where debris may ultimately end up.

To help us explore this topic, today we will be joined by Sherry Lippiatt. Sherry is joining us by phone as she is the California Regional Coordinator with the NOAA Marine Debris Program. Hi Sherry, welcome to our show.

SHERRY LIPPIATT: Hi Kate, thanks for inviting me here today.

HOST: So Sherry, to get us all on the same page, can you remind everyone what we mean when we say marine debris?

SHERRY LIPPIATT: Marine debris is any solid, man-made material in the marine environment that is not meant to be there. So, marine debris can be made of a number of different types of materials, like plastic, rubber, and metal. And, it can range in size from microscopic pieces of plastic to derelict fishing nets or abandoned vessels that are hundreds of feet long.

HOST: And how does this marine debris get in our environment in the first place?

SHERRY LIPPIATT: So, people are the ultimate source of all marine debris. And regardless of how far upstream it originates, debris can make its way from land into our oceans through runoff and storm drains or it can be disposed of or abandoned directly into the marine environment.

HOST: And Sherry, why are we concerned about marine debris?

SHERRY LIPPIATT: Marine debris has physical and chemical impacts on the marine environment and it can also have economic impacts on our coastal communities. For example, debris can damage habitats, fish and other marine species can ingest or become entangled in debris, and debris might act as a vector for contaminant transport.

And then there's also the human element, where there are known socioeconomic impacts from marine debris. For example, decreases in tourism, navigational hazards, and losses in catch to the fishing industry.

HOST: OK so it sounds like it can definitely be quite a nuisance, quite a problem then. Thanks so much for giving us that background on just marine debris in general. And now to get us to our real topic of the day, first, can you tell us about how marine debris behaves in the environment. Does it move from place to place or does debris tend to stay in just one place?

SHERRY LIPPIATT: Marine debris certainly moves throughout the marine environment. And debris that's made of persistent materials, like plastic, can travel long distances from far inland within a watershed through rivers and streams and out into the ocean. Once debris makes it to the ocean, it might be deposited back on shore or move very far offshore. And we know that debris can travel long distances because it's been found in these really remote regions of the world, like the Arctic and Antarctic. And, even on our shorelines here in California, we often find debris from overseas.

HOST: What kinds of things then cause marine debris to move?

SHERRY LIPPIATT: There's a number of factors that affect where a piece of marine debris will move and how long it will take to get there. And, along its journey, debris in the ocean will move both horizontally and vertically in the water column, and this movement depends on physical factors, like winds and currents, and characteristics of the debris itself. So, for example, marine debris that's denser than seawater will sink out of surface waters and debris that's less dense than seawater is going to remain floating and might travel very long distances with surface ocean currents.

Now, there's also something called the windage of an item, or how high a piece of debris floats above the surface of the water. And this windage determines how much of the debris movement is affected by the wind. So, something like a large buoy, which is exposed to the wind, will move faster in the downwind direction than say a piece of lumber that's mostly submerged beneath the surface of the water and is moved by the ocean surface currents.

HOST: So if we have this data on currents and winds, can we predict, almost like a forecast, where a piece of debris will move and maybe where it will ultimately end up?

SHERRY LIPPIATT: Yeah, we can use computer models to simulate the movement of debris. And, there are three key components that these models need to work properly. Those are data on winds, currents, and how the actual stuff you want to move around is going to behave in time. For example, you might have a large buoy with a known windage, but you also need to know what environmental forces are acting on it and how that will affect its trajectory.

Now, the same challenges that are faced by meteorologists in predicting the weather also apply to oceanographers. Because winds and ocean currents are really variable on smaller scales and are constantly changing even on large scales, we're limited in our ability to forecast debris movement. So, what NOAA and our partners are doing is using a tool called the General NOAA Operational Modeling Environment, which provides a hindcast, rather than a forecast, of the movement of debris. The model moves simulated particles under the influence of known wind and current data, and it tells us where these particles, which represent debris, have travelled over time up to the present day.

But, it's important to mention that even though we do have this data on how winds and currents have behaved in the past, there's always a degree of uncertainty associated with these hindcasts. One example is that the model doesn't account for debris degrading or sinking over time and the quality and resolution of the wind and current data will also affect the accuracy of the model.

HOST: OK, so still it's pretty cool even if it is a hindcast and we're able to get that data. Why do we need to know where marine debris is going? Why is this important?

SHERRY LIPPIATT: So the more information that we have about where debris tends to accumulate, the more prepared we are to respond. Whether it's a large amount of debris that's generated from a natural disaster or even if we're just talking about typical everyday debris, we want to be as prepared as possible to remove hazards to navigation and prevent other economic and environmental impacts that we talked about earlier. So having even a rough prediction of where debris might accumulate will help us guide any response efforts.

HOST: Sherry, what sorts of challenges do you face when you're trying to predict how marine debris will move in the environment?

SHERRY LIPPIATT: Predicting or forecasting the movement of marine debris is very difficult. So as I mentioned, the movement of debris in the ocean depends not only on winds and currents, which we know are variable on seasonal and other time scales, but the movement also depends on characteristics of the debris itself.

One key piece in predicting debris movement is having this data on the major sources and types of debris which tells us where it originated and what kind of material it might be composed of. But, even if we did have that information, we know very little about how long it takes for different materials to degrade in the marine environment and these rates of degradation or weathering are also affected by marine life that tends to colonize the surface of debris. So, using the same example of a large buoy, we might know where it came from and its initial windage, but that could change if barnacles cover the surface of the buoy and cause it to float lower in the water column. At the end of the day, there are a number of challenges and questions that modelers face in trying to predict debris movement, and our understanding of how this debris behaves is pretty limited.

HOST: So, just to make sure that I understand because we've touched on this a little bit, we've talked about where debris will end up or even starting there at the end in a sense and then going backwards with that, kind of a hindcast, rather than a forecast. Is it possible to tell where debris came from in the first place, where it originated?

SHERRY LIPPIATT: Debris can travel very far distances and persist in the environment for long periods of time. Given the vast size of our oceans and the number of potential types and sources of debris, in most cases it's really hard to tell where a particular item of debris originated and how much time it's spent in the ocean. However, there are some cases where debris might have unique identifying information that could be traced back to a specific source. For example, a registration number on a vessel or some other unique name or marking.

HOST: I think when folks think about marine debris right now, especially something that's in the news and people are hearing about is debris related to the Japan tsunami. For that event, you have that origin of the debris - so this kind of answers our first question - where did it come from. What have we learned about marine debris movement following the tsunami given that we have this crucial first piece of data?

SHERRY LIPPIATT: That's right, so in the case of Japan tsunami debris we know when and where the debris from this tragic event entered the ocean, but we really don't have a great idea of what and how much debris was washed out of the tsunami inundation zone. So in responding to this issue, one thing that we've been reminded of is how the small scale turbulence and variations in winds and currents can lead to big differences in when and where something may wash ashore. And one example is two 65-foot-long dock pieces that were both ripped away from the Port of Misawa in Japan, back on March 11, 2011. So, about 15 months after the tsunami occurred, back in June 2012, one of the docks washed ashore in Oregon near Newport, and then in December 2012, a second dock from Misawa washed up on a remote shoreline in Washington state. These two very similar items that left from the same location at the same time washed ashore more than 200 miles and 6 months apart. The fact that these two docks took such different paths across the ocean shows us just how hard it is to predict how a given item is going to behave at sea especially given the natural dispersion by winds and currents. But, to answer your question on what we've learned through the effort, the data that NOAA is gathering through these confirmed sightings of Japan tsunami debris is going to help us to refine our models, and be able to better predict debris movement in the future.

HOST: Well, thank you so much for those great examples and that really does paint the picture for us that these two docks, as you've said, it was the same time, the same origin, and then six months apart and totally different locations they wash up. That's really something. I could see how it's challenging to be able to predict this movement. What is needed to make our models stronger or really what do we need to have to help us better predict the movement of marine debris?

SHERRY LIPPIATT: Well, we talked about the three key components that we need to be able to predict how this debris is going to behave in the ocean, so that was winds, currents, and information about the debris itself which includes where it came from, what it is, and how it behaves in the ocean. And, of these three pieces, I think that the largest gap is the last one - a good understanding of the life cycle of these different types of debris. So this includes reliable data on the sources and sinks of marine debris and the time that different items will persist in the marine environment. Factors like debris degradation rates and the colonization or fouling of debris by marine life are all going to affect the amount and location of debris in the environment and also it'll determine whether the debris remains floating, submerged beneath the surface of the water, or falls to the ocean floor. And again, if we have a better idea of where debris is likely to end up, we'll be able to do a better job of managing the problem.

HOST: Sherry, just to close out our show today, I wanted to see if you had any final, closing words to leave our listeners with?

SHERRY LIPPIATT: Thanks Kate. The final thought that I'd like to leave is that outside of natural disasters, marine debris is completely preventable. And we can all make small changes in our daily lives, like consuming less, choosing to use reusable products, and responsibly disposing of our wastes. These small, easy steps will go a long way in preventing marine debris from making it into the ocean in the first place.

HOST: Thanks Sherry for joining us on Diving Deeper and talking about how marine debris moves in our environment. To learn more, please visit

And that's all for today's show. Remember, if you have questions on this episode or the National Ocean Service in general, you can contact us at And if you're on social media, don't forget you can find us, it's usoceangov, on Facebook, Flickr, and YouTube; and that's noaaocean on Twitter. Please join us for our next episode in two weeks.