Report on the Abundance of Floating Plastic Particles in the North Atlantic Ocean.

[NNadir]

The paper I'll discuss in this post is this one: Abundance of Floating Plastic Particles Is Increasing in the Western North Atlantic Ocean (Chris Wilcox*Britta Denise Hardesty*Kara Lavender Law, Environ. Sci. Technol. 2020, 54, 2, 790-796)

I recently had an outbreak of bravery and, albeit with some trepidation, ventured into the General Discussion forum here in a thread where a member of my generation, the so called "Baby Boomers," was trashing our most recent generation of adults, the "Millennial" generation, for not being more "activist." In a wonderful exchange there, which included the point that my generation's modern "activism" seems to consist of being the most reliable demographic for supporting the orange criminal in the White House, we have also been the most piggish generation of all, listing all the things we destroyed in our tenure of dominating the world, for example, the planetary atmosphere, the land, and the oceans, well, um, everything. As an example I referred to plastic pollution, placing a photograph of the Woodstock Rock Festival's garbage along side the garbage washed up recently on an uninhabited Hawaiian beach.

I noted that the world would be much improved if a large set of us baby boomers would just shut up and die. (People who find me unpleasant should feel free to offer advice along these lines.)

Anyway, about those of us of the "Woodstock Generation" ersatz peace and love and all that stuff:

We are not star dust, we are not golden, but we are carbon, too much of it.

The destruction of the ocean by my generation has very much involved the inventory of dumped plastic. Not so long ago I discussed and posted a link to a paper in this space about the distribution of surface, intermediate, and seafloor plastic in Hawaii.

That post is here: Distribution & Type of Marine Debris Polymers on Hawaiian Island Beaches, Sea Surface, and Seafloor.

Writing that post reminded of a basic fact that more or less slipped out of my mind, which is that many polymers are well known and widely used that are heavier than seawater and thus sink.

A table from that post is reproduced here for convenience:



This brings out an important point. Plastic pollution is not limited to floating plastics. Many important plastics sink.

Regrettably, the Pacific Ocean is not the only ocean being destroyed with plastic. The Atlantic is right up there, as the paper under discussion shows. From the introduction:

Plastic pollution in the ocean is of widespread concern, spurring a number of recent studies that attempted to estimate the extent of contamination at the sea surface. The first global estimation of the mass of floating plastic particles found 6350–32,000 tons,(1) a surprisingly low amount compared to the estimated input of plastic waste from land into the ocean of 4.8–12.7 million tons (Mt) in 2010 alone.(2) This raised a question originally posed a decade earlier when the first time series of ocean plastic particle abundance showed a significant increase from the 1960s and 1970s to the 1980s and 1990s but no clear increase between the latter two decades 3) where is all the plastic? Similarly, no temporal trend in surface plastic abundance could be detected in a 22 year data set (1986–2008) from the subtropical gyre of the western North Atlantic Ocean, where floating plastics accumulate,(4) or in an expanded analysis to 2012.(5) The lack of increased floating plastic particle abundance over time is puzzling since global plastics production increased by 562% between 1976 and 2014,(6) similar to the increase in the amount of plastics discarded in the United States municipal waste stream.(7) Moreover, the rate of plastic production is accelerating, with a doubling time in the order of 11 years,(6) implying that changes should be easier to detect with the passage of time. In addition, two recent global modeling analyses of ingestion rates by marine species have detected increases in ingestion rates over time,(8,9) although a regional long-term monitoring study of a single seabird species did not.(5)

It could be that plastics are removed from the sea surface at a rate that compensates for the increased input. Floating plastic particles may be removed by ingestion by marine organisms, buoyancy decrease and sinking, coastal deposition, or fragmentation to sizes smaller than the plankton nets typically used to collect them.(4) Evidence from a variety of laboratory and field studies supports the occurrence of each of these removal mechanisms,(10,11) but the removal rate in the ocean has not been satisfactorily quantified for any of these potential mechanisms. Unless removal rates collectively equal or exceed the input rate, one would expect to measure an increase in the abundance of floating plastics over time in the subtropical ocean gyres, where floating debris accumulates.
A second possible explanation for the lack of observed increase in abundance in time is the difficulty in separating the confounding effects of spatial and temporal variation in the observations. Previous studies have described large spatiotemporal variability in the amount of floating plastic debris collected using surface plankton nets,(12,13) even in the subtropical ocean gyres. Surface winds cause vertical mixing of particles(14,15) and appear to have other nonlinear effects on surface concentration with increasing wind speed.(16,17) Variability due to wind mixing, small-scale circulation features, variable input or removal, and other factors is difficult to quantify because evaluations of temporal trends to date have not been made using data sets from longitudinal studies at fixed locations. This implies that spatial variation in sampling over time will add further variance into the observations, making a time trend more difficult to detect.(11)

The goal of this work was to evaluate whether there is evidence of a time trend in floating surface plastic particles in the western Atlantic Ocean.

Plastic in the Altlantic ocean is decreasing or steady state? Let's see.

The paper offers some concentration data in graphic form:



The caption:

Figure 1. Ocean plastic concentration and global plastic production data included in the analysis. (A) Measured surface plastic concentrations from plankton net tows in the western North Atlantic (number of plastic pieces per km2). Letters indicate the location of time trends shown in Figure 4. (B) Global plastics production data,(6) interpolated production data, and cumulative production data calculated using interpolated values.

Of course, what you measure depends on how you measure it and when you measure it, and how often you measure it, a topic on which the author's discussion and graphic touches.

Figure 2 from the paper:



The caption:

Figure 2. Estimated change in surface plastic concentration since 1950 and the corresponding sample size by year. (A) Value of the time coefficient for surface plastic concentration with time since 1950 using the best fit base model with a static spatial surface. The 95% confidence intervals are shown as dotted lines. Note that smooth terms, such as this one, are forced to have a mean value of 0 for identifiability during estimation. (B) Number of surface plastic concentration measurements from plankton net tows in the data set for each year included in the analysis.

The quality of the measurement made at any time is actually subject to external trends that may not reflect the overall concentration averaged over time, but rather local conditions at the sampling time. For example, high winds may push plastic away or into a region if said winds are blowing at the time of sampling.

The authors thus write:

The best base model to remove variability not associated with a temporal trend, as determined by the Akaike information criterion (AIC),(18) included a 2D spline to account for spatial location and first-order linear terms for wind speed and tow length (Table S1). It also contained a smooth term for time of day, removing a daytime bias toward higher concentrations. The best fit model had negative coefficients for the wind speed and tow length terms, indicating a lower observed plastic concentration associated with higher wind speed and longer tow length. Comparing the product of the coefficient and the covariate at its median for these two terms, we found that they had similar magnitude effects on plastic concentration. The base model explained 43.7% of the variation in the data based on a deviance comparison. A Tweedie distribution with a scale of 1.6 was the best fitting model based on an examination of the mean–variance relationship. We rejected Poisson, quasi-Poisson, and negative binomial distributions as providing inadequate flexibility to accommodate the large probability mass at zero and the rare very high concentrations.

This graphic, which is based on some computational parameters, is not about plastic concentrations but rather about the nature of the measurements:



The caption:

Figure 3. Estimated spatial surface for plastic concentration. The plots are based on the best fit model with a two-dimensional spatial smooth for location, allowing the spatial surface to vary by decade. (A) 1986–1995; (B) 1996–2005; (C) 2006–2015. The spatial coefficient, as shown in the legend, gives the value of the contribution of position in the modeled region to the estimated concentration of plastic fragments. The spatial surfaces are constrained to have a mean value of 0 over all time; thus, the coefficients in the spatial surface represent deviations in the plastic concentration in space from the temporal mean and are therefore unitless. Values on the contour lines give the contribution to the overall model coefficient from the spatial surface. Black dots show the locations of samples in each of the decades.

The next graphic is about trends in the accumulations of plastic.



The caption:

Figure 4. Estimated time trends in surface plastic concentration at four locations under standardized conditions. The plots show the trend based on a parametric model for cumulative plastic production (blue) and a smooth model for year (brown). Locations are (A) coastal northwestern North Atlantic, (B) western North Atlantic subtropical gyre, (C) Florida Straits, and (D) eastern Caribbean Sea. The standardized conditions are a wind speed of 0, tow length at its median value (1852 m), and time of day at noon (12:00). Note the differences in scale on the abscissa of panels (A) through (D). Discontinuities reflect the transitions between spatial surfaces between 10 year intervals. The bars through each point provide the standard error for each estimated mean concentration. Typical for models of counting processes (Poisson, Tweedie, etc.), the standard errors of the estimates scale with the estimated mean. The distribution of samples in our data set and the locations of the four predictions are shown in Figure 1 (black letters).

From the author's discussion:

Using more than 8000 samples from plankton net data, we found clear support for the hypothesis that the abundance of plastics at the sea surface of the western North Atlantic Ocean has increased with time (Figures 2a and 4). The time trend is most strongly related to cumulative global plastics production. The better fit to cumulative rather than to annual production suggests that the particle loss rate from the sea surface is smaller than the input rate.

Furthermore, the relationship observed suggests that plastic concentration is accelerating compared to cumulative production. We hypothesize that this acceleration may result from particle fragmentation. Global plastics production is reported as mass (tons), whereas plastic particles are reported as a numerical concentration (number of particles per unit area). Most particles collected in plankton nets are ?0.35–10 mm in size and, based upon their size and shape, likely originated from fragmentation of larger objects,(19) which is known to occur when plastics undergo photodegradation and weaken upon exposure to sunlight and other physical processes.

To test the plausibility of this hypothesis, we built a hypothetical fragmentation model(18) (see detail provided in Figure S2), which indicates that, if the time to fragment from a large item (100 g) to smaller particles (0.00001 g) is sufficiently long, and particle removal is minimal, then the total number of particles will accelerate with respect to cumulative production. Furthermore, the model suggests that, if particles are lost from the system at any appreciable rate relative to inputs, either through flux away from the sea surface or by fragmentation to smaller sizes that can be captured by the plankton net, then the relationship between particle count and cumulative production will decelerate, rather than accelerate as observed.

We detected substantial variability associated with all sampling conditions tested: wind speed measured during the tow, tow length, and time of day. The inverse relationship between wind speed and measured surface concentration of microplastics is consistent with studies modeling the turbulent wind-driven mixing that submerges even buoyant materials below the sea surface where the measurements are made.(14,16) The mechanism driving the inverse relationship between tow length and measured surface concentration is unknown. We do, however, posit three hypotheses to explain the pattern. First, the efficiency of water passage through the net might be reduced on longer tows due to larger amounts of biological material accumulating in the net, which could cause a pressure wave at the mouth of the net that diverts seawater and suspended material around the net. A second related possibility is that larger volumes of material resulting from longer tows make visual sorting of the material for microplastics more difficult. Finally, surface concentrations of plankton and other floating materials typically exhibit patchiness or regions of high concentration separated by larger regions of very low concentration. A longer tow would be more likely to sample the larger areas of plastic-free water in between these patches, a hypothesis supported by the fact that the modal value in the data set is zero (35% of values). Finally, there are two potential explanations for the daytime bias in plastic particle concentration. Plankton net samples are typically collected twice per day, at noon and midnight local time, and samples are analyzed onboard the ship within 1–2 h of collection. It is possible that visual selection accuracy is reduced in midnight tows because of analyst fatigue and/or insufficient lighting conditions in the ship’s laboratory. An alternative explanation is physical in nature. There is evidence of a diurnal cycle in vertical mixing at the sea surface due to the diurnal daytime heating (nighttime cooling) cycle, which causes reduced (enhanced) turbulent mixing that submerges surface microplastics.(14)

It would seem to me, based on some recent experience in the lab, that the issue of "analyst fatigue" can be automated away. For roughly $10,000 plus or minus a few thousand, one can buy microscopes that are quite good at particle determinations, although plankton would be an obvious limitation on such an approach. There are also quite reliable particle size devices, which, albeit at higher expense count particles quite well. By comparing particle numbers with the optical density at several wavelengths to subtract out known plankton associated spectral lines, assuming that there is no interference one might be able to differentiate plastic from plankton, even if fish and crustaceans cannot do the same.

Of course, it is also possible that I don't know what I'm talking about in this case.

Irrespective of how one counts though, your seafood, if you eat seafood, contains plastic and the amount of plastic it contains will continue to rise.

The section of the paper called "Implications" has some good news with a huge caveat, which is that the estimates the authors made are an order of magnitude lower than other estimates about the rate of accumulation of plastic in the seawater.

Our results have two important implications. First, the accumulation over time suggests that floating plastics may have a residence time in the ocean equivalent to or greater than the sampling period of our data. This relatively long residence time implies that fluxes away from the sea surface, to the coasts, the seafloor, and the biota, are negligible with respect to the input rate of plastics to the surface ocean. Second, the significant relationship between cumulative plastic production (in tons) and measured ocean plastic concentration (in number per unit area) suggests that the input of plastics into the ocean has not slowed over time. Assuming that plastic waste input from land(2,21) is a major source of ocean plastics (either input in this size range or as larger items that generate smaller plastic fragments), our results imply that waste control efforts have not improved rapidly enough to compensate for increases in global production, a result consistent with recent findings that global plastic waste generation has outpaced plastics recycling and incineration rates.(22) Furthermore, fragmentation also contributes to an increase in ocean plastic counts (as detailed in the Supporting Information).

Based on our model, we estimate that, in 2010, the surface plastic concentration in the western North Atlantic increased by 0.1 particle/m2 for every ton of plastic produced globally. Using an average particle weight of 0.014 g(4) and a global ocean area of 361.9 million km2, this yields an increase of 506,000 tons of plastic in the ocean in 2010 or 0.2% of global production.(6) This is an order of magnitude lower than Jambeck et al.’s estimate that between 2% and 5% of global plastic production, by weight, entered the ocean in 2010.(2) The two estimates are not directly comparable since only buoyant plastics in a narrow size range are accounted for in the ocean data presented here. Furthermore, trends in other ocean basins may differ from our North Atlantic estimate because of differences in input rate (i.e., the largest sources of land-based waste are predicted to be Asian countries into the Indian and Pacific Oceans(2)) and transit times. However, this is a substantially better match than previous comparisons between estimated input and observed surface plastic concentrations in the open ocean.(1,17)

Plastics, of course, are sequestered carbon, and, if in some nuclear powered future they were made from carbon dioxide ultimately obtained from the air rather than from dangerous petroleum, they might help to mitigate climate change. This said, it is not acceptable for them to end up in our rivers, our lakes, our seas and, for that matter in our land. We need to close the plastic waste cycle completely. (The use of high temperatures in the absence of air can do this.)

In my studies over the years, I have come to feel that extraction of carbon dioxide from seawater may be the only feasible way to accomplish the task. One route to doing this involves raising seawater to supercritical temperatures, a topic to which I've alluded previously in this space. Under these circumstances, the plastic in seawater would be oxidized, although, were it to find its way back into the air, it would represent further destruction to the atmosphere, since it would liberate plastics obtained from dangerous fossil fuels, primarily petroleum, although some polymers are made using dangerous coal and dangerous natural gas.

I trust you're having a wonderful weekend.

[pbmus]

1. Before you boil the oceans, Worms, bacteria, and other physical removal methods ... are working

https://www.sciencedaily.com/releases/2017/04/170424141338.htm

Wax worm caterpillar will eat plastic shopping bags: New solution to plastic waste?
Date:
April 24, 2017
Source:
Cell Press
Summary:
Generally speaking, plastic is incredibly resistant to breaking down. That's certainly true of the trillion polyethylene plastic bags that people use each and every year. But researchers may be on track to find a solution to plastic waste. The key is a caterpillar commonly known as a wax worm.

[NNadir]

2. A statement about "boiling the oceans" is more than a little hyperbolic.

One can certainly choose where to have seawater intakes. If one's goal is to collect carbon from the atmosphere, an excellent place to do so would be portions of the oceans that have been killed by nutrient run-off, for example the Mississippi River delta.

Regrettably these dead zones are expanding all over the world.

Bioremediation schemes often get a lot of pop press, generally in the form of journalists focusing on press releases by universities hyping their research, but in general they are not practical, particularly to address diffuse pollution. Secondly this system injects the petroleum derived material as diluted carbon dioxide, and does not allow for the recovery of carbon dioxide for use.

I personally believe, our failure to address climate change with anything more than wishful thinking will certainly destabilize any reliance on any living thing, since organisms are heat sensitive. It is also true that many plastic objects are heterogenous composites.

The biggest problem with plastic is that it is widely distributed. If one were to have all the world's plastic in a single pile, it might be worth considering dealing with it using worms, but otherwise, it constitutes just more of the kind of wishful thinking that has brought us here.

Sorry, but my view is that the scheme in this press release will never be as clean and as sustainable as the use of supercritical seawater. The use of supercritical seawater has many advantages, including the recovery of resources other than carbon dioxide, notably phosphorous, uranium and most important of all, since this critical resource is being destroyed at a record pace, fresh water.

[pbmus]

3. Boiling is 212 ....