THEGREENGROK    Planetary Watch

Why’s the Ocean Less Green

by Bill Chameides | August 4th, 2010
posted by Erica Rowell (Editor)

Permalink | 25 comments


Is climate change causing an oceanic famine?

When I was a kid there was this commercial on television for encyclopedias in which a kid asks his dad, “Why’s the sky blue?” The dad isn’t able to answer until he goes and buys the encyclopedia — and then all is well, both dad and kid all smiles. Now the kid spends his free time reading the encyclopedia, and he’s going to grow up and be president or something. Meanwhile I’m just sitting there watching the stupid ad. Who wants to be president, anyway? Look at poor Barack.

Today it’s a different world and the dad would probably tell the kid to Google it, and since hope springs eternal, maybe his discoveries about the sky would pique his curiosity about other aspects of the earth. Maybe next he’d query cyberspace about the ocean — why is it green? He’d quickly learn that the ocean is green because of phytoplankton. If he keeps digging, he might come across a scientific paper that concludes the ocean is becoming less green. It could happen. In fact, that last bit, finding a paper stating that the ocean is becoming less green? That’s what happened to me over the weekend.

Microscopic Organisms Known As Phytoplankton Are Key to Underwater Life

When it comes to ocean life, phytoplankton are key — they exist at the bottom of the ocean’s food chain; the organic carbon they make through photosynthesis supports essentially all other life in the sea including the seafood we eat. To a first approximation, the less production from phytoplankton, the less fish there will be for us to eat.

There’s another reason to care about our green friends in the ocean. Microscopic phytoplankton help to transfer carbon dioxide (CO2) from the atmosphere to the deep ocean through something called the biological pump. (More on that in this post.) Fewer phytoplankton doing their thing in the ocean means more heat-trapping, global-warming CO2 in the atmosphere.

For those reasons the new paper by Daniel Boyce of Dalhousie University in Nova Scotia and colleagues published last week in the journal Nature is a bit of a shocker. The authors combined data from as far back as 1899 on the amount of phytoplankton in the ocean to determine if there has been any change in phytoplankton over the past 100+ years.

Chlorophyll Levels Used to Determine Amount of Phytoplankton

Marine biologists often use the amount of chlorophyll pigment (the thing that makes green plants green and allows them to be little photosynthesis machines) in the water column as a metric for the amount of phytoplankton there.

Since the 1950s scientists have quantified chlorophyll by collecting and analyzing water samples to measure concentrations of chlorophyll pigment. More recently (i.e., starting in the 1970s), we have also used satellite measurements of the intensity of the ocean’s green color to do the same with much greater spatial coverage.

While back in 1899 neither method was available to folks curious about the ocean, clever nineteenth century minds found clever, low-tech ways to study chlorophyll. Pietro Angelo Secchi, an Italian scientist and Jesuit priest, is credited with developing a simple but accurate method of determining chlorophyll levels: by lowering a white disk into the ocean until it disappeared, the water’s transparency can be determined and hence the amount of phytoplankton in the water column.

Scientists in the modern era have determined the specific quantitative relationship between the depth the white Secchi disk is no longer visible and the amount of chlorophyll by calibrating the results from the Secchi method with laboratory analysis of water from the same column.

And so, voila, we have more than 100 years of chlorophyll data and by extension data on the amount of chlorophyll in the ocean. Assembling such a record is no small feat — it requires carefully combining sundry data sets and making sure they are all appropriately calibrated to the same standard so they can be consistently compared. This Boyce and his colleagues did, and then examined the data for evidence of a long-term trend.

Declines in Phytoplankton Found to Be Extensive and Troubling

And evidence of a trend they did find. The authors found that oceanic productivity has declined; they found significant declines in the data spanning the period since 1899 to the present and, if you are suspicious of data from the Secchi method, they also found significant declines for the period from 1950 to the present. The declines were found for all the world’s oceans with the exception of the North and South Indian Oceans.

And by the way, we’re not talking about small changes. Globally the rate of decline was estimated at one percent per year since 1899. That might not seem like a lot but over 100 years it is; it adds up to a factor-of-two decrease.

What could have caused the decline? The authors found that chlorophyll declines were most closely correlated with increases in sea surface temperatures, and, as I’m sure you know, sea surface temperatures have been on the rise because of global warming. Such a result is not all that surprising.

I don’t find it all that surprising that phytoplankton would be unhappy with global warming. As the surface ocean heats up, the ocean becomes more stratified; there is less upwelling or mixing of nutrient-rich deep ocean water with surface waters and this tends to suppress photosynthesis. What I do find surprising, indeed astounding, is the size of the chlorophyll decline. If Boyce et al’s result is applicable to the total productivity of the ocean, it would imply that the productivity has decreased by a factor of two over the past 100 years. And that’s a huge decrease, more than enough to have had a large impact on ocean fisheries and CO2 uptake by the ocean.

In all likelihood the overall decrease was not quite so large. Ocean productivity varies spatially over the ocean. Much of the productivity occurs in specialized regions of the ocean such as coastal and shallow water areas — areas that Boyce et al excluded from their analysis. Much of the open oceans, where the authors found the largest decreases in chlorophyll, are veritable deserts with very low chlorophyll concentrations and productivity. Perhaps a careful weighting of the regional decreases with the amount of productivity in the regions would yield a more modest overall decrease.

So like the kid in the commercial this paper leaves with me some questions unanswered. I doubt if the answers can be found in an encyclopedia or on the Web. I’ll have to wait for additional research.

filed under: carbon dioxide, climate change, faculty, global warming, oceans, Planetary Watch
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  1. Hank Roberts
    Sep 14, 2010

    You’re right, misplaced comment, sorry; feel free to move or delete. I hope for more attention to both ocean and land work on trends in this.

  2. Hank Roberts
    Aug 30, 2010 “It is very likely that the previously demonstrated trend of increasing NPP has now slowed. It is possible that NPP is now actually decreasing, but the evidence for that is equivocal.” hat tip to: by way of:

    • Bill Chameides
      Sep 14, 2010

      Hank: Your comments/request are off topic. The post to which you responded was about ocean productivity from phytoplankton. The subject of your response is *terrestrial* productivity. I suspect you meant to comment on another post on that subject: . I gather you would like me to comment on the post from another blog on the subject. The discussion there is about looking at the data that Zhao and Running considered and I gather that the blogger eventually comes to the same conclusions as that of Zhao and Running; namely, that terrestrial NPP “is now decreasing.”

  3. Hank Roberts
    Aug 26, 2010 hat tip to

  4. Ken Towe
    Aug 17, 2010

    MattN… Jerry Jackson’s 2008 paper in PNAS is available to read at: Jerry wrote this: “…subsistence overfishing in developing nations is commonly a matter of survival, so that alternative sources of protein and livelihood are required to bring the situation under control. More fundamentally, however, wild fisheries cannot possibly sustain increasing global demand regardless of how well they are managed. the remainder of the century.” Also… …. “New research reveals hopeful signs that overfished marine ecosystems can recover provided adequate protections. The two-year study, published in the journal Science, found that efforts to reduce overfishing are beginning to succeed in five of the ten large marine ecosystems examined, suggesting that “sound management can contribute to the rebuilding of fisheries.” This indicates that it is overfishing resulting from the demand from a steadily increasing global population that is causing the decline. While CO2 has increased year after year in tandem with global population it does not seem to be the CO2 or the temperature or the pH of the water that is the proximate cause. In the words of Walt Kelly’s Pogo, “We have met the enemy and he is us.” Until we get a handle on population growth, sustainability will be “a tough row to hoe”, sound management, CO2, or not.

    • Hank Roberts
      Aug 17, 2010

      > This indicates that it is overfishing resulting from > the demand from a steadily increasing global population > that is causing the decline. Overfishing is causing the decline in big fish and big schools (and overhunting caused the decline in whales, as well) Could removal of the top predators be causing the decline in plankton? I’m not sure if that is what you mean. I suppose it could be a trophic cascade, from removing the top animals from the food chain (Aldo Leopold: “just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer.”). But is that what you mean? Any source of evidence for this compared to warming oceans causing the plankton change? Note the coral reef changes are clearly from warming.

      • Ken Towe
        Aug 19, 2010

        HANK…I’ll go with your quotes… “what might be seen as nitpicking by fellow scientists leads Pauly and his colleagues to strengthen their case that commercial fishing is endangering the global marine ecosystem.” and “We’ve removed the top predators from the oceans as well.” The fact that strict regulation can remediate the losses seems to contradict, or at least minimize, an environmental trigger. Boyce et al. have measured new productivity, not primary productivity, but it implies that global marine primary productivity has declined over the last 100 years. Since (a) coastal production is three times that of the open ocean and (b) they left out waters less than 20m deep or <1km from land, and (c) open ocean 'new' production sinks quickly, and (d) half of that is recycled in the upper 300 meters it will be difficult to decipher it all with much confidence. But, if it is true that net primary production has been decreasing and the sediment burial fraction hasn't changed much then so has the net loss of CO2 (and the gain in O2). This might mean that at least some of the increase in CO2 has come from other than fossil fuel burning. Some carbon isotope data support that.

        • Bill Chameides
          Aug 30, 2010

          Ken: I think you will find that the carbon isotope data in combination with the O2 data do not support that.

          • Ken Towe
            Sep 1, 2010

            At the very comprehensive UW lecture site you directed us to last December [University of Washington lecture [[…]/Topic_3A_Carbon_07.doc] on page 5, section C, item 5 the author uses pre-industrial values (275 ppm; C13 -6.2) and 1988 values (350 ppm; C13 -7.8) to ask what the C13 value of the 75 ppm increase should be. He derives –13.6 permil. It is IMPORTANT to note that this analysis MAKES THE IMPLICIT ASSUMPTION that 100% of the 75 ppm increase is due to anthropogenic CO2 (fossil fuel del C13 -28). The other approach uses the CDIAC pre-industrial start (288 ppm; -6.5) with the year 2000 values (370 ppm; -8.05), but asks HOW MUCH of the added 82 ppm (-13.4?) anthropogenic CO2 (–27 permil) is needed to derive the end result. This approach differs in that the latter question leaves open the possibility that some of the increase might, in fact, be natural. The former derives what it assumes. The CDIAC calculations intriguingly suggest that this might be so and the results I presented back then suggest that SOME of the increase could, indeed, be natural.

            • Bill Chameides
              Sep 22, 2010

              Ken: Asked and answered long ago in these posts. Your analysis is flawed. And you are still left with explaining O2 data.

    • Bill Chameides
      Aug 25, 2010

      Ken, Well yeah, the accepted wisdom has been that the declines in fisheries have been caused by overfishing. This paper by Boyce et al. suggests we may need to revise our thinking. However, with regard to all this discussion about fisheries it should be noted that Boyce and co. make no specific statement about the potential relevance of their work to fish populations.

  5. Hank Roberts
    Aug 12, 2010

    Why are grassland/pastureland areas less green when the top predators are removed? Alan Savory answered that convincingly by experiment. We’ve removed the top predators from the oceans as well. I suspect there’s a similar change in the entire trophic cascade for similar reasons. Some discussion here; of course you can find plenty more by looking. “People assume that removing the livestock would allow the land to recover, but in actuality, the complete removal of livestock accelerates the process of desertification. We are losing the land right out from beneath our feet, yet few people have even noticed. For more details please read my on-line article The American Sahara. Allan Savory discovered, or possibly re-discovered, the important link between hooves and the soil. In his book, Holistic Resource Management, he outlines the ways we can use livestock to restore the health of the land. Savory also puts forth a holistic system for making sound land management decisions, which could literally change the world… if more people knew about it. Allan Savory’s work has been highly influential to my own writing. I bought the first edition of Holistic Resource Management as soon as it came out in 1988. I read it many times over. The new edition, called Holistic Management: A New Framework for Decision Making is even better. …” Remove the top predators, the next level down no longer needs to concentrate in tight groups for survival and in fact is much safer by spreading out widely. That’s the difference between how deer react to wolves vs. hunters with guns. Perhaps schools of fish also are countersurvival tactics once big predator fish are removed and big net-dragging fish factory ships move in to go after the smaller fish by capturing whole schools. Spread out the fish, perhaps they graze differently enough to change the population structure of the upper ocean. Given the generation time (short) for small organisms, a day or two difference in average visits by a school of hungry fish could give some organisms a big advantage in numbers. Just speculation, for the fisheries. Savory has established it clearly for rangeland grazing animals and the plant ecologies they were part of. Joel Salatin of Polyface Farm in Virginia has applied Savory’s ideas in some fascinating ways. Can’t think of any way to apply this to the oceans, except the obvious — marine reserves, which do work — stop the big factory trawling and seining and go after individual fish with individual fishing rigs. Not likely I’m afraid.

  6. Hank Roberts
    Aug 12, 2010 quote follows: Five Easy Pieces features five contributions, originally published in Nature and Science, demonstrating the massive impacts of modern industrial fisheries on marine ecosystems. Initially published over an eight-year period, from 1995 to 2003, these articles illustrate a transition in scientific thought—from the initially-contested realization that the crisis of fisheries and their underlying ocean ecosystems was, in fact, global to its broad acceptance by mainstream scientific and public opinion. Daniel Pauly, a well-known fisheries expert who was a co-author of all five articles, presents each original article here and surrounds it with a rich array of contemporary comments, many of which led Pauly and his colleagues to further study. In addition, Pauly documents how popular media reported on the articles and their findings. By doing so, he demonstrates how science evolves. In one chapter, for example, the popular media pick up a contribution and use Pauly’s conclusions to contextualize current political disputes; in another, what might be seen as nitpicking by fellow scientists leads Pauly and his colleagues to strengthen their case that commercial fishing is endangering the global marine ecosystem. This structure also allows readers to see how scientists’ interactions with the popular media can shape the reception of their own, sometimes controversial, scientific studies. In an epilog, Pauly reflects on the ways that scientific consensus emerges from discussions both within and outside the scientific community.

  7. Hank Roberts
    Aug 12, 2010

    The slide in the Jeremy Jackson talk that you’re looking for is the one he describes this way in the transcript. It’s stunning. “And it’s hard to communicate this. And so, one way that I think is really interesting, is to talk about sport fish, because people like to go out and catch fish. It’s one of those things. This picture here shows the trophy fish, the biggest fish caught by people who pay a lot of money to get on a boat, go to a place off of Key West in Florida, drink a lot of beer, throw a lot of hooks and lines into the water, come back with the biggest and the best fish, and the champion trophy fish are put on this board, where people take a picture, and this guy is obviously really excited about that fish. Well, that’s what it’s like now, but this is what it was like in the 1950s, from the same boat in the same place on the same board on the same dock. And the trophy fish were so big, that you couldn’t put any of those small fish up on it. And the average size trophy fish weighed 250 to 300 lbs., goliath groper. And if you wanted to go out and kill something, you could pretty much count on being able to catch one of those fish. And they tasted really good. And people paid less in 1950 dollars to catch that than what people pay now to catch those little, tiny fish. And that’s everywhere.”

  8. Hank Roberts
    Aug 12, 2010

    > do not see You can look it up.” — that’s why people don’t see this happening. It’s not a matter of opinion, it’s just hard to see. A good reference librarian can help you far more than some guy on a blog, but let’s see what you can find if you try to look it up:“jeremy+jackson”+fish+number+size Here, video and transcript on the same page: Look at the video, read the transcript. Then google “Daniel Pauly” “In the past 50 years, we have reduced the populations of large commercial fish, such as BlueFin tuna, cod, and other favourites, by a staggering 90 percent. One study, published in the prestigious journal Science, forecast that, by 2048, all commercial fish stocks will have “collapsed,” meaning that they will be generating 10 percent or less of their peak catches. Whether or not that particular year, or even decade, is correct, one thing is clear: Fish are in dire peril, and, if they are, then so are we …. … there are fisheries scientists who, for example, write that cod have “recovered” or even “doubled” their numbers when, in fact, they have increased merely from 1 percent to 2 percent of their original abundance in the 1950s. … the evidence is overwhelming: Stocks are declining in most parts of the world….”

    • MattN
      Aug 18, 2010

      Cherry picking a few commercial fishing species does not prove anything. Furthermore, that reduction is because we’re taking them, not becuase there’s less food for them. Plankton is the base food for everything that lives in the ocean. If there is half the plankton there was in 1900, then the ENTIRE LIVING MASS IN ALL THE WORLD’S OCEANS must therefore be half. Not just a couple commercial fishes. Everything. Show me the TOTAL living mass of the planets oceans is half of what it was in 1900. If you can’t, then the claim that plankton population has been reduced by half is extremely questionable. No way around it. Show me the mass….

  9. MattN
    Aug 6, 2010

    Something is wrong with their math. I don’t know where exactly they went wrong, but they went wrong somewhere. Here’s why. Plankton are THE FOOD of the oceans. Every fish that swims either eats plankton, or eats something that ate plankton. So you can say that every fish has a direct relationship with plankton. This paper suggests that plankton has reduced by 50%. That is a big number. Now, what you don’t know is that Matt married into a farming family. We raise cows. 100% organic grassfed. The only one in the state of NC ( Here’s what is absolutely 100% true every time: if you only have half the normal amount of food, you can only have half the number of cows, or the cows you have are only going to gain half as much weight. Yes, it really is just that simple. I do NOT see any supporting evidence that there are HALF the number of fish in the ocean or the fish we are catching are weighing HALF as much. If YOU ate half as much food, what would the eventual outcome be? Somewhere, their math is wrong. It HAS to be. Either that or plankton is essentially meaningless for the health of ocean life, which we all know is not the case…

    • Bill Chameides
      Aug 18, 2010

      MattN – I also, as indicated in my post, am a little concerned about the size of the effect. But also be careful not to misinterpret what the authors were saying. Their analysis did not include the whole ocean, and specifically did not include some of the more productive regions of the world’s oceans.

      • MattN
        Aug 18, 2010

        …but from this article on the study: This statement: “The study, performed by Dalhousie researcher, Daniel Boyce, shows a forty percent decline in the amount of phytoplankton in the oceans since 1950.” Does not indicate to me that they excluded any areas. I take that statement to mean the whole ocean….

        • Bill Chameides
          Aug 30, 2010

          MattN: I guess you have to actually read the paper.

          • M_N
            Aug 31, 2010

            “The declines were found for all the world’s oceans with the exception of the North and South Indian Oceans.” You really didn’t mean “all the world’s oceans”? How about you specifically call out which ones you;re talking about? Because from YOUR own words and the press release on the paper, it sure sounds like “all the world’s oceans” means “all the world’s oceans”… Call me crazy, but I’m just reading what YOU wrote…

            • Bill Chameides
              Sep 14, 2010

              Declines were found in: Arctic Ocean, North Atlantic, South Atlantic, North Pacific, Equatorial Pacific, South Pacific and Southern Ocean. And as I said in the post, no declines in North and South Indian Oceans. Is there another ocean?

  10. Marcus
    Aug 5, 2010

    Typo: deserts, not desserts. (indeed, with a lack of plankton, they are liable to be less dessert-like for the ocean fauna)

    • Erica Rowell (Editor)
      Aug 5, 2010

      Don’t know how that slipped through, but I will fix it now. Thanks for the catch. – Erica

  11. Jim
    Aug 5, 2010

    If verified, could this be another feedback into global warming, such as permafrost melting? It just concerns me that all this could eventually lead to almost a runaway greenhouse effect if we continue on our current path. Of course that’s just speculation, but it seems like over time we have seen more and more mechanisms discovered that could potentially lead to such an effect.

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