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A warmer ocean is a less green one


The Earth’s oceans are mysterious and largely unexplored. Many of their inhabitants are familiar to us but their whereabouts and numbers are far less clear. This is starting to change. In two new studies, Boris Worm from Dalhousie University has revealed an unprecedentedly detailed portrait of the planet’s marine life, from tiny plankton to mighty whales. And with that knowledge comes concern, for neither study paints an optimistic picture about the fate of tomorrow’s seas, as changing climate slowly raises their temperature.

Graduate student Daniel Boyce focused on some of oceans’ smallest but most important denizens – the phytoplankton. These tiny creatures are the basis of marine food webs, the foundations upon which these watery ecosystems are built. They produce around half of the Earth’s organic matter and much of its oxygen. And they are disappearing. With a set of data that stretches back 100 years, Boyce found that phytoplankton numbers have fallen by around 1% per year over the last century as the oceans have become warmer, and if anything, their decline is getting faster.  Our blue planet is becoming less green with every year.

Meanwhile, post-doc Derek Tittensor has taken a broader view, looking at the worldwide distributions of over 11,500 seagoing species in 13 groups, from mangroves and seagrasses, to sharks, squids, and corals. His super-census reveals three general trends – coastal species are concentrated around the western Pacific, while ocean-going ones are mostly found at temperate latitudes, in two wide bands on either side of the equator. And the only thing that affected the distribution of all of these groups was temperature.

Together, the results from the two studies hammer home a familiar message – warmer oceans will be very different places. Rising sea temperatures could “rearrange the global distribution of life in the ocean” and destabilise their food webs at their very root. None of this knowledge was easily won – it’s the result of decades of monitoring and data collection, resulting in millions of measurements.

Boyce’s study, for example, really began in 1865, when an Italian priest and astronomer called Father Pietro Angelo Secchi invented a device for measuring water clarity. His “Secchi disk” is fantastically simple – it’s a black-and-white circle that is lowered until the observer can’t see it any more. This depth reveals how transparent the water is, which is directly related to how much phytoplankton it contains. This simple method has been used since 1899. Boyce combined it with measurements of the pigment chlorophyll taken from research vessels, and satellite data from the last decade.

Boyce’s data revealed a very disturbing trend. Phytoplankton numbers have fallen across the world over the last century, particularly towards the poles and in the open oceans. The decline has accelerated in some places, and total numbers have fallen by around 40% since the 1950s. Only in a few places have phytoplankton populations risen. These include parts of the Indian Ocean and some coastal areas where industrial run-off fertilises the water, producing choking blooms of plankton.

On a yearly basis, the rise and fall of the phytoplankton depends on big climate events like the El Nino Southern Oscillation. But in the long-term, nothing predicted the numbers of phytoplankton better than the surface temperature of the seas. Phytoplankton need sunlight to grow, so they’re constrained to the upper layers of the ocean and depends on nutrients welling up from below. But warmer waters are less likely to mix in this way, which starves the phytoplankton and limits their growth.


It’s not just the phytoplankton – Tittensor found that water temperature dictates the fate of all manner of marine species right up the food web, including animals like whales that are 10 billion times heavier. He studies 13 groups of plants and animals, including zooplankton, seagrasses, seals, billfishes, octopuses and sharks. On the whole, they were concentrated in predictable hotspots like the Caribbean, South-east Asia and the Australian coast.  Ocean wanderers like whales, squid and tuna were found at temperature latitudes away from the equator, while South-east Asia had the richest concentration of coast-lovers, like corals, mangroves and coastal fishes.

As you might imagine, several factors influence the distribution of these diverse species. Some parts of the ocean are more productive than others, some are richer in oxygen, and some have more stable climates. Some species might react to specific geographical features like length of coastline, while others may be limited to specific areas because of their evolutionary history. But the only thing that explained the patterns of diversity in all 13 groups was the surface temperature of the sea. None of the other factors had quite the same impact.

In general, warmer waters were more likely to be hotspots of diversity for marine species, with the exception of seals and sealions that are specially adapted to colder seas. But even with a census this big, Tittensor has merely glimpsed at the full panorama of ocean life through a keyhole. A more thorough survey would have to include groups that we don’t have a lot of data for, including deep-sea species, invertebrates other than cephalopods, bacteria and viruses. Meanwhile, the existing patterns are merely correlations and need to be checked at a more detailed, local level.

Nonetheless, the results suggest that changes in ocean temperatures could have a big impact on the spread of oceanic species. For the moment, the blue parts of the planet have to contend with more immediate threats. Tittensor found that the areas that are richest in life are also those that are most heavily affected by human activity, including pollution, habitat destruction and overharvesting. And as Boyce showed, warming waters have already taken their toll on the phytoplankton at the base of the food web. The time to act has already come, if the future of our marine life is to be preserved.


References: http://dx.doi.org/10.1038/nature09268 http://dx.doi.org/10.1038/nature09329

Images: Topmost phytoplankton images by Michael Stringer, Harry Taylor and Karl Bruun,

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19 thoughts on “A warmer ocean is a less green one

  1. Maybe things would have played out differently at CO2penhagen if these results had been available before the summit. … Oh wait a minute, this is the real world, I almost forgot it – nothing would have changed. Now a series of justified insults towards governments, multi-national companies, the economic system and the average voter should follow, but I am sure whoever has read this article is thinking more or less the same…
    Anyway, is acidification also covered in this study? I remember some recent research suggesting that acidification could be an even worse threat to marine biodiversity than global warming in the short term

  2. Decline of phytos at 1% per year for the past century would be tending toward zero left about now, not far to go. Low all right if accurate.

  3. I assumed the 1% per annum decrease would be compounded. Therefore:

    population(t) = population(0) * (1.0-decrease)^t

    which for t = 100years and decrease = 0.01 gives:

    pop(t) = pop(0) * 0.366

    i.e. 1% decrease per year means that approximately 63% have disappeared over the last 100 years

  4. IMHO, this is catastrophic! Massive loss of phytoplankton leads not only to profound negative impact on the the entire oceanic ecology (being the base of the food chain), but also indicates a devastating cascade effect for global warming. The oceans (that is, phytoplankton) are estimated to consume roughly 1/2 to 1/3rd of atmospheric CO2. We need more phytoplankton, not less — now more than ever.

    Policy-wise, in addition to reducing CO2 emissions (necessary, but not sufficient to stop climate change), we need to thoroughly understand the ocean carbon cycle. That is, essentially to understand marine ecology and dynamics. We need to begin micro, longitudinal and increasing scale research of safe and effective means to promote phytoplankton. We should be heavily investing in these studies (moonshot-scale), and using armies of robotic sensors, augmented by comprehensive space-based observations, as if the future of our planet depends on it — because it does.

  5. Premature conclusions on a minuscule amount of data that is meant to cite the conditions of a vast amount of ocean, none of which, from what I can tell, have been peer-reviewed. Previous claims by climate change scientists and environmentalists (including Al Gore) were that polar bears were near distinction as a result of melting, disappearing ice caps, but studies later proved that polar bear populations are presently at a 50-year record high. The ice caps, also revealed recently, have thickened and grown, flying in the face of previous reports. However, polar bears’ deaths are still used by eco-zealots to tug at heartstrings. I’ll postpone getting hysterical about phytoplankton until more research (replicated data & modelling, peer reviewed) is available.

    As was stated in the piece:

    But even with a census this big, Tittensor has merely glimpsed at the full panorama of ocean life through a keyhole. A more thorough survey would have to include groups that we don’t have a lot of data for, including deep-sea species, invertebrates other than cephalopods, bacteria and viruses. Meanwhile, the existing patterns are merely correlations and need to be checked at a more detailed, local level.

  6. @ClassicFilm What do you mean, ‘not peer reviewed’? Both studies are published in Nature, one of the top most high ranking scientific journals, known for its elaborate peer-reviewing. You would ‘ve seen this if you checked the reference links at the bottom of the article.

    I also don’t understand how you can call research that stretches back over more than a century, and which combines masses of measurements, minor. I’m talking about the phytoplankton study here. The other study analyses the global distribution of over 11,000 individual marine species, that together make up 13 species groups. Also not really ‘minuscule’.

  7. ClassicFilm’s potpurri aside, I have two questions. Oceans have been warmer in the past, do we have evidence of similar reduction in phytoplankton numbers in the fossil record?

    Also, the impact of a 63% reduction on the carbon cycle must have been just as massive (see #4). Has anybody investigated that?

    ps Nature throws those manuscripts up in the air and refuses publication to the inconvenient ones even if approved by both peer reviewers. Likewise for letters to the editor…

  8. Is this something that can be measured/investigated looking at the ice cores they drill in Antarctica?

    Don’t jump on me – I’m not a scientist – just trying to understand whether there is more than one way to cross check trends that go back farther than recorded time…

  9. I was also wondering what you think happened during the two periods in the past couple of millennia that were warmer than the present. The historical evidence for the medieval warm period shows a time of abundance, though this evidence is limited to the northern hemisphere (there’s nothing contradicting this from the south, just no historical evidence). Archaeological evidence from South America suggests this might have been true there, though. So far as I have been able to establish, all the proxy evidence from the southern hemisphere suggests there were warm periods there at the same sort of time as in the north.

    Why didn’t the oceans die then? Or did they? These aren’t antagonistic questions, I write this as someone who has an honorary share in a Greenpeace vessel, a thank-you for services rendered, but they do need to be addressed.

  10. There have been several severe rapid-onset climate perturbations throughout history. None of them were anthropogenic. However, it is not a logically valid construct to suggest that the one we are experiencing now cannot be anthropogenic…yet the point of the argument is moot.

    Whether we are the proximate cause or it is a natural phenomenon ignores the point that the previous rapid-onset, multi-degree warming (months/years as distinct from slow-onset events of hundreds/thousands of years) marked the beginning of a major extinction event in every case.

    I doubt there is a single person on earth who has not noticed the weather (differentiated from climate) is becoming more seriously erratic by the week. Floods occur where they didn’t before and the simple fact is that, since the hydrological cycle is fixed (as far as our experiments show), the water which is being dumped in floods instead of being spread out more evenly over a longer period means more runoff, more topsoil loss, less arable land, more fertilizer flowing into the oceans, more dead zones, more acidic oceans which will absorb less and less CO2 and more methane clathrate which warms and is beginning to be released in huge quantities. It also means more evaporation and more water vapor held by the atmosphere.

    I have stopped bothering with biosphere lectures. It doesn’t matter to me whether people believe their own thermometers or not or whether they believe we are entering an ice age. They are lost to reality. We are in the initial stages of a rapid-onset global extinction event caused by global warming. The reason doesn’t matter. By 2020 it will be well underway and obvious to everyone, and by 2034 it will peak. The earth will be fine. It doesn’t care what happens at the sea-air interface. It doesn’t care if the atmostphere contains O2, CO2, or CH4. The earth’s upper crust, including the oceans, is relatively equivalent to the thickness of the skin on an apple and the earth doesn’t care what the microscopic creatures on it’s skin do. It will all be replaced by subsidence eventually.

    This is the point. Even if we COULD stop it, we won’t make the attempt. People will continue to burn cheap fossil fuel and nothing will convince them otherwise. We probably have 600 years of fossil fuel left, 10 years of water (and grain crops), 200 years before ALL the arable land is gone and maybe thirty before the oceans turn to algae. At any of those time lengths, the only evolutionary imperative of EVERY living organism is to reproduce, not to save the world. So we will do nothing but watch in horror as we run out of natural resources. Water will be first. Watch it happen.

    As an analogy, we live on Easter Island and the last coconut tree has been cut down.

  11. PETM is a good example of what is happening today. It caused a major extinction event as we see in the ocean bottom core samples we have taken. Dead forams everywhere.

    Today we are going headlong into disaster about 10 times faster than natural events in the past, from what I have been able to understand. Blowing out the ocean’s thermodynamic base by killing the phytoplankton is a huge step towards mass extinction in my view. That is, everything: eats Phytoplankton, or eats something that eats Phytoplankton, or…. well, you get the picture. If Phytoplankton are reduced in numbers then everything else in the food chain above them must be reduced in numbers by starvation.

    We have lost 40% of our Phytoplankton since 1950 and currently the loss is 1% a year (source Nature). Seems the food they eat is located in the lower cool areas of the oceans but that food is not being delivered in great enough quantities to support a healthy biomass of Phytoplankton near the surface because the hotter surface water does not mix enough with the cooler layers.

    So what happens now? We have enough CO2 in the atmosphere to easily heat the planet another degree C even if we stop emitting CO2 completely right now. We are at about 0.7 degrees C over baseline and it is creating a loss of 1% a year in Phytoplankton. At 1.7 degrees C over baseline we will be killing Phytoplankton at 2 or even 3% or maybe more a year.

    So why am I concerned about these little plants you need a microscope to see?

    Without them the oceans will die … or more correctly the oceans will be inhabited with life we can’t use as a food source and which may even be toxic to us. And further, the oceans may give off gases that are toxic to us. Those ocean cruises in sealed vessels will be a real treat. “Please put on your life jacket and don’t forget your oxygen mask and hazmat suit!!”

    In short, if they go …. we go.

    For those interested take a look via Google at various mass deaths of sea creatures where, upon examination, it was determined that they died of starvation. Keep an eye on it for the next few years. These kinds of deaths will spike when the Phytoplankton reach critical levels in various parts of the world.

    Google “penguins falklands death starvation” and you get some idea of the problem as it appears today off the south-east coast of South America.

    This all reminds me of John Donne,

    “No man is an island, entire of itself; every man is a piece of the continent, a part of the main. If a clod be washed away by the sea, Europe is the less, as well as if a promontory were, as well as if a manor of thy friend’s or of thine own were. Any man’s death diminishes me, because I am involved in mankind; and therefore never send to know for whom the bell tolls; it tolls for

    The bell is now tolling for Mankind’s death.

    Absolutely incredible that it has come to this …

  12. @JohnnyC: Thank you. I tend not to be that verbal with people anymore. I can’t run that fast anymore and I’m too old to fight, so when they get upset and I haveta shoot ’em and then the anti-Second Amendment crowd gets upset. I don’t remember now whether those are liberals or conservatives but I know that each of them blame a global conspiracy of the other for all of the world’s problems. I feel a bit ostracized. I am an Independent and no one has ever invited me to join a global conspiracy.

    @CO2hound: I didn’t delve into that extensively in my post, but you covered it quite nicely. Since we have eaten all the fish, we had better get used to dining on what the fish used to eat and what thrive in a warm, acedic ocean….jellyfish. But that will only be a tempory fix. Salt-and-algae-flavored jellyfish will only work until ONE huge algae bloom fires the clathrate gun.

    The outcome is only incredible because we can project scenarios far into the future. We saw this coming a hundred years ago but no one cared then and no one cares now. People simply don’t care about threats they cannot see. It was an excellent survival strategy for millions of years, but it no longer works. As you mentioned, we have done it to ourselves. I really hope we don’t manage to kill off everything else on our way out but killing everything we see is something at which humans excel.

  13. The warming up of the air, as I feel it, doesn’t seem necessarily uniform over the years. I guess it depends on the solar activity as well. I would think the ocean waters follow similar trend. I note the fact that a study spanning over a century would average out the solar effects, if that cycle remains unchanged. But what I would be interested to know is if and how the ocean temperature affects the coastal waters’ bacterial content. It might be difficult, given that the coastal waters are increasingly getting contaminated with human wastes…

  14. I don’t deny a thing and I don’t believe in global conspiracies, yet despite or because of that I can’t help noticing the inherent non-scientific nature of statements such as “the weather is getting more erratic by the week”.

    Climate change is too important a topic to be pivoted around anecdotal hearsays and what was on the telly last night.

  15. There’s no doubt that man has raised the level of CO2 in the atmosphere and that this has led to a warming. The question is, why should this be catastrophic? It’s much less warming than the world has seen in the recent past (I’d class 500 years ago as recent for these purposes).

    Nobody has attempted to answer that question. Moreover, people have been warning of dire consequences for long enough now, since the mid-1980s, for us to have been able to see whether they were right in their 20 year projections of doom. They were not right. That doesn’t mean the projections people are making now are false, but it is good reason to be cautious.

    The original post is doubtful because for it to have any substance there would have to be a different reaction in the oceans now to the one the world saw last time that exactly the same climactic conditions prevailed. Isn’t that rather implausible?

  16. In other words, if I have to multiply 3876 by 18, I’ll quickly multiply 4000 by 20 to get an idea of the region my answer should be in. I don’t think anyone’s doing this sort of simple sanity check when they read these predictions of doom.

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