Six days from now, every one of the billions of phytoplankton alive today will be dead—eaten by zooplankton or having drifted to the bottom of the sea. In fact, some of these microscopic plants, which collectively perform as much as photosynthesis as all of Earth's land-based plants, live for just two days.

But these microscopic plants have an outsize effect on the levels of carbon dioxide in the atmosphere—both by sucking it up during photosynthesis and by helping to drive the natural circulation of the ocean that lets denser, cooler water that has absorbed CO2 drop to the bottom of the sea in places like the North Atlantic. This natural sink is one of the largest ways that CO2, the most abundant greenhouse gas responsible for climate change, exits the atmosphere. Understanding how and why the tiny plants bloom each spring is therefore critical to understanding how the planet's living systems—and therefore the planet's elemental cycles—might respond to global warming.

For decades scientists have assumed that springtime ocean conditions were responsible for the annual plankton blooms, thanks to pioneering work by oceanographer Harald Sverdrup in the 1950s. But a new analysis of satellite records suggests it may not be as simple as the advent of spring conditions unleashing the photosynthetic potential of phytoplankton, according to a paper in the April issue of Ecology.

Phytoplankton ecologist Michael Behrenfeld of Oregon State University studied nine years of data from the NASA satellite SeaStar and its Sea-viewing Wide Field-of-view Sensor (SeaWiFS). This tool allows researchers to estimate the total surface chlorophyll concentrations in the oceans as well as relative carbon concentration in phytoplankton. Focusing in on the North Atlantic, Behrenfeld found that the increase in numbers of plankton revealed by chlorophyll and carbon concentrations start in the middle of winter—when growth conditions are at their worst—rather than being initiated by the changing spring weather. The reason appears to be the deepwater mixing caused by winter storms churning the ocean, and thereby making it hard for the tiny animals that eat phytoplankton to find their prey.

"The fraction of phytoplankton growth lost to the grazers gets smaller and smaller as you go into winter and deeper mixing," Behrenfeld explains. In essence, because the phytoplankton are spread more thinly throughout more water, or diluted, the would-be grazers have a harder time finding them. That allows the phytoplankton to begin to build up in midwinter, a head start in growth that is a prelude to the massive bloom once the winter's storms cease mixing and conditions for growth improve.

By the end of spring, the grazers catch up, consuming as much plankton as grows and bringing the bloom to a close, as well. But the new hypothesis tweaks the old understanding that zooplankton grazers and other losses essentially eliminate the same amount of phytoplankton at all times, as Sverdrup proposed in 1953.

Biogeochemist Jorge Sarmiento of Princeton University's Atmospheric and Oceanic Sciences Program, who was not involved in the study, calls the new finding that blooms start in midwinter "a provocative idea…the only point in time when growing exceeds grazing is very early on." He adds: "Let's see what the data says in the long run."

Of course, this method of estimating plankton concentrations by interpreting chlorophyll and carbon concentrations remains to be verified by field-testing. "The North Atlantic is a pretty nasty place to go in winter, no one wants to go there. A satellite doesn't care how nasty conditions are," Behrenfeld says, and notes that a new study he is conducting with ocean floats has provided data that supports his new hypothesis. "Now we need to go into the field and make some measurements."

Climate change may also provide a test. If it is indeed the dilution caused by deepwater mixing as a result of winter storms that sets the stage for the annual bloom, then a warmer world with fewer storms in the North Atlantic "should reduce the bloom," Behrenfeld notes. "Winter mixing depths are already shallower in the southern end [of the North Atlantic]. Likewise, we see that the magnitude of the blooms are smaller in the southern end."

Adds Sarmiento: "If [the North Atlantic phytoplankton are] either becoming more efficient or less, there would be feedbacks to the Earth balance of CO2. It's really important to understand the system and understand it well enough that we can predict how it's going to respond to climate change."

After all, if the phytoplankton bloom is diminished Earth might lose two carbon sinks: there would be less dead plankton bodies (having avoided consumption by grazers) that fall to the ocean floor along with potentially less sinking of CO2-rich surface waters. And that, in turn, could further exacerbate the climate change caused by extra atmospheric greenhouse gases.

It is also important because phytoplankton form the base of the marine food web, meaning many of the world's most productive fisheries rely in large part on the activities of these microscopic plants. And other regions of the world's oceans with similar blooms may follow similar patterns, such as the Arabian Sea and its monsoon-related blooms.

The long lead-in and drivers of the phytoplankton bloom are hardly the only mystery of the North Atlantic. After all, these annual blooms show rapid changes in the dominance of one type of phytoplankton quickly followed by another—yet the overall population size grows relatively smoothly. Behrenfeld asks about that mechanism, "How does that actually work?"

15 Comments

1. 1. Acoyauh 12:57 PM 4/14/10

   "Six days from now, every one of the billions of phytoplankton alive today will be dead" sounds impressive, but it's either an editorial slip, or one of the greatest overstatements I've seen in SA.
   Nowhere close to the truth, even if you limit it to the North Atlantic area itself, let alone as open-ended as it is.
   
   OR, are we expecting a "Great Dying" like the end-Permian one? THAT would be news then...

   Reply | Report Abuse | Link to this

2. 2. candide in reply to Acoyauh 02:14 PM 4/14/10

   phytoplankton do not live that long, every one alive TODAY will be dead in 6 days - as their life span is 1 to 5 days.
   
   There will be other, newer, younger phytoplankton alive, billions of them, but none will be aged 6 days or more.

   Reply | Report Abuse | Link to this

3. 3. jtdwyer in reply to candide 02:49 PM 4/14/10

   candide - So, if these phytoplankton blooms do not directly represent an ongoing, more disperse population in the ocean that is continuously sequestering CO2, are scientists simply stopping to smell the flowers and missing the normal plant growth? Is the disperse population more significant to the biosphere than the occasional, more noticeable blooms?

   Reply | Report Abuse | Link to this

4. 4. candide in reply to jtdwyer 04:19 PM 4/14/10

   @jtdwyer -
   
   All good questions. As the article says much about phytoplankton is a mystery.
   
   My own guess would be that the dispersed population would have more of an effect that a bloom, but that is just a guess...

   Reply | Report Abuse | Link to this

5. 5. Acoyauh in reply to candide 04:19 PM 4/14/10

   Wrong. Again, and let me be clearer this time:
   Most internet searches will drop you the line "they typically live 1-5 days" if you superficially search for phytoplancton lifespan; but taking it as an absolute is rather simplystic. They are also typically asexual, unicellular organisms such as diatoms; but it does not mean diatoms are all there is out there, right? Phytoplancton is not only composed of diatoms, not even exclusively of unicellular plants - it is all sorts of microscopic and small algae, many of which live quite longer lives, have a healthy sex life and can even persist through full seasons.
   
   So, when you see "Typically" in a watered-down science article, do not take it as an absolute truth meaning "always".
   
   Again, the statement, as written here, is erroneous and probably based in such superficial interpretations of science texts as candide's. No, not all phytoplacton alive today will be dead in six days. Some could even outlive the author, for all we know.

   Reply | Report Abuse | Link to this

6. 6. Kevin Lately 04:54 PM 4/14/10

   The World is my Oyster & Plankton blooms are my Nemesis.

   Reply | Report Abuse | Link to this

7. 7. cloudman 05:52 PM 4/14/10

   The statement that warming 0cean waters would lead to less intense Atlantic storms is exactly opposite to what the global warming proponents predict.
   In reality, it's the clash between warm air and cold air plus vorticity that causes storms . One or two degrees of warming with a doubling of carbon dioxide---which would take 145 years---will make little difference.

   Reply | Report Abuse | Link to this

8. 8. candide in reply to Acoyauh 06:23 PM 4/14/10

   @Acoyauh -
   
   While I am not an expert on phytoplankton, it seems to me that your statement that "Some could even outlive the author, for all we know." is as simple, vague and "watered-down" as what you accuse this article of being.
   
   In addition your statement about another "Great Dying" like the end-Permian one" is, at best a huge exaggeration and miscomparison.
   
   If you portend to be accurate, you should try to be consistent about it.

   Reply | Report Abuse | Link to this

9. 9. Wayne Williamson 07:04 PM 4/14/10

   Interesting article...just wondering where the southern end of the North Atlantic is....

   Reply | Report Abuse | Link to this

10. 10. fisixisfun in reply to cloudman 10:01 PM 4/14/10

    @cloudman: More intense storms are predicted overall, not necessarily in the North Atlantic. A few years ago, Professor Immanuel at MIT, one of the leading hurricane experts in the world, said that wind-sheer effects could increase enough because of global climate change to kill off most hurricanes, but the article is not talking about hurricanes, it's talking about regular storms in the North Atlantic. Also, where did you get the idea that 1) It will take 145 years to double CO2 or 2) such an increase will only result in 1 or 2 degrees of warming? If by double you mean versus pre-industrial levels, that would be about 560 ppm, which the middle-of-the-road scenarios have happening towards the end of the century. If you mean double versus today's levels, that's about 760 ppm, and the worst-case scenarios have us reaching that level by the 2090's. Remember, a lot of the "worst-case scenario" predictions for the last few years have been beaten, as in glaciers retreating and sea levels rising by more than was expected even in the worst-case scenarios for that time. Also, the worst-case scenarios have temperatures rising by as much as 6-8 degrees Celsius, not 1 or 2.

    Reply | Report Abuse | Link to this

11. 11. Tardigrade 05:56 AM 4/15/10

    Candide:
    
    I see a noticeable difference between hyperbole (Acoyauh's statement of a "Great Dying") and statements of fact such as the author's "every plankton currently alive will be dead in 6 days".
    
    And while I agree that the "Some could even outlive the author" is a vague statement, Acoyauh isn't a journalist writing an article, but a commenter on that article. Given the specific purposes of articles of "fact" such as this article, and articles of opinion (Acoyauh's comment), it only seems natural to have distinct sets of standards for each type of article.

    Reply | Report Abuse | Link to this

12. 12. Tardigrade 05:58 AM 4/15/10

    Candide:
    
    I see a noticeable difference between hyperbole (Acoyauh's statement of a "Great Dying") and statements of fact such as the author's "every plankton currently alive will be dead in 6 days".
    
    And while I agree that the "Some could even outlive the author" is a vague statement,Acoyauh isn't a journalist writing an article, but a commenter on that article. Given the specific purposes of articles of "fact" such as this article, and articles of critique/opinion (Acoyauh's comment), it only seems natural to have distinct sets of standards for each type of article.

    Reply | Report Abuse | Link to this

13. 13. candide in reply to Tardigrade 04:42 PM 4/15/10

    @Tardigrade -
    
    The article was not written as well as it could have been, using superlatives (EVERY plankton) like they did.
    
    Still there have not been any facts presented to prove that wrong, just a couple opinions. I am not an expert on plankton so I cannot say if it is categorically true or false that "every plankton currently alive will be dead in 6 days."
    
    I do agree that the article writer should be held to higher standards than commenters. Beyond all that, IMO, one should try to be consistent.
    

    Reply | Report Abuse | Link to this

14. 14. jh443 06:27 PM 4/15/10

    I remember when all the science experts were convinced that these blooms were caused by phosphate in laundry detergent. I wonder what the experts will be wrong about this time.
    

    Reply | Report Abuse | Link to this

15. 15. Wayne Williamson 08:23 PM 4/15/10

    jh443...i think your thinking of the blooms at the mouth of rivers....

    Reply | Report Abuse | Link to this