Guest Post by Willis Eschenbach
Following on from Anthony’s article, here are my thoughts about the phytoplankton paper “Global phytoplankton decline over the past century”, by Daniel G. Boyce, Marlon R. Lewis & Boris Worm.
I started to write about this earlier, but I decided to wait until I had the actual paper. The paper in question is behind a paywall at Nature Magazine, but through my sub-oceanic channels (h/t to WS) I have obtained a copy. The paper makes two main claims, that: a) the numbers of phytoplankton have been cut by more than half since 1900, and b) the general warming of the global oceans is the reason for the declining numbers of phytoplankton.
First, what are phytoplankton when they are at home, and where is their home? Plankton are the ubiquitous soup of microscopic life in the ocean. Phytoplankon are the plant-like members of the plankton, the ones that contain chlorophyll and feed on sunshine. Phytoplankton are to the ocean what plant life is to the land. Almost all oceanic life depends on phytoplankton. Other than a thin strip of seaweeds and sea grasses along the coasts, phytoplankton are the microscopic plants that are the foundation of the vast entire oceanic food chain. Without phytoplankton there would be no deep water oceanic life to speak of. Figure 1 shows where you find phytoplankton:
Figure 1. Global distribution of phytoplankton. Lowest concentration is purple and blue, middle concentration is green, highest concentration is yellow and red. Source http://www.nasa.gov/vision/earth/environment/0702_planktoncloud.html
So where did the Nature paper go wrong?
The short answer is that I don’t know … but I don’t believe their results. The paper is very detailed, in particular the Supplementary Online Information (SOI). It all seems well thought out and investigated … but I don’t believe their results. They have noted and discussed various sources of error. They have compared the use of Secchi disks as a proxy, and covered most of the ground clearly … and I still don’t believe their results. Here’s exactly why I don’t believe them.
This is their abstract (emphasis mine):
In the oceans, ubiquitous microscopic phototrophs (phytoplankton) account for approximately half the production of organic matter on Earth. Analyses of satellite-derived phytoplankton concentration (available since 1979) have suggested decadal-scale fluctuations linked to climate forcing, but the length of this record is insufficient to resolve longer-term trends.
Here we combine available ocean transparency measurements and in situ chlorophyll observations to estimate the time dependence of phytoplankton biomass at local, regional and global scales since 1899. We observe declines in eight out of ten ocean regions, and estimate a global rate of decline of ~1% of the global median per year. Our analyses further reveal interannual to decadal phytoplankton fluctuations superimposed on long-term trends. These fluctuations are strongly correlated with basin-scale climate indices, whereas long-term declining trends are related to increasing sea surface temperatures. We conclude that global phytoplankton concentration has declined over the past century; this decline will need to be considered in future studies of marine ecosystems, geochemical cycling, ocean circulation and fisheries.
The first clue to where they went wrong is visible in Fig. 1. Although as you can see there is more phytoplankton in the cooler regions of the north, the same is not true in the corresponding regions in the south despite the ocean temperatures being very similar. In addition, there are many places where the ocean is warm (e.g. tropical coasts) that have lots of phytoplankton, while in other warm areas there is very little phytoplankton.
The rude truth of phytoplankton is this: phytoplankton growth is generally not limited by temperature. Instead, it is limited by nutrients. Where nutrients are plentiful, the phytoplankton grow regardless of temperature. Nutrients are more common along the coastline, where sub-oceanic currents come to the surface bringing nutrients from the deep ocean floor, and rivers bring nutrients from inland. For example, in Fig. 1 you can see the nutrients from the Amazon river causing the red area at the river mouth (north-east South American coast).
Indeed, the fact that phytoplankton are generally nutrient limited rather than temperature limited has been demonstrated in the “ocean fertilization” experiments using rust. If you spread a shipload of rust (iron oxide) out into the tropical ocean, you generally get an immediate bloom of phytoplankton. Temperature is not the problem.
So to start with, the idea that increasing temperature automatically leads to decreasing phytoplankton is not generally true. There are vast areas of the ocean where higher temperatures are correlated with more phytoplankton. For example, the warmer deep tropics generally have more phytoplankton than the cooler adjacent subtropics.
The paper’s most unbelievable claim, however, is their calculation that since 1899, the density of phytoplankon has been decreasing annually by 0.006 milligrams per cubic metre (mg m-3). They give the current global density of phytoplankton as being 0.56 mg m-3. Thus they are claiming that globally the concentration of phytoplankton has dropped by more than 50% over the last century.
Now, a half century ago I learned to sail on San Francisco Bay. Since then I’ve spent a good chunk of my lifetime at sea, as a commercial fisherman from California to the Bering Sea, as a sailboat delivery crewman, as a commercial and sport diver, and as a surfer. And call me crazy, but I simply don’t believe that the sea only has half the phytoplankton that it had in 1900. If that were true, it would not take satellites and complex mathematical analysis to show it. People would have noticed it many years ago.
I say this because phytoplankton are the base of almost the entire mass of oceanic life. They are what almost all other life in the ocean ultimately feeds on, predators and prey as well. The authors of the study do not seem to realize that if the total amount of phytoplankton were cut by more than half as they claim, the total mass of almost all living creatures in the open ocean would be cut about in half as well. No way around it, every farmer knows the equation. Half the feed means half the weight of the animals.
And I see no evidence of that having happened over the last century. It certainly does not accord with my own extensive practical experience of the ocean. And I see no one else making the claim that we only have half the total mass of deep-water oceanic life that we had a century ago..
The other thing that makes their claimed temperature/phytoplankton link very doubtful is that according to the HadISST dataset, the global ocean surface temperature has only increased by four tenths of a degree C in the last hundred years.
Four tenths of a degree … an almost un-noticeable amount. Yet their paper says (emphasis mine):
Our analyses further reveal interannual to decadal phytoplankton fluctuations superimposed on long-term trends. These fluctuations are strongly correlated with basin-scale climate indices, whereas long-term declining trends are related to increasing sea surface temperatures.
These kinds of claims drive me nuts. Is there anyone out there that truly believes that a change of global average ocean temperature of four tenths of a degree C over the last hundred years has cut the total mass of phytoplankton, and thus the total mass of all oceanic creatures, in half? Really?
So that’s why I say I don’t know where their math went wrong, but I don’t believe their results. I don’t believe we’ve lost about half the total mass of all oceanic creatures. Half the planet’s open ocean dwellers? Where is the evidence to support that outrageous claim? And I don’t believe that an ocean temperature change of four tenths of a degree over a century has made much difference to phytoplankton levels, as they grow at all temperatures.
Why don’t I know where their math went wrong? Unfortunately, they have not posted up the data that they actually used. Nor have they shown any of their data in the form of graphs or tables. Instead, they have shown model results, and merely pointed to general websites where a variety of datasets are maintained. So we don’t know, for example, whether they used the 1° grid version or the 2.5° grid version of a given dataset. Nor have they posted the computer code that they used in the analysis. Plus, the very first link in their paper to the first and most important data source is dead.
Grrrr … but dead link or not, pointing to a website as the data source in their kind of paper is meaningless. To do the analysis, they must have created a database of all of the observations, with the meta data, and the details for the type etc. for each observation. If they would include that database and their code in the SOI, then someone might be able to figure out where their math went wrong … my guess is that it may be due to overfitting or misfitting of their GAM model, but that’s just a wild guess.
It is a shame that they did not post their data and code, because other than the lack of data and code it is a fascinating analysis of a very interesting dataset. I don’t accept their analysis of the data because it doesn’t pass the “reasonableness” test, but that doesn’t mean that the dataset does not contain valuable information.
[Update] An alert reader noted that the image in Figure 1 was of a particular month and not a yearly average. So I’ve made a short movie of the variations in plankton over the year.
Figure 2. Monthly movie of plankton concentrations. Click on image to see animation.
“And I see no evidence of that having happened over the last century.”
Consider this year’s salmon run in Oregon. It was an all time record high greatly surpassing the previous record from the 1950’s.
Maybe there is less plankton today than there was before because there are more whales eating it. Whale populations have rebounded in many areas to the maximum sustainable by their food supply … which is in may cases, plankton. Maybe the plankton are being over grazed by whales.
@Willis Eschenbach, great post. If you keep this up, you may be awarded an honorary Knighthood. (reference to Hansen’s comment on “jousting with jesters.”)
see this link for more on jousting with jesters – and with Knights noble.
http://sowellslawblog.blogspot.com/2010/02/when-engineers-are-wrong-people-die.html
I’ll bet that at the beginning of the twentieth century there was a lot of organic pollution discharged from large cities near the coasts of the developed world. This sort of ocean fertilization probably led to local and large increases in the phytoplankton right off the coast, which may also be where most of the secchi disk and other phytoplankton measurements took place during the early years of the twentieth century. If this is so, I suspect that the decades-long time series on which the supposed drop of phytoplankton is based may be measuring nothing more than the drop in coastal pollution as the developed world’s sewage systems improved! I also like the point that Willis Eschenback makes implicitly, that phytoplankton obviously respond to the absolute temperature, not the temperature anomaly. Hence if the world’s oceans did get significantly warmer overall, we would expect to see tropical phytoplankton in temperate zones and temperate phytoplankton in polar zones, with little change — rather than a drop — in the overall amount of phytoplankton.
El Nino is a large variable in the availability of nutrients for phytoplankton off of the South American Pacific coast. The change in wind circulation kills the upwelling of the nutrient which deep water and can have a massive effect on the fisheries in the region.
There is also the problem of measuring phytoplankton over long timescales. The Secchi disk doesn’t measure phytoplankton, it measures turbidity – and the observers eyesight. Measurements done by chlorophyll extraction would be more recent and these measurements are also problematic in that there are a number of techniques which can give incommensurate answers.
Also, as pointed out, the growth of phytoplankton is not temperature dependent but more nutrient dependent. But of course it is also sunlight dependent. That’s right – sunlight. The more the better as far as phytoplankton are concerned.
I worked as a support scientist for many years in the field of Biological Oceanography. Most of my work was around the Great Barrier Reef, but I was involved in a number of ocean cruises in the Pacific. A secchi disk is a fairly crude measure of turbidity. In clear, oceanic water where suspended sediment levels are very low, the secchi-disk depth may be a proxy for phytoplankton levels. The secchi disk is streamed out on the up-swell side of the ship with the ship drifting, so it does not go straight down – but this should not be a major problem. However, there are other problems with its consistent use in oceanic waters. The biggest problem is the surface disturbance, which of course varies with the wind. On a calm day (no wind), you can see the disk to a much greater depth than on a day with wind-derived surface disturbance. In clear tropical waters with which I am familar, a calm day reading might be as high as 56m, while this reduces to 20-30m with surface wind. The time of the day, side of the ship with sunlight are other factors.
I too am very suspicious of the paper’s results, though I have not had a chance to see it. Is it available? The most pertinent question I would think is whether the secchi-disk history correlates with Chlorophyll-a measurements (a better proxy for phytoplankyon biomass). Did they do this comparison? There have been very many Chlorophyll measurements taken all over the world (I myself have made thousands) for a long time now and I would think that I would have heard of such a decline. Anyway, didn’t the study of satellite imagery show about a 6% worldwide INCREASE of chlorophyll (land and sea) over their 30-year history, possibly due to increasing CO2? By the way, as many readers have pointed out, phytoplankton growth is limited by nutrient availability, mostly N, P, Fe and Si.
I just thought of another issue. The modern trend of wearing polaroid sunglasses will of course give greater readings (i.e. less apparent phytoplankton) than older times when crew or scientific staff did not have them. We would deliberately not wear these sunglasses while taking such measurements, but would have to constantly remind people.
This paper should be brought to the attention of Michael Mann. Thoroughly bad science should not be published and he is just the MANN to fix it.
All good points Mike. So with this many variables in play, we are already calling into question the leap to temperature as the culprit.
There’s also a lot less sewerage sludge being dumped/piped offshore than there used to be, around the UK anyway.
If this were really true much of the increase of CO2 over the last century could be laid at the door of less sequestration by phytoplankton. If, in addition, the CO2 warming hypothesis was true the combination would lead to a positive feedback loop that would result in frequent periods of naturally occuring runnaway warming. There is zero evidence of this. Two wrongs definitely don’t make a right!
When I studied physics I would always ask myself: does this result look reasonable? Indeed we were encouraged to do a few back of the envelope calculations to check that we were in the right ball park. Clearly these researchers are not physicists.
Physics is considered to be a very difficult subject and it is. But in fact the systems that physicists study are generally simple. They are artificially constrained by strict boundary conditions and are simplified to special cases in order to make the problem soluble and reproduceable. The discipline and pure logic of a physicist can rarely deal with a complex unbounded system. The physicist can deal with the rules governing individual parts of the system but the phenomena which evolve from their interaction is normally left to others to study. The latter have equally rigourous approaches but their conclusions can never be as convincing. For example physicist might eventually define how individual neurones in the brain fire but they will never have much to say about the works of Shakespeare. Whether Shakespeare is a great writer or not is a a question physics can answer it is a matter of consensus. Where have I heard that before?
So it is with these so called studies. The data is useful but the conclusions are generally unimportant and, I think history shows, normally wrong. So conclusions without data are worse than useless.
I think they “got you” with the use of the “Median.”
Vast open stretches of Ocean with very little phytoplankton could cause the “Median” to be a very small number compared to the density in the area where phytoplankton actually hang out.
I would like to see their results expressed as a “percentage” of the “amount” of phytoplankton. It could look a lot more reasonable.
Sorry, correction to my last post. Second to last paragraph.
Whether Shakespeare is a great writer or not is a a question physics can NOT answer it is a matter of consensus. Got myself tied up in nots!
There must be a grain of truth in the claim that overall marine life has declined somewhat, although it seems improbable to state that this is due to a reduction in phytoplankton. In truth the culprit is over-fishing, an industry whose activities now range over all the world’s oceans, one example of its consequence surely being the decimation of cod numbers around Labrador, sharks too suffering as they are pursued solely for their fins, and all to satisfy some outlandish hunger for soup. While it is not all bad news, voicing uncertain and unproven concerns about about phytoplankton levels seems to distract from the real ssue.
“Analyses of satellite-derived phytoplankton concentration (available since 1979) have suggested decadal-scale fluctuations linked to climate forcing, ”
Decadal fluctuations do exist for reasons that are poorly understood,however the trends in the observational era show an increase in NCP eg Antoine et al 2005.
A comprehensive revision of the Coastal Zone Color Scanner (CZCS) data-processing algorithms has been undertaken to generate a revised level 2 data set from the near-8-year archive (1979–1986) collected during this ‘‘proof-of-concept’’ mission. The final goal of this work is to establish a baseline for a global, multiyear, multisensor ocean color record, to be built from observations of past (i.e., CZCS), present, and future missions. To produce an internally consistent time series, the same revised algorithms also have been applied to the first 5 years of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color observations (1998–2002). Such a database is necessary in order to determine whether or not the ocean biogeochemistry has evolved in the past years and, if so, to be able to detect near future trends. Algorithmic and calibration aspects, along with validation results presented in this paper, are tailored toward the identification of longterm trends, which mandated this reprocessing effort. The analysis of decadal changes from the CZCS to the SeaWiFS era shows an overall increase of the world ocean average chlorophyll concentration by about 22%, mainly due to large increases in the intertropical areas, where the seasonal cycles also substantially changed over the past 2 decades.
Increases in higher latitudes, where seasonal cycles did not change, contribute to a lesser extent to the general trend. In contrast, oligotrophic gyres display declining
concentrations
The authors are also the leaders in bio-optics ie water clarity and opacity eg Natural variability of bio-optical properties
http://www.biogeosciences.net/4/913/2007/bg-4-913-2007.pdf
In Variations of biological production and plankton biomass X. J. Wang et al. also found positive trends in the satellite era.
Recent studies indicate strengthened trade winds and intensified upwelling in the tropical Pacific since the late 1990s, suggesting implications for the biogeochemical processes. We employed a fully coupled physical-biogeochemical model to test the hy-
5 pothesis that there were climate driven decadal variations in biogeochemical fields
of the equatorial Pacific. We quantified changes in nitrate and iron concentrations,
primary and secondary productions, and phytoplankton and zooplankton biomass between 1988–1996 and 1999–2007. Our modeling simulation showed that the intensified upwelling during 1999–2007 resulted in significant increases of nitrate and iron 10 concentrations in the mixed layer of the central equatorial Pacific. In addition, the upwelling front moved westward, causing shifts of oligotrophic conditions to mesotrophic conditions in some parts of the western equatorial Pacific. As a result, there was an overall enhancement of biological activity in the western and central equatorial Pacific, leading to an increase in primary production and secondary production by 10–15% and 15 15–50%, respectively. Our study also indicated that there were changes in ecosystem states in the equatorial Pacific Ocean, suggesting alternative new states with more zooplankton biomass during 1999–2007. Additionally, our study showed significant changes in seasonal variations of biogeochemical fields. Particularly, there was a much stronger seasonality in biological production and plankton biomass near the dateline 20 during 1999–2007 relative to 1988–1996.
They are also add some interesting discussion
On the one hand, there is an increase in plankton biomass and enhancement in biological production in the upwelling region. In association with these changes, the ecosystem structure alters with more secondary producer and an increase of large cells. On the other hand, the upwelling front moves westward, causing shifts of oligotrophic condition to mesotrophic conditions in some parts of the western
equatorial Pacific. As a result, the whole basin has benefited with overall increases of
nutrient concentration and biological production in the euphotic zone.
Hensen et al 2009 suggest that no trends are distinguishable from annular or decadal trend as the time series is to short
We find that detection of real trends in the satellite data is confounded by the relatively short time series and large interannual 10 and decadal variability in productivity. Thus, recent observed changes in chlorophyll, primary production and the size of the oligotrophic gyres cannot be unequivocally attributed to the impact of global warming. Instead, our analyses suggest that a time series of 40 yr length is needed to distinguish a global warming trend from natural variability. Analysis of modelled chlorophyll and primary production from 2001–2100 suggests that, on average, the global warming trend will not be unambiguously separable from decadal variability until 2055. Because the magnitude of natural variability in chlorophyll and primary production is larger than, or similar to, the global warming trend, a consistent, decades-long data record must be established
Hence the Nature paper is an inverse reconstruction of what the biomass of phytoplankton and NCP was prior to the satellite era.
The paper ( which I have not read) would need to reconcile the Ar/o2 ratios concomitant to whatever historical observations they used .The additional O2 pulse from the SH Keeling et al., 1996 following Pinatubo and its natural Fe fertilzation experiment show potential uptake is availablem,
I wouldn’t worry about doing the maths Willis, because true believers everywhere use the same computer models and as you know computers never lie. Unfortunately for no comment Ministers for Gaia they don’t always tell the truth either-
http://www.theaustralian.com.au/national-affairs/people-in-politics/energy-star-ratings-in-disarray/story-fn5oa9p3-1225899270215
crosspatch says:
August 1, 2010 at 1:13 am
Consider this year’s salmon run in Oregon. It was an all time record high greatly surpassing the previous record from the 1950′s.
I think the problem with past low numbers is this:
http://tinyurl.com/27l5t4e
# W.E.: “And I don’t believe that an ocean temperature change of four tenths of a degree over a century has made much difference to phytoplankton levels.”
Agreed: it is naïve. And from where did they get any reliable phytoplankton data dating back 50, or even 100 years ago? Assessing such a question on a global basis is speculation in pure and worthless. The ocean is not a pond.
Hmm, it would appear from the analysis and the comments, that the only way that humans could have contributed, is by the act of cleaning up after ourselves and dumping less waste products into the sea, kind of like the way that some of the warming from the ’70s is believed to be caused by us putting up less aerosols. We’re damned if we do and damned if we don’t :-).
There’s a photo on wikipedia showing a plankton bloom in the Bering Sea. On the island in the middle of it, you could fit the entire human population an arms length apart, and still have space to spare. Kind of puts things into perspective.
/paulhan
Phytoplankton has at least two (2) defense systems
1) Umbrella defense system: When the UV gets to high, the phytoplankton release DMS and make it own low clouds as protection for the UV radiation.
2) Colony defense system: Phytoplankton is lowest in the marine food chain… when the plankton is treatened for the next chain, it builds colonies, clumps together, in a dramatic way. Imagine one mosquitoes transformed to 5 greenlandic whales in just 6 hours or to 50 big male elephants. When the threat is over they transform back to normal in antoher 6 hours.
With just one braincell.
I placed a wooden pole 5 meters long. 4 meters above ground and 1 meter underground in the middle of a field ( 4 hectares ) at the top, 3 meters, 2 meters I positioned 3 Barton temp. recorders, which have now been recording for 23 days, the variations over 24 hours/23 days in recoded temp. is 0.098c. Science anyone !
And I see no evidence of that having happened over the last century. It certainly does not accord with my own extensive practical experience of the ocean. And I see no one else making the claim that we only have half the total mass of deep-water oceanic life that we had a century ago..
Well I hold no brief for this paper but concern regarding the decline in major fisheries over the last couple of decades is widespread. Generally this is attributed to fishing pressure but this paper suggests that it isn’t that simple.
Collapse of N Sea fisheries
http://icesjms.oxfordjournals.org/cgi/reprint/53/6/1130.pdf
Decline in large game fish
http://www.bigmarinefish.com/extinction.html
Ziiex Zeburz:
Interesting. What is growing in the field? does it harbour plenty of moisture?
“Other than a thin strip of seaweeds and sea grasses along the coasts, phytoplankton are…”
Small point, you might want to add the Sargasso Sea.
http://www.straightdope.com/columns/read/2024/whats-the-story-on-the-sargasso-sea
That type map greatly exaggerates the area/volume of the Northern Oceans where phytoplankton is very prevalent.
You could change the “Median” 50%, and possibly only change the total mass of phytoplankton 2, or 3%.