New study reveals decline of marine phytoplankton over the past century

A new article published in the July 29 issue of the international journal Nature reveals for the first time that microscopic marine algae known as "phytoplankton" have been declining globally over the 20th century.

A new article published in the 29 July issue of the international journal Nature reveals for the first time that microscopic known as "" have been declining globally over the 20th century. Phytoplankton forms the basis of the and sustains diverse assemblages of species ranging from tiny zooplankton to large marine mammals, seabirds, and fish. Says lead author Daniel Boyce, "Phytoplankton is the fuel on which marine ecosystems run. A decline of phytoplankton affects everything up the food chain, including humans."

Using an unprecedented collection of historical and recent oceanographic data, a team from Canada's Dalhousie University documented phytoplankton declines of about 1% of the global average per year. This trend is particularly well documented in the and after 1950, and would translate into a decline of approximately 40% since 1950. The scientists found that long-term phytoplankton declines were negatively correlated with rising sea surface temperatures and changing oceanographic conditions.

The goal of the three-year analysis was to resolve one of the most pressing issues in oceanography, namely to answer the seemingly simple question of whether the ocean is becoming more (or less) „green' with algae. Previous analyses had been limited to more recent satellite data (consistently available since 1997) and have yielded variable results. To extend the record into the past, the authors analysed a unique compilation of historical measurements of ocean transparency going back to the very beginning of quantitative oceanography in the late 1800s, and combined these with additional samples of phytoplankton pigment („chlorophyll') from ocean-going research vessels. The end result was a database of just under half a million observations which enabled the scientists to estimate phytoplankton trends over the entire globe going back to the year 1899.

The scientists report that most phytoplankton declines occurred in polar and tropical regions and in the open oceans where most phytoplankton production occurs. Rising were negatively correlated with phytoplankton growth over most of the globe, especially close to the equator. Phytoplankton need both sunlight and nutrients to grow; warm oceans are strongly stratified, which limits the amount of nutrients that are delivered from deeper waters to the surface ocean. Rising temperatures may contribute to making the tropical oceans even more stratified, leading to increasing nutrient limitation and phytoplankton declines. The scientists also found that large-scale climate fluctuations, such as the El-Niño Southern Oscillation (ENSO), affect phytoplankton on a year-to-year basis, by changing short-term oceanographic conditions.

The findings contribute to a growing body of scientific evidence indicating that global warming is altering the fundamentals of marine ecosystems. Says co-author Marlon Lewis, "Climate-driven phytoplankton declines are another important dimension of global change in the oceans, which are already stressed by the effects of fishing and pollution. Better observational tools and scientific understanding are needed to enable accurate forecasts of the future health of the ocean." Explains co-author Boris Worm, "Phytoplankton are a critical part of our planetary life support system. They produce half of the oxygen we breathe, draw down surface CO2, and ultimately support all of our fisheries. An ocean with less phytoplankton will function differently, and this has to be accounted for in our management efforts."

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More information: Global phytoplankton decline over the past century, Nature, 466, 591-596 Date published: 29 July 2010. doi:10.1038/nature09268 … abs/nature09268.html
Provided by Dalhousie University
Citation: New study reveals decline of marine phytoplankton over the past century (2010, July 28) retrieved 18 October 2019 from
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Jul 29, 2010
Much of the global 'standing crop' of cyanobacteria are to be found around the continental shelves where the supplies of critical nutrients such as nitrogen, iron and silica are to be found in greatest abundance. The waters off Eastern Patagonia are a well known textbook example of this - where airborne dust from the Andean volcanos and glacial moraine runoff combines to increase the rate of nutrient export into that coastal shelf area. This study does not appear to have considered the very important coastal shelf regions at all. Ironically those are the very regions where the oceans have received, in recent centuries, the greatest input (and an increasing one) of such nutrients due to the expansion of the human race, much of which is concentrated around the continental margins and in great archipelagos such as Japan, Indonesia, the Philipines etc.

Jul 29, 2010
It is well known from numerous sea-based microcosm experiments that cyanobacterial primary productivity rises with increasing partial pressure of CO2 (just as it does with increasing levels of key nutrients). It is highly likely that this effect far outweighs any temperature-based effect. It can be shown that the NH oceans contain two great consortia of cyanobacteria which bloom in two different temperature bands of the annual cycle whereas the SH ocean has only one such consortium. Despite this, it is also possible to show that the rate at which the surface partial pressure of CO2 lags behind the global mean partial pressure over the Great Southern Ocean (SO) below 40 S has been actually slowly increasing since ~1980 not decreasing. This can only mean that the cyanobacterial primary productivity of the SO is increasing with increasing global partial pressure of CO2.

Jul 29, 2010
It is only in the last few decades that we have even approached a mature understanding of the major speciation of cyanobacterial species in the ocean and hence their often differing consortial/ecological relationships to 'traditional' gross parameters such as transparency and chlorophyll-a. Just a few decades ago, if one was to assert that seawater typically contained 100,000 cells/mL of the (tiny) picocyanobacterium Prochlorococcus and 10,000 cells/mL of the 'normal' cyanobacterium Synecchococcus one would have been laughed at quite simply because few were aware the major species Prochlorococcus was even present!

I fear this is just another one of those earnestly propagandist Nature AGW papers, readily revealing its origin in the fashionably domineering, socio-political movement of our times.

Jul 29, 2010
ecoeng, I trust you'll be publishing your rebuttal to this article, then?

Jul 29, 2010
I just published My Rebuttal. It was fully grounded in factual knowledge/mainstream literature.

You just read it.

Beyond this there is no such thing as 'absolutely transparent peer review and editorial' as Nature is not (yet) a fully transparent, free, online journal where all can read, and comment on, the 'peer reviews' and the editors' decisions.

There is no such viable thing as a partial, relative, conditional, managed, semi-secret, science.

We all, including you, must still wait for the realization of the Internet's potential to achieve true science.

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