On Coccolithophores and Climate Change

by EG

Al Gore discussed in his famous novel, “An Inconvenient Truth,” the impending doom of global warming stating “there is an air of unreality in debating these arcane points when the world is changing in such dramatic ways right in front of our eyes because of global warming.”  Global warming is the effect of several different factors including the Earth’s natural cycle, but the most prominent factor is due to us: greenhouse gas emissions such as water vapor, CO₂, and methane.  This is understood by most who believe in global warming; however, many may not be aware that microorganisms play a large role in the global warming cycle.  Soil-dwelling anaerobic organisms emit two of the major greenhouse gases previously mentioned: CO₂ and methane.  Organisms that reside in the ocean play an even larger part, considering the ocean is about 70% of the Earth’s surface¹. These organisms have a positive role in global warming; they commonly use photosynthesis to live, therefore using CO₂ and respiring oxygen, aiding in reducing the CO₂ levels.  This is important because the total CO₂ emitted accounts for 9-26% of the greenhouse effect².

Figure 1. EHUX cell. Photo from

  Dr. Marcus Geisen and the  National

 History Museum

A few organisms may, however, cause production of CO₂ in oceans,
 such as Emiliania huxleyi. E. huxleyi, EHUX for short, is a Eukaryotic coccolithophore that is a single-celled phytoplankton covered with ornamented calcite disks³ (Figure 1). EHUX is unusual in that not only its shell but the soft section inside can be found in sediment. This is possible because it produces chemical compounds resistant to decomposition, known as alkenones. These alkenones can be found in marine sediment long after the soft section of the organism has decomposed, making it very useful to scientists to estimate past sea surface temperatures⁴

Figure 2: EHUX bloom seen from space

 in the Barents Sea off the coast of Russia.

 Photo from  Jeff Schmaltz from the

 NASA Earth Observatory.

EHUX is the most abundant coccolithophore in Earth’s oceans and is found everywhere except the polar regions. These blooms are formed in nutrient rich waters, causing an extremely anoxic environment, thereby killing marine wildlife and other microorganisms that reduce CO₂ concentrations. The continual shedding of their coccolith disks makes the oceanic blooms visible from space, as seen in Figure 2. EHUXs’ ubiquity causes these blooms to be quite massive, sometimes spanning more than 100,000 square kilometers (over 38,600 square miles), accounting for approximately 75% of the photosynthetic plankton in that area⁵. This may seem advantageous to have a 38,000 square mile area of photosynthetic organisms that take up CO₂ and respire oxygen, but these organisms also produce dimethylsulfoniopropionate (DMSP). DMSP turns into dimethylsulfide (DMS) which can cause dense clouds to form over the ocean, blocking the sunlight used by the photosynthetic bacteria. Not all sunlight is blocked, but nonetheless, the heating of the ocean may decrease over time if this were to happen continually, resulting in a decrease in loss of polar ice caps and ice mass inhabited by penguins, polar bears and other polar wildlife. Unfortunately, since EHUX is not found at the poles due to its extreme cold temperature, this would not have a great effect on these regions.

Several research experiments have been conducted using E. huxleyi as a model organism for changing ocean conditions and its effects. A study led by Robert Charlson claims that DMS, a source of cloud condensation, affects the reflectance of the clouds and therefore the Earth’s radiation and temperature. Charlson et al claimed that to counteract global warming due to an increase of atmospheric CO₂, an equal amount of DMS would be needed⁶. This seems reasonable but their research on this subject matter has many inadequacies; it is still unknown how climate affects DMS emissions, or how the microbes react to the changing climate⁶. It is also unlikely that massive blooms would have more advantages than disadvantages in terms of other marine life.

In addition to the Charlson et al research, a study done by Marion van Rijssel and Winfried Gieskes showed that in higher temperatures the cell size of E. huxleyi decreased, but the amount of DMSP generated per cell increased⁷. However, they found that there was a two-fold drop in DMSP produced by EHUX in the temperature range of 5-15^oC which is the normal temperature of the euphotic (uppermost) layer of water where EHUX is found⁷.  This evidence supports the claim that because of global warming, the euphotic zone will be the warmest, resulting in an increase of DMSP production, thus an increase in DMS production to create clouds.  An important note the authors make is that only a small fraction of the total DMSP produced by all algal blooms, not solely EHUX blooms, will escape to the atmosphere.  Even in the atmosphere it is not guaranteed to create a cloud and if it does, it would likely be a very small cloud not nearly large enough to offset the effects of the heated ocean as Charlson et al claimed⁷. It is clear that research with EHUX and its ability to create safe byproducts for humans, wildlife, and the environment is limited. As of now there is much left unknown but if further research continues to show promising results, this organism may be our answer to ridding ourselves of, or delaying the monster hanging over our heads: global warming.

Two and a half billion years ago oxygen began to accumulate on this planet and 200,000 years ago when anatomically modern humans appeared, we began to destroy it. As technology has improved, one would think that ways to combat or decrease the amount of greenhouse gases emitted would be apparent but instead we put billions of dollars into war and absurd campaign ads. Before we leave our children, grandchildren, and even great grandchildren with a doomed planet, we need to take necessary steps to improve our energy use. This means using nuclear, solar, and wind energy and not relying on coal and oil. Now, with new research and discoveries of microorganisms that do amazing things, we may see ourselves turning to microbial engineering in order to delay the Earth’s inevitable fate. Organisms such as E. huxleyi demand further research but look promising in supplying us with naturally found compounds that, unlike CO₂, may help our planet. There are still many unanswered questions: will massive DMS clouds pollute our air and cause sickness? Will massive EHUX blooms kill off marine life and therefore our seafood industry and a major source of coastal economies? What about the potential of other organisms in the ocean or in the soil? These organisms and these questions demand attention; but like science, there will always be more to learn. It is up to us and the next generations to call attention to this global crisis and use our resources to find answers to these questions

References

1.     National Oceanic and Atmospheric Administration.  “Ocean.”  Date Accessed: November 15, 2012.  http://www.noaa.gov/ocean.html

2.     Russell, Randy. “The Greenhouse Effect & Greenhouse Gases.” Windows to the Universe.  June 1, 2007.

3.     Young, Jeremy.  “Emiliania huxleyi.” Natural History Museum. Date Accessed: November 15, 2012.  http://www.nhm.ac.uk/nature-online/species-of-the-day/biodiversity/climate-change/emiliania-huxleyi/index.html

4.     DOE Joint Genome Institute U.S. Department of Energy.  “Emiliania huxleyi CCMP1516 main genome assembly.”  Date Accessed: November 15, 2012.  http://genome.jgi-psf.org/Emihu1/Emihu1.home.html

5.     Tyrrell, T. and Merico, A. (2004) Emiliania huxleyi: bloom observations and the conditions that induce them. In,Thierstein, H.R. and Young, J.R. (eds.) Coccolithophores: from molecular processes to global impact. Berlin, Germany, Springer, 75-97.

6.     Charlson RJ, Lovelock JE, Andreae MO, & Warren SG.  1987.  “Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate.”  Nature. 326:655-661.

7.     Van Rijssel, Marion & Gieskes, Winfried W.C.  2002.  “Temperature, light, and the dimethylsulfoniopropionate (DMSP) content of Emiliania huxleyi (Prymnesiophyceae).” J of Sea Res.  48:17-27.