imageThank you for this opportunity to contribute to the briefing on Ocean Fertilization. My topic this morning is "Carbon Sequestration by the Ocean's Biological Pump: Present Understanding and Future Research Directions".

imageI would like to begin with my conclusions, just in case I run out of time at the end! It is important to emphasize that undersampling is a fact of life in oceanography. We have not yet sampled the ocean to the extent that will be required to validate comprehensive, predictive biogeochemical models.

Our understanding of carbon export, the cumulative effects of the biological pump, is presently limited by field observations, and in this regard I would say our ignorance greatly exceeds our knowledge. This is something that is very difficult to admit, but very important to keep in mind. The success of carbon sequestration by ocean fertilization demands an explicit understanding of the biological pump. We have not yet achieved that explicit understanding. Fertilization by iron (Fe) or other essential nutrients will certainly have an effect on the ocean and on the biological carbon pump, but the nature of the effect is poorly constrained as is our knowledge. The impacts on carbon sequestration cannot presently be predicted, and I would conclude that well-designed manipulation experiments, and systematic time-series observations will be needed to enhance our general understanding of the ocean's carbon cycle.

imageIn order to illustrate my comment about ignorance versus knowledge, I'd like to show what I call the Worldwide Web of oceanic microbes. For those of you who aren't microbiologists, you might not know that microorganisms have been around on Earth for a very long time, approximately 3.5 billion years. However, we didn't know about them until microscopes were invented in the 1600s by Van Leeuwenhoek. That was when microbes were first discovered and observed.

But it took us about another 150 years to describe them in any formal scientific sense. The first organism that was described, using what we now call bionominal nomenclature, was a marine microorganism in the early 1800s.


Over the next 100 years or so we conducted an intensive investigation of microorganisms so by the middle of the 20th century we thought we had a complete and fundamental understanding of microbes in the ocean. Then, in the mid 1980s, much to our amazement, we had what can only be called "microbiological revolution." First, we discovered the second-most and the first-most abundant groups of microorganisms in the ocean, that is, Synechococcus and Prochlorococcus, respectively. The latter group is affectionately also known as Pennychisholmcoccus, because it was discovered by Dr. Penny Chisholm, our workshop co-convenor! Prior to these discoveries we thought we had a balanced carbon cycle and a comprehensive inventory of marine life -- how wrong we were. It put us in awe because we had previously thought we understood marine life but, in retrospect, how could we have with such a large information gap?

So this was a major, unexpected discovery, and at that point we thought, well, now we must know just about everything there is to know about life in the sea. Then, just a few years later in 1992, we discovered planktonic Archaea - the third domain of life, which we never thought would be present in the ocean. We now recognize them as a dominant group of marine microbes in fact, below about 1500 m, the most dominant group. But we still don't know what they're doing in an ecological sense. We assume, but are not certain, that they are heterotrophic, competing with the bacteria.

Then, in 1996, through genetic techniques, we were able to get the first genome sequence of a marine microorganism, and we found out, again much to our amazement, that nearly 50% of the microbial genome was used to synthesize proteins that we didn't recognize. This genetic information appeared to be used for regulation and control of cellular activities which would be vital for successful ecological function and to respond to global environmental variability. In retrospect, it all makes sense yet we had not predicted this a priori.

So, again, we uncovered a fairly large information void about the ocean around us. Then, in 2000, we discovered a very interesting light-driven proton pump in a very widely distributed marine microorganism, uncovering a potentially new pathway of carbon and energy flow in the ocean.

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