By examining only the biomarker inventory, however, we can't say for certain which groups of cyanobacteria are actually responsible for this large change. Shown here are a few examples of important groups of known N2 fixing microorganisms: (1) Trichodesmium, a very large N2-fixing organism that's present in several different morphologies ranging from free trichomes (chains of cells) to the large (> 1 mm) aggregates or "bundles" shown in the slide, compared to the much smaller (3-5 mm) Synechococcus-like organisms that have recently been isolated by Dr. John Waterbury. The latter is a small unicellular N2-fixer, and this new organism was just discovered as an abundant component of the plankton at Station ALOHA (Zehr et al. 2001, Nature 412, 635-638). Both groups may contribute to the N2-primed prokaryote carbon pump discussed previously, but with fundamentally different ecological consequences due to variations in size.

imageAnother key group of microorganisms, the diatoms, also share a common biomarker pigment -- fucoxanthin. As with the cyanobacteria, not all diatoms are created equal; some are single-celled while others grow into long chains or large aggregates. Still others have endosymbiotic N2-fixing cyanobacteria living with them. These latter groups may, therefore, contribute to both the event driven and the N2-primed carbon pumps. As seen in this data set, there have been alternating 3-4 year periods of higher than average (the 12-yr climatology) and lower than average euphotic zone depth integrated inventories of fucoxanthin, again suggesting non steady-state population dynamics.

One major implication of this time variable population of diatoms is that if you fertilize at one point in time versus another point in time, you're likely to get a different result due to variations in the "seed" populations.


Species differences, even among the diatoms as a group, could also lead to variable response; e.g., presence or absence of species with endosymbiotic cyanobacteria. The variations observed at Station ALOHA are due to the natural variability of the ocean.

imageFinally, a third target group of microorganisms that are also very relevant to the ocean's carbon cycle share the common biomarker pigment 19-hexanoyloxyfucoxanthin (or simply, 19-Hex). This data set shows a different temporal pattern in abundance; relative to the long-term mean, the first seven years of data were lower than average, and then suddenly, there was nearly a doubling of this group biomarker. A key microorganism containing 19-Hex is the coccolithophores. The slide shows a satellite image of a very large bloom in the Bering Sea, so these are organisms are clearly visible from space. This group of organisms is also very important because they drive the calcification reaction shown; they consume alkalinity and they produce CO2 during growth and reproduction.

imageOver the last decade at Station ALOHA, we've also been measuring the particulate matter flux; the export of organic carbon as a manifestation of the biological pump. The interesting thing about this data set is that there are different phases over this 10-year cycle. For example, at Station ALOHA we began by having a peak in export each summer and each winter, and I wrote a paper about this because we thought this was the way it was going to be for the rest of the study period. Then, suddenly, we found a much lower flux and we lost the seasonality altogether. So much for accurate reporting from the field!

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