Methanol is an atmospheric volatile organic compound that contributes significantly to ozone production in the trophosphere. It has been thought that the ocean is a sink for methanol but recent studies suggest that ocean production of methanol could be important and that it exists in measurable quantities in surface ocean waters. Studies by the PI, from Woods Hole Oceanographic Institution, have recently shown that various genera of cyanobacteria and eukaryotic phytoplankton are capable of producing methanol. It is therefore hypothesized that methanol production by phytoplankton is a conserved phenomenon and that it comprises a significant portion of the photosynthetically fixed carbon in the marine environment. The PI proposes to use laboratory culture experiments to further elucidate what fraction of primary productivity is as methanol production, whether there is a diel cycle of production, and if it is stored or consumed or exuded from the microorganisms. The project will also examine the consumption of methanol as a carbon and energy source for microorganisms in the euphotic zone, and how environmental conditions affect this. Studies will involve both laboratory and field experiments. Methods developed by the PI will allow direct measurement of the rate of respiration, and the overall turnover rates of methanol in contrasting coastal and oligotrophic open ocean regimes. Results from this work will improve our understanding of the mechanisms controlling production and consumption of methanol, possibly a major fraction of dissolved organic matter that has been previously overlooked. The proposed project with fund a young investigator, contribute to student training at various levels and include outreach activities.

Project Report

Methanol is a major atmospheric volatile organic compound on the planet, second to methane in abundance and serves as an important substrate for certain abundant microbes. As the dominant Oxygenated Volatile Organic Compound (OVOC) in the atmosphere, methanol has been the subject of much climatological research. Methanol and other OVOCs have been shown to be significant contributors to ozone production in the trophosphere through the production of free radicals with oxygenated nitrogen species. Although well studied in terrestrial ecosystems, the sources of methanol are currently unknown in the marine environment. Modeling efforts have suggested that the marine contribution could be as large as from terrestrial sources. The following core discoveries were made during our award period: • We determined that a range of axenic phytoplankton cultures including diatoms, coccolithophores, cyanobacteria, cryptophytes and chlorophytes all produce methanol in significant amounts. • We found that methanol was produced in a punctuated fashion (not in a steady state), beginning during nutrient depletion and onset of photosystem decline- however, the cells are still fully pigmented and quite healthy at this point. Given this pulse of methanol (where typically >80% of methanol is produced in a matter of 1-2 days in the 14-20 days of a culture lifetime) it was not feasible to normalized methanol to primary productivity (as initially proposed), which is a rate type measurement. Rather, we decided to compare methanol production to the total fixed carbon of the culture. Here we determined that methanol consists of 0.4-0.9% of the total fixed carbon pool, which is a respectable amount and biogeochemically significant. This relates roughly to 10-50 micromolar amounts of methanol in a phytoplankton culture. • From our initial measurements we have determined that methanol is predominantly produced during the light cycle in the diatom Phaeodactylum tricornutum (P.t.) and are currently following up on measurements in other representative phytoplankton. • We have determined through 13C-labeled methanol incubation experiments that methanol is a true waste product and is not uptaken or consumed. This is significant as this waste product then fuels the surrounding C1 heterotrophic microbial community. Additionally, we found that other volatiles are produced, including ethanol and 2-methyl-2-propanol (tertiary butanol), albeit at about an order of magnitude lower amounts (in the low parts per thousand ranges of total fixed cellular carbon). This opens an avenue of exploration for determining microbial consumption of these volatile products-- an avenue that we intend to pursue in the near future.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Donald L. Rice
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Woods Hole Oceanographic Institution
Woods Hole
United States
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