by Adrienne Hoarfrost, University of North Carolina at Chapel Hill
|Adrienne puts some seawater into her |
autoclave—a machine used to sterilize
materials under very high temperature
and pressure. (Winn Johnson, WHOI)
As Gwenn masterfully explained in her post on the biological pump, phytoplankton at the surface of the ocean convert carbon dioxide into the material that makes up their bodies (organic carbon) via a process called photosynthesis, producing oxygen in the process. When they die, they sink into the deeper ocean, which sequesters carbon dioxide away from the atmosphere, and provides a source of food for organisms living below the surface. As this organic matter sinks, microorganisms at different depths consume and transform it still further. These organisms are called heterotrophs, meaning they use organic matter as a food source. (You and I are also heterotrophs, with the spaghetti, meatballs, and broccoli I had for dinner last night all qualifying as organic matter.
I’m interested in the appetites of these heterotrophs. Different microbes have varying abilities to eat different components of organic matter—not every heterotrophcan consume every organic molecule. Instead, the microbial community as a whole works together, cumulatively breaking down complex organic matter into smaller pieces that are easier to digest by a greater fraction of the community. Despite this communal effort, not every community can break down every component of organic matter.
|Adrienne samples her seawater-|
(Winn Johnson, WHOI)
On this cruise, I’m tracking microbial consumption of several high-molecular-weight polysaccharides in seawater from different latitudes and depths. I’m looking for differences in what organic materials get eaten, how much of it gets eaten how fast, and which microbes are doing the eating.
Because different microbes have varying abilities to eat different things, and microbial communities are different depending on latitude and depth, I expect this to be reflected in which and how much of my substrates are eaten. Ultimately, I want to understand what specific features of these substrates make one more tantalizing than the other and why different microbial communities have differing appetites according to latitude and depth. This might help us understand how biological activity, along with latitude- or depth-dependent variations in that activity, contributes to the composition and transformation of organic matter as it moves through the ocean and down the food chain from source to sink.