OCEAN-ATMOSPHERE CO2 EXCHANGE - AN ACCESSIBLE LAB SIMULATION FOR CONSIDERING BIOLOGICAL EFFECTS

Phytoplankton is considered a key component mediating the ocean-atmosp heric exchange of carbon dioxide and oxygen. Lab simulations which mod el biological responses to atmospheric change are difficult to transla te into natural settings owing in part to the vertical migration of ph ytoplankton. In the sea this vertical migration acts to regulate actua l carbon dioxide consumption. To capture some critical properties of t his vertical material transfer, we monitored the effects of atmospheri c CO2 on dense suspensions of bioconvecting microorganisms. Bioconvect ion refers to the spontaneous patterns of circulation which arise amon g such upwardly swimming cells as alga, protozoa, zoospore and large b acteria. Gravity, phototaxis and chemotaxis have all been implicated a s affecting pattern-forming ability. The ability of a biologically act ive suspension to detect atmospheric changes offers a unique method to quantify organism adjustment and vertical migration. With increasing CO2, bioconvection patterns in alga (P. parva) and protozoa (T. pyrifo rmis) lose their robustness, and surface cell populations retreat from the highest CO2 regions. Cell movement (both percent motile and mean velocity) generally diminishes. A general program of image analysis yi elds statistically significant variations in macroscopic migration pat terns; both fractal dimension and various crystallographic parameters correlate strongly with carbon dioxide content.