The cyanobacterium Oscillatoria (Trichodesmium) is the most abundant and active N2 fixing species in the plankton of tropical and subtropical seas. The frequency of blooms, distribution of the species and the estimates of rate of N2 fixation and primary production could be assessed more accurately by use of remote sensing when future satellites such as the ocean color scanner and Modus I satellites are launched. Trichodesmium has some ideal properties, a unique spectral signature and gas vesicles which bring it at or near the surface, thus facilitating remote sensing. This study will use an airborne spectrometer to map the spectral signature and ocean color in a field program at Barbados, West Indies. Ground truth data will be collected on density of Trichodesmium as well as rate of N2 fixation (acetylene reduction) and primary production while the spectrometer is operated in overflights. This information will be used in developing algorithms for the measurements of Trichodesmium distributions and rates of C and N2 fixation. In addition to the field studies, a search of existing images from the LANDSAT, CZCS, and manned spacecraft will be made to determine whether any images were taken during literature reported blooms. These images will be processed to determine the best modes of quantifying blooms. Results from this research will be directly relevant to the Global Ocean Flux (GOFS) program. The microscopic plants that are responsible for most of the ocean's biological production contain pigments for absorbing sunlight just as their terrestrial counterparts do. These pigments have long been used to quantify marine phytoplankton through direct chemical analysis of the chlorophyll present in a given body of water. Recently, the discovery that phytoplankton distributions can be measured remotely based on the color they impart to the water has opened up exciting opportunities for the large scale analysis of marine biological production. Dr. Carpenter and his co-workers seek to extend the use of remote biological sensing by developing optical methods for determining the spatial extent of a unique type of tropical microorganism known as Trichodesmium. Not only is the distribution of this organism of importance to the nutrient cycling and biological productivity of tropical areas, but the ability to differentiate among the different groups of floating organism in surface ocean water is an important area for future research.
