Data collected in the JGOFS field experiment conducted in 1989 indicated that bacteria process a large fraction of primary production even at the height of the North Atlantic spring bloom. Re-examination of those rates has raised several questions, and work since 1989 has discovered many new microbes and microbial processes not considered at the time. Some of the new microbes appear to be photoheterotrophic, such as the aerobic anoxygenic photosynthesizing (AAP) bacteria, which can be as abundant as Synechococcus and Prochlorococcus in the North Atlantic. These new findings indicate that it is essential to re-examine the role of bacteria (and archaea) during the North Atlantic spring bloom. In 2005, NSF-supported investigators and the EU CarboOcean project will address questions about the impact of pCO2 levels and temperature on algal community structure and biogeochemistry during the North Atlantic spring bloom. The investigators will join this effort and will explore how bacterial community structure changes in response to variation in phytoplankton biomass, growth, and community structure. Their working hypothesis is that Cytophaga-like bacteria are abundant during the height and waning stages of the spring bloom because of the use of high molecular weight dissolved organic matter, whereas SAR11 and other alpha-proteobacterial groups supported by low molecular weight DOM dominate non-bloom surface waters. The investigators will test this hypothesis using culture-independent methods, including microautoradiography and FISH (Micro-FISH) augmented by flow cytometry, and will also examine the uptake of select DOM components (amino acids, protein, glucose and polysaccharides) and CO2 by SAR11, Cytophaga-like bacteria, photoheterotrophs, and other abundant microbial groups.
The 1989 JGOFS field experiment was an important study of the North Atlantic Spring Bloom. The results of the study generated numerous hypotheses regarding the roles of bacteria in processing primary production, and these hypotheses have had a great influence on the subsequent development of marine microbial research. In 2005, researchers will revisit the North Atlantic Spring Bloom in an international collaboration designed to examine the influence of climate change on ocean processes, using the spring bloom as a proxy for longer-term climate change. In this project, the investigators will participate and examine explore how bacterial community structure changes in response to variation in phytoplankton biomass, growth, and community structure, using a combination of molecular genetic, ecological and biogeochemical approaches. The work is an essential addition to the NASB 2005 experiment and to the US/EU partnership to determine how the North Atlantic, an ecosystem that is shared by both North America and Europe, may react to climate regime changes during the coming century. The project will involve graduate and undergraduate students in research, and public outreach through a website.
