Joseph Montoya, Professor
Ph.D., Biology, Harvard University
Email:
Phone: 404-385-0479
Fax: 404-385-4440
Office: Environmental Science & Technology (ES&T) 1244
Research Interest
My lab group works at the interface between biological oceanography and biogeochemistry, with a strong focus on the role of nitrogen cycle processes in structuring the flow of biomass and energy through marine ecosystems.
Current Research
My research program is highly interdisciplinary, incorporating work in biological oceanography, marine chemistry, and isotope biogeochemistry on a variety of temporal and spatial scales. Much of our work at sea in the last several years has coupled integrative stable isotope measurements with short-term tracer experiments to study nitrogen cycle processes in the ocean, with a particular focus on the role of N2-fixation (diazotrophy) in structuring the flow of nitrogen and energy through planktonic ecosystems. Since carbon fixation is tightly linked to nitrogen supply in much of the ocean, our work on N2-fixation has broad relevance to questions of biological production and carbon cycling in the oceans.
In recent years, we have used the natural isotopic composition (δ15N ) of marine nitrogen to show that diazotrophy makes a significant contribution to the nitrogen budget of oligotrophic waters, and we have conducted extensive surveys of the overall impact and spatial extent of N2-fixation in the North Atlantic. These integrative, isotopic measurements bridge the gap between small-scale, biologically based estimates of diazotroph abundance and activity and the much higher rates of N2-fixation implied by geochemical studies of the Sargasso Sea and other waters. We are actively at work developing and refining techniques for measuring the δ15N of individual amino acids isolated from organic matter. These compound-specific isotope analyses provide information on the animal's trophic position as well as the sources of nitrogen supporting primary production in the ecosystem. We continue to develop and apply new methods in isotope ratio mass spectrometry, including analytical techniques for small sample analysis as well as compound specific work.
In shallower waters, we are involved in studies of the biogeochemistry and microbiology of cold seep systems in the northern Gulf of Mexico. These studies involve intensive sampling of sediments and organisms from both the bottom and the water column in the vicinity of oil-rich methane seeps. In addition to tracing the movement of carbon and nitrogen through the benthic food web, we have found clear evidence for the transfer of methane-derived carbon into the planktonic food web in the water column overlying the cold seeps.
In addition to our work in stable isotope biogeochemistry, my lab is involved in direct tracer measurements of N2-fixation in marine systems. We developed a high-sensitivity tracer assay for aquatic N2-fixation and have applied it in diverse oceanic regions to measure N2-fixation by recently discovered unicellular diazotrophs that are broadly distributed in oligotrophic waters. We have recently demonstrated that unicellular cyanobacteria may account for even more N2-fixation than the larger and better known Trichodesmium, dramatically increasing our estimates of the total oceanic potential for N2-fixation and new production of organic matter.
Recent Publications
Wilson, C., T.A. Villareal, N. Maximenko, S.J. Bograd, J.P. Montoya, and C.A. Schoenbaechler. In Press. Biological and physical forcings of late summer chlorophyll blooms at 30°N in the oligotrophic Pacific. J. Mar. Syst.
Burns, J.A., J.P. Zehr, J.P. Montoya, A.D. Kustka, and D.G. Capone. In Press. Effect of EDTA additions on natural Trichodesmium spp.(Cyanophyta) populations. J. Phycol.
Montoya, J.P., and M. Voss. 2006. Nitrogen cycling in anoxic waters: Isotopic signatures of nitrogen transformations in the Arabian Sea Oxygen Minimum Zone. In Past and Present Water Column Anoxia, Neretin, L.N, Ed. NATO Science Series IV: Earth and Environmental Sciences, 64. Springer, Dordrecht, Netherlands.
Krauk, J., T.A. Villareal, J.A. Sohm, J.P. Montoya, and D.G. Capone. 2006. Plasticity of N:P ratios in laboratory and field populations of Trichodesmium spp. Aquat. Microb. Ecol. 42: 243-253.
Garton, D.W., C.D. Payne, and J.P. Montoya. 2005. Flexible diet and trophic position of Dreissenid mussels inferred from stable isotopes of carbon and nitrogen. Can. J. Fish. Aquat. Sci. 62, 1119-1129.
Capone, D.G., J.A. Burns, C.A. Mahaffey, A.F. Michaels, J.P. Montoya, A. Subramaniam, and E.J. Carpenter. 2005. Nitrogen fixation by Trichodesmium spp.: An important source of new nitrogen to the tropical North Atlantic Ocean. Glob. Biogeochem. Cycles 19: GB2024, doi:10.1029/2004GB002331.
Holl, C.M. and J.P. Montoya. 2005. Interactions between nitrate uptake and N2-fixation in Trichodesmium. J. Phycol. 41: 1178-1183.
Joye, S.B., I.R. MacDonald, J.P. Montoya, and M. Peccini. 2005. Geophysical and geochemical signatures of Gulf of Mexico seafloor brines. Biogeosciences 2: 295-309.
Campbell L, E.J. Carpenter, J.P. Montoya, A.B. Kustka, and D.G. Capone. 2005. Picoplankton community structure within and outside a Trichodesmium bloom in the southwestern Pacific Ocean. Vie et Milieu 55: 185-195.
Joye, S.B., A. Boetius, B.N. Orcutt, J.P. Montoya, H.N. Schulz, M.J. Erickson, and S.K. Lugo. 2004. The anaerobic oxidation of methane and sulfate reduction in sediments from Gulf of Mexico cold seeps. Chemical Geology 205(3/4): 219-238.