Edward J. Carpenter
Douglas Capone
Raleigh Hood
Ajit Subramaniam

J. Montoya

Modeling of N2 and CO2 Fixation by the Oceanic Diazotroph Trichodesmium

NASA NAG5-6387, 36 months


N2 fixation by the marine cyanobacterium Trichodesmium has recently been recognized to provide an important source of new nitrogen in oligotrophic open ocean waters.  Along with atmospheric deposition of combined N, N2 fixation supports net uptake and export to depth of atmospheric CO2.  In contrast, new NO3- which enters the euphotic zone from below the thermocline is limited in its ability to sequester atmospheric CO2 because it is accompanied by an influx of dissolved inorganic carbon.

We here propose a synthesis and modelling effort with the following primary research objectives: 1) develop a global data base which incorporates all existing and accumulating field observations on Trichodesmium; 2) use this data base to improve existing algorithms for estimating Trichodesmium biomass from satellite ocean color measurements and for developing a new analytical model for predicting rates of N2 and CO2 fixation from satellite derived data; 3) use the analytical model to provide global estimates of CO2 and N2 fixation and thereby new production by Trichodesmium; 4) compare
satellite derived estimates of surface winds, temperature, chlorophyll and atmospheric dust (as a surrogate for iron) with satellite derived Trichodesmium biomass estimates, in order to examine the role of these factors as determinants for the distribution, abundance and bloom formation of Trichodesmium population and; 5) to interface our model as an input to the global marine carbon model being developed by Falkowski and Sarmiento.

We have undertaken quantitative field studies of the importance of the Trichodesmium as a primary producer and major source of new N in the tropical oligotrophic ocean in the N. Atlantic, Caribbean and Indian Ocean collecting data on biomass, depth distribution, N2 and CO2 fixation by Trichodesmium along with standard oceanographic data.  Relevant data are also available from the western Pacific, Caribbean and Sargasso Seas.  We currently have funding (through 2000) from NSF to undertake efforts in the SW Pacific and we have recently been funded by NASA/ SIMBIOS to incorporate satellite remote sensing in our Trichodesmium program, specifically to develop and verify (using surface spectrometer  measurements) algorithms to estimate Trichodesmium biomass by ocean color sensors (e.g. OCTS, SeaWiFS, MODIS).  A data base will be compiled from these studies and made available to other workers.  We will use the data base to develop an analytical model for estimating Trichodesmium-specific N2 and CO2 fixation rate from satellite-derived Trichodesmium biomass estimates.  This model will be analagous to the productivity algorithms which are being developed by P. Falkowski et al. as part of the current SeaWiFS science team efforts but it will be based upon measured Trichodesmium specific production and N2 fixation versus irradience relationships and observed Trichodesmium distributions.

The ultimate objective of our synthesis and modeling efforts will be to provide quantitative global estimates of N2 fixation rates as well as Trichodesmium-specific production, which will be coordinated, and intended to interface with, the efforts of P. Falkowski and J. Sarmiento who are developing a global oceanic productivity model.

Edward J. Carpenter
Marine Sciences Research Center
State University of New York at Stony Brook
145 Discovery Hall
Stony Brook, NY 11794-5000
tel: (516) 632-8696
fax: (516) 632-8915

Douglas G. Capone*
Chesapeake Biological Laboratory
University of Maryland Center for Environmental Science
P.O. Box 38
Solomons, MD 20688-0038
tel: (410) 326-7250
fax: (410) 326-7341

*note Dr. Capone's address will change in August 1998:
Wrigley Professor of Environmental Studies
Department of Biological Sciences &
The Wrigley Institute for Environmental Studies
University of Southern California
Los Angeles, CA  90089-0371

Raleigh R. Hood
Horn Point Environmental Laboratory
2020 Horns Point Rd
P.O. Box 775
Cambridge, MD 21613
tel: (410) 221-8434, 8497
fax: (410) 221-8490

Ajit Subramaniam
Chesapeake Biological Laboratory
University of Maryland Center for Environmental Science
P.O. Box 38
Solomons, MD 20688-0038
tel: (410) 326-7201

Joseph P. Montoya
Associate Professor of Biology and
    of Earth and Planetary Sciences
Harvard University
Bio. Labs 179, Ofc.
16 Divinity Ave.
Cambridge, MA 02138
tel:  (617) 496-8537
fax: (617) 496-5854