Mechanistic models of oceanic nitrogen fixation

Oceanic nitrogen fixation and biogeochemical interactions between the nitrogen, phosphorus and iron cycles have important implications for the control of primary production and carbon storage in the ocean. The biological process of nitrogen fixation is thought to be particularly important where the ocean is nitrogen limited and oligotrophic. This thesis examines some of the mechanisms responsible for the distribution, rates and temporal variability of nitrogen fixation and its geochemical signature in the modern ocean. I employ simple analytical theories and numerical models of ecosystems and biogeochemical cycles, and closely refer to direct observations of the phytoplanktonic community and geochemical tracers of the marine nitrogen cycle. Time-series observations of geochemical tracers and abundances of nitrogen fixers (or diazotrophs) in the northern subtropical gyres suggest variability in nitrogen fixation on interannual and longer timescales. I use a highly idealized, two-layer model of the nitrogen and phosphorus biogeochemistry and ecology of a subtropical gyre to explore the previously proposed hypothesis that such variability is regulated by an internal biogeochemical oscillator. I find, in certain parameter regimes, self-sustained oscillations in nitrogen fixation, community structure and biogeochemical cycles even with perfectly steady physical forcing. The period of the oscillations is strongly regulated by the exchange rate between the thermocline and mixed-layer waters, suggesting a period of several years to several decades for the North Pacific subtropical gyre regime, but would likely be shorter (only a year or so) for the North Atlantic Ocean.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Monteiro, Fanny Meline

Advisor dc:contributor.advisor

• Michael J. Follows.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/53104

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/53104