Montoya, J. P. Georgia Institute of Technology, j.montoya@biology.gatech.edu
Altabet, M. A. University of Massachusetts Dartmouth, maltabet@umassd.edu

 
NITROGEN ISOTOPE ABUNDANCES IN PELAGIC ECOSYSTEMS: BIOLOGICAL CONTROLS ON THE DELTA-15N OF THE OLIGOTROPHIC OCEAN
 
The stable isotope composition of marine organic matter reflects the isotopic composition of the sources of N supporting primary production as modified by the biological fractionations associated with the upper ocean N cycle. The low delta-15N typical of PN (ca. 1 to 2 permil) and zooplankton (ca. 2 to 5 permil) in the oligotrophic ocean have typically been attributed to trophic processes that preferentially export 15N-enriched material from the upper ocean, leading to a residual delta-15N lower than that of deep water nitrate (ca. 5 permil). However, a number of recent lines of evidence, including large-scale biogeochemical models, direct experimental studies, and measurements of the delta-15N of the major pools of marine N, all indicate that N2-fixation may make a large contribution to the nitrogen budget of the oligotrophic ocean. We have integrated the available isotope data, including time-series measurements of PN and sedimenting organic matter from the central Sargasso Sea and newer measurements providing broader geographic coverage, in order to assess the role of trophic and source influences in generating the low delta-15N typical of oligotrophic waters. These results clearly indicate that N2-fixation is a significant source of combined nitrogen to the Sargasso Sea and perhaps other oligotrophic systems.
 
Day: Tuesday, Feb. 2
Time: 09:00 - 09:15am
Location: Eldorado Hotel
 
Code: SS32TU0900E