The "DARK MATTER" of nitrogen fixation.

Großkopf, Tobias, Mohr, Wiebke, Baustian, Tina, Schunck, Harald, Gill, Diana, Kuypers, M. M. M., Lavik, G., Schmitz, R. A., Wallace, Douglas W.R. and LaRoche, Julie (2011) The "DARK MATTER" of nitrogen fixation. [Talk] In: SAME12 - 12. Symposium on Aquatic Microbial Ecology. , 28.08.-02.09.2011, Rostock/Warnemünde, Germany .

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Biological nitrogen fixation is the largest input of fixed nitrogen into the oceans and
thus a key parameter in controlling primary productivity. Despite the importance
of nitrogen fixation there is major controversy about its magnitude on a global
scale, due to a gap in the marine nitrogen cycle on the input side. While this gap
suggests that the nitrogen cycle is currently not in balance and the oceans are
losing more nitrogen than they gain, stable isotope measurements from sediment
cores suggest that the nitrogen cycle has been in balance over the last 3000 years.
To resolve this paradox it has been suggested that marine nitrogen fixation is
currently underestimated.
We used a revised method to measure nitrogen fixation and compared it with the
prior, widely applied method. Our study reveals that over the whole Atlantic Ocean
the prior method underestimated nitrogen fixation rates. In certain areas the mean
fixationrate increased over six fold when measured with the revised protocol. The
magnitude of the difference is not stable but rather highly variable on a coarse
geographic scale. We suspected that species composition has a great influence on
the magnitude of underestimation of nitrogen fixation rates by the prior method, a
theory we could confirm with a laboratory experiment.
Taken together, our results imply that there is an urgent need to agree on a common
protocol for nitrogen fixation rate measurements to assess the true potential of
this nitrogen input process and be able to model the future development, given
man-made climate changes

Document Type: Conference or Workshop Item (Talk)
Keywords: Aquatic microbial ecology
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Date Deposited: 09 Apr 2013 09:14
Last Modified: 09 Apr 2013 09:14

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