Biogeosciences
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5
1
2008
10.5194/bg-5-11-2008
http://www.biogeosciences.net/5/11/2008/
http://www.biogeosciences.net/5/11/2008/bg-5-11-2008.html
http://www.biogeosciences.net/5/11/2008/bg-5-11-2008.pdf
11
24
2008-01-11
Ocean biogeochemistry exhibits contrasting responses to a large scale reduction in dust deposition
A. Tagliabue
alessandro.tagliabue@lsce.ipsl.fr
L. Bopp
O. Aumont
Laboratoire des Sciences du Climat et de l'Environnement, IPSL-CNRS-CEA-UVSQ Orme des Merisiers, Bat 712, CEA/Saclay, 91198 Gif sur Yvette, France
Laboratoire d'Océanographie et Climatologie: Expérimentation et Approches Numériques, IRD/IPSL, Plouzané, France
Dust deposition of iron is thought to be an important control on ocean
biogeochemistry and air-sea CO<sub>2</sub> exchange. In this study, we examine the
impact of a large scale, yet climatically realistic, reduction in the
aeolian Fe input during a 240 year transient simulation. In contrast to
previous studies, we find that the ocean biogeochemical cycles of carbon and
nitrogen are relatively insensitive (globally) to a 60% reduction in Fe
input from dust. Net primary productivity (NPP) is reduced in the Fe limited
regions, but the excess macronutrients that result are able to fuel
additional NPP elsewhere. Overall, NPP and air-sea CO<sub>2</sub> exchange are
only reduced by around 3% between 1860 and 2100. While the nitrogen cycle
is perturbed more significantly (by ~15%), reduced N<sub>2</sub> fixation
is balanced by a concomitant decline in denitrification. Feedbacks between
N<sub>2</sub> fixation and denitrification are controlled by variability in
surface utilization of inorganic nitrogen and subsurface oxygen consumption,
as well as the direct influence of Fe on N<sub>2</sub> fixation. Overall, there is
relatively little impact of reduced aeolian Fe input (<4%) on
cumulative CO<sub>2</sub> fluxes over 240 years. The lower sensitivity of our
model to changes in dust input is primarily due to the more detailed
representation of the continental shelf Fe, which was absent in previous
models.
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