Biogeosciences
www.biogeosciences.net
1726-4170
1726-4189
3
4
2006
10.5194/bg-3-521-2006
http://www.biogeosciences.net/3/521/2006/
http://www.biogeosciences.net/3/521/2006/bg-3-521-2006.html
http://www.biogeosciences.net/3/521/2006/bg-3-521-2006.pdf
521
537
2006-11-09
Reconciling surface ocean productivity, export fluxes and sediment composition in a global biogeochemical ocean model
M. Gehlen
marion.gehlen@cea.fr
L. Bopp
N. Emprin
O. Aumont
C. Heinze
O. Ragueneau
LSCE/IPSL, Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ Orme des Merisiers, Bât. 712, CEA/Saclay 91198 Gif-sur-Yvette Cedex, France
LOCEAN/IPSL, Centre IRD de Bretagne, BP 70, 29280 Plouzané, France
University of Bergen, Geophysical Institute & Bjerkness Centre for Climate Research, Allegaten 70, 5007 Bergen, Norway
Institut Universitaire Européen de la Mer, Place Copernic, Technopôle Brest-Iroise, 29280 Plouzané, France
This study focuses on an improved representation of the biological soft
tissue pump in the global three-dimensional biogeochemical ocean model
PISCES. We compare three parameterizations of particle dynamics: (1) the
model standard version including two particle size classes,
aggregation-disaggregation and prescribed sinking speed; (2) an
aggregation-disaggregation model with a particle size spectrum and
prognostic sinking speed; (3) a mineral ballast parameterization with no
size classes, but prognostic sinking speed. In addition, the model includes
a description of surface sediments and organic carbon early diagenesis.
Model output is compared to data or data based estimates of ocean
productivity, pe-ratios, particle fluxes, surface sediment bulk composition
and benthic O<sub>2</sub> fluxes. Model results suggest that different processes
control POC fluxes at different depths. In the wind mixed layer turbulent
particle coagulation appears as key process in controlling pe-ratios.
Parameterization (2) yields simulated pe-ratios that compare well to
observations. Below the wind mixed layer, POC fluxes are most sensitive to
the intensity of zooplankton flux feeding, indicating the importance of
zooplankton community composition. All model parameters being kept constant,
the capability of the model to reproduce yearly mean POC fluxes below 2000 m
and benthic oxygen demand does at first order not dependent on the
resolution of the particle size spectrum. Aggregate formation appears
essential to initiate an intense biological pump. At great depth the
reported close to constant particle fluxes are most likely the result of the
combined effect of aggregate formation and mineral ballasting.
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