Biogeosciences
www.biogeosciences.net
1726-4170
1726-4189
5
1
2008
10.5194/bg-5-55-2008
http://www.biogeosciences.net/5/55/2008/
http://www.biogeosciences.net/5/55/2008/bg-5-55-2008.html
http://www.biogeosciences.net/5/55/2008/bg-5-55-2008.pdf
55
72
2008-01-25
On the treatment of particulate organic matter sinking in large-scale models of marine biogeochemical cycles
I. Kriest
ikriest@ifm-geomar.de
A. Oschlies
IFM-GEOMAR, Leibniz-Institut für Meereswissenschaften an der Universität Kiel, Kiel, Germany
Various functions have been suggested and applied to represent the
sedimentation and remineralisation of particulate organic matter (POM) in numerical ocean models. Here we
investigate some representations commonly used in large-scale biogeochemical models:
a constant sinking speed, a sinking speed increasing with depth, a spectrum of particles
with different size and different size-dependent sinking velocities, and a
model that assumes a power law particle size distribution everywhere
in the water column. The analysis is carried out for an idealised one-dimensional water column, under stationary
boundary conditions for surface POM.
It focuses on the intrinsic assumptions of the respective sedimentation function and their effect on POM mass,
mass flux, and remineralisation profiles.
<br><br>
A constant and uniform sinking speed does not appear appropriate for
simulations exceeding a few decades, as the sedimentation profile is not
consistent with observed profiles.
A spectrum of size classes, together with size-dependent sinking
and constant remineralisation, causes the sinking speed of total
POM to increase with depth.
This increase is not strictly linear with depth. Its particular form
will further depend on the size distribution of the POM ensemble at the surface.
Assuming a power law particle size spectrum at the surface, this model results in unimodal size
distributions in the ocean interior.
For the size-dependent sinking model, we present an
analytic integral over depth and size that can explain regional
variations of remineralisation length scales in response to regional patterns in
trophodynamic state.
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