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Modelling of the marine Si cycle within SINOPS
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Modelling Strategy
Basis of the modelling part of SINOPS is the Hamburg Carbon Cycle Model
(Maier-Reimer, 1993) which is coupled to an interactive sediment module
(Bareille et al., 1998; Heinze et al., 1999). The model covers the entire
globe and has a horizontal resolution of 3.5 by 3.5 degrees. Compared
to the work of Heinze et al. (1999), the model code was revised and accelarated
(about factor 2.7). An improved reference run was set up which serves
as a basis for further improvements. The model parameters will be optimised
with respect to the observed data collated by the partner in Brest. Later
on, the model will be applied to distinct paleoceanographic situations
(Last Glacial Maximum, closure of the Panama Isthmus).
Figure 1 shows the opal distribution as simulated by HAMOCC in its annually
averaged version. The velocity and thermohaline fields for this run are
provided by a run of the LSG-OGCM (Large Scale Geostrophic OGCM, Maier-Reimer
et al., 1993) which represents the modern ocean (Winguth et al., 1996).
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Fig. 1: Simulated opal distribution of the top
10 cm of sediment (in weight percent on a calcite free basis).
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Sensitivity Experiments
A set of sensitivity experiments was carried out to test the models behaviour
with respect to changes in single Si cycle relevant parameters. The ensemble
of available changes in tracer distributions and the prescribed changes
in governing parameters were used to set up a linear response model. In
a test this model was optimised with respect to reduced data set of observations
(silicic acid, opal sediment) using SVD technique. The resulting optimal
parameter set was then used in the full model to test the optimisation
method. The next step is a comprehensive comparison phase with the complete
data set provided by the Brest group. Afterwards additional sensitvity
tests will be carried out and the optimisation procedure will be applied
to the full observed data set.
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Fig. 2: Results of sensitivity experiments involving
Si cycle relevant parameters. Through the coupling of the rain ratio of
C (particulate organic carbon production versus calcium carbonate production)
to the opal production, changes in the marine Si budget affect also the
atmospheric carbon dioxide partial pressure. Further research is necessary
to confirm this interdependency. The sensitivity experiments are used for
a subsequent optimisation of the biogeochemical model. |
Comparison Model/Observations
The ongoing comprehensive comparison phase between model and observations
is carried out in order to identify specific key problem areas which will
be readdressed within the optimisation phase. |
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Fig. 3: Model results (upper row), observations
from the GEOSECS data set (Bainbridge, 1981; Broecker et al., 1982) (second
row), and differences model-obs (lower row) for silicic acid along merdional
cross sections in the Atlantic (left column), Pacific (central column) and
Indian Oceans (right column). |
References
- Bainbridge, A. E., 1981, GEOSECS Atlantic Expedition, volume 1: Hydrographic
data 1972-1973, National Science Foundation, Washington, D. C., 121
S..
- Bareille, G., M. Labracherie, P. N. Froelich, R. A. Mortlock, E.
Maier-Reimer, and L. D. Labeyrie, 1998, A test of (Ge/Si)opal as a paleorecorder
of (Ge/Si)seawater, Geology, 26, 179-182.
- Broecker, W. S., D. W. Spencer, and H. Craig, 1982, GEOSECS Pacific
expedition. Volume 3. Hydrographic data 1973-1974. National Science
Foundation. Superintendant of Documents, U.S. Government Priniting Office,
Washington D. C., 137 pp.eille, G., M. Labracherie, P. N. Froelich,
R. A. Mortlock, E. Maier-Reimer, and L. D. Labeyrie, 1998, A test of
(Ge/Si)opal as a paleorecorder of (Ge/Si)seawater, Geology, 26, 179-182.
- Maier-Reimer, E., 1993, Geochemical cycles in an ocean general circulation
model. Preindustrial Tracer Distributions, Global Biogeochemical Cycles,
645-677.
- Bareille, G., M. Labracherie, P. N. Froelich, R. A. Mortlock, E.
Maier-Reimer, and L. D. Labeyrie, 1998, A test of (Ge/Si)opal as a paleorecorder
of (Ge/Si)seawater, Geology, 26, 179-182.
- Maier-Reimer, E., U. Mikolajewicz, and K. Hasselmann, 1993, Mean
circulation of the Hamburg LSG OGCM and its sensitivity to the thermohaline
surface forcing, Journal of Physical Oceanography, 23, 731-757.
- Heinze, C., E. Maier-Reimer, A. M. E. Winguth, and D. Archer, 1999,
A global oceanic sediment model for longterm climate studies, Global
Biogeochemical Cycles, 13, 221-250.
- Winguth, A. M. E., E. Maier-Reimer, U. Mikolajewicz, and J.-C.\ Duplessy,
1996, On the sensitivity of an ocean general circulation model to glacial
boundary conditions, Max-Planck-Institut für Meteorologie, Report
No. 203, Hamburg, 48 pp.
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