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OCMIP: a proposed 5-yr GAIM-JGOFS project

Dear Colleagues,

        It has been proposed that the Ocean Carbon-Cycle  Intercomparison
Project be extended up to 2003 through joint participation of GAIM and

        A preliminary plan for this 5-yr is included below. Could you
please send to me your comments on this tentative proposition by Friday
June 6th.

        We need the revised version for the next GAIM Task Force meeting,
the following Monday.

                                                Patrick Monfray

The Ocean Carbon-Cycle Model Intercomparison Project:
A proposed GAIM-JGOFS framework for 1998-2002

Although GAIM's focus is to develop realistic earth-system models and
JGOFS studies have been more process oriented, both of these IGBP core
projects share the objective to improve prediction of atmospheric CO2
by better constraining the ocean carbon cycle.  For this reason, a
joint JGOFS-GAIM effort which was proposed at the 1st IGBP Conference
(Bad Munstereifeld, April 1996), and followed up by related proposals
at the last GAIM Task Force meeting (Barcelona, April 1997) and most
recently at the JGOFS Modelling Symposium (Oban, May 1997).  Such a
project is needed to better evaluate global ocean carbon-cycle models
used to predict evolution of atmospheric CO2.

During the first GAIM plan (1993-1997), the Ocean Carbon-Cycle Model
Intercomparison Project (OCMIP) was initiated in 1995 to intercompare
results from the four global ocean carbon-cycle models (OCCM's)
available at that time. This exploratory study found large
regional discrepancies between OCCM's to estimate CO2 fluxes and carbon

To better evaluate OCCM's, there exists a clear need for global
synthesis datasets, which JGOFS is now developing.  Likewise needed is
experience gained from JGOFS process oriented expertise and 1-D
modeling efforts to improve biogeochemical formulations in 3-D OCCM's.
Additionally, a more diverse group of OCCM's must participate, to
insure that the range of model predictions brackets real ocean
behavior and to develop standard protocols for simulations and
analysis and make them available to the entire ocean carbon-cycle
modeling community.

Thus we propose here a preliminary framework for a new 5-year OCMIP
project which will join activities of both JGOFS and GAIM.  The
preliminary plan given below is that developed by GAIM and JGOFS
participants at the recent JGOFS Modelling Symposium in Oban,
Scotland.  Once final, the plan may best be implemented by a joint
GAIM-JGOFS task team.  Thus it will be submitted to both the GAIM Task
Force and the JGOFS Steering Committee.

* There exist three main anthropogenic induced factors which can
perturb the ocean's distribution of carbon: (1) changes in atmospheric
climate (heat, fresh water, light), thereby affecting the natural
cycle; 2) changes in atmospheric composition (CO2, aerosols); and (3)
changes in river discharge (? water only) linking continent to the
open ocean through margin areas. The present GAIM-JGOFS project is
focused on the first two points affecting the open ocean by physical
and geochemical exchanges with the atmosphere.

* The main goals of OCMIP are to evaluate and intercompare Global
Ocean Carbon Cycle Models (OCCM) used to predict evolution of
atmospheric CO2.  We propose a new OCMIP project to be implemented in
two phases: A-1998 to 1999, and B-2000 to 2002. This new effort will
investigate the roles of the solubility pump, the biological pump, and
ocean circulation in controlling the distribution of oceanic carbon.
Eleven OCCM's, having horizontal resolution varying between 1 and 4,
will participate in phase A (Europe: EC-GOSAC, which has just been
funded; USA: NSF/JGOFS a new proposal).

* During phase A, the climatological present state of ocean carbon
cycle will be simulated from two basic simulations:
(1) a pre-industrial state estimated from solubility and biological
pumps, and
(2) a transient era corresponding to the atmospheric CO2 increase

* During phase B, variability induced by climate change will be
investigated through two types of simulations:
(1) Separating out anthropogenic from natural change during the 1980's
and 1990's (CO2 increase + natural climate variability, such as during
ENSO), and
(2) The XXI century in a changing climate.

Altough prediction of DecCen natural variability (North Atlantic
Oscillation-NAO) is of prime importance for such prediction, no OCMIP
simulations are currently planned because Ocean General Circulation
Models (OGCM's) are only beginning to investigate this problem, and ocean
carbon-cycle studies must follow these developments. On the other
hand, if OGCM studies do progress rapidly, OCMIP related work could be
included at a later date.

* A close interaction between GAIM and JGOFS will permit the three
following tasks:

1) The evaluation by global synthesis datasets:
        JGOFS and WOCE new synthesis datasets, along with satellite data,
will more fully test OCCM formulations for geochemistry, as well as
biology and chemistry. Following fields are crucial:
                - Fields of surface pCO2, nutrients (N, P, Si), oxygen,
carbonates and DOM fields;
                - Ocean sea colour maps;
                - Circulation tracers (14C,  CFCs); and
                - SST, salinity  and satellite altimetry.
        Seasonal fields are needed, and if accuracy permits
interannual and long-term trends would be most valuable.  Use of ocean
color in OCCM's requires determination of the spatial and temporal
variation of the C:Chl ratio; JGOFS dedicated studies will be
dedicated to this task.  Model evaluation often suffers because
uncertainites associated with some measurements, often makes principle
investigators hesitate long periods before releasing data sets, i.e.,
until the final result is as precise as possible.  Yet differences
between models are often many times larger.  For these data sets, such
as pCO2, preliminary release of non-final data, would be most helpful
to model evaluation.

2) The role of the ocean circulation:
        By using OCCM's with the same biogeochemistry, OCMIP will
focus on discrepancies due to differences in modeled circulation
fields.  During phase A, we will employ a diagnostic approach of
biological productivity, restoring a modeled phosphate at the surface
to seasonal observations.  In phase B, OCCM's will use a common
biogeochemical model, selected by the JGOFS 1-D intercomparison group,
for its robustness, its low number of parameters, and its portability in
different regime areas (evaluated against JGOFS time series).
        Additionally, because global OCCMs are of coarse resolution,
OCMIP will pay particular attention to the parametrization of sub-grid
scale processes through interaction with the JGOFS regional studies
group who use high-resolution OGCM's.

3) The role of the biogeochemical processes:
        The global impact of the relevant processes studied by JGOFS will
be investigated:
                - pCO2 fertilization effect, and C:N:P variability,
                - DOM/POM partionning, and lifetimes,
                - N/P/Si limitation,
                - N2/Fe/grazing intricate effects,
                - Nitrification/denitrification.

* In conclusion, the proposed OCMIP project will establish a strong
interaction between JGOFS and OCMIP in order that OCCM's be improved.
This will require rigorous evaluation with global synthesis datasets,
and improving global parametrizations through scaling up
biogeochemical models thoroughly tested at the local scale.  To aid
interaction between these two IGBP core projects, we propose the
following series of GAIM-JGOFS workshops:
        1998: Interaction between OCMIP and the JGOFS synthesis team-
Preliminary results of OCMIP phase A, evaluation by data.
        1999: Interaction between OCMIP and the JGOFS 1-D modelling team:
Results and integration plan.
        2000: OCMIP results phase A, and integration of new biogeochemical
        2001-2002: Preliminary results of OCMIP phase B.
        End 2003: Results of OCMIP phase B.

The new OCMIP project proposed above for 1998-2003 will help
ameliorate modeled biogeochemistry in 3-D OCCM's through the
interaction of GAIM and JGOFS.  Simultaneous collaboration between
OCMIP and WCRP/WOCE-CLIVAR/OMIP will be sought to improved modeled
circulation in OCCM's.

- ---------------------------------------------------------------------------
Centre des Faibles Radioactivites, CNRS-CEA
Laboratoire de Modelisation du Climat et de l'Environnement, CEA
Orme des Merisiers-Bat 709/LMCE
CE Saclay
F-91191 Gif-sur-Yvette Cedex

Work Phone:  (33) 1 69 08 77 24
FAX:              1 69 08 77 16
Internet:   monfray@cea.fr