[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

meeting minutes

- ----------
X-Sun-Data-Type: text
X-Sun-Data-Description: text
X-Sun-Data-Name: text
X-Sun-Charset: us-ascii
X-Sun-Content-Lines: 16

OCMIP members:

Attached are the long-awaited minutes of our February meeting.  Much was
covered, and I did my best to record it faithfully.  Jim Orr has been through
the minutes and has put his seal of approval on it all--except for how C-14
should be simulated in OCMIP.  Ken Caldeira has made some figures pertinent
to this and I will make them available to you shortly, at which time I suggest
we discuss the issue in more detail.


Raymond G. Najjar
Department of Meteorology            Phone: 814-863-1586
522 Walker Building                  Fax: 814-865-3663
The Pennsylvania State University    Email: najjar@essc.psu.edu 
University Park, PA 16802-5013       home page: http://www.essc.psu.edu/~najjar
- ----------
X-Sun-Data-Type: default
X-Sun-Data-Description: default
X-Sun-Data-Name: minutes.1.text
X-Sun-Charset: us-ascii
X-Sun-Content-Lines: 280

Minutes of the First OCMIP-2 Meeting
Recorded by Raymond Najjar
February 11, 1998. 8 AM - 1PM
Town and Country Hotel, San Diego, California

In attendance:  Jorge Sarmiento, Reiner Schlitzer, Roger Hanson, Anne Mouchet,
Ken Caldeira, Mick Follows, Helge Drange, Patrick Monfray, Jean-Claude Dutay,
Ferial Loanchi, Chris Sabine, Nicholas Gruber, Yasu Yamanaka, Fortunat Joos,
Ian Totterdell, Matthew Hecht, Martin Heimann, John Bullister, Rick Murnane,
Phil Duffy, James Orr, Raymond Najjar

We had several brief (thought not as brief as planned!) presentations by
several OCMIP participants, interweaved and followed by much discussion.

Jim Orr opened the meeting by stating that OCMIP is an open international
project.  Any modeling group can join and have access to OCMIP protocols
(subroutines, forcing functions, etc.), but there may be an upper limit as
to how many models can actually be analyzed.

OCMIP is a project of the GAIM (Global Analysis, Interpretation and Modeling)
task force, which is part of the IGBP (International Geosphere-Biosphere

As it now exists, OCMIP consists of several groups that are separately funded.
The European groups are funded by the European Commission under a project
called Global Ocean Storage of Anthropogenic Carbon (GOSAC).  US-OCMIP is
funded by NASA as part of the JGOFS Synthesis and Modeling Project (SMP).
There is also an effort headed by Yasu Yamanaka in Japan, as well as
an Australian effort headed by Richard Matear.  Ray Najjar noted that some
other US and Canadian groups have expressed interest in participating in OCMIP.
Jim noted that there are differences between GOSAC and US-OCMIP in terms of the
simulations that will be done, but there is much greater overlap. 

OCMIP-1, the first phase of OCMIP, could now be considered over, Jim noted.
Four groups participated in this project:  Hadley Centre, Princeton/GFDL,
IPSL/LSCE and Max Planck/Hamburg.  Most of the published work from this largely
unfunded effort is in reports and newsletters.  A number of manuscripts are
either complete or nearly so, and will be submitted to journals shortly.  A
few primary results from OCMIP-1 were noted:
	(1) The models showed little net interhemispheric transport of carbon
	(2) Modern uptake of anthropogenic CO2 predicted by the models is
            similar, at about 2 Gt C/yr 
	(3) There are large regional differences in anthropogenic CO2 uptake,
            particularly in the Southern Ocean, and these differences are
            expected to grow with time
	(4) Advection schemes used by the models appear to make large
            differences in terms of CO2 uptake
        (5) The similarity between bomb C-14 and anthropogenic
            CO2 increased with time in all models but there were large
            differences both regionally and between models

Jim noted that this meeting should be considered the end of OCMIP-1
and the beginning of OCMIP-2.  OCMIP-1 received minimal funding and,
understandably, output from simulations was sometimes not submitted on
time.  OCMIP-2 is quite different in that it is well funded (i.e.,
model groups are now supported to provide output).  Jim emphasized that
it is important for the success of the project that model results are
submitted in a timely manner.  It is also important that the same 
version of the circulation model is used for all simulations throughout
the duration of OCMIP-2.

Ray Najjar then discussed US-OCMIP plans for biological modelling.
US-OCMIP will have a two-tiered approach: (1) a simple
"nutrient-restoring" approach common to the modeling groups and (2)
"individual investigator" models that differ between groups. We had
some discussion as to how long these runs would be.  US plans were to
conduct long nutrient restoring runs and relatively short "individual
investigator" runs.  Some noted that in order to compute steady-state
air-sea CO2 fluxes, longer runs would be needed.  Helge Drange noted
that very long runs with complex ecosystem models could be highly
computationally demanding.  Sarmiento added that plans since the
beginning of OCMIP were to focus on runs to steady state.  Further
discussion is needed here concerning what the individual investigator
runs will be.

Ray Najjar also noted that there are now global seasonal data sets for oxygen
and nutrients that could be used, for the first time, to evaluate global marine
carbon cycle models.

There then followed some discussion as to how to model CaCO3 production and 
dissolution.  US-OCMIP plans are to use a simple scheme that guarantees 
agreement with the global mean alkalinity distribution.

After this presentation, Roger Hanson, the executive director for JGOFS, noted
that there appears to be a large "disconnect" between OCMIP and JGOFS.  There
was some discussion as to why this might be so.  Jorge noted that there will
be a close link between US-JGOFS and US-OCMIP, since PI meetings were included
in the SMP.  Patrick Monfray noted that there was a formal discussion at
the International JGOFS modeling meeting in Oban, Scotland about the role
that OCMIP could play as a bridge between GAIM and JGOFS, both of which are
programs of the IGBP.  There was a sense that more interaction is needed
between JGOFS and OCMIP, and Roger suggested that if OCMIP felt this was so,
that it could send a statement to the next international JGOFS steering
committee meeting this April 25-28.

Patrick Monfray then discussed atmospheric oxygen as a powerful tracer for
marine biogical processes, both in terms of seasonal and meridional variations
in atmospheric O2.  Ken Caldeira said that he would be willing to provide
O2 flux fields for any atmospheric transport modeler, but did not want to get
involved directly with such modeling.  Ray Najjar suggested that TRANSCOM, a
project for intercomparing atmospheric transport models (mainly for CO2), might
be interested in ocean model air-sea O2 flux fields.  Martin Heimann stated
that the next part of TRANSCOM will be devoted to atmospheric inversion.

Fortunat Joos then presented the utility of conducting pulse
simulations.  He showed that ocean GCM results for anthropogenic CO2
uptake could be reconstructed very well from pulse experiments.
Other scenarios for anthropogenic CO2 could easily be conducted
without running the GCM again, thereby saving vast amounts of computer
time.  He explained that "mixed-layer" pulse simulations, in contrast
to the more common atmospheric pulse simulations, solve the problems
with non-linearity of the carbonate equilibria.  Fortunat suggested
that the pulse simulations be conducted much sooner than planned.

Jim Orr then discussed simulations of purposeful CO2 sequestration.
He emphasized that GOSAC will only address the potential for the
global ocean to temporarily store additional CO2 from fossil
emissions.  With global models one cannot address the environmental,
economic, legal, or political concerns related to this issue.  There
was some discussion about potential biological impacts, and Helge
noted that some of his own research into the literature revealed that
modest pH changes (0.1) could have significant impacts.  Such pH changes would
occur even after dispersion of CO2 plumes to the grid sizes used in
ocean models.

Chris Sabine then summarized investigations into what set of equilibrium
constants are the best for the purposes of modeling in OCMIP.  He noted that
the carbonate constants in the DOE handbook (the Roy constants) do not
represent a community consensus.  There was a meeting of many inorganic
carbon chemists (Sabine, Wanninkhof, Takahashi, Goyet, Wallace, and others)
to discuss the equilibrium constants in which participants "agreed to
disagree."  That is, there is no consensus.  Chris presented calculations
using different sets of equilibrium constants.  It was clear that the most
consistent set, when computations involved alkalinity, pCO2 and DIC, was
the Mehrbach constants.  Specifically, these constants should be used
when Alk and pCO2 are used to compute DIC, and when DIC and Alk are used
to compute pCO2.  These computations are generally the most relevant for the
purposes of OCMIP.  It was then decided that the Mehrbach constants (K1 and
K2) would be adopted by OCMIP.  Chris emphasized that using the Mehrbach
constants for any calculations involving pH could be disastrous.  Uncertainties
in  constants for water, borate, or CO2 solubility tend to be either small or

Chris then shifted gears and talked about the data collected by WOCE and the
CO2 survey.  C-14 is rather densely sampled in the Pacific and Indian, but
there are no new data in the Atlantic.  TTO, SAVE and GEOSECS data must be
used for evaluating models in the Atlantic.  He showed a remarkable figure of
deep C-14, which revealed the deep circulation quite clearly.  For DIC and Alk,
all of the oceans are well sampled.  Gruber-type computations of anthropogenic
CO2 have been made in some regions.

Nicki Gruber then discussed some of these calculations, showing how uncertainty
in the C:O ratio can translate into a large uncertainty in the computed
CO2 uptake.  The Southern Ocean is where these calculations are probably the
most uncertain.  Ray Najjar suggested that these calculations could be tested
using simulated data from ocean GCMs.  Jim Orr then showed a few transparencies
revealing large differences between models and "data" for anthropogenic CO2

Rick Murnane suggested that OCMIP should include C-13 in its simulation suite.
The air-sea flux of 13-CO2 is critical to understanding the 13-CO2 distri-
bution in the atmosphere, and therefore for using this distribution for
constraining sources and sinks of CO2.

Ken Caldeira then discussed how increased in atmospheric CO2 will cause C-14
in the atmosphere to increase.  This is because CO2 increases are changing the
pH of the ocean and therefore the speciation of C-14, such that the
concentration of 14-CO2 in the ocean, and therefore in the atmosphere, will
increase.  The C-14 concentration in the atmosphere has been going down since
the bomb tests, but Ken's predictions are that it will go up and eventually
exceed the bomb peak for the business-as-usual scenario.  The 14C/C12 ratio,
however, will keep going down.

Jean-Claude Dutay then presented some general information about the utility of
CFCs for evaluating ocean circulation models.  He showed an evaluation of the
OPA model with CFCs which revealed that the model does a reasonable job
generally, but does not capture Antarctic Bottom Water formation.  Chris Sabine
noted that CFCs and anthropogenic CO2 are quite different due to their
different histories and equilibration times, so that one needs to be careful in
making assessments of one tracer based on the other.

Jean-Claude also discussed the utility of Helium-3 as a tracer of the deep
circulation, and suggested that this tracer would be useful for providing a
reality check of the purposeful CO2 sequestration simulations.  He-3 is 
produced at mid-ocean ridges.  There were some questions about contamination
from bomb tests, but this is apparently only relevant in the thermocline of
the Northern Hemisphere.  Modeling the source is tricky, but current thinking
is that the production rate is proportional to the spreading rate at the
ridges, thereby making the Southeastern Tropical Pacific the greatest source.
The only sink is gas transfer to the atmosphere.  Data are available from
GEOSECS and some from WOCE, but the latter does not have coverage comparable to
C-14. Some suggested that Bill Jenkins would be the person to contact for such

Jorge Sarmiento ended the presentations by making two main points.  First, the
Southern Ocean is perhaps the most important region for controlling the air-
sea partitioning of CO2.  OCMIP-1 results show that anthropogenic CO2 uptake
is greatest in the Southern Ocean, by virtue of its large area and vigorous
vertical exchange.  Simulations using coupled ocean-atmosphere GCMs show that
changes in the Southern Ocean could be dramatic, due largely to increased 
stabilization resulting from lower salinities.  The second point Jorge made was
that knowledge of air-sea CO2 fluxes is critical for inverting atmospheric CO2
observations in order to determine terrestrial sources and sinks of CO2.
His work shows a large sensitivity of inferred terrestrial sources and sinks
depending on rather modest changes in the air-sea CO2 flux.  Following this,
Jorge presented some preliminary ideas about how to apply inversion techniques
to oceanographic DIC observations in order to constrain air-sea CO2 fluxes.

Jim Orr then lead a discussion of the proposed OCMIP timetable, which was
distributed electronically before the meeting.  Additional copies (with slight
modifications) were distributed at the meeting itself.

There was a long discussion about the use of a common biological model.  US-
OCMIP plans are to use a nutrient-restoring approach.  It was suggested by
some that another approach, such as the original Hamburg formulation, might
be preferable.  Advantages and disadvantages of both approaches were discussed
for some time.  Mick Follows reiterated that the main point of using a simple
model was to compare the different capabilities of the physical model to 
deliver nutrients to surface waters.  After much discussion, it was decided 
that individuals could choose either model to run, but that it was preferable
for every group to run both models.  Jim Orr asked who would be running what
regarding the common biology model.

We had considerable discussion about DOM modeling.  The main two factors to
consider vis a vis such modeling is the fraction of new production that goes
to DOM (as opposed to POM) and the lifetime DOM.  There was disagreement as to
whether these parameters should come from the field (such as from JGOFS data
sets) or whether parameters should be chosen to fit the observed DOC data.
US-OCMIP plans were to use the parameters chosen by the Princeton/GFDL group,
which are based on fitting to DOC observations.  It seemed clear that field
observations show a much shorter DOC lifetime (months) than that used in most
models (years).  Ray Najjar said he would review the situation and come up with
a recommendation.  One point noted by Ray was that JGOFS data seem to show that
the fraction of new production that goes into DOC varies spatially: in the
Southern Ocean the fraction is much smaller than at Bermuda.

There was also considerable discussion about how to model radiocarbon in ocean
GCMs.  The debate was whether to use the "quick" method adopted by Toggweiler,
in which, effectively, the 14C/12C ratio is advected around and that 12C is
NOT carried as a separate tracer.  This shortcut was contrasted with carrying
separate tracers for 14C, 13C and 12C.  13C would be needed in order to
compute Big Delta C-14, which is most commonly reported in observations.  The
debate was effectively settled when Anne Mouchet showed a comparison of the
two approaches.  The differences were large enough, generally greater than
10 permil (even for natural C-14), that we were convinced that the quick
technique should not be adopted by OCMIP.  Rather, the carbon isotopes should
each be modeled separately.  This choice forces the biological simulations
to have high priority, because C-13 and C-14 concentrations have substantial
biological sources and sinks.  Adding C-13 to the suite, and modeling C-14
concentration, is a break from OCMIP-1 protocols, so there is a need for 
clear specification of how to model C-13 and C-14 concentrations.  Ken 
Caldeira agreed to propose specific algorithms for such modeling.

It was stated that for OCMIP-2 anthropogenic CO2 simulations, the natural
carbon cycle is needed for the initial conditions.  This places
even more priority on getting the natural carbon cycle runs done
sooner than others.

An urgent need was to have seasonal nutrient fields for conducting the 
nutrient-restoring simulations, and to have such fields for evaluating more
prognostic models.  Najjar and Louanchi agreed to provide such fields in about
two months.

We had some brief discussion about adding new "numerical" tracers, such as
age and dye tracers, to the OCMIP suite of simulations.  It was agreed that
there was enough work to do for now and to postpone discussion of such 
simulations to a later time.

There was one mistake in the timeline distibuted: the "solubility + arbitrary
biology" set of simulations should not appear.

Purposeful CO2 sequestration and natural He-3 were not proposed as part of
US-OCMIP.  Jim Orr asked individual US-OCMIP groups and Yasu Yamanaka whether
they plan to do these simulations.

There were some changes made to the time table handed out.  These
revisions are to be redistributed to all OCMIP groups.  Also to be
distributed is the table showing which groups will be doing what