|Understanding the marine ecosystem that drives biogeochemical general circulation
The annual amount of carbon dioxide (CO2)
generated by anthropogenic activities is said to be approximately
7.3 gigatons*1. Of this amount, the ocean's uptake is
approximately 2 gigatons. The Carbon Cycle Research Group of the
Global Warming Research Program has developed a general circulation*2
model that represents the marine ecosystem dynamics, and is engaged
in precise estimation of the amount of CO2
uptaken by the oceans. Dr. Yamanaka describes the importance of
clarifying the marine ecosystems and carbon cycle process*3,
and presents the group's future plans.
Dr. Yasuhiro Yamanaka Group Leader
Carbon Cycle Research Group, Global Warming Research Program
using a new model that representsthe marine ecosystem more precisely
|Our research group studies changes to the marine ecosystems such
as plankton and to CO2 circulation
due to global warming, and how the CO2
absorption in the oceans shifts accordingly. Until now, we used a
biogeochemical general circulation model in which the activity of
plankton is simplified. Currently, we have been developing a new biogeochemical
general circulation model that can represent the marine ecosystem
and sinking particles more precisely by classifying the various groups
of plankton. One factor is an increase in the "coccolithophorids"
plankton that favors warm ocean areas with small amounts of nutrients.
This increase is due to warming on the ocean surface water that leads
to an increase in CO2 concentration*4
and thus likely reduces the amount of CO2
uptaken in the ocean.
|Participation of the
ocean carbon cycle model in our international research project
|According to the IPCC Third Assessment Report published in 2001,
the amount of CO2 uptaken in the
ocean was "2 gigatons ± 0.6" after applying the values estimated
by ten research groups from countries around the world. Our group
was among the ten, and one of our members was among the few contributing
authors from Japan in the field of atmosphere and ocean science for
the Third Assessment Report.
The Groups from different countries studying the carbon cycle formed
a partnership to establish an international research project called
OCMIP*5. We are involved in the task force that will determine the
model and calculation method and expression of the analytical results
to be used within the organization.
In the IPCC Fourth Assessment Report, a predicted uptake of anthropogenic
CO2 will be presented using the aforementioned new biogeochemical
general circulation model that represents the marine ecosystem and
sinking particles more precisely.
the CO2 cyclesby setting a more realistic model
|One of the new research subjects we are engaged in is
an experiment focused on the "copepods" zooplankton, which
is born in the ocean deep layer at a depth of 400 m-1,500 m and rises
to the ocean surface as it grows. This plankton matures by eating
phytoplankton near the ocean surface during spring and summer, and
it returns to the ocean deep layer to breed in the autumn. Through
numerical calculation using the ecosystem model, we found that carbon
transport associated with the seasonal migration of copepod is equal
to an approximate 10% of marine snow. We will study changes brought
about by global warming on marine resources such as fish.
- Image of the carbon cycle in the ocean
- Differences in the partial pressure of CO2
between atmosphere and ocean surface
|The positive value near the equator indicates that the
CO2 concentration in the ocean is high and that CO2 is released into
the atmosphere. The negative value at the high latitudes indicates
that CO2 is uptaken by the ocean.
||1 gigaton=1 billion tons
||A part of the organic matter produced by phytoplankton. Some
parts become an organic matter that exists in a dissolved form
in the ocean. The other part settles into the deep layer of
the ocean in particle form and eventually decomposes into inorganic
matter, which is used again by phytoplankton. The accumulation
of these many processes is called general circulation.
||Explanation-Why is it important to clarify the marine ecosystem
and carbon cycle process to predict global change?
It is believed that oceans contain approximately 50 times more
CO2 than that in the atmosphere.
Marine ecosystems, including the phytoplankton, significantly
contribute to this fact. Phytoplankton takes in nutrients from
the ocean (nitrate, phosphate, silicate, etc.), performs photosynthesis,
and produces organic matter. In the photosynthesis process,
CO2 in the ocean is uptaken
by phytoplankton. Thus CO2
concentrations in the ocean are reduced, and atmospheric CO2
is more readily dissolved in the ocean. Phytoplankton that becomes
fecal pellets after being consumed by zooplankton falls to the
ocean deep layer; it is called marine snow. In this process,
CO2 is also carried to the
ocean deep water, creating a difference in CO2
concentrations between the ocean surface and deep layers. In
the absence of plankton activity, the CO2
concentration would be uniform throughout the ocean, and atmospheric
CO2 would be calculated at
twice the current amount.
||Cells of the coccolithophorids are covered by distinctive
disc-shaped plates made of calcium carbonate. As coccolithophorids
create calcium carbonate, they also produce CO2, rising the
partial pressure of CO2 in the sea water.
||Ocean Carbon-Cycle Model Intercomparison Project