To estimate the absorption by the ocean of the anthropogenic
carbon dioxyde. The first phase deals with the quantization of
the seasonal variation of oceanic sources and sinks at regional
scale. This is a companion study with part A : atmosphere and
part B : biosphere.
An experimental and a modelling approach are used to study the
exchange of CO2 between the ocean and the atmosphere, and the
natural carbon cycle in the ocean.
The CO2 flux exchanged
between ocean and atmosphere is most commonly derived from the
combination of the transfer velocity and of the air-sea gradient
of the CO2 partial pressure. The transfer velocity can be
deduced from the surface wind speed through a parametrization,
relating the wind speed to the turbulent exchange at the
air-sea interface. Experiments at sea are
carried out to improve this parametrization. Also,
the wind speed remotely sensed from satellite by microwave
instruments (radars and radiometers) is used to monitor the
transfer velocity on the global ocean.
The air-sea CO2 partial
pressure, which can only be measured in--situ, is monitored at
seasonal scale using ships of opportunity along a commercial line
in the north atlantic ocean and in the tropical pacific ocean and
also in the indian ocean. We intend to use satellite
measurements (ocean colour and SST) to help extrapolating these
measurements. In a near future automated buoys should complement
this monitoring. In addition, improved techniques to measure the
Dissolved Organic Carbon (DOC) are used on oceanographic cruises.
The knowledge of DOC composition and lifetime is of importance
for modelling the oceanic carbon cycle.
In parallel an important effort is done in modelling the natural
carbon cycle in the ocean. Process studies are carried out with
one dimensional models used in specific places, and descriptions
of the processes in the carbon cycle are implemented in two
different ocean global circulation models. One, in which the
representation of the biological processes is being improved,
will be used on the global scale. The other one is used at
regional scale (tropical atlantic ocean), the description of the
ocean circulation being tested at global scale. Finally,
assimilation techniques to constrain the models by measurements
(in particular of chlorophyll) are under development.
Funding SchemeCSC - Cost-sharing contracts
PL1 3DH Plymouth