Research Themes of the Chemical Oceanography Unit

One of the most challenging issues addressed to the oceanographic community is to budget atmospheric CO2 fluxes over the oceans. The open ocean has a major role in the global CO2 cycle, since it absorbs about 29% of the anthropogenic CO2 inputs (that contribute to 57% of the greenhouse forcing among all radiative gases). So far, one of the best methods is to compile worldwide measurements of the partial pressure of CO2 (pCO2) and to compute related CO2 fluxes using wind speed and well-constrained gas transfer velocity relationships. However, due to the large spatio-temporal variability of pCO2, budgeting CO2 fluxes requires huge data sets which cover satisfactorily both spatial and temporal changes.

The Chemical Oceanography Unit of the University of Liège aims to fill two crucial gaps in the present knowledge of global CO2 fluxes: the ignored Coastal Ocean and the remote Southern Ocean thought as the "last oceanic sink". In parallel, the Chemical Oceanography Unit also investigates the potential feed-backs between the oceanic biota and climate and their impact on global CO2 cycling.

Until recently, the Coastal Ocean was neglected from global CO2 budgets because it is difficult to include this region in global circulation models and because of the lack of field data on the spatial distribution and temporal variability of pCO2. During the last 10 years, the Chemical Oceanography Unit has investigated several European coastal regions (estuaries and open continental shelves), with sufficient spatial and temporal coverage to allow the integration of atmospheric CO2 fluxes. More recently, we have extended this research to tropical estuaries where dissolved inorganic carbon variability has seldom been investigated, although they could potentially be very important in the global carbon cycle.
The emerging picture of the functioning of the CO2 fluxes in the Coastal Ocean is that marginal shelves are net exporters of organic matter and sinks for atmospheric CO2, while near-shore ecosystems influenced by anthropogenic and/or terrestrial inputs are sources of CO2.
Air-water CO2 fluxes were recently up-scaled to take into account the latitudinal and ecosystem diversity of the coastal ocean, based on an exhaustive literature survey. Marginal seas at high and temperate latitudes act as sinks of CO2 from the atmosphere, in contrast to subtropical and tropical marginal seas that act as sources of CO2 to the atmosphere. Overall, marginal seas act as a strong sink of CO2 of about -0.45 Pg C yr-1. This sink could be almost fully compensated by the emission of CO2 from the ensemble of near-shore coastal ecosystems of about 0.40 Pg C yr-1. Although this value is subject to large uncertainty, it stresses the importance of the diversity of ecosystems, in particular near-shore systems, when integrating CO2 fluxes at global scale in the coastal ocean.

In the Southern Ocean, where adequate spatial coverage is logistically unreachable, we recently used remote sensing measurements of surface sea temperature chlorophyll a content and wind speed to assess CO2 fluxes by reconstructing CO2 fluxes fields over large areas from experimental measurements.
Recent research is concentrated on the dynamics of dissolved inorganic carbon within the Antartic sea-ice with particular emphasis on the exchange of CO2 between sea-ice and the atmosphere.

The Chemical Oceanography Unit has carried out pioneering research on dissolved inorganic carbon dynamics in coral reefs that highlighted the potential feed-back between the increase of atmospheric CO2 and the reduction of benthic calcification (resulting in turn on a decrease of the CO2 emission from coral reefs). This research has recently been extended to pelagic calcification (coccolithophorid Emiliania huxleyi) under experimental controlled conditions (mesocosms).

Research has also been devoted to the development of innovative CO2 measurement units complying with coastal environment particularities and constrains. Furthermore, making this equipment as versatile as possible so that CO2 measurements units can be either fully autonomous (on ships or fixed stations) or mounted on buoys. Such systems are essential to generate large and long-term data-sets to investigate seasonal variations of CO2 in such extremely dynamic environments and long-term patterns in strongly human impacted ecosystems.

The Chemical Oceanography Unit collaborates with the following institutions:



Powerpoint presentation of the Chemical Oceanography Unit

 

Alberto Vieira Borges& Bruno Delille, January 2006