Indirect Measurements of Air-Water CO2 Exchanges in a Tropical Coastal Area
Abstract
Depending on the latitude, coastal ecosystems (including reefs, estuaries, swamps, springs and rivers) behave differently with regard to CO2 flux between water surface and the atmosphere. Tropical areas are estimated to behave as sources for the atmosphere but are the poorest documented. We carried out a study focussed on such areas between April and July 2005 near the town of Kailua (21°40N-157°70W), Oahu, Hawai'i (USA). pH, total alkalinity, temperature and salinity were monitored at different sites in the water surface layer, to derive information on the carbonate system and estimate the magnitude of the CO2 exchange at the water/atmosphere interface. The difference between atmospheric and oceanic CO2 partial pressure (Δ pCO_2=pCO_2-pCO2atmos) at each monitoring sites was calculated using the carbonate system calculation program designed by C. Frankignoulle (2001). Measurements were made from the estuary to fresh-water springs, but also in a tidal swamp. For all of them positive Δ pCO_2 were calculated, indicating that this whole system behaves as a source for the atmosphere in term of CO2. Δ pCO_2 in the estuary and fresh-water rivers ranges between 0 and 5000 μatm as commonly observed in such situations. Very high Δ pCO_2 are reported (up to 70000~μatm) in the tidal swamp, featuring important spatial and temporal variability. The eastern and western side of the swamp behave differently, with larger Δ pCO_2 in the water from the western (30000 ± 25000~μatm) than the eastern (8000 ± 4000~μatm) side of the swamp. It is hypothesized that such high fluxes of CO2 result from an interaction between the marine calcerous grounds with water and also from the high rate of organic matter degradation associated with high water temperature. Our observations confirm that intertropical coastal areas generally behave as CO2 sources for the atmosphere. However, the large variability in the fluxes magnitude deserves to be studied more thoroughly in order to assess the globally integrated role of such areas in the perspective of an increasing CO2 load in the atmosphere.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMOS51C0571B
- Keywords:
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- 4217 Coastal processes;
- 4803 Analytical chemistry;
- 4805 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 1615;
- 4912);
- 4806 Carbon cycling (0428);
- 4835 Marine inorganic chemistry (1050)