Air-sea CO, exchanges and the part~al pressure of CO, were measured in surface water overlying 2 coral reefs: Moorea (French Polynesia, austl-a1 lvlnter, August 1992). where coral di\,ers~ty and surface cover are low, and Yonge Reef (Great Barr~er Reef, a~istral summer, December 1993), where coral diversity and cover are comparatively h~g h e r A procedure is proposed to estimate the potential CO2 exchange with the atmosphere by t a k~n g ~n t o account both the saturation level of oceanlc seawater and the equilibration process occurring after water leaves the reef. It is shown that both sites were net sources of CO2 to the atmosphere as a result of the effect of calcification on the dynamics of the inorganic carbon system. The potential global CO2 evasion from the ocean to the atmosphere is about 4 times higher at Yonge Reef than at Moorea. It is also demonstrated that, at both sites, the major exchange of CO2 from sea to air occurs as seacvater returns to chemical equilibrium after it has crossed and left the reef. The dynamics of inorganic carbon were studied using the so-called homogeneous buffer factor [P = dln(pC02)/dln(D1C)] (where pCO, 1s the CO2 partial pressure In surface ivdter and DIC 1s d~ssolved Inorganic carbon), which gave estimates that approximately 80% of the change In inorganic carbon was related to photosynthesis and respiration. This approach showed that the calc~fi-cation rate was proportional to the net organic production during the day and to the respiration rate at night.

Abstract}A new design of equilibrator for carbon dioxide monitoring in natural waters is described. It consists in a vertical tube filled with marbles through which water is flowing while equilibrating with a closed air circuit. It offers several advantages compared with classical equilibrators, among which is a fast response time (half-life constant % 30 s) and the potential to work in very turbid water. The proposed equilibrator is of particular interest to monitor carbon dioxide in coastal ecosystems, such as estuaries, which are known to be turbid and highly dynamic. Two performance tests and some field results are presented to illustrate the efficiency of the proposed system. #

No abstract

a b s t r a c tLevels of Be, Al, V, Mn, Co, As, Se, Mo, Ag, Sn, Sb, Bi as well as of Cr, Fe, Ni, Cu, Zn, Cd and Pb in Posidonia oceanica (L.) Delile from the Mediterranean French coast were analysed using DRC ICP-MS. The first twelve elements have not been well studied and can be considered to be potential pollutants as a result of potentially increased levels resulting from anthropogenic activities. Spatial variation and/or compartmentalization were found for all trace elements. Except for Al, Cr, Fe, Cu and Ag, most trace elements were preferentially accumulated in photosynthetic tissues, suggesting uptake from the water column. Moreover, for Be, V, Mn, Co, Ni, As, Mo, Sb, Sn and Pb, adult leaves had higher levels than intermediate leaves, suggesting low kinetics of accumulation. Levels in the third intermediate leaf were representative of the average levels of the integral shoot, and thus can be used alone in chemical biomonitoring. For most of the twelve little-studied trace elements, the background levels of the northwestern Mediterranean Sea can be measured, and their spatial variation can be related to anthropogenic activities. Levels of the seven widely studied trace elements seem to decrease or stabilize over time, probably due to their reduced anthropogenic use. These observations show that P. oceanica is a sensitive bioindicator for the monitoring of chemical contamination of a large number of trace elements.

No abstract