Carbon fluxes in coral reefs. II. Eulerian study of inorganic carbon dynamics and measurement of air-sea CO2 exchanges

Abstract

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.

Shifts in coral reef biogeochemistry and resulting acidification linked to offshore productivity

“…NEP mainly alters DIC, with net organic carbon production (NEP > 0) reducing DIC concentrations as CO 2 is used and increasing pH and Ω aragonite . Air-sea CO 2 gas exchange affects DIC only, but typically exerts minor influence on DIC relative to NEC and NEP in reef environments with residence times of a few days, such as Bermuda (17,18). Consequently, comparison of salinity normalized changes in seawater DIC and TA (nDIC and nTA) between the reef and offshore can be used to evaluate the relative contribution and variability in reef NEC and NEP over time and space.…”

Coral reef ecosystems in the South China Sea as a source of atmospheric CO2 in summer

“…Air-sea CO 2 flux values may be used to differentiate coral reefs that act as either sinks or sources of atmospheric CO 2 [6][7][8][9][10][11][12][13][14][15][16][17][18]. Positive values typically characterize coral reefs as a source of atmospheric CO 2 , whilst negative values may [20].…”

“…In recent years, several studies have examined the role of coral reefs and their contribution to atmospheric CO 2 by measuring seawater pCO 2 and atmospheric pCO 2 in coral reefs [6][7][8][9][10][11]. They indicate that although coral reefs are mostly net sources [7][8][9][10][11][12][13][14][15][16] of atmospheric CO 2 , they may also act as sinks [6,17,18] for atmospheric CO 2 . Suzuki et al [6] suggested that the contribution of coral reefs to atmospheric CO 2 is largely dependent on their topographic and oceanographic settings.…”

High‐resolution carbon budgets on a Palau back‐reef modulated by interactions between hydrodynamics and reef metabolism

“…However, both Eulerian (Atkinson and Bilger 1992; Gattuso et al 1993Gattuso et al , 1996 and Lagrangian (Barnes and Lazar 1993;Frankignoulle et al 1996) studies rely heavily on the assumption that the water column above the benthic community is fully mixed. Often in waters deeper than 3 m, the water column is sheared, so fluxes estimated from gradual changes in concentration using integration over the full depth of the environment can be erroneous.…”