Carbonate chemistry dynamics over a Caribbean shelf reef (Cayo Enrique) at the Atlantic Ocean Acidification Test-bed, La Parguera, Puerto Rico

Changes in surface ocean chemistry in direct response to rising atmospheric carbon dioxide (CO2) concentration may pose challenges to a range of marine ecosystems in coming decades. Monitoring this ocean acidification (OA) at regional and local-scales is an important requirement towards improving our understanding of the potential long-term consequences. Coral reef ecosystems are of particular concern given the potential effects OA may have on net community calcification and ultimately reef accretion rates. While the dynamics and trends in oceanic carbonate chemistry are reasonably well constrained, how OA is manifested within the shallow coastal waters where coral reef ecosystems reside is less understood. Community-scale metabolic processes impart an important control on near-reef carbonate chemistry. Constraining the near-reef variability in carbonate chemistry across diel, seasonal, and annual scales is a critical requirement towards assigning potential biogeochemical thresholds of OA. The Atlantic OA Test-bed in the La Parguera Marine Reserve, Puerto Rico was established in 2009 to provide sustained high temporal resolution monitoring of carbonate chemistry within an Atlantic tropical coral reef ecosystem. Presented here are the results of over a year’s worth of sustained monitoring at the Cayo Enrique forereef characterizing the temporal dynamics in carbonate chemistry. The Cayo Enrique reef is a source of CO2 to the atmosphere (1.7 mmol CO2 m-2 d-1, SE = 0.1) with both calcification and respiration serving to consistently elevate pCO2,sw relative to oceanic waters. Once pCO2,sw increase by a further 100 µatm in response to rising atmospheric CO2, these waters will likely reach undersaturation with respect to 13 mol % MgCO3 phases during winter months. While high-Mg calcites are prominent mineral phases of shallow tropical carbonate marine sediments, their relative importance as cementing agents of modern coral reef frameworks demands further investigation. Should their role prove significant, then the next several decades may represent an important geochemical threshold for Caribbean reef systems.

Gledhill, D. K., Corredor, J. E., Langdon, C., Manzello, D., Sabine, C. L., Hensley, V., Brocco, B., Musielewicz, S., Lawrence-Slavas, N. & Capella, J. E., 2010. Carbonate chemistry dynamics over a Caribbean shelf reef (Cayo Enrique) at the Atlantic Ocean Acidification Test-bed, La Parguera, Puerto Rico. American Geophysical Union, Fall Meeting 2010, abstract #OS21D-1541. Abstract.


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