| Summary: | Mangrove ecosystems were identified by recent research as capable of buffering coastal ocean acidification (OA) and acting as refugia for scleractinian corals, suggesting that sulfate reduction and carbonate sediment dissolution generated sufficient alkalinity to buffer OA. However, it remains unclear if said buffering capabilities are common to all coastal mangrove areas over extended time scales. This study describes the seasonal carbonate chemistry variability within a semi-enclosed tropical mangrove lagoon (BB) in southwestern Puerto Rico. Biweekly measurements of sea temperature and salinity, combined with water samples of pH, total alkalinity (TA), and dissolved inorganic carbon (DIC), were collected from 2014 to 2018. We investigated the mechanisms driving the carbonate variability using the salinity normalized DIC (nDIC) and TA (nTA) correlation and compared with an offshore reference station (SE) located approximately 11 km off the coast. Waters at BB showed mean pH (7.87±0.09) and mean aragonite saturation state levels (Ωarg, 2.96±0.47) that could be challenging to calcification. pCO2 data and nDIC vs. nTA analyses evidence that heterotrophic activity as the primary driver for the persistent acidification, which reaches its maximum expression during the wet season. We conclude that not all mangrove environments are capable of effectively buffering against OA. Lagoons with a limited exchange with nearshore water and high carbon input rates can show exacerbated OA levels relative to oceanic and mid-shelf environments. Los ecosistemas de manglar se identificaron recientemente como capaces de amortiguar la acidificación de los océanos (OA) costeros y actuar como refugio para los corales esclerocios, sugiriendo que la reducción de sulfato y la disolución de sedimentos de carbonato generan alcalinidad suficiente para amortiguar la OA. Sin embargo, no está claro si dichas capacidades de amortiguación son comunes a todas las áreas costeras de manglares en escalas de tiempo extendidas. En este estudio, ...
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