Carbonate chemistry seasonality in a tropical mangrove lagoon in La Parguera, Puerto Rico.

We investigated the seasonal carbonate chemistry variability within a semi-enclosed tropical mangrove lagoon in southwestern Puerto Rico. Biweekly measurements of seawater temperature, salinity, total alkalinity (TA), and dissolved inorganic carbon (DIC) were conducted from 2014 to 2018. We describe the possible mechanisms driving the observed variability by correlating the DIC/TA ratio with pH and Ωarg, suggesting that the mean pH (7.87 ± 0.09) and aragonite saturation state (Ωarg, 2.96 ± 0.47) of the mangrove lagoon negatively affected calcification. The measured pCO2 and DIC/TA ratios indicate that heterotrophic activity was the primary driver for persistent acidification, which reached its maximum expression during the wet season. We conclude that mangrove lagoons with limited seawater exchange and high carbon input will not mitigate ocean acidification.

Controls on surface water carbonate chemistry along North American ocean margins.

Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO2 (pCO2) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.

Rapid warming and salinity changes in the Gulf of Maine alter surface ocean carbonate parameters and hide ocean acidification.

A profound warming event in the Gulf of Maine during the last decade has caused sea surface temperatures to rise to levels exceeding any earlier observations recorded in the region over the last 150 years. This event dramatically affected CO2 solubility and, in turn, the status of the sea surface carbonate system. When combined with the concomitant increase in sea surface salinity and assumed rapid equilibration of carbon dioxide across the air sea interface, thermodynamic forcing partially mitigated the effects of ocean acidification for pH, while raising the saturation index of aragonite ( Ω AR ) by an average of 0.14 U. Although the recent event is categorically extreme, we find that carbonate system parameters also respond to interannual and decadal variability in temperature and salinity, and that such phenomena can mask the expression of ocean acidification caused by increasing atmospheric carbon dioxide. An analysis of a 34-year salinity and SST time series (1981-2014) shows instances of 5-10 years anomalies in temperature and salinity that perturb the carbonate system to an extent greater than that expected from ocean acidification. Because such conditions are not uncommon in our time series, it is critical to understand processes controlling the carbonate system and how ecosystems with calcifying organisms respond to its rapidly changing conditions. It is also imperative that regional and global models used to estimate carbonate system trends carefully resolve variations in the physical processes that control CO2 concentrations in the surface ocean on timescales from episodic events to decades and longer.

Ocean acidification in the coastal zone from an organism's perspective: multiple system parameters, frequency domains, and habitats.

Multiple natural and anthropogenic processes alter the carbonate chemistry of the coastal zone in ways that either exacerbate or mitigate ocean acidification effects. Freshwater inputs and multiple acid-base reactions change carbonate chemistry conditions, sometimes synergistically. The shallow nature of these systems results in strong benthic-pelagic coupling, and marine invertebrates at different life history stages rely on both benthic and pelagic habitats. Carbonate chemistry in coastal systems can be highly variable, responding to processes with temporal modes ranging from seconds to centuries. Identifying scales of variability relevant to levels of biological organization requires a fuller characterization of both the frequency and magnitude domains of processes contributing to or reducing acidification in pelagic and benthic habitats. We review the processes that contribute to coastal acidification with attention to timescales of variability and habitats relevant to marine bivalves.