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1. Carbonate Chemistry and the Potential for Acidification in Georgia Coastal Marshes and the South Atlantic Bight, USA

   https://doi.org/10.1007/s12237-023-01261-3  

   Reimer, Janet J. ; Medeiros, Patricia M. ; Hussain, Najid ; Gonski, Stephen F. ; Xu, Yuan-Yaun ; Huang, Ting-Hsuan ; Cai, Wei-Jun ( September 2023 , Estuaries and Coasts)

   In coastal regions and marginal bodies of water, the increase in partial pressure of carbon dioxide (pCO₂) in many instances is greater than that of the open ocean due to terrestrial (river, estuarine, and wetland) influences, decreasing buffering capacity and/or increasing water temperatures. Coastal oceans receive freshwater from rivers and groundwater as well as terrestrial-derived organic matter, both of which have a direct influence on coastal carbonate chemistry. The objective of this research is to determine if coastal marshes in Georgia, USA, may be “hot-spots” for acidification due to enhanced inorganic carbon sources and if there is terrestrial influence on offshore acidification in the South Atlantic Bight (SAB). The results of this study show that dissolved inorganic carbon (DIC) and total alkalinity (TA) are elevated in the marshes compared to predictions from conservative mixing of the freshwater and oceanic end-members, with accompanying pH around 7.2 to 7.6 within the marshes and aragonite saturation states (Ω_Ar) <1. In the marshes, there is a strong relationship between the terrestrial/estuarine-derived organic and inorganic carbon and acidification. Comparisons of pH, TA, and DIC to terrestrial organic material markers, however, show that there is little influence of terrestrial-derived organic matter on shelf acidification during thismore »period in 2014. In addition, Ω_Arincreases rapidly offshore, especially in drier months (July). River stream flow during 2014 was anomalously low compared to climatological means; therefore, offshore influences from terrestrial carbon could also be decreased. The SAB shelf may not be strongly influenced by terrestrial inputs to acidification during drier than normal periods; conversely, shelf waters that are well-buffered against acidification may not play a significant role in mitigating acidification within the Georgia marshes.

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2. A regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry, and ocean acidification in the Gulf of Alaska

   https://doi.org/10.5194/bg-17-3837-2020  

   Hauri, Claudine ; Schultz, Cristina ; Hedstrom, Katherine ; Danielson, Seth ; Irving, Brita ; Doney, Scott C. ; Dussin, Raphael ; Curchitser, Enrique N. ; Hill, David F. ; Stock, Charles A. ( January 2020 , Biogeosciences)

   Abstract. The coastal ecosystem of the Gulf of Alaska (GOA) is especially vulnerable to the effects of ocean acidification and climate change. Detection of these long-term trends requires a good understanding of the system’s natural state. The GOA is a highly dynamic system that exhibits large inorganic carbon variability on subseasonal to interannual timescales. This variability is poorly understood due to the lack of observations in this expansive and remote region. We developed a new model setup for the GOA that couples the three-dimensional Regional Oceanic Model System (ROMS) and the Carbon, Ocean Biogeochemistry and Lower Trophic (COBALT) ecosystem model. To improve our conceptual understanding of the system, we conducted a hindcast simulation from 1980 to 2013. The model was explicitly forced with temporally and spatially varying coastal freshwater discharges from a high-resolution terrestrial hydrological model, thereby affecting salinity, alkalinity, dissolved inorganic carbon, and nutrient concentrations. This represents a substantial improvement over previous GOA modeling attempts. Here, we evaluate the model on seasonal to interannual timescales using the best available inorganic carbon observations. The model was particularly successful in reproducing observed aragonite oversaturation and undersaturation of near-bottom water in May and September, respectively. The largest deficiency in the model ismore »its inability to adequately simulate springtime surface inorganic carbon chemistry, as it overestimates surface dissolved inorganic carbon, which translates into an underestimation of the surface aragonite saturation state at this time. We also use the model to describe the seasonal cycle and drivers of inorganic carbon parameters along the Seward Line transect in under-sampled months. Model output suggests that the majority of the near-bottom water along the Seward Line is seasonally undersaturated with respect to aragonite between June and January, as a result of upwelling and remineralization. Such an extensive period of reoccurring aragonite undersaturation may be harmful to ocean acidification-sensitive organisms. Furthermore, the influence of freshwater not only decreases the aragonite saturation state in coastal surface waters in summer and fall, but it simultaneously decreases the surface partial pressure of carbon dioxide (pCO2), thereby decoupling the aragonite saturation state from pCO2. The full seasonal cycle and geographic extent of the GOA region is under-sampled, and our model results give new and important insights for months of the year and areas that lack in situ inorganic carbon observations.« less
3. Mechanisms Driving Decadal Changes in the Carbonate System of a Coastal Plain Estuary

   https://doi.org/10.1029/2021JC017239  

   Da, Fei ; Friedrichs, Marjorie A. M. ; St‐Laurent, Pierre ; Shadwick, Elizabeth H. ; Najjar, Raymond G. ; Hinson, Kyle E. ( June 2021 , Journal of Geophysical Research: Oceans)

   Understanding decadal changes in the coastal carbonate system is essential for predicting how the health of these waters responds to anthropogenic drivers, such as changing atmospheric conditions and riverine inputs. However, studies that quantify the relative impacts of these drivers are lacking. In this study, the primary drivers of decadal trends in the surface carbonate system, and the spatiotemporal variability in these trends, are identified for a large coastal plain estuary: the Chesapeake Bay. Experiments using a coupled three‐dimensional hydrodynamic‐biogeochemical model highlight that, over the past three decades, the changes in the surface carbonate system of Chesapeake Bay have strong seasonal and spatial variability. The greatest surface pH and aragonite saturation state (Ω_AR) reductions have occurred in the summer in the middle (mesohaline) Bay: −0.24 and −0.9 per 30 years, respectively, with increases in atmospheric CO₂and reductions in nitrate loading both being primary drivers. Reductions in nitrate loading have a strong seasonal influence on the carbonate system, with the most pronounced decadal decreases in pH and Ω_ARoccurring during the summer when primary production is strongly dependent on nutrient availability. Increases in riverine total alkalinity and dissolved inorganic carbon have raised surface pH in the upper oligohaline Bay, while other driversmore »such as atmospheric warming and input of acidified ocean water through the Bay mouth have had comparatively minor impacts on the estuarine carbonate system. This work has significant implications for estuarine ecosystem services, which are typically most sensitive to surface acidification in the spring and summer seasons.

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4. Long-Term Trends in Estuarine Carbonate Chemistry in the Northwestern Gulf of Mexico

   https://doi.org/10.3389/fmars.2022.793065  

   McCutcheon, Melissa R. ; Hu, Xinping ( March 2022 , Frontiers in Marine Science)

   A four-decade dataset that spans seven estuaries along a latitudinal gradient in the northwestern Gulf of Mexico and includes measurements of pH and total alkalinity was used to calculate partial pressure of CO 2 ( p CO 2 ), dissolved inorganic carbon (DIC), saturation state of aragonite (Ω Ar ), and a buffer factor (β DIC , which measures the response of proton concentration or pH to DIC concentration change) and examine long-term trends and spatial patterns in these parameters. With the notable exception of the northernmost and southernmost estuaries (and selected stations near freshwater input), these estuaries have generally experienced long-term increases in p CO 2 and decreases in DIC, Ω Ar , and β DIC , with the magnitude of change generally increasing from north to south. At all stations with increasing p CO 2 , the rate of increase exceeded the rate of increase in atmospheric p CO 2 , indicating that these estuaries have become a greater source of CO 2 to the atmosphere over the last few decades. The decreases in Ω Ar have yet to cause Ω Ar to near undersaturation, but even the observed decreases may have the potential to decrease calcification ratesmore »in important estuarine calcifiers like oysters. The decreases in β DIC directly indicate that these estuaries have experienced continually greater change in pH in the context of ocean acidification.« less
5. Rapid Acidification of the Arctic Chukchi Sea Waters Driven by Anthropogenic Forcing and Biological Carbon Recycling

   https://doi.org/10.1029/2021GL097246  

   Qi, Di ; Wu, Yingxu ; Chen, Liqi ; Cai, Wei‐Jun ; Ouyang, Zhangxian ; Zhang, Yixing ; Anderson, Leif G. ; Feely, Richard A. ; Zhuang, Yanpei ; Lin, Hongmei ; et al ( February 2022 , Geophysical Research Letters)

   The acidification of coastal waters is distinguished from the open ocean because of much stronger synergistic effects between anthropogenic forcing and local biogeochemical processes. However, ocean acidification research is still rather limited in polar coastal oceans. Here, we present a 17‐year (2002–2019) observational data set in the Chukchi Sea to determine the long‐term changes in pH and aragonite saturation state (Ω_arag). We found that pH and Ω_aragdeclined in different water masses with average rates of −0.0047 ± 0.0026 years⁻¹and −0.017 ± 0.009 years⁻¹, respectively, and are ∼2–3 times faster than those solely due to increasing atmospheric CO₂. We attributed the rapid acidification to the increased dissolved inorganic carbon owing to a combination of ice melt‐induced increased atmospheric CO₂invasion and subsurface remineralization induced by a stronger surface biological production as a result of the increased inflow of the nutrient‐rich Pacific water.