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1. Upwelling intensity and source water properties drive high interannual variability of corrosive events in the California Current

   https://doi.org/10.1038/s41598-023-39691-5  

   Cheresh, Julia ; Kroeker, Kristy J. ; Fiechter, Jerome ( August 2023 , Scientific Reports)

   Ocean acidification is progressing rapidly in the California Current System (CCS), a region already susceptible to reduced aragonite saturation state due to seasonal coastal upwelling. Results from a high-resolution (~ 3 km), coupled physical-biogeochemical model highlight that the intensity, duration, and severity of undersaturation events exhibit high interannual variability along the central CCS shelfbreak. Variability in dissolved inorganic carbon (DIC) along the bottom of the 100-m isobath explains 70–90% of event severity variance over the range of latitudes where most severe conditions occur. An empirical orthogonal function (EOF) analysis further reveals that interannual event variability is explained by a combination coastal upwelling intensity and DIC content in upwelled source waters. Simulated regional DIC exhibits low frequency temporal variability resembling that of the Pacific Decadal Oscillation, and is explained by changes to water mass composition in the CCS. While regional DIC concentrations and upwelling intensity individually explain 9 and 43% of year-to-year variability in undersaturation event severity, their combined influence accounts for 66% of the variance. The mechanistic description of exposure to undersaturated conditions presented here provides important context for monitoring the progression of ocean acidification in the CCS and identifies conditions leading to increased vulnerability for ecologically and commercially important species.
2. Impact of local rivers on coastal acidification

   https://doi.org/10.1002/lno.12237  

   Savoie, Allison M. ; Moody, Amy ; Gilbert, Melissa ; Dillon, Kevin S. ; Howden, Stephan D. ; Shiller, Alan M. ; Hayes, Christopher T. ( October 2022 , Limnology and Oceanography)

   Coastal ecosystems are highly dynamic areas for carbon cycling and are likely to be negatively impacted by increasing ocean acidification. This research focused on dissolved inorganic carbon (DIC) and total alkalinity (TA) in the Mississippi Sound to understand the influence of local rivers on coastal acidification. This area receives large fluxes of freshwater from local rivers, in addition to episodic inputs from the Mississippi River through a human‐built diversion, the Bonnet Carré Spillway. Sites in the Sound were sampled monthly from August 2018 to November 2019 and weekly from June to August 2019 in response to an extended spillway opening. Prior to the 2019 spillway opening, the contribution of the local, lower alkalinity rivers to the Sound may have left the study area more susceptible to coastal acidification during winter months, with aragonite saturation states (Ω_ar) < 2. After the spillway opened, despite a large increase in TA throughout the Sound, aragonite saturation states remained low, likely due to hypoxia and increased CO₂concentrations in subsurface waters. Increased Mississippi River input could represent a new normal in the Sound's hydrography during spring and summer months. The spillway has been utilized more frequently over the last two decades due to increasing precipitation inmore »the Mississippi River watershed, which is primarily associated with climate change. Future increases in freshwater discharge and the associated declines in salinity, dissolved oxygen, and Ω_arin the Sound will likely be detrimental to oyster stocks and the resilience of similar ecosystems to coastal acidification.

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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. 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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