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1. Annual Mixed Layer Carbon Budget for the West Antarctic Peninsula Continental Shelf: Insights From Year‐Round Mooring Measurements

   https://doi.org/10.1029/2020JC016920  

   Yang, Bo; Shadwick, Elizabeth H.; Schultz, Cristina; Doney, Scott C. (April 2021, Journal of Geophysical Research: Oceans)

   Abstract For the first time the annual carbon budget on the West Antarctic Peninsula shelf was studied with continuously measured CO₂system parameters (pH andpCO₂) from a subsurface mooring. The temporal evolution of the mixed layer dissolved inorganic carbon (DIC) is investigated via a mass balance. The annual mixed layer DIC inventory change was 1.1 ± 0.4 mol m⁻² yr⁻¹, which was mainly regulated by biological drawdown (−2.8 ± 2.4 mol m⁻² yr⁻¹), diapycnal eddy diffusion (2.6 ± 1.3 mol m⁻² yr⁻¹), entrainment/detrainment (0.9 ± 0.4 mol m⁻² yr⁻¹), and air‐water gas exchange (0.4 ± 2.1 mol m⁻² yr⁻¹). Significant carbon drawdown was observed in the spring and summer, which was replenished by the physical processes mentioned above. These observations suggest this area is an annual atmosphere CO₂sink with a mixed layer net community production of 2.8 ± 2.4 mol m⁻² yr⁻¹. These results highlight the significant seasonality in the DIC mass balance and the necessity of year‐round continuous observations for robust assessments of biogeochemical cycling in this region. 

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2. Radium Inputs Into the Arctic Ocean From Rivers: A Basin‐Wide Estimate

   https://doi.org/10.1029/2022JC018964  

   Bullock, Emma J.; Kipp, Lauren; Moore, Willard; Brown, Kristina; Mann, Paul J.; Vonk, Jorien E.; Zimov, Nikita; Charette, Matthew A. (September 2022, Journal of Geophysical Research: Oceans)

   Abstract Radium isotopes have been used to trace nutrient, carbon, and trace metal fluxes inputs from ocean margins. However, these approaches require a full accounting of radium sources to the coastal ocean including rivers. Here, we aim to quantify river radium inputs into the Arctic Ocean for the first time for²²⁶Ra and to refine the estimates for²²⁸Ra. Using new and existing data, we find that the estimated combined (dissolved plus desorbed) annual²²⁶Ra and²²⁸Ra fluxes to the Arctic Ocean are [7.0–9.4] × 10¹⁴dpm y⁻¹and [15–18] × 10¹⁴dpm y⁻¹, respectively. Of these totals, 44% and 60% of the river²²⁶Ra and²²⁸Ra, respectively are from suspended sediment desorption, which were estimated from laboratory incubation experiments. Using Ra isotope data from 20 major rivers around the world, we derived global annual²²⁶Ra and²²⁸Ra fluxes of [7.4–17] × 10¹⁵and [15–27] × 10¹⁵dpm y⁻¹, respectively. As climate change spurs rapid Arctic warming, hydrological cycles are intensifying and coastal ice cover and permafrost are diminishing. These river radium inputs to the Arctic Ocean will serve as a valuable baseline as we attempt to understand the changes that warming temperatures are having on fluxes of biogeochemically important elements to the Arctic coastal zone. 

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3. 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)

   Abstract 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 this 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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4. Net Community Production and Inorganic Carbon Cycling in the Central Irminger Sea

   https://doi.org/10.1029/2024JC021027  

   Yoder, M_F; Palevsky, H_I; Fogaren, K_E (July 2024, Journal of Geophysical Research: Oceans)

   Abstract The subpolar North Atlantic plays an outsized role in the atmosphere‐to‐ocean carbon sink. The central Irminger Sea is home to well‐documented deep winter convection and high phytoplankton production, which drive strong seasonal and interannual variability in regional carbon cycling. We use observational data from moored carbonate chemistry system sensors and annual turn‐around cruise samples at the Ocean Observatories Initiative's Irminger Sea Array to construct a near‐continuous time series of mixed layer total dissolved inorganic carbon (DIC),pCO₂, and total alkalinity from summer 2015 to summer 2022. We use these carbonate chemistry system time series to deconvolve the physical and biological drivers of surface ocean carbon cycling in this region on seasonal, annual, and interannual time scales. We find high annual net community production within the seasonally varying mixed layer, averaging 9.8 ± 1.6 mol m⁻² yr⁻¹with high interannual variability (range of 6.0–13.9 mol m⁻² yr⁻¹). The highest daily net community production rates occur during the late winter and early spring, prior to the observed high chlorophyll concentrations associated with the spring phytoplankton bloom. As a result, the winter and early spring play a much larger role in biological carbon export from the mixed layer than traditionally thought. 

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5. Comparative Metabolism and Blue Carbon Sequestration of Two Wetland-Dominated Estuaries

   https://doi.org/10.34133/olar.0091  

   Hopkinson, Charles S; Weston, Nathaniel B; Vallino, Joseph J; Garritt, Robert H; Forbrich, Inke (January 2025, Ocean-Land-Atmosphere Research)

   Coastal tidal wetlands and estuaries play important roles in the global carbon budget by contributing to the net withdrawal of CO₂from the atmosphere. We quantified the linkages between terrestrial and oceanic systems, marsh-to-bay carbon exchange, and the uptake of CO₂from the atmosphere in the wetland-dominated Plum Island Sound (MA, USA) and Duplin River (GA, USA) estuaries. The C budgets revealed that autotrophic marshes [primary production:ecosystem respiration (P:R) ~1.3:1] are tightly coupled to heterotrophic aquatic systems (P:R ~0.6:1). Levels of marsh gross primary production are similar in these systems (865 ± 39 and 768 ± 74 gC m⁻²year⁻¹in Plum Island and the Duplin, respectively) even though they are in different biogeographic provinces. In contrast to inputs from rivers and coastal oceans, tidal marshes are the dominant source of allochthonous matter that supports heterotrophy in aquatic systems. Dissolved inorganic carbon (DIC) exported from marshes to the coastal ocean was a major flux pathway in the Duplin River; however, there was no evidence of DIC export from Plum Island marshes and only minor export to the ocean. Burial was a sink for 53% of marsh net ecosystem production (NEP) on Plum Island, but only 19% of marsh NEP in the Duplin. Burial was the dominant blue carbon sequestration pathway at Plum Island, whereas in the Duplin, DIC and organic carbon export to the ocean were equally important. Regional- and continental-scale C budgets should better reflect wetland-dominated systems to more accurately characterize their contribution to global CO₂sequestration. 

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