An official website of the United States government
With the increasing threat of ocean acidification and the important role of the oceans in the global carbon cycle, highly precise, accurate, and intercomparable determination of inorganic carbon system parameters is required. Thermodynamic relationships enable the system to be fully constrained using a combination of direct measurements and calculations. However, calculations are complicated by many formulations for dissociation constants (over 120 possible combinations). To address these important issues of uncertainty and comparability, we evaluated the various combinations of constants and their (dis)agreement with direct measurements over a range of temperature (−1.9–40 ◦C), practical salinity (15–39) and pCO2 (150–1200 μatm). The results demonstrate that differences between the calculations and measurements are significantly larger than measurement uncertainties, meaning the oft-stated paradigm that one only needs to measure two parameters and the others can be calculated does not apply for climate quality ocean acidification research. The uncertainties in calculated pHt prevent climate quality pHt from being calculated from total alkalinity (TA) and dissolved inorganic carbon (DIC) and should be directly measured instead. However, climate quality TA and DIC can often be calculated using measured pH and DIC or TA respectively. Calculations are notably biased at medium-to-high pCO2 values (~500–800 μatm) implying models underestimate future ocean acidification. Uncertainty in the dissociation constants leads to significant uncertainty in the depth of the aragonite saturation horizon (>500 m in the Southern Ocean) and must be considered when studying calcium carbonate cycling. Significant improvements in the precision of the thermodynamic constants are required to improve pHt calculations.
more »
« less
Coastal processes modify projections of some climate-driven stressors in the California Current System
Abstract. Global projections for ocean conditions in 2100 predict that the North Pacific will experience some of the largest changes. Coastal processes that drive variability in the region can alter these projected changes but are poorly resolved by global coarse-resolution models. We quantify the degree to which local processes modify biogeochemical changes in the eastern boundary California Current System (CCS) using multi-model regionally downscaled climate projections of multiple climate-associated stressors (temperature, O2, pH, saturation state (Ω), and CO2). The downscaled projections predict changes consistent with the directional change from the global projections for the same emissions scenario. However, the magnitude and spatial variability of projected changes are modified in the downscaled projections for carbon variables. Future changes in pCO2 and surface Ω are amplified, while changes in pH and upper 200 m Ω are dampened relative to the projected change in global models. Surface carbon variable changes are highly correlated to changes in dissolved inorganic carbon (DIC), pCO2 changes over the upper 200 m are correlated to total alkalinity (TA), and changes at the bottom are correlated to DIC and nutrient changes. The correlations in these latter two regions suggest that future changes in carbon variables are influenced by nutrient cycling, changes in benthic–pelagic coupling, and TA resolved by the downscaled projections. Within the CCS, differences in global and downscaled climate stressors are spatially variable, and the northern CCS experiences the most intense modification. These projected changes are consistent with the continued reduction in source water oxygen; increase in source water nutrients; and, combined with solubility-driven changes, altered future upwelled source waters in the CCS. The results presented here suggest that projections that resolve coastal processes are necessary for adequate representation of the magnitude of projected change in carbon stressors in the CCS.
more »
« less
- Award ID(s):
- 2048373
- PAR ID:
- 10348314
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 18
- Issue:
- 9
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 2871 to 2890
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Measuring, reporting, and verification (MRV) of ocean-based carbon dioxide removal (CDR) presents challenges due to the dynamic nature of the ocean and the complex processes influencing marine carbonate chemistry. Given these challenges, finding the optimal sampling strategies and suite of parameters to be measured is a timely research question. While traditional carbonate parameters such as total alkalinity (TA), dissolved inorganic carbon (DIC), pH, and seawater pCO2 are commonly considered, exploring the potential of carbon isotopes for quantifying additional CO2 uptake remains a relatively unexplored research avenue. In this study, we use a coupled physical-biogeochemical model of the California Current System (CCS) to run a suite of Ocean Alkalinity Enhancement (OAE) simulations. The physical circulation for the CCS is generated using a nested implementation of the Regional Ocean Modeling System (ROMS) with an outer domain of 1/10 ̊ (~10 km) and an inner domain of 1/30 ̊ (~3 km) resolution. The biogeochemical model, NEMUCSC, is a customized version of the North Pacific Ecosystem Model for Understanding Regional Oceanography (NEMURO) that includes carbon cycling and carbon isotopes. The CCS is one of four global eastern boundary upwelling systems characterized by high biological activity and CO2 concentrations. Consequently, the CCS represents an essential test case for investigating the efficacy and potential side effects of OAE deployments. The study aims to address two key questions: (1) the relative merit of OAE to counter ocean acidification versus the additional sequestration of CO2 from the atmosphere, and (2) the footprint of potentially harmful seawater chemistry adjacent to OAE deployments. We plan to leverage these high-resolution model results to competitively evaluate different MRV strategies, with a specific focus on analyzing the spatiotemporal distribution of carbon isotopic signatures following OAE. In this talk, we will showcase our initial results and discuss challenges in integrating high-resolution regional modeling into models of the global carbon cycle. More broadly, this work aims to provide insights into the plausibility of OAE as a climate solution that maintains ocean health and to inform accurate quantification of carbon uptake for MRV purposes. https://agu.confex.com/agu/fm23/meetingapp.cgi/Paper/1437343more » « less
-
Abstract Measuring, reporting, and verification (MRV) of ocean-based carbon dioxide removal (CDR) presents challenges due to the dynamic nature of the ocean and the complex processes influencing marine carbonate chemistry. Given these challenges, finding the optimal sampling strategies and suite of parameters to be measured is a timely research question. While traditional carbonate parameters such as total alkalinity (TA), dissolved inorganic carbon (DIC), pH, and seawater pCO2 are commonly considered, exploring the potential of carbon isotopes for quantifying additional CO2 uptake remains a relatively unexplored research avenue. In this study, we use a coupled physical-biogeochemical model of the California Current System (CCS) to run a suite of Ocean Alkalinity Enhancement (OAE) simulations. The physical circulation for the CCS is generated using a nested implementation of the Regional Ocean Modeling System (ROMS) with an outer domain of 1/10 ̊ (~10 km) and an inner domain of 1/30 ̊ (~3 km) resolution. The biogeochemical model, NEMUCSC, is a customized version of the North Pacific Ecosystem Model for Understanding Regional Oceanography (NEMURO) that includes carbon cycling and carbon isotopes. The CCS is one of four global eastern boundary upwelling systems characterized by high biological activity and CO2 concentrations. Consequently, the CCS represents an essential test case for investigating the efficacy and potential side effects of OAE deployments. The study aims to address two key questions: (1) the relative merit of OAE to counter ocean acidification versus the additional sequestration of CO2 from the atmosphere, and (2) the footprint of potentially harmful seawater chemistry adjacent to OAE deployments. We plan to leverage these high-resolution model results to competitively evaluate different MRV strategies, with a specific focus on analyzing the spatiotemporal distribution of carbon isotopic signatures following OAE. In this talk, we will showcase our initial results and discuss challenges in integrating high-resolution regional modeling into models of the global carbon cycle. More broadly, this work aims to provide insights into the plausibility of OAE as a climate solution that maintains ocean health and to inform accurate quantification of carbon uptake for MRV purposes. https://agu.confex.com/agu/OSM24/prelim.cgi/Paper/1491096more » « less
-
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 (ΩAr) <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, ΩArincreases 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.more » « less
-
Abstract Estuaries may be uniquely susceptible to the combined acidification pressures of atmospherically driven ocean acidification (OA), biologically driven CO 2 inputs from the estuary itself, and terrestrially derived freshwater inputs. This study utilized continuous measurements of total alkalinity (TA) and the partial pressure of carbon dioxide (pCO 2 ) from the mouth of Great Bay, a temperate northeastern U.S. estuary, to examine the potential influences of endmember mixing and biogeochemical transformation upon estuary buffering capacity ( β – H ). Observations were collected hourly over 28 months representing all seasons between May 2016 and December 2019. Results indicated that endmember mixing explained most of the observed variability in TA and dissolved inorganic carbon (DIC), concentrations of which varied strongly with season. For much of the year, mixing dictated the relative proportions of salinity‐normalized TA and DIC as well, but a fall season shift in these proportions indicated that aerobic respiration was observed, which would decrease β – H by decreasing TA and increasing DIC. However, fall was also the season of weakest statistical correspondence between salinity and both TA and DIC, as well as the overall highest salinity, TA and β – H . Potential biogeochemically driven β – H decreases were overshadowed by increased buffering capacity supplied by coastal ocean water. A simple modeling exercise showed that mixing processes controlled most monthly changes in TA and DIC, obscuring impacts from air–sea exchange or metabolic processes. Advective mixing contributions may be as important as biogeochemically driven changes to observe when evaluating local estuarine and coastal OA.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-18-2871-2021
