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Carbonate System Site Selection Characteristics for Ocean Alkalinity Enhancement in the US Northeast Shelf and Slope.

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Title: Carbonate System Site Selection Characteristics for Ocean Alkalinity Enhancement in the US Northeast Shelf and Slope.
Authors: Rheuban, Jennie E.1 (AUTHOR) jrheuban@whoi.edu, Kim, Heather H.1 (AUTHOR), Chen, Ke2 (AUTHOR), Lima, Ivan D.3 (AUTHOR), McCorkle, Daniel C.4 (AUTHOR), Michel, Anna P. M.5 (AUTHOR), Wang, Zhaohui Aleck1 (AUTHOR), Subhas, Adam V.1 (AUTHOR)
Source: Journal of Geophysical Research. Biogeosciences. Dec2025, Vol. 130 Issue 12, p1-21. 21p.
Subject Terms: *Carbon dioxide in seawater, *Climate change mitigation, *Ocean currents, Machine learning, Continental shelf, Carbonate minerals, Carbon dioxide reduction, Feasibility studies
Geographic Terms: United States
Abstract: Ocean alkalinity enhancement (OAE) is a marine carbon dioxide (CO2) removal strategy that relies on lowering the ocean's pCO2 via the addition of alkaline materials to facilitate enhanced CO2 uptake with the potential for durable, long‐term, storage. This strategy has gained recent scientific and private sector attention as a possible component of climate mitigation portfolios, yet many research questions remain. This work describes an analysis of historical reconstructions of regional carbonate chemistry developed via application of machine learning algorithms to an ocean reanalysis product. Model skill assessment demonstrated excellent performance when compared to regional observations, and this work focuses on four carbonate system variables that may influence OAE applications: total scale pH, calcite saturation state, the theoretical molar change in dissolved inorganic carbon associated with a molar change in total alkalinity (ΔDIC/ΔTA), and the timescale of CO2 equilibrium of the surface mixed layer (τCO2 ${\tau }_{{\text{CO}}_{2}}$). These metrics were combined into a suitability index to quantify locations and times of year more favorable for OAE. Much of the US Northeast Shelf and Slope region has seasonally similar suitability for small‐scale OAE applications, with nearshore environments exhibiting high suitability year‐round. Lagrangian particle tracking experiments show strong reductions in ΔDIC/ΔTA and increases in τCO2 ${\tau }_{{\text{CO}}_{2}}$ due to horizontal and vertical transport, suggesting that when water motion is accounted for, reduced efficiency and longer equilibration times may impact successful observations of carbon uptake and storage. This analysis and framework were developed with publicly available tools, data sets, and global data products allowing for global scalability and application. Plain Language Summary: Ocean alkalinity enhancement (OAE), a proposed marine carbon dioxide removal strategy, relies on altering ocean chemistry via the addition of alkaline materials to reduce pCO2 and allow for additional atmospheric CO2 uptake and storage. An understanding of historical regional ocean chemistry is necessary to inform planning and decision‐making. This manuscript applies machine learning models to a high‐spatial and temporal resolution ocean reanalysis to reconstruct chemistry on the US Northeast Shelf and Slope (NESS). We evaluated four ocean chemistry metrics, assessed regional thresholds to determine safe levels of alkalinity addition, and evaluated the effects of water motion on two of the four metrics. Ideal geochemical characteristics include: shallow, strong, and spatially‐consistent mixed layers, limited water movement, high alkalinity addition thresholds, low pH, low ΩCa, short mixed‐layer CO2 equilibration timescales, and high theoretical carbon uptake efficiency. We found, in the summertime, much of the NESS has similar suitability for OAE experiments, but in winter, only nearshore environments showed indices similar to summertime. When water motion was considered, both metrics evaluated suggested worse conditions, showing how water transport might influence OAE field experiments. This analysis was developed entirely with publicly available tools, data sets, and global data products allowing for global scalability and application. Key Points: Machine learning tools applied to a global ocean reanalysis product reconstruct ocean carbonate chemistry in the US Northeast Shelf and SlopeAssessment of background conditions identifies coastal regions as most suitable for ocean alkalinity enhancement applicationsConsideration of water movement reduces the efficacy and equilibration times of alkalinity‐enhanced parcels of water [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Biogeosciences is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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Items – Name: Title
  Label: Title
  Group: Ti
  Data: Carbonate System Site Selection Characteristics for Ocean Alkalinity Enhancement in the US Northeast Shelf and Slope.
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  Data: <searchLink fieldCode="AR" term="%22Rheuban%2C+Jennie+E%2E%22">Rheuban, Jennie E.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> jrheuban@whoi.edu</i><br /><searchLink fieldCode="AR" term="%22Kim%2C+Heather+H%2E%22">Kim, Heather H.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Chen%2C+Ke%22">Chen, Ke</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Lima%2C+Ivan+D%2E%22">Lima, Ivan D.</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22McCorkle%2C+Daniel+C%2E%22">McCorkle, Daniel C.</searchLink><relatesTo>4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Michel%2C+Anna+P%2E+M%2E%22">Michel, Anna P. M.</searchLink><relatesTo>5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Wang%2C+Zhaohui+Aleck%22">Wang, Zhaohui Aleck</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Subhas%2C+Adam+V%2E%22">Subhas, Adam V.</searchLink><relatesTo>1</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Biogeosciences%22">Journal of Geophysical Research. Biogeosciences</searchLink>. Dec2025, Vol. 130 Issue 12, p1-21. 21p.
– Name: Subject
  Label: Subject Terms
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  Data: *<searchLink fieldCode="DE" term="%22Carbon+dioxide+in+seawater%22">Carbon dioxide in seawater</searchLink><br />*<searchLink fieldCode="DE" term="%22Climate+change+mitigation%22">Climate change mitigation</searchLink><br />*<searchLink fieldCode="DE" term="%22Ocean+currents%22">Ocean currents</searchLink><br /><searchLink fieldCode="DE" term="%22Machine+learning%22">Machine learning</searchLink><br /><searchLink fieldCode="DE" term="%22Continental+shelf%22">Continental shelf</searchLink><br /><searchLink fieldCode="DE" term="%22Carbonate+minerals%22">Carbonate minerals</searchLink><br /><searchLink fieldCode="DE" term="%22Carbon+dioxide+reduction%22">Carbon dioxide reduction</searchLink><br /><searchLink fieldCode="DE" term="%22Feasibility+studies%22">Feasibility studies</searchLink>
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  Data: <searchLink fieldCode="DE" term="%22United+States%22">United States</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Ocean alkalinity enhancement (OAE) is a marine carbon dioxide (CO2) removal strategy that relies on lowering the ocean's pCO2 via the addition of alkaline materials to facilitate enhanced CO2 uptake with the potential for durable, long‐term, storage. This strategy has gained recent scientific and private sector attention as a possible component of climate mitigation portfolios, yet many research questions remain. This work describes an analysis of historical reconstructions of regional carbonate chemistry developed via application of machine learning algorithms to an ocean reanalysis product. Model skill assessment demonstrated excellent performance when compared to regional observations, and this work focuses on four carbonate system variables that may influence OAE applications: total scale pH, calcite saturation state, the theoretical molar change in dissolved inorganic carbon associated with a molar change in total alkalinity (ΔDIC/ΔTA), and the timescale of CO2 equilibrium of the surface mixed layer (τCO2 ${\tau }_{{\text{CO}}_{2}}$). These metrics were combined into a suitability index to quantify locations and times of year more favorable for OAE. Much of the US Northeast Shelf and Slope region has seasonally similar suitability for small‐scale OAE applications, with nearshore environments exhibiting high suitability year‐round. Lagrangian particle tracking experiments show strong reductions in ΔDIC/ΔTA and increases in τCO2 ${\tau }_{{\text{CO}}_{2}}$ due to horizontal and vertical transport, suggesting that when water motion is accounted for, reduced efficiency and longer equilibration times may impact successful observations of carbon uptake and storage. This analysis and framework were developed with publicly available tools, data sets, and global data products allowing for global scalability and application. Plain Language Summary: Ocean alkalinity enhancement (OAE), a proposed marine carbon dioxide removal strategy, relies on altering ocean chemistry via the addition of alkaline materials to reduce pCO2 and allow for additional atmospheric CO2 uptake and storage. An understanding of historical regional ocean chemistry is necessary to inform planning and decision‐making. This manuscript applies machine learning models to a high‐spatial and temporal resolution ocean reanalysis to reconstruct chemistry on the US Northeast Shelf and Slope (NESS). We evaluated four ocean chemistry metrics, assessed regional thresholds to determine safe levels of alkalinity addition, and evaluated the effects of water motion on two of the four metrics. Ideal geochemical characteristics include: shallow, strong, and spatially‐consistent mixed layers, limited water movement, high alkalinity addition thresholds, low pH, low ΩCa, short mixed‐layer CO2 equilibration timescales, and high theoretical carbon uptake efficiency. We found, in the summertime, much of the NESS has similar suitability for OAE experiments, but in winter, only nearshore environments showed indices similar to summertime. When water motion was considered, both metrics evaluated suggested worse conditions, showing how water transport might influence OAE field experiments. This analysis was developed entirely with publicly available tools, data sets, and global data products allowing for global scalability and application. Key Points: Machine learning tools applied to a global ocean reanalysis product reconstruct ocean carbonate chemistry in the US Northeast Shelf and SlopeAssessment of background conditions identifies coastal regions as most suitable for ocean alkalinity enhancement applicationsConsideration of water movement reduces the efficacy and equilibration times of alkalinity‐enhanced parcels of water [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Journal of Geophysical Research. Biogeosciences is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1029/2025JG009063
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 21
        StartPage: 1
    Subjects:
      – SubjectFull: Carbon dioxide in seawater
        Type: general
      – SubjectFull: Climate change mitigation
        Type: general
      – SubjectFull: Ocean currents
        Type: general
      – SubjectFull: Machine learning
        Type: general
      – SubjectFull: Continental shelf
        Type: general
      – SubjectFull: Carbonate minerals
        Type: general
      – SubjectFull: Carbon dioxide reduction
        Type: general
      – SubjectFull: Feasibility studies
        Type: general
      – SubjectFull: United States
        Type: general
    Titles:
      – TitleFull: Carbonate System Site Selection Characteristics for Ocean Alkalinity Enhancement in the US Northeast Shelf and Slope.
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              M: 12
              Text: Dec2025
              Type: published
              Y: 2025
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