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1. Multiple Ocean Equilibria and Decoupling of Miocene Atmospheric pCO ₂ and Regional Temperatures

   https://doi.org/10.1029/2025PA005126  

   Lee, Daeun; Sarr, Anta‐Clarisse; Acosta, R Paul; Poulsen, Christopher J (May 2025, Paleoceanography and Paleoclimatology)

   Abstract During the Middle Miocene Climate Transition (MMCT; ∼14.7–13.8 Ma), the global climate experienced rapid cooling, leading to modern‐like temperatures, precipitation patterns, and permanent ice sheets. However, proxy records indicate that atmospheric pCO₂and regional climate conditions (SST, ice volume) were highly variable from 17 to 12.5 Ma and these changes were not always synchronous. Here, we report on a series of middle Miocene (∼16–12.5 Ma) simulations using the water isotope enabled earth system model (iCESM1.2) to explore the potential for multiple equilibrium states to explain the observed decoupling between pCO₂and regional climates. Our simulations indicate that initial ocean conditions can significantly influence deep water formation in the North Atlantic and lead to multiple ocean equilibria. When the model is initiated from a cold state, residual cool surface water temperatures in the North Atlantic intensify Atlantic Meridional Ocean Circulation (AMOC) and inhibit Arctic sea‐ice formation. When initiated from a warm state, the AMOC remains weak. The different ocean states drive differences in equator‐to‐pole sea surface temperature gradients and sea ice distributions through heat redistribution changes. These equilibria cause variations in temperature gradients and sea ice distribution due to changes in heat redistribution. Additionally, changes in ocean circulation and a reduced temperature gradient in the North Atlantic increase North Atlantic precipitation when the AMOC is strong. These findings underscore the importance of the ocean's initial state in shaping regional climate responses to atmospheric pCO₂, potentially explaining regional climate pattern variability observed during the Miocene. 

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2. Short-term and seasonal pH, p CO ₂ and saturation state variability in a coral-reef ecosystem: CORAL REEF pCO ₂ , pH, SATURATION STATES

   https://doi.org/10.1029/2011GB004114  

   Gray, Sarah E.; DeGrandpre, Michael D.; Langdon, Chris; Corredor, Jorge E. (September 2012, Global Biogeochemical Cycles)
3. Drawdown of Atmospheric pCO ₂ Via Variable Particle Flux Stoichiometry in the Ocean Twilight Zone

   https://doi.org/10.1029/2021GL094924  

   Tanioka, Tatsuro; Matsumoto, Katsumi; Lomas, Michael W. (November 2021, Geophysical Research Letters)

   Abstract The strength of the biological soft tissue pump in the ocean critically depends on how much organic carbon is produced via photosynthesis and how efficiently the carbon is transferred to the ocean interior. For a given amount of limiting nutrient, phosphate, soft tissue pump would be strengthened if the carbon (C) to phosphorus (P) ratio of sinking organic matter increases as the remineralization length scale of C increases. Here, we present a new data compilation of particle flux stoichiometry and show that C:P of sinking particulate organic matter (POM) in the ocean twilight zone on average is likely to be higher than the C:P ratio of surface suspended POM. We further demonstrate using a physics‐biology coupled global ocean model combined with a theory from first principles that an increase in C:P export flux ratio in the ocean's twilight zone can lead to a considerable drawdown of atmosphericpCO₂. 

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4. Explicit Physical Knowledge in Machine Learning for Ocean Carbon Flux Reconstruction: The pCO ₂ ‐Residual Method

   https://doi.org/10.1029/2021MS002960  

   Bennington, Val; Galjanic, Tomislav; McKinley, Galen A. (October 2022, Journal of Advances in Modeling Earth Systems)
5. Upwelling‐level acidification and pH/ pCO₂ variability moderate effects of ocean acidification on brain gene expression in the temperate surfperch, Embiotoca jacksoni

   https://doi.org/10.1111/mec.16611  

   Toy, Jason A; Kroeker, Kristy J; Logan, Cheryl A; Takeshita, Yuichiro; Longo, Gary C; Bernardi, Giacomo (September 2022, Molecular Ecology)

   Acidification‐induced changes in neurological function have been documented in several tropical marine fishes. Here, we investigate whether similar patterns of neurological impacts are observed in a temperate Pacific fish that naturally experiences regular and often large shifts in environmental pH/pCO₂. In two laboratory experiments, we tested the effect of acidification, as well as pH/pCO₂variability, on gene expression in the brain tissue of a common temperate kelp forest/estuarine fish,Embiotoca jacksoni. Experiment 1 employed static pH treatments (target pH = 7.85/7.30), while Experiment 2 incorporated two variable treatments that oscillated around corresponding static treatments with the same mean (target pH = 7.85/7.70) in an eight‐day cycle (amplitude ± 0.15). We found that patterns of global gene expression differed across pH level treatments. Additionally, we identified differential expression of specific genes and enrichment of specific gene sets (GSEA) in comparisons of static pH treatments and in comparisons of static and variable pH treatments of the same mean pH. Importantly, we found that pH/pCO₂variability decreased the number of differentially expressed genes detected between high and low pH treatments, and that interindividual variability in gene expression was greater in variable treatments than static treatments. These results provide important confirmation of neurological impacts of acidification in a temperate fish species and, critically, that natural environmental variability may mediate the impacts of ocean acidification. 

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