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• The accelerated pace of natural and human-driven climate change presents profound challenges for Earth’s systems. Oceans and ice sheets are critical regulators of climate systems, functioning as carbon sinks and thermal reservoirs. However, they are increasingly vulnerable to warming and greenhouse gas emissions. Understanding the interrelations among oceanic carbon dynamics, ice sheet stability, and feedback mechanisms is essential for effective climate action. There are three primary carbon pumps in the global ocean that regulate carbon exchange. The solubility pump (physicochemical carbon pump) is controlled by Henry’s Law and the temperature-dependent solubility of CO₂ in seawater. The biological pump is driven by the transformation of dissolved CO₂ into organic carbon via photosynthesis, followed by its sequestration in deep-sea reservoirs. The carbonate pump involves the precipitation and dissolution of calcium carbonate (CaCO₃), affecting ocean alkalinity and carbon storage. Recent studies [1–3] suggest that climate change is altering the efficiency and balance of these carbon pumps through rising ocean temperatures, increased acidification, and ice sheet destabilization. We evaluate these findings from a chemical perspective, focusing on reaction kinetics, equilibrium shifts, and biogeochemical feedback loops that govern oceanic carbon sequestration.

  For the solubility pump (the role of temperature and CO₂ solubility), Ford et al. [1] demonstrate that near-surface temperature gradients significantly enhance CO₂ uptake, a process governed by Henry’s Law:

  $ C_{\mathrm{CO}_2}=k \cdot P_{\mathrm{CO}_2} $

  where C_co2 is the dissolved CO₂ concentration, k is the Henry’s Law constant (which decreases with temperature), ​P_co2 is the partial pressure of CO₂ in the atmosphere. The dissolution of CO₂ in seawater follows:

  $ \mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_2 \mathrm{CO}_3 \rightleftharpoons \mathrm{H}^{+}+\mathrm{HCO}_3^{-} \rightleftharpoons 2 \mathrm{H}^{+}+\mathrm{CO}_3^{2-} $

  A cooler near-surface layer favors CO₂ dissolution, shifting the equilibrium toward bicarbonate (HCO₃⁻) formation. This has implications for ocean acidification and carbonate compensation depth variations. As sea surface temperatures rise, CO₂ solubility decreases, reducing oceanic carbon uptake. However, Ford et al. [1] show that vertical temperature gradients create micro-scale regions where cooler surface layers enhance CO₂ solubility, contradicting conventional bulk estimates. This effect leads to an underestimation of global oceanic CO₂ uptake by 7% in the Atlantic and possibly 10%−31% globally. It reveals the underestimated role of near-surface temperature gradients in enhancing global CO₂ uptake (physical gas exchange carbon pump), challenging the conventional understanding of oceanic CO₂ uptake, emphasizing the role of near-surface temperature gradients in air-sea gas exchange. Incorporating micro-scale processes into broader oceanographic studies is meaningful for improving global carbon budget estimates.

  For the biological pump, Koeve et al. [2] uncover the dominance of the biological carbon pump as a carbon sink under net-negative CO₂ emissions, focusing on the biological carbon pump’s resilience during temperature overshoot scenarios. Biological carbon storage is closely tied to changes in upper-ocean stratification and vertical density gradients. These factors isolate organic carbon in the ocean interior, delaying outgassing to the atmosphere. While solubility-driven CO₂ uptake (physical pump) decreases during temperature overshoots, the biological pump continues sequestering carbon over multi-centennial timescales. Increased ocean stratification enhances organic matter degradation and CO₂ storage in deep waters, enhancing the biological pump’s efficacy. The biological pump retains CO₂ storage capacity even as physical processes weaken, ensuring oceanic sequestration during prolonged overshoot periods. The resilience of the biological pump under net-negative CO₂ emissions shows that organic carbon sequestration persists for centuries even as atmospheric CO₂ declines as being caused by thermally enhanced stratification reducing deep-ocean ventilation and increased organic matter remineralization at depth, preventing CO₂ from reentering the atmosphere. Therefore, maintaining biological pump efficiency requires policies that reduce nutrient runoff and deep-sea disturbance.

  The carbonate pump regulates ocean alkalinity through calcium carbonate formation and dissolution:

  $ \mathrm{Ca}^{2+}+2 \mathrm{HCO}_3^{-} \rightleftharpoons \mathrm{CaCO}_3+\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} $

  Under increasing ocean acidification, this reaction shifts left, reducing CaCO₃ deposition, increasing carbonate dissolution, and further lowering pH. Hill et al. [3] identify a direct chemical feedback between melting ice sheets and oceanic carbon cycling. Freshwater influx from melting ice dilutes ocean alkalinity, lowering carbonate saturation states. Iron-rich sediment exposure from ice sheet retreat stimulates phytoplankton blooms, which increase biological CO₂ drawdown but may also promote localized deoxygenation. It suggests that ice sheet stability is chemically linked to oceanic carbon sequestration efficiency, reinforcing the need for integrated climate-carbon models.

  While the solubility pump, biological pump, and carbonate pump are well-established components of the marine carbon cycle, recent advances suggest the need to revisit their interactions under climate change. The solubility and carbonate pumps are chemically integrated through temperature-dependent CO₂ solubility, carbonate equilibria, and buffering capacity. Ford et al. [1] demonstrate that micro-scale vertical temperature gradients near the sea surface significantly enhance CO₂ uptake by increasing solubility locally, refining classical solubility pump estimates and revealing an underappreciated interface with carbonate chemistry. Meanwhile, Koeve et al. [2] show that during temperature overshoot and net-negative CO₂ emission phases, the biological pump becomes the dominant mechanism for long-term carbon retention, as enhanced ocean stratification slows deep water ventilation, promoting organic matter remineralization and deep-sea carbon storage. This highlights a temporal decoupling. As the solubility and carbonate pumps weaken or reverse, the biological pump continues to sequester carbon on centennial timescales. Additionally, Hill et al. [3] demonstrate that ice sheet meltwater alters carbonate saturation and supplies bioavailable iron, indirectly stimulating phytoplankton blooms and enhancing the biological pump. These findings underscore the importance of viewing the ocean carbon system not as three isolated pumps but as a chemically and physically integrated network that evolves dynamically under climate stressors. We plot the following diagram to illustrate these relationships (Fig. 1).

  Figure 1

  

  Figure 1.  A chemical framework for the solubility, carbonate, and biological pumps.

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  In summary, we integrate recent research through a chemical framework, demonstrating that temperature-dependent solubility, biogeochemical stratification, and acidification feedbacks significantly influence global carbon sequestration. Temperature gradients in CO₂ uptake must be integrated into global carbon models. Biological pump resilience must be preserved through sustainable ocean management. Preventing Antarctic ice melt is crucial for maintaining carbonate pump stability. Addressing these processes within climate models is critical for accurate projections and effective mitigation strategies. By integrating chemical perspectives into climate action, policymakers can refine carbon sink efficiency and develop sustainable approaches to climate resilience and global futures.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Dongping Song: Writing – original draft, Investigation. Tao Tu: Writing – review & editing.

  
  
• 1. [1]

     D.J. Ford, J.D. Shutler, J. Blanco-Sacristán, et al., Nat. Geosci. 17 (2024) 1135–1140. doi: 10.1038/s41561-024-01570-7

  2. [2]

     W. Koeve, A. Landolfi, A. Oschlies, I. Frenger, Nature Geosci. 17 (2024) 1093–1099. doi: 10.1038/s41561-024-01541-y

  3. [3]

     E.A. Hill, G.H. Gudmundsson, D.M. Chandler, Nat. Clim. Change 14 (2024) 1165–1171. doi: 10.1038/s41558-024-02134-8

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  Figure 1  A chemical framework for the solubility, carbonate, and biological pumps.

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