Unlocking the Ocean's Potential for Large-Scale Carbon Removal: A Rigorous Exploration

As the world faces the intensifying challenge of climate change, the pursuit of effective carbon dioxide removal (CDR) strategies has accelerated. Among the innovative approaches, Ocean CDR has emerged as a promising avenue due to the ocean's central role in the Earth's carbon cycle and its expansive potential for scalability. Oceans, covering over 70% of the Earth's surface, are critical in absorbing and storing carbon dioxide (CO2) from the atmosphere, which has been instrumental in mitigating the effects of anthropogenic CO2 emissions. However, as atmospheric CO2 levels surge, the ocean's natural carbon sequestration capacity is under increasing pressure. Ocean CDR methodologies are being developed to enhance the ocean's ability to sequester and store carbon on a large scale, presenting a viable solution to combat climate change.

The Role of Oceans in the Global Carbon Cycle

The oceans play a pivotal role in the global carbon cycle, acting as a vast reservoir for carbon sequestration. Through natural processes such as the biological pump and the solubility pump, oceans have historically absorbed approximately one-third of anthropogenic CO2 emissions (Sabine et al., 2004). The biological pump involves the absorption of CO2 by phytoplankton through photosynthesis, with a portion of the carbon eventually sinking into the deep ocean, where it can be stored for centuries. On the other hand, the solubility pump is driven by the physical absorption of CO2 into the sea, where it reacts with water to form bicarbonate and carbonate ions, effectively sequestering carbon.

However, the oceans' capacity to continue functioning as an efficient carbon sink is under threat. Rising atmospheric CO2 levels lead to ocean acidification, which reduces the ocean's ability to absorb CO2 and negatively impacts marine ecosystems (Doney et al. 2009). Consequently, there is an urgent need to explore and develop methodologies to enhance the ocean's natural carbon sequestration capabilities, thereby contributing to global efforts to mitigate climate change.

Emerging Ocean CDR Methodologies

Ocean CDR encompasses a range of methods designed to enhance the ocean's capacity to absorb and store CO2. These methods vary in approach, potential impact, and technological maturity, but all share the goal of leveraging the ocean's vastness and natural carbon cycle to remove CO2 from the atmosphere.

1. Ocean Storage of Biomass (OSB): This method utilises photosynthesis as the primary mechanism for CO2 capture, with the captured CO2 being stored in a stabilised form in the ocean, typically in anoxic basins or deep-sea environments with suitable conditions. OSB has the potential for large-scale implementation due to its ability to utilise existing infrastructure and its promise of long-term carbon storage, where organic matter can be preserved for centuries or even millennia (Smith et al. 2021).
2. Electrochemical Methods: Electrochemical ocean CDR (EO-CDR) involves reactor-based processes that permanently sequester CO2 as bicarbonates and solid mineral carbonates. This method is notable for its potential precision, as the closed reactor environment allows for more straightforward measurement and reporting of carbon sequestration metrics. EO-CDR is still in the experimental stage, but its ability to sequester CO2 in a permanent and quantifiable form makes it a promising candidate for large-scale deployment (Rau et al. 2018).
3. Ocean Alkalinity Enhancement: This method increases the alkalinity of seawater by adding alkaline substances, thereby enhancing its capacity to absorb and store CO2 from the atmosphere. By promoting the conversion of CO2 into bicarbonate and carbonate ions, ocean alkalinity enhancement can provide long-term carbon storage and mitigate the effects of ocean acidification. However, the ecological impacts of large-scale alkalinity enhancement remain a topic of ongoing research (Feng et al. 2017).
4. Blue Carbon: This approach focuses on the conservation and restoration of coastal ecosystems, such as mangroves, seagrasses, and salt marshes, which are highly efficient at sequestering and storing carbon. These ecosystems act as significant carbon sinks and provide co-benefits such as biodiversity conservation, coastal protection, and support for local livelihoods (Nellemann et al. 2009). Blue carbon is an established method with proven efficacy, but its scalability is limited to coastal regions.
5. Ocean Fertilisation: Ocean fertilisation involves the addition of nutrients, such as iron, to the ocean to stimulate phytoplankton growth, which in turn absorbs CO2 through photosynthesis. While ocean fertilisation has the potential to enhance the ocean's carbon sink, concerns about its potential negative ecological impacts, such as harmful algal blooms and disruptions to marine food webs, have led to cautious exploration of this method (Buesseler et al. 2008).

The Need for Standardised Methodologies

As Ocean CDR methodologies continue to develop, there is a pressing need for standardised protocols to ensure carbon removal quantification and operations' safety. The lack of standardised methodologies challenges the credibility and scalability of these approaches, as stakeholders require robust and transparent metrics to assess their effectiveness and environmental impact.

One organisation in charge of this area is Puro, which specialises in carbon removal certification. Puro is actively working to develop comprehensive methodologies for emerging Ocean CDR methods, including OSB and EO-CDR. By establishing standardised protocols, Puro aims to provide a framework for monitoring, reporting, and verifying the climate impact of these methods, thereby facilitating their adoption at scale (Puro.earth 2023).

Investment and Commercial Viability

The potential of Ocean CDR is becoming increasingly apparent, attracting significant investment from both private and public sectors. In 2023, Ocean CDR companies secured over $200 million in funding, with major investors including Lowercarbon Capital, Counteract, Carbon Removal Partners, and the U.S. Department of Energy (ClimateTech VC, 2023). This influx of capital is driving research and development efforts, pilot projects, and early-stage deployments to advance Ocean CDR technologies toward commercial viability.

Investor support is crucial to bridging the gap between experimental research and large-scale implementation. However, the success of Ocean CDR will depend not only on technological advancements but also on establishing clear regulatory frameworks, public acceptance, and the development of a carbon market that values and incentivises carbon removal.

Conclusion

Ocean CDR represents a promising avenue for large-scale carbon removal as the world seeks practical solutions to combat climate change. By leveraging the ocean's natural carbon cycle, these methodologies have the potential to make a significant impact in reducing atmospheric CO2 levels. However, to realise this potential, it is essential to develop standardised methodologies that ensure Ocean CDR approaches' effectiveness, safety, and scalability. The ongoing efforts by organisations like Puro to establish robust protocols and the growing investment in the sector are positive steps toward unlocking the ocean's potential for carbon removal. Ocean CDR could play a vital role in achieving global climate goals with continued innovation and collaboration.

References

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Doney SC, Fabry VJ, Feely RA and Kleypas JA (2009) "Ocean Acidification: The Other CO2 Problem."?Annual Review of Marine Science, 1(1), pp.169-192.

Feng EY, Koeve W, Keller DP, Oschlies A and Rickels W (2017) "Could artificial ocean alkalinisation protect tropical coral ecosystems from ocean acidification?"?Environmental Research Letters, 12(3), pp.034009.

Nellemann C, Corcoran E, Duarte CM, Valdés L, De Young C, Fonseca L and Grimsditch, G. (eds) (2009)?Blue Carbon: A Rapid Response Assessment. United Nations Environment Programme, GRID-Arendal.

Puro. Earth (2023)?Puro is helping to pave the way for Ocean CDR. [online] Available at:?https://www.puro.earth/ocean-cdr ?[Accessed 1 Aug. 2024].

Rau GH, Carroll SA and Bourcier WL (2018) "Electrochemical CO2 Capture and Sequestration by Reacting with Dissolved Minerals in Seawater."?Environmental Science & Technology, 52(3), pp.1963-1971.

Sabine CL, Feely RA, Gruber N, Key RM, Lee K, Bullister JL, Wanninkhof R, Wong CS, Wallace DW and Tilbrook B (2004) "The oceanic sink for anthropogenic CO2."?Science, 305(5682), pp.367-371.

Smith P, Haszeldine RS, Smith SM and Haszeldine RS (2021) "Ocean-based Carbon Dioxide Removal: Getting the Balance Right."?Frontiers in Climate, 3, pp.659366.