The IDTechEx report “Carbon Dioxide Removal (CDR) 2024-2044” highlights three promising ocean-based carbon removal methods: ocean alkalinity enhancement, direct ocean capture, and seaweed sinking. These technologies offer significant potential for mitigating climate change by enhancing the ocean's natural CO2 absorption capabilities.

Every year, our oceans absorb 11-15 gigatonnes of CO2 as part of the Earth's natural carbon cycle. Despite its critical role in reducing climate change, the ocean's potential as a carbon sink still needs to be explored. Modern negative emission technologies are looking for ways to improve this natural process in an era of rising global temperatures. 

The most recent IDTechEx report, in assessing various methods for removing carbon dioxide, "Carbon Dioxide Removal (CDR) 2024-2044: Technologies, Players, Carbon Credit Markets, and Forecasts," highlights three promising ocean-based techniques: seaweed sinking, direct ocean capture, and ocean alkalinity enhancement.

Fighting Ocean Acidification with Ocean Alkalinity Enhancement (OAE)

Because of the increase in ocean acidity brought on by human-caused CO2 emissions over the past century, the concept of adding extra CO2 to the ocean may initially generate concerns. Ocean-based negative emission technologies must therefore refrain from accelerating this acidification.

Now for the enhancement of ocean alkalinity (OAE). Removing carbon dioxide boosts the ocean's ability to buffer CO2 by lowering its acidity and increasing seawater's alkalinity. By altering carbonate chemistry's balance, OAE promotes increased oceanic absorption of atmospheric CO2. Minerals like olivine or brine made electrochemically are sources of alkalinity.

OAE technologies are being developed by startups like Vesta, Planetary, and Vycarb, who are also undertaking field research. This method has eliminated hundreds of tonnes of CO2 so far. Effective alkaline material extraction and distribution are essential for OAE's future development. Before this technology is widely used, it is essential to ensure its security and benefit for ocean ecosystems.

Simpler and More Efficient: The Rise of Direct Ocean Capture (DOC)

Although investors and the media have focused a lot of emphasis on direct air capture due to its potential for large-scale carbon dioxide removal, CO2 removal from the ocean uses less energy than directly capturing carbon dioxide from ambient air. This is a result of the ocean's 100 times higher CO2 content than the atmosphere. Consequently, there has been an increase in players attempting to validate direct ocean capture (DOC). Technologies including calcium looping (created by CarbonBlue), electrodialysis (developed by Captura and SeaO2), electrolysis (developed by Equatic - green H2 is also generated using this approach), and photochemical addresses (developed by Banyu Carbon) are being investigated for commercialisation.

In the startup sector, Equatic is building a commercial DOC demonstration plant in Singapore with a capacity of 3,500 tpa (tonnes per annum of CO2). In a similar vein, Captura plans to establish a 1000 tpa pilot in Norway by the end of 2024. It took direct air capture pioneers about ten years to reach the kiloton per annum scale; if successful, direct ocean capture players will have done so in less than three years.

Players that engage in direct ocean capture are moving quickly; a number of them have stated that they hope to attain a megaton per year rate. Accelerating scale-up can be helped by already-existing water infrastructure, such as desalination facilities. By 2044, direct ocean capture technologies are expected to remove 40 million tonnes per year, according to IDTechEx forecasts.

Benefiting Communities with Seaweed Sinking

An easier but still promising technique for removing carbon dioxide from the water is seaweed sinking. The idea behind seaweed sinking is straightforward: grow seaweed, which absorbs carbon dioxide as it develops, and then sink it to the ocean floor to store carbon dioxide for extended periods of time. Although deep-sea food network disturbance has concerned scientists, there are some circumstances in which the advantages to the ecology are clear.

Every spring and summer since 2011, a huge seaweed nuisance bloom has formed in the middle Atlantic Ocean. The Great Atlantic Sargassum Belt is a result of intensive farming practices that release nitrogen and phosphorus fertilisers into rivers, together with an increase in world temperatures. Communities in the Caribbean and West Africa are badly impacted by the Sargassum Belt, particularly those whose economies depend on tourism, because of the stench, the insects it attracts, and the sheer amount of it that accumulates on beaches. Previous years have seen the US Virgin Islands declare a state of emergency and Guadeloupe issue a health advisory due to the nuisance bloom. Reefs and mangroves are infected by the Sargassum Belt, which fills up ecosystems and stops animals from breathing.

It seems obvious that Caribbean communities may gain a great deal from sinking invading seaweed before it reaches the coast and sequestering carbon dioxide in the process. This strategy is being developed by startups including Pull to Refresh, Seafields, and Seaweed Generation.

Navigating Challenges and Future Prospects

Ocean-based methods of removing carbon dioxide have limitations in terms of logistics and regulations, despite their potential. Regulations and laws controlling maritime areas frequently prohibit actions seen to be "dumping," which makes the implementation of technology such as ocean alkalinity enhancement more difficult. Furthermore, it is challenging to anticipate and lessen such unforeseen impacts due to the complexity of ocean ecosystems.

The business model for these technologies also remains a key question. As nascent technologies, they are not yet integrated into governmental climate strategies. Their growth will depend heavily on private sector investment, especially through the voluntary carbon market's purchase of carbon removal credits. The voluntary market had remarkable success in 2023, selling billions of dollars worth of long-lasting, designed removals, including technologies based on the ocean. However, gaining meaningful scale will require integrating these techniques into compliance marketplaces.

For more detailed information about the IDTechEx report “Carbon Dioxide Removal (CDR) 2024-2044: Technologies, Players, Carbon Credit Markets, and Forecasts,” including sample pages for download, visit [IDTechEx's official website]( 

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