It seemed to be simple: as people released more of carbon dioxide into the atmosphere through the burning of fossil fuels, the oceans were expected to absorb more of it. Approximately 30 percent of the carbon dioxide released into the atmosphere by human activities has found its way into the ocean through direct chemical exchange. This process involves the dissolution of carbon dioxide in the ocean, forming carbonic acid, which, in turn, elevates the acidity of the water. To put it differently, the ocean, which was slightly alkaline, has become slightly less alkaline. Since 1750, the pH of the ocean’s surface has experienced a decrease of 0.1, signifying a 30 percent change in acidity over this period. This shift in ocean chemistry is a consequence of human-induced carbon emissions and has implications for marine ecosystems and biodiversity. Importantly, ocean acidification reduces seawater buffering capacity, impeding the ocean’s ability to absorb carbon effectively. Paradoxically, this acts as a positive feedback mechanism, slowing down the oceanic carbon uptake, and increasing atmospheric CO2.
For oceanographers four decades ago, the primary concern was not how human emissions would alter the ocean carbon cycle, but rather, whether the ocean carbon cycle was already undergoing changes. This is an important question because if the ocean absorbs less carbon, there would be a higher concentration of carbon dioxide in the atmosphere, leading to increased global warming. Scientists needed to understand the changes in ocean carbon cycle to make accurate predictions about the trajectory of global warming. Motivated by this imperative, oceanographers initiated a series of research expeditions to collect data and insights into the evolving dynamics of the ocean carbon cycle. Concurrently, researchers on land have developed computer models for the same purpose. For example, The Surface Ocean CO2 Atlas (SOCAT) is a collaborative initiative driven by the community to measure the carbon absorption in the ocean and assess ocean acidification. The newest SOCAT version (Figure 1) contains 35.6 million observations spanning from 1957 to 2022 for global oceans and coastal seas. It includes 7.2 million calibrated sensor observations, providing a valuable dataset for studying surface ocean carbon dioxide concentrations.
The ocean surface CO2 data is necessary for human-led and engineered efforts to accelerate marine Carbon Dioxide Removal (mCDR) through Ocean Alkalinity Enhancement (OAE) approaches. OAE involves a strategy to mitigate climate change by leveraging the oceans’ natural processes. By enhancing the alkalinity of seawater through the addition of certain compounds, such as crushed minerals, the ocean’s capacity to absorb and store carbon dioxide is increased. This method aims to promote chemical reactions that convert carbon dioxide into dissolved bicarbonate ions, reducing its presence in the atmosphere. While still in the experimental stage, OAE holds promise as a potential tool for addressing the impacts of excessive carbon dioxide emissions on the climate. However, it requires careful consideration of environmental and ecological consequences before large-scale implementation.
Figure 1. Surface Ocean CO2 from ships, drifters and autonomous surface platforms and moorings for all data in SOCAT version 2023. (Credit: SOCAT Data Viewer)
In conclusion, the ongoing evolution of the carbon cycle, exacerbated by human-induced activities, underscores the critical need for advanced engineering of sensors and comprehensive ocean observation systems. As we face escalating challenges in climate change, these technological advancements play a pivotal role in monitoring, understanding, and mitigating the impacts of carbon emissions on our environment. Furthermore, these observations are essential for informing innovative strategies like Ocean Alkalinity Enhancement (OAE) for Carbon Dioxide Removal (CDR). By leveraging engineering solutions, oceanographers, researchers, and policymakers can work collectively to safeguard the delicate balance of the carbon cycle, ultimately contributing to the preservation of our planet and the mitigation of global warming.
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