## 5 Ocean-Based Climate Change Solutions Enhanced by DL
### Mitigation Strategies Using DL
#### 5.1.3. DL Applications in Ocean Carbon Sink  
Carbon sinks are natural or artificial reservoirs that absorb and store carbon from the atmosphere through physical and biological mechanisms. These sinks play a critical role in mitigating climate change by reducing the concentration of GHGs. Common examples of carbon sinks include forests, soils, and oceans. Forests capture carbon through photosynthesis, while soils store organic carbon from plant debris and biomass. Oceans, the largest carbon sink on Earth, have absorbed approximately \(25\pm 2\%\) of total human-induced CO\({}_{2}\) emissions from the early 1960s to the late 2010s [312; 313]. The oceans absorb CO\({}_{2}\) mainly through two mechanisms, including the physical and biological pumps. The physical pump dissolves CO\({}_{2}\) into surface waters, which are then transported to the deep ocean via large-scale circulation patterns. Specifically, when the partial pressure of CO\({}_{2}\) in seawater is lower than that in the atmosphere, CO\({}_{2}\) diffuses into the seawater and reacts with water to form carbonic acid and other derivatives. This process is more pronounced in cold, high-latitude regions since colder water can hold more CO\({}_{2}\) due to its higher solubility. As surface waters become cooler and denser, they sink, carrying the dissolved carbon into the deep ocean through thermohaline circulation. Once sequestered in the deep ocean, this carbon can remain trapped in cold, dense waters for hundreds to thousands of years, significantly contributing to long-term carbon storage. The biological pump, on the other hand, sequesters CO\({}_{2}\) through marine biological activity. Phytoplankton, the foundation of the oceanic food chain, use CO\({}_{2}\) for photosynthesis, producing organic carbon. This carbon is then transferred through the food chain to zooplankton and other marine organisms. When these organisms die, their remains sink to the ocean floor, depositing carbon in deep-sea sediments where it can be stored for long periods. In recent years, ocean fertilization has been explored as a geoengineering strategy to enhance the biological pump and increase the ocean's carbon storage capacity [314]. This technique involves adding nutrients, such as iron, nitrogen, or phosphorus, to the ocean's upper layers to stimulate phytoplankton growth and photosynthetic activity, thereby reducing atmospheric CO\({}_{2}\) levels. However, potential side effects, including harmful algal blooms, disruptions to fisheries, and ecological impacts, raise concerns. Further research and evaluation are necessary to fully understand the effectiveness and environmental risks of this approach. Researchers have employed various ML and DL techniques to process complex oceanic data, advancing our understanding of ocean carbon sinks and predicting their changes [315; 316; 317]. For example, the Southern Ocean, south of 35\({}^{\circ}\)S, is critical for studying oceanic carbon sinks, accounting for approximately 40% of the ocean's uptake of anthropogenic CO\({}_{2}\)[318]. However, the scarcity of in situ measurements in this region has posed challenges for accurately assessing changes in ocean carbon storage. To address this issue, [PERSON] et al. [297] applied a U-Net model combined with LSTM to estimate DIC concentrations down to 4 km depth in the Southern Ocean. Their model incorporated various