Oceans serve as significant carbon sinks, absorbing substantial amounts of carbon dioxide ($CO_2$) from the atmosphere through both physical and biological processes.

The world’s oceans are among the largest carbon sinks, meaning they absorb and store more carbon dioxide than they release. This phenomenon occurs primarily through two main mechanisms: physical absorption and biological uptake.

Physical absorption involves the straightforward process of carbon dioxide from the atmosphere dissolving into the ocean’s surface waters. This process is driven by the concentration gradient between the atmosphere and the ocean’s surface. When the concentration of carbon dioxide is higher in the atmosphere than in the ocean, the gas naturally diffuses from the area of higher concentration (the atmosphere) to the area of lower concentration (the ocean).

Biological uptake, in contrast, is mediated by marine organisms. Phytoplankton, which are tiny plant-like organisms residing in the upper layers of the ocean, absorb carbon dioxide for the process of photosynthesis. When these organisms die, they sink to the ocean floor, effectively trapping the carbon in the deep sea. This process is often referred to as the “biological pump.”

Although the carbon stored in the ocean does not remain there indefinitely, as some of it is eventually released back into the atmosphere through a process known as “outgassing.” Nevertheless, at present, the amount of carbon dioxide absorbed by the oceans exceeds the amount released, allowing the oceans to function as a net carbon sink.

It is crucial to recognize that the oceans’ capacity to absorb carbon dioxide is influenced by various factors, including temperature, salinity, and the availability of certain nutrients. Changes in these factors, potentially driven by human activities, could significantly impact the oceans’ ability to act as carbon sinks in the future.