A recent paper published in the Journal of Geophysical Research has shown a sudden decline in the uptake of carbon dioxide in the North Atlantic. Researchers Dr. Ute Schuster and Dr. Andrew Watson of the University of East Anglia analyzed almost a decade’s worth of data from merchant ships that frequently traverse the Atlantic. Using the data generated from automatic instruments on board, they discovered a dramatic decline in the uptake of carbon dioxide between the mid ‘90s and the early 2000s.
Historically, oceans have been the largest absorber— or sink—of carbon dioxide. Oceans and terrestrial ecosystems combined take in almost one half of total CO2 emissions, leaving the other half in the atmosphere.
Our oceans absorb almost one third of anthropogenic carbon dioxide emissions in two ways. The first is through the activity of phytoplankton flourishing in surface waters where sunlight is easily accessible. These gases are absorbed during photosynthesis and, once the phytoplankton die, carbon sinks into deeper parts of the ocean. Secondly, sea water can react with CO2 in the air, affected by differences in solubility within varying temperatures of water. The circulation of currents around the globe is an important aspect of this process. In the North Atlantic, where high salinity causes oceanic waters to sink, CO2 is more soluble and thus sinks along with the cold, create dense waters into deeper parts of the ocean.
The reasons for the North Atlantic’s decline in uptake are still unclear. It could be due to natural oscillations or global warming, but dire consequences may be seen if the oceans are indeed becoming “saturated”, as Schuster and Watson have suggested.
On the other side of the world, the Antarctic’s Southern Oceans have also seen a decline in CO2 uptake. Accounting for almost 15 per cent of the CO2 uptake by oceans and land combined, the effects of this decrease could produce some extreme results.
The Southern Oceans refer to a collective term within parts of the Indian, Atlantic, and Pacific oceans. Currently, they encompass approximately one-third less CO2 than expected. According to a paper published in Science, Dr. Corinne Le Quéré and her team found that the rate of atmospheric CO2 uptake has decreased by analyzing twenty-five years of data taken from stations all over the globe.
A possible explanation for this phenomenon may be increased temperatures that have led to the formation of intense winds over the surface of the waters. Normally, cool waters containing large amounts of dissolved CO2 would remain below the surface. However, these strong winds may churn up the water, causing the CO2-rich deep water to rise above. Since this water is already saturated with CO2, the end result is a decrease in uptake. If this is indeed the mechanism responsible for the decline, then this positive feedback cycle will cause the oceans to take in less and less CO2 over time.
The biological uptake by the oceans is also affected. When CO2 is dissolved in water, it forms bicarbonate, which causes it to become acidic. More acidic carbon-rich waters are mixed and left at the surface of the ocean, with the phytoplankton that reside near the surface unable to survive shifts in acidity.
This has profound implications for the rest of the earth. The saturation of ocean waters may be a sign that policies surrounding greenhouse gas emissions need to take into account anthropogenic aspects as well as the dynamic processes of the earth. If the problem is left unchecked, we may soon find ourselves in hot water—literally.
