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Ocean uptake of carbon likely to decrease by the year 2100

Dr. Megumi Chikamoto is an oceanographer and research scientist in the Plant, Soils and Climate department at USU who uses modeling to answer questions about the world’s oceans and climate.

Chikamoto’s recent study found that oceans will be able to uptake significantly less CO2 by the year 2100. The study simulated ocean responses to increasing atmospheric CO2, based on a number of things, including rainfall and CO2 levels recorded from 1850-2005. This particular simulation looked at the worst case scenario of increasing CO2 in the next several centuries.

“This is a very complicated system we have because basically, if atmospheric CO2 is increased compared to the ocean's CO2 levels, it's like an input from the high CO2 level from the atmosphere to the ocean-like input,” said Chikamoto.

Oceans play an essential role in carbon cycling by taking up atmospheric CO2. This is particularly important in limiting global warming, providing a buffer to rising levels of CO2. The oceans are able to uptake some of that increasing CO2, mildly alleviating climate change.

The ability of an ocean to do this is largely dependent on water temperatures. Warmer waters have lower alkalinity, which affects the ability water has to dissolve CO2. With an increase in global temperatures come increases in ocean temperatures, particularly on the surface layer. Those rising water temperatures affect the chemistry of oceans, making carbon uptake from atmospheric CO2 more difficult. Chikamoto and colleagues found that ocean uptake of CO2 will become particularly critical by the year 2100.

Furthermore, the study found that certain regions are likely to be impacted more than others due to water dynamics and ocean currents. The North Atlantic is often the focus of study in regard to carbon uptake, as water moves from the North Atlantic to deeper waters, with higher alkalinity. These deep, colder, alkaline waters can uptake more CO2. Simulations found that the North Atlantic in particular will not be able to uptake CO2 by 2100.

“So currently, the most research focuses on the North Atlantic, because this region is a main uptake region of CO2 compared to the global oceans. However, our research finds the North Atlantic becomes more stronger and no longer uptakes CO2 after 2100,” Chikamoto explained.

While this study stimulated warming temperatures and increasing CO2, it did not address other factors, such as ice melt, due to rising temperatures. Chikamoto emphasized the complexity of earth’s systems and that other things are likely to impact carbon uptake by causing changes to ocean chemistry.

The team hopes to continue this research, exploring further factors that may influence the uptake of carbon.

The article is called Long-Term Slowdown of Ocean Carbon Uptake by Alkalinity Dynamics.

Erin Lewis is a science reporter at Utah Public Radio and a PhD Candidate in the biology department at Utah State University. She is passionate about fostering curiosity and communicating science to the public. At USU she studies how anthropogenic disturbances are impacting wildlife, particularly the effects of tourism-induced dietary shifts in endangered Bahamian Rock Iguana populations. In her free time she enjoys reading, painting and getting outside with her dog, Hazel.