Global warming modifies the circulation patterns of the oceans and contributes to the loss of oxygen in the water, although current research models are not able to detect this phenomenon accurately, according to a study published today in the journal Nature.
Numerous works have shown in recent years that the oceans have lost 2% of their oxygen over the past five decades. Computer models also found that trend and predicted, in addition, that their level will continue to fall. However, the models have their limitations.
“They are not able to reproduce the recent decrease in oxygen exactly, on the contrary, they significantly underestimate the observed oxygen loss”, explains one of the authors of the study, Andreas Oschlies, from the GEOMAR Helmholtz Ocean Research Center in Kiel (Germany).
Consequently, future predictions are “problematic,” warn the experts, whose study shows the shortcomings of the models and, at the same time, identifies causes of deoxygenation ignored so far.
“The comparisons with our data show that there are several deficiencies in the models and they offer us clues as to the direction in which we should concentrate our research efforts,” another author, Peter Brandt, adds in a statement.
One of the main causes of deoxygenation in the oceans, remember, is global warming, which modifies the solubility of oxygen in water, because it absorbs less gas the higher the temperature rises.
This process affects, above all, the upper levels of the sea, “those that are in direct contact with the atmosphere”, and is responsible for up to 20% of the total loss of oxygen, as confirmed by current models, the researchers point out .
The warming also alters the circulation patterns of the oceans, since the complex system of surface and deep currents that supply oxygen to the seabed can affect the content of that gas globally.
“Many models have problems describing this effect in real terms because transport processes are often reproduced incorrectly,” says GEOMAR expert Lothar Stramma.
Likewise, they insist, the aforementioned models fail to represent the “extreme complexity” of the interactions between the “biological, chemical and physical” processes that intervene in deoxygenation.
To address these shortcomings, the authors stress the need to conduct “multidisciplinary process studies” to better understand the “delicate balance between oxygenation and oxygen consumption in the ocean.”
“International initiatives such as the Global Oxygen Network are very helpful,” says Oschlies, who adds that the improvement of current research models also has “another great advantage”.
Oxygen, he concludes, is “ideal” to “calibrate models that calculate the absorption of carbon dioxide by the oceans,” which “would increase our knowledge about the carbon cycle.”