Switzerland – A new study published in the Science Magazine showed the Southern Ocean works like a giant lung, for it absorbs vast amounts of carbon dioxide (CO2) from the atmosphere and then releases some of it back later in the year. It helps reduce a large part, around 40%, of CO2 that the human activities emit.

Scientists assumed that the higher the level of CO2 in the atmosphere, the higher the amount absorbed by the ocean. Since 2005, they had believed the Southern Ocean’s ability to absorb CO2 came to a limit, since some studies suggested the amount of carbon absorbed had not increased since 1980. In fact, they said the ocean had reduced its ability to absorb carbon dioxide by 30%.

Two Cape Petrels taking off from the sea in the Southern Ocean, near Elephant Island, South Shetland Islands, Antarctica. (Wikipedia)

However, the new research proves scientists were wrong. The absorption has become stronger since 2002 and by 2010 the ocean’s uptake was comparable to the level expected with the increase of CO2 in the atmosphere.

Lead author Nicolas Gruber, professor of environmental physics at ETH Zurich, explained in the study that the Southern Ocean carbon uptake decrease in periodic cycles, without depending on the amount of CO2 present  in the atmosphere. “We were surprised to see such large variations in this ocean’s net carbon uptake,” he said.

According to Gruber, a strong carbon sink in the Southern Ocean helps to mitigate climate change, although researchers are not sure if the uptake showed in the study will continue to increase or not. The effect seems to be temporary.

What causes these variations?

Since the creation of the world, it is known that the atmospheric pressure systems varies according to the place. Above the Atlantic sector, where the Southern Ocean is located, there is a powerful high pressure system, whereas a low pressure system has formed over the Pacific area.

The air pressure has caused wind patterns to change. While in 1990 winds tend to blow straight from the west to east, they now blow in an undulated pattern. Fifteen years ago these winds were also stronger over the Southern Ocean, which made the water “upwell” to the surface from depth.

Upwelling is the process in which deep, cold and usually nutrient-rich water rises toward the surface. These deeper waters contain higher concentrations of dissolved CO2, so when they rise, they released this gas into the atmosphere,  causing a decrease in the ocean’s net carbon uptake.

Is it really helpful?

There is another ongoing debate about how the acidity of the water, caused by the increase of CO2 levels present in it, could negatively affect sea animals in the ocean. For example, crabs, lobsters and mussels may have difficulties to grow their shelters, becoming vulnerable to predators.

There is still further investigation to make on this matter, although some scientists have already stated that this should not be a major concern.

“This announcement is good news, on the face of it, because we want this enormous carbon sink to keep working efficiently. It is not any reason to be complacent, however, because we still understand rather little about the internal workings of the Southern Ocean carbon cycle. For this reason we cannot be sure how resilient the Southern Ocean carbon sink will be in the future,” said Toby Tyrrell, professor in earth system science in ocean and earth science at the University of Southampton

Source: Science Magazine