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Why Have Earth's Oceans Lost 2 Percent Of Their Oxygen?

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New research has found that oxygen concentrations on Earth's oceans continue to diminish, losing as much as 2 percent over a span of 50 years.

What caused this phenomenon is less surprising: scientists said oceans' oxygen loss may be a result of climate change, which now threatens marine organisms all around the world.

Quantifying The Ocean's Oxygen Loss

Oxygen is as vital for life in the water as it is for life on land. However, past studies have found that the world's oceans have been steadily warming for half a century.

The warming of waters threatens marine life in two ways. First, warmer waters on the surface absorb less oxygen than colder waters. This stabilizes ocean stratification — the formation of water layers based on temperature and salinity — and weakens the flow that connects surface water to the deep ocean. Thus, less oxygen is transported deep below.

"The oxygen supply to the deep ocean is shut down or significantly reduced," said oceanographer Sunke Schmidtko.

In May 2016, scientists from the National Center for Atmospheric Research suggested that the world's oceans are bound to lose much of their oxygen concentrations by 2030. However, researchers were unable to quantify just how much.

In a new study, however, Schmidtko and his fellow oceanographers from Germany's GEOMAR Helmholtz Centre for Ocean Research confirmed the theory. For the first time, they successfully quantified the extent of oxygen loss on oceans.

By using historic oxygen data and modern ocean observations, Schmidtko and his colleagues - Martin Visbeck and Lothar Stramma - managed to build a global model that revealed oxygen levels have dropped 2 percent over the last 50 years. The study attributes about 15 percent of ocean deoxygenation to warmer temperatures, while the rest was attributed to other factors, including lack of mixing.

Greatest Oxygen Loss

The oceanographers discovered that the greatest oxygen loss occurred in the North Pacific Ocean. Although the levels of ocean deoxygenation there are still non-critical, the phenomenon can have long-term consequences on marine life because of the uneven oxygen distribution.

While researchers point to consistent climate change model predictions as the cause for oxygen loss, natural processes that occur over time may also have contributed to the phenomenon.

Furthermore, the study revealed that higher levels of atmospheric carbon dioxide and increasing global temperatures may have a hand on what's happening.

Scientist Denis Gilbert, who wrote an accompanying piece to the study, said the findings should alert the world about the impact of global warming on the world's oceans.

The findings of the new research are published in the journal Nature.

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