Researchers at the Helmholtz Centre for Ocean Research Kiel have found that oxygen concentrations in the Earth’s oceans have dropped as much as two percent over the last half-century, according to a recent paper published in the journal Nature.
This decrease is yet another shift caused by the climate change that is affecting marine organisms all over the world. It is problematic because, while most aquatic animals live underwater, they still need oxygen to survive.
Ocean temperatures have been steadily rising over the past 50 years. This is concerning to scientists because warmer waters absorb much less oxygen than cold ones. As a result, climate change stabilizes ocean stratification — the process by which water layers form based on temperature and salinity — and weakens the flow that connects surface water to the deep ocean. Without that flow, less oxygen is transferred underwater.
Though past studies have shown that oceans will likely lose most of their oxygen concentrations by 2030, nobody has been able to quantify just how much will disappear. To help with that problem, the team used past oxygen data and modern ocean observations to build a global model that showed oxygen levels have dropped two percent over the last 50 years.
“To quantify trends for the entire ocean…was more difficult since oxygen data from remote regions and the deep ocean is sparse,” said lead author Dr. Schmidtko, an oceanographer at Helmholtz Centre for Ocean Research, in a statement. “We were able to document the oxygen distribution and its changes for the entire ocean for the first time. These numbers are an essential prerequisite for improving forecasts for the ocean of the future.”
The team says that roughly 15 percent of ocean deoxygenation is the result of rising temperatures. The rest is caused by other factors, such as a lack of mixing. While the phenomenon is present all over the world, the largest decreases are happening in the North Pacific Ocean.
While current deoxygenation levels are still non-critical, the phenomenon does have long-term consequences. Uneven oxygen distribution negatively affects marine life and can seriously impact certain species, Tech Times reports.
However, though consistent climate change is likely the cause of oxygen loss, natural processes may also have contributed to the changes noted in the research.
“[W]ith measurements alone, we cannot explain all the causes,” added Professor Martin Visbeck, a researcher at the Helmholtz Centre for Ocean Research Kiel. “Natural processes occurring on timescales of a few decades may also have contributed to the observed decrease.”
The results of the study are consistent with most model calculations. Further decrease in oceanic oxygen levels is likely, especially as atmospheric carbon dioxide concentrations and global temperatures continue to rise.