For the first time, a team of researchers quantified global ocean oxygen content. In their study published in the Nature journal, Kiel, Germany researchers have found that less oxygen is present in the surface waters as well as in the deep sea.
The research team blames the current global change that causes an increase in ocean temperatures and alterations in the circulation of the ocean. This poses a significant threat to all living things in the ocean.
The researchers explain that warmer waters take up less oxygen compared to colder waters. This also stabilizes the ocean’s stratification, weakening the ocean circulation and transportation of oxygen into the deep sea.
Overall, the researchers from the GEOMAR Helmholtz Centre for Ocean Research Kiel, which includes oceanographers Dr. Sunke Schmidtko, Dr. Lothar Stramma and Prof. Dr. Martin Visbeck, found out that the global oceans has experienced more than two percent reduction of oxygen in the last 50 years. According to the study lead author Dr. Schmidtko, this will affect marine life, especially large fishes who do not easily survive in places with very low oxygen.
“While the slight decrease of oxygen in the atmosphere is currently considered non-critical, the oxygen losses in the ocean can have far-reaching consequences because of the uneven distribution. For fisheries and coastal economies this process may have detrimental consequences,” points out the study co-researcher Stramma.
The study involved utilizing all historic oxygen data available. They also observed that previous research has already shown that global ocean oxygen content has decreased.
“To quantify trends for the entire ocean, however, was more difficult since oxygen data from remote regions and the deep ocean is sparse,” states the lead author, “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 researchers also found out that during their study, the oxygen levels have also dropped. Although they cannot pinpoint all the causes for this, the researchers blame high carbon dioxide levels in the atmosphere as well as warmer global temperatures.
The researchers say that the findings contribute to the better understanding of the interaction between the climate and ocean’s biogeochemistry. They will also study tropical oxygen in the eastern Pacific off Peru. They hope to increase their data that will help them understand global trends on ocean oxygen levels.