Oxygen concentrations in bodies of water worldwide are decreasing at an alarming rate. This loss of oxygen, known as aquatic deoxygenation, seriously threatens ecosystems, livelihoods, and the entire planet. A new international study published in Nature Ecology & Evolution calls for recognizing aquatic deoxygenation as a planetary boundary.
Planetary boundaries are global-scale processes that regulate the Earth’s habitability and stability. When critical thresholds in these processes are crossed, the risk of large-scale, abrupt, or irreversible environmental changes increases. The study involved researchers from various institutions, including GEOMAR Helmholtz Centre for Ocean Research Kiel.
The lead author, Professor Dr. Rose from Rensselaer Polytechnic Institute in Troy, New York, emphasized the importance of adding aquatic deoxygenation to the list of planetary boundaries to support global monitoring, research, and policy efforts. Dissolved oxygen concentrations have declined sharply in recent decades across various aquatic ecosystems.
Since 1980, lakes and reservoirs have experienced oxygen losses of 5.5% and 18.6%, respectively. The ocean has reduced by around 2% since 1960, representing a significant mass of oxygen loss due to its vast volume.
Study reveals alarming aquatic deoxygenation
Some regions, like the midwaters off of Central California, have lost up to 40% of their oxygen in recent decades. The causes of aquatic oxygen loss are numerous. Dr. Andreas Oschlies, a Professor of Marine Biogeochemical Modeling at GEOMAR, explains that global warming enhances water column stratification, making it harder for oxygen-poor deep layers to exchange with oxygen-rich surface waters.
Nutrient inputs from land can also support algal blooms, leading to more oxygen consumption as organic material sinks and decomposes at depth. Areas in the sea with extremely low oxygen levels, known as “dead zones,” threaten organisms and ecosystem services such as fisheries, aquaculture, tourism, and cultural practices. Moreover, macrobiotic processes in oxygen-depleted regions can produce potent greenhouse gases, exacerbating global warming and further oxygen depletion.
Professor Dr. Rose warns that we are approaching critical thresholds of aquatic deoxygenation that will ultimately affect several other planetary boundaries. Improving oxygen concentrations depends on addressing root causes, including climate warming and runoff from developed landscapes.
Failure to address this issue will have global consequences for ecosystems, economic activity, and society. The study serves as a clear warning and a call to action, urging changes to mitigate this planetary boundary issue. It highlights the urgent need for global monitoring, research, and policy efforts to address the challenges brought on by rapid aquatic deoxygenation.
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