10th tipping point identified: aquatic deoxygenation on Earth

Researchers propose adding aquatic deoxygenation as a 10th planetary boundary, reporting measurable oxygen losses in lakes, reservoirs and the oceans and noting a 40% midwater decrease off California; the study is published in Nature Ecology & Evolution.

Scientists have proposed that widespread loss of dissolved oxygen in freshwater and marine systems should be considered a 10th planetary boundary. The Planetary Boundary framework originally described nine global thresholds; the study argues aquatic deoxygenation now meets criteria for an additional boundary. The research documents measurable declines in oxygen levels across lakes, reservoirs and the open ocean and links those changes to rising temperatures and nutrient inputs from land. The findings and author comments are reported in Nature Ecology & Evolution. Key findings: - Researchers document oxygen declines over recent decades, with reported losses of about 5.5% in lakes, 18.6% in reservoirs and about 2% in the oceans, and a reported 40% decline in midwaters off California since 1960. - The study proposes classifying aquatic deoxygenation as a planetary boundary alongside the existing nine to reflect its global-scale risks. - Authors attribute the trend mainly to warming (which reduces oxygen solubility and increases stratification) and to nutrient runoff that fuels decomposition, and note that lower oxygen can affect aquatic life and influence greenhouse gas production. Summary: The authors say aquatic deoxygenation is occurring at a scale that could warrant inclusion as a 10th planetary boundary and that the trend is linked to climate warming and land-derived nutrient inputs; the study appears in Nature Ecology & Evolution. Undetermined at this time.