Oxygen concentrations in both the open ocean and coastal waters have declined by 2-5% since at least the middle of the 20th century.
This is one of the most important changes occurring in an ocean becoming increasingly modified by human activities, with raised water temperatures, carbon dioxide content and nutrient inputs.
Through this, humans are altering the abundances and distributions of marine species but the decline in oxygen could pose a new set of threats to marine life.
Writing in Philosophical Transactions of the Royal Society B, scientists present support for the theory that marine invertebrates with larger body size are generally more sensitive to reductions in oxygen than smaller animals, and so will be more sensitive to future global climate change.
Read more at University of Plymouth
Image: John Spicer collecting intertidal amphipods from South Cove (Rothera Research Station, British Antarctic Survey) looking west to Ryder Bay on the Western Antarctic Peninsula. (Credit: Simon Morley)