Nature: Low-oxygen ‘underwater deserts’ in the tropical oceans have expanded over the past 50 years, according to new measurements. The most likely cause of the change is global warming, and climate models predict that the trend will continue, potentially threatening marine ecosystems. The discovery concerns a layer of the ocean called the ‘oxygen-minimum zone’, where concentrations of dissolved oxygen are particularly low. The new study shows that this zone has been expanding both upwards …