O2 Depletion (IMAGE) Arizona State University Caption Adding nutrients to the ocean causes increased production of organic matter such as phytoplankton. When these die, they sink to the bottom as "marine snow" and decompose, consuming oxygen in the process. This is thought to be primarily responsible for large-scale oxygen loss in ancient oceans, leading to mass extinctions in the marine environment. The modern ocean exhibits similar symptoms. Credit Natalie Renier, Woods Hole Oceanographic Institution Usage Restrictions No restrictions when used in connection with reportage on this story. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.