Oil at sea—how much is too much?

The anthropogenic share of marine oil discharge is much larger than previously thought Natural oil seepage from seafloor petroleum hydrocarbon reservoirs is a chemical stress on marine life ( 1 ). It also is a chemosynthetic energy source that allows the existence of chemosynthetic lifeforms and communities. These hydrocarbon emissions drive ecological adaptations and support high biomass ( 2 ). Additional oil enters the ocean from accidental and operational releases and primarily manifests as chronic and transient slicks found along shipping lanes and in coastal waters ( 3 ). Trends for small oil releases have been unclear because of the paucity of monitoring methods. Satellite synthetic aperture radar (SAR) is highly promising for monitoring small spills and oil seepage slicks. On page 1300 of this issue, Dong et al. ( 3 ) find that oil slicks are far more widespread than prior estimates ( 1 ). They analyzed more than 500,000 satellite SAR images from 2014 to 2019 and found over 450,000 oil slicks, with the vast majority originating from anthropogenic releases or discharges.