CMS - iron twilight zone - header.jpeg (IMAGE) University of South Florida Caption A conductivity, temperature and depth (CTD) rosette used to sample water from the ocean’s twilight zone during a GEOTRACES expedition in the Pacific Ocean. Credit Alex Fox Usage Restrictions NA License Original 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.