Although systematic soundings of the ocean bottom were initiated approximately 100 years ago, and although the United States Coast and Geodetic Survey took hundreds of ocean bottom samples beginning about 75 years ago, it was not until the ship CARNEGIE collected a number of bottom samples at great depths that information began to be available on the radioactive properties of deep ocean sediments....
Utterback, C. L., and L. A. Sanderman. 1948. "Radium analyses of marine sediments in Northern Pacific and adjacent waters." Journal of Marine Research 7, (3). https://elischolar.library.yale.edu/journal_of_marine_research/692