Radioactivity of the ocean floor and marine phosphorite deposits: Observations with a new deep‐towed scintillometer

Abstract

A new bottom‐towed scintillometer has been deployed in the tropical Atlantic to investigate whether lithological changes on the deep‐sea bed can be determined from variations in its natural radioactivity. Although count rates over the blanket of recent pelagic carbonates fall within the seawater background, high rates of gamma ray emission were detected on the crest of a seamount near 9° N, 21° W. Seismic profiles, bottom sampling and photography demonstrate that the radiometric anomalies coincide with areas in which the veneer of pelagic ooze is locally absent and phosphatized limestones of Cenozoic age (P2O5 > 14%) are exposed. The contrast in the U contents of the phosphorites (∼30 ppm) and pelagic carbonates (<3 ppm) appears to be responsible for producing the prominent radiometric signatures. Since phosphorites on continental margins and oceanic plateaus are generally more enriched in U than the seamount deposits (often >100 ppm), profiling the levels of seabed radioactivity would be a relatively rapid means of defining the distribution of phosphorite in many parts of the oceans.

Characterization of a CZT-based spectrometer for underwater operation via simulations and experiments

“…The most common ones involve the deployment of NaI(Tl) scintillators (see e.g. [6][7][8][9][10][11]), with the main limitation of such approaches residing in the generally poor energy resolution of the scintillator.…”