Shinn, E. A.1, M. Marot1, C. W. Holmes1
(1) USGS, St. Petersburg, FL
ABSTRACT: Solving the Whiting Problem with Short-Lived Isotopes: Still no Fish
The whiting problem has remained a controversial issue for more than 40 years. Proposed origins include 1) direct inorganic precipitation, 2) precipitation stimulated by cyanobacterial blooms, 3) mud suspension caused by fish, 4) mud suspended by sharks, and 5) microbursts in the water column. Resuspension hypotheses require source mud, such as breakdown of benthic organisms or precipitation from the water column. Traditional geochemical approaches (pH, carbonate saturation, 13C, and 14C), repeated for many years, negate a water-column source. Strontium and 210Pb analyses, aragonite architecture using SEM, and direct field observations indicate a water-column source. Presence of atmospherically derived short-lived isotopes (7Be, half-life 53 days) in whitings and absence in resuspended bottom sediment argue for direct precipitation in the water column. This ongoing study has consistently found elevated levels of 7Be activity (>5 dpm/g) in natural whiting aragonite filtered from the water column. 7Be was absent in bottom sediment and in bottom sediment collected from the water column after resuspension by storms. 7Be was also absent in bottom sediment filtered from the water column after artificial resuspension by a device that simulates fish schools and/or microbursts. Sequential acid stripping of whiting particles in the laboratory showed no decrease in 7Be activity as would be expected if epitaxial growth occurred during resuspension. In fact, 7Be activity increased (>12dpm/g) as outer layers were removed, suggesting constant depletion of the 7Be reservoir as carbonate precipitation continued within the whiting. The implications of this study are larger than the academic study of whitings.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.