J. Environ. Radioactivity, Vol. 39, No. 3, pp. 279 — 303, 1998  1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain PII: S0265-931X(96)00058-1 0265-931X/98 $19.00#0.00 The Distribution of Radiocesium and Plutonium in Sea Ice-entrained Arctic Sediments in Relation to Potential Sources and Sinks Lee W. Cooper,  I. L. Larsen, T. M. Beasley, Scott S. Dolvin, Jacqueline M. Grebmeier, J. M. Kelley, Martha Scott & A. Johnson-Pyrtle  Environmental Sciences Division, Oak Ridge National Laboratory, PO Box 2008, MS 6038, Oak Ridge, TN 37831-6038, USA  Environmental Measurements Laboratory, U.S. Department of Energy, 201 Varick Street, New York, NY 10014, USA  Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA  Pacific Northwest National Laboratory, Battelle Blvd., Richland, WA 99352, USA  Department of Oceanography, Texas A & M University, College Station, TX 77843-3146, USA (Received 10 July 1997; accepted 17 July 1997) ABS¹RAC¹ Gamma counting of a range of grain size fractions of sediments entrained in Arctic Ocean sea ice indicate that the wide range of radiocesium activities that are observed in bulk samples are primarily a function of the geographical origin of the sediment, rather than mineral composition, or physical processes that increase the content of fine clays in sediments. Plutonium isotope ratios ( 240 Pu: 239 Pu) of sea ice sediments are consistent with an ultimate origin of the plutonium from bomb fallout ( 240 Pu: 239 Pu"& 0)18), and these sediment ratios differ significantly in plutonium isotope ratios from deep sea sediments of the Arctic Ocean. Much lower plutonium activities were observed in deep sea sediments relative to the sea ice entrained sediments. These differences in isotopic ratios indicate that on decadal scales, sedimentation of bomb fallout plutonium is not the sole source of plutonium to deep Arctic Ocean sediments. The large differences in total plutonium activity between some of the sea ice entrained sediments and all of the deep Arctic Ocean sediments also suggest that the total flux of plutonium from sea ice entrained sediments to the deep sea may be relatively small. Radiocesium activity in the sea ice entrained sediments is well correlated with total plutonium abundance, but the best-fit 279