Chernobyl nuclide record from a North Sea sediment trap.

Nuclides liberated by explosion and subsequent fire at Chernobyl No. 4 reactor on 26 April 1986, travelled to Western Europe with lower tropospheric air masses. They reached the northern Alps and Paris on 30 April, southern Great Britain on 2 May, the southern North Sea on 3 May, and the northern North Sea on 3 May and again on 8 May. Levels of deposited activity varied by a factor of 30 or more over distances less than 100 km because of variability of rainfall. A sediment trap deployed 222-m-deep in the North Sea off Bergen recorded the onset and magnitude of the deposition of Chernobyl nuclides. The trap collected 13 samples between 24 April and 21 September 1986. The flux of nuclides adsorbed to particles sinking from surface waters to sediments started less than ten days after contaminated air reached the site. Maximum specific activity occurred on 16-27 May for 137Cs, 134Cs, 106Ru and 103Ru, and on 8-20 June for 144Ce, 95Nb and 95Zr. The highest activity was found for 103Ru. The highest total specific activity of these nuclides in depositing sediments reached 670,000 Bq kg-1, and the highest total activity flux for one day amounted to 50 Bq m-2.