Plutonium in the Russian Arctic, or How We Learned to Love the Bomb

Bradley Moran, Associate Professor
Graduate School of Oceanography

John N. Smith, Research Scientist
Bedford Instituteof Oceanography

Bradley Moran graduated from Concordia University and earned a PhD from Dalhousie University. He performed post-doctoral research at the Woods Hole Oceanographic Institution and came to GSO in 1994. His research interests include trace element geochemistry and using radionuclides as tracers of marine processes.

John Smith graduated from McGill University and earned a master's degree from the University of Chicago and a PhD from the University of Toronto. He has been at the Bedford Institute of Oceanography since 1976. His research includes studies of natural and artificial radionuclides in marine and freshwater systems.

Stanley Kubrick's film, Dr. Strangelove, a black comedy portraying tensions between the United States and the former Soviet Union during the height of the Cold War, is an extreme example of what can go wrong when an arsenal of nuclear weapons falls into the wrong hands. In Kubrick's model, a deranged U.S. Air Force captain orchestrates a series of miscommunications designed to trigger a nuclear holocaust, launched by Slim Pickins' rodeo-style delivery of The Bomb to unsuspecting Russkies. Fortunately, international relations have warmed since the 1950s and, following the collapse of the former Soviet Union in 1992, there is at least the possibility that we will not have global nuclear warfare in the near future. The environmental legacy of the Cold War endures, however, due to the extensive nuclear testing conducted by both superpowers. Ironically, this deliberate nuclear contamination has left scientists with a number of useful geochemical tracers with which to study the marine environment.
      In 1993, the Yablokov Report, which documented radioactive waste disposal in Russian waters, precipitated environmental concerns about radioactive contamination of the Russian Arctic Ocean and led to numerous scientific investigations. Among these are recent studies of the radioactive waste dumpsites in the Kara Sea, the downstream transport of radioactivity from nuclear facilities on the Ob and Yenesey rivers, long-range transport from European nuclear fuel reprocessing plants, and offshore transport of radioactivity into the Barents Sea from nuclear test sites on the southern coastline of the island of Novaya Zemlya. This last investigation revealed that some of the highest levels of radioactive plutonium (239,240Pu) ever measured in the marine environment can be found in the sediments of Chernaya Bay, a small (1-6km wide, 15km long) fjord on the southwestern coast of Novaya Zemlya (see Fig. 1). Chernaya Bay is a former Soviet Union nuclear weapons test site where at least two underwater nuclear tests were conducted in 1955 and 1957. The high level of radioactive plutonium measured in a single surface sediment sample collected from Chernaya Bay in 1992 indicated that radioactive plutonium from the nuclear tests may have been sequestered in bottom sediments. Chernaya Bay plutonium was also shown to be distinguished by a low 240Pu/239Pu isotope atom ratio (0.03, compared to typical global atomic fallout ratios of 0.18; the ratio of the two isotopes provides a signature that distinguishes plutonium originating at one source from all other plutonium) that is characteristic of low-yield nuclear tests. In addition, elevated levels of radioactive plutonium measured in sediments collected within 50km of Chernaya Bay indicated that transport had occurred from this embayment into the eastern Barents Sea (also known as the Pechora Sea) and could represent a potential radiological threat to the local commercial fishery.
      More extensive oceanographic investigations were undertaken aboard the R/V Geolog Fersman in 1993 and 1996 to collect seawater, sediment, and biota samples in Chernaya Bay and its surrounding approaches in the eastern Barents Sea. An important objective of these studies was to trace the transport of plutonium from Chernaya Bay using its characteristic plutonium isotopic signature. Specific questions that we addressed include: What is the magnitude, isotopic composition, and distribution within the sediments of the radionuclide inventory in Chernaya Bay? Has there been significant biological uptake of radioactive plutonium in the food chain? What is the magnitude of the radioactive plutonium flux from Chernaya Bay into the eastern Barents Sea and central Arctic Ocean?
      These questions have a bearing on radioactive plutonium in Arctic marine sediments and the environmental impact of the only recorded detonation of nuclear weapons in an Arctic Ocean fjord. They also address an important issue underlying many of the radionuclide studies in the Arctic Ocean: namely, the extent to which the Russian continental shelves represent a significant source of nuclear contamination for North American shelves and the central Arctic Ocean.
      Our investigations have produced some startling results. Radioactive plutonium levels in sediments from central Chernaya Bay are among the highest ever reported for the marine environment. Plutonium from Chernaya Bay is distinguished by 240Pu/239Pu atom ratios that are much lower than ratios typical of global fallout. High levels of radioactive cesium (137Cs) and cobalt (60Co) were also measured in surface sediments in the central regions of Chernaya Bay, near the presumed epicenter of the explosions. Most of the radioactive plutonium has been retained in the upper 20cm of the sediment column. Elevated levels of radioactive plutonium measured in benthic biota indicate that significant uptake has occurred in the food chain.
      Levels of radioactive plutonium in bottom water from Chernaya Bay are high because restricted exchange over the fjord sill limits the transport from contaminated sites in Chernaya Bay to the eastern Barents Sea. However, low 240Pu/ 239Pu ratios measured in sediment cores collected throughout the eastern Barents Sea indicate that significant offshore transport of plutonium from Chernaya Bay has occurred in the past, probably at the time of the original nuclear tests. Based on the large difference in end member 240Pu/239Pu atom ratios for Chernaya Bay fallout (0.03) and atmospheric fallout (0.18), we estimate that significant quantities of radioactive plutonium in Barents Sea sediments were originally derived from Chernaya Bay. Furthermore, a plume of low 240Pu/239Pu ratio plutonium is evident in sediments along the southern coastline of Novaya Zemlya. We are currently investigating the hypothesis that there is a plume of low 240Pu/239Pu ratio plutonium delineating the transport pathway from Chernaya Bay into the central Arctic Ocean.

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