Quarterdeck 3.2
by James M. Brooks and Michael A. Champ
[34K] Distributions of radioactive cesium-137 at sampling stations in the Kara Sea in 1993. Radioactivity is measured in Becquerels (Bq) per kilogram of sediment sampled. 3.7 x 10(10) Becquerels produce the radioactivity of approximately one gram of radium.
In 1993 and 1994 GERG's Russian Arctic expeditions provided some of the first samples taken by American scientists of the sediments, waters and biota from the region. The initial data indicate the presence of a lobe of radioactive cesium (Cs-137) deposited in sediments of the Yenisey River below the wedge of salt water which intrudes into the estuary at the river's mouth. Dr. Mahalingam Baskaran leads the analysis of these radionuclides (see Plutonium and Cesium in the Kara Sea).
In 1995 we plan to take sediment samples in the Laptev Sea to identify troughs and areas where fine-grained sediments have been deposited.
Colloids constitute one of the major routes through which transportation of reactor-derived radionuclides like plutonium takes place. In 1995 Drs. Mahalingam Baskaran and Peter Santschi will collect samples of particulates and colloidal material from the water column and analyze them for radionuclides. They hope to identify the isotopes present and determine the physical phases in which radionuclides move through the ecosystem.
To understand the dispersal pattern of reactor-derived, particle-reactive radionuclides we must comprehend the important mechanisms by which colloids adsorb them and the fate of colloids in the ecosystem. When we coordinate the radionuclide analysis with the sedimentological and geological data we can calculate the rates of radionuclide transport and deposition in the Russian marginal seas.
The results of this research will form the topic of graduate student Jon Schwantes' master's thesis. (For more information about colloid research see "The Laboratory for Oceanographic and Environmental Research at Texas A&M University in Galveston" in the Fall 1994 issue of Quarterdeck.)
Biology, chemistry, and geology in the oceans exist in a physical environment formed by mobile masses of water. Knowledge of this physical environment is essential to understand transport processes that affect the movement of radionuclides in the Russian marginal seas. Our physical oceanographic data has been used to support computer models of currents and water masses, including a study by Dr. David Brooks and graduate student Yao-Tsai Lo, supported by an Office of Naval Research subcontract from the University of Washington.
The features and properties of the seafloor form another oceanographic component which affects the transport and ultimate fate of contaminants. Drs. William Bryant and Niall Slowey are conducting geotechnical, geoacoustic, and seismic stratigraphic analysis of the Russian marginal seas and adjacent areas. Geotechnical features of the seafloor consist of its physical properties such as strength and texture. Geoacoustic properties determine how sound will travel through the sediment. Seismic stratigraphy is the technique of interpreting vast amounts of structural information from seismic signals reflected off different stratigraphic layers of the seafloor. These studies help oceanographers better understand the shape of the seafloor, its features, and its interaction with environmental processes.
Researchers survey parts of the seafloor using high-resolution, side-scan sonar and a vertical-incidence chirp sonar system (X Star). They can also sample sediments directly using wide-diameter gravity and vibra cores. With a device called a multi-sensor core logger the researchers test sediment properties such as the velocity of sound through the sediment, its density, porosity, and magnetic susceptibility over entire core lengths. Representative cores also provide valuable information about sediment shear strength, grain size, consolidation characteristics, permeability, overburden removed by erosion, clay mineralogy, cation exchange capacity, clay particle surface area, and the potential for the sediment particles to chemically bind with radioactive metals. Knowledge of these sediment parameters is required to assess the ability of various sediment types to absorb and retain radionuclides and other contaminants.
By correlating geologic, geotechnical and geoacoustic data with chirp and side-scan sonar results, it is possible to rapidly describe the local and regional distributions of sediment types on the seafloor and to depths of tens of meters below it. Chirp and side-scan sonar results also provide the means of characterizing seafloor structure and depth. We gain a great deal of basic information about recent environmental processes by interpretating high-resolution seismic data in terms of geological processes and correlating them with sediment characteristics.
In summary, this project provides a description of the current concentrations and types of radionuclides being discharged from Russian rivers into the Arctic marginal seas. The sampling plan allows us to assess the regional extent of radionuclide contamination at the mouth of and up-stream in a number of Russian rivers and their bay systems.
Initial results indicate that while man-derived radionuclides and other chemical contaminants (pesticides, hydrocarbons, and trace metals) can be easily detected in the Russian Arctic coastal environments, levels of contaminants are generally below those known to cause ecological or human-health risks. Continued monitoring is necessary, however, to protect the Arctic ecosystems and native peoples.
Oceanography, Texas A&M
University
rshatto@ocean.tamu.edu
URL=http://oceanography.tamu.edu/Quarterdeck/QD3.2/Brooks/brooks-b.html
Updated September 13, 1995
