In an article in this month's Journal Limnology and Oceanography, one of the world's most prestigious aquatic science magazines, Matthew Quigley, a graduate student at Texas A&M University at Galveston (TAMUG), working under radiochemist and oceanographer Peter Santschi, and three other research scientists report on how natural sugar-containing molecules found in the ocean strongly affect extents and rates at which radioactive tracer elements are converted into particulate matter.
"Oceanographers use radioactive isotopes of the element thorium to track the self-cleansing capacity of the ocean," Santschi said. "In particular, radioisotopes of thorium are used to clock the rate and extent at which organic particulate matter cycles in the ocean, helping to estimate, for example, the amount of particles settling to greater depths. This is called by oceanographers the biological pump, important in global carbon cycling models.
"However, accurate interpretation of data has been hampered by natural variabilities in the ratio of thorium to particulate organic carbon in the upper ocean," he continued. "Experiments by my graduate student, Matthew Quigley, and postdoctoral research associate Chin-Chang Hung have revealed that thorium (and many other metal ions) bind most strongly to acidic polysaccharide-containing biomolecules, which occur naturally in ocean water and are a billion times more abundant than thorium, and a thousand to a million times more abundant than many toxic metals in seawater. This discovery can help improve our general understanding of the role of macromolecular organic matter in metal-binding, trace metal speciation, bioavailability, and the natural self-cleaning capacity of natural waters.
"Natural organic matter of higher molecular weight is the least well understood fraction in the aquatic environment, and the normal approach of breaking down macromolecules into their monomers by organic geochemists is of little help when attempting to understand the role such compounds play in metal binding, as their biological and chemical actions depend on their three-dimensional structure."
Quigley used a novel application of two-dimensional polyacrylamide gel electrophoresis to study the binding of thorium with acid polysaccharide molecules, by separating the different kinds of molecules first in an electric field, according to the molecule's charge, then again based on its molecular weight.
Along with Quigley, Santschi and Hung, Laodong Guo of the International Arctic Research Center at the University of Alaska Fairbanks and Bruce D. Honeyman of the Colorado School of Mines' Department of Environmental Science and Engineering also contributed to the project.
"The significance of this work involves its potential use for determining metal and organic matter removal from the water column," Santschi said. "And the ability of thorium to trace this process could become a more powerful tool in the study of marine organic carbon cycling."
Contact: Terri Fowle, 409-740-4830, fowlet@tamu.edu;
Peter Santschi, 409-740-4476, santschip@tamug.tamu.edu.