Biocomplexity -- Incubation Activity - The Colloid Gap: Interfacial Phenomena Among Marine Biological, Chemical and Physical Environmental Systems and Their Role in Carbon Cycling

University Of Washington, Seattle WA

Investigators

Abstract

This project focuses on the intricate combination of biological and physicochemical processes by which dissolved organic matter (DOM) is formed and cycled in the ocean. The interlinked biological and physical processes by which bioactive elements are cycled in the ocean represent one of the most complicated and critical systems on earth. Although living organisms are the ultimate source and sink of the organic matter in which these elements primarily cycle, the major currency for both their active transfer and long?term storage in the ocean is as small, nonliving organic molecules. This "molecular prerogative" results because the biomacromolecules composing organisms and tissues must be broken down to inert subunits to pass bacterial cell walls prior to complete intracellular respiration. In the ocean, much of this molecular dismantling is accomplished by bacterial exoenzymes operating on organic substrates. Nutrient elements carried through this "bacterial loop" become available for conversion back to living particulate form either through photosynthesis or via transfer of bacterial production up food webs through protists and zooplankton. Such biologically mediated cycling between dissolved and particulate organic forms is critical on a larger scale to the transfer and fate of nutrients because only particles can sink to selectively transport bioactive elements from the lighted surface ocean into deep storage below the thermocline (i.e., the biological pump). Recent evidence for spontaneous assembly of colloidal marine molecules into microscopic polymer gels has fundamentally changed the way that oceanographers think about processes linking the microbial loop and biological pump to the rest of the biosphere and the geosphere. The key observation was that colloidal?size organic molecules found in surface seawater can coalesce spontaneously. The resulting particles (microgels) are sufficiently large to sink and might undergo other processes such as catastrophically collapsing to dense forms after passing sharp thresholds of temperature, pressure or pH. Our group has also recently found that these microgels are degraded approximately an order of magnitude faster by marine bacteria than the dispersed molecules from which they are formed, apparently by providing an effective means for abiotically concentrating substrate for efficient exoenzymatic dismantling. This project is an interdisciplinary focus on the role of these microgel particles in carbon cycling processes.