Ploug, H. University of Copenhagen, helle_ploug@inet.zitech.dk

 
DIFFUSION AND SHEAR IN THE PELAGIC ENVIRONMENT - IMPLICATIONS FOR THE BIOLOGICAL PROCESSES IN THE OCEAN.
 
Diffusive boundary layers (DBLs) with concentration gradients of solutes develop at small scale and at interfaces where flow and turbulence is limited by physical forces. The presence of DBLs surrounding small free-living organisms below the viscous length scale in the aquatic environment have been deduced from theoretical considerations since decades. The extent to which such boundary layers exist and interact with shear and the biological processes is important for our understanding of pelagic processes in the ocean. The recent development of new techniques have now enabled direct measurements of flow and microscale gradients of solutes in the vicinity of 0.5-5 mm large phytoplankton colonies and sinking particles. The oxygen distributions within and around sinking particles have been mapped in two dimensions by the use of microelectrodes. The data showed the existence of a DBL surrounding the particles, which indicate that the radial transport of solutes mainly occurs by molecular diffusion at the particle-water interface. The impact of particle size and sinking-induced shear on the DBL thickness were directly quantified. The measured DBLs and viscous boundary layers with velocity gradients of moving fluid in the vicinity of sinking particle will be demonstrated and discussed in relations to those predicted from theory.
 
Day: Tuesday, Feb. 2
Time: 11:00 - 11:15am
Location: Hilton of Santa Fe
 
Code: SS02TU1100H