Average Sinking Velocity Research Articles

Disequilibria between 226Ra, 210Pb and 210Po in the Arctic Ocean and the implications for chemical modification of the Pacific water inflow

Measurements have been made of 226Ra and both dissolved and particulate forms of 210Pb and 210Po in a vertical profile at 85°50′N, 108°50′W in the Arctic Ocean. In the upper water column 226Ra shows a concentration maximum that is coincident with one in the nutrients, silicate, phosphate, and nitrate, while at the same depth, dissolved and particulate 210Pb and 210Po all show minimum concentrations. It is suggested that the concentration maxima are partly due to sources of the respective elements in the continental shelf sediments, the shelf waters being subsequently advected into the Arctic Ocean basins. The 210Pb and 210Po minima have similarly been explained by interaction between the shelf sediments and overlying waters. An estimate is made of the possible contributions of shelf sediments to the layer of silica-rich water which covers the Canada Basin at a depth of 100–150 m. Residence times have been calculated for dissolved 210Pb and 210Po at various depths in the water column. Surface water residence times of dissolved and particulate forms of these radionuclides are longer than in surface Atlantic waters, probably due to lower biological activity in the surface waters of the Canada Basin. An estimatee has been made of the average sinking velocity of particulate material.

The form resistance of sinking algal chains

The relationship between sinking velocity and chain length was investigated in a species of Anabaena and with physical models constructed from glass beads. The sinking velocities of glass bead chains from one to 30 beads long were measured in tanks of glycerol, ensuring low Reynolds numbers, with the chains orientated in both horizontal and vertical directions. The coefficient of form resistance (⊘) for each length and attitude was calculated as a correction factor in the Stokes equation. Average sinking velocities of the Anabaena chains were found to fall within the range of velocities predicted from the Stokes equation with the appropriate values of ⊘ determined from measurements with the physical models.