Fine-scale oxygen variability in a stratified estuary: patchiness in aquatic environments

Abstract

Vertical and horizontal scales of oxygen patches in a strongly stratified, productive estuary were determined using current drogues and a C TD profiler equipped with a rapid response oxygen sensor. For the deep water layer, vertical and horizontal dimensions of oxygen patches were I to 2 m and 100 to 200 m respectively. Vertical diffusivities were also mapped from fine-scale measurements of temperature and salinity using calculated quantities of buoyancy frequency and dissipation rate per unit mass. Oxygen patch size was consistent with a model relating the vertical length scale of oxygen variability with vertical diffusivity, and the ratio of oxygen concentration differences between patches with the rate of oxygen metabolism. The observed oxygen patch size was consistent with the hypothesis that local oxygen production was balanced by vertical mixing. Vertical and horizontal distributions of soluble reactive phosphate were also determined but with greatly reduced resolution. Phosphate showed vertical variability consistent with the idea that it was extremely patchy. Large-scale horizontal distributions of mean oxygen and phosphate concentrations revealed a stoichiometery consistent with the remineralization of organic material in estuary bottom water.