The Effects of Internal Waves Shoaling over a Mid-shelf Submarine Bank as Assessed by Eddy Covariance Measurements of Benthic Oxygen Exchange Rates

During spring, summer and fall conditions, high-resolution measurements of current velocities and oxygen concentration were made at ~80 m off central Oregon in the benthic boundary layer over Hecata Bank using a tripod designed and equipped for eddy covariance (EC) studies. Time-lapse bottom photographs of the adjacent seafloor were also taken during the 18-24 hour deployments. These observations and repetitive CTD profiles of the water column at the study site show that near-bottom turbulence, oxygen concentrations, temperature, turbidity and groundfish densities were often highly variable within diurnal periods. Arrivals of shoaling internal waves are clearly seen in the velocity records and appear strongly linked to EC momentum and oxygen fluxes. Oxygen fluxes were observed to increase as much as 10-times over baseline levels. These non-steady state conditions allow investigation of different methods to interpret EC measurements, evaluate wave effects and determine if abrupt changes in sediment oxygen uptake may result from periods of high turbulence.