Spatial and temporal structure of fluxes between a lateral embayment and the Columbia River estuary channel

Estuary channels are often bordered by lateral bays and intertidal flats, which have shallow water depths but large surface areas compared to the neighboring estuary channel. Lateral bays play an important role in production of biogeochemicals in costal margins, and large biogeochemical fluxes are believed to be exchanged between lateral bays, estuary channels, and ultimately the coastal ocean. Due to seasonal weather variation, quantification of biogeochemical production is difficult. To quantify the spatial and temporal structure of water mass and biogeochemical fluxes between an intertidal lateral bay (Cathlamet Bay) and the main channel of the Columbia River estuary, surveys were conducted over semidiurnal tidal cycles during spring and neap tides and during high river flow (May/June) and low flow (September) conditions in 2012. A shipboard downward facing ADCP was used to take continuous measurements on current velocity while at three to five sampling stations along the transect a profiling package measured conductivity, temperature, water depth, dissolved oxygen concentration, chlorophyll fluorescence and optical backscatter. By comparing data from the wet and dry season, we study the influence of salt stratification and buoyancy forcing on the spatial and temporal structure of water mass exchange at the bay/estuary interface as well as gain an understanding of the role of lateral bays in biogeochemical production over the full range of seasonal weather variations.