The Columbia River brings buoyant fresh water to the Pacific Ocean, along with dissolved silicate and iron, crucial to phytoplankton growth. The plume increases near-surface stratification in coastal waters so may trap momentum, heat and biomass, and may inhibit turbulent exchanges with nutrient-rich subsurface waters.
Turbulence and acoustics measurements made during the River Influences in Shelf Ecosystems (RISE) experiment elucidate small-scale processes within the river-plume-ocean system, including:
turbulence in the estuary and nearfield plume
plume-driven bottom stress
frontal dynamics and nonlinear internal wave generation
mixing in the farfield plume
Columbia River Estuary
Tidally-resolving timeseries were aquired within the estuary during low (Aug 2005) and high (May 2006) river flows. While the salinity and stratification were markedly different, turbulence intensity within the estuary is dominated by the tidal dynamics and similar during both field seasons.
Contrasting the river estuary, the plume nearfield depends strongly on the near surface stratification. Under low river flows, turbulence extends from surface to bottom several kilometers from the river mouth. Under high flow conditions, the plume lift-off moves into the river mouth and the nearfield is more strongly stratified. Turbulence under high river flow conditions is trapped to the surface, having important consequences to sediment transport.