Spatio-temporal variability and ENSO modulation of turbid freshwater plumes along the Oregon coast

The influence of climate variability on the Northeast Pacific (NEP) ocean is mainly linked to the impact of El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and North Pacific Gyre Oscillation (NPGO) on the modulation of coastal circulation, coastal upwelling, and ecosystem response. The impact of climate variability on the interannual variability of freshwater river plumes has been largely unstudied. Here, 14.5 years of ocean color satellite imagery were used to study the interannual variability of turbid freshwater plumes off the Oregon coast. EOF analysis reveals two dominant modes associated with (i) the winter plumes of coastal rivers merged along the entire Oregon shelf (EOF1) in the downstream (northward) direction as coastal-attached buoyancy-driven plumes, and (ii) the offshore Columbia River plume occupying most of the coastal ocean off Oregon (EOF2) as result of its southward and offshore transport during spring-summer upwelling. Large plumes corresponded mainly with certain aspects of ENSO cycles. However, extended ocean time series are needed to better evaluate the influence of PDO and NPGO because of their dominant decadal variability. Anomalously large coastal plumes (EOF1) lagged the canonical El Niño primarily during fall and La Niña during winter. The largest offshore Columbia River plume events occurred after persistent La Niña conditions (e.g. 2008, 2011, 2014). •The interannual variability of freshwater turbid river plumes is evaluated off Oregon.•EOF modes separate small coastal rivers from the offshore Columbia River plume.•Anomalously large coastal plumes lagged El Niño in fall and La Niña in winter.•Major events of the offshore Columbia River plume occurred after strong La Niña.