Rain, Runoff, and Diatoms: the Effects of the North Pacific 2014–2015 Warm Anomaly on Particle Flux in a Canadian West Coast Fjord

Abstract

Sediment traps were deployed at 50 m depth in Douglas Channel, a fjord on the west coast of Canada, for 3 years (July 2013–July 2016). Particle flux was related to rain, freshwater discharge, and phytoplankton blooms. The North Pacific warm water anomaly (known popularly as the Blob) reached coastal waters during the second year of deployment, resulting in more autumn rain and less snow than during the other 2 years. The maximum particle flux was associated with the snowfed river freshet in May during the first year and with heavy October rains during the second and third years. A protracted sedimentation event consisting of copious diatoms occurred during the warm, second winter (December 2014–February 2015). Silica (empty diatom frustules) was exported, intercepting silicate from local rivers that might otherwise have reached the outer shelf. The effects of extreme climate events are experienced differently inshore than offshore, because they are mediated by local hydrology. During the Blob year, Douglas Channel experienced exceptionally high rainfall in October, which resulted in high particle flux. As the climate continues to warm, mild, rainy years like 2014–2015 will become more common, with the possibility of further winter blooms.