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Upwelling Controls HAB Movement toward Pacific NW Coast

Published on: 02/10/2015
Research Area(s): Coastal Change
Primary Contact(s): quay.dortch@noaa.gov

With upwelling, displaced surface waters are replaced by cold, nutrient-rich water that wells up from below. Credit: NOAA.

Models developed by NCCOS-sponsored researchers will predict the transport of harmful algal blooms (HABs) to coastal beaches or offshorefrom two locations off of Washington and Oregon, based on the influence of the Columbia River Plume and seasonal upwelling (displacement of surface water by cool, nutrient rich, deep water). A recent study determined that upwelling plays a dominant role in late summer and early fall in the shoreward transport of HABs, increasing their chance of impacting recreational and subsistence razor clamming on beaches.

Cross-shelf exchanges of water from offshore to inshore, and vice versa, is one of the most important, but least understood, physical phenomena in the coastal ocean. In the Pacific Northwest (PNW), seasonal upwelling, or the lack thereof, can determine the movement of plankton and larvae offshore or inshore. The study documents a dramatic seasonal change in upwelling flows across the PNW shelf, with onshore flows originating from much shallower in the water column late in the upwelling season (August and September). The findings imply less nutrient-rich water likely gets upwelled to the coast later in the season. Similarly, the shoreward transport of plankton and HABs originating in shallow layers just beneath the surface could be enhanced later in the upwelling season. The modelling results encourages managers to not only factor the location of the Columbia River plume into predictions of potential HAB landfalls but also the strength and depth of upwelling prior to opening beaches for harvesting of razor clams.

This study, part of the NCCOS-funded Ecology and Oceanography of Harmful Algal Blooms-Pacific Northwest project (‘PNWTOX’), is published in the Journal of Physical Oceanography .

For more information, contact Quay.Dortch@noaa.gov.

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