Chemical and Biological Impacts of ocean acidification Along the West Coast of North America

Chair: James Orr

Richard A. Feely (a)*, Simone Alin (a), Brendan Carter (b), and Nina Bednaršek (c)

a NOAA Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, USA
b Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA 98195, USA
c School of Marine and Environmental Affairs, University of Washington, Seattle, WA 98195, USA

Background
The continental shelf region off the Washington-Oregon-California coast is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of CO2-rich waters that can negatively impact juvenile and adult pteropods.

Methods
Seawater upwelling along the continental shelf of the west coast of North America comes from the thermocline waters of the North Pacific Gyre at depths between 150 and 300 m. Here we adapt the linear regression approach to utilize the GO-SHIP Repeat Hydrography data from the northeast Pacific to establish an annually updated relationship between the anthropogenic carbon (Canth) and potential density. This relationship was then used with the NOAA Ocean Acidification Program West Coast Ocean Acidification (WCOA) cruise data sets from 2007, 2011, 2012, and 2013 to determine the spatial variations of Canth along the coast.

Findings
Our results show large spatial differences in Canth in surface waters along the coast, with the lowest values in strong upwelling regions off northern California and southern Oregon and higher values to the north and south of this region. Coastal dissolved inorganic carbon concentrations are also elevated due to a natural respiration process. Average surface Canth more than doubles the surface respiration component. In contrast, Canth is only ~1/3rd and ~1/5th of the remineralized component at 50 m and 100 m depth, respectively. The Canth plays a significant role in causing the dissolution of pteropod shells in onshore and offshore waters.

Conclusions
Uptake of Canth has caused the aragonite saturation horizon to shoal by approximately 30–50 m since the preindustrial period so that undersaturated waters are well within the regions of the continental shelf that affect the dissolution of living pteropod shells. Our data shows that the most severe biological impacts occur in the onshore waters where corrosive waters are closest to the surface.