Science

Persistent spatial structuring of coastal ocean acidification in the California Current System

Across the CCLME, we observed near-shore pH that fell well below current global mean surface ocean pH of 8.1 (Fig. 1). Minimum pH reached as low as 7.43 at the most acidified site, and up to 18% of recorded values fell below 7.8 during the upwelling season (Table S1). These minima are among the lowest reported to date for the surface ocean and match levels not projected for the global surface ocean until atmospheric CO 2 exceeds 850 ppm.

(a) Intertidal pH_total variation across the CCLME study domain of contrasting shelf topography as delineated by the 75 m, 100 m, 200 m isobaths (magenta), and (b) wind-driven cross-shelf surface transport (m² s⁻¹) (see scale inset in a). Map was generated from the ETOPO1 dataset⁴² in Matlab v8.2. (c) Variation in pH at the event-scale during part of the 2013 upwelling season with asterisk denoting global mean surface pH¹² and (d) accompanying daily wind stress (N m⁻²) at 44.65°N, (e–g) severity of low pH exposure (lower 5th percentile) across three years of deployment and (h) pH variability. White dotted lines in pH panels denote station locations.

Exposure regimes to OA were also highly dynamic, exhibiting strong diel as well as event- (2 to 10 day), and intra-seasonal- (~15 to 40 day) scale variability. Daily pH ranges of up to 0.8 units were measured, as were rapid rates of change of up to 0.3 pH units per hour. Our findings indicate that coastal organisms in the CCLME face not only some of the lowest, but also some of the most dynamic pH environments currently known for surface marine systems (Fig. 2 ). Because variable pH exposure can affect organism response to OA, low and variable pH can further act as linked stressors.

Future biological impacts experiments should […]

Full article: Persistent spatial structuring of coastal ocean acidification in the California Current System