Rapid Progression of Ocean Acidification in the California Current System

Abstract

Nearshore waters of the California Current System (California CS) already have a low carbonate saturation state, making them particularly susceptible to ocean acidification. We used eddy-resolving model simulations to study the potential development of ocean acidification in this system up to the year 2050 under the Special Report on Emissions Scenarios A2 and B1 scenarios. In both scenarios, the saturation state of aragonite Ω(arag) is projected to drop rapidly, with much of the nearshore region developing summer-long undersaturation in the top 60 meters within the next 30 years. By 2050, waters with Ω(arag) above 1.5 will have largely disappeared, and more than half of the waters will be undersaturated year-round. Habitats along the sea floor will become exposed to year-round undersaturation within the next 20 to 30 years. These projected events have potentially major implications for the rich and diverse ecosystem that characterizes the California CS.

Limacina helicinashell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem

“…The conditions observed during the 2011 WCOA summer cruise were consistent with other observations and model results for the last several years during the upwelling season [11][12][13][14][15][16][17]. Water samples were collected from modified Niskin-type bottles and analysed for DIC, TA, oxygen, nutrients and dissolved and particulate organic carbon.…”

“…High-latitude areas of the open ocean will be the most affected by OA owing to the high solubility of CO 2 in cold waters [8][9][10]; however, the California Current Ecosystem (CCE) is already experiencing CO 2 concentrations similar to the projections for high-latitude regions, pointing towards enhanced vulnerability to OA [11][12][13][14]. This is, in part, owing to the natural process of upwelling, which brings already CO 2 -rich waters from the ocean interior to the shelf environment and adds to the anthropogenic CO 2 contribution.…”

“…The CCE is characterized by strong spatial (both horizontal and vertical) and temporal gradients in V ar [11,14], with the aragonite saturation shoaling closest to the surface during the summer upwelling season in the WashingtonOregon coastal regions and off northern California. Based on both discrete observations and model calculations, it has been suggested that the upwelled undersaturated sourcewaters were present 10% of the time at the shelf break in the pre-industrial era, and contemporary ocean source-waters are undersaturated approximately 30% of the time during the upwelling season at the shelf break [12][13][14]. The upwelled undersaturated waters reach their shallowest depths close to the coast where they occasionally reach the surface [4,11,14].…”

“…Their spatial habitat stretches along the CCE and their vertical habitat encompasses the upper 75-150 m during day and night, with some healthy individuals capable of vertically migrating much deeper [28,29]. The CCE is a major upwelling region that is already experiencing 'acidified' conditions [11][12][13][14] under which thin pteropod shells are vulnerable to dissolution [30][31][32], even by short-term exposures (4-14 days) to near-saturated waters (V ar 1), which makes them a suitable indicator for monitoring small-scale changes in the carbonate chemistry environment [30]. The existence of strong vertical gradients in aragonite saturation in the first 100 m of the CCE further accelerated by anthropogenic OA, where undersaturation protrudes into the pteropod vertical habitat provided a setting for estimating quantitative relationships between in situ undersaturation and shell dissolution.…”

Is Ocean Acidification an Open-Ocean Syndrome? Understanding Anthropogenic Impacts on Seawater pH

“…Accordingly, the pH of coastal waters affected by coastal upwelling is expected to decline in the future. A modelled simulation of the California Current upwelling region (Gruber et al 2012) forecasts that summer-long undersaturation will occur in the top 60 m of the water column by year 2040 and that by 2050 aragonite saturation states greater than 1.5 will have disappeared, driving more than one half of the water column to undersaturation year-round. Additionally, the seafloor will be undersaturated year-round within the next 20-30 years.…”