Spatiotemporal variability and long-term trends of ocean acidification in the California Current System

Abstract

Abstract. Due to seasonal upwelling, the upper ocean waters of the California Current System (CCS) have a naturally low pH and aragonite saturation state ( arag ), making this region particularly prone to the effects of ocean acidification. Here, we use the Regional Oceanic Modeling System (ROMS) to conduct preindustrial and transient simulations of ocean biogeochemistry in the CCS. The transient simulations were forced with increasing atmospheric pCO 2 and increasing oceanic dissolved inorganic carbon concentrations at the lateral boundaries, as projected by the NCAR CSM 1.4 model for the IPCC SRES A2 scenario. Our results show a large seasonal variability in pH (range of ∼ 0.14) and arag (∼ 0.2) for the nearshore areas (50 km from shore). This variability is created by the interplay of physical and biogeochemical processes. Despite this large variability, we find that present-day pH and arag have already moved outside of their simulated preindustrial variability envelopes (defined by ±1 temporal standard deviation) due to the rapidly increasing concentrations of atmospheric CO 2 . The nearshore surface pH of the northern and central CCS are simulated to move outside of their present-day variability envelopes by the mid-2040s and late 2030s, respectively. This transition may occur even earlier for nearshore surface arag , which is projected to depart from its present-day variability envelope by the early-to mid-2030s. The aragonite saturation horizon of the central CCS is projected to shoal into the upper 75 m within the next 25 yr, causing near-permanent undersaturation in subsurface waters. Due to the model's overestimation of arag , this transition may occur even earlier than simulated by the model. Overall, our study shows that the CCS joins the Arctic and Southern oceans as one of only a few known ocean regions presently approaching the dual threshold of widespread and near-permanent undersaturation with respect to aragonite and a departure from its variability envelope. In these regions, organisms may be forced to rapidly adjust to conditions that are both inherently chemically challenging and also substantially different from past conditions.

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.…”

“…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.…”

CO2-induced ocean acidification increases anxiety in Rockfish via alteration of GABAAreceptor functioning

“…7.8) and higher than normal pCO 2 that can reach as high as 820 matm at shallow depths (7 m) and as high as 1016 matm at greater depths (17 m) for at least 5-7 days [22]. Therefore, the California coast already regularly experiences CO 2 -acidified water and will be exposed to more extreme OA conditions earlier than in other locations [23,24].…”

Twenty Years of Marine Carbon Cycle Observations at Devils Hole Bermuda Provide Insights into Seasonal Hypoxia, Coral Reef Calcification, and Ocean Acidification

“…Time-series of seawater CO 2 -carbonate chemistry in the coastal marine environment tend to be relatively short (i.e., less than 10 years) with observation over an annual cycle (e.g., Johnson et al, 2013), a few years of regular sampling (e.g., Oregon coast, Harris et al, 2013;Santa Monica Bay, Leinweber and Gruber, 2013;Bermuda, Yeakel et al, 2015) that extends to 8 years of sampling (Bay of Bengal, Sarma et al, 2015). Other approaches include assessments of change from repeat sampling multi-year intervals between sampling (e.g., North Sea, (Clargo et al, 2015); coastal margin of the USA, Wanninkhof et al, 2015), or model assessments of longer-term change (e.g., California Current, Hauri et al, 2013;Turi et al, 2016).…”