Interpretation and design of ocean acidification experiments in upwelling systems in the context of carbonate chemistry co-variation with temperature and oxygen

Abstract

Coastal upwelling regimes are some of the most productive ecosystems in the ocean but are also among the most vulnerable to ocean acidification (OA) due to naturally high background concentrations of CO2. Yet our ability to predict how these ecosystems will respond to additional CO2 resulting from anthropogenic emissions is poor. To help address this uncertainty, researchers perform manipulative experiments where biological responses are evaluated across different CO2 partial pressure (pCO2) levels. In upwelling systems, however, contemporary carbonate chemistry variability remains only partly characterized and patterns of co-variation with other biologically important variables such as temperature and oxygen are just beginning to be explored in the context of OA experimental design. If co-variation among variables is prevalent, researchers risk performing OA experiments with control conditions that are not experienced by the focal species, potentially diminishing the ecological relevance of the experiment. Here, we synthesized a large carbonate chemistry dataset that consists of carbonate chemistry, temperature, and oxygen measurements from multiple moorings and ship-based sampling campaigns from the California Current Ecosystem (CCE), and includes fjord and tidal estuaries and open coastal waters. We evaluated patterns of pCO2 variability and highlight important co-variation between pCO2, temperature, and oxygen. We subsequently compared environmental pCO2–temperature measurements with conditions maintained in OA experiments that used organisms from the CCE. By drawing such comparisons, researchers can gain insight into the ecological relevance of previously published OA experiments, but also identify species or life history stages that may already be influenced by contemporary carbonate chemistry conditions. We illustrate the implications co-variation among environmental variables can have for the interpretation of OA experimental results and suggest an approach for designing experiments with pCO2 levels that better reflect OA hypotheses while simultaneously recognizing natural co-variation with other biologically relevant variables.

Using present-day observations to detect when anthropogenic change forces surface ocean carbonate chemistry outside preindustrial bounds

“…For example, ENSO is a driver of ocean conditions, including biogeochemistry, at CCE2 (Nam et al, 2011). While there were weak El Niño-like conditions that developed in the tropical Pacific in 2014 (McPhaden, 2015), there were no major La Niña or El Niño anomalies during the CCE2 time series used in this analysis (March 2012(March -2015. Hence, the estimate of interannual variability presented here is likely an underestimate of the true interannual signal at this location.…”

“…By resolving these scales of variability, researchers can start to refine biological experiments, ecosystem models, and economic vulnera-bility assessments in the context of full ecosystem variability and change. As evidence emerges that some shelled marine organisms are already being impacted by corrosive seawater chemistry conditions (Barton et al, 2012;Bednaršek et al, 2012Bednaršek et al, , 2014aReum et al, 2015) and stakeholders are seeking locally relevant solutions (Kelly and Caldwell, 2013;Kelly et al, 2011), these analyses are becoming increasingly important.…”

A multi-decade record of high-quality <i>f</i>CO<sub>2</sub> data in version 3 of the Surface Ocean CO<sub>2</sub> Atlas (SOCAT)

“…Regional f CO 2 values from SOCAT are used in diverse environmental studies with topics ranging from ocean acidification to genomics, gas transfer velocity and evaluation of independent measurements (Blomquist et al, 2014;Larsen et al, 2014;Holding et al, 2015;Marrec et al, 2015;Bonou et al, 2016;Reum et al, 2016). Reum et al (2016) assess the co-variance between pCO 2 , pH and other environmental parameters with the aim to improve the design of future ocean acidification incubation experiments. Larsen et al (2014) establish a significant correlation between gene expression for the relative turnover (synthesis or consumption) of CO 2 and surface ocean f CO 2 .…”

Species-specific responses to ocean acidification should account for local adaptation and adaptive plasticity

“…by a process of equilibration with the atmosphere 16,17 . This diversity of causative drivers and the high degree of variability in coastal environments, when compared with open ocean systems, limits the direct extrapolation of ocean acidification concepts and scenarios between these different environments 18 .…”