Tracking the Space‐Time Evolution of Ocean Acidification Extremes in the California Current System and Northeast Pacific

Abstract

Ocean acidification is punctuated by episodic extremes of low pH and saturation state with regard to aragonite (ΩA). Here, we use a hindcast simulation from 1984 to 2019 with a high‐resolution regional ocean model (ROMS‐BEC) to identify and track ocean acidification extremes (OAX) in the northeast Pacific and the California current system (CCS). In the first step, we identify all grid‐cells whose pH and ΩA are simultaneously below their first percentile over the analysis period (1984–2019). In the second step, we aggregate all neighboring cells with extreme conditions into three‐dimensional time evolving events, permitting us to track them in a Lagrangian manner over their lifetime. We detect more than 22 thousand events that occur at least once in the upper 100 m during their lifetime, with broad distributions in terms of size, duration, volume, and intensity, and with 26% of them harboring corrosive conditions (ΩA < 1). By clustering the OAXs, we find three types of extremes in the CCS. Near the coast, intense, shallow, and short‐lasting OAXs dominate, caused by strong upwelling. A second type consists of large and long‐lasting OAX events that are associated with westward propagating cyclonic eddies. They account for only 3% of all extremes, but are the most severe events. The third type is small extremes at depth arising from pycnocline heave. OAXs potentially have deleterious effects on marine life. Marine calcifiers, such as pteropods, might be especially impacted by the long‐lasting events with corrosive conditions.

Strong Habitat Compression by Extreme Shoaling Events of Hypoxic Waters in the Eastern Pacific

“…For example, strongly deoxygenated water masses trapped in eddy cores are partially the result of continuous oxygen consumption along the eddy trajectory (Fiedler et al., 2016; Frenger et al., 2018; Karstensen et al., 2015, 2017). A complementary Lagrangian analysis (Desmet et al., 2022) for each THREE would be required to account for non‐local oxygen consumption but would go beyond the scope of this study. Nonetheless, Montes et al.…”

“…For example, strongly deoxygenated water masses trapped in eddy cores are partially the result of continuous oxygen consumption along the eddy trajectory (Fiedler et al, 2016;Frenger et al, 2018;Karstensen et al, 2015Karstensen et al, , 2017. A complementary Lagrangian analysis (Desmet et al, 2022) for each THREE would be required to account for non-local oxygen consumption but would go beyond the scope of this study. Nonetheless, Montes et al (2014) show that the modeled variability of physical oxygen fluxes is about an order of magnitude larger than of biogeochemical oxygen fluxes in the ETSP ODZ, providing confidence, that physical processes are dominant in driving THREEs.…”

“…To date, only few studies exist that describe subsurface biogeochemical extreme events (see perspective by Gruber et al (2021)). Most of these studies focus on ocean acidification (e.g., Hauri et al, 2013;Hauri et al, 2021), analyze extreme events at a fixed depth level (Burger et al, 2020;Gruber et al, 2021) or track extremes through space and time in a Lagrangian framework (Desmet et al, 2022). Thus, as we analyze the variability of the spatially varying HI depth in a Eulerian framework, a direct comparison of THREE characteristics with previous findings is challenging.…”

“…Hence, the physical and biogeochemical characteristics of the compressed habitat co‐determine the biogeochemical and biological impacts of THREEs. Compound events, that is, simultaneous or successive occurrences of THREEs and other marine extremes (such as marine heatwaves (Frölicher et al., 2018; Oliver et al., 2018) or acidification extremes (Burger et al., 2020; Desmet et al., 2022; Hauri et al., 2013)), could thus have additive or even synergistic effects on epi‐ and mesopelagic ecosystems (Gruber et al., 2021).…”

Drivers of Surface Ocean Acidity Extremes in an Earth System Model

“…Extreme variations in ocean acidity, known as ocean acidity extreme (OAX) events, can amplify the impacts of long-term ocean acidification on marine organisms and ecosystems by pushing them beyond their limits of resilience (e.g., Bednaršek et al, 2022;Gruber et al, 2021;Spisla et al, 2021). These events can cause changes in hydrogen ion concentration ([H + ]) and other carbonate system variables of similar magnitude to those expected from long-term ocean acidification during the 21st century (Desmet et al, 2022;Hofmann et al, 2011;Leinweber & Gruber, 2013), particularly in coastal oceans (Torres et al, 2021). OAX events occur on much shorter timescales and can have detrimental impacts on marine organisms, as demonstrated, for example, by laboratory and field studies that show signs of shell dissolution in calcifying organisms after only a few days in undersaturated calcium carbonate waters (e.g., Bednaršek et al, 2012Bednaršek et al, , 2014.…”