Seasonal nearshore ocean acidification and deoxygenation in the Southern California Bight

Abstract

The California Current System experiences seasonal ocean acidification and hypoxia (OAH) owing to wind-driven upwelling, but little is known about the intensity, frequency, and depth distribution of OAH in the shallow nearshore environment. Here we present observations of OAH and dissolved inorganic carbon and nutrient parameters based on monthly transects from March 2017 to September 2018 extending from the surf zone to the ~ 40 m depth contour in La Jolla, California. Biologically concerning OAH conditions were observed at depths as shallow as 10 m and as close as 700 m to the shoreline. Below 20 m depth, 8% of observations were undersaturated with respect to aragonite, 28% of observations had a pHT less than 7.85, and 19% of observations were below the sublethal oxygen threshold of 157 µmol kg−1. These observations raise important questions about the impacts of OAH on coastal organisms and ecosystems and how future intensified upwelling may exacerbate these conditions.

Temperature-dependent feeding behavior in the brown box crab, Lopholithodes foraminatus

“…In Southern California, surface waters, down to about 10 m, exceed 20°C in summer months (Southwest Fisheries Science Center, 2023, Clements et al, 2023SOAR Dataset) or during episodic warm water events (Kekuewa et al, 2022). Yet, we found that brown box crabs are unable to survive long at 20°C in the lab but can subsist at 8°C and 15°C for extended periods of at least two months.…”

“…In deeper waters off the Southern California coast, brown box crabs are exposed to temperatures averaging 8°C (Southwest Fisheries Science Center, 2023). While brown box crabs are unlikely to experience temperatures above 15°C in the shallower part of their depth range (Donaldson and Byersdorfer, 2005;Southwest Fisheries Science Center, 2023), intertidal and subtidal waters in Southern California can reach temperatures of up to 24°C in the summer or during extreme marine heatwave events that can last for weeks to months (Kekuewa et al, 2022). Little is known about the migration behavior of brown box crabs, but their close relatives, several species of king crabs (Donaldson and Byersdorfer, 2005;Hall and Thatje, 2011), typically reside at depths below 100 m and have been observed migrating to mate and hatch in warmer, shallower waters (0 -100 m) (Stone et al, 1992;Donaldson and Byersdorfer, 2005).…”

Mississippi River Chemistry Impacts on the Interannual Variability of Aragonite Saturation State in the Northern Gulf of Mexico

“…DIC ratio), [Ca 2+ ] is the calcium ion concentration, which varies with salinity, and K Ar is the apparent solubility product of aragonite, a function of temperature, salinity, and pressure (Wang et al, 2013;Wanninkhof et al, 2015). Aragonite is prone to dissolve at Ω Ar values lower than one, but calcifying organisms may start experiencing stress under Ω Ar values lower than 2.0 (e.g., Kekuewa et al, 2022;Siedlecki et al, 2021). Quantifying the occurrence of those suboptimal levels (Ω Ar < 2.0) is therefore relevant for the management of shellfish and other important marine resources, such as the oyster Crassotea virginia, an important fishery resource along the northern GoM coast (Turner, 2006).…”

“…Ω Ar represents the solubility of aragonite, a specific mineral phase of CaCO 3 , which can be defined by: $$${{\Omega }}_{\text{Ar}}=\left[{{\text{CO}}_{3}}^{2\mbox{--}}\right]\cdot \,\left[{\text{Ca}}^{2+}\right]\cdot \,{{K}_{\text{Ar}}}^{\mbox{--}1}$$$ where $$\left[{{\text{CO}}_{3}}^{2\mbox{--}}\right]$$ is the carbonate ion concentration, a property strongly correlated to the Alk‐to‐DIC ratio (Alk:DIC ratio), [Ca 2+ ] is the calcium ion concentration, which varies with salinity, and K Ar is the apparent solubility product of aragonite, a function of temperature, salinity, and pressure (Wang et al., 2013; Wanninkhof et al., 2015). Aragonite is prone to dissolve at Ω Ar values lower than one, but calcifying organisms may start experiencing stress under Ω Ar values lower than 2.0 (e.g., Kekuewa et al., 2022; Siedlecki et al., 2021). Quantifying the occurrence of those suboptimal levels (Ω Ar < 2.0) is therefore relevant for the management of shellfish and other important marine resources, such as the oyster Crassotea virginia , an important fishery resource along the northern GoM coast (Turner, 2006).…”

A high-resolution synthesis dataset for multistressor analyses along the U.S. West Coast

“…Upwelling intensity varies across small spatial and temporal scales and is typically concentrated in the spring and early summer (Hickey, 1979;Marchesiello et al, 2003;Garciá-Reyes and Largier, 2012;Jacox et al, 2018;Cheresh and Fiechter, 2020). During upwelling, minimal values of seasonal dissolved oxygen and carbonate chemistry parameters such as pH are naturally close to biologically significant thresholds, making organisms in the CCS particularly vulnerable to ocean acidification and hypoxia (OAH) events (e.g., Chan et al, 2008;Connolly et al, 2010;Feely et al, 2008;Gruber et al, 2012;Low et al, 2021;Kekuewa et al, 2022). Local adaptation to high environmental variability may provide some ecological resilience (e.g., Sanford and Kelly, 2011;Kelly and Hofmann., 2013;Donham et al, 2023), but widespread die-offs are already a feature of some OAH events (e.g., Grantham et al, 2004;Barton et al, 2015).…”