Coupled CO<sub>2</sub> and O<sub>2</sub>-driven compromises to marine life in summer along the Chilean sector of the Humboldt Current System

Abstract

Abstract. Carbon dioxide and coupled CO 2 and O 2 -driven compromises to marine life were examined along the Chilean sector of the Humboldt Current System, a particularly vulnerable hypoxic and upwelling area, applying the Respiration index (RI = log 10 pO 2 pCO 2 ) and the pH-dependent aragonite saturation ( ) to delineate the water masses where aerobic and calcifying organisms are stressed. As expected, there was a strong negative relationship between oxygen concentration and pH or pCO 2 in the studied area, with the subsurface hypoxic Equatorial Subsurface Waters extending from 100 m to about 300 m depth and supporting elevated pCO 2 values. The lowest RI values, associated to aerobic stress, were found at about 200 m depth and decreased towards the Equator. Increased pCO 2 in the hypoxic water layer reduced the RI values by as much as 0.59 RI units, with the thickness of the upper water layer that presents conditions suitable for aerobic life (RI>0.7) declining by half between 42 • S and 28 • S. The intermediate waters hardly reached those stations closer to the equator so that the increased pCO 2 lowered pH and the saturation of aragonite. A significant fraction of the water column along the Chilean sector of the Humboldt Current System suffers from CO 2 -driven compromises to biota, including waters corrosive to calcifying organisms, stress to aerobic organisms or both. The habitat free of CO 2 -driven stresses was restricted to the upper mixed layer and to small water parcels at about 1000 m depth. Overall pCO 2 acts as a hinge connecting respiratory and calcification challenges expected to increase in the future, resulting in a spread of the challenges to aerobic organisms.

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

“…~42° S) up to Ecuador and the Galapagos Islands near the Equator (~5° N), and is one of the most productive marine ecosystems in the world 38 . This system, and particularly the coastal region off Chile, is characterized by large spatial-temporal heterogeneity in p CO2 conditions 39,40 , and is an area in which the effects of low pH/high p CO2 conditions can already be seen (Fig. 1).…”

Environmental pH, O2 and Capsular Effects on the Geochemical Composition of Statoliths of Embryonic Squid Doryteuthis opalescens

“…The only other known study that tested the effects of environmental pH on squid-embryo statolith geochemistry found that only 65 Zn significantly differed from an elemental suite that included 110m Ag, 109 Cd, 57 Co, 203 Hg and 54 Mn [49]. Evidence that environmental tracers in squid statoliths can track seawater pH and [O 2 ] is especially useful, because uranium has been shown to be promising for understanding squid life history, migrations and habitat use [88,90,91].…”

“…Low pH/high pCO 2 and low [O 2 ] (hereafter referred to as "low pHOx") can cause species-specific negative effects in isolation or in tandem, and the magnitude of each of these effects is likely to be habitat specific [65,66]. We conducted experiments to investigate whether statolith geochemistry can reveal squid exposure to low pHOx, low [O 2 ] only and/or low pH/high pCO 2 only (hereafter, referred to as "low pH") during benthic encapsulated stages.…”

Oxygen and indicators of stress for marine life in multi-model global warming projections

“…The combined mechanisms of global CO 2 (and f CO 2 ) increase and more local deoxygenation (and f O 2 decrease) have just begun to be addressed (e.g., Paulmier et al, 2011;Pörtner et al, 2011;Gruber, 2011;Mayol et al, 2012;Brewer and Peltzer, 2009) and need to be further investigated. Surprisingly, there is a lack of studies that project the combined evolution of these variables under global warming and anthropogenic carbon emissions using fully coupled Earth System Models.…”

“…Recently, observational studies focused on upwelling regions (Mayol et al, 2012;Paulmier et al, 2011), typical low-O 2 -high-CO 2 areas of particular vulnerability, where elevated f CO 2 levels represent a key threat connecting aerobic stress and calcification challenges. However, f CO 2 and CO 2 are not state variables in ocean biogeochemical models and coupled Earth System Models, and their distribution below the surface layer has been studied poorly.…”