Contrasting Impact of Future CO₂ Emission Scenarios on the Extent of CaCO₃ Mineral Undersaturation in the Humboldt Current System

Abstract

The eastern boundary upwelling systems are among those regions that are most vulnerable to an ocean acidification‐induced transition toward undersaturated conditions with respect to mineral CaCO3, but no assessment exists yet for the Humboldt Current System. Here we use a high‐resolution (∼7.5 km) regional ocean model to investigate past and future changes in ocean pH and CaCO3 saturation state in this system. We find that within the next few decades, the nearshore waters off Peru are projected to become corrosive year round with regard to aragonite, the more soluble form of CaCO3. The volume of aragonite undersaturated water off Peru will continue to increase in the future irrespective of the amount of CO2 emitted to the atmosphere. In contrast, the development of the saturation state with regard to calcite, a less soluble form of carbonate, depends strongly on the scenario followed. By 2050, calcite undersaturation appears in the nearshore waters off Peru occasionally, but by 2090 in a high‐emission scenario (RCP8.5), ∼60% of the water in the euphotic zone will become permanently calcite undersaturated. Most of this calcite undersaturation off Peru can likely be avoided if a low emission scenario (RCP2.6) consistent with the Paris Agreement is followed. The progression of ocean acidification off Chile follows a similar pattern, except that the saturation states are overall higher. But also here, calcite undersaturated waters will become common in the subsurface waters under the RCP8.5 scenario by the end of this century, while this can be avoided under the RCP2.6 scenario.

Processes Driving Global Interior Ocean pH Distribution

“…As shown by Negrete‐García et al () this natural gradient means that a very small anthropogenic perturbation is sufficient to shift the aragonite saturation horizon by several hundred meters from one year to the next. A similar effect has been shown by Hauri et al (), Feely et al (), and Franco et al () for Eastern Boundary Upwelling Systems, which are also regions where natural processes act to enhance the impact of ocean acidification. Such research highlights the fact that ocean acidification decreases natural pH distributions that result from ocean mixing, biological production and remineralization, mineral dissolution, temperature changes, and gas exchange.…”

Upwelling Amplifies Ocean Acidification on the East Australian Shelf: Implications for Marine Ecosystems

“…In the future ocean, upwelling events in these systems are projected to become more intense, more frequent and increase in duration (Hauri et al, 2013;Wang et al, 2015;Franco et al, 2018), although observational data hint at regional differences (Varela et al, 2015). While intensification will be driven by increasing amounts of anthropogenic CO 2 being absorbed by the world's oceans in a process termed ocean acidification (Doney et al, 2009), increases in frequency/duration are thought to be a result of enhanced land-ocean temperature gradients and alongshore winds (Di Lorenzo, 2015).…”

Dynamics of the Carbonate System Across the Peruvian Oxygen Minimum Zone

“…The upwelling region of Peru is one of the most important upwelling systems in the world due to its high productivity that supports abundant fisheries, particularly the Peruvian anchovy fishery (Chavez et al, 2008;Espinoza-Morriberon et al, 2017). Upwelling events mainly occur in spring and summer (Sobarzo and Djurfeldt, 2004;Franco et al, 2018). However, large and productive areas with important fisheries like Peru are considered to be zones that currently experience or that are projected to experience ocean acidification (Shen et al, 2017).…”

“…"Hotspots" of acidification, like the Peruvian regions, are thus predicted to occur in major fishery zones by mid-century when atmospheric CO 2 is projected to reach 650 µatm (McNeil and Sasse, 2016;Shen et al, 2017). In addition, ocean acidification modeling studies based on the oceanic uptake of anthropogenic CO 2 indicate that the upper water of the Humboldt Current is likely to become more corrosive with regard to mineral CaCO 3 (Franco et al, 2018).…”