Climate change feedbacks on future oceanic acidification

Abstract

Oceanic anthropogenic CO₂ uptake will decrease both the pH and the aragonite saturation state (Ω_arag) of seawater leading to an oceanic acidification. However, the factors controlling future changes in pH and Ω_arag are independent and will respond differently to oceanic climate change feedbacks such as ocean warming, circulation and biological changes.We examine the sensitivity of these two CO₂-related parameters to climate change feedbacks within a coupled atmosphere-ocean model. The ocean warming feedback was found to dominate the climate change responses in the surface ocean. Although surface pH is projected to decrease relatively uniformly by about 0.3 by the year ₂100, we find pH to be insensitive to climate change feedbacks, where as Ω_arag is buffered by˜15%. Ocean carbonate chemistry creates a situation whereby the direct pH changes due to ocean warming are almost cancelled by the pH changes associated with dissolved inorganic carbon concentrations changes via a reduction in CO₂ solubility from ocean warming. We show that the small climate change feedback on future surface ocean pH is independent to the amount of ocean warming. Our analysis therefore implies that future projections of surface ocean acidification only need to consider future atmospheric CO₂ levels, not climate change induced modifications in the ocean.