Anthropogenic CO2 uptake by the ocean will decrease both the pH
and the aragonite saturation state (Ωarag) of seawater. However, the factors controlling future changes
in pH and Ωarag 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 CO2-related parameters to climate change feedbacks within a
coupled atmosphere-ocean model. Although surface pH is projected to decrease
relatively uniformly by ~0.25 by the year 2100, we find pH to be insensitive to
climate change feedbacks, whereas Ωarag is buffered by ~15%. The independent
climate change response between pH and Ωarag is attributed solely to
the opposing effects associated with ocean warming, which increases Ωarag
but lowers pH. Our result implies that
future climate change projections for surface ocean pH can be adequately
simulated using ocean-only models, however for Ωarag more complex
coupled atmosphere-ocean models are required.
Author: B. I. McNeil and R. J. Matear
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