Carbon dioxide (CO2) from anthropogenic sources is emitted into the atmosphere before dissolving into the ocean to form carbonic acid. This increase in ocean acidity is known as Ocean Acidification (OA).
Marine calcifiers make their shells and skeletons using calcium carbonate, and may be particularly affected by OA. Although the recent rate of acidification is unprecedented in geological history, one way to get a better understanding of how the Earth system will respond to acidification in the future is to examine its behaviour in the geological and more recent historical past.
1. What was the magnitude and rate of ancient abrupt acidificaiton events? Do thresholds exist in the climate system with respect to OA?
2. Can we use geochemical techniques to reconstruct the magnitude of historical acidification? What does this historical acidification tell us about how organisms have already been impacted by OA?
How do we do it?
Quantitative reconstruction of the pH change during ancient OA events, such as the Palaeocene-Eocene thermal maximum (PETM), are lacking or limited.
Similarly, the magnitude of historical (i.e. last 200 years) acidification at any one location is unknown due to a lack of seawater pH measurements beyond the 1980's.
We use cutting edge boron isotopic techniques linked with ocean biogeochemical models to reconstruct the ocean pH change across these abrupt events.
Records of the biotic response to both ancient and historical OA can then used to identify critical thresholds and provide insights into the likely behaviour of marine calcifiers to future acidification.
Aze, T., Pearson, P.N., Dickson, A.J., Badger, M.P.S., Bown, P.R., Pancost, R.D., Gibbs, S.J., Huber, B.T., Leng, M.J., Coe, A.L., Cohen, A.S. and Foster, G.L. (2014) Extreme warming of tropical waters during the Paleocene-Eocene Thermal Maximum. Geology, 42, (9), 739-742. (doi:10.1130/G35637.1).
Honisch, B., Ridgwell, A., Schmidt, D.N., Thomas, E., Gibbs, S.J., Sluijs, A., Zeebe, R., Kump, L., Martindale, R.C., Greene, S.E., Kiessling, W., Ries, J., Zachos, J.C., Royer, D.L., Barker, S., Marchitto, T.M., Moyer, R., Pelejero, C., Ziveri, P., Foster, G.L. and Williams, B. (2012) The Geological Record of Ocean Acidification. Science, 335, (6072), 1058-1063. (doi:10.1126/science.1208277).