Reconstructing past seawater pH from boron isotopes in carbonates

Pelejero, C.; Calvo, E.
Contributions to Science
Since the Industrial Revolution, the CO2 concentration in the atmosphere has increased substantially, enhancing the greenhouse effect, which is very much related with the actual global warming. Fortunately, the Earth has a series of reservoirs, especially the oceans, which trap a significant amount of this excess of CO2. This marine absorption of CO2, however, results in the progressive acidification of the oceans, which has detrimental and possibly devastating effects for marine organisms, particularly those that construct a skeleton of calcium carbonate (corals, mussels, clams, etc.). To understand the magnitude of this problem, it is crucial to know how seawater pH has oscillated in the past, particularly during those periods of time that are not covered by instrumental measurements, which are restricted to the last decade. For this purpose, there is a geochemical indicator or proxy, the isotopic composition of boron in fossil biogenic carbonates, which allows the reconstruction of the past variations in seawater pH. In this review, we will explain the theoretical grounds of this proxy, we will show the empirical calibrations performed so far, we will briefly comment some aspects of the analysis of boron isotopes, and we will list the results on paleo-pH reconstructions published so far.
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