Evidence from Geological and Ice Core Records

Ice cores provide high resolution and accurate records of atmospheric CO2 concentrations over the last 650 000 a and together with marine paleo-proxies (e.g. boron isotopes) serve to arrive at a reasonable estimate of ocean carbonate chemistry over millions of years [14].

time/Ma before present

time/Ma before present

FIGURE 2 Past (white diamonds, data from Pearson and Palmer [14]) and contemporary varia bility of surface ocean pH (diamonds with dates). Future predictions are model derived values based on IPCC mean scenarios. Adapted from Turley et al. [15].

Such measurements indicate no major undersaturation of the surface ocean for at least the last 65 Ma and that the current rate and magnitude of CO2-induced chemical change occurring in the surface ocean are unprecedented for at least the past 25 Ma (Fig. 2).

Observations that CO2 variations in the glacial and inter-glacial periods of the last 50 000 a correlated with the shell weights of fossil planktonic forami-nifers [16] indicate that marine calcifiers are influenced by small fluctuations in atmospheric CO2 values and those effects are likely to progressively intensify with increasing CO2.

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