Evidence from Long Term Oceanographic Time Series

The Pacific time-series station, off Hawaii (Hawaii Ocean Time-Series, HOTS), shows an increase in seawater CO2 concurrent with the increase in atmospheric CO2 recorded at Mauna Loa. The resultant decrease in surface ocean pH is 0.0019 ± 0.00025 a 1 (Fig. 3a) [17]. Aragonite and calcite saturation states also both show a decline over the last 20 a (Fig. 3b and c).

The other two major time series stations, the Bermuda Atlantic Time-Series (BATS) and the European Station for Time-Series in the Ocean at the Canary Islands (ESTOC), located either side of the North Atlantic, show a decrease in the seawater pH of around 0.0012 ± 0.0006 a 1 at BATS, and 0.0017 ± 0.0004 a 1 at ESTOC due to increased uptake of CO2 [18]. These time-series data show that the Pacific and the subtropical gyre at both sites on the North Atlantic are becoming more acidic as predicted by ocean general-circulation models (OGCMs) (see below).

a 275 5.00

■^atm y = 174x - 3105-9 R2 = 0.94, st.err. = 0.029

■^atm y = 174x - 3105-9 R2 = 0.94, st.err. = 0.029

Mauna Loa CO2 Record

y = -0.0019x + 11.815 R2 = 0.2654, st. err. = 0.00025

6.50

GEOSECS

Calcite Saturation State

6.50

6.00

5.50

GEOSECS

Calcite Saturation State y = -0.011x + 27.7

T"

1950 1960 1970 1980 1990 2000 2010 2020 Year

FIGURE 3 (a) The Mauna Loa records of atmospheric CO2 over the last 50 a with the pCO2SW and surface ocean pH recorder during the last two decades from the Hawaii Ocean Time Series (HOTS) and the resultant changes to (b) Agaronite saturation state and (c) calcite saturation state over the same period. From Doney et al. [17].

Mauna Loa CO2 Record

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