Fig. 3
Temporal variability in sea surface pH, Ωarag, zonal wind speed and mixed layer depth (MLD) in January in three latitudinal bands. a–d Sea surface pH at in situ temperature (a, pH@in situ), sea surface aragonite saturation state at in situ temperature (b, Ωarag@in situ), zonal wind speed (c) and mixed layer depth (d, MLD) at 60°–55° S. e–h show the same parameters but at 55°–50° S; i–l shows the same parameters but at 50°–45° S. The vertical bars show one standard deviation, which reflects the spatial variability within each latitudinal band. Linear regression analyses were performed for the periods 1991–2000 (blue) and 2001–2011 (black). Slopes (s), and p-values of the regression analyses are also shown (differentiated with blue and black colors for the two periods). Trends of p-value < 0.1 are regarded as significant statistically (90% confidence interval) due to the small sample numbers (<10). The open gray circles indicate the values computed due solely to the atmospheric CO2 increase shown in Fig. 2c (see 'Methods'). Zonal wind speed and MLD are the mean values within 140°–148° E in the three latitudinal bands, respectively. Note by definition the trend of meridional Ekman transport is the same as that of zonal wind
