Fig. 1
(a) Alkalinity–salinity relationships of Koffi et al. (2010) and Takahashi et al. (2014). The dots correspond to the 190 data used (EGEE cruises from 2005 to 2007) for determining the Koffi et al.'s relationship and the crosses correspond to the 349 new data collected during the PIRATA FR cruises from 2009 to 2015. The 10-quantiles are indicated in red. (b) Differences between the observations and the alkalinity calculated with the relationship of Lee et al. (2006) as a function of salinity.
Fig. 2
Climatological surface velocity currents superimposed on the SST field for (a) January, (b) April, (c) July and (d) October. The climatology is calculated over the period January 2006–December 2013. The black circle indicates the position of the mooring. The surface velocity currents are from OSCAR and the SST climatology from GLORYS2v3 on a grid of 0.25° resolution.
Fig. 3
Hourly distribution of (a) SST, (b) SSS and (c) fCO2 from January to December for the years 2006 to 2013. From April 2012 the high resolution SSS is not available so mean daily data are plotted. Orange shaded areas correspond to high fCO2 associated with low SST (see text for details).
Fig. 4
(a) Daily difference of fCO2 between the ocean and the atmosphere (ΔfCO2) and (b) daily CO2 fluxes over the whole time series.
Fig. 5
Box and whisker plots of daily (a) SST, (b) SSS and (c) fCO2 for each month of the time series. The horizontal red line corresponds to the median, the blue box to the data between the first and third quartiles, the error bars to the minimum and maximum, and the crosses to outliers. The black line corresponds to the monthly climatology 2006–2013.
Table 1. Seasonal values of monthly climatological SST, SSS, fCO2, pH, TCO2, nTCO2 and TA calculated over 2006–2013 at 6°S, 10°W: minimum, maximum, range, mean, standard deviation (STD), median and interquartile range (IQR)
Table 2. Correlation between monthly variables calculated over the period 2006–2013
Fig. 6
Monthly distribution of (a) precipitation, (b) zonal wind and (c) meridional wind at the mooring. The precipitation from GPCP is represented in red and the precipitation at the PIRATA mooring in blue. The black line corresponds to the monthly climatology calculated over 2006–2013. The mean of the zonal and meridional wind components is −4.70 and 4.29 m/s, respectively. The zonal and meridional components of the wind are blue shaded with their respective 2006–2014 mean used as the base level. A zonal negative wind corresponds to a wind blowing westward and a positive meridional wind corresponds to a wind blowing northward. (d) Zonal wind anomaly and (e) meridional wind anomaly from 2006 to 2013.
Fig. 7
Hovmöller diagram of the meridional salinity anomaly advection (in s−1), averaged over the box 9°S–6°S and 10.5°W–9.5°W, from the surface to 50 m depth.
Fig. 8
Normalised fCO2 ((fCO2 – <fCO2>)/σ fCO2 ) and normalised SSS ((SSS – <SSS>)/σSSS) data at 6°S, 10°W from 14 August 2011 to 31 December 2011.
Fig. 9
Tropical South Atlantic index from 2006 to 2013. The index is calculated as the area-averaged monthly SST anomalies over the region 30°W–10°E, 20°S–0°. The anomalies are deviations from the 1951–2000 climatology (www.esrl.noaa.gov/psd).
Fig. 10
Time series of (a) fCO2, (b) pH, (c) TCO2 anomalies over the period 2006–2013 with regression line (green). (d) Time series of SST anomalies over the period 2000–2014. Solid lines correspond to the linear regressions for the periods 2000–2014 (red, SST=0.00516*time – 10.36352), 2006–2012 (green, SST=−0.0056*time+11.39793), 2006–2014 (blue) where time is in years; dashed lines correspond to the 95 % confidence intervals of the regressions over the various time segments, (e) time series of SSS anomalies over the period 2000–2014. Solid lines correspond to the linear regressions for the periods 2000–2014 (red, SSS=0.00575*time – 11.53567) and 2006–2014 (blue, SSS=0.00685*time – 13.75012); dashed lines correspond to the 95 % confidence intervals of the regressions over both time segments.