Variability and trends of carbon parameters at a time series in the eastern tropical Atlantic

Abstract

A B S T R A C THourly fCO 2 is recorded at a time series at the PIRATA buoy located at 68S 108W in the eastern tropical Atlantic since June 2006. This site is located south and west of the seasonal Atlantic cold tongue and is affected by its propagation from June to September. Using an alkalinityÁsalinity relationship determined for the eastern tropical Atlantic and the observed fCO 2 , pH and the inorganic carbon concentration are calculated. The time series is investigated to explore the intraseasonal, seasonal and interannual timescales for these parameters, and to detect any long-term trends. At intraseasonal timescales, fCO 2 and pH are strongly correlated. On seasonal timescales, the correlation still holds between fCO 2 and pH and their variations are in agreement with those of sea surface salinity. At interannual timescales, some important differences appear in 2011Á2012: lower fCO 2 and fluxes are observed from September to December 2011 and are explained by higher advection of salty waters at the mooring, in agreement with the wind. In early 2012, the anomaly is still present and associated with lower sea surface temperatures. No significant long-term trend is detected over the period 2006Á2013 on CO 2 and any other physical parameter. However, as atmospheric fCO 2 is increasing over time, the outgassing of CO 2 is reduced over the period 2006Á2013 as the flux is mainly controlled by the difference of fCO 2 between the ocean and the atmosphere. A longer time series is required to determine if any significant trend exists in this region.

The Tropical Atlantic Observing System

“…One of the longest moored pCO 2 time series in the tropical Atlantic is located at 6 • S, 10 • W and began in 2006. Acidification has been examined at this site, though the record is not long enough to detect any increase in CO 2 (or decrease of pH) given the strong natural variability of CO 2 (Lefevre et al, 2016). Documentation of the fate of organic matter (OM) in OMZs is also of paramount importance.…”

Detecting Regional Modes of Variability in Observation‐Based Surface Ocean pCO2

“…Furthermore, the majority of available measurements and auxiliary driver data is only available for the recent past (Bakker et al, ), limiting the time period the CO 2 flux can be estimated with a certain degree of confidence. Previously, regional studies have linked the air‐sea flux variability to atmospheric dynamics in the Tropical Pacific (Feely et al, ), the North Atlantic (Breeden & McKinley, ; Schuster & Watson, ), the Tropical Atlantic (Lefèvre et al, ), and the Southern Ocean (Le Quéré et al, ; Lovenduski et al, ). However, an attempt to attribute the dominant mode of variability on global scale to one single climate mode using empirical orthogonal function analysis has failed to identify a clear connection (Landschützer et al, ).…”

PIRATA: A Sustained Observing System for Tropical Atlantic Climate Research and Forecasting

“…High‐frequency fCO 2 variability is observed throughout the time series, but it is particularly pronounced after the upwelling season (Parard et al, ). The intraseasonal, seasonal, and interannual variability of fCO 2 at this site has been explored by Lefèvre et al (). On seasonal timescales, the fCO 2 variations are mainly correlated with SSS.…”

“…Orange shaded areas correspond to high fCO 2 associated with low SST. From Lefèvre et al (), their Figure 3 (reprinted by permission from Taylor and Francis Group).…”