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

Nathalie Lefèvre,Doris Veleda,Moacyr Araujo,Guy Caniaux

doi:10.3402/tellusb.v68.30305

Abstract

Hourly fCO2 is recorded at a time series at the PIRATA buoy located at 6°S 10°W 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 alkalinity–salinity relationship determined for the eastern tropical Atlantic and the observed fCO2, 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, fCO2 and pH are strongly correlated. On seasonal timescales, the correlation still holds between fCO2 and pH and their variations are in agreement with those of sea surface salinity. At interannual timescales, some important differences appear in 2011–2012: lower fCO2 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 2006–2013 on CO2 and any other physical parameter. However, as atmospheric fCO2 is increasing over time, the outgassing of CO2 is reduced over the period 2006–2013 as the flux is mainly controlled by the difference of fCO2 between the ocean and the atmosphere. A longer time series is required to determine if any significant trend exists in this region.

Highlights

Since the last decades, the continuous increase of global atmospheric CO2 has led to an increase of CO2 in the ocean reducing the CO2 concentration remaining in the atmosphere
When CO2 is absorbed by the ocean, it reacts with seawater to form carbonic acid, which increases ocean acidity by releasing H' ions, increases the inorganic carbon and decreases
sea surface temperature (SST), SSS, fugacity of CO2 (fCO2) variations are plotted for each year of the period 2006Á2013 (Fig. 3), in order to characterise the different scales of variability, from intraseasonal to interannual

Summary

Introduction

The continuous increase of global atmospheric CO2 has led to an increase of CO2 in the ocean reducing the CO2 concentration remaining in the atmosphere. This continuous absorption of CO2 has consequences on the chemistry of the ocean and on the biology. The decrease of CO23À reduces the saturation states of calcium carbonates (calcite and aragonite) This will lead to a shallower saturation horizon which will affect marine organisms that secrete CaCO3 to produce their shells or skeletons (Orr et al, 2005) and gradually slow down the production of calcium carbonate in the surface ocean (Riebesell et al, 2000).

Methods

Results

Conclusion