Global map of CO2 anomaly

'''DEFINITION'''

At each grid point, the time series of sea-to-air flux of CO2 between 1993 and 2017 is first detrended. The reference climatology is computed by averaging the detrended time series between 1993 and 2014. The sea-to-air CO2 flux anomaly is then obtained from the difference between the modelled sea-to-air CO2 flux in year 2017 (product GLOBAL_REANALYSIS_BIO_001_029) and the reference climatology (1993-2014). It is expressed in mole of carbon per square meter per year (mol C.m-2.yr-1). The signal is detrended in order to filter the model drift.

''''CONTEXT'''

The concentration of atmospheric CO2 has exceeded 400 ppm in 2015 and has thus increased by about 40% from about 280 ppmv in the pre-industrial era (Conway et al. 1994, Masarie and Tans 1995, www.esrl.noaa.gov/gmd/ccgg/trends/). This increase would have been much stronger without the contribution of the ocean and land biospheres which absorb each year roughly one half (25% ocean and 25% land) of the anthropogenic carbon emissions (Le Quéré et al. 2016, Ballantyne et al. 2012). The ocean acts as a carbon sink at high latitudes (40°- 60° in both hemispheres) due to the combined effect of cooling, formation of deep water in winter and of biological activity (strong seasonal bloom in these area) in spring (Takahashi 2002). Strong winds also blows over these waters which increase the ocean uptake (Takahashi 2002). In upwelling systems (equatorial upwelling, eastern boundary upwelling system, Arabian Sea upwelling), the ocean is a source of CO2 for the atmosphere due to the upwelling of CO2-rich waters. In the Pacific Ocean, the upwelled water masses at the equator are then advected westward and poleward due to equatorial divergence within the subtropical cells.

'''CMEMS KEY FINDINGS'''

In 2017 (unlike in year 2016), there is no significative anomaly of sea-to-air CO2 flux in the Tropical Pacific, corresponding to the absence of El Niño conditions.