Black Sea Chlorophyll-a anomalies

'''DEFINITION''' The regional annual chlorophyll anomaly is computed by subtracting a reference climatology (1997-2014) from the annual chlorophyll mean, on a pixel-by-pixel basis and in log10 space. Both the annual mean and the climatology are computed employing the regional products as distributed by CMEMS, derived by application of the regional chlorophyll algorithm over remote sensing reflectances produced by the Plymouth Marine Laboratory (PML) using the ESA Ocean Colour Climate Change Initiative processor (ESA OC-CCI, Sathyendranath et al., 2018a).

'''CONTEXT''' Phytoplankton and chlorophyll concentration as their proxy respond rapidly to changes in their physical environment. Some of those changes are seasonal and are determined by light and nutrient availability (Gregg and Rousseaux, 2014). By comparing annual mean values to the climatology, we effectively remove the seasonal signal at each grid point, while retaining information on peculiar events during the year. In particular, chlorophyll anomalies in the Black Sea can then be correlated with SST and the North Atlantic Oscillation (Oguz and Ediger, 2006).

'''CMEMS KEY FINDINGS''' The average chlorophyll anomaly 2019 in the Black Sea is 0.81 mg m-3(-0.1 log10 [mg m-3]), with a maximum value of 26.35 mg m-3 (1.42 log10 [mg m-3]) and a minimum value of 0.03 mg m-3 (-1.60 log10 (mg m-3). The negative anomaly, reported in 2016 and 2017 (Sathyendranath et al., 2018b) occurred also in 2019, especially for northern shelf areas. For the Open Waters, there is a central core in the basin where the signal is slightly positive.