Global map of Nitrate anomaly

DEFINITION''' At each grid point, the time series of surface nitrate concentration between 1993 and 2017 is first detrended. The reference climatology is computed by averaging the detrended time series between 1993 and 2014. The surface nitrate anomaly indicator is then obtained from the difference between the modelled surface nitrate concentration in year 2017 (product GLOBAL_REANALYSIS_BIO_001_029) and the reference climatology (1993-2014). It is expressed in milli mole per cubic meter (mmol.m-3). The signal is detrended in order to filter the model drift.

'''CONTEXT''' Mineral nutrients are key components of the oceanic biogeochemical cycles. They are assimilated by autotroph organisms to build living organic matter which is in turn recycled back into nutrients by bacteria at the end of the food web. Nitrate is one the main macro-nutrients limiting the growth of phytoplankton (primary production) that is why it has been defined as an Essential Ocean Variable (EOV). The variability of equatorial tongue of nitrate in the Tropical Pacific is mainly constrained by El Niño Southern Oscillation (ENSO). Respectively, in El Niño/La Nina conditions, the equatorial upwelling is reduced/strengthened and the nitrate anomaly is negative/positive.

'''CMEMS KEY FINDINGS''' In 2017, there is no significative anomaly of nitrate in the Tropical Pacific, corresponding to the absence of El Niño conditions.