Statement of main outcome: This section presents a satellite-based map of potential eutrophic and oligotrophic areas in the European Seas for the year 2020, together with time series of potential eutrophication in the past 23 years (1998-2020) averaged over Exclusive Economic Zones (EEZs) of each European country.The map and time series of potential eutrophication were generated on the basis of a comparison of the per-pixel chlorophyll-a data from remote sensing in the reporting year with the corresponding chlorophyll-a climatological 90th percentile (P90) established for a 20-year baseline (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017).The results showed few scattered potential eutrophic areas, while extensive coastal and shelf waters indicate a potential oligotrophic status.The distributions point to localities that should be on a watch to determine the in situ nutrient levels and whether the chlorophyll-a trend is sustained into the future.The time series of the potential eutrophication at the EEZ level showed low percentages across the area with some remarkable high potential eutrophic events occurring in the first decade of the study period, followed by an overall reduction in potential eutrophication from 2013 onwards.Furthermore, for several European countries, the eutrophication indicator at the EEZ level was often nil or never exceeded 1% of the EEZ area.Results are then compared with those from the Sustainable Development Goal (SDG, set by the United Nations General Assembly) 14 global satellite-derived eutrophication indicator (target 14.1).
Several data products, analysis software packages, and visualization tools have been released by the The Mediterranean Oceanic Data Base (MODB), a group that prepares hydrographic data sets and climatological fields for distribution to scientists working in the Mediterranean Sea. The climatological distributions of temperature and salinity in the Mediterranean that are available account for the regional properties of the water masses(Figure 1). These measurements should help refine the Mediterranean sector of the Climatological Atlas of the World Ocean published by S. Levitus in 1982. The Mediterranean gridded fields are represented in ASCII format on a 1/4‐degree grid and 19 levels on the vertical. The data sets also include the hydrographic profiles from which the analyzed fields were derived.
Abstract. In this paper, we investigate the influence of uncertainties in inherent optical properties on the modelling of radiometric quantities by an ocean radiative transfer model, in particular irradiance and reflectance. The radiative transfer model is coupled to a three-dimensional physical-biogeochemical model of the Black Sea. It describes the vertical propagation of incident irradiance within the water column along three streams in downward (direct and diffuse) and upward directions, with a spectral resolution of 25 nm in the visible range. The propagation of the irradiance streams is governed by the inherent optical properties of four major optically active constituents found in seawater and provided by the biogeochemical model: pure water, phytoplankton, non-algal particles and coloured dissolved organic matter. Sea surface reflectance is then derived as the ratio between simulated upward and downward irradiance streams, directly connecting the model with remote-sensed data. In this configuration, the coupling is in one-way: the radiative transfer model is only projecting model variables into the space of satellite observations, working as an observation operator. In the stochastic version of the model, uncertainties are injected in the form of random perturbations of inherent optical properties of water constituents. Different ensemble configurations are derived and their quality is assessed by comparison with in situ and remote-sensed observations. We find that the modelling of the uncertainties in the radiative model parameterisation allows to simulate distributions of radiative fields that are partially consistent with observations. Ensemble quality is consistent with remote-sensed reflectance data in summer and autumn, especially in the central parts of basin. The quality of the ensemble is lower in winter and early spring, suggesting the existence of another major source of uncertainty, or that the quality of the deterministic solution is insufficient. CDOM dominates absorption in short wavebands with relatively high uncertainty that influences irradiance and reflectance outputs. This dominant role calls better representation of CDOM to improve model calibration. Contributions from phytoplankton and non-algal particles are more significant for (back-)scattering. The results of this paper suggest that the integration of a radiative transfer model into a physical-biogeochemical model would be beneficial for calibration, validation and data assimilation purposes, offering a better link between model variables and radiometric observations.
Abstract The overturning circulation of the Southern Ocean has been investigated using eddying coupled ocean–sea ice models. The circulation is diagnosed in both density–latitude coordinates and in depth–density coordinates. Depth–density coordinates follow streamlines where the Antarctic Circumpolar Current is equivalent barotropic, capture the descent of Antarctic Bottom Water, follow density outcrops at the surface, and can be interpreted energetically. In density–latitude coordinates, wind-driven northward transport of light water and southward transport of dense water are compensated by standing meanders and to a lesser degree by transient eddies, consistent with previous results. In depth–density coordinates, however, wind-driven upwelling of dense water and downwelling of light water are compensated more strongly by transient eddy fluxes than fluxes because of standing meanders. Model realizations are discussed where the wind pattern of the southern annular mode is amplified. In density–latitude coordinates, meridional fluxes because of transient eddies can increase to counter changes in Ekman transport and decrease in response to changes in the standing meanders. In depth–density coordinates, vertical fluxes because of transient eddies directly counter changes in Ekman pumping.
Abstract. Today, the routine assimilation of satellite data into operational models of the ocean circulation is mature enough to enable the production of global reanalyses describing the ocean circulation variability during the past decades. The expansion of the "reanalysis" concept from ocean physics to biogeochemistry is a timely challenge that motivates the present study. The objective of this paper is to investigate the potential benefits of assimilating satellite-estimated chlorophyll data into a basin-scale three-dimensional coupled physical-biogeochemical model of the North-Atlantic. The aim is on one hand to improve forecasts of ocean biogeochemical properties and on the other hand to define a methodology for producing data-driven climatologies based on coupled physical-biogeochemical modelling. A simplified variant of the Kalman filter is used to assimilate ocean color data during a 9 year-long period. In this frame, two experiences are carried out, with and without anamorphic transformations of the state vector variables. Data assimilation efficiency is assessed with respect to the assimilated data set, the nitrate World Ocean Atlas database and a derived climatology. Along the simulation period, the non-linear assimilation scheme clearly improves the surface chlorophyll concentrations analysis and forecast, especially in the North Atlantic bloom region. Nitrate concentration forecasts are also improved thanks to the assimilation of ocean color data while this improvement is limited to the upper layer of the water column, in agreement with recent related litterature. This feature is explained by the weak correlation taken into account by the assimilation between surface phytoplankton and nitrate concentration deeper than 50 m. The assessement of the non-linear assimilation experiments indicates that the proposed methodology provides the skeleton of an assimilative system suitable for reanalysing the ocean biogeochemistry based on ocean color data.
