Mediterranean Sea - DIVAnd 4D 6-year seasonal analysis of Water body dissolved inorganic nitrogen (DIN) 1990/2023 v2025

Moving 6-year analysis of Water body dissolved inorganic nitrogen (DIN) in the Mediterranean Sea for each season:
- winter: January-March,
- spring: April-June,
- summer: July-September,
- autumn: October-December. 
Every year of the time dimension corresponds to the 6-year centered average of the season.
6-years periods span from 1990-1995 until 2018-2023.
Description of DIVA analysis: The computation was done with the DIVAnd (Data-Interpolating Variational Analysis in n dimensions), version 2.7.12, using GEBCO 30sec topography for the spatial connectivity of water masses.
The horizontal resolution of the produced DIVAnd maps grids is dx=dy=0.125 degrees (around 13.5km and 10.9km accordingly).
The vertical resolution is 21 depth levels: [0.,5.,10.,20.,30.,50.,75.,100.,125.,150.,200.,250.,300.,400.,500.,600.,700.,800.,900.,1000.,1100.].
The horizontal correlation length is 200km.
The vertical correlation length (in meters) was set twices the vertical resolution: [10.,10.,20.,20.,40.,50.,50.,50.,50.,100.,100.,100.,200.,200.,200.,200.,200.,200.,200.,200.,200.].
Duplicates check was performed using the following criteria for space and time: dlon=0.001deg., dlat=0.001deg., ddepth=1m, dtime=1hour, dvalue=0.1.
The error variance (epsilon2) was set equal to 1 for profiles and 10 for time series to reduce the influence of close data near the coasts.
An anamorphosis transformation was applied to the data (function DIVAnd.Anam.loglin) to avoid unrealistic negative values: threshold value=200.
A background analysis field was used for all years (1990-2023) with correlation length equal to 600km and error variance (epsilon2) equal to 20.
Quality control of the observations was applied using the interpolated field (QCMETHOD=3). Residuals (differences between the observations and the analysis (interpolated linearly to the location of the observations) were calculated. Observations with residuals outside the minimum and maximum values of the 99% quantile were discarded from the analysis. 
Originators of Italian data sets-List of contributors:
- Brunetti Fabio (OGS)
- Cardin Vanessa, Bensi Manuel doi:10.6092/36728450-4296-4e6a-967d-d5b6da55f306
- Cardin Vanessa, Bensi Manuel, Ursella Laura, Siena Giuseppe doi:10.6092/f8e6d18e-f877-4aa5-a983-a03b06ccb987
- Cataletto Bruno (OGS)
- Cinzia Comici Cinzia (OGS)
- Civitarese Giuseppe (OGS)
- DeVittor Cinzia (OGS)
- Giani Michele (OGS)
- Kovacevic Vedrana (OGS)
- Mosetti Renzo (OGS)
- Solidoro C.,Beran A.,Cataletto B.,Celussi M.,Cibic T.,Comici C.,Del Negro P.,De Vittor C.,Minocci M.,Monti M.,Fabbro C.,Falconi C.,Franzo A.,Libralato S.,Lipizer M.,Negussanti J.S.,Russel H.,Valli G., doi:10.6092/e5518899-b914-43b0-8139-023718aa63f5
- Celio Massimo (ARPA FVG)
- Malaguti Antonella (ENEA)
- Fonda Umani Serena (UNITS)
- Bignami Francesco (ISAC/CNR)
- Boldrini Alfredo (ISMAR/CNR)
- Marini Mauro (ISMAR/CNR)
- Miserocchi Stefano (ISMAR/CNR)
- Zaccone Renata (IAMC/CNR)
- Lavezza, R., Dubroca, L. F. C., Ludicone, D., Kress, N., Herut, B., Civitarese, G., Cruzado, A., Lefèvre, D.,Souvermezoglou, E., Yilmaz, A., Tugrul, S., and Ribera d'Alcala, M.: Compilation of quality controlled nutrient profiles from the Mediterranean Sea, doi:10.1594/PANGAEA.771907, 2011.