Average concentrations and trends of surface chlorophyll-a in transitional, coastal and marine waters surrounding Europe

Figure Created 24 Jan 2024 Published 07 May 2024 Last modified 08 May 2024
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Average summer surface chlorophyll-a concentration (left) and trends (right), in locations recently updated (last update>2016) with at least 5 years of observations, in the period between 1980 and 2021. Green circles indicate stations with significant (p<0.05) decreasing trends (i.e., improving); orange circles show stations with significant (p<0.05) increasing trends (i.e., deteriorating); and grey circles show stations with no significant trends. Colour keys of symbols and values are included in the legend.

European data


Additional information

• Average concentrations of chlorophyll-a (µg/l) and trends were calculated using data from observations in summer from the upper 10m of the water column, in locations with annual data for the last 5-year period (2016-2021).
• Growing season months considered are June-September for stations in the Baltic Sea north of 59 N and May–September for all other stations.
• Data were aggregated into squares with sides of 1.375km for coastal stations within 20km from the coastline and 5.5km for open water stations (more than 20km away from the coastline). A masking of 5km inwards from the coast was also applied.
• Temporal trends were estimated in locations with data for at least 5 years in the period 1980-2021 and updated in the last 5-year period (2017-2021), using the non-parametric Mann-Kendall test. A p-value <0.05 was considered to indicate a statistically significant trend.
• Results reflect data availability, which vary significantly across regions and over time.

Temporal coverage
1980-2021 (the temporal range specified is the maximum range of dates for raw observations but this range varies upon the availability of observations at each location).


Geographic coverage

Temporal coverage

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