Data and updating

Access and use

The data and resulting data products (tables, figures and maps) available on the indicator web page can be used freely given that the source is cited. The indicator should be cited as following: 

HELCOM (2018) Chlorophyll-a. HELCOM core indicator report. Online. [Date Viewed], [Web link].

ISSN 2343-2543



Result: Chlorophyll-a


Data source: The average chlorophyll-a was combined estimate of two types of data:

1) In-situ monitoring data provided by the HELCOM Contracting Parties, and kept in the HELCOM COMBINE database, hosted by ICES (, added with data from the Gulf of Finland year database, hosted by the Finnish Environment Institute.

2) The original source of the satellite-based EO-chl-a dataset is calculated at SYKE using ENVISAT/MERIS instrument data (2011). It has been validated by SYKE, and kept at the eutrophication assessment database hosted by ICES.  For the assessment period 2011-2016, data was available only during 2011.

3) FerryBox flow-through data is reported to ICES by Contracting Parties, to be included into the eutrophication assessment database. It is reported according to the QA/QC guidance for FerryBox Flow-through information, providing adequate metadata and quality information, including the following:

  • (arithmetic and) geometric mean
  • mode (most frequently occurring value in dataset)
  • standard deviation
  • percentiles (5,25, 50, 75, 95)
  • N of observations that were used to derive statistics

Geographical coverage: The observations are distributed in the sub-basins according to the HELCOM COMBINE programme, added occasionally with data from research cruises. In-situ data was used in all open-sea assessment units, while EO-data was applied only in SEA-001…003 and SEA-007…017.

Temporal coverage: The estimates are based on observations made between June – September. In-situ estimates include observations made during 2011-2016, whereas EO-data was available only during 2011.

Data aggregation: The 2011-2016 values for each sub-basin were estimated as an inter-annual summer (June-September) averages.