Blooms in the Baltic Sea

By Hajo Krasemann (HZG, Institute for Coastal Research)

Sentinel-3A carries several instruments to monitor the Earth's surface. One of them OLCI, the ocean and land colour instrument (OLCI), captured the imagery in Figure 1 and 2.

Captured by Sentinel-3A on 20 July, Figure 2 shows the colour of the sea in the Baltic and North Sea as it was detected by the satellite, cleared from influences by the atmosphere (Figure 1).

OLCI allows biogeochemical measurements like concentrations of chlorophyll - the photosynthetic pigment of phytoplankton (algae), and suspended sediments.

In this scene eddies are visible in the Baltic and filamentary structures west of the Danish coast both are formed by increased growing of algae called algae blooms.

This information can be used to predict harmful algal blooms, which is particularly relevant in the Baltic Sea where extreme blooms are a significant problem.

Information on health and vulnerability of marine ecosystems is fundamental to our knowledge of ocean productivity and, in turn, fish stocks.

Concurrently to the overflight of Sentinel-3A a local measurement of the ocean colour was taken in the German Bight between Cuxhaven and Helgoland to confirm the performance of the satellite derived values (Figure 3).

Note: Sentinel-3 data is currently test data, available only to selected expert users.