Beautiful phytoplankton – the basis of the marine food web

On the way to our intensive study area in Dronning Maud Land, the work package leaders on RV Kronprins Haakon constantly have to keep the cruise plan updated with the time schedule and with sea ice conditions, weather and whatever interesting is coming up on the way. Looking at satellite images, Sebastien Moreau (NPI) discovered a large phytoplankton bloom, which could provide a vital source of food to the ecosystem at the onset of winter as well as draw down a lot of atmospheric CO2 before sea ice caps the ocean for winter. We therefore changed the route slightly to cross through the bloom to take measurements and water samples.

Strong bloom (orange area) developing west of Droning Maud Land in our research area (SAR image, March 2019).

While inside the bloom, the observers on board spotted more than 100 whales, compared to about 5 on other days. The whales are there for one reason: food! And the food chain starts all the way down with primary producers that are the food for krill. The Antarctic krill has an estimated biomass of around 389 000 000 tonnes, which is more than the global population of humans! More than 50% of this mass fuels the ecosystem: the whales, seals, penguins, squid and fish.

Primary production in the Southern Ocean is generally low despite high nutrient concentrations. This is due to low iron concentrations. It increases close to islands, coasts, sea ice edge and icebergs. In Dronning Maud Land, many processes that increase primary production come together and green sea ice filaments can even be seen on satellite images.

Inside the giant phytoplankton plume, water samples were therefore taken and analysed with microscopy. It is incredible that nature can create those beautiful pieces of art that are so important for the life on earth!

Microscopy of phytoplankton from a giant plume in Dronning Maud Land. Photos: S. Moreau (NPI)


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