Published: 19.09.2023 Updated: 05.10.2023
Just beneath the ocean surface, a minke whale glides through the water.
A boat carefully approaches the big mammal.
At the bow stands whale scientist Audun Rikardsen from UiT The Arctic University of Norway – his eyes are tracking the whale as it swims. The boat adjusts its position: a little further, a little to the right. Finally, the boat is close enough.
Rikardsen pulls the trigger.
Success! The minke whale swims on, as nothing has happened, oblivious to the fact she is carrying a passenger: a satellite tag.
“It’s a challenge to tag these animals,” explains marine biologist Carla Freitas. “Minke whales are fast swimmers, and only spend few seconds at the surface”.
This minke whale is the first one tagged in the Horizon Europe project OceanICU, where the Institute of Marine Research (IMR) in Norway is one of 31 partners. The five-year project is led by NORCE.
“Our aim is to better understand of the oceanic carbon cycle – especially the biological carbon pump, which is more complex than previously assumed,” Freitas says. Previous research has mainly focused on how phytoplankton and bacteria affect the biological carbon cycle in the ocean – how phytoplankton through photosynthesis absorb CO₂, which then becomes part of the food chain or sinks to the deep sea, where it is stored. In recent years, scientists have highlighted the need for more extensive knowledge of how organisms at higher trophic levels – such as whales – contribute.
This is exactly what the IMR-scientists are investigating now as part of OceanICU. Their primary focus is the minke whale, as there is already good biological data for this species in the study area.
How do whales contribute to the biological carbon cycle?
When whales eat – either at the surface or at depth – they excrete a large amount of feces and urine. Minke whales around Svalbard, Norway excrete 600 tonnes of poo each day.
Scientists have a hypothesis that whale poo and urine are important for phytoplankton – that the poo fertilizes the ocean, similarly to how poo from cows and sheep fertilize land.
“We are estimating the amount of nutrients whales excrete; as currently there is a lack of good data,” Freitas says.
The whale tags will aid scientists to find out where whales acquire nutrients – how deep they dive, and where in the water column they eat.
“The next step is to investigate how phytoplankton absorbs the nutrients,” scientist Kjell Gundersen explains, the principal investigator in the phytoplankton experiments.
“In addition, we’ll investigate how much carbon sinks to the deep sea – both through whale excretions and when whales die and their bodies sink to the seabed,” Freitas adds.
Already, the first minke whale tagged outside Andenes in Norway has given useful information. Every time the whale surfaces, the tag sends data to scientists via satellite.
“The minke whale traveled fast northwards, and after a couple of days reached the northernmost parts of Russia,” Freitas says.
The tagged whale was most likely migrating to its summer feeding grounds in the Nordic Seas. During winter, minke whales use warmer waters in lower latitudes, where they mate and give birth.
The tag is programmed to collect a large amount of data on location and diving behavior during the first days; the tag will then fall on its own with no harm to the whale.
During the summer, two additional whales were tagged – and researchers hope to tag more.
The new data from the tags and from lab analyses, will end up in the hands of marine scientist Morten Skogen, who works with ecosystem models. He is part of the OceanICU project work group responsible for further developing current models with the new knowledge obtained in OceanICU.
“Our main goal is to investigate carbon cycling. To reduce uncertainties in climate forecasts, it is crucial to include all the most important processes,” Skogen says.
Global models, regional models and process models will all be examined.
Scientists will explore how the models can be improved, and how to better transfer knowledge from local processes to the global carbon budget – to improve our understanding of what role each part plays in the oceanic carbon cycle.
When Carla Freitas has collected data on where minke whales travel and where they eat, Skogen will include these data as a source in the models for the very first time.
Then he’ll run the same model twice: once with whales, then without – to see how important the poo is.
“There are whales in all oceans, so the big question is how much they contribute to carbon cycling globally,” Skogen says.