Exploring the Central Arctic Ocean from Svalbard shelf to the North Pole

The Arctic Ocean is shifting from white to blue during summer, with less sea ice and more open water, while boreal species expand northwards. This affects primary production and energy flow in the marine food web. Research cruises and long-term moorings provide information for future management.

The Arctic Ocean has been estimated to warm twice the global mean rate in the upper 2000 m. The blue waters are expanding into the currently ice-covered area of the Nansen Basin, which, together with the Amundsen Basin, forms the Eurasian part of the Central Arctic Ocean (CAO). The Arctic amplification is predicted to accelerate with increased transport of warm and saline Atlantic water into the CAO (Atlantification). A shift from ice-covered to open ocean during summer will have dramatic consequences for structure and functioning of the marine ecosystem and will particularly impact ice-associated organisms.

Knowledge- and capacity-building

To increase our knowledge about the CAO Large Marine Ecosystem, cruises with RV Kronprins Haakon were conducted in the Eurasian deep basins of the Arctic Ocean during July-August 2022 and 2023. The 2023 program included students from USA, Canada, Greenland, Iceland, Sweden, Finland, and Norway, to promote capacity- and network-building among students from circumpolar nations with Arctic connections.

Breaking the ice

During the 2022 expedition, Kronprins Haakon followed in the wake of the ice breaker Le Commandant Charcot all the way to the North Pole through relatively thin sea ice with leads. The sea ice was relatively thick and consolidated with large ridges in the northernmost part of the Amundsen Basin, while thinner ice with open leads dominated in the Nansen Basin. The 2023 cruise encompassed a shorter survey from the shelf and slope north of Svalbard.

Deep basins from top to bottom

In 2022, two long-term ocean observatories, the moorings Amundsen-1 (N87°31′ E5°36′) and Nansen-1 (N83°56′ E22°15′), were deployed to compare the marine environment between the two deep basins. These moorings are still in the water and are planned to be retrieved and re-deployed in the summer 2024.

Both years, hydrographic full-depth surveys of physical, chemical and biological properties were conducted to explore the marine system from the shelf slope and into the deep ocean, expanding the spatial perspectives of the two moorings. The transect of the prevailing water masses shows that the Amundsen Basin is characterised by low-salinity polar waters carried by the Transpolar Drift near the surface, and less influenced by warm and saline Atlantic water masses compared to the Nansen Basin. The polar water originates from the large Siberian rivers with a distinct terrestrial signal, visible in the high load of Coloured Dissolved Organic Matter (CDOM). The presence of this low-salinity water also results in different stratification regimes between the two basins. The core of the warm Atlantic waters flows along the Nansen Basin shelf slope while colder modified Atlantic water circulates in both basins as a layer below the polar waters. 

CAO marine ecological system

Both cruises were rather late in the season; ice algal growth was limited along the transect and bottom-ice algal production was greatest at the northern stations, close to the North Pole in 2022. The pelagic bloom had developed to a deep chlorophyll (chl) a maximum at 15-50 m depth, with remaining chl a in the water column being much less over the Amundsen Basin than in the Nansen Basin, where higher chl a prevailed near the ice edge at N82°.

Hydroacoustic surveys with a Simrad EK80 hull-mounted echo sounder were done to determine the distribution and biomass of zooplankton and fish from the surface to 500 m depth. Over the same depth range, pelagic trawling was conducted to sample fish and other organisms. Special ice-rigging enabled trawling in ice-covered waters, for the first time even at the North Pole!

Boreal zooplankton and fish have been reported to expand with increased inflow of Atlantic water from lower latitudes into the Nansen Basin. Capelin (Mallotus villosus) have expanded into the mesopelagic layer (300-500 m depth) near the slope, and will likely be the first fish species to expand further into the CAO. Other fishes in the catch were mostly juveniles of beaked redfish (Sebastes mentella) and Greenland halibut (Reinhardtius hippoglossoides), as well as a few larger cod (Gadus morhua). As we moved away from the slope and into the deep waters, the fishes associated with the mesopelagic layer diminished, and the last species to persist was the glacial lanternfish (Benthosema glaciale). With the fishes gone, their niche was occupied by pelagic amphipods, the large arrow worm Eukrohnia hamata and jellyplankton. The large helmet jellyfish (Periphylla periphylla) seems to have expanded into the CAO; it was caught in several pelagic trawl hauls in the Nansen Basin.

Management concerns

Our long-term commitment to study the CAO is expected to contribute to management concerns regarding ecosystem protection and sustainable exploitation of marine resources in light of rapid climate change. These efforts will contribute to the Joint Scientific Research and Management Programme linked to the CAO Fisheries Agreement. Less sea ice will open for oceanic sailing routes and other human activities, such as extraction of deep-sea minerals, fisheries, and tourism. Changes in teleconnections between an ice-free Arctic Ocean and the lower latitudes are expected to grandly affect marine ecosystems across latitudes.