URING THE NORWEGIAN young sea drift ex-pedition (N-ICE2015), when the research vessel Lance was frozen into the ice north of Svalbard, we studied the ocean’s invisible forest as the sun returned to the Arctic in spring after the long dark winter. The ice around us was our backyard and we took samples every day to discover how the complex ecosystem works. Excitement spread among the biologists when in late May, despite the thick snow cover, the water and the ice started to turn brownish-green. The invisi-ble forest was beginning to flourish.
Microscopic single-celled algae growing on and inside the sea ice (ice algae), and in the underlying water (phytoplankton), form the invisible forest of the Arctic Ocean and constitute the production base of its eco-system. The herbivores that eat them are small crus-taceans that fuel the ice-associated ecosystem, from
polar cod to polar bears. We humans rely on fish as an important source of protein and oils (lipids) in our diet, and as the sea ice retreats further north, com-mercial vessels have started to fish in arctic waters.
Factors that control algal productivity may determine whether the future Arctic Ocean will become a new food basket. With sea ice getting thinner, younger and more dynamic, and snow precipitation increas-ing due to climate change, the future arctic ice-scape will surely be different. During N-ICE2015, we had a unique opportunity to study the new ice regime dur-ing sprdur-ing 2015 and were able to get a “sneak preview”
of how the future seasonal ice zone may look.
SLIMY PHAEOCYSTIS RULES THE WATER COLUMN On 25 May, the water turned green. We were sudden-ly in the middle of a massive phytoplankton bloom Mar Fernández-Méndez, Lasse Mork Olsen, Hanna M. Kauko, Haakon Hop* and Philipp Assmy //
Norwegian Polar Institute
The frozen Arctic Ocean looks like a cold, white, inhospitable desert, yet seals, whales and polar bears appear there sporadically. The presence of large marine mammals tells us there must be an invisible
forest below the ice, producing the food they need to survive. In 2015, we explored that forest.
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*Haakan Hop is also affiliated with UiT The Arctic University of Norway
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growing below sea ice that was covered by thick snow (40 cm), allowing very little light to penetrate into the underlying water column. This came as a surprise to us, as previously observed under-ice blooms in the Canadian Arctic had formed much later in the season, and below transparent sea ice with no snow and many melt ponds. During N-ICE2015, however, the answer lay in the leads. Studying satellite images, we detect-ed many leads opening up during early spring. This promoted light transmission through the otherwise opaque ice pack and triggered the early phytoplank-ton under-ice bloom. These conditions favoured growth of the slimy phytoplankton species, Phaeo-cystis pouchetii, at the expense of pelagic diatoms, such as Thalassiosira spp., Fragilariopsis oceanica or Chaetoceros socialis, which usually dominate the arctic spring bloom. Shifts in species dominance could have important implications for the fate of the fixed
During the N-ICE2015 drift expedition, from January to June 2015, RV Lance was moored to four ice floes northwest of Svalbard and drift-ed with the pack ice for a total of 141 days. The aim of this multidisciplinary expedition was to understand the effects of the new arctic sea ice regime on energy flux, ice dynamics and the ice-associated ecosystem, by employing a suite of physical, chemical and biological measurements. The expedition began in the dead of the polar night and continued through the progression of spring.
More information: www.npolar.no/n-ice2015 FURTHER READING: https://eos.org/project- updates/arctic-research-on-thin-ice- consequences-of-arctic-sea-ice-loss Sampling the optical
prop-erties of the water column through a hole in the thin ice of the refrozen lead.
Photo: Alexey Pavlov / Norwegian Polar Institute
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RESEARCH NOTES FRAM FORUM 2017carbon as Phaeocystis is not relished by the dominant grazers (Calanus copepods) and does not sink to the deep ocean.
SUNSCREEN ON THIN ICE
From early May until early June, we had a unique opportunity to follow the progression of a thin-ice environment in a refrozen lead that had formed next to RV Lance. This allowed us to study in detail how leads act as windows into the ocean. Not only did the phytoplankton bloom profit, but also ice algae took advantage of the high light transmission through the thin lead ice and formed a small ice-algal bloom.
These ice algae had the highest concentrations of mycosporine-like amino acids (MAAs) ever recorded in sea ice. MAAs are water-soluble molecules that ab-sorb ultraviolet (UV) radiation and act like sunscreen
against damaging UV levels. On the other hand, the energy-demanding production of MAAs might have slowed algal growth, reducing the magnitude of the bloom.
OLD ICE: AN ALGAL SEED BANK IN WINTER Next to thin young ice, we also sampled older ice, mainly second-year ice. The detailed time-series en-abled us to identify how the life cycles of a dominant ice algal species are geared to the sea-ice environ-ment. The diatom Nitzschia frigida is the champion of the sea ice invisible forest, but how this species adapts to the ice melt season and winter is still unknown.
According to our observations, ice that survives the summer melt season acts as a repository for N. frigida that will serve as the seed bank for next year’s spring bloom of ice algae when the sun returns. However, if Ice that survives the summer melt acts as an algal seed bank.
Nitzschia frigida resides there during the winter and seeds the ice algal bloom in new ice in spring.
Photo: Philipp Assmy / Norwegian Polar Institute
Under-ice bloom dominated by Phaeo-cystis pouchetii.
Photo: Philipp Assmy / Norwegian Polar Institute
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conditions in the future Arctic Ocean mean that less ice survives the summer, this seed bank will progres-sively disappear, threatening the long-term survival of ice-associated species like Nitzschia frigida.
ANTARCTIFICATION OF ARCTIC ICE ECOSYSTEMS In June, the sea ice started to melt from below. As the thick snow pushed the ice under the water surface, the ice became flooded with seawater. In particular, cracks in the ice enabled algae from the water col-umn to infiltrate the snow-ice interface. We got very excited about the rich brownish-green soup below the snow, but even more interesting was that the algal species growing there were pelagic diatoms, includ-ing Thalassiosira species and Fragilariopsis oceanica!
Yes, exactly the ones that were outcompeted below the ice by Phaeocystis pouchetii. They seemed to be
doing fine at the snow-ice interface, closer to the light, where they were protected from grazers and replen-ished with nutrients. These types of communities are known from the Antarctic, but have rarely been observed in the Arctic.
Changes in the Arctic ice-scape are happening fast and our new observations indicate that we must constant-ly update our knowledge in order to make predictions about the future arctic ecosystem. Thus, it is crucial to continue performing research expeditions to the white desert to unveil the secrets of its invisible forest.
Navicula sp. with sunglasses and sunscreen tube with MAAs.
Credit: Mar Fernández-Méndez / Norwegian Polar Institute
Mar Fernández-Méndez (left) and Hanna Kauko sampling the snow-ice interface.
Photo: Marcel Nicolaus