(text by Philipp Assmy)

Hanna, Lasse, Mar, and Philipp from the Norwegian Polar Institute study the world of microscopic algae floating in the water column (phytoplankton) and living inside the sea ice (ice algae).

The NPI team enjoying the visit of the Polish Research Station in Hornsund (from left to right: Mar, Hanna, Philipp and Lasse, picture by Morten Iversen)
The NPI team enjoying the visit of the Polish Research Station in Hornsund (from left to right: Mar, Hanna, Philipp and Lasse, picture by Morten Iversen)

The ARCEx cruise comes just at the right timing for us as we observed the phytoplankton spring bloom at various stages of development at the stations we occupied so far. The world of the phytoplankton fully reveals itself under the microscope with its multitude of species that come in various sizes and shapes. At most stations during the ARCEx cruise, the phytoplankton community was dominated by a mix of diatoms and Phaeocystis pouchetii.

Overview pictures taken at low magnification (40x) showing a diatom dominated (A) and a Phaeocystis (B) dominated community (Phaeocystis colony highlighted with red arrow). Chain-forming diatoms under transmitted light (C&E) and excited with UV-light showing the autofluorescence of their chloroplasts (D&F). Scale bar in A corresponds to 0.5 mm and in C-F to 0.1 mm. (pictures by Philipp Assmy).
Overview pictures taken at low magnification (40x) showing a diatom dominated (A) and a Phaeocystis (B) dominated community (Phaeocystis colony highlighted with red arrow). Chain-forming diatoms under transmitted light (C&E) and excited with UV-light showing the autofluorescence of their chloroplasts (D&F). Scale bar in A corresponds to 0.5 mm and in C-F to 0.1 mm. (pictures by Philipp Assmy).

Diatoms live inside a glass house made of silica and make long cell chains under favorable growth conditions while P. pouchetii forms large (>1 mm in diameter) floating colonies containing hundreds of individual cells. Both taxa are the working horses of the Arctic marine ecosystem as they build up a lot of biomass in spring that feeds pelagic grazers but also transport organic matter from sunlit surface waters into the deep ocean and eventually to the seafloor. These linkages are studied by our colleagues from UiT and Akvaplan-niva and our international partners, making this cruise a truly interdisciplinary experience. Apart from counting phytoplankton under the microscope, we study their production rates and optical properties and perform manipulation experiments in the lab to study the combined effects of light, nutrients and grazers on phytoplankton community composition (see also earlier blog).

Unfortunately, we were less lucky with respect to ice algae due to the unusually poor ice conditions for this time of the year. We steamed into a large patch of sea ice southeast of Nordaustlandet to find an appropriate ice floe for an extended ice station, but ice turned out to be highly fragmented and the swell was quite considerable. A proper ice station was thus not possible but the distinct brown color of the ice and slush prompted us to collect material for closer inspection. So, we decided to use the ice we have – and take our samples there.

Mar and Philipp using the transporting basket on the crane to get to the ice floe (picture by Ingrid Wiedmann).
Mar and Philipp using the transporting basket on the crane to get to the ice floe (picture by Ingrid Wiedmann).

And, it turned out that the sea ice community was composed of an interesting mix of diatoms, flagellates and green algae that awaits further investigation – making the “ice soup” a very unusual and exciting ice environment to study.