Blog from RV Lance: Plankton and sea ice ecology
Air temperature -8 °C, but feeling colder due to the wind chill; water temperature close to freezing, overcast skies, and three people (Harvey, Mirko and Philipp) in survival suits close to the edge of a large ice flow.
We are about to deploy water samples under the ice through an ice hole, which was drilled before by our experienced polar bear guide Jago. It’s always good to have a polar bear guide with you, since the buoy, marking the incubation spot, seem to be of interest for polar bears, as we have seen a few days ago. This is our third under ice incubation experiment. This time we are also investigating primary productivity and diatom growth rates in different depths in the water column. So far we worked on ice floes of different size and snow thickness causing a range of under ice light intensities. These differences in the light climate are reflected in the spatial patchiness of ice algal assemblages and under ice communities. The dive team (Haakon, Peter, Sanna and Ireen) collects under ice water samples from these patches for our experimental work. The water samples contain microplankton, small algae and bacteria, which represent the basis of the marine food web in the Arctic. As marine ecologists we are mainly interested in how this small organisms (only 1/10–1/1000 mm in size), are involved in the transformation of carbon and nitrogen, which are main elements of life. Therefore we add tracer amounts of carbon and nitrogen isotopes, followed by incubation at in situ environmental conditions. Our aim is to quantify the incorporation of these elements into biomass and to study the release of nutrients by algae and the recycling of organic and inorganic matter by bacteria. Unfortunately, analyzes can be not carried out on board, but have to be done once we are back in our home laboratory. Here on board our main business is filtration, a rather monotonous and time consuming task.
Besides the experimental work we are also involved in the biological and chemical characterization of the sea ice. Together with Daiki and Mats we are drilling ice cores, which are split into appropriate sections and melted at 4 °C. We will measure nutrients, particulate and dissolved matter and cell counts for ice algae and bacteria from these ice cores. First microscopic investigations revealed that Nitzschia cf. frigida (a colony forming pennate diatom commonly found in Arctic sea ice communities) is the dominant species in the ice algal community. Furthermore we look for ikaite crystals (calcium carbonate which forms at low temperatures) in the upper 15–20 cm of ice cores collected by Daiki and Mats. We are planning further experiments and sea ice sampling during the next two ice stations.
Meanwhile the phytoplankton bloom is rapidly developing in the water column as indicated by the increasing fluorescence in the shallow surface mixed layer and biomass build-up of bloom forming diatom species (e.g. Thalassiosira spp. and Chaetoceros socialis) as well as the colonial Haptophyte Phaeocystis pouchetii. Following the progression of the phytoplankton spring bloom will be the main objective of the cross-slope CTD transect at the end of the cruise. The CTD team (Arild, Vladimir and Alexey) will continue to provide us with water samples. We are sort of looking forward to this upcoming intensive filtration marathon… However, we really appreciate the good spirit and constant support of the zooplankton team (Anette, Malin and Ingeborg), with whom we share our cozy lab.