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Final conclusions of the biological group.
link to publications resulted from this workSummary:
General studies:
Biological experiments were carried out in the HSVA environmental basin to determine whether a large ice tank can also be utilized for solving polar biological scientific questions. The drawback of field studies lies in the notoriously high variability of samples and the insufficient knowledge on the history of the sampled ice. Ice tanks pose a unique opportunity to study processes with a high temporal resolution. The goal of our studies was to establish a growing ice community and study its spatial and temporal variabilities. Based on these data we wanted to test the applicability of such a system to conduct detailed, temporarily high resolved biological experiments in conjunction with physical and chemical investigations. Every second day from the commence of ice formation to a stagnant phase of an ice thickness of 21 cm followed by a melting period of ten days photopigments, bacterial and primary production as well as nutrient concentrations, temperature, salinity and light (PAR) in the ice and water were measured with a vertical resolution of 2 to 10 cm. The tank was divided into two fields; one with a water velocity of 4 cm s-1 and another without water current.
During ice growth, algal abundances and activity remained low, whereas bacterial production was elevated. An increase in the biomass of ice organisms was resolved when the ice growth had ceased and warming of the ice sheet commenced during later stages of the experiment (Fig. 1 b). The increase in temperature from -20 °C to -5°C caused a doubling of the light intensity from 6.5 to 15.7 µE m2 s-1 (Fig. 1a) which can be attributed to technical properties of neon lamps. Higher air temperatures resulted in a uniform temperature distribution and a reduction of brine salinity (Fig. 1c) in the upper part of the ice sheet. The biological data propose (Fig. 1 b and Fig 2) , that the vertical stabilization of the brine is a key factor triggering the onset of growth of the ice algal community beginning at day 10 of the experiment. Doubling time of algae biomass after day 10 was comparable to field data. It can not be ruled out that the increased light intensities is also responsible for the observed increase of algae biomass. Bacterial production developed opposite to the production of phytoplankton. Phytoplankton production coincided with increased Chl-a concentrations in the ice whereas bacterial production dwindled significantly during the warming period.
Water current (4 cm/sec) did not have a significant influence on the development, variability or onset of ice the algal community when both experimental fields were compared. Ice sheets displayed little spatial and temporal variability throughout the growth of the ice, which was also unrelated to the sampling size that was selected (12 x 12 to 4 x 4 cm). Artificially introduced disturbances of the ice sheet where current was present created increased variability in the Chl-a distribution inside the ice. Also topographic features of the ice underside underwent morphological changes over time. We speculate that variations in algal pigments and bulk salinity can be attributed to altered hydrodynamic conditions within the brine channels.Continued sample and data analysis:
Microscopic analysis of the species composition will determine whether Arctic species were responsible for the colonization of the ice. Summarizing conducted productivity measurements will determine the physiological state of the established community. A combination of our findings with physical data sets (porosity, brine flux, inner surface) will provide potential information on key processes in the habitat of the organisms that accounted for their successful growth.Methodology:
Success: It was possible to transport organisms from the field (Laptev Sea) to Hamburg. Artificial sea water (Instant Ocean) proofed to be suitable for the growth of an ice community inside the Environmental ice tank. In both areas, still water and currents, the spatial variability of Chl-a concentration in the ice was very low which is the prerequisite for biological experimental studies in the ice. Repetitive sampling of an uniformly inhabited ice sheet allows high temporal resolution of biological parameters and sensitive experiments in which designed altered environmental conditions can potentially render very insightful results.Drawbacks:
Production measurements with radioactive labeled substances turned out to be very difficult due to logistical constrains. Trace element studies (micro-nutrients such as iron) are difficult due to the many different materials used for installations in the tank. Temporal scales for biological processes require a certain time. Experimental time was on the lowest limit suitable for biological experiments. Cautious ice removal should be conducted since we experienced that drilling and sawing introduced air bubbles below the ice. Walking on the ice created pressure differences which might have artificially induced brine fluxes throughout the ice sheet. In addition, light should have been kept at an constant level throughout the entire experiment.
Fig. 1: Temporal evolution of a) air temperature and radiation (in air and under the ice sheet), b) ice algal biomass in terms of chlorophyll a, and c) brine salinity in the current field of the HSVA environmental tank.
Fig. 2: Ice algal growth in the current field of the HSVA environmental tank.
link to publications resulted from this work
