Sea ice microbial communities
This process forms an initial semisolid matrix of approximately 1 meter in thickness with strong temperature, salinity, light and nutrient gradients.
The fraction of irradiance reaching the sea ice matrix is thus also controlled by the amount of snowfall and varies from <0.01% to 5% depending on the thickness and density of the snowpack.
[7] High brine salinity combined with an elevated pH reduces the rate at which gases and inorganic nutrients diffuse into the ice matrix.
[4] Winters are typically characterized by moderate oxygen levels that are accompanied by nutrient and inorganic carbon concentrations that are not growth limiting to phytoplankton.
[5] Studies have shown that sea ice microbial retention can be enhanced by the presence of extracellular polymeric substance/polysaccharides (EPS) on the walls of the brine channels.
[10] Both the Antarctic and Arctic sea ice environments present strong vertical gradients of salinity, temperature, light, nutrients and DOM.
[11][12] Microbial abundance declines significantly with depth in the upper and middle ice, but not in the lowest, suggesting that much of the prokaryotic bacterial community is resistant to extreme environmental conditions.
[12] The temporal distribution of microbial community composition in the Antarctic and Arctic sea ice does not present significant seasonal variability, despite extremes in environmental conditions.
Previous studies of sea ice habitats have shown that the composition of SIMCO in early fall is identical to the source seawater community.
[13] The microbial community composition does not seem to change significantly in fall and winter, despite the extreme variability in irradiance, temperature, salinity and nutrient concentrations.
Studies have shown that sea ice microalgae provide a platform and organic nutrient source for bacterial growth, therefore increasing community diversity and abundance.
[13][14] It has also been proven that microbes produce extracellular polymeric substances (EPS) to help retain nutrients and survive under high salinity and low temperature conditions.
[5] The increase in irradiance levels in late spring promotes ice algal photosynthesis which in turn affects the microbial community abundance and composition.
[15] A majority of the information on sea ice microbial community composition comes from 16S ribosomal RNA taxonomic marker genes and metagenomic analyses.
Genera of the Alphaproteobacteria class were shown to include Loktanella, Octadecabacter, Roseobacter, Sulfitobacter and Methylobacterium and to agree with previous phylogenetic analyses of sea ice around the Antarctic.
A study of the SIMCO 16S ribosomal RNA at Cape Hallett in the Antarctic has shown that aerobic oxygenic phototrophic bacteria may be equally abundant.
A large proportion of the identified SIMCO in these studies were shown to belong to phylotypes associated with heterotrophic taxa[20] While this gives researchers an insight into the microbial community composition of the Antarctic sea ice, there are clear shifts between locations in the Southern Ocean.
These factors include the composition of the microbial communities in place at the moment of sea ice formation, and the regional weather and wind patterns affecting the transport of snow and aerosols.
[21] Studies of the 16s ribosomal RNA subunits found in the sea ice cover of Terra Nova Bay have shown that archaea consist of ≤ 6.6% of the total prokaryotic community in this environment.
Animals found in the extreme polar environments depend on the high bacterial production as a food source, despite the slow turnover of DOM.
