Bacterial communities of the Arctic sea ice, drifting towards an age of uncertainty

• Author / Creator

  Hatam, Ido

• The Arctic Ocean sea ice is shifting from a system dominated by thick perennial ice (multiyear ice –MYI) to one dominated by thinner, seasonal ice (first year ice – FYI). The effects of this shift on the bacterial constituents of the Arctic sea ice have been grossly under studied, although it is a vast habitat for a bacterial community. This community plays a key role in the biogeochemical cycles and energy flux of the Arctic Ocean via regulating and reseeding the spring and summer algal bloom. Furthermore bacterial secondary productivity supplies the water column with nutrients during the polar winter. MYI and FYI are similar in that both are cold, semi-solid habitats originating from the freezing of sea water; however, they differ in many of their chemical and physical attributes. MYI has lower bulk salinity and volume than FYI mainly due to seasonal flushing with melt water; the temperature gradient is steeper and there is less light attenuation in FYI than MYI because FYI is thinner; and MYI has features, such as freshwater surface melt ponds and annual growth layers, that are absent from FYI. To date, there has been almost no comparing and contrasting the structure and composition of microbial communities from both ice types. I contend that, given the importance of sea ice bacterial communities to the ecological functioning of the Arctic Ocean, such a comparison is crucial to our understanding of the repercussions of declining MYI cover to the Arctic Ocean environment. Therefore, I tested whether bacterial communities in Arctic MYI and FYI differ in composition and membership, as well as richness and diversity. Furthermore, I tested the response of these bacterial communities to environmental disturbance. To test this, MYI and FYI cores were sampled from land-fast ice in the Lincoln Sea off the shore of Northern Ellesmere Island, NU, Canada, during the months of April and May in four consecutive field seasons (2010-2013). For depth-specific assessments, cores were sectioned into 30 cm sub-sections; for assessment of FYI vs. MYI bacterial structure, whole cores were assessed. To simulate environmental disturbance, cores from MYI and FYI sites where inserted inverted back to the borehole to disrupt the temperature and brine salinity gradients that occur in sea ice.. Assessment of microbial community structure was performed by analysis of 16S rRNA gene sequences. Bacterial communities from MYI cluster to three statistically distinct communities representing the top, middle, and bottom of the ice. Bacteria from the classes Flavobacteria, Bacteroidetes, Actinobacteria and Betaproteobacteria dominated the top communities and decreased in relative abundance with depth, where as Gammaproteobacteria and Alphaproteobacteria increased in relative abundance with depth. Rather than associating with gradients in salinity or temperature, these changes in bacterial communities were associated with three distinct layers within the ice: melt pond ice, old (i.e. more than one year) ice, or new (i.e. formed over the winter season prior to sampling) ice. My results also show that in contrast to MYI samples, communities from FYI do not show distinct top to bottom clustering, supporting my second hypothesis. Though communities from both ice types were dominated by members of similar class level groups, FYI and MYI had distinct membership at the operational taxonomic unit (OTU) level. Bacterial composition was highly variable in FYI from different sites and field seasons; however, bacterial community composition in MYI samples was much more similar to each other. Treatments designed to simulate environmental disturbance had mixed effects. Core inversion transplantation resulted in changes to the membership and composition of the top communities from the MYI core making them similar to communities from the middle sections of the core. Results from similar disruption experiments on FYI cores were confounded by the highly variable community composition and lack of vertical structure in the communities. Taken together, these results indicate that the shift from a MYI dominated Arctic to seasonal ice dominated Arctic will lead to a sea ice bacterial community with more variability and less predictability. This shift may indicate a transition to a community less able to rebound from environmental disturbance. I discuss potential implications of these findings for understanding and modeling responses of the Arctic Ocean ecosystem to the challenge of a changing climate and proposed future directions for this research.

• Subjects / Keywords

  • Sea ice
  • Arctic
  • Microbial ecology
  • High throughput sequencing

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3183472T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.