Factors influecing the abundance of microorganisms in icy environments
Santibanez-Avila, Pamela Alejandra
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Microbial life can easily live without us; we, however, cannot survive without the global catalysis and environmental transformations it provides' (Falkowski et al., 2008). Despite of the key role of microbes on Earth, microbial community characteristics are not explicitly part of climate models because our understanding of their responses to long-term environmental and climatic processes is limited. In this study, I developed a Flow Cytometric protocol to access a long-term record of non-photosynthetic prokaryotic cell concentration archived in the West Antarctic Ice-Sheet (WAIS; chapter 2). The WD ice core was retrieved between 2009 and 2011 to a depth of 3,405 m, extending back to 68,000 before 1950. Once a 17,400 year-record of prokaryotic cell concentration was acquired, I investigated its temporal variability and patterns, determined the potential sources of prokaryotic cells between the Last Glacial Maximum and the early Holocene, and assessed the environmental factors that might have the largest influence on the prokaryotic response (chapter 3). The observed patterns in the prokaryotic record are linked to large-scale controls of the Southern Ocean and West Antarctica Ice-Sheet. The main research findings presented here about the first prokaryotic record are: (i) airborne prokaryotic cell concentration does respond to long-term climatic and environmental processes, (ii) the processes of deglaciation, sea level rise and sea-ice fluctuation were key; the abundance of prokaryotic cells covariate with ssNa and black carbon, and (iii) the prokaryotic cell record variate on millennial time scale with cycles of 1,490-years. In addition, I studied 'congelation ice' (i.e., ice forms as liquid water freezes) from ice-covered lakes to understand prokaryotic cell segregation between liquid and solid phases during the physical freezing process. Five mesocosm experiments were designed to understand prokaryotic responses to the progressive freezing in concert with field observations from ice-covered lakes from Barrow, Alaska. As a result of this last study (chapter 4), I concluded that prokaryotic cells are preferentially incorporated in the ice with segregation coefficients (K eff) between 0.8 - 4.4, which are higher than for major ions. Prokaryotic cells avoid rejection more effectively from the ice matrix.