Different Environmental Stressors and their Effect on TEX86 Signature of Marine Ammonia-Oxidizing Archaea
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Marine ammonia-oxidizing archaea (AOA) compose their cell membranes with glycerol dialkyl glycerol tetraethers (GDGTs). These lipids are useful biomarkers for developing a paleo-climatological proxy for sea surface temperature. Through the TEX86 temperature proxy, GDGTs have been able to provide insight into historic patterns of sea surface temperature through the relationship between annual average sea surface temperature and the composition of GDGTs. To better understand how GDGTs change according to environmental pressures we conducted experiments with varying levels of light, pH, salinity, ammonia and peroxide to test their effect on TEX86 on strains of AOA (Qin et. al 2014 & 2015). Light levels influenced the total GDGT composition, where the composition was relatively higher for when the light was present but did not have a significant effect on the calculated TEX86 temperature. Salinity concentrations below and above optimal salinity at 25 ppt resulted in lower GDGT compositions and TEX86 sea surface temperatures (below 17 °C). As for pH, peroxide and ammonia levels, there appeared to be no major effect on calculated TEX86 temperatures with fluctuating concentrations, which suggest the presence of different adaptations that allow for archaea to acclimate to relatively extreme conditions. This will provide more understanding of TEX86 and archaeal physiology and more specifically the effect that different environmental stressors have on lipid composition, which ultimately relates to archaeal growth rates. In light of the conducted culture treatments, natural samples from the Northern Pacific Ocean were analyzed for their TEX86 temperatures. In situ temperatures did not correlate well with TEX86 for surficial nor subsurface temperatures in the water column suggesting that the TEX86 proxy may not be as direct of a correlation as originally determined.