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Africa's climate became progressively drier and more variable in the last few million years (e.g., deMenocal, 2004). Of particular interest, is a shift to drier and more variable conditions in the Olorgesailie Formation (Kenya) between 500 and 300 thousand years ago (ka) in which Potts et al. (2018) observed a turnover of ~85% of large-body mammalian fauna to smaller-body related taxa, suggesting that the shift was an evolutionary response to better adapt to the changing climate. However, a hiatus in the Olorgesailie record means that the cause of this faunal shift is still an outstanding question. Here, we analyze Lake Malawi drill core MAL 05–1 (~11ºS, 34ºE) to investigate if a specific climatic event stands out as a possible driver of the dramatic change observed in the East African mammal community. We use organic geochemical proxies including branched glycerol diaklyl glycerol tetraethers (GDGTs), leaf wax carbon and deuterium isotopic records to develop high-resolution temperature, vegetation, and precipitation records, respectively, between 600 and 200 ka. Results show a dramatic and abrupt temperature increase of ~6°C occurring in less than 3000 years during Glacial Termination V, which is the Marine Isotope Stage (MIS) 12 to MIS 11 transition at ~430 ka. Notably, this deglacial warming coincides with enriched leaf wax deuterium isotopic values suggesting a shift to more arid conditions in interglacial MIS 11 than in glacial MIS 12. Results also show another abrupt warming period in which temperature increased ~9°C around MIS 7 (~240 ka). We propose that the major warming and drying during Termination V in East Africa represents a significant abrupt change in the climate of eastern Africa and was a likely driver of the major faunal turnover noted in the Olorgesailie Basin.

The global climate is strongly regulated by the oceans, which store carbon away from the atmosphere for long periods. In an effort to understand the role of the oceans in the carbon cycle, it is necessary to understand the nuances of specific regional and functional marine ecosystems. The continental shelf of the West Antarctic Peninsula (WAP) is one particularly important regional ecosystem that plays a vital role in the Southern Ocean carbon export. Within the seasonally productive marginal ice zone of the WAP, I sought to identify the long-term drivers of particulate organic carbon (POC) flux. The vast majority of exported POC on the WAP was previously found to be made up of krill fecal pellets. I provide evidence that supports the hypothesis that the inherent life cycle of krill drives the observed 5-year oscillation in POC export. At the end of their life cycle, when krill are at their largest body size, the WAP experiences anomalously high POC export events through the production and sinking of large, carbon-rich krill fecal pellets. Conversely, when krill are young and small, POC export is anomalously low. This pattern shows that ecology exerts a first-order control on the the biogeochemical cycles of the WAP. Upon identifying the source and driver of POC export on the WAP, I set out to determine the role heterotrophic bacteria play in POC flux attenuation. I collected krill fecal pellets on the WAP over three years and measured bacterial metabolic activity in terms of bacterial production and respiration, thereby identifying the amount of organic carbon within the sinking fecal pellets that is lost due to bacteria. Overall, fecal pellet POC turnover rate by bacteria is very low. The relationship between bacteria and POC is complex with each having an affect on the other. Despite varied reactions of the free-living bacterial populations to the presence of krill fecal pellets, a consistent pattern emerged in the concentration of nucleic acid within each bacterial cell. Access to fecal pellets increased the metabolic activity of the free-living bacterial population. This finding shows that the egestion of krill fecal pellets metabolically stimulates the surrounding bacterial community, even though bacteria play a minor role in fecal pellet POC flux attenuation. Though bacteria were found to play a minimal role in organic carbon uptake on krill fecal pellets, they are still vital members of the WAP ecosystem and biological pump. I next sought to identify which bacteria in particular were responsible for colonizing and consuming the fecal pellet POC. Krill fecal pellets were genetically sequenced after timed exposure to the free-living water column bacterial community. I found that there is an endemic population of bacteria that are associated with each population of krill and their fecal pellets. This community of fecal pellet-associated bacteria does not change over time, indicating little colonization by free-living bacteria. Krill fecal pellets, aside from being good agents of POC export, seem to be selective environments for certain specialized copiotrophic bacteria. Further, I find that only a small subset of these endemic copiotrophs actively partake in carbon consumption on krill fecal pellets. Overall, these results show that a small endemic, specialized bacterial community play an outsized role in krill fecal pellet POC degradation and flux attenuation, but that krill fecal pellets remain efficient agents of carbon export to the deep ocean.

<p>Surface mining of Alberta’s oil sands has led to significant land disturbance, making reclamation and sustainable development of this resource one of the largest challenges facing the industry today. Syncrude Canada Ltd. has developed an innovative technique to reclaim composite tailings (CT) through constructed wetland landscapes and is currently investigating the viability of a pilot-scale freshwater fen built over sandcapped CT. Unpredicted by abiotic geochemical modelling of CT behaviour, a minor episode of hydrogen sulfide (H₂S) gas release was encountered during the initial stages of fen construction indicating microbial activity was likely involved in H₂S generation within CT. This thesis investigates the S geochemistry of CT with depth and employed 454 pyrosequencing and functional enrichments to characterize the associated microbial communities in the first S biogeochemical study of oil sands CT. Porewater H₂S was detected extensively throughout the deposit with background levels ranging from 14 – 23 µM and a maximum of 301.5 µM detected at 22-24 m of depth. Reduced Fe (Fe²⁺) was also detected, but confined within surficial depths sampled, ranging from 1.2 – 38.5 µM. Mass balance calculations identify that the Fe²⁺ generated within the surficial zone of the CT deposit is sufficient to effectively sequester ambient concentrations H₂S generated in this deposit through FeS precipitates. Results identifying (1) distinct zones of porewater Fe²⁺ and H₂S, (2) co-occurrence of the highest [H₂S] and lowest dissolved organic C (DOC) at 22-24 m consistent with heterotrophic sulfate reducing bacteria (SRB) activity, and (3) the presence of mixed valence Fe biomineral, magnetite, throughout the deposit, are all consistent with microbially-mediated Fe and S cycling occurring within this CT deposit. The cultivation independent identification of several known iron reducing bacteria (IRB) and SRB within CT microbial communities, in conjunction with observed positive growth of IRB and SRB functional metabolic enrichments, demonstrates widespread capacity for microbial Fe and S activity throughout the CT deposit. Metagenomic characterization of CT microbial communities revealed high diversity (over 20 phyla) over the 5 depths examined. Multivariate statistical analyses (Unifrac) revealed that bacterial community composition and structure was driven by changed in DOC, ORP and salinity and that structuring corresponded with a surficial zone of Fe³⁺ reduction and an underlying zone of SO₄^2- reduction. Despite the high organic carbon (OC) content of oil sands tailings, much of that C is not considered to be labile and accessible to microbes. Based on the results of this thesis, CT SRB appear to have a greater ability than IRB to utilize recalcitrant OC (e.g. bitumen, naphthenic acids) given the widespread occurrence of porewater [H₂S] and surficially restricted [Fe²⁺] despite accessible pools of Fe³⁺ and OC with depth. This enhanced understanding of biogeochemical S cycling within CT newly establishes the importance of microbial activity in these processes, identifying the need to incorporate microbially based understanding into on-going development of reclamation strategies in order to manage these waste materials effectively.</p> / Master of Science (MSc)

The role of aquifer microorganisms in controlling arsenic contamination of Bangladesh aquifers via oxidation of organic carbon coupled with reduction of sedimentary iron oxyhydroxides and concomitant arsenic dissolution is generally accepted. What remains to be ascertained is the in situ biogeochemical mechanisms of cycling different carbon sources and directly relating indigenous microbiota to arsenic release. Using biomarker fingerprint approaches, this dissertation expanded the presently growing research in the biogeochemical carbon cycling controlling arsenic contamination in Bangladesh aquifers. Comprehensive profiles of microbial cell membrane components (PLFA and sterols) at three different aquifers tested the regional distribution of aquifer microbial community abundance, structure, and organic input potential across Araihazar. The highly variable bulk viable microbial biomass observed across these three sites confer both regional-scale and localized heterogeneous distributions of in-aquifer microbial communities which control carbon cycling in the aquifer. The lack of correlation between PLFA biomarkers and dissolved arsenic challenges the assumption that greater extent of microbial community metabolism results in an increase in arsenic in groundwater. Natural abundance radiocarbon isotope Δ14C analysis of cell membrane PLFA and available carbon pools (SOC, DOC, DIC) confirmed that young organic carbon substrates are being cycled at two of the three sites investigated here. This corroborates previous reports at nearby sites (Site B and F) thereby contributing to a well-constrained carbon source which actively support microbial metabolism over a regional scale. Sterol biomarker distributions were characterized to determine potential sources of organic input into the aquifer. In particular, the importance of raw human and/or animal sewage waste as a source of labile carbon was assessed by measuring the faecal biomarker Coprostanol and comparing its abundance to other sources of biogenic sterols using sewage input proxies (Sewage Contamination Index, Coprostanol/Cholesterol ratio). This was motivated by previous findings which correlated sewage contamination with dissolved arsenic at depth at nearby sites. While sewage contamination was low in the shallow aquifers at these sites, it is more likely that plant organic matter supported the elevated microbial abundance at shallow depths. On the other hand, evidence presented in this project suggests that sewage contamination intrudes into deeper aquifers (e.g. buried Pleistocene) and contributes to the vulnerability of previous pristine aquifers to future arsenic contamination. / Thesis / Master of Science (MSc)