S. Lalonde - Academia.edu (original) (raw)

Papers by S. Lalonde

Proceedings of the National Academy of Sciences of the United States of America, Jan 27, 2015

The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmosphe... more The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmospheric oxygen increased above ∼10(-5) times the present atmospheric level (PAL). This threshold represents an estimated upper limit for sulfur isotope mass-independent fractionation (S-MIF), an Archean signature of atmospheric anoxia that begins to disappear from the rock record at 2.45 Ga. However, an increasing number of papers have suggested that the timing for oxidative continental weathering, and by conventional thinking the onset of atmospheric oxygenation, was hundreds of million years earlier than previously thought despite the presence of S-MIF. We suggest that this apparent discrepancy can be resolved by the earliest oxidative-weathering reactions occurring in benthic and soil environments at profound redox disequilibrium with the atmosphere, such as biological soil crusts and freshwater microbial mats covering riverbed, lacustrine, and estuarine sediments. We calculate that oxyge...

Palaios, 2007

Seasonally sampled cores of burrowed sediment containing chirono- mid larvae were collected from ... more Seasonally sampled cores of burrowed sediment containing chirono- mid larvae were collected from Cooking Lake, Alberta, and analyzed to (1) assess and establish the typical burrowing behavior and burrow architecture of chironomid larvae; (2) record micrometer-scale geo- chemical profiles of O 2 ,H 2S, and pH in the uppermost sedimentary layers throughout a seasonal cycle; and (3) link changing geochemical

Palaios, 2011

Many infaunal marine invertebrates produce mucous excretions, composed primarily of the glycoprot... more Many infaunal marine invertebrates produce mucous excretions, composed primarily of the glycoprotein mucin, that play important roles in burrow stabilization. As with other biopolymers, the ionization of mucin provides highly reactive organic ligands that enable the sorption of metal cations from seawater. Owing to the difficulties in its isolation, however, the specific role of mucin in the adsorptive properties of animal secretions in marine environments is poorly understood. Here we apply a surface complexation approach to model proton and Cd adsorption behavior of partially purified Type III porcine gastric mucin (PGM), a commercially available analog to natural infaunal mucus. FTIR, proton and cadmium adsorption experiments indicate that Type III PGM mimics the acid-base and metal complexation behavior of natural mucous gels excreted by terebellid polychaete worms. At marine pH, nearly two-thirds of the total ligands in mucin-type glycoproteins are deprotonated and thus available to participate in metal cation adsorption reactions. Importantly, the concentration of available organic ligands in mucin exceeds (by up to 5 times) that of a variety of other metal-reactive organic compounds comprising the organic fraction of marine sediments. A substantial fraction of the dissolved organic matter in the bioturbated zone of marine sediments occurs in the form of mucin-associated glycoproteins; the availability of such organic materials may strongly influence the distribution of cations at the burrow margin.

Sedimentary Geology, 2012

Meter-sized thrombolites coated by well developed zonally differentiated microbial mats have been... more Meter-sized thrombolites coated by well developed zonally differentiated microbial mats have been found growing in the shallow waters (depth b 1 m) of a restricted hypersaline lagoon on the Archipelago Los Roques in Venezuela. By contrast, within the deeper parts of the studied lagoon, sedimentation is characterized by several decimeters of organic-rich material containing gypsum granules lacking carbonate cementation. The lithification of the thrombolites is thought to have proceeded as follows. First, extracellular polymeric substances (EPS) comprising the microbial mat concentrate Ca 2 + and other metal cations by adsorption from the hypersaline waters. Second, some of these bound metals then serve as nucleation sites for primary calcium carbonate (CaCO 3 ) precipitation. Third, while carbonate phases are forming in some zones of the mat, in others zones they are being re-dissolved due to the acidity generated through the metabolism of sulfide-oxidizing bacteria, Fourth, as the dissolved sulfide is oxidized into sulfate, the pore-water become saturated with respect to gypsum (CaSO 4 ·2H 2 O). Fifth, as primary gypsum precipitates within the structures, endolithic sulfate-reducing bacteria metabolize the sulfate moiety in the mineral phase, while simultaneously oxidizing the EPS trapped during accretion. Sixth, as microbial EPS degradation proceeds, the anaerobic oxidation of specific protein fractions of the EPS matrix leads to increased alkalinity, the partial dissolution of gypsum, supersaturation with respect to calcium carbonate, and ultimately pseudomorphic aragonite replacement; this differs from secondary calcite cements in being enriched in 12 C, and depleted in minor and trace metals initially associated with the EPS. The biogeochemical processes occurring in this thromboliteconstructing lagoon represent a novel field site for studying the chemical and isotopic processes characterizing early diagenetic gypsum and the role microbes play in its precipitation, dissolution and calcification. In this regard, insights gained from this modern field site will help to better understand mechanisms by which some Precambrian microbialites were lithified.

Nature Geoscience, 2014

The early Earth was characterized by the absence of oxygen in the ocean-atmosphere system, in con... more The early Earth was characterized by the absence of oxygen in the ocean-atmosphere system, in contrast to the well-oxygenated conditions that prevail today. Atmospheric concentrations first rose to appreciable levels during the Great Oxidation Event, roughly 2.5-2.3 Gyr ago. The evolution of oxygenic photosynthesis is generally accepted to have been the ultimate cause of this rise, but it has proved di cult to constrain the timing of this evolutionary innovation 1,2 . The oxidation of manganese in the water column requires substantial free oxygen concentrations, and thus any indication that Mn oxides were present in ancient environments would imply that oxygenic photosynthesis was ongoing. Mn oxides are not commonly preserved in ancient rocks, but there is a large fractionation of molybdenum isotopes associated with the sorption of Mo onto the Mn oxides that would be retained. Here we report Mo isotopes from rocks of the Sinqeni Formation, Pongola Supergroup, South Africa. These rocks formed no less than 2.95 Gyr ago 3 in a nearshore setting. The Mo isotopic signature is consistent with interaction with Mn oxides. We therefore infer that oxygen produced through oxygenic photosynthesis began to accumulate in shallow marine settings at least half a billion years before the accumulation of significant levels of atmospheric oxygen.

Nature Geoscience, 2011

Complex animals first evolved during the Ediacaran period, between 635 and 542 million years ago,... more Complex animals first evolved during the Ediacaran period, between 635 and 542 million years ago, when the oceans were just becoming fully oxygenated. In situ fossils of the mobile forms of these animals are associated with microbial sedimentary structures 1-3 , and the animal's trace fossils generally were formed parallel to the surface of the seabed, at or below the sediment-water interface 4,5 . This evidence suggests the earliest mobile animals inhabited settings with high microbial populations, and may have mined microbially bound sediments for food resources 6-8 . Here we report the association of mobile animals-insect larvae, oligochaetes and burrowing shore crabs-with microbial mats in a modern hypersaline lagoon in Venezuela. The lagoon is characterized by low concentrations of dissolved O 2 and pervasive biomats dominated by oxygen-producing cyanobacteria, both analogous to conditions during the Ediacaran. We find that, during the day, O 2 levels in the biomats are four times higher than in the overlying water column. We therefore conclude that the animals harvest both food and O 2 from the biomats. In doing so, the animals produce horizontal burrows similar to those found in Ediacaran-aged rocks. We suggest that early mobile animals may have evolved in similar environments during the Ediacaran, effectively exploiting oases rich in O 2 that formed within low oxygen settings.

Nature, 2009

the probable eruption temperatures, plotted (filled circles) as a function of age. Eruption tempe... more the probable eruption temperatures, plotted (filled circles) as a function of age. Eruption temperatures T were calculated using the relation T 5 1,000 1 20MgO (where T is in uC, and MgO in wt%; ref. 18), assuming essentially anhydrous magmas. Open circle, recent data by Berry et al. 13 . MORB, mid-ocean-ridge basalts; OIB, oceanic island basalt.

Journal of Paleolimnology, 2010

The quality and interpretability of the paleobiological record depends on the preservation of mor... more The quality and interpretability of the paleobiological record depends on the preservation of morphological and geochemical fossils. Siliceous microfossils and sedimentary pigments are often cornerstones in paleoecology, although the microbial and geochemical processes conducive to their preservation remain poorly constrained. We examined sediments from an alpine lake in Banff National Park (Alberta, Canada) where diatom frustules are completely dissolved within 50 years of deposition. Diatom dissolution, silica recycling, and diagenetic alteration of algal pigments were investigated, in conjunction with porewater geochemistry and microelectrode profiling of the sediment-water interface. Analysis of sediment trap material showed *90% of biogenic silica (BSi) production is lost prior to burial. Silica flux calculations, based on dissolved silica (as H 4 SiO 4 ) in pore-waters, show a further *6% of total BSi is returned to the water column from the upper 4 cm of sediments, implying that only *4% of total BSi is permanently archived in sediments. In situ sediment pH and O 2 profiles reveal that aerobic respiration by bacteria fully consumes oxygen by a depth of 4 mm into the sediment, with associated strong pH and redox gradients. During sedimentation and early diagenesis, diatoms undergo loss of extracellular polymeric substances that coat their frustules, promoting silica dissolution and leading to the loss of the microfossil record by a depth of 3.25 cm. Sedimentary pigments similarly undergo rapid degradation, but diatom-related carotenoids persist below the depth of silica dissolution. This work provides new insights on diagenetic processes in lakes, with broad implications for the interpretation of sedimentary proxies for algal production.

Geomicrobiology Journal, 2011

Geochimica et Cosmochimica Acta, 2008

Significant efforts have been made to elucidate the chemical properties of bacterial surfaces for... more Significant efforts have been made to elucidate the chemical properties of bacterial surfaces for the purposes of refining surface complexation models that can account for their metal sorptive behavior under diverse conditions. However, the influence of culturing conditions on surface chemical parameters that are modeled from the potentiometric titration of bacterial surfaces has received little regard. While culture age and metabolic pathway have been considered as factors potentially influencing cell surface reactivity, statistical treatments have been incomplete and variability has remained unconfirmed. In this study, we employ potentiometric titrations to evaluate variations in bacterial surface ligand distributions using live cells of the sheathless cyanobacterium Anabaena sp. strain PCC 7120, grown under a variety of batch culture conditions. We evaluate the ability for a single set of modeled parameters, describing acid-base surface properties averaged over all culture conditions tested, to accurately account for the ligand distributions modeled for each individual culture condition. In addition to considering growth phase, we assess the role of the various assimilatory nitrogen metabolisms available to this organism as potential determinants of surface reactivity. We observe statistically significant variability in site distribution between the majority of conditions assessed. By employing post hoc Tukey-Kramer analysis for all possible pair-wise condition comparisons, we conclude that the average parameters are inadequate for the accurate chemical description of this cyanobacterial surface. It was determined that for this Gram-negative bacterium in batch culture, ligand distributions were influenced to a greater extent by nitrogen assimilation pathway than by growth phase.

Geobiology, 2013

Here, we explore enrichments in paleomarine Zn as recorded by authigenic iron oxides including Pr... more Here, we explore enrichments in paleomarine Zn as recorded by authigenic iron oxides including Precambrian iron formations, ironstones, and Phanerozoic hydrothermal exhalites. This compilation of new and literature-based iron formation analyses track dissolved Zn abundances and constrain the magnitude of the marine reservoir over geological time. Overall, the iron formation record is characterized by a fairly static range in Zn/Fe ratios throughout the Precambrian, consistent with the shale record (Scott et al., 2013, Nature Geoscience, 6, 125-128). When hypothetical partitioning scenarios are applied to this record, paleomarine Zn concentrations within about an order of magnitude of modern are indicated. We couple this examination with new chemical speciation models to interpret the iron formation record. We present two scenarios: first, under all but the most sulfidic conditions and with Zn-binding organic ligand concentrations similar to modern oceans, the amount of bioavailable Zn remained relatively unchanged through time. Late proliferation of Zn in eukaryotic metallomes has previously been linked to marine Zn biolimitation, but under this scenario the expansion in eukaryotic Zn metallomes may be better linked to biologically intrinsic evolutionary factors. In this case, zinc's geochemical and biological evolution may be decoupled and viewed as a function of increasing need for genome regulation and diversification of Zn-binding transcription factors. In the second scenario, we consider Archean organic ligand complexation in such excess that it may render Zn bioavailability low. However, this is dependent on Zn-organic ligand complexes not being bioavailable, which remains unclear. In this case, although bioavailability may be low, sphalerite precipitation is prevented, thereby maintaining a constant Zn inventory throughout both ferruginous and euxinic conditions. These results provide new perspectives and constraints on potential couplings between the trajectory of biological and marine geochemical coevolution.

Geobiology, 2005

Archean microfossils provide some of the earliest physical evidence for life on Earth, yet there ... more Archean microfossils provide some of the earliest physical evidence for life on Earth, yet there remains a great deal of uncertainty regarding which micro-organisms were actually preserved. Because of the limited cellular detail remaining, interpretation of those microfossils has been based solely on size and morphology. This has led to significant controversy surrounding the presence or absence of cyanobacteria as early as 3.5 billion years. Accordingly, there has been an experimental bias towards studying their silicification. Here we report the very first findings on thermophilic bacteria-silica interactions, and investigate how Sulfurihydrogenibium azorense , a representative of the Aquificales often found as prominent members of modern hot spring vent communities, interacts with highly siliceous hydrothermal fluids. We show that adsorption of silica is limited to silica polymers and colloids, and that the magnitude of silica adsorption is dependent on its chemolithoautotrophic pathway. Intriguingly, when S. azorense is grown as a H 2 -oxidizer, it responds to increasing silica concentrations by producing a protein-rich biofilm that may afford the cells protection against cell wall silicification. Although the biofilms of Aquificales could potentially contribute to or accelerate siliceous sinter formation under certain growth conditions, the cells themselves show a low preservation potential and are unlikely to have been preserved in the ancient rock record, despite phylogenetic analyses suggesting that they represent one of the most primordial life forms.