- Department of Earth and Planetary Sciences
McGill University
3450 University Street
Montreal, QC
Canada
H3A 0E8 - +1 514-398-4892
Alfonso Mucci
McGill University, Earth and Planetary Sciences, Faculty Member
The Labrador Current transports cold, relatively fresh, and well-oxygenated waters within the subpolar North Atlantic and towards the eastern American continental shelf. The relative contribution of these waters to either region depends... more
The Labrador Current transports cold, relatively fresh, and well-oxygenated waters within the subpolar North Atlantic and towards the eastern American continental shelf. The relative contribution of these waters to either region depends on the eastward retroflection of the Labrador Current at the Grand Banks of Newfoundland. Here, we develop a retroflection index based on the pathway of virtual Lagrangian particles and show that strong retroflection generally occurs when a large-scale circulation adjustment, related to the subpolar gyre, accelerates the Labrador Current and shifts the Gulf Stream northward, partly driven by a northward shift of the wind patterns in the western North Atlantic. Starting in 2008, a particularly strong northward shift of the Gulf Stream dominates the other drivers. A mechanistic understanding of the drivers of the Labrador Current retroflection should help predict changes in the water properties in both export regions, and anticipate their impacts on ma...
Research Interests:
Research Interests:
The Labrador Current carries cold, relatively fresh, and well-oxygenated waters into the subpolar North Atlantic and into the Slope Sea. The relative contribution of these waters to either region depends on the eastward retroflection of... more
The Labrador Current carries cold, relatively fresh, and well-oxygenated waters into the subpolar North Atlantic and into the Slope Sea. The relative contribution of these waters to either region depends on the eastward retroflection of the Labrador Current at the Grand Banks. We develop a retroflection index based on virtual Lagrangian particles and show that the amplitude of the retroflection is mostly controlled remotely by large-scale forcing, related to winds over the Labrador Shelf and to subpolar gyre dynamics, whereas eddies and meanders arising from interactions between the Labrador Current and the Gulf Stream play a secondary role. The mechanistic understanding of the drivers of the Labrador Current retroflection should help to predict changes in the water properties of both export regions, and anticipating their important consequences on marine life and deep-water formation.
Research Interests:
The global carbon cycle is strongly modulated by organic carbon (OC) sequestration and decomposition. Whereas OC sequestration is relatively well constrained, there are few quantitative estimates of its susceptibility to decomposition.... more
The global carbon cycle is strongly modulated by organic carbon (OC) sequestration and decomposition. Whereas OC sequestration is relatively well constrained, there are few quantitative estimates of its susceptibility to decomposition. Fjords are hot spots of sedimentation and OC sequestration in marine sediments. Here, we adopt fjords as model systems to investigate the reactivity of sedimentary OC by assessing the distribution of the activation energy required to break OC bonds. Our results reveal that OC in fjord sediments is more thermally labile than that in global sediments, which is governed by its unique provenance and organo-mineral interactions. We estimate that 61 ± 16% of the sedimentary OC in fjords is degradable. Once this OC is remobilized and remineralized during glacial maxima, the resulting metabolic CO 2 could counterbalance up to 50 ppm of the atmospheric CO 2 decrease during glacial times, making fjords critical actors in dampening glacial-interglacial climate f...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
<p>Oxygen concentrations in the deep waters of the Lower St. Lawrence Estuary, in eastern Canada, have decreased by 50% over the past century, reaching hypoxic levels. To study the causes of this deoxygenation, we applied a mixing... more
<p>Oxygen concentrations in the deep waters of the Lower St. Lawrence Estuary, in eastern Canada, have decreased by 50% over the past century, reaching hypoxic levels. To study the causes of this deoxygenation, we applied a mixing model (an extended multi-parameter analysis - eOMP) to data collected in the St. Lawrence Estuary since the 1970s and from the late 1990s to 2018. This method accounts for diapycnal mixing and can distinguish between the physical and biogeochemical causes of deoxygenation. The eOMP reveals that, in recent years, most of the deoxygenation of deep waters of the St. Lawrence Estuary is due to a change in the circulation pattern in the western North Atlantic. Since 2008, the Slope Sea and the deep waters of the St. Lawrence Estuary are fed by an increasing amount of oxygen-poor North Atlantic Central Waters (NACW), transported by the Gulf Stream, at the expense of oxygen-rich Labrador Current Waters (LCW). The oxygenation level of the St. Lawrence Estuary therefore reflects what is happening in the western North Atlantic. In contrast, the eOMP shows that, from the 1970s to the late 1990s, biogeochemical changes such as local eutrophication and variations in oxygen consumption rates in the North Atlantic dominated the deoxygenation.&#160;</p><p>Further analyses suggest that the variability in the LCW:NACW ratio in the Slope Waters is mainly controlled by the Scotian Shelf-break Current, an extension of the Labrador Current, and not by the position or strength of the Gulf Stream, as often suggested. When the Labrador Current is strong, little of the southward flowing Labrador Current waters follow the coast all the way to the Scotian Shelf, and most of these waters are deviated east towards the North Atlantic. The opposite is true when the Labrador Current is weak. We will present some analysis of LCW trajectories in different conditions and discuss their potential drivers, based on a high resolution model. Overall, our results highlight the primary role of the Labrador Current in determining (i) the oxygen concentration and other water properties on the western North Atlantic continental shelf and slope, and (ii) the advection of fresh Labrador Current Water into the subpolar North Atlantic, with possible implications on the thermohaline and gyre circulation.</p>
Research Interests:
Over the past century, dissolved oxygen concentrations have decreased and metabolic CO2 has accumulated in the bottom waters of the Gulf of St. Lawrence (GSL) and Lower St. Lawrence Estuary (LSLE). Oxygen depletion has been attributed... more
Over the past century, dissolved oxygen concentrations have decreased and metabolic CO2 has accumulated in the bottom waters of the Gulf of St. Lawrence (GSL) and Lower St. Lawrence Estuary (LSLE). Oxygen depletion has been attributed primarily to changes in ocean circulation in the northwest Atlantic Ocean, as well as an increase in the flux of organic matter at or near the seafloor and its accompanying biological oxygen demand. The accumulation of metabolic CO2 in these waters has led to their progressive acidification and a decrease in pH (0.3–0.4 pH unit) commensurate to the variation expected for global oceanic surface waters by the end of this century, albeit by a different mechanism (anthropogenic CO2 uptake from the atmosphere). The decrease in bottom-water pH of the GSL and LSLE is accompanied by a decrease in the carbonate ion concentration and the saturation state of the waters with respect to both calcite and aragonite (ΩC and ΩA). Although the Laurentian Trough sediment...
Research Interests:
Research Interests:
Oxygen concentrations in the deep waters of the Lower St. Lawrence Estuary have decreased by 50% over the past century. The drivers of this decrease are investigated by applying an extended Optimum Multiparameter analysis to a time series... more
Oxygen concentrations in the deep waters of the Lower St. Lawrence Estuary have decreased by 50% over the past century. The drivers of this decrease are investigated by applying an extended Optimum Multiparameter analysis to a time series of physical and biogeochemical observations of the St. Lawrence Estuarine System in the 1970s and from late 1990s to 2018. This method reconstructs the relative contributions of the two major water masses feeding the system, the Labrador Current Waters (LCW) and the North Atlantic Central Waters (NACW), as well as oxygen utilization, and accounts for diapycnal mixing. The causes of the oxygen decline varied over the last 5 decades. Between the 1970s and late 1990s, the decrease was mainly driven by biogeochemical changes through an increase in microbial oxygen utilization in the St. Lawrence Estuary in response to warmer temperatures and eutrophication and lower oxygen concentrations in LCW and NACW. Between 2008 and 2018, the decrease was mainly d...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Nitrogen is a limiting nutrient for primary production in the western Arctic Ocean. Measurements of the nitrogen (15N/14N) and oxygen (18O/16O) isotope ratios of nitrate in the southeastern Beaufort Sea provide insight into biogeochemical... more
Nitrogen is a limiting nutrient for primary production in the western Arctic Ocean. Measurements of the nitrogen (15N/14N) and oxygen (18O/16O) isotope ratios of nitrate in the southeastern Beaufort Sea provide insight into biogeochemical cycling of nitrogen in the western Arctic Ocean. Nitrate O isotope ratios in the Pacific halocline evidence a highly regenerated reservoir. Coincident peaks in nutrient concentrations and reduced dissolved oxygen concentrations suggest that nitrate accrues from organic matter remineralization in bottom waters of the Chukchi shelf and that these ventilate the basin predominantly in summer, when isolated from the atmosphere. Preformed nitrate in Pacific Winter Water lacks 18O/16O elevation from nitrate assimilation, contrasting with preformed nitrate in other ocean regions. A reactive N deficit and elevated nitrate N isotope ratios in the Pacific halocline further indicate substantial N loss to coupled nitrification‐denitrification in shelf sediments...
Research Interests:
Research Interests:
Research Interests:
The Mackenzie Shelf in the southeastern Beaufort Sea is a region that has experienced large changes in the past several decades as warming, sea-ice loss, and increased river discharge have altered carbon cycling. Upwelling and downwelling... more
The Mackenzie Shelf in the southeastern Beaufort Sea is a region that has experienced large changes in the past several decades as warming, sea-ice loss, and increased river discharge have altered carbon cycling. Upwelling and downwelling events are common on the shelf, caused by strong, fluctuating along-shore winds, resulting in cross-shelf Ekman transport, and an alternating estuarine and anti-estuarine circulation. Downwelling carries inorganic carbon and other remineralization products off the shelf and into the deep basin for possible long-term storage in the world oceans. Upwelling carries dissolved inorganic carbon (DIC) and nutrient-rich waters from the Pacific-origin upper halocline layer (UHL) onto the shelf. Profiles of DIC and total alkalinity (TA) taken in August and September of 2014 are used to investigate the cycling of inorganic carbon on the Mackenzie Shelf. The along-shore transport of water and the cross-shelf transport of inorganic carbon are quantified using v...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Over the past century, an increase in temperatures and a decrease in dissolved oxygen concentrations have been observed in the bottom waters of the Laurentian Channel (LC), throughout the Lower St. Lawrence Estuary (LSLE) and the Gulf of... more
Over the past century, an increase in temperatures and a decrease in dissolved oxygen concentrations have been observed in the bottom waters of the Laurentian Channel (LC), throughout the Lower St. Lawrence Estuary (LSLE) and the Gulf of St. Lawrence (GSL), eastern Canada. To document the impact of these changes, we analyzed the benthic foraminiferal assemblages and geochemical signatures of four sediment cores taken in the LC. Radiometric measurements (210Pb, 226Ra, 137Cs) indicate that the studied cores encompass the last 50 years of sedimentation in the LSLE and the last ∼160 years in the GSL. The sedimentary record shows a 60 to 65% decrease in benthic foraminiferal taxonomic diversity in the LC since the 1960s. An accelerated change in the foraminiferal assemblages is observed at approximately the same time at all studied sites, around the late 1990s and the early 2000s, towards populations dominated by the hypoxia-tolerant indicator taxa Brizalina subaenariensis, Eubuliminella...
Research Interests:
Given the current threat of fast-paced global change, it has become urgent to understand the biogeochemical response of the Arctic environment to external forcing. The Canadian Arctic Shelf Exchange Study (CASES) is an interdisciplinary... more
Given the current threat of fast-paced global change, it has become urgent to understand the biogeochemical response of the Arctic environment to external forcing. The Canadian Arctic Shelf Exchange Study (CASES) is an interdisciplinary project put together by scientists from across Canada whose primary goal is to gain a better understanding of the Canadian Arctic environment. Objectives include evaluating issues such as the impact of climate change – extent of sea ice cover - on biological productivity and the carbon cycle. In order to predict the potential evolution of the complex Canadian Arctic system, the intricacies of its current dynamics must first be understood.
Research Interests:
Research Interests:
Research Interests:
Research Interests: Environmental Science, Oceanography, Phytoplankton, Sea Ice, Arctic, and 4 moreCruise, Bloom, Bay, and spring bloom
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Abstract The important changes that took place in the glacial cycle at the termination, from the Last Glacial Maximum to the present interglacial, deserve an examination of ocean sedimentary records that document past productivity, carbon... more
Abstract The important changes that took place in the glacial cycle at the termination, from the Last Glacial Maximum to the present interglacial, deserve an examination of ocean sedimentary records that document past productivity, carbon fluxes, and carbonate preservation. In this study, we analyzed coccoliths, alkenones, and foraminifers in core HU2008–029-004 PC (61.46°N and 58.04°W, water depth = 2,674 m) from the northwestern Labrador Sea to document linkages between hydrographic conditions, biogenic carbonate fluxes to the seafloor, and their preservation/dissolution during the last 25,000 years. Large changes in coccolith and foraminifer concentrations are recorded, with sediments from the last glacial interval containing significantly less carbonate microfossils (9.5 ± 3.9 × 105 coccoliths g−1 and 2,860 ± 580 planktonic foraminifers g−1) than sediments from the deglacial and postglacial intervals (up to 3.1 × 108 coccoliths g−1 and 2.9 × 104 foraminifers g−1). Three foraminifer-based calcite dissolution indices were used to evaluate biogenic carbonate preservation: the planktonic foraminifer fragmentation index, the ratio of benthic-to-planktonic foraminifers (B/P), and the ratio of organic linings to benthic foraminifers (OL/B). Fragmentation remained low throughout the postglacial (mean of 4%) but reached up to 8% in the deglacial and peaked at 16% in samples from the Bolling-Allerod of the late glacial interval. Samples from the Bolling-Allerod and the deglacial interval also display a slightly elevated B/P index (>0.15), which suggests that some dissolution may have occurred. In contrast, with the exception of the Bolling-Allerod and the deglacial interval, near zero OL/B values characterize most of the sequence, suggesting good biogenic carbonate preservation, which implies that the low biogenic carbonate and coccolith content in sediments of the glacial stage mirror low productivity of calcifying organisms. The elevated fragmentation of foraminifers during the Bolling-Allerod and the deglacial interval, a time of elevated productivity and low percentages of ice-rafted debris, may indicate the development of calcite undersaturated porewaters and consequent dissolution resulting from oxic remineralization of sedimentary organic matter. We also identify a significant decoupling of coccolith and alkenone concentrations throughout the core. Colder-than-expected UK37-SST estimates from the alkenones of the glacial interval rule out possible allochthonous inputs from lower-latitude locations. Instead, our records imply that at least during the glacial interval, alkenones were produced by non-calcifying haptophytes that may not follow the canonical UK37-based temperature calibrations.
Research Interests:
Abstract We determined the abundances and concentrations of coccoliths and alkenones in 66 surface sediment samples from the northwest North Atlantic to evaluate the role that surface ocean temperature, salinity, sea-ice cover, and... more
Abstract We determined the abundances and concentrations of coccoliths and alkenones in 66 surface sediment samples from the northwest North Atlantic to evaluate the role that surface ocean temperature, salinity, sea-ice cover, and productivity have on the regional distribution of these two biological remains produced by haptophytes in the photic zone. In areas with sea-ice cover of more than 1 month per year, coccolith and alkenone concentrations in sediments are extremely low to nil. Elsewhere, the distribution of coccolith taxa generally displays strong relationships to water temperature, salinity, and productivity. Coccolithus pelagicus is associated with low summer sea-surface temperatures ( 33.5), whereas Helicosphaera carteri seems to follow the path of the North Atlantic Drift. The distribution of Emiliania huxleyi, the dominant alkenone producer, is not strongly correlated with that of alkenones. Calcite dissolution in shelf sediments could explain the occurrence of alkenones in the absence of coccoliths but alkenone production by non-calcifying haptophytes seems to also exert some control on alkenone concentrations in surface sediments, thus blurring alkenone abundance links to coccolithophorid production and their relative preservation.
Research Interests:
The oceanic phosphorus cycle describes how phosphorus moves through the ocean, accumulates with the sediments on the sea floor, and participates in biogeochemical reactions. We propose a new two-re...
Research Interests:
Research Interests:
Research Interests:
Significance The geological record contains numerous examples of “greenhouse periods” and ocean acidification episodes, where the spreading of corrosive (CO 2 -enriched) bottom waters enhances the dissolution of CaCO 3 minerals delivered... more
Significance The geological record contains numerous examples of “greenhouse periods” and ocean acidification episodes, where the spreading of corrosive (CO 2 -enriched) bottom waters enhances the dissolution of CaCO 3 minerals delivered to the seafloor or contained within deep-sea sediments. The dissolution of sedimentary CaCO 3 neutralizes excess CO 2 , thus preventing runaway acidification, and acts as a negative-feedback mechanism in regulating atmospheric CO 2 levels over timescales of centuries to millennia. We report an observation-based indication and quantification of significant CaCO 3 dissolution at the seafloor caused by man-made CO 2 . This dissolution is already occurring at various locations in the deep ocean, particularly in the northern Atlantic and near the Southern Ocean, where the bottom waters are young and rich in anthropogenic CO 2 .
Research Interests:
Research Interests:
Research Interests:
In an experimental assessment of the potential impact of Arctic Ocean acidification on seasonal phytoplankton blooms and associated dimethylsulfide (DMS) dynamics, we incubated water from Baffin Bay under conditions representing an... more
In an experimental assessment of the potential impact of Arctic Ocean acidification on seasonal phytoplankton blooms and associated dimethylsulfide (DMS) dynamics, we incubated water from Baffin Bay under conditions representing an acidified Arctic Ocean. Using two light regimes simulating under-ice/ subsurface chlorophyll maxima (low light; Low PAR and no UVB) and ice-free (high light; High PAR + UVA + UVB) conditions, water collected at 38 m was exposed over 9 days to 6 levels of decreasing pH from 8.1 to 7.2. A phytoplankton bloom dominated by the centric diatoms Chaetoceros spp. reaching up to 7.5 µg chlorophyll a L<sup>−1</sup> took place in all experimental bags. Total dimethylsulfoniopropionate (DMSPT) and DMS concentrations reached 155 nmol L<sup>−1</sup> and 19 nmol L<sup>−1</sup>, respectively. Under both light regimes, chlorophyll a and DMS concentrations decreased linearly with increasing proton concentration at all p...
Research Interests:
Research Interests:
Helene Tremblay, 1 Gaston Desrosiers, Jacques Locat, 3 Alfonso Mucci, 4 and Emilien Pelletier2 Characterization of a Catastrophic Flood Sediment Layer: Geological, Geotechnical ... of the fjord (in the Bras Nord) to less than 0.1 cm/yr in... more
Helene Tremblay, 1 Gaston Desrosiers, Jacques Locat, 3 Alfonso Mucci, 4 and Emilien Pelletier2 Characterization of a Catastrophic Flood Sediment Layer: Geological, Geotechnical ... of the fjord (in the Bras Nord) to less than 0.1 cm/yr in the deepest basin (Smith and Walton 1980 ...
Research Interests:
The biogeochemical cycles of iron (Fe) and organic carbon (OC) are strongly interlinked. In oceanic waters, organic ligands have been shown to control the concentration of dissolved Fe [1], whereas in soils, solid Fe phases provide a... more
The biogeochemical cycles of iron (Fe) and organic carbon (OC) are strongly interlinked. In oceanic waters, organic ligands have been shown to control the concentration of dissolved Fe [1], whereas in soils, solid Fe phases provide a sheltering and preservative effect for organic matter [2]. Until now however, the role of iron in the preservation of OC in sediments has not been clearly established. Here we show that 21.5 ± 8.6% of the OC in sediments is directly bound to reactive iron phases, which promote the preservation of OC in sediments. Iron-bound OC represents a global mass of 19 to 45 × 10^15 g of OC in surface marine sediments. This pool of OC is different from the rest of sedimentary OC, with 13C and nitrogen-enriched organic matter preferentially bound to Fe which suggests that biochemical fractionation occurs with OC-Fe binding. Preferential binding also affects the recovery of high molecular weight lipid biomarkers and acidic lignin oxidation products, changing the envi...
Research Interests:
Des analyses physiques (susceptibilité magnétique, densité, porosité et couleur), géochimiques (C org. , C inorg. , N), isotopiques ( 13 C et 15 N de la matière organique) et micropaléontologiques (foraminifères, diatomées, kystes de... more
Des analyses physiques (susceptibilité magnétique, densité, porosité et couleur), géochimiques (C org. , C inorg. , N), isotopiques ( 13 C et 15 N de la matière organique) et micropaléontologiques (foraminifères, diatomées, kystes de dinoflagellés, pollen, spores etc.) ont été réalisées dans les sédiments d'une carotte de ~2 m prélevée dans le bassin supérieur du fjord du Saguenay. La séquence étudiée représente environ 330 ans de sédimentation. Deux unités sédimentaires peuvent y être définies. Elles indiquent des changements majeurs dans la dynamique sédimentaire. La base de la séquence (endessous de ~70 cm) renferme des apports terrigènes dominants dont témoignent de faibles teneurs en 13 C et 15N de la matière organique, des rapports C/N élevés, la présence de carbonates détritiques et une faible concentration de microfossiles marins. Cette unité aurait été mise en place à la suite du tremblement de terre de 1663. La deuxième unité (~70-0 cm) présente de fortes teneurs en C ...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The head of the Laurentian Channel is a very dynamic region of exceptional biological richness. To evaluate the impact of freshwater discharge, tidal mixing, and biological activity on the pH of surface waters in this region, a suite of... more
The head of the Laurentian Channel is a very dynamic region of exceptional biological richness. To evaluate the impact of freshwater discharge, tidal mixing, and biological activity on the pH of surface waters in this region, a suite of physical and chemical variables was measured throughout the water column over two tidal cycles. The relative contributions to the water column of the four source-water types that converge in this region were evaluated using an optimum multiparameter algorithm (OMP). Results of the OMP analysis were used to reconstruct the water column properties assuming conservative mixing, and the difference between the model properties and field measurements served to identify factors that control the pH of the surface waters. These surface waters are generally undersaturated with respect to aragonite, mostly due to the intrusion of waters from the Upper St. Lawrence Estuary and the Saguenay Fjord. The presence of a cold intermediate layer impedes the upwelling of...
Research Interests:
... Moritz F. Lehmann,a,b,* Bruce Barnett,c Y. Gélinas,b,d Denis Gilbert,e Roxane J. Maranger,f Alfonso Mucci,b,g Bjorn ... by the diffusive supply of oxygen, and, therefore, the community (or apparent) O-isotope effect can be... more
... Moritz F. Lehmann,a,b,* Bruce Barnett,c Y. Gélinas,b,d Denis Gilbert,e Roxane J. Maranger,f Alfonso Mucci,b,g Bjorn ... by the diffusive supply of oxygen, and, therefore, the community (or apparent) O-isotope effect can be significantly reduced (Bender 1990; Brandes and Devol ...
Research Interests:
ABSTRACT Upon inundation, the soils in a hydroelectric reservoir are subjected to several years of physical, biological, and chemical changes as the transition from a terrestrial to an aquatic ecosystem is achieved. It is suspected that... more
ABSTRACT Upon inundation, the soils in a hydroelectric reservoir are subjected to several years of physical, biological, and chemical changes as the transition from a terrestrial to an aquatic ecosystem is achieved. It is suspected that changes in soil Eh and pH alter the metal binding capacity of organic matter, reactive iron (Fe) oxides/oxyhydroxides, and clay minerals, and may cause the mercury associated with these phases to be remobilized. Four cores were collected along a transect from an unflooded forest soil to a pre-impoundment lake bottom sediment. They were subjected to a customized sequential extraction procedure to determine the distribution of Hg between three operationally-defined solid compartments: organic carbon, reactive Fe oxides/hydroxides, and the solid (clay and sulfide) residue. Results indicate that up to 80% of the Hg in the O-horizon of forest soils and flooded soils and up to 85% of the Hg in lake sediments is bound to the NaOH-extractable organic carbon fraction. Furthermore, it was observed that the highest Hg concentrations are associated with degraded organic matter. In the B-horizon of a podzol, 40–60% of the total Hg was found associated with reactive Fe minerals. In contrast, the flooded podzol contains almost no reactive Fe at any depth and associated Hg concentrations are low. We propose that upon inundation, Fe oxides are reduced and Hg released to the pore waters where it is rapidly bound to other available substrates. Analyses of the extractions residues suggest that there is an enrichment of Hg in this fraction immediately above the B-horizon in a flooded soil.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
This study investigates the influence of EDTA and the Gram-positive cell walls of Bacillus subtilis on the dissolution rates and development of morphological features on the calcite [1014] surface. The calcite dissolution rates are... more
This study investigates the influence of EDTA and the Gram-positive cell walls of Bacillus subtilis on the dissolution rates and development of morphological features on the calcite [1014] surface. The calcite dissolution rates are compared at equivalent saturation indicies (SI) and relative to its dissolution behavior in distilled water (DW). Results indicate that the presence of metabolically inactive B. subtilis does not affect the dissolution rates significantly. Apparent increases in dissolution rates in the presence of the dead bacterial cells can be accounted for by a decrease of the saturation state of the solution with respect to calcite resulting from bonding of dissolved Ca2+ by functional groups on the cell walls. In contrast, the addition of EDTA to the experimental solutions results in a distinct increase in dissolution rates relative to those measured in DW and the bacterial cell suspensions. These results are partly explained by the 6.5-8 orders of magnitude greater stability of the Ca-EDTA complex relative to the Ca-B. subtilis complexes as well as its free diffusion to and direct attack of the calcite surface. Atomic force microscopy images of the [1014] surface of calcite crystals exposed to our experimental solutions reveal the development of dissolution pits with different morphologies according to the nature and concentration of the ligand. Highly anisotropic dissolution pits develop in the early stages of the dissolution reaction at low B. subtilis concentrations (0.004 mM functional group sites) and in DW. In contrast, at high functional group concentrations (4.0 mM EDTA or equivalent B. subtilis functional group sites), dissolution pits are more isotropic. These results suggest that the mechanism of calcite dissolution is modified by the presence of high concentrations of organic ligands. Since all the pits that developed on the calcite surfaces display some degree of anisotropy and dissolution rates are strongly SI dependent, the rate-limiting step is most likely a surface reaction for all systems investigated in this study. Results of this study emphasize the importance of solution chemistry and speciation in determining calcite reaction rates and give a more accurate and thermodynamically sound representation of dead bacterial cell wall-mineral interactions. In studies of natural aquatic systems, the presence of organic ligands is most often ignored in speciation calculations. This study clearly demonstrates that this oversight may lead to an overestimation of the saturation state of the solutions with respect to calcite and thermodynamic inconsistencies.
Research Interests:
Research Interests:
Research Interests: Earth Sciences, Environmental Science, Geology, Oceanography, Limnology, and 15 moreMixing, Biological Sciences, Phosphorus, Environmental Sciences, Far East, Depth, Diffusion, Ground Water, Deuterium, Hydrodynamics, Aquifers, Difusion, Biological Oceanography and Limnology, Lac, and Biogeochemical Cycle
Research Interests:
Research Interests:
Limrtol Oceanogì . 43(1), 1998, 53-64 © 1998, by the American Society of Limnology and Oceanography, Ine Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments Pierre Anschutz,1 Shaojun Zhong,2 and... more
Limrtol Oceanogì . 43(1), 1998, 53-64 © 1998, by the American Society of Limnology and Oceanography, Ine Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments Pierre Anschutz,1 Shaojun Zhong,2 and Bj0rn Sundby ...
Research Interests: Earth Sciences, Limnology, Biological Sciences, Concentration, Phosphorus, and 13 moreEnvironmental Sciences, Iron Oxide, Iron, Sorption, Dissolution, Biological Oceanography and Limnology, Chesapeake Bay, Acid Volatile Sulfide, Marine Environment, P/BV Ratio, Continental Margin, Pore Water, and Sediment-Water Interface
Research Interests: Geology and Geochemistry
The incomplete spatial coverage of CO<sub>2</sub> partial pressure (<i>p</i>CO<sub>2</sub>) measurements across estuary types represents a significant knowledge gap in current regional- and global-scale... more
The incomplete spatial coverage of CO<sub>2</sub> partial pressure (<i>p</i>CO<sub>2</sub>) measurements across estuary types represents a significant knowledge gap in current regional- and global-scale estimates of estuarine CO<sub>2</sub> emissions. Given the limited research on CO<sub>2</sub> dynamics in large estuaries and bay systems, as well as the sources of error in the calculation of <i>p</i>CO<sub>2</sub> (carbonic acid dissociation constants, organic alkalinity), estimates of air–sea CO<sub>2</sub> fluxes in estuaries are subject to large uncertainties. The Estuary and Gulf of St. Lawrence (EGSL) at the lower limit of the subarctic region in eastern Canada is the world's largest estuarine system, and is characterized by an exceptional richness in environmental diversity. It is among the world's most intensively studied estuaries, yet there are no published data on its s...
Research Interests:
Research Interests:
Research Interests:
ABSTRACT The stoichiometric solubility of fluorite was measured in a variety of aqueous solutions, including artificial seawater at 25°C and 1 atm total pressure in order to determine the effect of ionic strength and the potential... more
ABSTRACT The stoichiometric solubility of fluorite was measured in a variety of aqueous solutions, including artificial seawater at 25°C and 1 atm total pressure in order to determine the effect of ionic strength and the potential co-precipitation of seawater constituents on the equilibrium ion concentration product. The ion concentration products (ICP=[Ca2+][F−]2) measured after 32 weeks of equilibration converged to constant values. Extrapolation of the results in pure water and simple salt solutions (i.e., Na–Cl) to infinite dilution using the general specific ion interaction theory (SIT) or model estimates of the single ion activity coefficients of F− and Ca2+, yield an average Ksp° of 3.08±0.08×10−11 (or −log Ksp°=10.51±0.01).Application of speciation models to estimate the CaF2 ion activity coefficient product (i.e., (γCa2+)(γF−)2) in a high ionic strength Na–Mg–Ca–Cl solution (It=0.6951 m) failed to reproduce the values calculated from the ratio of the thermodynamic to the stoichiometric solubility constants (i.e., Ksp°/Ksp*) measured in this study. The discrepancy is attributed to the formation of a Mg-bearing CaF2 solid solution in the Na–Mg–Ca–Cl solution. Despite the close agreement between estimated and measured CaF2 activity coefficient products in artificial seawater, a more complex (i.e., containing Mg but also Sr and possibly other seawater constituents) CaF2 solid solution must also be precipitated on the surface of the fluorite in this solution.
Research Interests:
Research Interests:
Research Interests:
ABSTRACT Increase in bottom water temperatures in the St. Lawrence Estuary and Gulf over the last century: results of an oxygen isotopic study of benthic foraminifers.
Research Interests:
Research Interests:
Research Interests: Geology and Geochemistry
Research Interests:
Research Interests:
Research Interests:
Gaspeite is a low reactivity, rhombohedral carbonate mineral and a suitable surrogate to investigate the surface properties of other more ubiquitous carbonate minerals, such as calcite, in aqueous solutions. In this study, the acid-base... more
Gaspeite is a low reactivity, rhombohedral carbonate mineral and a suitable surrogate to investigate the surface properties of other more ubiquitous carbonate minerals, such as calcite, in aqueous solutions. In this study, the acid-base properties of the gaspeite surface were investigated over a pH range of 5 to 10 in NaCl solutions (0.001, 0.01, and 0.1 M) at near ambient conditions (25 +/- 3 degrees C and 1 atm) by means of conventional acidimetric and alkalimetric titration techniques and microelectrophoresis. Over the entire experimental pH range, surface protonation and electrokinetic mobility are strongly affected by the background electrolyte, leading to a significant decrease of the pH of zero net proton charge (PZNPC) and the pH of isoelectric point (pH(iep)) at increasing NaCl concentrations. This challenges the conventional idea that carbonate mineral surfaces are chemically inert to background electrolyte ions. Multiple sets of surface complexation reactions (i.e., ionization and ion adsorption) were formulated within the framework of three electrostatic models (CCM, BSM, and TLM) and their ability to simulate proton adsorption and electrokinetic data was evaluated. A one-site, 3-pK, constant capacitance surface complexation model (SCM) reproduces the proton adsorption data at all ionic strengths and qualitatively predicts the electrokinetic behavior of gaspeite suspensions. Nevertheless, the strong ionic strength dependence exhibited by the optimized SCM parameters reveals that the influence of the background electrolyte on the surface reactivity of gaspeite is not fully accounted for by conventional electrostatic and surface complexation models and suggests that future refinements to the underlying theories are warranted.
Research Interests:
Research Interests:
Mucci, A., Forest, A., Fortier, L., Fukuchi, M., Grant, J., Hattori, H., Hill, P., Lintern, G., Makabe, R., Magen, C., Miller, L., Sampei, M., Sasaki, H., Sundby, B., Walker, T.R., Wassmann, P. (2009) Chapter 7: Organic and Inorganic fluxes. In: On Thin Ice: a synthesis of the Canadian Arctic She...more
Research Interests:
Research Interests:
Research Interests:
Research Interests:
... Synthetic, a, 25, 11.01, 2, 0.01, Kim and O&#x27;Neil (1997). Calcite (CaCO 3 ), Natural, a, 25, 95, 10.10, 1, –, Das Sharma et al. (2002). Natural, ... Synthetic, a, 25, 10.44(ave.), 8, 0.10, Kim andO&#x27;Neil (1997). NBS... more
... Synthetic, a, 25, 11.01, 2, 0.01, Kim and O&#x27;Neil (1997). Calcite (CaCO 3 ), Natural, a, 25, 95, 10.10, 1, –, Das Sharma et al. (2002). Natural, ... Synthetic, a, 25, 10.44(ave.), 8, 0.10, Kim andO&#x27;Neil (1997). NBS 20, a, 25, 10.52, 6, N/A, Land (1980). Cerussite ...
Research Interests:
ABSTRACT Recent measurements show that an estimated 1300 km2 of the bottom of the St. Lawrence Estuary is now bathed by hypoxic waters (i.e., waters containing less than 62.5 mu M or 2 mg/l of dissolved oxygen). Eutrophication is one of... more
ABSTRACT Recent measurements show that an estimated 1300 km2 of the bottom of the St. Lawrence Estuary is now bathed by hypoxic waters (i.e., waters containing less than 62.5 mu M or 2 mg/l of dissolved oxygen). Eutrophication is one of the possible causes of hypoxia. An increased flux of nutrients from the watershed would lead to an increase surface productivity and organic carbon flux to the bottom waters. The microbially-mediated remineralization of this organic carbon will result in the progressive depletion of dissolved oxygen in the bottom waters. We have analysed sediment cores collected in the lower St. Lawrence Estuary in order to investigate temporal changes in productivity since the pre-colonial period and to identify evidence of eutrophication. The chronology of the cores is based on 210Pb measurements. The upper part of the box cores (upper 20 cm) is characterized by a very high sedimentation rate of 0.74 cm/yr. In the lower part of the core, sedimentation rates decreased to 0.28 cm/yr. Organic carbon content and its Delta 13C signature were used to reconstruct the fluxes, provenance and nature of the organic matter. The concentration and assemblages of dinoflagellates cysts served to estimate the variation in planktonic productivity whereas the abundance of benthic foraminifera and their organic linings were used to estimate variations in benthic production. The data clearly show an increase in the Delta 13C of preserved organic matter since the 70&#39;s, which we interpret as a shift toward enhanced contribution from a marine source of organic carbon. This shift corresponds to a significant increase in dinocyst concentration, possibly reflecting an increase in primary production of the surface waters. Moreover, there is an increase in the concentration of organic linings of benthic foraminifera suggesting a concomitant increase of benthic production.
Research Interests:
Research Interests: Marine Biology, Indonesia, Multidisciplinary, Archaea, Sulfides, and 15 moreLight, Surface Water, Iron Oxide, Iron, Banded Iron Formation, Water Microbiology, Sulfate reduction, Low Light, Sunlight, Environment, Oxidation-Reduction, Chlorophyll a, Microbial community, Green Sulfur Bacteria, and Molecular Sequence Data
Research Interests: Marine Biology, Indonesia, Multidisciplinary, Archaea, Sulfides, and 15 moreLight, Surface Water, Iron Oxide, Iron, Banded Iron Formation, Water Microbiology, Sulfate reduction, Low Light, Sunlight, Environment, Oxidation-Reduction, Chlorophyll a, Microbial community, Green Sulfur Bacteria, and Molecular Sequence Data
Research Interests:
Research Interests: Geology and Sedimentology
Research Interests:
ABSTRACT
Research Interests:
Page 1. [American Journal of Science, Vol. 285, April, 1985, P. 306-317] AUGER SPECTROSCOPY DETERMINATION OF THE SURFACE-MOST ADSORBED LAYER COMPOSITION ON ARAGONITE, CALCITE, DOLOMITE ...
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Geochemical (organic and inorganic carbon contents), isotopic (13C content of organic matter, 210Pb, 14C), micropaleontological (foraminifera, pollen) and sedimentological analysis of several sedimentary sequences (box and piston cores)... more
Geochemical (organic and inorganic carbon contents), isotopic (13C content of organic matter, 210Pb, 14C), micropaleontological (foraminifera, pollen) and sedimentological analysis of several sedimentary sequences (box and piston cores) were used to determine the chronology of land use change and industrial activity in the St. Lawrence Estuary and Saguenay Fjord from the European settlement to the present. In the St. Lawrence Estuary, the chronostratigraphy was derived from 210Pb and AMS 14C measurements, geochemical and isotopic correlations and the relative abundance of the pollen Ambrosia, whereas the Saguenay Fjord chronological framework was derived from chronostratigraphic markers associated with the 1663 (M~7) earthquake, 1971 St-Jean-Vianney landslide and the flood of 1996. In both area, paper mill and industrial activity during the 20th century is reflected by the organic carbon (OC) and 13C content profiles and has resulted in terrestrial OC contents growing almost exponentially until the 1970's, when major changes in industrial practices and the implementation of environmental regulations reduced the amount of industrial OC discharged into the Fjord and St. Lawrence River. This reduction of industrial waste inputs is also depicted in the Saguenay Fjord sediments by the decline in the relative abundance of the benthic foraminifera Spiroplectammina biformis, an opportunistic and tolerant species previously associated with polluted benthic environments. In addition, major changes in grain size are recorded in a core sampled at the head of the Fjord and probably reflect the impact of dam construction on the Saguenay River discharge. Finally, the chronology of deforestation and agricultural development linked to the European settlement in the St. Lawrence Lowlands as well as the industrial development of the second half of the 20th century are highlighted in the St. Lawrence Estuary sediments by the increase in the relative abundance of the pollen Ambrosia and by the two-step increase in sedimentation rates from 0.15 to 0.28 cm/yr and finally to 0.74 cm/yr.
Research Interests:
Field evidence suggests that the fate of sedimentary DOC is intimately linked to the diagenetic cycles of iron and manganese in marine sediments. Co-variations of their concentrations in sediment pore water [1], as well as the release of... more
Field evidence suggests that the fate of sedimentary DOC is intimately linked to the diagenetic cycles of iron and manganese in marine sediments. Co-variations of their concentrations in sediment pore water [1], as well as the release of DOC upon the reductive dissolution of authigenic iron and manganese oxides [1] suggest that sorption (i.e., co-precipitation and/or adsorption) onto these oxides
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Redox-sensitive elements (RSEs) are potentially powerful paleo-redox tracers [1]. To realize this potential requires an improved understanding on their geochemical properties and the chemical reactions they participate in during early... more
Redox-sensitive elements (RSEs) are potentially powerful paleo-redox tracers [1]. To realize this potential requires an improved understanding on their geochemical properties and the chemical reactions they participate in during early diagenesis. We measured the distributions of Fe, Mn, U, Mo, Re, and Cd in solid phase sediment and their porewaters in six cores collected along the Laurentian Trough of the Estuary and Gulf of St. Lawrence and the Eastern Canadian continental shelf. The data were obtained via ICP-MS analysis of porewaters and buffered-ascorbate and 1 N HCl extractible solid phase components. The results are consistent with the conclusions of a previous investigation that the accumulation rates of U, Mo, Re, and Cd are controlled by slow precipitation kinetics [2]. At the most landward station, where the sedimentation rate is highest (~4 mm/yr) and the bottom water dissolved oxygen concentration is lowest (~60 µM), the porewater U, Mo and Re concentrations decrease gra...
Research Interests:
Research Interests: Oceanography and Polar
A complex soup of assorted dissolved organic compounds can be found in lakes, rivers and oceans. Some of this organic matter (OM) is associated to mineral phases and the composition of the dissolved organic compound mixture is largely... more
A complex soup of assorted dissolved organic compounds can be found in lakes, rivers and oceans. Some of this organic matter (OM) is associated to mineral phases and the composition of the dissolved organic compound mixture is largely dictated by the adsorption efficacy and availability of mineral surfaces. In sediments, about 90% of the OM is bound - to some
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Geology and Geochemistry
Research Interests:
Research Interests:
Research Interests: Geology and Geochemistry
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Zoology, Biomass, Ecology, Periphyton, Canadian, and 5 moreMercury, Fisheries Sciences, Watershed, Lac, and Short Term
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.
Research Interests:
The solubilities of synthetic, natural and biogenic aragonite and calcite, in natural seawater of 35o/oo salinity at 25°C and 1 atm pressure, were measured using a closed system technique. Equilibration times ranged up to several months.... more
The solubilities of synthetic, natural and biogenic aragonite and calcite, in natural seawater of 35o/oo salinity at 25°C and 1 atm pressure, were measured using a closed system technique. Equilibration times ranged up to several months. The apparent solubility constant determined for calcite of 4.39(+/- 0.20) x 10-7 moI2 kg-2 is in good agreement with other recent solubility measurements and is constant after 5 days equilibration. When we measured aragonite solubility we observed that it decreased with increasing time of equilibration. The value of 6.65(+/- 0.12) x 10-7 mol2 kg--2determined for equilibration times in excess of 2 months, is significantly less than that found in other recent measurements, which employed equilibration times of only a few hours to days. No statistically significant difference was found among the synthetic, natural and biogenic material. Solid to solution ratio, contamination of aragonite with up to 10 wt% calcite and recycling of the aragonite made no statistically significant difference in solubility when long equilibration times were used. Measured apparent solubility constants of aragonite and calcite are respectively 22(+/- 3)% and 20(+/- 2)% less than apparent solubility constants calculated from thermodynamic equilibrium constants and seawater total activity coefficients. These large differences in measured and calculated apparent solubility constants may be the result of the formation of surface layers of lower solubility than the bulk solid.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Geology and Sedimentology
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Applied Mathematics, Geology, Algorithms, Thermodynamics, Speciation, and 21 moreMining, Hazardous Waste, Genetic Algorithm, Adsorption, Optimization, Models, Industry, Calibration, Data Bases, Aquifers, Efficiency, Simple Genetic Algorithm, Data Fitting, Inverse Modeling, Newton-Raphson algorithm, Evolutionary optimization, Industrie, Evolutionary Programming, Hazardous Wastes, Mathematical Geosciences, and Pore Water
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Geology and Geochemistry
Research Interests:
Research Interests:
Research Interests:
Research Interests: Geochemistry, Oceanography, Ecology, Carbon Cycle, Nova Scotia, and 14 moreHistorical Data, Sediment Traps, Continental Slope, Primary Production, Total Organic Carbon, Dissolved Oxygen, Organic carbon, Carbon Budget, Sedimentation Rate, Organic Matter, Dissolved Inorganic Carbon, Nitrate Uptake, Continental Margin, and Oxygen uptake rate
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Earth Sciences and Earth
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
6.1 Abstract Organic carbon is oxidized by microorganisms that use a series of terminal electron acceptors defined by free energy yield and availability. Methanogenesis by highly specialized Archea occurs once the availability of these... more
6.1 Abstract Organic carbon is oxidized by microorganisms that use a series of terminal electron acceptors defined by free energy yield and availability. Methanogenesis by highly specialized Archea occurs once the availability of these electron acceptors is diminished beyond a thermodynamic threshold which renders the energy yield to low to sustain microbial respiration. In the deep waters of the persistently stratified and Fe-rich Lake Matano, Indonesia, authigenic organic matter is largely degraded through ...