Papers by Maurice Levasseur
Simultaneous nitrogen and silicate deficiency of a phytoplankton community in a coastal jet-front
Marine Biology, Jun 1, 1990
Page 1. Marine Biology 104, 329-338 (1990) Marine o°-.o-.... B iology © Springer-Verlag 1990 Simu... more Page 1. Marine Biology 104, 329-338 (1990) Marine o°-.o-.... B iology © Springer-Verlag 1990 Simultaneous nitrogen and silicate deficiency of a phytoplankton community in a coastal jet-front ME Levasseur 1, 2, pj Harrison t, BR Heimdal 3 and J.-C. Therriault 2 ...

Limits to Microalgal Growth
Our objectives were to determine: 1) the influence of different N forms (NH4 +, NO3, and urea) on... more Our objectives were to determine: 1) the influence of different N forms (NH4 +, NO3, and urea) on the growth rate and on the nitrogen and carbon content of four microalgae, and 2) to relate the N form-induced physiological and biochemical differences to a shortage in energy (presumably reductant for NO3 − reduction), or a rate-limiting step in the N uptake and/or assimilation. The use of NO3 − instead of NH4 + resulted in a decrease in growth rate in Thalassiosira pseudonana and in significantly smaller N quotas and higher C:N ratios in T. pseudonana and Chaetoceros gracilis. Growth on urea instead of NH4 + resulted in a lower growth rate in C. gracilis and Gymnodinium sanguineum and in a lower N quota and a higher C:N ratio in most species tested. Growth on NO3 − rather than on NH4 + often resulted in a smaller (less chlorophyll a cell−1) and less efficient (lower quantum yield for oxygen production, higher chlorophyll a fluorescence yield) photosynthetic system, suggesting that NO...

Decreasing sea ice and increasing marine navigability in northern latitudes have changed Arctic s... more Decreasing sea ice and increasing marine navigability in northern latitudes have changed Arctic ship traffic patterns in recent years and are predicted to increase annual ship traffic in the Arctic in the future. Development of effective regulations to manage environmental impacts of shipping requires an understanding of ship emissions and atmospheric processing in the Arctic environment. As part of the summer 2014 NETCARE (Network on Climate and Aerosols) campaign, the plume dispersion and gas and particle emission factors of emissions originating from the Canadian Coast Guard Amundsen icebreaker operating near Resolute Bay, NU, Canada have been investigated. The Amundsen burnt distillate fuel with 1.5 wt % sulfur. Emissions were studied via plume intercepts using aircraft measurements, an analytical plume dispersion model, and using the FLEXPART-WRF Lagrangian particle dispersion model. The first plume intercepts by research aircraft were carried out on 19 July 2014 during the operation of the Amundsen in the open water. The second and third plume intercept measurements were carried out on 20 and 21 July 2014 when the Amundsen had reached the ice edge and operated under icebreaking conditions. Typical of Arctic marine navigation, the engine load was low compared to cruising conditions for all of the plume intercepts. The measured species included mixing ratios of CO 2 , NO x , CO, SO 2 , particle number concentration (CN), refractory Black Carbon (rBC), and Cloud Condensation Nuclei (CCN). The results were compared to similar experimental studies in mid latitudes.

The Lifetime of DMS in Northern Latitudes: Results from Four Shipboard Experiments
ABSTRACT The lifetime of dimethylsulfide (DMS) is usually referred to as being a day or more and ... more ABSTRACT The lifetime of dimethylsulfide (DMS) is usually referred to as being a day or more and is typically based on oxidation by OH and nitrate. However, the definition of DMS lifetime is not simply academic. It is an essential component for climate models attempting to estimate the effect of DMS oxidation as a feedback to global warming: an effect that is of increasing importance at high latitudes. The relevance of DMS oxidation by halogens, which are present at concentrations below detection limits of most current instrumentation, has largely been left as a modeling exercise. However, recent results from studies incorporating DMS flux from surface water and atmospheric measurements at mid to high latitudes permit a closer examination of the assumptions surrounding oxidation. A unique series of atmospheric and ocean DMS measurements were performed as part of Canadian Surface Ocean Lower Atmosphere Study (C-SOLAS) in 2002 and 2003 to clarify new aerosol formation. Month-long shipboard campaigns were conducted in the summer of 2002 over the North Pacific and a seasonal study with three campaigns was performed in 2003 above the NW Atlantic. Land- and ship-based measurements of the oxidation products sulphur dioxide, aerosol sulphate, and methane sulfonic acid provide a larger context in which to place the results. Sulphur isotope apportionment was used to quantify the contribution of DMS to sulphate and sulphur dioxide to link gas concentrations with biogenic aerosol formation.

Sources of Dimethyl Sulfide in the Canadian Arctic Archipelago and Baffin Bay
AGU Fall Meeting Abstracts, Dec 14, 2015
International audienceDimethyl sulfide plays a major role in the global sulfur cycle, meaning tha... more International audienceDimethyl sulfide plays a major role in the global sulfur cycle, meaning that it is important to the formation of sulfate aerosol and thus to cloud condensation nuclei populations and cloud formation. The summertime Arctic atmosphere sometimes resides in a cloud condensation nuclei limited regime, making it very susceptible to changes in their number. Despite the interest generated by this situation, dimethyl sulfide has only rarely been measured in the summertime Arctic. This work presents the first high time resolution (10 Hz) DMS mixing ratio measurements for the Eastern Canadian Archipelago and Baffin Bay in summer performed on an icebreaker cruise as one component of the Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments (NETCARE). Measured mixing ratios ranged from below the detection limit of 4 pptv to 1155 pptv with a median value of 186 pptv. We used transfer velocity parameterizations from the literature to generate the first flux estimates for this region in summer, which ranged from 0.02-12 μmol m-2 d-1. DMS has a lifetime against OH oxidation of 1-2 days, allowing both local sources and transport to play roles in its atmospheric mixing ratio. Through air mass trajectory analysis using FLEXPART-WRF and chemical transport modeling using GEOS-Chem, we have identified the relative contributions of local sources (Lancaster Sound and Baffin Bay) as well as transport from further afield (the Hudson Bay System and the Beaufort Sea) and find that the local sources dominate. GEOS-Chem is able to reproduce the major features of the measured time series, but is biased low overall (median 72 pptv). We discuss non-marine sources that could account for this low bias and estimate the possible contributions to DMS mixing ratios from lakes, biomass burning, melt ponds and coastal tundra. Our results show that local marine sources of DMS dominate the summer Arctic atmosphere, but that non-local and possibly non-marine contributions have a detectable influence

Ammonia in the summer Arctic marine boundary layer: Sources, Sinks and Implications
2015 AGU Fall Meeting, Dec 14, 2015
International audienceThe abundance of NH3 can influence new particle formation rates, aerosol ch... more International audienceThe abundance of NH3 can influence new particle formation rates, aerosol chemical and optical properties, as well as N-sensitive ecosystems via deposition. Sources and sinks of gas-phase ammonia (NH3) are poorly constrained in the High Arctic due to a lack of field observations. In particular, both the magnitude and direction of sea-air NH3 exchange are highly uncertain, although previous studies suggest the open ocean is likely to act as a net sink at high latitudes.In order to investigate potential NH3 sources, sinks and impacts, hourly gas-phase NH3 and particulate-phase NH4+ and SO42- measurements were taken from 13 July to 7 August 2014 aboard a research cruise throughout Baffin Bay and the eastern Canadian Arctic Archipelago. Simultaneous measurements of total seawater ammonium, pH and sea surface temperature were used to compute the compensation point (χ), which is the ambient NH3 concentration at which sea-air fluxes change direction. Ambient NH3 ranged from 30-650 ng m-3 throughout the cruise and was several orders of magnitude larger than measured χ values (0.4-10 ng m-3). Hence, the summertime Arctic Ocean is a strong net sink of NH3.GEOS-Chem (a chemical transport model) was employed to examine the impact of seabird guano (feces) on surface NH3 concentrations. A simulation without guano-derived NH3 emissions yielded highly acidic aerosol and underestimated surface NH3 by several orders of magnitude. Including NH3 emission estimates from seabird guano greatly improved model-measurement comparison. The importance of seabird guano as an NH3 source was also investigated using the FLEXible PARTicle dispersion model driven by WRF meteorology (FLEXPART-WRF). FLEXPART-WRF results confirm that air masses with origins co-located with large seabird colonies were enriched in NH3, whereas those originating over the open ocean were depleted in NH3. The influence of NH3 from wildfires, as well as implications for N-deposition and aerosol neutralization are also discussed

Elementa: Science of the Anthropocene, 2021
Phytoplankton blooms in the Arctic marginal ice zone (MIZ) can be prolific dimethylsulfide (DMS) ... more Phytoplankton blooms in the Arctic marginal ice zone (MIZ) can be prolific dimethylsulfide (DMS) producers, thereby influencing regional aerosol formation and cloud radiative forcing. Here we describe the distribution of DMS and its precursor dimethylsulfoniopropionate (DMSP) across the Baffin Bay receding ice edge in early summer 2016. Overall, DMS and total DMSP (DMSPt) increased towards warmer waters of Atlantic origin concurrently with more advanced ice-melt and bloom stages. Relatively high DMS and DMSPt (medians of 6.3 and 70 nM, respectively) were observed in the surface layer (0–9 m depth), and very high values (reaching 74 and 524 nM, respectively) at the subsurface biomass maximum (15–30 m depth). Microscopic and pigment analyses indicated that subsurface DMS and DMSPt peaks were associated with Phaeocystis pouchetii, which bloomed in Atlantic-influenced waters and reached unprecedented biomass levels in Baffin Bay. In surface waters, DMS concentrations and DMS:DMSPt ratio...
Global Ocean Dimethylsulfide Observations and Climatology
Dimethylsulfide (DMS) measurements (15748 samples) made in the surface global oceans during 1972-... more Dimethylsulfide (DMS) measurements (15748 samples) made in the surface global oceans during 1972-1998 are given as raw data samples, along with the associated environmental data data at the time of data collection, and as 1-degree by 1-degree global objectively analyzed grids. The grids are for both a monthly climatology (12 monthly grids), and an overall annual mean.
Dust in an acidified ocean: iron bioavailability, phytoplankton growth and DMS
Earth System Science Data Discussions, 2019
The Green Edge initiative was developed to investigate the processes controlling the primary prod... more The Green Edge initiative was developed to investigate the processes controlling the primary productivity and the fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797N, 63.7895W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea ice cover from the surface

Elementa: Science of the Anthropocene, 2019
This paper presents the first empirical estimates of dimethyl sulfide (DMS) gas fluxes across per... more This paper presents the first empirical estimates of dimethyl sulfide (DMS) gas fluxes across permeable sea ice in the Arctic. DMS is known to act as a major potential source of aerosols that strongly influence the Earth’s radiative balance in remote marine regions during the ice-free season. Results from a sampling campaign, undertaken in 2015 between June 2 and June 28 in the ice-covered Western Baffin Bay, revealed the presence of high algal biomass in the bottom 0.1-m section of sea ice (21 to 380 µg Chl a L–1) combined with the presence of high DMS concentrations (212–840 nmol L–1). While ice algae acted as local sources of DMS in bottom sea ice, thermohaline changes within the brine network, from gravity drainage to vertical stabilization, exerted strong control on the distribution of DMS within the interior of the ice. We estimated both the mean DMS molecular diffusion coefficient in brine (5.2 × 10–5 cm2 s–1 ± 51% relative S.D., n = 10) and the mean bulk transport coefficien...

Atmospheric Chemistry and Physics Discussions, 2019
Atmospheric dimethyl sulfide, DMS(g), is a climatically important sulfur compound and is the main... more Atmospheric dimethyl sulfide, DMS(g), is a climatically important sulfur compound and is the main source of biogenic sulfate aerosol in the Arctic atmosphere. DMS(g) production and emission to the atmosphere increase during the summer due to greater ice-free sea surface and higher biological activity. We implemented DMS(g) in the GEM-MACH model (GEM: Global Environmental Multiscale-Environment and Climate Change Canada's (ECCC) numerical weather forecast model, MACH: ECCC's Modelling Air quality and CHemistrychemistry and aerosol microphysics) for the Arctic region, and compared model simulations with DMS(g) measurements made in Baffin Bay and the Canadian Arctic Archipelago in July and August 2014. Two sea water DMS(aq) datasets were used as input to the simulations: 1) DMS(aq) climatology dataset based on seawater concentration measurements (Lana et al., 2011) and 2) DMS(aq) dataset based on satellite detection (Galí et al., 2018). In general, GEM-MACH simulations underpredict DMS(g) measurements, likely due to negative biases in both DMS(aq) datasets. Yet, higher correlation and smaller bias were obtained with the satellite dataset. Agreement with the observations improved by replacing climatological values with in situ measured DMS(aq) concurrently with atmospheric observations over Baffin Bay and Lancaster Sound area in July 2014. The addition of DMS(g) to the GEM-MACH model resulted in a significant increase in atmospheric SO2 for some regions in the Canadian Arctic (up to 100%). Analysis of the size-segregated sulfate aerosol in the model shows that a significant increase in sulfate mass occurs for particles with a diameter smaller than 200 nm due to formation and growth of biogenic aerosol at high latitudes (> 70º N). The enhancement in sulfate particles is most significant in the size range of 50 to 100 nm, however, this enhancement is stronger in the 200-1000 nm size range at lower latitudes (< 70º N). These results emphasise the important role of DMS(g) in the formation and growth of fine and ultrafine sulfate-containing particles in the Arctic during the month of July.

Biogeosciences, 2018
We investigated the combined effect of ocean acidification and warming on the dynamics of the phy... more We investigated the combined effect of ocean acidification and warming on the dynamics of the phytoplankton fall bloom in the Lower St. Lawrence Estuary (LSLE), Canada. Twelve 2600 L mesocosms were set to initially cover a wide range of pH T (pH on the total proton scale) from 8.0 to 7.2 corresponding to a range of pCO 2 from 440 to 2900 µatm, and two temperatures (in situ and +5 • C). The 13-day experiment captured the development and decline of a nanophytoplankton bloom dominated by the chainforming diatom Skeletonema costatum. During the development phase of the bloom, increasing pCO 2 influenced neither the magnitude nor the net growth rate of the nanophytoplankton bloom, whereas increasing the temperature by 5 • C stimulated the chlorophyll a (Chl a) growth rate and maximal particulate primary production (P P) by 76 % and 63 %, respectively. During the declining phase of the bloom, warming accelerated the loss of diatom cells, paralleled by a gradual decrease in the abundance of photosynthetic picoeukaryotes and a bloom of picocyanobacteria. Increasing pCO 2 and warming did not influence the abundance of picoeukaryotes, while picocyanobacteria abundance was reduced by the increase in pCO 2 when combined with warming in the latter phase of the experiment. Over the full duration of the experiment, the time-integrated net primary production was not significantly affected by the pCO 2 treatments or warming. Overall, our results suggest that warming, rather than acidification, is more likely to alter phytoplankton autumnal bloom development in the LSLE in the decades to come. Future studies examining a broader gradient of temperatures should be conducted over a larger seasonal window in order to better constrain the potential effect of warming on the development of blooms in the LSLE and its impact on the fate of primary production.
Atmospheric Chemistry and Physics Discussions, 2018
*This paper is dedicated to Eric Girard, a NETCARE scientist who died July 10, 2018. Eric contrib... more *This paper is dedicated to Eric Girard, a NETCARE scientist who died July 10, 2018. Eric contributed greatly to the field of Arctic cloud and aerosol microphysics during his research career.

Atmospheric Chemistry and Physics Discussions, 2015
Dimethyl sulfide (DMS) plays a major role in the global sulfur cycle. In addition, its atmospheri... more Dimethyl sulfide (DMS) plays a major role in the global sulfur cycle. In addition, its atmospheric oxidation products contribute to the formation and growth of atmospheric aerosol particles, thereby influencing cloud condensation nuclei (CCN) populations and thus cloud formation. The pristine summertime Arctic atmosphere is a CCN-limited regime, and is thus very susceptible to the influence of DMS. However, atmospheric DMS mixing ratios have only rarely been measured in the summertime Arctic. During July-August 2014, we conducted the first high time resolution (10 Hz) DMS mixing ratio measurements for the Eastern Canadian Archipelago and Baffin Bay as one component of the Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments (NETCARE). DMS mixing ratios ranged from below the detection limit of 4 to 1155 pptv (median 186 pptv). A set of transfer velocity parameterizations from the literature coupled with our atmospheric and coincident seawater DMS measurements yielded air-sea DMS flux estimates ranging from 0.02-12 µmol m −2 d −1 , the first published for this region in summer. Airmass trajectory analysis using FLEXPART-WRF and chemical transport modeling using GEOS-Chem indicated that local sources (Lancaster Sound and Baffin Bay) were the dominant contributors to the DMS measured along the 21 day ship track, with episodic transport from the Hudson Bay System. After adjusting GEOS-Chem oceanic DMS values in the region to match measurements, GEOS-Chem reproduced the major features of the measured time series, but remained biased low overall (median 67 pptv). We investigated non-marine sources that might contribute to this bias, such as DMS emissions from lakes, biomass burning, melt ponds and coastal tundra. While the local marine sources of DMS dominated overall, our results suggest that non-local and possibly non-marine sources episodically contributed strongly to the observed summertime Arctic DMS mixing ratios.

Canadian Journal of Fisheries and Aquatic Sciences, 2017
The head of the Laurentian Channel is a very dynamic region of exceptional biological richness. T... 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...
Atmospheric Chemistry and Physics Discussions, 2017
Vertical distributions of atmospheric dimethyl sulfide (DMS(g)) were sampled aboard the research ... more Vertical distributions of atmospheric dimethyl sulfide (DMS(g)) were sampled aboard the research aircraft Polar 6 near Lancaster Sound, Nunavut, Canada in July 2014 and on pan-Arctic flights in April 2015 that started from Longyearbyen, Spitzbergen, and passed through Alert and Eureka, Nunavut and Inuvik, Northwest Territories. Larger mean DMS(g) mixing ratios were present during April 2015 (campaign-mean of 116±8 pptv) compared to July 2014 (campaign-mean of 20±6 pptv). Observations in July 2014 indicated a decrease in DMS(g) mixing ratios with altitude up to about 3 km, and the largest

Marine Ecology Progress Series, 2016
Sea ice-derived particulate organic carbon (iPOC) represents an important contribution of carbon ... more Sea ice-derived particulate organic carbon (iPOC) represents an important contribution of carbon to Arctic ecosystems, yet our ability to obtain realistic quantitative estimates of iPOC outside the sea ice matrix is currently somewhat limited. To address this challenge, we applied a novel approach to quantifying iPOC within the water column under melting sea ice by first measuring the proportion of the sea ice diatom biomarker IP 25 within iPOC in bottom ice samples obtained from Resolute Passage during spring 2012. We then compared this value with corresponding values obtained from a time series of water samples. Together, these reflected a period of ice melt and rapid release of iPOC, indicated by changing ice temperature and thickness, in addition to changes in the stable carbon isotope composition and concentration of iPOC, IP 25 and chlorophyll a within bottom ice. Estimates of iPOC in seawater were highest (0.15 to 0.22 mg l −1) in the upper 2 m, coincident with the reduction of iPOC in sea ice near the beginning of sampling, with iPOC accounting for an estimated 84 to 125% of total POC (tPOC). Collectively, this biomarker approach yielded realistic estimates of %iPOC, both numerically and in the context of melting sea ice following a spring bloom in the Canadian Arctic. We describe some assumptions of this approach and consider the impacts of possible caveats on quantitative estimates of iPOC derived using this methodology.
Uploads
Papers by Maurice Levasseur