Christine Michel - Academia.edu (original) (raw)

Papers by Christine Michel

Environmental Research Letters, 2019

Progress in Oceanography, Dec 1, 2016

Sea ice algae are a characteristic feature in ice-covered seas, contributing a significant fracti... more Sea ice algae are a characteristic feature in ice-covered seas, contributing a significant fraction of the total primary production in many areas and providing a concentrated food source of high nutritional value to grazers in the spring. Algae respond to physical changes in the sea ice environment by modifying their cellular carbon, nitrogen and pigment content, and by adjusting their photophysiological characteristics. In this study we examined how the ratios of particulate organic carbon (POC) to nitrogen (PON), and POC to chlorophyll a (chl a), responded to the evolving snow-covered sea ice environment near Cambridge Bay, Nunavut, during spring 2014. We also estimated photosynthesis-irradiance (PI) curves using oxygen-optodes and evaluated the resulting time-series of PI parameters under thin and thick snow-covered sites. There were no significant differences in PI parameters between samples from different overlying snow depths, and only the maximum photosynthetic rates in the absence of photoinhibition (P ! !) and photoacclimation (I S) parameters changed significantly over the spring bloom. Furthermore, we found that both these parameters increased over time in response to increasing percent transmission of photosynthetically active radiation (T PAR) through the ice, indicating that light was a limiting factor of photosynthesis and was an important driver of temporal (over the spring) rather than spatial (between snow depths) variability in photophysiological response. However, we note that spatial variability in primary production was evident. Higher T PAR over the spring and under thin snow affected the composition of algae over both time and space, causing greater POC:chl a estimates in late spring and under thin snow cover. Nitrogen limitation was pronounced in this study, likely reducing P ! ! and algal photosynthetic rates, and increasing POC:PON ratios to over Photosynthetic response of ice algae 3 six times the Redfield average. Our results highlight the influence of both light and nutrients on ice algal biomass composition and photophysiology, and suggest a limitation by both resources over a diel period.

Authors Hans Meltofte, Tom Barry, Dominique Berteaux, Helga Bültmann, Jørgen S. Christiansen, Jos... more Authors Hans Meltofte, Tom Barry, Dominique Berteaux, Helga Bültmann, Jørgen S. Christiansen, Joseph A. Cook, Anders Dahlberg, Fred J.A. Daniëls, Dorothee Ehrich, Finnur Friðriksson, Barbara Ganter, Anthony J. Gaston, Lynn Gillespie, Lenore Grenoble, Eric P. Hoberg, Ian D. Hodkinson, Henry P. Huntington, Rolf A. Ims, Alf B. Josefson, Susan J. Kutz, Sergius L. Kuzmin, Kristin L. Laidre, Dennis R. Lassuy, Patrick N. Lewis, Connie Lovejoy, Christine Michel, Vadim Mokievsky, Tero Mustonen, David C. Payer, Michel Poulin, Donald Reid, James D. Reist, David F. Tessler and Frederick J. Wrona

and Wells, T. 2020. Marine harmful algal blooms and phycotoxins of concern to Canada. Can. Tech. ... more and Wells, T. 2020. Marine harmful algal blooms and phycotoxins of concern to Canada. Can. Tech. Rep. Fish. Aquat. Sci. 3384: x + 322 p. In Canada, reports of marine harmful algal blooms (HABs) have increased over the past few decades. HABs are caused by the growth of certain phytoplankton that produce phycotoxins or otherwise cause harm. Phycotoxins are problematic to human health, and their cumulative effects are stressors to marine ecosystems by causing the mortality of marine fish, birds and mammals, including species designated at risk. Paralytic Shellfish Poisoning (caused by saxitoxin group toxins produced by Alexandrium spp.) has been problematic for years on both the east and west Canadian coasts. Amnesic Shellfish Poisoning (caused by domoic acid produced by Pseudo-nitzschia spp.) was identified for the first time worldwide following consumption of blue mussels from eastern Canada in 1987. Domoic acid has since also been found on the west coast. Diarrhetic Shellfish Poisoning (caused by okadaic acid group toxins produced by Dinophysis spp. and Prorocentrum spp.) was first recognized as a hazard in eastern Canadian waters in 1990, and these phycotoxins have since been found on both the east and west Canadian coasts. Other phycotoxins that may cause harm to human health in Canada include pectenotoxins, yessotoxins, azaspiracids, and cyclic imine group toxins (spirolide toxins, pinnatoxins, and gymnodimines). Multiple harmful algal species have been associated with fish-killing blooms on both east and west Canadian coasts. The range of exotic toxic/harmful algae is expanding in Canadian waters due in part to introductions from ships' ballast water and climate change. The detection of domoic acid and the discovery of several toxigenic diatoms and dinoflagellates in the Canadian Arctic is of increasing concern because of the limited knowledge of HABs in this region. Canada's experience in dealing with toxic events resulted in research and monitoring programs designed to understand HABs and to assist the fishing and aquaculture industries. In spite of decreases in research and phytoplankton monitoring efforts, consumers of molluscan shellfish are still protected by phycotoxin monitoring, which is conducted by the Canadian Food Inspection Agency. Novel phycotoxins and toxic algae will continue to be discovered. Continued vigilance and the maintenance of an effective capacity to manage developing problems via strategic research programs is essential. This document reviews Canadian marine HABs and phycotoxins up to late 2018, and provides a foundation for any future research in this area.

Marine Ecology Progress Series, 2018

Elem Sci Anth

Ice algae are critical components to the lipid-driven Arctic marine food web, particularly early ... more Ice algae are critical components to the lipid-driven Arctic marine food web, particularly early in the spring. As little is known about these communities in multiyear ice (MYI), we aimed to provide a baseline of fatty acid (FA) and stable isotope signatures of sea-ice communities in MYI from the Lincoln Sea and compare these biomarkers to first-year ice (FYI). Significant differences in the relative proportions of approximately 25% of the identified FAs and significantly higher nitrogen stable isotope values (δ15N) in bottom-ice samples of FYI (δ15N = 6.4 ± 0.7%) compared to MYI (δ15N = 5.0 ± 0.4%) reflect different community compositions in the two ice types. Yet, the relative proportion of diatom- and dinoflagellate-associated FAs, as well as their bulk and most of the FA-specific carbon stable isotope compositions (δ13C) were not significantly different between bottom FYI (bulk δ13C: –28.4% to –26.7%, FA average δ13C: –34.4% to –31.7%) and MYI (bulk δ13C: –27.6% to –27.2%, FA av...

Marine Ecology Progress Series, 2008

The variability of particulate organic carbon (POC) sinking flux and its relationship to primary ... more The variability of particulate organic carbon (POC) sinking flux and its relationship to primary production were investigated in the upper twilight zone of the northwest Atlantic Ocean on 4 occasions during a Lagrangian study of the decline of a spring diatom bloom and its transition towards post-bloom conditions. POC sinking fluxes below the euphotic zone (50 to 75 m depth) decreased from (mean ± SD) 674 ± 105 to 281 ± 17 mg C m-2 d-1 throughout the senescence of the bloom and further decreased to 197 ± 2 mg C m-2 d-1 under post-bloom conditions. POC sinking fluxes below the euphotic zone were positively correlated to the production of large phytoplankton cells (≥5 µm) throughout the study period, highlighting the importance of the size structure of primary producers in shaping the export of POC from the euphotic zone. In contrast, POC sinking fluxes at 150 m depth showed little variation throughout the study period. Analysis of the vertical profiles of POC sinking flux revealed an increase in POC transfer efficiency from 50 to 150 m depth due to a decrease in POC recycling within the upper twilight zone throughout the decline of the bloom. Moreover, POC recycling within the upper twilight zone was positively correlated with POC sinking fluxes below the euphotic zone throughout the study period, suggesting that recycling processes in the upper twilight zone respond rapidly and proportionally to the export of POC from the euphotic zone. It is hypothesized that the concomitant decreases in POC sinking fluxes below the euphotic zone and in POC recycling within the upper twilight zone compensated each other and could explain the fairly constant POC sinking fluxes at 150 m depth that were observed throughout the study period. Our results shed light on the importance of short-term variability in organic matter recycling within the upper twilight zone for the efficiency of POC export to depth.

Journal of Geophysical Research: Oceans, 2015

Snow is a principal factor in controlling heat and light fluxes through sea ice. With the goal of... more Snow is a principal factor in controlling heat and light fluxes through sea ice. With the goal of improving radiative and heat flux estimates through sea ice in regional and global models without the need of detailed snow property descriptions, a new parameterization including subgrid-scale snow thickness variability is presented. One-parameter snow thickness distributions depending only on the gridbox-mean snow thickness are introduced resulting in analytical solutions for the fluxes of heat and light through the snow layer. As the snowpack melts, these snow thickness distributions ensure a smooth seasonal transition of the light field under sea ice. Spatially homogenous melting applied to an inhomogeneous distribution of snow thicknesses allows the appearance of bare sea ice areas and melt ponds before all snow has melted. In comparison to uniform-thickness snow used in previous models, the bias in the under sea-ice light field is halved with this parameterization. Model results from a one-dimensional ocean turbulence model coupled with a thermodynamic sea ice model are compared to observations near Resolute in the Canadian High Arctic. The simulations show substantial improvements not only to the light field at the sea ice base which will affect ice algal growth but also to the sea ice and seasonal snowpack evolution. During melting periods, the snowpack can survive longer while sea ice thickness starts to reduce earlier.

Reviews of Geophysics, 2014

Sea ice in the Arctic is one of the most rapidly changing components of the global climate system... more Sea ice in the Arctic is one of the most rapidly changing components of the global climate system. Over the past few decades, summer areal extent has declined over 30%, and all months show statistically significant declining trends. New satellite missions and techniques have greatly expanded information on sea ice thickness, but many uncertainties remain in the satellite data and long-term records are sparse. However, thickness observations and other satellite-derived data indicate a 40% decline in thickness, due in large part to the loss of thicker, older ice cover. The changes in sea ice are happening faster than models have projected. With continued increasing temperatures, summer ice-free conditions are likely sometime in the coming decades, though there are substantial uncertainties in the exact timing and high interannual variability will remain as sea ice decreases. The changes in Arctic sea ice are already having an impact on flora and fauna in the Arctic. Some species will face increasing challenges in the future, while new habitat will open up for other species. The changes are also affecting people living and working in the Arctic. Native communities are facing challenges to their traditional ways of life, while new opportunities open for shipping, fishing, and natural resource extraction. Significant progress has been made in recent years in understanding of Arctic sea ice and its role in climate, the ecosystem, and human activities. However, significant challenges remain in furthering the knowledge of the processes, impacts, and future evolution of the system. MEIER ET AL.

Quaternary Science Reviews, 2013

Contents 4 3.8 Sea ice surface, bromine and tropospheric ozone chemistry 4. Modelling and up-scal... more Contents 4 3.8 Sea ice surface, bromine and tropospheric ozone chemistry 4. Modelling and up-scaling the role of sea ice in the marine biogeochemical cycles 5. Discussion and outlook References Tables and Figures

Polar Biology, 1993

, in southeastern Hudson Bay (Canadian Arctic). The taxonomic similarity between samples from the... more , in southeastern Hudson Bay (Canadian Arctic). The taxonomic similarity between samples from the three environments was assessed using a clustering procedure. There were two groups that comprised samples from both the ice-water interface and the water column, while five other groups were made of samples originating from a single environment. Taxonomic compositions of the two mixed groups suggest two types of connexion between the ice-water interface and the water column, i.e. before the phytoplankton bloom, there was seeding of the water column by ice algae and, during ice melt, interfacial algae contributed to the water column communities that were otherwise typically phytoplankton. Overall, the phytoplankton community underwent a succession from pennate to centric diatoms. Sinking rates of algae from the ice-water interface were estimated using settling columns (SETCOL). The sinking rates increased seasonally (0.4-2.7 m d-1), which enhanced accessibility of ice-algal cells to the pelagic grazers. Ice algae contributed to water column production as they became accessible to the pelagic grazers, and also by seeding the water column before the phytoplankton bloom. Recent biological studies in ice-covered seas have mainly focussed on the ecology and physiology of ice-algal communities which comprise, according to the terminology of

Polar Biology, 2007

Microscale photographs were taken of the ice bottom to examine linkages of algal chlorophyll a (c... more Microscale photographs were taken of the ice bottom to examine linkages of algal chlorophyll a (chl a) biomass distribution with bottom ice features in thick Arctic first-year sea ice during a spring field program which took place from May 5 to 21, 2003. The photographic technique developed in this paper has resulted in the first in situ observations of microscale variability in bottom ice algae distribution in Arctic first-year sea ice in relation to ice morphology. Observations of brine channel diameter (1.65-2.68 mm) and number density (5.33-10.35 per 100 cm 2) showed that the number of these channels at the bottom of thick first-year sea ice may be greater than previously measured on extracted ice samples. A variogram analysis showed that over areas of low chl a biomass (£20.7 mg chl a m-2), patchiness in bottom ice chl a biomass was at the scale of brine layer spacing and small brine channels (~1-3 mm). Over areas of high chl a biomass (‡34.6 mg chl a m-2), patchiness in biomass was related to the spacing of larger brine channels on the ice bottom (~10-26 mm). Brine layers and channels are thought to provide microscale maxima of light, nutrient replenishment and space availability which would explain the small scale patchiness over areas of low algal biomass. However, ice melt and erosion near brine channels may play a more important role in areas with high algal biomass and low snow cover.

Marine Ecology Progress Series, 2010

Comprehensive investigations of the Canadian Arctic during late summer and early fall revealed th... more Comprehensive investigations of the Canadian Arctic during late summer and early fall revealed the widespread occurrence of long-lived subsurface chlorophyll maxima (SCM) in seasonally ice-free waters. The vertical position of the SCM corresponded with the depth of the subsurface biomass maximum (SBM), at least in Baffin Bay, suggesting that SCM could be an important source of carbon for the food web. Most of these SCM were located well below the pycnocline in close association with the nitracline, implying that their vertical position was driven mainly by a shortage of inorganic nitrogen in the upper euphotic zone. The diversity of SCM configurations with respect to physical properties of the water column complicates the estimation of euphotic-zone chlorophyll and primary production from surface properties. High photosynthetic yields (F v /F m) showed the phytoplankton to be photosynthetically competent and well acclimated to conditions of irradiance and nutrient supply near the surface and at the SCM. A well-defined primary nitrite maximum was associated with the SCM in the southwest Canadian Arctic, but not in the northeast where nitrite concentrations were highest much below the euphotic zone. This contrast is consistent with differences in vertical stratification, the light-dark cycle and, possibly, the physiological state and taxonomic composition of the phytoplankton community at the SCM. This study demonstrates that the SCM, once regarded as anecdotal due to under-sampling, are a dominant feature of the Arctic Ocean that should be considered in remote sensing studies and biogeochemical models.

Marine Ecology Progress Series, 2004

The downward export of organic material was assessed during the productive period (late spring to... more The downward export of organic material was assessed during the productive period (late spring to early autumn) in the North Water polynya area (NOW; northern Baffin Bay). Freedrifting short-term particle interceptor traps were deployed at 3 depths below the euphotic zone (50, 100 and 150 m) for 12 to 24 h at 19 stations from June to July in 1998 and at 12 stations during August and September in 1999. The sinking material was analyzed for particulate organic carbon (POC) and pigments (chlorophyll a and pheopigments), and for phytoplankton and fecal pellet enumerations. POC and pigment sinking fluxes at 50 m averaged 337 and 8 mg m-2 d-1 , respectively. The maximum sinking fluxes of organic matter (ca. 554 mg C m-2 d-1 and 14 mg pigments m-2 d-1) were observed in June, after which they decreased and remained relatively constant (ca. 219 to 240 mg C m-2 d-1 and 3.9 to 4.1 mg pigments m-2 d-1). Phytoplankton carbon flux decreased while fecal carbon flux increased during the study. In June, intact diatom cells and fecal pellets made up 50 and 4% of the total POC sinking flux, respectively. During the following months, they made up ≤10% (diatoms) and 30 to 50% (fecal pellets) of the total POC flux. A rapid increase in sinking cell numbers and fecal pellets at the end of the sampling season points to a late summer-early autumn bloom in the NOW. The dominant pathway of carbon cycling changed during the study, from export in spring to retention afterwards. From July on, the retention of particulate organic matter in the upper 100 m of the water column was favored by the low sinking velocities of POC and chlorophyll a, which averaged ≤1.3 m d-1. Over the whole sampling period, 35% of the particulate phytoplankton production was exported through sinking, while 65% was recycled or remained suspended in the euphotic zone. The organic carbon produced in the euphotic zone was, thus, mainly available to pelagic grazers rather than being exported to the benthic community. These results are in agreement with the abundance of higher trophic level pelagic organisms observed in this region.

Marine Ecology Progress Series, 1988

Photoadaptive responses of sea-ice microalgae in springtime were observed in southeastern Hudson ... more Photoadaptive responses of sea-ice microalgae in springtime were observed in southeastern Hudson Bay (Canadian Arctic). The responses included changes in pigment composition (chlorophyll a, carotenoids), photosynthetic parameters (Pmax, Ik, a, p) and carboxylating enzymes The complete transition from shade to light adaptation took place over 1 generation time while susceptibility to photoinhibition decreased more rapidly. Activities of carboxylating enzymes were never the ratelimiting step of photosynthesis. At low irradiances, increased pigments in the cells and modifications of the photosynthetic parameters suggest that photosynthesis did depend on the trapping of light energy and on the rate of electron transport. With increased irradiances, light energy harvested by the cells exceeded their energetic requirements, so that photosynthesis was only related to the rate of electron transport. These results emphasize the ability of sea-ice mlcroalgae to photoadapt to the seasonally increasing under-ice irradiance, showing that they are not an obligate shade flora in southeastern Hudson Bay.

Journal of Plankton Research, 1999

The abundances and chlorophyll a concentrations (Chl a) of ultraphytoplankton (<5 µm) were determ... more The abundances and chlorophyll a concentrations (Chl a) of ultraphytoplankton (<5 µm) were determined at four ice-covered sites in northern seas, i.e. southeastern Hudson Bay, Saroma-ko Lagoon, Resolute Passage and the Northeast Water Polynya. Numbers of total ultraphytoplankton were low, ranging from 3.6 ϫ 10 7 to 9.7 ϫ 10 9 cells m-3 , which confirms the overall paucity of ultraphytoplankton in cold waters. Concentrations of <5 µm Chl a varied between 0.002 and 10.8 mg m-3 , which accounted for 0.2-99.7% of total Chl a. Chlorophyll a concentrations of ultraphytoplankton can thus reach high values and make up a substantial fraction of total Chl a. Ultraphytoplankton were ubiquitous, but they showed high among-and within-site variability in abundance, biomass and contribution to total Chl a concentrations. The ultraphytoplankton comprised primarily eukaryotes and prokaryotic phycoerythrin-rich cyanobacteria, but also some cryptomonads and phycocyanin-rich cyanobacteria. Concentrations of ultraplanktonic eukaryotes reached 7.8 ϫ 10 9 cells m-3 , but were generally <5 ϫ 10 9 cells m-3 , whereas the maximum concentration of prokaryotes was 6.2 ϫ 10 9 cells m-3. The concentrations of eukaryotes and prokaryotes were related, overall, to water mass characteristics, i.e. temperature, salinity, percent irradiance, and concentrations of nitrate and ammonium. Depending on sites, the abundances of eukaryotes were positively linked to salinity, percent irradiance, nitrate and ammonium, whereas the abundances of prokaryotes were positively correlated with ammonium and nitrate. Phycocyanin-rich cyanobacteria were generally confined to brackish waters (Hudson Bay). The highest cell numbers of ultraphytoplankton were found at temperatures of <0.5°C and salinities of >30 p.s.u. Fig. 1. Locations of the four study sites: southeastern Hudson Bay, Saroma-ko Lagoon, Resolute Passage and the Northeast Water Polynya (NEWP).

Journal of Plankton Research, 2005

Community structure of pelagic copepods was investigated in the upper 200 m in the Disko Bay, Wes... more Community structure of pelagic copepods was investigated in the upper 200 m in the Disko Bay, Western Greenland, during the post-spring bloom period in June, 2001. This was the first study of the copepod community in West Greenland coastal waters sampled using smaller mesh sizes (50 m as opposed to 200 m). The mesozooplankton was dominated by copepods who constituted 82% of the total abundance and 95% of the total mesozooplankton biomass (>50 m). Nauplii of Calanus, Pseudocalanus and Oithona dominated by number and the copepodites and adults were dominated by Oithona spp., Oncaea sp., Pseudocalanus sp., harpacticoids, Calanus finmarchicus, C. glacialis, and C. hyperboreus. Multivariate tests showed that the species/stage abundance composition of copepods changed significantly with depth. With one exception, all depth intervals showed unique significantly different compositions. Accordingly, the copepod community structure was influenced primarily by depth rather than by chlorophyll a concentration. Factors other than herbivorous grazing, such as omnivory, predator avoidance or association to marine snow aggregates of specific species, may have influenced the depth distribution of the total copepod community in the Disko Bay. Nevertheless, subsequent Pearson product moment correlations showed positive significant correlations between the vertical distribution of the three Calanus spp. and Pseudocalanus spp. and chlorophyll a concentrations, which points towards these species as prime components in the classic diatom-copepod food chain.

Journal of Marine Systems, 1996

Analysis of sea ice cover, runoff and air temperature observations in Hudson Bay shows marked int... more Analysis of sea ice cover, runoff and air temperature observations in Hudson Bay shows marked interannual variability. This variability is thought to play a major role in determining overall productivity of the coastal ecosystem by changes to river plume extent, under-ice light conditions and nutrient levels during spring. Extensive field work off the Great Whale River in southeastern Hudson Bay

Estuarine, Coastal and Shelf Science, 2008

The Arctic is currently undergoing rapid environmental and economic transformations. Recent and o... more The Arctic is currently undergoing rapid environmental and economic transformations. Recent and ongoing climate warming which is simplifying access to oil and gas resources, enabling trans-Arctic shipping and shifting the distribution of harvestable ...