Research - Dr. Elisabeth Levac
Research Links:
Abrupt Climatic Changes and Meltwater Discharges along the Eastern Canadian Margin
Dr. Elisabeth Levac
Department of Environmental Studies and Geography
Dr. Levac is studying the sources and path of large meltwater discharges to the North Atlantic during the last deglaciation to clarify the role of these events in the natural climatic variability and latitudinal differences along the Eastern Canadian Margin. More specifically, her research intends to reconstruct sea surface conditions (temperature, salinity) from high resolution sedimentary records to precisely document the timing and duration of abrupt climatic change, and shed light on their causes. Professor Levac’s studies target different climatic events, time intervals, and locations.
1- The age and path of Lake Agassiz meltwater drainage
Glacial Lake Agassiz, formed by the accumulation of meltwater and impounded by the Laurentide Ice Sheet, drained catastrophically around 8200 years ago. It is widely believed that the release of freshwater into the North Atlantic Ocean was responsible for a reduction in northward heat transport in the upper limb of the Atlantic meridional overturning circulation (i.e. the big conveyor belt transporting heat towards northern Europe). However, evidence for this event was lacking in records from the Labrador Sea.
A collaborative effort with researchers from the Geological Survey of Canada-Atlantic allowed to assemble evidence for the meltwater drainage event and to re-assess its age. Analysis of 10 sediment cores revealed distinct beds originating from erosion of carbonate bedrock in the Hudson Bay region. We revised the age of the floods at 8330 cal years (7500 14C years) and we showed that the Agassiz floodwater and icebergs have travelled southward in the Labrador Current (rather than directly into the Labrador Sea) before being incorporated into the North Atlantic Current and transported to the Nordic seas (see Lewis, Miller, Levac, Piper and Sonnichsen 2012).
2- The impact of Lake Agassiz meltwater drainage on sea surface conditions
By reconstructing sea surface conditions at strategic locations along the path of the Outer Labrador Current, Dr. Levac was able to determine the impact of the meltwater influx on the Labrador Current. On the Northeast Newfoundland Shelf, the meltwater drainage caused significant changes in dinoflagellate cyst assemblages, indicating that sea surface temperature and salinity dropped by 3°C and 10‰, respectively (see Levac, Lewis and Miller 2011). On the Scotian Shelf, the drop in temperature was similar (2-3°C) and the drop in salinity was smaller (2‰). This study suggests that most of the meltwater from the final drainage of Lake Agassiz flowed south over the the Labrador and Northeast Newfoundland shelves and was not dispersed directly into the Labrador Sea. This is the first paper presenting paleoecological evidence for the presence of the Agassiz meltwater along the eastern Canadian margin.
3- Meltwater drainage via the St. Lawrence River at the time of the Younger Dryas (ongoing)
The objectives of this project are to determine if meltwater was released through the St. Lawrence River at the time of the Younger Dryas and Preboreal Oscillation (two important climatic events), and the impact of this meltwater influx on sea surface conditions over the Gulf of St. Lawrence, the Scotian Shelf and other key areas along the East Coast of Canada.
Professor Levac’s studies will provide better paleoclimatic data against which numerical models of global warming can be tested. Professor Levac’s research will also contribute towards a better understanding of global warming’s potential impact on the climate of Eastern Canada and East Coast fisheries.
This project is funded by two grants and funds are available for graduate students:
(NSERC discovery grant) 2007-2012; $109,000)
Acquisition of a microscope and a microwave digester for the study of abrupt climatic events in the last 11,000 years. (NSERC Research Tools and Instrument, Category 1 2007; $19,250)
More about the Younger Dryas
The Younger Dryas cold climate event (Broecker et al. 1989) was the largest climatic event since the ice age. The Younger Dryas interrupted the postglacial warming trend, causing a return to glacial conditions between 11,000 to 10,000 years ago. Broecker (1989) proposed that an interruption of the North Atlantic thermohaline circulation, caused by a large input of freshwater (Lake Agassiz meltwater) induced the cold event. Thermohaline circulation is a planetary mechanism responsible for the circulation of water masses and distribution of heat in regions around the North Atlantic.
During deglaciation, meltwater from the Laurentide Ice Sheet accumulated in deglaciated basins and over land areas that had previously been depressed by the weight of the ice sheet. One of these large lakes, Lake Agassiz, existed for over 5000 years. Flow of meltwater was re-routed (either to the Mississippi, St. Lawrence, Mackenzie, or Hudson Rivers) on different occasions as spillways opened in newly deglaciated areas (Teller et al. 2005). At about 10,900 radiocarbon years ago, the level of Lake Agassiz suddenly dropped by 100 m, suggesting a large and rapid meltwater release through a new outlet (Teller et al. 2005). For a century, it was widely accepted that the meltwater flowed via the St. Lawrence River (Clarke et al. 2001; Teller et al. 2002) to the North Atlantic, causing the Younger Dryas cold climate event (Broecker et al. 1989). The evidence supporting a large meltwater flow via the St. Lawrence River at the time of the Younger Dryas is now debated and evidence for meltwater flow at other locations have been found.
The lack of evidence for a freshwater flow via the Gulf of St. Lawrence might be explained by the location of the marine records used. Dr. Levac is presently examining strategic locations providing sedimentary records with a much higher time resolution. Dr. Levac will use reconstructions of sea surface conditions at locations along the expected path of the meltwater: the Western Laurentian Channel and the Northern Scotian Shelf.
The Role of Weather Patterns on the Production of
Allergenic Airborne Pollen and Spores
Dr. Elisabeth Levac
Department of Environmental Studies and Geography
Dr. Levac started monitoring airborne pollen and spores at Bishop's University in 2006. Data collected was used to create a pollen calendar for the borough of Lennoxville (see Levac and others 2011 in the list of publications). A new project, the Sherbrooke Aerobiological Surveillance was launched in 2012.
Why monitor airborne pollen and spores?
It is estimated that 15% of Canadians suffer from allergic rhinitis also known as hay fever. Pollen and spores released in the air are inhaled and trigger allergies in sensitive individuals and can even trigger asthma and chronic obstructive pulmonary disease. Real time pollen monitoring is critical to help allergy sufferers reduce their exposure and manage their symptoms more efficiently. Daily pollen counts and forecasts were provided from 2006-2008 by the Lennoxville Experimental Pollen and Spore Forecast. Dr. Levac is presently collecting data for downtown Sherbrooke and plans to provide forecasts for both Lennoxville and Sherbrooke in 2012.
The role of weather
Weather is an important variable in the occurrence of rhinitis, therefore forecasting is not easy. Anemophilous (wind pollinated) plants want to maximize fertilisation chances and therefore release massive amounts of pollen when weather conditions are optimal for dispersal towards other individuals of the same species. Pollen concentrations also show a diurnal cycle, with peaks usually occurring in the early afternoon. Weather patterns can affect the timing of this peak: concentrations of pollen will be high on sunny days, low on rainy days. Finally, the start of the flowering season will vary for each plant and from year to year at a given location with climatic conditions.
Acknowledgments
Funding from the ETRC, the SRC and the Faculty of Social Sciences at Bishop`s University are acknowledged. We thank the Musée de la Nature et des Sciences (season 2012) and from the département de Géomatique de l`université de Sherbrooke (season 2009) for providing roof access and technical assistance.
The following Bishop's University students were involved in the data collection and their help is greatly acknowledged: Amber Ashley ('06), Simone Sandercombe ('08), Vanessa Stretch ('09), Vanessa Asselin ('10), Thomas Neulieb ('10), Annie Chouinard ('11), Kathleen Chan ('12), Rebecca Pelletier-Allard ('12), Katie Duchesne ('12).
