High-resolution paleoenvironmental record of Late Holocene storm activity in coastal lagoons

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Hurricanes and intense "post-tropical" cyclones are a major cause of severe weather in eastern Canada. Climate models predict that there will be an increase in the frequency of destructive hurricanes in the future due to climate warming. Some models suggest possible linkages with human-induced climate warming and the production of greenhouse gases. However, the available record of past storm events in North America (< 150 years) is too short to evaluate long-term trends. The NSERC-funded research will employ measurements of the geochemical and magnetic properties of sediments in lakes and coastal lagoons to better understand the frequency of large storm events over the last 5000 years. During large storm events, storm waves overtop sandy beach barriers depositing distinctive “overwash” sand sheets on the lake floor. Storm sediment layers are also deposited in lakes by the flood discharge of rivers. Storm overwash and flood deposits can be identified in sediment cores extracted from the lake bed and by dating of the storm event layers, the past frequency of storm events can be determined. Identification of storm layers can be difficult, however, based on the visible characteristics of the sediments alone. In order to obtain more detailed and reliable records of past storm frequency, Boyce and research team (1 Ph.D., 2 M.Sc., 5 B.Sc. students) will investigate the geochemical and magnetic properties of storm sediment layers in coastal lagoons. By determining the abundance of distinctive elements and magnetic minerals carried by storm events, the researchers will be able geochemically “finger-print” the storm deposits. In order to obtain a detailed record of storm events, researchers will employ the new ITRAX core scanning facility at McMaster. The ITRAX core scanner uses an X-ray beam to measure very precisely the abundance of a wide range of elements in core samples. The scanner also records changes in the magnetization of the core and produces a high-resolution colour image that can be used to identify changes in sediment texture and colour. Using the combined properties, it is possible to detect very thin storm event layers (less than 2/10 of a millimetre), yielding a very detailed record of past storm events. Using this new technique, the researchers will develop a detailed history of past storm events in Lake Ontario and on the Atlantic coast of Canada (Nova Scotia, Newfoundland). The detailed long-term record of storm events produced with the ITRAX facility will allow McMaster researchers to assess whether the frequency of storms has been different in the past, and whether the variability in storminess is linked to other climate variables, such as past changes in temperature and precipitation. These data are critical for evaluating future changes in storm frequency predicted by climate models and will assist in the development of appropriate emergency planning for heavily populated areas of eastern Canada that are at risk from severe weather.