HR: 1340h
AN: PP43A-0621    [Abstracts]
TI: The Oxygen and Hydrogen Isotope Composition of Lake Huron
AU: * Macdonald, R A
EM: rmacdo@uwo.ca
AF: Department of Earth Sciences, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7 Canada
AU: Longstaffe, F J
EM: flongsta@uwo.ca
AF: Department of Earth Sciences, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7 Canada
AB: Over 150 water samples collected along transects of Lake Huron and Georgian Bay during late April-early May 2004 have average oxygen and hydrogen isotope compositions of -7.5 and -57$\permil$ (VSMOW), respectively. These values are very similar to averages obtained using monthly samples collected over the last seven years from a single location (Grand Bend, Ontario) near Lake Huron's southern outlet. At the time of the 2004 sampling, Lake Huron and Georgian Bay were receiving waters with lower-than-average oxygen and hydrogen isotope compositions, both from Lake Superior (via the St. Mary's River), and from fluvial inputs into the North Channel and Saginaw Bay. Conversely, inflow from Lake Michigan via the Straits of Mackinac supplied waters with higher-than-average oxygen and hydrogen isotope values. These regions of contrasting isotopic composition were localized, and the lake was regulated to values typical of the average within a short distance from these inputs. Vertical profiles from several locations throughout Lake Huron and Georgian Bay likewise showed little variation in oxygen and hydrogen isotope composition from top to bottom of the water column. Porewater samples were also extracted at 10-cm intervals from two Lake Huron sediment cores, which were obtained from the Manitoulin and Goderich basins in spring 2004. In the Manitoulin basin, the oxygen isotope values of porewater decreased systematically from about -7.2$\permil$ at the sediment-water interface to about -9.0$\permil$ at 11 m depth. Porewater from the Goderich basin showed similar variation in oxygen isotope values, from about -7.6$\permil$ at the sediment-water interface to -9.7$\permil$ at 12.3 m depth. The oxygen isotope composition of porewater then increased to -9.3$\permil$ by the core's end at 13.3 m. This latter variation may reflect upward infiltration of groundwater or contamination during coring. Overall, however, we suggest that these changes in porewater oxygen isotope composition may be a useful proxy for variations in the composition of Lake Huron over the time required to deposit these sediments.
DE: 3344 Paleoclimatology
DE: 1806 Chemistry of fresh water
DE: 1845 Limnology
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting