New results from our research indicate that water levels in the Great Lakes have, in the past, dropped several metres and have even become isolated from each other in response to drier than present climate conditions. Since some future climate change scenarios now indicate that the water levels in the Great Lakes may drop below levels that are within the range of variability that is presently considered normal, knowledge of historical events of rapid hydrological change is very important. It has been hypothesized by our team that the water levels in the Great Lakes fell below their outlet levels, thus allowing no outflow, after 9000 cal BP due to the effects of increased incursions of dry arctic air during late deglaciation in Hudson Bay and flows of warm-dry Pacific air. Despite the fact that these events took place thousands of years ago, they are still useful examples of severe hydrological change since the present non-glacial conditions of the Great Lakes had already been reached.
Digital elevation model of the Great Lakes region showing the 5 major lake basins and their water surface elevations (Superior, Michigan, Huron and Georgian Bay, Erie, Ontario), direction of water flow (blue arrows), and locations of subsequent figures (numerals). Boundaries of the Great Lake’s watersheds are shown by white lines. SLR = St. Lawrence River. Index map from The Great Lakes Environmental Atlas (1995).
Evidence for low early Holocene lake levels in the Huron and Georgian Bay basins.
a. the Stanley unconformity in northwestern Lake Huron comprising shallow-water sand over eroded red clay and under silty clay with black specks of FeS (core at left) expressed also as a strong subsurface seismic reflector (right) (Moore et al., 1994); sand and reflector represent a former lake level 50 m below present at about 7900±300 14C BP.
b. upper: two in situ tree stumps on the lakefloor at the entrance to Georgian Bay, found in water depths of 3 to 43 m and ranging in radiocarbon age from 7230 ±90 to 9360 ±80 years BP, lower right: sidescan record showing beach ridges in 48 to 53 m water depths (Blasco, 2001).
Ultimately, the intent of this research is to use the geological record to enhance understanding of the sensitivity of the Great Lakes to climate change. Objectives are one, to corroborate and test closed lowstands in the Great Lakes, two, to use multi-proxy data from small lakes within the Great Lakes watershed to evaluate paleoclimate change, and three, to reconstruct the paleogeography of the Great Lakes and then model the relationship between paleoclimate and hydrology.
Reconstructed paleogeographic map showing shorelines (yellow) of closed lake lowstands at 7900 14C BP. Red lines are inferred shorelines at the lowest possible overflow sill elevation. Present lake shores are shown as white lines.
E = Erie basin,
G = Georgian Bay basin,
H = Huron basin, and
O = Ontario basin.
In order to corroborate interpretations of existing data about past low-lake levels and to ensure that the water sources for the Great Lakes during the modelled periods were from non-glacial hydrological processes, seismic profiles and sediment cores obtained for prior studies will be re-analyzed. Also, a limited number of new cores and seismic surveys will be taken for paleoclimatic analysis using fossil organisms such as pollen, to supplement the existing data. The time interval of the past low-lake levels will be identified in the sediment cores using AMS 14C and paleomagnetic methods, and they will be analysed using isotopic geochemical methods and paleoecological transfer functions in order to correlate historical hydrological and atmospheric conditions with Great Lake water level oscillations. The data generated by these analyses will allow for the relationship between climate and the hydrology of the Great Lakes to be modelled using an operational hydrological process model (NOAA).
Multibeam sonar image looking west from Georgian Bay at the submerged Niagara escarpment and the sill between the Huron and Georgian Bay basins (Parks Canada, Canadian Hydrographic Service and Tekmap Consulting). White lines indicate the 35 m and 90 m isobaths. Note channels across the sill, probably eroded by waters overflowing from the Huron basin when lake levels were descending to or rising from the closed lowstands.
The aim of this research is to determine how sensitive the hydrology of the Great Lakes watershed is to rapid climate changes. In order to accomplish this, it was necessary first, to demonstrate that it was possible to force the closure of the Great Lakes with climate changes using the NOAA hydrological process model. Existing models for the current large basin runoff as it applies to all 121 watersheds that drain into the Great Lakes, models for the thermodynamics and water balance of each of the Great Lakes, and models for the channel flows and outflows were integrated. This new integrated hydrology model was tested against recorded meteorology, and was found to be an acceptable model for water levels in the Great Lakes. Climate change scenarios were constructed for warmer and drier climates using decrements of precipitation and increments of temperature, relative to the present mean climate. The integrated hydrology model was then applied to each scenario to produce projections of lake levels under each set of conditions. It was shown that such climate changes were capable of causing terminal Great Lakes (Croley and Lewis, 2006).
Corroboration of lowstands in the Huron and Georgian Bay basins.
a. sand with detrital organic matter (dark) overlying and overlain by clastic clay sediment (light gray) indicating former occurrences of early Holocene low water levels in the lower French River northeast of Georgian Bay,
b. seismic profile from Lake Simcoe showing truncated reflectors at arrow heads in glaciolacustrine sediment (surface of green unit at 25 m depth) beneath deepwater sediment (blue) indicating early Holocene erosion, probably by waves on a former low level lake (Todd et al. in press,
c. seismic profile (Coakley and Lewis, 1985) from eastern Lake Erie (depths in m below present lake surface at left) showing erosion (sloping subsurface that truncates underlying flat-lying reflectors) by waves in a former low level lake shoreface, shown by pollen stratigraphy and radiocarbon dating to be of early Holocene age.
Quantitative climate estimates from 11 000 14C BP (bottom) to present (top) based on transfer function analysis of pollen assemblage data in a small lake (Porqui Pond) near southeastern Georgian Bay. Graphs portray (left) January mean temperature, (middle) July mean temperature, and (right) mean annual precipitation (courtesy of J.H. McAndrews and F.M.G. McCarthy). At the time of the Huron-Georgian Bay early Holocene lowstands marked by horizontal gray bands, winter temperatures
a. were colder, summer temperatures
b. were slightly warmer, and annual precipitation
c. was substantially less than at present, in a climate similar to that of Minneapolis MN today.
- Mike Lewis, Geological Survey of Canada (GSC web site)
- Tom Croley, NOAA / GLERL
- Dave Rea, U. Michigan (U of M web site)
- John King, U. Rhode Island
- Kathryn Moran, U. Rhode Island (URI web site)
- Ted Moore, U. Michigan
- Dave Dettman, U. Arizona (UA web site)
- Alison Smith, Kent State U. (KSU web site)
- Steve Blasco, Geological Survey of Canada
- John Coakley, Environment Canada (EC web site)
- Tom Edwards, U. Waterloo (UW web site)
- Kathleen Laird, Queens U. (QU web site)
- John McAndrews, U. Toronto (U of T web site)
- Francine McCarthy, Brock U. (Brock U web site)
- Croley II, T.E. and Lewis, C.F.M. 2006. Warmer and Drier Climates that Make Terminal Great Lakes 2006. Journal of Great Lakes Research 32(4):852-869. ABSTRACT
- Lewis, C.F.M., Blasco, S.M. and Gareau, P.L. 2007. Glacial isostatic adjustment of the Laurentian Great
Lakes basin: using the empirical record of strandline deformation for reconstruction of early Holocene
paleo-lakes and discovery of a hydrologically closed phase. Géographie physique et Quaternaire, 2005, vol. 59, nos. 203, p. 167-210.
- Lewis, C.F.M., Heil Jr., C.W., Hubeny, J.B., King, J.W., Moore Jr, T.C. and Rea, D.K. 2007. The Stanley unconformity in Lake Huron basin, evidence for a climate-driven closed lowstand about 7900 14C BP, with similar implications for the Chippewa lowstand in Lake Michigan basin. Journal of Paleolimnology.
Published online. Doi 10.1007s 10933-006-9049-y. ABSTRACT
- Blasco, S.M. 2001. Geological history of Fathom Five National Marine Park over the past 15000 years. In: Parker S, Munawar M (Eds.) Ecology, Culture and Conservation of a Protected Area: Fathom Five National Marine Park, Canada. Ecovision Monograph Series, Backhuys Publishers, Leiden, pp. 45-62.
- Coakley, J.P. and Lewis, C.F.M. 1985. Postglacial lake levels in the Erie basin. In Karrow, P.F. and Calkin, P.E. (Eds.) Quaternary Evolution of the Great Lakes, Geological Association of Canada Special Paper 30, pp. 195-212.
- Moore Jr., T.C., Rea, D.K., Mayer, L.A., Lewis, C.F.M., Dobson, D.M. 1994. Seismic stratigraphy of Lake Huron - Georgian Bay and postglacial lake history. Canadian Journal of Earth Sciences 31:1606-1617.
- The Great Lakes Environmental Atlas, 1995. The Great Lakes, An Environmental Atlas and Resource Book, Third edition. Government of Canada, Toronto, Ontario and United States Environmental Protection Agency, Chicago, Illinois. Online Version
- Todd, B.J., Lewis, C.F.M. and Anderson, T.W. in press. Quaternary features beneath Lake Simcoe, Ontario, Canada: drumlins, tunnel channels, and records of proglacial to postglacial closed and overflowing lakes. Journal of Paleolimnology.