Water isotope partitioning in aquitards and precipitation on the northern Great Plains

The isotopic composition of water preserved in low-permeability deposits from glacial Lake Agassiz has already been used to obtain important information about late-glacial climate. The objectives of this research were to assess the capability of resolving finer-scale features in the porewater isotope record in Lake Agassiz deposits and also to use modern local and regional isotope-climate relations to improve our understanding of how changes in climate affect the partitioning of the isotopomers of water in the hydrological cycle.; Sediment cores from Montcalm, located on Lake Agassiz deposits in southern Manitoba, were collected to better characterize the diffusion coefficients of the heavy isotopomers of water and obtain detailed profiles of delta 18O, delta2H and d-excess.; Modern isotope-climate relations in precipitation on the Great Plains were evaluated at local and regional scales to develop more physically based conceptual models to explain variations in the distribution of isotopes in precipitation. Anomalously enriched precipitation was associated with periods of meridional atmospheric circulation, and more depleted precipitation with zonal atmospheric circulation.; The isotopic composition of daily precipitation from Glenlea, Manitoba, revealed systematic differences in the isotopic composition of precipitation related to the origin and air-mass history of the precipitation events. Precipitation trajectory as well as the type of precipitation influenced the delta 18O-delta2H and delta18O-T relations.; Comparisons of distributions of delta18O, delta 2H and d-excess in monthly precipitation across Canada with the distribution of climate parameters confirmed the potential for the northern Great Plains to receive moisture from a variety of sources, and were useful in identifying changes in moisture source or trajectory.; Two co-existing isotopic archives of the isotopic composition of Lake Agassiz, porewater and cellulose, were used to infer lake water compositions for the early lake phase. These results showed how comparison of the inferred isotopic composition of Lake Agassiz from two contemporaneous archives yielded new information about the paleolimnology of this major glacial lake and provides a unifying conceptual model that reconciles differing estimates of Lake Agassiz isotopic composition. (Abstract shortened by UMI.)...