2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 10
Presentation Time: 1:30 PM-5:30 PM

POSSIBLE EVIDENCE FOR ISOTOPIC STRATIFICATION OF GLACIAL LAKE AGASSIZ, 11,000-9,900 14C YR BP


BIRKS, S.J.1, EDWARDS, T.W.D.1 and REMENDA, V.H.2, (1)Department of Earth Sciences, Univ of Waterloo, Waterloo, ON N2L 3G1, Canada, (2)Department of Geological Sciences, Queen's Univ, Kingston, ON K7L 3N6, Canada, sjbirks@sciborg.uwaterloo.ca

A significant difference exists between the isotopic composition of glacial Lake Agassiz during the interval 11,000-9,900 14 C yr BP, as inferred from the oxygen isotope composition of algal cellulose preserved in a sediment core from the south basin of the lake (d18Olake water = –15 to –19‰ VSMOW), versus that of connate porewaters extracted from the same core (d18O = -24‰ VSMOW). This substantial discrepancy may reflect the existence of isotopic stratification in the south basin of Lake Agassiz during this time of rapid detrital sedimentation, with algal cellulose recording the isotopic signature of relatively warm, evaporatively-enriched waters of the epilimnion, while sediment porewaters preserve the composition of hypolimnion waters fed primarily by cold, dense, non-evaporated glacial meltwater issuing from the ice front.