Holocene hydrologic and hydrochemical changes of the South Basin of Lake Manitoba, Canada, inferred from ostracode shell chemistry and autoecology

Abstract

Holocene record of ostracode shell chemistry from the South Basin of Lake Manitoba shows how isostatically and climatically induced changes in the surface and groundwater input to the overall hydrologic budget affected the hydrochemistry. The shallow South Basin experienced periods of extensive shell transport from isolated pools and groundwater seeps, as suggested by disparate chemistry of Fabaerformiscandona rawsoni shells from the same 1-cm-thick sediment sample. Temporal changes reconstructed from ostracode species and F. rawsoni shell chemistry include, for some depth intervals, shells of individuals that were not living at the same time or were not living at the core site. Shell chemistry before the South and North Basins became connected at 1850 BP broadly show a hydrologically closed-basin behavior with alternating periods of a more and less stressful environment to ostracodes. F. rawsoni with high δ 18O and low Mg/Ca or low δ 18O and high Mg/Ca were likely transported from marginal evaporated pools or groundwater seeps. Overall δ 18O and δ 13C values increase over time, but at levels for which multiple analyses were made, the values show a wide range, and indicate a highly variable hydrochemical environment both spatially and temporally (over one summer or multiple summers).