CLIMATE RECORDS IN WETLAND SEDIMENTS

This study compares components from the sediment records in two semi-permanent wetlands on the Missouri Coteau in North Dakota to determine how adjacent, but hydrologically different settings record climate. Both wetlands receive the bulk of their waters from spring rains and snow melt and are underlain with glacial till. However, one wetland loses most of its water by evaporation and the other loses some water by outflow. Yet, because the hydrologic budgets of these wetlands respond immediately to climate change (seasonal, annual, decadal, longer) and because climate input to both wetlands is identical, we would expect the components of their sediments to tell a similar climate story. Short cores from the centers of the two wetlands (P1 and P8) do not have similar records: (1) An order of magnitude difference in magnetic susceptibility. (2) Lithology of one wetland is dominated by organic material. (3) The mollusks and ostracodes also differ considerably between these two wetlands. (4) Stable isotopes of O and C from carbonate mud in the basin also show an offset of up to several per mil between the two cores. Despite similarities in these two wetlands physical, geological, and climatic settings, their sedimentary records do not share a common climate story. The primary reason for the differences between the records can be attributed to the differences in the hydrology of each wetland. Therefore, climate studies that derive their data from proxies in the sediments of lakes and wetlands need to understand how the hydrology of the system modifies the climate signal.