2 Trinity College, 300 Summit St., Hartford, CT 06106 United States, christoph.geiss@trincoll.edu

We conducted a multi-proxy study of 18 glacial lakes from southern Minnesota combining sedimentological, palynological and rock magnetic analyses to constrain the nature of links between environmental change and sediment magnetic properties. Pollen analyses record a shift to a more forested landscape ~ 1000-1100 AD corresponding to the Medieval Climate Optimum and onset of the Little Ice Age, and pollen analysis was used to identify the Ambrosia-rise in each core which corresponds to the onset of Euroamerican agriculture in 1860 AD. Broadly speaking, magnetic concentrations increased while magnetic grain size decreased with the onset of the LIA. This change was most evident for lakes that are presently situated in forested watersheds, which is suggestive of a subtle vegetation feedback, probably due to changes in water and sediment chemistry. With the onset of plow agriculture high rates of soil erosion initially increase the supply of highly magnetic sediment, but ultimately lead to increases in organic productivity and the dilution or reductive dissolution of magnetic minerals. This process is reflected in a decrease of concentration dependent parameters, such as magnetic susceptibility and SIRM, and coincides with a shift to coarser grain sizes as evidenced in lower ratios of ARM/IRM.