TEMPORALLY CONSTRAINED SAND SIGNALS AND THEIR RELATIONSHIP TO CLIMATIC TRENDS IN SOUTHWESTERN MICHIGAN, USA

Lake sediment downwind of foredunes, which began forming around 1920 AD, was sampled to compare eolian sand concentrations (sand signals) with known climate proxies. This study tests the hypothesis that increased sand input to these downwind lakes follows highstands in Lake Michigan, and periods of severe storminess. Sand signals (percent sand by weight) were calculated for five cores from Oxbow Lake, once the Kalamazoo River mouth. A time scale was assigned to the sand signals using an age model derived from ²¹⁰Pb/¹³⁷Cs/⁷Be dating. Core stratigraphy was consistent across all cores, with a basal, massive pebbly sand, overlain by laminated, to very-finely bedded sand and silt with interspersed organics, capped by a shelly, sandy sapropel. Massive pebbly sand is a fluvial unit recording last flows in the Kalamazoo River before it was cut off. The laminated, to very-finely bedded sand and silt with interspersed organics are interpreted as transitional periods recording fluvial and lacustrine conditions, as well as storm surges before the river mouth was closed by littoral drift and foredunes were established. The sapropel represents the time after separation of Oxbow Lake from Lake Michigan; thus, sand signals in the lacustrine deposits are interpreted as eolian from surrounding dunes. The dated sand signals were compared to trends in annually averaged temperature, precipitation, evaporation, and lake level (datasets from NOAA GLERL). A relatively positive correlation was found between lake level and sand concentrations for years 1960–2011 AD. This can be interpreted as an increase in eolian sand transport associated with lake level highstands.