EVIDENCE OF DRYING IN NORTHERN OHIO DURING THE EARLY HOLOCENE

It has been suggested that Lake Erie experienced a drying event during the Early Holocene (Lewis et al., 2012). We wonder if these effects are expressed elsewhere. To address this question sediment cores were taken from a kettle lake in Northwest Ohio, Browns Bog, in January 2014. From the five meters of core that represent the Early Holocene, magnetic susceptibility (MS), loss on ignition (LOI), carbon to nitrogen ratios (C:N), and grain size were analyzed to see if any of these properties indicate drier conditions.

These analyses revealed three major units covering the interval from 11,000 to 6,600 cal yr BP. The oldest unit ranges from 11000 to 9700 cal yr BP, and is composed of dark brown silt with some laminations at the beginning and the end of the section. The unit displays low MS, a slight increase in C:N from 11 to 12, a decrease of LOI from 60% to 40% and the largest grain size with a mean of 250-500 µm. The next unit was deposited between 9700 to 9100 cal yr BP, and is a brittle olive green silt with strong laminations throughout. This unit shows a defined jump then fall in both MS and C:N (from 13 to 11). At 9200 cal yr BP peaks in both LOI (up to 60%) and grain size (to 600 µm) occur. The uppermost Early Holocene unit spans from 9100 to 6600 cal yr BP and is a dark green grey slit, with strong laminations and some texture changes. This unit has the highest MS values with sharp oscillations, a high and consistent C:N between 11-12, a low LOI ranging from 20-30%, and the lowest mean grain size of 100-200 µm. Sediments deposited after 6,600 cal yr BP have simple trends: decreases MS and C:N with rising in LOI and grain sizes.

We interpret the higher, variable MS pattern from 9,100 to 6,600 cal yr BP as the typical pattern of windblown processes. Lower LOI values may reflect decreased influx of clastic sediments with a smaller, well sorted distribution. C:N values reflect increased terrestrial sources, which may be a result from intervals of erosion during drier periods. Our working hypothesis is that these results reflect relatively dry conditions from 9100 to 6600 cal yr BP. We plan to test this with additional analyses from horizon above and below presented here. If our hypothesis is correct, it implies that the hydrologic conditions that lowered Lake Erie are also expressed on the landscape south of Lake Erie.