EXPLORING THE CHARCOAL RECORD IN FLAT IRON LAKE, MICHIGAN, USA

Charcoal is frequently found in post glacial lake sediment and interpreted as a proxy for fire in the watershed. The focus of this study is to describe the charcoal record in Flat Iron Lake (43.123227, -85.384526), a kettle lake in western Michigan, and secondarily to evaluate if charcoal interacts with other sedimentary components in the lake archive. Using a Livingstone corer we collected 8 m of sediment from the deepest portion of the lake. Individual drives were split and described using smear slides and visual observations. The lake sediment consists of laminated silty sapropel until refusal was met in unstratified silty clay. The laminations alternate between dark colored organics and light colored calcite and diatom laminations and charcoal was observed in several centimeter thick layers in multiple drives. From the cores we collected samples for charcoal, loss on ignition and XRD analyses, and radiocarbon dating. We sampled the core for charcoal in continuous 5 cm long x 0.5 cm deep increments (2.5 cc samples), treated the samples with hydrogen peroxide and sieved to 125 μm then counted the charcoal fragments under a microscope. The charcoal counts varied throughout the sedimentary record. For example in the first meter, out of 20 samples, the charcoal counts range from 1426 to 109 and the most common morphotype was varieties of wood. The other sedimentary components are primarily organic, authigenic minerals, and small amounts of clastic inputs. The paucity of allochthonous material in the lake suggests that charcoal is the main external contribution to the sedimentary archive and it could yield important paleofire information. However, the charcoal record could indicate more than just the paleofire record, we suspect it could also help determine if broader climate history is archived in the lake.