CONTRASTING INLAND AND COASTAL AEOLIAN RECORDS IN SW MICHIGAN, USA: IMPLICATIONS FOR TRIGGERS OF DUNE MOBILITY

A history of dune mobility in the coastal dune field along Lake Michigan southwest of Holland has been reconstructed using OSL ages on dune sand, radiocarbon ages from dune paleosols and sand concentrations in sediment cores from small dune lakes. Collectively, the data records periods of extensive dune mobility with the record beginning at 5.7 cal ka BP until 3.8, renewed activity at 3.3–1.8 and more recently at 0.5–0 cal ka BP, during which dune mobility was episodic on a quasi-periodic cycle. The environmental factor(s) driving variability in dune activity remain equivocal. Processes suggested include lake level fluctuations (of Lake Michigan) and storminess. In an effort to remove any direct lake level effect from the record, aeolian sand concentrations were determined from a sediment core collected near the center of a small sedge peat bog at the edge of a forested interior dune field, 20 km southeast of the coastal dunes. Peaks in sand concentration in the upper 3.6 m throughout the past 8,200 years represent episodes of increased sand influx into the bog. Lower background concentrations of sand occur in the interval deposited from 8.0–7.4 and 3.0–0.5 cal ka BP, which correlate with the disappearance of siliceous microfossils (sponge spicules and diatoms) in the peat, suggesting that the center of the bog was emergent during these periods. Variations in aeolian transport at the inland site reveals a quasi-periodic ~250 yr cycle in the interval throughout the peat and the decreased sand in the past 3 ka may be a result of bog emergence and reduced ability to saltate sand grains. But, unlike the record in the coastal dunes, there is no indication of a decrease in aeolian activity between 1.8 and 0.5 ka. This may suggest that conditions controlling aeolian activity are more sensitive inland than at the coast, and that if wind, or storminess is controlling the inland aeolian record, then storminess alone can not explain the coastal dune record, and dominating wind direction and coastal processes may also play an important role.