Abstract
Investigations of the geology and physical limnology of a field of sedimentary furrows in Lake Superior have provided information on the characteristics of these bedforms and their relationship to the wind‐driven currents and associated turbulence structures in the bottom boundary layer. The results generally support the existing conceptual model for furrow formation. Furrows in the study area (2 km2) at 100‐m depth are spaced 20–100 m apart and exceed 800 m long, the troughs being ∼0.5 m deep and 3–5 m wide. Sediment cores collected by submersible are poorly sorted, cohesive, terrigenous silts with a mean grain size of 20 µm. Relative to sediments in the interfurrow area, those in the trough contain higher fractions of sand and coarse debris and accumulate at a rate 15% slower. Strong bottom currents (speed > 6 cm s−1) usually flow within 20° of the furrow direction and are most frequent between late October and early February, when wind‐forced currents reach the bottom; annual peak speeds approach 30 cm The relationship of the current and temperature records to the wind field is consistent with predictions of coastal jet theory. Profiling current meters deployed on either side of a furrow showed near‐bottom, cross‐stream flow converging over the furrow with divergence higher in the boundary layer when the current speed exceeded 6 cm s−1. A preliminary numerical model exhibits a cross‐stream flow pattern consistent with the profiler observations.
