Nepheloid and suspended particulate matter in south‐eastern Lake Michigan*

A persistent benthic nepheloid layer with high total suspended matter (TSM) and high total particulate surface area was observed in south‐eastern Lake Michigan. The layer thickens from a few metres near the shelf‐slope boundary to greater than 10 m at the base of the slope. When compared to the hypolimnion, TSM increases by a factor of 2‐20 at 1 m above the bottom, the greatest increase detected at the slope‐basin boundary. Sediment trap profiles within the nepheloid layer show that the particulate flux increases exponentially from about 10 m above the bottom to 1 m above the bottom, suggesting that a large fraction of the collected material came from resuspension. A nepheloid layer is created during the formation of the thermal bar and maintained during the stratified period, apparently through the action of weak but persistent currents. This layer is supplemented by lakeward transport of fine particles resuspended near the shelf‐slope boundary due to impingement of the thermocline on the bottom, or during higher energy events.