Large-scale transport phenomena in the Keweenaw Region of Lake Superior: The Ontonagon Plume and the Keweenaw Eddy

Large-scale transport phenomena in the Keweenaw region of Lake Superior are examined using multi-sensor satellite remote sensing. Satellite-based estimates of chlorophyll a (C-OC2) and total suspended matter (TSMSAT) concentrations are obtained from Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) imagery, while lake surface temperatures (LST) are obtained from, Advanced Very High Resolution Radiometer (AVHRR) imagery. Analysis of 2 years of temperature, chlorophyll, and sediment maps reveal several potentially important features in central Lake Superior. SeaWiFS TSMSAT images indicate the presence of an offshore sediment plume originating near Ontonagon, Michigan that was observed on multiple occasions in March, April, and May of both years. Plume materials were observed northeastward of Ontonagon at distances of 80-100 km off shore, although reversals in the pattern were observed. During summer months, the Keweenaw current culminated in a clockwise rotating eddy east of the tip of the Keweenaw Peninsula. The Keweenaw eddy, identified in both A VHRR LST and Sea WiFS C-OC2 Maps, was 50-75 km in diameter, and it changed shape and location during July, August, and September of both years. In August and September 1999, warm waters originating near the southern shore of Isle Royale and in central Lake Superior extended in a southeasterly direction toward the tip of the Keweenaw and were subsequently entrained in the Keweenaw eddy. The physical mechanisms that create the eddy and its potential biological significance for lower trophic food web interactions are not understood at this time.