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Cross shore transport by wind-driven turbidity plumes in western Lake Superior*
Citation:
McKinney, P., J. Austin, AND F. Gills. Cross shore transport by wind-driven turbidity plumes in western Lake Superior*. Presented at Ocean Sciences Meeting, Portland, OR, February 11 - 16, 2018.
Impact/Purpose:
Turbidity plumes may represent a significant cross shelf transport mechanism in the western arm of Lake Superior, however basic questions regarding their formation and offshore transport volume are unknown. This work develops a simple linear model for evaluating the offshore transport using in situ and satellite remote sensing observations. Cross shore transport varied by an order of magnitude between 2008- 2016 depending on the strength and frequency of springtime NE wind events and nearshore ice cover. The results suggest these events play a role in the interannual variability of ecosystem functioning in the lake.
Description:
Turbidity plumes frequently occur in the western arm of Lake Superior and may represent a significant cross shelf transport mechanism for sediment, nutrient and biota. We characterize a plume that formed in late April 2016 using observations from in situ sensors and remote sensing imagery, and estimate the volume of cross shelf transport using both remote sensing and an idealized analytical model of plume formation. The analytical model represents the western arm as a channel in which coastal flows are aligned with the northeast wind stress whereas plume waters are driven offshore up the middle of the lake in the opposite direction of the wind stress by an along-lake pressure gradient. The volume of cross shelf transport associated with the 2016 plume is estimated, by both methods, to have been on the order of 1010m3. We investigate the hypothesis that the total volume transported offshore during a plume event is proportional to the specific impulse of the event. Analysis of springtime events from 2008-2016 displays a strong relationship between the specific wind impulse and plume volume, consistent with the simple linear theory. The total annual transport varied by nearly an order of magnitude over the time period studied. This raises the possibility that these sorts of wind-driven processes may play a role in the interannual variability of ecosystem functioning in the lake.