Observations of near-inertial energy in Lake Superior

• Published in: Limnology and oceanography Vol. 58; no. 2; pp. 715 - 728
• Main Author: Austin, Jay
• Format: Journal Article
• Language: English
• Published: Waco, TX John Wiley and Sons, Inc 01-03-2013; American Society of Limnology and Oceanography
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Hydrology; Hydrology. Hydrogeology; Canada; Lake Superior; United States; Great Lakes; wavelength; waves; fresh-water environment; stratification; thermocline; near-field; hydrodynamics; velocity; North America; currents; amplitude; vertical variations; oscillations; direction; energy
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2013.58.2.0715

Directly measured velocity data collected in Lake Superior between 2008 and 2011 show that currents in the open waters of the lake are dominated by near-inertial energy. The near-inertial signal is composed almost entirely of clockwise rotation, with vertical structure dominated by the first baroclinic mode, where waters above and below the thermocline are roughly 180° out of phase with each other. The strength of the oscillations is strongly related to the strength of the stratification; in periods of the year when the water column is well-mixed (typically late autumn and late spring) the near-inertial signal is very weak; when stratification exists, near-inertial oscillations can occur. Combining the velocity amplitudes with an estimate of the thermocline displacement allows estimation of the dominant direction and horizontal wavelength of the near-inertial field, showing that horizontal wavelengths are on the order of 50–100 km, and the direction of the waves veers counter-clockwise over the course of the season with a period of ∼ 1 month. Observations of backscatter suggest that inertial oscillations may be responsible for re-suspension of bottom sediments, which could have significant ecological consequences.