Abstract
Here, we report large, near-daily oscillations of near-bottom temperatures, with ranges of up to 11.5 °C at depths of 30–60 m in September 2011 around the Saint Pierre and Miquelon archipelago (south-eastern Canada). These oscillations were detected on velocity and temperature profiles from moorings in Miquelon Bay and on an array of near-bottom temperature sensors around the archipelago. The oscillations coincided with the seasonal stratification period. In addition to their remarkable range, they exhibited a near-diurnal period centred on the O1 tidal component (~26 h), contrasting with the dominant semi-diurnal sea-level periodicity in the area. They appear to be the manifestation of an internal wave, triggered by the diurnal surface tide and trapped by the bathymetric configuration of the area. We argue that the archipelago is nearly resonant for island-trapped waves at near-diurnal frequencies. Our data demonstrate that these coastal-trapped waves propagate clockwise around the archipelago in roughly two days, and thus approximate an azimuthal, mode 2 pattern. Simplified calculations show that cross-shore motions are bottom-amplified. In addition, bottom friction acts to rotate the axes of the diurnal tidal current ellipses with depth, and this combination of effects explains the large range of observed bottom temperature oscillations.
Highlights
Large seabed temperature oscillations have been observed in shallow waters at many locations around the world
Under sufficiently strong stratification, topography may be neglected and waves become very similar to Kelvin waves (KWs), where the sloping bottom has a purely geometric effect
The current and temperature oscillations displayed a peak at the O1 tidal frequency, suggesting tidal forcing
Summary
Large seabed temperature oscillations have been observed in shallow waters at many locations around the world. At mid-latitudes, diurnal tides are sub-inertial, and strong currents have been frequently reported, e.g. in the North-east Atlantic Ocean[14,15,16], on the west coast of Vancouver Island[17,18], near the Kuril Islands (North Pacific Ocean)[19] and other locations often characterised by curved shelf breaks on a scale of 10–100 km. These currents are typically attributed to CTWs20. They open the possibility of resonant forcing and amplification of CTWs around a seamount or island[3,4,25]
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