Credit: © 2007 AGU

The 16.8-metre tidal range in Ungava Bay, off Hudson Strait, is one of the world's two largest tidal elevations because the bay's natural period resonates with the principal lunar tide.

Using a combination of data and numerical analyses, Brian Arbic at the Institute for Geophysics at the University of Texas, USA and colleagues1 determined the natural period of the Ungava Bay tides to be 12.7 hours — very close to the period of the principal lunar tidal cycle of 12.4 hours. This near-resonance means that incoming and outgoing tides reinforce each other, so tidal friction is the primary limitation on the height of the tides. Potential future rises in sea levels would bring Ungava Bay even closer to resonance — it was found that a 7 metre rise would shift the bay to full resonance and result in a ∼2% increase in tidal range. Deeper water in the bay would also reduce friction, causing a further amplification of the tidal fluctuations.

The strong tides in Hudson Bay and the northern Labrador Sea are globally important in dissipating tidal energy. Moreover, Ungava Bay's resonance may significantly influence tidal dynamics in the Atlantic Ocean via a coupled-oscillator phenomenon.