Shelf/fjord exchange driven by coastal-trapped waves in the Arctic

Abstract

In this article, we show that the class of low frequency (subinertial) waves known as coastal-trapped waves (CTWs) are a significant agent of water volume exchange in a west Svalbard fjord, and by extension more widely along the west Svalbard and east Greenland margins where similar conditions prevail. We show that CTWs generated by weather systems passing across the sloping topography of the shelf break propagate into the fjord, steered by the topography of an across-shelf trough. The CTWs have characteristic periods of ∼2 days, set by the passage time of weather systems. Phase speeds and wavelengths vary seasonally by a factor of two, according to stratification: winter (summer) values are C_p = 0.25 ms⁻¹ (0.5 ms⁻¹) and λ = 40 km (84 km). CTW-induced flow velocities in excess of 0.2 ms⁻¹ at 100 m water depth are recorded. Observationally scaled CTW model results allow their explicit role in volume exchange to be quantified. Of the estimated exchange terms, estuarine exchange is weakest (Q_est=0.62x10³ m³s^-1), followed by barotropic tidal pumping (Q_bt=2.5x10³ m³s^-1)with intermediary exchange dominating (Q_i=2.4x10⁴ m³s^-1). Oscillatory flows display greatest activity in the 1–5 day period band, and CTW activity is identified as the likely source of variability in the 40–60 h period band. Within that band, intermediary exchange driven by CTWs is estimated as Q_i^CTW_ave=0.82x10⁴ m³s^-1; an exchange rate exceeding both barotropic and estuarine exchange estimates.