ABSTRACT

Seasonal and tidal variability of temperature, salinity, and currents were measured from spring to fall 2017, and during spring 2018 in the Bay of Sept-Îles (BSI), located in the northwest of the Gulf of St. Lawrence, Canada. Surface drifters were deployed to measure surface current velocities and CTD profiles were recorded regularly at 21 stations across the bay and the archipelago. Repeated passages along a transect at the mouth of the bay were conducted for 12 hours with a towed acoustic Doppler current profiler. During these transects, regular stops were made for CTD profiling. The bay was found to be a two-layer system, with a pycnocline near a depth of 10 m. There was a horizontal temperature and salinity front near the tributary rivers separating them from the surface waters of the Gulf of St. Lawrence; however, this front was outside the bay during the spring freshet. Tide-averaged currents were seaward near the surface (2–10 m) and shoreward in deeper waters (10–30 m), suggesting an estuarine circulation in the BSI. Average and maximum surface drifter speeds were 17.4 cm s${}^{-1}$ and 86.6 cm s${}^{-1}$. Instantaneous drifter velocity was coarsely ($25\pm {25}^{\circ }$ west of it) but steadily aligned with the direction of the wind, and average surface currents seemed to follow the dominant wind directions (SSE and WNW), since drifters often (in 22/46 cases) shoaled on their leeward beaches. Currents were dominated by tides locally but usually resulted from the complex interaction of tides with estuarine circulation, winds and effects of the Earth's rotation. Usual alignment of currents with coasts and bathymetry emphasized the key role of topographic steering on bay scale flow patterns. The bulk flushing time of water in the BSI was estimated to $\tau =5.6\pm 3.5$ days.

摘要

2017 年春季至秋季以及 2018 年春季在位于加拿大圣劳伦斯湾西北部的七岛湾 (BSI) 测量了温度、盐度和洋流的季节性和潮汐变化。部署表面漂移器以测量表面电流速度，并在整个海湾和群岛的 21 个站点定期记录 CTD 剖面。使用拖曳声学多普勒电流剖面仪沿着海湾口处的横断面重复通过 12 小时。在这些横断面期间，定期停止进行 CTD 剖析。发现该海湾是一个两层系统，在 10 m 深度附近有一个密度跃层。支流附近有一个水平的温度和盐度前沿，将它们与圣劳伦斯湾的地表水分开；然而，在春天的新鲜空气中，这条锋面位于海湾之外。潮汐平均流在表面附近 (2-10 m) 向海，在较深的水域 (10-30 m) 向岸，表明 BSI 中存在河口环流。平均和最大表面漂流速度为 17.4 cm s${}^{-\mathrm{1个}}$和 86.6 厘米${}^{-\mathrm{1个}}$. 瞬时漂流速度粗略地（$25\pm {25}^{\circ }$它以西）但稳定地与风向一致，平均表面流似乎遵循主导风向（SSE 和 WNW），因为漂流者经常（在 22/46 的情况下）在他们的背风海滩上浅滩。洋流在当地以潮汐为主，但通常是潮汐与河口环流、风和地球自转影响的复杂相互作用的结果。洋流与海岸和测深的通常对齐强调了地形导向对海湾尺度流动模式的关键作用。BSI 中水的大量冲洗时间估计为$\tau =5.6\pm 3.5$天。