Transverse variability of flow on both sides of a sill/contraction combination in a fjord-like inlet of southern Chile

Abstract

Water velocity and density profiles were obtained over a semidiurnal tidal cycle to describe the transverse variability of flow in either side of Galvarino Pass, a sill/contraction combination in a fjord-like inlet in southern Chile (44.4°S). Velocity profiles were obtained with a 614.4 kHz Acoustic Doppler Current Profiler (ADCP) during eight repetitions of a circuit that consisted of along-fjord transects along the pass and cross-fjord transects at either side of the pass. The geomorphology in Galvarino Pass represents a coastline contraction of about 90%, decreasing from 2000 m to 200 m in just 1500 m in the along-channel direction. Depth varies from 40 m on the landward side of the pass to 10 m at the shallowest portion of the sill to 80 m south of the pass. The mean flow in the northern side of the pass showed a tendency of the flow to rotate anticlockwise throughout the water column. This feature should result in a sluggish flushing of the northern side. South of the pass, mean surface outflow and mean bottom inflow (at 20 m) developed near the western side of the fjord. Within the pass, the shallowest and narrowest section represented a boundary between inflows and outflows. The strongest net inflows (∼15 cm/s) were observed in the sill region and the strongest outflows (∼10 cm/s) were seen to the south of the pass. The magnitude of the tidal flows increased inside the pass, reaching a maximum over the sill, and then decreased northward owing to conservation of mass. In the across-channel momentum balance the advective terms seemed to be greater than the rest of the terms in the northern end of the pass and over the sill. Magnitudes of the terms in the along-channel momentum balance were comparable to those in the across-channel direction, highlighting the importance of the transverse dimension under strong geometric constraints.