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Exploratory Observations of Winter Oceanographic Conditions in the Saguenay Fjord

2012; Taylor & Francis; Volume: 50; Issue: 1 Linguagem: Inglês

10.1080/07055900.2012.659844

1488-7576

Daniel Bourgault, Peter S. Galbraith, Gesche Winkler,

Oceanographic and Atmospheric Processes

A literature review and a search through public databases revealed that little attention had been paid to the winter oceanographic conditions of the Saguenay Fjord. This observation led to an exploratory survey carried out in the Saguenay Fjord during winter 2010, providing the first historical winter measurements throughout the entire water column. Contrary to hypotheses raised about 40 years earlier, the winter water column was well stratified both in temperature and salinity with a dynamically stable pycnocline. The water column was, in fact, more stratified than during the previous summer with a thinner and fresher surface layer lying above a sharper halocline. This stronger winter stratification is attributed to the shielding effect of sea ice to wind-induced mixing. An intermediate water mass lying between 20 and 60 m, called the Saguenay Intermediate Water (SIW), is identified and documented. This water mass appeared clearly as a warm intermediate layer during winter 2010. It is hypothesized that SIW was formed during the previous summer as a mixture of St. Lawrence Estuary Cold Intermediate Layer (CIL), found at flood tide near the mouth of the fjord, and surface water from the Saguenay Fjord. It is further hypothesized that during winter the SIW is eroded and mixed with cold and salty water from the St. Lawrence Estuary found near the mouth of the fjord. This new mixture creates the T-S characteristics of the Saguenay Deep Water (i.e., the water mass that fills the bottom of the Saguenay Fjord). A wintertime water-column echogram is also presented. The echogram reveals a series of biological strata with small fish near the top of the water column (5–20 m), showing little movement, and active larger fish at mid-depth (below 80 m). The echogram also shows vertical migration of zooplankton, possibly euphausiids, mysids or hyperiid amphipod occurring at sunset. Turbulence measured through the migration does not show evidence of enhanced turbulent diffusivity.