Large-Scale Atmospheric and Oceanic Control on Krill Transport into the St. Lawrence Estuary Evidenced with Three-Dimensional Numerical Modelling

A three-dimensional circulation model, coupled to a Lagrangian particle drift model, is used to understand the processes leading to krill transport from the northwest Gulf of St. Lawrence (nwGSL) towards the head of the Lower St. Lawrence Estuary (LSLE), a well-known site of krill accumulation. An analysis of the circulation at the scale of the Gulf of St. Lawrence (GSL) over five years (2006 to 2010) evidenced four major findings. (i) There are two main seasonal circulation patterns, one in winter-spring and one in summer-fall, driven by local wind forcing and transport at Cabot Strait and at the Strait of Belle Isle. (ii) The freshwater runoff variability does not control the observed inflow events at the mouth of the LSLE. (iii) Extratropical storms passing over the GSL are important for the transport of krill into the LSLE through the generation of inflow events at Pointe-des-Monts. (iv) The contribution of the transport in the surface layer ( where krill are found at night) during these inflow events is also important in modulating the variability of the transport of krill into the LSLE. The inflow events, combined with the presence or absence of high krill densities in the nwGSL, partly control the interannual variability of the transport of krill into the LSLE.