Stevens, Samuel W., Pawlowicz, Rich, Tanhua, Toste , Gerke, Lennart, Nesbitt, William A., Drozdowski, Adam, Chassé, Joël and Wallace, Douglas W. R. (2024) Deep inflow transport and dispersion in the Gulf of St. Lawrence revealed by a tracer release experiment. Communications Earth & Environment, 5 . Art.Nr. 338 (2024). DOI 10.1038/s43247-024-01505-5.

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Abstract

The Gulf of St. Lawrence is increasingly affected by bottom water hypoxia; however, the timescales and pathways of deep water transport remain unclear. Here, we present results from the Deep Tracer Release eXperiment (TReX Deep), during which an inert SF 5 CF 3 tracer was released inshore of Cabot Strait at 279 m depth to investigate deep inflow transport and mixing rates. Dispersion was also assessed via neutrally-buoyant Swish floats. Our findings indicate that the tracer moves inland at 0.5 cm s −1 , with an effective lateral diffusivity of 2 × 10 2 m 2 s −1 over 1 year. Simplified 1D simulations suggest inflow water should reach the estuary head in 1.7 years, with the bulk arriving after 4.7 years. Basin-wide effective vertical diffusivity is around 10 −5 m 2 s −1 over 1 year; however, vertical diffusivity increases near the basin slopes, suggesting that turbulent boundary processes influence mixing. These results are compared to Lagrangian simulations in a regional 3D model to evaluate the capacity to model dispersion in the Gulf.

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