17 Jul 2023
 | 17 Jul 2023
Status: this preprint is open for discussion.

Influence of a small submarine canyon on biogenic matter export flux in the Lower St. Lawrence Estuary, eastern Canada

Hannah Sharpe, Michel Gosselin, Catherine Lalande, Alexandre Normandeau, Jean-Carlos Montero-Serrano, Khouloud Baccara, Daniel Bourgault, Owen Sherwood, and Audrey Limoges

Abstract. Submarine canyons enhance shelf-slope sediment exchange and influence hydrodynamic processes, with consequences for biogeochemical cycles. This work documents variations in the vertical export of biogenic matter on the northern shore of the Lower St. Lawrence Estuary (LSLE, Quebec, eastern Canada), which is characterized by the presence of an active submarine canyon system. A total of three moorings were deployed from November 2020 to September 2021. One nearshore mooring was deployed in the main axis of the Pointe-des-Monts (PDM) canyon system and was equipped with an Acoustic Doppler Current Profiler (ADCP), and two moorings equipped with sediment traps were deployed in the distal PDM canyon system and offshore Baie-Comeau (BC). The ADCP data revealed the occurrence of a minor sediment remobilization event (December 2020) and a small turbidity current (February 2021) in the canyon. Concurrent elevated fluxes of total particulate matter, particulate organic carbon, particulate nitrogen, and chloropigments showed that these events left a signature in the distal PDM sediment trap located >2.6 km further offshore. The composition of diatom and dinoflagellate assemblages was similar in the canyon system and offshore BC, but the diatom bloom occurred two weeks earlier (in mid-April) at the PDM site, where annual diatom and dinoflagellate fluxes were almost 2 times lower than at the BC site. A bloom of the potentially toxic diatom Pseudo-nitzschia seriata was also observed during the second half of September 2021 at the BC site. This study notably helps identify the relationship between near-bed canyon processes and biogenic matter export in the water column, thereby directly influencing the regional ecosystem. The study period further covered an anomalously nearly ice-free winter and thus, in the context of climate change, provides valuable insight into future trends of biogenic matter export in the LSLE.

Hannah Sharpe et al.

Status: open (until 04 Oct 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1538', Kyung-Hoon Shin, 16 Sep 2023 reply

Hannah Sharpe et al.

Hannah Sharpe et al.


Total article views: 226 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
173 42 11 226 6 6
  • HTML: 173
  • PDF: 42
  • XML: 11
  • Total: 226
  • BibTeX: 6
  • EndNote: 6
Views and downloads (calculated since 17 Jul 2023)
Cumulative views and downloads (calculated since 17 Jul 2023)

Viewed (geographical distribution)

Total article views: 220 (including HTML, PDF, and XML) Thereof 220 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 22 Sep 2023
Short summary
We studied the impact of submarine canyon processes within the Pointe-des-Monts system on biogenic matter export and phytoplankton assemblages. Using data from three oceanographic moorings, we show that the canyon experienced two low-amplitude sediment remobilization events in 2020–2021, that led to enhanced particle fluxes in the deep-water column layer >2.6 km offshore. Sinking phytoplankton fluxes were lower near the canyon compared to background values from the Lower St. Lawrence Estuary.