05 Sep 2023
 | 05 Sep 2023
Status: this preprint is open for discussion.

Persistence of a Subsurface Water Mass in a Deep Mid-Latitude Fjord

Laura Bianucci, Jennifer Jackson, Susan Elizabeth Allen, Maxim Krassovski, and Ian Giesbrecht

Abstract. Fjords are common geomorphological coastal features in the mid- and high-latitudes, carved by glacial erosion. These deep nearshore zones connect watersheds and oceans, typically behaving as an estuary. Many fjords in the world have shown concerning warming and deoxygenation trends in their deep waters, sometimes at faster rates than the open ocean. While that is the case in several fjords of British Columbia (BC), Canada, some of the same fjords have shown that strong Arctic outflow wind events in winter can lead to cooling and reoxygenation of subsurface waters, with effects lasting until the following autumn. The latter was observed in Bute Inlet, BC in 2019. We used a high-resolution, three-dimensional ocean model to investigate the mechanisms allowing for the persistence of these subsurface conditions through the year. The presence of the subsurface cold water mass reduced the already weak residual circulation, changing its vertical structure from three to four layers. The reduction of mixing and advection allowed for the water mass to stay in place until autumn conditions arrived (i.e., strong wind mixing and reduced freshwater forcing). The identification of mechanisms that allow for the persistence of cold and oxygenated conditions are key to understand potential areas of ecological refugia in a warming and deoxygenating ocean.

Laura Bianucci et al.

Status: open (until 31 Oct 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2014', Anonymous Referee #1, 12 Sep 2023 reply
  • RC2: 'Comment on egusphere-2023-2014', Anonymous Referee #2, 30 Sep 2023 reply

Laura Bianucci et al.

Laura Bianucci et al.


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Short summary
Fjords are deep coastal features in the nearshore that provide much ecological, economical, and social value despite their relatively small areas. While the deeper waters in the coastal ocean show signs of climate change-induced warming and deoxygenation, this modelling paper highlights a process that can cool and reoxygenate subsurface waters in a fjord for a whole year. We explain how a cold, oxygen-rich water mass originated in winter is able to persist until the next fall in a Canadian fjord.