Where and Why Do Submarine Canyons Remain Connected to the Shore During Sea-level Rise? - Insights from Global Topographic Analysis and Bayesian Regression

Abstract

Submarine canyons are prime conduits for sediment-laden flows that link terrestrial sediment sources with deep-marine depocenters. The efficiency at which canyons route sediments is at least partly controlled by how far they extend into the shelf. If the distance between the canyon head and the shore is short, terrestrial sediment, associated pollutants, and organic carbon can be efficiently delivered to the deep ocean (Azaroff et al.

Controls on submarine canyon connection to the shoreline: a numerical modelling approach

“…These results show that shore-connected submarine canyons are most likely to form when; 1) shelves are narrow, 2) shelves are steep, 3) sediment supply is high, and 4) the magnitude of sea-level change is high. This is in agreement with observations from the Quaternary shore-connected canyons (Sweet and Blum, 2018;Bernhardt and Schwanghart, 2021), indicating that the physical principles underlying these models reflect shore-connected canyon evolution in the natural world. Since gravity flow triggering mechanisms are simplified in these models, this indicates that sediment supply and basin physiography are more important controls on submarine connection to the shoreline than the exact triggering mechanism, e.g., hyperpycnal flows or delta-front failure, over millennial timescales.…”

“…Three key factors have been suggested to increase the prevalence of shore-connected canyons; 1) narrow shelves, 2) high supply of coarse-grained sediment, and 3) high magnitude relative sea-level change (Harris and Whiteway, 2011;Sweet and Blum, 2018;Smith et al, 2017;2018). This is supported by analysis of present-day canyons, with canyons formed on narrow shelves, steep shelves, and subject to high subaerial discharge from relatively unerodible bedrock hinterlands more likely to remain connected to the shoreline (Bernhardt and Schwanghart, 2021), which is also reflected in the prevalence of river-associated canyons on active margins characterised by these factors (Fig. 1B) (Harris and Whiteway, 2011).…”

The Concavity of Submarine Canyon Longitudinal Profiles

“…The present-day global highstand has therefore resulted in an abandonment of many canyons that were primarily active during the last lowstand, when sea-levels were up to 120 m lower than present (Miller et al, 2020). This will have a particular impact on long and low-gradient systems with wide shelves, such as passive margins and foreland basins (Nyberg et al, 2018), as canyons will be less able to keep pace with sea-level rise (Bernhardt & Schwanghart, 2021). This may contribute to high concavity values measured in these settings.…”

“…On active margins, where incised valleys are expected to be deeper owing to steeper river gradients, canyons can be more easily traced onto the shelf as the incised valley is less likely to be fully buried during transgression and highstand (Fagherazzi et al, 2004;Harris & Whiteway, 2011; Figure 10e). Canyons formed on active margins with narrow and steep shelves are also more prone to maintaining connection with the shoreline during Holocene transgression (Bernhardt & Schwanghart, 2021). Therefore, some of the lower concavity values seen on active margin canyons may be attributed to the combination of preferential preservation of incised valley relief on the shelf and an increased ability of these canyons to incise across the shelf (Figure 10e).…”

Tectonics dominates over climatic and oceanographic factors in controlling the physiography of the Americas shelf-break at a continental scale

“…The influences of these processes on shelf and shelf-break physiography have been studied along sections of continental margins with similar tectonic and climatic conditions, including the northern Canadian passive margin (15), NE Atlantic passive margin (16) and western American active margin (17), through global mapping of shelfincising submarine canyons (3,18), and through discrete morphological classifications of global continental shelves (6). However, the continuous impact of these processes on shelf-break relief along continental margins with vastly different tectonic and climatic settings has not been quantified.…”