Different frequencies and triggers of canyon filling and flushing events in Nazaré Canyon, offshore Portugal

Abstract

Submarine canyons are one of the most important pathways for sediment transport into ocean basins. For this reason, understanding canyon architecture and sedimentary processes has importance for sediment budgets, carbon cycling, and geohazard assessment. Despite increasing knowledge of turbidity current triggers, the down-canyon variability in turbidity current frequency within most canyon systems is not well constrained.NewAMS radiocarbon chronologies from canyon sediment cores illustrate significant variability in turbidity current frequency within Nazaré Canyon through time. Generalised linear models and Cox proportional hazardsmodels indicate a strong influence of global sea level on the frequency of turbidity currents that fill the canyon.Radiocarbon ages from basin sediment cores indicate that larger, canyon-flushing turbidity currents reachingthe Iberian Abyssal Plain have a significantly longer average recurrence interval than turbidity currents that fillthe canyon. The recurrence intervals of these canyon-flushing turbidity currents also appear to be unaffectedby long-term changes in global sea level. Furthermore, canyon-flushing and canyon-filling have very differentstatistical distributions of recurrence intervals. This indicates that the factors triggering, and thus controllingthe frequency of canyon-flushing and canyon-filling events are very different. Canyon-filling appears to be predominantly triggered by sediment instability during sea level lowstand, and by storm and nepheloid transportduring the present day highstand. Canyon-flushing exhibits time-independent behaviour. This indicates that atemporally random process, signal shredding, or summation of non-random processes that cannot be discerned from a random signal, are triggering canyon flushing events.

Durable Terrestrial Bedrock Predicts Submarine Canyon Formation

“…If more than half of the sampling points had adjacent canyons, we assigned that interval to have a canyon (24%). Though this procedure resulted in averaging of terrestrial parameters and does not assign particular rivers to particular canyons, we believe that averaging is justified by the paleogeographic uncertainty concerning specific river‐canyon connections (Fagherazzi et al, ), by the offset of canyons by transform faulting (Nagel et al, ), and by the possibility for long distance littoral transport of sediment delivered by rivers into nearby active canyons (Allin et al, ; Covault & Fildani, ). To assess the effects of this approach, we also conducted several sensitivity analyses in which we varied the spatial extent of averaging and the method of assigning canyon presence versus absence (see section 3).…”

How turbidity current frequency and character varies down a fjord‐delta system: Combining direct monitoring, deposits and seismic data

“…Their volume suggests that these mega‐beds are mostly sourced from distinctly larger scale failures on the Squamish Delta (see section on Sources of flows ). Previous work has suggested that submarine canyon systems experience two scales of event, which either fill or flush the canyon and may be related to different triggering mechanisms (Arzola et al ., ; Allin et al ., ). Similar bimodality of flows occurs in this fjord‐delta system.…”

“…Changes in flow frequency are also key for understanding fundamental flow behaviour; such as how often flows erode and accelerate (ignite; Parker, ), or deposit sediment and dissipate, and the length scales over which such changes occur. It has also been proposed that turbidity currents in larger submarine canyon fed systems are strongly bimodal, such that most events are canyon filling, whilst only a few much larger flows flush sediment out of canyons (Arzola et al ., ; Allin et al ., ). More generally, flow frequency has important implications for the tempo of organic carbon and nutrient transport into deeper water (Galy et al ., ) and the physical disturbance of benthic ecosystems (Paull et al ., ).…”

Origin of mud in turbidites and hybrid event beds: Insight from ponded mudstone caps of the Castagnola turbidite system (north‐west Italy)

“…In addition, phenomena like liquefaction of mud usually only occur up to 25 days from deposition (Mehta, 2014), so are unlikely to happen under a turbidity current unless the frequency of large events is very high (cf. Gutierrez-Pastor et al, 2009;Allin et al, 2016).…”