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

Abstract

8Submarine canyons are one of the most important pathways for sediment transport into ocean 9 basins. For this reason, understanding canyon architecture and sedimentary processes has 10 importance for sediment budgets, carbon cycling, and geohazard assessment. Despite increasing 11 knowledge of turbidity current triggers, the down-canyon variability in turbidity current frequency 12 within most canyon systems is not well constrained. New AMS radiocarbon chronologies from 13 canyon sediment cores illustrate significant variability in turbidity current frequency within Nazaré 14 Canyon through time. Generalised linear models and Cox proportional hazards models indicate a 15 strong influence of global sea level on the frequency of turbidity currents within the canyon. 16Radiocarbon chronologies from basin sediment cores indicate that larger, canyon-flushing turbidity 17 currents reaching the Iberian Abyssal Plain have a significantly longer average recurrence interval 18 than turbidity currents that fill the canyon. The recurrence intervals of these larger turbidity currents 19 also appear to be unaffected by long-term changes in global sea level. This indicates that the factors 20 triggering, and thus controlling, the frequency of canyon-flushing and canyon-filling events are very 21 different. Canyon-filling appears to be predominantly controlled by sediment instability during sea 22 level lowstand and by storm and nepheloid transport during the present day highstand. Canyon-23 flushing exhibits time-independent behaviour. This indicates that a temporally random process, or 24 summation of non-random processes that cannot be discerned from a random signal, are triggering 25 canyon flushing events. 26

Eustatic sea-level controls on the flushing of a shelf-incising submarine canyon

“…Turbidity currents that fill, or recharge, Nazaré Canyon have previously been analyzed using sediment cores obtained from the canyon levees. These filling turbidity currents are predominantly active during sea-level lowstand, and their recurrences conform to a normal distribution (Allin et al, 2016). Larger turbidity currents that flush Nazaré Canyon periodically have been inferred from thick (>20 cm) turbidites in the central Iberian Abyssal Plain, 140 km from the mouth of the canyon.…”

“…Turbidity currents in submarine canyons are proposed to be one of two broad end-member types: those that are restricted to, and fill or recharge the canyon with sediment, and those that flush sediment from the canyon and continue into deeper water (Parker, 1982;Piper and Savoye, 1993;Canals et al, 2006;Piper and Normark, 2009;Talling et al, 2012;Allin et al, 2016). "Filling" turbidity currents triggered by localized failures, hyperpycnal river discharge, or storms accumulate sediment within canyons over hundreds or even thousands of years (Paull et al, 2005;Canals et al, 2006;Arzola et al, 2008;Khripounoff et al, 2009;Masson et al, 2011;Talling et al, 2012;Talling, 2014).…”

“…However, whether or not factors like eustatic sea-level change are a control on the recurrence rates of large-volume landslides and turbidity currents worldwide has little empirical support, based upon few well-dated examples that do not provide the required statistical power for testing (Urlaub et al, 2013;Pope et al, 2015). Furthermore, it is also unclear whether or not signals of environmental change that propagate into deep water (>4000 m) are recorded and preserved in distal marine sedimentary archives Romans and Graham, 2013;Allin et al, 2016;Romans et al, 2016).…”

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

“…Changes in flow frequency are also key for understanding fundamental flow behaviour; such as how often flows erode and accelerate (ignite; Parker, 1982), 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, 2008;Allin et al, 2016). More generally, flow frequency has important implications for the tempo of organic carbon and nutrient transport into deeper water (Galy et al, 2007) and the physical disturbance of benthic ecosystems (Paull et al, 2010).…”

Volume and recurrence of submarine‐fan‐building turbidity currents

“…Event recurrence is better constrained, with Quaternary core-based studies providing recurrence interval data from multiple basins (Clare et al, 2014;Clare et al, 2016;Paull et al, 2014). Studies have also focused on the distribution of event recurrence and how allogenic forcing and position along the sediment-routing system can affect the recurrence distribution (Allin et al, 2017;Allin et al, 2016;Clare et al, 2015).…”