Dynamic near-seafloor sediment transport in Kaikōura Canyon following a large canyon-flushing event

Abstract

ABSTRACT Submarine canyons are important deep-sea environments and conduits for transferring and accumulating sediment and organic matter and pollutants. Recent advances in observing, sampling, and analyzing modern canyon sediment transport systems illustrate near-seafloor dynamics and highlight the potential roles of submarine canyons in transporting and storing organic carbon, nutrients, and contaminants in the deep sea, with implications for deep-sea ecosystems and global carbon budgets. Kaikōura Canyon, offshore northeastern Te Waipounamu South Island, Aotearoa New Zealand, is a benthic biomass hotspot that experienced an earthquake-triggered, canyon-flushing event in 2016. On return to the canyon in October 2020, benthic landers, with sediment traps at 2 m above the seafloor, were deployed along the canyon axis in ∼ 900–1500 m water depths for a period of three weeks. These instrumented platforms provide a detailed view of near-seafloor sediment and organic-carbon transport between canyon-flushing events, showing that the canyon environment hosts dynamic physical processes and short-term sediment fluxes and transport. Variations in sediment and organic carbon flux down-canyon and over time include small-scale sediment transport events, some of which are interpreted as turbidity currents, occurring on much shorter timescales than earthquake recurrence. We compare Kaikōura Canyon results with other longshore-fed, shelf-incised global submarine canyons and deep-ocean sites, revealing differences and likely multiple controlling factors for near-seafloor sediment flux. This Kaikōura Canyon high-resolution, benthic lander timeseries dataset highlights the complexity of submarine canyons and their role in organic carbon flux to the deep ocean, even under high present-day sea-level conditions. Evolving insights underscore the need for more observational data and samples to further quantify submarine canyon sediment and organic-carbon transport and contribute to global evaluations of deep-sea canyon distributary systems.