Controls on the global distribution of contourite drifts: Insights from an eddy-resolving ocean model

Abstract

Contourite drifts are anomalously high sediment accumulations that form due to reworking by bottom currents. Due to the lack of a comprehensive contourite database, the link between vigorous bottom water activity and drift occurrence has yet to be demonstrated on a global scale. Using an eddyresolving ocean model and a new georeferenced database of 267 contourites, we show that the global distribution of modern contourite drifts strongly depends on the configuration of the world's most powerful bottom currents. Bathymetric obstacles frequently modify flow direction and intensity, imposing additional finer-scale control on drift occurrence. Mean bottom current speed over contourite-covered areas is only slightly higher (2.2 cm/s) than the rest of the global ocean (1.1 cm/s), falling below proposed thresholds deemed necessary to re-suspend and redistribute sediments (10-15 cm/s). However, currents fluctuate more frequently and intensely over areas with drifts, highlighting the role of intermittent, high-energy bottom current events in sediment erosion, transport, and subsequent drift accumulation. We identify eddies as a major driver of these bottom current fluctuations, and we find that simulated bottom eddy kinetic energy is over three times higher in contourite-covered areas in comparison to the rest of the ocean. Our work supports previous hypotheses which suggest that contourite deposition predominantly occurs due to repeated acute events as opposed to continuous reworking under averageintensity background flow conditions. This suggests that the contourite record should be interpreted in terms of a bottom current's susceptibility to experiencing periodic, high-speed current events. Our results also highlight the potential role of upper ocean dynamics in contourite sedimentation through its direct influence on deep eddy circulation.

The influence of bottom currents on the Zambezi Valley morphology (Mozambique Channel, SW Indian Ocean): In situ current observations and hydrodynamic modelling

“…events of strong currents capable of eroding the seafloor and generating benthic nepheloid layers) in areas with high sea-surface eddy kinetic energy, related to the Gulf Stream or its associated rings. The importance of eddies in controlling deep-sea sedimentation is also supported by a global comparison of contourite distribution and hydrodynamic modelling, which showed that contourites are located in areas with high simulated bottom eddy kinetic energy (Thran et al, 2018).…”

“…Bottom currents are often considered as permanent steady flows, in contrast to the more episodic nature of gravity-flows (Rebesco et al, 2014). Nevertheless, both short-term and seasonal variations may also be involved in controlling the formation of sediment drifts (Zhang et al, 2016;Thran et al, 2018). More studies based on in situ current measurements and hydrodynamic modelling are needed to better understand the intensity and variability of bottom currents and their effect on deep-sea sedimentation.…”

Hybrid turbidite-drift channel complexes: An integrated multiscale model

“…Sedimentary facies and architecture of the hybrid turbidite-drift channel systems are therefore controlled by the frequency of sediment gravity flow activity and the relative persistence and strength of bottom currents. Deposit modification would mostly occur during periods when bottom currents dominate; during this time, the strength and character or direction of the bottom current system would be variable due to, for example, seasonal eddies and benthic storms (Thran et al, 2018;Miramontes, et al, 2019). However, changes in sediment flux (i.e., frequency of sediment gravity flows) and fluctuation of bottom currents over geological time scales (10 6 m.y.)…”

Geochemical Signatures of Paleoclimate Changes in the Sediment Cores from the Gloria and Snorri Drifts (Northwest Atlantic) over the Holocene-Mid Pleistocene

“…The contourite drifts were discovered about 50 years ago [7]. They are defined as sedimentary bodies formed under the influence of the system of the along-slope near-bottom currents, so contourite drifts are usually investigated to reconstruct near-bottom paleocurrents speed [8][9][10][11]. In the North Atlantic, the contourite drifts have been formed due to the inflow of deep Arctic waters with bottom currents, the speed of which was increased during warming and decreased during glaciation [12][13][14][15].…”