On the Magnitude of Canyon‐Induced Mixing

Nazarian, Robert; Burns, Christian; Legg, Sonya; Buijsman, Maarten C.; Kaur, Harpreet; Arbic, Brian K.

doi:10.1029/2021jc017671

Cited by 8 publications

(3 citation statements)

References 66 publications

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“…hills, canyons, channels, sills, or seamounts) contribute the most to abyssal watermass transformations (e.g. Armi and D'Asaro 1980;Bryden and Nurser 2003;Thurnherr et al 2005;Legg et al 2009;Nazarian et al 2021;Mashayek et al 2021) and 2) what are the dynamics that support finite watermass transformations in these regions (Garrett 1979(Garrett , 1990Callies 2018;Drake et al 2020)?…”

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confidence: 99%

Dynamics of eddying abyssal mixing layers over sloping rough topography

Drake

Ruan

Callies

et al. 2022

Journal of Physical Oceanography

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The abyssal overturning circulation is thought to be primarily driven by small-scale turbulent mixing. Diagnosed watermass transformations are dominated by rough topography “hotspots”, where the bottom-enhancement of mixing causes the diffusive buoyancy flux to diverge, driving widespread downwelling in the interior—only to be overwhelmed by an even stronger up-welling in a thin Bottom Boundary Layer (BBL). These watermass transformations are significantly underestimated by one-dimensional (1D) sloping boundary layer solutions, suggesting the importance of three-dimensional physics. Here, we use a hierarchy of models to generalize this 1D boundary layer approach to three-dimensional eddying flows over realistically rough topography. When applied to the Mid-Atlantic Ridge in the Brazil Basin, the idealized simulation results are roughly consistent with available observations. Integral buoyancy budgets isolate the physical processes that contribute to realistically strong BBL upwelling. The downwards diffusion of buoyancy is primarily balanced by upwelling along the sloping canyon sidewalls and the surrounding abyssal hills. These flows are strengthened by the restratifying effects of submesoscale baroclinic eddies and by the blocking of along-ridge thermal wind within the canyon. Major topographic sills block along-thalweg flows from restratifying the canyon trough, resulting in the continual erosion of the trough’s stratification. We propose simple modifications to the 1D boundary layer model which approximate each of these three-dimensional effects. These results provide local dynamical insights into mixing-driven abyssal overturning, but a complete theory will also require the non-local coupling to the basin-scale circulation.

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confidence: 99%

Dynamics of eddying abyssal mixing layers over sloping rough topography

Drake

Ruan

Callies

et al. 2022

Journal of Physical Oceanography

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“…Submarine canyons are narrow, V-shaped valleys incised into lithified rock or sediment that typically occur on upper continental slopes and connect directly to the shelf edge (Daly, 1936;Shepard, 1972;Wynn et al, 2007;Fildani, 2017). They are globally important as conduits that transfer vast amounts of sediment and pollutants from continents to deep-marine basins (Harris et al, 2014;Amaro et al, 2016;Mountjoy et al, 2018;Zhong and Peng, 2021), as efficient sites of organic carbon burial (Masson et al, 2010;Maier et al, 2019), biodiversity hotspots (Cunha et al, 2011;Bianchelli and Danovaro, 2019;De Leo et al, 2020), and dynamic areas of ocean mixing (Allen and Durrieu de Madron, 2009;Zhu et al, 2010;Nazarian et al, 2021). Therefore, it is important to understand the processes that transport, capture and redistribute particulates within submarine canyons, and how they ultimately contribute to the erosion and/or depositional fill over time (Puig et al, 2014).…”

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confidence: 99%

Evolution and architecture of an overbank in an ocean-facing canyon-fill.

Taylor,

Hodgson,

Peakall

et al. 2024

Preprint

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Submarine canyon-fills comprise substantial volumes of thin-bedded successions deposited by sediment gravity flows that are either stripped or overspill from adjacent channels into highly confined, topographically complex overbank settings. Here, we document the Punta Baja Formation, a rare example of an exhumed canyon-confined overbank succession with good 3D constraints from the Mesozoic Peninsular Ranges Forearc, Mexico. High-resolution sedimentary logging and drone-captured photogrammetric models reveal that the overbank was a highly dynamic environment, where different bed types point to a variety of flow transformations and complex topographical interactions that evolved through time. The lower overbank is characterised by variable bed thicknesses, grain-sizes and palaeocurrent directions, which point to a wide range of unfiltered flows that overspilled from channels. Thick sandstone beds contain distinct hummock-like bedforms, representing high energy combined flows that repeatedly deflected and reflected against the high relief canyon margin, suggesting complete confinement within the conduit. Locally, thinner beds are disrupted by slides, debrites and scour surfaces on the canyon floor. As the canyon system matured, constituent channels migrated laterally and aggraded. Here, the character of the overbank changes, developing distinct fining- and thinning-upward packages that decay in thickness and grain-size away from the channel axis. Packages are more mud-rich and beds contain mixed grain-size bedforms indicating smaller magnitude, rapidly decelerated transitional flows that failed to interact with the canyon margin. In more quiescent parts of the upper overbank, beds containing rhythmic bundles of silt-rich, mud-draped bedforms are interpreted to be the product of sediments reworked by internal tides. This is the first detailed study of fine-grained fills in an ancient ocean-facing submarine canyon. Canyon-confined overbanks offer a more diverse fill, with flow transformations that demonstrate a complex balance between erosion and deposition, and an absence of discrete internal levée or depositional terrace elements that have been identified in more distal confined overbank settings.

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“…Submarine canyons funnel large volumes of sediment from continents to oceans via gravity flows (Daly, 1936;Kuenen, 1938;Shepard, 1972;Fildani, 2017;Fisher et al, 2021). More than 9,500 submarine canyons mapped along the Earth's continental margins (Harris et al, 2014) are now recognised to play an important role in ocean circulation patterns (Allen & Durrieu De Madron, 2009;Zhu et al, 2010;Nazarian et al, 2021), marine biodiversity (Schlacher et al, 2007;Bianchelli et al, 2010;Vetter et al, 2010;Fernandez-Arcaya et al, 2017), and carbon and pollutant export from shelves to deep water locations (Palanques et al, 2008;Pham et al, 2014;Puig et al, 2014;Hage et al, 2020;Taviani et al, 2023). Despite their size and ubiquity, little is known about how sediment in submarine canyons is stored and transferred into the stratigraphic record on geological timescales.…”

Section: Introductionmentioning

confidence: 99%

Evolution and architecture of an exhumed ocean-facing coarse-grained submarine canyon fill, Baja California, Mexico

Bouwmeester,

Kane,

Hodgson

et al. 2024

Preprint

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Present day submarine canyons are active conduits for large volumes of sediment, carbon, and pollutants from continents to oceans. However, the evolution of submarine canyons over geological timescales remains poorly understood due to their erosional nature and low preservation potential. The Late Cretaceous Punta Baja Formation represents a well-preserved submarine canyon-fill on a tectonically-active ocean-facing margin. Outcrops provide km-scale continuous strike and dip sections of the 120 m thick and 1.2 km wide feature. An inherited tectonic fabric influenced the location and orientation of canyon incision into fluvial bedrock. The stratigraphic evolution of the Punta Baja submarine canyon is reconstructed from incision to fill, and shows that it remained an active sediment conduit throughout the time period represented by the preserved fill. The depositional architecture of the north-south oriented erosionally confined canyon-fill is asymmetric, with sub-vertically stacked channel-fills to the west, and an overbank confined by the canyon margin in the east. Sedimentary process interactions led to depositional patterns that we consider distinct to submarine canyon fills. Dynamic topography created by mass wasting processes captured sediment and drove knickpoint development, an autogenic mechanism that modifies sediment delivery to the ocean floor. We interpret widespread upstream dipping surfaces in channel-fills as the stratigraphic expression of migrating supercritical-flow bedforms, playing an important role in sediment storage and transport in the canyon. The proximal location of canyons and unique confinement configuration impact transverse and lateral gravity flow filtering, causing depositional patterns in the intra-canyon overbank areas that are less well organised than in published examples of external levees and which were previously poorly characterised for submarine canyons. This study provides insight into how processes that are observed in modern canyons are selectively preserved through the lifetime of the canyon and construct or destroy stratigraphy on geological timescales.

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On the Magnitude of Canyon‐Induced Mixing

Cited by 8 publications

References 66 publications

Dynamics of eddying abyssal mixing layers over sloping rough topography

Dynamics of eddying abyssal mixing layers over sloping rough topography

Evolution and architecture of an overbank in an ocean-facing canyon-fill.

Evolution and architecture of an exhumed ocean-facing coarse-grained submarine canyon fill, Baja California, Mexico

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