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Abstract Arctic coastlines are known to be rapidly eroding, but the fate of this material in the coastal ocean (and the sedimentary dynamics of Arctic continental shelves in general) is less well‐constrained. This study used summertime mooring data from the Alaskan Beaufort Shelf to study sediment‐transport patterns which are dominated by waves and wind‐driven currents. Easterly wind events account for most of the seasonal sediment transport, and serve to focus sediment on the inner shelf. This is a key finding because it means that sediment is readily available for wave‐driven resuspension and sea‐ice entrainment during fall storms. Sediment‐ice entrainment has been previously implicated as a major mechanism for Arctic Shelf erosion—and so the summertime focusing of sediment observed in this study may actually serve to enhance shelf erosion rather than promote shelf sediment accumulation. In a pan‐Arctic context, the Alaskan Beaufort Shelf is somewhat similar to the Laptev Sea Shelf, where previous work has shown that sediment is also focused during the summer months (but for different reasons related to estuarine‐like circulation under the Laptev plume). The Alaskan Beaufort Shelf example contrasts with previous work on the Canadian Beaufort Shelf, where dominant winds from the opposite direction (northwest) likely promote strong seaward dispersal of sediment rather than inner‐shelf convergence. This study thus highlights the importance of understanding dominant wind patterns when considering seasonal and inter‐annual storage, transport, and erosion of sediments from Arctic continental shelves.
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Data-Driven, Multi-Model Workflow Suggests Strong Influence from Hurricanes on the Generation of Turbidity Currents in the Gulf of Mexico
Turbidity currents deliver sediment rapidly from the continental shelf to the slope and beyond; and can be triggered by processes such as shelf resuspension during oceanic storms; mass failure of slope deposits due to sediment- and wave-pressure loadings; and localized events that grow into sustained currents via self-amplifying ignition. Because these operate over multiple spatial and temporal scales, ranging from the eddy-scale to continental-scale; coupled numerical models that represent the full transport pathway have proved elusive though individual models have been developed to describe each of these processes. Toward a more holistic tool, a numerical workflow was developed to address pathways for sediment routing from terrestrial and coastal sources, across the continental shelf and ultimately down continental slope canyons of the northern Gulf of Mexico, where offshore infrastructure is susceptible to damage by turbidity currents. Workflow components included: (1) a calibrated simulator for fluvial discharge (Water Balance Model - Sediment; WBMsed); (2) domain grids for seabed sediment textures (dbSEABED); bathymetry, and channelization; (3) a simulator for ocean dynamics and resuspension (the Regional Ocean Modeling System; ROMS); (4) A simulator (HurriSlip) of seafloor failure and flow ignition; and (5) A Reynolds-averaged Navier–Stokes (RANS) turbidity current model (TURBINS). Model simulations explored physical oceanic conditions that might generate turbidity currents, and allowed the workflow to be tested for a year that included two hurricanes. Results showed that extreme storms were especially effective at delivering sediment from coastal source areas to the deep sea, at timescales that ranged from individual wave events (~hours), to the settling lag of fine sediment (~days).
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- Award ID(s):
- 1831623
- PAR ID:
- 10252505
- Date Published:
- Journal Name:
- Journal of Marine Science and Engineering
- Volume:
- 8
- Issue:
- 8
- ISSN:
- 2077-1312
- Page Range / eLocation ID:
- 586
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Wave‐ and current‐supported turbidity currents (WCSTCs) are one of the sediment delivery mechanisms from the inner shelf to the shelf break. Therefore, they play a significant role in the global cycles of geo‐chemically important particulate matter. Recent observations suggest that WCSTCs can transform into self‐driven turbidity currents close to the continental margin. However, little is known regarding the critical conditions that grow self‐driven turbidity currents out of WCSTCs. This is in part due to the knowledge gaps in the dynamics of WCSTCs regarding the role of density stratification. Especially the effect of sediment entrainment on the amount of sediment suspension has been overlooked. To this end, this study revisits the existing theoretical framework for a simplified WCSTC, in which waves are absent, that is, along‐shelf current‐supported turbidity current. A depth‐integrated advection model is developed for suspended sediment concentration. The model results, which are verified by turbulence‐resolving simulations, indicate that the amount of suspended sediment load is regulated by the equilibrium among positive/negative feedback between entrainment and cross‐shelf gravity force/density stratification, and settling flux dissociated with density stratification. It is also found that critical density stratification is not a necessary condition for equilibrium. A quantitative relation is developed for the critical conditions for self‐driven turbidity currents, which is a function of bed shear stress, entrainment parameters, bed slope, and sediment settling velocity. In addition, the suspended sediment load is analytically estimated from the model developed.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/jmse8080586
