Scales of seafloor sediment resuspension in the northern Gulf of Mexico

Abstract

Diercks, A-R, et al. 2018 Scales of seafloor sediment resuspension in the northern Gulf of Mexico. Elem Sci Anth, 6: 32. DOI: https://doi. org/10.1525/elementa.285 IntroductionThe sedimentation of large amounts of oil via marine snow and its accumulation on the deep seafloor (>1,200 m) during and after the Deepwater Horizon (DwH) oil spill (Passow et al., 2012;Valentine et al., 2014;Brooks et al., 2015;Chanton et al., 2015;Daly et al., 2016;Joye, 2016;Joye et al., 2016;Passow, 2016) raised questions regarding the distribution and re-distribution processes of freshly sedimented material (marine snow) on the seafloor. Once on the seafloor, marine snow contributes to unconsolidated fluffy sediment layers (Gardner, 1978;Gardner et al., 1984;1985;Walsh et al., 1988;Pilskaln et al., 1998;Newell et al., 2005) that are subject to resuspension and the production of benthic nepheloid layers (BNLs).Resuspension leads to the re-invigoration of degradation processes, which would impact the degradation rates of the oil associated with marine snow following the DwH accident (Ziervogel et al., 2016). Additionally, resuspension leads to lateral transport and redistribution of the material that sank to the seafloor. After the DwH accident such re-distribution processes make it especially difficult to estimate the total amount of Macondo oil that reached the seafloor (Passow and Hetland, 2016).BNLs, which are formed when the frictional stress of water motion strips sediment off the seafloor, therewith carrying particles into the overlying water layer, exist near the seafloor, but may reach tens to hundreds of meters upward into the water column (McCave et al., 1976). The thickness of the BNL extending above the seafloor scales with the strength of the bottom currents and the particle composition. Bottom currents >10 cm s -1 may cause resuspension events (Gardner et al., 2017), especially when low density phytodetritus or fine silt covers sediments, but large benthic storms reach 20 cm s -1 (Gardner et al., 1985). Besides locally resuspended material, particles in the BNL also include aggregates settling from the upper ocean as Time-series data of size-specific in-situ settling speeds of marine snow in the benthic nepheloid layer (moored flux cameras), particle size distributions (profiling camera), currents (various current meters) and stacked time-series flux data (sediment traps) were combined to recognize resuspension events ranging from small-scale local, to small-scale far-field to hurricane-scale. One smallscale local resuspension event caused by inertial currents was identified based on local high current speeds (>10 cm s -1) and trap data. Low POC content combined with high lithogenic silica flux at 30 m above bottom (mab) compared to the flux at 120 mab, suggested local resuspension reaching 30 mab, but not 120 mab. Another similar event was detected by the changes in particle size distribution and settling speeds of particles in the benthic nepheloid layer. Flux data indicated two other small-scale events, which occurre...

Aggregation and sedimentation of shattered graphene oxide nanoparticles in dynamic environments: a solid-body rotational approach

“…Additionally, it is critical to investigate how resuspension phenomenon occurring within surface water (SW) bodies, such as lakes, river, and sea at various scales, influences the aggregation of NP in these environments. [34][35][36][37] Typically, current experimental techniques investigating NP aggregation dynamics are limited to simple quiescent or turbulent mixing batch experiments which may not adequately capture aggregation conditions in real systems. 38,39 Whilst research into incorporating aggregation models within porous media transport models continues, 38,40,41 steps must be taken to validate the individual aspects of aggregation models in dynamic media.…”

“…38,39 Whilst research into incorporating aggregation models within porous media transport models continues, 38,40,41 steps must be taken to validate the individual aspects of aggregation models in dynamic media. One of these impacts can be the heterogeneous or anisotropic mixing in the population of nanoaggregates induced by the environmental dynamics such as cascading/cycling conditions within GW and SW systems [27][28][29][30]32,33,36,37,[42][43][44] that can modify the particle size distribution (PSD) evolution trends under aggregation/sedimentation conditions. To investigate such systems, we used a slow rotating cylinder in which these impacts are simulated by slow continuous revolutions of the cylinder.…”

Temporal Variability of Polycyclic Aromatic Hydrocarbons in Deep-Sea Cephalopods of the Northern Gulf of Mexico

“…Of all the species studied, H. corona is the only one that lives in the mesopelagic zone and does not migrate to the surface to feed ( Supplementary Table S1). Oil-residues have been observed in the water column years after the spill (Walker et al, 2017), probably from resuspension of contaminated sediments (Romero et al, 2017;Diercks et al, 2018). It is possible that the dietary intake for H. corona was affected like the other species studied (Figure 3), but with an extended period of exposure to oilresidues persistent at depth.…”

A First Comprehensive Baseline of Hydrocarbon Pollution in Gulf of Mexico Fishes

“…These locations are either near major population www.nature.com/scientificreports www.nature.com/scientificreports/ centers (e.g., Tampa Bay, Florida), along marine traffic thoroughfares (e.g Yucatán Shelf), or within an area of high density oil and gas infrastructure (e.g., northwest and north central region). The large hotspot of mean naphthalene equivalent concentrations in the north central region is likely a combination of the resuspension of DWH contaminated sediments, additional oil spills, leaking wells (e.g., Taylor Energy's Saratoga platform MC20), and riverine inputs from the Mississippi River Delta 41,42 . The naphthalene hotspot off the northern tip of the Yucatán Shelf is somewhat enigmatic as it is located far from both coastal populations and the extant Mexican oil infrastructure.…”

“…Between 2012 and 2014, the pattern of increasing PAHs has www.nature.com/scientificreports www.nature.com/scientificreports/ been observed in sediments, fishes and birds 3,48-53 . These increases have been attributed to the resuspension of contaminated sediments that often occur following natural disturbances (e.g., bioturbation, tropical storms and hurricanes, currents and waves) 41,52,53 . However, the ongoing release of oil and gas from the 2004 toppled Taylor Energy Company's Saratoga oil platform (MC20) 42,54 and the lingering leak of DWH until at least 2012 55 cannot be dismissed as possible sources.…”