Abstract
Seafloor sediment resuspension events of different scales and magnitudes and the resulting deep (>1,000 m) benthic nepheloid layers were investigated in the northern Gulf of Mexico during Fall 2012 to Summer 2013. 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 small-scale 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 occurred at some distance, rather than locally. Inertia-driven resuspension of material in shallower areas surrounding the traps presumably transported this material downslope leaving a resuspension signal at 120 mab, but not at 30 mab. The passage of hurricane Isaac left a larger scale resuspension event that lasted a few days and was recorded in both traps. Although hurricanes cause large-scale events readily observable in sediment trap samples, resuspension events small in temporal and spatial scale are not easily recognizable in trapped material as they tend to provide less material and become part of the background signal in the long-term averaged trap samples. We suggest that these small-scale resuspension events, mostly unnoticed in conventional time-series sampling, play an important role in the redistribution and ultimate fate of sediment distribution on the seafloor.
Highlights
The 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 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)
The formation of a deep BNL was recorded in our camera data, and the subsequently observed change over time in particle size distribution within that layer we attribute to lateral advection, to the formation of nepheloid layers, observed in less than 70 m of water depth in the Baltic Sea, which reportedly moved along haloclines as intermediate nepheloid layers and contributed through lateral advection to the deposition of material in the deeper portions of the Baltic Sea (Tamelander et al, 2017)
Summary
The 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. 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). 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). 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). Particles in the BNL include aggregates settling from the upper ocean as
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
