Fate of Ayeyarwady and Thanlwin River Sediment: Relative Importance of Oceanographic and Tectonic Controls - Associated Dataset

Data set archive associated with Kuehl et al. (2019) collected as part of NSF award OCE-1737221. Core and CTD data are from a two-week oceanographic research cruise which was conducted in December 2017 in the Northern Andaman Sea and Bay of Bengal, using a locally hired vessel. Overall, we occupied 30 stations and collected ~50 sediment cores (kasten, gravity and box), along with CTD profiles on the shelf and inside the Yangon River estuary. The area covered includes both the western and eastern sides of the delta, almost 250 nm across, and southward across the continental shelf to a major submarine canyon at the shelf edge in the northern Andaman Sea. The data set represents both electronic and physical archives

Across-shelf sediment transport: Interactions between suspended sediment and bed sediment

[1] We use a two-dimensional, time-dependent sediment-transport model to quantify across-shelf transport, deposition, and sorting during wave-driven resuspension events characteristic of those that dominate sediment transport on many continental shelves. Decreases in wave-orbital velocities as water depth increases, and the resulting cross-shelf gradient in bed shear stress favor a net offshore transport of sediment. On wide, flat shelves (slopes similar to0.1%), these gradients are low, and the depth to which the seabed is reworked depends mainly on bottom shear stress and local sediment availability. On narrow, steep shelves (slopes similar to0.5%), however, the gradient in bottom stress generates significant cross-shelf suspended sediment flux gradients that create regions of net erosion and deposition. While the magnitude of waves generally determines the water depth to which sediment can be resuspended, erosional and depositional patterns on narrow shelves are sensitive to cross-shelf gradients in wave energy, nonlocal sediment availability, and the direction and magnitude of the cross-shelf current. During energetic waves, cross-shelf divergence of suspended sediment flux can create a coarsened, erosional area on the inner shelf that abuts a region of fine-grained sediment deposition on the mid-to-outer shelf. If currents are strongly shoreward, however, flux divergence leads to erosion over the entire shelf

Event-to-seasonal sediment dispersal on the Waipaoa River Shelf, New Zealand: A numerical modeling study

The formation of the geologic record offshore of small mountainous rivers is event-driven and, more so than many other environments, can result in relatively complete sequences. One such river, the Waipaoa in New Zealand, has been studied from its terrestrial source to its oceanic sink over timescales spanning storms, seasons, and the Holocene. This study focused on the formation of riverine deposits on the Waipaoa Shelf during episodic flood and wave events, contrasting deposition during short-lived events to accumulation patterns created over thirteen months. Sediment fluxes and fate were estimated using the numerical hydrodynamic and sediment transport model ROMS, the Regional Ocean Modeling System, using CSTMS, the Community Sediment Transport Modeling System. During the study period (January 2010-February 2011), the model indicated that initial flood deposition generally occurred near the river mouth and along the coast in water shallower than 40 m, and that deposition during any one event was sensitive to variations in shelf currents and wave energy. Also, the sedimentation due to plume settling and suspended transport during these relatively short flood and wave events were not aligned with longer time-scale accumulation patterns (months or greater) previously reported for the Waipaoa shelf. In the days to months following a flood pulse, waves episodically reworked this initial deposit, resuspending centimeter-scale layers of sediment during energetic periods. Frequent and intense resuspension occurred in shallow areas where bed stresses were high. This encouraged redistribution of material toward deeper areas having lower near-bed wave stresses, including continental shelf depocenters and offshore areas. While fast settling material was preferentially retained near the river mouth, currents dispersed slower settling sediment farther before deposition. Overall, accumulation depended on characteristics of oceanographic transport (wave energy, current velocities), not just source characteristics (flood size, sediment size distribution). (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.orgilicensesiby-nc-nd/4.0/)

A Hydrodynamic-Sediment Transport Numerical Model for the Waipaoa Shelf, New Zealand: Model Archive

These files are compressed versions of input files, model code, and output used for two publications: Moriarty, J. M., Harris, C. K., and Hadfield, M. G. (2014). A hydrodynamic and sediment transport model for the Waipaoa Shelf, New Zealand: Sensitivity of fluxes to spatially-varying erodibility and model nesting. Journal of Marine Science and Engineering, 2 (2): 336-369. Doi:10.3390/jmse2020336 Moriarty, J. M., Harris, C. K., and Hadfield, M. G. (2015). Event-to-seasonal sediment dispersal on the Waipaoa River Shelf, New Zealand: A numerical modeling study. Continental Shelf Research, 110: 108-123. Doi: 10.1016/j.csr2015.10.005 Compressed files with the .gz file extension can be opened with Gzip GNU software (open source). Compressed files with the .tar file extension can be opened with Gzip Tar software (open source). Many of the input / output files use the NetCDF (Network Common Data Form) file format. These have "nc" as a file extension and can be read using a variety of open source tools: see http://www.unidata.ucar.edu/software/netcdf/docs/ . For information about the Regional Ocean Modeling System (ROMS), its model code and input / output, see www.myroms.org

Formation of Oil-Particle-Aggregates: Numerical Model Formulation and Calibration

When oil spills occur in turbid waters, the oil droplets and mineral grains can combine to form oil-particle aggregates (OPAs). The formation of OPAs impacts the vertical transport of both the oil and the mineral grains; especially increasing deposition of oil to the seabed. Though the coastal oceans can be very turbid, to date, few numerical ocean models have accounted for aggregation processes that form OPAs. However, interactions between oil and mineral aggregates may be represented using techniques developed to account for sediment aggregation. As part of Consortium for Simulation of Oil Microbial Interactions in the Ocean (CSOMIO), we modified an existing, population dynamics-based sediment flocculation model to develop OPAMOD, a module that accounts for the formation of OPAs. A zero-dimensional model using OPAMOD is shown to be capable of reproducing the size distribution of aggregates from existing laboratory experimental results. Also using the zero-dimensional model, sensitivity tests were performed on two model parameters, the fractal dimension and collision efficiency. Results showed that fractal dimension played a role in the OPA size distribution by influencing the effective particle density, which modified the number concentration of flocs for a given mass concentration. However, the modeled particle characteristics and oil sequestration were relatively insensitive to collision efficiency. To explore OPA formation for an outer continental shelf site, two simulations were conducted using a one-dimensional (vertical) implementation of the model. One scenario had high sediment concentration near the seabed to mimic storm-induced resuspension. The other scenario represented river plume sediment delivery by having high sediment concentration in surface waters. Results showed that OPA formation was sensitive to the vertical distribution of suspended sediment, with the river plume scenario creating more OPA, and sequestering more oil within OPA than the storm resuspension scenario. OPAMOD was developed within the Coupled Ocean-Atmosphere-Wave-and-Sediment Transport (COAWST) modeling system, therefore the methods and parameterizations from this study are transferrable to a three-dimensional coupled oil-sediment-microbial model developed by CSOMIO within the COAWST framework

A Model Archive for Simulations in a Partially-Mixed Idealized Estuary using the COAWST System: Model Code and Output

This dataset includes model input, code and output used in the publication Tarpley et al. (2019, Journal of Marine Science and Engineering), which used a coupled hydrodynamic-sediment transport model to investigate the roles of flocculation, bed consolidation and sediment-induced stratification on changes in fine-grained sediment distribution in an idealized estuarine model. The modeling system used in the development was the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) framework

The Impact of Winter Storms on Sediment Transport Through a Narrow Strait, Bohai, China

The Yellow River is one of the most significant sources of terrestrial sediment to the global seas, and the Bohai Strait is the only pathway that delivers Yellow River‐derived sediments from the shallow Bohai Sea to the Yellow Sea. To investigate sediment transport processes through the strait under the influence of storms (strong northerly winds) that frequently occur in winter, we deployed two sets of observing platforms equipped with Acoustic Doppler Current Profilers (ADCP) and a suite of other sensors in the strait in January 2018. Aided by a system of high‐resolution models, we reconstructed sediment dynamics in response to the strong northerly wind of a winter storm. Model results show that the instantaneous suspended sediment flux (SSF) is highly aligned with tidal currents, while the net sediment flux has a clear dependence on variations in exchange flow and sediment resuspension. Enhanced coastal currents, intensified wave motions, and higher suspended sediment concentrations indicate that the through‐strait sediment flux during outflows is greater than during inflow conditions. Such SSF asymmetries are believed responsible for the net sediment export through the Bohai Strait in wintertime. Diagnostic analyses provided insights into the dynamic mechanisms of exchange flow variations influenced by both the strong northerly winds and the wind‐triggered coastal trapped waves in the shallow, narrow strait via geostrophic effects. This study highlights the importance of storm‐induced horizontal exchange processes in a coupled bay‐shelf system

Numerical Model of Geochronological Tracers for Deposition and Reworking Applied to the Mississippi Subaqueous Delta

Measurements of naturally occurring, short-lived radioisotopes from sediment cores on the Mississippi subaqueous delta have been used to infer event bed characteristics such as depositional thicknesses and accumulation rates. Specifically, the presence of Beryllium-7 (Be-7) indicates recent riverine-derived terrestrial sediment deposition; while Thorium-234 (Th-234) provides evidence of recent suspension in marine waters. Sediment transport models typically represent coastal flood and storm deposition via estimated grain size patterns and deposit thicknesses, however, and do not directly calculate radioisotope activities and profiles, which leads to a disconnect between the numerical model and field observations. Here, observed radioisotopic profiles from the Mississippi subaqueous delta cores were directly related to a numerical model that represented resuspension and deposition using a new approach to account for the behavior of short-lived radioisotopes. Appropriate selection of parameters such as the bioditfusion coefficient, sediment accumulation rate, and radioisotopic source terms enabled a good match between the modeled and observed cores. Comparisons of modelled profiles with geochronological analytical models that estimate accumulation rate and flood layer thickness revealed potential avenues for refining these tools, and highlight the importance of constraining the biodiffusion coefficient

Seabed Resuspension in the Chesapeake Bay: Implications for Biogeochemical Cycling and Hypoxia

Sediment processes, including resuspension and transport, affect water quality in estuaries by altering light attenuation, primary productivity, and organic matter remineralization, which then influence oxygen and nitrogen dynamics. The relative importance of these processes on oxygen and nitrogen dynamics varies in space and time due to multiple factors and is difficult to measure, however, motivating a modeling approach to quantify how sediment resuspension and transport affect estuarine biogeochemistry. Results from a coupled hydrodynamic-sediment transport-biogeochemical model of the Chesapeake Bay for the summers of 2002 and 2003 showed that resuspension increased light attenuation, especially in the northernmost portion of the Bay, shifting primary production downstream. Resuspension also increased remineralization in the central Bay, which experienced larger organic matter concentrations due to the downstream shift in primary productivity and estuarine circulation. As a result, oxygen decreased and ammonium increased throughout the Bay in the bottom portion of the water column, due to reduced photosynthesis in the northernmost portion of the Bay and increased remineralization in the central Bay. Averaged over the channel, resuspension decreased oxygen by similar to 25% and increased ammonium by similar to 50% for the bottom water column. Changes due to resuspension were of the same order of magnitude as, and generally exceeded, short-term variations within individual summers, as well as interannual variability between 2002 and 2003, which were wet and dry years, respectively. Our results quantify the degree to which sediment resuspension and transport affect biogeochemistry, and provide insight into how coastal systems may respond to management efforts and environmental changes. Model datasets are available through W&M ScholarWorks : https://doi.org/10.25773/hamz-zc5