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1. Equilibrium sediment exchange in the earth’s critical zone: evidence from sediment fingerprinting with stable isotopes and watershed modeling

   https://doi.org/10.1007/s11368-018-2208-8  

   Mahoney, David Tyler; Al Aamery, Nabil; Fox, James Forrest; Riddle, Brenden; Ford, William; Wang, Y. T. (June 2019, Journal of Soils and Sediments)

   Abstract Purpose The equilibrium sediment exchange process is defined as instantaneous deposition of suspended sediment to the streambed countered by equal erosion of sediment from the streambed. Equilibrium exchange has rarely been included in sediment transport studies but is needed when the sediment continuum is used to investigate the earth’s critical zone. Materials and methods Numericalmodeling in the watershed uplands and streamcorridor simulates sediment yield and sediment source partitioning for the Upper South Elkhorn watershed in Kentucky, USA.We simulate equilibrium exchange when uplandderived sediment simultaneously deposits to the streambed while streambed sediments erode. Sediment fingerprinting with stable carbon isotopes allowed constraint of the process in a gently rolling watershed. Results and discussion Carbon isotopes work well to partition upland sediment versus streambed sediment because sediment deposited in the streambed accrues a unique autotrophic, i.e., algal, fingerprint. Stable nitrogen isotopes do not work well to partition the sources in this study because the nitrogen isotope fingerprint of algae falls in the middle of the nitrogen isotope fingerprint of upland sediment. The source of sediment depends on flow intensity for the gently rolling watershed. Streambed sediments dominate the fluvial load for low and moderate events, while upland sediments become increasingly important during high flows and extreme events.We used sediment fingerprinting results to calibrate the equilibrium sediment exchange rate in the watershed sediment transport model. Conclusions Our sediment fingerprinting and modeling evidence suggest equilibrium sediment exchange is a substantial process occurring in the system studied. The process does not change the sediment load or streambed sediment storage but does impact the quality of sediment residing in the streambed. Therefore, we suggest equilibrium sediment exchange should be considered when the sediment continuumis used to investigate the critical zone.We conclude the paper by outlining future research priorities for coupling sediment fingerprinting with watershed modeling. 

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2. Summertime Sediment Storage on the Alaskan Beaufort Shelf and Implications for Ice‐Sediment Rafting and Shelf Erosion

   https://doi.org/10.1029/2025JC022624  

   Eidam, E F (July 2025, Journal of Geophysical Research: Oceans)

   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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3. Sediment Routing and Floodplain Exchange (SeRFE): A Spatially Explicit Model of Sediment Balance and Connectivity Through River Networks

   https://doi.org/10.1029/2020MS002048  

   Gilbert, Jordan_T; Wilcox, Andrew_C (September 2020, Journal of Advances in Modeling Earth Systems)

   Abstract Sediment regimes, i.e., the processes that recruit, transport, and store sediment, create the physical habitats that underpin river‐floodplain ecosystems. Natural and human‐induced disturbances that alter sediment regimes can have cascading effects on river and floodplain morphology, ecosystems, and a river's ability to provide ecosystem services, yet prediction of the response of sediment dynamics to disturbance is challenging. We developed the Sediment Routing and Floodplain Exchange (SeRFE) model, which is a network‐based, spatially explicit framework for modeling sediment recruitment to and subsequent transport through drainage networks. SeRFE additionally tracks the spatially and temporally variable balance between sediment supply and transport capacity. Simulations using SeRFE can account for various types of watershed disturbance and for channel‐floodplain sediment exchange. SeRFE is simple, adaptable, and can be run with widely available geospatial data and limited field data. The model is driven by real or user‐generated hydrographs, allowing the user to assess the combined effects of disturbance, channel‐floodplain interactions and particular flow scenarios on the propagation of disturbances throughout a drainage network, and the resulting impacts to reaches of interest. We tested the model in the Santa Clara River basin, Southern California, in subbasins affected by large dams and wildfire. Model results highlight the importance of hydrologic conditions on postwildfire sediment yield and illustrate the spatial extent of dam‐induced sediment deficit during a flood. SeRFE can provide contextual information on reach‐scale sediment balance conditions, sensitivity to altered sediment regimes, and potential for morphologic change for managers and practitioners working in disturbed watersheds. 

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4. ADCP Observations of Currents and Suspended Sediment in the Macrotidal Gulf of Martaban, Myanmar

   https://doi.org/10.3389/feart.2022.820326  

   Harris, Courtney K; Wacht, Jacob T; Fair, Matthew J; Côté, Jessica M (April 2022, Frontiers in Earth Science)

   The Ayeyarwady and Thanlwin Rivers, which drain Myanmar, together form one of the largest point sources of freshwater and sediment to the global ocean. Combined, these rivers annually deliver an estimated 485 Mt of sediment to the northern Andaman Sea. This sediment contributes to a perennially muddy zone within the macro-tidal Gulf of Martaban, but little is known about the processes that dominate dispersal and trapping of sediment there, as very few water column observations are available. A research cruise in December 2017 provided a rare opportunity to obtain Acoustic Doppler Current Profiler (ADCP) data along transects from the Gulf of Martaban and adjacent continental shelf. Two transects were obtained from the outer portion of the Gulf of Martaban in water depths that ranged from about 20–35 m. These showed very fast currents, especially during flood tide conditions, exceeding 1.5 m/s. The backscatter record from the ADCP indicated asymmetries in distribution of suspended sediment during the ebb versus flood phase of the tide. During ebb tidal conditions, the backscatter record indicated that sediment was transported in either a surface advected layer, or fairly well-mixed throughout the water column. In contrast, during flood tidal conditions, sediment was confined to the bottom boundary layer, even though the velocities were faster during flood than the ebb conditions. The vertical structure of the currents during flood tide conditions indicated the presence of sediment–induced stratification because currents within the near-bed turbid layers were relatively slow, but speeds increased markedly above these layers. This albeit limited dataset provides an exciting glimpse into the dynamics of sediment transport within the muddy, macrotidal Gulf of Martaban, and implies the importance of tidal straining and bottom nepheloid layer formation there. 

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5. On the Evolution and Fate of Sediment Diapirs in Subduction Zones

   https://doi.org/10.1029/2021GC009873  

   Klein, Benjamin Z.; Behn, Mark D. (November 2021, Geochemistry, Geophysics, Geosystems)

   Abstract At subduction zones, significant volumes of sediments and other crustal material are carried on top of the downgoing plate past the trench and into the mantle. This represents the dominant process by which material from the Earth's surface is recycled to the interior. However, the fate of these recycled materials is uncertain. Subducted material may be carried with the slab into the deep mantle, or it may form diapirs that ascend into the hotter portions of the mantle wedge, where they can melt and/or be relaminated to the base of the arc crust. While this material can be a mixture (or “mélange”) of sediments, oceanic crust and mantle rocks, here we focus on the dynamics of the uppermost layer of sediments on the downgoing slab. We modified a thermodynamic model to accurately predict the equilibrium mineral assemblage, melting behavior, and density of a range of subducted sediment compositions at pressure and temperature conditions relevant to subduction zones. Using this thermodynamic model, we constructed a coupled dynamic model of sediment diapirs and identified the primary parameters that control diapir behavior: sediment thickness and composition, and the thermal state of the subduction zone. Relamination of ascending diapirs is favored by greater sediment thicknesses, more felsic compositions, and warmer thermal conditions. By contrast, diapirism is suppressed in colder arcs, or where subducted sediment layers are thin or more mafic. Applying this model to modern subduction zones suggests that multiple processes are active today, with relamination occurring in a significant subset of modern arcs. 

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