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1. Bedform segregation and locking increase storage of natural and synthetic particles in rivers

   https://doi.org/10.1038/s41467-021-27554-4  

   Dallmann, J.; Phillips, C. B.; Teitelbaum, Y.; Saavedra Cifuentes, Edwin Y.; Sund, N.; Schumer, R.; Arnon, S.; Packman, A. I. (December 2021, Nature Communications)

   Abstract While the ecological significance of hyporheic exchange and fine particle transport in rivers is well established, these processes are generally considered irrelevant to riverbed morphodynamics. We show that coupling between hyporheic exchange, suspended sediment deposition, and sand bedform motion strongly modulates morphodynamics and sorts bed sediments. Hyporheic exchange focuses fine-particle deposition within and below mobile bedforms, which suppresses bed mobility. However, deposited fines are also remobilized by bedform motion, providing a mechanism for segregating coarse and fine particles in the bed. Surprisingly, two distinct end states emerge from the competing interplay of bed stabilization and remobilization: a locked state in which fine particle deposition completely stabilizes the bed, and a dynamic equilibrium in which frequent remobilization sorts the bed and restores mobility. These findings demonstrate the significance of hyporheic exchange to riverbed morphodynamics and clarify how dynamic interactions between coarse and fine particles produce sedimentary patterns commonly found in rivers. 

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2. Land2Sea database, Version 2.0. PANGAEA

   https://doi.org/10.1594/PANGAEA.892680  

   Peucker-Ehrenbrink, Bernhard (January 2018, Pangaea)

   Expansion (version 2.0) of the original Land2Sea database of exorheic rivers (Peucker-Ehrenbrink, 2009, doi:10.1029/2008GC002356) that contains information on 1519 rivers, with additional literature estimates of basin size, water discharge (runoff) under current conditions and prior to human intervention, suspended sediment discharge under current conditions and prior to human intervention, estimate of sediment bedload flux, dissolved strontium concentration and radiogenic isotope value as well as particulate (silt or clay) neodymium concentration, isotope composition and Nd model ages. A large addition to the original river database that contains a significant amount of data from the compilation of Meybeck and Ragu (1996) is from Milliman and Farnsworth (2011). The compilation is not yet geo-referenced. The 2156 rivers are sorted alphabetically within each large-scale drainage region (Graham et al., 1999, 2000). In addition, the compilation includes data on sizes of, and sediment discharge from 48 small islands in Oceania with very high sediment yields. Any errors in transcribing data or converting units from their primary sources into this compilation are entirely mine. Acknowledgements: BPE acknowledges financial support from NSR-EAR-0087697, -0125873, -1226818 and ICER-1639557, as well as from WHOI's Investment in Research and Development Fund. 

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3. Experimental Observations of Bedload Tracer Movement: Effects of Mixed Particle Sizes and Bedforms

   https://doi.org/10.1029/2022WR033114  

   Singh, Arvind; Wu, Zi; Wilcock, Peter; Foufoula‐Georgiou, Efi (May 2023, Water Resources Research)

   Abstract Predicting the transport of bedload tracer particles is a problem of significant theoretical and practical interest. Yet, little understanding exists for transport in rivers in the presence of bedforms, which may trap grains and thereby influence travel distance. In a series of flume experiments with a sandy gravel bed in a large experimental flume, bed elevation and tracer travel distances were measured at high resolution for a range of discharges. As discharge increased, bedform height increased and bedform length decreased, increasing bedform steepness. For all tracer sizes and flow conditions, bedforms act as primary controls on the tracer travel distances. Bedform trapping increases linearly with the ratio of bedform height to tracer grain size, with 50% trapping efficiency for a ratio of two and 90% trapping efficiency for a ratio of four. A theoretical model based on the extended active layer formulation for sediment transport is able to capture much of the distribution of measured travel distances for all tracer sizes and discharges, providing a first connection between tracer transport theory and bedform trapping and indicating normal diffusion of tracers at relatively small timescales. Variable bedform geometry can influence trap efficiency for individual bedforms and the theoretical model can help identify “preferential trapping” conditions. The distribution of tracer travel distances for a mixture of grain sizes and variable discharge, as expected in natural rivers, displays heavy tail characteristics. 

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4. Efficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits

   https://doi.org/10.1130/G47320.1  

   Hage, S.; Galy, V.V.; Cartigny, M.J.B.; Acikalin, S.; Clare, M.A.; Gröcke, D.R.; Hilton, R.G.; Hunt, J.E.; Lintern, D.G.; McGhee, C.A.; et al (May 2020, Geology)

   null (Ed.)

   Abstract Burial of terrestrial biospheric particulate organic carbon in marine sediments removes CO2 from the atmosphere, regulating climate over geologic time scales. Rivers deliver terrestrial organic carbon to the sea, while turbidity currents transport river sediment further offshore. Previous studies have suggested that most organic carbon resides in muddy marine sediment. However, turbidity currents can carry a significant component of coarser sediment, which is commonly assumed to be organic carbon poor. Here, using data from a Canadian fjord, we show that young woody debris can be rapidly buried in sandy layers of turbidity current deposits (turbidites). These layers have organic carbon contents 10× higher than the overlying mud layer, and overall, woody debris makes up >70% of the organic carbon preserved in the deposits. Burial of woody debris in sands overlain by mud caps reduces their exposure to oxygen, increasing organic carbon burial efficiency. Sandy turbidity current channels are common in fjords and the deep sea; hence we suggest that previous global organic carbon burial budgets may have been underestimated. 

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5. Data report: reconnaissance of bulk sediment composition and clay mineral assemblages: inputs to the Hikurangi subduction system

   https://doi.org/10.14379/iodp.proc.372B375.203.2020  

   Underwood, M.B. (March 2020, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   This report provides a reconnaissance-scale assessment of bulk mineralogy and clay mineral assemblages in sediments and sedimentary rocks that are entering the Hikurangi subduction zone, offshore North Island, New Zealand. Samples were obtained from three sites drilled during Leg 181 of the Ocean Drilling Program (Sites 1123, 1124, and 1125) and 38 piston/gravity cores that are distributed across the strike-length of the margin. Results from bulk-powder X-ray diffraction show large variations in normalized abundances of total clay minerals and calcite. The typical lithologies range from clay-rich hemipelagic mud (i.e., mixtures of terrigenous silt and clay with lesser amounts of biogenic carbonate) to calcareous mud, muddy calcareous ooze, and nearly pure nannofossil ooze. Basement highs (Chatham Rise and Hikurangi Plateau) are dominated by biocalcareous sediment, whereas most deposits in the trench (Hikurangi Trough and Hikurangi Channel) and on the insular trench slope are hemipelagic. Clay mineral assemblages (<2 µm) change markedly as a function of geographic position. Sediment entering the southwest side of the Hikurangi subduction system is enriched in detrital illite (>60 wt%) relative to chlorite, kaolinite, and smectite. Normalized proportions of detrital smectite increase significantly toward the northeast to reach values of 40–55 wt% offshore Hawkes Bay and across the transect area for Expeditions 372 and 375 of the International Ocean Discovery Program. 

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