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1. Widespread Deposition in a Coastal Bay Following Three Major 2017 Hurricanes (Irma, Jose, and Maria)

   https://doi.org/10.1038/s41598-019-43062-4  

   Browning, Trevor N.; Sawyer, Derek E.; Brooks, Gregg R.; Larson, Rebekka A.; Ramos-Scharrón, Carlos E.; Canals-Silander, Miguel (May 2019, Scientific Reports)

   Abstract In 2017, three major hurricanes (Irma, Jose, and Maria) impacted the Northeastern Caribbean within a 2-week span. Hurricane waves can cause physical damage to coastal ecosystems, re-suspend and transport antecedent seafloor sediment, while the associated intense rainfall can yield large influxes of land-derived sediment to the coast (e.g. burial of ecosystems). To understand sedimentation provenance (terrestrial or marine) and changes induced by the hurricanes, we collected bathymetry surveys and sediment samples of Coral Bay, St. John, US Virgin Islands in August 2017, (pre-storms) and repeated it in November 2017 (post-storms). Comparison reveals morphologic seafloor changes and widespread aggradation with an average of ~25 cm of sediment deposited over a 1.28 km²benthic zone. Despite an annual amount of precipitation between surveys, sediment yield modeling suggests watersheds contributed <0.2% of the total depositional volume. Considering locally established accumulation rates, this multi-hurricane event equates to ~1–3 centuries of deposition. Critical benthic communities (corals, seagrasses) can be partially or fully buried by deposits of this thickness and previous studies demonstrate that prolonged burial of similar organisms often leads to mortality. This study illuminates how storm events can result in major sediment deposition, which can significantly impact seafloor morphology and composition and benthic ecosystems. 

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2. Recent Acceleration of Wetland Accretion and Carbon Accumulation Along the U.S. East Coast

   https://doi.org/10.1029/2022EF003037  

   Weston, Nathaniel B.; Rodriguez, Elise; Donnelly, Brian; Solohin, Elena; Jezycki, Kristen; Demberger, Sandra; Sutter, Lori A.; Morris, James T.; Neubauer, Scott C.; Craft, Christopher B. (March 2023, Earth's Future)

   Abstract The long‐term stability of coastal wetlands is determined by interactions among sea level, plant primary production, sediment supply, and wetland vertical accretion. Human activities in watersheds have significantly altered sediment delivery from the landscape to the coastal ocean, with declines along much of the U.S. East Coast. Tidal wetlands in coastal systems with low sediment supply may have limited ability to keep pace with accelerating rates of sea‐level rise (SLR). Here, we show that rates of vertical accretion and carbon accumulation in nine tidal wetland systems along the U.S. East Coast from Maine to Georgia can be explained by differences in the rate of relative SLR (RSLR), the concentration of suspended sediments in the rivers draining to the coast, and temperature in the coastal region. Further, we show that rates of vertical accretion have accelerated over the past century by between 0.010 and 0.083 mm yr⁻², at roughly the same pace as the acceleration of global SLR. We estimate that rates of carbon sequestration in these wetland soils have accelerated (more than doubling at several sites) along with accelerating accretion. Wetland accretion and carbon accumulation have accelerated more rapidly in coastal systems with greater relative RSLR, higher watershed sediment availability, and lower temperatures. These findings suggest that the biogeomorphic feedback processes that control accretion and carbon accumulation in these tidal wetlands have responded to accelerating RSLR, and that changes to RSLR, watershed sediment supply, and temperature interact to determine wetland vulnerability across broad geographic scales. 

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3. Silicate Weathering and Diagenetic Reaction Balances in Deltaic Muds

   https://doi.org/10.2475/001c.134118  

   Trapp-Müller, Gerrit; Aller, Robert C; Sluijs, Appy; Middelburg, Jack J (January 2025, American Journal of Science)

   Reactions between terrigenous sediments, marine-biogenic substances and seawater modulate multiple biogeochemical cycles, but the dynamics and factors governing these reactions are poorly constrained. Deltaic mobile muds are a major sedimentary facies along river-dominated ocean margins through which most terrigenous sediment transits and mixes with marine-biogenic matter, representing efficient and globally significant batch reactors. Here, we present a process-based model that combines equilibrium aqueous chemistry with kinetic concepts from sediment biogeochemistry and mineral sciences to explore the solution-mediated interplay of organic and inorganic matter alteration in episodically reworked deltaic muds. The model reproduces observed diagenetic conditions and product suites over the seasonal timescales relevant to deltaic systems and indicates a systematic and dynamic coupling between the sedimentary cycles of H⁺, C, P, Fe, S, Si, Mg, K, and Ca. We used the model in combination with published field observations and concepts of authigenic mineral occurrences to develop a generalized explanatory framework for silicate weathering fluxes and diagenetic reaction balances in marine sediments. Diagenetic silicate weathering is represented by a continuum of reaction balances with acid (reverse) and alkaline (forward) endmembers that is moderated by sediment sources, which determine the sediment’s weatheringpotential, and depositional environments, which govern theexpressionof this potential. Reverse weathering dominates in seasonally reworked, low-latitude deltaic muds, where green clays form rapidly from lateritic river sediments and biogenic silica under suboxic conditions. High mineral precipitation rates and protracted sediment remobilization drive large solute fluxes from/to these sediments. Net forward silicate weathering becomes more likely under steady, sustained anoxic conditions, particularly in volcanically-influenced settings and at minimal pre-weathering of sediment sources. These results further our understanding of the role silicate weathering and marine sediments play in global biogeochemistry and Earth system evolution, and can aid targeted ‘enhanced weathering’ strategies to environmental governance. 

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4. Seasonal growth and senescence of seagrass alters sediment accumulation rates and carbon burial in a coastal lagoon

   https://doi.org/10.1002/lno.12178  

   Zhu, Qingguang; Wiberg, Patricia L.; McGlathery, Karen J. (July 2022, Limnology and Oceanography)

   Abstract Seagrass meadows are important carbon sinks in the global coastal carbon cycle yet are also among the most rapidly declining marine habitats. Their ability to sequester carbon depends on flow–sediment–vegetation interactions that facilitate net deposition, as well as high rates of primary production. However, the effects of seasonal and episodic variations in seagrass density on net sediment and carbon accumulation have not been well quantified. Understanding these dynamics provides insight into how carbon accumulation in seagrass meadows responds to disturbance events and climate change. Here, we apply a spatially resolved sediment transport model that includes coupling of seagrass effects on flow, waves, and sediment resuspension in a seagrass meadow to quantify seasonal rates of sediment and carbon accumulation in the meadow. Our results show that organic carbon accumulation rates were largely determined by sediment accumulation and that they both changed non‐linearly as a function of seagrass shoot density. While seagrass meadows effectively trapped sediment at meadow edges during spring–summer growth seasons, during winter senescence low‐density meadows (< 160 shoots m⁻²) were erosional with rates sensitive to density. Small variations in winter densities resulted in large changes in annual sediment and carbon accumulation in the meadow; meadow‐scale (hundreds of square meters) summer seagrass dieback due to marine heatwaves can result in annual erosion and carbon loss. Our findings highlight the strong temporal and spatial variability in sediment accumulation within seagrass meadows and the implications for annual sediment carbon burial rates and the resilience of seagrass carbon stocks under future climate change. 

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5. Offshore transport of particulate organic carbon in the California Current System by mesoscale eddies

   https://doi.org/10.1038/s41467-019-12783-5  

   Amos, Caitlin M.; Castelao, Renato M.; Medeiros, Patricia M. (October 2019, Nature Communications)

   Abstract The California Current System is characterized by upwelling and rich mesoscale eddy activity. Cyclonic eddies generally pinch off from meanders in the California Current, potentially trapping upwelled water along the coast and transporting it offshore. Here, we use satellite-derived measurements of particulate organic carbon (POC) as a tracer of coastal water to show that cyclones located offshore that were generated near the coast contain higher carbon concentrations in their interior than cyclones of the same amplitude generated offshore. This indicates that eddies are in fact trapping and transporting coastal water offshore, resulting in an offshore POC enrichment of 20.9 ± 11 Gg year⁻¹. This POC enrichment due to the coastally-generated eddies extends for 1000 km from shore. This analysis provides large-scale observational-based evidence that eddies play a quantitatively important role in the offshore transport of coastal water, substantially widening the area influenced by highly productive upwelled waters in the California Current System. 

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