Oceanic sediment accumulation rates predicted via machine learning algorithm: towards sediment characterization on a global scale

AbstractObserved vertical sediment accumulation rates (n = 1031) were gathered from ~ 55 years of peer reviewed literature. Original methods of rate calculation include long-term isotope geochronology (14C,210Pb, and137Cs), pollen analysis, horizon markers, and box coring. These observations are used to create a database of global, contemporary vertical sediment accumulation rates. Rates were converted to cm year−1, paired with the observation's longitude and latitude, and placed into a machine learning–based Global Predictive Seabed Model (GPSM). GPSM finds correlations between the data and established global "predictors" (quantities known or estimable everywhere, e.g., distance from coastline and river mouths). The result, using a k-nearest neighbor (k-NN) algorithm, is a 5-arc-minute global map of predicted benthic vertical sediment accumulation rates. The map generated provides a global reference for vertical sedimentation from coastal to abyssal depths. Areas of highest sedimentation, ~ 3–8 cm year−1, are generally river mouth proximal coastal zones draining relatively large areas with high maximum elevations and with wide, shallow continental shelves (e.g., the Gulf of Mexico and the Amazon Delta), with rates falling exponentially towards the deepest parts of the oceans. The exception is Oceania, which displays significant vertical sedimentation over a large area without draining the large drainage basins seen in other regions. Coastal zones with relatively small drainage basins and steep shelves display vertical sedimentation of ~ 1 cm year−1, which is limited to the near shore when compared with shallow, wide margins (e.g., the western coasts of North and South America). Abyssal depth rates are functionally zero at the time scale examined (~ 10−4 cm year−1) and increase one order of magnitude near the Mid-Atlantic Ridge and at the Galapagos Triple Junction

A machine-learning derived model of seafloor sediment accumulation

Abstract Previous studies regarding the depositional pattern and quantity of accumulated seafloor sediment tend to be regional, limited in scope and involving costly and time-consuming geologic field campaigns and laboratory work. Presented herein is a global map of predicted modern (postindustrial, 20th and 21st century) oceanic mass accumulation rates of 5-arc-minute pitch and in log10-space, trained on observed marine mass accumulation rates from 43 peer reviewed sources (n = 1744) and predicted using a k-nearest neighbor geospatial algorithm. The resultant model predicts ~3.3 × 104 Mt. yr−1 of sediment accumulating onto the sea floor (R2 = 0.88). Most sediment accumulates proximal to major river outlets and deltas. Continental regions with the highest sediment accumulation are Asia and Oceania. This model is the first of its kind to predict the rate and quantity of sediment accumulating on to the ocean floor, globally, using decades of regional real-world observations. The generated global map of modern, benthic mass accumulation rates also serves to highlight areas of interest for future study in related fields, such as sediment dynamics and seafloor stability

Deltaic Wetland Dynamics from Seasonal to Centennial Scales

The lower plain of the Mississippi River Delta contains approximately five coastal sedimentary basins that are topographically defined, and one shelf-crossing depocenter (the Birds Foot Delta). These depositional systems receive varying quantities of sediment from fluvial and marine sources and have rates of coastal land loss that are roughly inversely proportional to fluvial sediment supply. To combat land loss along these regions, Louisiana has launched a historic campaign to sustain and regrow coastal lands using, in part, river sediment diversions. Fine sediments constitute the majority of sediment load in the Mississippi River, but are under-studied with respect to dispersal processes, particularly in terms of sediment supply to distal deltaic bays and wetlands. To expand the knowledge of fine sediment dynamics along distal coastal marshes, two distinct, contrasting field areas along southeastern Louisiana are studied. The first, Fourleague Bay, is actively nourished by fresh sediment from the Atchafalaya River. The second, Terrebonne Bay, has not had an active fluvial connection in over a century. Using push cores, vibracores, carbon dating, grain size analysis, loss-on-ignition testing, bulk density, seismic CHIRP data, and natural and anthropogenic radioisotopes 7-beryllium, 210-lead, and 137-cesium, rates and patterns of sediment accumulation on both the shallow bay bottom and marsh platforms are calculated from seasonal to centennial timescales. Results indicate 1) riverine sphere of influence for nourishing mineral sediments is at least 25 km from the river mouth; 2) there exists a synergistic relationship between mineral sediment input and organic sediment production; 3) paleochannels may provide resiliency for marsh platforms established above them; 4) environmental processes control the physical properties of sediment

Riverine Sediment Contribution to Distal Deltaic Wetlands: Fourleague Bay, LA

© 2018, Coastal and Estuarine Research Federation. To combat land loss along the Mississippi River Delta, Louisiana has launched a historic campaign to sustain and regrow coastal lands using, in part, sediment diversions. Previous research has focused primarily on sand-sized sediment load, which is usually deposited proximal to a river’s delta or a diversion’s outlet. Fine sediments constitute the majority of sediment load delivered by rivers, but are understudied with respect to dispersal processes, particularly in terms of sediment supply to distal deltaic bays and wetlands. The Atchafalaya River and associated wetlands serve as prime study areas for this purpose. Fourleague Bay has remained stable against the deteriorative effects of relative sea level rise, standing out along Louisiana’s declining coastline. Push cores were collected once every 2 months, from May 2015 to May 2016, along five central bay sites and five adjacent marsh sites within Fourleague Bay, Louisiana. All sites fall within ~ 10 to 30 km of the Atchafalaya Delta, extending south towards the Gulf of Mexico. Cores were extruded in 2-cm intervals, dried, ground, and analyzed via gamma spectrometry for the presence of 7 Be. Inventories of 7 Be were then calculated and used to determine daily apparent mass deposition rates (AMDR) over 12 months. Average AMDR values for the bay and the marshes are compared with Atchafalaya River discharge, wind data, and atmospheric pressure through the year of sampling. Peak marsh AMDR, 0.7 ± 0.2 kg m −2 d −1 , occurred just after historically high river discharge. Peak bay AMDR, 1.2 ± 0.7 kg m −2 d −1 , occurred during seasonal low river discharge and calm winds. Average bay and marsh AMDRs have a moderate negative correlation (r = − 0.51) when compared. Results indicate that, during periods of moderate to high river discharge, sediment bypasses the bay floor and enters the marshes directly when inundation occurs, a process enhanced by the passage of strong atmospheric fronts. During periods of low river discharge and relatively calm winds, riverine sediments aggregate directly onto the bay floor

The coupling of bay hydrodynamics to sediment transport and its implication in micro-tidal wetland sustainability

© 2018 Elsevier B.V. To investigate bay hydrodynamics and its impacts on the adjacent micro-tidal wetland sustainability, hourly measurements of wave, tidal current, and benthic suspended sediment concentration in summer, winter, and spring of 2015–2016 were conducted in Fourleague Bay, Louisiana, USA. High-temporal resolution data indicate that benthic suspended sediment resuspension had a dominant periodicity of 4.8-d, which was mainly caused by wind-driven waves. Sediment flux reached 28 g·m−2·s−1 during events. Net sediment flux direction is northwestward in summer, and southeastward in winter and spring. Potential depth-integrated sediment flux to surrounding wetland varied within 0–500 g·m−1·s−1. Seasonal variations of river discharge and wind direction (particularly speed \u3e3 m·s−1) dominated potential sediment contribution from the bay to the surrounding wetland. Three sediment transport regimes were delineated: ‘bypassing’ season, resuspension-accumulation season, and combined ‘bypassing’ and resuspension-accumulation season. This study couples bay hydrodynamics to the sediment transport processes and sustainability of adjacent wetlands in a micro tidal environment. It sheds light on the understanding of natural feedback mechanisms and how estuarine-marsh system survive high relative sea level rising scenario in micro tidal environment, which could aid in the design of future ecological engineering restoration strategies