Why do shelf-incising submarine canyons form? - Insights from global topographic analyses and regression trees

2020 ◽  
Author(s):  
Anne Bernhardt ◽  
Wolfgang Schwanghart
Keyword(s):  
Continental Slope ◽  
Regression Trees ◽  
Signal Propagation ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Slope Gradient ◽  
Submarine Canyons ◽  
Data Set ◽  
Sediment Routing ◽  
River Mouths

<p>The efficiency of environmental signal propagation from terrestrial sources to marine sinks highly depends on the connectivity of the sediment-routing system. Submarine canyons that couple river outlets with marine depocenters are particularly crucial links in the routing network as they convey terrestrial sediment, associated pollutants and organic carbon to the deep ocean. However, why and where submarine canyons incise into shelves is still poorly understood. Several factors were proposed, including narrow shelves along active continental margins, onshore sediment flux, more proximal sediment supply during sea-level lowstands, mass wasting along high-gradient continental slopes, and the occurrence of durable bedrock in adjacent catchments. In this study, we test whether we can predict shelf incision of submarine canyons from onshore and offshore parameters.</p> <p>We used maps of global elevation and bathymetry and analyzed them together with a global compilation of 5900 submarine canyon heads. The analysis relies on bagged regression trees that predict the distance of each canyon head from the shelf edge as a function of numerous candidate predictor variables. These variables describe spatial relations of river mouths and canyons, shelf geometry, continental slope gradient, as well as numerous terrestrial catchment properties. Moreover, we added 120 m to the elevation of the present-day topography to simulate a coastal landscape during the Last Glacial Maximum (LGM) and recalculated the topographic terrestrial parameters and the shelf width.</p> <p>The trained model explains 66% (R<sup>2</sup>) of the variance within the data set with a root mean square error (RMSE) of 31 km and a mean absolute error (MAE, less sensitive to outliers) of 17 km. The highest predictor importance is consistently reported for the weighted distance from canyon heads to the adjacent river mouths during the LGM and the present-day catchment gradient. We find no significant influence of shelf width, continental slope gradient and sediment load, and the moderate fit of the model indicates that we are still missing one or more important controls on the spatial location of canyon heads. Our predictions may be refined by including a more detailed assessment of catchment lithologies, locations of submarine groundwater discharge, locations of tectonic faults, and longshore current directions. Notwithstanding, we conclude that our model identifies important controls on the spatial occurrence and shelf incision of submarine canyons and sorts out much debated but seemingly unimportant variables.  </p>

Quantifying environmental signal propagation and preservation in ancient sediment routing systems using field data

2021 ◽  
Author(s):  
Robert Duller ◽  
Stephan Toby ◽  
Silvio De Angelis ◽  
Kyle Straub
Keyword(s):  
Temporal Resolution ◽  
Numerical Models ◽  
Signal Propagation ◽  
Sediment Flux ◽  
Threshold Condition ◽  
Environmental Signals ◽  
Sediment Routing ◽  
Environmental Signal ◽  
Spatio Temporal

<p>The assertion that stratigraphy will store environmental signals, such as sediment flux signals related to paleoclimate and tectonics, is debatable because that same stratigraphy can also store signals of autogenic processes that overprint and replace allogenic signals (“shred”). To establish the likelihood that strata will contain allogenic signals, the focus should be on quantifying autogenic processes. Models show that stratigraphic storage of allogenic sediment flux signals will only take place if it exceeds a threshold condition set by autogenic processes. This is supported by experimental and numerical models but its validation is hindered by low spatio-temporal resolution of stratigraphic datasets. We address this by reformulating a theoretical framework that dispenses with the need for exquisite temporal resolution. To demonstrate the applicability of our approach we explore the potential for environmental signal propagation and preservation in two ancient field systems: a small Pleistocene delta in Greece and a larger Eocene sediment routing system in the Spanish Pyrenees. This work demonstrates how short-term system dynamics can be integrated with long-term basin dynamics to provide a framework that assesses the capacity of sedimentary systems to store environmental signals.</p>

scholarly journals Which Drivers Control the Suspended Sediment Flux in a High Arctic Glacierized Basin (Werenskioldbreen, Spitsbergen)?

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1408
Author(s):  
Elżbieta Łepkowska ◽  
Łukasz Stachnik
Keyword(s):  
Suspended Sediment ◽  
High Arctic ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Mineral Matter ◽  
Suspended Sediment Transport ◽  
Positive Trend ◽  
Precipitation Trend ◽  
Data Set ◽  
Active Season

A unique data set of suspended sediment transport from the Breelva, which drains the Werenskioldbreen (Southwestern Spitsbergen), is reported for the period 2007–2012. This basin is thoroughly described hydrologically, glaciologically, and chemically. However, until now there was a lack of full recognition of mechanical denudation. This study extends the information on quantitative suspended sediment load (SSL), amounting to 37.30–130.94 kt per year, and also underlines the importance of its modification by high discharge events, triggered by intense snowmelt or heavy rainfall. The large floods during the hydrologically active season transported even 83% of the total SSL. The variability of the SSL is controlled by glacial storage and release mechanisms. Particularly interesting is the second half of the hydrologically active season when intense rainfall events plays a key role in shaping the sediment supply pattern. The main source of fine mineral matter is the basal moraine, drained by subglacial outflows. Their higher mobilization occurs when the hydrostatic pressure increases, often as a result of rainwater supply to the glacier system. An increasing precipitation trend for Hornsund fjord region determines a positive trend predicted for sediment flux.

Transient landscape response to abrupt precipitation increase at the Pleistocene-Holocene transition, offshore Sumatra

2021 ◽  
Author(s):  
Sarah Mosser ◽  
Anne Bernhardt ◽  
Mahyar Mohtadi ◽  
Tilmann Schwenk
Keyword(s):  
High Resolution ◽  
Time Scale ◽  
Landscape Evolution ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Sediment Routing ◽  
Precipitation Increase ◽  
Compositional Changes

<p>Active continental margins play a major role in exporting terrestrial sediment to the oceans. Yet, the response of a sediment-routing system to a specific climate change is poorly quantified. The terrestrial-to-marine sediment-routing systems on West Sumatra can be used as a natural laboratory to quantify these changes. Rivers efficiently deliver sediment from the high-relief Barisan mountains to the enclosed marine forearc Mentawai Basin along this active subduction margin. The Holocene climatic history of the region is well known and shows an abrupt precipitation increase at the Pleistocene-Holocene transition (~12 ka BP) as recorded previously in δ<sup>18</sup>O time-series measured on planktonic foraminifera.</p><p>Here we analyze multiple late Quaternary sediment records spanning the last 14 ka from the Mentawai Basin, offshore Sumatra. We use volumetric sediment budgets and multivariate statistics on high-resolution elemental compositions to assess changes in sediment flux and composition based on ~150 km of high-resolution sub-bottom sediment profiles (covering 435 km²) and six sediment cores. Radiocarbon ages were taken at every ~35 cm within the sediment cores.</p><p>Our results, from sediment budget calculation and sedimentation rates within the cores, show that absolute rates of sediment supply to the marine forearc basin remained constant throughout the Holocene (542-566 g/m²/yr, 68% quantile, 0.1 and 0.2 cm/yr, respectively). However, the sediment composition varies drastically with comparable patterns all over the basin. The compositional changes are characterized by an 8000-year damped oscillation between terrestrial clastic (Al, Si, Ti, Zr, Fe, K, Rb) and marine authigenic (Ca, Sr) sediment supply. From ~12 to 8 ka BP, the relative amount of clastic rock-forming elements is increasing, then decreasing from ~8 to 4 ka BP, and finally increasing again from 4 ka BP to the present. Using a dynamical system modeling approach, we link the beginning of this oscillation to the abrupt precipitation increase at the interglacial transition at ~ 12 ka BP. We interpret the oscillation to reflect a persistent erosional feedback between physical and chemical weathering caused by ongoing landscape adaptation to the abrupt Pleistocene-Holocene transition. The total amount of sediment accumulation, however, does not follow this trend. Thus, the sedimentary composition shows ongoing landscape transience, whereas the uniform sediment accumulation rates imply a landscape in steady state.</p><p>These results have two major implications for future landscape evolution: a) the time scale of landscape transience far exceeds the time scale of abrupt climate transition, b) in this study, the sediment flux to the ocean floor does not mirror landscape transience because the excess terrestrial clastic sediment is compensated by decreased deposition of marine carbonates. These implications call for the implementation of compositional changes of exported sediments into landscape evolution models since so far most landscape models focus on the amount of exported sediment.</p>

scholarly journals Morphodynamic limits to environmental signal propagation across landscapes and into strata

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Stephan C. Toby ◽  
Robert A. Duller ◽  
Silvio De Angelis ◽  
Kyle M. Straub
Keyword(s):  
Signal Propagation ◽  
Sediment Flux ◽  
Scale Analysis ◽  
Field Scale ◽  
Short Term ◽  
Environmental Forcing ◽  
Environmental Signals ◽  
Sediment Routing ◽  
Environmental Signal ◽  
Landscape Response

AbstractThe sedimentary record contains unique information about landscape response to environmental forcing at timescales that far exceed landscape observations over human timescales. However, stochastic processes can overprint and shred evidence of environmental signals, such as sediment flux signals, and so inhibit their transfer to strata. Our community currently lacks a quantitative framework to differentiate between environmental signals and autogenic signals in field-scale analysis of strata. Here we develop a framework and workflow to estimate autogenic thresholds for ancient sediment routing systems. Crucially these thresholds can be approximated using measurements that are readily attainable from field systems, circumventing the low temporal resolution offered by strata. This work demonstrates how short-term system dynamics can be accessed from ancient sediment routing systems to place morphodynamic limits on environmental signal propagation across ancient landscapes and into strata.

scholarly journals Tracking the <sup>26</sup>Al/<sup>10</sup>Be source-area signal in sediment-routing systems of arid central Australia

2018 ◽  
Author(s):  
Martin Struck ◽  
John D. Jansen ◽  
Toshiyuki Fujioka ◽  
Alexandru T. Codilean ◽  
David Fink ◽  
...  
Keyword(s):  
Source Area ◽  
Stream Sediments ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Environmental Signals ◽  
Source Areas ◽  
Sediment Routing ◽  
Aeolian Dunes ◽  
Central Australia ◽  
Cosmogenic 10Be

Abstract. Sediment-routing systems continuously transfer information and mass from eroding source areas to depositional sinks. Understanding how these systems alter environmental signals is critical when it comes to inferring source-area properties from the sedimentary record. We measure cosmogenic 10Be and 26Al along three large sediment-routing systems (~ 100,000 km2) in central Australia with the aim of tracking downstream variations in 26Al/10Be inventories and to identify the factors responsible. By comparing 56 new cosmogenic 10Be and 26Al measurements in stream sediments with matching data (n = 55) from source areas, we show that 26Al/10Be inventories in hillslope bedrock and soils set the benchmark for relative downstream modifications. Lithology is the primary determinant of erosion-rate variations in source areas and despite sediment mixing over hundreds of kilometres downstream a distinct lithological signal is retained. Postorogenic ranges yield catchment erosion rates of ~ 6–11 m/m.y. and silcrete-dominant areas erode as slow as ~ 0.2 m/m.y. 26Al/10Be inventories in stream-sediments reveal overall downstream-increasing minimum cumulative burial terms up to ~ 1.1 m.y. but more generally ~ 400–800 k.y. The magnitude of the burial signal correlates with increasing sediment cover downstream and reflects assimilation from storages with long exposure histories, such as alluvial fans, desert pavements, alluvial plains, and aeolian dunes. We propose that the tendency for large alluvial rivers to mask their 26Al/10Be source-area signal differs according to geomorphic setting. Signal preservation is favoured by i) high sediment supply rates, ii) high mean runoff, and iii) a thick sedimentary basin pile. Conversely, signal masking prevails in landscapes of i) low sediment supply, ii) discontinuous sediment flux, and iii) juxtaposition of sediment storages with notably different exposure histories.

scholarly journals Global estimation of burned area using MODIS active fire observations

2006 ◽  
Vol 6 (4) ◽  
pp. 957-974 ◽  
Author(s):  
L. Giglio ◽  
G. R. van der Werf ◽  
J. T. Randerson ◽  
G. J. Collatz ◽  
P. Kasibhatla
Keyword(s):  
Vegetation Cover ◽  
Regression Trees ◽  
The United States ◽  
Tree Cover ◽  
Burned Area ◽  
Data Set ◽  
Active Fire ◽  
Terra Modis ◽  
Good Agreement ◽  
Area Data

Abstract. We present a method for estimating monthly burned area globally at 1° spatial resolution using Terra MODIS data and ancillary vegetation cover information. Using regression trees constructed for 14 different global regions, MODIS active fire observations were calibrated to burned area estimates derived from 500-m MODIS imagery based on the assumption that burned area is proportional to counts of fire pixels. Unlike earlier methods, we allow the constant of proportionality to vary as a function of tree and herbaceous vegetation cover, and the mean size of monthly cumulative fire-pixel clusters. In areas undergoing active deforestation, we implemented a subsequent correction based on tree cover information and a simple measure of fire persistence. Regions showing good agreement between predicted and observed burned area included Boreal Asia, Central Asia, Europe, and Temperate North America, where the estimates produced by the regression trees were relatively accurate and precise. Poorest agreement was found for southern-hemisphere South America, where predicted values of burned area are both inaccurate and imprecise; this is most likely a consequence of multiple factors that include extremely persistent cloud cover, and lower quality of the 500-m burned area maps used for calibration. Application of our approach to the nine remaining regions yielded comparatively accurate, but less precise, estimates of monthly burned area. We applied the regional regression trees to the entire archive of Terra MODIS fire data to produce a monthly global burned area data set spanning late 2000 through mid-2005. Annual totals derived from this approach showed good agreement with independent annual estimates available for nine Canadian provinces, the United States, and Russia. With our data set we estimate the global annual burned area for the years 2001-2004 to vary between 2.97 million and 3.74 million km2, with the maximum occurring in 2001. These coarse-resolution burned area estimates may serve as a useful interim product until long-term burned area data sets from multiple sensors and retrieval approaches become available.

Feasibility of sedimentation strategies for the Mekong delta to counterbalance relative sea-level rise

2021 ◽  
Author(s):  
Frances E. Dunn ◽  
Philip S. J. Minderhoud
Keyword(s):  
Land Use ◽  
Sea Level Rise ◽  
Sea Level ◽  
Mekong Delta ◽  
Sediment Deposition ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Relative Sea Level ◽  
Fluvial Sediment ◽  
Relative Sea Level Rise

&lt;p&gt;As one of the largest deltas in the world, the Mekong delta is home to over 17 million people and supports internationally important agriculture. Recently deposited sediment compacts and causes subsidence in deltas, so they require regular sediment input to maintain elevation relative to sea level. These processes are complicated by human activities, which prevent sediment deposition indirectly through reducing fluvial sediment supply and directly through the construction of flood defence infrastructure on deltas, impeding floods which deliver sediment to the land. Additionally, anthropogenic activities increase the rate of subsidence through the extraction of groundwater and other land-use practices.&lt;/p&gt;&lt;p&gt;This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise.&lt;/p&gt;

Sediment slugs: large-scale fluctuations in fluvial sediment transport rates and storage volumes

1995 ◽  
Vol 19 (4) ◽  
pp. 500-519 ◽  
Author(s):  
A.P. Nicholas ◽  
P.J. Ashworth ◽  
M.J. Kirkby ◽  
M.G. Macklin ◽  
T. Murray
Keyword(s):  
Sediment Transport ◽  
Sediment Supply ◽  
Fluvial Systems ◽  
Event Scale ◽  
Fluvial Sediment ◽  
Sediment Routing ◽  
Basin Scale ◽  
Wide Range ◽  
And Storage ◽  
Fluvial Sediment Transport

Variations in fluvial sediment transport rates and storage volumes have been described previously as sediment waves or pulses. These features have been identified over a wide range of temporal and spatial scales and have been categorized using existing bedform classifications. Here we describe the factors controlling the generation and propagation of what we term sediment slugs. These can be defined as bodies of clastic material associated with disequilibrium conditions in fluvial systems over time periods above the event scale. Slugs range in magnitude from unit bars (Smith, 1974) up to sedimentary features generated by basin-scale sediment supply disturbances (Trimble, 1981). At lower slug magnitudes, perturbations in sediment transport are generated by local riverbank and/or bed erosion. Larger-scale features result from the occurrence of rare high- magnitude geomorphic events, and the impacts on water and sediment production of tectonics, glaciation, climate change and anthropogenic influences. Simple sediment routing functions are presented which may be used to describe the propagation of sediment slugs in fluvial systems. Attention is drawn to components of the fluvial system where future research is urgently required to improve our quantitative understanding of drainage-basin sediment dynamics.

scholarly journals Conceptual model of sedimentgraph from flood events in a small agricultural watershed

2008 ◽  
Vol 39 (1) ◽  
pp. 49-57 ◽  
Author(s):  
Kazimierz Banasik ◽  
J. Mitchell
Keyword(s):  
Conceptual Model ◽  
Suspended Sediment ◽  
Sediment Concentration ◽  
Agricultural Watershed ◽  
Sediment Flux ◽  
Flood Events ◽  
Rainfall Events ◽  
Sediment Routing ◽  
Suspended Sediment Flux ◽  
Lag Times

Conceptual model of sedimentgraph from flood events in a small agricultural watershed A procedure for predicting the sediment graph (i.e. the suspended sediment flux), from a small river catchment by heavy rainfall, has been developed using the concept of an instantaneous unit hydrograph (IUH) and dimensionless sediment concentration distribution (DSCD). A formula for instantaneous unit sedimentgraph (IUSG) is presented, and a procedure for estimating the sediment routing coefficient, which is a key parameter of the IUSG, based on measured data of rainfall-runoff-suspended sediment is applied. Field data from a small, field sized agricultural basin, lacated in center of Illinois has been used for analizing lag times for runoff (LAG) and sediment yield (LAGs). Assumptions about sediment generated during rainfall events are discussed.

Relating sediment supply to the morphological and hydro-meteorological characteristics of torrent catchments

2021 ◽  
Author(s):  
Maxime Morel ◽  
Guillaume Piton ◽  
Caroline Le Bouteiller ◽  
Alexandre Mas ◽  
Guillaume Evin
Keyword(s):  
Sediment Yield ◽  
Prediction Method ◽  
Original Data ◽  
Sediment Supply ◽  
Set Covering ◽  
Sediment Retention ◽  
Multivariate Statistical ◽  
Catchment Basin ◽  
Mountain Areas ◽  
Data Set

&lt;p&gt;In mountain areas, the quantification of sediment yield is essential in the diagnosis of a torrential watershed. The objective of this study is to present a prediction method based on multivariate statistical models calibrated from an original data set covering nearly 130 torrential basins in the Northern French Alps. Data on sediment yield and occurrence of torrential events were collected on these catchments thanks to registries from sediment retention basins (average monitoring period of 20 years) and historical archives of the catchment basin managers. On these catchments, several morphological and hydro-meteorological characteristics were calculated (e.g. geological and sediment connectivity indices, the rate of connected eroding areas in the catchment, the Melton index, the slope of the fan, etc.) in order to relate them to sediment production and the frequency of occurrence of torrential events. These models allow the estimation of quantiles of the sediment yield in small torrent catchments. These models could be useful to evaluate sediment yield and the occurrence of torrential events on catchment not equipped with sedimentation structures.&lt;/p&gt;

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