Transport of particles across continental shelves

Abstract

Transport of participate material across continental shelves is well demonstrated by the distributions on the seabed and in the water column of geological, chemical, or biological components, whose sources are found farther landward or farther seaward. This paper addresses passive (incapable of swimming) particles and their transport across (not necessarily off) continental shelves during high stands of sea level. Among the general factors that influence across‐shelf transport are shelf geometry, latitudinal constraints, and the timescale of interest. Research studies have investigated the physical mechanisms of transport and have made quantitative estimates of mass flux across continental shelves. Important mechanisms include wind‐driven flows, internal waves, wave‐orbital flows, infragravity phenomena, buoyant plumes, and surf zone processes. Most particulate transport occurs in the portion of the water column closest to the seabed. Therefore physical processes are effective where and when they influence the bottom boundary layer, causing shear stresses sufficient to erode and transport particulate material. Biological and geological processes at the seabed play important roles within the boundary layer. The coupling of hydrodynamic forces from currents and surface gravity waves has a particularly strong influence on across‐shelf transport; during storm events, the combined effect can transport particles tens of kilometers seaward. Several important mechanisms can cause bidirectional (seaward and landward) transport, and estimates of the net flux are difficult to obtain. Also, measurements of across‐shelf transport are made difficult by the dominance of along‐shelf transport. Geological parameters are often the best indicators of net across‐shelf transport integrated over time scales longer than a month. For example, fluvially discharged particles with distinct composition commonly accumulate in the midshelf region. Across‐shelf transport of particulate material has important implications for basic and applied oceanographic research (e.g., dispersal of planktonic larvae and particle‐reactive pollutants). Continued research is needed to understand the salient mechanisms and to monitor them over a range of timescales.

Clinoform development by advection‐diffusion of suspended sediment: Modeling and comparison to natural systems

“…The latter is the consequence of more rapid seaward expansion of the flow field as the relief between the topset and bottomset increases basinward. This type of foreset steepening is clearly observed in clinoforms of the Lake Mead delta (Figures 3a and 3e), where repeat surveys were carried out since the damming of the lake, showing progressively steeper clinoform fronts advancing over the Colorado River valley (mean gradient of 0.02ø; Table 1 In natural systems, say over a continental shelf or enclosed lake basin, near-bed shear stresses generated by stirring waves and tides will also diminish with increasing water depth [Nittrouer and Wright, 1994;Dyer, 1989]. The net transport of sediment due to waves over a period of time can be negligible, but the important effect of wave motion stirring is that once in suspension, sediments will be advected by even very small lateral currents [Grant and Madsen, 1979].…”

Fate of sediments delivered to the sea by Asian large rivers: Long-distance transport and formation of remote alongshore clinothems

“…It is the nearshore oceanographic processes that transport fluvial sediments across the shallow-water topset area to the deep-water bottomsets that result in rapid accumulation on the middle shelf and development of the sigmoid-shaped ("S") clinoform (i.e., Kuehl et al, 1986). Important mechanisms that influence across-shelf sediment transport include wind-driven flows, internal waves, wave-orbital flows, infragravity phenomena, buoyant plumes, and surf-zone processes (Nittrouer and Wright, 1994).…”

Using MODIS Terra 250 m imagery to map concentrations of total suspended matter in coastal waters

“…The most common limitation is an instrument's spatial or ground resolution. For example, the nominal spatial resolution of data from the AVHRR (Advanced Very High Resolution Radiometer), and SeaWiFS (Sea-viewing Wide Field-of-view Sensor) instruments is 1 km, an area typically too large to examine coastal horizontal gradients, particularly in estuaries and bays (Nittrouer and Wright, 1994 define instrument deployment parameters (e.g., time flown, area covered, and spatial resolution), most airborne systems are expensive to operate and processing the data is often costly and difficult. Generally, the limited availability of remote sensing data and processing software has also restricted the widespread application of remote sensing to coastal studies (Miller 1993 The use of remote sensing to map suspended sediment concentration is well established for a variety of water types.…”