Matter sedimentary particulate

In order to study aspects of the fate of these sediments, we have studied sedimentary particulate matter from sites in the estuary of the Rhine downstream from Rotterdam, from several dredging spoil dunqtsites offshore (Loswal Noord), and from sediments of the Flemish... 

Measurements of radionuclides and metals in marine sediments and particulate matter are conducted for a variety of purposes, including the determination of sedimentation rates, trace metal and radionuclide fluxes through the water column, enrichment of metals in specific phases of the sediments, and examination of new sedimentary phases produced after sediment deposition. Such studies address fundamental questions concerning the chronology of deep-sea and near-shore sedimentary deposits, removal mechanisms and cycling of metals in the ocean, and diagenesis within deep-sea sediments. 

Wakeham, S.G., and C. Lee. 1989. Organic geochemistry of particulate matter in the ocean The role of particles in oceanic sedimentary cycles. Organic Geochemistry 14 83-96. 

Particulate matter that reaches the seafloor becomes part of the blanket of sediments that lie atop the crust. If bottom currents are strong, some of these particles can become resuspended and transported laterally until the currents weaken and the particles settle back out onto the seafloor. The sedimentary blanket ranges in thickness from 500 m at the foot of the continental rise to 0 m at the top of the mid-ocean ridges and rises. Marine scientists refer to this blanket as the sedimentary column. Like the water column, the sediments contain vertical gradients in their physical and chemical characteristics. Similar to the vertical profile convention used in the water column, depth in the sediments is expressed as an increasing distance beneath the seafloor. 

It can be seen in Table 9.7 that the particulate load constitutes by far the most important contribution (88%) of total river discharge of materials to the ocean. The amount carried as solids should be increased by bed load transport, which usually is considered to be about 10% of the total suspended load (Blatt et al 1980). The mean chemical composition of river suspended matter closely approximates that of average shale (Table 9.8). This resemblance is expected because suspended solids in rivers are derived mainly from shales. Sedimentary rocks constitute about 66% of the rocks exposed at the Earth s surface fine-grained rocks, like shales, comprise at least 65% of the sedimentary rock mass. Thus, roughly 50% of surface erosion products come from shaly rocks. 

The identification of C-depleted (fi C values as low as -58 per mil) archeal cyclic biphytanes in particulate matter from the Black Sea, where more than 98% of the methane released from sediments is apparently oxidized anaerobically (Reeburgh et al., 1991), provides evidence for AMO in euxinic waters (Schouten et al., 2001). However, the same isotopically depleted compounds were not detected in the underlying sediments, suggesting that the responsible organisms are in low abundance and/or leave no characteristic molecular fingerprint in the sedimentary record. 

The Cu concentration of crustal rocks (32 34 p,g g ) is approximately equivalent to that for average soils (25 4 p,g g ). However, as the earth material is weathered and transported to streams-lakes-shaUow marine sediments there is a minimal enrichment in Cu concentration (39 = 34 = 43 p,g g ) (Table 4). And, as for Pb-Zn-Cd, riverine particulate matter is greatly enriched (100p,gg ) relative to the other sedimentary materials. While the Pb-Zn-Cd concentrations of deep-sea clay are enriched 1.5 times that of the continental sedimentary materials, Cu is enriched approximately five times. The substantial enrichment of Cu in oceanic pelagic clay relative to terrestrial earth materials is due to the presence of ubiquitous quantities of ferromanganese oxides in surficial ocean sediments (Drever, 1988). 

The Ni concentration of crustal rocks (58 53 p,g g ) is substantially greater than the average world soils (23 3 p,g g ), but essentially equal to continental sedimentary materials (49 13 p,gg ). Riverine particulate matter (90p,gg ) is nearly twice the Ni concentration of these continental sedimentary materials and deep-sea clay is nearly three times (230 p-g g ) that concentration. As noted for Cu, the substantial Ni enrichment of deep-sea clays is due to the presence of ferromanganese micronodules in the oxidized surficial sediment column (Drever, 1988). 

In these examples as well as for most aquatic sediments, the principal diagenetic reactions that occur in these sediments are aerobic respiration and the reduction of Mn and Fe oxides. Under the slower sedimentation conditions in natural lakes and estuaries, there is sufficient time (years) for particulate organic matter to decompose and create a diagenetic environment where metal oxides may not be stable. When faster sedimentation prevails, such as in reservoirs, there is less time (months) for bacteria to perform their metabohc functions due to the fact that the organisms do not occupy a sediment layer for any length of time before a new sediment is added (Callender, 2000). Also, sedimentary organic matter in reservoir sediments is considerably more recalcitrant than that in natural lacustrine and estuarine sediments as reservoirs receive more terrestrial organic matter (Callender, 2000). 

However, I2 and HOI are the likely intermediates formed by both abiotic and biotic processes during L oxidation. These intermediates, if formed, can be reduced back to I react with organic matter to form particulate or dissolved organic iodine (RI) compounds or be volatilized to the atmosphere as I2, HOI, or CH3I. Iodate can also react directly with humic material during reduction to form RI (58), but this reaction is more important in sedimentary environments and has not been documented in the photic zone. 

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