Burial efficiency

Anschutz, P., Zihong, S., Sundby, B., Mucci, A., and Gobeil, C. (1998). Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments. Limnol. Oceanogr. 43,53-64. 

The iron-based redox cycle depicted in Figure 18.9 provides an effective preconcentrating step for phosphorus by trapping remineralized phosphate in oxic sediments. The conversion of phosphorus from POM to Fe(lll)OOH to CFA is referred to as sink switching. Overall this process acts to convert phosphorus from unstable particulate phases (POM to Fe(lll)OOH) into a stable particulate phase (CFA) that acts to permanently remove bioavailable phosphorus from the ocean. This is pretty important because most of the particulate phosphate delivered to the seafloor is reminer-alized. Without a trapping mechanism, the remineralized phosphate would diffuse back into the bottom waters of the ocean, greatly reducing the burial efficiency of phosphorus. 

Some component of the terrestrial POM must be extremely nonreactive to enable a higher burial efficiency as compared to autochthonous POM. A possible candidate for this nonreactive terrestrial POM is black carbon. This material is a carbon-rich residue produced by biomass burning and fossil fuel combustion. Some black carbon also appears to be derived from graphite weathered from rocks. It is widely distributed in marine sediments and possibly carried to the open ocean via aeolian transport. 

Carbon and Phosphorus Burial Efficiencies. The estimate of diatom carbon demand (12-15 g/m2 per year) is consistent with the flux of carbon to the sediment surface. With sediment-trap fluxes corrected for resuspension, we measured a total annual deposition flux of 12.5 g of C/m2. In comparison, Eadie et al. (24) obtained 23 g of C/m2 for a 100-m station, based on three midsummer metalimnion deployments. Of our total, 83% of the carbon was associated with diatoms, and the primary diatom carbon flux was 10.3 g of C/m2. Thus, about 15-30% of the diatom carbon was regenerated in the water column during sedimentation. Approximately 10% of the diatom flux reached the sediment surface encapsulated in copepod fecal pellets the remaining 90% was unpackaged. 

Residence Times. Phosphorus residence times with respect to major depositional processes (see Tables II and IV) are summarized in Table VI. In comparison, the total-P residence time based on external loading is about 4.5 years. Residence times were calculated for a mean water-column depth of 85 m, and steady state was assumed. Although transport of P to the sediment surface by the combination of diatoms, calcite, and terrigenous material is relatively rapid, the low burial efficiency results in a relatively long residence time for total P (about 5 years). In comparison, the residence time for Pb is about 0.6 years (20). Thus, the response time for P changes with respect to loading should be on the order of 5-15 years. 

Huber C, Wachtershauser G (2006) a-hydroxy and a-amino acids under possible Hadean, volcanic origin-of-life conditions. Science 314 630-632 Huber H, Stetter KO (1998) Hyperthermophiles and their possible potential in biotechnology. J Biotechnol 64 39-52 Hurtgen MT, Arthur MA, Halverson GP (2005) Neoproterozoic sulfur isotopes, the evolution of microbial sulfur species, and the burial efficiency of sulfide as sedimentary pyrite. Geology 33 41-44 Husain V, Winkler O (2007) Semiclassical states for quantum cosmology. Phys Rev D 75 024014... 

The first evidence for enhanced preservation with high net sediment accumulation rates in oceanic environments was presented in the context of organic burial efficiency—to... 

Organic burial efficiency the accumulation rate of organic matter below the active zone of diagenesis divided by the organic matter flux to surface sediments. 

The magnitude of this loss is thus substantial, and comparable to flux estimates for the delivery of terrigenous OC to the oceans (Figure 1). However, while the above studies imply low burial efficiencies for fluvial POM in deltaic environments, it is uncertain whether the apparent losses of riverine POM reflect its complete mineralization or export to the ocean interior either in dissolved or particulate form (Edmond et al., 1981). Moreover, the extent of terrestrial OC export and burial from river systems that do not form deltaic deposits is less weU constrained. 

Betts J. N. and Holland H. D. (1991) The oxygen content of bottom waters, the burial efficiency of organic carbon, and the regulation of atmospheric oxygen. Global Planet. Change 5, 5-18. 

The range of riverine suspended particulate matter that may be solubilized once it enters the marine realm (e.g., the so-called reactive-F ) is derived from three sources. Colman and Holland (2000) estimate that 45% may be reactive, based on RSPM-P compositional data from a number of rivers and estimated burial efficiency of this material in marine sediments. Bemer and Rao (1994) and Ruttenberg and Canfield (1994) estimate that 35% and 31% of RSPM-P is released upon entering the ocean, based on comparison of RSPM-P and adjacent deltaic surface sediment phosphorus in the Amazon and Mississippi systems, respectively. Lower estimates have been published (8% Ramirez and Rose (1992) 18% Froelich (1988) 18% Compton et al. (2000). Higher estimates have also been published (69% Howarth et al. (1995). 

Mobilization of sedimentary phosphorus by microbial activity during diagenesis causes dissolved phosphate buildup in sediment pore waters, promoting benthic efflux of phosphate to bottom waters or incorporation in secondary authigenic minerals. The combined benthic flux from coastal (sFcbf) and abyssal (sFabf) sediments is estimated to exceed the total riverine-P flux (F24(d+p>) to the ocean. Reprecipitation of diagenetically mobilized phosphorus in secondary phases significantly enhances phosphorus burial efficiency, impeding return of phosphate to the water column (see Section 8.13.3.3.2). Both processes impact the... 

Fig. 12.12 Simplified representation of the burial efficiency of reactive substances (e.g. dependent on the...

In general, the diffusive fluxes (DF) of different forms of nitrogen in the sediments of the same region are the same. The nitrogen burial efficiency in different regions would be accounted for by the formula (Table 3.19, Lu et al., 2002)... 

Table 3.19. The nitrogen burial efficiency in the three regions surface sediments of the SYS...

Apparentiy, the product of/cs and/s must be small to create low S/C ratios. Assuming an S/C ratio of 1/30, which is the mean of TS/TOC of our samples, one can get a value of 0.24 for sfn- This value is considerably lower than that (>2) predicted for normal marine sediments at similar (Morse and Berner, 1995). There are two possibilities that may result in this low value. The first possibility, opting for a normal value of/cs, requires a very low value of/g, which is caused probably by a high rate of sulfide re-oxidation the other requires a low value of /cs under a normal burial efficiency (/b). We discuss the two possibilities below. 

---