Phosphorus Burial Fluxes

Mass accumulation rate (MAR) in the ECS varied from 2 to 0.05 g/(cm -yr). The maximum MAR appeared in the mouth of the Changjiang River, and the value generally decreased southward along the inner shelf and eastward offshore. Based on this valuable published data, Fang et al. (2007) calculated the phosphorus burial flux in the ECS. To facilitate the calculation, the calculated area is divided into five boxes estuary (box I), inner shelf (box II), middle shelf (boxes III and IV), and outer shelf (box V) (Fig. 4.43), according to the value of MAR in each box observed by Huh and Su (1999) and to the phosphorus content in surface sediments found by Fang et al. (2007). 

The total P concentration in the sediments in the ECS area remained within a narrow range, 14 23 pmol/g. Thus, the error in calculation caused by the variation in the total P concentration in sediments in different boxes was probably less than 20%. Table 4.14 (Fang et al., 2007) shows the values of the parameters used in the calculations and the calculated results. The 

Box Area (km=) Mass accum. rate (g/(cm yr)) P total cone, (jlmol/g) P accum. rate (Hmol/(cm yr)) P burial flux (xlO mol/yr)  

P burial flux was found to be in the range of 9.03xl0 26.68xl0 mol/yr (average 16.5x10 mol/yr) for the calculated area. 

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Phosphorus reservoir Phosphorus burial flux Method of determination (10 ° mol yr ) ... 

The revised, larger burial flux cannot be balanced by the dissolved riverine input alone. However, when the fraction of riverine particulate phosphorus that is believed to be released upon entering the marine realm is taken into account, the possibility of a balance between inputs and outputs becomes more feasible. Residence times estimated on the basis of phosphorus inputs that include this releasable riverine particulate phosphorus fall within the range of residence time estimates derived from phosphorus burial fluxes (Table 5). Despite the large uncertainties associated with these numbers, as evidenced by the maximum and minimum values derived from both input and removal fluxes, these updated residence times are all significantly shorter than the canonical value of 100 000 years. Revised residence times on the order of 10 000-17 000 y make phosphorus-perturbations of the ocean-atmosphere CO2... 

These estimates are favored by the author, and reflect the minimum sF and maximum sF fluxes given in Table 2. Because the reactive phosphorus contents of continental margin and abyssal sediments differ (see Table 2 and note d, below), these fluxes must be listed separately in order to calculate the whole-ocean reactive phosphorus burial flux. See note (j) in Table 2 for other published estimates of reactive-phosphorus burial flux. 

As noted in Table 2, between 40% and 75% of phosphorus buried in continental margin sediments is potentially reactive, and 90% to 100% of phosphorus buried in abyssal sediments is potentially reactive. The reactive phosphorus fraction of the total sedimentary phosphorus reservoir represents that which may have passed through the dissolved state in oceanic waters, and thus represents a true phosphorus sink from the ocean. The minimum reactive phosphorus burial flux was calculated as the sum of 0.4(sFjs) -I- 0.9 (sF ) the maximum reactive phosphorus burial flux was calculated as the sum of 0.75(sFes) -i- 1(sF ). Both the flux estimates and the % reactive phosphorus estimates have large uncertainties associated with them. 

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. 

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... 

Phosphorus Biogeochemistry and Cycling Current Research Table 4 Geochemical partitioning of reactive-P burial fluxes. 

Fig. 3.56. The burial fluxes of phosphorus at different periods in Jiaozhou Bay sediments (Li et ah, 2006) (With permission from Springer)...

Fig. 4.43. The area within the ECS was divided into five boxes for burial flux calculations. The five boxes representing different MAR area and phosphorus content are (I) estuary (II) inner shelf (III) middle shelf (IV) middle shelf (V) outer shelf (Fang et al., 2007) (With permission from Elsevier s Copyright Clearance Center)...

Carbon burial separates oxygen from carbon. It takes time for the reactants to get back together. Processes that increase the burial flux or increase the duration of burial thus increase the amount of oxygen in the air. I discuss the coupling of the carbonate cycle with the organic carbon cycle before discussing more traditional topics of the sites for carbon burial and the effect of phosphorus. 

Reservoir fluxes (F) represent the P-flux between reservoirs R1—R8 defined in Table 1. The sub-reservoir fluxes (sF) refer to the flux of phosphorus into the marine sediment portion of reservoir 1 via sediment burial,... 

Implications of these results are that phosphorus removed from the surface waters as biological flux is 30-65 times more hkely to come from upwelling than from rivers (1.3-3.0 x 10 /4.6 x 10 ), indicating that ocean circulation is far more important in regulating biological productivity than river inflow. Also, only 1 in 30-65 atoms of P that rains to the deep ocean is actually buried the rest are degraded in the deep and recycled back to surface waters. This results in a residence time for phosphorus with respect to burial of 30 000-65 000 y 30-65 times the ocean circulation rate. 

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