Sediment traps

Rivers transport suspended sediments derived from the disintegration of basin surface layers. With reduced velocity, sediment is deposited in the river channel. The finest material is carried to the sea. It has been estimated that the average mechanical denudation rate for continents is 0.056 mm year (35). This is based on a total suspended load of 13.5 x 10 metric tons year (S). Presently, about two-thirds of the world s total suspended sediment load derives from Southern Asia and large Pacific Islands. Berner has estimated the increase in sediment loss in the U.S. and world since prehuman times to be approximately 200% (35). Current estimated erosion rate from the major land forms is provided in Table I. The relatively recent construction of large sediment trapping dams that normally caused sediment to be deposited in river valleys or transported to the ocean has drastically reduced sediment yields in great rivers. 

The quantity of primary production that is exported from the upper ocean is said to be equivalent to new production (18, 19) New primary production is that associated with allocthonous nutrients (i.e., those upwelled or mixed into the euphotic zone or input via rivers and rain). In order for steady state to be maintained, an equivalent flux out of the euphotic zone is required. Earlier studies (19) suggested that sediment-trap measurements of particulate organic carbon (POC) flux were equivalent to new primary production however, recently it has become clear that these measurements probably represent only a... 

Sediment trap studies in the open ocean show that the flux of organic carbon at any depth is directly proportional to the rate of primary productivity in the surface water and inversely proportional to the depth of the water column (Suess, 1980) ... 

Fig. 10-15 Organic carbon fluxes with depth in the water column normalized to mean annual primary production rates at the sites of sediment trap deployment. The undulating line indicates the base of the euphotic zone the horizontal error bars reflect variations in mean annual productivity as well as replicate flux measurements during the same season or over several seasons vertical error bars are depth ranges of several sediment trap deployments and uncertainities in the exact depth location. (Reproduced with permission from E. Suess (1980). Particulate organic carbon flux in the oceans - surface productivity and oxygen utilization, Nature 288 260-263, Macmillan Magazines.)...

Figure 5. Comparison between fluxes measured in shallow sediment traps and those calcnlated for the same depth and time from the " Th deficit in the overlying water colnmn. The data were compiled from many studies and the right-hand scale shows the factor of positive or negative offset between the two data sets. Significant differences are common and are linked to the varions assumptions and constraints of the two approaches for measnring POC finx. [Reprinted from Nature, Vol. 353, Buesseler, pp. 420-423, 1991, Macmillan Publishers Ltd.]...

The fluxes of POC determined by the " Th method applied to the world s oceans are summarized in Table 1. Where possible we have tabulated the ratio of Th-derived POC export to independent estimates of primary production. As noted above, this ratio, termed the 77i ratio (Buesseler 1998), is important in the euphotic zone carbon balance as it represents the leakage of POC out of the euphotic zone (The ThE ratio is so named to evoke the e ratio, which is defined as the ratio of POC flux measured with sediment traps to primary production). 

B Bottle IM In situ pump/membrane filter (53, 70 p,m) 1C In situ pump/cartridge filter (0.5,1 am) ST sediment trap 5°S-5°Nand25°W-5°E... 

Broecker WS, Kaufman A, Trier RM (1973) The residence time of Thorium in surface sea-water and its implications regarding the fate of reactive pollutants. Earth Planet Sci Lett 20 35-44 Buesseler KO (1991) Do upper-ocean sediment traps provide an accurate record of particle flux Nature 353 420-423... 

Buesseler KO, Charette MA (2000) Commentary on How accurate are the based particulate residence times in the ocean by G. Kim, N. Hussain and T. Church. Geophys Res Lett 27 1939-1940 Buesseler KO, Steinberg DK, Michaels AF, Jonson RJ, Andrews JE, Valdes JR, Price JF (2000) A comparison of the quantity and quality of material caught in a neutrally buoyant versus surface-tethered sediment trap. Deep-Sea Res 147 277-294... 

Heussner S, Cherry RD, Heyraud M (1990) Po-210 and Pb-210 in sediment trap particles on a Mediterranean continental margin. Cont. Shelf Res 10 989-100 Heyraud M, Cherry RD (1983) Correlation of Po-210 and Pb-210 enrichments in the sea-surface microlayer with neuston biomass. Cont Shelf Res 1 283-293 Honeyman BD, Santschi PH (1989)The role of particles and colloids in the transport of radionuclides and trace metals in the oceans. In Environmental particles. Buffle J, van Leewen HP (eds) Lewis Publishers, Boca Raton, p 379-423... 

Vxh can then be compared to Pph to assess the magnitude of lateral °Thxs advection, or with the measured sediment-trap °Thxs flux to assess the trapping efficiency. 

A correlation exists between the flux of particles collected by sediment traps and the ( Paxs/ °Thxs) of these particles (Kumar et al. 1995). In pelagic regions, particulate material settling through the deep sea is almost entirely of biogenic origin. A... 

Much of the geographic variability in sedimentary ( Paxs/ °Thxs) observed in modern sediments may be explained by variability in the composition of biogenic particles arising from variability in the structure of the planktonic ecosystem. This can be inferred from the composition-dependence of F(Th/Pa) (Fig. 8), and is shown explicitly by the relationship between sediment trap ( Paxs/ °Thxs) and the opal/calcite ratio of the trapped particles (Fig. 9). Sediment trap ( Paxs/ °Thxs) also exhibits a positive relationship with the mass flux of particles, but the correlation is poorer than that with particle composition (Fig. 9). Indeed, the relationship between particulate ( Paxs/ °Thxs)... 

Figure 9. A log-log plot of the annual average ( Paxs/ °Thxs) as a function of sediment trap particle composition, and as a function of total mass flux. Note the importance of particle composition on the ( Paxs/ °Thxs) of trapped material, with a high opal fraction leading to higher ratios. Note also the poor relationship between ( Paxs/ °Thxs) and mass flux. This data was compiled by Chase et al. (in press-b) and includes data from that study, as well as from Lao et al. (1993), Scholten et al. (2001), and Yu et al. (2001a).

Cochran JK, Krishnaswami S (1980) Radium, thorium, uranium and °Pb in deep-sea sediments and sediment pore waters from the north equatorial Pacific. Am J Sci 280 849-889 Cochran JK, Masque P (2003) Short-lived U/Th-series radionuchdes in the ocean tracers for scavenging rates, export fluxes and particle dynamics. Rev Mineral Geochem 52 461-492 Colley S, Thomson J, Newton PP (1995) Detailed °Th, Th and °Pb fluxes recorded by the 1989/90 BQFS sediment trap time-series at 48°N, 20°W. Deep-Sea Res 42(6) 833-848... 

Scholten JC, Fietzke J, Vogler A, Rutgers van der Loeff MM, Mangini A, Koeve W, Waniek J, Staffers P, Antia A, Kuss J (2001) Trapping efficiencies of sediment traps from the deep Eastern North Atlantic The °Th calibration. Deep-Sea Res II 48 2383-2408... 

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