Sinking POC flux

The potential underestimation of Phaeocystis spp. carbon by only including cell carbon is thus not likely to be >40%. Based on measurements of vertical flux around 100 m depth from Antarctica, the coastal North Sea, North Norwegian fjords, the Barents Sea and the Arctic Ocean (Fig. 5), the average carbon contribution from Phaeocystis spp. to the POC flux will increase from 3% to <5% by including mucus carbon. Despite the lack of appropriate species-specific carbon conversion rates for all Phaeocystis species, the evidence clearly indicates that Phaeocystis spp. mucus, sinking as intact colonies with cells, is not significantly contributing to the total POC export. 

In Ullfjord, Phaeocystis comprised a major fraction of the sinking particles (Reigstad et al. 2000). Sedimentation of these cells may account for the high DMSP and POC fluxes and low POC/234Th ratio measured in the traps with the highest rates in Ullsfjord. 

Zooplankton actively swimming into sediment traps also serve as a source of error in flux measurements. It is impossible to differentiate these swimmers from zooplankton that have settled passively into the cup as part of the sinking POM flux. Swimmers may constitute as much as a quarter of the POC collected by the trap (Steinberg et al, 1998) and are generally removed from trap material prior to analysis. This introduces minimal error into the trap estimates of POC flux, as detrital zooplankton likely only comprise... 

Figure 14 Fluxes and composition of particulate organic carbon in the equatorial Pacific Ocean, (a) POC fluxes (mgm d ). (b) Corresponding fractions of amino acid, carbohydrate, lipid, and molecularly uncharacterized carbon (biochemical class-carbon as a percentage of total OC) in plankton, sediment traps (105 m, l,000m, >3,500 m) and surface sediment samples. The fraction of molecularly uncharacterized organic carbon (calculated as the difference between total OC and the sum of amino acid - - carbohydrate - - Upid) increases with more extensive degradation to become the major constituent in deeper POC samples (after Wakeham et al., 1997). (c) Calculated weight percentages of amino acid, carbohydrate, and lipid in plankton and in sinking (sediment trap) particles in the upper and lower water column as determined by solid-state C-NMR spectroscopy (source Hedges et al., 2001).

Deep seafloor communities are shaped by a number of key parameters that directly affect the nature and abundance of living organisms and their interactions with seafloor geochemistry. These parameters include (a) substratum type, (b) near-bottom hydrodynamic regime, (c) bottom-water oxygen concentration, (d) sinking particulate-organic-carbon (POC) flux, and (e) sediment redox conditions. Below, we describe these parameters and their variation in the northeastern abyssal Pacific. 

Buesseler et al. (1992b) proposed a method to circumvent these difficulties in comparing residence times. They argued that the deficiency in total " Th with respect to indicates a flux of " Th in association with particles sinking out of the euphotic zone. If the POC (or particulate organic nitrogen, PON)/ Th ratio of these sinking particles is known, a POC (or PON) flux can be calculated as ... 

Evidence for seasonal fluctuations in the export of sinking POM from the euphotic zone has been obtained from sediment trap studies. As shown in Figure 23.3, seasonal variations in the flux of sinking biogenic hard and soft parts are detectable even in the deep zone. Furthermore, interannual variations in POC and PIC production lead to similar shifts in the deepwater fluxes of these particles. 

Bloesch, J., and M. Sturm, Settling flux and sinking velocities of particulate phosphorus (PP) and particulate organic carbon (POC) in Lake Zug, Switzerland . In Sediments and Water Interactions, P. G. Sly, Ed., Springer, New York, 1986, pp. 481-490. 

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