Benthic flux measurements

Fl ur6 3 3 Iron concentrations in surface waters versus distance offshore on a transect from central California to Hawaii. Elrod et al. (2004) used benthic flux measurements and these water column data to make a case for transport of Fe from shelf sediments out into the open ocean gyre. Elrod et al. (2004), Geophysical Research Letters 31 L12307. 

Jahnke (1996) extrapolated available benthic-flux measurements from landers and pore-water determinations into a global map of benthic oxygen flux for sediments deeper than 1,000 m. When compared with global primary production rates and sediment-trap particle fluxes, these data indicate that 1% of the primary production reaches deep-sea sediments and is oxidized there (Table 3). Also —45% of respiration in the ocean below 1,000 m occurs within sediments. 

There is, however, a fly in the ointment. Benthic flux measurements made by deploying chambers... 

CovELLi S, Faganeli j, Horvat M and Brambati A (1999) Pore water distribution and benthic fluxes measurements of mercury and methylmercury in the Gulf of Trieste (northern Adriatic Sea). Estuar Coast Shelf Sci 48 415 —428. 

Study included flux measurements at sites characterized by six different sediment-plant types Enteromorpha sp., phytoplankton detritus, seagrass + epiphytes, seagrass, Gradlaria sp., and benthic microalgae. Incubations were done in the light and dark net release rates are reported. 

Upon settling to the surface sediments, trace metals can be recycled back into the dissolved phase and act as a source to the deep ocean. Pore-water concentrations of trace metals can be significantly higher than that observed in the overlying water column. Elevated pore-water concentrations suggested a potential for benthic fluxes of dissolved metals out of the sediment, which has been verified by direct measurements (Elderfield et al., 1981 Westerlund et al., 1986). 

Archer D. E. and Devol A. (1992) Benthic oxygen fluxes on the Washington shelf and slope a comparison of in situ microelectrode and chamber flux measurements. Limnol. Oceanogr. 37, 614-629. 

Understanding of sediment diagenesis and benthic fluxes has evolved with advances in both experimental methods and modeling. Measurements of chemical concentrations in sediments, their associated pore waters and fluxes at the sediment-water interface have been used to identify the most important reactions. Because transport in pore waters is usually by molecular diffusion, this medium is conducive to interpretation by models of heterogeneous chemical equilibrium and kinetics. Large chemical changes... 

Figure 6 Oxygen fluxes determined from benthic lander measurements (X) and calculated from microelectrode oxygen gradients measured in the top few centimeters of pore waters (O) as a function of latitude and depth on the northwest US continental margin. Error bars are the standard deviation of replicate measurements (after Archer and Devol, 1992).

Figure 11 Relationship between the rain of opal and the burial flux of opal normalized to (sedimentation rate (cm kyr )). The figure is taken from Sayles et al. (2001, figure 14(b)). The rain of opal is measured either with sediment traps (direct) or estimated from the Si02 reminerahzation flux plus opal burial flux, as indicated below. The linear regressions shown use different data sets as indicated. Where the data are designated A, they are from Sayles et al. (2001). (D/L rain—Dymond and Lyle (1994) R rain—Rabouille et al. (1997) A rain—uses benthic Si02 remineralization and °Th-normalized sedimentation rates and opal burial rates (Sayles et al., 2001.) A trap(l k) uses particle flux measured in sediment traps at 1 km depth (Honjo et al, 2000) together with °Th-normalized sedimentation rates and opal burial rates. AESOPS —uses Si02 remineralization together with C-derived...

Observations from benthic flux experiments in which Ai and Ca fluxes have been measured both below and above the calcite saturation horizon confirm the effect of organic matter degradation on the dissolution of CaCOs in most but not all situations. Jahnke and Jahnke... 

Measurements of Diffusive Fluxes. Benthic chamber experiments were carried out by using an automatic flux chamber (sediment lander). Our lander followed closely the design of Devol (43). The two benthic flux chambers have an area of 400 cm2 each. They penetrated the sediment to a... 

Benthic flux chamber experiments measure the loss or gain of various dissolved species from a fixed container on the seafloor, thus yielding instantaneous measurements of P cycling. A benthic flux chamber deployment in the Saanich Inlet in summer, 1997... 

Sediments are a sink or source for many solutes in the water column. Thus, they can play an important role in regulating the composition of the overlying waters. This approach provides information that can be compared to direct measurements of benthic fluxes. 

Diffusion flux can be made by measuring solute gradients using pore water equilibrator, benthic flux chamber, and core incubation. 

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