Saanich Inlet, British Columbia

In this discussion, I will examine the cycling of C and P and C P ratios in sediments from the anoxic Saanich Inlet (located near Victoria on Vancouver Island, British Columbia, Canada). This basin was cored by Ocean Drilling Program (ODP) Leg 169S in 1996 at two sites (Bomhold et al. 1998). The blue-gray silty sediments in the lower part 

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Table 8.5. Sulfate concentrations Cs°4 (mmol l 1) at depth z (cm) in pore waters from the Saanich Inlet, British Columbia (Murray et al., 1978).

Saanich Inlet British Columbia, Canada bottom waters... 

Saanich Inlet British Columbia, Canada 22 analyses from 1.3-16 Peterson and Carpenter (1986)... 

Presley, B.J., Kolodny, Y., Nissenbaum, A., and Kaplan, I.R. (1972) Early diagenesis in a reducing fjord, Saanich Inlet, British Columbia—II. Trace element distribution in interstitial water and sediment. Geochim. Cosmochim. Acta 36, 1073-1090. 

Todd, J.F., Elsinger, R.J., and Moore, W.S. (1988) The distributions of uranium, radium, and thorium isotopes in two anoxic fjords Framvaren Fjord (Norway) and Saanich Inlet (British Columbia). Mar. Chem. 23, 393—415. 

Tunnicliffe, V. (2000) A fine-scale record of 130 years of organic carbon deposition in an anoxic fjord, Saanich Inlet, British Columbia. Limnol. Oceanogr. 45, 1380-1387. 

German C. R. and Elderfield H. (1989s) Rare earth elements in Saanich Inlet, British Columbia, a seasonally anoxic basin. Geochim. Cosmochim. Acta 53, 2561—2571. 

Filippelli G. M. (2001) Carbon and phosphorus cycling in anoxic sediments of the Saanich Inlet. British Columbia. Mar. Geol. 174, 307-321. 

Diagenesis in a Reducing Fjord, Saanich Inlet, British Columbia—III , Geochim. Cosmochim. Acta 1972, 36, 1185-1203. 

With suitable anoxic conditions and abundant organic matter, the pore waters in sediments may be totally depleted of sulfate within a depth of 1 to 2 m. In pore waters of Saanich Inlet, British Columbia, where organic carbon contents reached 5%, Nissenbaum et al. (1972) found essentially total sulfate depletion at depths of less than 0.5 m. This depth corresponds to a time span of hundreds of years. In contrast, some off-shore cores from the JOIDES Deep Sea Drilling Programme show that, in more slowly accumulating sediments, there is negligible sulfate depletion despite apparent continuation of sulfate reduction for millions of years, and to depths of several hundred meters. A number of these extreme, as well as intermediate cases are summarised by Goldhaber and Kaplan (1974). 

If metals, particularly iron, are not available to precipitate the biogenic sulfide, then dissolved sulfide builds up in the pore waters and may even reach toxic levels. When iron is present the dissolved sulfide is significantly lower in concentration. The concentration profiles for dissolved sulfide in sediments often show a depletion in the upper layers and a maximum at a depth of a meter or less. The depletion is interpreted by Goldhaber and Kaplan (1974) to reflect reactions between iron oxide and dissolved sulfide to yield iron sulfides. As a consequence of different reactivities of iron oxides to aqueous sulfide, a depth may be reached where the sulfide production rate exceeds removal as iron sulfide. Volkov et al. (1972) reported that, in sediments off the Japan Depression, the free hydrogen sulfide concentration reaches as high as 150 mg h which is roughly 50% higher than that found in the Black Sea and is comparable to the maximum concentration observed at Saanich Inlet, British Columbia, by Nissenbaum et al. (1972). The... 

These changes were thought to be either by natural climate-induced variability or by a decrease in river inflow from Europe (25). The new appearance of a suboxic zone and the increase in salinity were possibly related because the increase in salinity of the surface layer could change the rate and depth of ventilation of the pycnocline. Mixing events in other anoxic basins like Saanich Inlet, British Columbia, have been known to result in similar suboxic zones (26-28). 

Russell, A.D. and Morford, J.L. (2001) The behavior of redox-sensitive metals across a laminated-massive-laminated transition in Saanich Inlet, British Columbia. Marine Geology, 174, 341-354. 

Nissenbaum A, Presley BJ, Kaplan IR (1972) Early diagenesis in a reducing Fjord, Saanich Inlet, British Columbia I Chemical and isotopic changes in major components of interstitial water. Geochim Cosmochim Acta 36 1007-1027. 

Birkeland PW (1984) Soils and Geomorphology. Oxford University Press, New York Blaise-Stevens A, Bomhold BD, Kemp AES, Dean JM, Vaan AA (2001) Overview of Later Quaternary stratigraphy in Saanich Inlet, British Columbia Results of the Ocean Drilling Program Leg 169S. Mar Geol 174 27-41... 

Figure 4. Laminated sediment from Saanich Inlet, British Columbia, Ocean Drilling Program drill Site 1093 ...

Blais-Stevens.A., J. J. Clague, P. T. Brobowsky R. T. Patterson, 1997. Late Holocene sedimentation in Saanich Inlet, British Columbia, and its paleoseismic implications. Can. J. Earth Sci. 34 1345-1357. 

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