Addendum
Addendum to ``Molecular and isotopic characterization
of organic matter in Recent and sub-Recent sediments from
the Dead Sea''
[Organic Geochemistry, 31 (2000) 251±265]
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T.B.P. Oldenburg, J. RullkoÈtter *, M.E. BoÈttcher, A. Nissenbaum
Institute of Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, PO Box 2503, D-26111 Oldenburg, Germany
This Addendum, giving some recent measurements on the stable sulfur isotope ratios of reduced sulfur species from Recent and sub-Recent sediments of the Dead Sea, should be read in conjunction with our original paper (Oldenburg et al., 2000). Pyrite (FeS2) sulfur on the one hand, and the sum of acid volatile sul®des (AVS= FeS+H2S) and elemental sulfur on the other, were separated from freeze-dried sediments by cold and hot Cr(II) chloride distillation, respectively, and converted into Ag2S. Stable isotope measurements were carried out by means of combustion-isotope-ratio monitoring mass spectrometry (C-irmMS). Sul®des were converted to SO2in a EuroVector elemental analyzer coupled to a Finnigan MAT Delta+ mass spectrometer via a Finni-gan MAT Con¯o II interface. Results are reported in the usuald-notation versus the V-CDT standard: repli-cate measurements agreed within0.3%.
The reduced sulfur species in the sediments consisted mainly of pyrite (Table 2 in Oldenburg et al., 2000) and were generally depleted in34S with respect to the com-positions of dissolved sulfate in the water column and pore waters measured previously (d34S between +10 and +20%; Table 1). This con®rms that the sulfur species originate from the dissimilatory activity of halophilic or halo-tolerant microorganisms in relation to the degra-dation of organic matter. Indeed, for shallow sediments of the southern Dead Sea basin (Fig. 1 in Oldenburg et al., 2000), Lerman (1967) calculated sulfate reduction
rates similar to results observed in basins o southern California. The d34S values of the uppermost and the deepest sections of the `canyon core' (Fig. 1) are close to isotopic results reported by Nissenbaum and Kaplan (1976). The intermediate `canyon' sections and the `black mud' samples, however, are much more enriched in34S (Fig. 1). The downcore variations in total reduced inorganic sulfur (TIRS) and the sulfur isotope data are not consistent with steady-state microbial reduction of sulfate in the sediments as de®ned by Hartmann and Nielsen (1969) and Jùrgensen (1979). It is known that most of the pyrite found in sediments is formed close to the sediment-water interface (e.g. BoÈttcher and Lepland, 2000). Therefore, the depth pro®les re¯ect the dierences in the sedimentary conditions between the `canyon' and the `black mud' pro®les and, most importantly, changes in the near-surface sulfur cycle over time. This may have been caused by varying concentrations of dissolved sulfate available to the microbes (dierent signi®cance of reservoir eects) or changes in the microbial activity and cellular sulfate reduction rates (Chambers and Tru-dinger, 1979). These parameters may have been in¯u-enced by changes in the salinity, the Dead Sea water level, the sedimentation rate, the microbial community structure, and/or the relative abundance of auto-chthonous to terrestrial organic matter. Additionally, sediment reworking may have in¯uenced the sediment pro®les.
Microbial sulfate reduction in the Dead Sea water column is accompanied by a sulfur isotope eect of about ÿ35% (Nissenbaum and Kaplan, 1976). Con-sidering ad34S value between +10 and +20%for pore water sulfate close to the sediment±water interface (Table 1; Fig. 1), an isotope enrichment factor of
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Organic Geochemistry 31 (2000) 773±774
www.elsevier.nl/locate/orggeochem
* Corresponding author. Tel.: 441-798-5359; fax: +49-441-798-3404.
ÿ305% was calculated from the isotope value of the metastable reduced sulfur fraction in the shallowest section of the `canyon' core (Table 1) which brackets the water column result. Lower isotope fractionation is found for the shallowest sample of the `black mud' core
(ÿ205%), most likely indicating higher cellular sulfate reduction rates.
References
BoÈttcher, M.E., Lepland, A., in press. Biogeochemistry of sul-fur in a sediment core from the west-central Baltic Sea: Evi-dence from stable isotopes and pyrite textures. Journal of Marine Systems.
Chambers, L.A., Trudinger, P.A., 1979. Microbiological frac-tionation of stable sulfur isotopes: a review and critique. Geomicrobiological Journal 1, 249±293.
Hartmann, M., Nielsen, H., 1969. d34S-Werte in rezenten
Meeressedimenten und ihre Deutung am Beispiel einiger Sedimentpro®le aus der westlichen Ostsee. Geologische Rundschau 58, 621±655.
Jùrgensen, B.B., 1979. A theoretical model of the stable sulfur isotope distribution in marine sediments. Geochimica et Cosmochimica Acta 43, 363±374.
Lerman, A., 1967. Model for the evolution of a chloride lake-the Dead Sea. Geochimica et Cosmochimia Acta 31, 2309± 2330.
Nissenbaum, A., Kaplan, I.R., 1976. Sulfur and carbon iso-topic evidence for biogeochemical processes in the Dead Sea ecosystem. In: Nriagu, J.O. (Ed.), Environmental Bio-geochemistry Vol. 1. Ann Arbor Science, MI, pp. 309±325. Oldenburg, Th.B.P., RullkoÈtter, J., BoÈttcher, M.E.,
Nissen-baum, A., 2000. Molecular and isotopic characterisation of organic matter in recent and sub-recent sediments from the Dead Sea. Organic Geochemistry 31, 251±265.
Fig. 1. Sedimentary sulfur species vs. depth for two sediment cores. Closed symbols: `Canyon' core; open symbols: `Black mud' core. Left: concentrations of TIRS (total inorganic reduced sulfur). Right: sulfur isotopic compositions of pyrite (circles) and the sum of AVS+S(diamonds).
Table 1
Range of stable sulfur isotope data for sulfur species in the water column and sediments from the Dead Seaa
Sulfur species d34S (%) Reference
Dead Sea water column
Dissolved sulfate +10.3 to+15.9 b
Dissolved sul®de ÿ19.6 toÿ21.7 b
Dead Sea sediments
Dissolved sulfate +10.0 to+20.0 b
Gypsum +12.7 to+15.8 b
Dissolved sul®de ÿ12.7 toÿ16.3 b
AVS ÿ15.9 toÿ16.3 b
AVS+S ÿ15.7 to+3.1 c
FeS2 ÿ13.5 to+2.8 c
TIRS ÿ14.5 to+3.0 b
Organic sulfur ÿ19.6 c
a Dissolved sulfate concentrations in the water column range
between 409 and 560 mg lÿ1(Nissenbaum and Kaplan, 1976). b Nissenbaum and Kaplan (1976); excluding data from the
southern basin.
c This study.
