Environmental Engineering Reference
In-Depth Information
34
S of sulfate in pore waters is in the range between 0.8‰ in the upper
sediments due to the influence of river water and 53.8‰ in the pore water of
shallow-water sediments with active sulfate reduction. The range of δ
The δ
34
Sof
pyrite is very wide: 1.5‰ in littoral sediments of the north-western shelf and
up to -43‰ in surface layers of continental slope and shelf sediments (Table
5).
34
S of pyrite, are compared
with the daily production of sulfate reduction in the upper 30 cm layer, the
relationship between the isotopic composition of pyrite and sulfate reduction
rate is evident. The most isotopically heavy pyrite was found in sediments close
to river mouth and in coastal marine sediments with the maximum intensities
of H
2
S production (with the average δ
When both, the average and the range of δ
34
S values of pyrite ranged from -10.1 to
-11.0‰ - Table 5, No. 1-3). In sediments on the north-western and Bulgarian
shelf (Table 5, No. 4-6), pyrite was less enriched with
34
S as the intensity of
sulfate reduction decreased from 2.6 to 0.89 mmol m
−
2
day
−
1
. The difference
34
S of sulfate from the pore water and pyrite was maximal (61.4‰
- Table 5, No. 5) in shelf sediments with the minimum sulfate reduction rate.
Pyrite in sediments of the continental slope and deep water zone of the Black
Sea was less depleted in
between δ
34
S varied from -29.7 to -32.8‰;
the maximum values were higher than -40.0‰ (Table 5, No. 8-10).
Hence, in lithologically homogeneous sediments (aleuropelitic shelf sed-
iments with shell fragments of benthic clams - Table 5, No. 3-7, and car-
bonate/clay sediments of the hydrogen sulfide zone - Table 5, No. 8-10), the
isotopic composition of the pyrite sulfur depends entirely on the intensity of
sulfate reduction.
Unlike the Black Sea water column, where the isotopic composition of the
sulfate sulfur is not affected by sulfate reduction, considerable and regular
changes in the δ
34
S: the average δ
34
S of sulfate of pore waters are observed in bottom sediments
with depth. Table 6 shows changes in δ
34
S values of pore water sulfate, acid-
volatile sulfides, and the sum of elemental, pyrite, and organic sulfur in bottom
sediments of various zones of the Black Sea. The data presented (Table 6, No.
1-5) indicate that at all stations on the north-western shelf (depths less than 80
m), consumption of sulfate along with changes in its isotopic compositions have
been observed in the upper 0-1 cm. Shallow-water sediments were anaerobic
except of a brownish thin layer at the interface with the oxygen-containing
water. Active SRR was measured in surface sediments (Table 6, No. 2-5).
A group of German scientists also detected active sulfate reduction in the
surface layer (fluff layer) of sediments on the north-western shelf during the
R/V “Petr Kottsov” cruise in September 1997 [54, 97]. Significant changes in
the isotopic composition of sulfate of pore waters were detected only in 5-10
and 10-15 cm layers of deep-sea sediments (Table 6, stations 616 and 601).
Residual sulfate was significantly depleted in
32
S at all shallow-water stations
