154
0.4
0.3
l c:
l c:
8.
S. Wakeham
-
Inshore - - .
4
14
0 " " " " ,
3
""""" CL""""
l'
/ /
/ /
.... ,,-/
13
12
e 0.2
.&
~ 2
.!:!
/
//
/ /
~
·2
iii
~
0.1
c:
III
E'
o
//
b. ........ _-_._._._. __ ._ ..... _ .... .t:s.
___ Organic carbon
-0- Total nitrogen
··b·· (ON).
11
10
o
o
9
Station
B54-15
Depth (m)
198
Oxygen (mll-1)
0
B54-16B
160
0.05*
B54-16
128
0.68
B54-17
97
1.27
. .
Fig. 6.6. Organic carbon and total nitrogen concentrations and atomic C/N ratios for fluff samples from
sediment cores spanning the oxic/anoxic interface in the Black Sea. Also shown are the water depths and
bottom water dissolved oxygen concentrations overlying the cores (redrawn from Cowie and Hedges 1991)
delivered to the sediments is uniform across the transect and differences in organic
composition reflect different processes as a function of oxygen content. Decreasing
OC and TN concentrations and increasing C/N(a) of interfacial "fluff" samples from
the deepest, anoxic (BS4-15) to the shallowest, most oxygenated (BS4-17) coring stations are consistent with typical diagenetic trends. Accordingly, the extent of degradation in the fluff material varied with oxygen availability. OC and TN concentrations
were also determined as a function of depth in the five cores (Fig. 6.7). OC and TN
generally decreased with depth in the core and with bottom water oxygen present. For
all five cores, there were substantial decreases in wt% OC and TN between the fluff
layer and the underlying 0-0.5 em sediment, confirming that most degradation takes
place near the water-sediment interface.
Laboratory simulations have been useful for evaluating changes in elemental composition during organic matter diagenesis and possible effects of oxic and anoxic conditions on decomposition, although results regarding oxygen have been equivocal
(Henrichs 1993). In a recent study, Harvey et al. (1995) examined the decay of two marine phytoplankton, the diatom Thallasiosira weissflogii, and the cyanobacterium
Synechococcus sp., by measuring particulate organic carbon (POC), particulate organic
nitrogen (PON) and biochemical compositions (discussed below) in oxic and anoxic
treatments over the 3-month time-course of the experiment. First order decay con-
0.4
0.3
l c:
l c:
8.
S. Wakeham
-
Inshore - - .
4
14
0 " " " " ,
3
""""" CL""""
l'
/ /
/ /
.... ,,-/
13
12
e 0.2
.&
~ 2
.!:!
/
//
/ /
~
·2
iii
~
0.1
c:
III
E'
o
//
b. ........ _-_._._._. __ ._ ..... _ .... .t:s.
___ Organic carbon
-0- Total nitrogen
··b·· (ON).
11
10
o
o
9
Station
B54-15
Depth (m)
198
Oxygen (mll-1)
0
B54-16B
160
0.05*
B54-16
128
0.68
B54-17
97
1.27
. .
Fig. 6.6. Organic carbon and total nitrogen concentrations and atomic C/N ratios for fluff samples from
sediment cores spanning the oxic/anoxic interface in the Black Sea. Also shown are the water depths and
bottom water dissolved oxygen concentrations overlying the cores (redrawn from Cowie and Hedges 1991)
delivered to the sediments is uniform across the transect and differences in organic
composition reflect different processes as a function of oxygen content. Decreasing
OC and TN concentrations and increasing C/N(a) of interfacial "fluff" samples from
the deepest, anoxic (BS4-15) to the shallowest, most oxygenated (BS4-17) coring stations are consistent with typical diagenetic trends. Accordingly, the extent of degradation in the fluff material varied with oxygen availability. OC and TN concentrations
were also determined as a function of depth in the five cores (Fig. 6.7). OC and TN
generally decreased with depth in the core and with bottom water oxygen present. For
all five cores, there were substantial decreases in wt% OC and TN between the fluff
layer and the underlying 0-0.5 em sediment, confirming that most degradation takes
place near the water-sediment interface.
Laboratory simulations have been useful for evaluating changes in elemental composition during organic matter diagenesis and possible effects of oxic and anoxic conditions on decomposition, although results regarding oxygen have been equivocal
(Henrichs 1993). In a recent study, Harvey et al. (1995) examined the decay of two marine phytoplankton, the diatom Thallasiosira weissflogii, and the cyanobacterium
Synechococcus sp., by measuring particulate organic carbon (POC), particulate organic
nitrogen (PON) and biochemical compositions (discussed below) in oxic and anoxic
treatments over the 3-month time-course of the experiment. First order decay con-