area, it increased more than fourfold and reached its maximum of 590. We assume
an increasing ratio of freshly formed detritus in SOM in the photosynthetic layer in
the western area.
During the autumn period, the average C SOM and C Chl concentrations in the
surface water layer decreased by 1.2–2.5 times compared to the summertime, and
N SOM , by 60 to 80% (Figs. 10.3g,h and 10.4d; Table 10.1). The average C/Chl ratios
also decreased in both areas and varied as 126–161. Since the average C/N ratio in
the northern area was 7.5, this testified to both phytoplankton and freshly formed
detritus here during the autumn period. In the western area, the detritus was well
transformed (C/N ¼ 10.5).
As was found for the surface layer, the concentrations of SOM components also
decreased in the photosynthetic layer compared to the summer period. In the
western area, the weighted average C SOM concentration decreased by 1.7 times,
but the C Chl concentration changed insignificantly. In the northern area, these
parameters decreased by 4.4. and 2.7 times, respectively. The weighted average
N SOM concentrations in both areas decreased by approximately four times. An
insignificant difference between the average SOM concentrations in the surface
and photosynthetic water layers was a peculiarity of the autumn period. The
average C/Chl ratio in the photosynthetic layer decreased significantly and was
even lower (103–143) than in the surface water layer (126–161). The average C/N
ratio increased up to 9.7 (western area) and 7.0 (northern area). This may evidence
that phytoplankton and freshly formed detritus constituted a large part of SOM in
the northern area; in contrast, well-transformed detritus together with the phytoplankton was the major component of SOM in the western area.
Central and the eastern areas were less affected by riverine discharge. The
transformed riverine water masses came to the central area in the late spring and
summer periods. The area affected by this intrusion depended on the wind conditions, which in turn influenced the water circulation peculiarities in the NWBS
(Bol’shakov 1970; Kukushkin et al. 2004, 2006).
During the winter, the concentrations of SOM components in the surface water
layer of the central and eastern areas were lower compared to other areas of the
NWBS (Figs. 10.3a,b and 10.4a; Table 10.1). The lowest concentrations of C SOM
(4.3 μM), N SOM (0.25–0.50 μM), and C Chl (0.35–0.55 mg/m
3 ) were recorded in the
northern part of the central area in December 1987 (Kukushkin et al. 2004). The
average C/Chl ratios in both areas were 146–173; average C/N, 8.7–9.2. This may
testify to well transformed detritus as the main SOM components.
The weighted averages of the SOM components in the photosynthetic water
layer (0–40 m) in the central area were similar compared to those observed in the
surface water layer; however, in the eastern area, the C SOM and N SOM concentrations increased by 1.2 times, but C Chl remained the same. The C/Chl ratio slightly
decreased in the central area and slightly increased in the eastern area, but the C/N
ratios decreased in both areas. This pertains to the relative similarity of the SOM
composition in the photosynthetic layer of the central area to the SOM composition
of the surface layer in the eastern area. The detritus rate increased slightly in the
162
A.S. Kukushkin
an increasing ratio of freshly formed detritus in SOM in the photosynthetic layer in
the western area.
During the autumn period, the average C SOM and C Chl concentrations in the
surface water layer decreased by 1.2–2.5 times compared to the summertime, and
N SOM , by 60 to 80% (Figs. 10.3g,h and 10.4d; Table 10.1). The average C/Chl ratios
also decreased in both areas and varied as 126–161. Since the average C/N ratio in
the northern area was 7.5, this testified to both phytoplankton and freshly formed
detritus here during the autumn period. In the western area, the detritus was well
transformed (C/N ¼ 10.5).
As was found for the surface layer, the concentrations of SOM components also
decreased in the photosynthetic layer compared to the summer period. In the
western area, the weighted average C SOM concentration decreased by 1.7 times,
but the C Chl concentration changed insignificantly. In the northern area, these
parameters decreased by 4.4. and 2.7 times, respectively. The weighted average
N SOM concentrations in both areas decreased by approximately four times. An
insignificant difference between the average SOM concentrations in the surface
and photosynthetic water layers was a peculiarity of the autumn period. The
average C/Chl ratio in the photosynthetic layer decreased significantly and was
even lower (103–143) than in the surface water layer (126–161). The average C/N
ratio increased up to 9.7 (western area) and 7.0 (northern area). This may evidence
that phytoplankton and freshly formed detritus constituted a large part of SOM in
the northern area; in contrast, well-transformed detritus together with the phytoplankton was the major component of SOM in the western area.
Central and the eastern areas were less affected by riverine discharge. The
transformed riverine water masses came to the central area in the late spring and
summer periods. The area affected by this intrusion depended on the wind conditions, which in turn influenced the water circulation peculiarities in the NWBS
(Bol’shakov 1970; Kukushkin et al. 2004, 2006).
During the winter, the concentrations of SOM components in the surface water
layer of the central and eastern areas were lower compared to other areas of the
NWBS (Figs. 10.3a,b and 10.4a; Table 10.1). The lowest concentrations of C SOM
(4.3 μM), N SOM (0.25–0.50 μM), and C Chl (0.35–0.55 mg/m
3 ) were recorded in the
northern part of the central area in December 1987 (Kukushkin et al. 2004). The
average C/Chl ratios in both areas were 146–173; average C/N, 8.7–9.2. This may
testify to well transformed detritus as the main SOM components.
The weighted averages of the SOM components in the photosynthetic water
layer (0–40 m) in the central area were similar compared to those observed in the
surface water layer; however, in the eastern area, the C SOM and N SOM concentrations increased by 1.2 times, but C Chl remained the same. The C/Chl ratio slightly
decreased in the central area and slightly increased in the eastern area, but the C/N
ratios decreased in both areas. This pertains to the relative similarity of the SOM
composition in the photosynthetic layer of the central area to the SOM composition
of the surface layer in the eastern area. The detritus rate increased slightly in the
162
A.S. Kukushkin