CHAPTER 53
Sediment Community Oxygen Consumption
along a Shelf-slope Transect in the Western Gulf of Lions
P. Picon1,A.Accornerol,F. de Bovee3,B. Charriere 1, and R. Buscail 1
ABSTRACT
seoe measurements were carried out on a seasonal basis during 1997 and 1998 along a transect
from the shelf to the slope of the western Gulf of Lions (northwestern Mediterranean). Values ranged from 0.6 to 48.0 mmol 02 m- 2 d- 1 and decreased with increasing depth. The overall mean was
11.2 ± '.0 mmol 02 m- 2 d- 1 for the shelf and 2.3 ± 1.9 mmol 02 m- 2 d- 1 for the slope, with a significant difference between canyon axis (average 3.7 ± 2.1 mmol0 2 m- 2 d-') and open slope sites
(average 1.2 ± 0.8 mmol 02 m- 2 d-'). The highest values were registered in all stations in late spring,
when they were 1.5 to 4.2 times higher than in other seasons, except for the shelf deepest station,
which showed a slight temporal variation. Temporal and spatial variations appeared to be related
to the benthic biological activity and organic matter input. Our data confirm previous findings
from other authors in the Gulf of Lions and highlight the importance of organic matter mineralization in this area in the frame of the processes occurring at the sediment-water interface.
I ntrod uction
Despite the fact that they represent less than 20%
of the world ocean area, continental margins
have been demonstrated to play an important
role in the marine biogeochemical carbon cycle
(Walsh et al. 1981; Smith and MacKenzie 1981;
Walsh 1991; Wollast 1991; Bauer and Druffel
1998). In this cycle the sediment-water interface
can be considered as a key zone, because it represents the link between the carbon which is supplied from the water column, by downward particle fluxes, and the carbon which accumulates in
marine deposits.
Once in the sediments, a part of this carbon
undergoes deep burial and is thus substracted
from the ocean -atmosphere system for periods
ranging on geological time scales. Hence, the
sediment-water interface constitutes a transitional zone between pelagic and sedimentary carbon pools. Once deposited at the seafloor, organic matter can follow different pathways, depending on its quality (e.g. labile molecules vs
refractory compounds), the characteristics of the
environment (e.g. temperature, reducing/oxidizing conditions) and the types and relative abundances of benthic organisms (heterotrophic bacteria, meio- and macrofauna). The extent and
type of these transformations also depend on the
rate at which organic matter is supplied, on the
proportion of co-sedimenting inorganic material
and on the presence of physical forcing factors
(e.g. turbidity currents and resuspension events).
Excellent review articles on the physical, chemical and biological processes which regulate the
organic carbon cycling at the sediment-water
interface can be found in Mantoura et al. (1991).
In Fig. 1 fluxes of the different carbon forms
across the sediment-water interface are schematized. The particulate organic carbon (POe) freshly deposited at the seafloor is subject to extensive degradation prior to burial: the largest portion of the metabolizable (i.e. not refractory)
organic matter is mineralized by aerobic bacterial respiration in the oxic layer of surficial sediments, and thus partially returned to the water
column (directly or via pore water) as dissolved
inorganic carbon (DIe). Dissolved carbon can
1 CEFREM, CNRS, Universite de Perpignan. 52 avenue de VIlleneuve, 66860 Perpignan cedex, France
2 Istituto
F.M. Faranda, L. Guglielmo, G. Spezie (eas)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag Italia. 2001
Sediment Community Oxygen Consumption
along a Shelf-slope Transect in the Western Gulf of Lions
P. Picon1,A.Accornerol,F. de Bovee3,B. Charriere 1, and R. Buscail 1
ABSTRACT
seoe measurements were carried out on a seasonal basis during 1997 and 1998 along a transect
from the shelf to the slope of the western Gulf of Lions (northwestern Mediterranean). Values ranged from 0.6 to 48.0 mmol 02 m- 2 d- 1 and decreased with increasing depth. The overall mean was
11.2 ± '.0 mmol 02 m- 2 d- 1 for the shelf and 2.3 ± 1.9 mmol 02 m- 2 d- 1 for the slope, with a significant difference between canyon axis (average 3.7 ± 2.1 mmol0 2 m- 2 d-') and open slope sites
(average 1.2 ± 0.8 mmol 02 m- 2 d-'). The highest values were registered in all stations in late spring,
when they were 1.5 to 4.2 times higher than in other seasons, except for the shelf deepest station,
which showed a slight temporal variation. Temporal and spatial variations appeared to be related
to the benthic biological activity and organic matter input. Our data confirm previous findings
from other authors in the Gulf of Lions and highlight the importance of organic matter mineralization in this area in the frame of the processes occurring at the sediment-water interface.
I ntrod uction
Despite the fact that they represent less than 20%
of the world ocean area, continental margins
have been demonstrated to play an important
role in the marine biogeochemical carbon cycle
(Walsh et al. 1981; Smith and MacKenzie 1981;
Walsh 1991; Wollast 1991; Bauer and Druffel
1998). In this cycle the sediment-water interface
can be considered as a key zone, because it represents the link between the carbon which is supplied from the water column, by downward particle fluxes, and the carbon which accumulates in
marine deposits.
Once in the sediments, a part of this carbon
undergoes deep burial and is thus substracted
from the ocean -atmosphere system for periods
ranging on geological time scales. Hence, the
sediment-water interface constitutes a transitional zone between pelagic and sedimentary carbon pools. Once deposited at the seafloor, organic matter can follow different pathways, depending on its quality (e.g. labile molecules vs
refractory compounds), the characteristics of the
environment (e.g. temperature, reducing/oxidizing conditions) and the types and relative abundances of benthic organisms (heterotrophic bacteria, meio- and macrofauna). The extent and
type of these transformations also depend on the
rate at which organic matter is supplied, on the
proportion of co-sedimenting inorganic material
and on the presence of physical forcing factors
(e.g. turbidity currents and resuspension events).
Excellent review articles on the physical, chemical and biological processes which regulate the
organic carbon cycling at the sediment-water
interface can be found in Mantoura et al. (1991).
In Fig. 1 fluxes of the different carbon forms
across the sediment-water interface are schematized. The particulate organic carbon (POe) freshly deposited at the seafloor is subject to extensive degradation prior to burial: the largest portion of the metabolizable (i.e. not refractory)
organic matter is mineralized by aerobic bacterial respiration in the oxic layer of surficial sediments, and thus partially returned to the water
column (directly or via pore water) as dissolved
inorganic carbon (DIe). Dissolved carbon can
1 CEFREM, CNRS, Universite de Perpignan. 52 avenue de VIlleneuve, 66860 Perpignan cedex, France
2 Istituto
F.M. Faranda, L. Guglielmo, G. Spezie (eas)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag Italia. 2001