Using a time dependent model, we investigate seasonal and interannual variations of oxygen, nitra... more Using a time dependent model, we investigate seasonal and interannual variations of oxygen, nitrate and organic carbon profiles in sediment in which the supply of particulate organic matter (POM) exhibits temporal variations. Model parameters are estimated using sediment and porewater composition obtained during the BENGAL program at a deep-sea site in the North Atlantic. Time-dependent simulations are performed using the seasonal pattern of fluxes recorded in sediment traps as forcing functions. With the diagenetic conditions recorded at the BENGAL site, i.e deep oxygen penetration, low denitrification rate, the model indicates that sediment solute fluxes (oxygen and nitrate) should not exhibit large variation (less than ±20%). Little variation of the sediment and porewater composition is calculated by the model for the seasonal variation of the POM flux. Oxygen concentration varies by 14 μmol/l in the upper layer of the sediment while nitrate concentration changes by less than 2 μmol/l over the year. When time-variable bioturbation is introduced in the model, our simulations indicate that enhanced bioturbation during high flux periods could generate larger changes in porewater composition. Oxygen concentration would vary by 25 μmol/l at 1.5 cm depth in the sediment. The model with variable bioturbation reproduces the main feature of the data set obtained during the BENGAL programme where large pulses of phytodetritus were not observed, i.e. a relative constancy of oxygen fluxes from the sediment and of the oxygen and organic carbon profiles. A large event of phytodetritus deposition is simulated by imposing a flux of POM in summer which is six times greater than the flux recorded. The response of oxygen and nitrate fluxes is much larger, as these fluxes increase by a factor of 3 after the pulse deposition. The simulated concentration profiles of oxygen and nitrate also show large variations after the deposition event. The model with large supply of phytodetritus captures the features observed on the labile organic carbon data, i.e. a continuous quasi-exponential decrease of the labile (bioavailable) carbon over the course of the program. This simulation also provides steeper oxygen gradients in the porewaters after the deposition such as observed during a cruise in September 1996. This certainly points towards large deposition of phytodetritus before the programme began and suggests that the diagenetic system in this region might be dominated by interannual, rather that seasonal, variability.
Deep-sea Research Part Ii-topical Studies in Oceanography, 1997
During the Netherlands Indian Ocean Project (NIOP, 1992–1993) sediment community oxygen consumpti... more During the Netherlands Indian Ocean Project (NIOP, 1992–1993) sediment community oxygen consumption (SCOC) was measured on two continental margins in the Indian Ocean with different productivity: the productive upwelling region off Yemen-Somalia and the supposedly less productive Kenyan margin, which lacks upwelling. The two margins also differ in terms of river input (Kenya) and the more severe oxygen minimum in
In the period 1993–1995 the OMEX area has been visited 3 times to address the question of across-... more In the period 1993–1995 the OMEX area has been visited 3 times to address the question of across-slope transport of suspended matter from the shelf to the deep sea. By analyzing phytopigments and nucleic acids in the sediment and water of the N.W. European Continental slope and rise seasonal patterns of benthic food input were investigated and relation between input
On the SE slope of Rockall Bank, cold-water corals form dense aggregations on the top of elevated... more On the SE slope of Rockall Bank, cold-water corals form dense aggregations on the top of elevated mounds supposedly because mounds give rise to topographically accelerated currents and thus enhanced particle supply. In 2005, a study was made of the trophic structure of a Rockall coral mound community by means of (15)N stable isotope signatures. Simultaneously near-bottom current speed, turbidity, and temperature were measured on and off the mound to search for links between the predominant feeding mode of the coral community, the particle supply, and the physical factors governing the supply. The range of delta(15)N in the coral community was small in comparison to other deep habitats due to the absence of deposit-feeders. The delta(15)N of corals was very close to those of obligate filter-feeders (tunicate, bivalves) indicating that corals assimilate similar types of particles as these filter-feeders. Benthic lander deployments on the mound and in the adjacent gully and plains show...
Quantitative information on particle fluxes, sedimentary OM composition, microbial and meiofaunal... more Quantitative information on particle fluxes, sedimentary OM composition, microbial and meiofaunal parameters is summarised from various stations in the Gulf of Lions and Catalan Sea (North-Western Mediterranean) and in the Cretan Sea (Eastern Mediterranean), investigated between 1993 and 1996. Benthic responses in relation to the different trophic conditions in the two areas were compared in terms of: (1) temporal and
Using a time dependent model, we investigate seasonal and interannual variations of oxygen, nitra... more Using a time dependent model, we investigate seasonal and interannual variations of oxygen, nitrate and organic carbon profiles in sediment in which the supply of particulate organic matter (POM) exhibits temporal variations. Model parameters are estimated using sediment and porewater composition obtained during the BENGAL program at a deep-sea site in the North Atlantic. Time-dependent simulations are performed using the seasonal pattern of fluxes recorded in sediment traps as forcing functions. With the diagenetic conditions recorded at the BENGAL site, i.e deep oxygen penetration, low denitrification rate, the model indicates that sediment solute fluxes (oxygen and nitrate) should not exhibit large variation (less than ±20%). Little variation of the sediment and porewater composition is calculated by the model for the seasonal variation of the POM flux. Oxygen concentration varies by 14 μmol/l in the upper layer of the sediment while nitrate concentration changes by less than 2 μmol/l over the year. When time-variable bioturbation is introduced in the model, our simulations indicate that enhanced bioturbation during high flux periods could generate larger changes in porewater composition. Oxygen concentration would vary by 25 μmol/l at 1.5 cm depth in the sediment. The model with variable bioturbation reproduces the main feature of the data set obtained during the BENGAL programme where large pulses of phytodetritus were not observed, i.e. a relative constancy of oxygen fluxes from the sediment and of the oxygen and organic carbon profiles. A large event of phytodetritus deposition is simulated by imposing a flux of POM in summer which is six times greater than the flux recorded. The response of oxygen and nitrate fluxes is much larger, as these fluxes increase by a factor of 3 after the pulse deposition. The simulated concentration profiles of oxygen and nitrate also show large variations after the deposition event. The model with large supply of phytodetritus captures the features observed on the labile organic carbon data, i.e. a continuous quasi-exponential decrease of the labile (bioavailable) carbon over the course of the program. This simulation also provides steeper oxygen gradients in the porewaters after the deposition such as observed during a cruise in September 1996. This certainly points towards large deposition of phytodetritus before the programme began and suggests that the diagenetic system in this region might be dominated by interannual, rather that seasonal, variability.
Deep-sea Research Part Ii-topical Studies in Oceanography, 1997
During the Netherlands Indian Ocean Project (NIOP, 1992–1993) sediment community oxygen consumpti... more During the Netherlands Indian Ocean Project (NIOP, 1992–1993) sediment community oxygen consumption (SCOC) was measured on two continental margins in the Indian Ocean with different productivity: the productive upwelling region off Yemen-Somalia and the supposedly less productive Kenyan margin, which lacks upwelling. The two margins also differ in terms of river input (Kenya) and the more severe oxygen minimum in
In the period 1993–1995 the OMEX area has been visited 3 times to address the question of across-... more In the period 1993–1995 the OMEX area has been visited 3 times to address the question of across-slope transport of suspended matter from the shelf to the deep sea. By analyzing phytopigments and nucleic acids in the sediment and water of the N.W. European Continental slope and rise seasonal patterns of benthic food input were investigated and relation between input
On the SE slope of Rockall Bank, cold-water corals form dense aggregations on the top of elevated... more On the SE slope of Rockall Bank, cold-water corals form dense aggregations on the top of elevated mounds supposedly because mounds give rise to topographically accelerated currents and thus enhanced particle supply. In 2005, a study was made of the trophic structure of a Rockall coral mound community by means of (15)N stable isotope signatures. Simultaneously near-bottom current speed, turbidity, and temperature were measured on and off the mound to search for links between the predominant feeding mode of the coral community, the particle supply, and the physical factors governing the supply. The range of delta(15)N in the coral community was small in comparison to other deep habitats due to the absence of deposit-feeders. The delta(15)N of corals was very close to those of obligate filter-feeders (tunicate, bivalves) indicating that corals assimilate similar types of particles as these filter-feeders. Benthic lander deployments on the mound and in the adjacent gully and plains show...
Quantitative information on particle fluxes, sedimentary OM composition, microbial and meiofaunal... more Quantitative information on particle fluxes, sedimentary OM composition, microbial and meiofaunal parameters is summarised from various stations in the Gulf of Lions and Catalan Sea (North-Western Mediterranean) and in the Cretan Sea (Eastern Mediterranean), investigated between 1993 and 1996. Benthic responses in relation to the different trophic conditions in the two areas were compared in terms of: (1) temporal and
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