An array of six time series sediment traps and current meters was deployed in water depths of 230... more An array of six time series sediment traps and current meters was deployed in water depths of 2300 and 3000 m on two bottom-mounted moorings along the axis of the Cap-Ferret Canyon, a large depression in the southeastern part of the Bay of Biscay (northeastern Atlantic), as part of the ECOMARGE Atlantic experiment ECOFER. The 14-month experiment consisted of three successive deployments during which particle #uxes were collected over sampling periods of 16}27 d. Two large-aperture traps also were deployed to measure #uxes at a faster sampling rate (4}7 d). The recovered samples were analyzed for total mass, concentration of major constituents (organic and inorganic carbon, opal), activity of
Terrestrial Atmospheric and Oceanic Sciences, 2008
The western Pacific Ocean plays an important role in regulating and modulating the global climate... more The western Pacific Ocean plays an important role in regulating and modulating the global climate system on in- terannual to geological timescales. Excellent records have been acquired by coring high sedimentation rate sites in the marginal seas of the western Pacific Ocean during IMAGES cruises. This special section has been proposed to publish papers presenting high-resolution records and the interpreta-
The mismatch between the 100 and 400 k.y. components of Pleistocene climate and the relative powe... more The mismatch between the 100 and 400 k.y. components of Pleistocene climate and the relative power of those terms from the eccentricity of the Earth's orbit remains a challenge to the Milankovitch hypothesis. Coccolithophores have the potential to respond to parameters of orbital forcing other than insolation, and, as a critical component of the ocean carbon cycle, can act to modify
Système de Reconnaissance Automatique de Coccolithes (SYRACO) is a tool for automatic recognition... more Système de Reconnaissance Automatique de Coccolithes (SYRACO) is a tool for automatic recognition of coccoliths by neural networks. Previous versions of this tool were able to identify individual species of coccoliths with a high reliability, but failed in that many coccoliths were overlooked. SYRACO was able to identify only about half the coccoliths present in a field of view. We have now developed a new type of Neural Network, which includes a dynamic view of the object analysed. We have added parallel neural networks, which perform five types of simple image transformation to the general back-propagation neural network. This new dynamic version of SYRACO is able to identify individual coccoliths even more reliably at the same time as it is able to recognize almost all coccoliths present in a field of view. The only remaining problem concerns the inclusion of objects that are not coccoliths. This problem can be solved partly by performing a secondary SYRACO analysis of output ima...
Neural networks: the official journal of the International Neural Network Society
THE DESIGN OF A RECOGNITION SYSTEM FOR NATURAL OBJECTS IS DIFFICULT, MAINLY BECAUSE SUCH OBJECTS ... more THE DESIGN OF A RECOGNITION SYSTEM FOR NATURAL OBJECTS IS DIFFICULT, MAINLY BECAUSE SUCH OBJECTS ARE SUBJECT TO A STRONG VARIABILITY THAT CANNOT BE EASILY MODELLED: planktonic species possess such highly variable forms. Existing plankton recognition systems usually comprise feature extraction processing upstream of a classifier. Drawbacks of such an approach are that the design of relevant feature extraction processes may be very difficult, especially if classes are numerous and if intra-class variability is high, so that the system becomes specific to the problem for which features have been tuned. The opposite course that we take is based on a structured multi-layer neural network with no shared weights, which generates its own features during training. Such a large parameterised-fat-network exhibits good generalisation capabilities for pattern recognition problems dealing with position-normalised objects, even with as many as one thousand weights as training examples. The advanta...
ABSTRACT Coccolithophores, major pelagic carbonate producers, underwent important changes during ... more ABSTRACT Coccolithophores, major pelagic carbonate producers, underwent important changes during the latest Aalenian-Early Bajocian (ca.-170 Ma, Middle Jurassic). Specifically, a new genus called Watznaueria diversified and started dominating the coccolith assemblages. While this change in the coccolith assemblages is already known, the impact on coccolith absolute abundances and fluxes is still misunderstood. Here we tested for the first time on Mesozoic deposits an automated counting method using the SYRACO system, and then compared these results with a classic counting method. Two neural networks were created based on the shape, birefringence and size of coccoliths, the first of which contained only one class and the second of which was composed of six classes. Based on the morphological criteria used for the neural networks, coccoliths were not identified at the species level. We quantified coccolith absolute abundances and estimated fluxes for the latest Aalenian-Early Bajocian in two well-dated and correlated sections, Cabo Mondego in Portugal and Chaudon-Norante in France. There is a strong linear correlation between classic and automatic counting (r > 0.8) supporting automatic counting as a reliable method for coccolith absolute abundance and flux quantification. In spite of under- or over-estimation by automatic counting with respect to classic counting, the absolute abundance stratigraphic trends are remarkably similar. Under- or over-estimation may be reduced by further technical improvements such as automatic focus. At Cabo Mondego, coccolith fluxes increased from 0.2x109 coccoliths/m2/yr in the latest Aalenian to 700x109 coccoliths/m2/yr in the middle of the Laeviuscula ammonite Zone (Early Bajocian), remaining high for the rest of the Early Bajocian. At Chaudon-Norante, a similar trend was observed. This coccolith flux increase is therefore considered to be a supra-regional event matching an important δ13CBulk carbonate positive excursion. The carbon isotopic positive excursion, along with the onset of radiolarian sedimentation and coccolith fluxes is related to a gradual increase in the fertility of the oceans during the Early Bajocian and is likely associated with warmer and more humid climates and associated enhanced continental weathering.
ABSTRACT Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have reveal... more ABSTRACT Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have revealed wide-scale changes in past convective activity in response to orbital and sub-orbital climate forcings. However, attributing proxy responses to regional changes in WPWP hydrology versus local variations in precipitation requires independent records linking the terrestrial and marine realms. We present high-resolution stable isotope, UK’37 sea-surface temperature, X-ray fluorescence (XRF) core scanning and coccolithophore-derived paleoproductivity records covering the past 120 ka from International Marine Global Change (IMAGES) Program Core MD06-3075 (6°29' N, 125°50' E, water depth 1878 m), situated in the Davao Gulf on the southern side of Mindanao. XRF-derived log(Fe/Ca) records provide a robust proxy for runoff-driven sedimentary discharge from Mindanao, whilst past changes in local productivity are associated with variable freshwater runoff and stratification of the surface layer. Significant precessional-scale variability in sedimentary discharge occurred during Marine Isotope Stage (MIS) 5, with peaks in discharge contemporaneous with Northern Hemisphere summer insolation minima. We attribute these changes to the latitudinal migration of the Intertropical Convergence Zone (ITCZ) over the WPWP together with variability in the strength of the Walker circulation acting on precessional timescales. Between 60 and 15 ka sedimentary discharge at Mindanao was muted, displaying little orbital- or millennial-scale variability, likely in response to weakened precessional insolation forcing and lower sea level driving increased subsidence of air masses over the exposed Sunda Shelf. These results highlight the high degree of local variability in the precipitation response to past climate changes in the WPWP.
ABSTRACT Fifty calcareous nannofossil species were listed in the upper Miocene deposits of the No... more ABSTRACT Fifty calcareous nannofossil species were listed in the upper Miocene deposits of the Northern Chelif Basin (Dahra, Ben Dourda section). The frequence of some of them (Discoaster loeblichii, D. quinqueramus, Amaurolithus primus and A. amplificus) suggests the presence of four subzones (NN 10a, NN 10b, NN 11b, NN 11 c) which are assigned to the Tortonian and Messinian stages. The NN 11 a subzone is absent (hiatus), testified by the (first) simultaneous occurrence (FO) of D. quinqueramus and A. primus. In the same samples, planktonic foraminifera analysis revealed a comparable succession of biozones (Neogloboquadrina acostaensis, N. humerosa-N. dutertrei and Globorotalia mediterranea) which make possible a good calibration between biostratigraphic scales (calcareous nannofossils, foraminifera). The Tortonian-Messinian boundary is pointed out at the sample 28 of the section and characterized by the first occurrence (FO) of A. delicatus and Reticulo/enestra rotaria on the one hand and G. mediterranea on the other hand. The assemblage analysis and relative abundance fluctuations of Coccolithus pelagicus and R. pseudo-umbilicus show evidence of seven successive phases which are characterized, alternately, by cold and hot water marine masses, light intensity variations and nutrient availability.
An array of six time series sediment traps and current meters was deployed in water depths of 230... more An array of six time series sediment traps and current meters was deployed in water depths of 2300 and 3000 m on two bottom-mounted moorings along the axis of the Cap-Ferret Canyon, a large depression in the southeastern part of the Bay of Biscay (northeastern Atlantic), as part of the ECOMARGE Atlantic experiment ECOFER. The 14-month experiment consisted of three successive deployments during which particle #uxes were collected over sampling periods of 16}27 d. Two large-aperture traps also were deployed to measure #uxes at a faster sampling rate (4}7 d). The recovered samples were analyzed for total mass, concentration of major constituents (organic and inorganic carbon, opal), activity of
Terrestrial Atmospheric and Oceanic Sciences, 2008
The western Pacific Ocean plays an important role in regulating and modulating the global climate... more The western Pacific Ocean plays an important role in regulating and modulating the global climate system on in- terannual to geological timescales. Excellent records have been acquired by coring high sedimentation rate sites in the marginal seas of the western Pacific Ocean during IMAGES cruises. This special section has been proposed to publish papers presenting high-resolution records and the interpreta-
The mismatch between the 100 and 400 k.y. components of Pleistocene climate and the relative powe... more The mismatch between the 100 and 400 k.y. components of Pleistocene climate and the relative power of those terms from the eccentricity of the Earth's orbit remains a challenge to the Milankovitch hypothesis. Coccolithophores have the potential to respond to parameters of orbital forcing other than insolation, and, as a critical component of the ocean carbon cycle, can act to modify
Système de Reconnaissance Automatique de Coccolithes (SYRACO) is a tool for automatic recognition... more Système de Reconnaissance Automatique de Coccolithes (SYRACO) is a tool for automatic recognition of coccoliths by neural networks. Previous versions of this tool were able to identify individual species of coccoliths with a high reliability, but failed in that many coccoliths were overlooked. SYRACO was able to identify only about half the coccoliths present in a field of view. We have now developed a new type of Neural Network, which includes a dynamic view of the object analysed. We have added parallel neural networks, which perform five types of simple image transformation to the general back-propagation neural network. This new dynamic version of SYRACO is able to identify individual coccoliths even more reliably at the same time as it is able to recognize almost all coccoliths present in a field of view. The only remaining problem concerns the inclusion of objects that are not coccoliths. This problem can be solved partly by performing a secondary SYRACO analysis of output ima...
Neural networks: the official journal of the International Neural Network Society
THE DESIGN OF A RECOGNITION SYSTEM FOR NATURAL OBJECTS IS DIFFICULT, MAINLY BECAUSE SUCH OBJECTS ... more THE DESIGN OF A RECOGNITION SYSTEM FOR NATURAL OBJECTS IS DIFFICULT, MAINLY BECAUSE SUCH OBJECTS ARE SUBJECT TO A STRONG VARIABILITY THAT CANNOT BE EASILY MODELLED: planktonic species possess such highly variable forms. Existing plankton recognition systems usually comprise feature extraction processing upstream of a classifier. Drawbacks of such an approach are that the design of relevant feature extraction processes may be very difficult, especially if classes are numerous and if intra-class variability is high, so that the system becomes specific to the problem for which features have been tuned. The opposite course that we take is based on a structured multi-layer neural network with no shared weights, which generates its own features during training. Such a large parameterised-fat-network exhibits good generalisation capabilities for pattern recognition problems dealing with position-normalised objects, even with as many as one thousand weights as training examples. The advanta...
ABSTRACT Coccolithophores, major pelagic carbonate producers, underwent important changes during ... more ABSTRACT Coccolithophores, major pelagic carbonate producers, underwent important changes during the latest Aalenian-Early Bajocian (ca.-170 Ma, Middle Jurassic). Specifically, a new genus called Watznaueria diversified and started dominating the coccolith assemblages. While this change in the coccolith assemblages is already known, the impact on coccolith absolute abundances and fluxes is still misunderstood. Here we tested for the first time on Mesozoic deposits an automated counting method using the SYRACO system, and then compared these results with a classic counting method. Two neural networks were created based on the shape, birefringence and size of coccoliths, the first of which contained only one class and the second of which was composed of six classes. Based on the morphological criteria used for the neural networks, coccoliths were not identified at the species level. We quantified coccolith absolute abundances and estimated fluxes for the latest Aalenian-Early Bajocian in two well-dated and correlated sections, Cabo Mondego in Portugal and Chaudon-Norante in France. There is a strong linear correlation between classic and automatic counting (r > 0.8) supporting automatic counting as a reliable method for coccolith absolute abundance and flux quantification. In spite of under- or over-estimation by automatic counting with respect to classic counting, the absolute abundance stratigraphic trends are remarkably similar. Under- or over-estimation may be reduced by further technical improvements such as automatic focus. At Cabo Mondego, coccolith fluxes increased from 0.2x109 coccoliths/m2/yr in the latest Aalenian to 700x109 coccoliths/m2/yr in the middle of the Laeviuscula ammonite Zone (Early Bajocian), remaining high for the rest of the Early Bajocian. At Chaudon-Norante, a similar trend was observed. This coccolith flux increase is therefore considered to be a supra-regional event matching an important δ13CBulk carbonate positive excursion. The carbon isotopic positive excursion, along with the onset of radiolarian sedimentation and coccolith fluxes is related to a gradual increase in the fertility of the oceans during the Early Bajocian and is likely associated with warmer and more humid climates and associated enhanced continental weathering.
ABSTRACT Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have reveal... more ABSTRACT Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have revealed wide-scale changes in past convective activity in response to orbital and sub-orbital climate forcings. However, attributing proxy responses to regional changes in WPWP hydrology versus local variations in precipitation requires independent records linking the terrestrial and marine realms. We present high-resolution stable isotope, UK’37 sea-surface temperature, X-ray fluorescence (XRF) core scanning and coccolithophore-derived paleoproductivity records covering the past 120 ka from International Marine Global Change (IMAGES) Program Core MD06-3075 (6°29' N, 125°50' E, water depth 1878 m), situated in the Davao Gulf on the southern side of Mindanao. XRF-derived log(Fe/Ca) records provide a robust proxy for runoff-driven sedimentary discharge from Mindanao, whilst past changes in local productivity are associated with variable freshwater runoff and stratification of the surface layer. Significant precessional-scale variability in sedimentary discharge occurred during Marine Isotope Stage (MIS) 5, with peaks in discharge contemporaneous with Northern Hemisphere summer insolation minima. We attribute these changes to the latitudinal migration of the Intertropical Convergence Zone (ITCZ) over the WPWP together with variability in the strength of the Walker circulation acting on precessional timescales. Between 60 and 15 ka sedimentary discharge at Mindanao was muted, displaying little orbital- or millennial-scale variability, likely in response to weakened precessional insolation forcing and lower sea level driving increased subsidence of air masses over the exposed Sunda Shelf. These results highlight the high degree of local variability in the precipitation response to past climate changes in the WPWP.
ABSTRACT Fifty calcareous nannofossil species were listed in the upper Miocene deposits of the No... more ABSTRACT Fifty calcareous nannofossil species were listed in the upper Miocene deposits of the Northern Chelif Basin (Dahra, Ben Dourda section). The frequence of some of them (Discoaster loeblichii, D. quinqueramus, Amaurolithus primus and A. amplificus) suggests the presence of four subzones (NN 10a, NN 10b, NN 11b, NN 11 c) which are assigned to the Tortonian and Messinian stages. The NN 11 a subzone is absent (hiatus), testified by the (first) simultaneous occurrence (FO) of D. quinqueramus and A. primus. In the same samples, planktonic foraminifera analysis revealed a comparable succession of biozones (Neogloboquadrina acostaensis, N. humerosa-N. dutertrei and Globorotalia mediterranea) which make possible a good calibration between biostratigraphic scales (calcareous nannofossils, foraminifera). The Tortonian-Messinian boundary is pointed out at the sample 28 of the section and characterized by the first occurrence (FO) of A. delicatus and Reticulo/enestra rotaria on the one hand and G. mediterranea on the other hand. The assemblage analysis and relative abundance fluctuations of Coccolithus pelagicus and R. pseudo-umbilicus show evidence of seven successive phases which are characterized, alternately, by cold and hot water marine masses, light intensity variations and nutrient availability.
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