Biomedical subjects

L Beaufort

Publications and source records attributed to L Beaufort.

4 recordsLinked to original sources

PubMed2006

Climatically driven emissions of hydrocarbons from marine sediments during deglaciation.

Marine hydrocarbon seepage emits oil and gas, including methane ( approximately 30 Tg of CH(4) per year), to the ocean and atmosphere. Sediments from the California margin contain preserved tar, primarily formed through hydrocarbon weathering at the sea surface. We present a record of variation in the abundance of tar in sediments for the past 32,000 years, providing evidence for increases in hydrocarbon emissions before and during Termination IA [16,000 years ago (16 ka) to 14 ka] and again over Termination IB (11-10 ka). Our study provides direct evidence for increased hydrocarbon seepage associated with deglacial warming through tar abundance in marine sediments, independent of previous geochemical proxies. Climate-sensitive gas hydrates may modulate thermogenic hydrocarbon seepage during deglaciation.

Journal Article↗

PubMed2001

ENSO-like forcing on oceanic primary production during the Late Pleistocene.

Late Pleistocene changes in oceanic primary productivity along the equator in the Indian and Pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep-sea cores. We show that variations in equatorial productivity are primarily caused by glacial-interglacial variability and by precession-controlled changes in the east-west thermocline slope of the Indo-Pacific. The precession-controlled variations in productivity are linked to processes similar to the Southern Oscillation phenomenon, and they precede changes in the oxygen isotopic ratio, which indicates that they are not the result of ice sheet fluctuations. The 30,000-year spectral peak in the tropical Indo-Pacific Ocean productivity records is also present in the Antarctica atmospheric CO2 record, suggesting an important role for equatorial biological productivity in modifying atmospheric CO2.

Animals↗

PubMed1999

Fat neural network for recognition of position-normalised objects.

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 advantage of such large networks, in terms of generalisation efficiency, adaptability and classification time, is demonstrated by applying the network to three plankton recognition and face recognition problems. Its ability to perform good generalisation with few training examples, but many weights, is an open theoretical problem.

Journal Article↗

PubMed1997

Insolation cycles as a major control of equatorial indian ocean primary production

Analysis of a continuous sedimentary record taken in the Maldives indicates that strong primary production fluctuations (70 to 390 grams of carbon per square meter per year) have occurred in the equatorial Indian Ocean during the past 910,000 years. The record of primary production is coherent and in phase with the February equatorial insolation, whereas it shows diverse phase behavior with delta18O, depending on the orbital frequency (eccentricity, obliquity, or precession) examined. These observations imply a direct control of productivity in the equatorial oceanic system by insolation. In the equatorial Indian Ocean, productivity is driven by the wind intensity of westerlies, which is related to the Southern Oscillation; therefore, it is suggested that a precession forcing on the Southern Oscillation is responsible for the observed paleoproductivity dynamics.

Journal Article↗