Deep Chlorophyll Maxima in the Global Ocean: Occurrences, Drivers and Characteristics.

Stratified oceanic systems are characterized by the presence of a so-called Deep Chlorophyll a Maximum (DCM) not detectable by ocean color satellites. A DCM can either be a phytoplankton (carbon) biomass maximum (Deep Biomass Maximum, DBM), or the consequence of photoacclimation processes (Deep photoAcclimation Maximum, DAM) resulting in the increase of chlorophyll a per phytoplankton carbon. Even though these DCM (further qualified as either DBMs or DAMs) have long been studied, no global-scale assessment has yet been undertaken and large knowledge gaps still remain in relation to the environmental drivers responsible for their formation and maintenance. In order to investigate their spatial and temporal variability in the open ocean, we use a global data set acquired by more than 500 Biogeochemical-Argo floats given that DCMs can be detected from the comparative vertical distribution of chlorophyll a concentrations and particulate backscattering coefficients. Our findings show that the seasonal dynamics of the DCMs are clearly region-dependent. High-latitude environments are characterized by a low occurrence of intense DBMs, restricted to summer. Meanwhile, oligotrophic regions host permanent DAMs, occasionally replaced by DBMs in summer, while subequatorial waters are characterized by permanent DBMs benefiting from favorable conditions in terms of both light and nutrients. Overall, the appearance and depth of DCMs are primarily driven by light attenuation in the upper layer. Our present assessment of DCM occurrence and of environmental conditions prevailing in their development lay the basis for a better understanding and quantification of their role in carbon budgets (primary production and export).

Detection of Coccolithophore Blooms With BioGeoChemical-Argo Floats.

Coccolithophores (calcifying phytoplankton) form extensive blooms in temperate and subpolar oceans as evidenced from ocean-color satellites. This study examines the potential to detect coccolithophore blooms with BioGeoChemical-Argo (BGC-Argo) floats, autonomous ocean profilers equipped with bio-optical and physicochemical sensors. We first matched float data to ocean-color satellite data of calcite concentration to select floats that sampled coccolithophore blooms. We identified two floats in the Southern Ocean, which measured the particulate beam attenuation coefficient (c p) in addition to two core BGC-Argo variables, Chlorophyll-a concentration ([Chl-a]) and the particle backscattering coefficient (b bp). We show that coccolithophore blooms can be identified from floats by distinctively high values of (1) the b bp/c p ratio, a proxy for the refractive index of suspended particles, and (2) the b bp/[Chl-a] ratio, measurable by any BGC-Argo float. The latter thus paves the way to global investigations of environmental control of coccolithophore blooms and their role in carbon export.

Adsorption Dynamics of alpha-Lactalbumin and beta-Lactoglobulin at Air-Water Interfaces.

Dynamics of adsorption of 14C radiolabeled beta-lactoglobulin and alpha-lactalbumin at the air-water interface was investigated through the measurement of surface pressure (pi) and surface concentration (Gamma) via a radiotracer technique. Adsorption was diffusion controlled at short times, the rates of increase of pi and Gamma being lower at longer times because of an energy barrier. At low concentrations, an apparent time lag was observed in the evolution of pi for beta-lactoglobulin but not for alpha-lactalbumin which was shown to be due to the nonlinear nature of the pi-Gamma relationship for the former. The area per molecule of an adsorbed beta-lactoglobulin during the dynamics of adsorption was smaller than that for spread monolayer since beta-lactoglobulin was not fully unfolded during adsorption. For alpha-lactalbumin, however, no such difference in the molecular areas for adsorbed and spread monolayer was observed indicating thereby that alpha-lactalbumin unfolded much more rapidly than beta-lactoglobulin. Evolution of Gamma for alpha-lactalbumin was found to occur in two steps possibly due to the change in the orientation of the adsorbed protein from a side-on to an end-on orientation. A previously developed mechanistic model (G. Narsimhan and F. Uraizee, Biotechnology Prog. 8, 187 (1992)) was improved to account for the presence of hydrophobic patches on the surface of the protein molecule as well as an adsorbed protein layer at the air-water interface. The model predictions agreed quite well with the experimental evolution of Gamma for beta-lactoglobulin and alpha-lactalbumin. The model calculations seem to indicate that alpha-lactalbumin changes its orientation at the air-water interface from side-on to other orientations at higher surface concentrations. Copyright 1999 Academic Press.

Relations between aggregative, viscoelastic and molecular properties in gluten from genetic variants of bread wheat.

Glutens differing in their low- and high-molecular-weight glutenin subunits (LMW-GS and HMW-GS) were extracted from genetic variants of bread wheat. Their composition was analysed by electrophoresis, the glutenin size distribution was determined by size-exclusion chromatography. Rheological measurements in the dynamic regime and electron spin resonance spin-labelling experiments gave data on the viscoelasticity and the protein flexibility of the glutens, respectively. In glutens differing in their HMW-GS, a relation is observed between the composition, aggregative properties, segmental flexibility and viscoelastic behaviour. This is not found in glutens with different LMW-GS. However, the proportion of rigid polypeptide segment is related to the height of the elastic plateau in all cases. The organisation of the protein network in gluten is discussed in reference to this data.

[The value of the treatment of post-radiotherapy hyposialorrhoea by dihydroergotamine (author's transl)]. / Intérêt du traitement des hyposialorrhées post-radiothérapiques par la dihydroergotamine.

This study of the Rennes anti-cancer Center reports the results of a clinical and isotope scan study of Dihydroergotamine-Sandoz in the treatment of post-radiotherapy hyposialorrhoea. Dihydroergotamine was used at an initial dose of 100 drops 3 times per day for two weeks, then 60 drops 3 times per day. Treatment must be continued for several months. The results of such treatment given to 11 patients in comparison with a "control" group of 19 patients were evaluated objectively using isotope studies of salivary function. It was found, in addition, that the interruption of treatment might be associated with a relapse of symptoms, reversible when the drug was restarted. Finally, and in the light of the results of this study, it would appear to be logical to treat patients immediately following the end of radiotherapy without awaiting the first symptoms of hyposialorrhoea.