Atmospheric triggers of the Brunt Ice Shelf calving in February 2021

The calving of Antarctic ice shelves remains unpredictable to date due to a lack of understanding of the role of the different climatic components in such events. In this study, the role of atmospheric forcing in the calving of the Brunt Ice Shelf (BIS) in February 2021 is investigated using a combination of observational and reanalysis data. The occurrence of a series of extreme cyclones around the time of the calving induced an oceanward sea surface slope of more than 0.08º leading to the calving along a pre-existing rift. The severe storms were sustained by the development of a pressure dipole on both sides of the BIS associated with a La Niña event and the positive phase of the Southern Annular Mode. Poleward advection of warm and moist low-latitude air over the BIS area just before the calving was also observed in association with atmospheric rivers accompanying the cyclones. Immediately after the calving, strong offshore winds continued and promoted the drift of the iceberg A-74 in the Weddell Sea at a speed up to 700 m day-1. This study highlights the contribution of local atmospheric conditions to ice-shelf dynamics. The link to the larger scale circulation patterns indicates that both need to be accounted for in the projections of Antarctic ice shelf evolution

The dust load and radiative impact associated with the June 2020 historical Saharan dust storm

International audienceIn June 2020, a major dust outbreak occurred in the Sahara that impacted the tropical Atlantic Ocean. In this study, the dust load and radiative forcing of the dust plumes on both the atmosphere and ocean surface is investigated by means of observations and modelling. We estimated dust loadings in excess of 8 Tg over the eastern tropical Atlantic, comparable to those observed over the desert during major Saharan dust storms. The dust induced an up to 1.1 K net warming of the ocean surface and a 1.8K warming of the air temperature (i.e., two to three times the respective climatological standard deviations), with a +14 W m−2 (∼28% of the mean value) increase in the surface net radiation flux at night. As the dust plumes extended all the way to the Caribbean, it is possible that this historical dust event helped fuel the record-breaking 2020 Atlantic hurricane season

Detecting and Predicting Archaeological Sites Using Remote Sensing and Machine Learning—Application to the Saruq Al-Hadid Site, Dubai, UAE

In this paper, the feasibility of satellite remote sensing in detecting and predicting locations of buried objects in the archaeological site of Saruq Al-Hadid, United Arab Emirates (UAE) was investigated. Satellite-borne synthetic aperture radar (SAR) is proposed as the main technology for this initial investigation. In fact, SAR is the only satellite-based technology able to detect buried artefacts from space, and it is expected that fine-resolution images of ALOS/PALSAR-2 (L-band SAR) would be able to detect large features (>1 m) that might be buried in the subsurface (<2 m) under optimum conditions, i.e., dry and bare soil. SAR data were complemented with very high-resolution Worldview-3 multispectral images (0.31 m panchromatic, 1.24 m VNIR) to obtain a visual assessment of the study area and its land cover features. An integrated approach, featuring the application of advanced image processing techniques and geospatial analysis using machine learning, was adopted to characterise the site while automating the process and investigating its applicability. Results from SAR feature extraction and geospatial analyses showed detection of the areas on the site that were already under excavation and predicted new, hitherto unexplored archaeological areas. The validation of these results was performed using previous archaeological works as well as geological and geomorphological field surveys. The modelling and prediction accuracies are expected to improve with the insertion of a neural network and backpropagation algorithms based on the performed cluster groups following more recent field surveys. The validated results can provide guidance for future on-site archaeological work. The pilot process developed in this work can therefore be applied to similar arid environments for the detection of archaeological features and guidance of on-site investigations

Haplotypic classification of dystrophic epidermolysis bullosa in Tunisian consanguineous families: implication for diagnosis

International audienceDystrophic epidermolysis bullosa (DEB) is a rare genodermatosis caused by mutations in the type VII collagen gene COL7A1. Clinical diagnosis of DEB should be confirmed by histopathological and electron microscopy analysis, which is not always accessible. We report here a genetic investigation of DEB consanguineous families in Tunisia. A total of 23 EB families were genotyped with 5 microsatellite markers overlapping the COL7A1 gene. Among these families, 19 presented with the dystrophic form of EB, 9 were diagnosed by histopathological examination, 2 had the simplex form, 1 had a junctional EB, and 1 was affected by an unclassified form of EB. The informativeness of the markers was studied and allowed us to select three markers for genetic testing of DEB in Tunisian families at risk. Haplotype analysis and homozygosity by descent suggest that all families classified clinically as having DEB and the patient who presented with an unclassified form of EB are likely linked to the COL7A1 gene, and showed evidence for exclusion for the simplex and junctional cases. For COL7A1 linked families, two main haplotypes were shared by eight families. For all the other cases, haplotypic heterogeneity was observed, thus suggesting a mutational heterogeneity among Tunisian DEB families. The genetic results matched with the ultrastructural analysis in all the DEB families and with the clinical examination in 94.7% of all studied DEB families. This study is to our knowledge the first genetic investigation of DEB in the Maghrebian population. We propose a selection of informative markers and show the importance of haplotype analysis as a relatively easy and cost and time effective method for carrier screening and prenatal diagnosis of DEB in consanguineous families at risk

Mutation spectrum of glycogen storage disease type Ia in Tunisia: implication for molecular diagnosis.

International audienceGlycogen storage disease type Ia (GSD Ia; OMIM 232200) is an autosomal recessive disorder of glycogen metabolism caused by a deficiency of the microsomal glucose-6-phosphatase (G6Pase). It is characterized by short stature, hepatomegaly, hypoglycaemia, hyperuricaemia, and lactic acidaemia. Various mutations have been reported in the G6Pase gene (G6PC). In order to determine the mutation spectrum in Tunisia, we performed mutation analysis in 22 Tunisian type I glycogen storage disease (GSD I) patients belonging to 18 unrelated families. All patients were clinically classified as GSD Ia. The R83C mutation was found to be the major cause of GSD Ia, accounting for 24 of 36 mutant alleles (66.6%), The R170Q mutation was the second most frequent mutation; it accounts for 10 of 36 mutant alleles (27.7%). The R83C and R170Q mutations could be rapidly detected by PCR/RFLP. Since the majority of Tunisian patients carried R83C and/or R170Q mutations, we propose direct screening of these mutations as a rapid, valuable and noninvasive tool for diagnosis of GSD Ia in Tunisian as well as in Northern African populations

Molecular and biochemical characterization of Tunisian patients with glycogen storage disease type III

Glycogen storage disease type III (GSD III) is an autosomal recessive inborn error of metabolism caused by mutations in the glycogen debranching enzyme amylo-1,6-glucosidase gene, which is located on chromosome 1p21.2. GSD III is characterized by the storage of structurally abnormal glycogen, termed limit dextrin, in both skeletal and cardiac muscle and/or liver, with great variability in resultant organ dysfunction. The spectrum of AGL gene mutations in GSD III patients depends on ethnic group. The most prevalent mutations have been reported in the North African Jewish population and in an isolate such as the Faroe Islands. Here, we present the molecular and biochemical analyses of 22 Tunisian GSD III patients. Molecular analysis revealed three novel mutations: nonsense (Tyr1148X) and two deletions (3033_3036del AATT and 3216_3217del GA) and five known mutations: three nonsense (R864X, W1327X and W255X), a missense (R524H) and an acceptor splice-site mutation (IVS32-12A > G). Each mutation is associated to a specific haplotype