RESUMO
Carbon and other volatiles in the form of gases, fluids or mineral phases are transported from Earth's surface into the mantle at convergent margins, where the oceanic crust subducts beneath the continental crust. The efficiency of this transfer has profound implications for the nature and scale of geochemical heterogeneities in Earth's deep mantle and shallow crustal reservoirs, as well as Earth's oxidation state. However, the proportions of volatiles released from the forearc and backarc are not well constrained compared to fluxes from the volcanic arc front. Here we use helium and carbon isotope data from deeply sourced springs along two cross-arc transects to show that about 91 per cent of carbon released from the slab and mantle beneath the Costa Rican forearc is sequestered within the crust by calcite deposition. Around an additional three per cent is incorporated into the biomass through microbial chemolithoautotrophy, whereby microbes assimilate inorganic carbon into biomass. We estimate that between 1.2 × 108 and 1.3 × 1010 moles of carbon dioxide per year are released from the slab beneath the forearc, and thus up to about 19 per cent less carbon is being transferred into Earth's deep mantle than previously estimated.
Assuntos
Dióxido de Carbono/análise , Sequestro de Carbono , Sedimentos Geológicos/química , Biomassa , Isótopos de Carbono , Costa Rica , Sedimentos Geológicos/microbiologia , HélioRESUMO
AIM: The mechanism by which unilateral testicular torsion leads to injury of the contralateral testis is still controversial. The present study aimed to evaluate immunohistopathological changes in the contralateral testis of rats after acute testicular torsion. METHODS: 40 pubertal rats were randomly divided into 3 groups. Group 1 (n=10) functioned as controls. Group 2 rats (n=10) underwent a sham operation, and Group 3 (n=20) underwent 720° torsion of the left spermatic cord (3 h) followed by detorsion (24 h). RESULTS: Immunofluorescence tests were done to investigate contralateral lesions in half of the animals in Group 3. Nitro blue tetrazolium (NBT) was injected in both testes to identify the presence of oxygen-derived free radicals. 24 h after reperfusion, bilateral samples of the testes were obtained for histological analysis. Fisher's exact test was used for statistical analysis with p-values <0.05 considered significant.Immunofluorescence tests were positive for the contralateral (right) testis but with a lower intensity than that of the testis submitted to torsion. NBT reaction was intense all over the left testis while a minor reaction was visible in the right testis. In Group 3 the left distorted testicle showed diffuse edema with cell elimination and extensive necrosis of the seminiferous tubules. Histological lesions were moderate to mild in the contralateral testis. CONCLUSION: An autoimmune IgG-mediated mechanism deposited on the basement membrane of seminiferous tubules seems to be involved in the genesis of contralateral testis injury.