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Unraveling the origin(s) of carbon on Earth has remained challenging, not only because of the multiple isotopic fractionation episodes that may have occurred during planet formation processes but also because the end point of these processes, the current isotopic value of Earth’s deep carbon reservoirs remains poorly constrained. Here, we present carbon isotopic measurements on rare undegassed mid-ocean ridge basalts from the Pacific, Atlantic, and Arctic Oceans that have preserved the isotopic signature of their mantle source. We find that Earth’s present-day convecting upper mantle has variable δ¹³C value from ~−10 to −4‰, significantly different from the δ¹³C value of peridotitic diamonds and with the highest values being restricted to the Atlantic. Evidence for significant mantle heterogeneity contrasts with previous assumptions and its origin remains puzzling being uncorrelated with geochemical markers associated with either subduction and surficial recycling processes or lower mantle contributions. The data do not preclude other causes such as primordial mantle heterogeneity. We suggest that the δ¹³C value of the bulk silicate Earth may need to be revised. 

Magma ascent rate is a challenging parameter to constrain yet a crucial element to investigate magma dynamics. The 1600 eruption of the Huaynaputina volcano was the largest recorded eruption in South America, with an impact area that now hosts approximately a quarter of Peru's population. The aim of this study is to investigate the magma ascent rate of the initial Plinian phase of the eruption using pyroclast texture. Scanning electron microscopy (SEM) was employed to image several pumice clasts. The images were then cleaned and processed using the Fast Object Acquisition and Measurement System (FOAMS) to obtain a vesicle number density. Melt inclusions in crystals were identified and double polished, and their H₂O content was analyzed using infrared spectroscopy (FTIR). The mean value of the BND is 4.09×10 6 mm⁻³, while the mean value of the H₂O content is 3.05%. According to the nucleation theory, the average decompression rate is thus calculated to be 13.47 MPa/s (ascent rate of 548 m/s). An alternative equation, which relies solely on the BND, provides a decompression rate of 9.06 MPa/s (ascent rate of 362 m/s). Both calculated values are high, but remain within a reasonable range for eruptions of this magnitude. If this eruption were to occur today, it would have a catastrophic impact. These results emphasize the necessity for further research to provide a deeper understanding of such destructive eruptions.