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Although the Po river is the most important fluvial system of Northern Italy, the systematic geochemical and isotopic investigations of its water are rare and were never reported for the whole basin. The present contribution aims to fill this knowledge gap, reporting a comprehensive data set including oxygen and hydrogen stable isotopes as well as major and trace element concentration of dissolved species for 54 Po river water samples, mainly collected in different hydrological conditions (peak discharge in April, drought in August) at increasing distance from the source, i.e., from the upper part of the catchment to the terminal (deltaic) part of the river at the confluence with the Adriatic Sea. The isotopic compositions demonstrate that the predominant part of the runoff derives from the Alpine sector of the catchment through important tributaries such as the Dora Baltea, Ticino, Adda, and Tanaro rivers, whereas the contribution from the Apennines tributaries is less important. The geochemical and isotopic compositions show that the Po river water attains a homogeneous composition at ca. 100 km from the source. The average composition is characterized by δ(18)O -9.8‰, δD -66.2‰, total dissolved solid (TDS) 268 mg/L, and chloride 17 mg/L and by a general Ca-HCO3 hydrochemical facies, which is maintained for most of the river stream, only varying in the terminal part where the river is diverted in a complex deltaic system affected by more significant evaporation and mixing with saline water evidenced by higher TDS and chloride content (up to 8198 and 4197 mg/L, respectively). Geochemical and isotopic maps have been drawn to visualize spatial gradients, which reflect the evolution of the river water composition at progressive distance from the source; more detailed maps were focused on the deltaic part in order to visualize the processes occurring in the transitional zone toward the Adriatic Sea. The data also highlight anthropogenic contributions, mainly represented by significant concentrations of nitrate (average 8 mg/L) and possibly arsenic (average 12 μg/L). These data allow the calculation of geochemical fluxes transferred from the river to the sea, and generally, they contribute to the definition of a "hydro-archive" which is useful to highlight ongoing variations in the related ecosystems.

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The Adige River flows from the Eastern Alps to the Adriatic Sea and the understanding of its fluvial dynamics can be improved by geochemical and O-H isotopic investigation. The most negative isotopic compositions are recorded close to the source (δ(18)O between -14.1 and -13.8 ‰, δD between -100.3 and -97.0 ‰), and δD and δ(18)O values generally increase downstream through the upper part (UP, the mountainous sector), stabilizing along the lower part (LP, the alluvial plain) of the river with δ(18)O between -12.4 and -11.8 ‰, δD between -86.9 and -83.7 ‰. The isotopic variations along the stream path (δ(18)O-δD vs distance from the source) depict subparallel distributions for all the investigated periods, with less negative values recorded in winter. Total dissolved solids (TDS) concentration shows the lowest value (<100 mg/l) at the river source, jumping to 310 mg/l at the Rio Ram inflow, then decreasing down to the Isarco River confluence; from here, we observed an increase toward the river mouth, with different values in the distinct sampling periods. The lowest values (140-170 mg/l) were recorded during high discharge in spring, whereas higher TDS values (up to 250 mg/l) were recorded during winter low flow conditions. Extreme TDS values were observed in the estuarine samples (up to 450 mg/l), as result of mixing with seawater. The results allow for the identification of distinct water end-members: glacio-nival component(s) characterized by the most negative isotopic composition and extremely low TDS, a rainfall component characterized by intermediate isotopic and elemental composition and groundwater characterized by the less negative isotopic composition and comparatively higher TDS. An additional component is represented by seawater, which is recorded at the lowest reach of the river during drought periods. These contributions variously mix along the stream path in the distinct hydrological periods, and the presented data are a snapshot of the current hydroclimatic conditions. Future investigations will evaluate possible hydrological variations related to meteo-climatic changes. Monitoring is fundamental for future water management to overcome the vanishing of a significant water end-member of the basin, i.e., the glacio-nival reservoir that is severely affected by the ongoing climatic changes.

11A comprehensive petrological and geochemical dataset is reported in order to define the 12 thermo-compositional characteristics of Ti (Fe)-enriched picrite-basalt lavas (HT2, TiO 2 3-7 13 wt%), erupted close to the axial zone of the inferred Afar mantle plume, at the centre of the 14 originally continuous Ethiopian-Yemeni CFB plateau (ca. 30Ma) which is zonally arranged 15 with progressively lower Ti basalts (HT1, TiO 2 2-4 wt%; LT, TiO 2 1-3 wt%) toward the 16 periphery. Integrated petrogenetic modelling based on major and trace element analyses of 17 bulk rocks, minerals and melt inclusions in olivines, as well as Sr-Nd-Pb-He-O isotope 18 compositional variations enables us to make several conclusions. 1) The phase equilibria 19 constraints indicate that HT2 primary picrites were generated at ca. 1570°C mantle potential 20 temperatures (T p ) in the pressure range 4-5 GPa whereas the HT1 and LT primary melts 21 formed at shallower level (<2 to 3 GPa, T p 1530 °C for HT1 and 1430°C for LT). Thus the 22Afar plume head was a thermally and compositionally zoned melting region with maximum 23 excess temperatures of 300-350°C with respect to the ambient mantle. 2) The HT2 primary 24 melts upwelled nearly adiabatically to the base of the continental crust (ca. 1 GPa) where 25 *Revised manuscript with no changes marked Click here to view linked References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 fractionation of olivine, followed by clinopyroxene, led to variably differentiated picritic and 26 basaltic magmas. 3) Trace element modelling requires that the primary HT2 melts were 27 generated -either by fractional or batch melting (F 9-10%) -from a mixed garnet peridotite 28 source (85%) with 15% eclogite (derived from transitional MORB protoliths included in 29Panafrican terranes) that has to be considered a specific Ti-Fe and incompatible element