Sea surface reservoir ages must be known to establish a common chronological framework for marine, continental, and cryospheric paleoproxies, and are crucial for understanding ocean-continent climatic relationships and the paleoventilation of the ocean. Radiocarbon dates of planktonic foraminifera and tephra contemporaneously deposited over Mediterranean marine and terrestrial regions reveal that the reservoir ages were similar to the modern one (∼400 years) during most of the past 18,000 carbon-14 years. However, reservoir ages increased by a factor of 2 at the beginning of the last deglaciation. This is attributed to changes of the North Atlantic thermohaline circulation during the massive ice discharge event Heinrich 1.

A detailed study of the pyroclastic deposits of the AD 79 ‘Pompei’ Plinian eruption of Vesuvius has allowed: (1) reconstruction of the thermal, compositional and isotopic (87Sr/86Sr) pre-eruptive layering of the shallow magma chamber; (2) quantitative definition of the syn-eruptive mixing between the different magmas occupying the chamber, and its relationships with eruption dynamics; (3) recognition of the variability of mafic magma batches supplying the chamber. During the different phases of the eruption ∼25–30% of the magma was ejected as white K-phonolitic pumice, and 70–75% as grey K-tephri-phonolitic pumice. The white pumice results from the tapping of progressively deeper magma from a body (T = 850–900%C) consisting of two distinct layers mainly formed by crystal fractionation. The grey pumice results from syn-eruptive mixing involving three main end-members: the phonolitic ‘white’ magmas (salic end-member, SEM), mafic cumulates (cumulate end-member, CEM) and a crystal-poor ‘grey’ phono-tephritic magma (mafic end-member, MEM), which was never erupted without first being mixed with ‘white’ magma. Evidence is provided that mixing occurred within the chamber and was characterized by a transition with time from physical mixing at a microscopic scale to chemical hybridization. The MEM magma had a homogeneous composition and constant 87Sr86Sr isotopic ratio, possibly as a result of sustained convection. No unambiguous liquidus phases were found, suggesting that the MEM magma was superheated (T = 1000–1100°C); its very low viscosity was a main cause in the establishment of a physical discontinuity separating the white and the grey magmas. The white-grey boundary layer possibly consisted of a multiply diffusive interface, periodically broken and recreated, supplying the phonolitic body through mixing of moderate amounts of fractionated grey melts with the overlying white magma. The presence of a large overheated mass indicates the young, growing stage of the AD 79 chamber, whose main engine was the periodic arrival of hot mafic magma batches. These were characterized by K-tephritic to K-basanitic compositions, high temperatures (>1150°C), high volatile contents (2·0−2·5% H2O +Cl+F+S), low viscosities [(1+2 × 102 poises)] and relatively low densities (2500–2600 kg/m3). The birth of the Pompei chamber followed the repeated arrival of these batches (on average characterized by 87Sr/86Sr≈0·70729) into a reservoir containing a tephriticphonolitic, crystal-enriched, magma, a residue from the preceding ‘Avellino’ Plinian eruption (3400 BP).In fact, about half of magma ejected during the AD 79 eruption could have been inherited from pre-Avellino times.