Understanding ice-volume (sea-level) and deep-sea temperature variations over the past 40 million years is important for many lines of research. For example, it will lead to (a) a better understanding of ice sheet (in-)stability under different climate conditions, with implications for sea-level responses to anthropogenic warming (e.g.,

Deciphering the dynamics of sub-volcanic magmatic processes requires a detailed understanding of the compositional and textural relationships between melt and crystals. To examine these relationships, we investigated material from one of the largest caldera-forming explosive eruptions on the ocean island of Tenerife, the 312 ka Fasnia event. This eruption ejected juvenile pyroclasts of melt-bearing, partially crystalline cumulate nodules alongside phonolitic pumice and accidental lithic clasts. Nodules contain an average of 26% melt which is preserved as vesiculated and microcrystalline basanite in segregations, pathways and interstitial domains. Both the microcrystalline groundmass and crystal framework are generally unaltered as this crystal ‘mush’ remained supra-solidus until the eruption. We find no surficial or intrinsic evidence that the nodules were transported from their reservoir in a ‘carrier’ magma, and it is most likely that the mush was in situ when it was explosively fragmented and ejected during eruption. As such, the nodules preserve a record of the proportions and relationships between the crystal framework and pre-eruptive melt in an active magma mush reservoir; importantly, capturing a snapshot of the sub-volcanic system at a single point in time. We have analysed >100 of the mush nodules from the massive lithic breccia facies within the Fasnia Member of the Diego Hernández Formation. These cumulates span a diverse range of alkaline plutonic lithologies, from wehrlite and pyroxenite, through hornblende gabbros, to monzodiorite and syenite. Their textures record a range of crystallisation environments, including both crystal- and melt-rich groundmass domains, and invasion of near-solidus domains by ascending reactive melts. In addition, the cumulus phases record complex interactions between felsic and mafic magmas throughout their development, providing evidence for mush remobilization and disequilibrium. Relative homogeneity of melt compositions through the mafic and felsic lithologies testifies to melt mobility through the cumulates. Nevertheless, all melts are of different basanite-intermediate composition to the juvenile phonolitic pumice ejected during the same eruption. This observation implies that the mafic-felsic cumulate mush and the phonolite did not experience significant two-way mixing and existed as separate crustal reservoirs. However, the Fasnia eruption simultaneously fragmented and removed material from both reservoirs, implying the mafic system was subjacent to the felsic, but they did not form a contiguous body.

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Global ice volume (sea level) and deep-sea temperature are key measures of Earth's climatic state. We synthesize evidence for multi-centennial to millennial ice-volume and deep-sea temperature variations over the past 40 million years, which encompass the early glaciation of Antarctica at ˜34 million years ago (Ma), the end of the Middle Miocene Climate Optimum, and the descent into the bipolar glaciation state from ˜3.4 Ma. We compare different sea-level and deep-water temperature reconstructions that are grounded in data to build a resource for validation of long-term numerical model-based approaches. We present: (a) a new ice-volume and deep-sea temperature synthesis for the past 5.3 million years; (b) a single template reconstruction of ice-volume and deep-sea temperature for the interval between 5.3 and 40 Ma; and (c) a discussion of uncertainties and limitations. We highlight key issues associated with glacial state changes in the geological record from 40 Ma to the present that require specific attention in further research. These include offsets between calibration-sensitive versus more thermodynamically guided deep-sea paleothermometry proxy measurements; a conundrum related to the magnitudes of sea-level and deep-sea temperature change at the Eocene-Oligocene transition at 34 Ma; a discrepancy in deep-sea temperature levels during the Middle Miocene between proxy reconstructions and model-based deconvolutions of deep-sea oxygen isotope data; and a hitherto unquantified non-linear reduction of glacial deep-sea temperatures through the past 3.4 million years toward a near-freezing deep-sea temperature asymptote, while sea level stepped down in a more linear manner.

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