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Biomass burning source identification through molecular markers in cryoconites over the Tibetan Plateau
No full textCryoconite is a dark, dusty aggregate of mineral particles, organic matter, and microorganisms transported by wind and deposited on glacier surfaces. It can accelerate glacier melting and alter glacier mass balances by reducing the surface albedo of glaciers. Biomass burning in the Tibetan Plateau, especially in the glacier cryoconites, is poorly understood. Retene, levoglucosan, mannosan and galactosan can be generated by the local fires or transported from the biomass burning regions over long distances. In the present study, we analyzed these four molecular markers in cryoconites of seven glaciers from the northern to southern Tibetan Plateau. The highest levels of levoglucosan and retene were found in cryoconites of the Yulong Snow Mountain and Tienshan glaciers with 171.4 ± 159.4 ng g−1 and 47.0 ± 10.5 ng g−1 dry weight (d.w.), respectively. The Muztag glacier in the central Tibetan Plateau contained the lowest levels of levoglucosan and retene with mean values of 59.8 ng g−1 and 0.4 ± 0.1 ng g−1 d.w., respectively. In addition, the vegetation changes and the ratios of levoglucosan to mannosan and retene indicate that combustion of conifers significantly contributes to biomass burning of the cryoconites in the Yulong Snow Mountain and Tienshan glacier. Conversely, biomass burning tracers in cryoconites of Dongkemadi, Yuzhufeng, Muztag, Qiyi and Laohugou glaciers are derived from the combustion of different types of biomass including softwood, hardwood and grass
Providential desorder in Plato's Timaeus
No full textPlato tries to explain the becoming of the cosmos by referring to the concepts of order and disorder. Scholars have usually focused on the relationship between the cosmos and the demiurge that Plato puts forward to explain the reasonable (i.e., well-ordered) development. Along these lines, scholarship has examined the providential role played by both the demiurge and the soul of the world. Yet, an interesting problem still remains open: what exactly is the function of disorder? What is the sense of the concept of a perfectly established order if we do not know the manner in which it is achieved, since we have no understanding of the conditions that make it possible? Pursuing this line of thought, one may point to a providential role of the disorder given the balance of forces that operates in Plato’s cosmic becoming
Maria Carolina ‘sposa’ e ‘madre’: la rappresentazione del potere virtuoso tra Vienna e Napoli
No full textMare nostro, mare amico. La longue durée delle rappresentazioni francesi del Mediterraneo (1830-1930)
No full textAbrupt ice-age shifts in southern westerly winds and Antarctic climate forced from the north
No full textThe mid-latitude westerly winds of the Southern Hemisphere play a central role in the global climate system via Southern Ocean upwelling1, carbon exchange with the deep ocean2, Agulhas leakage (transport of Indian Ocean waters into the Atlantic)3 and possibly Antarctic ice-sheet stability4. Meridional shifts of the Southern Hemisphere westerly winds have been hypothesized to occur5,6 in parallel with the well-documented shifts of the intertropical convergence zone7 in response to Dansgaard–Oeschger (DO) events— abrupt North Atlantic climate change events of the last ice age. Shifting moisture pathways to West Antarctica8 are consistent with this view but may represent a Pacific teleconnection pattern forced from the tropics9. The full response of the Southern Hemisphere atmospheric circulation to the DO cycle and its impact on Antarctic temperature remain unclear10. Here we use five ice cores synchronized via volcanic markers to show that the Antarctic temperature response to the DO cycle can be understood as the superposition of two modes: a spatially homogeneous oceanic ‘bipolar seesaw’ mode that lags behind Northern Hemisphere climate by about 200 years, and a spatially heterogeneous atmospheric mode that is synchronous with abrupt events in the Northern Hemisphere. Temperature anomalies of the atmospheric mode are similar to those associated with present-day Southern Annular Mode variability, rather than the Pacific–South American pattern. Moreover, deuterium-excess records suggest a zonally coherent migration of the Southern Hemisphere westerly winds over all ocean basins in phase with Northern Hemisphere climate. Our work provides a simple conceptual framework for understanding circum-Antarctic temperature variations forced by abrupt Northern Hemisphere climate change. We provide observational evidence of abrupt shifts in the Southern Hemisphere westerly winds, which have previously documented1–3 ramifications for global ocean circulation and atmospheric carbon dioxide. These coupled changes highlight the necessity of a global, rather than a purely North Atlantic, perspective on the DO cycle
The Early Issues of the Fiorino Piccolo or Denaro of Florence (c. 1255-1303)
No full textLa circolazione del fiorino piccolo è chiaramente documentata dal 1256, però solo dal primo semestre 1315 troviamo testimonianza della sua coniazione nel Libro della Zecca, che contiene registrazioni relative agli anni successivi al 1303. Le liste di monete presenti in alcune pratiche di mercatura e trattati di aritmetica redatti tra il 1280 circa ed il 1315 indicano, comunque, che durante la seconda metà del Duecento questo nominale fu soggetto ad una serie di svalutazioni che dettero probabilmente luogo ad emissioni distinte. Questo articolo presenta una proposta di classificazione dei fiorini piccoli duecenteschi basata sui dati archeologici disponibili e sull’analisi delle caratteristiche stilistiche, epigrafiche e pondometriche, con la distinzione in tre gruppi distinti di emissioni. Ne emerge un quadro piuttosto completo, con le prime emissioni
appartenenti agli anni ’50 e ’60 caratterizzate dal busto del santo in stile arcaico, e con la identificazione di una nuova serie coniata con numerosi segni di zecca e databile tra la fine degli anni ’60 ed il 1303. Il confronto tra quest’ultima ed i fiorini piccoli coniati a partire dal 1315 rivela, infine, caratteristiche e differenze utili per la loro classificazione
