Beyond one-way determinism: San Frediano's miracle and climate change in Central and Northern Italy in late antiquity.

Integrating palaeoclimatological proxies and historical records, which is necessary to achieve a more complete understanding of climate impacts on past societies, is a challenging task, often leading to unsatisfactory and even contradictory conclusions. This has until recently been the case for Italy, the heart of the Roman Empire, during the transition between Antiquity and the Middle Ages. In this paper, we present new high-resolution speleothem data from the Apuan Alps (Central Italy). The data document a period of very wet conditions in the sixth c. AD, probably related to synoptic atmospheric conditions similar to a negative phase of the North Atlantic Oscillation. For this century, there also exist a significant number of historical records of extreme hydroclimatic events, previously discarded as anecdotal. We show that this varied evidence reflects the increased frequency of floods and extreme rainfall events in Central and Northern Italy at the time. Moreover, we also show that these unusual hydroclimatic conditions overlapped with the increased presence of "water miracles" in Italian hagiographical accounts and social imagination. The miracles, performed by local Church leaders, strengthened the already growing authority of holy bishops and monks in Italian society during the crucial centuries that followed the "Fall of the Roman Empire". Thus, the combination of natural and historical data allows us to show the degree to which the impact of climate variability on historical societies is determined not by the nature of the climatic phenomena per se, but by the culture and the structure of the society that experienced it. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10584-021-03043-x.

Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition.

Radiometric dating of glacial terminations over the past 640,000 years suggests pacing by Earth's climatic precession, with each glacial-interglacial period spanning four or five cycles of ~20,000 years. However, the lack of firm age estimates for older Pleistocene terminations confounds attempts to test the persistence of precession forcing. We combine an Italian speleothem record anchored by a uranium-lead chronology with North Atlantic ocean data to show that the first two deglaciations of the so-called 100,000-year world are separated by two obliquity cycles, with each termination starting at the same high phase of obliquity, but at opposing phases of precession. An assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration.

Sulphur stable isotope systematics in diagenetic pyrite from the North Sea hydrocarbon reservoirs revealed by laser combustion analysis.

Our study focuses on pyrite nodules developed in the Brent Group sandstones, which host the Brent Oilfield, one of the North Sea's greatest oil and gas producers. Timing of nodule formation is equivocal, but due to the forceful, penetrative textures that abound, it is considered late. This pyrite offers a research opportunity because it records the development of the supply of H(2)S in a hydrocarbon reservoir and its sulphur isotopic composition. Laser-based analysis of δ(34)S reveals an extraordinary diversity in values and patterns. The values range from-27 to+72‰, covering half the terrestrial range, with large variations at the submillimetre scale. Isotopically heavy (δ(34)S ∼+30‰ or higher) sulphide is endemic, but low δ(34)S pyrite is also present and appears to represent a temporally though not spatially (on the ∼cm scale) distinct pyritisation event. The distribution of δ(34)S values within individual concretions can be normal (Gaussian), but in some cases may reflect progressive isotope fractionation process(es), conceivably of Rayleigh type. The source of the sulphur and the identity of the isotope fractionation process(es) remain enigmatic.

Stable isotopes reveal Holocene changes in the diet of Adélie penguins in Northern Victoria Land (Ross Sea, Antarctica).

Adélie penguin (Pygoscelis adeliae) modern and fossil eggshells and guano samples collected from ornithogenic soils in Terra Nova Bay (Victoria Land, Ross Sea) were processed for carbon and nitrogen isotopic ratios with the aim of detecting past penguin dietary changes. A detailed and greatly expanded Adélie penguin dietary record dated back to 7,200 years BP has been reconstructed for the investigated area. Our data indicate a significant dietary shift between fish and krill, with a gradual decrease from past to present time in the proportion of fish compared to krill in Adélie penguin diet. From 7,200 to 2,000 years BP, δ(13)C and δ(15)N values indicate fish as the most eaten prey. The dietary contribution of lower-trophic prey in penguin diet started becoming evident not earlier than 2,000 years BP, when the δ(13)C values reveal a change in the penguin feeding behavior. Modern eggshell and guano samples reveal a major dietary contribution of krill but not a krill-dominated diet, since δ(13)C values remain much too high if krill prevail in the diet. According to the Holocene environmental background attested for Victoria Land, Adélie penguin dietary shifts between fish and krill seem to reflect penguin paleoecological responses to different paleoenvironmental settings with different conditions of sea-ice extension and persistence. Furthermore, Adélie penguin diet appears to be particularly affected by environmental changes in a very specific period within the breeding season, namely the egg-laying period when penguin dietary and feeding habit shifts are clearly documented by the δ(13)C of eggshell carbonate.

Subsurface filamentous fabrics: an evaluation of origins based on morphological and geochemical criteria, with implications for exopaleontology.

The fossil record of the subsurface biosphere is sparse. Results obtained on subsurface filamentous fabrics (SFF) from >225 paleosubsurface sites in volcanics, oxidized ores, and paleokarst of subrecent to Proterozoic age are presented. SFF are mineral encrustations on filamentous or fibrous substrates that formed in subsurface environments. SFF occur in association with low-temperature aqueous mineral assemblages and consist of tubular, micron-thick (median 1.6 micron) filaments in high spatial density, which occur as irregular masses, matted fabrics, and vertically draped features that resemble stalactites. Micron-sized filamentous centers rule out a stalactitic origin. Morphometric analysis of SFF filamentous forms demonstrates that their shape more closely resembles microbial filaments than fibrous minerals. Abiogenic filament-like forms are considered unlikely precursors of most SFF, because abiogenic forms differ in the distribution of widths and have a lower degree of curvature and a lower number of direction changes. Elemental analyses of SFF show depletion in immobile elements (e.g., Al, Th) and a systematic enrichment in As and Sb, which demonstrates a relation to environments with high flows of water. Sulfur isotopic analyses are consistent with a biological origin of a SFF sample from a Mississippi Valley-Type deposit, which is consistent with data in the literature. Fe isotopes in SFF and active analogue systems, however, allow no discrimination between biogenic and abiogenic origins. The origin of most SFF is explained as permineralized remains of microbial filaments that possibly record rapid growth during phases of high water flow that released chemical energy. It is possible that some SFF formed due to encrustation of mineral fibers. SFF share similarities with Microcodium from soil environments. SFF are a logical target in the search for past life on Mars. The macroscopic nature of many SFF allows for their relatively easy in situ recognition and targeting for more detailed microstructural and geochemical analysis.

Identifying source correlation parameters for hydrocarbon wastes using compound-specific isotope analysis.

A preliminary evaluation of compound-specific isotope analysis (CSIA) as a novel, alternative method for identifying source correlation compounds in soils contaminated with residual heavy or weathered petroleum wastes is presented. Oil-contaminated soil microcosms were established using soil (sandy-loam, non-carbonaceous cley) amended with ballast-, crude- or No.6 fuel oil. Microcosms were periodically sampled over 256 days and delta(13)C values (which express the ratio of (13)C to (12)C) determined at each time point for five n-alkanes and the isoprenoid norpristane using gas chromatography-isotope ratio mass spectrometry (GC-IRMS). Although some temporal variation was observed, no significant temporal shifts in the delta(13)C values for the five n-alkanes were measured in all three oils. Isoprenoid isotope ratios (delta(13)C) appeared to be least affected by biotransformation, especially in the No.6 fuel oil. The research suggests that the delta(13)C of isoprenoids such as norpristane, may be of use as source correlation parameters.

Determination of rhizosphere 13C pulse signals in soil thin sections by laser ablation isotope ratio mass spectrometry.

In grassland ecosystems, soil animals act as key soil engineers and architects. The diversity of soil animals is also a regulator of ecosystem carbon flow. However, our understanding of the link between soil animals, carbon fluxes and soil physical organisation remains poor. An integrated approach based on soil micromorphology and laser ablation stable isotope ratio mass spectrometry (LA-IRMS) was developed to provide spatially distributed data of pulse-derived (13)C tracer from roots in the soil environment. This paper describes the development and testing of a LA-IRMS (13)C/(12)C analytical method on soil thin sections as a means to determine the fate of root carbon derived from photosynthesis into soil. Results from this work demonstrated (1) that micro-scale delta(13)C (per thousand) analysis could be made on targeted features located within a soil thin section and (2) that LA-IRMS delta(13)C (per thousand) measurements made on samples obtained from (13)CO(2) pulse labelled plant-soil blocks confirmed the presence of recent photosynthates in the rhizosphere (1 and 4 weeks post-pulse).