School of Geography - Research Publications

Permanent URI for this collection

Search Results

Now showing 1 - 10 of 15
  • Item
    Thumbnail Image
    SISALv2: A comprehensive speleothem isotope database with multiple age-depth models
    Comas-Bru, L ; Rehfeld, K ; Roesch, C ; Amirnezhad-Mozhdehi, S ; Harrison, SP ; Atsawawaranunt, K ; Ahmad, SM ; Brahim, YA ; Baker, A ; Bosomworth, M ; Breitenbach, SFM ; Burstyn, Y ; Columbu, A ; Deininger, M ; Demény, A ; Dixon, B ; Fohlmeister, J ; Hatvani, IG ; Hu, J ; Kaushal, N ; Kern, Z ; Labuhn, I ; Lechleitner, FA ; Lorrey, A ; Martrat, B ; Novello, VF ; Oster, J ; Pérez-Mejías, C ; Scholz, D ; Scroxton, N ; Sinha, N ; Ward, BM ; Warken, S ; Zhang, H ; Apaéstegui, J ; Baldini, LM ; Band, S ; Blaauw, M ; Boch, R ; Borsato, A ; Budsky, A ; Rosell, MGB ; Chawchai, S ; Constantin, S ; Denniston, R ; Dragusin, V ; Drysdale, R ; Dumitru, O ; Frappier, A ; Gandhi, N ; Gautam, P ; Hanying, L ; Isola, I ; Jiang, X ; Jingyao, Z ; Johnson, K ; Vanessa Johnston, ; Kathayat, G ; Klose, J ; Krause, C ; Lachniet, M ; Laskar, A ; Lauritzen, SE ; Lončar, N ; Moseley, G ; Narayana, AC ; Onac, BP ; Racovitǎ, E ; Pawlak, J ; Ramsey, CB ; Rivera-Collazo, I ; Rossi, C ; Rowe, PJ ; Stríkis, NM ; Tan, L ; Verheyden, S ; Vonhof, H ; Weber, M ; Wendt, K ; Wilcox, P ; Winter, A ; Wu, J ; Wynn, P ; Yadava, MG (Copernicus Publications, 2020-10-27)
    Characterizing the temporal uncertainty in palaeoclimate records is crucial for analysing past climate change, correlating climate events between records, assessing climate periodicities, identifying potential triggers and evaluating climate model simulations. The first global compilation of speleothem isotope records by the SISAL (Speleothem Isotope Synthesis and Analysis) working group showed that age model uncertainties are not systematically reported in the published literature, and these are only available for a limited number of records (ca. 15 %, n = 107/691). To improve the usefulness of the SISAL database, we have (i) improved the database's spatio-temporal coverage and (ii) created new chronologies using seven different approaches for age- depth modelling. We have applied these alternative chronologies to the records from the first version of the SISAL database (SISALv1) and to new records compiled since the release of SISALv1. This paper documents the necessary changes in the structure of the SISAL database to accommodate the inclusion of the new age models and their uncertainties as well as the expansion of the database to include new records and the qualitycontrol measures applied. This paper also documents the age-depth model approaches used to calculate the new chronologies. The updated version of the SISAL database (SISALv2) contains isotopic data from 691 speleothem records from 294 cave sites and new age-depth models, including age-depth temporal uncertainties for 512 speleothems.
  • Item
    Thumbnail Image
    Beyond one-way determinism: San Frediano’s miracle and climate change in Central and Northern Italy in late antiquity
    Zanchetta, G ; Bini, M ; Bloomfield, K ; Izdebski, A ; Vivoli, N ; Regattieri, E ; Isola, I ; Drysdale, RN ; Bajo, P ; Hellstrom, JC ; Wiśniewski, R ; Fallick, AE ; Natali, S ; Luppichini, M (Springer (part of Springer Nature), 2021-03-20)
    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.
  • Item
    Thumbnail Image
    Subglacial carbonate deposits as a potential proxy for a glacier's former presence
    Lipar, M ; Martin-Perez, A ; Ticar, J ; Pavsek, M ; Gabrovec, M ; Hrvatin, M ; Komac, B ; Zorn, M ; Hajna, NZ ; Zhao, J-X ; Drysdale, RN ; Ferk, M (Copernicus Publications, 2021-01-04)
    The retreat of ice shelves and glaciers over the last century provides unequivocal evidence of recent global warming. Glacierets (miniature glaciers) and ice patches are important components of the cryosphere that highlight the global retreat of glaciers, but knowledge of their behaviour prior to the Little Ice Age is lacking. Here, we report the uranium–thorium age of subglacial carbonate deposits from a recently exposed surface previously occupied by the disappearing Triglav Glacier (southeastern European Alps) that may elucidate the glacier's presence throughout the entire Holocene. The ages suggest the deposits' possible preservation since the Last Glacial Maximum and Younger Dryas. These thin deposits, formed by regelation, are easily eroded if exposed during previous Holocene climatic optima. The age data indicate the glacier's present unprecedented level of retreat since the Last Glacial Maximum and the potential of subglacial carbonates as additional proxies to highlight the extraordinary nature of the current global climatic changes.
  • Item
    No Preview Available
    Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition
    Bajo, P ; Drysdale, RN ; Woodhead, JD ; Hellstrom, JC ; Hodell, D ; Ferretti, P ; Voelker, AHL ; Zanchetta, G ; Rodrigues, T ; Wolff, E ; Tyler, J ; Frisia, S ; Spotl, C ; Fallick, AE (AMER ASSOC ADVANCEMENT SCIENCE, 2020-03-13)
    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.
  • Item
    Thumbnail Image
    Magnesium in subaqueous speleothems as a potential palaeotemperature proxy
    Drysdale, R ; Couchoud, I ; Zanchetta, G ; Isola, I ; Regattieri, E ; Hellstrom, J ; Govin, A ; Tzedakis, PC ; Ireland, T ; Corrick, E ; Greig, A ; Wong, H ; Piccini, L ; Holden, P ; Woodhead, J (NATURE RESEARCH, 2020-10-06)
    Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca. Subaqueous speleothems from similar deep-cave environments should be capable of providing palaeotemperature information over multiple glacial-interglacial cycles.
  • Item
    Thumbnail Image
    New constraints on the source, composition, and post-emplacement modification of kimberlites from in situ C-O-Sr-isotope analyses of carbonates from the Benfontein sills (South Africa)
    Castillo-Oliver, M ; Giuliani, A ; Griffin, WL ; O'Reilly, SY ; Drysdale, RN ; Abersteiner, A ; Thomassot, E ; Li, X-H (SPRINGER, 2020-03-19)
    Primary carbonates in kimberlites are the main CO2 carriers in kimberlites and thus can be used to constrain the original carbon and oxygen-isotope composition of kimberlite melts and their deep mantle sources. However, the contribution of syn- and post-emplacement processes to the modification of the C–O-isotope composition of kimberlites is yet to be fully constrained. This study aims to shed new light on this topic through a detailed textural, compositional (major and trace elements), and in situ C–O–Sr isotopic characterisation of carbonates in the Benfontein kimberlite sills (Kimberley, South Africa). Our multi-technique approach not only reveals the petrographic and geochemical complexity of carbonates in kimberlites in unprecedented detail, but also allows identification of the processes that led to their formation, including: (1) magmatic crystallisation of Sr-rich calcite laths and groundmass; (2) crystallisation of late groundmass calcite from hydrothermal fluids; and (3) variable degrees of crustal contamination in carbonate-rich diapirs and secondary veins. These diapirs most likely resulted from a residual C–O–H fluid or carbonate melt with contributions from methane-rich fluids from the Dwyka shale wall rock, leading to higher 87Sr/86Sr and δ18O, but lower δ13C values than in pristine magmatic calcite. Before coalescing into the diapiric segregations, these fluids/melts also variably entrained early formed calcite laths and groundmass phases. Comparison between in situ and bulk-carbonate analyses confirms that O isotopic analyses of bulk carbonates from kimberlite rocks are not representative of the original isotopic signature of the kimberlite magma, whereas bulk C-isotope compositions are similar to those of the pristine magmatic carbonates. Calcite laths and most groundmass grains at Benfontein preserve isotopic values (δ18O = 6–8‰ and δ13C = − 4 to − 6‰), similar to those of unaltered carbonatites worldwide, which, therefore, probably correspond to those of their parental melts. This narrow range suggests kimberlite derivation from a mantle source with little contribution from recycled crustal material unless the recycled material had isotopic composition indistinguishable from typical mantle values.
  • Item
    Thumbnail Image
    Hydrological changes during the Roman Climatic Optimum in northern Tuscany (Central Italy) as evidenced by speleothem records and archaeological data
    Bini, M ; Zanchetta, G ; Regattieri, E ; Isola, I ; Drysdale, RN ; Fabiani, F ; Genovesi, S ; Hellstrom, JC (WILEY, 2020-08)
    ABSTRACT Study of the climate in the Mediterranean basin during different historical periods has taken on a particular importance, particularly regarding its role (together with other factors) in the evolution of human settlement patterns. Although the Roman age is traditionally considered a period with a favourable climate, recent studies have revealed considerable complexity in terms of regional climate variations. In this paper, we compare the hydrological change from speleothem proxy records with flood reconstructions from archaeological sites for Northern Tuscany (central Italy). We identify a period of oscillating climatic conditions culminating in a multidecadal dry event during the 1st century bc, followed by a century of increased precipitation at the beginning of the Roman Empire and subsequently a return to drier conditions in the 2nd century ad. The period of rainfall increase documented by the speleothems agrees with both the archaeological flood record as well as historical flood data available for the Tiber River, ca. 300 km to the south. These data also suggest a return to wetter conditions following the 3nd and 4rd centuries ad.
  • Item
    Thumbnail Image
    Effects of organic removal techniques prior to carbonate stable isotope analysis of lacustrine marls: A case study from palaeo-lake Fucino (central Italy)
    Mannella, G ; Zanchetta, G ; Regattieri, E ; Perchiazzi, N ; Drysdale, RN ; Giaccio, B ; Leng, MJ ; Wagner, B (WILEY, 2020-04-15)
    RATIONALE: The suitability of organic matter (OM) removal pre-treatments in isotopic studies of lacustrine carbonates is currently under debate. Naturally occurring OM seems to have a negligible effect on the bulk isotopic composition of carbonates compared with changes induced by pre-treatments. This study provides further insights into the possible effects induced by commonly used pre-treatments on natural lacustrine carbonates. METHODS: Sixteen samples from the Fucino F1-F3 lacustrine succession (Abruzzo, central Italy) were characterised for their mineralogical and geochemical composition and each was split into three identical aliquots. One aliquot was left untreated while the remaining two were treated with NaOCl and H2 O2 dilutions. The same treatment was applied to an internal standard consisting of pure Carrara marble. The treated and untreated samples were analysed for their carbon (δ13 C values) and oxygen (δ18 O values) isotope compositions using an Analytical Precision AP2003 isotope ratio mass spectrometer. RESULTS: The samples had variable proportions of endogenic and detrital components, the detrital portion being more (less) abundant during colder (warmer) climate phases. We observed that neither the NaOCl nor the H2 O2 treatment was able to completely remove OM and therefore there was selective removal of compounds within the OM pool. A possible effect of pre-treatment is the loss of carbonates intimately interspersed within the OM, as suggested by the evolution of isotopic ratios towards the local detrital array. CONCLUSIONS: Our study highlights sample-specific changes in geochemistry associated with sample pre-treatments; however, such changes do not seem to lead to either systematic and/or predictable isotopic shifts. We suggest that the suitability of NaOCl or H2 O2 pre-treatments for OM removal should be evaluated on a case-by-case basis. In the specific case of lacustrine marls from palaeo-lake Fucino containing relatively low amounts of OM and in which both detrital and endogenic carbonates occur, both pre-treatments should be avoided.
  • Item
    Thumbnail Image
    Holocene Critical Zone dynamics in an Alpine catchment inferred from a speleothem multiproxy record: disentangling climate and human influences
    Regattieri, E ; Zanchetta, G ; Isola, I ; Zanella, E ; Drysdale, RN ; Hellstrom, JC ; Zerboni, A ; Dallai, L ; Tema, E ; Lanci, L ; Costa, E ; Magri, F (NATURE PUBLISHING GROUP, 2019-11-28)
    Disentangling the effects of climate and human impact on the long-term evolution of the Earth Critical Zone is crucial to understand the array of its potential responses to the ongoing Global Change. This task requires natural archives from which local information about soil and vegetation can be linked directly to climate parameters. Here we present a high-resolution, well-dated, speleothem multiproxy record from the SW Italian Alps, spanning the last ~10,000 years of the present interglacial (Holocene). We correlate magnetic properties and the carbon stable isotope ratio to soil stability and pedogenesis, whereas the oxygen isotope composition is interpreted as primarily related to precipitation amount, modulated at different timescales by changes in precipitation source and seasonality. During the 9.7-2.8 ka period, when anthropic pressure over the catchment was scarce, intervals of enhanced soil erosion are related to climate-driven vegetation contractions and occurred during drier periods. Immediately following the onset of the Iron Age (ca. 2.8 ka), by contrast, periods of enhanced soil erosion coincided with a wetter climate. We propose that the observed changes in the soil response to climate forcing were related to early anthropogenic manipulations of Earth's surface, which made the ECZ more sensitive to climate oscillations.
  • Item
    Thumbnail Image
    Most Earth-surface calcites precipitate out of isotopic equilibrium
    Daeron, M ; Drysdale, RN ; Peral, M ; Huyghe, D ; Blamart, D ; Coplen, TB ; Lartaud, F ; Zanchetta, G (NATURE PUBLISHING GROUP, 2019-01-25)
    Oxygen-isotope thermometry played a critical role in the rise of modern geochemistry and remains extensively used in (bio-)geoscience. Its theoretical foundations rest on the assumption that 18O/16O partitioning among water and carbonate minerals primarily reflects thermodynamic equilibrium. However, after decades of research, there is no consensus on the true equilibrium 18O/16O fractionation between calcite and water (18αcc/w). Here, we constrain the equilibrium relations linking temperature, 18αcc/w, and clumped isotopes (Δ47) based on the composition of extremely slow-growing calcites from Devils Hole and Laghetto Basso (Corchia Cave). Equilibrium 18αcc/w values are systematically ~1.5‰ greater than those in biogenic and synthetic calcite traditionally considered to approach oxygen-isotope equilibrium. We further demonstrate that subtle disequilibria also affect Δ47 in biogenic calcite. These observations provide evidence that most Earth-surface calcites fail to achieve isotopic equilibrium, highlighting the need to improve our quantitative understanding of non-equilibrium isotope fractionation effects instead of relying on phenomenological calibrations.