John C Hellstrom

John C Hellstrom
University of Melbourne | MSD · School of Earth Sciences

PhD Isotope Geochemistry and Geochronology

About

255
Publications
54,773
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12,294
Citations
Additional affiliations
January 2002 - present
University of Melbourne
Position
  • Research Associate

Publications

Publications (255)
Article
Full-text available
Detailed, well-dated palaeoclimate and archaeological records are critical for understanding the impact of environmental change on human evolution. Ga-Mohana Hill, in the southern Kalahari, South Africa, preserves a Pleistocene archaeological sequence. Relict tufas at the site are evidence of past flowing streams, waterfalls, and shallow pools. Her...
Preprint
The 8.2 ka event is regarded as the most prominent climate anomaly of the Holocene, and is thought to have been triggered by a meltwater release to the North Atlantic that was of sufficient magnitude to disrupt the Atlantic Meridional Overturning Circulation (AMOC). It is most clearly captured in Greenland ice-core records, where it is reported as...
Preprint
A better understanding of ENSO dynamics is essential for modelling future climate change and its impacts on the ecosystems and lives of the inhabitants of the tropical Pacific islands, which face considerable environmental risk in the coming decades. This study reconstructs past ENSO dynamics using a multi-proxy approach applied to a stalagmite fro...
Article
The Tamala Limestone, a vast Quaternary carbonate sequence exposed on the coast of Western Australia, forms one of the most geographically-extensive deposits of carbonate aeolianite in the world. It is also considered an excellent example of so-called ‘syngenetic karstification’, where the processes of lithification and karst development occur in c...
Article
Speleoseismology reconstructs palaeo-earthquake records from damage preserved in caves, such as rockfall and broken or deformed speleothems (i.e., stalagmites and stalactites), which are uranium-series dated by analysis of pre- and post-damage speleothem calcite. However, in regions of low strain and infrequent damaging earthquakes, there is potent...
Article
Speleothems are increasingly valued as important paleoclimate archives and yet the removal of samples from caves can come at a cost to natural heritage, impacting delicate environments with limited mechanisms for repair. Conservation of cave environments is a key responsibility for scientists and, with this in mind, we are working to develop and im...
Conference Paper
The last deglaciation (Termination I, T-I) was the most recent global-scale climate transition. It involved a drastic temperature increase guiding massive melting of ice sheets, with a concurrent reorganization of inter- and intrahemispherical atmospheric and ocean circulation patterns. T-I lasted ~3.0 ka (ka = kiloyears before present) in Greenlan...
Poster
Speleothems from coastal caves are useful sources of sea-level data. Ages from submerged speleothems indicate that the relative sea level was lower than the (corrected) elevation of the speleothem, but there is no certainty that the speleothem was still growing during the transgression. More powerful age constraints could be derived if the speleoth...
Article
We present the first stable isotope (δ13C and δ18O) speleothem record from continental Croatia retrieved from two coeval stalagmites from Nova Grgosova Cave. U-Th dates constrain the stalagmite growth history from 10ka to the present, revealing coeval growth between 7.8 and 5.6ka. We interpret δ18O as an autumn/winter hydrological proxy related to...
Article
Full-text available
Lignin oxidation products (LOPs) are widely used as vegetation proxies in climate archives, such as sediment and peat cores. The total LOP concentration, Σ8, provides information on the abundance of vegetation, while the ratios C/V and S/V of the different LOP groups also provide information on the type of vegetation. Recently, LOP analysis has bee...
Poster
Full-text available
In Europe, the scarcity of last glacial speleothem palaeoclimate/palaeoenvironmental records is attributable to the generally dry and cold climate that hampered soil bioproductivity, karst dissolution and carbonate deposition in caves. However, at southern Mediterranean latitudes, glacial climate was milder than in central or northern Europe and sp...
Article
Full-text available
A sedimentary sequence of fluvial deposits preserved in the Corchia Cave (Alpi Apuane) provides new chronological constraints for the evolution of the cave system and the timing and rate of uplift of this sector of the Alpi Apuane since the late Pliocene. Supported by magnetostratigraphic analysis performed on fine-grained fluvial deposits, and by...
Article
Understanding of Late Pleistocene megafaunal extinctions in Australia and New Guinea (Sahul) suffers from a paucity of reliably dated bone deposits. Researchers are divided as to when, and why, large-bodied species became extinct. Critical to these interpretations are so-called ‘late survivors’, megafauna that are thought to have persisted for tens...
Article
Both the distribution of mapped glacial landforms and ice sheet modelling point to an absence of ice over the White Peak during the last glacial period, but intermittent permafrost conditions are expected. Water Icicle Close Cavern is an ancient cave system in the central White Peak that is thought to have been drained for several hundred thousand...
Article
Full-text available
Insects form an important source of food for many people around the world, but little is known of the deep-time history of insect harvesting from the archaeological record. In Australia, early settler writings from the 1830s to mid-1800s reported congregations of Aboriginal groups from multiple clans and language groups taking advantage of the annu...
Conference Paper
Full-text available
The Last Interglacial (LIG) was the last time that temperatures were warmer than present, making it an interesting target for better understanding the consequences of global warming. Of particular interest is the smaller global ice volume which, in combination with ocean thermal expansion, contributed to sea levels reaching 6 to 9 metres above pres...
Preprint
Full-text available
Lignin oxidation products (LOPs) are widely used as vegetation proxies in climate archives, such as sediment and peat cores. The total LOP concentration, Σ8, provides information on the abundance of vegetation, while the ratios C / V and S / V of the different LOP groups also provide information on the type of vegetation. Recently, LOP analysis has...
Article
Full-text available
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...
Article
Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Article
Full-text available
Age distributions of speleothem growth frequency are often employed as proxies for past climate variation. However, their interpretation can be influenced by many variables such as the type of probability density estimator used, the number of samples studied, and indeed the nature of the sampling itself. In order to explore the utility of speleothe...
Article
Full-text available
Cave microclimate and geochemical monitoring is vitally important for correct interpretations of proxy time series from speleothems with regard to past climatic and environmental dynamics. We present results of a comprehensive cave-monitoring programme in Waipuna Cave in the North Island of New Zealand, a region that is strongly influenced by the S...
Article
The utility of speleothems as environmental and geological archives has greatly expanded with recent advances in geochronology. Here we reevaluate their ability to constrain late Cenozoic uplift in karst terranes. Using combined U-Th and U-Pb speleothem chronologies for the Buchan karst along the passive margin of southeastern Australia, we calcula...
Article
The Carpathian island-type glaciokarst has a great potential of preserving signals of past environments, archived in cave deposits like speleothems and clastic infills. We present here the geomorphology and structural control of several relict alpine caves and the surrounding glaciated marble karst in the Făgăraș Mountains. Four truncated and parti...
Article
Full-text available
Flowstone speleothem growth beneath Mount Arthur, New Zealand shows a clear relationship to vegetation density and soil development on the surface above. Flowstone does not currently form beneath sub-alpine Nothofagus forest above ca. 1000–1100 m altitude but U-Th dating shows it has formed there during past intervals of warmer-than-present conditi...
Preprint
Full-text available
Abstract. Cave microclimatic and geochemical monitoring is vitally important for correct interpretations of proxy time series from speleothems with regard to past climatic and environmental dynamics. We present results of a comprehensive cave monitoring programme in Waipuna Cave in the North Island of New Zealand, a region that is strongly influenc...
Article
This study explores the climatic variability in the Iberian Peninsula (IP) and its surrounding seas from 140 to 65 kyr BP. Marine sediment cores and cave speleothems are used to reconstruct changes in sea surface water conditions, deep sea current intensities and atmospheric moisture availability based on stable isotopes, trace elements, grain size...
Poster
Full-text available
Using groundwater δ18O to constrain a speleothem record
Article
The accuracy of ages produced by the U-Pb speleothem chronometer is influenced by initial disequilibrium effects resulting from weathering and transit of water through the epikarst. If some residual disequilibrium remains at the time of measurement, corrections can be made. However, once the system reaches equilibrium, the initial state has to be e...
Article
Full-text available
The previous ‘Journal peer review information’ for this Letter was incorrect. The correct statement is “Nature Climate Change thanks Jie He, Hanh Nguyen, Caroline Ummenhofer and other anonymous reviewer(s) for their contribution to the peer review of this work.” This statement has now been amended.
Article
High-resolution U-Th and 14C dating of two calcite flowstones (RTf: Last Interglacial; RTy: Late Holocene) from the Re Tiberio – Monte Tondo karst system (North Italy) is presented to investigate the palaeoclimate potential of speleothems from gypsum caves. To date, there is a lack of information regarding the dating potential of calcite speleothem...
Article
Synchrotron high‐resolution and micro‐X‐ray fluorescence elemental mapping of two coeval coralloid speleothems from Lamalunga Cave (Italy) are complemented with petrographic, morphological and microstratigraphic studies. The importance of these speleothems relies on their direct and indirect association with a complete Neanderthal skeleton (‘Altamu...
Article
Aragonite speleothems are increasingly being used as high-resolution climate proxies; however, aragonite is unstable and susceptible to diagenetic transformation into calcite leading to mineralogical, textural and geochemical alterations that have not been fully investigated. To provide some insights to these modifications, this study combines stab...
Article
Full-text available
Climate projections 1–3 and observations over recent decades 4,5 indicate that precipitation in subtropical latitudes declines in response to anthropogenic warming, with significant implications for food production and population sustainability. However, this conclusion is derived from emissions scenarios with rapidly increasing radiative forcing t...
Article
Full-text available
The nature and duration of the Last Glacial Maximum (LGM) in Australia are poorly understood, with little regional agreement on the timing and direction of LGM climate changes. One reason for this is that Australian Late Pleistocene terrestrial sediments typically are both sparse and inorganic, inhibiting the development of detailed radiocarbon chr...
Article
Full-text available
Speleothems represent important archives of terrestrial climate variation that host a variety of proxy signals and are also highly amenable to radiometric age determination. Although speleothems have been forming on Earth for at least 400 million years, most studies rely upon the U-Th chronometer which extends only to the mid Pleistocene, leaving i...
Article
A stalagmite (FR16) from Frasassi Cave, located near the Adriatic coast of the Italian peninsula, offers a 16 kyr petrographic and stable isotope record spanning from 112.8 ± 1.5 ka to 96.6 ± 1.0 ka, corresponding to the interval from marine isotope stage (MIS) 5c to MIS 5d. The physical characteristics of FR16 calcite, allowed for a thorough under...
Article
Oxygen and carbon (d 18 Ο/d 13 C) isotope, growth rate and trace element data are reported for a U-Th dated, annually-laminated stalagmite, GM1 from Goda Mea Cave, Ethiopia. The stalagmite grew intermittently around the last interglacial. The proxy records are used to develop a conceptual growth model of the stalagmite and to assess its potential f...
Conference Paper
Stalagmites are valuable Quaternary palaeoclimate archives because: 1) cave calcite dating is highly precise and accurate; 2) geochemical (oxygen and carbon stable isotopes, trace elements, etc.) and physical (growth rate, fabric, shape and size, etc.) properties are often related to environmental changes at the surface, such as rainfall and temper...
Article
Full-text available
Little is known about terrestrial climate dynamics in the Levant during the penultimate interglacial-glacial period. To decipher the palaeoclimatic history of the Marine Oxygen Isotope Stage (MIS) 6 glacial period, a well-dated stalagmite (~194 to ~154 ka) from Kanaan Cave on the Mediterranean coast in Lebanon was analyzed for its petrography, grow...
Article
An unusual shell deposit at Moyjil (Point Ritchie), Warrnambool, in western Victoria, has previously been dated at 67±10 ka and has features suggesting a human origin. If human, the site would be one of Australia’s oldest, justifying a redetermination of age using amino acid racemisation (AAR) dating of Lunella undulata (syn. Turbo undulatus) operc...
Article
New speleothem records from northeastern Iberian caves provide data to explore the climatic patterns during the Holocene. We present δ ¹³ C and Mg/Ca from three speleothems from two different caves located in the Iberian Range allowing replication of the climatic signal for several millennia. Through the integration of those stalagmites covering si...
Conference Paper
Full-text available
More than 600 caves have been surveyed in the Triassic and Messinian gypsum beds of the Northern Apennines (Emilia-Romagna region, N Italy). Despite the fact that these caves have been studied for a very long time, their age was inaccurately believed to be Late Glacial. In fact, the fast dissolution of gypsum and the regional uplift of the mountain...
Article
Full-text available
Marine sediment records suggest that episodes of major atmospheric CO2 drawdown during the last glacial period were linked to iron (Fe) fertilization of subantarctic surface waters. The principal source of this Fe is thought to be dust transported from southern mid-latitude deserts. However, uncertainty exists over contributions to CO2 sequestratio...
Data
Supplementary Figures, Supplementary Table and Supplementary References
Data
list of Boggs Valley subglacial calcite samples analysed for DNA. Sample BV11, consisting of angular clasts cemented by microsparite, is sterile (see text for details.)
Data
OTU data in .Biom format relative to samples BV8a and BV9b.
Data
OTU .txt file relative to the DNA data for Boggs Valley calcite samples BV8a and BV9b. BV 11 is sterile.
Article
Chemical and physical proxy data from a precisely dated early last glacial (~113e110 ka, MIS5d) Sardinian stalagmite reveal a sub-millennial-scale, cool-dry climate event centered at 112.0 þ0.52 /-0.59 ka, followed by a rapid return to warm-wet conditions at 111.76 þ0.43 /-0.45 ka. Comparison with regional speleothem records and the palaeotemperatu...
Article
Full-text available
New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted...
Article
In this study, the ‘dead carbon proportion’ (DCP) calculated from combined U-Th and radiocarbon analyses was used to explore the carbon isotope systematics in Corchia Cave (Italy) speleothems, using the example of stalagmite CC26 which grew during the last ~12 ka. The DCP values in CC26 are among the highest ever recorded in a stalagmite, spanning...
Article
Full-text available
Speleothems may preserve geochemical information at annual resolution, preserving information about past hydrology, environment and climate. In this study, we advance information-extraction from speleothems in two ways. First, the limitations in dating modern stalagmites are overcome by refining a dating method that uses annual trace element cycles...
Article
Speleothems and other carbonate deposits such as tufa containing high proportions of detrital material can be difficult to chemically date due to detrital thorium levels causing a high level of error in conventional U-Th disequilibrium dating. Here we investigate the use of an alternative technique centring on radiocarbon dating of organic matter p...