Mid-Holocene thinning of David Glacier, Antarctica: chronology and controls

Quantitative satellite observations only provide an assessment of ice sheet mass loss over the last four decades. To assess long-term drivers of ice sheet change, geological records are needed. Here we present the first millennial-scale reconstruction of David Glacier, the largest East Antarctic outlet glacier in Victoria Land. To reconstruct changes in ice thickness, we use surface exposure ages of glacial erratics deposited on nunataks adjacent to fast-flowing sections of David Glacier. We then use numerical modelling experiments to determine the drivers of glacial thinning. Thinning profiles derived from 45 10Be and 3He surface exposure ages show David Glacier experienced rapid thinning of up to 2 m/yr during the mid-Holocene (∼ 6.5 ka). Thinning slowed at 6 ka, suggesting the initial formation of the Drygalski Ice Tongue at this time. Our work, along with ice thinning records from adjacent glaciers, shows simultaneous glacier thinning in this sector of the Transantarctic Mountains occurred 4–7 kyr after the peak period of ice thinning indicated in a suite of published ice sheet models. The timing and rapidity of the reconstructed thinning at David Glacier is similar to reconstructions in the Amundsen and Weddell embayments. To identify the drivers of glacier thinning along the David Glacier, we use a glacier flowline model designed for calving glaciers and compare modelled results against our geological data. We show that glacier thinning and marine-based grounding-line retreat are controlled by either enhanced sub-ice-shelf melting, reduced lateral buttressing or a combination of the two, leading to marine ice sheet instability. Such rapid glacier thinning events during the mid-Holocene are not fully captured in continental- or catchment-scale numerical modelling reconstructions. Together, our chronology and modelling identify and constrain the drivers of a ∼ 2000-year period of dynamic glacier thinning in the recent geological past.

Human Distribution in Caucasia in the Coldest and Driest Period of the Last Glacial

Since the period the modern human originated anatomically, genetic diversity was accumulated in the hereditarily transferred DNA (e.g., Y-chromosome and mitochondrial DNA), which makes it possible to estimate the ways of human origination and evolution. The research presented in the article uses the branches of Y-chromosome (or paternal branches) which originated in the period of the Last Glaciation. According to the hypothesis to be researched, the major phenomenon in the geological past which could have caused genetic differences by means of reproductive distancing of human populations (i.e., isolation) was the succession of minimal temperatures over the period of glaciation. The author’s hypothesis was motivated by the fact that the dates of temperature minimums almost coincided with the times of origination of paternal branches presumed by other scholars (Fig. 1). Consequently, it was the distribution of the biomes during these minimums that must have affected creation and dissemination of paternal branches.

Arc eruptions deliver ‘first blow’ in the pulsed end-Permian mass extinction

Brief pulses of intense magmatic activity (flare-ups) along convergent margins represent drivers for climatic excursions that can lead to major extinction events. However, correlating volcanic outpouring to environmental crises in the geological past is often difficult due to poor preservation of volcanic sequences. Herein, we present a high-fidelity, CA-TIMS U–Pb zircon record of an end-Permian flare-up event in Eastern Australia, that involved the eruption of >39,000–150,000 km3 of silicic magma in c. 4.21 million years. A correlated high-resolution tephra record (c. 260–249 Ma) in the proximal sedimentary basins suggests recurrence of eruptions from the volcanic field in intervals of ~51,000–145,000 years. Peak eruption activity at 253 Ma is chronologically associated with the pulsed stages of the Permian mass extinction event. The ferocity of the 253 Ma eruption cycle in Eastern Australia is identified as a driver of greenhouse crises and ecosystem stress that led to the reduction in diversity of genera and the demise of the Glossopteris Forests. Simultaneous global continental margin arc flare-up events could thus present an additional agent to trigger greenhouse warming and ecosystem stress that preceded the catastrophic eruption of the Siberian Traps.

A Natural Colonisation of Asia: Phylogenomic and Biogeographic History of Coin Spiders (Araneae: Nephilidae: Herennia)

Reconstructing biogeographic history is challenging when dispersal biology of studied species is poorly understood, and they have undergone a complex geological past. Here, we reconstruct the origin and subsequent dispersal of coin spiders (Nephilidae: Herennia Thorell), a clade of 14 species inhabiting tropical Asia and Australasia. Specifically, we test whether the all-Asian range of Herennia multipuncta is natural vs. anthropogenic. We combine Anchored Hybrid Enrichment phylogenomic and classical marker phylogenetic data to infer species and population phylogenies. Our biogeographical analyses follow two alternative dispersal models: ballooning vs. walking. Following these assumptions and considering measured distances between geographical areas through temporal intervals, these models infer ancestral areas based on varying dispersal probabilities through geological time. We recover a wide ancestral range of Herennia including Australia, mainland SE Asia and the Philippines. Both models agree that H. multipuncta internal splits are generally too old to be influenced by humans, thereby implying its natural colonisation of Asia, but suggest quite different colonisation routes of H. multipuncta populations. The results of the ballooning model are more parsimonious as they invoke fewer chance dispersals over large distances. We speculate that coin spiders’ ancestor may have lost the ability to balloon, but that H. multipuncta regained it, thereby colonising and maintaining larger areas.

Thermochronology of Alkali Feldspar and Muscovite at T > 150 °C Using the 40Ar/39Ar Method: A Review

The 40Ar/39Ar method applied to K-feldspars and muscovite has been often used to construct continuous thermal history paths between ~150–600 °C, which are usually applied to structural and tectonic questions in many varied geological settings. However, other authors contest the use of 40Ar/39Ar thermochronology because they argue that the assumptions are rarely valid. Here we review and evaluate the key assumptions, which are that (i) 40Ar is dominantly redistributed in K-feldspars and muscovite by thermally-driven volume diffusion, and (ii) laboratory experiments (high temperatures and short time scales) can accurately recover intrinsic diffusion parameters that apply to geological settings (lower temperatures over longer time scales). Studies do not entirely negate the application of diffusion theory to recover thermal histories, although they reveal the paramount importance of first accounting for fluid interaction and secondary reaction products via a detailed textural study of single crystals. Furthermore, an expanding database of experimental evidence shows that laboratory step-heating can induce structural and textural changes, and thus extreme caution must be made when extrapolating laboratory derived rate loss constants to the geological past. We conclude with a set of recommendations that include minimum sample characterisation prior to degassing, an assessment of mineralogical transformations during degassing and the use of in situ dating.

The Reading Palaeofire database: an expanded global resource to document changes in fire regimes from sedimentary charcoal records

Sedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using INTCAL2020 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1681 records (entities) from 1477 sites worldwide. The database (DOI: 10.17864/1947.319) is available from https://researchdata.reading.ac.uk/id/eprint/319.

At the crossroads: early Miocene marine fishes of the proto-Mediterranean Sea

Connectivity and climate control fish distribution today as well as in the geological past. We present here the Aquitanian (early Miocene) marine fish of the Mesohellenic Basin, a restricted basin at the border between the proto-Mediterranean and Paratethyan seas. Based on fish otoliths, we were able to identify 19 species from 17 genera, including two new species: Ariosoma mesohellenica and Gnathophis elongatus. This fish assemblage, in conjunction with the accompanying molluscan assemblage, indicates a variable shelf paleoenvironment with easy access to the open ocean. Although available data on the Indo-Pacific fishes of the early Miocene are very limited, the fish fauna of the Mesohellenic Basin has many elements in common with the North Sea, the NE Atlantic, and the Paratethys.

Tectono-Thermal Evolution of the Red Sea Rift

The Oligocene-Recent Red Sea rift is one of the preeminent examples of lithospheric rupture in the recent geological past, forming the basis for many models of how continental breakup occurs and progresses to the formation of new oceanic crust. Utilisation of low-temperature thermochronology in the Red Sea Rift since the 1980s has been key to constraining its spatio-temporal evolution, providing constraints for the propagation of strain and geomorphological development of its margins where datable syn-tectonic strata and/or markers are absent. We review the wealth of published apatite fission track and (U-Th-Sm)/He data from along the Red Sea, affording insights into the Oligocene-Recent thermo-tectonic evolution of the Nubian and Arabian margins. A regional interpolation protocol was employed to synthesise time-temperature reconstructions generated from the mined thermochronology data and burial histories produced from vitrinite reflectance and well data. These cooling-heating maps record a series of pronounced episodes of upper crustal thermal flux related to the development of the Oligocene-Recent Red Sea Rift. Assimilation of these regional thermal history maps with paleogeographic reconstructions and regional magmatic and strain histories provide regional perspectives on the roles of tectonism and geodynamic activity in Red Sea formation and their effects on rift margin development.