The Eocene-Oligocene boundary climate transition:an Antarctic perspective

Antarctica underwent a complex evolution over the course of the Cenozoic, which influenced the history of the Earth’s climate system. The Eocene-Oligocene boundary is a divide of this history when the ice-free ‘greenhouse world’ transitioned to the ‘icehouse’ with the glaciation of Antarctica. Prior to this, Antarctica experienced warm climates, peaking during Early Eocene when tropical-like conditions existed at the margins of the continent where geological evidence is present. Climate signals in the geological record show that the climate then cooled, but not enough to allow the existence of significant ice until the latest Eocene. Glacial deposits from several areas around the continental margin indicate that ice was present by the earliest Oligocene. This matches the major oxygen isotope positive shift captured by marine records. On land, vegetation was able to persist, but the thermophylic plants of the Eocene were replaced by shrubby vegetation with the southern beech Nothofagus, mosses and ferns, which survived in tundra-like conditions. Coupled climate–ice sheet modelling indicates that changing levels of atmospheric CO2 controlled Antarctica’s climate and the onset of glaciation. Factors such as mountain uplift, vegetation changes, ocean gateway opening and orbital forcing all played a part in cooling the polar climate, but only when CO2 levels reached critical thresholds was Antarctica tipped into an icy glacial world.CE acknowledges funding by the Spanish Ministry of Economy, Industry and Competitivity (grants CTM2017-89711-C2-1/2-P), cofunded by the European Union through FEDER funds. IS was supported by the Australian Research Council Discovery Project 180102280. A.T. Kennedy Asser was supported by NERC funding (grant no. NE/L002434/1) Edward Gasson is funded by the Royal Society. EG is funded by the Royal Society. AS thanks the European Research Council for Consolidator Grant #771497 (SPANC)

Bedrock erosion surfaces record former East Antarctic Ice Sheet extent

East Antarctica hosts large subglacial basins into which the East Antarctic Ice Sheet (EAIS) likely retreated during past warmer climates. However, the extent of retreat remains poorly constrained, making quantifying past and predicted future contributions to global sea level rise from these marine basins challenging. Geomorphological analysis and flexural modeling within the Wilkes Subglacial Basin is used to reconstruct the ice margin during warm intervals of the Oligocene–Miocene. Flat‐lying bedrock plateaus are indicative of an ice sheet margin positioned >400–500 km inland of the modern grounding zone for extended periods of the Oligocene–Miocene, equivalent to a 2 meter rise in global sea level. Our findings imply that if major EAIS retreat occurs in the future, isostatic rebound will enable the plateau surfaces to act as seeding points for extensive ice rises, thus limiting extensive ice margin retreat of the scale seen during the early EAIS

Genomic Diversity and Evolution of Mycobacterium ulcerans Revealed by Next-Generation Sequencing

Mycobacterium ulcerans is the causative agent of Buruli ulcer, the third most common mycobacterial disease after tuberculosis and leprosy. It is an emerging infectious disease that afflicts mainly children and youths in West Africa. Little is known about the evolution and transmission mode of M. ulcerans, partially due to the lack of known genetic polymorphisms among isolates, limiting the application of genetic epidemiology. To systematically profile single nucleotide polymorphisms (SNPs), we sequenced the genomes of three M. ulcerans strains using 454 and Solexa technologies. Comparison with the reference genome of the Ghanaian classical lineage isolate Agy99 revealed 26,564 SNPs in a Japanese strain representing the ancestral lineage. Only 173 SNPs were found when comparing Agy99 with two other Ghanaian isolates, which belong to the two other types previously distinguished in Ghana by variable number tandem repeat typing. We further analyzed a collection of Ghanaian strains using the SNPs discovered. With 68 SNP loci, we were able to differentiate 54 strains into 13 distinct SNP haplotypes. The average SNP nucleotide diversity was low (average 0.06–0.09 across 68 SNP loci), and 96% of the SNP locus pairs were in complete linkage disequilibrium. We estimated that the divergence of the M. ulcerans Ghanaian clade from the Japanese strain occurred 394 to 529 thousand years ago. The Ghanaian subtypes diverged about 1000 to 3000 years ago, or even much more recently, because we found evidence that they evolved significantly faster than average. Our results offer significant insight into the evolution of M. ulcerans and provide a comprehensive report on genetic diversity within a highly clonal M. ulcerans population from a Buruli ulcer endemic region, which can facilitate further epidemiological studies of this pathogen through the development of high-resolution tools

Idealized steady-state and transient simulations of Miocene Antarctic ice-sheet variability using 3D thermodynamical ice-sheet model IMAU-ICE

We present results from simulations of the Miocene Antarctic ice sheet, that were performed using the 3D thermodynamical ice-sheet model IMAU-ICE (v1.1.1-MIO). Five steady-state present-day simulations were conducted for reference (PI_ref), and 13 experiments using Miocene settings. Each Miocene experiment comprises 11 steady-state and 4 transient simulations. In the README file, the experiments and simulations are listed. IMAU-ICE was run using a 40x40km grid covering the Antarctic continent. Initial conditions were obtained from reconstructions of the Antarctic bathymetry and bedrock topography pertaining to 23 to 24 million years (Myr) ago from Hochmuth et al. (2020; doi:10.1594/PANGAEA.923109). The simulations were forced by climate input data obtained from GENESIS simulations with varying CO2 levels (280 to 840 ppm) and Antarctic ice sheet cover (no ice to a large ice sheet), and with present-day insolation. We utilized a matrix interpolation method to construct the time-varying climate forcing, based on the prescribed CO2 levels and ice cover simulated by IMAU-ICE. For each simulation, we provide the run script, 1D output variables including CO2 level and the sea level contribution of the Antarctic ice sheet, and 3D output variables including ice thickness, bedrock and surface height, surface mass balance, basal mass balance, ice velocities, and ice temperatures