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In less than a decade, analyses of ancient genomes have transformed our understanding of the Indigenous peopling and population history of the Americas. These studies have shown that this history, which began in the late Pleistocene epoch and continued episodically into the Holocene epoch, was far more complex than previously thought. It is now evident that the initial dispersal involved the movement from northeast Asia of distinct and previously unknown populations, including some for whom there are no currently known descendants. The first peoples, once south of the continental ice sheets, spread widely, expanded rapidly and branched into multiple populations. Their descendants--over the next fifteen millennia--experienced varying degrees of isolation, admixture, continuity and replacement, and their genomes help to illuminate the relationships among major subgroups of Native American populations. Notably, all ancient individuals in the Americas, save for later-arriving Arctic peoples, are more closely related to contemporary Indigenous American individuals than to any other population elsewhere, which challenges the claim--which is based on anatomical evidence--that there was an early, non-Native American population in the Americas. Here we review the patterns revealed by ancient genomics that help to shed light on the past peoples who created the archaeological landscape, and together lead to deeper insights into the population and cultural history of the Americas. A review of the ancient human genomic record sheds light on the peopling processes of the Americas., Author(s): Eske Willerslev [sup.1] [sup.2] [sup.3] , David J. Meltzer [sup.2] [sup.4] Author Affiliations: (1) GeoGenetics Group, Department of Zoology, University of Cambridge, Cambridge, UK (2) Lundbeck Foundation GeoGenetics Centre, [...]

Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6-9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics--including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs--that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years. Climate and ice-sheet modelling that includes ice fracture dynamics reveals that Antarctica could contribute more than a metre of sea-level rise by 2100 and more than 13 metres by 2500, if greenhouse gas emissions continue unabated. A 500-year model of Antarctica's contribution to future sea-level rise Robert DeConto and David Pollard use a newly improved numerical ice-sheet model calibrated to Pliocene and Last Interglacial sea-level estimates to develop projections of Antarctica's evolution over the next five centuries, driven by a range of greenhouse gas scenarios. The modelling shows that the Antarctic ice sheet has the potential to contribute between almost nothing, to contributing more than a metre of sea-level rise by 2100 and more than 15 metres by 2500. The startling high-end estimate arises from unabated emissions and previously underappreciated mechanisms: ice-fracturing by surface meltwater and collapse of large ice cliffs. The low end shows that a scenario of strong climate mitigation can radically reduce societal exposure to higher sea levels., Author(s): Robert M. DeConto [sup.1] , David Pollard [sup.2] Author Affiliations: (1) Department of Geosciences, University of Massachusetts, Amherst, USA (2) Earth and Environmental Systems Institute, Pennsylvania State University, University [...]

A synthesis of new and existing data allows Heinrich Stadial 11 (HS11), a prominent Northern Hemisphere cold event, to be linked to the timing of peak sea-level rise during glacial termination T-II, whereas rapid sea-level rise in T-I is shown to clearly post-date Heinrich Stadial 1, so fundamentally different mechanisms seem to be at work during glacial terminations. Anatomy of a glacial termination A central goal of palaeoclimate research is that of deciphering the mechanisms responsible for major state shifts in the Earth system, such as between glacial and interglacial conditions. This has proven difficult enough even for the last glacial termination (T-I), much less termination II (T-II), which ended glacial conditions about 130,000 years ago. Gianluca Marino et al. use new and existing data to demonstrate a link, within uncertainties, between Heinrich Stadial 11 (HS11) -- a prominent Northern Hemisphere cold event -- and the timing of peak sea level rise during T-II. A strong Southern Hemisphere warming also occurred during HS11, consistent with the idea of a bipolar seesaw that would probably have promoted Antarctic ice sheet melting. In contrast, rapid sea level rise in T-1 clearly postdated Heinrich Stadial 1. Possibly in response to differing CO.sub.2 and insolation conditions during T-I and T-II, fundamentally different mechanisms seem to be at work in triggering glacial terminations. Our current understanding of ocean-atmosphere-cryosphere interactions at ice-age terminations relies largely on assessments of the most recent (last) glacial-interglacial transition.sup.1,2,3, Termination I (T-I). But the extent to which T-I is representative of previous terminations remains unclear. Testing the consistency of termination processes requires comparison of time series of critical climate parameters with detailed absolute and relative age control. However, such age control has been lacking for even the penultimate glacial termination (T-II), which culminated in a sea-level highstand during the last interglacial period that was several metres above present.sup.4. Here we show that Heinrich Stadial 11 (HS11), a prominent North Atlantic cold episode.sup.5,6, occurred between 135 [plus or minus] 1 and 130 [plus or minus] 2 thousand years ago and was linked with rapid sea-level rise during T-II. Our conclusions are based on new and existing.sup.6,7,8,9 data for T-II and the last interglacial that we collate onto a single, radiometrically constrained chronology. The HS11 cold episode.sup.5,6 punctuated T-II and coincided directly with a major deglacial meltwater pulse, which predominantly entered the North Atlantic Ocean and accounted for about 70 per cent of the glacial-interglacial sea-level rise.sup.8,9. We conclude that, possibly in response to stronger insolation and CO.sub.2 forcing earlier in T-II, the relationship between climate and ice-volume changes differed fundamentally from that of T-I. In T-I, the major sea-level rise clearly post-dates.sup.3,10,11 Heinrich Stadial 1. We also find that HS11 coincided with sustained Antarctic warming, probably through a bipolar seesaw temperature response.sup.12, and propose that this heat gain at high southern latitudes promoted Antarctic ice-sheet melting that fuelled the last interglacial sea-level peak., Author(s): G. Marino [sup.1] , E. J. Rohling [sup.1] [sup.2] , L. Rodríguez-Sanz [sup.1] , K. M. Grant [sup.1] , D. Heslop [sup.1] , A. P. Roberts [sup.1] , J. [...]

Way down south The recent discovery of active water-venting from the surface of Saturn's icy moon Enceladus has caused a ripple of excitement as it suggests the possibility of subsurface liquid water. Geologically, Enceladus poses problems. One, the reason why the hotspot of geological activity is centred precisely on the south pole, has been tackled by Francis Nimmo and Robert T. Pappalardo. They identify reorientation of Enceladus's rotation axis as the likely cause, and an upwelling of low-density material to the surface as the cause of that reorientation. Comparison of the distribution of impact craters on the 'leading' and 'trailing' hemispheres will be a good test of the reorientation part of the theory. Enceladus is a small icy satellite of Saturn. Its south polar region consists of young, tectonically deformed terrain and has an anomalously high heat flux.sup.1,2. This heat flux is probably due to localized tidal dissipation within either the ice shell.sup.3 or the underlying silicate core.sup.4. The surface deformation is plausibly due to upwelling of low-density material (diapirism.sup.5) as a result of this tidal heating. Here we show that the current polar location of the hotspot can be explained by reorientation of the satellite's rotation axis because of the presence of a low-density diapir. If the diapir is in the ice shell, then the shell must be relatively thick and maintain significant rigidity (elastic thickness greater than ~0.5 km); if the diapir is in the silicate core, then Enceladus cannot possess a global subsurface ocean, because the core must be coupled to the overlying ice for reorientation to occur. The reorientation generates large (~10 MPa) tectonic stress patterns.sup.6 that are compatible with the observed deformation of the south polar region.sup.2. We predict that the distribution of impact craters on the surface will not show the usual leading hemisphere-trailing hemisphere asymmetry. A low-density diapir also yields a potentially observable negative gravity anomaly., Author(s): Francis Nimmo [sup.1] , Robert T. Pappalardo [sup.2] [sup.3] Author Affiliations: (1) Department of Earth Sciences, University of California Santa Cruz, Santa Cruz, USA (2) Laboratory for Atmospheric and [...]

It is difficult to obtain a dynamic picture of the Earth's mantle. A study involving geophysical observations with geochemical implications shows that compositionally distinct megablobs contribute to the ebb and flow., Author(s): Michael Manga [sup.1] Author Affiliations: (1) Department of Earth and Planetary Sciences, University of California, Berkeley, USA The slow and continual deformation of the Earth's mantle is seen in [...]

Researchers struggle to project how fast, how high and how far the oceans will rise., Author(s): Nicola Jones [sup.1] Author Affiliations: (1) Nicola Jones is a freelance writer near Vancouver, Canada., PETE RYAN/NATL GEOGRAPHIC/GETTY The world's leading climate scientists kicked up a storm in 2007, [...]