Two global glaciations occurred during the Neoproterozoic. Snowball Earth theory posits that these were terminated after millions of years of frigidity when initial warming from rising atmospheric CO2 concentrations was amplified by the reduction of ice cover and hence a reduction in planetary albedo1, 2. This scenario implies that most of the geological record of ice cover was deposited in a brief period of melt-back3. However, deposits in low palaeo-latitudes show evidence of glacial?interglacial cycles4, 5, 6. Here we analyse the sedimentology and oxygen and sulphur isotopic signatures of Marinoan Snowball glaciation deposits from Svalbard, in the Norwegian High Arctic. The deposits preserve a record of oscillations in glacier extent and hydrologic conditions under uniformly high atmospheric CO2 concentrations. We use simulations from a coupled three-dimensional ice sheet and atmospheric general circulation model to show that such oscillations can be explained by orbital forcing in the late stages of a Snowball glaciation. The simulations suggest that while atmospheric CO2 concentrations were rising, but not yet at the threshold required for complete melt-back, the ice sheets would have been sensitive to orbital forcing. We conclude that a similar dynamic can potentially explain the complex successions observed at other localities. Document embargo 24/02/2016.Peer reviewe

SummaryOsteoporosis and the associated risk of fracture are major clinical challenges in the elderly. Telomeres shorten with age in most human tissues, including bone, and because telomere shortening is a cause of cellular replicative senescence or apoptosis in cultured cells, including mesenchymal stem cells (MSCs) and osteoblasts, it is hypothesized that telomere shortening contributes to the aging of bone. Osteoporosis is common in the Werner (Wrn) and dyskeratosis congenita premature aging syndromes, which are characterized by telomere dysfunction.

Each of two calcitic stalagmites from Grotte de Clamouse, Herault, southern France, displays a discrete aragonite layer dated at around 1100 yr BP. The layer of fanning aragonite ray crystals is immediately preceded by calcite with Mg and Sr compositions that are uniquely high for the past 3 kyr. Trace element compositions close to the boundary between original aragonite and calcite are consistent with quasi-equilibrium partitioning of trace elements between the phases. Study of modern dripwaters demonstrates that pronounced covariation of Mg/Ca and Sr/Ca ratios in dripwater occurs owing to large amounts of calcite precipitation upflow of the drips that fed the stalagmites. Trace element to Ca ratios are enhanced during seasonally dry periods. Ion microprobe data demonstrate a pronounced covariation of trace elements, including Mg and Sr in calcite, and Sr, U and Ba in aragonite. The mean peak spacing is close to the long-term mean of annual growth rates determined by differences in U-series ages and so the trace element peaks are interpreted as annual. The trace element chemistry of the stalagmites on annual to inter-annual scales thus directly reflects the amounts of prior calcite precipitation, interpreted as an index of aridity. The longer-term context is a multi-decadal period of aridity (1200-1100 yr BP) possibly correlated with an analogous episode in Central America. The arid period culminated in the nucleation of aragonite, but within a decade was followed by a return to precursor conditions.

This is the peer reviewed version of the following article: Fairchild, I. J., Fleming, E. J., Bao, H., Benn, D. I., Boomer, I., Dublyansky, Y. V., Halverson, G. P., Hambrey, M., Hendy, C., Mcmillan, E. A., Sp?tl, C., Stevenson, C. T. E. & Wynn, P. M. (2015). Continental carbonate facies of a Neoproterozoic panglaciation, north-east Svalbard. Sedimentology., which has been published in final form at http://dx.doi.org/doi:10.1111/sed.12252. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The Marinoan panglaciation (?650 to 635 Ma) is represented in north-east Svalbard by the 130 to 175 m thick Wilsonbreen Formation which contains syn-glacial carbonates in its upper 100 m. These sediments are now known to have been deposited under a CO2-rich atmosphere, late in the glaciation, and global climate models facilitate testing of proposed analogues. Precipitated carbonates occur in four of the seven facies associations identified: Fluvial Channel (including stromatolitic and intraclastic limestones in ephemeral stream deposits); Dolomitic Floodplain (dolomite-cemented sand and siltstones, and microbial dolomites); Calcareous Lake Margin (intraclastic dolomite and wave-rippled or aeolian siliciclastic facies); and Calcareous Lake (slump-folded and locally re-sedimented rhythmic/stromatolitic limestones and dolomites associated with ice-rafted sediment). There is no strong cyclicity, and modern analogues suggest that sudden changes in lake level may exert a strong control on facies geometry. Both calcite and dolomite in stromatolites and rhythmites display either primary or early diagenetic replacive growth. Oxygen isotope values (-12 to +15?VPDB) broadly covary with ?13C. High ?13C values of +3.5 to +4.5? correspond to equilibration with an atmosphere dominated by volcanically degassed CO2 with ?13C of -6 to -7?. Limestones have consistently negative ?18O values, whilst rhythmic and playa dolomites preserve intermediate compositions, and dolocretes possess slightly negative to strongly positive ?18O signatures, reflecting significant evaporation under hyperarid conditions. Inferred meltwater compositions (-8 to -15.5?) could reflect smaller Rayleigh fractionation related to more limited cooling than in modern polar regions. A common pseudomorph morphology is interpreted as a replacement of ikaite (CaCO3.H2O), which may also have been the precursor for widespread replacive calcite mosaics. Local dolomitization of lacustrine facies is interpreted to reflect microenvironments with fluctuating redox conditions. Although differing in (palaeo)latitude and carbonate abundance, the Wilsonbreen carbonates provide strong parallels with the McMurdo Dry Valleys of Antarctica.authorsversionpublishersversionPeer reviewe

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