• Recent enhancement of central Pacific El Nino variability relative to last eight centuries

      Liu, Yu; Cobb, Kim M.; Song, Huiming; Li, Qiang; Li, Ching-Yao; Nakatsuka, Takeshi; An, Zhisheng; Zhou, Weijian; Cai, Qiufang; Li, Jinbao; et al. (NATURE PUBLISHING GROUP, 2017-05-30)
      The far-reaching impacts of central Pacific El Nino events on global climate differ appreciably from those associated with eastern Pacific El Nino events. Central Pacific El Nino events may become more frequent in coming decades as atmospheric greenhouse gas concentrations rise, but the instrumental record of central Pacific sea-surface temperatures is too short to detect potential trends. Here we present an annually resolved reconstruction of NINO4 sea-surface temperature, located in the central equatorial Pacific, based on oxygen isotopic time series from Taiwan tree cellulose that span from 1190 AD to 2007 AD. Our reconstruction indicates that relatively warm Nino4 sea-surface temperature values over the late twentieth century are accompanied by higher levels of interannual variability than observed in other intervals of the 818-year-long reconstruction. Our results imply that anthropogenic greenhouse forcing may be driving an increase in central Pacific El Nino-Southern Oscillation variability and/or its hydrological impacts, consistent with recent modelling studies.
    • Resilience of the Asian atmospheric circulation shown by Paleogene dust provenance

      Licht, A.; Dupont-Nivet, G.; Pullen, A.; Kapp, P.; Abels, H. A.; Lai, Z.; Guo, Z.; Abell, J.; Giesler, D.; Univ Arizona, Dept Geosci (NATURE PUBLISHING GROUP, 2016-08-04)
      The onset of modern central Asian atmospheric circulation is traditionally linked to the interplay of surface uplift of the Mongolian and Tibetan-Himalayan orogens, retreat of the Paratethys sea from central Asia and Cenozoic global cooling. Although the role of these players has not yet been unravelled, the vast dust deposits of central China support the presence of arid conditions and modern atmospheric pathways for the last 25 million years (Myr). Here, we present provenance data from older (42-33 Myr) dust deposits, at a time when the Tibetan Plateau was less developed, the Paratethys sea still present in central Asia and atmospheric pCO(2) much higher. Our results show that dust sources and near-surface atmospheric circulation have changed little since at least 42 Myr. Our findings indicate that the locus of central Asian high pressures and concurrent aridity is a resilient feature only modulated by mountain building, global cooling and sea retreat.
    • Seismic evidence for a cold serpentinized mantle wedge beneath Mount St Helens

      Hansen, S. M.; Schmandt, B.; Levander, A.; Kiser, E.; Vidale, J. E.; Abers, G. A.; Creager, K. C.; Univ Arizona, Dept Geosci (NATURE PUBLISHING GROUP, 2016-11-01)
      Mount St Helens is the most active volcano within the Cascade arc; however, its location is unusual because it lies 50 km west of the main axis of arc volcanism. Subduction zone thermal models indicate that the down-going slab is decoupled from the overriding mantle wedge beneath the forearc, resulting in a cold mantle wedge that is unlikely to generate melt. Consequently, the forearc location of Mount St Helens raises questions regarding the extent of the cold mantle wedge and the source region of melts that are responsible for volcanism. Here using, high-resolution active-source seismic data, we show that Mount St Helens sits atop a sharp lateral boundary in Moho reflectivity. Weak-to-absent PmP reflections to the west are attributed to serpentinite in the mantle-wedge, which requires a cold hydrated mantle wedge beneath Mount St Helens (V similar to 700 degrees C). These results suggest that the melt source region lies east towards Mount Adams.
    • Shear-induced Notch-Cx37-p27 axis arrests endothelial cell cycle to enable arterial specification

      Fang, Jennifer S.; Coon, Brian G.; Gillis, Noelle; Chen, Zehua; Qiu, Jingyao; Chittenden, Thomas W.; Burt, Janis M.; Schwartz, Martin A.; Hirschi, Karen K.; Univ Arizona, Dept Physiol, Coll Med (NATURE PUBLISHING GROUP, 2017-12-15)
      Establishment of a functional vascular network is rate-limiting in embryonic development, tissue repair and engineering. During blood vessel formation, newly generated endothelial cells rapidly expand into primitive plexi that undergo vascular remodeling into circulatory networks, requiring coordinated growth inhibition and arterial-venous specification. Whether the mechanisms controlling endothelial cell cycle arrest and acquisition of specialized phenotypes are interdependent is unknown. Here we demonstrate that fluid shear stress, at arterial flow magnitudes, maximally activates NOTCH signaling, which upregulates GJA4 (commonly, Cx37) and downstream cell cycle inhibitor CDKN1B (p27). Blockade of any of these steps causes hyperproliferation and loss of arterial specification. Re-expression of GJA4 or CDKN1B, or chemical cell cycle inhibition, restores endothelial growth control and arterial gene expression. Thus, we elucidate a mechanochemical pathway in which arterial shear activates a NOTCH-GJA4-CDKN1B axis that promotes endothelial cell cycle arrest to enable arterial gene expression. These insights will guide vascular regeneration and engineering.
    • Surface uplift in the Central Andes driven by growth of the Altiplano Puna Magma Body

      Perkins, Jonathan P.; Ward, Kevin M.; de Silva, Shanaka L.; Zandt, George; Beck, Susan L.; Finnegan, Noah J.; Univ Arizona, Dept Geosci (NATURE PUBLISHING GROUP, 2016-10-25)
      The Altiplano-Puna Magma Body (APMB) in the Central Andes is the largest imaged magma reservoir on Earth, and is located within the second highest orogenic plateau on Earth, the Altiplano-Puna. Although the APMB is a first-order geologic feature similar to the Sierra Nevada batholith, its role in the surface uplift history of the Central Andes remains uncertain. Here we show that a long-wavelength topographic dome overlies the seismically measured extent of the APMB, and gravity data suggest that the uplift is isostatically compensated. Isostatic modelling of the magmatic contribution to dome growth yields melt volumes comparable to those estimated from tomography, and suggests that the APMB growth rate exceeds the peak Cretaceous magmatic flare-up in the Sierran batholith. Our analysis reveals that magmatic addition may provide a contribution to surface uplift on par with lithospheric removal, and illustrates that surface topography may help constrain the magnitude of pluton-scale melt production.
    • Temperature mediates continental-scale diversity of microbes in forest soils

      Zhou, Jizhong; Deng, Ye; Shen, Lina; Wen, Chongqing; Yan, Qingyun; Ning, Daliang; Qin, Yujia; Xue, Kai; Wu, Liyou; He, Zhili; et al. (NATURE PUBLISHING GROUP, 2016-07-05)
      Climate warming is increasingly leading to marked changes in plant and animal biodiversity, but it remains unclear how temperatures affect microbial biodiversity, particularly in terrestrial soils. Here we show that, in accordance with metabolic theory of ecology, taxonomic and phylogenetic diversity of soil bacteria, fungi and nitrogen fixers are all better predicted by variation in environmental temperature than pH. However, the rates of diversity turnover across the global temperature gradients are substantially lower than those recorded for trees and animals, suggesting that the diversity of plant, animal and soil microbial communities show differential responses to climate change. To the best of our knowledge, this is the first study demonstrating that the diversity of different microbial groups has significantly lower rates of turnover across temperature gradients than other major taxa, which has important implications for assessing the effects of human-caused changes in climate, land use and other factors.
    • Ultra-strong nonlinear optical processes and trigonal warping in MoS2 layers

      Säynätjoki, Antti; Karvonen, Lasse; Rostami, Habib; Autere, Anton; Mehravar, Soroush; Lombardo, Antonio; Norwood, Robert A.; Hasan, Tawfique; Peyghambarian, Nasser; Lipsanen, Harri; et al. (NATURE PUBLISHING GROUP, 2017-10-12)
      Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e. g., microscopy, therapy, and frequency conversion. However, high-order harmonic conversion is typically much less efficient than low-order, due to the weak intrinsic response of the higher-order nonlinear processes. Here we report ultra-strong optical nonlinearities in monolayer MoS2 (1L-MoS2): the third harmonic is 30 times stronger than the second, and the fourth is comparable to the second. The third harmonic generation efficiency for 1L-MoS2 is approximately three times higher than that for graphene, which was reported to have a large chi((3)). We explain this by calculating the nonlinear response functions of 1L-MoS2 with a continuum-model Hamiltonian and quantum mechanical diagrammatic perturbation theory, highlighting the role of trigonal warping. A similar effect is expected in all other transition-metal dichalcogenides. Our results pave the way for efficient harmonic generation based on layered materials for applications such as microscopy and imaging.
    • Voltage-controlled interlayer coupling in perpendicularly magnetized magnetic tunnel junctions

      Newhouse-Illige, T.; Liu, Yaohua; Xu, M.; Reifsnyder Hickey, D.; Kundu, A.; Almasi, H.; Bi, Chong; Wang, X.; Freeland, J. W.; Keavney, D. J.; et al. (NATURE PUBLISHING GROUP, 2017-05-16)
      Magnetic interlayer coupling is one of the central phenomena in spintronics. It has been predicted that the sign of interlayer coupling can be manipulated by electric fields, instead of electric currents, thereby offering a promising low energy magnetization switching mechanism. Here we present the experimental demonstration of voltage-controlled interlayer coupling in a new perpendicular magnetic tunnel junction system with a GdOx tunnel barrier, where a large perpendicular magnetic anisotropy and a sizable tunnelling magnetoresistance have been achieved at room temperature. Owing to the interfacial nature of the magnetism, the ability to move oxygen vacancies within the barrier, and a large proximity-induced magnetization of GdOx, both the magnitude and the sign of the interlayer coupling in these junctions can be directly controlled by voltage. These results pave a new path towards achieving energy-efficient magnetization switching by controlling interlayer coupling.
    • Western Pacific hydroclimate linked to global climate variability over the past two millennia

      Griffiths, Michael L.; Kimbrough, Alena K.; Gagan, Michael K.; Drysdale, Russell N.; Cole, Julia E.; Johnson, Kathleen R.; Zhao, Jian-Xin; Cook, Benjamin I.; Hellstrom, John C.; Hantoro, Wahyoe S.; et al. (NATURE PUBLISHING GROUP, 2016-06-08)
      Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known. Here we present a 2,000-year, multiproxy reconstruction of western Pacific hydroclimate from two speleothem records for southeastern Indonesia. The composite record shows pronounced shifts in monsoon rainfall that are antiphased with precipitation records for East Asia and the central-eastern equatorial Pacific. These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between similar to 1000 and 1500 CE Conversely, an equatorward contraction of the Intertropical Convergence Zone and strengthened PWC occurred between similar to 1500 and 1900 CE. Our findings, together with climate model simulations, highlight the likelihood that century-scale variations in tropical Pacific climate modes can significantly modulate radiatively forced shifts in global temperature.