Oxygen stable isotope ratios from British oak tree-rings provide a strong and consistent record of past changes in summer rainfall

United Kingdom (UK) summers dominated by anti-cyclonic circulation patterns are characterised by clear skies, warm temperatures, low precipitation totals, low air humidity and more enriched oxygen isotope ratios (δ18O) in precipitation. Such conditions usually result in relatively more positive (enriched) oxygen isotope ratios in tree leaf sugars and ultimately in the tree-ring cellulose formed in that year, the converse being true in cooler, wet summers dominated by westerly air flow and cyclonic conditions. There should therefore be a strong link between tree-ring δ18O and the amount of summer precipitation. Stable oxygen isotope ratios from the latewood cellulose of 40 oak trees sampled at eight locations across Great Britain produce a mean δ18O chronology that correlates strongly and significantly with summer indices of total shear vorticity, surface air pressure, and the amount of summer precipitation across the England and Wales region of the United Kingdom. The isotope-based rainfall signal is stronger and much more stable over time than reconstructions based upon oak ring widths. Using recently developed methods that are precise, efficient and highly cost-effective it is possible to measure both carbon (δ13C) and oxygen (δ18O) isotope ratios simultaneously from the same tree-ring cellulose. In our study region, these two measurements from multiple trees can be used to reconstruct summer temperature (δ13C) and summer precipitation (δ18O) with sufficient independence to allow the evolution of these climate parameters to be reconstructed with high levels of confidence. The existence of long, well-replicated oak tree-ring chronologies across the British Isles mean that it should now be possible to reconstruct both summer temperature and precipitation over many centuries and potentially millennia

Can oxygen stable isotopes be used to track precipitation moisture

Variations in the isotopic composition of precipitation are determined by fractionation processes which occur during temperature- and humidity-dependent phase changes associated with evaporation and condensation. Oxygen stable isotope ratios have therefore been frequently used as a source of palaeoclimate data from a variety of proxy archives, which integrate this signal over time. Applications from ombrotrophic peatlands, where the source water used in cellulose synthesis is derived solely from precipitation, have been mostly limited to Northern Hemisphere Sphagnum-dominated bogs, with few in the Southern Hemisphere or in peatlands dominated by vascular plants. New Zealand (NZ) provides an ideal location to undertake empirical research into oxygen isotope fractionation in vascular peatlands because single taxon analysis can be easily carried out, in particular using the preserved root matrix of the restionaceous wire rush (Empodisma spp.) that forms deep Holocene peat deposits throughout the country. Furthermore, large gradients are observed in the mean isotopic composition of precipitation across NZ, caused primarily by the relative influence of different climate modes. Here, we test whether δ18O of Empodisma α-cellulose from ombrotrophic restiad peatlands in NZ can provide a methodology for developing palaeoclimate records of past precipitation δ18O. Surface plant, water and precipitation samples were taken over spatial (six sites spanning >10◦ latitude) and temporal (monthly measurements over one year) gradients. A link between the isotopic composition of root-associated water, the most likely source water for plant growth, and precipitation in both datasets was found. Back-trajectory modelling of precipitation moisture source for rain days prior to sampling showed clear seasonality in the temporal data that was reflected in root-associated water. The link between source water and plant cellulose was less clear, although mechanistic modelling predicted mean cellulose values within published error margins for both datasets. Improved physiological understanding and modelling of δ18O in restiad peatlands should enable use of this approach as a new source of palaeoclimate data to reconstruct changes in past atmospheric circulation

Scanning Angle Plasmon Waveguide Resonance Raman Spectroscopy for the Analysis of Thin Polystyrene Films

Scanning angle (SA) Raman spectroscopy was used to characterize thin polymer films at a sapphire/50 nm gold film/polystyrene/air interface. When the polymer thickness is greater than ∼260 nm, this interface behaves as a plasmon waveguide; Raman scatter is greatly enhanced with both p- and s-polarized excitation compared to an interface without the gold film. In this study, the reflected light intensities from the interface and Raman spectra were collected as a function of incident angle for three samples with different polystyrene thicknesses. The Raman peak areas were well modeled with the calculated mean-square electric field (MSEF) integrated over the polymer film at varying incident angles. A 412 nm polystyrene plasmon waveguide generated 3.34× the Raman signal at 40.52° (the plasmon waveguide resonance angle) compared to the signal measured at 70.4° (the surface plasmon resonance angle). None of the studied polystyrene plasmon waveguides produced detectable Raman scatter using a 180° backscatter collection geometry, demonstrating the sensitivity of the SA Raman technique. The data highlight the ability to measure polymer thickness, chemical content, and, when combined with calculations of MSEF as a function of distance from the interface, details of polymer structure and order. The SA Raman spectroscopy thickness measurements agreed with those obtained from optical interferometery with an average difference of 2.6%. This technique has the potential to impact the rapidly developing technologies utilizing metal/polymer films for energy storage and electronic devices

Complex-valued wavelet lifting and applications

Signals with irregular sampling structures arise naturally in many fields. In applications such as spectral decomposition and nonparametric regression, classical methods often assume a regular sampling pattern, thus cannot be applied without prior data processing. This work proposes new complex-valued analysis techniques based on the wavelet lifting scheme that removes ‘one coefficient at a time’. Our proposed lifting transform can be applied directly to irregularly sampled data and is able to adapt to the signal(s)’ characteristics. As our new lifting scheme produces complex-valued wavelet coefficients, it provides an alternative to the Fourier transform for irregular designs, allowing phase or directional information to be represented. We discuss applications in bivariate time series analysis, where the complex-valued lifting construction allows for coherence and phase quantification. We also demonstrate the potential of this flexible methodology over real-valued analysis in the nonparametric regression context

Tropical tree growth driven by dry-season climate variability

Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink.We acknowledge financial support to the co-authors provided by Agencia Nacional de Promoción Científica y Tecnológica, Argentina (PICT 2014-2797) to M.E.F.; Alberta Mennega Stichting to P.G.; BBVA Foundation to H.A.M. and J.J.C.; Belspo BRAIN project: BR/143/A3/HERBAXYLAREDD to H.B.; Confederação da Agricultura e Pecuária do Brasil - CNA to C.F.; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES, Brazil (PDSE 15011/13-5 to M.A.P.; 88881.135931/2016-01 to C.F.; 88887.199858/2018-00 to G.A.-P.; Finance Code 001 for all Brazilian collaborators); Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq, Brazil (ENV 42 to O.D.; 1009/4785031-2 to G.C.; 311874/2017-7 to J.S.); CONACYT-CB-2016-283134 to J.V.-D.; CONICET to F.A.R.; CUOMO FOUNDATION (IPCC scholarship) to M.M.; Deutsche Forschungsgemeinschaft - DFG (BR 1895/15-1 to A.B.; BR 1895/23-1 to A.B.; BR 1895/29-1 to A.B.; BR 1895/24-1 to M.M.); DGD-RMCA PilotMAB to B.T.; Dirección General de Asuntos del Personal Académico of the UNAM (Mexico) to R.B.; Elsa-Neumann-Scholarship of the Federal State of Berlin to F.S.; EMBRAPA Brazilian Agricultural Research Corporation to C.F.; Equatorian Dirección de Investigación UNL (21-DI-FARNR-2019) to D.P.-C.; São Paulo Research Foundation FAPESP (2009/53951-7 to M.T.-F.; 2012/50457-4 to G.C.; 2018/01847‐0 to P.G.; 2018/24514-7 to J.R.V.A.; 2019/08783-0 to G.M.L.; 2019/27110-7 to C.F.); FAPESP-NERC 18/50080-4 to G.C.; FAPITEC/SE/FUNTEC no. 01/2011 to M.A.P.; Fulbright Fellowship to B.J.E.; German Academic Exchange Service (DAAD) to M.I. and M.R.; German Ministry of Education, Science, Research, and Technology (FRG 0339638) to O.D.; ICRAF through the Forests, Trees, and Agroforestry research programme of the CGIAR to M.M.; Inter-American Institute for Global Change Research (IAI-SGP-CRA 2047) to J.V.-D.; International Foundation for Science (D/5466-1) to M.I.; Lamont Climate Center to B.M.B.; Miquelfonds to P.G.; National Geographic Global Exploration Fund (GEFNE80-13) to I.R.; USA’s National Science Foundation NSF (IBN-9801287 to A.J.L.; GER 9553623 and a postdoctoral fellowship to B.J.E.); NSF P2C2 (AGS-1501321) to A.C.B., D.G.-S. and G.A.-P.; NSF-FAPESP PIRE 2017/50085-3 to M.T.-F., G.C. and G.M.L.; NUFFIC-NICHE programme (HEART project) to B.K., E.M., J.H.S., J.N. and R. Vinya; Peru ‘s CONCYTEC and World Bank (043-2019-FONDECYT-BM-INC.INV.) to J.G.I.; Peru’s Fondo Nacional de Desarrollo Científico, Tecnológico y de Innovación Tecnológica (FONDECYT-BM-INC.INV 039-2019) to E.J.R.-R. and M.E.F.; Programa Bosques Andinos - HELVETAS Swiss Intercooperation to M.E.F.; Programa Nacional de Becas y Crédito Educativo - PRONABEC to J.G.I.; Schlumberger Foundation Faculty for the Future to J.N.; Sigma Xi to A.J.L.; Smithsonian Tropical Research Institute to R. Alfaro-Sánchez.; Spanish Ministry of Foreign Affairs AECID (11-CAP2-1730) to H.A.M. and J.J.C.; UK NERC grant NE/K01353X/1 to E.G.Peer reviewe

Mineral indicators of porphyry Cu fertility

‘Fertile’ magmas which generate metal-rich porphyry Cu deposits are thought to form by similar processes to normal ‘barren’ arc magmas which are unrelated to mineralisation. However, fertile magmas contain distinctive trace element signatures, which highlight the processes by which they achieved high ore-forming potential. These ‘indicators of fertility’ make potentially useful tools to be used in the exploration of porphyry systems and may be amplified in minerals within these rocks. Intrusive rocks were collected from the Resolution and Oyu Tolgoi porphyry Cu deposits. A combination of whole rock geochemistry, and trace element analyses of apatite and zircon were carried out, and these data were compared to literature data for barren rocks. Rocks from both systems indicators of fertility, some of which (especially Sr/Y) were found to be susceptible to feldspar-destructive hydrothermal alteration. The presence of these anomalies (e.g. La/Yb, Eu/Eu*, V/Sc) is indicative of garnet control on deep crustal fractionation, which may occur due to loaclised increases in melt H2O. Zircons from Oyu Tolgoi show that Eu/Eu* and Ce4+/Ce3+ ratios in zircon were strongly controlled by the co-crystallisation of titanite, limiting their utility as measures of redox. Ce/Ce* may provide a better measure of melt redox in zircon, but is difficult to measure. Eu/Eu* may still be useful for distinguishing barren and fertile systems. Igneous apatite has high Sr and Eu/Eu* compared to barren systems. Hydrothermal apatite from a number of porphyry systems were found to contain uniquely high Fe, Mn, Pb, Sr, and Eu/Eu*, which possibly relate to their precipitation from metal rich brines. The magnitude of Mn enrichment may also be sensitive to bulk rock Cu content. These results highlight the potential of apatite and zircon as mineral indicators of porphyry fertility, and recommendations are made for how they may be used in exploration.Open Acces

Multi-proxy evidence of a mid-Holocene shift in the climatic system of Maritime Canada at ca. 6.8 ka BP

Persistent cyclical patterns of centennial- to millennial-scale changes in key climate drivers, such as North Atlantic Deep Water formation and the Atlantic Meridional Overturning Circulation, have frequently been identified in Holocene palaeorecords of the mid- and eastern-Atlantic region. Given its proximity to the major discharge routes of the Laurentide Ice Sheet and repeated meltwater discharge of varying magnitude, the western Atlantic region, however, experienced disruptions to such cyclical climate patterns during the early Holocene. Here we present evidence of a shift in the climate system of Maritime Canada coinciding with the end of meltwater discharge at ca. 6.8 ka BP. Petite Bog (45°8'43"N, 63°56'36"W), a large ombrotrophic plateau bog in central Nova Scotia, was cored and analysed as part of the PRECIP (Palaeo- REconstructions of ocean-atmosphere Coupling In Peat) project, which aims to reconstruct the spatial-temporal pattern of moisture balance changes on the eastern seaboard of North America. A multi-proxy approach using stable isotope (C, H, and O) from Sphagnum cellulose, testate amoebae and plant macrofossil analysis was used to reconstruct palaeoclimatic changes at Petite Bog. Peat accumulation of ca. 1 yr.mm-1 was consistent and near-linear throughout most of the Holocene with the exception of a clear 1,400 year long slowing to ca. 10 yr.mm-1 following the ‘8.2 ka BP cold event’. A robust chronology, constrained by 34 14C radiocarbon dates, 3 typed tephra layers and an uncut surface, provides a suitable platform for palaeoclimatic reconstructions and multi-centennial to millennial-scale time series analysis. Results show a 325-year cyclicity in bog surface wetness (BSW), and consequently atmospheric moisture availability, following the mid-Holocene slow down in accumulation. This multi-centennial cycle is not present prior to ca. 6.8 ka BP, suggesting that the end of the meltwater influence marks a distinct shift in the regional climatic regime. Underlying the entire Holocene record is a cycle with a periodicity of ca. 2,800 years. However, no evidence of the well-documented millennial-scale climate cycles was found, suggesting that Petite Bog was either insensitive to or outwith the reach of the forcing factor responsible for such climate variability in the North Atlantic region. This stands in stark contrast to the millennial-scale climate cycle identified in BSW reconstructions at Nordan’s Pond Bog, Newfoundland. Findings from Petite Bog show a clear shift to a multi-centennial cyclicity in the regional climate system following the end of meltwater influence and highlight the complexity of Holocene climate in Atlantic Canada

Genetic sampling identifies canid predators of koalas (Phascolarctos cinereus) in peri-urban areas

An understanding of the threats to threatened species in urban and peri-urban areas is essential to develop successful management approaches. Dog attacks are considered to be a major contributor to koala (Phascolarctos cinereus) mortalities in peri-urban areas of north-eastern Australia. Predation could be due to either domestic dogs or wild dogs (dingoes and dingo-domestic dog hybrids), gentically-identifiable groups of Canis familiaris. Here, we aimed to use genetic sampling methods to determine or verify the identity, number and successful removal of canid predators of koalas in a peri-urban environment in south-eastern Queensland. Genetic samples were taken from the remains of 12 koalas suspected to have died from predation. Canine genotypes were present on 11 of 12 predated koalas (∼92%) and were from wild dogs, not domestic dogs. Most koalas had only one canine genotype identified, suggesting they were killed by a single dog. Our results show that DNA samples collected from deceased prey species can be used to identify the predator, and distinguish between closely-related species, and hybrids of the two. Genetic methods confirmed the identification of the predator obtained through conventional necropsy and support growing evidence that wild dog predation is a significant cause of koala mortality in this region. Strategies to reduce predation on koalas should therefore focus on reducing the impact of free-ranging wild dog populations. This approach is important to identify and target those canids responsible for predation of threatened prey populations, particularly where multiple predators are present and/or predator removals may be controversial