interdecadal changes in the enso teleconnection to the caribbean region and the north atlantic oscillation abstract the el nino southern oscillation enso phenomenon and variability in the subtropical north atlantic high sea level pressure slp are known to affect rainfall in the caribbean region an el nino event is associated with drier than average conditions during the boreal summer of year 0 and wetter than average conditions during the spring of year 1 dry conditions during the summer of year 0 of an el nino are associated with the locally divergent surface circulation engendered by the eastward shift of deep convection in the pacific ocean wet conditions during the spring of year 1 of an el nino are associated with the lagged warming of the tropical north atlantic ocean variability in the strength of the north atlantic high is governed mainly by the north atlantic oscillation nao with a positive nao phase implying a stronger than normal high and vice versa the nao is negatively correlated with caribbean rainfall indirectly via anomalous sea surface temperatures sst associated with a

ejecta from impact craters an important feature of impacts into solar system bodies is the fate of crater ejecta the near surface material launched during the highly dynamic crater formation process laboratory measurements of impact crater ejecta from 18 studies are summarized the data are examined and used to assess our understanding of how the ejecta velocity and mass distributions depend on the conditions of an impact event the effects of impact speed on the ejecta are reasonably well understood but the dependences on target properties such as strength and porosity are only poorly constrained a point source scaling model for the ejecta mass and velocity distributions is developed and fit to the data for several classes of materials distinguished by porosity

density porosity and magnetic susceptibility of carbonaceous chondrites abstract we report physical properties bulk and grain density magnetic susceptibility and porosity measured using nondestructive and noncontaminating methods for 195 stones from 63 carbonaceous chondrites grain densities over the whole population average 3 44 g cm 3 ranging from 2 42 g cm 3 ci1 orgueil to 5 66 g cm 3 cb bencubbin magnetic susceptibilities in log units of 10 9 m3 kg 1 averaged log 4 22 ranging from 3 23 cv3 axtell to 5 79 cb bencubbin porosities averaged 17 ranging from 0 for a number of meteorites to 41 for one stone of the co ornans notably we found significant differences in porosity between the oxidized and reduced cv subgroups with the porosities of cvo averaging approximately 20 and cvr porosities approximately 4 overall porosities of carbonaceous chondrite falls trend with petrographic type from type 1 ci near 35 type 2 cm cr averaging 23 type 3 cv co 21 to type 4 ck and some co averaging 15 there is also a significant decrease in porosity between meteorites of shock stage s1 and those of s2 indicative of shock compression

holocene climate and seasonality of shell collection at the dundas islands group northern british columbia canada a bivalve sclerochronological approach article i nfo to analyze environmental changes and the seasonality of shell collection in british columbia during the ho locene oxygen isotopes were measured from modern and archeological 1337 7438 cal yr bp shells of the butter clam saxidomus gigantea 1697 discrete isotope samples were taken from two modern and 27 arche ological shells with a high temporal resolution sub seasonal up to daily archeological shells were collected from five shell midden sites on the dundas islands group northern british columbia canada the oxygen iso tope data reveal clear annual cycles with the most positive 18 oshell values occurring during the cold season slower growth annual growth line formation and the most negative 18 oshell values during the warm sea son period of faster growth whereas the most positive 18 oshell values remained relatively constant throughout the holocene the warm season 18 oshell values reflected considerable variability summer values observed in the early and late holocene became approximately 1 more negative around 2500 3000 and 5500 6000 bp implying lower salinity during the mid holocene variations in the oxygen isotopic composi tion of marine shells reflect changes in temperature and salinity such large changes in 18 oshell are unlikely being caused by temperature changes alone furthermore the large annual 18

late holocene teleconnections between tropical pacific climatic variability and precipitation in the western usa evidence from proxy records decadal to multidecadal fluctuations between drought and relatively more moist conditions are a defining characteristic of precipitation variability in the western usa in an attempt to better understand the forcing mechanisms responsible for producing this variability relationships between proxy indices of tropical climatic variability and precipitation related reconstructions in the western usa are examined the tropical proxies include the o record from the quelccaya ice cap southern subtropical andes and the lacustrine sedimentation record from laguna pallcacocha near equatorial andes the precipi tation related records are tree ring reconstructions of river flow drought severity and precipitation over the contiguo usa one new finding is a consistent relation between decadal variability in el ninno activity and precipitation related proxies through much of the western usa during the past 1200 years surpris ingly the proxy records do not show a systematic link between inferred el ninno activity and precipitation in the interior southwest usa a second new result is the existence of relationships at decadal to multidecadal timescales between fluctuations in quelccaya o precipitation related proxies from the western usa and proxy records from the pacific basin this finding links the quelccaya record to the transhemi spheric pacific decadal scale climatic variability documented from proxy records by villalba et al 2001 and suggests that similar changes in the large scale circulation changes accompany both the decadal and multidecadal signals a composite constructed using gridded proxy precipitation constructed on the basis of decadal scale fluctuations in inferred el ninno activity shows a pattern rather different to ninno based teleconnection maps for the instrumental record in the proxy based composite positive values cover much of the extreme western west central and southeastern usa with negative values in the central mis sissippi valley the interior southwest shows essentially no response a second composite based on multi decadal variability in quelccaya o shows a well developed dipole pattern across the western usa with opposing centres in the interior southwest and northwest it is suggested that this dipole pattern results from multidecadal variability in tropical pacific ssts and resulting changes in the strength of the northeast pacific high and the latitudinal distribution of cool season westerlies across the eastern north pacific and western usa

hydroclimatic change in southern manitoba since a d 1409 inferred from tree rings abstract a record of estimated annual prior august to current july precipitation derived from a regional bur oak quercus macrocarpa michx tree ring chronology indicates that southern manitoba s hydroclimate has been relatively stable over the last 200 yr although this stability was interrupted briefly by pronounced wet intervals in the late a d 1820s and 1850s hydroclimatic conditions since permanent euro canadian settlement were much less variable and persistent than those prior to a d 1790 the reconstruction indicates that the red river basin experienced extremely dry conditions between a d 1670 and 1775 with below normal precipitation occurring approximately 2 years out of 3 annual precipitation was estimated at more than two standard deviations below the mean during a d 1477 1485 1556 1595 1612 1644 1661 1743 1900 and 1980 comparisons with limnological records from north dakota and minnesota suggest that multidecadal fluctuations in regional hydroclimate have been remarkably coherent across the northeastern great plains during the last 600 yr however individual dry years in the red river basin were usually associated with larger scale drought across much of the north american interior

convection in a volatile nitrogen ice rich layer drives pluto s geological vigour the volatile ice filled basin informally named sputnik planum is central to pluto s geological activity this ice layer is organized into cells or polygons and it is now shown that convective overturn in a several kilometre thick layer of solid nitrogen can explain both the presence of the cells and their great width nasa s new horizons spacecraft has revealed fascinating details of the surface of pluto including a vast ice filled basin known as sputnik planum which is central to pluto s geological activity much of the surface of sputnik planum consisting mostly of nitrogen ice is divided into irregular polygons that are tens of kilometres in diameter and whose centres rise tens of metres above their sides two papers in this issue of nature analyse new horizons images of this polygonal terrain both conclude that it is continually being resurfaced by convection but arrive at contrasting models for the process alexander trowbridge et al report a parameterized convection model in which the nitrogen ice is vigorously convecting ten or more kilometres thick and about a million years old william mckinnon et al from the new horizons team show that sluggish lid convective overturn in a several kilometre thick layer of solid nitrogen can explain both the presence of the cells and their great width the vast deep volatile ice filled basin informally named sputnik planum is central to pluto s vigorous geological activity1 2 composed of molecular nitrogen methane and carbon monoxide ices3 but dominated by nitrogen ice this layer is organized into cells or polygons typically about 10 to 40 kilometres across that resemble the surface manifestation of solid state convection1 2 here we report on the basis of available rheological measurements4 that solid layers of nitrogen ice with a thickness in excess of about one kilometre should undergo convection for estimated present day heat flow conditions on pluto more importantly we show numerically that convective overturn in a several kilometre thick layer of solid nitrogen can explain the great lateral width of the cells the temperature dependence of nitrogen ice viscosity implies that the ice layer convects in the so called sluggish lid regime5 a unique convective mode not previously definitively observed in the solar system average surface horizontal velocities of a few centimetres a year imply surface transport or renewal times of about 500 000 years well under the ten million year upper limit crater retention age for sputnik planum2 similar convective surface renewal may also occur on other dwarf planets in the kuiper belt which may help to explain the high albedos shown by some of these bodies

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

accretion timescales and style of asteroidal differentiation in an 26al poor protoplanetary disk the decay of radioactive 26al to 26mg half life of 730 000 years is postulated to have been the main energy source promoting asteroidal melting and differentiation in the nascent solar system high resolution chronological information provided by the 26al 26mg decay system is therefore intrinsically linked to the thermal evolution of early formed planetesimals in this paper we explore the timing and style of asteroidal differentiation by combining high precision mg isotope measurements of meteorites with thermal evolution models for planetesimals in detail we report mg isotope data for a suite of olivine rich al mg 0 achondritic meteorites as well as a few chondrites main group pyroxene and the zinder pallasites as well as the lodranite all record deficits in the mass independent component of 26mg 26mg relative to chondrites and earth this isotope signal is expected for the retarded ingrowth of radiogenic 26mg in olivine rich residues produced through partial silicate melting during 26al decay and consistent with their marginally heavy mg isotope composition relative to ordinary chondrites which may reflect the early extraction of isotopically light partial melts from the source rock we propose that their parent planetesimals started forming within 250 000 years of solar system formation from a hot 500 k inner protoplanetary disk region characterized by a reduced initial 26al 27al 0 abundance 1 2 10 5 relative to the 26al 27al 0 value in cais of 5 25 10 5 this effectively reduced the total heat production and allowed for the preservation of solid residues produced through progressive silicate melting with depth within the planetesimals these non carbonaceous planetesimals acquired their mass throughout an extended period 3 myr of continuous accretion thereby generating onion shell structures of incompletely differentiated zones consisting of olivine rich residues overlaid by metachondrites and undifferentiated chondritic crusts in contrast individual olivine crystals from eagle station pallasites record variable 26mg excesses suggesting that these crystals captured the 26mg evolution of a magmatic reservoir controlled by fractional crystallization processes during the lifespan of 26al similar to previous suggestions based on isotopic evidence we suggest that eagle station pallasites formed from precursor material similar in composition to carbonaceous chondrites from a cool outer protoplanetary disk region characterized by 26al 27al 0 2 7 10 5 protracted planetesimal accretion timescales at large orbital distances with onset of accretion 0 3 1 myr post cais may have resulted in significant radiative heat loss and thus efficient early interior cooling of slowly accreting carbonaceous planetesimals

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

three layered models of ganymede and callisto compositions structures and aspects of evolution abstract three layered structural models are determined for ganymede and callisto each consists of a rock core a mixed ice rock lower mantle and a pure ice upper mantle this structure results from differentiation subsequent to accretional melting attention is given to evaluating various candidates for the rock component and three alternatives representing various degrees of silicate hydration and oxidation are modeled and incorporated structures are calculated on the basis of a 250 k isotherm which is a reasonablev approximation to the gentle adiabats expected to occur in icy satellites differentiation of an ice rock satellite generally involves an increase in radius and the three layered approach allows this process to be examined in some detail it is determined that satellite expansion is most significant early in the process and much less so as differentiation proceeds to completion if tectonics are due to global expansion distinguishing on this basis between a completely differentiated satellite and one that is only partially differentiated is difficult the postaccretional global expansion of ganymede which may have left a tectonic record was probably limited to 1 in radius in agreement with observed limits useful quantities such as silicate mass and volume fraction uncompressed density j2 c22 binding energy and surface heat flow are also determined nonhydrostatic contributions to j2 and c22 are estimated and shown to be nonnegligible encounters with jupiter orbiting spacecraft are unlikely to determine callisto s degree of central condensation we conclude by calculating the relative likelihood of postaccretional melting caused by radiogenic heating three layered satellites have generally hotter interiors because additional thermal boundary layers divide the separately convecting upper and lower mantles inhibiting heat transport ganymedes and callistos that are less than about 1 3 differentiated by mass should experience a second episode of melting as these boundary layers are either above the level of the water ice minimum melting temperature or intersect the melting curve at deeper levels runaway differentiation to at least a depth corresponding to a pressure in the ice v stability field is likely the main point here is that if satellite tectonics are tied to differentiation by melting or its aftermath as in the instability following ocean closure of kirk and stevenson moderate or small amounts of accretional differentiation are unlikely to explain an absence of tectonics as in callisto because extensive differentiation ultimately occurs

the changing relationship between enso variability and moisture balance in the continental united states the el nino southern oscillation enso system orchestrates a well documented suite of climate anomalies worldwide the details of enso s extratropical influence vary among events but this variability has not been described or diagnosed beyond the past few decades and previous descriptions have looked at inter event differences rather than decadal patterns we use a new tree ring based drought reconstruction for the continental u s and instrumental enso indices to document systematic decadal changes in the u s drought enso relationship since the late 19th century significant enso drought correlation occurs consistently in the southwest u s but the strength of penetration of moisture anomalies into the continent varies substantially the most striking change over the past 130 years is the initiation of a bipolar enso drought signature around 1920 producing opposite sign moisture anomalies in the southwest and mid atlantic states shifts in teleconnection patterns coincide with variations in the strength of enso and in a north pacific mode

the fall recovery orbit and composition of the tagish lake meteorite a new type of carbonaceous chondrite the preatmospheric mass of the tagish lake meteoroid was about 200 000 kilograms its calculated orbit indicates affinity to the apollo asteroids with a semimajor axis in the middle of the asteroid belt consistent with a linkage to low albedo c d and p type asteroids the mineralogy oxygen isotope and bulk chemical composition of recovered samples of the tagish lake meteorite are intermediate between cm and ci meteorites these data suggest that the tagish lake meteorite may be one of the most primitive solar system materials yet studied

satellite radar interferometry for assessing coseismic liquefaction in portoviejo city induced by the mw 7 8 2016 pedernales ecuador earthquake the portoviejo city located in the central part of the ecuadorian pacific coast province of manabi was severely affected during the pedernales mw 7 8 earthquake of april 16 2016 accompanied by coseismic liquefaction phenomena that induced processes of ground subsidence lateral spreading sinkhole and sand boils the present study proposes the detection and delimitation of the areas affected by the relief deformation associated liquefaction processes which occurred in the urban area of portoviejo city and especially in the zero zone of greater destruction after the earthquake through the application of differential interferometry synthetic aperture radar insar methodology using sentinel 1a satellite images plus the support of geological geotechnical data obtained from boreholes and standard penetration tests to evaluate the liquefaction potential of the layers of the subsoil based on the potential liquefaction index considering the seismic scenario of amax 0 5 g for the urban area and the zero zone this procedure allowed the delimitation of areas of high seismic risk for the proper coordination and management of the construction and reconstruction processes in the city of portoviejo and specifically in the ground zero

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

reconstruction of drought variability in north china and its association with sea surface temperature in the joining area of asia and indian pacific ocean abstract using tree ring data from the northernmost marginal area of the east asian summer monsoon easm in north china may july mean palmer drought severity index pdsi was reconstructed back to 1767 ad the reconstruction captured 52 8 of the variance over the calibration period from 1945 to 2005 ad and showed pronounced pluvial periods during 1850 1905 1803 1811 and 1940 1961 and dry periods during 1814 1844 1916 1932 and 1984 2012 these anomalous periods have previously been reported in other parts of north china spatial correlation analyses and comparisons with other hydroclimatic indices in north china indicated that our new pdsi reconstruction could represent spatial and temporal drought variability in this region well our work also suggested that the drying tendency currently observed in the northern part of north china including the study area is consistent with the weakening of the easm meanwhile the drying trend was seemingly restrained at present in the southern part of north china spatial correlation patterns with global sea surface temperature sst indicated that the regional hydroclimatic variability in north china was tightly linked to sst over the joining area of asia and indian pacific ocean aipo especially over the tropical western pacific when sst from prior november to current july nj sst in the aipo area was anomalously high low the thermal contrast between asian land and ocean was weakened strengthened and the easm was correspondingly weakened strengthened thereby causing droughts pluvials in north china the results of this study do not only provide useful information for assessing the long term climate change in north china but also suggest that abnormal variability in nj sst over the aipo area could be used to forecast hydroclimatic conditions in north china

recent tectonic activity on pluto driven by phase changes in the ice shell the new horizons spacecraft has found evidence for geologic activity on the surface of pluto including extensional tectonic deformation of its water ice bedrock see moore et al 2016 one mechanism that could drive extensional tectonic activity is global surface expansion due to the partial freezing of an ocean we use updated physical properties for pluto and simulate its thermal evolution to understand the survival of a possible subsurface ocean for thermal conductivities of rock less than 3 w m 1 k 1 an ocean forms and at least partially freezes leading to recent extensional stresses in the ice shell in scenarios where the ocean freezes and the ice shell is thicker than 260 km ice ii forms and causes global volume contraction since there is no evidence for recent compressional tectonic features we argue that ice ii has not formed and that pluto s ocean has likely survived to present day

the nature and origin of charon s smooth plains charon displays extensive plains that cover the equatorial area and south to the terminator on the sub pluto hemisphere observed by new horizons we hypothesize that these plains are a result of charon s global extension and early subsurface ocean yielding a large cryoflow that completely resurfaced this area leaving the plains and other features that we observe today the cryoflow consisted of ammonia rich material and could have resurfaced this area either by cryovolcanic effusion similar to lunar maria emplacement or a mechanism similar to magmatic stoping where lithospheric blocks foundered geological observations modeling of possible flow rheology and an analysis of rille orientations support these hypotheses

environmental reconstruction from a varve network in the southern coast mountains british columbia canada cores of annually laminated sediments varves from five lakes in the southern coast mountains of british columbia canada document clastic sediment response to climate and geomorphic change over the past 120 years interannual varve thickness correlates with annual flood magnitude interdecadal trends in varve thickness are influenced by other environmental factors such as glacier recession despite major differences in the lakes and their contributing watersheds substantial concordance is observed among the records a pronounced change in the nature of lake sedimentation accompanied by higher interannual variability occurred in 1980 the change coincides with an increase in the magnitude of autumn flooding and major re organization of the north pacific climate system these results highlight new directions for palaeoenvironmental research using varved sediment records specifically to study the magnitude and spatial extent of past hydro climatic events

geology before pluto pre encounter considerations the cameras of new horizons will provide robust data sets that should be imminently amenable to geological analysis of the pluto system s landscapes in this paper we begin with a brief discussion of the planned observations by the new horizons cameras that will bear most directly on geological interpretability then we broadly review the major geological processes that could potentially operate on the surfaces of pluto and its major moon charon we first survey exogenic processes i e those for which energy for surface modification is supplied externally to the planetary surface impact cratering sedimentary processes including volatile migration and the work of wind we conclude with an assessment of the prospects for endogenic activity in the form of tectonics and cryovolcanism

using the density of kuiper belt objects to constrain their composition and formation history telescopic observations of kuiper belt objects have enabled bulk density determinations for 17 objects these densities vary systematically with size perhaps suggesting systematic variations in bulk composition we find this trend can be explained instead by variations in porosity arising from the higher pressures and warmer temperatures in larger objects we are able to match the density of 14 of 17 kbos within their 2 errors with a constant rock mass fraction of 70 suggesting a compositionally homogeneous rock rich reservoir because early 26al would have removed too much porosity in small 100 km kbos we find the minimum formation time to be 4 myr after solar system formation this suggests that coagulation and not gravitational collapse was the dominant mechanism for kbo formation we also use this model to make predictions for the density of makemake 2007 or10 and mu69

drought variability in the pacific northwest from a 6 000 yr lake sediment record we present a 6 000 yr record of changing water balance in the pacific northwest inferred from measurements of carbonate 18o and grayscale on a sediment core collected from castor lake washington this subdecadally resolved drought record tracks the 1 500 yr tree ring based palmer drought severity index reconstructions of cook et al cook er woodhouse ca eakin cm meko dm stahle dw 2004 science 306 1015 1018 in the pacific northwest and extends our knowledge back to 6 000 yr b p the results demonstrate that low frequency drought pluvial cycles with occasional long duration multidecadal events are a persistent feature of regional climate furthermore the average duration of multidecadal wet dry cycles has increased since the middle holocene which has acted to increase the amplitude and impact of these events this is especially apparent during the last 1 000 yr we suggest these transitions were driven by changes in the tropical and extratropical pacific and are related to apparent intensification of the el nino southern oscillation over this interval and its related effects on the pacific decadal oscillation the castor lake record also corroborates the notion that the 20th century prior to recent aridity was a relatively wet period compared to the last 6 000 yr our findings suggest that the hydroclimate response in the pacific northwest to future warming will be intimately tied to the impact of warming on the el nino southern oscillation

the geology of pluto and charon through the eyes of new horizons nasa s new horizons spacecraft has revealed the complex geology of pluto and charon pluto s encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection with a crater retention age no greater than 10 million years surrounding terrains show active glacial flow apparent transport and rotation of large buoyant water ice crustal blocks and pitting the latter likely caused by sublimation erosion and or collapse more enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures pluto also has ancient cratered terrains up to 4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes charon does not appear to be currently active but experienced major extensional tectonism and resurfacing probably cryovolcanic nearly 4 billion years ago impact crater populations on pluto and charon are not consistent with the steepest impactor size frequency distributions proposed for the kuiper belt

antarctic station based seasonal pressure reconstructions since 1905 1 reconstruction evaluation seasonal mean antarctic pressures at 17 stations are reconstructed based on the method of principal component regression employing midlatitude pressure data as predictors several reconstruction methods were performed in order to assess the stability and reliability of the reconstructions obtained including performing the reconstructions over a shorter 30 year window and withholding the remaining data for an independent validation generally there were small differences between the various approaches but typically reconstructions conducted on data with the trends still present and over the full period of observations achieved the highest skill seasonally reconstruction skill was high in austral summer across the entire antarctic continent reconstructions that employed gridded pressure data over oceans as well as the observations here termed pseudoreconstructions also performed remarkably well in austral winter spatially the reconstruction skill was highest near the antarctic peninsula in all seasons and weakest in coastal east antarctica and the antarctic interior during austral spring and autumn the spatial variability of the skill in part reflects the distance to the nearest midlatitude predictor nonetheless for nearly all seasons and locations the observed trends since 1957 were well captured by the reconstructions as was the low frequency decadal scale variability these results suggest antarctic pressure observations can be extended throughout the twentieth century with high confidence especially in summer allowing for a more precise understanding of the role and magnitude of natural atmospheric circulation variability across antarctica

thermal evolution of pluto and implications for surface tectonics and a subsurface ocean abstract determining whether or not pluto possesses or once possessed a subsurface ocean is crucial to understanding its astrobiological potential in this study we use a 3d convection model to investigate pluto s thermal and spin evolution and the present day observational consequences of different evolutionary pathways we test the sensitivity of our model results to different initial temperature profiles initial spin periods silicate potassium concentrations and ice reference viscosities the ice reference viscosity is the primary factor controlling whether or not an ocean develops and whether that ocean survives to the present day in most of our models present day pluto consists of a convective ice shell without an ocean however if the reference viscosity is higher than 5 10 15 pa s the shell will be conductive and an ocean should be present for the nominal potassium concentration the present day ocean and conductive shell thickness are both about 165 km in conductive cases an ocean will be present unless the potassium content of the silicate mantle is less than 10 of its nominal value if pluto never developed an ocean predominantly extensional surface tectonics should result and a fossil rotational bulge will be present for the cases which possess or once possessed an ocean no fossil bulge should exist a present day ocean implies that compressional surface stresses should dominate perhaps with minor recent extension an ocean that formed and then re froze should result in a roughly equal balance between older compressional and younger extensional features these predictions may be tested by the new horizons mission

a tree ring based record of annual mass balance changes for the ts tuyuksuyskiy glacier and its linkages to climate change in the tianshan mountains abstract fluctuations in glacier mass and volume are indicative of changes in the climate system they also strongly affect regional climate and hydrology in this paper we explore possible relationships between the radial growth of schrenk spruce picea schrenkiana fisch et mey and the mass balance of the tsentralniy tuyuksuyskiy ts tuyuksuyskiy glacier which is located on the northern slopes of the tianshan mountains in arid central asia we attempt to reconstruct the historical mass balance variability of the ts tuyuksuyskiy glacier using tree ring widths and stable carbon isotope chronologies the reconstruction is able to explain 62 1 of the variance in the annual glacier mass balance record over the 1965 2014 calibration period we also analyzed centennial mass balance variability and its linkages to climate change the ts tuyuksuyskiy glacier has a negative annual mass balance in most years and since 1968 has undergone the most rapid and longest melting process in the past 166 years the mass balance change of the glacier is controlled by the combination of temperature and precipitation conditions this study could be useful for more detailed glaciological hydrological and climatological assessments in this portion of the tianshan mountains

evidence for a hot start and early ocean formation on pluto pluto is thought to possess a present day ocean beneath a thick ice shell it has generally been assumed that pluto accreted from cold material and then later developed its ocean due to warming from radioactive decay in this cold start scenario the ice shell would have experienced early compression and more recent extension here we compare thermal model simulations with geological observations from the new horizons mission to suggest that pluto was instead relatively hot when it formed with an early subsurface ocean such a hot start pluto produces an early rapid phase of extension followed by a more prolonged extensional phase which totals 0 5 linear strain over the last 3 5 gyr the amount of second phase extension is consistent with that inferred from extensional faults on pluto we suggest that an enigmatic ridge trough system recently identified on pluto is indicative of early extensional tectonics a hot initial start can be achieved with the gravitational energy released during accretion if the final stage of pluto s accretion is rapid 30 kyr a fast final stage of growth is in agreement with models of the formation of kuiper belt objects via gravitational collapse followed by pebble accretion and implies that early oceans may have been common in the interiors of large kuiper belt objects pluto s subsurface ocean may have formed early due to accretionary heating a comparison of thermal evolution modelling with observed tectonic structures suggests

reconstructed summer temperatures over the last 400 years based on larch ring widths sakhalin island russian far east a new ring width record from the eastern flanks of the eastern sakhalin range sakhalin island russian federation is significantly correlated with summer temperatures and allows for the reconstruction of may july average temperatures for the past 400 years the reconstruction explains 37 of the variance in may july temperatures and shows a strong cooling between 1680 and 1710 ce coincident with the maunder solar minimum and in agreement with other independent tree ring reconstructions and glacier histories from sites along the margin of the sea of okhotsk while recent decades are among the warmest in the record they are rivaled by periods centered on 1650 and 1850 ce warming in the observational record and the reconstruction is consistent with the influence of the declining strength of the siberian high and loss of sea ice over the same interval decadal 17 25 year variability persists throughout the reconstruction at interannual timescales the sakhalin reconstruction is most strongly correlated with local and central north pacific sea surface temperatures over the past 120 years whereas at decadal timescales there is an additional association with asian land surface temperatures

earthquake ground effects and intensity of the 16 april 2016 mw 7 8 pedernales ecuador earthquake implications for the source characterization of large subduction earthquakes

el nino phases embedded in asian and north american drought reconstructions abstract the amplitude of el nino southern oscillation enso varies substantially at each phase of its evolution affecting the timing and patterns of atmospheric teleconnections around the globe instrumental records are too short to capture the full behavior of enso variability here we use the well validated monsoon asia drought atlas mada and north america drought atlas nada for the past 700 years and show that tree ring records from different regions represent tropical sea surface temperature sst conditions at various phases of enso three modes of tree ring based summer drought variability are found to be correlated with enso summer droughts over the maritime continent and southwest north america na and a dipole mode between central and south asia a lagged correlation analysis is performed to determine the time when precipitation and temperature anomaly imprints on summer droughts as recorded in tree rings drought anomalies in the maritime continent and southwest na represent enso at the developing and peak phases respectively while those over central south asia are associated with tropical wide sst anomalies including the indian ocean at the decay phase of enso thus proxy records from different regions can provide valuable information on long term behavior of enso at different phases

primordial n2 provides a cosmochemical explanation for the existence of sputnik planitia pluto abstract the presence of n2 in the surface environment of pluto is critical in creating pluto s richness of features and processes here we propose that the nitrogen atoms in the n2 observed on pluto were accreted in that chemical form during the formation of pluto we use new horizons data and models to estimate the amounts of n2 in the following exterior reservoirs atmosphere escape photochemistry and surface the total exterior inventory is deduced to be dominated by a glacial sheet of n2 rich ices at sputnik planitia or by atmospheric escape if past rates of escape were much faster than at present pluto s atmosphere is a negligible reservoir of n2 and photochemical destruction of n2 may also be of little consequence estimates are made of the amount of n2 accreted by pluto based on cometary and solar compositions it is found that the cometary model can account for the amount of n2 in sputnik planitia while the solar model can provide a large initial inventory of n2 that would make prodigious atmospheric escape possible these consistencies can be considered preliminary evidence in support of a primordial origin of pluto s n2 however both models predict accreted ratios of co n2 that are much higher than that in pluto s atmosphere possible processes to explain missing co that are given quantitative support here are fractional crystallization from the atmosphere resulting in co burial at the surface and aqueous destruction reactions of co subject to metastable thermodynamic equilibrium in the subsurface the plausibility of primordial n2 as the primary source of pluto s nitrogen vs nh3 or organic n can be tested more rigorously using future constraints on the 14 n 15 n ratio in n2 and the 36ar n2 ratio

coherence between the great salt lake level and the pacific quasi decadal oscillation the lake level elevation of the great salt lake gsl a large closed basin lake in the arid western united states is characterized by a pronounced quasi decadal oscillation qdo the variation of the gsl elevation is very coherent with the qdo of sea surface temperature anomalies in the tropical central pacific also known as the pacific qdo however such coherence denies any direct association between the precipitation in the gsl watershed and the pacific qdo because in a given frequency the precipitation variation always leads the gsl elevation variation therefore the precipitation variation is phase shifted from the pacific qdo this study investigates the physical mechanism forming the coherence between the gsl elevation and the pacific qdo pronounced and coherent quasi decadal signals in precipitation streamflow water vapor flux and drought conditions are found throughout the great basin recurrent atmospheric circulation patterns develop over the gulf of alaska during the warm to cool and cool to warm transition phases of the pacific qdo these circulation patterns modulate the water vapor flux associated with synoptic transient activities over the western united states and in turn lead to the qdo in the hydrological cycle of the great basin as the gsl integrates the hydrological responses in the great basin the hydrological qdo is then transferred to the gsl elevation because the gsl elevation consistently lags the precipitation by a quarter phase about 3 yr in the quasidecadal time scale these processes take an average of 6 yr for the gsl elevation to eventually respond to the pacific qdo this creates a half phase delay of the gsl elevation from the pacific qdo thereby forming the inverse yet coherent relationship between them tree ring reconstructed precipitation records confirm that the quasi decadal signal in precipitation is a prominent feature in this region

reconstructed may july mean maximum temperature since 1745ad based on tree ring width of pinus tabulaeformis in qianshan mountain china abstract a tree ring width chronology of pinus tabulaeformis was developed from the qianshan mountain liaoning province northeastern china based on the correlation between the ring width and instrumental data a transfer function was designed and the may july mean maximum temperature mmt from 1745 to 2012 was reconstructed the reconstruction explains 42 7 of the instrumental variance during the calibration period 41 7 after adjusting for the loss of the degrees of freedom the reconstructed mmt is similar to several observed mmt series and the temperature index in north central china which indicated that the decrease in summer temperatures in the 20th century was a large scale phenomenon the reconstruction also showed that high mmt values corresponded to historical drought events in liaoning in addition a spatial correlation analyses revealed that the mmt reconstruction is regionally representative significant 128 2 64 1 18 6 3 46 3 19 2 43 2 15 and 2 10 year cycles were detected in the reconstructed mmt series from qianshan mountain

convection driven compaction as a possible origin of enceladus s long wavelength topography 1 the long wavelength surface topography of enceladus shows depressions about 1 km in depth and 102 km wide one possible cause of this topography is spatially variable amounts of compaction of an initially porous ice shell driven by spatial variations in heat flux here we show that the heat flux variations associated with convection in the shell can quantitatively match the observed features we develop a simple model of viscous compaction that includes the effect of porosity on thermal conductivity and find that an initial shell porosity of at least 20 25 is required to develop the observed topography over 1 ga this mechanism produces topographic depressions not rises above convective upwellings and does not generate detectable gravity anomalies unlike transient dynamic topography it can potentially leave a permanent record of ancient convective processes in the shallow lithospheres of icy satellites

origin of the pluto charon system constraints from the new horizons flyby abstract new horizon s accurate determination of the sizes and densities of pluto and charon now permit precise internal models of both bodies to be constructed assuming differentiated rock ice structures we find that pluto is close to 2 3 solar composition anhydrous rock by mass and charon 3 5 solar composition anhydrous rock by mass pluto and charon are closer to each other in density than to other large 1000 km diameter kuiper belt bodies despite this we show that neither the possible presence of an ocean under pluto s water ice shell and no ocean within charon nor enhanced porosity at depth in charon s icy crust compared with that of pluto are sufficient to make pluto and charon s rock mass fractions match all four small satellites styx nix kerberos hydra appear much icier in comparison with either pluto or charon in terms of a giant impact origin both these inferences are most consistent with the relatively slow collision of partly differentiated precursor bodies canup astrophys j 141 35 2011 this is in turn consistent with dynamical conditions in the ancestral kuiper belt but implies that the impact precursors themselves accreted relatively late and slowly to limit 26 al and accretional heating the iciness of the small satellites is not consistent with direct formation of the pluto charon system from a streaming instability in the solar nebula followed by prompt collapse of gravitationally bound pebble piles a proposed formation mechanism for kuiper belt binaries nesvorn et al astron j 140 785 793 2010 growth of pluto scale bodies by accretion of pebbles in the ancestral kuiper belt is not ruled out however and may be needed to prevent the precursor bodies from fully differentiating due to buried accretional heat prior to the charon forming impact

the pluto system initial results from its exploration by new horizons the pluto system was recently explored by nasa s new horizons spacecraft making closest approach on 14 july 2015 pluto s surface displays diverse landforms terrain ages albedos colors and composition gradients evidence is found for a water ice crust geologically young surface units surface ice convection wind streaks volatile transport and glacial flow pluto s atmosphere is highly extended with trace hydrocarbons a global haze layer and a surface pressure near 10 microbars pluto s diverse surface geology and long term activity raise fundamental questions about how small planets remain active many billions of years after formation pluto s large moon charon displays tectonics and evidence for a heterogeneous crustal composition its north pole displays puzzling dark terrain small satellites hydra and nix have higher albedos than expected

reorientation of sputnik planitia implies a subsurface ocean on pluto to explain the position of the sputnik planitia basin on pluto the feature would need to have formed via impact and pluto would need to have a subsurface ocean the present location of sputnik planitia the prominent deep icy basin on pluto is close to one of the longitudes of the dwarf planet s tidal axis by analogy with other large basins in the solar system it is thought to be an impact feature although reorientation arising from tidal and rotational torques can explain the present day location of the basin it requires the feature to be a positive gravity anomaly despite its negative topography francis nimmo et al argue that if sputnik planitia formed via impact and if pluto possesses a subsurface ocean a positive gravity anomaly would naturally result because of shell thinning and ocean uplift followed by later modest nitrogen deposition this is one of four papers on the geology of sputnik planitia in this issue of nature in news views amy barr puts these latest contributions into context the deep nitrogen covered basin on pluto informally named sputnik planitia is located very close to the longitude of pluto s tidal axis1 and may be an impact feature2 by analogy with other large basins in the solar system3 4 reorientation5 6 7 of sputnik planitia arising from tidal and rotational torques can explain the basin s present day location but requires the feature to be a positive gravity anomaly7 despite its negative topography here we argue that if sputnik planitia did indeed form as a result of an impact and if pluto possesses a subsurface ocean the required positive gravity anomaly would naturally result because of shell thinning and ocean uplift followed by later modest nitrogen deposition without a subsurface ocean a positive gravity anomaly requires an implausibly thick nitrogen layer exceeding 40 kilometres to prolong the lifetime of such a subsurface ocean to the present day8 and to maintain ocean uplift a rigid conductive water ice shell is required because nitrogen deposition is latitude dependent9 nitrogen loading and reorientation may have exhibited complex feedbacks7

planetesimal sulfate and aqueous alteration in cm and ci carbonaceous chondrites water soluble sulfate salts extracted from six cm chondrites have oxygen isotope compositions that are consistent with an extraterrestrial origin the 17 o of sulfate are correlated with previously reported whole rock 18 o and with an index of meteorite alteration and may display a correlation with the date of the fall the enrichments and depletions for 17 o of water soluble sulfate from the cm chondrites relative to the terrestrial mass dependent fractionation line are consistent with sulfate formation in a rock dominated asteroidal environment and from aqueous fluids that had undergone relatively low amounts of oxygen isotope exchange and little reaction with anhydrous components of the meteorites it is unresolved how the oxidation of sulfide to sulfate can be reconciled with the inferred low oxidation state during the extraterrestrial alteration process oxygen isotope data for two ci chondrites orgueil and ivuna as well as the ungrouped c2 chondrite essebi are indistinguishable from sulfate of terrestrial origin and may be terrestrial weathering products consistent with previous assertions our oxygen isotope data however can not rule out a preterrestrial origin either copyright 2005 elsevier ltd

properties of the 67p churyumov gerasimenko interior revealed by consert radar the philae lander provides a unique opportunity to investigate the internal structure of a comet nucleus providing information about its formation and evolution in the early solar system we present comet nucleus sounding experiment by radiowave transmission consert measurements of the interior of comet 67p churyumov gerasimenko from the propagation time and form of the signals the upper part of the head of 67p is fairly homogeneous on a spatial scale of tens of meters consert also reduced the size of the uncertainty of philae s final landing site down to approximately 21 by 34 square meters the average permittivity is about 1 27 suggesting that this region has a volumetric dust ice ratio of 0 4 to 2 6 and a porosity of 75 to 85 the dust component may be comparable to that of carbonaceous chondrites

a terrestrial origin for sulfate veins in ci1 chondrites white sulfate veins are a very well known petrological feature of the chemically primitive ci1 carbonaceous chondrites sulfate veins were first described in the orgueil meteorite in 1961 almost one century after its fall however we have observed such veins to form easily during typical sample storage we suggest that all ci1 sulfate veins formed during the terrestrial residence of these heavily brecciated porous stones reacting with atmospheric water sulfates originally present in the meteorites dissolved and remobilized and or sulfides oxidised filling the many open spaces offered to them by the very porous rock sulfate veins in ci1 chondrites can no longer be used as evidence of a late stage oxidation event in the ci1 parent body or of centimeter scale fluid transport on the parent asteroid

a tree ring based precipitation reconstruction for the baluntai region on the southern slope of the central tien shan mountains china since a d 1464 abstract july june precipitation has been reconstructed back to a d 1464 for the baluntai region on the southern slope of the central tien shan mountains china using the picea schrenkiana tree ring width the reconstruction explains the variance of 51 in the observed precipitation from 1959 to 2005 by employing a 21 year moving average to the reconstruction nine periods with above average reconstructed precipitation comprised 1474 1503 1550 1577 1588 1619 1658 1713 1790 1812 1833 1867 1890 1907 1923 1944 and 1988 1995 eight periods with below average reconstruction consisted of 1504 1549 1578 1587 1620 1657 1714 1789 1813 1832 1868 1889 1908 1922 and 1945 1987 the wet dry periods of the reconstructed precipitation correspond well with other reconstructions some droughts in the historical documents are also precisely captured in the reconstruction precipitation variations for the southern slope of the central tien shan mountains are roughly synchronous with that of the northern slope in the recent 300 year power spectral and wavelet analysis demonstrated the existence of significant 100 y 60 y 50 y 16 y 10 y and 2 y cycles of variability

modeling kuiper belt objects charon orcus and salacia by means of a new equation of state for porous icy bodies abstract we use a one dimensional adaptive grid thermal evolution code to model kuiper belt objects charon orcus and salacia and compare their measured bulk densities with those resulting from evolutionary calculations at the end of 4 6 gyr our model assumes an initial homogeneous composition of mixed ice and rock and follows the multiphase flow of water through the porous rocky medium consequent differentiation and aqueous chemical alterations in the rock heating sources include long lived radionuclides serpentinization reactions release of gravitational potential energy due to compaction and crystallization of amorphous ice the density profile is calculated by assuming hydrostatic equilibrium to be maintained through changes in composition pressure and temperature to this purpose we construct an equation of state suitable for porous icy bodies with radii of a few hundred km based on the best available empirical studies of ice and rock compaction and on comparisons with rock porosities in earth analog and solar system silicates we show that the observed bulk densities can be reproduced by assuming the same set of initial and physical parameters including the same rock ice mass ratio for all three bodies we conclude that the mass of the object uniquely determines the evolution of porosity and thus explains the observed differences in bulk density the final structure of all three objects is differentiated with an inner rocky core and outer ice enriched mantle the degree of differentiation too is determined by the object s mass

differential hydrogen isotopic ratios of sphagnum and vascular plant biomarkers in ombrotrophic peatlands as a quantitative proxy for precipitation evaporation balance abstract we have developed a new approach to quantitatively reconstruct past changes in evaporation based on compound specific hydrogen isotope ratios of vascular plant and sphagnum biomarkers in ombrotrophic peatland sediments we show that the contrast in h isotopic ratios of water available to living sphagnum top 20 cm and in the rooting zone of peatland vascular plants can be used to estimate the fraction of water remaining after evaporation vascular plant leaf waxes record h isotopic ratios of acrotelm water which carries the d h ratio signature of precipitation and is little affected by evaporation whereas the sphagnum biomarker c 23 n alkane records h isotopic ratios of the water inside its cells and between its leaves which is strongly affected by evaporation at the bog surface evaporation changes can then be deduced by comparing h isotopic ratios of the two types of biomarkers we calibrated d h ratios of c 23 n alkane to source water with lab grown sphagnum we also tested our isotopic model using modern surface samples from 18 ombrotrophic peatlands in the midwestern united states finally we generated a 3000 year downcore reconstruction from minden bog michigan usa our new record is consistent with records of other parameters from the same peatland derived from different proxies and allows us to differentiate precipitation supply and evaporative loss

reconstructed summer temperature in the northern rocky mountains wilderness usa ring widths from whitebark pine pinus albicaulis englem and subalpine larch larix lyallii parl collected at three high elevation sites were used to develop tree growth chronologies to reconstruct summer temperature anomalies a step wise multiple regression procedure was used to screen potential predictor variables to generate a transfer function capable of skillfully reconstructing summer temperature the resulting regression model explained approximately 38 of the adjusted variance in the instrumental temperature record the fidelity of the reconstruction was verified using product mean and sign tests both of which suggested significant predictive power in the reconstructions p 0 05 reduction of error re and coefficient of efficiency ce measures were both positive indicating the reconstruction contained useful climate information cool periods often coincided with reduced solar activity and or periods of increased volcanic activity differences between this reconstruction and others encompassing a broader geographic scale highlight the importance of developing local reconstructions of climate variability particularly when used in conjunction with ecological data sets that describe the occurrence of fires or insect epidemics mixed and divergent climate response relationships were evident in the whitebark pine chronologies and suggest subalpine larch may be a more useful species than whitebark pine to target for the development of temperature reconstructions in this region

abundance distribution and origin of 60fe in the solar protoplanetary disk abstract meteorites contain relict decay products of short lived radionuclides that were present in the protoplanetary disk when asteroids and planets formed several studies reported a high abundance of 60fe t1 2 2 62 0 04 myr in chondrites 60fe 56fe 6 10 7 suggesting that planetary materials incorporated fresh products of stellar nucleosynthesis ejected by one or several massive stars that exploded in the vicinity of the newborn sun we measured 58fe 54fe and 60ni 58ni isotope ratios in whole rocks and constituents of differentiated achondrites ureilites aubrites heds and angrites unequilibrated ordinary chondrites semarkona ll3 0 and nwa 5717 ungrouped petrologic type 3 05 metal rich carbonaceous chondrite gujba cba and several other meteorites cv el h ll chondrites iiiab iva ivb iron meteorites we derive from these measurements a much lower initial 60fe 56fe ratio of 11 5 2 6 10 9 and conclude that 60fe was homogeneously distributed among planetary bodies this low ratio is consistent with derivation of 60fe from galactic background 60fe 56fe 2 8 10 7 in the interstellar medium from ray observations and can be reconciled with high 26al 27al 5 10 5 in chondrites if solar material was contaminated through winds by outer layers of one or several massive stars e g a wolf rayet star rich in 26al and poor in 60fe we present the first chronological application of the 60fe 60ni decay system to establish the time of core formation on vesta at 3 7 1 7 2 5 myr after condensation of calcium aluminum rich inclusions cais

subduction of the eastern panama basin and seismotectonics of northwestern south america spreading along the cocos nazca plate boundary since the breakup of the farallon plate in the miocene has resulted in the formation of the panama basin and a complex interaction of plates in and near northwestern south america current plate boundaries have been defined and segments of subducted lithosphere identified through selection of hypocentral locations of earthquakes considering only well located events and through focal mechanism determinations the existence of relict plate boundaries bathymetric features and the panamanian isthmus has affected the subduction process of the nazca plate beneath south america and determined the present day configuration of the subducting lithospheric plate there is no single triple junction separating the caribbean south american and nazca plates instead the panamanian isthmus and surrounding areas are accommodating east west compression and a lesser degree of north south compression along a series of thrust faults striking nw to ne and the andean ranges of ecuador colombia and venezeula are moving as a block nne relative to the rest of the south american plates along a system of faults following the front of the eastern cordillera the subducted portions of the panama basin and old farallon plate have become segmented into three pieces recognized in this study from north to south they are 1 a bucaramanga segment continuous with the caribbean seafloor northwest of colombia 2 a cauca segment continuous with oceanic crust nazca plate currently being subducted beneath south america at the colombia ecuador trench and 3 an ecuador segment at the northern end of the subducted lithospheric plate which is dipping at a small angle to the east beneath northern peru the segmentation of the subducted plate can be explained by the buoyancy of bathymetric features which have been partially subducted

a 1000 year record of temperature and precipitation in the sierra nevada abstract tree ring data from subalpine conifers in the southern sierra nevada were used to reconstruct temperature and precipitation back to a d 800 tree growth of foxtail pine pinus balfouriana and western juniper juniperus occidentalis ssp australis is influenced by nonlinear interactions between summer temperature and winter precipitation reconstruction of the separate histories of temperature and precipitation is feasible by explicitly modeling species and site differences in climatic response using response surfaces the summer temperature reconstruction shows fluctuations on centennial and longer time scales including a period with temperatures exceeding late 20th century values from ca 1100 to 1375 a d corresponding to the medieval warm period identified in other proxy data sources and a period of cold temperatures from ca 1450 to 1850 corresponding to the little ice age precipitation variation is dominated by shorter period decadal scale oscillations the long term record presented here indicates that the 20th century is anomalous with respect to precipitation variation a tabulation of 20 and 50 yr means indicates that precipitation equaling or exceeding 20th century levels occurred infrequently in the 1000 yr record

a euro mediterranean tree ring reconstruction of the winter nao index since 910 c e we develop a new reconstruction of the winter north atlantic oscillation nao index using a network of 97 euro mediterranean tree ring series the reconstruction covers the period 910 2018 c e making it the longest annually resolved estimate of winter nao variability available we use nested correlation weighted principal components regression and the maximum entropy bootstrap method to generate a 2400 member ensemble of reconstructions for estimating the final reconstruction and its quantile uncertainties extensive validation testing of the new reconstruction against data withheld from the calibration exercise demonstrates its skill the skill level of the new reconstruction is also an improvement over two nao reconstructions published earlier spectral analyses indicate that the new reconstruction behaves like a white noise process with intermittent band limited power suggesting that the winter nao is stochastically forced the white noise properties of our reconstruction are also shown to be consistent with the spectral properties of long instrumental nao indices extending back to 1781 and nao indices extracted from a large number of forced climate model runs covering the last millennium in contrast an annually resolved multi proxy nao reconstruction of comparable length based in part on speleothem data behaves more like externally forced red noise process which is inconsistent with our reconstruction long observations and forced model runs

fennoscandia revisited a spatially improved tree ring reconstruction of summer temperatures for the last 900 years despite the spatially homogenous summer temperature pattern in fennoscandia there are large spreads among the many existing reconstructions resulting in an uncertainty in the timing and amplitude of past changes also there has been a general bias towards northernmost fennoscandia in an attempt to provide a more spatially coherent view of summer june august jja temperature variability within the last millennium we utilized seven density and three blue intensity scots pine pinus sylvestris l chronologies collected from the altitudinal scandinavian mountains and latitudinal northernmost part treeline to attain a jja temperature signal as strong as possible as well as preserving multicentury scale variability we used a new tree ring parameter where the earlywood information is removed from the maximum density and blue intensity and a modified signal free standardization method two skilful reconstructions for the period 1100 2006 ce were made one regional reconstruction based on an average of the chronologies and one field gridded reconstruction the new reconstructions were shown to have much improved spatial representations compared to those based on data from only northern sites thus making it more valid for the whole region an examination of some of the forcings of jja mean temperatures in the region shows an association with sea surface temperature over the eastern north atlantic but also the subpolar and subtropical gyres moreover using superposed epoch analysis a significant cooling in the year following a volcanic eruption was noted and for the largest explosive eruptions the effect could remain for up to 4 years this new improved reconstruction provides a mean to reinforce our understanding of forcings on summer temperatures in the north european sector