reconstructing el nino southern oscillation using data from ships logbooks 1815 1854 part ii comparisons with existing enso reconstructions and implications for reconstructing enso diversity a systematic comparison of el nino southern oscillation reconstructions during the early to mid nineteenth century is presented using a range of proxy and documentary sources reconstructions of the boreal winter southern oscillation index soi using data from ships logbooks presented in a companion paper are evaluated and compared to previous enso reconstructions comparisons between enso reconstructions and the instrumental soi during a period of overlap 1876 1977 are made these same proxy and documentary reconstructions are then compared to the logbook based reconstructions over 1815 1854 the logbook based reconstructions compare best with a recent multi proxy reconstruction that used signals taken from different teleconnection regions and they have an improved agreement with multi proxy records compared to a previous attempt to reconstruct the soi from ships logbook data the logbook based and the multi proxy reconstructions are found to capture el nino events better than la nina events and east pacific el nino events better than central pacific el nino events thus suggesting a degree of bias in the historical reconstructions these findings have important implications for future enso reconstructions with a need for an increased understanding of the effects of different enso flavours for future reconstructions

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

coordinated hydrological regimes in the indo pacific region during the past two millennia instrumental data suggest that major shifts in tropical pacific atmospheric dynamics and hydrology have occurred within the past century potentially in response to anthropogenic warming to better understand these trends we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes delta d wax in marine sediments from southwest sulawesi indonesia to compile a detailed reconstruction of central indo pacific warm pool ipwp hydrologic variability spanning most of the last two millennia our paleodata are highly correlated with a monsoon reconstruction from southeast asia indicating that intervals of strong east asian summer monsoon easm activity are associated with a weaker indonesian monsoon im furthermore the centennial scale oscillations in our data follow known changes in northern hemisphere climate e g the little ice age and medieval warm period implying a dynamic link between northern hemisphere temperatures and ipwp hydrology the inverse relationship between the easm and im suggests that migrations of the intertropical convergence zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the ipwp throughout most of the past two millennia

a major holocene enso anomaly during the medieval period 1 here we present a high resolution marine el nino flood record from peru a period of extreme drought without strong flooding occurred from a d 800 1250 anomalous precipitation patterns characterized the entire indo pacific enso domain with dry events in the northern arabian sea and the mid latitudes of both americas coinciding with wet periods in the atlantic cariaco basin the occurrence of contemporaneous moisture anomalies in other archives in the enso region highlights the role of el nino strength in global climate evolution during the late medieval period when temperature reconstructions show a rather heterogeneous pattern

tropical sea surface temperatures for the past four centuries reconstructed from coral archives most annually resolved climate reconstructions of the common era are based on terrestrial data making it a challenge to independently assess how recent climate changes have affected the oceans here as part of the past global changes ocean2k project we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives validation exercises suggest that our reconstructions are interpretable for much of the past 400 years depending on the availability of paleoclimate data within and the reconstruction validation statistics for each target region analysis of the trends in the data suggests that the indian western pacific and western atlantic ocean regions were cooling until modern warming began around the 1830s the early 1800s were an exceptionally cool period in the indo pacific region likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century decadal scale variability is a quasi persistent feature of all basins twentieth century warming associated with greenhouse gas emissions is apparent in the indian west pacific and western atlantic oceans but we find no evidence that either natural or anthropogenic forcings have altered el nino southern oscillation related variance in tropical sea surface temperatures our marine based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change

intercolony δ18o and sr ca variability among porites spp corals at palmyra atoll toward more robust coral based estimates of climate

dynamical response of the tropical pacific ocean to solar forcing during the early holocene we present a high resolution magnesium calcium proxy record of holocene sea surface temperature sst from off the west coast of baja california sur mexico a region where interannual sst variability is dominated today by the influence of the el nino southern oscillation enso temperatures were lowest during the early to middle holocene consistent with documented eastern equatorial pacific cooling and numerical model simulations of orbital forcing into a la nina like state at that time the early holocene ssts were also characterized by millennial scale fluctuations that correlate with cosmogenic nuclide proxies of solar variability with inferred solar minima corresponding to el nino like warm conditions in apparent agreement with the theoretical ocean dynamical thermostat response of enso to exogenous radiative forcing

a coral oxygen isotope record from the northern red sea documenting nao enso and north pacific teleconnections on middle east climate variability since the year 1750 a 245 year coral oxygen isotope record from the northern red sea ras umm sidd egypt 28 n in bimonthly resolution is presented the mean annual coral 18o signal apparently reflects varying proportions of both sea surface temperature and 18oseawater variability in conjunction with instrumental observations of climate the coral record suggests for interannual and longer timescales that colder periods are accompanied by more arid conditions in the northern red sea but increased rainfall in the southeastern mediterranean whereas warmer periods are accompanied by decreased rainfall in the latter and less arid conditions in the northern red sea a 70 year oscillation of probably north atlantic origin dominates the coral time series interannual to interdecadal variability is correlated with instrumental indices of the north atlantic oscillation nao the el nino southern oscillation enso and north pacific climate variability the results suggest that these modes contributed consistently to middle east climate variability since at least 1750 preferentially at a period of 5 7 years

coral derived western pacific tropical sea surface temperatures during the last millennium reconstructions of ocean temperatures prior to the industrial era serve to constrain natural climate variability on decadal to centennial timescales yet relatively few such observations are available from the west pacific warm pool here we present multiple coral based sea surface temperature reconstructions from yongle atoll in the south china sea over the last 1 250 years 762 2013 common era ce reconstructed coral sr ca sea surface temperatures indicate that the little ice age 1711 1817 ce period was 0 7 c cooler than the medieval climate anomaly 913 1132 ce and that late 20th century warming of the western pacific is likely unprecedented over the past millennium our findings suggest that the western pacific warm pool may have expanded contracted during the medieval climate anomaly little ice age leading to a strengthening weakening of the asian summer monsoon as recorded in chinese stalagmites

estimating central equatorial pacific sst variability over the past millennium part ii reconstructions and implications abstractreducing the uncertainties surrounding the impacts of anthropogenic climate change requires vetting general circulation models gcms against long records of past natural climate variability this is particularly challenging in the tropical pacific ocean where short sparse instrumental data preclude gcm validation on multidecadal to centennial time scales this two part paper demonstrates the application of two statistical methodologies to a network of accurately dated tropical climate records to reconstruct sea surface temperature sst variability in the nino 3 4 region over the past millennium while part i described the methods and established their validity and limitations this paper presents several reconstructions of nino 3 4 analyzes their sensitivity to procedural choices and input data and compares them to climate forcing time series and previously published tropical pacific sst reconstructions the reconstructions herein show remarkably similar behavior at decadal to multidecadal s

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

reprocessing of deep seismic reflection data from the north german basin with the common reflection surface stack abstract the common reflection surface crs stack is a promising alternative stacking technique for reflection data this technique is an automatic multi parameter stack that does not require the explicit knowledge of a stacking velocity model furthermore it significantly improves the signal to noise ratio as it considers more traces during the zero offset stacking than the conventional cmp stack especially for low fold data in heterogeneous settings the crs stack is able to further enhance reflections recently the crs stack was applied to reflection data from sedimentary basins for oil and gas exploration purposes it was not yet applied to crustal and deeper reflection data we used the crs stack for deep reflection data from the north german basin the data were acquired in the late 1970 s and early 1980 s with recording times down to 15 s twt and mean cmp folds of about 20 we reprocessed the data focusing on lower crustal and deeper structures compared to the conventional cmp processing of the 1980 s the reprocessed sections show an improved image quality at all time levels i e from the sedimentary cover down to the crust and upper mantle especially the reflections from the salt structures and moho events are enhanced further a constrained crs stack was applied to the data using a stacking velocity model from conventional velocity analysis the latter further improved the coherency and visibility of the reflections especially in the area of the salt plugs and in the upper crust where multiples were suppressed the data examples demonstrate that the crs stack is a suitable tool for improving the quality of seismic images especially for deep reflection data from low low fold data acquisitions

climate change and solar variability what s new under the sun the sun has an obvious effect on climate since its radiation is the main energy source for the outer envelopes of our planet nevertheless there is a long standing controversy on whether solar variability can significantly generate climate change and how this might occur this is a crucial issue not only in the field of paleoclimatology but also for predicting the future of the earth s climate which will be subject to perturbations by anthropogenic greenhouse gases indeed if climate changes due to the sun were large and rapid this would make it more difficult to extract the anthropogenic effects from precise records of instrumental data over the past century hence sun climate relationships have never been so controversial as today forming a debate that often escapes the scientific arena here we provide a review of this problem by considering changes on different time scales from the last million years up to recent decades in doing so we also critically assess recent claims that the variability of the sun has had a significant impact on global climate the different studied records also illustrate the multi disciplinary nature of this difficult problem requiring knowledge in several fields such as astronomy and astrophysics atmospheric dynamics and microphysics isotope geochemistry and geochronology as well as geophysics paleoceanography and glaciology overall the role of solar activity in climate changes such as the quaternary glaciations or the present global warming remains unproven and most probably represents a second order effect although we still require even more and better data the weight of evidence suggests that solar changes have contributed to small climate oscillations occurring on time scales of a few centuries similar in type to the fluctuations classically described for the last millennium the so called medieval warm period 900 1400 a d followed on by the little ice age 1500 1800 a d

proxy based northern hemisphere surface temperature reconstructions sensitivity to method predictor network target season and target domain abstract results are presented from a set of experiments designed to investigate factors that may influence proxy based reconstructions of large scale temperature patterns in past centuries the factors investigated include 1 the method used to assimilate proxy data into a climate reconstruction 2 the proxy data network used 3 the target season and 4 the spatial domain of the reconstruction estimates of hemispheric mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach the experiments compare results based on the global multiproxy dataset used by mann and coworkers with results obtained using the extratropical northern hemisphere nh maximum latewood tree ring density set used by briffa and coworkers mean temperature reconstructions are compared for the full nh tropics and extratropics land and ocean and ext

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

a multicentury stable isotope record from a new caledonia coral interannual and decadal sea surface temperature variability in the southwest pacific since 1657 a d a 335 year stable isotope record from a new caledonia coral 22 s 166 e helps fill a large gap in historical climate reconstructions although the long term coral 18o based sea surface temperature sst trend is one of warming there are notable decadal fluctuations especially in the early 18th and early 19th centuries mean annual ssts between 1658 and 1900 are estimated to be 0 3 c lower than the 20th century average with interdecadal excursions of 0 5 0 8 c time series analyses of the coral isotope record reveals significant concentrations of variance in the el nino band an inderdecadal spectral peak is present but its robustness requires additional statistical evaluation a secular but irregular decrease in coral 13c values begins in the mid 1800s and may reflect the anthropogenic perturbation of the carbon reservoir these and other results indicate that the new caledonia coral isotope record is a valuable source of information on southwest pacific climate history

a multiproxy index of the el nino southern oscillation a d 1525 1982 1 an understanding of past variability in the el nino southern oscillation enso on interannual interdecadal and longer time scales would be useful in assessing recent observed changes to enso and in determining the realism of climate model simulations using tree ring coral and ice core data we reconstruct a proxy based enso index between a d 1525 and 1982 unlike most previous studies which have drawn climate proxies from limited geographic regions our network is pacific basin wide using enso sensitive proxies from the western equatorial pacific new zealand the central pacific and subtropical north america by considering multiple teleconnection regions this network provides a more robust proxy enso signal the common signal recorded in the multiproxy network has a high correlation with the southern oscillation index soi nino 3 4 sea surface temperature nino3 4 sst and a combined ocean atmosphere enso index cei the proportion of instrumental variance explained is 47 for the soi 48 for nino3 4 sst and 52 for the cei the proxy enso index also displays skill in reproducing warm and cold extremes of the soi the proxy enso index over the last 450 years shows considerable amplitude and frequency modulation in the 3 10 year band on multidecadal time scales there is a relative reduction in the amplitude of high frequency variability during the sixteenth early seventeenth and mid eighteenth centuries in contrast high frequency enso variability has increased over the last 200 years variability during the first half of the twentieth century is similar to that evident in the nineteenth century

underestimation of volcanic cooling in tree ring based reconstructions of hemispheric temperatures a large volcanic eruption in ad 1258 1259 is expected to have caused substantial climate cooling but evidence for this effect is absent from tree ring based temperature reconstructions numerical modelling of tree growth shows that the lack of cooling is probably an artefact caused by low sensitivity to cooling in trees growing near the treeline

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

does the el nino southern oscillation control the interhemispheric radiocarbon offset since the 1970s it has been recognised that southern hemisphere samples have a lower radiocarbon content than contemporaneous material in the northern hemisphere this interhemispheric radiocarbon offset has traditionally been considered to be the result of a greater surface area in the southern ocean and high latitude deepwater formation this is despite the fact that the el nino southern oscillation enso is known to play a significant role in controlling the interannual variability of atmospheric carbon dioxide by changing the flux of old co2 from the tropical pacific here we demonstrate that over the past millennium the southern hemisphere radiocarbon offset is characterised by a pervasive 80 yr cycle with a step shift in mean values coinciding with the transition from the medieval warm period to the little ice age the observed changes suggest an enso like role in influencing the interhemispheric radiocarbon difference most probably modulated by the interdecadal pacific oscillation and supports a tropical role in forcing centennial scale global climate change

presence of the solar de vries cycle 205 years during the last ice age certain characteristic periodicities in the 14c record from tree rings such as the well known 11 yr schwabe cycle are known to be of solar origin the origin of longer period cycles such as the 205 yr de vries cycle in the 14c record was less certain and it was possible to attribute it either to solar or climatic variability here we demonstrate that the de vries cycle is present in 10be data from the grip ice core during the last ice age 25 to 50 kyr bp analysis of the amplitude of variation of this cycle shows it to be modulated by the geomagnetic field indicating that the de vries cycle is indeed of solar rather than climatic origin

holocene paleomagnetic records from the st lawrence estuary eastern canada centennial to millennial scale geomagnetic modulation of cosmogenic isotopes two long holocene piston cores md99 2220 and md99 2221 were raised from the st lawrence estuary eastern canada because of the expanded holocene sediment sequence this location provides a u channel based paleomagnetic study supported by an accelerator mass spectrometry ams 14c chronology rock magnetic and sedimentological data indicates that these sediments provide a paleomagnetic directional secular variation psv and relative paleointensity rpi proxy records for the last 8500 cal bp sedimentation rates vary from 1 2 to 4 2 m kyr comparison of inclination and declination features with other north american holocene psv records are generally consistent and temporal offsets are within chronological uncertainties the normalized natural remanent magnetization intensity record a rpi proxy from the postglacial sediments of core 2220 compares favorably with north american and european holocene rpi records at millennial and even some centennial timescales comparisons between core 2220 rpi proxy and the 10be flux record from the greenland summit gisp2 ice core finkel and nishiizumi j geophys res 102 1997 26699 26706 and a 14c production rate record bond et al science 294 2001 2130 2136 suggest that geomagnetic modulation may control the millennial and even some centennial scale variability within cosmogenic isotope records this implies that the core 2220 rpi record reflects changes in global scale geomagnetic field at these timescales

characterizing decadal to centennial variability in the equatorial pacific during the last millennium 1 the magnitude of sea surface temperature variability in the nino3 4 region of the equatorial pacific on decadal and longer timescales is assessed in observational data state of the art coupled model intercomparison project 5 climate model simulations and a new ensemble of paleoclimate reconstructions on decadal to multidecadal timescales variability in these records is consistent with the null hypothesis that it arises from multivariate red noise a multivariate ornstein uhlenbeck process generated from a linear inverse model of tropical ocean atmosphere dynamics on centennial and longer timescales both a last millennium simulation performed using the community climate system model 4 ccsm4 and the paleoclimate reconstructions have variability that is significantly stronger than the null hypothesis however the time series of the model and the reconstruction do not agree with each other in the model variability primarily reflects a thermodynamic response to reconstructed solar and volcanic activity whereas in the reconstruction variability arises from either internal climate processes forced responses that differ from those in ccsm4 or nonclimatic proxy processes that are not yet understood these findings imply that the response of the tropical pacific to future forcings may be even more uncertain than portrayed by state of the art models because there are potentially important sources of century scale variability that these models do not simulate