spatio temporal structure of the pentadecadal variability over the north pacific abstract using a multi taper frequency domain singular value decomposition mtm svd a pentadecadal oscillation was detected in the winter spring sea level pressure slp field over the north pacific and surface air temperature in north america which was significant at the 95 confidence level the mtm svd captured the different slp and air temperature distributions between the winter and spring seasons in a consistent manner the pentadecadal slp signature in the spring season is centered nearer the west coast of north america than in the winter season this zonal displacement is consistent with the prominent springtime pentadecadal air temperature variability in mid latitude western north america a wavelet analysis of the pacific decadal oscillation index pdoi showed that the regime shifts in the 1920s 1940s and 1970s involved simultaneous phase reversals of the bidecadal and pentadecadal variations the two interdecadal variations are synchronized with one another such that a half period of the pentadecadal oscillation one epoch of an individual regime corresponds to one and half periods of the bidecadal oscillation these results are consistent with the wavelet analysis of the north pacific index npi similar resonance between the bidecadal and pentadecadal variations is evident in air temperatures over alaska the bidecadal and pentadecadal signals have different seasonality in these time series suggesting that although the two interdecadal variations arise from two different physical mechanisms they interact with each other the most distinct seasonal difference was observed in mid latitude western north america where the bidecadal variation prevails only in the winter season and the pentadecadal variation only in the spring season alaska air temperatures in the winter and winter spring of 1999 were the coldest since 1977 as were springtime air temperatures in mid latitude western north america in contrast to the warm anomalies that prevailed in this region during 1977 98 the npi and pdoi also exhibited an opposite polarity in 1999 to the respective regime mean polarities these anomalous conditions in winter and spring seasons of 1999 may signify a major regime shift in 1998 1999 in order to verify whether or not a regime shift did occur in 1998 1999 a careful examination of additional data in coming ten or so years will be necessary

temperature variability over the past millennium inferred from northwestern alaska tree rings we describe a new tree ring width data set of 14 white spruce chronologies for the seward peninsula sp alaska based on living and subfossil wood dating from 1358 to 2001 ad a composite chronology derived from these data correlates positively and significantly with summer temperatures at nome from 1910 to 1970 after which there is some loss of positive temperature response there is inferred cooling during periods within the little ice age lia from the early to middle 1600s and late 1700s to middle 1800s and warming from the middle 1600s to early 1700s we also present a larger composite data set covering 978 2001 ad utilizing the sp ring width data in combination with archaeological wood measurements and other recent collections from northwestern alaska the regional curve standardization rcs method was employed to maximize potential low frequency information in this data set the rcs chronology shows intervals of persistent above average growth around the time of the medieval warm period mwp early in the millennium which are comparable to growth levels in recent centuries there is a more sustained cold interval during the lia inferred from the rcs record as compared to the sp ring width series the chronologies correlate significantly with bering and chukchi sea sea surface temperatures and with the pacific decadal oscillation index these atmosphere ocean linkages probably account for the differences between these records and large scale reconstructions of arctic and northern hemisphere temperatures based largely on continental interior proxy data

kunashir kuriles oak 400 year reconstruction of temperature and relation to the pacific decadal oscillation paleoclimatic records of northwest pacific variations are scarce but can be extended by proxy records from old aged trees around the north pacific rim in july of 2001 on kunashir island at the southern extent of the kuriles tree cores were extracted from century old oaks quercus crispula and developed into a 400 year tree ring width index series analyses showed the ringwidth indices to correlate strongly with summer june september temperatures as recorded at ugno kurilsky on the island the summer temperatures were reconstructed using the tree ring data and 52 of the variance was explained by the tree ring indices the recorded temperature data and the tree ring data show similar correlation patterns with sea surface temperatures ssts of the north pacific studies of north pacific variations as quantified by the pacific decadal oscillation pdo show the pdo to be an important index of large scale climate variation the tree ring series explains more than 33 of the variance of the july september pacific decadal oscillation and has similar spectral properties further supporting the concept of multidecadal variation or shifts in north pacific climate for four centuries d 2004 elsevier b v all rights reserved

diatom bound 15n 14n new support for enhanced nutrient consumption in the ice age subantarctic 1 diatom bound 15n 14n was used to reconstruct the glacial nutrient status of the subantarctic zone in the southern ocean down core records from both the pacific and indian sectors show 15n of 5 to 6 during the last glacial maximum and a decrease coincident with the glacial termination to values as low as 2 the effect of either diatom assemblage or physiological change on the diatom bound 15n 14n is unknown and cannot yet be ruled out as a possible explanation for the observed change however the consistency between indian and pacific sector records and with other paleoceanographic data suggests that the glacial interglacial difference in diatom bound 15n 14n was driven by higher consumption of nitrate in the subantarctic surface during the last ice age such a change in nutrient consumption may have resulted from atmospheric iron fertilization and or decreased glacial mixed layer depths associated with sea ice melting enhanced nutrient consumption in the glacial subantarctic would have worked to lower the concentration of co2 in the ice age atmosphere it also would have reduced the preformed nutrient content of the low latitude thermocline leading to decreases in low latitude productivity suboxia and denitrification

developing millennial tree ring chronologies in the fire prone north american boreal forest a denser global network of millennial tree ring chronologies is needed to verify whether the warming of the last century is anomalously rapid or of large amplitude in the context of the last millennium the north american boreal forest in particular has been poorly represented in long climatic reconstructions based on tree rings because of short tree longevity as well as frequent and severe wildfires in this study we exhaustively sampled tree remains in the littoral zone of two lakes and partially sampled seven additional lakes in the northern boreal forest of eastern canada to verify if highly replicated millennial tree ring chronologies could be developed in total 989 black spruce picea mariana mill bsp tree remains were sampled of which 529 could be crossdated providing a master chronology spanning the ad 676 1991 time period radiocarbon dating of a floating chronology indicates that maximum residence time of tree remains outside of sediments is at least 1500 years past fires halted or reduced wood inputs at least once at all but one site and thus influenced the replication of local chronologies however fire effects can be minimized using appropriate site selection criteria old growth forest on the leeward shore sharp deepening of the littoral zone burial of tree remains by fine sediments such that it would be possible to develop a network of several highly and evenly replicated multi century local chronologies these tree ring chronologies would have desirable properties for extracting low frequency tree growth trends and for reconstructing forest disturbance histories copyright 2013 john wiley sons ltd

boreal temperature variability inferred from maximum latewood density and tree ring width data wrangell mountain region alaska abstract variations in both width and density of annual rings from a network of tree chronologies were used to develop high resolution proxies to extend the climate record in the wrangell mountain region of alaska we developed a warm season july september temperature reconstruction that spans a d 1593 1992 based on the first eigenvector from principal component analysis of six maximum latewood density mxd chronologies the climate tree growth model accounts for 51 of the temperature variance from 1958 to 1992 and shows cold in the late 1600s early 1700s followed by a warmer period cooling in the late 1700s early 1800s and warming in the 20th century the 20th century is the warmest of the past four centuries several severely cold warm seasons coincide with major volcanic eruptions the first eigenvector from a ring width rw network based on nine chronologies from the wrangell mountain region a d 1550 1970 is correlated positively with both reconstructed and recorded northern hemisphere temperatures rw shows a temporal history similar to that of mxd by increased growth warmer and decreased growth cooler intervals and trends after around 1970 the rw series show a decrease in growth while station data show continued warming which may be related to increasing moisture stress or other factors both the temperature history based on mxd and the growth trends from the rw series are consistent with well dated glacier fluctuations in the wrangell mountains and some of the temperature variations also correspond to variations in solar activity

diachronous evolution of late jurassic cretaceous continental rifting in the northeast atlantic west iberian margin 1 regional 2 d seismic reflection profiles outcrop and borehole data are used to characterize the evolution of deep offshore sedimentary basins in southwest iberia alentejo basin the interpreted data indicate the bulk of late jurassic earliest cretaceous subsidence occurred in the present day continental slope area as shown by 1 significant thickening of synrift strata basinward from a slope bounding fault system sfs west of which the total thickness of sediment can reach more than 9 0 km and 2 relatively thin mesozoic strata east of the sfs where thickening of synrift units against principal faults is limited five principal regressive events and their basal unconformities reflect tectonic uplift and relative emersion in proximal basins which were located on the rift shoulder to subsiding tilt blocks west of the sfs these regressive events are correlated with major rift related events occurring on the deeper margin direct comparisons with the peniche basin of northwest iberia reveal that significant portions of the iberian lower plate margin were uplifted and eroded during the last stages of continental rifting this process was repeated at different times and in different areas as the locus of rifting and continental breakup migrated northward as a result two distinct rift axes are recognized in west iberia a first axis extending from the porto basin to the alentejo basin and a second axis located on the outer proximal margin north of 38 30n in addition the sfs delimited 1 prograding deposits of cretaceous paleogene age and 2 late cenozoic deposits draping the modern continental slope these latter facts demonstrate that on lower plate passive margins the relative position of the continental slope is established during the final rifting episode s preceding continental breakup

fennoscandian summers from ad 500 temperature changes on short and long timescales quantitative estimates of 1480 years of summer temperatures in northern fennoscandia have previously been derived from continuous treering records from northern sweden here we show the results of spectral analyses of these data only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub periods relatively timestable peaks are apparent at periods of 2 1 2 5 3 1 3 6 4 8 32 33 and for a range between 55 100 years these results offer no strong evidence for solar related forcing of summer temperatures in these regions our previously published reconstruction was limited in its ability to represent long timescale temperature change because of the method used to standardize the original tree ring data here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales considerable variance is now reconstructed on timescales of several centuries in comparison with modern normals 1951 70 generally extended periods when cool conditions prevailed prior to the start of the instrumental record include 500 700 790 870 1110 1150 1190 1360 1570 1750 a d with the most significant cold troughs centred on about 660 800 1140 1580 1620 and 1640 predominantly warm conditions occurred in 720 790 870 1110 and 1360 1570 with peaks of warmth around 750 930 990 1060 1090 1160 1410 1430 1760 and 1820

3d data derived lithospheric structure of the central andes and its implications for deformation insights from gravity and geodynamic modelling abstract we present a new three dimensional density model of the central andes characterizing the structure and composition of the lithosphere together with a geodynamic simulation subjected to continental intraplate shortening the principal aim of this study is to assess the link between heterogeneities in the lithosphere and different deformation patterns and styles along the orogen foreland system of the central andes first we performed a 3d integration of new geological and geophysical data with previous models through forward modelling of bouguer anomalies subsequently a geodynamic model was set up and parametrized from the previously obtained 3d structure and composition we do not find a unambigous correlation between the resulting density configuration and terrane boundaries proposed by other authors our models reproduce the observed bouguer anomaly and deformation patterns in the foreland we find that thin skinned deformation in the subandean fold and thrust belt is controlled by a thick sedimentary layer and coeval underthrusting of thin crust of the foreland beneath the thick crust of the andean plateau in the adjacent thick skinned deformation province of the inverted cretaceous extensional santa barbara system sedimentary strata are much thinner and crustal thickness transitions from greater values in the andean to a more reduced thickness in the foreland our results show that deformation processes occur where the highest gradients of lithospheric strength are present between the orogen and the foreland thus suggesting a spatial correlation between deformation and lithospheric strength

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

reconstructed warm season temperatures for nome seward peninsula alaska 1 understanding of past climate variability in the bering strait region and adjacent land areas is limited by a paucity of long instrumental and paleoclimatic records here we describe a reconstruction of may august temperatures for nome seward peninsula alaska based on maximum latewood density data which considerably extends the available climatic information the reconstruction shows warm conditions in the late 1600s and middle 20th century and cooler conditions in the 1800s the summer of 1783 coinciding with the laki iceland volcanic event is among the coldest in the reconstruction statistically significant relationships with the north pacific index and bering chukchi sea surface temperatures indicate that the seward tree ring data are potentially useful as long term indices of atmosphere ocean variability in the region

summer temperatures in the canadian rockies during the last millennium a revised record we present a significant update to a millennial summer temperature reconstruction 1073 1983 that was originally published in 1997 utilising new tree ring data predominantly picea engelmannii the reconstruction is not only better replicated but has been extended 950 1994 and is now more regionally representative calibration and verification statistics were improved with the new model explaining 53 of may august maximum temperature variation compared to the original 39 of april august mean temperatures the maximum latewood density data which are weighted more strongly in the regression model than ringwidth were processed using regional curve standardisation to capture potential centennial to millennial scale variability the reconstruction shows warm intervals comparable to twentieth century values for the first half of the eleventh century the late 1300s and early 1400s the bulk of the record however is below the 1901 1980 normals with prolonged cool periods from 1200 to 1350 and from 1450 to the late 19th century the most extreme cool period is observed to be in the 1690s these reconstructed cool periods compare well with known regional records of glacier advances between 1150 and the 1300s possibly in the early 1500s early 1700s and 1800s evidence is also presented of the influence of solar activity and volcanic events on summer temperature in the canadian rockies over the last 1 000 years although this reconstruction is regional in scope it compares well at multi decadal to centennial scales with northern hemisphere temperature proxies and at millennial scales with reconstructions that were also processed to capture longer timescale variability this coherence suggests that this series is globally important for the assessment of natural temperature variability over the last 1 000 years

multi proxy reconstructions of northeastern pacific sea surface temperature data from trees and pacific geoduck abstract we demonstrate the potential for developing sea surface temperature sst reconstructions in the northeast pacific from combinations of tree ring and growth increment chronologies of the long lived marine bivalve the pacific geoduck six pacific geoduck chronologies developed from site along the washington british columbia coast are compared and combined with tree ring chronologies from california to alaska all chronologies are annually resolved and strongly relate to local to regional scale sst though differences in the response season as well as the spectral properties of the two proxies are observed both proxy types closely track sst and when used in combination yield a more robust sst reconstruction than tree ring or geoduck chronologies could provide alone in total variance explained in sst is 63 9 at the regional scale and 68 2 at a local scale providing sst estimates for more than 60 years prior to the start of continuous instrumental records in this region this study represents one of the few climate reconstructions where both proxies are annually resolved and is the first to integrate regional networks of geoduck chronologies and tree ring chronologies

tree ring width based precipitation reconstruction in zhaogaoguan china since 1805 ad abstract in order to further understand the past climate variation especially the history of drought and flood events in the east asian summer monsoon easm marginal area precipitation from previous august to current july for the period of 1805 2014 ad was reconstructed from a ring width chronology of pinus tabulaeformis in zhaogaoguan zgg a site located in the easm marginal area in northern china the transfer function can explain 46 4 adjusted to 45 4 for the loss of degrees of freedom of the variance of the observed precipitation during the calibration period 1958 2014 ad the reconstructed precipitation series revealed that the inter annual variability was very prominent 1843 and 1844 ad were the two wettest years while 1931 and 1999 ad were the two driest years we noticed that the droughts in 1900 1906 1931 1955 and 1999 ad in the reconstruction series corresponded to the severe floods in the yangtze river watershed in southern china during those same years this phenomenon confirmed the typical climate pattern of northern droughts and southern floods in china moreover the reconstructed precipitation series in zgg showed synchronous variation patterns with the other tree ring based hydrological reconstructions in the marginal area of easm on both inter annual and inter decadal scales indicating the common precipitation variation characteristics of the easm marginal area

the sines contourite depositional system along the sw portuguese margin onset evolution and conceptual implications abstract the sines contourite depositional system located in the southwest portuguese margin is a central segment of the iberian contourite depositional complex built under the influence of the mediterranean outflow water mow this work presents the onset and evolution of this system using multibeam bathymetry multichannel seismic reflection lines sediment cores and well data six seismic units of late miocene through holocene age have been identified which defined three evolutionary stages for drift construction a an onset and initial stage from the latest miocene to the late pliocene 5 33 2 5 ma where a sheeted drift was built under a weak flowing mow b a growing stage from the early to middle quaternary 2 5 0 7 ma characterized by the deposition of a mounded drift in the south and a sheeted drift in the north which is correlated with a strengthening of the mow and c a maintenance stage between the middle pleistocene and holocene 0 7 ma present where the modern depositional and erosional contourite features developed associated with three intensification periods of the mow at 0 7 ma 0 4 ma and 20 ka the development of the sines contourite depositional system was constrained in the long term by seafloor paleomorphologies inherited from the mesozoic rifting phases of the southwest portuguese margin the nnw sse horsts and grabens built during the mesozoic rifting provided accommodation for drift growth with limited lateral migration and locally enhanced the alongslope bottom current in short term environmental climate and sea level fluctuations modulated changes in bottom current density and intensity determining sedimentary cycles in the depositional record especially during the quaternary our findings emphasize the occurrence of three main plastered morphologies throughout the seismic record which were compared with other plastered drifts in different continental margins to establish a conceptual model

august temperature variability in the southeastern tibetan plateau since ad 1385 inferred from tree rings long term high resolution climate proxies are essential for understanding climate variability on the tibetan plateau tp where few long term climate records are available in this paper we describe a summer august temperature reconstruction over the period 1385 2002 based on a tree ring width chronology of balfour spruce picea likiangensis var balfouriana on the southeastern tp created using the regional curve standardization method the reconstruction explains 44 7 of the variance in the instrumental temperature records during the calibration period 1962 2002 and captures temperature variability over a broad region of the tp warmer than average augusts were found during the periods 1446 1494 1509 1522 1553 1567 1797 1812 1845 1905 and 1918 2002 cooler than average augusts occurred from 1385 1416 1426 1445 1495 1508 1523 1552 1568 1686 1695 1718 1725 1796 1813 1844 and 1906 1917 a warming trend in the 20th century was unprecedented during the past six centuries the reconstruction closely matched other tree ring summer temperature reconstructions from neighboring regions as well as patterns from ice core delta 18 o data and fluctuated in synchrony with northern hemisphere temperature reconstructions c 2011 elsevier b v all rights reserved

glacial to interglacial changes in the settling depth of the mediterranean outflow plume we present micropalaeontological and grain size records for a set of sediment cores from the gulf of cadiz southwest spain that reflect changes in the position and strength of the mediterranean outflow mo current the cores sample a sediment drift the gil eanes drift that is positioned lower on the slope in the gulf of cadiz than the position of the main current today the data indicate that the drift is of glacial age and that the glacial mo current was positioned lower on the slope than today but also that it was active over a considerably reduced area of the slope we argue that this observation is consistent with physical constraints on the gibraltar exchange and on the likely settling and spreading behavior of the mo plume along the iberian margin under glacial environmental and sea level conditions the deeper settling of the mo is likely to have influenced the formation of glacial north atlantic intermediate water and also may have exerted indirect influence on the formation of glacial north atlantic deep water

changes in northeast pacific marine ecosystems over the last 4500 years evidence from stable isotope analysis of bone collagen from archeological middens changes in food web dynamics and ocean productivity over the past 4500 years are investigated using stable isotope analysis of nitrogen and carbon in collagen from animal bones preserved in coastal arche ological middens on sanak island along the eastern edge of the aleutian archipelgo samples included steller sea lions harbor seals northern fur seals sea otters pacific cod and sockeye salmon sea otters had the high est 13 c 11 9 0 7 and lowest 15 n values 14 5 1 4 northern fur seals had the lowest 13 c values 13 6 1 4 and steller sea lions had the highest 15 n values 18 4 1 4 of the marine mammals cod isotope values were consistent with those of demersal organisms from near shore habitats 12 5 0 9 13 c 16 1 1 4 15 n while salmon values were consistent with those of organisms existing in an open ocean habi c corrected for the oceanic suess effect of modern specimens of all species except northern fur seals were sig nificantly lower than prehistoric animals several hypotheses are explored to explain these differences includ ing a reduction in productivity during the twentieth century in this region of the gulf of alaska if true this sug gests that north pacific climate regimes experienced during the twentieth century may not be good analogs of north pacific marine ecosystems during the late holocene

high resolution dinoflagellate cyst record of environmental change in effingham inlet british columbia canada over the last millennium abstract we present a high resolution sedimentary record of dinoflagellate cysts spanning the last 900 years recovered from effingham inlet a glacial fjord on the west coast of vancouver island canada the combination of seasonal coastal upwelling supporting high levels of marine primary productivity in surface waters together with restricted bottom water circulation in the silled fjord fosters the preservation of laminated sediments in the inner basin of effingham inlet geochemical data are used to assess the sedimentary facies of the core which is composed primarily of laminated units 50 2 occasionally interrupted by seismites 39 5 and homogenous units 10 2 the chronology of the 2 m long core is based on varve counting and fifteen 14c dates and is anchored by a seismite previously dated at ad 1946 the dinoflagellate cyst assemblages are diverse total of 47 taxa abundant average concentrations of 102 900 cyst g 1 of dry sediment and characterized by a proportionally equal contribution of autotrophic and heterotrophic cyst taxa in most samples overall cyst assemblages are characterized by operculodinium centrocarpum 36 2 accompanied by brigantedinium spp 18 0 and dubridinium spp 6 6 multivariate analyses are used to extract the dominant patterns of variability in autotrophic and heterotrophic dinoflagellate cyst assemblages separately and help in identifying the temperature and primary productivity gradients encoded in the cyst sedimentary record in this particular estuary specific intervals identified in the dinoflagellate cyst record are interpreted to represent the local expression of the medieval climate anomaly from the base of the record ad 1090 to 1230 the little ice age ad 1230 to late 19th century and warming in the second half of the 20th century the timing of these intervals are consistent with the regional paleoclimate and help constrain past climatic and oceanographic variability on the west coast of vancouver island the origin of homogenous units in the sedimentary record of effingham inlet and paleoseismicity in the region are also discussed

mechanisms of hemispherically symmetric climate variability inspired by paleoclimate evidence that much past climate change has been symmetric about the equator the causes of hemispherically symmetric variability in the recent observational record are examined using the national centers for environmental prediction national center for atmospheric research reanalysis dataset and numerical models it was found that the dominant cause of hemispherically symmetric variability is the el nino southern oscillation during an el nino event the tropics warm at all longitudes and the subtropical jets in both hemi spheres strengthen on their equatorward flanks poleward of the tropical warming there are latitude belts of marked cooling extending from the surface to the tropopause in both hemispheres at all longitudes and in all seasons the midlatitude cooling is caused by changes in the eddy driven mean meridional circulation changes in the transient eddy momentum fluxes during an el nino event force upper tropospheric ascent in midlatitudes through a balance between the eddy fluxes and the coriolis torque the eddy driven ascent causes anomalous adiabatic cooling which is primarily balanced by anomalous diabatic heating using a quasigeostrophic spherical model forced by an imposed surface eddy disturbance of chosen wave number and frequency it is shown that the anomalous eddy momentum fluxes are caused by the impact that the changes in the tropically forced subtropical jets have on the propagation in the latitude height plane of transient eddies changes in zonal winds and associated changes in the meridional gradient of potential vorticity create an anomalous region of low meridional wavenumber in the midlatitudes that refracts waves away both poleward and equatorward tropical forcing of variability in the eddy driven mean meridional circulation is another way in addition to rossby wave teleconnections whereby the tropics can influence extratropical climate unlike teleconnections this mechanism causes climate variability that has strong zonally and hemispherically symmetric components and operates throughout the seasonal cycle