archaeological implications of a widespread 13th century tephra marker across the central indonesian archipelago abstract despite the occurrence of exceptionally large eruptions in the indonesian archipelago in recent historic times i e krakatoa 1883 tambora 1815 no historic tephra beds have been widely identified in the terrestrial realm that could facilitate the correlation of equivalent aged sequences and or archaeological remains this study has identified one such tephra bed of 13th century age that can be correlated throughout central east java and now can be unequivocally correlated with the samalas 1257 a d tephra recently described from lombok the occurrence of this historic tephra marker extending 650 km west from its eruptive source provides the first opportunity to effect inter regional correlation over large swathes of central indonesia it remains entirely conceivable that in the aftermath of this exceptionally large eruptive event there was considerable westward disruption to subsistence agriculture and trade food shortages and famine dislocation of affected populations and socio political unrest on a scale that equalled or exceeded the catastrophic effects documented from the more recent tambora 1815 a d eruption indeed the effects of this mid 13th century eruption can be registered globally in a variety of records from antarctica europe middle east and the americas unfortunately archaeological evidence indicating such disruption in mid 13th century indonesia is yet to be deciphered from the so far sparse accounts and inscriptions of that time however this paucity of evidence does not diminish the utility of this widespread tephra bed as a unique chronostratigraphic marker for archaeological studies across large areas of central indonesia

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

the equatorial atlantic oscillation and its response to enso an internal equatorial atlantic oscillation has been identified by analyzing sea surface temperature sst observations the equatorial atlantic oscillation can be viewed as the atlantic analogue of the el nino southern oscillation enso phenomenon in the equatorial pacific but it is much less vigorous the equatorial atlantic oscillation is strongly influenced by the pacific enso with the equatorial atlantic sea surface temperature lagging by about six months this lag can be explained by the dynamical adjustment time of the equatorial atlantic to low frequency wind stress variations and the seasonally varying background state which favours strongest growth of perturbations in summer results of an extended range simulation with a coupled ocean atmosphere gcm support this picture

monsoonal variability in the northeastern arabian sea during the past 5000years geochemical evidence from laminated sediments abstract a high resolution laminated sediment record from the oxygen minimum zone in the northeastern arabian sea off pakistan was studied to reconstruct climatic variations to infer the monsoon driven moisture history in the northeastern arabian sea during the past 5000 years we have used three types of independant proxies 1 varve thickness 2 stable isotope ratios of planktic foraminifera and 3 inorganic geochemical composition on the basis of these proxies we have subdivided the sedimentary record into five intervals the first time interval from 5000 to 3900 yr bp period i is dominated by summer monsoon activity deduced from ti al zr al k al and sr ca ratios and oxygen isotope data of planktonic foraminifera slightly enhanced winter monsoon conditions can be inferred for the period from 3900 to about 3000 yr bp period ii maximum precipitation during enhanced winter monsoon activity at about 3100 yr bp was followed by an onset of aridification at 3000 yr bp which continued until about 2000 2200 yr bp period iii the textural mineralogical and geochemical data suggest that this aridification was a gradual century scale process rather than an abrupt event comparison to late holocene records in nw and sw india the near east and tropical africa supports our interpretation that period iii from 3000 to 2000 yr bp is characterized by a gradual change in the atmospherical moisture budget over much of this area reduced monsoonal rainfall may be linked to variations of eurasian snow cover as deduced from varve thickness and element to al ratios period iv from 2000 to about 1500 yr bp is characterized by a summer monsoon dominated sequence with higher precipitation than during period iii the 18o record shows an abrupt shift at 2000 yr bp coinciding with an increase of varve thickness which suggests a cooling of surface waters in the northern arabian sea present day conditions in the makran area were established at 1500 yr bp period v based on inorganic geochemical data and meteorological records at several stations in the makran we conclude that period v is dominated by precipitation during the winter season here declined rainfall associated with the summer monsoon may be related to a less northward position of the intertropical convergence zone itcz during summer and a stronger influence of winter monsoon linked phenomenona

dispersal and deposition of eolian and fluvial sediments off peru and northern chile relative abundances of quartz and feldspar in fine grained terrigenous sediments have been used to recognize specific continental sediment sources along northwestern south america and to trace the dispersal of specific grain size fractions from these sources to adjacent continental margin and deep sea sedimentary environments quartz feldspar ratios are low 0 6 for all fractions of sediments derived from southern peru and northern chile but such ratios increase systematically in central and northern peru as the importance of granitic and related intrusives increases relative to more basaltic extrusives and gabbroic equivalents limited published analyses of dusts collected offshore prospero and bonatti 1969 are also consistent with a latitudinally varying continental sediment source we find that clay

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

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

dating methods and geomorphic evidence of palaeoenvironmental changes at the eastern margin of the south peruvian coastal desert 14 30 s before and during the little ice age abstract the atacama desert is known to be one of the driest places on earth however in the study area between ica and nasca south peru 75 76 w 14 15 s palaeoclimate proxies show several semi arid phases during the holocene a more humid period during the early holocene favoured an open grass land which allowed the accumulation of desert loess eitel b hecht s machtle b schukraft g kadereit a wagner g kromer b unkel i reindel m 2005 geoarchaeological evidence from desert loess in the nazca palpa region southern peru palaeoenvironmental changes and their impact on pre columbian cultures archaeometry 47 137 158 the paracas and nasca cultures existing in that region between the 9th century bc and 7th century ad had propitious conditions to evolve and to settle close to the rivers fed by the monsoonal precipitation in the cordillera occidental culminating aridity after 600 ad might have caused the collapse of the nasca civilization the onset of semi arid climate towards the end of the late intermediate period 14th century ad allowed a reoccupation of the area here we present 14c and osl data from sediments of river terraces a debris flow and loess snails scutalus sp indicating appreciable geomorphic activity between 1390 and 1714 cal ad this phase is isochronous to the little ice age period on the northern hemisphere and to an increase in the ice accumulation on the quelccaya glacier in the peruvian altiplano thompson l g mosley thompson e bolzan j f koci b r 1985 a 1500 year record of tropical precipitation in ice cores from the quelccaya ice cap peru science 229 971 973

environmental context for late holocene human occupation of the south wellesley archipelago gulf of carpentaria northern australia a 2400 year record of environmental change is reported from a wetland on bentinck island in the southern gulf of carpentaria northern australia three phases of wetland development are identified with a protected coastal setting from ca 2400 to 500 years ago transitioning into an estuarine mangrove forest from ca 500 years ago to the 1940s and finally to a freshwater swamp over the past 60 years this sequence reflects the influence of falling sea levels development of a coastal dune barrier system prograding shorelines and an extreme storm cyclone event in addition there is clear evidence of the impacts that human abandonment and resettlement have on the island s fire regimes and vegetation a dramatic increase in burning and vegetation thickening was observed after the cessation of traditional indigenous kaiadilt fire management practices in the 1940s and was then reversed when people returned to the island in the 1980s in terms of the longer context for human occupation of the south wellesley archipelago it is apparent that the mangrove phase provided a stable and productive environment that was conducive for human settlement of this region over the past 1000 years

mount logan ice core record of tropical and solar influences on aleutian low variability 500 1998 a d continuous high resolution paleoclimate records from the north pacific region spanning the past 1500 years are rare and the behavior of the aleutian low alow pressure center the dominant climatological feature in the gulf of alaska remains poorly constrained here we present a continuous 1500 year long calibrated proxy record for the strength of the wintertime december march alow from the mount logan summit pr col 5200 m asl ice core soluble sodium time series we show that ice core sodium concentrations are statistically correlated with north pacific sea level pressure and zonal wind speed our alow proxy record reveals a weak alow from circa 900 1300 a d and 1575 1675 a d and a comparatively stronger alow from circa 500 900 a d 1300 1575 a d and 1675 a d to present the mount logan alow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the el nino southern oscillation and is consistent with the hypothesis that the medieval climate anomaly was characterized by more persistent la nina like conditions while the little ice age was characterized by at least two intervals of more persistent el nino like conditions the mount logan alow proxy record is significantly p 0 05 correlated and coherent with solar irradiance proxy records over various time scales with stronger solar irradiance generally associated with a weaker alow and la nina like tropical conditions however a step like increase in alow strength during the dalton solar minimum circa 1820 is associated with enhanced walker circulation furthermore rising co2 forcing or internal variability may be masking the twentieth century rise in solar irradiance

oceanic cooling recorded in shells spanning the medieval climate anomaly in the subtropical eastern north atlantic ocean abstract the medieval climate anomaly mca 900 1300 ad was the most recent period of pre industrial climatic warming in the northern hemisphere and thus estimations of mca signals can illuminate possible impacts of anthropogenic climate change current high resolution mca climate signals are restricted to mid and high latitude regions which confounds inferences of how the mca impacted some global hemispheric climate mechanisms e g north atlantic oscillation nao to address this knowledge gap we estimate seasonally resolved sea surface temperatures ssts from the oxygen isotope composition 18o of serially sampled phorcus atratus shells from archaeological sites spanning the mca in the canary islands twelve archaeological and six modern p atratus shells were analyzed and archaeological shells were dated using carbonate target radiocarbon dating ssts were estimated using the published aragonite water equilibrium fractionation equation modern shells showed a mean sst of 20 0 1 5 c with a seasonal amplitude of 5 3 0 9 c archaeological shells exhibited a mean sst of 18 2 0 7 c with a mean seasonal amplitude of 5 5 1 0 c thus shells that span the mca in the canary islands recorded ssts that were significantly cooler than the modern p

a 350014c yr high resolution record of water level changes in lake titicaca bolivia peru abstract sediment cores collected from the southern basin of lake titicaca bolivia peru on a transect from 4 6 m above overflow level to 15 1 m below overflow level are used to identify a new century scale chronology of holocene lake level variations the results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century scale lake level changes detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores a chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water level fluctuations two methods were used to estimate the14c reservoir age both indicate that it has remained nearly constant at 25014c yr during the late holocene core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level implying negative moisture balance for the northern andean altiplano over the last 3500 cal yr between 3500 and 3350 cal yr b p a transition from massive inorganic clay facies to laminated organic matter rich silts in each of the four cores signals a water level rise after a prolonged mid holocene dry phase evidence of other significant low lake levels occurs 2900 2800 2400 2200 2000 1700 and 900 500 cal yr b p several of the low lake levels coincided with cultural changes in the region including the collapse of the tiwanaku civilization

exploring the relationship between aboriginal population indices and fire in australia over the last 20 000 years abstract the extent of prehistoric human impact on the environment is a contentious topic in various palaeo environmental sciences the long history of humans in australia and its extensive fire prone biota makes this continent a key research area for better characterization of prehistoric human fire interactions here we use statistically robust cross correlation of archaeological radiocarbon data n 4102 ages from 1616 sites and a new synthesis of charcoal records n 155 sites to test for any relationship between people and fire over the last 20 000 years at continental and regional 25 45 s scales we find that the statistical correlation between the two datasets is weak at both spatial scales with short lived synchronous responses only in the terminal pleistocene holocene transition at the onset of the mid holocene climatic optimum 10 7 ka and during significant transitions of el nino southern oscillation 5 4 ka and 1 2 0 8 ka one interpretation of this is that aboriginal populations were implementing fire stick farming only intermittently during periods of societal stress resulting from climatic variability however the synchronicity of the correlations with climate changes along with the low populations through much of this time suggests that both datasets were independently responding to external climatic forcing under either scenario a lack of significant change in the charcoal record implies that there were no long lasting impacts to the environmental biota and macro scale palaeoenvironmental records prior to european colonization largely reflect responses to non human influences while we do not discount the possibility of systematic or deliberate manipulation of fire regimes at local spatial scales we conclude that human control of fire by prehistoric people in australia is not evident at broad landscape levels this conclusion contradicts persistent suggestions of australian wide land management and the pervasiveness of the impacts of fire stick farming

subtropical sea level history from coral microatolls in the southern cook islands since 300 ad abstract relative sea level rsl history is reconstructed for the southern cook islands since 300 ad using porites sp coral microatolls the upper surface or height of living coral of the modern microatolls on rarotonga was rigorously determined by 400 laser survey measurements to be constrained by the sea level 0 36 m below mean sea level with a standard deviation of 0 008 m that is equivalent to midway between mean low water neaps and mean low water springs tidal datums fossil microatoll history on the fringing reefs is fragmentary due to multi decadal to centennial windows of microatoll growth cyclone destruction and preservation through coastal progradation the mid late holocene highstand ceased prior to 500 bc and rsl fell from 1 3 0 1 m to 0 45 0 15 m by 1000 ad at a rate of 0 5 mm yr the rsl minimum occurred during the late 1700s to 1800s ad at 0 2 m below present before rising during the 1900s during the past 500 yr rsl fluctuated including an abrupt fall at 1750 ad following a sustained multi decadal high anomaly similarly low rsl anomalies and slow coral growth rates during the 950 to 1000 ad period are indicative of pacific basin wide climate variability and are consistent with extreme la nina like climate anomalies previously reported around the pacific basin the fall in rsl during the first millennium ad crossed over tidal thresholds for rapid coastal progradation when ambient mean high water neaps and mean high water springs fell below the low tide level of the mid late holocene high stand this coastal response is inversely analogous to the projected response to sea level rise during the latter part of the modern century

multiproxy summer and winter surface air temperature field reconstructions for southern south america covering the past centuries we statistically reconstruct austral summer winter surface air temperature fields back to ad 900 1706 using 22 20 annually resolved predictors from natural and human archives from southern south america ssa this represents the first regional scale climate field reconstruction for parts of the southern hemisphere at this high temporal resolution we apply three different recon struction techniques multivariate principal component regression composite plus scaling and regularized expectation maximization there is generally good

subdecadally resolved paleoceanography of the peru margin during the last two millennia 1 using multiproxy sediment core data from the el nino southern oscillation enso sensitive peru margin subdecadally resolved down to 0 6 year surface productivity and subsurface denitrification are reconstructed for the last 2300 years scanning xrf generated major elemental data ti fe si correlate well with discrete inductively coupled plasma atomic emission spectometry icp aes analyses and together with x radiography core density are used as productivity indices as surface productivity in this marine region is strongly impacted by enso higher lower periods of surface productivity are inferred to represent a persistent normal la nina el nino like state surface productivity and subsurface denitrification appear to have remained intimately coupled during this period due to direct stimulation of requisite subsurface suboxia and or hydrographic restructuring the late holocene peru margin is characterized by persistent moderate productivity and subsurface denitrification punctuated at centennial scale by shorter duration periods of high production and intense denitrification these centennial scale events are likely analogous to modern observations of decadal scale regime shifts but of higher amplitude and provide a background history for future natural changes to this system solar irradiance variability is suggested to have influenced peru productivity as evidenced in numerous high resolution paleorecords from the northern hemisphere

el nino as a mediator of the solar influence on climate 1 using a climate model of intermediate complexity we simulate the response of the el nino southern oscillation enso system to solar and orbital forcing over the holocene solar forcing is reconstructed from radiocarbon production rate data using various scaling factors to account for the conflicting estimates of solar irradiance variability as estimates of the difference since the maunder minimum range from 0 05 to 0 5 of the solar constant we consider these two extreme scenarios along with the intermediate case of 0 2 we show that for large or moderate forcings the low pass filtered east west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing with a short phase lag about a decade wavelet analysis shows a statistically significant enhancement of the century to millennial scale enso variability for even a moderate irradiance forcing in contrast the 0 05 case displays no such enhancement orbitally driven insolation forcing is found to produce a long term increase of enso variability from the early holocene onward in accordance with previous findings when both forcings are combined the superposition is approximately linear in the strong scaling case overall the sea surface temperature response is of the magnitude required and is persistent enough to induce important climatic perturbations worldwide the results suggest that enso may plausibly have acted as a mediator between the sun and the earth s climate a comparison to key holocene climate records from the northern hemisphere subtropics and midlatitudes shows support for this hypothesis

el nino variability off peru during the last 20 000 years here we present a high resolution marine sediment record from the el nino region off the coast of peru spanning the last 20 000 years sea surface temperature photosynthetic pigments and a lithic proxy for el nino flood events on the continent are used as paleo el nino southern oscillation proxy data the onset of stronger el nino activity in peru started around 17 000 calibrated years before the present which is later than modeling experiments show but contemporaneous with the heinrich event 1 maximum el nino activity occurred during the early and late holocene especially during the second and third millennium b p the recurrence period of very strong el nino events is 60 80 years el nino events were weak before and during the beginning of the younger dryas during the middle of the holocene and during medieval times the strength of el nino flood events during the last millennium has positive and negative relationships to global and northern hemisphere temperature reconstructions

holocene history of the el nino phenomenon as recorded in flood sediments of northern coastal peru significant precipitation along the north central coast of peru lat 5 10 s occurs exclusively during el nino incursions of warm water into the peruvian littoral flood deposits from this region therefore provide a proxy record of extreme el nino events i present a 3500 yr chronology of the extreme events based on radiocarbon dating of overbank flood sediments from the rio casma lat 9 2 s the flood plain stratigraphy suggests that the el nino phenomenon has occurred throughout the holocene and that flood events much larger than that which occurred during 1982 1983 occur here at least once every 1000 yr

south asian monsoon climate change and radiocarbon in the arabian sea during early and middle holocene the 1 4 c ages of planktonic foraminifers globigerinoides sacculifer bracketing the younger dryas in a 1 8 o record of globigerinoides ruber from a laminated sediment core on the pakistani continental margin suggest thatsurface reservoir ages in the arabian sea were in excess of 1000 years during the deglaciation a least squares error fit of a detailed 1 4 c chronology to the atmospheric tree ring record gave variable early holocene reservoir ages between 780 and 1120 years well above the prebomb value of 640 years mid holocene reservoir ages are less well constrained but were probably closer to the prebomb value the method used to fit individual core sections to the tree ring record was designed to require only a rough a priori estimate of the time spans which in the core presented here were taken from each section s range of 1 4 c ages a significant 220 year quasi oscillation was present in the 1 8 o record during the early holocene but not thereafter this frequency and amplitude pattern resembles an early holocene 207 to 227 year oscillation previously observed in the atmospheric 1 4 c record which is generally interpreted as reflecting solar irradiance variability an early holocene climate event at 8150 8400 calendar years b p observed elsewhere within the asian east african monsoon system was again found in our record suggesting a reduction in precipitation over nw india and pakistan

interaction between the enso and the asian monsoon in a coral record of tropical climate the oxygen isotopic composition of a banded coral from the western equatorial indian ocean provides a 150 year long history of the relation between the el nino southern oscillation enso phenomenon and the asian monsoon interannual cycles in the coral time series were found to correlate with pacific coral and instrumental climate records suggesting a consistent linkage across ocean basins despite the changing frequency and amplitude of the enso however decadal variability that is characteristic of the monsoon system also dominates the coral record which implies important interactions between tropical and midlatitude climate variability one prominent manifestation of this interaction is the strong amplitude modulation of the quasi biennial cycle

a late quaternary record of monsoon variability in the northwest kimberley australia abstract understanding of the late quaternary environment of australia s vast kimberley region has to date been hindered by the region s lack of classic palaeoenvironmental archives such as deep lake sediments however mound spring peat deposits in the region have been found to be a potentially rich archive of palaeoenvironmental data here we present a high resolution record from black springs mound spring in the kimberley s northwest filling some of the current gaps in knowledge of the region s environmental history this builds on a 6000 year record developed from the same site and indicates that since the last glacial interglacial transition the australian summer monsoon has varied greatly in intensity with an increase in monsoonal precipitation from 14 000 yr bp and pronounced drying in the late holocene despite some chronological uncertainties thought to be due to the inclusion of younger microscopic root fragments changes in the record compare well with other records of climatic change from the kimberley and across tropical northern australia

late holocene paleoenvironmental change at mid elevation on the caribbean slope of the cordillera central dominican republic a multi site multi proxy analysis abstract high resolution proxy records from the circum caribbean region indicate significant variation in late holocene climate especially precipitation attributed primarily to shifts in the mean annual position of the intertropical convergence zone itcz the paleoenvironmental and cultural impacts of this late holocene climate variability have been analyzed intensively in the western caribbean and to a lesser extent in the southern caribbean however the occurrence and impacts of late holocene climate shifts in the eastern caribbean especially in island interiors has not been well documented here we present sediment records of late holocene paleoenvironmental change from two lakes located on the caribbean slope of the cordillera central in the dominican republic that span the last 3000 years sediment characteristics pollen charcoal biogenic carbonate assemblages and isotopic composition and bulk sedimentary carbon isotope values in laguna castilla and laguna de salvador indicate extreme shifts in hydrology vegetation and disturbance regimes in response to climate change and human activity in the lake watersheds close correspondence between the hydrological histories of the lakes and trace metal concentrations in sediments of the cariaco basin indicate that precipitation variability here responds to the same controls and may similarly reflect shifts in the mean annual position of the itcz human occupation of the watersheds appears to be closely linked to severe dry periods and may indicate larger scale cultural responses to precipitation variability on the island of hispaniola prehistoric human populations strongly affected vegetation and disturbance regimes in the lake watersheds impacts may have lasted several centuries and may have been more severe than impacts of modern populations

geomorphology internal structure and successive development of a glacier foreland in the semiarid chilean andes cerro tapado upper elqui valley 30 08 s 69 55 w we use geomorphological analysis sedimentological survey remote sensing and ground penetrating radar gpr in order to understand the complex landform assemblage found in front of the cerro tapado glacier in the upper elqui river catchment semiarid andes of chile the geomorphological analysis highlights prominent boundaries dividing the landform assemblage into from the upper part to the lower part an upper latero frontal moraine complex an upper debris covered glacier a lower debris covered glacier two rock glaciers and a lower morainic complex the sedimentological survey highlights the rather small size of the surface debris in general 400 m receding of the glacier occurred along with downslope displacements dm m y 1 of most of the landform units and a significant evolution of the thermokarst features on the debris covered glaciers considerable surface lowering occurred in the upper part of the assemblage while localized bulging is seen along the morphological boundaries in the lower units the gpr profiles highlight spectacular internal structure in the upper debris covered glacier with up to 80 m of buried ice in the other landform units the internal structure is less visible and more heterogeneous the analysis of the radar wave velocity along the gpr profiles reveals the occurrence of air filled and moist zones in the internal structure the geomorphological assemblage is fundamentally characterized by its morphological structural and dynamical boundaries and defined as a young probably 2000 years polygenetic construction with landform units having added to overlapped one another the rock glaciers do not derive from the present debris covered glacier but preexist to it

evidence for pacific modulated precipitation variability during the late holocene from the southwestern usa 1 the mechanisms driving late holocene drought cycles in the western united states are not well known due to the general scarcity of long term high resolution absolutely dateable proxies for precipitation in continental interiors here we show that late holocene precipitation variability in the southwestern united states has been caused by changes in the pacific ocean we present a stalagmite based annually resolved moisture record that indicates large shifts from pluvial to drought conditions alternating with periods of dampened near average precipitation over the last 3000 years significant spectral peaks at decadal scale 20 50 70 80 year frequencies likely correspond to modern frequencies of the pacific decadal oscillation or a low frequency component of the el nino southern oscillation and are dominant during episodes of large precipitation shifts overall pluvial conditions punctuated by severe droughts may have challenged the adaptive capacities of emerging agrarian communities of ancestral americans

late holocene flood probabilities in the black hills south dakota with emphasis on the medieval climate anomaly abstract a stratigraphic record of 35 large paleofloods and four large historical floods during the last 2000 years for four basins in the black hills of south dakota reveals three long term flooding episodes identified using probability distributions at a d 120 395 900 1290 and 1410 to present during the medieval climate anomaly a d 900 1300 the four basins collectively experienced 13 large floods compared to nine large floods in the previous 800 years including the largest floods of the last 2000 years for two of the four basins this high concentration of extreme floods is likely caused by one or more of the following 1 instability of air masses caused by stronger than normal westerlies 2 larger or more frequent hurricanes in the gulf of mexico and atlantic ocean and or 3 reduced land covering vegetation or increased forest fires caused by persistent regional drought

solar forcing of centennial scale east asian winter monsoon variability in the mid to late holocene abstract centennial scale variability of the east asian winter monsoon during the holocene is poorly understood because suitable archives and proxies are lacking here we present a high resolution 30 yr spacing planktonic foraminiferal o 18 record of neogloboquadrina incompta dextral form which reflects sea surface temperature during the winter season for the last 6000 yrs from marine sediments in the western north pacific stronger winter monsoons indicated by cooler winter ssts correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial scale variability the variability also shows good correlation with o 18 records in lake sediments and ice cores from the yukon territory canada spanning the last 4500 yrs suggesting east west climate coupling across the north pacific furthermore the climate changes across the north pacific co vary over widespread regions such as the eastern tropical pacific and the northern red sea and the reconstructed solar activity the cross spectral and wavelet analyses show that the east asian winter monsoon shares some cyclicity with the solar variability our results suggest that the solar activity is a fundamental forcing producing the centennial scale eawm variability mediated by the large scale climate linkages

wave climate sand budget and shoreline alignment evolution of the iluka woody bay sand barrier northern new south wales australia since 3000 yr bp abstract multi centennial fluctuations in the northern new south wales nsw coastline alignment are interpreted from a detailed reconstruction of the morphological and depositional evolution of the iluka to woody bay barrier during the late holocene the regional coastline is aligned obliquely to the south east inner shelf modal wave direction and hence sediment is transported obliquely on the shoreface with a net northward movement on centennial to millennial time scales the coastline is shown to have responded to fluctuations in mean wave direction longshore gradients in sand transport and headland sand bypassing processes overall barrier progradation has been punctuated by episodes of shoreline recession and realignment throughout the late holocene a prolonged shoreline recessional phase occurred at 1500 yr bp in response to a rotation in modal wave direction from more southerly towards east south easterly subsequent to this realignment renewed shoreline progradation occurred along the east aspect coastline after 1400 yr bp whilst the north east aspect coastline remained in a receded alignment until after 1000 yr bp when renewed progradation occurred progradation rates increased throughout the past millennium driven by changes to the alongshore gradient in sand transport under an implied shift to a more southerly and energetic modal wave climate in the past 50 yrs the north east aspect shoreline has experienced a rapid recessional trend which is associated with a shift in modal wave climate to a more east southeasterly direction and a reduction in headland sand bypassing the average sand supply rate to the iluka to woody head section of the northern nsw shoreline is 4 1 m3 m yr since 3000 yr bp

nature and causes of quaternary climate variation of tropical south america abstract this selective review of the quaternary paleoclimate of the south american summer monsoon sasm domain presents viewpoints regarding a range of key issues in the field many of which are unresolved and some of which are controversial 1 el nino southern oscillation variability while the most important global scale mode of interannual climate variation is insufficient to explain most of the variation of tropical south american climate observed in both the instrumental and the paleoclimate records 2 significant climate variation in tropical south america occurs on seasonal to orbital i e multi millennial time scales as a result of sea surface temperature sst variation and ocean atmosphere interactions of the tropical atlantic 3 decadal scale climate variability linked with this tropical atlantic variability has been a persistent characteristic of climate in tropical south america for at least the past half millennium and likely far beyond 4 centennial to millennial climate events in tropical south america were of longer duration and perhaps larger amplitude than any observed in the instrumental period which is little more than a century long in tropical south america these were superimposed upon both precession paced insolation changes that caused significant variation in sasm precipitation and eccentricity paced global glacial boundary conditions that caused significant changes in the tropical south american moisture balance as a result river sediment and water discharge increased and decreased across tropical south america lake levels rose and fell paleolakes arose and disappeared on the altiplano glaciers waxed and waned in the tropical andes and the tropical rainforest underwent significant changes in composition and extent to further evaluate climate forcing over the last glacial cycle 125 ka we developed a climate forcing model that combines summer insolation forcing and a proxy for north atlantic sst forcing to reconstruct long term precipitation variation in the sasm domain the success of this model reinforces our confidence in assigning causation to observed reconstructions of precipitation in addition we propose a critical correction for speleothem stable oxygen isotopic ratios which are among the most significant of paleoclimate proxies in tropical south america for reconstruction of variation of paleo precipitation or sasm intensity however it is already well known that any particular 18o value observed in speleothem carbonate is affected by two processes that have nothing to do with changes in precipitation amount the influence of temperature on carbonate water isotopic fractionation in the cave and the influence of changing 18o of seawater quantitatively accounting for both artifacts can significantly alter the interpretations of speleothem records in tropical south america both adjustments act in the same direction and have the tendency to increase the true amplitude of the paleo hydrologic signal but by different amounts in glacial and inter glacial stages these corrections have even graver implications for the interpretation of tropical northern hemisphere speleothem records e g chinese speleothems where the combined adjustments tend to decrease or even eliminate the true signal amplitude

solar and tropical ocean forcing of late holocene climate change in coastal east asia abstract in this study paleoclimate signals were extracted from high resolution sediment records very recently produced from the mulyoungari swamp on jeju island south korea and examined to determine the main factors driving late holocene climate change in east asia the high resolution of the mulyoungari records allows the detection of multidecadal to centennial scale climate change with various cycles this enables comparisons with important paleoclimate proxies such as total solar irradiation tsi and sea surface temperatures ssts in the western tropical pacific wtp spectral analyses of pollen and magnetic susceptibility ms data identify significant periodicities of 780 470 135 145 and 50 70 years the mulyoungari swamp responded sensitively to global climate change during the holocene showing well known holocene cycles in the results our tree pollen index of warmness tpiw shows important late holocene cold events associated with low sunspot periods such as oort wolf sporer and maunder minimum comparisons among standard z scores of filtered tpiw tsi and other paleoclimate records from central and northeastern china off the coast of northern japan southern philippines and peru all demonstrate significant relationships this suggests that solar activity drove holocene variations in both east asian monsoon eam and el nino southern oscillation enso in particular the latter seems to have predominantly controlled the coastal climate of east asia to the extent that the influence of precession was nearly muted during the late holocene

cooling of the southern high latitudes during the medieval period and its effect on enso abstract a high resolution multiproxy study performed on a marine record from se pacific off southern south america was used to reconstruct past regional environmental changes and their relation to global climate particularly to el nino southern oscillation enso phenomenon during the last 2200 years our results suggest a sustained northward shift in the position of the zonal systems i e the southern westerly wind belt and the antarctic circumpolar current which occurred between 1300 and 750 yr bp the synchrony of the latitudinal shift with cooling in antarctica and reduced enso activity observed in several marine and terrestrial archives across south america suggests a causal link between enso and the proposed displacement of the zonal systems this shift might have acted as a positive feedback to more la nina like conditions between 1300 and 750 yr bp by steepening the hemispheric and tropical pacific zonal sea surface temperature gradient this scenario further suggests different boundary conditions for enso before 1300 and after 750 yr bp

widening of the krafla fissure swarm during the 1975 1981 volcano tectonic episode frequent distance measurements across the krafla fissure swarm north iceland recorded the extension accompanying the sequence of rifting events which started in december 1975 and lasted for 6 years an 80 to 90 km long section of the fissure swarm extended during this sequence of rifting and volcanic events maximum widening of about 8 m occurred 10 to 12 km north of leirhnjukur which is located above the center of the krafla magma reservoir from that location the amount of widening decreased north wards and is estimated to exceed 2 m where the seismicity indicated the northern termination of the present rifting off the north coast about 70 km north of leirhnjukur the amount of widening also decreased southwards and approached zero at 15 to 20 km south of leirhnjukur the ground deformation associated with these rifting events can be summarised as a narrow strip 1 to 2 km wide along the fissure swarm is heavily fractured with numerous open cracks parallel to the fissure swarm this fractured strip has subsided 2 to 3 m relative to its flanks the flanks of the fractured zone have been uplifted relative to regions farther away the uplift is not well constrained but tilt observations at several locations indicate about 1 m uplift the flanks of the rift zone have contracted perpendicular to the fissure swarm the maximum contractional strain exceeds 300 mm per km the amount of areal expansion windening of the fissure swarm times the length of the fractured zone associated with these rifting events is estimated to be about 0 30 km2 for individual events the area of expansion has been roungly proportional to the volume of subsidence above the krafla magma reservoir if the width of a new dike is equal widening of surface fissures the ratio of the subsidence volume to the area of expansion for the best observed events indicated a height of a new dike system as 2 4 to 2 8 km this ratio is significantly less for events of large lava production but even during these events the majority of magma leaving the krafla reservoir was apparently emplaced in subsurface fissures

postglacial changes in el nino and la nina behavior paleoclimate reconstructions suggest distinctive changes in the el nino southern oscillation enso the dominant mode of tropical climate variability over the last glacial cycle and throughout the holocene however to the best of our knowledge no studies provide parallel reconstructions of warm el nino and cold la nina phase variability thus precluding distinction between variations in enso activity and the mean state of the tropical pacific here we provide the first such records generated using molecular organic geochemical proxies in a sediment core from the peru margin region the opposing influences of el nino and la nina on coastal upwelling and phytoplankton community structure produce distinct sedimentary sterol records describing the evolution of each enso phase we document changes in surface ocean productivity on the peru margin over the past 16 ka that indicate enhanced la nina like conditions alone during deglaciation but concomitant increases in both el nino and la nina activity during the past 2 ka we propose that the preponderance of la nina like conditions prior to 11 5 ka reflects the influence of waning glacial boundary conditions by contrast warm and cold phase covariability during the late holocene suggests centennial scale changes in enso activity rather than the pacific mean state driven by tropical insolation

perennial stream discharge in the hyperarid atacama desert of northern chile during the latest pleistocene abstract a large fraction of the vital groundwater in the atacama desert of northern chile is likely composed of fossil or ancient reserves that receive little or no recharge in today s hyperarid climate here we present evidence for latest pleistocene perennial streamflow in canyons from the hyperarid core of the atacama desert in northern chile fluvial terraces in the pampa del tamarugal pdt basin 21 s contain widespread fossil wood in situ roots and well preserved leaf litter deposits indicative of perennial surface flow currently absent in these channels nineteen radiocarbon dates on these deposits from four separate drainages within this endorheic basin indicate ages from 16 380 to 13 740 cal yr bp synchronous with paleolake tauca on the bolivian altiplano and other regional evidence for wetter conditions during the latest pleistocene groundwater fed riparian ecosystems and associated fluvial deposits abound today in the absence of direct rainfall in northern atacama canyons with perennial discharge our relict riparian ecosystems from the pdt basin are indicative of conditions similar to these northern canyons given that discharge was higher than present during this time we propose that these deposits represent the most important groundwater recharge events of the last 18 000 years a lesser recharge event occurred during the holocene when phreatophytic trees also grew in these drainages between 1 070 and 700 cal yr bp during the medieval climatic anomaly taken together our evidence lends further support for gradient changes in the equatorial pacific as a major driver of hydrologic change in the atacama on both centennial and millennial time scales central andes hyperaridity riparian ecosystems late quaternary fluvial terraces

cross stratigraphies from a seismically active mud lens off peru indicate horizontal extensions of laminae missing sequences and a need for multiple cores for high resolution records abstract marine laminated sediments in dysoxic areas of the ocean floor are an excellent archive for high resolution climate reconstructions while the existence of discontinuities produced by natural events such as underwater landslides slumps strong bottom currents and or bioturbation is usually acknowledged for long records the extent of their influence on high resolution sequences is usually not considered in the present work we show strong evidence for multiple stratigraphic discontinuities in different gravity and box cores retrieved off pisco peru covering the last 600 years chronostratigraphies are largely based on cross correlation of distinct sedimentary structures determined by x ray image analysis and validated using 210 pb 241 am and 14 c profiles as well as proxy records the cross correlation of distinct stratigraphic layers allows for chronostratigraphic tie points and clearly shows that some sedimentary sequences are continuous across scales of tens of kilometers indicating that regional processes often determine laminae formation some differences in laminae thickness were found among cores which could be explained by different sedimentation rates spatially variable deposition of diatom blooms changes in silica dissolution and partial deposition erosion caused by bottom currents using multiple stratigraphic tie points provides clear evidence for laminated sequences present in some cores to be missing in other cores moreover instantaneous depositions from upslope were identified in all the cores disrupting the continuity of the sediment records these discontinuities instantaneous deposits and missing sequences may be due to slumps possibly triggered by earthquakes and or erosion by strong bottom currents in spite of the missing sequences in some cores a continuous composite record of the last six centuries was reconstructed from spliced sequences of the different cores which provides a well constrained temporal framework to develop further high resolution proxies in this region the present work shows that paleoreconstructions developed from single cores particularly in areas with strong seismic activity and or strong bottom currents are subject to both temporal gaps and instantaneous depositions from upslope both of which could be misinterpreted as abrupt climate changes or anomalous climate events we stress the need for multiple cores to determine the stratigraphic continuity and chronologies for high resolution records

a reconstruction of extratropical indo pacific sea level pressure patterns during the medieval climate anomaly subtropical and extratropical proxy records of wind field sea level pressure slp temperature and hydrological anomalies from south africa australia new zealand patagonian south america and antarctica were used to reconstruct the indo pacific extratropical southern hemisphere sea level pressure anomaly slpa fields for the medieval climate anomaly mca 700 1350 ce and transition to the little ice age lia 1350 1450 ce the multivariate array of proxy data were simultaneously evaluated against global climate model output in order to identify climate state analogues that are most consistent with the majority of proxy data the mean slp and slp anomaly patterns derived from these analogues illustrate the evolution of low frequency changes in the extratropics the indo pacific extratropical mean climate state was dominated by a strong tropical interaction with antarctica emanating from 1 the eastern indian and south west pacific regions prior to 1100 ce then 2 the eastern pacific evolving to the central pacific la nina like pattern interacting with a ve sam to 1300 ce a relatively abrupt shift to ve sam and the central pacific el nino like pattern occurred at 1300 a poleward equatorward shift in the subtropical ridge occurred during the mca mca lia transition the hadley cell expansion in the australian and southwest pacific region together with the poleward shift of the zonal westerlies is contemporaneous with previously reported hadley cell expansion in the north pacific and atlantic regions and suggests that bipolar climate symmetry was a feature of the mca

decadal periodicities of nile river historical discharge a d 622 1470 and climatic implications the roda nilometer cairo egypt has recorded more than 2 000 gauge readings i e annual low water and flood levels from a d 622 to the beginning of this century spectral analysis of the a d 622 1470 data set yields several statistically significant periodicities for both low water 256 75 9 52 6 38 28 9 20 9 18 5 and 13 4 yr and flood levels 75 9 33 6 21 4 14 7 13 7 9 7 and 8 1 yr evolutionary multi taper method analysis suggests that shifts or disappearances of spectral peaks occur in sub intervals of the studied time span this is noticeable for the low frequency peaks in the sub interval a d similar to 950 similar to 1250 which corresponds to the medieval warm period in europe by contrast a remarkable time stability is observed for the 5 yr period that could confirm the existence of a robust enso like forcing during the studied period

el nino floods and culture change a late holocene flood history for the rio moquegua southern peru the 1997 1998 el nino generated large floods throughout southern peru especially in inland locations along rio moquegua using remote sensing hydraulic modeling field surveying and stratigraphic analyses we estimate the magnitude and frequency of this flood and determine a late holocene flood history for main stem and tributary sections modeling indicates a peak discharge of 450 m3 s for the 1998 flood with an estimated recurrence interval between 50 and 100 yr flood deposits for two large events dated to a d 690 and a d 1300 respectively exist in a small tributary system tiwanaku site abandonment ca a d 1000 predates the younger flood indicating that stratigraphically recognizable el nino driven floods were not a causal mechanism for abandonment although possessing three flood units main stem alluvium is considerably younger 320 14c yr b p than tributary alluvium evidencing the major channel widening and lateral reworking of the main stem

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

late quaternary hydroclimatology of a hyper arid andean watershed climate change floods and hydrologic responses to the el nino southern oscillation in the atacama desert abstract although certain characteristics of the el nino southern oscillation enso are well known on contemporary timescales less is known about the magnitude frequency relationships of this atmospheric phenomenon on longer timescales or its relationship to widespread flooding especially in its core zone along the sub tropical andes where la nina or el nino episodes control regional hydroclimatology using a combination of stratigraphic evidence geochronologic dating 14c and osl stable isotope analyses and water geochemistry along the rio moquegua in the northern fringes of the atacama desert we assemble a paleoflood chronology for mainstem and tributary sections for the past ca 20 ka and ascertain the variation in enso frequency and magnitude because of the inherent watershed structure and regional hydroclimatology mid valley tributaries of the rio moquegua only flood during el nino episodes and thus provide an important proxy of extreme el ninos while mainstem stratigraphy records both la nina and el nino episodes el nino floods appear to have been pronounced during the late pleistocene and up to at least the younger dryas 12 000 cal yr bp while stratigraphic evidence of large el nino floods is lacking in tributary systems during the mid holocene flood stratigraphy in a 2 ka 7 m high terrace along the mainstem indicates an increased frequency and magnitude of large floods between ca 700 and 1610 ad as compared to the period from ca 160 bce to 700 ad with mega ninos occurring ca 1330 ad and ca 1650 ad water geochemistry and radiocarbon dating indicate that at least two major aquifers exist with wells and springs in the mid valley dating to 710 and 3100 14c yr bp respectively while water from a spring in the headwaters dates to 10 320 14c yr bp this range in dates suggests that groundwater flow in the mid valley is neither fossil water nor exclusively recharged from local precipitation while the older date for headwater sections suggests a more fossil groundwater source and lack of contemporary recharge the 18o similarity between groundwater in the mid valley and the regional meteoric water line mwl suggests a pacific moisture source and the role of el nino precipitation in recharging local aquifers thus el ninos and pacific sourced moisture are an important component of the regional hydroclimatology and the variation in enso frequency and intensity has significant social and hydrologic repercussions in these hyper arid settings

lacustrine record from the eastern tibetan plateau associated with asian summer monsoon changes over the past 6 ka and its links with solar and enso activity a multi parameter absolute dated lacustrine record from the eastern tibetan plateau provides a continuous history of the asian summer monsoon asm over the past 6000 years the record broadly follows the trend in northern hemisphere summer insolation however it diverges during a period of increased moisture and thermal conditions during the past 1300 years broadly corresponding to the asm 2 kyr shift this shift as referred by cheng et al nature 534 640 646 10 1038 nature18591 2016 may be related to atlantic meridional overturning circulation variations and potentially to increased forcing by greenhouse gases coincident with reduced enso activity the record is punctuated by several weak monsoon intervals cross correlation of the sub millennial scale monsoon record with solar activity and enso records shows that most of the monsoon variability potentially results from changes in solar irradiation and has a strong teleconnection with enso activity

multicentennial megadrought in northern europe coincided with a global el nino southern oscillation drought pattern during the medieval climate anomaly the el nino southern oscillation enso is a pacemaker of global climate and the accu rate prediction of future climate change requires an understanding of the enso variability recently much debated aspects of the enso have included its long term past and future changes and its associations with the north atlantic and european sectors potentially in inter action with the north atlantic oscillation and the atlantic multidecadal oscillation here we present the fi rst european dendroclimatic precipitation reconstruction that extends through the alternating climate phases of the medieval climate anomaly and the little ice age we show that northern europe underwent a severe precipitation defi cit during the medieval climate anomaly which was synchronous with droughts in various enso sensitive regions worldwide while the subsequent centuries during the little ice age were markedly wetter we attribute this drought primarily to an interaction between the enso and the north atlantic oscillation and to a lesser or negligible degree to an interaction between the enso and the atlantic multidecadal oscillation

late holocene sea surface temperature and precipitation variability in northern patagonia chile jacaf fjord 44 s abstract a high resolution multi proxy study including the elemental and isotopic composition of bulk organic matter land plant derived biomarkers and alkenone based sea surface temperature sst from a marine sedimentary record obtained from the jacaf fjord in northern chilean patagonia 44 20 s provided a detailed reconstruction of continental runoff precipitation and summer sst spanning the last 1750 yr we observed two different regimes of climate variability in our record a relatively dry warm period before 900 cal yr bp lower runoff and average sst 1 c warmer than present day and a wet cold period after 750 cal yr bp higher runoff and average sst 1 c colder than present day relatively colder ssts were found during 750 600 and 450 250 cal yr bp where the latter period roughly corresponds to the interval defined for the little ice age lia similar climatic swings have been observed previously in continental and marine archives of the last two millennia from central and southern chile suggesting a strong latitudinal sensitivity to changes in the southern westerly winds the main source of precipitation in southern chile and validating the regional nature of the lia our results reveal the importance of the chilean fjord system for recording climate changes of regional and global significance

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

global surface temperatures over the past two millennia 1 we present reconstructions of northern and southern hemisphere mean surface temperature over the past two millennia based on high resolution proxy temperature data which retain millennial scale variability these reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the northern hemisphere conclusions for the southern hemisphere and global mean temperature are limited by the sparseness of available proxy data in the southern hemisphere at present

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

establishment and formation of fog dependent tillandsia landbeckii dunes in the atacama desert evidence from radiocarbon and stable isotopes 1 extensive dune fields made up exclusively of the bromeliad tillandsia landbeckii thrive in the atacama desert one of the most extreme landscapes on earth these plants survive by adapting exclusively to take in abundant advective fog and dew as moisture sources although some information has been gathered regarding their modern distribution and adaptations very little is known about how these dune systems actually form and accumulate over time we present evidence based on 20 radiocarbon dates for the establishment age and development of five different such dune systems located along a 215 km transect in northern chile using stratigraphy geochronology and stable c and n isotopes we 1 develop an establishment chronology of these ecosystems 2 explain how the unique t landbeckii dunes form and 3 link changes in foliar 15n values to moisture availability in buried fossil t landbeckii layers we conclude by pointing out the potential that these systems have for reconstructing past climate change along coastal northern chile during the late holocene

continuous measurements of microtremors on sediments and basement in los angeles california abstract continuous measurement of microtremors at two sites on basement rock and sediments was carried out in los angeles california in order to understand the fundamental characteristics of microtremors a predominant peak with a period of about 6 5 sec was found in the microtremor spectra in both media the spectral amplitude of the peaks varied gradually with time in a similar manner at the two sites their time variant characteristics are in agreement with change in oceanic swell height observed at an oceanic buoy in the southwest of los angeles this suggests that they originate from an oceanic disturbance on the other hand a clear daily variation of spectral amplitudes at a period of 0 3 sec indicates that short period microtremors are caused by cultural noises it was found that the spectral ratio of long period microtremors between the basement and the sediments was repeatable although the spectral amplitudes at the two sites were time variant the spectral ratio of the long period microtremors was similar to that derived from strong motion records this suggests the applicability of spectral ratios of microtremors to assess the effects of deep sediments on long period earthquake ground motion

the las salinas palaeo lagoon in the sechura desert peru evolution during the last two millennia the sechura desert provides a unique example of a vast palaeo lagoon system on the peruvian coast that was active during the first millennium ad reconstruction of coastal evolution is made possible by the good resolution of the sedimentary records of the las salinas noroeste coastal plain evidence from morphostratigraphy and sedimentary facies indicates marked environmental diversity between the 3rd and the 8th centuries ad and a wide variability of sedimentary dynamics lagoon foreshores received alternately fine distal marine sediments and coarser continental sediments in pro deltaic sheets evaporation phases periodically occurred in these foreshores causing the formation of salt crusts after a last high water level in the 8th century ad the lagoon ultimately dried out and remains dry today the malacofauna and sedimentary facies indicate that marine marshes bordered by vegetation perhaps mangrove developed in the higher parts of these lagoons this palaeogeography is explained by the progressive build up of a sand bar which started at least in the middle holocene from the 3rd to 8th centuries ad the lagoon had limited connection to the sea in its northern end and hosted a warm water and productive ecosystem that was exploited by pre hispanic populations wetter conditions in the andes and occasional el nino rainfalls maintained the lagoon during this period the freshwater input likely stopped in the 8th century ad which led to the closing of the shore bar under the influence of the longshore drift rapidly followed by the drying up of the lagoon and the abandonment of the archaeological site

fish scales in sediments from off callao central peru abstract we study fish scales as a proxy of fish abundance and preservation biases together with phosphorus from fish remains p fish in a sediment core retrieved off callao peru 12 1 s 77 42 w water depth 179 m core length 52 cm we interpret our results as a function of changing redox conditions based on ratios of redox sensitive trace elements cu al mo al ni al zn al v al terrigenous indicators fe in clays ti al and biogenic proxies caco 3 biogenic opal total nitrogen organic carbon barite ba the core covers roughly 700 years of deposition based on 210 pb activities extrapolated downcore and 14 c dating at selected intervals our fish scale record is dominated by anchovy engraulis ringens scales followed by hake merluccius gayii scales the core presented an abrupt lithological change at 17 cm corresponding to the early 19th century above that depth it was laminated and was more organic rich 10 15 organic carbon than below where the core was partly laminated and less organic rich fish p total ratios were also observed within the upper 17 cm of the core the behavior of biogenic proxies and redox sensitive trace elements was similar more reduced conditions corresponded to higher contents of caco 3 c org total nitrogen and fish scales suggesting that these proxies might convey an important preservation signal

annually resolved ice core records of tropical climate variability over the past 1800 years ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics but they are difficult to recover and few exist here we report annually resolved ice core records from the quelccaya ice cap 5670 meters above sea level in peru that extend back 1800 years and provide a high resolution record of climate variability there oxygen isotopic ratios 18 o are linked to sea surface temperatures in the tropical eastern pacific whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the intertropical convergence zone in the region of the tropical andes quelccaya continues to retreat and thin radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia

peruvian sediments as recorders of an evolving hiatus for the last 22 thousand years highlights review of sediment archives from the peruvian margin since the lgm focus on the evolutionary feature of the hiatus found in archives modern analogue for current dominated environments for paleo reconstructions new results for erosional potential of the non linear internal waves nliws abstract the peruvian continental margin is characterized by the presence of one of the strongest and most distinct oxygen minimum zones omzs in today s oceans therefore it has long been in the focus of oceanographic and geological investigations observations indicate that omzs are expanding in relation with currently changing climate to advance understanding of the temporal evolution of omzs and climate change complete paleoceanographic and palaeoclimatological reconstructions are needed however the development of paleoenvironmental scenarios for the period since the last glacial maximum at this region was hampered by a ubiquitous hiatus and short term interruptions of the stratigraphical record in the present study we combined the stratigraphical information from 31 sediment cores from the peruvian margin located between 3 and 18 s and water depths of 90 to 1300 m within and below today s omz in order to determine the extent of the hiatus and assess the responsible mechanisms a widespread unconformity and related erosional features omission surfaces and phosphorites were observed in sediment cores from the area south of 7 s depicting a prograding feature on the continental slope from south to north during the deglaciation combining recent oceanographic and sedimentological observations it is inferred that tide topography interaction and resulting non linear internal waves nliws shape the slope by erosion carry sediments upslope or downslope and leave widespread phosphoritic lag sediments while the peru chile undercurrent pcuc transports the resuspended sediments southward causing non deposition this exceptional sedimentary regime makes the peruvian margin a modern analogue for such environments overall our compilation of downcore records showed that enhanced bottom currents due to tide topography interaction were progressively evolving and affected a wider area with the onset of the last deglaciation elevated tidal amplitudes and variability of mid depth water masses i e density changes and hydrodynamics in relation with changing climate were potential reasons of this evolving feature of erosion and reworking additionally erosion and non deposition was observed widest and even was encountered on the continental shelf during the early holocene potentially indicating a strong phase of the pcuc mirroring today s el nino like conditions

3500 yr record of centennial scale climate variability from the western pacific warm pool we use geochemical data from a sediment core in the shallowsilled and intermittently dysoxic kau bay in halmahera indo nesia lat 1 n long 127 5 e to reconstruct century scale climate variability within the western pacifi c warm pool over the past 3500 yr downcore variations in bulk sedimentary 15 n appear to refl ect century scale variability in basin ventilation attributed to changes in oceanographic conditions related to century scale fl uctuations in el nino southern oscillation enso we infer an increase in century scale el nino activity beginning ca 1700 yr b p with peaks in el nino activity ca 1500 yr b p 1150 yr b p and ca 700 yr b p the kau bay results suggest that there was diminished enso amplitude or frequency or a departure from el nino like conditions during the medieval warm period and distinctive but steadily decreasing el nino activity during and after the little ice age

climate variation and the rise and fall of an andean civilization paleolimnological and archaeological records that span 3500 years from lake titicaca and the surrounding bolivian peruvian altiplano demonstrate that the emergence of agriculture ca 1500 b c and the collapse of the tiwanaku civilization ca a d 1100 coincided with periods of abrupt profound climate change the timing and magnitude of climate changes are inferred from stratigraphic evidence of lake level variation recorded in14c dated lake sediment cores paleo lake levels provide estimates of drainage basin water balance archaeological evidence establishes spatial and temporal patterns of agricultural field use and abandonment prior to 1500 b c aridity in the altiplano precluded intensive agriculture during a wetter period from 1500 b c to a d 1100 the tiwanaku civilization and its immediate predecessors developed specialized agricultural methods that stimulated population growth and sustained large human settlements a prolonged drier period ca a d 1100 1400 caused declining agricultural production field abandonment and cultural collapse