the evolution of oceanic and atmospheric anomalies in the northeast pacific during the el nino and la nina events of 1995 2001 abstract from late 1995 through early 2001 three major interannual climate events occurred in the tropical pacific the 1995 97 la nina ln 1997 98 el nino en and 1998 2001 ln we analyze atmospheric and upper oceanic anomalies in the northeast pacific nep during these events and compare them to anomalies both elsewhere in the north and tropical pacific and to typical en and ln anomaly patterns the atmospheric and oceanic anomalies varied strongly on intraseasonal and interannual scales during the 1995 97 ln and 1997 98 en the northeast pacific was dominated by negative slp and cyclonic wind anomalies and by upper ocean temperature and sea surface height ssh anomalies the latter were positive along the north american west coast and in the nep thermal anomaly pool between hawaii vancouver island and baja california and negative in the central north pacific this atmospheric oceanic anomaly pattern is typical of en an eastward shift in the atmospheric teleconnection from east asia created en like anomalies in the nep during the 1995 97 ln well before the 1997 98 en had begun the persistence of negative sea level pressure slp and cyclonic wind anomalies in the nep during the 1997 98 en intensified pre existing upper oceanic anomalies atmospheric anomalies were shifted eastward during late 1996 early 1998 leading to a similar onshore shift of oceanic anomalies this produced exceptionally strong positive upper ocean temperature and ssh anomalies along the west coast during the 1997 98 en and explains the unusual coastal occurrences of several species of large pelagic warm water fishes the growth and eastward shift of these pre existing anomalies does not appear to have been linked to tropical pacific en anomalies until late 1997 when a clear atmospheric teleconnection between the two regions developed prior to this remote atmospheric impacts on the nep were primarily from east asia as the 1998 2001 ln developed nep anomalies began reversing toward the typical ln pattern this led to predominantly negative slp and cyclonic wind anomalies in the nep and upper ocean temperature and ssh anomalies that were mainly negative along the west coast and positive in the central north pacific the persistence of these anomalies into mid 2001 and a number of concurrent biological changes in the nep suggest that a decadal climate shift may have occurred in late 1998 during 1995 2001 nep oceanic anomalies tracked the overlying atmospheric anomalies as indicated by the maintenance of a characteristic spatial relationship between these anomalies in particular wind stress curl and ssh anomalies in the nep maintained an inverse relationship that strengthened and shifted eastward toward the west coast during late 1996 early 1998 this consistent relationship indicates that anomalous ekman transport driven by regional atmospheric forcing was an important contributor to temperature and ssh anomalies in the nep and ccs during the 1997 98 en other studies have shown that coastal propagations originating from the tropical pacific also may have contributed to coastal nep anomalies during this en our results indicate that at least some of this coastal anomaly signal may have been generated by regional atmospheric forcing within the nep

a 160 k y old record of el nino southern oscillation in marine production and coastal runoff from santa barbara basin california usa a 160 k y old laminated sediment record from the santa barbara basin california analyzed using scanning electron microscope techniques provides a history of interannual variability of marine production and coastal runoff we used backscatter electron imagery to measure the components of the varve these include a terrigenous lamina formed by seasonal runoff from winter rains together with a diatomaceous lamina that records marine production during the spring and early summer spectral analysis of terrigenous and diatomaceous laminae thickness reveals significant periodicities of 3 1 and 8 4 yr in the terrigenous series these are indistinguishable within the frequency resolution of the spectra from significant periodicities of 3 5 and 7 6 yr in the diatomaceous series the 3 1 and 3 5 yr periodicities record el nino modulation of coastal runoff and marine production the 8 4 and 7 6 yr periodicities are consistent with modulation by strong to very strong el nino events this is supported by the results of cross spectral analysis of the terrigenous and diatomaceous records which reveal inverse or antiphase relationships at 3 5 and 7 6 yr our work adds to a body of evidence that suggests that el nino has been a persistent feature of late quaternary climate variability

mid holocene climate in the south central andes humid or dry have concluded thatgenerally drier conditions prevailed we argue that wet conditions result in high er river discharge and erosion whereas accu mulation of fine materials in a steep valleyrequires overall decreased river flow and a low energy environment with dry conditions fine grained but permeable sediments that accumu late in the valley bottom may form local aqui fers and raise the groundwater table despite alarger cross section in the valley and reduceddischarge overall modern analogs show thatgroundwater tables in such wetlands are oftenself sustained very local and disconnectedfrom their surroundings and are thus difficult tointerpret in terms of climate conditions today the rivers in both the tula n and puripica valleysare erosive and have dissected the mid holo cene sediments down to bedrock typically sediments from between 14 and 9 ky b p aperiod of well documented extreme humidity are missing in these valleys because of strongerosion whereas as expected sediments fromthis humid period are present in fossil springcomplexes tilomonte springs figure 4 in

human populations and environments during the middle holocene in the south central andes fil mondini nora mariana consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico cordoba instituto de antropologia de cordoba argentina universidad nacional de cordoba facultad de filosofia y humanidades museo de antropologia argentina

new archeointensity data from nw argentina 1300 1500 ce abstract a good characterization of the geomagnetic field strength at centennial to millennial time scales in the southern hemisphere is particularly crucial to disentangle the long term evolution of the south atlantic anomaly saa an intriguing geomagnetic feature currently observed at the earth s surface here we present 59 new archeointensities obtained from four well dated groups of potteries with ages ranging between 1300 and 1500 ce and collected in northwest argentina the new data were obtained in accordance with the thellier paleointensity method including partial thermoremanent magnetization ptrm checks and trm anisotropy and cooling rate corrections we have also performed a comparative study of the efficiency of magnetic susceptibility arm and trm anisotropy tensors to correct the trm anisotropy effect upon intensity estimates our results suggest that the magnetic susceptibility tensor systematically underestimates the trm anisotropy effect by 10 30 our new data together with selected archeointensities already published confirm that the decrease of the geomagnetic field intensity in south america started around 1600 1650 ce due to the arrival of the saa

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

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

late quaternary sea levels and crustal movements coastal british columbia late quaternary sea level fluctuations on the british columbia coast have been established from studies of terrestrial and marine sediments and landforms these studies indicate that the sea level history of mainland british columbia and eastern vancouver island is very different from that of the queen charlotte islands and western vancouver island specifically in the former areas there was a rapid rise of submerged coastal lowlands between about 13 000 and 10 000 years ago emergence culminated about 6000 9000 years ago depending on the locality when the sea relative to the land was 12 m or more lower than at present in some areas during middle and late holocene time relative sea level rose on the mainland coast and at least locally on eastern vancouver island resulting in inundation of coastal archaeological sites and low lying terrestrial vegetation tidal records and precise levelling suggest ongoing submergence of at least part of this region in contrast shorelines on the queen charlotte i

biological forcing of hemipelagic sedimentary laminae evidence from odp site 893 santa barbara basin california core observation x radiography and scanning electron microanalysis of distinctly laminated indistinctly laminated and nonlaminated sediments from odp site 893 show that laminated as well as nonlaminated i e massive hemipelagic sediments can form in the absence of bioturbation this view contrasts with conventional sedimentological interpretations equating laminated hemipelagic sediments with anoxic water masses i e absence of bioturbation and nonlaminated sedimentary intervals exclusively with oxygenation episodes that permitted infaunal colonization we conclude that heterogeneities in the texture and or composition of sediment supply are necessary for the production of laminated sediments the absence of hydraulic and biological reworking permits their preservation laminae at site 893 have two prominent components biosilica and terrigenous detritus compositional contrasts between adjacent laminae in x radiographs reflect short term seasonal and subseasonal heterogeneities in sediment flux core intervals with large contrasts in density and or composition between adjacent laminae are termed as having high bimodality hb hb couplets produce distinctly laminated sediments that intergrade vertically with indistinctly laminated and nonlaminated sediments adjacent laminae in indistinctly laminated sediments possess minimal contrasts in bulk density and composition nonlaminated sediments are compositionally and texturally homogeneous many biosiliceous laminae responsible for distinctly laminated hb couplets record mass flocculation and sedimentation of ungrazed diatom frustules formed during discrete bloom events ecological interpretation of diatomite laminae suggests that many were effectively self sedimenting i e the production of gelatinous exudates by phytoplankton facilitated their aggregation and rapid sedimentation the results indicate that lamination style preserves meaningful ocean climate data concerning episodicity heterogeneity and export efficiency of biologically mediated sedimentary flux in upwelling dominated coastal ecosystems

mid holocene climate and culture change in the atacama desert northern chile abstract twenty archaeological campsites intercalated between more than 30 debris flows caused by heavy rainfall events between 6200 and 310014c yr b p have recently been discovered at quebrada puripica in the atacama desert of northern chile this record provides detailed information about extreme short lived climatic events during the hyperarid mid holocene period for the first time we found evidence of continuous human occupation in this area filling the regional hiatus in the atacama basin silencio arqueologico between 8000 and 480014c yr b p the transformation of early archaic hunters into the complex late archaic cultural tradition was an adaptive process during this time the site was a local ecological refuge with abundant resources in a generally hostile environment

hunter gatherer mobility decisions and synchronous climate change in the southern andes the early and middle holocene occupations of arq 18 san juan argentina 29 5 s abstract in the southern andes holocene climate records show drastic changes in moisture during the early and middle holocene to generate a more refined chronology of climate changes in this region we present a bayesian model that combines published cosmogenic dates from the encierro valley 29 1 s and radiocarbon dates on peat and soils from the western slope of the andes 27 33 s we compare this to a similar model from the high altitude archaeological site arq 18 in the las taguas valley 29 5 s san juan argentina these chronologies indicate synchronous changes in climate and occupational intensity which shed light on hunter gatherer mobility decisions this site was first occupied in the early holocene when nearby valleys were deglaciated by around 10 700 cal bp arq 18 was occupied a few centuries later around 10 100 cal bp the site was first colonized during a regional wet phase probably by hunters from the highlands to north who moved quickly among humid high altitude valleys as regional moisture began dropping around 8700 7800 cal bp occupational intensity at arq 18 reached a maximum as diverse groups gathered in the valley at this point an important environmental threshold was crossed as groups reversed their mobility patterns and decisions and did not occupy the site for 1700 years this archaeological silence correlates closely with the middle holocene s hyperaridity during 7800 5700 cal bp as soon as humidity returned groups began visiting the site again from this point on strategies increasingly incorporated herding in response to less stable environmental conditions

archaeological silence and ecorefuges arid events in the puna of atacama during the middle holocene this paper briefly summarizes presearch concerning the mid holocene in the western slope of the puna de atacama 20 25 s proxy data and dates from palynological limnological geomorphological archives were compared with data recovered from the archaeological sites in high altitude basins intermediate ravines and piemontane paleowetlands due to exceptionally favorable conditions numerous early holocene archaeological sites were found in contrast the lack of occupations in previously populated areas suggests a decline in human activity during the arid mid holocene in this context two key concepts are introduced ecorefuge or ecological refuge and archaeological silence silencio arqueologico the first refers to the particular favorable locations occupied by human groups during the mid holocene the second provides a better understanding about the impact of the arid interval during this period on human adaptations in the most barren territories of the new world

mid holocene occupation of the dry puna in nw argentina evidence from the hornillos 2 rockshelter abstract this paper summarizes the results of the research carried out during a decade at the hornillos 2 rock shelter located at 4020 m asl in the dry puna of argentina the human occupations in this site arebracketed between the pleistoceneeholocene boundary and the mid holocene challenging the idea ofa widespread abandonment of the andes highlands during mid holocene due to extreme arid conditions i e the silencio arqueologico or archaeological silence hypothesis nine occupational levels have beenrecognized in the timed span at the site the result of hunteregatherer activities carried out in a highlyoscillating and changing environment here we present the mean trends and patterns observed in the full set of lines of inquiry applied in thesite lithic evidence zooarchaeological analysis rock art stratigraphic and spatial analysis and isotopicdata the outcomes of these studies together with the site location features known raw materialssources and regional archaeological evidence indicate that hunteregatherer groups reduced theirresidential mobility and increased the intensity of their occupations and the rate of technologicalinnovations in the arid and unstable mid holocene landscapes 2012 elsevier ltd and inqua all rights reserved

moving obsidian the case of antofagasta de la sierra basin southern argentinean puna during the late middle and late holocene abstract this paper presents the results of an xrf analysis on the provenience of 118 obsidian artifacts from archaeological sites of the antofagasta de la sierra basin catamarca province argentina dating to the late middle and late holocene c 4500 1100 bp the time span considered encompasses a local process of gradual transformation from hunter gatherer early agro pastoral groups to consolidated agro pastoral societies for this study non destructive elemental analysis of obsidian artifacts was conducted using two different x ray fluorescence spectrometers ed xrf this information was then supplemented by previous provenience results undertaken on 59 obsidian archaeological artifacts from the same area a comparative synthesis of chemical and macroscopic characterization of five obsidian sources located in southern argentinean puna is also presented the provenance of archaeological materials was assigned by comparison with twelve presently known argentine sources on this basis late middle and late holocene obsidian regional movement patterns differential distribution and use of this raw material are discussed furthermore this obsidian research lends support to the existence of exchange networks based on the use of different extra regional obsidian sources located in the northern argentinean puna

spectral characteristics of sea level variability along the west coast of north america during the 1982 83 and 1997 98 el nino events abstract we use hourly sea level records from southern california to the aleutian islands to examine low frequency variability in the northeast pacific during the 1982 83 and 1997 98 el nino events comparison between events is facilitated by long term records for yakutat tofino neah bay and san francisco which appear to be representative of distinct coastal oceanic regimes residual tide removed time series reveal that the anomalously high sea levels of the 1997 98 el nino persisted from the spring of 1997 to the spring of 1998 and this event was more protracted than the 1982 83 el nino during both major events the annual sa semiannual ssa and synoptic scale sea level constituents were amplified relative to non el nino years with synoptic fluctuations in sea level height and sea level pressure for mid latitude sites tofino and neah bay strongly correlated through the inverted barometer response the spectral anomaly coefficient sjr rj 1 rj 1 where r j s j s j is the spectral ratio between the el nino spectrum sj and the time averaged non el nino spectrum s j for tide gauge site j indicates that both events gave rise to enhanced sea level variability at periods of days to weeks because of passing atmospheric systems however the 1982 83 el nino generated greater signal variance at seasonal scales periods of months while the 1997 98 el nino generated greater variance at synoptic scales periods of days findings further indicate that poleward oceanic propagation of the 1982 83 and 1997 98 events terminated near central california and that much of the enhanced sea level variability observed at mid to high latitudes was associated with atmospheric teleconnection responses that gave rise to amplified variations in coastal sea level pressure and or surface wind stress

obsidian use and mobility during the early and middle holocene in the salt puna nw argentina abstract we discuss the use of obsidian as a tool to understand the mobility range of hunter gatherers living in a high elevation desert in the salt puna specifically in the area of antofagasta de la sierra catamarca between ca 9000 and 6000 bp xrf analyses of a vertical sample of obsidian artifacts pertaining to early and middle holocene contexts from three archaeological sites show the use of various sources within a range of 40 95 km respectively from the study area our analyses suggest that mobility patterns during the early colonization phase early holocene of this high elevation region included two sources located in the eastern and northwestern areas of the salt puna and reveal a process of landscape learning by contrast during the phase of effective occupation middle holocene a period coinciding with climatic fluctuations and decreasing rainfall a greater number of obsidian sources were used suggesting increased knowledge of the landscape as well as a pattern of territorial range shifting

the pleistocene holocene transition in peru and its effects upon human use of the landscape abstract this paper reviews the state of our knowledge regarding the effects of the pleistocene holocene transition on the kinds and range of human adaptations in what is now peru following a discussion of geological paleoclimatic and archaeological data the paper focuses upon four aspects of environmental change with specific regard to how these would have affected human adaptations environmental changes on the pacific littoral the extinction of pleistocene faunal and floral species and their replacement with modern faunas the adaptive radiation of these modern flora and fauna especially into the andean highlands and characteristics of newly available high elevation environments that would have affected the process by which foraging peoples moved into them although pleistocene fauna have been discovered in peru none of these finds have been made in the context of indisputable human activity and therefore the effect of their extinction on early foraging peoples is unknown the earliest acceptable archaeological sites in peru date around 11 12 000 years ago and are found on the coastal lowlands the highlands were not occupied until after 11 000 years ago while high elevation environments were attractive after 11 000 years ago they were only slowly occupied by humans due to the constraints of the combined effects of hypoxia and cold

in stream wetland deposits megadroughts and cultural change in the northern atacama desert chile a key concern regarding current and future climate change is the possibility of sustained droughts that can have profound impacts on societies as such multiple paleoclimatic proxies are needed to identify megadroughts the synoptic climatology responsible for these droughts and their impacts on past and future societies in the hyperarid atacama desert of northern chile many streams are characterized by perennial flow and support dense in stream wetlands these streams possess sequences of wetland deposits as fluvial terraces that record past changes in the water table we mapped and radiocarbon dated a well preserved sequence of in stream wetland deposits along a 4 3 km reach of the rio san salvador in the calama basin to determine the relationship between regional climate change and the incision of in stream wetlands the rio san salvador supported dense wetlands from 11 1 to 9 8 6 4 to 3 5 2 8 to 1 3 and 1 0 to 0 5 ka and incised at the end of each of these intervals comparison with other in stream wetland sequences in the atacama desert and with regional paleoclimatic archives indicates that in stream wetlands responded similarly to climatic changes by incising during periods of extended drought at 9 8 3 5 1 3 and 0 5 ka

a perched high elevation wetland complex in the atacama desert northern chile and its implications for past human settlement a previously undocumented type of wetland is described from the atacama desert in northern chile 3000 m above sea level sustained exclusively by direct precipitation and perched above the regional water table geomorphological mapping pedostratigraphy geochemistry and analysis of contemporary vegetation is used to understand wetland formation and dynamics during historical and present time periods the paleowetland deposits overlie a miocene tuff that acts as an impermeable barrier to water transfer and creates conditions for local shallow ground water these deposits include several paleosols that were formed during periods when precipitation increased regionally at 7755 7300 1270 545 and 400 300 cal yr bp the similarity in timing with other palaeohydrological records for the atacama implies that paleosols from this wetland are proxies for reconstructing past changes in local and regional hydrological cycle archaeological investigations have revealed the presence of two small farms from the late intermediate period i e during the earliest wetter phase represented by the paleosols both farms are located near the paleowetland deposits which suggests that local inhabitants exploited these water sources during late pre hispanic times results of this study improve knowledge of settlement patterns during this and earlier cultural periods

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses cappa et al modelling pressure pulses in rock fractures estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses frederic cappa 1 yves guglielmi 2 jonny rutqvist 3 chin fu tsang 3 and alain thoraval 4 geosciences azur university of nice sophia antipolis sophia antipolis france geologie des systemes et des reservoirs carbonates university of provence aix marseille france earth sciences division lawrence berkeley national laboratory berkeley usa ineris ecole national superieure des mines de nancy parc de saurupt nancy france corresponding author fax 33 4 92 94 26 10 e mail address cappa geoazur unice fr f cappa

high resolution seismic reflection profiles from lake titicaca peru bolivia evidence for holocene aridity in the tropical andes high resolution seismic reflection profiles of the sediments of lake titicaca peru bolivia suggest that lake levels in the recent past were considerably lower than today incised channels on the major deltas extend to depths of 85 m below modern lake level erosional truncation of onlapping seismic reflectors is found at similar depths this interpretation of the seismic data is supported by analyses of sediment cores from the lake which indicate that there was a significant drop in lake level during the early to mid holocene

rapid sea level change and coastal evolution on the pacific margin of canada a rapid regression occurred off the northern pacific margin of canada approximately between 14 600 and 12 500 14c years b p contemporary with the deglaciation of the continental shelf primarily due to the rapid isostatic rebound sea level had reached a maximum lowering of greater than 150 m and remained low until approximately 12 400 14c years b p after which a rapid transgression occurred at 12 500 14c years b p the shelf tilt across the northern pacific margin of canada ranged between 50 m of submergence at prince rupert on the british columbia mainland to greater than 150 m of emergence on the western edge of the queen charlotte islands this regressive transgressive cycle lasted only from 5200 to 5500 14c years a result of the development and collapse of a glacioisostatic forebulge sediment supply wave action and tidal current energy are the primary factors that controlled the coastal response to these late quaternary relative sea level changes plate tectonics on the other hand played a secondary role in coastal evolution during deglacial regression extensive glacial outwash and glaciomarine deposition occurred except on the outer coast where sediment was transferred to the shelf break during the transgression of the shelf the sediment supply was primarily restricted to the erosion of the previously deposited deglacial deposits resulting in the formation of drowned wave cut terraces spit platforms and modification of estuarine environments as the sea level rose in steps the present unconsolidated coastline is mostly erosional during the most recent enso event the sea level rise of up to 0 4 m resulted in as much as 12 m of coastal retreat

evidence for abrupt climate changes in annually laminated marine sediments annually laminated sediments from marine or lacustrine settings represent valuable high resolution archives of climate change that record variation due to changing precipitation and run off from land or variation in biological productivity and flux in the water column because of their annual resolution such sediments may capture abrupt changes of interannual to decadal scales rivaling corals and ice cores in resolution laminated sediments often occur intermittently in the sediment column and the onset and cessation of laminae commonly record the abrupt crossing of thresholds related to climate change for example in the degree of oxygenation of bottom waters such records from marginal basins and continental margins have been pivotal in demonstrating that abrupt changes hitherto documented only in high latitude ice cores are synchronous with climatic change at low latitudes these insights into global teleconnections have improved our understanding of the mechanisms of rapid climate change in deep sea settings the discovery of the episodic occurrence of laminated diatom rich sediments in the equatorial pacific and southern ocean provides evidence for massive climate related biogeochemical excursions tied to abrupt changes in the input distribution and availability of nutrients in the oceans

late holocene sedimentation in saanich inlet british columbia and its paleoseismic implications eight piston cores of sediment spanning the last 1500 years were collected from saanich inlet an anoxic fiord on southern vancouver island to obtain information on sedimentation and prehistoric earthquake activity the cores consist mainly of fine grained varved sediments but include massive layers deposited by subaqueous debris flows the debris flows may have been triggered by earthquakes or by the buildup of fine sediment on the walls of the inlet cesium 137 and 2bopb data i4c ages and varve counts were used to date and correlate massive layers in the eight cores the uppermost massive layer in two cores may record a magnitude 7 2 earthquake that occurred in 5946 near comox british columbia 200 km north northwest of saanich inlet seven older layers are found in two or more cores and are about 200 440 550 800 850 1050 1100 1100 1150 and 1450 1500 years old two of these older layers may correlate with previously documented earthquakes in the region there is an average of one massive layer per 116 varves in the core with the greatest number of such layers which is broadly consistent with the expected periodicity of moderate to large earthquakes in the region on average one earthquake producing local modified mercalli intensity vii or viii per century saanich inlet may contain a proxy record of all moderate and large earthquakes that have affected southwestern british columbia during holocene time but some of the massive layers do not appear to correlate from core to core and undoubtedly are nonseismically generated deposits

records of seasonal flux in holocene laminated sediments gulf of california holocene laminated sediments from guaymas basin gulf of california mexico have in the past been described as annual couplets of sedimentation couplets comprise an alternation of diatom and terrigenous rich sediment reflecting winter and summer flux to the sediment respectively new data from backscattered electron imagery bsei show that a three component pattern of sedimentation is preserved comprising 1 a lithogenic lamina consisting of clays silt and minor diatomaceous material deposited during the summer and autumn wet season 2 a mixed flora diatomaceous lamina deposited during the early winter collapse of the thermocline and onset of water column mixing and 3 a near monospecific flora lamina of chaetoceros resting spores or more rarely skeletonema costatum representing deposition from or at the end of the spring coastal upwelling bloom recent sediment trap biogenic and terrigenous flux data also show three to four major flux events per year direct comparisons are possible between bsei records and recent sediment trap flux data to facilitate high resolution palaeoceanaographic and palaeoclimatic reconstructions throughout the holocene

late quaternary vegetation and climate history of a perennial river canyon in the rio salado basin 22 s of northern chile abstract plant macrofossils from 33 rodent middens sampled at three sites between 2910 and 3150 m elevation in the main canyon of the rio salado northern chile yield a unique record of vegetation and climate over the past 22 000 cal yr bp presence of low elevation prepuna taxa throughout the record suggests that mean annual temperature never cooled by more than 5 c and may have been near modern at 16 270 cal yr bp displacements in the lower limits of andean steppe and puna taxa indicate that mean annual rainfall was twice modern at 17 520 16 270 cal yr bp this pluvial event coincides with infilling of paleolake tauca on the bolivian altiplano increased enso activity inferred from a marine core near lima abrupt deglaciation in southern chile and heinrich event 1 moderate to large increases in precipitation also occurred at 11 770 9550 central atacama pluvial event 7330 6720 3490 2320 and at 800 cal yr bp desiccation occurred at 14 180 8910 8640 and 4865 cal yr bp compared to other midden sites in the region early holocene desiccation seems to have happened progressively earlier farther south emerging trends from the cumulative midden record in the central atacama agree at millennial timescales with improved paleolake chronologies for the bolivian altiplano implying common forcing through changes in equatorial pacific sea surface temperature gradients

preparation and analysis techniques for studies of laminated sediments laminated sediments commonly represent the highest resolution continuous records available of marine and lacustrine variability to exploit this information effectively careful sampling and preparation procedures must be followed thus the method of analysis chosen must have sufficient resolution to recover the data the scanning electron microscope because of its good spatial resolution is an ideal tool for analyzing laminated sediment fabric backscattered electron imagery produces preserved flux data on intra annual time scales which enables high resolution fabric studies palaeoenvironmental reconstructions and compilation of data for time series analysis this contribution summarizes the techniques used for laminated sediment fabric investigation and discusses the use of the scanning electron microscope including the best preparation method for thin sections and the procedure for backscattered electron imagery analysis

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

an assessment of the megathrust earthquake potential of the cascadia subduction zone the active tectonic setting of the southwest coast of canada and the pacific northwest coast of the united states is dominated by the cascadia subduction zone the zone can be divided into four segments where oceanic lithosphere is converging independently with the north american plate the winona and the explorer segments in the north the larger juan de fuca segment that extends into both canada and the united states and the gorda segment in the south the oceanic lithosphere entering the cascadia subduction zone in all segments is extremely young less than 10 ma of the other six zones around the pacific where young 20 ma lithosphere is being subducted five have had major thrust earthquakes megathrust events on the subduction interface in historic time an estimation based on potential area of rupture gives maximum possible earthquake magnitudes along the cascadia subducting margin of 8 2 for the winona segment 8 5 for the explorer segment 9 1 for the juan de fuca segment and 8 3 for the so

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

deposition of ungraded muds from high density non turbulent turbidity currents turbidity current deposits of mud have recently been found up to 10m in thickness resulting from single depositional events1 2 turbidites 1 5 m thick from the madeira abyssal plain3 4 display long segments with little vertical change of grain size5 6 this suggests that the currents froze in some way making them unable to sort sediment here we suggest that a decline in flow speed of these currents led to a concentration gradient in silt close to the bed that was sufficiently steep to stratify the flow a concentration gradient of 18 kg m 3 over 1 5 m height gives a layer richardson number above the critical value of 0 25 for damping of turbulence we propose that with turbulence severely damped a dense suspension of fine material consolidates like a static suspension while continuing to flow downslope the current changes from a fully turbulent flow to a decelerating flow with suppressed turbulence and increasing density in the latter state interparticle forces prevent differential settling of the coarser grains

a holocene record of diatom and silicoflagellate microfossils in sediments of saanich inlet odp leg 169s odp leg 169s laminated sediment cores provided a unique opportunity to examine changes in the siliceous phytoplankton community of saanich inlet these laminated sediments are rich in diatom and silicoflagellate remains as a result of the inlet s high production and excellent preservation our results suggest that species composition and abundance of diatoms and silicoflagellates in the inlet have changed very little since the inlet s formation carbon and opal data indicate an increase in primary productivity with time which is not apparent in the fossil data however the discrepancy between data sets may be due to changes in grazer activity which could have reduced the number of identifiable fossils individual species were useful for identifying changes in the inlet some planktonic diatoms suggest that nutrient supply was highest in the early mid holocene increases in the abundance of a partially benthic diatom paralia sulcata follow variations in sea level and availability of benthic habitat in the inlet a large peak of the silicoflagellate dictyocha fibula corresponds to a catastrophic flood event in the early holocene which probably washed terrestrial material and low salinity water from the british columbia mainland into saanich inlet fossil data were also analyzed to infer past changes in the environment using a weighted averaging calibration and regression technique these data suggest that only minor variations in sea surface temperature have occurred

paleohydrology of the laguna lejia north chilean altiplano and climatic implications for late glacial times paleoenvironmental and sedimentological data from laguna lejia 23 30 s 67 42 w 4325 m in the high altiplano of the chilean atacama desert indicate that climatic conditions during late glacial times were significantly wetter than today a water and energy budget model was used to simulate climatic scenarios that would have resulted in the observed changes in the water levels water surfaces water volumes and salinity during the time interval different climatic scenarios for the laguna lejia catchment include precipitation increases of over 100 up to 400 500 mm yr today 200 mm yr to account for the late glacial lake levels with shorelines 15 25 m higher than at present and a lake surface of 9 11 km2 compared to the present 2 km2 during the lake maximum about 13 500 11 300 yr b p finely laminated sediments consisting of mg calcite diatoms and sometimes gypsum were deposited the paleoenvironmental evidence indicates that north easterly wind direction prevailed and the summer rainfall resulted from a seasonal poleward shift of the tropical circulation the lake history of laguna lejia is representative for the altiplano area between 21 and 24 s

holocene paleohydrology and glacial history of the central andes using multiproxy lake sediment studies here we document at century to millennial scale the regional changes of precipitation evaporation from the late pleistocene to present with multiproxy methods on a north south transect of lake sites across the eastern cordillera of the central andes the transect of study sites covers the area from v14 s to 20 s and includes core studies from seven lakes and modern calibration water samples from twenty three watersheds analyzed to constrain the down core interpretations of stable isotopes and diatoms we selected lakes in different hydrologic settings spanning a range of sensitivity to changes in the moisture balance these include 1 lakes directly receiving glacial meltwater 2 overflowing lakes in glaciated watersheds 3 overflowing lakes in watersheds without active glaciers and 4 lakes that become closed basins during the dry season the results of our current work on multiple lakes in the bolivian andes show that while the overall pattern of holocene environmental change is consistent within the region conditions were not always stable over centennial to over millennial timescales and considerable decadal to centuryscale climate variability is evident abbott et al quat res 47 1997 70 80 quat res 47 1997 169 180 quat sci rev 19 2000 1801 1820 polissar master s thesis university of massachusetts 1999 comparison of the paleoclimate record from one well studied site lago taypi chaka kkota ltck with others within the region illustrates a consistent overall pattern of aridity from the late glacial through the middle holocene previous work noted a difference between the timing of water level rise in lake titicaca v5 0 3 5 ka b p abbott et al quat res 47 1997 169 180 cross et al holocene 10 2000 21 32 rowe et al clim change 52 2002 175 199 and the onset of wetter conditions at 2 3 ka b p in ltck a lake that drains into the southern end of lake titicaca abbott et al quat res 47 1997 70 80 sedimentary and oxygen isotope evidence from paco cocha 13 54ps located in the northern reaches of the expansive 57 000 km 2 titicaca watershed which spans v14 s to 17 s indicates that

liquefaction features on the fraser delta evidence for prehistoric earthquakes sand dykes and sills and vented sand boils on the fraser river delta and adjacent serpentine river floodplain in southwestern british columbia record one or more major liquefaction events the source of the dykes is a shallow subsurface saturated sand unit that was deposited in foreslope and distributary channel environments during holocene progradation of the fraser delta the dykes cut steeply through a crust of delta topset muds and locally flatten out as sills in overlying peaty sediments at two sites evidence was found for venting of sand onto a subaerial or intertidal surface liquefaction and upward movement of sand and water locally deformed the intruded sediments causing some subsidence and uplift of the delta surface all observed liquefaction features are younger than ca 3500 bp and at least some are younger than 2400 bp it is not clear however whether they formed during one or several separate events a review of possible causes suggests that the liquefaction features probably are seis

a 106ka paleoclimate record from drill core of the salar de atacama northern chile abstract a 100 m long salt core sqm 2005 from the salar de atacama northern chile 23 s 68 w a dry lake bed contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central andes of south america six u series disequilibrium dates range sequentially from 106 1 6 4 to 5 4 2 7 ka based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods saline lakes and expanded mudflats existed in the salar de atacama from 75 7 to 60 7 ka and from 53 4 to 15 3 ka with the wettest perennial lake interval from 26 7 to 16 5 ka short relatively wet periods also occurred in the holocene from 11 4 to 10 2 ka and from 6 2 to 3 5 ka these wet periods at salar de atacama correspond well with other late pleistocene climate records from the central andes that are a function of the net hydrologic budget the minchin tauca lake sequence from salar de uyuni bolivia is synchronous with the 53 4 15 3 ka saline lake wet period at salar de atacama the tauca phase coincided with the wettest perennial lake interval at salar de atacama from 26 7 to 16 5 ka the coipasa lake phase from uyuni was probably contemporaneous with the early holocene wet period at salar de atacama from 11 4 to 10 2 ka the early holocene wet interval at salar de atacama was also synchronous with the maximum holocene lake levels of the chilean altiplano lakes to the east and with grass rich rodent middens between 11 8 and 10 5 ka in age from the atacama basin the lake period at salar de atacama between 26 7 and 15 3 ka compares closely with low 18o values low anion concentrations and high accumulation rates from the sajama glacial ice core southwestern bolivia between 25 and 15 5 ka it is concluded that wet and dry phases were synchronous in the central andean plateau of southwestern bolivia and along the western flank of the andes of northern chile over the past 50 kyr this region which today receives its moisture from the amazon basin to the east probably also did so in the past the wet periods at salar de atacama are in phase with january insolation maxima at 15 s at 70 45 and 20 ka which suggests that past changes in summer insolation influenced precipitation patterns in the central andes however there are no major wet periods linked to the january insolation maximum at 93 ka and the present day extremely dry climate in the atacama desert is associated with a peak in summer insolation therefore there must be other important influences over precipitation in the central andes which modify the first order insolation controls

late quaternary glaciation and postglacial stratigraphy of the northern pacific margin of canada abstract areas of southeastern alaska and the queen charlotte islands of the northwestern pacific coast of north america were considered to be ice free during the late wisconsinan glaciation and glacial refugia existed however a glacier extended from mainland north america to the shelfbreak in dixon entrance separating alaska and the queen charlotte islands glacial retreat to the east began sometime after 15 000 to 16 000 14 c yr b p and ice had completely left dixon entrance by 13 500 to 13 000 14 c yr b p a rapid sea level regression occurred soon after deglaciation began due to isostatic rebound with relative sea level falling to approximately 150 m below present in central dixon entrance decreasing the size of the inlet by about 30 percent by 12 400 14 c yr b p the late quaternary glacial and postglacial stratigraphic sequence is more than 100 m thick overlying older pleistocene sediments and tertiary bedrock a late wisconsinan diamicton is overlain by glaciomarine muds formed between approximately 14 400 and 13 000 14 c yr b p contemporaneous with the deposition of the glaciomarine muds an extensive outwash deposit formed off the northern coast of the queen charlotte islands to a present depth of 150 m during the sea level lowstand and subsequent transgression a reworked sand unit was deposited over much of the seafloor to depths greater than 450 m the unit is exposed at the seafloor over much of the region suggesting that seabed hydrodynamic energy levels were high after 13 000 14 c yr b p and remain so today

composition and origins of laminae in late quaternary and holocene sediments from the santa barbara basin late quaternary and holocene sediments from the santa barbara basin have been analyzed using back scattered electron imaging bsei techniques to identify the origins of laminae and document intra and interannual ocean climate variability over the last glacial cycle laminae observed in x ray radiography and bsei are entirely defined by variations in the relative abundance and grain size of biogenic and terrigenous components there is no evidence to suggest that bacterial mat mediation may have played a role in lamina formation the simplest lamination type comprises silt rich silt poor couplets that originate from seasonal variation in the supply of silt to the basin the second lamination type contains an additional lamina of diatom ooze to form terrigenous sediment diatomaceous triplets the thicker diatom ooze laminae commonly exhibit a vertical succession of diatom floras which represents intra annual variation in productivity the variation in thickness and assemblage of diatom ooze laminae is probably a function of the amount of diatom flux which is controlled by upwelling dri ven primary productivity in the basin laminated sediments deposited during cooler periods generally contain thicker diatom ooze laminae consistent with more vigorous regional circulation and increased upwelling

overview of late quaternary stratigraphy in saanich inlet british columbia results of ocean drilling program leg 169s abstract continuous coring in saanich inlet ocean drilling program odp leg 169s british columbia canada yielded a detailed record of late quaternary climate oceanography marine productivity and terrestrial vegetation two sites 1033 and 1034 were drilled to maximum depths of 105 and 118 m recovering sediments ranging in age from 13 300 to less than 300 14 c yr earliest sediments consist of dense largely massive gray glaciomarine muds with dropstones and sand and silt laminae deposited during the waning stages of glaciation deposition of organic rich olive gray sediments began in the fjord about 12 000 14 c yr ago under well oxygenated conditions as reflected by the presence of bioturbation and a diverse infaunal bivalve community at about 10 500 14 c yr a massive gray unit 40 50 cm thick was emplaced in a very short span of time the unit is marked by a sharp lower contact a gradational upper contact and an abundance of reworked tertiary microfossils it has been interpreted as resulting from massive flood events caused by the collapse of glacial dams in the fraser valley of mainland british columbia progressively greater anoxia in bottom waters of saanich inlet began about 7000 14 c yr ago this is reflected in the preservation of varved sediments consisting of diatomaceous spring summer laminae and terrigenous winter laminae correlation of the sediments was based on marked lithologic changes the presence of massive intervals reflecting localized sediment gravity flow events the mazama ash occasional thin gray laminae indicative of abnormal flood events in nearby watersheds varve counts between marker horizons and 71 accelerator mass spectrometry ams radiocarbon dates

a basin scale oceanic instability event in the gulf of alaska a composite noaa 14 satellite advanced very high resolution radiometer image of the gulf of alaska for early march 1995 reveals a sequence of six anticyclonic oceanic eddies spanning more than 1500 km of the continental margin of north america from central british columbia to central alaska although isolated mesoscale eddies have previously been documented for this eastern boundary region the composite image provides the first evidence that trains of such eddies can develop simultaneously along the entire coast the 80 km radius and 250 km spacing of these warm core eddies are consistent with a baroclinic instability event in the poleward coastal current that prevails along the northwest continental margin of north america in winter roughly october through march wind data from offshore meteorological buoys combined with partial cloud free thermal images for january and february suggest that the event was triggered in mid january by an abrupt coast wide reversal in the prevailing poleward wind the instability event disrupted the alongshore transport of relatively warm high salinity water and presumably resulted in a greatly enhanced cross shore flux of brackish nutrient rich coastal water into the open ocean on the basis of its basin scale extent and more than 2 month duration it is feasible that the event had a major impact on the early spring recruitment and survival of zooplankton and pelagic fish within the highly productive fishery zones of coastal british columbia and alaska less extensive eddy sequences found in several earlier satellite images for the region suggest that these instability events are fairly common if so this indicates that the poleward current that forms over the eastern pacific continental slope in late fall herein the northeast pacific coastal current is marginally stable and likely to deform into a series of mesoscale eddies following abrupt basin scale reversals in the seasonally dominant wind provided these wind events occur early enough in the season the coastal current could reform with the onset of poleward winter winds

paleoseismic signature in late holocene sediment cores from saanich inlet british columbia abstract this paper explores the paleoseismic record potentially preserved in the upper 40 m of hydraulic piston cores collected in 1996 at two sites in saanich inlet british columbia during ocean drilling program odp leg 169s the odp cores are missing 1 2 m of water rich sediment directly underlying the seafloor but this sediment is preserved in shorter piston cores collected in 1989 and 1991 the upper part of the odp cores consists of rhythmically laminated varved marine mud with intercalated massive beds interpreted to be debris flow deposits some of the debris flow deposits are linked to past earthquakes including the 1946 vancouver island earthquake m7 2 a great m8 9 plate boundary earthquake at the cascadia subduction zone in january 1700 and a large crustal or plate boundary earthquake about 1000 yr ago earthquakes may also be responsible for debris flows in about ad 1600 1500 1250 1150 850 450 350 180 and bc 200 220 500 900 and 1050 if so the average recurrence interval for moderate to large earthquakes which trigger debris flows in saanich inlet is about 150 yr this recurrence interval is broadly consistent with the frequency of moderate to large earthquakes in the region during the historical period debris flows however can also be triggered by non seismic processes making it difficult to assemble a complete earthquake record from the saanich inlet cores we propose that extensive debris flow deposits emplaced by single large failures or many smaller coincident failures probably have a seismic origin

late quaternary paleohydrology of the central atacama desert lat 22 24 s chile in northern chile precipitation in the high andes 3500 m recharges groundwater systems that flow down the pacific slope and feed large aquifers in the hyperarid atacama desert wetlands which are often found along the base of the andes mark locations where the water table intersects the land surface at these locations paleo wetland deposits which are present as terraces between 3 and 20 m above modern wetlands record past water table heights along the andean front and are used to reconstruct changes in groundwater discharge paleo wetland deposits in the central atacama desert lat 22 24 s record an episode 15 4 9 ka of high water tables followed by an episode 8 3 ka of moderately high water tables elevated water tables result from increased groundwater discharge and ultimately from enhanced recharge in the andes the concordance of results from three separate hydrologic systems suggests that changes in groundwater discharge and recharge are regional and reflect climatic fluctuations this interpretation is supported by close agreement with other paleoclimatic records in the region the periods of greater groundwater discharge were separated by episodes 9 8 and 3 0 ka of significant groundwater lowering and stream incision implying greatly diminished discharge the central atacama and andes lat 22 24 s receive precipitation mainly from moist air masses transported from the amazon basin by the south american summer monsoon sasm increases in groundwater recharge are therefore thought to reflect an increase in the frequency and or moisture content of sasm air masses crossing the andes fluctuations in sasm precipitation have previously been linked to summer insolation in the southern hemisphere the wettest period in the central atacama 15 4 9 ka however coincides with a minimum in austral summer insolation at 10 ka suggesting that regional summer insolation is not a dominant influence on the sasm instead intensification of the sasm may be linked to extraregional forcings such as the walker circulation

introduction to the 1997 8 el nino atlas of oceanographic conditions along the west coast of north america 23 n 50 n abstract hydrographic data collected along the west coast of north america between january 1997 and january 1999 have been compiled into a web based atlas of the 1997 8 el nino event this paper discusses the organization of the atlas describes the data that were incorporated into the atlas and explains how vertical and horizontal distributions for the different properties were constructed examples of figures from the atlas are shown

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

from proxy data to paleoclimate interpretation the mid holocene paradox of the atacama desert northern chile abstract the question whether the mid holocene climate between ca 9 and 4 cal kyr b p in the atacama desert and the central andes in general was humid or dry has wide implications with regard to the understanding of long term climate variability in south america paleosols regional groundwater tables abiotic proxy data and pollen of aquatic plants in lake sediments show a marked and rapid shift from very humid late glacial early holocene climatic conditions between ca 14 and 9 5 kyr b p to extremely dry mid holocene conditions more arid than today between ca 9 and 4 kyr b p an exception during this hyperarid period is a century scale more humid interval around ca 5 5 6 kyr b p that appears systematically in lake sediment archives in contrast pollen for most terrestrial plants preserved in lake sediments do not show major changes during the holocene whereas more humid mid holocene conditions compared with late holocene conditions were inferred from plant macrofossils in rodent middens is the reason for this disagreement to be attributed to misinterpretation of the paleoenvironments or of the proxy records themselves or to incomplete paleoclimatic interpretation of the paleoenvironments we argue that these different paleoclimate archives record different aspects and facets of climate while paleosols and groundwater in the atacama desert record low frequency climate variability at century to millennium scales lake sediments on the altiplano record decade to century scale variability terrestrial vegetation responds to shorter high frequency climate variability at seasonal to inter annual scales and preferably to humid years vegetation remains in hibernation or does not germinate during arid years thus information from these three types of archives is not a priori comparable and requires careful site specific archive specific and time scale specific evaluation what is natural in modern climatology is also true for paleoclimatology a comprehensive assessment must account for the complex daily and seasonal cycles for the range of climate variability and trends at different scales in space and time for impacts of short term extreme events and for specific often non linear responses of individual bio geo physical archives to any of the numerous aspects of climate

a record of past ocean atmosphere radiocarbon differences from the northeast pacific a record of the 14c age differences between atmosphere and the mixed layer of the northeast pacific ocean was obtained from 58 radiocarbon measurements on shells and associated wood from coastal sediments in british columbia this series of mixed layer reservoir ages spans the holocene and extends into the period of the younger dryas cold event in the north atlantic and surrounding regions the data reflect the extent of upwelling in the northeast pacific and thus constrain models of carbon cycling and ocean circulation most of the reservoir ages are only slightly less than than the present preindustrial value of about 800 years and may be identical when probable sampling errors are taken into account either the north pacific reached a state close to its present mode of circulation at or before the end of the younger dryas or a different circulation fortuitously produced a similar reservoir age our results support the hypothesis that slow changes in atmospheric radiocarbon concentrations over the holocene arose from 14c production rate changes data corresponding to a radiocarbon age of around 6400 years b p give a reservoir age of 1200 years if this result is confirmed it indicates a much greater variability for the holocene ocean circulation than was previously believed possible

radiocarbon reservoir effect and the timing of the late glacial early holocene humid phase in the atacama desert northern chile we revise substantially the regional chronology of lake level fluctuations from the late glacial early holocene humid phase along a high altitude transect 3500 to 4500 m between 18 s and 28 s in the southwestern altiplano of northern chile radiocarbon dates and 210pb profiles for limnic and terrestrial materials allow us to estimate and justify reservoir correction values for conventional 14c dates our chronology suggests that the latest pleistocene early holocene humid phase started between 13 000 and 12 000 14c yr b p and that maximum lake levels were reached between 10 800 and 9200 14c yr b p this is significantly younger than what has been established so far for the titicaca uyuni basin in bolivia the paleolakes disappeared sometime between 8400 and 8000 14c yr b p our revised chronology agrees with the regional history of human occupation and is broadly synchronous with vegetation changes in subtropical continental south america and with the onset of wetland expansion in the northern hemisphere tropics

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

distribution of diatom surface sediment assemblages within effingham inlet a temperate fjord on the west coast of vancouver island canada abstract twenty nine surface sediment samples from effingham inlet a small fjord on the west coast of vancouver island british columbia were analyzed for diatoms this fjord has been selected for paleoceanographic investigation due to the presence of laminated sediments resulting from the dysoxic to anoxic bottom water conditions in the inner and outer basins of the inlet distributional patterns of the diatom microflora reflected proximity to littoral regions phytoplankton production and marine influence from outside the fjord principal components and cluster analyses of the microflora established four diatom assemblages with a clear separation between the inner and outer basin diatom floras inner basin stations were characterized by elevated absolute abundance with assemblages dominated by spring early summer bloom taxa including skeletonema costatum thalassiosira nordenskioeldii and thalassiosira pacifica chaetoceros spp resting spores were abundant throughout effingham inlet with the exception of the stations closest to the fjord head stations located in the outer basin and towards the fjord mouth had relatively lower absolute abundance yet showed a higher relative and absolute abundance of thalassionema nitzschioides rhizosolenia setigera coscinodiscus radiatus ditylum brightwellii odontella longicruris and paralia sulcata in relation to the inner basin many of these latter taxa are often associated with late summer and autumn conditions in fjords along coastal british columbia oceanographic data for effingham inlet suggest that increased offshore penetration is more likely to occur from summer to early fall with a more restricted offshore influence in the inner basin diatom surface sediment assemblages in effingham inlet appear to reflect incursions of offshore waters into the fjord absolute abundance estimates and the preservation of lightly silicified taxa suggest excellent preservation of fossil material in the sediments of the predominantly anoxic inner basin preservation in the outer basin is reduced reflecting more frequent recharge by oxygenated waters spilling over the outer sill into the basin our findings suggest the inner basin should be an optimal site for reconstruction of diatom production with records from the outer basin providing more consistent information about offshore influence and coastal upwelling conditions over the holocene estimates of diatom abundance within the inner basin sediment may serve as a good proxy of production although proxy tracers of bottom water conditions and sedimentological analyses must be coupled to the diatom record to ensure depositional conditions were not influencing valve preservation or abundance our results suggest that fjords can serve as good environments for paleoceanographic reconstructions of both inshore and offshore conditions although careful site selection and understanding of processes affecting the microfossil record are essential

modern to late holocene deposition in an anoxic fjord on the west coast of canada implications for regional oceanography climate and paleoseismic history laminated sediments preserved in the anoxic inner basin of effingham inlet on the pacific coast of vancouver island british columbia canada yield a high resolution sediment deposition record spanning about 6000 yr the varying thickness of diatom terrigenous mud varves in sediment cores from the basin can be interpreted in terms of annual changes in surface productivity and freshwater input within the inlet similarly the occurrence of unlaminated mud units homogenites intercalated amongst the laminated sediments can be interpreted in terms of oceanic and climatic changes these units appear to be associated with coastal upwelling events that result infrequently in highly oxygenated oceanic water penetrating to the bottom of the inner and outer basins of the inlet the sedimentary record also contains massive and graded mud units considered to arise from debris flows and turbidity currents some of which were probably initiated by seismic events including a major event about 4500 14 c yr bp which may be earthquake related a total of seventeen oceanographic surveys of the inlet beginning in 1995 characterize the modern seasonal coastal upwelling regime and a unique bottom water oxygenation event which was

late quaternary environmental dynamics in the atacama desert reconstructed from rodent midden pollen records in the past two decades much has been learned about the late quaternary climate history of the atacama desert with some details still unclear about the seasonality timing and extent of wet and dry phases modern climate studies reveal that far from exhibiting a unique pattern seasonal precipitation originates from many sources and mechanisms for the last 16 ka we attempt to sort out these complexities in pollen records from four fossil rodent midden series spanning 22 25 s in northern chile widespread wet conditions prevailed during the late pleistocene and early holocene particularly between 13 and 9 ka evidenced by 400 m lowering of pollen zones plant communities compared to today regional differences in the timing and magnitude of this displacement may be related to the prevailing source tropical extra tropical or mode nnw se of tropical precipitation through time wet conditions persisted well into the early holocene lasting 1 1 5 ka longer than previously suggested the pollen record suggests extreme drying 8 ka possibly associated with a northward shift of the inter tropical convergence zone tracking minimum insolation values at subtropical latitudes during the austral summer the establishment of conditions similar to today happened 4 ka copyright 2017 john wiley sons ltd

prosopis sp tree ring oxygen and carbon isotope record of regional scale hydroclimate variability during the last 9500 years in the atacama desert abstract the hyper arid core of the atacama desert is one of the most persistently arid environments in the world yet there is evidence of significant hydroclimate variability during the holocene the timing of regional scale pluvial or humid periods has important implications for understanding the drivers of south american climate variability as well as the development of agriculture by prehistoric cultures here we present oxygen 18o and carbon 13c isotope values from ancient prosopis sp tree ring cellulose as a record relative humidity rh and water availability via intrinsic water use efficiency over century long intervals throughout the past 9 5 ka in the northern atacama desert 19 21 s these data provide the first high resolution ca annual evidence for decreasing water availability and increasing climate variability in the atacama from the early to late holocene intrinsic water use efficiency steadily increases over the holocene indicating a lowering of the water table and a reduction in the availability of groundwater resources in the region as water availability decreases 18o based estimates of rh show increased variance beginning 4 9 ka this change in rh coincides with the onset of modern day central andean atmospheric circulation patterns and previously documented humid periods in the southern altiplano 22 24 s subannual tree ring isotope analysis of modern and early holocene 8 3 ka trees show a similar seasonal cycle in carbon isotope values that correlates with modern annual changes in temperature however the early holocene interseasonal variability is greater than modern seasonality 18o values of the atacama tree rings are highly correlated with those of the sajama ice core from the bolivian andes demonstrating a teleconnection between high altitude andean precipitation and water availability in the atacama desert these reconstructions together provide a record of holocene water availability and ephemeral recharge related to changes in enso and south american monsoon

self sedimentation of phytoplankton blooms in the geologic record abstract understanding the formation of laminated organic rich sediments is an essential topic for researchers interested in fossil fuels biogeochemical cycles earth s environmental history and global change biologists have very recently demonstrated that some marine phytoplankton blooms actively govern their own sedimentation by the formation of sticky transparent gels that facilitate rapid aggregation accelerated sinking and efficient export flux here we present fossil evidence of unfragmented low diversity phytoplankton assemblages preserved as sedimentary laminae and irregular flocs that are attributable to a similar phytoplankton driven sedimentary mechanism we term self sedimentation the geological evidence suggests that self sedimentation precludes significant heterotrophic grazing propels the formation of some conspicuous hemipelagic sedimentary laminae and results in efficient carbon and opal flux to the sediments we suggest that the self sedimentation phenomenon may have broad implications for the geological history of biogeochemical cycling oceanic ecological dynamics and abrupt atmospheric environmental change broader recognition of the self sedimentation phenomenon as explicitly defined here is a prerequisite to testing these unconventional hypotheses

palaeoindian occupation of the atacama desert northern chile palaeoindian occupation of the atacama desert in northern chile has been found between 12 600 and 10 200 cal yr bp the new site at salar punta negra 24 28 s 60 53 w 2976 m includes about 1000 classifiable mostly unifacial artefacts and uniquely three different diagnostic types of early projectile points two of the lateglacial early holocene projectile types have wide distribution and are known from different geographical areas in south america the palaeoindian fell fish tail point mainly from the southern cone of south america and the triangular tuina points typical of the puna of the south central andes in northern chile and northwestern argentina in addition we found a third type a stemmed point typical for the salar punta negra filling a large geographical gap of fell occupation the site at salar punta negra provides evidence for generally much higher mobility and diversity of early cultures and supports an andean pacific route for early human exploration of south america to the south through the desert at intermediate altitudes contemporaneous high amplitude climatic changes were fundamental preconditions to provide adequate environments and habitats and to make palaeoindian hunting gathering occupation possible in the atacama desert copyright 2005 john wiley sons ltd

a large california flood and correlative global climatic events 400 years ago a gray silt layer 1 2 cm thick in the central santa barbara basin dated by varve counts to a d 1605 5 yr implies an intensity of precipitation flooding of regional rivers and transport of terrigenous detritus unmatched in the last 1000 yr the inferred flood may correlate with the reported rare occurrence of a perennial lake 14c dated to 390 90 b p in california s mojave desert 300 km east of the area draining into the santa barbara basin the dating of the a d 1605 5 yr flood event is consistent with tree ring evidence for a wet and cold paleoclimate elsewhere in the region regional and global climate evidence indicates that much of the world also experienced rapid intense cooling around a d 1605 this cooling was probably accompanied by an equatorward shift of prevailing wind patterns and associated storm tracks

paleowetlands and regional climate change in the central atacama desert northern chile abstract widespread organic rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central atacama desert one of the driest places on earth today we mapped and dated these paleowetland deposits at three presently waterless locations near salar de punta negra 24 5 s on the western slope of the andes elevated groundwater levels supported phreatic discharge into wetlands during two periods 15 900 to 13 800 and 12 700 to 9700 cal yr bp dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase 11 000 9700 cal yr bp water tables dropped below the surface before 15 900 and since 8100 cal yr bp and briefly between 13 800 and 12 700 cal yr bp this temporal pattern is repeated with some slight differences in rodent middens from the study area in both paleowetland and rodent midden deposits north and south of the study area and in lake level fluctuations on the adjacent bolivian altiplano the regional synchroneity of these changes points to a strengthening of the south american monsoon which we term the central andean pluvial event in two distinct intervals 15 900 13 800 and 12 700 9700 cal yr bp probably induced by steepened sst gradients across the tropical pacific i e la nina like conditions

vegetation invasions into absolute desert a 45 th000 yr rodent midden record from the calama salar de atacama basins northern chile lat 22 24 s plant macrofossils percentage abundance of grass taxa fecal pellet d13 c and plant cuticle contents from 49 fossil rodent middens dated by 14 c record changes in local vegetation and precipitation since 45 ka calibrated or measured to thousands of calendar years before present in the central atacama desert lat 228 248s of northern chile the midden sites are along the hyperarid upper margin 2400 3100 m of the absolute desert in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs conditions between 40 and 22 ka may have been at least intermittently dry and possibly cooler as implied by four middens with low species richness we infer a large increase in summer rainfall between 16 2 and 10 5 ka on the basis of the lowering of steppe grasses by as much as 1000 m prominence of c4 grasses and summer annuals high species richness and displacement of northern species at least 50 km south of their modern ranges the precipitation increase was greatest for a cluster of middens between 11 8 and 10 5 ka abrupt drying evident in a dramatic decrease in grass abundance occurred after 10 5 ka at all four midden localities increased percentages of