direct correlation of millennial scale changes in western north american vegetation and climate with changes in the california current system over the past 60 kyr terrestrial pollen and marine climate proxies from seven sediment cores taken on the continental margin of western north america between 32 and 43 n show systematically related short term changes superposed on milankovitch scale oscillations of the past 60 kyr during oxygen isotope stage 3 brief warming events in california and oregon appear correlative with interstadial events in waters offshore as do the rapid climate oscillations of the last glacial transition 14 10 ka estimated temperature depression of the coastal lowlands ranges from 10 c in southern california to 5 c in oregon during the last glacial the absence of long distance migration of pacific coastal plant assemblages concurs with marine evidence that southward movement of the polar front during the last glacial maximum was limited correlative changes in terrestrial and marine ecosystems imply that broad reorganizations of circulation in the northeast pacific ocean were synchronous with reorganizations of atmospheric circulation over western north america

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

late holocene environmental changes in arid southwestern madagascar a 5000 yr stratigraphic record containing fossil pollen charcoal and bones of the extinct quaternary megafauna from andolonomby a hypersaline pond in arid southwestern madagascar shows evidence for climatic desiccation beginning about 3000 yr b p pollen spectra shift at this time from primarily arboreal taxa characteristic of forests and woodlands of more mesic western madagascar to wooded savanna typical of somewhat drier localities between 3000 and 2000 yr b p the site became increasingly arid charcoal and pollen evidence indicates that increased fire and disturbance occurred at the site beginning ca 1900 yr b p probably signaling the beginning of human settlement in the area the fossil record suggests that various human and natural factors on the island may have interacted in the subsequent millennium to culminate in the extinction of the entire endemic megafauna

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

human responses to middle holocene climate change on california s channel islands abstract high resolution archaeological and paleoenvironmental records from california s channel islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses available climate records in western north america 7 3 8 ka indicate a severe dry interval between 6 3 and 4 8 ka embedded within a generally warm and dry middle holocene very dry conditions in western north america between 6 3 and 4 8 ka correlate with cold to moderate sea surface temperatures sst along the southern california coast evident in ocean drilling program odp core 893a b santa barbara basin an episode of inferred high marine productivity between 6 3 and 5 8 ka corresponds with the coldest estimated ssts of the middle holocene otherwise marked by warm low productivity marine conditions 7 5 3 8 ka the impact of this severe aridity on humans was different between the northern and southern channel islands apparently related to degree of island isolation size and productivity of islands relative to population fresh water availability and on going social relationships between island and continental populations northern channel islanders seem to have been largely unaffected by this severe arid phase in contrast cultural changes on the southern channel islands were likely influenced by the climatically induced environmental changes we suggest that productive marine conditions coupled with a dry terrestrial climate between 6 3 and 5 8 ka stimulated early village development and intensified fishing on the more remote southern islands contact with people on the adjacent southern california coast increased during this time with increased participation in a down the line trade network extending into the western great basin and central oregon genetic similarities between middle holocene burial populations on the southern channel islands and modern california uto aztecan populations suggest middle holocene movement of people at this time from southern california desert environs westward to the southern islands a migration perhaps stimulated by increased continental aridity

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

holocene environment changes around the sara us river northern china revealed by optical dating of lacustrine aeolian sediments abstract the sara us river is located along the boundary of the mu us desert and the chinese loess plateau in northern china the river has cut down through quaternary sediments creating 70 80 m deep valleys with thick lacustrine aeolian sequences exposed we applied optical stimulated luminescence on sediments from a holocene section of aeolian sand lacustrine deposits in the top of the river valley the dating results show that a humid period existed from 7 1 to 2 0 ka ago as evidenced by two layers of peat and lacustrine sediments however compared to other published holocene sections in the sara us river valleys close to the section under studying the local environment experienced very complicated changes during the holocene all of the sections recorded a period with drought and or cold before the holocene at around 13 ka and an episode of aridity after about 2 ka ago as evidenced by the layers of aeolian sand however the ages of the lacustrine and peat layers in these sections are substantially different geomorphological analysis by digital elevation models does not support the existence of a mega lake covering the study area at 2 ka the intricate environmental changes may have been caused by the meandering of the sara us river environmental changes also strongly affected human migration in this area which is documented by chinese historical records

latest quaternary north pacific surface water responses imply atmosphere driven climate instability a full sequence of brief interstadials dansgaard oeschger d o cycles are recorded from 60 to 25 ka in santa barbara basin california ocean drilling program hole 893a by planktonic foraminiferal isotopic and assemblage changes at unparalleled high resolution for the oceans synchronous climatic response between north pacific surface waters and the greenland ice sheet during d o cycling is strongly indicated by remarkable similarities in speed magnitude and character of rapid oceanic and atmospheric reorganizations inferred sea surface temperature warmings of as much as 5 c within a few decades and brief warming overshoots of as much as 3 c suggest involvement of an atmospheric amplification top down in situ atmospheric warming of the ocean is implied by differential responses partial decoupling in the changes recorded in surface and thermoclinal waters

was the younger dryas triggered by a flood draining of a huge lake into the northern atlantic may have triggered a cold period 12 900 years ago the route taken by the flood waters remains unknown

new pygmy mammoth mammuthus exilis localities and radiocarbon dates from san miguel santa rosa and santa cruz islands california abstract the 1994 discovery and excavation on santa rosa island of the most complete pygmy mammoth mammuthus exilis skeleton yet recovered prompted additional research of the california channel islands an intensive pedestrian survey of mammoth localities tied to gps coordinates was initiated for the first time in the history of the island mammoth research and has resulted in the discovery and documentation of more than 100 new localities several mainland size mammoth mammuthus columbi elements were recovered these may represent 1 ancestral animals 2 contemporary animals or 3 late migrant animals dental and osteological metric analyses in progress will allow comparisons and contrasts to mainland m columbi populations six new radiocarbon dates from san miguel and santa rosa islands have been added to the eleven published dates for mammoth and mammoth associated material these new dates include an ams bone collagen date of 12 840 410 yr b p cams 24429 derived from the right femur of the 1994 skeleton

evidence for temporal fluctuations in marine radiocarbon reservoir ages in the santa barbara channel southern california abstract differences in the 14 c ages of closely associated marine shell and carbonized plant material from stratified archaeological deposits on san miguel island california suggest holocene 10 000 present fluctuations in marine 14 c reservoir ages these fluctuations coincide with 18 o and 13 c shifts measured in mytilus californianus shells from the same stratigraphic contexts and general atmospheric oceanic circulation models for the region based on these data we make three primary observations 1 significant changes appear to have occurred in the radiocarbon reservoir during the holocene 2 these fluctuations appear to correlate with regional oceanographic changes and 3 high resolution 14 c dating of marine shells may require different r values for different periods of time

evidence from western north america for rapid shifts in climate during the last glacial maximum the estancia basin in southwestern united states contains evidence for strong and rapid pulsations in the supply of moisture brought into the region during the last ice age the pulses were recorded during episodes of stream discharge that spread plumes of fresh water laden with quartz sand over the saline lake the largest pulses in stream discharge lasted only a few decades were organized into cycles that were spaced approximately 200 to 250 and 2000 years apart and were of sufficient magnitude to freshen and maintain the lake at its maximum recorded elevation

intermittent existence of a southern californian upwelling cell during submillennial climate change of the last 60 kyr 1 application of a high resolution multiproxy approach to a sedimentary section drilled at ocean drilling program site 1017 located under a highly active upwelling cell off point conception california provides clear evidence for surface ocean productivity shifts on submillennial timescales during the last 60 kyr the proxies include bulk sediment major and minor elements organic carbon and carbonate concentrations 15n and planktonic foraminiferal species assemblage and carbon isotope determinations the collective results demonstrate that marine productivity in this area was not simply linearly related to cold and warm cycles except during the millennial scale climate oscillations of marine isotope stage mis 3 during that interval the upwelling cell and resulting high productivity were active during warm interstadial events and were largely inactive during cool stadial events however the last glacial maximum was also relatively productive productivity increased dramatically during the bolling warm interval while the allerod and younger dryas were much less productive high coccolithophorid abundance commenced during the earliest holocene after 10 ka the complexity of the productivity response was probably related to interplay between local winds as well as california undercurrent strength

paleoproductivity ventilation and organic carbon burial in the santa barbara basin odp site 893 off california since the last glacial biogenic burial rates and coccolith assemblage data were generated for the past 16 ka at odp site 893 in the santa barbara basin off california to determine if dysoxic events in the basin were related to changes in marine productivity coccolith abundance data show that changes in surface water conditions did indeed change in concert with oxygen levels at the sea floor however organic carbon burial rates varied independently indicating that oxygenation of the water column is related mainly to intermediate water ventilation a strong correlation of organic carbon burial rates with lithogenic and to a lesser extent with carbonate and opal accumulation rates confirms recent conclusions that the export of organic carbon from the sea surface is largely controlled by the presence of ballast minerals

apparent synchroneity of submillennial scale climate events between greenland and santa barbara basin california from 30 10 ka abstract evidence is presented from odp hole 893a santa barbara basin for possible synchroneity between greenland and california margin submillennial climate change records during termination 1 and the last glacial maximum lgm planktonic foraminiferal isotope and faunal records are compared to the gisp2 18o records greenland for the interval between 30 and 10 ka using a new chronology based on 38 planktonic 14c dates apparent synchronous climatic events include interstadial is events 2 3 and 4 a broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka bolling and allerod warm episodes separated by the cooler older dryas event younger dryas cool episode and the preboreal the resulting tight correlation supports an intimate teleconnection between santa barbara basin surface waters and greenland air temperatures differences between greenland and santa barbara basin suggest that some regional variations were superimposed on the global pattern of climate change e g the pre bolling warming

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

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

carbonate deposition pyramid lake subbasin nevada 4 comparison of the stable isotope values of carbonate deposits tufas and the lahontan lake level record abstract in this paper the fundamental importance of changes in hydrologic balance and hydrologic state on the 18o and 13c values of water and dissolved inorganic carbon dic in lakes of the lahontan basin is illustrated abrupt changes in 18o and 13c values of carbonate deposits tufas from the pyramid lake subbasin nevada coincide with abrupt changes in lake level and hydrologic state minima in lake level at 26 000 15 500 and 12 000 yr b p are associated with relatively heavy 18o and 13c values maxima in the lake level record at 14 000 and 10 500 yr b p are associated with relatively light 18o and 13c values we believe that the correlation between maxima and minima in the lake level and 18o records reflect the fundamental effect of lake level dynamics on the 18o value of lake water evaporation increases the 18o value of lake water whereas streamflow discharge and on lake precipitation decrease the 18o value variation in the 18o value of lake water therefore indicates change in the hydrologic balance increases in 18o accompany decreases in lake volume and decreases in 18o accompany increases in lake volume covariance of 13c and 18o indicates that change in 13c values of dic also accompany change in lake volume we offer the hypothesis first put forward by j a mckenzie that change in the productivity photosynthesis respiration balance is responsible for much of the observed variation in 13c most great basin lakes including lake lahontan experienced changes in hydrologic state during the late wisconsin when a lake becomes hydrologically open the residence time of water decreases the greater the rate of spill the greater the volume of evaporated 18o enriched water removed from the spilling lake and the more negative the 18o value of water remaining in the spilling lake the concentration of dic as well as the concentrations of photosynthesis limiting nutrients e g phosphorus nitrogen silica molybdenum decrease as spill increases increasing rates of spill therefore lead to overall decreases in photosynthetic rates relative to respiration rates and as a consequence the 13c values of dic become more negative

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

wildfire and abrupt ecosystem disruption on california s northern channel islands at the allerod younger dryas boundary 13 0 12 9 ka abstract sedimentary records from california s northern channel islands and the adjacent santa barbara basin sbb indicate intense regional biomass burning wildfire at the allerod younger dryas boundary 13 0 12 9 ka all age ranges in this paper are expressed in thousands of calendar years before present ka radiocarbon ages will be identified and clearly marked 14c years multiproxy records in sbb ocean drilling project odp site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats abrupt ecosystem disruption is evident on the northern channel islands at the allerod younger dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape these wildfires coincide with the extinction of mammuthus exilis pygmy mammoth the earliest evidence for human presence on these islands at 13 1 12 9 ka 11 000 10 900 14c years is followed by an apparent 600 800 year gap in the archaeological record which is followed by indications of a larger scale colonization after 12 2 ka although a number of processes could have contributed to a post 18 ka decline in m exilis populations e g reduction of habitat due to sea level rise and human exploitation of limited insular populations we argue that the ultimate demise of m exilis was more likely a result of continental scale ecosystem disruption that registered across north america at the onset of the younger dryas cooling episode contemporaneous with the extinction of other megafaunal taxa evidence for ecosystem disruption at 13 12 9 ka on these offshore islands is consistent with the younger dryas boundary cosmic impact hypothesis firestone r b west a kennett j p becker l bunch t e revay z s schultz p h belgya t kennett d j erlandson j m dickenson o j goodyear a a harris r s howard g a kloosterman j b lechler p mayewski p a montgomery j poreda r darrah t que hee s s smith a r stich a topping w wittke j h wolbach w s 2007 evidence for an extraterrestrial impact 12 900 years ago that contributed to the megafaunal extinctions and younger dryas cooling proceedings of the national academy of sciences 104 16016 16021

geographic coherence of millennial scale climate cycles during the holocene varve thickness measurements and variation in sediment texture have been compiled for an intermittently varved sequence of holocene sediments at odp site 893 in the santa barbara basin sbb off california a varve based age model is generated from the varve counts using interpolation across homogeneous intervals with this age model the varve thickness and sediment texture time series are compared to published gisp2 stable oxygen isotope and aerosol data as well as to the atmospheric 14c record variation in sediment texture at site 893 shows the presence of a 1000 year cycle which is attributed to fluctuations in the degree of ventilation of the basin cross spectral analysis shows that this cycle is coherent with the gisp2 18o record and with atmospheric 14c throughout the holocene the correlation with the 14c record indicates that this 1000 year cycle is related to solar cycles which appear to have a noticeable impact especially on circum north atlantic climate the presence of the 1000 year cycle in the sbb is attributed to a tele connection with the northern high latitudes most likely via intermediate water formation in the north pacific in contrast the gisp2 aerosol record and variation in varve thickness at odp site 893 show a coherent 2750 year cycle which does not correlate with the 1000 year cycle varve thickness in sbb has been shown to correlate with annual rainfall which occurs mainly during winter when prevailing winds slacken both the gisp2 aerosol and sbb varve thickness records are therefore interpreted as a measure for a combination of wind stress and aridity the correlation is negative in that thick varves wet climate in sbb occur during times that the aerosol load is high at gisp2 dry the presence of two distinct patterns of millennial scale variation points to regional trends in climate change during the holocene however the fact that both patterns occur at two distant localities suggest that they represent differential behaviour of supra regional climate systems of which the effects can be traced over large parts of the globe

radiocarbon dating and the old wood problem the case of the hohokam chronology abstract many archaeological chronologies including that of the hohokam in southern arizona are based on a series of radiocarbon dates on wood this paper argues that because of variability in rates of wood decay processes in the environment and in systemic context such archaeological chronologies are potentially biased towards excessive antiquity by an old wood problem and must be reassessed following the theoretical insights of dean 1978 this paper sets forth principles and procedures for relating radiocarbon dates to cultural events emphasis is placed on identifying and taking into account the formation processes of 1 the dated specimens and 2 the deposits that yielded them this methodological framework is applied to hohokam radiocarbon dates and a chronology much shorter than the original gladwin haury formulation is supported

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

biotic response to late quaternary rapid climate switches in santa barbara basin ecological and evolutionary implications benthic foraminiferal assemblages from santa barbara basin exhibit major faunal and ecological switches associated with late quaternary millennial to decadal scale global climate oscillations repeated turnovers of entire faunas occurred rapidly 40 400 yr without extinction or speciation in conjunction with dansgaard oeschger shifts in thermohaline circulation ventilation and climate confirming evolutionary model predictions of roy et al consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late quaternary and possibly other transitional intervals in the history of the earth s ocean atmosphere cryosphere system these data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change

archaeological geology of the lubbock lake site southern high plains of texas the lubbock lake site is a well stratified archaeological locality in yellowhouse draw on the southern high plains of texas it has a cultural record that spans the past 11 000 yr that is contained within a thick sequence of sediments and soils the sequence at lubbock lake is one of the most closely integrated records of late quaternary human occupation sedimentation and soil formation documented in north america stratum 1 11000 yr b p and older was deposited by a meandering stream and contains clovis age cultural remains stratum 2 is composed of lacustrine sediments 11000 to 10000 yr b p and overlying marsh deposits 10000 to 8500 yr b p with paleoindian material in both units the firstview soil 8500 to 6300 yr b p formed in the top of stratum 2 stratum 3 6300 to 5000 yr b p contains early archaic material eolian and marsh deposits suggestive of warm arid conditions and the yellowhouse soil indicating a brief period of landscape stability stratum 4 5000 to 4500 yr b p is primarily an eolian unit that marks the second of two periods of severe drought in the middle holocene the lubbock lake soil formed in stratum 4 beginning 4500 yr b p coincides with the late archaic and ceramic periods and documents landscape stability and a return to climatic conditions similar to those of today stratum 5 contains late ceramic protohistoric and historic archaeological material within eolian and slopewash sediments and the apache and singer soils which indicate several shifts toward aridity within the past 1 000 yr

rancho la brea stable isotope biogeochemistry and its implications for the palaeoecology of late pleistocene coastal southern california abstract we sampled 143 individuals from rancho la brea rlb large faunal collections for bone collagen stable carbon 13c and nitrogen 15n isotope ratios these collections were recovered from asphalt seeps in the los angeles basin california usa and date from 40 to 12 ka our findings indicate that despite a slight reduction in collagen nitrogen content rlb skeletal remains are relatively well preserved and most yield proteins diagnostic of diet herbivore 13c and 15n values covary with rumination and are consistent with changes in late pleistocene vegetation reconstructed from pollen profiles we find no evidence for reliance on c4 grasses at rlb despite low atmospheric co2 concentrations carnivore 15n values indicate canis dirus smilodon fatalis and panthera leo atrox competed for similar prey sets and were equally reliant on ruminant and nonruminant prey types the 15n values of mammut americanum indicate partial reliance on vegetation with lower 15n values such as nitrogen fixing taxa distinguishing them from the remainder of the study population a comparison of rlb and european faunal 15n values from the late pleistocene suggests that coastal southern california experienced greater aridity

the millennium uranium deposit athabasca basin saskatchewan canada an atypical basement hosted unconformity related uranium deposit the millennium uranium basement hosted unconformity related deposit is one of the most recent discoveries of basement hosted deposits and may hold as much as 46 8 million pounds 18 000 metric tonnes u at an average grade of 4 53 percent u3o8 the alteration zone associated with the deposit is atypical as it consists predominantly of muscovite rather than the chlorite and muscovite commonly found in the other basement hosted deposits of the athabasca basin the preore stage consists of early minor clinochlore alteration at temperatures of about 275 c interpreted to result from retrograde metamorphism of the basement rocks prior to the deposition of the athabasca basin this clinochlore event is followed by an extensive 1mc muscovite alteration of the basement rocks by na k fe rich basinal brines at temperatures of about 250 c creating up to 25 percent void space in the basement rocks subsequently a weak chamoisite alteration resulted from fe mg ca rich fluids with temperatures of about 300 c that evolved from reactions between the basinal brines and the basement rocks ore stage uraninite has an extrapolated chemical age of 1590 ma and is contemporaneous with synore 1mc muscovite and iron oxide deposited at temperatures near 250 c from fluids with similar 18o but lower d values to preore basinal fluids the low d values indicate postdepositional exchange of h isotopes with cenozoic fluids postore alteration consists of dravite and sudoite precipitated from mg ca rich fluids from the same evolved basinal brines that precipitated preore chamoisite at temperatures of about 185 c filling voids created during the preore stage our results indicate that the pre and synore minerals were formed dominantly by basinal fluids with no contribution from basement fluids which differ from some other basement hosted deposits in the athabasca basin where basement derived fluid influx was more significant several u pb and ar ar resetting events recorded on preore muscovite and on uraninite are coincident with fluid flow induced by distal orogenies remobilizing radiogenic pb from the deposit the radiogenic pb remobilization events were not widespread as the presence of radiogenic pb is restricted to basement rocks proximal to the deposit and along the unconformity

deep dwelling planktonic foraminifera of the northeastern pacific ocean reveal environmental control of oxygen and carbon isotopic disequilibria abstract we assess the utility of four species of living planktonic foraminifera as tracers of thermocline and intermediate water masses in the northern pacific ocean based on their water column distribution and shell isotopic composition assuming oxygen isotopic equilibria with the water column we infer apparent calcification depths this allows an estimate of apparent carbon isotopic disequilibria we then relax the assumption of oxygen isotopic equilibrium to examine habitat effects on kinetic disequilibrium processes in the california current left coiling neogloboquadrina pachyderma and globigerina calida calcify in the upper thermocline globorotalia scitula resides within the shallow salinity minumum potential density 25 1 26 7 while globoquadrina hexagona is associated with the deeper north pacific intermediate water 26 7 26 9 apparent carbon isotopic disequilibria corrected for oxygen isotopic disequilibria range from 1 0 1 9 in these asymbiotic species the carbon isotopic disequilibrium can be modeled as a single exponential function of temperature or a logarithmic function of potential food supply we infer that carbon isotopic disequilibrium increases with metabolic rate related to temperature and or food supply kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen carbon isotopic shift is about 0 35 consistent with culture data our finding of a link between environment metabolism and isotopic disequilibrium observed in oceanic settings suggests the potential to better reconstruct the structure and biological processes of the upper water column from geologic data

tree rings and ice cores reveal c 14 calibration uncertainties during the younger dryas the younger dryas interval during the last glacial termination was an abrupt return to glacial like conditions punctuating the transition to a warmer interglacial climate despite recent advances in the layer counting of ice core records of the termination the timing and length of the younger dryas remain controversial also a steep rise in the concentration of atmospheric radiocarbon at the onset of the interval recorded primarily in the cariaco basin has been difficult to reconcile with simulations of the younger dryas carbon cycle here we discuss a radiocarbon chronology from a tree ring record covering the late glacial period that has not been absolutely dated we correlate the chronology to ice core timescales using the common cosmic production signal in tree ring 14c and ice core 10be concentrations the results of this correlation suggest that the cariaco record may be biased by changes in the concentration of radiocarbon in the upper ocean during the early phase of the younger dryas climate reversal in the cariaco basin this bias in the marine record may also affect the accuracy of a widely used radiocarbon calibration curve over this interval our tree ring based radiocarbon record is easily reconciled with simulated production rates and carbon cycle changes associated with reduced ocean ventilation during the younger dryas attaching a floating tree ring chronology to ice core records that cover the abrupt younger dryas cold interval during the last glacial termination provides a better estimate of the onset and duration of the radiocarbon anomaly the chronology suggests that marine records may be biased by changes in the concentration of radiocarbon in the ocean which may affect the accuracy of a popular radiocarbon calibration program during this interval

fault related fold growth and isostatic subsidence california channel islands in the northern channel islands of california preservation of paleo shoreline features both as uplifted landforms onshore and subsided depositional features offshore has allowed precise measurement of late quaternary fold growth relative to sea level and has helped to disentangle the relative contributions of tectonic forcing and isostatic response we precisely measured several hundred points on uplifted pleistocene coastal terraces of santa cruz and anacapa islands the elevations of which document anticlinal growth of the islands since at least 400 ka we also interpreted a dense grid of seismic reflection profiles that image a complex of eustatic lowstand deltas that record regional subsidence surrounding the uplifting structure we combined onshore uplift with offshore subsidence measurements to produce a quantitative mass balance of structural growth since 400 ka the data outlined above were then used to test the hypothesis that subsidence around the northern channel islands represents the flexural isostatic response to tectonic loading of the islands calculations of cumulative uplifted mass and cumulative subsided mass across the structure closely match the values predicted for density driven isostatic compensation and local flexural support although the wavelength of flexure predicted for the study area suggests that an additional component of flexural support may extend distally 10s of kilometers into the surrounding offshore basins in the northern channel islands isostatic subsidence is explicitly manifested because erosional mass removal is small because the crust here is relatively thin and weak and most importantly because sea level provides an absolute datum against which to measure vertical deformation an explicit treatment of the interplay between crustal thickening erosional denudation surface uplift and isostatic response helps to illustrate the conditions under which isostatic subsidence may or may not be a significant process where surface denudation rates approach the rate of rock uplift for example isostatic subsidence will approach zero in contrast failure to recognize isostatic subsidence in earthquake hazard studies can lead to order of magnitude errors in slip rate and hazard estimates

black mats spring fed streams and late glacial age recharge in the southern great basin black mats are prominent features of the late pleistocene and holocene stratigraphic record in the southern great basin faunal geochemical and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge ranging from wet meadows to shallow ponds small land snails such asgastrocopta tappanianaandvertigo berryiare the most common mollusk taxa present semiaquatic and aquatic taxa are less abundant and include catinellids fossaria parva gyraulus parvus and others living today in and around perennial seeps and ponds the ostracodescypridopsis okeechobiandscottia tumida typical of seeps and low discharge springs today as well as other taxa typical of springs and wetlands are common in the black mats several new species that lived in the saturated subsurface also are present but lacustrine ostracodes are absent the 13c values of organic matter in the black mats range from 12 to 26 reflecting contributions of tissue from both c3 sedges most shrubs and trees and c4 saltbush saltgrass plants carbon 14 dates on the humate fraction of 55 black mats fall between 11 800 to 6300 and 230014c yr b p to modern the total absence of mats in our sample between 6300 and 230014c yr b p likely reflects increased aridity associated with the mid holocene altithermal the oldest black mats date to 11 800 11 60014c yr b p and the peak in the14c black mat distribution falls at 10 00014c yr b p as the formation of black mats is spring related their abundance reflects refilling of valley aquifers starting no later than 11 800 and peaking after 11 00014c yr b p reactivation of spring fed channels shortly before 11 20014c yr b p is also apparent in the stratigraphic records from the las vegas and pahrump valleys this age distribution suggests that black mats and related spring fed channels in part may have formed in response to younger dryas yd age recharge in the region however the inception of black mat formation precedes that of the yd by at least 40014c yr and hydrological change is gradual not rapid