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

dietary reconstruction of an early to middle holocene human population from the central california coast insights from advanced stable isotope mixing models the inherent sampling and preservational biases of the archaeological record make it difficult to quantify prehistoric human diets especially in coastal settings where populations had access to a wide range of marine and terrestrial food sources in certain cases geochemical proxies such as stable isotope ratios may be utilized to provide robust estimates on the relative proportions of various food resources consumed by prehistoric populations the harkins slough archaeological site scr 60 130 is an early to middle holocene coastal assemblage located on monterey bay in central ca the carbon d 13 c and nitrogen d 15 n isotope composition of human burials and associated archaeofauna excavated from the site were measured for input into a concentration dependent isotope mixing model that is able to statistically discriminate among multiple o3 food sources the human burials segregate into two distinct groups an early w7000 bp and middle w4500 bp holocene population with significant dietary differences stable isotope analyses indicate a 70e84 marine food source contribution for the early holocene group ehg but only a 48e58 marine dietary contribution for the middle holocene group mhg results also suggest that pinnipeds were an important marine food source for both groups modeling results are in agreement with archaeological evidence from southern ca suggesting that early holocene coastal populations were highly dependent on marine resources with the ability to procure both littoral and pelagic species further the use of terrestrial plant sources likely increased over time with the feasible contribution range doubling from the ehg 4e30 mean 19 to mhg 10e52 mean 38 this trend is supported by regional archaeological evidence for the advent of technological innovations linked to intensive terrestrial plant processing beginning in the middle holocene methodologically this work demonstrated the utility of a concentration dependent stable isotope mixing model in an iterative framework to provide feasible ranges of dietary contribution when the number of food sources is too high to allow a unique solution 2004 published by elsevier ltd

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

millennial scale climate variability of the northeast pacific ocean and northwest north america based on radiolaria and pollen abstract radiolaria and pollen abundances in marine sediment cores from the northeast pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle 0 150 kyr these data allow direct comparison of the climate response of continental and oceanic systems detailed 18 o and ams 14 c measurements provide a link into global stratigraphic frameworks canonical correlation analysis extracts two modes of variation common to both the radiolaria and pollen records the first mode of variation correlates an assemblage of radiolaria associated with coastal upwelling with increased redwood western hemlock and alder pollen this association is consistent with the modern relationship between coastal upwelling coastal fog and redwood forests a second canonical mode relates an oceanic fauna now found in highest abundance in the far north pacific with reduced pine and western hemlock pollen abundance comparison of these records to an ice core 18 o record suggests that at wavelengths 3000 years warm events in greenland are correlated to intervals of increased coastal upwelling off oregon decreases in importance of very cold north pacific fauna suggesting warming and increases in pollen associated with wetter coastal environments radiolarian based sea surface temperature estimates suggest that the variability of the northeast pacific on this time scale is about 2 c warming in the coastal regions reflects reduced advection of the california current but is moderated by increases in cool coastal upwelling we infer that the response of the northeast pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid to high latitudes preliminary analysis suggests that oceanic variability off oregon at wavelengths 18 o records this variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements this finding suggests that unlike longer period millennial scale events the propagation of the shorter wavelength events to the northeast pacific is through subtropical or tropical teleconnections

devils hole nevada δ18o record extended to the mid holocene abstract the mid to late pleistocene devils hole 18 o record has been extended from 60 000 to 4500 yr ago the new 18 o time series in conjunction with the one previously published is shown to be a proxy of pacific ocean sea surface temperature sst off the coast of california during marine oxygen isotope stages mis 2 and 6 the devil hole and sst time series exhibit a steady warming that began 5000 to 10 000 yr prior to the last and penultimate deglaciations several possible proximate causes for this early warming are evaluated the magnitude of the peak 18 o or sst during the last interglacial lig is significantly greater 1 per mill and 2 to 3 c respectively than the peak value of these parameters for the holocene in contrast benthic 18 o records of ice volume show only a few tenths per mill difference in the peak value for these interglacials statistical analysis provides an estimate of the large shared information variation between the devils hole and eastern pacific sst time series from 41 to 2 n and enforces the concept of a common forcing among all of these records the extended devils hole record adds to evidence of the importance of uplands bordering the eastern pacific as a source of archives for reconstructing pacific climate variability

antarctic peninsula and south america patagonia paleogene terrestrial faunas and environments biogeographic relationships abstract the eocene of seymour island contains the only association of cenozoic plants and land vertebrates known from anywhere in antarctica and lies at about latitude 63 south the late early to latest eocene la meseta formation fills an incised valley and comprises sediments representing deltaic estuarine and very shallow marine environments the paleogene sequence in southern south america patagonia and the antarctic peninsula reveals floristically distinct periods late paleocene early and middle eocene and latest eocene based largely on leaf assemblages the late paleocene cross valley flora seymour island contains ferns and other elements suggesting a much warmer climate than at this latitude today the middle eocene fossil hill south shetland islands and the rio turbio santa cruz province southern patagonia floras have a mixture of both neotropical and antarctic elements the la meseta paleoflora is distinctive in having a predominance of antarctic taxa especially nothofagus podocarps and araucarian conifers in the eocene deciduous and evergreen forests this suggests a cooling trend during the eocene of antarctica with mid to late eocene seasonal cool temperate rainy climates and latitudinal and altitudinal gradients the seymour island la meseta fauna cucullaea allomember middle eocene contains at least 10 mammal taxa predominantly tiny marsupials mostly endemic and new taxa the endemism of these marsupials suggests the existence of some form of isolating barrier climatic and or geographic during the eocene faunal similarity between the la meseta fauna and the fauna assigned to the riochican late paleocene south american land mammal age of patagonia strongly suggests that the former derived from the latter the occurrence on seymour island of sudamericids that had become extinct in south america in the paleocene also indicates that isolation may have allowed extended survival of this gondwanan group in the eocene of antarctica and the factors that caused their extinction did not affect this continent global warming and intercontinental dispersal have been major influences on the timing and magnitude of terrestrial biotic change in the late paleocene and early eocene epochs the faunistic evidence indicates that the la meseta mammalian fauna derived from late paleocene early eocene riochican vacan faunas the dispersal and vicariance events may have occurred during the onset of the climatic optimum of the cenozoic late paleocene early eocene when major regressive events are recorded either in the northern antarctic peninsula and southernmost patagonia between 58 5 and 56 5 ma the absence of notoungulates in the la meseta fauna is noteworthy we speculate that the notoungulates could have passed into antarctica during the latest part of the paleocene when the environmental conditions were warmer and then became extinct at the onset of the climatic deterioration during the early eocene

the california current system during the last 136 000 years response of the north pacific high to precessional forcing abstract alkenone sea surface temperature sst records were generated from the ocean drilling program s odp sites 1014 and 1016 to examine the response of the california current system to global climate change during the last 136 ka the temperature differences between these sites sstnep sstodp1014 sstodp1016 reflected the intensity of the california current and varied between 0 4 and 6 1 c a high sstnep weaker california current was found for late marine isotope stage mis 2 and early mis 5e while a low sstnep stronger california current was detected for mid mis 5e and mis 1 spectral analysis indicated that this variation pattern dominated 23 precession and 30 ka periods comparison of the sstnep and sst based on data from core md01 2421 at the japan margin revealed anti phase variation the high sstnep weakening of the california current corresponded to the low sst at the japan margin the southward displacement of the nw pacific subarctic boundary and vice versa this variation was synchronous with a model prediction of the tropical el nino southern oscillation behavior these findings suggest that the intensity of the north pacific high varied in response to precessional forcing and also that the response has been linked with the changes of tropical ocean atmosphere interactions

water mass conversion in the glacial subarctic pacific 54 n 148 w physical constraints and the benthic planktonic stable isotope record benthic uvigerina spp cibicidoides spp gyroidinoides spp and planktonic n pachyderma sinistral g bulloides stable isotope records from three core sites in the central gulf of alaska are used to infer mixed layer and deepwater properties of the late glacial subarctic pacific glacial interglacial amplitudes of the planktonic 18o records are 1 1 1 3 less than half the amplitude observed at core sites at similar latitudes in the north atlantic these data imply that a strong negative w anomaly existed in the glacial subarctic mixed layer during the summer which points to a much stronger low salinity anomaly than exists today if true the upper water column in the north pacific would have been statically more stable than today thus suppressing convection even more efficiently this scenario is further supported by vertical i e planktic versus benthic 18o and 13c gradients of 1 which suggest that a thermohaline link between pacific deep waters and the subarctic pacific mixed layer did not exist during the late glacial epibenthic 13c in the subarctic pacific is more negative than at tropical subtropical pacific sites but similar to that recorded at southern ocean sites suggesting ventilation of the deep central pacific from mid latitude sources e g from the sea of japan and sea of okhotsk still convection to intermediate depths could have occurred in the subarctic during the winter months when heat loss to the atmosphere sea ice formation and wind driven upwelling of saline deep waters would have been most intense this would be beyond the grasp of our planktonic records which only document mixed layer temperature salinity fields extant during the warmer seasons also we do not have benthic isotope records from true intermediate water depths of the subarctic pacific

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

micropaleontology and palynology of core par87a 10 a 23 000 year record of paleoenvironmental changes in the gulf of alaska northeast north pacific micropaleontological data of core par87a 10 reveal that the last glacial interval prior to 13 ka was marked by low biogenic fluxes and poor caco3 preservation quantitative estimates of sea surface conditions based on dinocyst assemblages suggest that cold temperatures and freezing winter conditions existed during this period the glacial to interglacial transition i e the 13 8 ka interval was characterized by an increase in fluxes of microfossils indicating enhanced productivity in surface waters a higher biogenic carbonate production probably resulted in better preservation of caco3 this interval was marked by relatively low salinity and by sea surface temperatures increasing toward modern values relatively high pollen flux during the transition suggests nutrient inputs through atmospheric and or fluvial transport from the adjacent north american continent after 8 ka diminished fluxes of plankton concomitant with a decline in pollen input are associated with decreasing nutrient supply as predominantly eastward winds became established over the north pacific

middle pleistocene to holocene palynostratigraphy of ocean drilling program site 887 in the gulf of alaska northeastern north pacific a palynological investigation was undertaken on the upper 29 m of sediment at ocean drilling program odp site 887 spanning the last 430 000 years i e isotopic stages 12 to 1 pollen and dinocyst assemblages reveal a major ecostratigraphical boundary at the middle late pleistocene transition the middle pleistocene pollen data doc ument the occurrence of a spruce forest vegetation in the source area likely located on the adjacent alaskan coast whereas the late pleistocene is marked by higher inputs of pine shrub and herb taxa suggesting predominant inputs from a more open landscape the middle pleistocene is characterized by a low diversity in dinocyst assemblages which are dominated by operculodinium centrocarpum whereas the late pleistocene is marked by the significant oc currence of pentapharsodinium dalei pyxidinopsis reticulata and by high percentages of brigantedinium spp such as semblages suggest open oceanic and cool temperate conditions during the middle pleistocene changing toward generally colder and less saline conditions during the late pleistocene in addition large fluctuations in the dinocyst assemblages during the late pleistocene are recorded in phase with the main shifts in the isotopic stratigraphy a new dinocyst taxon spiniferites alaskensis sp nov exclusively recorded in sediments of the isotopic substage 5e is de scribed herein resume une analyse palynologique a ete realisee sur une sequence sedimentaire de 29 metres prelevee au site odp 887 et couvrant les derniers 430 000 ans soit les stades isotopiques 12 a 1 les assemblages de pollen et de dinokystes revelent une transition ecostratigraphique majeure entre le pleistocene moyen et le pleistocene superieur les assembla ges polliniques du pleistocene moyen indiquent la presence d une vegetation dominee par l epinette et l aulne dans la region source qui etait sans doute localisee le long des cotes de l alaska de forts pourcentages de pin et des taxons arbustifs et herbaces au pleistocene superieur indiquent des apports issus d un paysage plus ouvert le pleistocene moyen est caracterise par une faible diversite dans les assemblages de dinokystes et par la dominance de operculodi nium centrocarpum tandis que le pleistocene superieur est marque par pentapharsodinium dalei pyxidinopsis reticulata et des pourcentages eleves de brigantedinium spp les assemblages suggerent des conditions oceaniques temperees fraiches pendant le pleistocene moyen et des eaux de surface plus froides et moins salines au cours du pleistocene su perieur par ailleurs de larges fluctuations sont enregistrees dans les assemblages de dinokystes au pleistocene supe rieur en phase avec la stratigraphie isotopique parmi les dinokystes une nouvelle espece spiniferites alaskensis sp nov observee exclusivement pendant le sous stade isotopique 5e est decrite ici marret et al 386

late quaternary sea level change in southern beringia postglacial emergence of the western alaska peninsula abstract postglacial sea level trends have varied dramatically across the bering platform because of differences in coastal and shelf geologic settings emergent shorelines and basal peats along the western alaska peninsula indicate that relative sea level has fallen since regional deglaciation occurred ca 13 000 cal yr bp age elevation determinations on four shorelines 25 m 10 ka 16 m 9 6 6 ka 6 m 2 1 ka and 2 3 m 1 8 0 6 ka in the vicinity of cold and morzhovoi bays provide an estimate of the pace and timing of of sea level change since the last glacial maximum lgm 22 17 ka isostatic recovery and shoreline regression following the disintegration of continental and alpine ice has been interrupted by transgressive conditions at least twice since deglaciation changes in the balance between eustatic sea level rise and isostatic uplift resulted in the reactivation of marine scarps during the early to middle holocene but terrace cutting and a gap in the archaeological record about 2 1 ka suggest that sudden tectonic displacements also influence the record reconstructions of coastal paleogeography constrain the timing and distribution of regional archaeological settlement periods of shoreline erosion during stillstands or transgressions and the episodic reorganization of intertidal environments that accompanies tectonic displacements have conditioned site preservation potential and long term adaptive strategies

sediment geochemical records of productivity and oxygen depletion along the margin of western north america during the past 60 000 years teleconnections with greenland ice and the cariaco basin abstract many sediment records from the margins of the californias alta and baja collected in water depths between 60 and 1200 m contain anoxic intervals laminated sediments that can be correlated with interstadial intervals as defined by the oxygen isotope composition of greenland ice dansgaard oeschger d o cycles these intervals include all or parts of oxygen isotope stage 3 ois3 60 24 cal ka the bolling allerod warm interval b a 15 13 cal ka and the holocene this study uses organic carbon corg and trace element proxies for anoxia and productivity namely elevated concentrations and accumulation rates of molybdenum and cadmium in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom water oxygen bwo conditions on open highly productive continental margins the main conclusion from these proxies is that during the last glacial interval lgi 24 15 cal ka and the younger dryas cold interval yd 13 11 6 cal ka productivity was lower and bwo levels were higher than during ois3 the b a and the holocene on all margins of the californias the corg and trace element profiles in the lgi b a holocene transition in the cariaco basin on the margin of northern venezuela are remarkably similar to those in the transition on the northern california margin correlation between d o cycles in greenland ice with gray scale measurements in varved sediments in the cariaco basin also is well established synchronous climate driven changes as recorded in the sediments on the margins of the californias sediments from the cariaco basin and in the gisp 2 greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka millennial scale cycles in productivity and oxygen depletion on the margins of the californias demonstrate that the california current system was poised at a threshold whereby perturbations of atmospheric circulation produced rapid changes in circulation in the eastern north pacific ocean it is likely that the pacific and atlantic oceans were linked through the atmosphere warmer air temperatures during interstadials would have strengthened hadley and walker circulations which in turn would have strengthened the subtropical high pressure systems in both the north pacific and the north atlantic producing increased rainfall over the cariaco basin and increased upwelling along the margins of the californias

effects of late neogene climatic cooling on north pacific radiolarian assemblages and oceanographic conditions abstract radiolarian census and abundance data were collected from three deep sea cores drilled by the ocean drilling program sites 884 887 and 1151 to investigate patterns of ecologic changes in space and time during the last 16 million years for the mid latitude to subarctic north pacific high concentrations of radiolarians occurred between 9 0 and 2 7 ma radiolarian species richness was highest in the early middle miocene at each site and gradually decreased up to about 7 ma coinciding with a well established global cooling trend a degree of overlap index calculated for radiolarian assemblages revealed 11 faunal change events of which 8 corresponded to global cooling events and expansions of polar ice sheets three of the faunal change events were observed within the peak of radiolarian accumulation rate and were ascribed to changes in primary productivity in the north pacific rather than global climatic changes our assemblage analyses revealed that north south differentiation in radiolarian assemblages in the northwestern pacific has existed since 16 ma and became more distinct via major steps at 6 8 ma and 2 7 ma coinciding with major glaciation events and that east west faunal contrasts in the subarctic region became obvious beginning at 11 7 ma and changed to a different mode around 6 8 ma the observed east west faunal differences possibly reflect east to west climate differences that were characterized by cooler temperatures in the east than the west during the late miocene 11 7 6 8 ma and then by the opposite temperature trend 6 8 ma recent a severe glaciation at 2 7 ma played a large role particularly in temporal changes in radiolarian accumulation rate and assemblage composition

intensification of the oxygen minimum zone in the northeast pacific off vancouver island during the last deglaciation ventilation and or export production 1 the oxygen minimum zone omz off vancouver island was more oxygen depleted relative to modern conditions during the allerod 13 5 to 12 6 calendar kyr and again from 11 to 10 kyr the timing of omz intensification is similar to that seen throughout the north pacific although the onset appears to have been delayed by 1500 years off vancouver island radiocarbon dating of coeval benthic and planktonic foraminifera shows that between 16 0 and 12 6 kyr the age contrast between surface and intermediate waters 920 m depth off vancouver island was similar to or slightly less than that today there is no evidence of an increased age difference i e decreased ventilation during the deglaciation particularly during the allerod however sedimentary marine organic carbon concentration and mass accumulation rate increased substantially in the allerod suggesting that increased organic matter export was the principal cause of late pleistocene omz intensification off vancouver island

stable isotope and minor element proxies for eocene climate of seymour island antarctica 1 abundant and well preserved marine macrofossils on seymour island antarctica provide a valuable resource to establish paleoenvironmental conditions at high southern latitudes during the warm paleogene stable isotope minor element and 8 7 sr 8 6 sr compositions have been measured for the aragonite bivalve cucullaea from the eocene la meseta formation the 8 7 sr 8 6 sr stratigraphy suggests an early to late eocene age for the la meseta formation sea surface temperature estimates based on 1 8 o values range from 14 5 to 15 5 c in the early and middle eocene to 10 5 c in the late eocene high resolution sampling along growth structures provides estimates of seasonality in temperature which decrease considerably up section to address the relative contribution of temperature and ice volume or salinity to the 1 8 o record sr ca was measured and evaluated as a potential independent paleothermometer for cucullaea

timing and extent of allerod and younger dryas age ca 12 500 10 000 14c yr b p oscillations of the cordilleran ice sheet in the fraser lowland western north america the use of shaded digital topographic models to visualizes suites of topographic features stratigraphy and field mapping reveals newly recognized multiple moraines associated with oscillations of the remnants of the cordilleran ice sheet in the fraser lowland along the western washington british columbia border morphologic features show the extent of ice represented by sumas drift ca 11 600 10 000 14c yr b p following ca 3000 yr of retreat from the glacial maximum fraser glaciation positions 80 km south of seattle and in the strait of juan de fuca the paleogeography of the ice margin and timing of ice retreat during the sumas stade is reconstructed and bracketed by 70 radiocarbon dates 24 on marine shells 46 on wood and peat which are secured by morphologic and stratigraphic evidence four topographically distinct phases of the sumas deglaciation model are suggested phase si 11 600 11 400 14c yr b p outermost drift scattered remnants of ice contact deposits phase sii 11 600 11 400 14c yr b p glacier readvance building prominent moraine followed by glacier retreat phase siii 10 980 10 250 14c yr b p glacier readvance building of multiple moraines followed by glacier retreat phase siv 10 250 10 000 14c yr b p glacier readvance building of inner moraine followed by glacier retreat

early retreat of the alaska peninsula glacier complex and the implications for coastal migrations of first americans abstract the debate over a coastal migration route for the first americans revolves around two major points seafaring technology and a viable landscape and resource base three lake cores from sanak island in the western gulf of alaska yield the first radiocarbon ages from the continental shelf of the northeast pacific and record deglaciation nearly 17 ka bp thousands of calendar years ago much earlier than previous estimates based on extrapolated data from other sites outside the coastal corridor in the gulf of alaska pollen data suggest an arid terrestrial ecosystem by 16 3 ka bp therefore glaciers would not have hindered the movement of humans along the southern edge of the bering land bridge for two millennia before the first well recognized new world archaeological sites were inhabited

tyrrhenian holocene palaeoclimate trends from spelean serpulids abstract in tropical regions changes in sea level and sea surface temperature sst can be obtained from coral reefs in temperate seas such as the mediterranean where there are neither fossil nor actively growing coral reefs palaeoclimatic trends and associated sea level rise can be reconstructed through radiocarbon ages and the geochemical properties of serpulid calcite tubes from colonies that dwell in submerged caves in the present work we reconstructed holocene palaeoclimate trends for the tyrrhenian sea through the oxygen isotopic composition of marine polychaete serpulids that colonised continental speleothems when the sea invaded the caves which open along the italian coast the long term 18 o trend extracted from multiple serpulid skeletons of 0 7 per mil increase over the last 8 kyr can be interpreted in terms of temperature change but could also be due to long term changes in the salinity balance of the mediterranean if the 18 o trends recorded by serpulid calcite reflected changes in mediterranean sst starting at 8200 cal yr bp it would coincide with the cooling trend recorded in the tropics and in greenland ice cores spelean serpulids radiocarbon ages allowed us to reconstruct a tyrrhenian sea level curve comparable to that recorded along the french mediterranean coast spelean serpulid calcite therefore can be used as a useful tool to reconstruct paleoclimate and sea level changes in temperate coastal karst regions

organic carbon accumulation over the last 16 kyr off vancouver island canada evidence for increased marine productivity during the deglacial abstract the organic carbon content of marine sediments is commonly used as a proxy for export production however in continental margin sediments a large fraction of the organic matter may be of terrestrial origin and it is necessary to correct the total organic carbon data accordingly radiocarbon dating of bulk organic carbon organic geochemistry and isotope data 13c and 15n are used here to characterize the type of organic matter present in core jt96 09 collected at a water depth of 920 m on the slope off western canada the quantities of marine and terrestrial organic carbon are then estimated using the 13c data the 16 kyr record obtained from core jt96 09 suggests that accumulation of total organic carbon was highest during the late glacial and deglacial but geochemical data indicate that as much as 70 of this carbon is terrestrial in origin when the palaeo record is corrected for this terrigenous input it is observed that accumulation of marine organic matter and presumably marine export production increased at the end of the last glacial contemporaneous with the bolling and that it peaked during the allerod data from other palaeoproductivity proxies i e bio barium opal and alkenones also indicate relatively high productivity during the deglacial these results indicate a return to modern upwelling conditions and high marine export production at 14 3 calendar kyr bp and a period of enhanced upwelling relative to the present during the allerod

radiolaria and pollen records from 0 to 50 ka at odp site 1233 continental and marine climate records from the southeast pacific abstract site 1233 drilled during leg 202 of the ocean drilling program provides a detailed record of marine and continental climate change in the southeast pacific and south american continent splits from over 500 samples taken at 20 cm intervals for quantitative analysis of radiolarian and pollen populations yield a temporal resolution of 200 400 years in each sample 39 pollen taxa and 40 radiolarian species and genera were evaluated age control is provided by 25 ams 14c dates lamy f kaiser j ninnemann u hebbeln d arz h w stoner j 2004 science 304 1959 1962 multivariate statistical analyses of these data allow us to conclude the following 1 during the past 50 ka the region of the central chile coast is not directly influenced by polar water from the antarctic region 2 changes in ocean conditions off central chile during this time interval primarily reflect north south shifts in the position of the south pacific transition zone 3 changes in chilean vegetation reflect comparable latitudinal shifts in precipitation and the position of the southern westerlies 4 the first canonical variate of radiolarian and pollen records extracted from site 1233 are remarkably similar to each other as well as to temperature records from the antarctic which suggests that marine and continental climate variability in the region is tightly coupled at periods longer than 3000 years 5 the phase coupling of these climate records which lead variations of continental erosion based on iron abundance at the same site are consistent with a hypothesis that erosion is linked to relatively long i e few thousand years response times of the patagonian ice sheet and thus is not a direct indicator of regional climate

assessment of sea surface temperature at 42 n in the california current over the last 30 000 years assessment of changes in surface ocean conditions in particular sea surface temperature sst is essential to understand long term changes in climate especially in regions where continental climate is strongly influenced by oceanographic processes to evaluate changes in sst in the northeast pacific we have analyzed long chain alkenones of prymnesiophyte origin at 38 depths in a piston and associated trigger core collected beneath the contemporary core of the california current system at 42 n 270 km off the coast of oregon california the samples span 30 000 years of deposition at this location unsaturation patterns u37k in the alkenone series display a statistically significant difference p 0 001 between interglacial 0 44 0 02 n 11 and glacial 0 29 0 04 n 20 intervals of the cores detailed examination of other compositional features of the c37 c38 c39 alkenone series and a related c36 alkenoate series measured downcore suggests the published u37k temperature calibration u37k 0 034 t 0 039 defined for cultures of a strain of emiliania huxleyi isolated from the subarctic pacific provides best estimates of winter sst at our study site this inference is purely statistical and does not imply however that the phytoplankton source of these biomarkers is most productive in winter or at the ocean surface the temperature record for u37k implies 1 an 4 c shift occurred in winter sst from 7 5 1 1 c at the last glacial maximum to 11 7 0 7 c in the present interglacial period and 2 this warming trend was confined to the time frame 14 10 ka within the glacial to interglacial transition period these conclusions are corroborated entirely by results from an independent sst transformation of radiolarian species assemblage data obtained from the same core materials

ages and inferred causes of late pleistocene glaciations on mauna kea hawai i glacial landforms on mauna kea hawai i show that the summit area of the volcano was covered intermittently by ice caps during the late pleistocene cosmogenic 36 cl dating of terminal moraines and other glacial landforms indicates that the last two ice caps called older makanaka and younger makanaka retreated from their maximum positions approximately 23 ka and 13 ka respectively the margins and equilibrium line altitudes of these ice caps on the remote tropical pacific island were nearly identical which would seem to imply the same mechanism for ice growth but modelling of glacier mass balance combined with palaeotemperature proxy data from the subtropical north pacific suggests that the causes of the two glacial expansions may have been different older makanaka air atop mauna kea was likely wetter than today and cold whereas younger makanaka times were slightly warmer but significantly wetter than the previous glaciation the modelled increase in precipitation rates atop mauna kea during the late pleistocene is consistent with that near sea level inferred from pollen data which suggests that the additional precipitation was due to more frequent and or intense tropical storms associated with eastward moving cold fronts these conditions were similar to modern la nina weak enso conditions but persisted for millennia rather than years increased precipitation rates and the resulting steeper temperature lapse rates created glacial conditions atop mauna kea in the absence of sufficient cooling at sea level suggesting that if similar correlations existed elsewhere in the tropics the precipitation dependent lapse rates could reconcile the apparent difference between glacial time cooling of the tropics at low and high altitudes copyright 2008 john wiley sons ltd

sea level paleogeography and archeology on california s northern channel islands abstract sea level rise during the late pleistocene and early holocene inundated nearshore areas in many parts of the world producing drastic changes in local ecosystems and obscuring significant portions of the archeological record although global forces are at play the effects of sea level rise are highly localized due to variability in glacial isostatic adjustment gia effects interpretations of coastal paleoecology and archeology require reliable estimates of ancient shorelines that account for gia effects here we build on previous models for california s northern channel islands producing more accurate late pleistocene and holocene paleogeographic reconstructions adjusted for regional gia variability this region has contributed significantly to our understanding of early new world coastal foragers sea level that was about 80 85 m lower than present at the time of the first known human occupation brought about a landscape and ecology substantially different than today during the late pleistocene large tracts of coastal lowlands were exposed while a colder wetter climate and fluctuating marine conditions interacted with rapidly evolving littoral environments at the close of the pleistocene and start of the holocene people in coastal california faced shrinking land intertidal and subtidal zones with important implications for resource availability and distribution

paleoceanographic changes on the farallon escarpment off central california during the last 16 000 years abstract new benthic and planktic foraminiferal assemblage census data and benthic foraminiferal oxygen index bfoi values previously published marine climate proxy data stable isotopes and ca cd and unpublished results of total carbon organic carbon and calcium carbonate analyses of sediments recovered off central california on the farallon escarpment 1605 m water depth 37 13 4 n 123 14 6 w core f 8 90 g21 document paleoceanographic changes during the latest quaternary which reflect the intensity and source of north pacific intermediate water npiw and surface productivity accelerator mass spectrometry radiocarbon dates of both benthic and planktic species provide an excellent age depth model for the last 16 000 years covering the latest glacial bolling allerod younger dryas and early middle and late holocene intervals a q mode cluster analysis separated the benthic fauna into three clusters one pleistocene and two holocene whereas the planktic fauna was divided only into pleistocene and holocene clusters stable oxygen isotope values show an increase in water temperature of 1 c from the late glacial to late holocene and a change in faunal composition of the planktic assemblage implies surface waters warmed as well a general trend of decreasing dissolved oxygen concentration from the pleistocene high oxic 3 0 6 0 ml l o2 to the holocene low oxic 1 5 3 0 ml l o2 suggested by the bfoi and cd ca data reflect decreased ventilation as the source of the npiw shifted from the sea of okhotsk to the tropical east pacific at 11 000 cal bp the middle holocene cooling reported in other central and northern california margin studies is not apparent in f 8 90 g21 which compares more favorably with studies from southern california and british columbia total carbon and organic carbon values are highest in the bolling allerod early holocene and late holocene similarly calcium carbonate values are high in the bolling allerod and peak in the early holocene but decrease significantly in the latest middle and late holocene which coincides with a depauparate planktic foraminiferal fauna in the upper 60 cm 70000 0 cal bp of the core and poor preservation of the benthic foraminiferal fauna at 40 cm 3000 cal bp decoupling is evident between the planktic and benthic faunal response to changing climatic conditions with the surface dwelling assemblage often leading the bottom dwelling assemblage by several millennia

a framework for interpreting paleoclimatic variations in eastern beringia abstract paleoclimatic variations in a particular region can be viewed as the outcome of the superimposition of the effects of a number of large scale controls a framework for understanding paleoclimatic variations in a region can be established by considering the long term history of those controls jointly with climatic modeling results that illustrate how regional climates respond to changes of individual controls the relevant controls of late quaternary paleoclimatic variations in eastern beringia include 1 the size of the ice sheet which influences both atmospheric circulation and temperature 2 insolation which influences mainly temperature and seasonality 3 carbon dioxide concentration in the atmosphere which influences temperature and 4 feedbacks involving sea ice sea surface temperatures and snow cover which reinforce the insolation effects we review the results of a number of paleoclimatic experiments with general circulation models to illustrate the potential response of eastern beringia to the variations of these controls we then present a framework for understanding paleoclimatic variations in eastern beringia by describing the likely responses of the climate of this region to the known variations in the controls in addition we discuss key times during the quaternary when particular combinations of the controls give rise to natural experiments which lend themselves to the testing of particular hypotheses our understanding of the nature of climatic variations at high latitudes should increase through examination of paleoclimatic evidence that documents the response of the region at those key times

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

paleodeviations of radiocarbon marine reservoir values for the northeast pacific differences in the radiocarbon ages of coeval marine shells and wood from emergent glaciomarine sediments in the fraser lowland of southwestern british columbia and northwest washington indicate that a total marine radiocarbon reservoir value of 1 1 1 k y is applicable in the region this is 40 greater 300 yr than the 800 yr value currently used to correct the ages of both modern and late pleistocene marine shells from this area the glaciomarine sediments were deposited rapidly between ca 12 5 and 11 5 1 4 c k y b p paleodeviations of the marine reservoir value may illustrate that rapid environmental changes occurred during the last glacial to interglacial transition these variations are thought to have been caused by changes in both deep and surface ocean circulation and by variations in the production of atmospheric radiocarbon 1 4 c these findings may indicate a rapid reordering of oceanic atmospheric circulation in the region

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

glacial lake evolution in the southeastern tibetan plateau and the cause of rapid expansion of proglacial lakes linked to glacial hydrogeomorphic processes abstract glacial lakes as an important component of the cryosphere in the southeastern tibetan plateau setp in response to climate change pose significant threats to the downstream lives and properties of people engineering construction and ecological environment via outburst floods yet we currently have limited knowledge of their distribution evolution and the driving mechanism of rapid expansions due to the low accessibility and harsh natural conditions by integrating optical imagery satellite altimetry and digital elevation model dem this study presents a regional scale investigation of glacial lake dynamics across two river basins of the setp during 1988 2013 and further explores the glacial hydrogeomorphic process of rapidly expanding lakes in total 1278 and 1396 glacial lakes were inventoried in 1988 and 2013 respectively approximately 92 4 of the lakes in 2013 are not in contact with modern glaciers and the remaining 7 6 includes 27 1 9 debris contact lakes in contact with debris covered ice and 80 5 7 cirque lakes in categorizing lake variations we found that debris contact proglacial lakes experienced much more rapid expansions 75 than cirque lakes 7 and non glacier contact lakes 3 to explore the cause of rapid expansion for these debris contact lakes we further investigated the mass balance of parent glaciers and elevation changes in lake surfaces and debris covered glacier tongues using time series landsat images icesat altimetry and dem results reveal that the upstream expansion of debris contact proglacial lakes was not directly associated with rising water levels but with a geomorphological alternation of upstream lake basins caused by melting induced debris subsidence at glacier termini this suggests that the hydrogeomorphic process of glacier thinning and retreat in comparison with direct glacial meltwater alone may have played a dominant role in the recent glacial lake expansion observed across the setp our findings assist in understanding the expansion mechanism of debris contact proglacial lakes which facilitates early recognition of potential glacial lake hazards in this region

a late quaternary pollen record from ka au crater o ahu hawai i abstract a pollen record from ka au crater o ahu hawai i contains evidence for changes in vegetation and climate since about 28 000 14c yr b p zone 1 ca 28 100 ca 22 800 14c yr b p has pollen of dry to mesic forest species including pipturus type dodonaea viscosa acacia koa chenopodium oahuense claoxylon sandwicense myrsine and metrosideros type in zone 2 ca 22 800 ca 16 200 14c yr b p myrsine and coprosma increase with herbs fern allies and grammitidaceae suggesting open canopies zone 3 ca 16 200 ca 9700 14c yr b p has pollen of wet forest species including freycinetia arborea abundant pritchardia and metrosideros type zone 4 ca 9700 ca 7000 14c yr b p is similar with less pritchardia and more metrosideros type climate reconstruction was based on modern climatic ranges of flowering plants and an index derived from abundance of pollen in surface samples both methods agree on a qualitative reconstruction although the ages are poorly constrained 28 000 25 000 14c yr b p cool and dry 25 000 23 000 14c yr b p dry and warmer 23 000 20 000 14c yr b p moderately dry with declining temperature 20 000 16 000 14c yr b p moderately dry and cool 16 000 9000 14c yr b p warm and wet 9000 7000 14c yr b p warm and possibly drier lower precipitation at ka au crater during the late glacial period and last glacial maximum is consistent with the interpretation that the north pacific subtropical anticyclone was south of its present position the pollen derived temperature index yields an estimate of 3 5 c temperature depression during the last glacial maximum

orbital suppression of wind driven upwelling in the california current at 6 ka 1 marine records clearly show activity in the california current cc system to have been altered during the mid holocene however the specific nature of cc activity during this period remains ambiguous as proxies that suggest cooler than present sea surface temperatures co occur in mid holocene marine sediments with multiple proxies that suggest decreased coastal upwelling to test the sensitivity of wind driven upwelling in the cc to mid holocene orbital forcing we have employed a high resolution regional climate model rcm the seasonality of modern cc wind driven coastal upwelling simulated by the rcm is in strong agreement with observational data further we show that changes in the seasonality of solar insolation induced by mid holocene milankovitch forcing decrease early and peak season coastal upwelling in the cc along with increasing late season coastal upwelling these results are in agreement with several marine and terrestrial proxies suggesting that relative to present cc activity during the mid holocene was characterized by a longer and less vigorous upwelling season with decreased seasonal contrast

younger dryas environments and human adaptations on the west coast of the united states and baja california on the pacific coast of the united states and baja california the younger dryas was one component of dynamic late pleistocene and holocene environmental changes changing climate sea level rise and shifting shorelines created ecological challenges for ancient coastal peoples and daunting challenges for archaeologists searching for early coastal sites this paper reviews the evidence for ecological change in this west coast region including shoreline changes that may have submerged or destroyed archaeological sites from this time period examining the regional record of human occupation dating to the younger dryas well dated coastal sites are limited to california s northern channel islands and isla cedros off baja california a small number of fluted points found in coastal areas may also date to the younger dryas but their context and chronology is not well defined review of the implications of these two data sets considers whether the early but discontinuous younger dryas archaeological record from the west coast might result from a migration of maritime peoples from northeast asia into the americas

sea surface temperature changes in the northeastern pacific ocean during the past 20 000 years and their relationship to climate change in northwestern north america abstract modern ocean atmosphere interactions in the northeastern pacific ocean have a significant effect on the climate of the west coast of north america we present radiolarian microfossil based temperature reconstructions for the eastern north pacific spanning the past 20 000 yr to examine possible correlations and linkages between continental climate change and changes in sea surface temperature sst in the northeastern pacific ocean on millennial time scales the reconstructions indicate that the regional pattern of ocean circulation off the west coast of north america was further south 15 000 cal yr b p than it is today and reached its present location 13 000 cal yr b p the north pacific drift and transition zone were further south as a result of a more southerly north pacific high pressure cell prior to 13 000 cal yr b p while two continental paleoclimate records from northwestern north america show regional differences they also can be correlated to the sst changes a coastal site at 48 n shows similar patterns in summer temperatures as observed in offshore marine records of ssts however an inland continental record seems to reflect more regional scale changes in sea surface conditions showing a thermal maximum centered at 10 000 cal yr b p which is observed in the marine transect south of 42 n we conclude based on the pattern of oceanographic change as reflected in radiolarian assemblages that changes in the past latitudinal position of the north pacific drift played a significant role in controlling continental climate immediately to its east as it does in the present environment we also conclude that during the past 20 000 yr much of the evolution of oceanographic change is related to the migration of the atmospheric pressure cells the north pacific high and aleutian low of the northeastern pacific

radiolarian based transfer functions for estimating mean surface ocean temperatures and seasonal range new radiolarian based transfer functions to estimate sea surface temperature sst and seasonal range are presented the transfer fonctions are based on the approach originated by imbrie and kipp 1971 the transfer functions differ from previous studies in the following three important ways 1 extensions to q mode factor analysis provide an objective method to cull species in the very diverse radiolarian population 2 a log transform of the relative abundance data is used to normalize the species percent data and 3 rather than writing equations for specific seasons which are not independent data sets statistically independent equations are developed to predict mean annual sea surface temperatures as well as seasonal temperature range one hundred and seventy surface sediment samples from the pacific ocean are used to generate the sst and season temperature range transfer functions all samples were counted using a standardized radiolarian taxonomy forty one radiolarian species were used in the final regression equation q mode factor analysis of this data set identified seven assemblages these assemblages the tropical transitional antarctic bering sea western pacific central gyre and eastern boundary current are named for the oceanographic regions where these assemblages are important the seven assemblages are used in a regression analysis to predict sst and seasonal temperature range the standard error of estimates for both mean sst and seasonal temperature range is 1 6 c comparison between radiolarian based ssts and sst estimates from alkenone uk37 in a 20 000 year long record from the northeast pacific shows excellent agreement comparison of mean sst estimates for the last glacial maximum lgm based on radiolarian and foraminifera in 10 eastern equatorial pacific also show excellent concordance these new lgm estimates suggest that the original climate long range investigation mapping and prediction climap reconstruction for this region underestimated surface ocean cooling

deglacial subarctic pacific surface water hydrography and nutrient dynamics and links to north atlantic climate variability and atmospheric co2 the glacial to holocene evolution of subarctic pacific surface water stratification and silicic acid si dynamics is investigated based on new combined diatom oxygen 18odiat and silicon 30sidiat isotope records along with new biogenic opal subsurface foraminiferal 18o alkenone based sea surface temperature sea ice diatom and core logging data from the ne pacific our results suggest that 18odiat values are primarily influenced by changes in freshwater discharge from the cordilleran ice sheet cis while corresponding 30sidiat are primarily influenced by changes in si supply to surface waters our data indicate enhanced glacial to mid heinrich stadial 1 hs1 ne pacific surface water stratification generally limiting the si supply to surface waters however we suggest that an increase in si supply during early hs1 when surface waters were still stratified is linked to increased north pacific intermediate water formation the coincidence between fresh surface waters during hs1 and enhanced ice rafted debris sedimentation in the north atlantic indicates a close link between cis and laurentide ice sheet dynamics and a dominant atmospheric control on cis deglaciation the bolling allerod b a is characterized by destratification in the subarctic pacific and an increased supply of saline si rich waters to surface waters this change toward increased convection occurred prior to the bolling warming and is likely triggered by a switch to sea ice free conditions during late hs1 our results furthermore indicate a decreased efficiency of the biological pump during late hs1 and the b a possibly also the younger dryas suggesting that the subarctic pacific has then been a source region of atmospheric co2

sea surface temperatures in the subarctic northeast pacific reflect millennial scale climate oscillations during the last 16 kyrs changes of sea surface temperature sst in the subarctic ne pacific over the last 16 000 calendar years before present 16 kyr bp have been inferred from the study of c 37 alkenone unsaturation in a sediment core from the western canadian continental slope between 16 0 and 11 0 kyr three distinct cold phases 6 7 c interrupt two warmer periods 9 10 c within the 2 range of the radiocarbon based time control the observed sst oscillations correspond to the oldest dryas the bolling the older dryas the allerod and the younger dryas periods in the gisp2 18 o record these results represent the first high resolution marine paleotemperature estimates off the northern west coast of north america and imply that the climate of this region may be very strongly coupled to that of the north atlantic given the fast rates of sst change 1 c 40 80 yr such coupling must be controlled by atmospheric transmission of the climate signal

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

quaternary surface water temperature estimations calibration of a diatom transfer function for the southern ocean the quantitative diatom analysis of 218 surface sediment samples recovered in the atlantic and western indian sector of the southern ocean is used to define a base of reference data for paleotemperature estimations from diatom assemblages using the imbrie and kipp transfer function method the criteria which justify the exclusion of samples and species out of the raw data set in order to define a reference database are outlined and discussed sensitivity tests with eight data sets were achieved evaluating the effects of overall dominance of single species different methods of species abundance ranking and no analog conditions e g eucampia antarctica on the estimated paleotemperatures the defined transfer functions were applied on a sediment core from the northern antarctic zone overall dominance of fragilariopsis kerguelensis in the diatom assemblages resulted in a close affinity between paleotemperature curve and relative abundance pattern of this species downcore logarithmic conversion of counting data applied with other ranking methods in order to compensate the dominance of f kerguelensis revealed the best statistical results a reliable diatom transfer function for future paleotemperature estimations is presented

development of the california current during the past 12 000 yr based on diatoms and silicoflagellates detailed diatom and silicoflagellates records in three cores from the offshore region of southern oregon to central california reveal the evolution of the northern part of the california current during the past 12 000 yr the early holocene prior to 9 ka was characterizedbyrelativelywarmseasurfacetemperatures sst owingtoenhancednortherlyflowofthesubtropicalwaterscomparable tothemoderndavidsoncurrent progressivestrengtheningof thenorthpacifichighleadtointensificationofthesouthwardflowofthe california current at 8 ka resulting in increased coastal upwelling and relatively cooler sst which persisted until 5 ka reduced southward flow of the california current between 4 8 ka and 3 6 ka may have been responsible for a period of decreased upwelling modern seasonal oceanographic cycles as evidenced by increased spring early summer coastal upwelling and warming of early fall sst evolved between 3 5 and 3 2 ka widespread occurrence of paleoceanographic and paleoclimatic change between 3 5 3 0 ka along the eastern margins of the north pacific was likely a response to increasing enso variability in the tropical pacific published by elsevier b v

tropical forcing of north pacific intermediate water distribution during late quaternary rapid climate change abstract evidence is presented demonstrating intermediate water 500 m temperature variability at odp hole 893a in santa barbara basin during submillennial climate change 11 60 ka benthic 18 o oscillations are considered to result primarily from shifts in intermediate water temperature at the site detailed comparison of both benthic and planktonic records from the basin provide crucial evidence for differing surface and intermediate water mass temporal responses to rapid climate change gradual warming of intermediate water compared to abrupt cooling suggests mechanistic differences between processes controlling north pacific intermediate water expansion and contraction relative to southern component intermediate waters comparisons suggest intermediate water warming preceded by 60 200 years the most rapid interval of surface warming inferred to be associated with north pacific atmospheric reorganization tropical forcing of sea level anomalies in the eastern pacific via trade wind strength may control california undercurrent flow 300 500 m and be the cause of early intermediate water warming in santa barbara basin

radiolarian assemblages in surface sediments along longitude 175 e in the pacific ocean abstract this study of 24 surface sediment samples along longitude 175 e between latitudes 48 n and 14 s in the western pacific ocean documents the relationship between the modern distribution of radiolarian assemblages and present oceanographic conditions ninety two species were classified into eight clusters by using r mode cluster analysis q mode cluster analysis was used to distinguish five geographical zones which were interpreted to represent the tropical southern subtropical northern subtropical transitional and subarctic climatic zones species richness diversity and equitability are highest in the tropical and transitional zones we attempted to formulate new regression equations considering ecological information on the vertical distribution of radiolarian species transfer functions were derived from regression analysis of radiolarian assemblages to observed sea surface temperature sst values the transfer functions have a standard error of 1 16 c in the estimate of winter sst 0 81 c in that of summer sst

the california current of the last glacial maximum reconstruction at 42 n based on multiple proxies multiple paleoceanographic proxies in a zonal transect across the california current near 42 n record modern and last glacial maximum lgm thermal and nutrient gradients the offshore thermal gradient derived from foraminiferal species assemblages and oxygen isotope data was similar at the lgm to that at present warmer offshore but average temperatures were 3 3 1 5 c colder observed gradients require that the sites remained under the southward flow of the california current and thus that the polar front remained north of 42 n during the lgm carbon isotopic and foraminiferal flux data suggests enhanced nutrients and productivity of foraminfera in the northern california current up to 650 km offshore in contrast marine organic carbon and coastal diatom burial rates decreased during the lgm these seemingly contradictory results are reconciled by model simulations of the lgm wind field which suggest that wind stress curl at 42 n and thus open ocean upwelling increased while offshore ekman transport and thus coastal upwelling decreased during the last ice age the ecosystem of the northern california current during the lgm approximated that of the modern gulf of alaska cooling and production in this region was thus driven by stronger open ocean upwelling and or southward flow of high latitude water masses rather than by coastal upwelling

radiolarian based sea surface temperatures and paleoceanographic changes during the late pleistocene holocene in the subantarctic southwest pacific abstract a high resolution record of radiolarian faunal changes from site y8 south of the subtropical front stf offshore eastern new zealand provides insight into the paleoceanographic history of the last 265 kyrs quantitative analysis of radiolarian paleotemperature indicators and radiolarian based sea surface temperature sst estimates reveal distinct shifts during glacial interglacial g i climate cycles encompassing marine isotope stages mis 8 1 faunas at site y8 are abundant and diverse and consist of a mixture of species typical of the subantarctic transitional and subtropical zones which is characteristic of subantarctic waters just south of the stf during interglacials diverse radiolarian faunas have increased numbers of warm water taxa 15 while cool water taxa decrease to 11 of the assemblage warmest climate conditions occurred during mis 5 5 and the early holocene climatic optimum hco at the onset of mis 1 where ssts reach maxima of 12 8 and 12 9 c respectively this suggests that temperatures during the hco were comparable to the eemian one of the warmest interglacial intervals of the late quaternary glacials are characterized by less diverse radiolarian faunas with cool water taxa increasing to 49 of the assemblage coolest climate conditions occurred in mis 4 and 2 where ssts are reduced to 5 4 c and 4 3 c respectively radiolarian faunal changes and sst estimates clearly identify major water masses and oceanic fronts in the offshore eastern new zealand area during warmest mis 5 5 and early mis 1 substantial influence of northern sourced subtropical surface water stw is evident at site y8 this implies southward incursions of stw around the eastern crest of chatham rise with the stf displaced towards higher latitudes and spinning off eddies as far south as campbell plateau additionally increased flow of the southland current sc might have enhanced the local occurrence of warm water radiolarians derived from the subtropical tasman sea coolest glacials are marked by a strong inflow of cool southern sourced waters at site y8 indicating a more vigorous flow along the subantarctic front saf

high resolution migration history of the subtropical high trade wind system of the northeastern pacific during the last 55 years implications for glacial atmospheric reorganization 1 guaymas basin gulf of california is a restricted basin located under the present day wet dry subtropical divide 27 n and is ideally circumstanced for detecting variations in the north pacific subtropical high npsh trade wind system controlled by climate cell boundary displacement npsh midwinter location was the primary influence on timing and intensity of upwelling seasons in guaymas basin analysis of high resolution x ray fluoresence data and sediment fabric log from 75 laminated core md02 2517 2515 western guaymas basin reveals systematic changes in npsh behavior over the last 55 kyr bp southward displacement of the wet dry subtropical divide controlled upwelling related diatom productivity while sea level and regional rainfall controlled terrigenous supply the basin was oxic during the glacial and preservation was ensured by high burial rate due to the increased deposition of terrigenous sediment sediment fabric style number and or thickness of laminae plus color banding and homogeneous intervals changes systematically through the core and gives insights into the number of seasons occurring in guaymas basin and the occurrence and intensity of the upwelling season five millennial scale low flux events with close timing to heinrich events and ten decadal centennial scale low biogenic silica events occurring in the interval 33 16 5000 years before present kyr bp are interpreted as times of extreme aridity at 16 5 kyr bp a regime shift from terrigenous dominated oxic to evenly balanced biogenic terrigenous dysoxic conditions occurred although there was a further extreme arid event at 11 5 kyr bp 16 5 kyr bp was essentially the beginning of the interglacial

paleoproductivity and carbon burial across the california current the multitracers transect 42 n the multitracers experiment studied a transect of water column sediment trap and sediment data taken across the california current to develop quantitative methods for hindcasting paleoproductivity the experiment used three sediment trap moorings located 120 km 270 km and 630 km from shore at the oregon california border in north america we report here about the sedimentation and burial of particulate organic carbon corg and caco3 in order to observe how the integrated caco3 and corg burial across the transect has changed since the last glacial maximum we have correlated core from the three sites using time scales constrained by both radiocarbon and oxygen isotopes by comparing surface sediments to a two and a half year sediment trap record we have also defined the modern preservation rates for many of the labile sedimentary materials our analysis of the corg data indicates that significant amounts 20 40 of the total corg being buried today in surface sediments is terrestrial at the last glacial maximum the terrestrial corg fraction within 300 km of the coast was about twice as large such large fluxes of terrestrial corg obscure the marine corg record which can be interpreted as productivity when we corrected for the terrestrial organic matter we found that the mass accumulation rate of marine corg roughly doubled from the glacial maximum to the present because preservation rates of organic carbon are high in the high sedimentation rate cores corrections for degradation are straightforward and we can be confident that organic carbon rain rate new productivity also doubled as confirmation the highest burial fluxes of other biogenic components opal and ba also occur in the holocene productivity off oregon has thus increased dramatically since the last glacial maximum caco3 fluxes also changed radically through the deglaciation however they are linked not to caco3 production but rather to changes in deepwater carbonate chemistry between 18 ka and now

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation