age distribution and stratigraphy of glacier peak tephra in eastern washington and western montana united states tephra layers from williams lake fen wildcat lake and east wenatchee washington and kearns basin lost trail pass sheep mountain bog and marys frog pond montana were analyzed by electron mi

postglacial wetland succession carbon accumulation and forest dynamics on the east coast of vancouver island british columbia canada peatland development and carbon accumulation on the pacific coast of canada have received little attention in paleoecological studies despite wetlands being common landscape features here we present a multi proxy paleoenvironmental study of an ombrotrophic bog in coastal british columbia following decreases in relative sea level the wetland was isolated from marine waters by 13 300 cal yr bp peat composition non pollen palynomorph and c and n analyses demonstrate terrestrialization from an oligotrophic lake to a marsh by 11 600 cal yr bp followed by development of a poor fen and then a drier ombrotrophic bog by 8700 cal yr bp maximum carbon accumulation occurred during the early holocene fen stage when seasonal differences in insolation were amplified this highlights the importance of seasonality in constraining peatland carbon sequestration by enhancing productivity during summer and reducing decomposition during winter pollen analysis shows that pinus contorta dominated regional forests by 14 000 cal yr bp warm and relatively dry summers in the early holocene allowed pseudotsuga menziesii to dominate lowland forests 11 200 7000 cal yr bp tsuga heterophylla and p menziesii formed coniferous forest in the mid and late holocene tephra matching the mid holocene glacier peak dusty creek assemblage provides evidence of its most northwesterly occurrence to date

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

late glacial vegetation and climate at the manis mastodon site olympic peninsula washington abstract as the late wisconsin cordilleran ice sheet retreated sediment accumulated in shallow depressions at the manis mastodon archaeological site on the olympic peninsula near sequim washington pollen plant macrofossils and bones of mastodon caribou and bison occur within the lower 47 cm of these deposits the fossil pollen and seed assemblages indicate persistence for 1000 yr 11 000 12 000 yr b p of an herb and shrub dominated landscape at a time when forest species appear elsewhere in washington and in adjacent british columbia at present sequim is near the northern coastal limits of both cactaceae and ceratophyllum mean annual precipitation is 42 7 cm and summer temperatures average 15 16 c in july the absence of coniferous trees and the presence of cactus and ceratophyllum in late glacial sediments are explained by a regional climate that was drier and at least as warm as today these conditions persisted in the rain shadow of the olympic mountains until at least 11 000 yr b p

an observational and modeling study of the interaction of low level southwesterly flow with the olympic mountains during coast iop 4 abstract this paper presents an observational and modeling study of the three dimensional flow and precipitation around the olympic mountains of northwest washington state for a case of relatively steady south southwesterly flow this study utilized data from coast iop 4 the fourth intensive observing period during the coastal observation and simulation with topography field experiment that took place during 9 10 december 1993 one of the most important data sources was the noaa p 3 aircraft which provided flight level data reflectivity and doppler winds as it flew around the olympics features that were mapped successfully with the noaa p 3 included flow splitting around the windward pressure ridge strong southeasterlies to approximately 25 m s 1 northeast of the olympics caused by downgradient acceleration into the lee trough the rapid transition from strong southeasterlies to lighter easterlies 5 10 m s 1 in the strait of juan de fuca strong downslope flow and a hydraulic jump like transiti

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

postglacial vegetation and climate of the cascade range central oregon abstract pollen data from two sites provide information on the postglacial vegetation and climate history of the cascade range indian prairie in the western cascade range was colonized by subalpine forests of pinus picea and tsuga and open meadows prior to ca 12 400 14 c yr b p the treeline lay 500 to 1000 m below its modern elevation and conditions were cooler than at present from ca 12 400 to ca 9950 14 c yr b p abies became important and the forest resembled that presently found at middle elevations in the western cascade range the pollen record implies a rise in treeline and warmer conditions than before from ca 10 000 to 4000 4500 14 c yr b p conditions that were warmer and effectively drier than today led to the establishment of a closed forest composed of pseudotsuga abies and at lower elevations quercus and corylus during this period gold lake bog in the high cascades was surrounded by closed forest of pinus and abies the early holocene pollen assemblages at both indian prairie and gold lake bog lack modern analogues and it is likely that greater than present summer radiation fostered unique climatic conditions and vegetation associations at middle and high elevations in the late holocene beginning ca 4000 4500 14 c yr b p cooler and more humid conditions prevailed and the modern vegetation was established a comparison of these sites with others in the pacific northwest suggests that major patterns of vegetational change at individual sites were a response to large scale changes in the climate system that affected the entire region

late glacial vegetation and climate change in western oregon abstract pollen records from two sites in western oregon provide information on late glacial variations in vegetation and climate and on the extent and character of younger dryas cooling in the pacific northwest a subalpine forest was present at little lake central coast range between 15 700 and 14 850 cal yr b p a warm period between 14 850 and 14 500 cal yr b p is suggested by an increase inpseudotsugapollen and charcoal the recurrence of subalpine forest at 14 500 cal yr b p implies a return to cool conditions another warming trend is evidenced by the reestablishment ofpseudotsugaforest at 14 250 cal yr b p increased haploxylonpinuspollen between 12 400 and 11 000 cal yr b p indicates cooler winters than before after 11 000 cal yr b p warm dry conditions are implied by the expansion ofpseudotsuga a subalpine parkland occupied gordon lake western cascade range until 14 500 cal yr b p when it was replaced during a warming trend by a montane forest a rise inpinuspollen from 12 800 to 11 000 cal yr b p suggests increased summer aridity pseudotsugadominated the vegetation after 11 000 cal yr b p other records from the pacific northwest show an expansion ofpinusfrom ca 13 000 to 11 000 cal yr b p this expansion may be a response either to submillennial climate changes of younger dryas age or to millennial scale climatic variations

late quaternary vegetation in the southwestern columbia basin washington abstract a 33 000 yr pollen record from carp lake provides information on the vegetation history of the forest steppe border in the southwestern columbia basin the site is located in the pinus ponderosa zone but through much of late quaternary time the area was probably treeless pollen assemblages in sediments dating from 33 000 to 23 500 yr b p suggest a period of temperate climate and steppe coinciding with the end of the olympia interglaciation the fraser glaciation ca 25 000 10 000 yr b p was a period of periglacial steppe or tundra vegetation and conditions too dry and cold to support forests at low altitudes aridity is also inferred from the low level of the lake between 21 000 and 8500 yr b p and especially after about 13 500 yr b p about 10 000 yr b p chenopodiineae and other temperate taxa spread locally providing palynological evidence for a shift from cold dry to warm dry conditions pine woodland developed at the site with the onset of humid conditions at 8500 yr b p further cooling is suggested at 4000 yr b p when pseudotsuga and abies were established locally

palynology and paleoecology of postglacial sediments in an anoxic basin saanich inlet british columbia varved black clayey silts deposited in the marine waters of saanich inlet yield unusually abundant and diverse pollen assemblages derived from the coastal douglas fir pseudotsuga and western hemlock tsuga heterophylla forests of southwestern british columbia the 12 000 year palynological record chronicles the development of vegetation since ice left saanich inlet the succession of pine pinus contorta and alder alnus rubra woodlands by forests characterized by douglas fir and oak quercus and later by western hemlock and red cedar thuja plicata rapid deposition of annual layers of pollen charcoal and other terrigenous particles provides detailed evidence of changes in land use during the past few hundred years settlement logging farming and urbanization vegetational and climatic changes inferred from pollen spectra in the marine sediments of saanich inlet compare favorably with changes inferred from correlative pollen assemblages previously described from adjacent parts of vancouver i

postglacial vegetation fire and climate history of the siskiyou mountains oregon usa the forests of the siskiyou mountains are among the most diverse in north america yet the long term relationship among climate diversity and natural disturbance is not well known pollen plant macrofossils and high resolution charcoal data from bolan lake oregon were analyzed to reconstruct a 17 000 yr long environmental history of high elevation forests in the region in the late glacial period the presence of a subalpine parkland of artemisia poaceae pinus and tsuga with infrequent fires suggests cool dry conditions after 14 500 cal yr b p a closed forest of abies pseudotsuga tsuga and alnus rubra with more frequent fires developed which indicates more mesic conditions than before an open woodland of pinus quercus and cupressaceae with higher fire activity than before characterized the early holocene and implies warmer and drier conditions than at present in the late holocene abies and picea were more prevalent in the forest suggesting a return to cool wet conditions although fire episode frequency remained relatively high the modern forest of abies and pseudotsuga and the present day fire regime developed ca 2100 cal yr b p and indicates that conditions had become slightly drier than before sub millennial scale fluctuations in vegetation and fire activity suggest climatic variations during the younger dryas interval and within the early holocene period the timing of vegetation changes in the bolan lake record is similar to that of other sites in the pacific northwest and klamath region and indicates that local vegetation communities were responding to regional scale climate changes the record implies that climate driven millennial to centennial scale vegetation and fire change should be considered when explaining the high floristic diversity observed at present in the siskiyou mountains d 2005 university of washington all rights reserved

new accelerator mass spectrometry radiocarbon ages for the mazama tephra layer from kootenay national park british columbia canada charcoal fragments recovered from the mazama air fall tephra layer in cores from dog and cobb lakes kootenay national park british columbia yielded accelerator mass spectrometry ages of 6720 70 and 6760 70 14c years bp respectively these two new ages together with other previously published radiocarbon ages on charcoal and twig fragments from mazama air fall deposits indicate that the climactic eruption of mount mazama occurred 6730 40 14c years bp

little ice age glacial activity in strathcona provincial park vancouver island british columbia canada dendroglaciological and lichenometric techniques are used to establish the little ice age lia history of two glaciers colonel foster and septimus in strathcona provincial park vancouver island british columbia our lichenometric investigations were preceded by the development of a locally calibrated rhizocarpon geographicum growth curve 1708 1998 a d documentation of a 3 4 year ecesis interval for both trees and lichen greatly reduces one of the main uncertainties in using geobotanical methods for dating lia landforms the moraine dates provided therefore give a good approximation of the shift in climate conditions that lead to the retreat of the glaciers and subsequent moraine stabilization geobotanical evidence records three synchronous episodes of lia moraine deposition at both glaciers two prominent moraines at each site are dated to the early 1700s and late 1800s with a third smaller moraine dated to the mid 1930s moraines deposited prior to 1397 a d were also recorded at colonel foster glacier however precise dating of these moraines was not possible the moraine records from strathcona provincial park suggest two possible modes of glacier response i synchronous responses to larger scale climatic forcing and ii asynchronous responses to local factors such as microclimate topography and glacier geometry the vancouver island lia record was evaluated in the context of lia results from the pacific north american pna cordillera it compares well with regional moraine records from coastal british columbia washington alaska and the canadian rocky mountains suggesting a regional response of pna glaciers to climate change associated with the lia

an improved method for computing horizontal diffusion in a sigma coordinate model and its application to simulations over mountainous topography abstract a set of modifications is presented to reduce the unphysical impact of horizontal diffusion in numerical models with a terrain following sigma coordinate system at model levels sufficiently far away from the ground vertical interpolation is used to compute diffusion truly horizontally when the coordinate surfaces are sloping close to the ground where truly horizontal computation of diffusion is not everywhere possible without intersecting the topography a combination of one sided truly horizontal diffusion and orography adjusted diffusion along the sigma surfaces is used for most of the variables the latter means that the diffusion coefficient is reduced strongly when the grid points involved in the computation of horizontal diffusion are located at greatly different heights for temperature one sided horizontal diffusion is not used because it damps the slope wind circulation in an unphysical way however a temperature gradient correction is applied to the terrain following part of the t

a 14 300 year long record of fire vegetation climate linkages at battle ground lake southwestern washington high resolution macroscopic charcoal analysis was used to reconstruct a 14 300 year long fire history record from the lower columbia river valley in southwestern washington which was compared to a previous vegetation reconstruction for the site in the late glacial period ca 14 300 13 100 cal yr bp pinus picea dominated parkland supported little to no fire activity from the late glacial to the early holocene ca 13 100 10 800 cal yr bp pseudotsuga abies dominated forest featured more frequent fire episodes that burned mostly woody vegetation in the early to middle holocene ca 10 800 5200 cal yr bp quercus dominated savanna was associated with frequent fire episodes of low to moderate severity with an increased herbaceous i e grass charcoal content from the middle to late holocene ca 5200 cal yr bp to present forest dominated by pseudotsuga thuja type and tsuga heterophylla supported less frequent but mostly large or high severity fire episodes fire episodes were least frequent but were largest or most severe after ca 2500 cal yr bp the fire history at battle ground lake was apparently driven by climate directly through the length and severity of the fire season and indirectly through climate driven vegetation shifts which affected available fuel biomass

conodonts and radiolarians from pelagic cherts of the frasnian famennian boundary interval at bancheng guangxi china global recognition of the upper kellwasser event abstract the recognition of five standard conodont biozones and five radiolarian zones in the same set of samples from cherts within the frasnian famennian f f boundary interval at bancheng southeastern guangxi china allowed precise placement of the f f boundary and demonstrated the multi episodic pattern of the f f mass extinction frasnian pelagic radiolarian and conodont faunas had an acme in the lower palmatolepis linguiformis zone in the upper pa linguiformis zone until the level of the upper kellwasser extinction kw members of the radiolarian family ceratoikiscidae and of the conodont frasnian populations disappeared above the kw in the lower palmatolepis triangularis zone new populations of the conodont pa triangularis gradually appeared and the survivor radiolarian genus trilonche gradually re appeared both blooming in the lower part of the middle pa triangularis zone the nehden extinction nd in the uppermost middle pa triangularis zone interrupted the recovery of the conodont and radiolarian faunas but above this level the conodont species became more numerous and the post extinction radiolarian faunas including entactiniidae recovered gradually

atmospheric structure and momentum balance during a gap wind event in shelikof strait alaska abstract gap winds occur in topographically restricted channels when a component of the pressure gradient is parallel to the channel axis aircraft flight level data are used to examine atmospheric structure and momentum balance during an early spring gap wind event in shelikof strait alaska alongshore sea level pressure ridging was observed vertical cross sections show that across strait gradients of boundary layer temperature and depth accounted for the pressure distribution geostrophic adjustment of the mass field to the along strait wind component contributed to development of the observed pressure pattern boundary layer structure and force balance during this event was similar to that often observed along isolated barriers however the rossby radius was lager than the strait width and atmospheric structure in the strait exit region indicates transition of the flow to open coastline conditions two across strait momentum budgets show that the coriolis force and across strait pressure gradient w

dielectric constant as a predictor of porosity in dry volcanic rocks x measurements of dielectric constant k are made on 34 samples of volcanic rocks at frequencies of 0 01 to 10 mhz

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

structure of a low level jet over lower cook inlet alaska abstract during february 1982 a noaa research aircraft investigated a cold low level jet blowing from a gap between mountain ranges on line west side of cook inlet alaska the jet blew 200 km southeastward across cook inlet between the kenai peninsula and the kodiak archipelago passing into the gulf of alaska where it merged with the large scale marine wind field measurement commenced 35 km downstream of the seaward end of the gap the jet s internal boundary layer accelerated by 5 and grew 20 in depth for 50 km thereafter wind speed and boundary layer depth were nearly constant for the next 100 km the strongest winds 20 m s 1 at a height of 80 m were observed on the south side of the jet s thermal axis and 90 km downstream from the coast budget analyses reveal that the down gradient acceleration within the jet was principally opposed by surface friction and the cold air advection was balanced by a strong upward directed sensible heat flux from cook inlet and entrainment of warmer air from

timing and patterns of the frasnian famennian event evidences from high resolution conodont biostratigraphy and event stratigraphy at the yangdi section guangxi south china abstract continuous centimeter scale sampling for conodonts with microfacies and carbon isotope analysis has been carried out across the frasnian famennian f f transition at the yangdi section guangxi south china the newly revised conodont biostratigraphy reveals a succession of six zones ranging from the upper palmatolepis rhenana zone to lower palmatolepis crepida zone in ascending order based on a detailed analysis of conodont abundance and diversity changes through the section two intervals involving significant conodont faunal changes were recognized in the uppermost palmatolepis linguiformis zone at the yangdi section the first conodont change occurred at the transition between the lower and upper pa linguiformis zone and is marked by the disappearance of pa linguiformis accompanied by the successive disappearances of pa eureka pa rhenana pa nasuta pa gigas ad ioides and ad nodosa the second conodont change appeared in a horizon equivalent to the uppermost upper kellwasser horizon ukh and is indicated by the elimination of nearly all frasnian palmatolepids ancyrodellids and polygnathids furthermore the second conodont change is coincident with the decimation of ostracods and tentaculitids and is synchronous with the turnovers of conodont biofacies in addition the onset of the 13 c carb perturbation is a little earlier than the second conodont change with the maximum amplitude of excursion right at the start of the famennian therefore we conclude that the second conodont change represents the f f mass extinction based on the temporal correlation among 13 c carb excursions pelagic faunal changes and conodont biofacies turnovers during the f f boundary interval according to the high resolution conodont biostratigraphy together with cyclostratigraphy the uppermost ukh and whole ukh contain 1 and 12 bundle cycles respectively thus the time span of the mass extinction and the entire upper kellwasser crisis lasted 16 18 kyr and 200 kyr respectively

holocene vegetation history and fire regimes of pseudotsuga menziesii forests in the gulf islands national park reserve southwestern british columbia canada article i nfo pollen analysis of a 9 03 m long lake sediment core from pender island on the south coast of british columbia was used to reconstruct the island s vegetation history over the last 10 000 years the early holocene was characterized by open mixed woodlands with abundant pseudotsuga menziesii and a diverse understory in cluding salix and rosaceae shrubs and pteridium aquilinum ferns the establishment of quercus garryana savanna woodland with p menziesii and acer macrophyllum followed deposition of the mazama tephra until 5500 cal yr bp when these communities gave way to modern mixed p menziesii forest charcoal anal yses of the uppermost sediments revealed low charcoal accumulation over the last 1300 years with a mean fire return interval mfri of 88 years fires were more frequent mfri 50 yr during the medieval climate anomaly mca with warm dry conditions facilitating a higher fire frequency than during the little ice age when fires were infrequent given the projected warming for the next 50 100 years land managers considering the reintroduction of fire to the gulf islands national park reserve may want to consider using the mfri of the mca as a baseline reference in prescribed burning strategies

observations and scale analysis of coastal wind jets abstract blocking of onshore flow by coastal mountains was observed south of vancouver island british columbia by the noaa p 3 aircraft on 1 december 1993 winds increased from 10 m s 1 offshore to 15 m s 1 nearshore and became more parallel to shore in the blocked region which had a vertical scale of 500 m and an offshore scale of 40 50 km these length scale and velocity increases are comparable to theory the flow was semigeostrophic with the coast being hydrodynamically steep that is the coast acts like a wall and the alongshore momentum balance is ageostrophic this is shown by the nondimensional slope parameter the burger number b hmn flm being greater than 1 where hm and lm are the height and half width of the mountain n is the stability frequency and f is the coriolis parameter the height scale is given by setting the local froude number equal to 1 that is hl u n 500 m where u is the onshore component of velocity this scale is appropriate when hl is less than the mountain height

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

late quaternary vegetation near battle ground lake southern puget trough washington pollen and plant macrofossil records from battle ground lake along with published data are used to reconstruct the late quaternary vegetation history of the nonglaciated southern puget trough coinciding with the end of the evans creek stade circa 20 000 17 000 yr b p of fraser glaciation gramineae artemisia herbs and picea cf engelmannii grew in a parkland tundra around battle ground this assemblage recorded throughout the southern puget trough implies cold relatively dry conditions similar to subalpine environments east of the cascade range the presence of pseudotsuga picea sitchensis and alnus rubra as macrofossils suggests a slight interstadial warming between 17 000 and 15 000 yr b p cool humid conditions prevailed during the vashon stade when south of the cordilleran ice sheet open forest or parkland featured mesophytic subalpine taxa at battle ground lake temperate conifers were part of forest communities circa 11 200 yr b p but elsewhere they were present as early as 12 500 yr b p from 10 000 to 4500 yr b p pseudotsuga quercus savannah spread into the battle ground area offering evidence for summer drought more severe than today pseudotsuga and thuja forest was established in the late holocene with the introduction of the modern humid climate consideration of all the pollen data from the southern puget trough and the available radiometric chronology suggests that postglacial migration of most lowland conifers into the puget trough was rapid and not necessarily from southern refugia

effects of coastal orography on landfalling cold fronts part ii effects of surface friction abstract the role of surface friction in modifying cold fronts as they make landfall in regions of steep coastal orography is examined by means of idealized simulations both the effects of the surface roughness change at the coast in the absence of orography and the effects of orography are considered flow over a large and abrupt change in surface roughness generates an inertia gravity wave above the boundary layer with characteristics similar to that associated with flow over a plateau deceleration of the cross coast flow occurs over land as well as for a short distance upstream and causes retardation of frontal motion a prescribed northerly postfrontal jet weakens rapidly after landfall maximum vertical motions are several centimeters per second however only small rainfall enhancement is expected since the updraft is very narrow and produces only small vertical displacements friction modifies the flow over the orography by increasing the upstream flow deceleration and reducing the magnitude of

holocene precipitation in the coastal temperate rainforest complex of southern british columbia canada abstract pollen data from 69 surface samples from vancouver island canada were used to develop a ratio index of precipitation douglas fir western hemlock index dwhi dwhi ratios were combined with interpolated estimates of mean annual precipitation to develop pollen based precipitation transfer functions the optimal regression model with a predictive range of 960 2600 mm was applied to 10 holocene lake sediment records distributed across a 150 km long coastal inland precipitation gradient predicted precipitation was spatially modelled in a geographic information system to examine the spatio temporal history of precipitation from this representative portion of the coastal temperate rainforest ctr complex of western north america the reconstructions show widespread early holocene dry conditions coupled with a steep east west precipitation gradient thereafter the modern precipitation gradient established 7000 years ago illustrating that the ctr complex has experienced marked short distance east west changes in precipitation in the past changes in the abundance of arboreal and non arboreal vegetation as well as fire disturbance are often concomitant with changes in holocene precipitation given the precipitation and vegetation history of the region conservation initiatives should focus on the moist outer coastal zone since it appears to have the greatest amount of resilience to perturbations in precipitation whereas monitoring programs for signs of climate change should be initiated in central and eastern areas as they appear sensitive to changes in the moisture regime

revised correlation of the frasnian famennian boundary and kellwasser events upper devonian in shallow marine paleoenvironments of new york state abstract the frasnian famennian boundary upper devonian is exposed in a 200 km long outcrop belt in new york state with deeper paleoenvironments to the west and shallower ones to the east geochronology in the eastern end of the outcrop belt has been based primarily on lithostratigraphic correlation with western sections which were dated using conodonts we collected conodonts and brachiopods from several measured sections and numerous other localities and these collections suggest that these east west lithostratigraphic correlations require revision we correlate the wiscoy formation with the upper angola formation and the canaseraga with the upper hanover thus the canaseraga formation contains the frasnian famennian boundary and upper kellwasser event and the dark shale above the wiscoy is equivalent to the pipe creek formation and lower kellwasser event these new correlations imply that the lower kellwasser event had greater impact on the shelly benthos of new york than the upper kellwasser at least for the subset of taxa examined here all strophomenid brachiopods and rugose corals were extirpated at the lower kellwasser along with numerous other brachiopods the final species of atrypid brachiopod persisted to the upper kellwasser

boundary layer effects on fronts over topography abstract a hydrostatic primitive equation model with frontogenetical deformation forcing is used to study the effects of surface friction on fronts passing over a two dimensional ridge surface friction is parameterized using a k theory planetary boundary layer bl parameterization with implicitly defined diffusion coefficients following keyser and anthes previous studies without surface friction such as williams et al show that a cold front weakens on the upwind slope and intensifies on the lee slope this is in part due to a superposition effect of mountain flow where colder temperatures exist over the crest and in part due to the divergence pattern caused by the basic flow over the mountain divergence on the upwind slope and convergence on the lee slope in williams et al the final intensity of a front after passing a symmetric mountain is the same as a front moving over flat land for no mountain simulations the inclusion of the bl results in a more realistic frontal structure and the fron

effects of coastal orography on landfalling cold fronts part i dry inviscid dynamics abstract in this study the interaction of cold fronts with idealized coastal terrain typical of the western united states and canada is considered two issues are examined first what are the factors that determine the strength of the coastal winds and second what are the orographic effects on the frontal evolution to address these issues the authors utilize a two dimensional boussinesq terrain following coordinate numerical model in which a uniform prescribed flow is forced to move over a plateau the resultant across mountain velocities are characterized by a zone of strongly decelerated flow upstream of the windward slope and a train of inertia gravity waves downstream a barrier jet oriented parallel to the mountain is produced by the coriolis force the variations of the magnitude of the upstream deceleration and the barrier jet over a wide range of froude numbers and rossby numbers are described steady linear theory applied to flow over a plateau shows that the upstream deceleration is dete

three dimensional idealized simulations of barrier jets along the southeast coast of alaska abstract three dimensional idealized simulations using the fifth generation pennsylvania state university ncar mesoscale model mm5 down to 6 km grid spacing were performed in order to understand how different ambient conditions wind speed and direction stability and inland cold pool and terrain characteristics impact barrier jets along the southeastern alaskan coast the broad inland terrain of western north america is important in alaskan jet development since it rotates the impinging flow cyclonically more coast parallel well upstream of the coast thus favoring more low level flow blocking while also adding momentum and width to the barrier jet near the steep coastal terrain the largest wind speed enhancement factor 1 9 2 0 in the terrain parallel direction relative to the ambient onshore directed wind speed occurs at relatively low froude numbers fr 0 3 0 4 these low froude numbers are associated with 10 15 m s 1 ambient wind speeds and wind directions orientated 30 45 from terra

a record of late quaternary vegetation from davis lake southern puget lowland washington abstract pollen and macrofossil analyses of a core spanning 26 000 yr from davis lake reveal late pleistocene and holocene vegetational patterns in the puget lowland the core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units the late pleistocene pollen sequence records two intervals of tundra parkland vegetation the earlier of these has high percentages of picea gramineae and artemisia pollen and represents the vegetation during the evans creek stade fraser glaciation ca 25 000 17 000 yr b p the later parkland interval is dominated by picea tsuga mertensiana and gramineae it corresponds to the maximum ice advance in the puget lowland during the vashon stade fraser glaciation ca 14 000 yr b p an increase in pinus ontorta pollen between the two tundra parkland intervals suggests a temporary rise in treeline during an unnamed interstade after 13 500 yr b p a mixed woodland of subalpine and lowland conifers grew at davis lake during a period of rapid climatic amelioration in the early holocene the prolonged expansion of pseudotsuga and alnus woodland suggests dry temperate conditions similar to those of present rainshadow sites in the puget lowland more mesic forests of tsuga eterophylla thuja plicata and pseudotsuga similar to present lowland vegetation appeared in the late holocene ca 5500 yr b p

1200 years of fire and vegetation history in the willamette valley oregon and washington reconstructed using high resolution macroscopic charcoal and pollen analysis article high resolution macroscopic charcoal and pollen analyses were used to reconstruct the fire and vegetation history of the willamette valley for the last 1200 years presented in this paper are three new paleoecological reconstructions from lake oswego porter lake and warner lake oregon and portions of previous reconstructions from battle ground lake washington and beaver lake oregon the reconstructions show that prior to euro american settlement vegetation and fire regimes were influenced by a combination of natural and anthropogenic factors battle ground lake shows a stronger influence from climate while lake oswego beaver lake porter lake and warner lake were more controlled by human activity however human set fires were also modulated by regional climate variability during the medieval climate anomaly and the little ice age fire reconstructions from battle ground lake lake oswego beaver lake and porter lake imply that fires were infrequent in the willamette valley 200 300 years prior to euro american settlement the decline of native american populations due to introduced disease may have led to this reduction in fire activity the prehistoric record from warner lake however indicates that fires in the foothills of the cascade range were more frequent than on the valley floor at least until ca ad 1800 the historic portions of the reconstructions indicate that euro american land clearance for agriculture and logging produced the most dramatic shifts in vegetation and fire regimes all five records indicate that few fires in the willamette valley have occurred since ca ad 1930 and fires today are predominantly grass fires 2010 elsevier b v all rights reserved

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

the impact of upstream blocking drainage flow and the geostrophic pressure gradient on the persistence of cold air pools idealized numerical simulations are performed to investigate dynamical mechanisms affecting the persistence of cold air pools in basins and valleys the first orography type considered is a shallow elongated basin located upstream of a mountain ridge for sensitivity tests the mountain ridge is removed the second type is a basin embedded in a plateau like mountain ridge in part of the simulations this basin has an outflow towards the lee side plain so as to assess the impact of the drainage flow the large scale flow is taken to be in geostrophic balance in the standard setting it is perpendicular to the basin and the ridge the main effect of a large scale pressure gradient is to induce a circulation within a cold air pool until the upper boundary of the cold pool is inclined such as to compensate for the ambient pressure gradient the cold air accumulates where the ambient pressure is lowest for a shallow basin this means that part of the cold air may be lost due to advection out of the basin the upstream influence of a mountain ridge in the lee of a shallow basin is found to be twofold it tends to deflect the low level flow towards the lower pressure leading to an additional ridge parallel force on the cold air pool on the other hand the absolute wind speed is reduced diminishing the turbulent mixing near the top of the cold pool the simulations show that the first effect prevails for ridge normal flow while second effect may dominate for other flow directions drainage flow out of a valley is found to be very important as it promotes the penetration of warm air into valleys very effectively it may cause a cold pool in a deep valley to disappear more quickly than a cold pool in a shallow basin sensitivity tests show that the persistence of a cold pool depends on its depth on its vertically integrated heat deficit and on the maximum heat deficit at the bottom of the cold pool copyright 2003 royal meteorological society

regional and local controls on postglacial vegetation and fire in the siskiyou mountains northern california usa article i nfo the siskiyou mountains of northwestern california and southwestern oregon are a floristic hotspot and the high diversity of conifers there likely results from a combination of geological ecological climatological and historical factors to evaluate how past climate variability has influenced the composition structure and fire regime of the siskiyou forests pollen charcoal and lithological evidence was examined from two lakes along a moisture gradient to reconstruct the vegetation fire and climate history the late glacial period was characterized by subalpine parkland and infrequent fire at both sites during the late glacial early holocene transition period subalpine parkland was replaced by a closed forest of pinus cupressaceae abies and pseudotsuga and more frequent fires a 1000 years earlier at the wetter site and it is likely that reduced pacific ocean upwelling created warmer drier conditions at the coast in the early holocene pinus cupressaceae were less abundant and fire less frequent at the coastal site during a period of increased coastal upwelling and fog production in the late holocene abies pseudotsuga pinus and quercus vaccinifolia increased in the forest at both sites suggesting a widespread response to cooling fewer fires at the wetter site may account for the abundance of picea breweriana within the last 1000 years the comparison of the two records implies that large scale controls in climate during the last 14 000 cal yr bp have resulted in major changes in vegetation and fire regime asynchrony in the ecosystem response of wetter and drier sites arises from small scale spatial variations in effective moisture and temperature resulting from topographically influenced microclimates and coastal to inland climate gradients

the influence of coastal orography the yakutat storm abstract an unforecast windstorm in the vicinity of yakutat alaska on 14 march 1979 illustrates the importance of ageostrophic dynamics within a coastal zone proximal to significant terrain large pressure rises greater than 4 mb 3 h 1 were observed along the southeastern alaska coast after passage of a cold front when the low level geostrophic flow was directed onshore these pressure rises did not occur simultaneously along the coast but rather propagated northward along the coast as a coherent pulse or surge strong surface winds approximately 25 30 m s 1 were observed in the region of laid sea level pressure gradient at the leading edge of the surge and occurred after the passage of the synoptic front although the sparseness of the observations prevent definite conclusions this feature resembles a kelvin wave more than a density current omega dropwindsonde observations collected along the coast of alaska during two other less dramatic situations suggest damming and downslope flow structu

numerical simulations of a landfalling cold front observed during coast rapid evolution and responsible mechanisms abstract this paper identifies mechanisms that led to the observed rapid evolution of a landfalling weak cold front along the steep mountainous northern california coast on 1 december 1995 this event was simulated down to 3 km horizontal grid spacing using the pennsylvania state university ncar mesoscale model version 5 mm5 the mm5 simulation reproduced the basic features such as the timing location and orientation of the cold front and associated precipitation evolution as well as the tendency for enhanced precipitation to extend 50 100 km upwind of the coastal barrier with the heaviest amounts occurring over the windward slopes 0 20 km inland locally however the model underestimated the magnitude of the prefrontal terrain enhanced flow by as much as 30 since the simulated low level static stability was weaker than observed the mm5 simulations illustrate the complex thermal wind and precipitation structures in the coastal zone upstream flow blocking by the steep coastal terrain led to

history and isostatic effects of the last ice sheet in southern british columbia abstract the late wisconsinan cordilleran ice sheet covered british columbia southern yukon territory and parts of alaska washington idaho and montana its major source areas were the high mountain ranges of the canadian cordillera and flow was strongly controlled by topography the last ice sheet began to develop about 30 000 25 000 14c yr ago but it did not achieve its maximum extent until 15 000 14 000 14c yr bp ice sheet growth was interrupted locally by stillstands and retreat ice sheet decay was rapid and was characterized by complex frontal retreat at the periphery accompanied locally by brief readvances and by downwasting and stagnation by 10 000 14c yr bp

climatology of barrier jets along the alaskan coast part i spatial and temporal distributions abstract this paper investigates the temporal and spatial climatology of coastal barrier jets in the gulf of alaska the jets are divided into two categories based upon the origin of the air involved classic barrier jets fed primarily by onshore flow and hybrid jets fed primarily by gap flow from the continental interior the analyses are compiled from five years 1998 2003 of synthetic aperture radar images from the radarsat 1 satellite totaling 3000 images thermodynamic and kinematic data from the ncep reanalysis is used in the interpretation of the results the majority of coastal barrier jets occur during the cool season with the coastline near mount fairweather and the valdez cordova mountains experiencing the greatest number of barrier jets hybrid jets are even more strongly restricted to the cool season and are commonly found to the west of cross sound yakutat bay and icy bay some interannual variability in the total number of jets is observed coastal barrier jet formation is associate

postglacial vegetation and fire history eastern klamath mountains california usa pollen and high resolution charcoal data from bluff lake and crater lake california indicate simi lar changes in climate vegetation and fire history during the last 15 500 years pollen data at bluff lake suggest that the vegetation between c 15 500 and 13 100 cal bp consisted of subalpine parkland with scattered pinus and abies after 13 100 cal bp a relatively closed forest of p monticola p contorta and abies developed and fire event frequency was low the inferred climate then was cooler and wetter than present pinus and quercus vaccinifoliadominated at both sites during the early holocene when conditions were warm and dry as climate became wetter and cooler in the late holocene abies spp at both sites and tsuga mertensi ana at crater lake increased in importance displacing pinus and quercus the two lake records have similar trends in fire history with high event frequencies at c 8400 4000 and 1000 cal bp and low values at c 4800 cal bp the fire and vegetation history at both sites suggests a similar response to large scale changes in climate during the holocene

time specific facies and biological crises the kellwasser event interval near the frasnian famennian boundary late devonian abstract features which may be called time specific facies tsf can be linked to global bioevents or better biological crises the late devonian kellwasser kw event is a classic example of such a crisis this geologically short lived event shows recurring patterns within the critical time interval including patterns that are often minute not only do the well known lower and upper kw horizons yield specific features but also the adjacent sedimentary rocks show characteristic markers such observations were first made in facies settings of submarine rises with preferably carbonate rocks mainly cephalopod limestones but these features can now also be traced into basinal sections characterized by fine grained pelitic rocks these beds and markers are crossing traditional facies borders at exactly the same time making them perfect examples of tsf

the late devonian frasnian famennian f f biotic crisis insights from δ13ccarb δ13corg and 87sr 86sr isotopic systematics a severe biotic crisis occurred during the late devonian frasnian famennian f f transition f367 myr here we present d 13 ccarb d 13 corg and 87 sr 86 sr isotopic systematics from identical samples of two sections across f f boundary in south china which directly demonstrate large and frequent climatic fluctuations 200 kyr from warming to cooling during the f f transition these climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land which would have increased riverine delivery to oceans and primary bioproductivity and subsequent burial of organic matter thereby resulting in climate cooling such large and frequent climatic fluctuations together with volcanic induced increases in nutrient e g biolimiting fe toxin sulfide and anoxic water supply and subsequent enhanced riverine fluxes and microbial bloom were likely responsible for the stepwise faunal demise of f f biotic crisis d 2005 elsevier b v all rights reserved

postglacial vegetation history of orcas island northwestern washington abstract the revegetation of islands following retreat of pleistocene glaciers is of great biogeographical interest the san juan islands washington feature regionally distinctive xerophytic plant communities yet their vegetation history as it relates to past climate and sea level is poorly known we describe a 13 700 year old pollen record from killebrew lake fen and compare the vegetation reconstruction with others from the region the data suggest that the narrow channels surrounding orcas island were not a barrier to early postglacial immigration of plants between 13 700 and 12 000 cal yr bp pinus tsuga picea alnus viridis and possibly juniperus maritima were present in a mosaic that supported bison antiquus and megalonyx the rise of alnus rubra type pollen and pteridium spores at ca 12 000 cal yr bp suggests a warming trend and probably more fires temperate conifer taxa including cupressaceae pseudotsuga tsuga heterophylla and abies increased after 11 000 cal yr bp and especially in the last 7000 cal yr bp after 6000 cal yr bp pseudotsuga and cupressaceae dominated the vegetation the last 1500 yr were the wettest period of the record due to its rain shadow location orcas island experienced drier conditions than on the mainland during most of the postglacial period

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

high resolution holocene vegetation history and climate from hole 1034b odp leg 169s saanich inlet canada abstract high resolution pollen analysis of laminated marine sediments from odp hole 1034b in saanich inlet british columbia reveals changes in vegetation and inferred climate during the holocene four main pollen zones are discerned using constrained cluster analysis although the timing of major vegetation changes at the saanich inlet is similar to other study sites in the pacific northwest the composition of pollen assemblage zones is different from the mainland sites vegetation assemblages reconstructed from the pollen and spore record include a douglas fir pseudotsuga menziesii parkland with abundant grass poaceae and bracken pteridium between 11 450 and 8300 bp all ages are calibrated calendar years oak quercus savanna or parkland with high grass and bracken 8300 7040 bp a mixed deciduous coniferous forest with oak western hemlock tsuga heterophylla and douglas fir 7040 5750 bp and the development of modern coastal temperate forest with the marked expansion of cedar cupressaceae western hemlock spruce picea and douglas fir 5750 1050 bp climatic periods inferred from the cores include an early holocene warm dry interval 11 450 8300 bp a warm period with mild winters 8300 7040 bp a period of transitional mid holocene climate 7040 5750 bp and the advent of a relatively cool wet neoglacial climate after 5750 bp modern conifer forests and oak savannas became established by about 3800 bp the saanich inlet pollen record indicates that vegetation and inferred climate change was particularly rapid between 8700 and 8300 bp when grass and bracken abruptly decrease and oak becomes a significant component of the paleovegetation because neoglacial conditions have prevailed from 3800 years to present in the pacific northwest factors other than climate such as anthropogenic modification of the landscape may be responsible for the persistence of oak savannas

the frasnian famennian boundary interval in the south polish moravian shelf basins integrated event stratigraphical approach abstract the late devonian mass extinction event near the frasnian famennian f f boundary has been analysed using conodont biostratigraphy and biofacies sedimentology magnetic susceptibility and geochemistry in reference sections of the south polish moravian shelf holy cross mountains cracow and brno areas high resolution biostratigraphic study revealed difficulties in the precise recognition of this natural stage boundary but confirmed the occurrence of a major third order sequence boundary in the f f transition in an active synsedimentary tectonic setting marked by erosional discontinuities hardgrounds and brecciation or omission surfaces conclusive evidence of an extraterrestrial impact has not been found among earth bound factors the main devastating role in the shelf habitats is ascribed to fluctuating anoxia and or nutrient dynamics in a disturbed greenhouse climatic setting the long term facies changes were determined by a conspicuous break in carbonate production accompanied by replacement of mature stromatoporoid coral reefs by pioneer shelly crinoid banks microbial mounds and localised oolitic bars the key f f passage interval was marked by intermittent but generally accelerated periplatform ooze debris input and severe storm events as well as by probably highly fluctuating oxygenation and biological overproduction best manifested in radiolarian silicisponge and cephalopod acmes eutrophication phenomena at least partly stimulated by various hydrothermal and volcanic processes were one of the major biogeochemical processes during this climax of the late devonian biotic crisis however significant oceanographic perturbations were also linked with the onset of the transgressive hypoxic upper kellwasser event still within the latest frasnian linguiformis zone i e well before the f f conodont collapse implied variations in the redox state of seawater through the kellwasser timespan probably in regionally highly variable temporal scales are in agreement with recent palaeoecological and biogeochemical inferences in particular suggesting recovering oxygenation just prior to the f f boundary in the other laurussian intrashelf basins all the data support a long time multicausal earth bound crisis instead a worldwide cosmic catastrophe

a 14 000 year vegetation history of a hypermaritime island on the outer pacific coast of canada based on fossil pollen spores and conifer stomata abstract pollen and conifer stomata analyses of lake sediments from hippa island on the north coast of british columbia were used to reconstruct the vegetation history of this small hypermaritime island between 14 000 and 13 230 cal yr bp the island supported diverse herb shrub communities dominated by cyperaceae artemisia and salix pinus contorta and picea sitchensis stomata indicate that these conifers were present among the herb shrub communities likely as scattered individuals transition to open p contorta woodland by 13 000 cal yr bp was followed by increases in alnus viridis alnus rubra and p sitchensis after 12 000 cal yr bp pinus dominated communities were replaced by dense p sitchensis and tsuga heterophylla forest with lysichiton americanus and fern understory thuja plicata stomata indicate that this species was present by 8700 cal yr bp but the pollen record suggests that its populations did not expand to dominate regional rainforests along with tsuga and picea until after 6600 cal yr bp conifer stomata indicate that species may be locally present for hundreds to thousands of years before pollen exceed thresholds routinely used to infer local species arrival when combined pollen and conifer stomata can provide a more accurate record of paleovegetation than either when used alone

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

humptulips revisited a revised interpretation of quaternary vegetation and climate of western washington usa abstract new pollen data from a 770 cm core of a mire at humptulips on the southwestern olympic peninsula 47 17 00 n 123 54 40 w and from a nearby deposit regarded as interglacial in age on the west fork of the humptulips river provide evidence for a reinterpretation of previous accounts of the quaternary vegetation and climate using a new age model the highly variable record at humptulips is here correlated with marine oxygen isotope stages ois 1 5a vegetation during ois 5a was pine dominated mixed woodland and tundra in ois 4 3 and 2 oscillations in pollen assemblages imply repeated intervals of mountain hemlock parkland and tundra pine as an indicator of openness is also abundant in these stages interstadial fluctuations in ois 3 reflect episodes of lowland western hemlock communities the earliest of the episodes is of infinite radiocarbon age and the latest dates to approximately 30 000 14 c yr b p parkland in ois 2 occurring after 24 600 until at least 18 440 14 c yr b p was replaced by transitional pine alder in ois 1 holocene which unlike any of the earlier stages conveys the development of modern lowland forest dominated by western hemlock pollen assemblages over the length of record imply that temperature and humidity at no time were as high as at present only in ois 3 do conditions approach those occurring in ois 1 during ois 2 3 and 4 when tree line apparently stood at the location of the site climate was colder and drier temperatures were depressed an estimated 5 c with precipitation close to 1000 mm compared with 2000 3000 mm at present atmospheric circulation during ois 2 appears to have been much controlled by the location of the laurentide ice sheet in the continental interior whereas under the current climatic regime beginning in the early holocene westerly air flow has dominated regulated by interplay between the north pacific high in summer and the wintertime aleutian low

global estimates of lunar iron and titanium contents from the chang e 1 iim data 1 until recently global high spatial resolution maps of feo and tio2 of the moon were only derived from clementine data in this study we show global maps of feo and tio2 using chang e 1 interference imaging spectrometer iim at a spatial resolution of 200 m pixel with a newly developed calibration presented here spectra obtained by iim compare well with telescopic spectra spectral parameters previously shown to be sensitive to iron and titanium derived from the calibrated iim data are highly correlated with the measured elemental concentration with r2 0 96 for feo and 0 95 for tio2 the maps were developed using this calibration histograms of basalt feo estimates have a negatively skewed distribution while tio2 distributions are unimodal they also revealed that the lunar highland crust is relatively uniform on the quadrant scale several hundred to thousand kilometers scale but inhomogenous on the global scale the area of highest elevation of the moon has very low feo and tio2 raising the question about south pole aitken spa whether its ejecta deposits covered the highest elevation and when it was formed although the average feo and tio2 abundances for basalts are highly correlated local areas of elevated iron can be associated with both high and low titanium

the persian gulf summertime low level jet over sloping terrain there are few observational and numerical studies of the summertime low level jet llj over the persian gulf known as the shamal in this study the weather research and forecasting wrf model accurately simulates the llj s vertical structure nocturnal features and strong diurnal variation of the wind the case study period is divided into a period during which the shamal is spatially extended strong winds over the gulf and iraq and a period during which it is less spatially extended strong flow only over the gulf orography mountain slope and land sea breeze are found to be key factors for the shamal diurnal variation of wind speed and wind direction the blackadar mechanism appears to be secondary to the heating in forcing the shamal the zagros mountains not only channel the northwesterly winds but also provide a barrier for the easterly monsoon airflow which maximizes the wind speed only during the less extensive period does the zagros mountains slope significantly affect the shamal wind intensity and direction both shallow and steep mountain slope sensitivity studies feature a jet like flow over the persian gulf the steep slopes cause larger wind speeds however the shallow slopes reveal a stronger diurnally varying wind direction due to larger heating and cooling of the sloping terrain it is also shown that during the less extensive period the land breeze and the lower friction over the sea increase the intensity of the nocturnal jet over the gulf copyright 2011 royal meteorological society

airborne dual doppler observations of an intense frontal system approaching the pacific northwest coast airborne doppler radar data collected off the pacific northwest coast by a noaa wp 3d orion aircraft over an 8 h period on 8 december 1993 during the coastal observations and simulations with topography experiment reveal the mesoscale structure of an intense frontal system while it was well offshore and as it approached within 20 km of the oregon coastline during the offshore stage a portion of the narrow coldfrontal rainband was characterized by deep convective cores pseudo dual doppler analyses characterize the kinematic and precipitation structure of the deep convection pseudo dual doppler analyses describe the subsequent evolution of the narrow cold frontal rainband as it approached to within 20 km of the oregon coast deformation of the frontal zone appeared to cause the dissipation of one of three precipitation cores contained within the dual doppler area the precipitation cores and the strong convergence zone associated with the front conformed to some degree to the shape of the coastline near cape blanco oregon as the front neared the coast changes in the prefrontal flow that occurred as the front approached the coast were qualitatively consistent with theoretical and numerical studies of upstream orographic influence comparison of pseudo dual doppler derived velocity profiles with idealized numerical model calculations suggests that the nearshore evolution of the frontal rainband was significantly affected by an upstream influence of the coastal orography

late quaternary dynamics of forest vegetation on northern vancouver island british columbia canada abstract pollen analysis of radiocarbon dated lake sediment from northern vancouver island southwest british columbia reveals regional changes in forest vegetation over the last 12 200 14c yr 14 900 cal yr between at least 12 200 and 11 700 14c yr bp 14 900 13 930 cal yr bp open woodlands were dominated by pinus contorta alnus crispa and various ferns as p contorta decreased in abundance alnus rubra and more shade tolerant conifers i e picea and tsuga mertensiana increased increases in t mertensiana p contorta and a crispa pollen accumulation rates pars between 10 600 and 10 400 14c yr bp 11 660 11 480 cal yr bp reflect a cool and moist climate during the younger dryas chronozone orbitally induced warming around 10 000 14c yr bp 11 090 cal yr bp allowed the northward extension of pseudotsuga menziesii although picea tsuga heterophylla and a rubra dominated early holocene forests by 7500 14c yr bp 8215 cal yr bp shade tolerant t heterophylla was the dominant forest tree cupressaceae thuja plicata and chamaecyparis nootkatensis was present by 7500 14c yr bp but reached its maximum after 3500 14c yr bp 3600 cal yr bp when a cooler and wetter regional climate facilitated the development of temperate rainforest the highest rates of vegetation change are associated with lateglacial climate change and species with rapid growth rates and short life spans

postglacial vegetation and climate dynamics in the seymour belize inlet complex central coastal british columbia canada palynological evidence from tiny lake a pollen based study from tiny lake in the seymour belize inlet complex of central coastal british columbia canada permits an evaluation of the dynamic response of coastal temperate rainforests to postglacial climate change open pinus parklands grew at the site during the early lateglacial when the climate was cool and dry but more humid conditions in the later phases of the lateglacial permitted mesophytic conifers to colonise the region early holocene conditions were warmer than present and a successional mosaic oftsugaheterophylla andalnus occurred at tiny lake climate cooling and moistening at 8740 70 14 c a bp initiated the development of closed late successional t heterophylla cupressaceae forests which achieved modern character after 6860 50 14 c a bp when a temperate and very wet climate became established the onset of early holocene climate cooling and moistening at tiny lake may have preceded change at more southern locations including within the seymour belize inlet complex on a meso to synoptic scale this would suggest that an early holocene intensification of the aleutian low pressure system was an important influence on forest dynamics in the seymour belize inlet complex and that the study region was located near the southern extent of immediate influence of this semi permanent air mass copyright 2008 john wiley sons ltd

carbon isotopic evidence for the associations of decreasing atmospheric co2level with the frasnian famennian mass extinction 1 a perturbation of the global carbon cycle has often been used for interpreting the frasnian famennian f f mass extinction however the changes of atmospheric co2 level pco2 during this interval are much debatable to illustrate the carbon cycle during f f transition paired inorganic 13ccarb and organic 13corg carbon isotope analyses were carried out on two late devonian carbonate sequences dongcun and yangdi from south china the larger amplitude shift of 13corg compared to 13ccarb and its resultant 13c 13c 13ccarb 13corg decrease indicate decreased atmospheric co2level around the f f boundary the onset ofpco2 level decrease predates that of marine regressions which coincide with the beginning of conodont extinctions suggesting that temperature decrease induced by decreased greenhouse effect of atmospheric co2might have contributed to the f f mass extinction

pedogenic processes and soil landscape relationships in north cascades national park washington thunder creek watershed tcw in the northern cascade range washington state provides a complex environment for studying soil formation approximately 15 000 cal yrs b p the cordilleran ice sheet cis overrode the watershed during the last glacial maximum and deposited glacial drift that provides the substratum for soil formation today since then the watershed has been blanketed by tephra from mount mazama glacier peak and mount st helens soils with the gross morphology of spodosols podzols and andisols andosols occur in a complex landscape mosaic in tcw and along the entire washington cascade range the pedologic conundrum addressed in this paper is whether true spodosols are forming in these areas or are they mimics of spodosols based on field morphology and lab analysis soils in tcw are andic subgroups of spodosols and andisols in approximately equal abundance with lesser areas of inceptisols cambisols and some entisols gleysols field morphology and electron microprobe analysis of glass shards shows that the major volume of tephra about 8 cm compacted thickness is predominantly from the eruption of mount mazama 7600 cal yrs bp tephra from this eruption has been mixed into the upper 50 cm of glacial drift and colluvium fallout from other eruptions in tcw had individual compacted thicknesses less than 2 cm we conclude that true spodosols are widespread in tcw they have albic and spodic horizons no pseudo albic horizons of white unweathered tephra layers were found in tcw the cold wet and dominantly conifer covered landscape supports podzolization in tephra rich materials on parts of landforms that have been stable for several thousand years andisols are forming in drier microclimates on gravitationally active landscapes and under herbaceous vegetation inceptisols dominate landforms controlled by water erosion and deposition where tephra has not been preserved in the soil and on active avalanche chutes entisols were found only on active or recent floodplains the distribution of each soil order in tcw corresponds to the preservation of tephra vegetation type and stability of the landform

the effect of upstream wind direction on atmospheric flow in the vicinity of a large mountain a series of idealized simulations is conducted to investigate how the upstream wind direction impacts on the flow in the vicinity of a large elliptical mountain oriented north south the upstream wind speed and stability are kept constant there is no surface friction the rossby number is low and the non dimensional mountain height nh u is varied from 1 to 4 5 the flow pattern varies greatly with wind direction and a number of features of orographic flows where the coriolis force is important are found for a given the flow is blocked for low aspect ratio while it is not blocked for high aspect ratio furthermore the upstream barrier wind is more pronounced when the upstream flow is from the south west than from the north west both these features are linked to the interaction of the coriolis force with the mountain induced flow anomalies the drag force and the pressure deficit in the wake are greater in the south west cases than in the north west cases these features are linked as the main contribution to the drag being greater in the south west cases is a negative pressure anomaly over the lee slope the difference downstream of the mountain is linked to the interaction of the low level flow anomalies and the coriolis force copyright 2005 royal meteorological society

microtektites and mass extinctions evidence for a late devonian asteroid impact glass spherules similar to microtektites have been found near the frasnian famennian boundary f f upper devonian at senzeilles belgium contemporaneous with one of the largest marine mass extinctions of the phanerozoic these spherules exhibit a wide range of compositions and display teardrop dumbbell and compound morphologies analogous to microtektites in addition they lack crystallites have few or no vesicles and have a low content of volatile material these characteristics are supportive of an impact origin the siljan ring sweden and charlevoix structure quebec canada are candidate craters of this age the presence of microtektites near the f f boundary supports the hypothesis that an impact caused the upper devonian worldwide benthic mass extinctions

turbulent large eddy momentum flux divergence during high wind events abstractmomentum transport by energy containing turbulent eddies in the oceanic mixed layer were investigated during high wind events in the northern gulf of alaska off kayak island sixteen high wind events with magnitudes ranging from 7 to 22 m s 1 were examined winds from the southeast prevailed from one to several days with significant wave heights of 5 9 m and turbulent langmuir numbers of about 0 2 0 4 surface buoyancy forcing was much weaker than the wind stress forcing the water column was well mixed to the bottom depth of about 73 m spectral analyses indicate that a major part of the turbulent momentum flux was concentrated on 10 30 min time scales the ratio of horizontal scale to mixed layer depth was from 2 to 8 turbulent shear stresses in the mixed layer were horizontally asymmetric the downwind turbulent stress at 10 20 m below the surface was approximately 40 of the averaged wind stress and was reduced to 5 10 of the wind stress near the bottom turbulent kinetic energy in the cros

on the spatial distribution of high winds off southeast greenland 1 the spatial distribution of barrier winds along southeast greenland has been investigated through idealized modeling of unidirectional flow towards an isolated mountain the regions of enhanced surface wind speed seen in previous studies are reproduced and shown to be primarily the result of promontories in the orography along the southeast coast the maxima disappear in experiments without the promontories two mechanisms are proposed to explain these enhancements firstly a reduction in pressure experienced by the flow as it passes a promontory results in an acceleration akin to that of easterly tip jets at cape farewell secondly mountain waves observed along the southeast coast are accompanied by strong low level downslope winds in the lee of the promontories both mechanisms contribute to the simulated wind speed maxima

a modified approach to initialize an idealized extratropical cyclone within a mesoscale model abstract a technique for initializing realistic idealized extratropical cyclones for short term 0 72 h numerical simulations is described the approach modifies select methods from two previous studies to provide more control over the initial cyclone structure additional features added to the technique include 1 deformation functions to initialize more realistic low level fronts tropopause structure and enhanced jet maximum at upper levels 2 a barotropic shear function to help develop different cyclone and frontal geometries and 3 damping functions to create an isolated baroclinic wave in the horizontal therefore the initialized cyclone is not influenced by the domain boundaries for relatively short simulations since this procedure allows for control of the initialized cyclone structures it may be useful for studies of frontal and cyclone interaction with topography and mesoscale predictability the initialization system produces a variety of basic states and synoptic disturbances ranging f

postglacial history of subalpine forests olympic peninsula washington usa to investigate subalpine vegetation history on the olympic peninsula washington usa two pol len macrofossil and charcoal records were studied in climatically distinct zones martins lake 1415 m in the moist tsuga mertensianazone and moose lake 1508 m in the drier abies lasiocarpa zone the interpret ation of fossil pollen assemblages was aided by comparisons with 308 modern assemblages from the olympic peninsula and western north america both pollen records show a cold dry period following deglaciation 10 000 radiocarbon years bp with sparse tundra and little similarity to any modern pollen assemblage in the early holocene when summer temperatures are thought to have been higher than present high percentages of alnus sinuata type pollen at both lakes suggest increased avalanche activity at martins lake warmer summers were not accompanied by forest establishment possibly because persistent spring snow pack snow avalanches and or edaphic constraints limited tree establishment at this site the martins lake record shows a steplike shift in vegetation to modern tsuga mertensiana abies amabilis parkland across the mazama tephra 6730 bp in contrast to martins lake abies lasiocarpa forest quickly established at moose lake in the early holocene though forests were probably initially open and fires may have been frequent from 7800 to 5100 bp forests near moose lake shifted gradually to cooler and moister species composition with the addition of chamaecyparis nootkatensis tsuga mertensianaand pinus though abies lasiocarpa remained dominant for est cover was probably greatest during this transition with parklike conditions at moose lake beginning at c 5100 bp the major differences in the records between the two sites may be due to differences in the local expression of regional climatic change and or differences in soil development and stabilization

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

a 4000 year record of hydrologic variability from the olympic mountains washington usa sedimentological and geochemical analyses of gravity and piston cores retrieved from lake quinault washington reveal an 4000 year flood dominated depositional record individual flood event laye

a comparison of two coastal barrier jet events along the southeast alaskan coast during the sarjet field experiment abstract the southeastern alaskan regional jets experiment investigated the structures and physical processes of barrier jets along the coastal fairweather mountains near juneau alaska from 24 september to 21 october 2004 this paper compares in situ aircraft data and high resolution simulations from the first intensive observation period iop1 which featured a nearly terrain parallel barrier jet classical jet with another coastal jet event iop7 that was influenced by offshore directed gap flows at the coast hybrid jet iop1 featured southerly onshore flow preceding a landfalling trough which was blocked by the coastal terrain and accelerated down the pressure gradient to produce a 5 10 m s 1 wind enhancement in the alongshore direction in the lowest 1 km msl in contrast iop7 featured higher surface pressure and colder low level temperatures to the east inland of the study area than did iop1 which resulted in offshore directed coastal gap flow exiting cross sound below 500 m that turned a

dendroglaciological investigations of mid to late holocene glacial activity in the mt waddington area british columbia coast mountains canada dendroglaciological investigations near mt waddington in the central british columbia coast mountains provide an enhanced perspective of holocene glacial activity field investigations at confederation franklin and jambeau glaciers led to the discovery of subfossil wood mats encased in glacial deposits and glacially sheared stumps buried beneath till radiocarbon dated wood collected from valley bottom and lateral moraine sites at confederation glacier suggest that an early holocene advance occurred at c 5665 cal yr bp followed by succeeding intervals of glacier expansion at c 3700 and 3500 cal yr bp at jambeau glacier detrital wood mats buried close to the contemporary lateral moraine crests document glacier expansion at c 3000 cal yr bp detrital subfossil wood buried in lateral moraines at the confluence of confederation and franklin glaciers records distinct episodes of little ice age glacier expansion as early as c 1212 cal yr ad and suggests the glacier surface continued to thicken u

an 11 000 year long record of fire and vegetation history at beaver lake oregon central willamette valley high resolution macroscopic charcoal and pollen analysis were used to reconstruct an 11 000 year long record of fire and vegetation history from beaver lake oregon the first complete holocene paleoecological record from the floor of the willamette valley in the early holocene ca 11 000e7500 calendar years before present cal yr bp warmer drier summers than at present led to the establishment of xeric woodland of quercus corylus and pseudotsuga near the site disturbances i e floods fires were common at this time and as a result alnus rubra grew nearby high fire frequency occurred in the early holocene from ca 11 200e9300 cal yr bp riparian forest and wet prairie developed in the middle holocene ca 7500 cal yr bp likely the result of a decrease in the frequency of flooding and a shift to effectively cooler wetter conditions than before the vegetation at beaver lake remained generally unchanged into the late holocene from 4000 cal yr bp to present with the exception of land clearance associated with euro american settlement of the valley ca 160 cal yr bp middle to late holocene increases in fire frequency coupled with abrupt shifts in fire episode magnitude and charcoal composition likely indicate the influence anthropogenic burning near the site the paleoecological record from beaver lake and in particular the general increase in fire frequency over the last 8500 years differs significantly from other low elevation sites in the pacific northwest which suggests that local controls e g shifts in vegetation structure intensification of human land use rather than regional climatic controls more strongly influenced its environmental history

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

upper kellwasser carbon isotope excursion pre dates the f f boundary in the upper devonian lennard shelf carbonate system canning basin western australia abstract here we report four high resolution carbon isotope records in addition to trace element data for the frasnian famennian f f boundary interval in the lennard shelf carbonate system of the canning basin western australia this region lacks the characteristic black shale horizons associated with the global late devonian kellwasser extinction events yet still exhibits a trend in carbon isotope character similar to what has been reported from elsewhere in the world two positive 13c excursions with 3 4 amplitudes enrichments in select trace element ratios suggest that both excursions are related to periods of oxygen deprivation and perhaps increased biological productivity given the continuous and stratigraphically expanded nature of lennard shelf sections together with high density sampling constrained by both conodont biostratigraphy and magnetostratigraphy we observe that the upper kellwasser isotope excursion maximum 13c values and associated trace element enrichments occur distinctly lower than the f f boundary level these results have implications for the paleoenvironmental conditions leading up to the late devonian mass extinction in terms of ocean chemistry and circulation patterns this data set allows for a rare detailed look at the temporal relationship between the kellwasser events and the f f boundary and constrains the pattern of carbon isotope perturbations at the intra zonal scale

sea level change and paleogeographic reconstructions southern vancouver island british columbia canada abstract forty eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern vancouver island british columbia sea level fell rapidly from its high stand of about 75 m elevation just before 14 000 cal bp 12 000 radiocarbon yrs bp to below the present shoreline by 13 200 cal bp 11 400 radiocarbon years bp the sea fell below its present level 1000 years later in the central strait of georgia and 2000 years later in the northern strait of georgia reflecting regional differences in ice sheet retreat and downwasting direct observations only constrain the low stand to be below 11 m and above 40 m analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the cascadia subduction zone however places the low stand at 30 5 m at about 11 200 cal bp 9800 bp the inferred low stand for southern vancouver island when compared to the sea level curve previously derived for the central strait of georgia to the northwest generates differential isostatic depression that is consistent with the expected crustal response between the two regions morphologic and sub bottom features previously interpreted to indicate a low stand of 50 to 65 m are re evaluated and found to be consistent with a low stand of 30 5 m submarine banks in eastern juan de fuca strait were emergent at the time of the low stand but marine passages persisted between southern vancouver island and the mainland the crustal uplift presently occurring in response to the late pleistocene collapse of the southwestern sector of the cordilleran ice sheet amounts to about 0 1 mm yr the small glacial isostatic adjustment rate is a consequence of low viscosity mantle in this tectonically active region

kinematic and thermodynamic structures of sierra barrier jets and overrunning atmospheric rivers during a landfalling winter storm in northern california abstractthis study characterizes kinematic and thermodynamic structures of sierra barrier jets sbjs atmospheric rivers ars and their interaction over the period 14 16 february 2011 when a winter storm made landfall in northern california a suite of scanning and profiling doppler radars rawinsondes and gps receivers is used to document these structures across the central valley and up the western sierra slope to the crest along an 200 km segment of the sierra the winter storm is grouped into two episodes each having an ar that made landfall low level winds in the sbj observed during episode 1 were southeasterly and embedded in a stably stratified air mass along barrier wind speeds u340 reached maximum values of 25 30 m s 1 as low as 0 2 km msl over the central valley and as high as 1 5 km msl over the western sierra slope southwesterly winds associated with the ar overlaid the sbj along an interface that sloped upward from southwest to northeast with a southwestern extent at the western

numerical simulations of the barrier jet over northwestern taiwan during the mei yu season orographic effects on the airflow over taiwan under the prevailing southwesterly monsoon flow are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 in particular the orographically induced low level strong winds along the northwestern coast of taiwan are simulated in the absence of radiative forcing thermal forcing from the surface and synoptic forcing the momentum balance for the low level strong winds along the northwest coast of taiwan shows that above the mixed layer the alongshore force balance is dominated by the inertial advection term and the pressure gradient force term the significant lagrangian flow acceleration of the northern branch of the deflected airflow along the northwest coast is mainly related to the pressure gradient force as the airflow moves down the orographically induced pressure ridge along the windward coast even though the alongshore pressure gradient force along the northwest coast is largest at the surface the observed and simulated wind profiles show that the wind speed maximum in the vertical of the barrier jet occurs at a height of 800 m primarily due to frictional retardation in the lowest levels within the well mixed layer the alongshore force balance is a threeway balance between inertial advection pressure gradient force and frictional force normal to the northwest coast the force balance is approximately geostrophic in addition the location and the strength of the orographically induced low level strong winds along the northwest coast of taiwan also depend on the impinging angle and the wind speed of the prevailing winds

prefrontal and postfrontal boundary layer processes over the ocean abstract measurements taken during the storm transfer and response experiment strex are used to analyse boundary layer structures and processes in north pacific storms heat and moisture transfers at the surface and through the top of the boundary layer are evaluated for three cases with warm southerly flow ahead of cold fronts and two cases of cooler westerly and northerly flow behind fronts the prefrontal boundary layers are nearly neutrally stratified and surface heat and moisture fluxes are small surface fluxes tend to be downward just ahead of the fronts and are of greater magnitude during stronger storms entrainment fluxes at the top of the prefrontal boundary layers are generally larger than surface fluxes and are the dominant sources of heating for the boundary layers entrainment rates determined from budgets compare well with laboratory studies of shear driven entrainment in the postfrontal cases surface heat and moisture fluxes are the dominant sources of total heating within the bound

late quaternary vegetation and climate history near little lake central coast range oregon pollen and plant macrofossils recovered from little lake oregon provide the first record of late quaternary climate and vegetation changes in oregon9s central coast range the pollen data suggest that the period from ca 42 000 to 24 770 yr b p featured an open forest of western white pine western hemlock and fir the inferred climate was cooler and wetter than today the full glacial period was characterized by a parkland of spruce lodgepole pine and mountain hemlock which suggests that the climate was colder and possibly drier than today the oregon coast range was not a glacial refugium for temperate conifers as has been proposed by 16 000 yr b p the pollen and plant macrofossil data suggest the development of a montane forest composed of pine fir western hemlock and mountain hemlock temperate taxa were present in the vegetation at 13 500 yr b p during a period of climatic amelioration a reversal in this warming trend may have occurred between 11 000 and 10 500 yr b p when pine western and mountain hemlock and spruce were slightly more abundant early holocene forests featured douglas fir red alder and bracken fern implying more severe summer drought and more frequent fires after 5600 yr b p douglas fir western hemlock and western red cedar dominated the record marking the introduction of the present day cool moist climate however during the past 2800 yr increased douglas fir and decreased cedar suggest the possibility of reduced effective moisture at little lake

climatology of barrier jets along the alaskan coast part ii large scale and sounding composites abstract this paper investigates the large scale flow and thermodynamic structures associated with barrier jets along the alaskan coast using the national centers for environmental prediction ncep reanalysis as well as the average wind moisture and thermodynamic soundings at yakutat alaska yak and whitehorse yukon territory canada yxy large scale and sounding composites are constructed for all barrier jets objectively identified around yak using synthetic aperture radar sar imagery during the cool and warm seasons of 1998 2003 during the cool season the jet events are separated into those with sharp upstream wind gradients shock jets highly variable gustlike surface winds variable jets and the other jet events other jets those cool season barrier jets without shock or variable characteristics are associated with an anomalously deep upper level trough approaching the gulf of alaska and an anomalous ridge over western canada and interior alaska the associated surface cyclone a

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

analysis of the ross ice shelf airstream forcing mechanisms using self organizing maps abstractthe ross ice shelf airstream ras a prominent transport mechanism of cold continental air to the north is the most common wind pattern over the ross ice shelf antarctica the forcing mechanisms of the ras include katabatic drainage mesoscale forcing and synoptic forcing this paper uses the 15 km output from the antarctic mesoscale prediction system amps and the method of self organizing maps som to analyze how the combination of these forcing mechanisms impacts the strength and position of the ras it is found that the strength and position of the ras is mainly driven by the thermal forcing in the region of the transantarctic mountains this forcing includes the pressure gradient associated with cold air pooling at the base of the transantarctic mountains as well as the pressure gradient associated with the temperature contrast between the cold air located over the east antarctic plateau and the warm ambient air over the ross ice shelf these forcing mechanisms are analyzed in a regi