response of the chydorid faunas to rapid climatic changes in four alpine lakes at different altitudes abstract the subfossil assemblages of chydoridae from late glacial preboreal sediments of four sites from 603 m to 2290 m asl were analysed to trace the community response to rapid climatic warming that occurred at this period of time in each site distinct signals at the younger dryas preboreal boundary were recorded by density of remains species diversity or community composition however responses varied considerably among the sites this variation was attributed to the situation that the chydorid community structure is determined not only by temporal younger dryas preboreal boundary and spatial among the sites temperature gradients but also by the specific local ecological conditions at the sites in some species the classification with respect to cold tolerance should be reconsidered

size fractionated iron distribution on the northern gulf of alaska 1 concentrations of soluble 0 4 m and colloidal 0 025 0 4 m fe size fractions were removed from surface waters within the inner and mid shelf as a result the contribution of soluble fe to the total fe concentration increased from the inner shelf to the shelf break slope waters surface water dissolved fe concentrations on the northern goa continental slope were higher than those previously observed in the central goa gyre variations in surface water fe concentrations from spring through summer appear to result from the changes in freshwater discharge and physical processes on the shelf

seasonal cross shelf distribution of major zooplankton taxa on the northern gulf of alaska shelf relative to water mass properties species depth preferences and vertical migration behavior the cross shelf distribution of major zooplankton species was examined on the northern gulf of alaska goa shelf during the production season for four years between october 1997 and october 2001 the zooplankton community on the northern goa shelf consisted of oceanic and neritic species of the north pacific subarctic species complex cross shelf distribution of the major zooplankton species was influenced by their depth preferences vertical migration behavior salinity temperature preferences and by cross shelf water mass distribution and movement the neritic community dominated by pseudocalanus spp metridia pacifica and calanus marshallae had highest abundances on the inner shelf in the alaska coastal current and in the adjacent fjords in late spring and early summer the oceanic community which contained primarily neocalanus cristatus and eucalanus bungii was observed in the alaskan stream and adjacent waters near the shelf break a mid shelf transition zone contained a mixture of oceanic and neritic species prince william sound pws contained a unique species complex of large mesopelagic copepods amphipods and shrimp neocalanus flemingeri and oithona similis were abundant in all four regions during spring and early summer the transition zone commonly crossed much of the shelf between the shelf break and the acc but satellite images and ctd data indicate that occasionally a narrow shelf break front can form in which case distinct zooplankton species groups are observed on either side of the front satellite data also revealed numerous large and small eddies which probably contribute to cross shelf mixing in the transition zone

low frequency current regimes over the bering sea shelf abstract using direct current measurements made during the period 1975 81 we describe the general circulation over the southeastern bering sea and differentiate it by regimes related to depth and forcing mechanisms three regimes are present delineated by water depth z the coastal z 50 m the middle shelf 50 z 100 m and the outer shelf z 100 m these are nearly coincident with previously described hydrographic domains statistically significant mean flow 1 to 10 cm s 1 exists over the outer shelf generally directed toward the northwest but with a cross isobath component flow of similar magnitude 1 6 cm s 1 occurs in the coastal regime paralleling the 50 m isobath in a counterclockwise sense around the shelf mean flow in the middle shelf is insignificant kinetic energy at frequencies 0 5 cycle per day cpd is greater over the outer shelf than in the other two regimes suggesting that oceanic forcing is important there but does not affect the remainder of the shelf kinetic

vegetation responses to rapid warming and to minor climatic fluctuations during the late glacial interstadial gi 1 at gerzensee switzerland abstract high resolution pollen analyses made on the same samples on which the ratios of oxygen isotopes were measured that provided the time scale and a temperature proxy after correlation to northgrip 1 a primary succession the vegetation responded to the rapid rise of temperatures around 14 685 yr bp with a primary succession on a decadal to centennial time scale the succession between ca 15 600 and 13 000 yr bp included 1 1 the replacement of shrub tundra by woodland of juniperus and tree birch around 14 665 yr bp 1 2 the response of juniperus pollen to the shift in oxygen isotopes in less than 20 yr 1 3 a sequence of population increases of hippophae rhamnoides ca 14 600 yr bp salix spp ca 14 600 yr bp betula trees ca 14 480 yr bp populus cf tremula ca 14 300 yr bp and pinus cf sylvestris ca 13 830 yr bp 2 biological processes plants responded to the rapid increase of summer temperatures on all organisational levels 2 1 individuals may have produced more pollen e g juniperus 2 2 populations increased or decreased e g juniperus betula later pinus and 2 3 populations changed their biogeographical range and may show migrational lags 2 4 plant communities changed in their composition because the species pools changed through immigration and local extinction some plant communities may have been without modern analogue these mechanisms require increasing amounts of time 2 5 processes on the level of ecosystems with species interactions may involve various time scales besides competition and facilitation nitrogen fixation is discussed 3 the minor fluctuations of temperature during the late glacial interstadial which are recorded in 18o resulted in only very minor changes in pollen during the aegelsee oscillation older dryas biozone gi 1d and the gerzensee oscillation gi 1b 4 biodiversity the afforestation at the onset of bolling coincided with a gradual increase of taxonomic diversity up to the time of the major pinus expansion

quantification of biotic responses to rapid climatic changes around the younger dryas a synthesis to assess the presence or absence of lags in biotic responses to rapid climatic changes we 1 assume that the 18o in biogenically precipitated carbonates record global or hemispheric climatic change at the beginning and at the end of the younger dryas without any lag at our two study sites of gerzensee and leysin switzerland 2 derive a time scale by correlating the 18o record from these two sites with the 18o record of the grip ice core 3 measure 18o records in ostracods and molluscs to check the record in the bulk samples and to detect possible hydrological changes 4 analyse at gerzensee and leysin as well as at two additional sites that lack carbonates and hence a 18o record pollen plant macrofossils chironomids beetles and other insects and cladocera 5 estimate our sampling resolution using the grip time scale for the isotope stratigraphies and the biostratigraphies and 6 summarise the major patterns of compositional change in the biostratigraphies by principal component analysis or correspondence analysis we conclude that at the major climatic shifts at the beginning and end of the younger dryas hardly any biotic lags occur within the sampling resolution of 8 30 years and that upland vegetation responded as fast as aquatic invertebrates we suggest that the minor climatic changes associated with the gerzensee and preboreal oscillations were weakly recorded in the biostratigraphies at the lowland site but were more distinct at higher altitudes individualistic responses of plant and animal species to climatic change may reflect processes in individuals e g productivity and phenology in populations e g population dynamics in spatial distributions e g migrations and in ecosystems e g trophic state we suggest that biotic responses may be telescoped together into relatively short periods 50 to 150 years perhaps disrupting functional interactions among species and thus destabilising ecosystems

acceleration of near surface strong winds in a dry idealised extratropical cyclone to understand near surface strong winds in extratropical cyclones a simulation of a dry idealised baroclinic wave is presented the forces that accelerate the winds are analysed using the terms in the horizontal momentum equation two regions of strong near surface winds developed within the simulation one to the east of the low centre and the other to the southwest the flow to the east resembling the cold conveyor belt accelerated as it passed through the strong pressure gradient associated with the warm frontal zone this acceleration was reduced by friction near the surface the winds to the southwest were characterised by three airstreams one airstream consisted of air parcels that started north of the warm front near the surface accelerated north of the warm front encircled the low and continued to accelerate to the southwest of the low the increases in wind speed in this airstream also part of the cold conveyor belt resulted from the along flow pressure gradient force being greater than friction the second airstream consisted of air parcels that descended west of the cold front and maintained their speed during descent until they were slowed either by friction in the boundary layer or as they moved southward against the local pressure gradient between these two airstreams a third airstream was characterised by air parcels that accelerated during descent from the mid to lower troposphere whilst moving around the bent back front this airstream bears some resemblance to the sting jet and was accelerated by the pressure gradient force on descent until it encountered increased friction or moved against the local pressure gradient

younger dryas and allerod summer temperatures at gerzensee switzerland inferred from fossil pollen and cladoceran assemblages linear and unimodal based inference models for mean summer temperatures partial least squares weighted averaging and weighted averaging partial least squares models were applied to a high resolution pollen and cladoceran stratigraphy from gerzensee switzerland the time window of investigation included the allerod the younger dryas and the preboreal characteristic major and minor oscillations in the oxygen isotope stratigraphy such as the gerzensee oscillation the onset and end of the younger dryas stadial and the preboreal oscillation were identified by isotope analysis of bulk sediment carbonates of the same core and were used as independent indicators for hemispheric or global scale climatic change in general the pollen inferred mean summer temperature reconstruction using all three inference models follows the oxygen isotope curve more closely than the cladoceran curve the cladoceran inferred reconstruction suggests generally warmer summers than the pollen based reconstructions which may be an effect of terrestrial vegetation not being in equilibrium with climate due to migrational lags during the late glacial and early holocene allerod summer temperatures range between 11 and 12 c based on pollen whereas the cladoceran inferred temperatures lie between 11 and 13 c pollen and cladocera inferred reconstructions both suggest a drop to 9 10 c at the beginning of the younger dryas although the allerod younger dryas transition lasted 150 160 years in the oxygen isotope stratigraphy the pollen inferred cooling took 180 190 years and the cladoceran inferred cooling lasted 250 260 years the pollen inferred summer temperature rise to 11 5 12 c at the transition from the younger dryas to the preboreal preceded the oxygen isotope signal by several decades whereas the cladoceran inferred warming lagged major discrepancies between the pollen and cladoceran inference models are observed for the preboreal where the cladoceran inference model suggests mean summer temperatures of up to 14 15 c both pollen and cladoceran inferred reconstructions suggest a cooling that may be related to the gerzensee oscillation but there is no evidence for a cooling synchronous with the preboreal oscillation as recorded in the oxygen isotope record for the gerzensee oscillation the inferred cooling was ca 1 and 0 5 c based on pollen and cladocera respectively which lies well within the inherent prediction errors of the inference models

younger dryas event recorded by the mirabilite deposition in huahai lake hexi corridor nw china abstract deposits from the huahai ancient lake in the hexi corridor were dated using conventional and ams 14c a 2500a carbon storage effect was defined at 9 25 m depth according to the 14c age difference between a plant macrofragment and detrital organic matter from the same layer the chronology of this strata indicated that the mirabilite layer at the depth of 8 05 m 9 15 m had formed during the younger dryas yd event the formation of the mirabilite layer indicated that the mean annual temperature in the hexi corridor dropped by 11 c during the yd event compared with today the lowest cold event occurred early in the yd which is consistent with what has been revealed by other high resolution records such as those of arctic ice cores and stalagmites in mid latitude regions

biotic responses to rapid warming about 14 685 yr bp introduction to a case study at gerzensee switzerland abstract the late glacial climatic warming indicated in the greenland ice core record about 14 685 years before 1950 ad belongs to a type of very rapid high amplitude warming similar the onsets of dansgaard oeschger events during marine isotope stage 3 mis 3 in order to estimate the nature and rates of change of biotic responses to such a major climatic shift we need a reliable time scale as well as climatic indicators independent of the biota both are provided by a high resolution oxygen isotope record from precipitated carbonates of lake marl in gerzensee switzerland van raden et al 2013 this issue on the basis of the assumption of synchronous climatic changes between greenland and gerzensee the close correlation of the oxygen isotope changes at the two sites allows the use of the ngrip gicc05 timescale at gerzensee with the zero point at 1950 ad to maintain comparability with the numerous radiocarbon dates in europe the 18o record measured in precipitated carbonates is checked and refined by the 18o measured in mono specific ostracod samples von grafenstein et al 2013 in this issue the shift of 3 6 18o pdb in only about 112 years at the end of the gs 2 represents a very rapid temperature increase of at least 6 2 c this increase is confirmed by reconstructions based on transfer functions for pollen and chironomids by lotter et al 2012 possibly 4 7 c in the annual mean and 2 5 c in summer temperatures after this major shift the greenland late glacial interstadial gi 1 corresponding to the regional biozones bolling and allerod 18o records of both greenland and gerzensee exhibit four minor fluctuations about 1 0 1 2 18o of which the second and the fourth are especially clearly correlated with several of terrestrial records in the northern hemisphere the oxygen isotope record is used as a template for all these sediment and bio stratigraphies the biotic responses may include at least five types of process 1 changes in productivity of individuals within a year or two 2 changes in populations usually somewhat slower depending on life cycles and environmental constraints 3 changes due to migration often rather slow depending again on life cycles and environmental constraints 4 changes in the terrestrial and aquatic communities and 5 changes on the level of ecosystems including pedogenesis nutrient cycling and species interactions these biotic responses to the early rapid warming about 14 685 ka bp are elaborated in subsequent papers for plants chironomids ostracods and cladocera ammann et al 2013 a brooks and heiri in this issue von grafenstein et al in this issue novakova et al 2013 this issue in addition lake levels are reconstructed by magny 2013 this issue and vegetation dynamics and n2o emissions are modelled lischke et al 2013 pfeiffer et al 2013 the changes in the mammal fauna of the swiss plateau are summarized by nielsen 2013 this issue

responses to rapid warming at termination 1a at gerzensee central europe primary succession albedo soils lake development and ecological interactions the transition from the oldest dryas to the bolling around 14 685 cal yr bp was a period of extremely rapid climatic warming from a single core of lake marl taken at gerzensee switzerland we studied the transition in stable isotopes of oxygen and carbon on bulk sediment and charophyte remains as well as on monospecific samples of ostracods after pisidium a in addition pollen chironomids and cladocera were analyzed the 18o record serves as an estimate of mean air temperature and by correlation to the one from ngrip in greenland it provides a timescale the timing of responses the statistically significant zone boundaries of the biostratigraphies are telescoped at the rapid increase of about 3 in 18o at the onset of bolling biotic responses may have occurred within sampling resolution 8 to 16 years although younger zone boundaries are less synchronous gradual and longer lasting responses include complex processes such as primary or secular succession during the late glacial interstadial of bolling and allerod two stronger and two weaker cool phases were found biological processes involved in the responses occurred on levels of individuals e g pollen productivity of populations increases or decreases immigration or extinction and on the ecosystem level species interactions such as facilitation or competition abiotic and biotic interactions include pedogenesis nitrogen fixation nutrient cycling catchment hydrology water chemistry of the lake and albedo controlled by the transition from tundra to forest for the swiss plateau this major change in vegetation induced a change in the mammal fauna which in turn led to changes in the tool making by paleolithic people

late glacial and early holocene development of lakes in northeastern poland in view of plant macrofossil analyses the late glacial history of the development of seven extant or former now sediment filled lakes in northeastern poland was investigated based on high resolution plant macrofossil analyses and ams radiocarbon dating according to palaeobotanical data and ams dating the accumulation of organic sediments began during the bolling period the bottom sediments of all studied lakes contain plant macrofossils typical of late glacial vegetation such as betula nana dryas octopetala potamogeton filiformis and potamogeton alpinus the first plants to occur in the lakes were chara sp p filiformis and batrachium sp the late glacial sediments included rarely encountered macrofossils of sphagnum teres at the beginning of the holocene the water level in the studied northeastern polish lakes decreased significantly this was manifested in a change in the type of sediment transformation of small lakes into peatland in places and expansion of typical indicator plants of shallow waters

a census of mesoscale eddies in shelikof strait alaska during 1989 over a 5 month period in the spring and summer of 1989 12 mesoscale eddies were identified crossing a section of moored current meters in the shelikof sea valley this represents the first census of mesoscale eddies on the northwestern gulf of alaska continental shelf the majority of eddies 7 were observed in may and june anticyclonic eddies outnumbered cyclonic eddies two to one but all had characteristics similar to eddies previously observed in the region analysis of the current meter time series revealed that the mean speeds volume transport and the structure of the flow at the present location were similar to current meter and hydrographic measurements during other years in the sea valley we suggest that 1989 was a typical year in terms of eddy formation as well the proliferation of mesoscale eddies in this region in spring has an impact on the larval dispersal and eventual recruitment of walleye pollock

living diatom assemblages from north pacific and bering sea surface waters during summer 1999 diatom assemblages collected during july august 1999 along an e w transect comprising sixty two north pacific and bering sea surface water samples were identified and enumerated absolute abundance profiles of centric and raphid pennate diatoms show that the former group dominates in shallow coastal waters and through island passes whilst the latter group though less numerous dominates the oceanic regions this pattern is interpreted as nutrient related with centric diatoms especially chaetoceros section hyalochaete minidiscus and thalassiosira spp preferring eutrophic and upwelling conditions and raphid pennate diatoms especially nitzschioid genera like fragilariopsis neodenticula and pseudo nitzschia preferring oligotrophic pelagic conditions the absolute abundances of the two sections of chaetoceros chaetoceros ex phaeoceros and hyalochaete and some species belonging to the thalassiosirales and bacillariaceae show distribution patterns that can be interpreted as preferences for shallow or oceanic waters subtropical or subarctic waters or ice related arctic conditions r 2005 elsevier ltd all rights reserved

the large scale coastal wind field along the west coast of north america 1981 1982 we study the statistical properties of the coastal wind field along the west coast of north america for two summers 1981 and 1982 coastal ocean dynamics experiments 1 and 2 respectively and the intervening winter using measured winds and geostrophic winds calculated from fleet numerical oceanography center atmospheric pressure analyses summer wind fluctuations are driven primarily by the interaction between two relatively stationary pressure systems the north pacific subtropical high and southwest u s thermal low and by their interactions with propagating atmospheric systems to the north in particular propagating cyclones and associated fronts are often followed by a northeastward intensification of the high producing strong upwelling events along the california coast this summer event sequence occurs more frequently and is displaced farther to the south on average during summer 1981 winter wind fluctuations are primarily driven by propagating cyclones and anticyclones and they tend to have larger variance and space scales than in summer a preference for poleward equatorward propagation exists in summer winter and the largest time scales are observed in summer 1982 coastal atmospheric boundary layer processes substantially modify winds within 100 200 km of the coast consequently measured wind fluctuations are strongly polarized in the alongshore direction and have means and rms amplitudes that can vary considerably between nearby stations along the coast calculated wind fluctuations are less polarized in the alongshore direction and have alongshore correlation scales about 60 larger than those for measured winds they represent fluctuations with alongshore wavelengths of 900 km rather well but represent poorly those with smaller wavelengths and those due to coastal atmospheric boundary layer effects

coastal atmospheric forcing in the northern gulf of alaska a comparison of winds over the northern gulf of alaska found measured winds to be significantly weaker than calculated geostrophic winds the latter required more than the standard 30 reduction to correct for frictional effects in the maritime boundary layer an additional 11 is calculated based on principal axis analysis a counterclockwise rotation of the instantaneous geostrophic wind vectors of 44 59 total beyond the standard 15 was required to align them with those measured at a coastal weather station however events in these two wind sets were well correlated throughout the year and the rotary coherence was significant for frequencies lower than 0 895 cpd on the basis of empirical orthogonal function analysis most of the seasonal variability in this coastal current is associated with wind changes freshwater discharge is also important in driving the alongshore baroclinic flow and a secondary cross shelf flow

an eddy resolving model of circulation on the western gulf of alaska shelf 1 model development and sensitivity analyses an eddy resolving primitive equation model was used to simulate circulation on the shelf in the western gulf of alaska this paper describes the development and sensitivity analysis of the model while a companion paper stabeno and hermann this issue demonstrates correspondence with measured currents in specific years the model is initialized with a salinity field derived from local conductivity temperature depth surveys and forced with an idealized alongshore wind stress pattern buoyancy forcing is achieved by freshening the salinity field along a portion of the coastal wall the model exhibits many of the patterns evident in observations including mean flows and mesoscale eddies associated with the alaska coastal current acc sensitivity studies suggest a strong dependence of the barotropic flux of the acc on local winds and weak dependence on upstream buoyancy forcing both wind and buoyancy forcing significantly affect the generation of eddies strong northeasterly winds enhance cross shelf flow of the acc to the west of shelikof strait where isobaths veer southward strong buoyancy forcing also favors cross shelf flow in that region and enhances the formation of eddies

palaeoclimate records 60 8 ka in the austrian and swiss alps and their forelands abstract the european alps and their forelands provide a range of different archives and climate proxies for developing climate records in the time interval 60 8 thousand years ka ago we review quantitative and semi quantitative approaches for reconstructing climatic variables in the austrian and swiss sector of the alpine region within this time interval available quantitative to semi quantitative climate records in this region are mainly based on fossil assemblages of biota such as chironomids cladocerans coleopterans diatoms and pollen preserved in lake sediments and peat the analysis of oxygen isotopes in speleothems and lake sediment records the reconstruction of past variations in treeline altitude the reconstruction of past equilibrium line altitude and extent of glaciers based on geomorphological evidence and the interpretation of past soil formation processes dust deposition and permafrost as apparent in loess palaeosol sequences palaeoclimate reconstructions in the alpine region are affected by dating uncertainties increasing with age the fragmentary nature of most of the available records which typically only incorporate a fraction of the time interval of interest and the limited replication of records within and between regions furthermore there have been few attempts to cross validate different approaches across this time interval to confirm reconstructed patterns of climatic change by several independent lines of evidence based on our review we identify a number of developments that would provide major advances for palaeoclimate reconstruction for the period 60 8 ka in the alps and their forelands these include 1 the compilation of individual fragmentary records to longer and continuous reconstructions 2 replication of climate records and the development of regional reconstructions for different parts of the alps 3 the cross validation of different proxy types and approaches and 4 the reconstruction of past variations in climate gradients across the alps and their forelands furthermore the development of downscaled climate model runs for the alpine region 60 8 ka and of forward modelling approaches for climate proxies would expand the opportunities for quantitative assessments of climatic conditions in europe within this time interval

baroclinic instability in a downstream varying channel shelikof strait alaska abstract moored current meter observations obtained from upstream and downstream locations in shelikof strait between kodiak and afognak islands and the alaskan mainland in the northwest gulf of alaska show a considerable amount of low frequency variability superimposed upon the mean southwestward along channel flow moreover the spectral properties of these low frequency current fluctuations varied seasonally and according to location within the channel during fag 1976 the variance spectra of the along channel fluctuations at the upstream end of shelikof strait were sharply peaked at 2 86 days at the downstream end of the strait some 150 km to the southwest the variance spectrum of the cross channel fluctuations at 100 m was peaked at 6 15 days however the upstream 2 86 day signal was coherent with 2 86 day fluctuations downstream and the phase relationship between the two locations implied the presence of a downstream traveling wave with a wavelength of 74 km and a phase speed of 26 km day 1

coupling global and regional circulation models in the coastal gulf of alaska abstract as part of the us globec ne pacific program we are simulating currents in the coastal gulf of alaska cgoa to explore sources of interannual and interdecadal variability to do so we have developed a coupled modeling system composed of linked regional and global circulation models the regional model configured with 13 22 km resolution in the cgoa is forced at the surface by observed heat fluxes and wind stresses at the continental boundaries by observed runoff and at the open ocean boundaries by a combination of tracer climatologies and sub tidal velocity and tidal elevation provided by a global finite element model in this communication we describe the coupled system including its present method of intermodel coupling describe a series of multi year model hindcasts compare hindcast results with eulerian and lagrangian field data obtained in the cgoa in fall 1996 and assess the impact of global information barotropic sub tidal velocities and tidal elevations on the regional model under the present coupling strategy we find that the regional model produces appropriate current systems alaskan stream alaska coastal current and scalar fields but with mesoscale variability of ssh and velocities at somewhat reduced strength relative to data and with temperature gradients somewhat larger than those observed barotropic sub tidal information from the global model penetrates the regional model interior supplying additional mesoscale variability and modifying regional velocity and scalar fields in both shallow and deep areas tidal information exerts a significant influence on sub tidal scalar and velocity structure only in specific shallow areas where the tides and tidal mixing are strongest pending the exploration of alternate coupling schemes we infer from these results that on a time scale of months purely barotropic information from outside the cgoa will have a modest impact on its mean regional circulation but a potentially stronger impact on the statistics and details of mesoscale eddies

a comparison of gradient and observed over the water winds along a mountainous coast surface winds measured from april 11 1987 through august 16 1987 at five locations off the southeastern coast of the alaska peninsula indicate the complexity of coastal wind structure as a function of proximity to a mountainous coast proxy winds were computed for the same five locations from digitized sea level pressure fields using a simple geotriptic wind model shoreward of the rossby deformation radius the friction parameters of the geotriptic model vary from their open ocean values slowing the winds and rotating them farther counterclockwise these changing friction parameters account for the effect of the mountains on the surface wind distribution proxy winds and observed surface winds are coherent for periods longer than about 2 days and are better correlated farther seaward from the coast and for northeasterly alongshore winds and southeasterly onshore winds estimates of numbers of storms regional wind stress and regional vorticity determined from proxy winds are qualitatively accurate

distribution and transport patterns of northern rock sole lepidopsetta polyxystra larvae in the southeastern bering sea abstract we report the size abundance and distribution horizontal vertical of northern rock sole lepidopsetta polyxystra larvae collected from ichthyoplankton surveys on the southeastern bering sea shelf near unimak island in unimak pass and in the gulf of alaska south of unimak island the greatest abundances of larvae occurred within unimak pass and in the bering sea northeast of unimak island larvae were smaller and more abundant in 2002 than in 2003 larval abundance and size varied with depth highest abundances were at depths of 10 30 m during the day and larger fish appeared to migrate from below 20 m to 0 10 m at night there was evidence of multiple spawning locales and larval dispersal pathways that were depth and area specific northern rock sole larvae spawned west of unimak pass along the aleutian islands may be transported northward by the bering slope current larvae spawned in the gulf of alaska and advected through unimak pass are differentially dispersed primarily to the middle and outer shelves along the 100 m and 200 m isobaths or along the alaska peninsula larvae spawned along the alaska peninsula east of unimak island appear to have the greatest chance of being transported to nursery areas in the coastal domain dispersal of near surface northern rock sole larvae in any of these locations is likely influenced by wind driven advection but below surface 10 m northern rock sole larval transport is probably more affected by factors that modulate geostrophic flow rather than wind driven surface currents

near surface strong winds in a marine extratropical cyclone acceleration of the winds and the importance of surface fluxes a rapidly developing extratropical cyclone named tini brought strong winds to ireland and the united kingdom on 12 february 2014 a mesoscale model simulation is used to analyze the development of the strong winds through the terms in the horizontal momentum equation the maximum of near surface wind speed equatorward of the cyclone was composed of two different airstreams that underwent different paths to acceleration first horizontally moving air in the cold conveyor belt was accelerated by the along flow pressure gradient force but was decelerated by friction second descending air accelerated into the eastern end of the maximum of near surface wind speed and was associated in part with a sting jet caused by the increasing along flow horizontal pressure gradient force at lower levels when this descending air entered the boundary layer it too was decelerated by surface friction surface fluxes of heat and moisture were necessary to destabilize and deepen the boundary layer allowing mixing of the strongest winds from the free troposphere down to the surface a simulation with the surface fluxes turned off during cyclogenesis showed a more stable boundary layer around the bent back front which inhibited the strongest winds from reaching the surface the descent of the sting jet air was associated with a maximum in quasigeostrophic omega which consisted of both synoptic scale and mesoscale descent the latter associated with frontolysis occurring at the end of the bent back front thus the near surface wind maximum was created by the synoptic scale and mesoscale dynamics whereas localized moist processes were negligible

altimeter derived surface circulation in the large scale ne pacific gyres part 1 seasonal variability abstract the seasonal variability of sea surface height ssh and currents are defined by analysis of altimeter data in the ne pacific ocean over the region from central america to the alaska gyre the results help to clarify questions about the timing of seasonal maxima in the boundary currents as explained below the long term temporal mean of the ssh values must be removed at each spatial point to remove the temporally invariant and large signal caused by the marine geoid we refer to the resulting ssh values which contain all of the temporal variations as the residual ssh our main findings are 1 the maximum surface velocities around the boundaries of the cyclonic alaska gyre the alaska current and the alaska stream occur in winter at the same time that the equatorward california current is weakest or reversed forming the poleward davidson current the maximum surface velocities in the california current occur in summer these seasonal maxima are coincident with the large scale atmospheric wind forcing over each region 2 most of the seasonal variability occurs as strong residuals in alongshore surface currents around the boundaries of the ne pacific basin directly connecting the boundaries of the subpolar gyre the subtropical gyre and the equatorial current system 3 seasonal variability in the surface velocities of the eastward north pacific current west wind drift is weak in comparison to seasonal changes in the surface currents along the boundaries 4 there is an initial appearance next to the coast and offshore migration of seasonal highs and lows in ssh alongshore velocity and eddy kinetic energy eke in the alaska gyre similar to the previously described seasonal offshore migration in the california current 5 the seasonal development of high ssh and poleward current residuals next to the coast appear first off central america and mainland mexico in may june prior to their appearance in the southern part of the california current in july august and their eventual spread around the entire basin in november december similarly low ssh and equatorward transport residuals appear first off central america and mexico in january february before spreading farther north in spring and summer 6 the maximum values of eke occur when each of the boundary currents are maximum

three dimensional mesoscale circulation within a convective post frontal system possible role of conditional symmetric instability for triggering convective motion the role of the conditional symmetric instability csi in the formation of convective systems in the cold airmass located at the rear of a secondary cold frontal system is evaluated this study is based on observations made on 4 june 1984 during the french experiment landes fronts 84 in particular the mesoscale three dimensional circulation deduced from doppler radar data within one of these convective systems is studied in detail and compared with that predicted by the csi theory in spite of the fact that on the one hand notable convective scale motion masks the mesoscale circulation and that on the other hand the synoptic scale circulation is poorly described this comparison shows that among the various theories involved at the mesoscale only csi gives a proper account of the observed mesoscale circulation

holocene climate fire and vegetation dynamics at the tree line in the northwestern swiss alps treelines are expected to rise to higher elevations with climate warming the rate and extent however are still largely unknown here we present the first multi proxy palaeoecological study from the treeline in the northwestern swiss alps that covers the entire holocene we reconstructed climate fire and vegetation dynamics at iffigsee an alpine lake at 2 065 m a s l by using seismic sedimentary surveys loss on ignition visible spectrum reflectance spectroscopy pollen spore macrofossil and charcoal analyses afforestation with larix decidua and tree betula probably b pendula started at 9 800 cal b p more than 1 000 years later than at similar elevations in the central and southern alps indicating cooler temperatures and or a high seasonality highest biomass production and forest position of 2 100 2 300 m a s l are inferred during the holocene thermal maximum from 7 000 to 5 000 cal b p with the onset of pastoralism and transhumance at 6 800 6 500 cal b p human impact became an important factor in the vegetation dynamics at iffigsee this early evidence of pastoralism is documented by the presence of grazing indicators pollen spores as well as a wealth of archaeological finds at the nearby mountain pass of schnidejoch human and fire impact during the neolithic and bronze ages led to the establishment of pastures and facilitated the expansion of picea abies and alnus viridis we expect that in mountain areas with land abandonment the treeline will react quickly to future climate warming by shifting to higher elevations causing drastic changes in species distribution and composition as well as severe biodiversity losses

three dimensional structure of mesoscale eddies in the norwegian coastal current abstract an eddy tracking experiment was carried out in the norwegian coastal current during a 10 day field investigation period in february march 1986 noaa satellite infrared data were used in near real time to direct the r v h kon mosby into the position of four mesoscale eddy features at the front between the coastal water and atlantic water combined acoustic doppler current profiler towed undulating ctd and satellite infrared data provide three dimensional velocity and thermohaline structure of these eddies the upper layer of the eddies is strongly asymmetric with maximum speed of about 1 m s 1 while the barotropic component is about 0 20 0 30 m s 1 after removing the effect of the asymmetry the ratio of baroclinic to barotropic speed is about 0 5 northward eddy propagation speed of about 5 km day 1 is observed during the investigation period structural changes are minor bottom steering of atlantic water leads to convergence with the coastal current in turn the thickness of the two layers

some characteristics of yakutat eddies propagating along the continental slope of the northern gulf of alaska abstract data from array for real time geostrophic oceanography argo profiling floats oil tanker thermosalinographs shipboard adcp and towed ctd surveys and satellite altimetry are used to examine properties of two 200 km diameter anticyclonic yakutat eddies that propagated westward at 1 5 km day 1 along the continental slope of the northern gulf of alaska goa in 2001 and 2003 the eddies had lifetimes of up to 5 years remained close to the shelfbreak and had relatively constant size and strength until they encountered the alaskan stream where they appeared to spawn smaller shorter lived anticyclones the azimuthal velocity field was vigorous 25 40 cm s 1 and in gradient wind balance with rossby numbers of 0 05 conservation of salt and azimuthal mass transports between 20 m and the depth of the 32 2 isohaline from shipboard surveys in may and august 2003 suggest little mass exchange occurred between the surface layers of the eddy and ambient waters chlorophyll concentrations were greater in the eddy than in ambient waters in both may and august in may the chlorophyll was patchily distributed while in august dense chlorophyll concentrations occurred in and beneath the seasonal thermocline within 50 km of the eddy center the high august chlorophyll concentrations might have been fostered by a broad and shallow it appears likely that as yakutat eddies approach the shelfbreak non linear processes will modify the slope flow field and the stability and structure of the shelfbreak front leading to cross slope flows and flow reversals this interaction may induce 30 km wide streamers of shelf water to flow around the trailing edge of the anticyclone the role of streamers in the freshwater and nutrient budgets of the goa shelf and basin is unknown but their contribution to these budgets will depend on the trajectory of a yakutat eddy especially its proximity to the shelfbreak as the eddy propagates along the goa continental slope

effects of sea level sea ice extent and nutrient availability on primary production at the umnak plateau bering sea iodp site u1339 during marine isotope stage mis 5 abstract this study investigates how primary production responded to changes in nutrient availability sea level and sea ice coverage at the umnak plateau during marine isotope stage mis 5 and parts of mis 4 and mis 6 the umnak plateau during mis 4 and mis 6 had low primary production resulting from extensive sea ice coverage that enhanced stratification and limited nutrient replenishment this nutrient limitation was relieved during the deglaciation going into mis 5 when previously exposed continental shelves were flooded and the eastern aleutian island passes were opened by an increase in sea level resulting in an increase in productivity opening and closing of the eastern aleutian island passes during the rest of mis 5 reflected fluctuations in sea level and likely affected nutrient sources and productivity at the umnak plateau nutrients during sea level lowstands were likely sourced by the aleutian north slope current whereas most of the sea level high stands throughout mis 5 had nitrogen sourced by an increase in nitrogen fixation and the assimilation of remineralized nitrogen which led to highly depleted nitrogen isotope values never before seen for the northern pacific higher sea level and productivity near the beginning of mis 5 likely reflected mis 5e however a discrepancy between two diatom productivity proxies suggests that changing environmental conditions stimulated a change in the dominant diatom species this highlights the complexities associated with productivity in the bering sea and emphasizes the need to continue studying how productivity and ecosystems changed during previous warm periods

late glacial climatic oscillations as recorded in swiss lake sediments regional pollen assemblage zones for the late glacial period of the swiss plateau are introduced and defined they include four major zones artemisia juniperus hippophae betula pinus paz with several subzones pollen and oxygen isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000 9500 yr bp the first oscillation termed the aegelsee fluctuation occurs shortly before 12 000 yr bp and varve counts suggest its duration was ca 100 yr it is characterised by a short decrease in the oxygen isotopes as well as a short increase in nap associated with a depression in birch pollen values the second oscillation which occurs in the 18o record shortly before the deposition of the laacher see tephra ca 11 000 yr bp is termed the gerzensee fluctuation it occurs during a pine dominated phase and its vegetational effects cannot be determined palynologically the most prominent regressive phase is the younger dryas biozone ca 10 700 10 000 yr bp characterised by an increase in heliophilous nap and low 18o values the younger dryas biozone can often be subdivided palynologically into two parts a first part rich in grasses and juniper and a second part with higher filipendula and birch values during the preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios comparison of the swiss oxygen isotope profiles with the greenland dye 3 record suggests that not only the three major shifts in the 18o curves but also the minor ones are closely comparable suggesting some common climatic control

circulation in shelikof strait alaska abstract extensive hydrographic surveys were conducted in shelikof strait in march and october 1985 the data are used to describe circulation and property distributions and the changes that occurred the upper layer flows to the southwest throughout the year but greatest speeds occur in the fall when surface waters are least saline because of a maximum in freshwater discharge the deep water has its source to the south and the properties seem to result from vertical mixing of this southern water thus shelikof strait has an estuarine like circulation with a northward deep inflow property distribution showed that isolines were usually deepest on the right side of the channel looking to the southwest greatest baroclinic speeds were often there also differential ekman pumping may contribute to the development of this structure and its changes volume transport estimates varied considerably in october the southwest flow bifurcated with part continuing along the alaska peninsula and the rest exiting t

vegetational response to climatic changes recorded in swiss late glacial lake sediments abstract high resolution pollen analysis at five lakes on an altitudinal transect in switzerland gerzensee 603 m leysin 1230 m regenmoos 1260 m zeneggen 1510 m heremence 2290 m focused on the vegetational response to the rapid climatic changes at the end and beginning of the younger dryas and to the minor gerzensee and preboreal climatic oscillations an absolute time scale transferred from the greenland grip ice core to the gerzensee and leysin records by wiggle matching the oxygen isotope stratigraphies facilitates the estimation of pollen influx and rates of change the climatic warming at the end of the younger dryas indicated by increases in oxygen isotope values and or the beginning of organic sedimentation in the lakes was immediately reflected in the vegetation at all the sites investigated the time lags at sites situated above the timberline during the younger dryas are considered to be migrational lags at the onset of the younger dryas a time lag of several decades occurred between the oxygen isotope record of climatic cooling and the major response of the vegetation whereas minor vegetation changes occurred with or without short time lags betula reacted earlier to the new environmental conditions within about 40 50 yr at gerzensee and within less than 36 yr at leysin than pinus and artemisia about 170 yr suggesting that time lags are due to the ecological requirements of the different taxa for the gerzensee and preboreal oscillations little or no change can be observed in the pollen record from gerzensee whereas at leysin both climatic oscillations produced a statistically significant vegetational response to both climatic oscillations generally the vegetation responses to climatic changes are more pronounced near vegetation ecotones at medium and higher altitudes than in the lowlands

currents and transport on the eastern bering sea shelf an integration of over 20 years of data abstract more than 20 years of data from moorings satellite tracked drifters and hydrographic surveys are integrated to provide a comprehensive view of currents and transport on the eastern bering sea shelf the major sources of water onto the eastern bering sea shelf are north pacific water flowing through unimak pass and bering slope water flowing onto the shelf usually via the canyons that intersect the shelf break absolute geostrophic transport through unimak pass varies from an average of 0 25 106 m3 s 1 sv in the warm months to 0 43 sv in the cold months flow along the 50 m isobath is weak with a transport of 13 months and from amukta pass to bering strait via the bering slope current is 8 months consequently the source of most of the heat transported into the arctic through bering strait is a result of air sea interactions local to the northern bering sea analysis of the currents and water properties on the southern shelf indicates that 50 of the shelf water is exchanged with slope water during october january each year this exchange elevates the october mid shelf average nitrate level from 6 m to 14 16 m by the end of january

coastal temperature and salinity in the northern gulf of alaska 1970 1983 analysis of the time series of the temperature and salinity in the northern gulf of alaska from december 1970 to september 1983 shows annual signals in water properties with warm low salinity surface water in summer and cold high salinity surface water in late winter the mean surface temperature and salinity were 11 5 c and 27 33 in summer and 4 3 c and 31 16 in winter over the nearly 13 year observational period the surface temperature range was from 2 to 14 c and the surface salinity range was 26 to 31 5 abnormal warming throughout the water column was evident in 1976 1977 and 1983 these thermal features appear to be caused by advection rather than local effects the salinity anomalies in the upper 50 m are primarily correlated with freshwater discharge and secondarily with wind stress

the relevance of conditional symmetric instability to the prediction of mesoscale frontal rainbands this paper examines the theory of conditional symmetric instability bennetts and hoskins 1979 and considers its relevance to meso scale frontal rainbands the theoretical growth rate of the instability is evaluated from synoptic scale data obtained from a numerical forecast model and compared with observations of the horizontal structure of rainfall observed by radar one case study is presented in detail and a further 44 cases summarized rainbands were observed on 80 of the occasions on which they were predicted

evolution of mesoscale precipitation band environments within the comma head of northeast u s cyclones abstract this paper explores the mesoscale forcing and stability evolution of intense precipitation bands in the comma head sector of extratropical cyclones using the 32 km north american regional reanalysis hourly 20 km rapid update cycle analyses and 2 km composite radar reflectivity data a statistical and composite analysis of 36 banded events occurring during the 2002 08 cool seasons reveals a common cyclone evolution and associated band life cycle a majority 61 of banded events develop along the northern portion of a hook shaped upper level potential vorticity pv anomaly during the 6 h leading up to band formation lower tropospheric frontogenesis nearly doubles and the conditional stability above the frontal zone is reduced the frontogenesis increase is primarily due to changes in the kinematic flow associated with the development of a mesoscale geopotential height trough this trough extends poleward of the 700 hpa low and is the vertical extension of the surface warm front and surface

on the seasonal variability of the alaska coastal current current measurements of the alaska coastal current were analyzed for their mean structures and seasonal cycles the current is westward alongshore at the surface 25 to 175 cm s 1 with a baroclinic shear of 30 cm s 1 in the upper 70 m the amplitude of the seasonal variation of the flow decreases with depth and its maximum phase delay of 3 months occurs at 175 m relative to the surface the amplitude of the seasonal cycle of the north south cross shore flow is a minimum at mid depth the phase of this seasonal cycle is also delayed at deeper depths but the maximum shift relative to the surface occurs at 110 m rather than at the bottom 175 m empirical orthogonal function analysis indicates that the first mode of the alongshore flow has nearly constant amplitude with depth barotropic variations and is related to the east west wind the second mode explains significant variance of the surface current and the freshwater discharge the cross shore flow analysis shows that the first mode is again nearly barotropic and is principally related to the east west wind with increased southward flow when the winds are increased westward the second mode of the cross shore flow fluctuates with runoff such that the offshore flow at the surface and the onshore flow near to the bottom coincide with increased freshwater discharge

patterns of flow in the canyons of the northern gulf of alaska abstract the continental shelf around kodiak island is incised with numerous submarine canyons which play an important role in the cross shelf transport of heat salt and nutrients and the transport of ichthyoplankton of deep spawning fish from the slope region into the shallow nursery grounds surrounding kodiak island to explore the pathways and variability of flow and the extent of tidal mixing within the canyons moorings were placed in the chiniak barnabas and amatuli troughs and off the shelf from resurrection bay seward line and the kenai peninsula gore point in the troughs intensified flow was evident near the trough walls and flow was directed by bathymetry with inflow along the upstream northern side and outflow along the downstream southern side the presence of mesoscale eddies in the gulf had no unique influence on currents or salinity in the troughs tidal mixing was strongest in chiniak trough and this introduced cold nutrient rich bottom waters into the upper water column intensified bottom flow associated with the alaskan coastal current was evident along the seward line and gore point and directed toward the kennedy stevenson entrances which are also regions of strong tidal mixing observations of tidal mixing were consistent with model results and satellite images showing cooler phytoplankton rich water in summer in the nursery grounds that surround kodiak island patterns of flow within the troughs and in shelikof strait were consistent with the springtime advance of ichthyoplankton across the shelf

transport through unimak pass alaska we examined inflow through unimak pass 200 m deep which is the only major connection between the shelves of the north pacific ocean and the eastern bering sea geostrophic transport was generally northward from the gulf of alaska into the bering sea the flow through the pass appeared to be modulated by the seasonal cycle of freshwater discharge on shorter time scales transport also was affected by semi daily variations in tidal mixing this effect was significant and not anticipated near bottom currents measured from moorings were maximum during winter and significantly correlated r 0 7 with the alongshore winds although the flow through unimak pass transported some nutrients from the north pacific ocean the gulf of alaska shelf is not the major source of nutrients to the bering sea shelf

the alaska coastal current continuity of transport and forcing current moorings were deployed on the continental shelf at 13 locations in the northwest gulf of alaska they measured the alaska coastal current at three positions along the coast during april october 1991 the strongest currents were in the confined region of shelikof strait mean daily transport was as large as 2 5 106 m3 s 1 mean transport over the 6 month period ranged from 0 85 106 m3 s 1 at the easternmost line off gore point to 0 64 106 m3 s1 at the westernmost section shelikof strait indicating significant transport to the south of kodiak island the transports were well correlated r 0 8 and in phase with each other and were also correlated with wind r 0 6 data suggest that in shelikof strait and off gore point baroclinic flow is 75 and 40 respectively of total transport

holocene tree immigration and the chironomid fauna of a small swiss subalpine lake hinterburgsee 1515 m asl early holocene reforestation by stone pine pinus cembra and tree birch betula pubescens took place ca 500 years after the end of the younger dryas at hinterburgsee a small subalpine lake in the northern swiss alps during the next ca 3000 years the local vegetation consisted of open woodlands with many pioneer dwarf shrubs and herbs the expansion of silver fir abies alba at ca 7400 calibrated radiocarbon years before present cal bp and norway spruce picea abies at ca 6000 cal bp in hinterburgsee s catchment led to a closing of the local forests with a successive decrease in erosion and a distinct change in hinterburgsee s sediment composition first signs of probably human induced openings of the catchment forest are apparent at ca 2500 cal bp but it is not until the past ca 800 years that pollen analysis suggests strong local and regional anthropogenic activity the strongest and most abrupt changes in the holocene development of hinterburgsee s chironomid fauna took place at ca 11 500 cal bp and at ca 10 000 cal bp when parts of the alpine taxa that were dominant during the younger dryas disappeared from the lake the first change is most likely related to the increasing temperatures after the end of the younger dryas the second possibly to decreasing lake depth and increasing summer insolation in the early holocene that may have led to warmer bottom water temperatures in the lake no clear relationship between the changes in catchment vegetation and the development of the chironomid fauna was found possibly the increase in sediment organic matter associated with the denser catchment forests was responsible for a succession in the chironomid stratigraphy between 7000 and 4500 cal bp however due to the high sedimentation rates in hinterburgsee this trend could also be a consequence of or be promoted by the sediment infilling of the lake basin this conjecture is supported by the increasing importance of tanytarsus lugens type a chironomid taxon dominant in the extant chironomid assemblages of shallow mountain lakes in switzerland the only shift in the chironomid fauna that clearly parallels a change in catchment vegetation is found during the past ca 800 years we discuss possible reasons for the comparatively weak influence of catchment vegetation on the chironomid fauna of hinterburgsee and the implications of our results for multi proxy studies on past climate involving both palaeobotanical and chironomid based reconstructions 2002 elsevier science b v all rights reserved

aircraft observations of offshore directed flow near wide bay alaska abstract the effects of the upstream orography of the alaska peninsula on the low level flow in the coastal region are studied using observations from two noaa p 3 research flights the terrain in this region includes a low sill at wide day approximately 300 m high and 80 km wide which is flanked by moderate terrain to the southwest 900 m high and higher terrain to the northeast 1500 m high for the case of 26 february 1987 a large froude number fr 1 6 characterized the incident flow boundary layer wind speeds were approximately 30 m s 1 downstream of the gap at wide bay and the moderate terrain the cross terrain component of the wind above the boundary layer was 24 m s 1 upstream of the barrier and as lame as 45 m s 1 approximately 70 km downstream of the barrier wind speeds were significantly less above and downstream of this wind maximum as with a hydraulic jump a prominent trough in sea level pressure was observed in the lee of the higher terrain the largest 100 m wind speeds 34

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

modification of a kenai eddy along the alaskan stream 1 a kenai eddy was studied through analyses of satellite altimeter data and hydrographic data from shipboard and argo float observations this eddy formed in december 2006 south of the kenai peninsula and propagated southwestward along the alaskan stream the eddy held horizontally uniform warm core water in january 2007 in late winter 2007 this core water was cooled from the top and a subsurface temperature maximum was formed around 26 5 two years later in summer 2009 warm and low dissolved oxygen low do water characterized by a temperature maximum around 26 5 was observed again in the eddy core and was likely the remnant of original core water at the same time cold and high do water intrusions occurred in the eddy core suggesting that strong modification of core water was ongoing after summer 2009 the core water was fully changed through interaction with another eddy

long term observations of alaska coastal current in the northern gulf of alaska abstract the alaska coastal current is a continuous well defined system extending for 1700 km along the coast of alaska from seward alaska to samalga pass in the aleutian islands the currents in this region are examined using data collected at 20 mooring sites and from 400 satellite tracked drifters while not continuous the mooring data span a 30 year period 1984 2014 using current meter data collected at a dozen mooring sites spread over four lines seward gore point kennedy and stevenson entrances and the exit to shelikof strait total transport was calculated transport was significantly correlated with alongshore winds although the correlation at the seward line was weak the largest mean transport in the alaska coastal current occurred at gore point 1 4 10 6 m 3 s 1 in winter and 0 6 10 6 m 3 s 1 in summer with the transport at the exit to shelikof strait 1 3 10 6 m 3 s 1 in winter and 0 6 10 6 m 3 s 1 in summer only slightly less the transport was modified at the seward line in late summer and fall by frontal undulations associated with strong river discharge that enters onto the shelf at that time of year the interaction of the alaska coastal current and tidal currents with shallow banks in the vicinity of kodiak archipeligo and in kennedy stevenson entrance results in mixing and prolonged primary production throughout the summer

offshore directed winds in the vicinity of prince william sound alaska abstract the thermal contrast between cold air over continental alaska and relatively warm marine air over the gulf of alaska causes frequent low level offshore directed winds over the south central alaskan coast during the cold season coastal mountains affect these winds by inhibiting low level mixing of continental and marine air masses near the coast by providing channels that focus and accelerate drainage winds and by exciting mountain lee waves offshore directed winds were observed twice with a research aircraft the strongest winds were measured at the mouth of the copper river and over and downwind of resurrection bay the synoptic weather pattern and its orientation to local topographic features influenced wind magnitude with the pressure gradient perpendicular to the coast offshore directed flow was light except at the copper river and resurrection bay drainages when the pressure gradient was aligned with the shore regional surface winds were stronger and more uniform although the copp

the influence of several factors controlling the interactions between prince william sound alaska and the northern gulf of alaska abstract interactions between the circulation of prince william sound pws alaska and that of the continental shelf region of the northern gulf of alaska are studied numerically the focus is on the flow structure at hinchinbrook entrance he and montague strait ms and the associated pws interior circulation under various initial state and forcing configurations bottom topography inhibits flow into pws under barotropic conditions while stratification very much facilitates flow into pws layered flow develops at he and ms under baroclinic conditions with two four layers under march september stratification conditions in both baroclinic cases the top layer transports inflow and a cyclonic eddy develops over the central basin of pws westward wind the predominant direction enhances this upper layer inflow and the lower layer outflow eastward wind completely reverses the flow direction not only at he but also inside pws remarkably the total outflow through ms is consistently less than the

the importance of plant macrofossils in late glacial climatic reconstructions an example from western norway a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract late glacial pollen diagrams from two sites on the outermost coast of western norway are discussed on the islands of utsira paus 1990 and blomoy mangerud 1970 during the allerod chronozone 12 000 11 000 bp their climatic reconstructions depend on the assumed local occurrence of tree betula b pubescens at blomoy and on the presence of pollen of thermophilous taxa at utsira the plant macrofossil analyses at these same sites do not indicate the presence of betula at either during the allerod reconstruction of the local vegetation is of willow shrubs and empetrum dwarf shrub heath at utsira and of salix herbacea dominated vegetation at blomoy these reconstructions accord well with modern analogues above the tree line in the west norwegian mountains the inferred summer temperatures during the allerod are thus 2 6 c lower than had been proposed from pollen evidence alone late glacial plant macrofossil assemblages can generally be easily matched with modern vegetation analogues on the west norwegian coast it would appear that the pollen of betula and thermophilous indicators arrived by long distance dispersal facilitated by the strong winds during the late glacial the frequently found no analogue pollen assemblages of the late glacial period may therefore be due to their previously unsuspected content of extra regional pollen dispersed by strong winds this emphasises that climatic reconstructions should only be made using taxa that were certainly growing locally it demonstrates the importance of using locally derived ecologically sound vegetational reconstructions for the reconstruction of late glacial climates and for this plant macrofossil analysis is invaluable

climatic and human impacts on mountain vegetation at lauenensee bernese alps switzerland during the last 14 000 years lake sediments from lauenensee 1381 m a s l a small lake in the bernese alps were analysed to reconstruct the vegetation and fire history the chronology is based on 11 calibrated radiocarbon

wave current interaction study in the gulf of alaska for detection of eddies by synthetic aperture radar high resolution ers i synthetic aperture radar sar images are used to detect a mesoscale eddy such features limit dispersal of pollock larvae and therefore likely influence recruitment of fish in the gulf of alaska during high sea states and high winds the direct surface signature of the eddy was not clearly visible but the wave refraction in the eddy area was observed the rays of the wave field are traced out directly from the sar image the ray pattern gives information on the refraction pattern and on the relative variation of the wave energy along a ray through wave current interaction these observations are simulated by a ray tracing model which incorporates a surface current field associated with the eddy the numerical results of the model show that the waves are refracted and diverge in the eddy field with energy density decreasing the model data comparison for each ray shows the model predictions are in good agreement with the sar data

environmental changes of a shallow kettle lake catchment in a young glacial landscape sumowskie lake catchment north central poland abstract on the basis of detailed analysis sedimentological palynological macroremains geochemical and gis analysis the development of the sumowskie paleolake was reconstructed obtained results led to distinguish three main stages of the evolution of the basin and its catchment during the late glacial and the holocene the lacustrine stage the lake overgrowth stage and the post lacustrine stage study site is located in the western part of the brodnica lakeland north eastern poland within the former sumowskie lake bottom multidisciplinary research was conducted for two cores sedimentological palynological plant macroremains sum a 149 cm and sum c 51 cm and the soil profile sum 3 sedimentological geochemical gis analyses land cover and water level changes were carried out for the nowadays sumowskie lakes catchment it was confirmed that climate was the most important factor influencing the evolution of the lake and its surrounding although the role of this factor decreased in the neo holocene period in favor of rapidly growing human impact changes of the water level were much more abrupt and lasted longer e g 9500 5000 bp hiatus caused by the water level decrease than in other described basins of the region due to the specific geomorphologic situation shallow kettle basins could alternately act as lakes and wetlands as they are well spread in the young glacial area the strong influence of this abrupt and long term events should be reconsidered

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

satellite observations of small coastal ocean eddies in the southern california bight this study describes the characteristics of extensive small scale coastal ocean eddies in the southern california bight these surface features were primarily detected by using ers 1 and ers 2 synthetic aperture radar sar satellite imagery from 1992 to 1998 the eddies predominantly cyclonic in their rotation appeared to result from several forcing mechanisms they were mainly observed within the santa barbara channel and the santa monica san pedro basin regions and appeared to be seasonal in their distribution observed eddy diameters were all less than 50 km with over 70 less than 10 km the sar data were complemented by sea surface temperature measurements derived from advanced very high resolution radiometer satellite imagery as well as in situ data from moorings and drifters that provided substantial verification of the small scale eddies these findings are significant in that the eddies were in general smaller in size and more abundant than previously reported additionally these results provide further evidence of the complex near surface circulation within the southern california bight with important implications for nutrient flux productivity plankton patchiness larval transport and recruitment and dispersal of pollutants

scale analysis of marine winds in straits and along mountainous coasts abstract the complicated wind regimes in straits which develop in response to different large scale pressure fields are investigated by scale analysis of the equations of motion adjustment of the mass and motion fields in straits o los km in width is governed by four nondimensional numbers separate along and cross strait rossby numbers a strait drag coefficient and a stratification parameter which relates the internal rossby radius of deformation to the width of the strait the wind field is in approximate geostrophic balance with an imposed cross channel pressure gradient an along channel pressure gradient is primarily balanced by ageostrophic acceleration of the wind field down the axis of the strait the gap wind vertical motion and the accompanying horizontal divergence in the near surface wind field can be large even for moderately stable stratification as a consequence there may be particularly abrupt transitions of the surface wind field at the exits of straits where there is a rapid c

biotic responses to rapid climatic changes abstract qualitative and quantitative changes in fossil flora and fauna have been used in many studies to infer climatic change here we ask a different question how do flora and fauna respond to climatic changes such as rapid warming or cooling as an independent proxy for paleotemperature we take the ratio of oxygen isotopes in biogenically precipitated lake marl and in ostracod shells this introductory paper describes the project design and the five sites on an altitudinal transect from 600 m to about 2300 m asl in the western swiss alps as cases of climatic cooling and warming we use the beginning and end of the younger dryas as major changes and the gerzensee and preboreal oscillations as minor changes at the two sites of gerzensee and leysin these changes are recorded in stable isotope ratios and there the time scales can be derived by correlations to the grip ice core schwander et al 2000 von grafenstein et al 2000 biotic responses to climate changes are treated in individual papers using pollen wick 2000 plant macrofossils tobolski and ammann 2000 and remains of chironomids brooks 2000 beetles and other insects lemdahl 2000 and chydorid cladocera hofmann 2000 they are followed by a synthesis focusing on quantification of biotic responses ammann et al 2000 in addition a reconstruction of summer temperatures for the allerod and the younger dryas at gerzensee is provided by lotter et al 2000

macrofossils as records of plant responses to rapid late glacial climatic changes at three sites in the swiss alps plant macrofossils from the end of the younger dryas were analysed at three sites gerzensee 603 m asl leysin 1230 m asl and zeneggen 1510 m asl for the first two sites an oxygen isotope record is also available that was used to develop a time scale schwander et al this volume dates refer therefore to calibrated years according to the grip time scale around gerzensee a pine forest with some tree birches grew during the younger dryas with the onset of the isotopic shift initiating the rapid warming about 11 535 cal years before 1950 the pine forest became more productive and denser at leysin no trees except some juniper scrub grew during the younger dryas tree birches pine and poplar immigrated from lower altitudes and arrived after the end of the isotopic shift about 11 487 b p i e at the beginning of the preboreal at about 11 420 b p zeneggen is situated somewhat higher than leysin but single tree birches and pines survived the younger dryas at the site at the beginning of the preboreal their productivity and population densities increased simultaneously shifts from nitella to chara and from silt to gyttja are recorded all indicating rapidly warming conditions and higher nutrient levels of the lake water and probably of the soils in the catchment at gerzensee the beginning of the younger dryas was also analysed the beginning of the isotopic shift correlates within one sample about 15 years to rapid decreases of macrofossils of pines and tree birches

a comparison of observed and geostrophically calculated wintertime surface winds over the east china sea wintertime geostrophic winds calculated over the east china sea from surface pressure maps are compared to observed winds from the region for mean winds the average counterclockwise veering angle from to is 37 and the average reduction in amplitude is 39 for fluctuating winds the average veering and attenuation are 25 and 55 the greatest reduction occurs for land stations while the lowest 33 occurs at an offshore buoy station evidence from power spectral computations suggests that the spectral contents of and are very similar even for cases where observed winds are of much lower amplitude and do not appear to be reliable

mesoscale dynamics in the palm sunday tornado outbreak abstract radar and satellite imagery suggest that strong mesoscale forcing occurred in the palm sunday tornado outbreak on 27 march 1994 parallel lines of severe thunderstorms within each of three mesoscale convective systems developed just ahead of a cold front in mississippi and alabama on this date analyses of routine meteorological observations barograph data and forecasts from the eta and ngm models and a mesoscale research model mass are used to examine the relative roles of large scale dynamics and mesoscale processes in triggering and organizing the mesoscale convection quasigeostrophic forcing was absent in the outbreak region likewise a thermally direct circulation system transverse to the upper level jet that was present to the northwest of the outbreak region was decoupled from the strong low level ascent occurring in northern alabama and mississippi at the time of the outbreak strong ageostrophic frontogenesis in the presence of conditional symmetric instability csi was the chief

the record of hydroclimatic changes in the sediments of a kettle hole in a young glacial landscape north central poland abstract multidisciplinary research on the bottom sediments of a kettle hole at the retno site the brodnica lake district north central poland provided some information about changes in hydroclimatic conditions in the late glacial and the holocene detailed analysis sedimentological palynological macroremains geochemical and radiocarbon dating helped to identify 6 stages in the development of the depression in the village of gaj near retno lake with 11 phases of hydroclimatic conditions sediments of the retno profile with a total thickness of 6 72 m reflected individual natural stages in the development of the depression from a lake to a peat bog most of the environmental changes were gradual a sequence of late glacial and early holocene lacustrine sediments mainly gyttja occurred in the floor of the profile the upper 4 10 m consisted of paludal deposits peat of transitional and raised bogs divided at a depth of 1 56 1 54 m b g l by a thin layer of clay dated late subboreal early subatlantic the presence of this layer indicates a sudden change in the environmental conditions associated with a water level rise at that time denudation processes started within the drainage basin probably induced by human activity the important effects related to contemporary anthropopressure included desiccation of the peat bog muck formation in the uppermost 10 cm layer and elevated trophic conditions resulting in a change of the vegetation cover

on the nature of winter cooling and the recent temperature shift on the northern gulf of alaska shelf 1 in spring 2006 and 2007 northern gulf of alaska goa shelf waters were 1 5 c below average throughout the 250 m deep shelf and the salinity dependent winter stratification was anomalously weak due to above below average surface bottom salinities spring 2007 and 2008 temperatures were also 1 5 c below average but the anomalies were confined to the upper 100 m due to moderate salt stratification shelf temperatures in these 2 years were among the lowest observed since the early 1970s thus interrupting an approximately 30 year warming trend we examined winter cooling processes using historical conductivity temperature depth ctd profiles and mooring data from hydrographic station gak1 the 2006 and 2007 cooling was associated with anomalously strong atmospheric heat loss in november 2006 and march 2007 and below average fall runoff which weakened winter stratification and allowed the late cooling to penetrate throughout the water column in 2007 and 2008 early winter cooling was weak fall runoff large and stratification moderate at 100 m so that spring temperature anomalies were trapped to the upper 100 m analysis of the 40 year gak1 ctd record indicates that winter averaged air sea heat flux and salinity stratification anomalies explain 81 of the variation in deep 100 250 m goa temperatures although the timing and magnitude of winter runoff influences the shelf temperature distribution temperature anomalies are a consequence of three dimensional circulation and mixing processes these involve the complex but poorly understood interplay among the air sea heat flux the ocean heat flux convergences the stabilizing influence of runoff and the destabilizing effects of cooling vertical mixing and the wind driven cross shelf buoyancy flux

the response of a shallow lake and its catchment to late glacial climate changes a case study from eastern poland in this study we investigate how climate fluctuation in the late glacial period influenced the development of a lake and its catchment located in the east european plain we analyzed the sediments of the lake for pollen subfossil cladocera macrofossils and chemical composition we aimed at disentangling 1 the climate changes and their limno ecological responses 2 temperature dynamics with the use of cladocera based transfer function mjt and macrofossil based reconstruction of mean minimum july temperature mmjt 3 timing of the response of different proxies to environmental changes the results of multiproxy analyses explicitly suggest that the main driver for changes in aquatic and terrestrial ecosystems as well as geomorphological processes in the catchment was climate reconstructed temperatures generally follow the known trends showing the increase at the beginning of the allerod and decrease at the beginning of the younger dryas however there are some discrepancies between the two reconstructions as well as between the generally accepted temperature trends in late glacial the timing of the proxy response to climate change differs the aquatic proxies responding first

dynamics of a low level jet observed during the fronts 87 experiment a study of the internal dynamics of a low level jet its role on the frontal discontinuity evolution and its relevance to the organization of convection at mesoscale and small scale is presented the low level jet studied is associated with an active cold front that was observed during the french british co operative field experiment fronts 87 the originality of the present low level jet description lies in the fact that it is observed not only by means of soundings but also by means of a new tool for mesoscale meteorology observations a wind profiler stratospheric tropospheric uhf radar the high resolution of the wind profiler data in both time and height allows one to assess in precipitating as well as in clear sky areas a detailed image of the low level jet and the associated mesoscale and convective scale circulations the comparison between observations and predictions of various theories provides information on the physical mechanisms responsible for the initiation and maintenance of the observed mesoscale features the flow resulting from the presence of the low level jet produces inertial acceleration and baroclinic symmetric instability which lead to a narrow mesoscale line of sloping motions moreover the interaction of the cold surface outflow with the low level vertical shear below the jet maximum is found to be crucial in the intensification and maintenance of the observed narrow cold frontal rainband

some mesoscale features of flow in shelikof strait alaska moored current observations were obtained from a small region of shelikof strait during 1986 1987 results from two sites 11 km however correlations were quite weak a new feature intense 13 day spectral peaks of narrow horizontal and vertical scale was also revealed the feature appears to be a baroclinic residual flow linked to tidal currents

lateglacial and early holocene insect assemblages from sites at different altitudes in the swiss alps implications on climate and environment insect analyses from four sites at differentaltitudes in the swissalps are presented the dominant insect group considered here is coleoptera beetles though other insect orders are also recorded

the effect of abrupt climatic warming on biogeochemical cycling and n2o emissions in a terrestrial ecosystem the large rapid increase in atmospheric n2o concentrations that occurred concurrent with the abrupt warming at the end of the last glacial period might have been the result of a reorganization in global biogeochemical cycles to explore the sensitivity of nitrogen cycling in terrestrial ecosystems to abrupt warming we combined a scenario of climate and vegetation composition change based on multiproxy data for the oldest dryas bolling abrupt warming event at gerzensee switzerland with a biogeochemical model that simulates terrestrial n uptake and release including n2o emissions as for many central european sites the pollen record at the gerzensee is remarkable for the abundant presence of the symbiotic nitrogen fixer hippophae rhamnoides l during the abrupt warming that also marks the beginning of primary succession on immature glacial soils here we show that without additional nitrogen fixation climate change results in a significant increase of n2o emissions of approximately factor 3 4 from 6 4 1 9 to 21 6 5 9 mg n2o n m 2 yr 1 each additional 1000 mg m 2 yr 1 of nitrogen added to the ecosystem through n fixation results in additional n2o emissions of 1 6 mg n2o n m 2 yr 1 for the time with maximum h rhamnoides coverage our results suggest that local reactions of emissions to abrupt climate change could have been considerably faster than the overall atmospheric concentration changes observed in polar ice nitrogen enrichment of soils due to the presence of symbiotic n fixers during early primary succession not only facilitates the establishment of vegetation on soils in their initial stage of development but can also have considerable influence on biogeochemical cycles and the release of reactive nitrogen trace gases to the atmosphere c 2012 elsevier b v all rights reserved

an eddy resolving model of circulation on the western gulf of alaska shelf 2 comparison of results to oceanographic observations currents generated by an eddy resolving semispectral primitive equation model are compared with those measured by moored current meters 1989 and 1991 and satellite tracked drifting buoys 1987 from shelikof strait alaska the model reproduced many of the dominant circulation features including the cross sectional spatial structure of the alaskan coastal current the estuarine inflow at the bottom of the sea valley and the mean transport the first mode empirical orthogonal functions of the model and of the observed data represent similar spatial structures and were significantly correlated in time while the model produced eddies 20 km diameter at a similar rate as observed the timing did not generally match the observations as a result correlations between the measured currents and model generated currents usually were not significant correlations between modeled and measured transport through the sea valley however were significant for both years

idealized three dimensional modeling of seasonal variation in the alaska coastal current 1 seasonal variation of the buoyancy and downwelling wind forced alaska coastal current acc and the fate of freshwater contained in it is considered using idealized analytical and numerical models of the acc formed from a half line source of buoyant inflow the coastal current initially develops two dimensionally but becomes three dimensional from a balance between coastal influx of buoyancy and its downstream transport which leads to a coastal current depth limit hmax 1 2 where x is along shelf distance q is the line source strength for unit length f is the coriolis frequency and g is the reduced gravity of the buoyant inflow this limit is unchanged under downwelling wind stress and is reached on timescales of less than 1 month for the acc the coastal current width is roughly constant in x and increases in time at the same rate as the two dimensional solution imposition of a downwelling wind stress results in an approximate balance among wind stress and along and cross shelf momentum advection so that the current width is reduced to ywind ld 1 2 where ld is the rossby radius of deformation is the wind stress and 0 is a reference density waves eddying motions eventually grow in the half line source coastal current with wavelengths proportional to the coastal current width and with a downstream phase speed slower than the maximum current speed these features cause an offshore flux of buoyant water a broader coastal current and further accumulation of buoyancy on the shelf increasing downwelling wind stress reduces the effects of the instabilities continual accumulation of buoyancy on the shelf occurs during all model runs but is nearly absent under maximum winter downwelling wind stress it is suggested that freshwater accumulation on the shelf during spring summer and fall may be largely lost downstream during winter

oxygen isotopes of lake marl at gerzensee and leysin switzerland covering the younger dryas and two minor oscillations and their correlation to the grip ice core the ratio of oxygen isotopes is a temperature proxy both in precipitation and in the calcite of lacustrine sediments the very similar oxygen isotope records from greenland ice cores and european lake sediments during the last glacial termination suggest that the drastic climatic changes occurred quasi simultaneously on an extra regional probably hemispheric scale in order to study temporal relations of the different parameters recorded in lake sediments for example biotic response times to rapid climatic changes a precise chronology is required in unlaminated lake sediments there is not yet available a method to provide a high resolution chronology especially for periods with radiocarbon plateaux alternatively an indirect time scale can be constructed by linking the lake stratigraphy with other well dated climate records new oxygen isotope records from gerzensee and leysin with an estimated sampling resolution of between 15 and 40 years match the greenlandic isotope record in many details under the assumption that the main variations in temperature and thus in oxygen isotopes occurred about simultaneously in greenland and switzerland we have assigned a time scale to the lake sediments of gerzensee and leysin by wiggle matching their stable isotope records with those of greenland ice cores which are among the best dated climatic archives we estimate a precision of 20 to 100 years during the last glacial termination

anticyclonic eddies in the alaskan stream abstract anticyclonic eddies propagating southwestward in the alaskan stream as were investigated through analysis of altimetry data from satellite observations during 1992 2006 and hydrographic data from profiling float observations during 2001 06 fifteen long lived eddies were identified and categorized based on their area of first appearance three eddies were present at the beginning of the satellite observations another three formed in the eastern gulf of alaska off sitka alaska and four were first detected at the head of the gulf of alaska near yakutat alaska the other five eddies formed along the as between 157 and 169 w and were named as eddies while the eddies that formed in the gulf of alaska mainly decayed before exiting the gulf of alaska the as eddies mostly crossed the 180 meridian and reached the western subarctic gyre four of five as eddies formed under negative or weakly positive wind stress curls which possibly caused as separation from the coast comparison of eddy propag

isotope signature of the younger dryas and two minor oscillations at gerzensee switzerland palaeoclimatic and palaeolimnologic interpretation based on bulk and biogenic carbonates oxygen and carbon isotope ratios in the carbonate of benthic ostracodes pseudocandona marchica and molluscs pisidium ssp were measured across the transitions bordering the younger dryas chronozone in littoral lacustrine cores from gerzensee switzerland the specific biogenic carbonate records confirm the major shifts already visible in the continuous bulk carbonate oxygen isotope record 18occ if corrected for their vital offsets oxygen isotope ratios of pisidium and juvenile p marchica both formed in summer are almost identical to 18occ this bulk carbonate is mainly composed of encrustations of benthic macrophythes chara ssp also mainly produced during summer adult p marchica which calcify in winter show consistently higher 18o larger shifts across both transitions and short positive excursions compared with the summer forms especially during early preboreal despite such complexity the 18o of adult p marchica probably reflects more accurately the variations of the 18o of former lake water because during winter calcification temperatures are less variable and the water column isotopically uniform the difference between normalised 18o of calcite precipitated in winter to that formed in summer can be used to estimate the minimum difference between summer and winter water temperatures in general the results indicate warmer summers during the late allerod and early preboreal compared with the younger dryas altogether the isotopic composition of lake water 18ol and of the dissolved inorganic carbonate 13cdic reconstructed from adult pseudocandona marchica as well as the seasonal water temperature contrasts indicate that the major shifts in the 18o of local precipitation at gerzensee were augmented by changes of the lake s water balance with relatively higher evaporative loss occurring during the allerod compared with the younger dryas it is possible that during the early preboreal the lake might even have been hydrologically closed for a short period we speculate that such hydrologic changes reflect a combination of varying evapotranspiration and a rearrangement of groundwater recharge during those climatic shifts

early holocene afforestation processes in the lower subalpine belt of the central swiss alps as inferred from macrofossil and pollen records to reconstruct the vegetation history of the upper engadine continuous sediment cores covering the past 11 800 years from lej da champfer and lej da san murezzan upper engadine valley c 1800 m a s l southeastern switzerland have been analysed for pollen and plant macrofossils the chronologies of the cores are based on 16 and 22 radiocarbon dates respectively the palaeobotanical records of both lakes are in agreement for the holocene but remarkable differences exist between the sites during the period 11 100 to 10 500 cal bp when lej da champfer was affected by re sedimentation processes macrofossil data suggest that holocene afforestation began at around 11400 cal bp a climatic deterioration the preboreal oscillation stopped and subsequently delayed the establishment of trees until c 11000 cal bp when first betula then pinus sylvestrislmugo then larix 300 years later and finally pinus cembra expanded within the lake catchment treeline was at c 1500 m during the younger dryas 12 542 11 550 cal bp in the central alps our results along with other macrofossil studies from the alps suggest a nearly simultaneous afforestation e g by pinus sylvestris in the lower subalpine belt between 1500 and 2340 m a s l at around 11 400 to 11 300 cal bp we suggest that forest limit species e g pinus cembra larix decidua could expand faster at today s treeline c 2350 m a s l than 550 m lower earlier expansions at higher altitudes probably resulted from reduced competition with low altitude trees e g pinus sylvestris and herbaceous species comparison with other proxies such as oxygen isotopes residual a14c glacier fluctuations and alpine climatic cooling phases suggests climatic sensitivity of vegetation during the early holocene

southeast alaskan shelf from southern tip of baranof island to kayak island currents mixing and chlorophyll a abstract during 2011 and 2013 an integrated ecosystem study was undertaken on the southeast alaska shelf and slope as part of that study a total of 8 moorings were deployed each year along the coast of baranof and chichagof islands in cross sound and at icy point in addition 18 satellite tracked drifters were deployed during the two field years the goals of this manuscript are to describe the coastal currents in southeastern alaska the processes affecting them and how the physics modify the nutrients and primary production in the region mixing in cross sound is an important source of nutrients for the shelf north of the sound resulting in prolonged production during summer while the alaska coastal current is not a continuous feature along the entire gulf of alaska coast it does exist from southern tip of baranof island to cross sound and again northwest of yakutat the narrowness of this shelf coupled with the meanders and eddies in the alaska current result in large amounts of on shelf flow of slope water and off shelf flow of coastal water while local currents and summer winds were similar in 2011 and 2013 2011 was characterized by low chlorophyll a concentrations throughout the spring summer while chlorophyll concentrations in 2013 were typical the cause of this difference remains unclear but bottom up processes likely contributed to the low chlorophyll a concentrations in 2011

sea level variations in relation to coastal flow around the gulf of alaska adjusted sea level deviations at six tide stations around the gulf of alaska were examined in light of our recent knowledge of the flow regime on the east side of the gulf a maximum in the deviations seems to be caused by winter barotropic flow on the shelf on the north side of the gulf the maximum in fall is apparently produced by a marked increase in flow of the baroclinic coastal current farther west the seasonal sea level signal is appreciably reduced

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