the north atlantic jet stream a look at preferred positions paths and transitions preferred jet stream positions and their link to regional circulation patterns over the winter north atlantic european sector are investigated to corroborate findings of multimodal behaviour of the

late quaternary plume nepheloid and turbidite sedimentation and effect of the gulf stream near the tail of the grand banks newfoundland abstract cores collected from the tops of the fogo seamounts southwest of the grand banks of newfoundland contain considerable amounts of detrital clay the seamounts rise at least 1 km above the surrounding sea floor and are an unlikely place for sedimentation by turbidity currents sedimentological and micropaleontological evidence suggests that large amounts of detrital clay were injected into the system during glacial and interglacial stages by turbidity currents and surface sediment plumes the main source of sediment was the laurentian channel although some sediment was injected through the canyons around the grand banks surface sediment plumes were strongly influenced by the labrador current and by the surface circulation of the gulf stream fine grained sediments injected into the system by turbidity currents through the laurentian channel were probably trapped by the deep circulation of the gulf stream and dispersed to the northeast effects of the sediment drift induced by the deep gulf stream circulation is also reflected in an abrupt eastward bent of the depositional lobes of the laurentian fan and in the shape of the newfoundland ridge

variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

downward coupling between the stratosphere and troposphere the relative roles of wave and zonal mean processes abstract wave and zonal mean features of the downward dynamic coupling between the stratosphere and troposphere are compared by applying a time lagged singular value decomposition analysis to northern hemisphere height fields decomposed into zonal mean and its deviations it is found that both zonal and wave components contribute to the downward interaction with zonal wave 1 due to reflection dominating on the short time scale up to 12 days and the zonal mean due to wave mean flow interaction dominating on the longer time scale it is further shown that the two processes dominate during different years depending on the state of the stratosphere winters characterized by a basic state that is reflective for wave 1 show a strong relationship between stratospheric and tropospheric wave 1 fields when the stratosphere is leading and show no significant correlations in the zonal mean fields on the other hand winters characterized by a stratospheric state that does not reflect waves show a strong relat

contemporary changes in sediment yield in an alpine mountain basin due to afforestation the upper drome in france abstract the baurieres plain within the upper drome river basin was used to reconstruct recent changes in sediment supply in relation to changes in land use within an alpine catchment a considerable body of archival information is available furthermore the plain acts as a natural sediment trap and the reach basin interaction has not been disrupted by human activity based on archival data channel geometry measurements dendrogeomorphological and radionuclide analysis cs137 and unsupported pb210 the trends in channel change and sediment supply over the past two centuries are assessed and their causes are interpreted dendrogeomorphology and radionuclide profiles show that the floodplain is characterised by a decrease in sedimentation rate in the 1960s the ex pb210 profiles also suggest a spatial modification of the relative contribution in sediment supply of the catchment bedload yields are estimated to be at least 26 m3 km 2 year 1 between 1928 and 1996 based on an estimate of storage over a channel length of 11 5 km archival data concerning bedload removal from traps yields an estimate of 25 6 m3 km 2 year 1 between 1993 and 2001 these two values are very comparable suggesting no major modification in bedload transport within the reach during the 20th century if the bedload supply has not strongly decreased in the studied reach during this period the bedload sources have changed the volume of sediment stored in the beaurieres area between 1928 and 1996 corresponds to at least 40 of the sediment delivered by channel degradation from an upstream alluvial reach both changes in floodplain sedimentation as well as changes in bedload and suspended contributions from catchment sources are interpreted as responses to land use but also flow regime hillslope sediment production strongly decreased due to planned hillslope afforestation and torrent regulation at the end of the 19th century and spontaneous hillslope afforestation resulting from grazing decline mainly in the two decades following world war ii the observed change in suspended sediment supply which occurred around 1960 1965 has a clear synchronicity with spontaneous catchment afforestation following world war ii after this period a decrease in sediment supply a change in source but also a decrease in peak flow were observed changes in run off are complex and cannot be caused with only land use change flood hydrographs underwent peak decreases and duration increases through the 20th century because of increase in water retention capacity of the forested catchment in addition flood seasonality has changed with september and october flood events being much less frequent in the last part of the 20th century

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

the life cycle of the northern hemisphere sudden stratospheric warmings motivated by recent evidence of strong stratospheric tropospheric coupling during the northern hemisphere winter this study examines the evolution of the atmospheric flow and wave fluxes at levels throughout the stratosphere and troposphere during the composite life cycle of a sudden stratospheric warming the composite comprises 39 major and minor warming events using 44 years of ncep ncar reanalysis data the incipient stage of the life cycle is characterized by preconditioning of the stratospheric zonal flow and anomalous quasistationary wavenumber 1 forcing in both the stratosphere and troposphere as the life cycle intensifies planetary wave driving gives rise to weakening of the stratospheric polar vortex and downward propagation of the attendant easterly wind and positive temperature anomalies when these anomalies reach the tropopause the life cycle is marked by momentum flux and mean meridional circulation anomalies at tropospheric levels that are consistent with the negative phase of the northern hemisphere annular mode the anomalous momentum fluxes are largest over the atlantic half of the hemisphere and are associated primarily with waves of wavenumber 3 and higher

a model of channel response in disturbed alluvial channels dredging and straightening of alluvial channels between 1959 and 1978 in west tennessee caused a series of morphologic changes along modified reaches and tributary streams degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed levels by as much as 6 1 m following degradation reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction aggradation downstream of the area of maximum disturbance reached 0 12 m per year with the greatest rates occurring near the stream mouths the adjustment of channel geometry and phases of channel evolution are characterized by six process oriented stages of morphologic development premodified constructed degradation threshold aggradation and restabilization down cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded threshold stage channel widening continues through the aggradation stage as the slough line develops as an initial site of lower bank stability the bank profile develops three dynamic elements 1 vertical face 70 to 90 2 upper bank 25 to 50 and 3 slough line 20 to 25 alternate channel bars form during the restabilization stage and represent incipient meandering of the channel

orographic constraints on a modeled siberian snow tropospheric stratospheric teleconnection pathway previous modeling studies have identified a teleconnection pathway linking observation based early season siberian snow perturbations to a modulation of the winter arctic oscillation ao mode in this study the key role of orography in producing this modeled teleconnection is explicitly investigated using numerical experiments analogous to the previous studies the climatic response to the same snow perturbation is investigated under modified orographic barriers in southern and eastern siberia reducing these barriers results in a weakening of the prevailing orographically forced region of stationary wave activity centered over siberia as well as the snow forced upward wave flux anomaly that initiates the teleconnection this diminished anomaly propagates upward but does not extend into the stratosphere to weaken the polar vortex consequently poleward refraction of upper tropospheric waves and downward propagation of coupled wave mean flow anomalies which ultimately produce the negative winter ao response fail to develop thus the mountains represent an orographic constraint on the snow ao teleconnection pathway by reducing the orographic barrier the snow forced influx of wave energy remains in the troposphere and instead produces a hemispheric scale equatorward wave refraction

the geomorphic evolution and sediment balance of the lower rhone river southern france over the last 130 years hydropower dams versus other control factors article i nfo atthe end of thelittleice age lia agriculturalpractices and successive phasesof channel management involv ing embankments and dams however the respective roles of these various control factors in modifying sedi ment storage and channel stability are often difficult to identify the aim of this paper is to determine the main factors that have driven morphological changes over the past 130 years on the 120 km long downstream reach of the rhone river a gis based analysis of maps and aerial photographs available since 1860 coupled with chrono stratigraphic data on the river s alluvial deposits has enabled quantification of sediment storage and erosion in different morphological units changes measured include riverbed incision narrowing of the main channel in relation with accumulation of fine sediments along the channel margins and reduction of sed iment input at the mouth on the basis of local and reach scale sediment balances we show that these changes are synchronous with engineering works carried out at the end of the nineteenth century and beginning of the twentieth century a period that coincided with a decline in river sediment inputs largely generated by human activities the early stabilisation of mountain slopesresulting from a decline inrural agriculture rural exodus re forestation and engineered torrent control has had a much greater impact in geomorphically transforming the rhone than dams and gravel mining the major identified causes of river destabilisation in the world this calls for caution in the all too common and wholesale attribution of declining sediment budgets of european rivers

paleoceanographic significance of sediment color on western north atlantic drifts ii late pliocene pleistocene sedimentation abstract color variations were interpreted in paleoceanographic terms for the late pliocene pleistocene sediments recovered by odp leg 172 on deep sea drifts at blake bahama outer ridge and northeastern bermuda rise the color derived parameters used in interpretation included predicted carbonate content terrigenous fluxes and hematite content abundance of upper carboniferous spores indicates that the hematite is probably derived from the permo carboniferous red beds of the canadian maritimes in the last 800 kyr sedimentation pattern changes on the blake bahama outer ridge were determined by the sediment delivery to the deep basin as well as circulation changes sediment delivery increased during glacials especially during the last 500 kyr and particularly since stage 6 a fundamental change in the thermohaline circulation occurred at about 500 ka corresponding to the end of the mid pleistocene transition period at the onset of the predominant 100 kyr climate cyclicity sedimentation related to wbuc had intensified at that time and had become more focused at depths below 3000 m changes in hematite content and sedimentation rate show a pulse of sediment via the st lawrence outlet at the pliocene pleistocene boundary suggesting that a likely change in the hydrography physiography of the laurentide ice sheet could have been involved in the climatic and ocean circulation changes at that time

glacial to interglacial changes in carbonate and clay sedimentation in the atlantic ocean estimated from 230th measurements abstract the cause of the climatically controlled fluctuations in the carbonate content of deep sea sediments remains the subject of uncertainty and debate three variables are involved supply of biogenic carbonate loss by dissolution and dilution by non carbonate phases it is suggested that 230 th which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale results of a preliminary analysis based on published data indicate that for depths at and above the lysocline the carbonate fluctuations observed in cores from the north atlantic ocean are due primarily to variations in the terrigenous clay input which was 2 5 times higher during glacials than during interglacials carbonate deposition appears to have been somewhat reduced during glacials but probably not by more than a factor of 2 from published 230 th 232 th profiles it appears that the south atlantic ocean also received increased inputs of terrigenous clay during glacial periods

high resolution isotope study of the latest deglaciation based on bermuda rise cores abstract a stable isotope and 14c investigation of carbonates from three late quaternary cores with high rates of sedimentation from the northeastern bermuda rise has produced the highest resolution record of the glacial maximum to holocene stable isotope change yet obtained from an open ocean location the record includes a three step termination and the first direct evidence of an early deglacial meltwater spike in the open sea

structure composition and bulk properties of upland stream gravels upland gravel bedded streams in the u k have received only scant attention from both hydrologists and sedimentologists but are worthy of further investigation the sedimentology of three small streams in teesdale in the pennines has been examined in detail grain size characteristics bedforms structure composition and packing characteristics of these deposits are described and compared where appropriate with published information it is argued that a fuller appreciation of gravel bed composition and morphology should eventually contribute to an improved understanding of sediment transport and deposition mechanisms and hence to improved accuracy in sediment transport and deposition estimates

seismic evidence for early tertlary bottom current controlled deposition in the charlie gibbs fracture zone abstract buried mounded and acoustically transparent sediment bodies banked up against a basement ridge at the eastern end of the charlie gibbs fracture zone are interpreted as a type of contourite drift as they are probably of eocene palaeocene age their origin has implications for the little known deep circulation pattern in the ne atlantic during this period possible sources for the bottom currents responsible for these drifts include labrador sea water norwegian sea overflow water antarctic bottom water or a gulf stream deep gyre system the preferred source is an early development of antarctic bottom water or an arm of a gulf stream gyre flowing eastwards through the fracture zone

interdecadal arctic oscillation in twentieth century climate simulations viewed as internal variability and response to external forcing 1 interdecadal variations similar to the arctic oscillation ao are investigated for internal variability intv and response to external forcing rext in an ensemble simulation of twentieth century climate the significant trend in rext implies that a sizeable part of the observed ao trend in recent decades can also be attributed to anthropogenic forcing intv is characterized by a barotropic dipole of zonal wind anomalies and associated wave propagation suggesting a mechanism similar to the month to month ao its thermal structure can be attributed to dynamic processes rext exhibits a thermal structure that can be explained by responses to the forcing due to increased greenhouse gases a westerly wind anomaly in the stratosphere as a thermal response corresponds to anomalies in wave propagation and meridional circulation that are similar to intv which may induce the ao like annular pattern

effect of madden julian oscillation occurrence frequency on the interannual variability of northern hemisphere stratospheric wave activity in winter abstractthis study uses reanalysis datasets and numerical experiments to investigate the influence of the occurrence frequency of the individual phases of the madden julian oscillation mjo on the interannual variability of stratospheric wave activity in the middle and high latitudes of the northern hemisphere during boreal winter november february ndjf our analysis reveals that the occurrence frequency of mjo phase 4 in winter is significantly positively correlated with the interannual variability of the eliassen palm e p flux divergence anomalies in the northern extratropical stratosphere that is higher lower occurrence frequency of mjo phase 4 corresponds to weaker stronger upward wave fluxes and increased decreased e p flux divergence anomalies in the middle and upper stratosphere at mid to high latitudes which implies depressed enhanced wave activity accompanied by a stronger weaker polar vortex in that region the convection anomalies over the maritime continent related to mjo p

role of planetary waves in the stratosphere troposphere coupled variability in the northern hemisphere winter the role of planetary waves in stratosphere troposphere coupled variability is investigated using an extended singular value decomposition analysis of zonal mean zonal wind and the vertical component of the eliassen palm e p flux for the winters from 1979 80 to 1995 96 the results suggest a close relationship between anomalies of zonal mean zonal wind and the convergence zone of e p flux which together shift poleward and downward from the stratosphere to the troposphere as time advances following enhanced vertical propagation of waves into the stratosphere the arctic oscillation ao pattern is seen in the 500 hpa geopotential height field in association with an increased poleward propagation of tropospheric waves

upward and downward injection of rossby wave activity across the tropopause a new aspect of the troposphere stratosphere dynamical linkage propagation of zonally confined rossby wave activity between the troposphere and lower stratosphere of the southern hemisphere during austral winter and spring of 1997 is studied by using a wave activity flux and refractive index both defined for stationary rossby waves on a zonally asymmetric time mean flow a particular event of large scale quasi stationary cyclogenesis in the troposphere is discussed to which downward wave activity injection from anticyclonic anomalies upstream that had developed in the exit region of the lower stratospheric polar night jet pnj contributed substantially consistent with that downward injection phase lines of observed stream function anomalies exhibited a distinct eastward tilt with height the development of the anticyclonic anomalies occurred at the leading edge of a quasi stationary rossby wave train propagating along the pnj that had originated from a tropospheric blocking ridge farther upstream though less common than upward wave activity injection across the tropopause similar events of downward wave activity injection occurred several times during that season primarily in the regions south of australia and over the central south pacific over each of which the pnj exit overlapped with a tropospheric subpolar jet to form a vertical waveguide locally it is argued that the downward wave activity propagation is essentially due to refraction in the vertically sheared westerlies and the zonal asymmetries in the time mean flow are a likely factor for the observed geographical preference of the downward wave activity injection copyright 2005 royal meteorological society

deglacial diatom productivity and surface ocean properties over the bermuda rise northeast sargasso sea 1 diatom assemblages document surface hydrographic changes over the bermuda rise between 19 2 and 14 5 ka subtropical diatom species and chaetoceros resting spores dominate the flora as in north atlantic productive regions today from 16 9 to 14 6 ka brackish and fresh water diatoms are common and their contribution is generally coupled with total diatom abundance this same interval also contains rare grains of ice rafted debris coupling between those proxies suggests that successive discharge of icebergs might have stimulated productivity during heinrich event 1 h1 iceberg migration to the subtropics likely created an isolated environment involving turbulent mixing upwelled water and nutrient rich meltwater supporting diatom productivity in an otherwise oligotrophic setting in addition the occurrence of mode water eddies likely brought silica rich waters of southern ocean origin to the euphotic zone the persistence of lower salinity surface water beyond the last ice rafting suggests continued injection of fresh water by cold core rings and advection around the subtropical gyre these results indicate that opal productivity may have biased estimates of meridional overturning based on 231pa 230th ratios in bermuda rise sediments during h1

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

arctic oscillation and the autumn winter snow depth over the tibetan plateau 1 the present study examines the relationship between the arctic oscillation ao and the autumn winter snow depth over the tibetan plateau results show that there exists significant correlation between the ao and the tibetan plateau snow depth on interdecadal timescale the ao and the snow depth over the tibetan plateau experienced interdecadal regime shift in the late 1970s before the late 1970s when the ao was in its interdecadal negative phase the snow depth over the tibetan plateau increased in fall and then decreased in the following winter conversely when the ao has entered its interdecadal positive phase since the early 1980s the snow depth decreased in fall but increased in winter the vertical propagation of rossby waves is proposed to explain the physical process linking the ao with the snow depth anomalously excessive fall snow depth over the tibetan plateau amplifies orographically forced upward stationary waves the snow forced changes in stratosphere are not identified until later in the winter season when rossby waves propagate into the stratosphere and the ao becomes negative in winter when the troposphere and stratosphere are actively coupled the downward propagation of rossby waves associated with the positive ao phase modulates the atmospheric circulation in the troposphere and causes the abnormal increase of snow depth over the tibetan plateau

alkenones and multiproxy strategies in paleoceanographic studies 1 we assess multiproxy strategies involving alkenone based and other paleoceanographic indicators in an effort to define uncertainties and to advance understanding of past oceanic and climatic changes looking to the future we recommend a parallel strategy of applying proxies to the geologic record while continuously seeking refinements in methods and understanding of mechanisms that control each proxy a multiproxy strategy increases confidence in results and provides oceanographic context for more effective interpretation of processes a combination of proxies allows derivation of additional properties such as upper ocean paleosalinity or paleo pco2 for a more complete view of the oceanographic and climate mechanisms involved in changing earth s environment

a poisoned chalice deep sea sediments often carry information about past temperatures in the upper ocean directly above their location but as mccave cautions in this perspective interpretation of the sediments can be complicated by deep sea processes for example material transported laterally in the deep ocean may distort the upper ocean signal in the sediments a report by ohkouchi illustrates such processes at bermuda rise the study yields a detailed understanding of deep sea sediment transport processes aiding the interpretation of sediment records at this site and sounding a warning for others

early middle pleistocene deep circulation in the western subtropical atlantic southern hemisphere modulation of the north atlantic ocean early middle pleistocene climate and deep ocean hydrography have been reconstructed using oxygen and carbon isotope ratio measurements in planktonic and benthic foraminifera from a high deposition rate sedimentary succession recovered at the bermuda rise in the northern sargasso sea ocean drilling program leg 172 site 1063 the site s water depth makes it sensitive to changes in the balance between north atlantic deep water nadw and antarctic bottom water aabw in the deep north atlantic allowing the evaluation of perturbations in deep water production at different timescales millennial scale fluctuations superimposed on the longer period oscillations of orbital origin occurred during all the observed climate states the highest amplitude sub milankovitch fluctuations were mainly associated with interglacials particularly after the intensification of the glacial regime at c 900 ka using the benthic carbon isotope signal as a water mass tracer and by comparing the delta 13c record to a suite of drill sites in the north atlantic and pacific oceans it has been possible to infer that the relative strength of aabw production varied through time as did that of nadw a scenario in which the two different source components of deep water can undergo dramatic changes in their circulation regime through time should be taken into consideration when evaluating the role of thermohaline circulation in global climate change

tropospheric precursors of anomalous northern hemisphere stratospheric polar vortices regional extratropical tropospheric variability in the north pacific and eastern europe is well correlated with variability in the northern hemisphere wintertime stratospheric polar vortex in both the ecmwf reanalysis record and in the whole atmosphere community climate model to explain this correlation the link between stratospheric vertical eliassen palm flux variability and tropospheric variability is analyzed simple reasoning shows that variability in the north pacific and eastern europe can deepen or flatten the wintertime tropospheric stationary waves and in particular its wavenumber 1 and 2 components thus providing a physical explanation for the correlation between these regions and vortex weakening these two pathways begin to weaken the upper stratospheric vortex nearly immediately with a peak influence apparent after a lag of some 20 days the influence then appears to propagate downward in time as expected from wave mean flow interaction theory these patterns are influenced by enso and october eurasian snow cover perturbations in the vortex induced by the two regions add linearly these two patterns and the quasi biennial oscillation qbo are linearly related to 40 of polar vortex variability during winter in the reanalysis record

a meta analysis of soil erosion rates across the world abstract over the last century extraordinary efforts have been devoted to determining soil erosion rates in units of mass per area and time under a large range of climatic conditions and land uses and involving various measurement methods we undertook a meta analysis of published data from more than 4000 sites worldwide the results show that there is extraordinarily high variability in erosion rates with almost any rate apparently possible irrespective of slope climate scale land use land cover and other environmental characteristics however detailed analysis revealed a number of general features including positive relationships of erosion rate with slope and annual precipitation and a significant effect of land use with agricultural lands yielding the highest erosion rates and forest and shrublands yielding the lowest despite these general trends there is much variability that is not explained by this combination of factors but is related at least partially to the experimental conditions our analysis revealed a negative relationship between erosion rate and the size of the study area involved significant differences associated with differing measurement methods with direct sediment measurement yielding the lowest erosion rates and bathymetric radioisotope and modeling methods yielding the highest rates and a very important effect of the duration of the experiment our results highlight that when interpreting erosion rates the experimental conditions involved must be taken into account even so the data suggest that only order of magnitude approximations of erosion rates are possible and these retain a very large degree of uncertainty consequently for practical purposes such as calculation of global sediment budgets empirical equations are not a substitute for direct measurements our results also show that a large proportion of the experiments have been short term less than 3 years which reduces dramatically the reliability of the estimated erosion rates given the highly non normal behavior of soil erosion time dependency despite the efforts already made more long term measurement experiments need to be performed especially in regions of the world that are under represented in global datasets in addition protocols need to be established for standardizing the measurement methods and reporting the results to enable data to be compared among diverse sites

northern hemisphere winter circulation associated with the north atlantic oscillation and stratospheric polar night jet the interannual variability of the atmospheric winter circulation as characterized by the geopotential height at 500 hpa and temperature at 850 hpa associated with the north atlantic oscillation nao and stratospheric polar night jet pnj is examined it is suggested that the wintertime atmospheric circulation related to the nao index can be separated into two different modes of variability one is a regional mode characterized by a meridional dipole type pattern in the 500 hpa geopotential height anomaly field over the atlantic region the other having more zonal structure extends over wider region of the northern hemisphere this is also related to the lower stratospheric polar night jet air temperature near the surface over the eastern part of the eurasian continent is more closely correlated with the above mentioned hemispheric mode of variability than the regional nao

month to month variability of winter temperature over northeast china linked to sea ice over the davis strait baffin bay and the barents kara sea abstractthis study focuses on the month to month variability of winter temperature anomalies over northeast china necta especially the out of phase change between december and january february

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

the statistical connection between tropospheric and stratospheric circulation of the northern hemisphere in winter abstract the associated anomaly patterns of the stratospheric geopotential height field and the tropospheric geopetential and temperature height fields of the northern hemisphere are determined applying the canonical correlation analysis with this linear multivariate technique the coupled modes of variability of lime series of two fields are isolated in the space of empirical orthogonal functions the one dataset is the 50 hpa geopotential height field the other set consists of different height fields of the tropospheric pressure levels 200 500 700 and 850 hpa and the temperature of the 850 hpa pressure level for the winter months december january february two natural coupled modes a barotropic and a baroclinic one of linear relationship between stratospheric and tropospheric circulation are found the baroclinic mode describes a connection between the strength of the stratospheric cyclonic winter vortex and the tropospheric circulation over the north atlantic the corresponding temperature

downward migration of extratropical zonal wind anomalies 1 we show in confirmation of previous work using one and three dimensional models that extratropical zonal wind anomalies produced by fluctuating rossby wave forcing in the troposphere appear first in the stratosphere and migrate downward into the troposphere by systematically eliminating wave reflection and downward control through an induced meridional circulation it is shown that the downward migration is dependent on neither process rather the mechanism appears to rely on local wave mean flow interaction just as in the similar downward migration evident in the tropical quasi biennial oscillation in particular these results imply that the similar downward migration observed in the arctic oscillation should not be taken to indicate any controlling influence of the stratosphere on the troposphere

the influence of autumnal eurasian snow cover on climate and its link with arctic sea ice cover abstractthe relationship between eurasian snow cover extent sce and northern hemisphere atmospheric circulation is studied in reanalysis during 1979 2014 and in cmip5 preindustrial control runs in observations dipolar sce anomalies in november with negative anomalies over eastern europe and positive anomalies over eastern siberia are followed by a negative phase of the arctic oscillation ao one and two months later in models this effect is largely underestimated but four models simulate such a relationship in observations and these models the sce influence is primarily due to the eastern siberian pole which is itself driven by the scandinavian pattern sca with a large anticyclonic anomaly over the urals the sca is also responsible for a link between eurasian sce anomalies and sea ice concentration sic anomalies in the barents kara sea increasing sce over siberia leads to a local cooling of the lower troposphere and is associated with warm conditions over the eastern arctic this is fol

late quaternary sedimentation on the southern sohm abyssal plain six closely spaced sediment cores taken below the carbonate compensation depth penetrated fine silty muds and entered sandy sediment at 10 12 m below the seafloor foraminiferal assemblages and 8o analyses on planktonic foraminifera indicated that the surface muds down to 2 m are holocene and derived from local promontories above the ccd below these sediments are about 6 m of clays deposited during the late wisconsin these are unfossiliferous and have a possible northern source suggested by the higher chlorite content sandy sediments below 9 m in the cores contain well preserved benthic foraminifera from the scotian shelf glacial 18o values on planktonic tests indicate the sandy sediments are most likely of latest wisconsin age thus during the recent interglacial the sand fraction of the southern sohm abyssal plain sediments is mostly locally derived but during glacial periods the sediments have a distant northern source containing quartz sand that was initially deposited on the scotian shelf 1 500 km to the north

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

comments on the life cycle of the northern hemisphere sudden stratospheric warmings limpasuvan et al 2004 hereafter lth consider thelife cycle of sudden stratospheric warmings ssws from onset to maturity and eventually decay by com positing multiple events over the course of 80 days their main emphasis is on the mature phases of the lifecycle when there is a clear chain of downward strato sphere to troposphere propagation of anomalies inthis comment we aim to focus on the onset resultsreported in lth by placing the results in the context ofmore regional phenomena reported in earlier studiesand providing a more comprehensive framework forunderstanding wintertime northern hemisphere cli mate variability and improved predictability among the results presented lth show that sswsare associated with antecedent eliassen palm ep fluxconvergence from the troposphere these upward propagating ep flux anomalies precede the large scaleanomalies in the stratosphere and subsequent down ward propagating anomalies yield an arctic oscillation ao signal in the lower troposphere a number ofprevious studies provide evidence that the forcing forthe real or apparent downward propagation of zonallysymmetric large scale height and wind anomalies fromthe stratosphere to the troposphere has its origins re gionally in the lower troposphere kuroda and kodera1999 cohen et al 2002 furthermore these lower tropospheric precursors have also been linked toanomalies in eurasian snow cover saito et al 2001 gong et al 2003 which antecede even the atmosphericprecursors the ep flux anomalies shown in lth aresimilar to the wave fluxes presented in kuroda andkodera 1999 saito et al 2001 and gong et al 2003 which were shown to perturb the stratosphereand originate over eurasia but were not considered bylth who limit their analysis to zonal means kurodaand kodera 1999 also show wave fluxes over the at lantic sector but these are observed only during themature phase of an ao event and their influence isconfined to the troposphere also lth show statistically significant heightanomalies in the both the stratosphere and the tropo

use of grain size and magnetic fabric analyses to distinguish among depositional environments the combined use of grain size and magnetic fabric analyses provides the ability to discriminate among depositional environments in deep sea terrigenous sediments we analyzed samples from three different depositional settings turbidites pelagic or hemipelagic interlayers and sediment drifts results indicate that sediment samples from these different environments can be distinguished from each other on the basis of their median grain size sorting as well as the intensity and shape of magnetic fabric as determined from an examination of the anisotropy of magnetic susceptibility we use these discriminators to interpret downcore samples from the bermuda rise sediment drift we find that the finer grains of the bermuda rise relative to the blake outer ridge do not result from lower depositional energy current speed and so may reflect a difference in the nature of sediment being delivered to the site i e distance from source between the two locations

internal variability of the troposphere stratosphere coupled system simulated in a simple global circulation model internal variability of a troposphere stratosphere coupled system is investigated in a series of numerical experiments with a simple global circulation model under a perpetual winter condition in order to examine the relative importance of forced planetary waves in the interaction with the zonal mean zonal flow and baroclinic disturbances amplitude of a sinusoidal surface topography of zonal wavenumber 1 or 2 is swept as an experimental parameter 1000 day integrations are performed for 110 combinations of the external parameters intraseasonal variability of the extratropical winter stratosphere in the parameter sweep experiment of the zonal wavenumber 1 topography is classified into four regimes dependent on the topographic amplitude i a nearly radiative equilibrium state ii small undulations of the polar vortex iii intermittent breakdowns of the polar vortex or occurrence of stratospheric sudden warming events and iv a usually weak and warm state of the polar vortex the behavior of planetary waves in the stratosphere is characterized by linear propagation in regime i and by quasi linear or weakly nonlinear wave mean flow interaction in regime ii in regimes iii and iv on the other hand it is in a highly nonlinear state reflecting the occurrence of sudden warming events and the usually distorted polar vortex respectively the northern hemisphere winter stratosphere corresponds to regime iii in the intraseasonal variations while the southern counterpart is close to regime ii a lag correlation analysis shows that the dynamical linkage between the stratosphere and the troposphere is also dependent on the regimes the vertical linkage is primarily the upward control in regime i planetary waves are generated by nonlinear interaction of baroclinic disturbances in the troposphere and propagate into the stratosphere in regime ii stratospheric variations are largely confined in the stratosphere although planetary waves are generated in the troposphere the linkage in regime iii on the other hand is inevitably two way planetary wave variability has upward influence from the troposphere to the stratosphere as well as the zonal mean zonal wind shows preconditioning in the troposphere before stratospheric sudden warming events downward propagation of signals to the upper troposphere are also seen in the zonal mean temperature in high latitudes it is higher than normal at the final stage of the sequence of sudden warming events the linkage is also two way in regime iv

a mechanistic model study of slowly propagating coupled stratosphere troposphere variability observational studies reveal the oscillatory nature of coupled stratosphere troposphere variability which is characterized by a slowly downward propagating anomalous zonal mean zonal wind during the winter the term slowly is employed compared to the rapid variation associated with stratospheric sudden warmings in fact strong stratospheric warming events are embedded in this slowly propagating variability as is shown in a companion paper kodera et al this issue in the present study the mechanism producing such variability at all levels of the atmosphere is investigated by developing a simple model that extends from the earth s surface to 80 km altitude the model is a quasi geostrophic channel model similar to that used by holton and mass 1976 but it includes two meridional fourier components and latitudinal variation in the gradient of the coriolis parameter by this extension the present model can incorporate both the subtropical and polar night jet and also treat the horizontal propagation of planetary waves as well as vertical propagation the results of the simulation reproduce qualitatively well the main observed features interaction between the planetary waves and zonal mean flow produces oscillations in the winter stratosphere and zonal wind anomalies created in the subtropics of the stratopause propagate downward into the polar region of the troposphere which provoke changes in the meridional propagation of tropospheric planetary waves

a possible mechanism of solar modulation of the spatial structure of the north atlantic oscillation 1 the spatial structure of the north atlantic oscillation nao in winter differs significantly according to the solar cycle the nao is confined to the atlantic sector during low solar activity ls whereas it has a hemispherical structure during high solar activity hs the present study focuses on identifying the involved processes the results of analyses suggest that the solar activity influence originates in the stratopause region where the mode of interannual variation in the zonal mean zonal winds changes according to solar activity in the early winter of hs the leading zonal wind mode has a meridional dipole type structure that extends downward from the stratosphere to the troposphere through interaction with planetary waves the dipole type anomaly in the zonal winds produces a hemispherical scale seesaw pattern in the surface pressure between the polar region and surrounding regions thus the nao during hs has a hemispherical pattern during ls the downward extension of zonal mean zonal wind anomalies is weak so the regional scale variation becomes dominant in the troposphere

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

analysis of the coupling between the stratospheric meridional wind and the surface level zonal wind during 1979 93 northern hemisphere extratropical winters the coupling between the stratosphere and the troposphere has been investigated by analysing low frequency variations in 1 the meridional mass flux into the polar cap north of 60 n computed separately for the stratosphere and the troposphere 2 the polar cap mean surface pressure and 3 the surface level meridional pressure gradient and zonal wind around 60 n the analysis has been done for the 1979 93 northern hemisphere nh winters using ecmwf reanalysis data the results show that for all winters the meridional mass flux variations in the stratosphere precede those in the troposphere by about one day this result can also be obtained qualitatively with a very simple model based on the zonally averaged zonal and meridional momentum equations the lag is not very sensitive to the latitude of the southern boundary of the polar cap the analysed variations in the polar cap mean surface pressure associated with variations in the meridional mass flux determine most of the variability in the analysed meridional surface pressure gradient and the associated surface zonal wind around 60 n the results also show that in the stratosphere the coriolis force associated with the zonal mean meridional wind is in near balance with the convergence of the eddy momentum flux and in the lower troposphere with the zonal frictional force in summary the results indicate that in the extratropical northern winter hemisphere low frequency variations in the meridional wind in the stratosphere induce low frequency variations in the zonal wind near the surface

measurement of the degree of smoothing in sediment paleomagnetic secular variation records an example from late quaternary deep sea sediments of the bermuda rise western north atlantic ocean abstract replicate paleomagnetic secular variation psv records for the last 15 000 yr have been recovered from two deep sea sediment gravity cores on the bermuda rise western north atlantic ocean the records have been correlated using several different parameters and dated by correlation to a nearby piston core which has a high resolution 14 c chronology the psv records are systematically subdued with respect to the expected local magnetic field variability during the holocene when sedimentation rates were about 10 cm kyr during the late pleistocene when sedimentation rates were a factor of 2 3 higher the psv variability was significantly larger we attribute this to smoothing of the psv records by a depositional post depositional remanence drm pdrm acquisition process with a 10 20 cm lock in interval the degree of psv smoothing was evaluated by comparing the vgp angular dispersion and vector spectral content of the bermuda rise cores with high resolution psv records from north america and great britain these results suggest a 50 reduction in the drm pdrm recording of vector variability during the holocene on the bermuda rise with most of the psv reduction occurring for features of less than 2000 yr in duration we can reproduce the subdued psv pattern with a mathematical model that simulates the site drm pdrm remanence acquisition process finally the replicate gravity cores document that psv records may be reproducible on a local scale even though they only retain a low pass filtered record of true magnetic field variability

the association between stratospheric weak polar vortex events and cold air outbreaks in the northern hemisphere previous studies have identified an association between temperature anomalies in the northern hemisphere and the strength of stratospheric polar westerlies large regions in northern asia europe and north america have been found to cool during the mature and late stages of weak vortex events in the stratosphere a substantial part of the temperature changes are associated with changes in the northern annular mode nam and north atlantic oscillation nao pressure patterns in the troposphere the apparent coupling between the stratosphere and the troposphere may be of relevance for weather forecasting but only if the temporal and spatial nature of the coupling is known using 51 winters of re analysis data we show that the development of the lower tropospheric temperature relative to stratospheric weak polar vortex events goes through a series of well defined stages including the formation of geographically distinct cold air outbreaks at the inception of weak vortex events a precursor signal in the form of a strong high pressure anomaly over northwest eurasia is associated with long lived and robust cold anomalies over asia and europe a few weeks later near the mature stage of the weak vortex events a shorter lived cold anomaly emerges off the east coast of north america the probability of cold air outbreaks increases by more than 50 in one or more of these regions during all phases of the weak vortex events this shows that the stratospheric polar vortex contains information that can be used to enhance forecasts of cold air outbreaks as large changes in the frequency of extremes are involved this process is important for the medium range and seasonal prediction of extreme cold winter days three hundred year pre industrial control simulations by 13 coupled climate models corroborate our results copyright 2010 royal meteorological society and crown copyright

a magnetic signature of bottom current erosion abstract to characterize the magnetic signal associated with bottom current erosion we have conducted downcore measurements of magnetic texture and fabric in three cores containing known erosional hiatuses using biostratigraphic and magnetostratigraphic analysis erosional hiatuses were identified for three cores from two current dominated environments the northern bermuda rise and the south indian basin the cores were contiguously subsampled and the magnetic susceptibility k the anisotropy of magnetic susceptibility ams and the anhysteretic susceptibility k arm were measured the ams parameters h and q were used to describe the relative magnitude and the shape respectively of the representative susceptibility ellipsoid the concentration independent and dimensionless ratio k arm k was used to indicate relative changes in magnetic grain size hiatuses in the three cores were marked by unusually high values of h and q indicating a greater development of internal fabric with a more linear fabric representation depressed values of k arm k indicated a coarser mean magnetic grain size the magnitude of this signal however did not have a simple relationship with hiatus duration t test results statistically confirmed the existence of an erosional signature to enhance the applicability of this technique a quantitative discriminant model was constructed and calibrated using the magnetic characteristics of erosion since this model was constructed from samples of known erosional and non erosional character the discriminant functions could then be used as reference equations to identify erosion in other cores biostratigraphic and oxygen isotopic data from a 14 m core from the northern bermuda rise extending back to isotopic stage 8 250 ka bp indicate two short intervals of low accumulation rate which for this region are most probably attributable to bottom current erosion magnetic data for this core were entered into the reference discriminant model and the two zones of suspected erosion were classified by the functions as being highly crosional in character zones of probable erosion were identified at several other levels in the core the timing of these short term crosional events was found to coincide closely with glacial intervals suggesting that bottom currents active on the northern bermuda rise were invigorated periodically during glacial maxima at c 18 58 64 85 130 140 165 180 225 and 250 ka bp

abyssal currents and advection of resuspended sediment along the northeastern bermuda rise abstract an integrated study using current meters time series nephelometers and water samplers for measurements of particulate matter concentration revealed an intense nepheloid layer centered on the slopes of the eastward scarp the northeastern boundary of the bermuda rise these slopes also contained extensive furrows truncated seismic reflectors and wisconsin age and older surface sediments the abyssal circulation in this region appears to be accelerated when it encounters the steep topography of the eastward scarp eroding sediments creating the erosional furrows and moving eroded sediment upslope instruments on top of the bermuda rise recorded episodic events benthic storms where particle concentrations at 25 m above the bottom increased from a background level of 60 g 1 1 to maximum of 251 g 1 1 and current velocities were nearly 20 cm s 1 net transport of both water and entrained sediment was to the west northwest during the largest benthic storm water temperature decreased by 0 1 c consistent with a 300 600 m upslope transport of water and resuspended sediments from the upper slopes of the eastward scarp when currents carry resuspended sediment over the rim of the eastward scarp to the plateau region the current slows depositing its sediment load thus the plateau is growing upwards slowly at the expense of the surrounding scarps

understanding the variation of stratosphere troposphere coupling during stratospheric northern annular mode events from a mass circulation perspective we revisit the various stratosphere troposphere coupling relation from the perspective of the meridional mass circulation we constructed 10 hpa northern annular mode nam phase composites to show the typical spatiotemporal evolution of circulation anomalies during the nam s life cycle our results indicate that there is large case to case difference in the temporal evolution and vertical profile of polar temperature anomalies during nam events which shows no strong dependence on the intensity and duration of nam events but agrees well with the variations of the three branches of mass circulation at 60 n the stratospheric poleward warm air branch st the poleward warm air branch in the upper troposphere wb and the equatorward cold air branch in the lower troposphere cb such correspondence is due to the dynamic heating and cooling anomalies associated with the redistribution of air masses by the anomalous meridional mass circulation in different isentropic layers the various relationship among the three mass circulation branches is attributed to anomalous wave activities the amplitude and westward tilt of waves are always stronger weaker throughout the stratosphere before after the peak time of negative nam events leading to a stronger weaker st before after the peak time variations in wb and cb are mostly dependent on wave variabilities in the mid to lower troposphere leading to variations in the timing of in or out of phase coupling of the st with the wb and cb and thus various thermostructure during nam events at a later stage of the negative nam events when the polar temperature becomes colder and the polar jet recovers the weakened baroclinic instability in the lower stratosphere provides favorable conditions for the strengthening of the wb and cb if wave activities strengthen in the troposphere during that period

variability of the polar night jet in the northern and southern hemispheres the spatial and temporal characteristics of the month to month variability of the polar night jet and its relationship with tropospheric circulation is investigated for both the northern and southern hemispheres the variabilities of the hemispheres have many common characteristics of the polar night jet oscillation pjo these common characteristics include the following 1 the anomalous zonal mean zonal winds shift poleward and downward 2 the anomalous polar temperatures propagate downward from the stratopause to the upper troposphere and 3 they are made through a wave mean flow interaction with mainly the planetary wave of zonal wave number one annular modes associated with the pjos appear in both hemispheres when the zones of maximum polar temperature anomaly descend to the lowermost stratosphere and upper troposphere the major difference in the pjos of the two hemispheres is found in their temporal characteristics in the southern hemisphere the phase of the pjo is closely locked to the annual cycle while in the northern hemisphere it exhibits quasiperiodic variability with its envelope controlled by the annual cycle the origin of the differences between the pjos is discussed based on the theory of the wave mean flow interaction

coherent deep flow variation in the iceland and american basins during the last interglacial the first direct evidence that the deepflow speed of north atlantic deep water nadw in the south iceland and north americanbasins declined dramatically over a period of a few hundred years at about 120 000 years ago is presented the flow rate inferred from silt grain size then rose into the subsequent cool period stage 5d these changes are clear and synchronous in records from both locations these circulation events are recorded less markedly in chemical and isotopic proxies for the nutrient status of water masses the congruence of flowvariation and hydrography at the two separated sites suggests they are primarily controlled by variation in the deep thermohaline circulation

characteristics of the deep ocean carbon system during the past 150 000 years σco2 distributions deep water flow patterns and abrupt climate change abstract studies of carbon isotopes and cadmium in bottom dwelling foraminifera from ocean sediment cores have advanced our knowledge of ocean chemical distributions during the late pleistocene last glacial maximum data are consistent with a persistent high co2 state for eastern pacific deep water both tracers indicate that the mid depth north and tropical atlantic ocean almost always has lower co2 levels than those in the pacific upper waters of the last glacial maximum atlantic are more co2 depleted and deep waters are co2 enriched compared with the waters of the present in the northern indian ocean 13c and cd data are consistent with upper water co2 depletion relative to the present there is no evident proximate source of this co2 depleted water so i suggest that co2 depleted north atlantic intermediate deep water turns northward around the southern tip of africa and moves toward the equator as a western boundary current at long periods 15 000 years milankovitch cycle variability is evident in paleochemical time series but rapid millennial scale variability can be seen in cores from high accumulation rate series atlantic deep water chemical properties are seen to change in as little as a few hundred years or less an extraordinary new 52 7 m long core from the bermuda rise contains a faithful record of climate variability with century scale resolution sediment composition can be linked in detail with the isotope stage 3 interstadials recorded in greenland ice cores this new record shows at least 12 major climate fluctuations within marine isotope stage 5 about 70 000 130 000 years before the present

effects of check dams reforestation and land use changes on river channel morphology case study of the rogativa catchment murcia spain this work has been financially supported by the project respuesta hidrologica y geomorfologica de los sistemas fluvio torrenciales afectados por proyectos de restauracion hidrologico forestal en cuencas semiaridas del sureste peninsular of the fundacion instituto euromediterraneo de hidrotecnia ce the first author was financially supported by an i3p postdoc contract csic ce and a ramon y cajal contract from the education and science ministry spain gonzalo g barbera also was supported by i3p postdoc contract

the response of the north pacific decadal variability to strong tropical volcanic eruptions in this study the effects of volcanic forcing on north pacific climate variability on interannual to decadal time scales are examined using climate model simulations covering the last 600 years the model used is the bergen climate model a fully coupled atmosphere ocean general circulation model it is found that natural external forcings such as tropical strong volcanic eruptions sves and variations in total solar irradiance play an important role in regulating north pacific decadal variability npdv in response to tropical sves the lower stratospheric pole to equator temperature gradient is enhanced the north polar vortex is strengthened which forces a significant positive arctic oscillation at the same time dipole zonal wind anomalies associated with strong polar vortex propagate downward from the lower stratosphere through positive feedbacks in the troposphere the surface westerly winds across the central north pacific are significantly weakened and positive sea level pressure anomalies are formed in the north pacific this anomalous surface circulation results in changes in the net heat fluxes and the oceanic advection across the north pacific as a result of this warm water converges in the subtropical western north pacific where the surface waters in addition are heated by significantly reduced latent and sensible heat fluxes from the ocean in the eastern and high latitude north pacific the ocean loses more heat and large scale decreases in sea surface temperatures are found the overall response of this chain of events is that the north pacific enters a negative phase of the pacific decadal oscillation pdo and this negative phase of the pdo is maintained for several years it is thus concluded that the volcanic forcing plays a key role in the phasing of the pdo the model results furthermore highlight the important role of troposphere stratosphere coupling tropical extratropical teleconnections and extratropical ocean atmosphere interactions for describing npdv

solar influence on the spatial structure of the nao during the winter 1900 1999 1 the solar influence on the north atlantic oscillation nao reported in a previous study based on 39 years of data was confirmed by using 100 years of historical data during the low solar activity winters the nao signal in the sea level pressure is confined in the atlantic sector while during the high solar activity winters nao related anomalies extend over the northern hemisphere in particular over the polar region and eurasian continent it was also found that the solar influence on the nao originates from the eurasian continent in early winter in addition two prolonged periods of high nao index in the early and late 1900s showed spatial structures that were quite different and similar to those that occur during the low and high solar activity winters respectively

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to nam and sst 1 with the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data from 1958 to 1998 two teleconnection patterns in the eliassen palm ep flux divergence field due to stationary planetary waves with wavenumbers wns 1 to 3 are studied in the northern hemisphere winter both patterns appear as dipole structures with divergence of ep flux in the north and convergence in the south or vice versa one dipole evolves mainly in the stratosphere and is referred to as the stratospheric interannual oscillation sio the other evolves mostly in the troposphere and is referred to as the tropospheric interannual oscillation tio the tio and the sio are shown to be associated with anomalous meridional planetary wave propagation in the troposphere and stratosphere respectively the upward and poleward refraction of planetary waves into the polar waveguide across the tropopause is closely linked to the tio examination of individual waves indicates that the tropospheric dipole ofep flux divergence comes basically from wn 3 whereas the stratospheric one comes totally from wns 1 and 2 the reduced refraction of planetary waves into the polar waveguide across the tropopause associated with positive tio index is dominantly contributed from both wns 1 and 2 regression and correlation analyses suggest that the tio is closely related to the northern annular mode nam its relation to the sea surface temperature sst is consistent with previous studies on the relation of nam to sst on the other hand the sio is shown to be closely associated with anomalous zonal mean winds in the subtropics of the midstratosphere and has a moderate correlation with an augmented pacific north american pna pattern in 500 hpa geopotential height for the leading eof of stratospheric u variability the sio accounts for a smaller fraction than the tio however with the teleconnectivity in stratospheric ep flux divergence one can distinguish a stratospheric variation of anomalous north south planetary wave propagation from the total amount of wave activity entering the stratosphere which may help us to understand the variability of transport circulation in the stratosphere significant correlation of sio with tropical sst reveals that tropical sst is leading the sio by up to around 9 months which suggests a strong impact of el nino southern oscillation enso on the sio planetary waves tend to be bent poleward in the midstratosphere when there is a warm event the situation tends to be reverse during a cold event

assessment of channel changes due to long term bedload supply decrease roubion river france this paper presents the observations made in the watershed of the upper roubion river which drains a submediterranean mountainous environment and in two of its main tributaries the soubrion and bine creeks our aim was to analyze contemporary morphological and sedimentary changes in response to a progressive decrease in bedload supply this decrease is linked to an increase of forest cover in the watershed during the 20th century following rural depopulation and to a correlated decrease in peak flows several variables were systematically measured width slope bed level change sediment size along 23 km of river whereas dendrochronological data floodplain cross sections and estimated recurrence intervals of sediment entrainment based on critical shear stress calculations were also produced for specific sites to complete our analysis evidence of three major phenomena was obtained on both the roubion and its tributaries i bed degradation ii development of stable pavement in incised reaches and iii channel narrowing associated with the development of alluvial forest on recently abandoned portions of the pre existing active channel forest development began in the 1950s these three phenomena show positively covariant relationships that lead us to propose a descriptive model of mountain fluvial system adjustments to progressive decrease of bedload

incision and morphologic evolution of an alluvial channel recovering from hydraulic mining sediment hydraulic gold mining in the sierra nevada california produced such a large volume of sediment from 1853 to 1884 that channels could not carry a substantial proportion of the delivered sediment the lower bear river aggraded as much as 5 m and underwent a major avulsion during the 1870s channel morphology continues to respond to these changes more than 100 years after the cessation of most hydraulic mining textures of mine tailings and older alluvium are contrasted and channel incision and channel shape changes from 1930 to 1985 are documented unlike the yuba and sacramento rivers the lower bear river had not returned to pre mining base levels by 1950 as sediment loads decreased nor were incision rates or morphological change governed by reduced sediment loads below dams built in 1928 and in the mid 1960s channel stability was due to resistance of a cohesive stratum on the channel bed an episode of channel down cutting was instigated by a moderately large flood in december 1955 that pierced the cohesive layer and was sustained through the 1970s by moderate magnitude floods the 1955 flood did not directly erode large volumes of sediment but it destabilized the channel allowing smaller floods to erode the channel at an accelerated rate episodic channel bed incision is contrasted to progressive morphologic changes cross section shape narrowed and deepened steadily from 1930 through the mid 1970s as the channel was superimposed onto cohesive older alluvium progressive deepening set up a positive feedback that ensured the ultimate penetration of the paved bed channel morphologic readjustment from the avulsion thus was both progressive and episodic

geophysical evidence for widespread cenozoic bottom current activity from the continental margin of nova scotia canada abstract two dimensional and three dimensional multichannel seismic reflection data are utilized to examine previously unrecognized contourite depositional systems along the continental margin of nova scotia canada prior to this study these features were thought to be of limited extent in the study area the new data show that contourite drifts are widespread with greatest drift development during the late miocene to pliocene giant sediment waves form stacked aggrading sequences of bedforms and their development is linked to pre existing seafloor morphology small sediment drifts developed locally throughout the late paleogene and neogene either southwest and down current of seafloor obstacles or form channel fills major erosional pulses form regional seismic markers first along the continental rise in the early oligocene then along the continental slope during the late miocene and pliocene three dimensional seismic data show that erosion surfaces preserve along slope amplitude anomalies two dimensional low relief sediment waves and barchanoid bedforms the geophysical evidence implies that a northeast to southwest along slope bottom current influenced cenozoic depositional patterns throughout the study area

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

alkenones as paleoceanographic proxies 1 alkenone derived estimates of temperature and co2 are contributing to our understanding of earth s climate history in order to increase confidence in alkenone based climate proxies we recommend the following actions first the sedimentary component or fraction containing alkenones should be identified in order to assess the impact of horizontal advection and vertical mixing on alkenone derived temperature and co2 estimates second differential mixing rates of alkenone containing particles and sand sized foraminifera should be quantified by independent dating of the two phases until that is accomplished apparent temporal offsets of climate proxies in the two phases should be interpreted cautiously third the stability of the unsaturation ratio and carbon isotopic compositions of alkenones during all phases of diagenesis should be confirmed both field and laboratory observations are required fourth future alkenone investigations should be coupled with other paleoclimate proxy measurements at high deposition rate sites in a variety of oceanographic settings in upwelling regions and in the vicinity of river plumes salinity and nutrient proxies should be measured since changes in these parameters may affect alkenone biosynthesis

determination of sediment provenance at drift sites using hydrogen isotopes and unsaturation ratios in alkenones the large 20 hydrogen isotopic gradient in surface waters of the northwest atlantic ocean is exploited to track changes in the source of alkenones to the bermuda rise sediment drift cultures of the predominant alkenone producing coccolithophorid e huxleyi were grown in deuterium enriched seawater and shown to possess alkenones with a d h ratio that closely tracked the water d h ratio r 2 0 999 n 5 isotopic enrichments with a fractionation factor between 0 732 and 0 775 a hydrogen isotopic depletion of 193 3 n 9 was measured in alkenones from suspended particles relative to seawater in the subpolar and subtropical northwest atlantic ocean this value was used to calculate the water d values in which alkenones from bermuda rise sediment were synthesized and by extension the water mass in which they were produced applying this technique we find that 60 to 100 of the alkenones in late holocene bermuda rise sediment were produced in deuterium depleted subpolar water to the northwest of the drift to reconcile values of the alkenone unsaturation ratio u k 37 a widely used proxy for sea surface temperature with the d values of alkenones in late holocene sediments from the bermuda rise at least three sources of sediment must be invoked a cold very isotopically depleted source almost certain to be the scotian margin a warm moderately isotopically depleted source likely to be the northwestern edge of the subtropical gyre and a cold isotopically enriched source which we hypothesize to be the subpolar waters overlying the main branch of north atlantic deep water flowing southwest from the nordic seas copyright 2005 elsevier ltd paleoclimate records with sufficient length and temporal resolution to study the occurrence and causal mechanisms of abrupt climate change are exceedingly rare rapidly deposited ocean sediments provide the best archive for studying these events through geologic time but such sites in the open ocean are limited to sediment drift deposits such as the bermuda rise in the northwest atlantic using multiple climate proxies in a single core is becoming more common in high resolution pa leoclimate investigations but a major potential concern for this approach arises from the possibility that the fine fraction of sediment e g 63 m and the climate proxies within it may represent conditions far from the deposition site here we propose and test the hypothesis that hydrogen isotope ratios of alkenones a class of lipids from phytoplankton may provide insight into the source of fine grained sediment because of their restricted sources broad geographic distri bution and excellent preservation properties alkenones are of particular interest in the emerging field of compound specific hydrogen isotopic analysis the sedimentary abundances ex tents of unsaturations and isotopic compositions of alkenones provide quantitative and near continuous records we isolated alkenones from cultured unicellular algae haptophyte emil iania huxleyi surface ocean particulate material and open ocean sediments to determine the extent and variability of hydrogen isotopic fractionation in the di tri and tetraunsat urated c37 compounds we then compared the d values of the alkenones in surface sediments between the bermuda rise and the scotian margin above which a large 20 d gradient exists we determined the fractionation between alkenones from suspended particulate samples and the water in which the phytoplanton lived and examined the variability of alkenone d values during the medieval warm period little ice age climate transition cf keigwin 1996 at the bermuda rise

stratosphere troposphere evolution during polar vortex intensification stratosphere troposphere evolution associated with polar vortex intensification vi events is examined during the northern hemisphere winter the incipient stage of a vi event is marked by anomalously low wave activity and descending westerly anomalies over the depth of the polar stratosphere reduced poleward planetary wave heat flux occurs as the circumpolar wind becomes strongest and pressure anomalies penetrate toward the surface descending pressure patterns project strongly onto the positive state of the northern hemisphere annular mode nam concurrently anomalous poleward momentum flux develops in the upper troposphere and the related tropospheric mean meridional circulation maintains the attendant wind and temperature anomalies against surface drag the gross behavior of the composite vi event is similar in shape but opposite in sign to that associated with sudden stratospheric warming events ssws however the descent of the wind and temperature anomalies over the vi life cycle is generally weaker and slower than its ssw counterpart preceding the maximum vortex anomaly similarly after the maximum wind event the weakening of the winds is faster than the strengthening of the winds after a ssw this is because stratospheric wind reduction anomalies are produced by wave driving which can be rapid and increases in wind speed are associated with the radiative cooling of the polar cap which happens more gradually while the contributions of the anomalous momentum fluxes by the quasi stationary and synoptic eddies are similar to ssws the much stronger anomalous momentum flux observed during vi can be attributed to the larger role of eddies with timescales between 15 and 40 days and of wave number 2 scale notable differences between vi and ssw appear in the tropical region in particular anomalous vortex intensification seems to occur preferentially during la nina conditions

geological effects of the gulf stream system on the northern bermuda rise abstract the gulf stream system contains a clockwise rotating set of bottom currents which influence the sea bed in the northern north american basin it is possible to interpret the present day and historical record of current activity in this basin in terms of the deep flow of the gulf stream this interpretation provides a much more satisfactory and consistent explanation of the geologic record than previous interpretations based strictly on the influence of the classic abyssal circulation the present day circulation of the gulf stream actively resuspends large quantities of sediment on and near the northern bermuda rise and it is suggested that this resuspension may be due to the eddy field which is embedded in the westward flowing return flow during the late cenozoic the gulf stream system was responsible for depositing and shaping the major acoustic sedimentological units on the relatively smooth surface of the horizon a complex fine grained mont morillionite rich sediments derived from the chemically weathered saprolites of the hudson and st lawrence drainage basins were injected into the deep ocean basins by turbidity currents during the late paleogene and the neogene fine grained turbidites from the st lawrence spread southward down the southeastern sohm abyssal plain across the eastward flowing gulf stream and its westward flowing return flows portions of these fine grained sediments were entrained by the main and return flows and deposited downstream as acoustically non laminated accumulations on the corner and bermuda rises respectively the hudson river input was injected into the deep basin through the hudson canyon system the interaction of these fine grained turbidites with the northward flowing deep flow of the gulf stream system led to the formation of the gulf stream outer ridge here defined for the first time during the late neogene or early pleistocene the gulf stream outer ridge was partially eroded by the gulf stream system and portions subsequently covered by coarse grained pleistocene turbidites the coarse grained illite rich turbidites that flowed across the southeastern sohm abyssal plain also crossed the main and return flows of the gulf stream system the finer portions of these sediments were entrained and deposited as pleistocene acoustically laminated sediments on the plateaus of the bermuda and corner rises

floods in mountain environments a synthesis floods are a crucial agent of geomorphic change in the channels and valley floors of mountains watercourses at the same time they can be highly damaging to property infrastructure and life because of their high energy mountain watercourses are highly vulnerable to environmental changes affecting their catchments and channels many factors have modified and frequently still tend to modify the environmental conditions in mountain areas with impacts on geomorphic processes and the frequency magnitude and timing of floods in mountain watercourses the ongoing climate changes vary between regions but may affect floods in mountain areas in many ways in many mountain regions of europe widespread afforestation took place over the twentieth century considerably increasing the amounts of large wood delivered to the channels and the likelihood of jamming bridges at the same time deforestation continues in other mountain areas accelerating runoff and amplifying the magnitude and frequency of floods in foreland areas in many countries in channel gravel mining has been a common practice during recent decades the resultant deficit of bed material in the affected channels may suddenly manifest during flood events resulting in the failure of scoured bridges or catastrophic channel widening during the past century many rivers in mountain and foreland areas incised deeply the resultant loss of floodplain water storage has decreased attenuation of flood waves hence increasing flood hazard to downstream river reaches on the other hand a large amount of recent river restoration activities worldwide may provide examples of beneficial changes to flood risk attained as a result of increased channel storage or reestablished floodplain water storage relations between geomorphic processes and floods operate in both directions which means that changes in flood probability or the character of floods e g increased wood load may significantly modify the morphology of mountain rivers but morphological changes of rivers can also affect hydrological properties of floods and the associated risk for societies this paper provides a review of research in the field of floods in mountain environments and puts the papers of this special issue dedicated to the same topic into context it also provides insight into innovative studies methods or emerging aspects of the relations between environmental changes geomorphic processes and the occurrence of floods in mountain rivers

geological interpretations based on deep two single channel and multichannel seismic data from the bermuda rise abstract multichannel seismic data taken with a deep tow system approximately 170 n mile south southwest of bermuda reveal the upper 300 m of sediment in detail unachievable by conventional single channel and multichannel seismic reflection methods these data show the upper sediments to be largely undisturbed although faulting and basement uplift are evident the acoustic reflectivity of the sediments and nature of the reflectors are consistent with dsdp data from the region horizons a v a t and a c of the horizon a complex are observed in addition to numerous reflecting horizons associated with porcellanitic chert limestone and cemented claystone layers of a c seismic velocity inversions observed generally beneath a c are thought to result from sediment loading and buildup of excess pore pressures in the sediments below horizon a v upward migration of these fluids may account for localized zones of little or no subbottom acoustic reflectivity seafloor structural details resolved include erosional channels or slump scars mud waves and possible furrows

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

direct observation of subtropical mode water circulation in the western north atlantic ocean abstract eighteen degree water edw is the dominant subtropical mode water of the north atlantic subtropical gyre and is hypothesized as an interannual reservoir of anomalous heat nutrients and co2 although isolated beneath the stratified upper ocean at the end of each winter edw may re emerge in subsequent years to influence mixed layer properties and consequently air sea interaction and primary productivity here we report on recent quasi lagrangian measurements of edw circulation and stratification in the western subtropical gyre using an array of acoustically tracked isotherm following bobbing profiling floats programmed to track and intensively sample the vertically homogenized edw layer and directly measure velocity on the 18 5 c isothermal surface the majority of the clivar mode water dynamics experiment climode bobbers drifted within the subtropical gyre for 2 5 3 5 years many exhibiting complex looping patterns indicative of an energetic eddy field bobber derived lagrangian integral time and length scales 3 days 68 km associated with motion on 18 5 c were consistent with previous measurements in the gulf stream extension region and fall between previous estimates at the ocean surface and thermocline depth several bobbers provided evidence of long lived submesoscale coherent vortices associated with substantial edw thickness while the relative importance of such vortices remains to be determined our observations indicate that these features can have a profound effect on edw distribution edw thickness defined using a vertical temperature gradient criterion exhibits seasonal changes in opposition to a layer bounded by the 17 c and 19 c isotherms in particular edw thickness is generally greatest in winter as a result of buoyancy forced convection while the 17 19 c layer is thickest in summer consistent with seasonal ekman pumping contrary to previous hypotheses the bobber data suggest that a substantial fraction of subducted edw is isolated from the atmosphere for periods of less than 24 months seasonal to biennial re emergence principally within the recirculation region south of the gulf stream appears to be a common scenario which should be considered when assessing the climatic and biogeochemical consequences of edw

tropospheric impact of reflected planetary waves from the stratosphere 1 a reflection of stratospheric planetary waves and its impact on the troposphere during a stratospheric sudden warming of march 2007 are investigated zonal propagation and reflection of the planetary waves is clearly seen in the longitude height sections of the eddy geopotential height and the vertical and zonal component of the three dimensional wave activity flux a wave packet propagating upward and eastward from eurasian continent was reflected by a negative wind shear in the upper stratospheric westerly jet caused by stratospheric warming waves then propagated downward to the american atlantic sector of the troposphere which led to the formation of a deep trough over the atlantic and brought cold weather to the northeastern part of the american continent

seismic stratigraphy of the northern bermuda rise abstract analysis of low frequency seismic profiles from the northern bermuda rise has led to the recognition of several seismic horizons and determination of a regional seismic stratigraphic framework horizon a is the deepest regionally significant reflector identified and horizon a c a t and a v of the horizon a complex are also mappable reflectors in the study area three additional regionally significant reflectors named yellow purple and silver have been identified in the area these seven reflectors allow speculation on the sedimentary evolution of the area sedimentation below the horizon a complex was primarily pelagic the distribution of reflectors within the horizon a complex indicates the area experienced turbidite deposition from both the u s east coast continental margin and nearby bermuda as well as pelagic deposition during the eocene sedimentation subsequently has been dominated by at least two distinct periods of abyssal current flow initially bottom currents brought in sediments from the north or west creating an anomalously thick accumulation of seismically poorly stratified sediments on the rise this period of accumulation was punctuated by an episode of erosion in latest miocene or earliest pliocene the most recent sediments are seismically well stratified sediments of primarily quaternary age carried from the east by the gulf stream system

the life cycle of northern hemisphere downward wave coupling between the stratosphere and troposphere abstractthe life cycle of northern hemisphere downward wave coupling between the stratosphere and troposphere via wave reflection is analyzed downward wave coupling events are defined by extreme negative values of a wave coupling index based on the leading principal component of the daily wave 1 heat flux at 30 hpa the life cycle occurs over a 28 day period in the stratosphere there is a transition from positive to negative total wave 1 heat flux and westward to eastward phase tilt with height of the wave 1 geopotential height field in addition the zonal mean zonal wind in the upper stratosphere weakens leading to negative vertical shear following the evolution in the stratosphere there is a shift toward the positive phase of the north atlantic oscillation nao in the troposphere the pattern develops from a large westward propagating wave 1 anomaly in the high latitude north atlantic sector the subsequent equatorward propagation leads to a positive anomaly in midlatitudes the near surface tempera

variability of clay mineral composition on carolina slope nw atlantic during marine isotope stages 1 3 and its paleoceanographic significance abstract the clay mineral composition of marine isotope stages 1 3 sediments at the ocean drilling program odp site 1055 on the carolina slope consists mainly of illite kaolinite chlorite and smectite clay mineral variability is marked by a distinct increase in the relative amounts of kaolinite and smectite during the holocene and by high illite and to a lesser extent chlorite relative amounts during marine isotopic stages 2 and 3 this grouping of clay minerals as two different assemblages during different isotopic stages suggest their different source affinities the increase in the kaolinite smectite assemblage in the holocene is accompanied by a significant increase in the sedimentation rate the change in the sedimentation regime after the last glacial maximum is interpreted to be related to resuspension and advection of clays and silts by increased deep water activity over the bermuda rise followed by their transport to site 1055 on the carolina slope by shallow elements of the north atlantic deep water high amplitude variations with high illite amounts characterize marine isotope stage 3 and appear to be related to heinrich events

sensitivity of the boreal winter circulation in the middle atmosphere to the quasi biennial oscillation in maecham5 simulations the polar vortex in the northern hemisphere exhibits high intraseasonal and interannual variability which to some degree may be controlled by the quasi biennial oscillation qbo in the tropical stratosphere here we analyze the qbo signal in the northern hemisphere polar vortex in a model simulation using the general circulation model maecham5 middle atmosphere european center hamburg model which simulates the qbo as an internal mode of variability composites have been computed for the westerly and easterly qbo phases from early winter to late winter november december december january and january february of a 50 year experiment containing 20 complete qbo cycles this method identifies tropical and midlatitude patterns in wind and temperature that are related to the secondary meridional circulation of the qbo extending towards the winter pole in the tropics significant qbo signature is observed in the mesosphere up to 0 05 hpa only in early winter and mainly in the easterly qbo phase forced by the parameterized gravity waves mean flow interaction at high latitudes maecham5 shows a significantly warmer colder polar stratosphere in the easterly westerly qbo phase at 30 hpa accompanied by a weaker stronger polar vortex in the late winter months from december to february december to january in the easterly westerly phase of the qbo in early winter there is no significant change in temperature and zonal mean zonal wind in the polar stratosphere the analysis of ep fluxes shows a different behavior between qbo phases with changes in the waveguide wave propagation occurs upwards and polewards in the easterly qbo phase at 30 hpa while waves are refracted equatorward in the westerly phase no relationship has been found between the tropical qbo and the final warming at the end of the boreal winter

fluvialcorridor a new arcgis toolbox package for multiscale riverscape exploration abstract both for scientists and river basin managers development of automated geographic information system gis tools is essential today to characterize riverscapes and explore biogeomorphologic processes over large channel networks since the 1990s gis toolboxes and add in programs have been used to characterize catchments however there is currently no equivalent to a planimetric and longitudinal characterization of fluvial corridor networks at multiple scales this paper describes fluvialcorridor a new gis toolbox this package allows the user i to extract a large set of riverscape features such as the main components of fluvial corridors from dem and vector layers e g stream network or valley bottom and ii to aggregate spatial features into homogeneous segments and metrics characterizing each of them the methodological frameworks involved have been previously described by alber and piegay 2011 leviandier et al 2012 and bertrand et al 2013 and this contribution focuses on the gis tools allowing the user to automatically operate them a case study on the drome river france is provided to illustrate the potential of the package both for geomorphologic understanding and target management actions fluvialcorridor has been developed for arcgis with the related native python library named arcpy and tested on arcgis 10 0 and 10 1 obviously each component of the package can be used separately however it also provides a complete workflow for fluvial corridor characterization even as the toolbox is continually under development and revision case study database fluvialcorridor package and guidelines are available online at http umrevs isig fr