the corresponding tropospheric environments during downward extending and nondownward extending events of stratospheric northern annular mode anomalies abstractusing the ncep ncar reanalysis dataset this study classifies stratospheric northern annular mode nam anomalies during the negative or positive phase into two categories anomalies extendi

biogenic sedimentation and geochemical properties of deep sea sediments of the demerara slope abyssal plain influence of the amazon river plume abstract the amazon river plume has a major impact on sedimentation at abyssal depths throughout a broad area 450 000 km2 and far 500 1000 km from the river mouth as the plume mixes into the north atlantic ocean it may support ecological niches favorable for n2 fixation driven by the symbiosis between diatoms and diazotrophic cyanobacteria this proposed diatom diazotroph association dda should result in increased carbon export from a limited region of plume influence here we used 32 multicores collected throughout the demerara abyssal slope and plain at depths ranging from 3000 to 5000m to assess patterns and rates of export and accumulation of organic carbon corg or poc and biogenic sio2 bsi sediment accumulation rates were determined from 14c ages of foraminifera obtained at 2 5 depths from 9 cores and were further constrained by 230th measurements the sedimentation rate 1 5 cm ky 1 representing the average accumulation over the past 8000 years was combined with corg and bsi sediment concentrations to establish biogenic matter burial fluxes burial of poc represents 4 16 of the corg raining to the deep sea floor which is high for water depths 4000 m burial of bsi represents 1 9 of the total bsi rain clastic sedimentation dominates regions underlying the plume while carbonate sedimentation dominated otherwise sediment mixing bioturbation was studied in 13 cores using 210pb as a tracer and showed no spatial patterns diffusional mixing coefficients ranged from 0 03 to 3 2 cm year 1 values consistent with other deep sea mixing rates however sites with the highest mixing rates did not have the highest corg content sediment focusing was studied in at 7 sites using 230th as a tracer surficial sediments had focusing factors that ranged from 1 to 2 indicating little sediment redistribution biogenic sedimentation in general and bsi deposition in particular is not concentrated in the region of dda abundance the nw axis of primary plume trajectory is coincident with the maximum deposition and burial of poc and bsi but not caco3

a study of planetary waves in the southern winter troposphere and stratosphere part i wave structure and vertical propagation abstract planetary wave propagation in the southern winter troposphere and stratosphere is studied in an attempt to trace the origins of upward propagating disturbance daily geopotential girds from 1000 to 1 mb are analyzed for two 120 day winter seasons a cross correlation analysis technique is developed which allows coherent wave structure to be traced in time significant correlations are observed between the troposphere and stratosphere at finite time lags indicative of vertically propagating waves the observed vertical propagation time scales between the middle troposphere and middle stratosphere are on the order of 4 days for zonal wavenumber 1 k 1 1 2 days for k 2 and 1 day for k 3 the cross correlation analysis also delineates the meridional and vertical structures of the transient in time planetary waves zonal wavenumber 1 fluctuations exhibit a vertical out of phase relationship between the midlatitude troposphere and atmosphere three out of phase maxima in latitude are observed in

meridional and downward propagation of atmospheric circulation anomalies part ii southern hemisphere cold season variability abstract as in the northern hemisphere there exists a simultaneous poleward propagation of temperature anomalies in the stratosphere and equatorward propagation in the troposphere in the southern hemisphere s cold season it takes about 110 days for anomalies of one polarity to propagate from the equator to the pole or half the period of the complete cycle nearly twice as long as in the northern hemisphere the earlier poleward propagation of temperature anomalies in upper levels compared with those in lower levels results in an apparent downward propagation in the stratosphere accompanying the poleward and downward propagating warm cold anomalies is a successive leveling steepening of isentropic surfaces reflecting a simultaneous reduction strengthening of the meridional temperature gradient and increase decrease of the vertical static stability following changes in the thermal fields are poleward and downward propagating zonal wind anomalies of the opposite sign the arrival of the pole

sudden stratospheric warmings and tropospheric blockings in a multi century simulation of the ipsl cm5a coupled climate model the relation between sudden stratospheric warmings ssws and blocking events is analyzed in a multi centennial pre industrial simulation of the institut pierre simon laplace coupled model ipsl cm5a prepared for the fifth phase of the coupled model intercomparison project the ipsl model captures a fairly realistic distribution of both ssws and tropospheric blocking events albeit with a tendency to overestimate the frequency of blocking in the western pacific and underestimate it in the euro atlantic sector the 1000 year long simulation reveals statistically significant differences in blocking frequency and duration over the 40 day periods preceding and following the onset of ssws more specifically there is an enhanced blocking frequency over eurasia before ssws followed by an westward displacement of blocking anomalies over the atlantic region as ssws evolve and then decline the frequency of blocking is reduced over the western pacific sector during the life cycle of ssws while the model simulates no significant relationship with eastern pacific blocks finally these changes in blocking frequency tend to be associated with a shift in the distribution of blocking lifetime toward longer lasting blocking events before the onset of ssws and shorter lived blocks after the warmings this study systematically verifies that the results are consistent with the two pictures that 1 blockings produce planetary scale anomalies that can force vertically propagating rossby waves and then ssws when the waves break and 2 ssws affect blockings in return for instance via the effect they have on the north atlantic oscillation

glacial interglacial productivity and environmental changes in lake biwa japan a sediment core study of organic carbon chlorins and biomarkers abstract temporal changes in paleoproductivity of lake biwa japan over the past 32 kyr have been studied by analyzing bulk organic carbon and photosynthetic pigments chlorins in the biw95 5 core primary productivity was estimated on the assumption of c norg values of 8 for autochthonous organic matter om and 25 for allochthonous om and using an equation developed for the marine environment the estimate indicates that primary productivity ranges from 50 to 90 g c m 2 yr 1 in the holocene while it is 60 g c m 2 yr 1 on average in the last glacial pheophytin a and pheophorbide a are the major chlorins a downcore profile of chlorin concentration normalized to autochthonous organic carbon oc shows a decreasing trend chlorin productivity was corrected by removal of the effect of post burial chlorin degradation the temporal profile of chlorin productivity thereby obtained resembles that from autochthonous oc the difference in primary productivity between the holocene and the glacial for the lake is markedly smaller than that for lake baikal situated in the boreal zone this difference between the two lakes is probably caused by the difference in their climatic conditions such as temperature and precipitation precipitation at lake biwa is relatively large during the glacial and the holocene because of the continuous influence of the east asian monsoon lake baikal precipitation is generally small as a result of control by the continental siberia climate regime in addition a significant difference in productivity between the glacial and the holocene for lake baikal may be essentially controlled by the hydrodynamic systems in the lake lake biwa terrigenous om input events occurred at least five times over the period 11 32 kyr bp suggesting enhanced monsoon activity molecular examination of the layer with a large input of terrigenous om during the younger dryas indicates that concentrations of terrigenous biomarkers such as n c27 c31 alkanes lignin phenols cutin acids hydroxy acids and c29 sterols are high suggesting that soil om with peat like material entered the lake as a result of flooding an enhanced sedimentation rate in the last 3000 years might have been partially caused by agricultural activity around the lake

viable diatoms and chlorophylla in continental slope sediments off cape hatteras north carolina abstract continental slope sediments off cape hatteras north carolina were sampled by coring in late summer 1992 the chlorophylla concentrations measured in sediments from 16 sites at depths ranging from 530 to 2003 m averaged 19 9 mg chla m 2 a concentration much higher than observed elsewhere on the eastern u s continental slope indicating high depositional rates for microalgal material the variability in the chlorophylla values suggests strong environmental heterogeneity at both small and large spatial scales in this slope habitat probably a consequence of both topography and bioturbation viable diatoms were found in sediment samples across the range of depths sampled and up to 14 cm deep in sediments indicating high rates of deposition and bioturbation bulk sediment samples contained planktonic tychopelagic and benthic diatoms indicating that both phytoplankton and benthic microalgae from the continental shelf may be sources of organic matter for these slope sediments

evidence for nonlinear climate change two stratospheric regimes and a regime shift two regimes are found in the interannual variability of the large scale stratospheric flow in the northern hemisphere cold season the regimes are identified by studying the probability distribution of the leading principal component of the geopotential height which explains approximately 50 of the variance the probability distribution has a bimodal structure with two clearly separated peaks corresponding to two circulation regimes the two regimes are characterized by a strong and a weak vortex respectively and they therefore resemble the two phases of the stratospheric part of the arctic oscillation while the upper troposphere and the lower stratosphere are colder in the strong vortex regime than in the weak vortex regime the lower troposphere is warmer in particular over the continents an abrupt regime shift took place in the last half of the 1970s in favor of the more zonal regime the shift is manifested by a substantial change in the frequencies of the two regimes strong statistical significance for the two separate regimes is obtained by a monte carlo approach the regimes and the regime shift are found in two different datasets reducing the possibility that the results are due to inhomogeneities in the data the results support the nonlinear dynamical perspective on climate change suggested by t n palmer according to this idea the response to a weak forcing would be seen mainly in a change of the frequencies of the climate regimes while the spatial structure of the regimes would be relatively insensitive to the forcing

altered atmospheric responses to eastern pacific and central pacific el ninos over the north atlantic region due to stratospheric interference the two types of el nino that have been identified namely the eastern pacific ep and central pacific cp el ninos are known to exert different climatic impacts on the north atlantic region during winter here we investigate the characteristics of the teleconnection of the two el nino types with a focus on the stratosphere troposphere coupling during the ep el nino polar stratospheric warming and polar vortex weakening frequently occur with a strong tendency for downward propagation near the tropopause consequently the atmospheric pattern within the troposphere over the north atlantic sector during midwinter closely resembles the negative north atlantic oscillation pattern in contrast during cp el nino events stratospheric warming events exhibit a much weaker downward propagation tendency this difference in the stratospheric circulation response arises from the different seasonal evolution of the tropospheric wave response to the two el nino types for the ep el nino the aleutian low begins growing during december and is sustained throughout the entire winter december to february which provides favorable conditions for the continuous downward propagation of the stratospheric warming we also discuss the origin of the difference in the teleconnections from the two types of el nino associated with the distinct longitudinal position of the warm sst anomaly that determines troposphere stratosphere coupling

pigment preservation and remineralization in oxic coastal marine sediments abstract complex mixtures of sedimentary chlorophyll degradation products were measured using high performance liquid chromatography hplc in 210 pb dated box and piston core sediments sediments were collected from dabob bay washington a coastal marine fjord conducive to studies yielding an understanding of the remineralization and diagenesis of organic carbon greater than 99 of the pheopigment flux out of the water column does not accumulate in the top 2 cm of sediment surface sediment pigment profiles indicate that pheophorbides are the dominant pheopigments observed with concentrations decreasing rapidly with depth concentrations of chlorophyll c derivatives also decrease rapidly but ratios of a c pheopigments remain within ranges reported for natural and cultured phytoplankton sharp pheopigment concentration decreases within the bioturbated surface sediments as defined by 210 pb activities were modeled using a one dimensional mixing model the in situ pheopigment decomposition rate corrected for bioturbation and sediment accumulation corresponds to an approximate half life of 40 days sedimentary humic acid fulvic acid and residual humin associated pheopigments in sediments which had been previously acetone extracted to remove the lipophilic pheopigment fraction were typed by chromic acid oxidation and release of pyrrole derived maleimides this humic associated pyrrole derived nitrogen while a small fraction of total sedimentary or humic nitrogen accounted for 16 75 of the total sedimentary pheopigment accumulation and may be significant in understanding the diagenetic fate and transformation of pheopigments to petroporphyrins

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

zonal mean dynamics of extended recoveries from stratospheric sudden warmings abstractthe recovery of the arctic polar vortex following stratospheric sudden warmings is found to take upward of 3 months in a particular subset of cases termed here polar night jet oscillation pjo events the anomalous zonal mean circulation above the pole during this recovery is characterized by a persistently warm lower stratosphere and above this a cold midstratosphere and anomalously high stratopause which descends as the event unfolds composites of these events in the canadian middle atmosphere model show the persistence of the lower stratospheric anomaly is a result of strongly suppressed wave driving and weak radiative cooling at these heights the upper stratospheric and lower mesospheric anomalies are driven immediately following the warming by anomalous planetary scale eddies following which anomalous parameterized nonorographic and orographic gravity waves play an important role these details are found to be robust for pjo events as opposed to sudden warmings in general in that ma

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

molecular carbon isotopic fractionation of algal lipids during decomposition in natural oxic and anoxic seawaters abstract to evaluate molecular carbon isotopic fractionation of algal lipids during oxic and anoxic degradation emiliania huxleyi a marine haptophyte was incubated in seawater collected from two depths 30 and 930 m in the cariaco basin three classes of algal lipids alkenones fatty acids and sterols showed a degradation pattern characterized by complete loss in oxic seawater within 2 3 months the only exception was 16 0 fatty acid but 10 40 of initial algal lipids remained in the anoxic seawater after 3 months incubation oxic degradation rate constants of alkenones and fatty acids were generally 2 3 times higher than those derived from anoxic incubations however two sterols had similar degradation rate constants in oxic and anoxic seawater there was little preferential degradation of 37 3 relative to 37 2 alkenone in oxic and anoxic seawater leading to insignificant changes for u 37 k paleotemperature indicator in spite of alkenone degradation during oxic and anoxic degradation the same three classes of algal lipids exhibited different patterns of molecular carbon isotopic fractionation depletion 4 to 6 relative to initial value in 13 c for alkenones enrichment 2 to 7 relative to initial value for fatty acids and no change for sterols we postulate that the contrasting molecular isotopic fractionation patterns which depend on the structure of the lipid compounds are likely caused by different degradation reactions at specific functional groups where the carbon atoms may have dissimilar isotopic ratios from other carbon atoms in the molecules due to the differences in original precursors and synthesis pathways laboratory observation of these patterns of lipid fractionations during decomposition of a single phytoplankton material suggests that diagenetic processes can alter the molecular isotopic signals of preserved organic matter in a variety of ways

suction controlled multistage triaxial testing on clayey silty soil abstract multistage triaxial testing offers a potentially reliable and time saving alternative method of determining the shear strength of soils under suction controlled conditions while addressing the issues related to soil variability and lack of replicates however evidence of its suitability for testing geomaterials in unsaturated conditions is rather limited in this work a series of suction controlled multistage triaxial tests were performed on compacted specimens of clayey silty soil wherein each test was performed on the same soil specimen at a constant suction under drained condition but at varying net confining pressures the point of termination of the shearing stage was defined through a selection process involving either the stiffness or the volume change in monotonically sheared specimen based on whichever prevents premature failure of the specimen this was the first attempt where all the stages of a multistage triaxial test were compared against that from single stage triaxial tests for validation of the approach moreover the influence of errors introduced by multistage triaxial testing on the shear strength predictions of unsaturated soil was considered by constructing a three dimensional failure envelope on p s space using a well known relation and comparing them against those obtained from single stage triaxial tests it was also noted that for determining the shear strength parameters of soil the multistage testing reduced the testing times to half of that required by single stage triaxial testing which would translate into significant reduction of cost of testing thereby making unsaturated soil testing much more appealing to the practitioners

observational evidence of preferred flow regimes in the northern hemisphere winter stratosphere abstract ten yeah of stratosphere geopotential height data are analyzed in an attempt to determine whether there are preferred flow regimes in the northern hemisphere winter stratosphere the data are taken from stratospheric sounding units on board noaa satellites the probability density estimate of the amplitude of the wavenumber 1 10 mb height is found to be bimodal the density distribution is composed of a dominant large amplitude mode and a less frequent low amplitude mode when the wavenumber 1 10 mb height data are projected onto the phase plant defined by the 10 mb zonal mean winds and wavenumber 1 100 mb heights three preferred regimes are evident the small amplitude mode separates into a strong zonal wind weak wave regime and a weak zonal wind weak wave regime the large amplitude mode is an intermediate zonal wind strong wave regime transitions between the large amplitude regime and the weak zonal wind weak wave regime are found to be associated with major stratospheric warnings the clust

how depositional conditions control input composition and degradation of organic matter in sediments from the chilean coastal upwelling region abstract in a comprehensive study we compared depositional conditions organic matter om composition and organic carbon turnover in sediments from two different depositional systems along the chilean continental margin at 23 s off antofagasta and at 36 s off concepcion both sites lie within the chilean coastal upwelling system and have an extended oxygen minimum zone in the water column however the northern site 23 s borders the atacama desert while the southern site 36 s has a humid hinterland eight surface sediment cores up to 30 cm long from water depths of 126 1350 m were investigated for excess 210pb 210pbxs activity total organic and total inorganic carbon concentrations toc and tic respectively c n ratios organic carbon isotopic compositions 13c chlorin concentrations chlorin indices ci and sulfate reduction rates srr sediment accumulation rates obtained from 210pb analysis were similar in both regions 0 04 0 15 cm yr 1 at 23 s 0 10 0 19 cm yr 1 at 36 s although total 210pbxs fluxes indicated that the vertical particle flux was higher at 36 s than at 23 s we propose that sediment focusing in isolated deposition centers led to high sediment accumulation rates at 23 s furthermore there were no indications for sediment mixing at 23 s while bioturbation was intense at 36 s 13c values 24 5 to 20 1 vs vpdb and c n ratios molar 8 6 12 8 were characteristic of a predominantly marine origin of the sedimentary om in both investigated areas the extent of om alteration in the water column was partly reflected in the surface sediments as chlorin concentrations decreased and c n ratios and ci increased with increasing water depth of the sampling site srr were lower at 23 s areal srr 0 12 0 60 mmol m 2 d 1 than at 36 s areal srr 0 82 1 18 mmol m 2 d 1 which was partly due to the greater water depth of most of the sediments investigated in the northern region and consistent with a lower quality of the sedimentary om at 23 s reaction rate constants for toc degradation that were obtained from measured srr ksrr 0 0004 0 0022 yr 1 showed a good correspondence to ktoc that were derived from the depth profiles of toc 0 0003 0 0014 yr 1 both ksrr and ktoc reflect differences in om composition at 36 s they were related to the degradation state of bulk om represented by c n ratios whereas near 23 s they were related to the freshness of a small fraction of labile om represented by ci our study shows that although rates of organic carbon accumulation were similar in both investigated sites the extent and kinetics of organic carbon degradation were closely linked to differing depositional conditions

chlorophyll a and pheopigments as tracers of labile organic carbon at the central equatorial pacific seafloor high rates of primary production and fast sinking rates lead to the deposition of phytodetritus and highly reactive organic matter to the sediments of the central equatorial pacific these substances are responsible for driving important chemical fluxes and fueling benthic organisms chloropigments have proven useful as tracers of similar highly reactive organic carbon components in lacustrine and nearshore marine sediments in this study we investigate the degradation of chlorophyll a and pheopigments a at four abyssal sites on the jgofs equatorial pacific transect along 140 w and explore the usefulness of these chloropigments as tracers of the most reactive component of the deep sea particulate organic carbon poc rain first order reaction rate constants k 1 75 yr 1 half life 3 250 d and relative reactivities chlorophyll a allomer and pheophorbide a pheophytin a derived from most of the sedimentary profiles are similar to those found in laboratory and other field lake and coastal marine studies however in some profiles the rate constants determined by fitting data below 0 5 cm are slower by up to 3 orders of magnitude despite an apparent abundance of bacteria macrofauna and porewater oxygen model results assuming multi g kinetics suggest that these chloropigments degrade as two components one which accounts for at least 99 of the degradation and 11 57 of the sediment inventory degrades with a half life of 4 120 days the other component degrades with a half life of up to 440 years these results suggest that some otherwise labile poc may be protected and escape rapid degradation near the sediment water interface if phytodetritus is deposited continuously throughout the year our model calculated chlorophyll a fluxes indicate that it could account for 25 100 of the annual poc flux at sites close to the equator

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

effect of compaction pressure on consolidation behaviour of unsaturated silty soil the effect of compaction pressure on subsequent soil behaviour during isotropic consolidation has been investigated by conducting controlled suction triaxial tests on samples of an unsaturated compacted silty soil a comprehensive set of laboratory experiments was carried out in a double walled triaxial apparatus on samples of unsaturated soil that were prepared using two different compaction pressures the axis translation technique was used for creating the desired suctions in the samples in the experiments the soil samples were subjected to isotropic consolidation under constant suctions the results show that different compaction pressures produce different fabrics in a soil and therefore affect the behaviour of the soil the results also show that the value of yield stress and the location of the loading collapse lc yield curve are functions of soil fabric furthermore it is shown that the slopes of normal consolidation lines for densely and loosely compacted samples differ in unsaturated condit

planetary scale wave activity as a source of varying tropospheric response to stratospheric sudden warming events a case study 1 stratospheric sudden warming ssw events are typically but not always accompanied by negative northern annular mode anomalies in the troposphere however large uncertainties remain as to which dynamical processes are responsible for those anomalies in order to highlight sources of variability in stratosphere troposphere coupling among ssw events we present a case study of three selected events and show detailed transformed eulerian mean diagnostics for momentum changes in the stratosphere and troposphere in the course of those events our results suggest that planetary scale waves especially the zonal wave number 2 component may play an important role not only for the onset of tropospheric anomalies in response to ssw events but also for introducing variability in the vertical coupling i e whether the tropospheric circulation anomalies lag lead or occur simultaneous to the weakening of the vortex particularly the meridional propagation of those waves in the upper troposphere could be an important factor that determines whether ssw events lag or lead tropospheric anomalies

climatology of the stratospheric polar vortex and planetary wave breaking abstract we use the distribution of ertel s potential vorticity pv on the 850 k isentropic surface to establish a climatology for the transient evolution of the planetary scale circulation in the northern hemisphere winter midstratosphere we compute pv distribution from gridded nmc daily temperature and height maps for the 10 and 30 mb levels and show that a very good approximation for 850 k pv can be derived from 10 mb heights and temperatures alone we assume that reversals of the latitudinal gradient of pv localized in longitude and latitude may be regarded as signatures of planetary wave breaking wave breaking identified by such signatures tends to occur mainly in the vicinity of the aleutian anticyclone with a secondary maximum over europe the area of the polar vortex defined as the area enclosed by pv contours greater than a certain critical value is strongly influenced by wave breaking erosion of the polar vortex due to transport and mixing of pv leads to a preconditioned state when def

influence of compaction procedure on the mechanical behaviour of an unsaturated compacted clay part 1 wetting and isotropic compression the influence of compaction pressure compaction water content and type of compaction static or dynamic on subsequent soil behaviour during wetting and isotropic loading has been investigated by conducting controlled suction tests on samples of unsaturated compacted speswhite kaolin the results are interpreted within the context of an elastoplastic framework for unsaturated soils to examine which compaction induced effects can be explained simply by variation in the initial state of the soil and which require that soils produced by different compaction procedures are modelled as fundamentally different materials the compaction pressure influences initial state by affecting the initial position of the yield surface but it also influences to a limited degree the positions of the normal compression lines for different values of suction the compaction water content influences the initial suction but also has a significant influence greater than does compaction pressure on the positions of the nor

bioturbation short lived radioisotopes and the tracer dependence of biodiffusion coefficients bioturbation refers to the mixing of sediment particles resulting from benthic faunal activity it is the dominant particle mixing process in most marine sediments and exerts an important control on diagenetic processes in models bioturbation is usually treated as a diffusive process where the biodiffusion coefficient db characterizes the biological mixing intensity biodiffusion coefficients are classically computed by fitting a diffusive model to vertical profiles of particle bound radioisotopes one peculiar observation is tracer dependence db values from short lived tracers tend to be larger than those obtained from long lived tracers from the same site recent theoretical work based on random walk theory and lattice automaton bioturbation simulations labs has suggested that this tracer dependence is simply a model artifact and has concluded that the biodiffusion model is not applicable to the short observational time scales associated with short lived radioisotopes here we have compiled a global dataset of db values obtained from different radiotracers to assess tracer dependence from a data perspective tracer dependence is significant in low mixing environments like slope and deep sea sediments but is not present in intensely mixed coastal areas tracer dependence is absent when the number of mixing events is larger than 20 or the potential length scale is greater than 0 5 cm roughly this comes down to tracer derived db values greater than 2 cm2 yr 1 this condition is met for 68 50 and 8 of published db values obtained from coastal continental slope and abyssal environments respectively these results show that short lived radioisotopes are suitable to quantify biodiffusion mixing in sedimentary environments featuring intense bioturbation

tropospheric response to stratospheric sudden warmings in a simple global circulation model abstract a composite analysis is made of 132 stratospheric sudden warming ssw events obtained in a 10 000 day integration with a simple global circulation model under a perpetual winter condition the analysis confirms general features of the ssws such as enhanced upward propagation of planetary wave activity from the troposphere to the stratosphere before the ssws and downward propagation of warming signals to the lower stratosphere after the events a further dynamical diagnosis shows that the tropospheric circulation is quite different between pre ssw and post ssw periods in terms of the zonal mean zonal wind planetary wave and synoptic scale waves in the pre ssw period the planetary wave is more active than normal in relation to the tropospheric westerly jet that shifts poleward in the post ssw period on the other hand the planetary wave is less active while the mean zonal wind is close to the climatology synoptic scale waves also exhibit anomalous features in both periods corresponding to

role of the quasi biennial oscillation in the downward extension of stratospheric northern annular mode anomalies using the jra 55 reanalysis datasets and radiosonde observations the impact of the quasi biennial oscillation qbo on the downward extension of stratospheric northern annular mode nam signals in its positive and negative phases positive and negative nam hereafter is examined the results show that the average number of days per month on which stratospheric negative nam signals extend downward into the troposphere is more than twice as large during the easterly phase of the qbo eqbo as those during the westerly phase of the qbo wqbo the increasing likelihood of downward extension of stratospheric negative nam signals during the eqbo is related to three factors enhanced upward wave 1 fluxes entering the stratosphere anomalous poleward wave fluxes below 100 hpa and eqbo induced residual circulation it is also revealed that the eqbo induced subtropical tropospheric easterly anomalies lead to positive height anomalies over the subtropical north atlantic which are amplified by transient eddies and maintained by convection these subtropical positive height anomalies further stimulate an anomalous wave train forcing subpolar positive height anomalies over the euro atlantic sector and enhancing wave 1 over the pacific the eqbo could also induce positive height anomalies in the tropical troposphere and these anomalies are related to convection and vertical motion the positive height anomalies can induce anomalous poleward propagating waves forcing negative height anomalies over the north pacific at mid high latitudes and the enhancing wave 1 fewer stratospheric positive nam signals extend downward into the troposphere during the eqbo than during the wqbo with mechanisms similar to those of negative nam

bioturbation in shelf slope sediments off cape hatteras north carolina the use of 234th chl a and br to evaluate rates of particle and solute transport abstract biogenic particle reworking 234 th chl a chloropigment distributions and pore water irrigation rates br tracer were examined in the continental shelf break upper slope region off the north carolina cape hatteras coastline sediment cores were obtained along three primary east west transects water depth 75 800 m 36 20 n 35 50 n 35 25 n at additional shallow stations along 35 40 n and at slope stations within a region of complex topography known as the manteo lease block samples were collected during august 1994 july 1996 and august 1996 and were recovered using two shipboard techniques haps corer and box corer as well as by the deep submersible johnson sea link natural and experimental tracer distributions demonstrate that with few exceptions surface deposits throughout this region are rapidly reworked and irrigated by abundant infaunal benthos excess 234 th t 1 2 24 1 days was present at all stations with surface activities 0 0 5 cm ranging from 2 to 62 dpm cm 3 5 54 dpm g 1 average inventories of 28 21 median 24 dpm cm 2 and typical penetration depths of 5 7 cm steady state particle mixing coefficients d b estimated using excess 234 th ranged from 1 to 200 cm 2 yr 1 although the highest mixing intensities were found between 300 and 500 m water depths rates were locally variable and there was little or no evidence for any consistent attenuation with bathymetric depth in either 234 th inventories or mixing intensity estimates of d b made using chl a distributions are similar to those estimated using 234 th ranging from 36 to 110 cm 2 yr 1 added br tracer penetrated 7 cm in 24 h periods in shipboard incubated sediment cores representing rates ranging from 1 5 to 38x molecular diffusion mean 13 1 13 0 median 11x sedimentary chl a and phaeophytin a distributions below the photic zone are indicative of high input of fresh planktonic debris and rapid remineralization these inputs presumably fuel the abundant benthic fauna which rework sediments on the hatteras slope at some of the highest mixing rates yet reported

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

the undrained shear strength of soils containing large gas bubbles measurements of undrained shear strength are reported from a series of triaxial tests on reconstituted soil samples containing large bubbles of methane gas the experimental results indicate that the undrained strength can be either increased or reduced by the presence of large gas bubbles depending upon the values of the consolidation pressure and the initial pore water pressure a conceptual model for soils containing large gas bubbles developed in the companion paper is analysed to provide theoretical predictions for the undrained shear strength the analysis leads to theoretical upper and lower bounds for the undrained strength which show good agreement with the experimental data the experimental and theoretical developments have led to a better understanding of the strength of soils containing large gas bubbles this could be of considerable benefit to the offshore construction industry if platforms pipelines and other structures are to be built in areas of gas bearing sediments l article pre

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

the netherlands indian ocean expedition 1992 1993 first results and an introduction the netherlands indian ocean programme was carried out with the rv tyro in the nw indian ocean the arabian sea and off kenya and the seychelles during 1992 1993 with the objective to study the effect on both spatial and temporal scales of the monsoon on the climate system in the northern indian ocean the programme included five research foci studied in different projects project a was directed towards the effects of the seasonally reversing monsoonal system on the coastal ecosystems in kenya especially to gain a clear understanding of the physical chemical and biological processes occurring in the coastal zone this includes the development of the marine flora and fauna in response to the changing conditions in the coastal zone the second project b aimed at a study of the dynamics of the pelagic system including a quantification of the carbon flux and biogeographical studies with the emphasis on distribution and taxonomy of plankton part of this project was designed as pilot project for the jgofs northwest indian ocean study carried out in 1994 95 covering most of the jgofs core measurements these studies were planned in close cooperation with the geological project c tracing a seasonal upwelling system aimed at determining the spatial and temporal variability of biological chemical and geological parameters that define an upwelling system and recognizing these in the sedimentary record as proxies for upwelling in the waters off somalia and yemen project d concentrated on two main issues the first was the late quaternary productivity and the dynamics of the oxygen minimum zone in the northeast arabian sea the second was the depositional architecture and sediment facies of the middle and lower indus fan the biology of oceanic reef systems of the seychelles formed the last project e within the netherlands indian ocean programme and was mainly directed towards biogeographical taxonomical and ecological studies of the reefs the studies comprised within these projects were and are being carried out at a range of different institutes and preliminary results were discussed at an arabian sea workshop held at nioz texel the netherlands from 13 16 february 1995 the papers in this special form the first group of results from the progamme and as a consequence the articles have a strongly variable character the first paper by kromkamp et al describes temporal and spatial variability of primary production along the kenyan coast and their relationship to the development of the cyanobacterium trichodesmium

temporal changes in the phytoplankton community of the southern basin of lake baikal over the last 24 000 years recorded by photosynthetic pigments in a sediment core abstract photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of lake baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial post glacial transition the sedimentation age of the core spans the last 24 14c ka chlorophyll a its derivatives carotenoids and total organic carbon toc started to increase after 15 14c ka and the onset of biogenic silica occurred at 10 14c ka this indicated that the post glacial growth of diatoms was preceded by that of other phytoplankton groups in the record of the pigments and toc a temporary decrease was observed in the period 11 5 10 5 14c ka corresponding to the younger dryas cold period the similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of toc suggested the important contribution of fecal pellets to sedimentary organic matter in the lake

sedimentary pigments on the pakistan margin controlling factors and organic matter dynamics abstract sedimentary pigments can provide information on various aspects of benthic processes and biogeochemistry in this study sediments from sites at depths of 140 to 1850 m spanning the pakistan margin oxygen minimum zone omz and representing dramatic contrasts in depositional conditions and benthic communities were analysed for pigment yields and compositions this has allowed a rare consideration of how different factors including oxygen concentration organic matter om supply and biological activity e g degree of bioturbation may influence sedimentary pigment distribution in a continental margin environment it has also allowed one of the first efforts to study the impact of biological activity on pigment concentrations in the natural environment rather than in a microcosm setting total extractable surface sediment pigment concentrations showed a range of 1 5 49 g g 1 of dry sediment the pigment suite was dominated by pheophytin and pheophorbide which together constituted 75 of total pigments with minor amounts of chlorophyll a alloxanthin diatoxanthin zeaxanthin and carotene low oxygen concentration appeared to influence pigment abundance by increasing the concentration of refractory pigments ultimately buried in addition maximal pigment abundances were associated with minimal amounts of sediment mixing by macrofauna and at one site macrofaunal digestion may have altered the relative dominance of the different pheopigments in contrast the lack of a marked increase in pigment concentrations after the summer monsoon plus the lack of a correlation between pigment concentration and water depth suggest that om supply plays a relatively small role in controlling sedimentary pigments pigment concentrations and suites together with modelled decay half lives 0 8 15 years suggest that in general om on the pakistan margin despite the low oxygen concentrations and monsoon driven productivity is surprisingly degraded compared to that on other continental margins with om rich sediments as an exception to this general situation pigment suites appeared to be relatively fresh i e contained more labile components compared to those found on the oman margin of the arabian sea but overall concentrations were lower this is consistent with the higher oxygen concentrations productivity and macrofaunal abundances found on the western margin of the arabian sea principle component analysis of pigment suites showed that they correlated with an amino acid based degradation index di thus the pigment composition of marine sediments is related to and may serve as an indicator of the state of decay of sedimentary om

a study of oxic anoxic effects on degradation of sterols at the simulated sediment water interface of coastal sediments laboratory incubation experiments were conducted to determine the behavior of sterols at the sediment water interface in oxic and anoxic sediments both plankton and 4 14c cholesterol were used as tracers cholesterol was rapidly degraded at the sediment water interface 55 of 14c cholesterol was lost from sediments under anoxic conditions and 78 under oxic conditions over three and one half months about 3 of initially added free radiolabel was incorporated into a bound pool that was released only by saponification of solvent extracted sediment less than 1 of initially added radiolabel remained in pore waters after three and one half months rate constants for degradation of cholesterol in oxic and anoxic surficial sediments were estimated by tracking variations in radioactivity and sterol concentration as a function of time we discuss our results in terms of factors affecting sterol degradation in coastal marine sediments including molecular structure sediment matrix effect and redox conditions

propagation of planetary waves between the troposphere and stratosphere abstract the propagation of planetary waves between the troposphere and stratosphere is investigated using a linear time dependent primitive equation model it is found that the tropopause acts like a valve for the propagation of planetary waves the key parameters controlling the valve are the vertical gradient of buoyancy frequency and the vertical shear of the zonal winds at the tropopause for a given wind profile smaller gradient of buoyancy frequency enhances the propagation of planetary waves for a given profile of buoyancy frequency the larger the shear the more the wave activity is trapped in the troposphere and therefore there is less left to propagate into the stratosphere the transmission across the tropopause is however not sensitive to zonal winds in the upper stratosphere the propagation of planetary waves is very sensitive to transience more transient waves propagate more vertically within the troposphere and for more transient waves more wave activity is transferred into the

influence of sediment permeability and mineral composition on organic matter degradation in three sediments from the gulf of aqaba red sea abstract in order to investigate the influence of sediment physical and chemical characteristics on the degradation of deposited organic matter decomposition in three sediments from the gulf of aqaba red sea that differ in permeability and mineral composition were compared freeze dried spirulina was added to coarse carbonate and silicate sands from a shallow nearshore region and silt clay sediment from the deeper center region of the gulf incubated in laboratory chambers the stirring in the chambers caused higher solute exchange in the coarse permeable sands relative to the fine less permeable silt due to the generation of advective fluid exchange between the sediment and overlying water this enhanced exchange increased the decomposition rates of organic matter in the incubated sands the decomposition rates of total organic carbon in the permeable carbonate 3 0 mg c m 2 d 1 and silicate sands 2 0 mg c m 2 d 1 exceeded that in the fine grained sediment 1 4 mg c m 2 d 1 oxygen consumption in the coarse sands was 3 fold higher than in the silt clay sediment with highest rates in the carbonate sand in carbonate and silicate sands of the same grain size the carbonate sediment was more permeable than the silicate resulting in 1 4 fold higher fluid exchange rates and 1 4 fold larger sedimentary organic matter mineralization rates an in situ experiment comparing trapping efficiencies in carbonate and silicate sands showed that the higher fluid exchange rate in the carbonate sand results in larger filtration rates and a faster accumulation of particulate organic matter from the boundary layer these experiments demonstrate that with respect to sedimentary mineralization rates higher transport rates in permeable coarse sediments can outweigh the effect of a higher specific surface area in fine grained silt sediments in permeable sands however the higher specific surface area and fluid exchange in biogenic carbonate sands result in higher mineralization rates than in silicate sands of the same grain size

how permeable is the edge of the arctic vortex model studies of winter 1999 2000 1 the edge of the arctic vortex constitutes a strong barrier to transport however the extent of isolation of the vortex air as a function of altitude and season is relatively poorly quantified in this study by examining the transport of midlatitude air parcels across the vortex edge into the vortex we analyze the permeability of the vortex edge with the three dimensional version of clams chemical lagrangian model of the stratosphere we explore the dilution of the vortex air due to mixing in winter 1999 2000 an artificial passive tracer was initialized on 1 december 1999 inside the polar vortex with a value of 100 and with a value of zero outside the polar vortex using several different definitions of the vortex edge the resulting intrusions of midlatitude air into the vortex show the same mean features this demonstrates that the diagnosed dilution does not strongly depend on the details of the definition of the vortex edge at about the end of march 2000 the vertical structure of the vortex consisted of well isolated pure vortex layers around 500 k and 750 k with some more diluted layers in between and at the vortex bottom the influence of wave activity on the evolution of the intrusion layers is studied the divergence of the eliassen palm flux shows such a high variability during the whole period that it is not possible to assess a direct causality of certain intrusion layers and some specific patterns some characteristics of the vortex edge in particular the shape of the gradient of potential vorticity pv can influence the dilution of the vortex in cases without a distinct maximum in the pv gradient the defined vortex edge may vary substantially from day to day the comparison of some properties of the vortex wind speed pv field area of the vortex the maximum of the pv gradient of undisturbed versus diluted layers and the variation in time of the intrusions were analyzed all observed intrusions begin in conditions of weak pv gradient indicating that the value of the maximum of the pv gradient may be used as a quantitative measure of the permeability of the vortex edge

aragonite cycles diagenesis caught in the act organic biomarker and nannofossil assemblages are used in combination with sedimentary petrology to identify the role of diagenesis for the formation of a rhythmic calcareous succession a record from the early pliocene of the maldives ocean drilling program odp leg 115 is presented containing precession and eccentricity cycles expressed as variable aragonite content additional sub milankovitch cycles are caused by rhythmic precipitation of calcite cement in the lower part of the interval comparison with palaeo productivity indicators nannofossils chlorin total organic carbon suggests that cementation occurs preferentially in intervals characterized by increasing or decreasing productivity the coupled variability in productivity and carbonate diagenesis is attributed to the effect of organic matter degradation in the sediment the observed combination of primary and diagenetic factors hampers the interpretation of the cyclicity on milankovitch and sub milankovitch scales diagenetically stable proxies for palaeo productivity such as nannofossil assemblage data were used to distinguish between palaeoclimate and diagenetic influences

carotenoid diagenesis in recent marine sediments i the peru continental shelf 15 s 75 w abstract we report here the distribution of carotenoids in peru marine surface sediments including partial identification of 37 pigments 33 of which have not been previously reported to occur in marine sediments our analysis demonstrates that zooplanktonic crustacea diatoms dinoflagellates cryptomonads purple nonsulfur photosynthetic bacteria and unidentified species of photosynthetic bacteria are contributors to sedimentary organic matter fucoxanthin fucoxanthinol diadinoxanthin peridinin and peridininol the principal carotenoids of diatoms and dinoflagellates observed in sediment traps are nearly absent from our sample even though these phytoplankton are the primary source of organic matter we attribute this to the presence of 5 6 epoxides in these pigments a feature which causes rapid cleavage of the polyene and fragmentation to low molecular weight compounds

climatology of planetary waves in the northern stratosphere a 30 year record of subjectively analyzed daily temperature and geopotential height data from the lower and middle stratosphere 50 30 and 10 hpa is used to derive a climatology of planetary waves with zonal wavenumbers s 1 2 and 3 of temperature t and geopotential height z this should be useful as 1 a reference data set for intercomparison with shorter records and validation of general circulation models and 2 for fundamental understanding of the nature of stratospheric wave disturbances first seasonal december january and february statistics are presented the steady standing waves are strongest at 60 70 n and generally lead to northward eddy heat and momentum fluxes consistent with vertically propagating dissipated disturbances in broad agreement with previous studies based on shorter data sets at 30 hpa the stationary eddies provide about 50 60 of the net northward heat flux but the transients contribute a similar proportion to the net northward momentum flux statistical analysis of the transient wave amplitudes reveals unimodal distributions which are skew for higher wavenumbers transient variations in the eddy fluxes are shown to be mainly due to amplitude variations rather than changes in the barotropic or baroclinic structure of the eddies it is shown that changes in the geographical location of the waves contribute a considerable amount to the transience so that a composite mean based on the wave amplitude maximum contributes a much larger fraction of the net eddy fluxes than the stationary waves the importance of the long data record for these statistical distributions is emphasized by examining a 10 year subsample finally the occurrence of preferred flow regimes through the 30 year data record is examined neither trends nor definite links with possible external forcing mechanisms are found despite considerable low frequency biennial to decadal variability

biomarker evidence for heinrich events the so called heinrich layers found in north atlantic sediments have been attributed to quasi periodic discharges of armadas of icebergs originating from the laurentide ice sheet using the distribution of biomarkers in a sediment core bofs 5k we have attempted to provide more information about their origin and the effect of the heinrich events on oceanic circulation and the climatic system estimates of sea surface temperature changes via u3k7 measurements show that the surface ocean underwent significant cooling during the events probably as a result of incoming iceberg meltwater the low sea temperatures and the rapid variation in the accumulation of chlorophyll derived pigments suggest that the events provoked a major change in oceanographic conditions which may have affected the thermohaline circulation in the atlantic ocean within the most recent layers we have also found vanadyl alkyl porphyrins and aryl isoprenoid hydrocarbons diagenetic products of photosynthetic pig ments chlorophylls and carotenoids respectively these components are not expected to occur in late quaternary sediments so their presence demonstrates a contribution to the layers of ancient organic rich sedimentary material of continental origin the presence of vanadyl porphyrins and absence of their nickel counterparts and the distributional features of the aryl isoprenoids e g presence of the c40 reduced carotenoid isorenieratane of green sulphur bacterial origin indicate the existence of anoxic conditions in the photic zone of a marine water column in the original depositional setting of the contributed ancient sediment these results suggest that it should be possible using a biomarker correla tion approach to determine the source area of the ancient sediment eroded by the icebergs copyright 1997 elsevier science ltd

vortex dynamics and the evolution of water vapour in the stratosphere of the southern hemisphere the seasonal evolution of water vapour in the stratosphere of the southern hemisphere is studied by using water vapour measurements made by the microwave limb sounder on the upper atmosphere research satellite this evolution is interpreted with the aid of meteorological fields produced at the uk meteorological office by data assimilation the processes governing the distribution of water vapour are clarified by focusing on the physical and dynamical conditions in and around the stratospheric polar vortex sustained diabatic descent in the vortex causes isopleths of water vapour mixing ratio to dip down markedly in the polar vortex strengthening radial gradients of water vapour in the westerly jet while stretching and folding of material lines in anticyclones adjacent to the polar vortex leads to a widening zone of weak horizontal gradients of water vapour the circulation is discussed in terms of the dynamics of interacting vortices two different flow regimes are identified a mid and late southern winter with a strong polar vortex and one or more eastward travelling anticyclone and b spring with a relatively weak polar vortex and a quasi stationary anticyclone the phenomenon of merger of anticyclones already observed in the stratosphere of the northern hemisphere is documented for the southern hemisphere a detailed study of the tracer transport during merger is made by computing the isentropic advection of many thousands of particles a comparison is made of the seasonal evolution of water vapour in the stratosphere of the southern and northern hemispheres

organic matter diagenesis in shallow water carbonate sediments muddy carbonate deposits near the dry tortugas florida are characterized by high organic carbon remineralization rates however approximately half of the total sedimentary organic matter potentially supporting remineralization is occluded in caco3 minerals intracrystalline while a portion of nonintracrystalline organic matter appears to cycle rapidly intracrystalline organic matter has an approximately constant concentration with depth suggesting that as long as its protective mineral matrix is intact it is not readily remineralized organic matter in excess of intracrystalline organic matter that is preserved may have a variety of mineral associations e g intercrystalline adsorbed or detrital in surface sediment aspartic acid contributed 22 mole and 50 mole to nonintracrystalline and intracrystalline pools respectively in deeper sediment 1 6 1 7m the composition of hydrolyzable amino acids in both pools was similar aspartic acid 40 mole like amino acids intracrystalline and nonintracrystalline fatty acids have different compositions in surface sediments but are indistinguishable at depth these data suggest that preserved organic matter in the nonintracrystalline pool is stabilized by its interactions with caco3 neutral lipids are present in very low abundances in the intracrystalline pool and are extensively degraded in both the intracrystalline and nonintracrystalline pools suggesting that mineral interactions do not protect these compounds from degradation the presence of chlorophyll a but absence of phytol in the intracrystalline lipid pool demonstrates that chloropigments are present only in the nonintracrystalline pool sedimentary chloropigments decrease with depth at similar rates in dry tortugas sediments as found in alumino silicate sediments from the long island sound suggesting that chloropigment degradation is largely unaffected by mineral interactions overall however inclusion and protection of organic matter by biominerals is a major pathway for organic matter preservation in this low organic carbon biomineral rich regime

benthic organic matter supply and metabolism at depositional and non depositional areas in the north sea in 1994 four stations in the southern north sea the german bight and the skagerrak were visited with the aim to get insight into spatial and temporal variation in the supply of fresh organic matter to the benthos and its subsequent metabolic reaction stations were chosen on the basis of differences in sediment type depth and depositional regime sediments were sampled sliced and analysed for phytopigments fatty acids and nucleic acids on deck sediment core incubations provided the sediment oxygen demand sod fatty acids as well as chlorophyll a indicated a seasonal variation of phytodetritus sedimentation with highest values in may reflecting the spring bloom sedimentation the two stations in the depositional areas german bight and skagerrak had the highest input of algal detritus into the sediment these stations also contained higher concentrations of bacterial and long chain fatty acids probably related to the relatively higher proportion of fine particles in the sediment and to the input of terrestrial organic matter and or refractory marine organic matter respectively the metabolic indices viz the sod and the rna concentrations reflected the benthic metabolic reaction to the labile organic matter supply the three stations in the southern and south eastern north sea had a sod congruent with the phytodetrital inventories with highest sod measured at the german bight surprisingly the skagerrak sediment did not have a high oxygen demand although it contained the highest inventory of labile organic matter and high rna concentrations the fluxes of carbon to the sediment at station sk calculated from the chlorophyll a inventory were about four times higher than the sediment oxygen demand we hypothesise two mechanisms for this discrepancy one is the decreased mineralisation rate of labile organic matter due to sorption to clayey sediment particles the other is advection of labile organic matter from the shallower coastal waters of northern denmark to and subsequent removal from the deeper skagerrak sediments by periodically occurring high near bottom water currents

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

organic matter reactivity indicators in sediments of the st lawrence estuary here we report multiple parameters used to describe the diagenetic state of sediments including total hydrolyzable amino acid thaa amino acid enantiomer chlorin ci and amino acid degradation di ri indices along a transect between the upper st lawrence estuary and the gulf of st lawrence canada the study area is characterized by gradients in water oxygen concentration water depth organic matter om source primary productivity and sedimentation rate both ci and di indicate a decline in om reactivity with the transition from a more terrestrial to a more marine dominated sedimentation regime as one moves from the shallow upper estuary 23 95 m to the hypoxic mid depth lower estuary and to the deep 400 m well oxygenated gulf whereas the ci more accurately reflected om reactivity in surface sediments and sediments down to 5 cm the amino acid based degradation indices di and ri better described degradation in sediments down to 35 cm systematic variations in the amino acid composition along the laurentian channel confirmed the increased diagenesis of om with distance from the upper st lawrence estuary the ratio of d l stereoisomers of alanine increased along the transect and the co variation between di and the d l ala suggest a close coupling between the extent of diagenesis and the accumulation and selective preservation of bacterially derived cell wall material in the sediments the same patterns that we observed along the estuarine transect were present down core in two sediment cores confirming the robustness of our reactivity indices oxygen exposure time of the sediments appears to strongly determine sediment om reactivity in the st lawrence estuary the sediment oxygen regime itself is related to the interplay between water column depth vertical om flux and reactivity of settling om

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

phytodetritus at the abyssal seafloor across 10 of latitude in the central equatorial pacific fresh phytoplankton detritus or phytodetritus has been reported from numerous deep seafloor sites in the temperate north atlantic and pacific oceans following seasonal phytoplankton blooms here we report the first strong evidence for abyssal accumulations of phytodetritus in the tropics in the central equatorial pacific in november december 1992 we obtained photographs and or sediment core samples from 61 abyssal stations water depths of 4280 5012 m between 12 s and 9 n along 140 w greenish flocculent material was recovered from the top of multiple core samples from 5 s to 5 n this material was most abundant from 2 s to 2 n in some areas forming continuous layers at least 5 mm thick and individual aggregates 1 cm in diameter the greenish material was clearly visible in bottom photographs as a green veneer that covered 95 of the seafloor near the equator and as individual cm scale aggregates covering 1 of the seafloor occasionally thick accumulations of cm scale aggregates occurred in biogenic pits cleared trails and feeding traces suggest that surface deposit feeding holothurians and echiurans grazed the greenish material microscopic examination of greenish material recovered from core tops and a burrow lumen revealed relatively intact diatoms including rhizosolenia sp and other microalgae with chloroplasts containing chlorophyll the greenish material was 1 12 5 organic carbon by weight i e 5 39 times richer than associated seafloor sediments it also contained high excess activities of 234th suggesting arrival from the water column in the previous 100 days samples of the greenish flocculent material from 0 and 5 n incubated at simulated environmental pressure and temperature with 14c labeled glutamate exhibited 5 fold higher rates of microbial activity than underlying sediments or brown floc from 9 n surface sediment samples which included the greenish flocculent material from 5 s to 5 n also contained significant concentrations of chlorophyll a and other chloropigments the chloropigment concentrations were roughly comparable to deep sea phytodetritus collected in the north atlantic we conclude that fresh organic rich phytodetritus was present on the seafloor from 5 s to 5 n along 140 w in november december 1992 with highest concentrations within 2 3 of the equator this material is likely to be a concentrated high quality food resource for deep sea microbes and metazoans we estimate an upper limit for the standing stock of this phytodetritus to be 2 6 mmol corg m2 this corresponds to 3 of the annual flux of organic carbon to the seafloor at these latitudes in 1992 because the degradation rate of this material appears to be very high its presence at the seafloor for several months per year could yield significant phytodetrital contributions to the annual seafloor organic carbon budget we also suggest that the phytodetrital aggregates are formed at intense convergence zones resulting from seasonal passage of tropical instability waves within 5 of the equator if so phytodetrital accumulations are likely to recur seasonally over broad areas of the abyssal equatorial pacific

diagnostic case studies of the northern annular mode abstract recent observational studies of the northern annular mode nam indicate that significant case to case variability exists in the structural evolution of individual events in particular certain nam events remain confined to stratospheric altitudes whereas others readily penetrate downward into the troposphere we perform observational diagnostic analyses that are targeted at identifying the physical mechanisms behind this distinction our results thereby provide a test of the different existing theories regarding stratospheric influences upon tropospheric climate we contrast robust stratospheric nam events with differing tropospheric signals in order to identify the underlying dynamical reasons for the observed differences piecewise potential vorticity pv inversions and eliassen palm flux analyses are performed to study the roles of different forcing mechanisms during nam onset our results indicate that variations in the tropospheric response are readily explained on the basis of piecewise

statistical characterization of arctic polar night jet oscillation events abstracta novel diagnostic tool is presented based on polar cap temperature anomalies for visualizing daily variability of the arctic stratospheric polar vortex over multiple decades this visualization illustrates the ubiquity of extended time scale recoveries from stratospheric sudden warmings termed here polar night jet oscillation pjo events these are characterized by an anomalously warm polar lower stratosphere that persists for several months following the initial warming a cold anomaly forms in the middle stratosphere as does an anomalously high stratopause both of which descend while the lower stratospheric anomaly persists these events are characterized in four datasets microwave limb sounder mls temperature observations the 40 yr ecmwf re analysis era 40 and modern era retrospective analysis for research and applications merra reanalyses and an ensemble of three 150 yr simulations from the canadian middle atmosphere model the statistics of pjo events in the model are found t

sources and preservation of organic matter in plum island salt marsh sediments ma usa long chain n alkanes and stable carbon isotope compositions elemental toc tn c n and stable carbon isotopic delta 13 c compositions and n alkane nc 16 38 concentrations were measured for spartina alterniflora a c 4 marsh grass typha latifolia a c 3 marsh grass and three sediment cores collected from middle and upper estuarine sites from the plum island salt marshes our results indicated that the organic matter preserved in the sediments was highly affected by the marsh plants that dominated the sampling sites delta 13 c values of organic matter preserved in the upper fresh water site sediment were more negative 23 0 0 3 as affected by the c 3 plants than the values of organic matter preserved in the sediments of middle 18 9 0 8 and mud flat sites 19 4 0 1 as influenced mainly by the c4 marsh plants the distribution of n alkanes measured in all sediments showed similar patterns as those determined in the marsh grasses s alterniflora and t latifolia and nc 21 to nc 33 long chain n alkanes were the major compounds determined in all sediment samples the strong odd to even carbon numbered n alkane predominance was found in all three sediments and nc 29 was the most abundant homologue in all samples measured both delta 13 c compositions of organic matter and n alkane distributions in these sediments indicate that the marsh plants could contribute significant amount of organic matter preserved in plum island salt marsh sediments this suggests that salt marshes play an important role in the cycling of nutrients and organic carbon in the estuary and adjacent coastal waters c 2003 elsevier ltd all rights reserved

laboratory studies of oxic and anoxic degradation of chlorophyll a in long island sound sediments abstract laboratory incubations of long island sound lis sediments show that chlorophyll a chla degradation generally follows first order kinetics but that the rates and mechanisms of degradation differ under oxic and anoxic conditions chl a in fresh sediment can be operationally defined as being present in three pools bound chl a nonextractable by acetone free acetone extractable anoxically degradable chl a and free anoxically stable chl a a major pathway of degradation is initial release of bound chl a into the free pool the release rate constants of bound chl a into free chl a are remarkably faster 10 under oxic 4 d 1 compared to anoxic 0 1 d 1 conditions and a much greater fraction of total chl a degrades under oxic conditions however the apparent degradation rate constants of free chl a are two to three times higher in the absence of oxygen in sediments with high bound chla 0 2 0 3 d 1 for anoxic 0 1 d 1 for oxic and about seven times higher in sediments without bound chl a 0 3 d 1 for anoxic 0 04 d 1 for oxic the differences between anoxic and oxic decomposition in incubation experiments together with naturally observed concentration profiles which reach low levels of chl a imply that chl a in natural sediments degrades during the oscillation between oxic and anoxic conditions caused by physical and biological mixing processes oscillation experiments oxic vs anoxic and anoxic vs oxic suggest that the activities of aerobic organisms may be an important factor affecting chl a degradation examination of effects of meiofauna on chl a degradation under oxic conditions implies that microorganisms may play a stronger role in chl a degradation than meiofauna 0 125 mm the relative temperature independence of anoxic degradation and temperature dependence of oxic degradation suggest that anoxic degradation may be controlled largely by chemical factors while oxic degradation may be more strongly controlled by biophysical and biochemical processes

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

response of the stratosphere to interannual variability of tropospheric planetary waves a primitive equation global model of the middle atmosphere is used to investigate the response of the extratropical stratosphere to different levels of wave forcing from steady perturbations of the geopotential height near the tropopause the response of the stratosphere is compared to that in quasi geostrophic beta plane models used in previous studies the primitive equation model exhibits three flow regimes under perpetual january conditions strong westerly steady flow for small wave amplitude forcing strong westerly but unsteady flow for moderate wave amplitude forcing and oscillations between easterly and westerly flow for large wave amplitude forcing the regimes for low and high forcing are analogous to solutions of the simpler holton mass hm quasi geostrophic model the moderate forcing regime does not occur in the hm model and it is attributed to instability of the strongly sheared flow generated by planetary waves in the upper stratosphere we also show how the observed patterns of interannual variability in the winter stratosphere can be explained in terms of these three flow regimes in the northern hemisphere the flow often enters the high forcing regime where variations in conditions in the early winter flow or quasi steady upper tropospheric planetary wave amplitudes make similar contributions to the interannual variability in the stratospheric circulation for the southern hemisphere we suggest that the flow alternates between the low and moderate forcing regimes through year to year changes in the amplitude of quasi steady waves near the tropopause this mechanism produces large enough changes to explain the interannual variability in the southern stratosphere

climatology of arctic and antarctic polar vortices using elliptical diagnostics abstract the climatological structure and interannual variability of the arctic and antarctic stratospheric polar vortices are examined by analysis of elliptical diagnostics applied to over 19 yr of potential vorticity data the elliptical diagnostics define the area center elongation and orientation of each vortex and are used to quantify their structure and evolution the diagnostics offer a novel view of the well known differences in the climatological structure of the polar vortices although both vortices form in autumn to early winter the arctic vortex has a shorter life span and breaks down over a month before the antarctic vortex there are substantial differences in the distortion of the vortices from zonal symmetry the arctic vortex is displaced farther off the pole and is more elongated than the antarctic vortex while there is a midwinter minimum in the distortion of the antarctic vortex the distortion of the arctic vortex increases during its life cycle there are also large differenc

the early major warming in december 2001 exceptional the early major warming in december 2001 is described and compared to the two other december major warmings in 1998 and 1987 showing a strong tropospheric stratospheric coupling in all three cases we argue that the occurrence of free westward propagating rossby waves interacting with a forced quasi stationary wave number 1 led to these three early events the possible excitation of these waves is discussed with respect to the tropospheric circulation which showed strong blockings over the northern atlantic prior to the early major warmings

response of phytoplankton productivity to climate change recorded by sedimentary photosynthetic pigments in lake hovsgol mongolia for the last 23 000 years abstract we analyzed photosynthetic pigments total organic carbon toc and total nitrogen tn in two radiocarbon dated sediment cores of lake hovsgol nw mongolia covering the period of the last glacial post glacial transition since 23 14c ka the sedimentary profiles of total chlorophyll a derivatives tchl a toc and tn reflect productivity increase during the last glacial post glacial transition between 15 and 10 14c ka in response to regional climate warming and enhanced precipitation correlation between tchl a and toc was high r 2 0 934 n 74 with a zero intercept of a regression line suggests that total organic carbon in lake hovsgol sediments is of autochthonous origin the depth profiles of toc tn ratio showed increases toward the core top in parallel with other paleoproductivity proxies serving as an indicator of climatic transition quite similar to lake baikal sedimentary record the primary reason for the shifts of this parameter is still not clear however chlorophyll b derivatives and some algal carotenoids such as lutein zeaxanthin diatoxanthin and canthxanthin were detected although in concentrations lower than that of tchl a these biomarkers indicate that green algae cyanobacteria and diatoms were present in phytoplankton during the post glacial period significantly pre dating the beginning of the holocene abrupt drops of biomarker profiles at ca 1 2 and 10 14c ka due to decreased productivity in the lake or enhanced degradation of the biomarkers likely record short term climatic events

nitrogen isotope and chlorin paleoproductivity records from the northern south china sea remote vs local forcing of millennial and orbital scale variability abstract variations in nitrogen isotopic composition 15n and total chlorin accumulation rate ar are employed as proxies to reconstruct oceanic nitrate inventory the balance between denitrification and n fixation and paleoproductivity in a rapidly accumulating sediment drift deposit beneath the western pacific warm pool for the last 145 kyr subsurface and deep waters of the northern south china sea scs are sourced from the shallow kuroshio current kc and pacific intermediate water respectively their relative importance in determining sedimentary 15n and paleoproductivity have been altered by changes in equatorial circulation summer and winter monsoon intensity and relative sea level the location and basin configuration of the marginal scs renders it especially sensitive to such changes assuming complete annual nitrate utilization low 15n values during glacial stages are interpreted as a reflection of reduced remote denitrification in the eastern tropical north pacific etnp source waters while much of marine isotope stage mis 3 and the last interglacial were characterized by high denitrification however intervals of anomalously low 15n values are interpreted as reflecting the contribution from regional n fixation in west pacific surface waters transmitted to the site by the shallow kc unusually the holocene is characterized by declining 15n values and an inverse correlation with organic matter content since ca 8 2 ka millennial scale variations during mis 3 indicate higher frequency variations in both etnp denitrification and local n fixation which may be coherent with a hemispheric response to dansgaard oeschger events recorded at high latitudes for much of the last 145 kyr paleoproductivity was decoupled from 15n and instead seems to reflect the extent of the global nitrate inventory stimulated by elevated dust fertilization and regional mixed layer deepening associated with the relative intensity of the se asian winter monsoon despite evaluation of possible conflicting influences on the record of each proxy we interpret our data as clear evidence of glacial interglacial changes in marine nutrient inventory across the whole of the north pacific with a corresponding biogeochemical response and important implications for global co2 drawdown via an invigorated biological pump the relative importance of local regional and global contributions to our records appears to be strongly modulated by relative sea level controlling trans and extra basinal circulation in the scs

sedimentary pigments and nature of organic matter within the oxygen minimum zone omz of the eastern arabian sea indian margin abstract sedimentary pigments carbon and nitrogen content and their stable isotopes were studied in three short cores collected from the oxygen minimum zone omz of the eastern arabian sea eas nine pigments including chlorophyll a and their degradation products were quantified using high performance liquid chromatography hplc astaxanthin followed by canthaxanthin and zeaxanthin were the major carotenoids detected in these cores the total pigment concentration was high in the core collected from 500 m water depth 6 5 gg 1 followed by 800 m 1 7 gg 1 and 1100 m 1 1 gg 1 depths respectively the organic carbon did not have considerable control on sedimentary pigments preservation pigment degradation was comparatively high in the core collected from the 800 m site which depended not only the bottom dissolved oxygen levels but also on the faunal activity as reported earlier the bottom water dissolved oxygen and presence of fauna have good control on the organic carbon accumulation and preservation at indian margin omz sediments the c n ratios and 13 c values for all the cores conclude the marine origin of organic matter and 15 n profiles revealed signature of upwelling associated denitrification within the water column

wave maintained annular modes of climate variability abstract the leading modes of month to month variability in the northern and southern hemispheres are examined by comparing a 100 yr run of the geophysical fluid dynamics laboratory gcm with the ncep ncar reanalyses of observations the model simulation is a control experiment in which the ssts are fixed to the climatological annual cycle without any interannual variability the leading modes contain a strong zonally symmetric or annular component that describes an expansion and contraction of the polar vortex as the midlatitude jet shifts equatorward and poleward this fluctuation is strongest during the winter months the structure and amplitude of the simulated modes are very similar to those derived from observations indicating that these modes arise from the internal dynamics of the atmosphere dynamical diagnosis of both observations and model simulation indicates that variations in the zonally symmetric flow associated with the annular modes are forced by eddy fluxes in the free troposphere while

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

early diagenesis of redox sensitive trace metals in the peru upwelling area response to enso related oxygen fluctuations in the water column pore water and solid phase data for redox sensitive metals mn fe v mo and u were collected on a transect across the peru upwelling area 11 s at water depths between 78 and 2025 m and bottom water oxygen concentrations ranging from 0 to 93 m by comparing authigenic mass accumulation rates and diffusive benthic fluxes we evaluate the respective mechanisms of trace metal accumulation retention and remobilization across the oxygen minimum zone omz and with respect to oxygen fluctuations in the water column related to the el nino southern oscillation enso sediments within the permanent omz are characterized by diffusive uptake and authigenic fixation of u v and mo as well as diffusive loss of mn and fe across the benthic boundary some of the dissolved mn and fe in the water column re precipitate at the oxycline and shuttle particle reactive trace metals to the sediment surface at the lower and upper boundary of the omz at the lower boundary pore waters are not sufficiently sulfidic as to enable an efficient authigenic v and mo fixation as a consequence sediments below the omz are preferentially enriched in u which is delivered via both in situ pre cipitation and lateral supply of u rich phosphorites from further upslope trace metal cycling on the peruvian shelf is strongly affected by enso related oxygen fluctuations in bottom water during periods of shelf oxygenation surface sediments receive particulate v and mo with metal oxyhydr oxides that derive from both terrigenous sources and precipitation at the retreating oxycline after the recurrence of anoxic conditions metal oxyhydr oxides are reductively dissolved and the hereby liberated v and mo are authigenically removed this alternation between supply of particle reactive trace metals during oxic periods and fixation during anoxic periods leads to a preferential accumulation of v and mo compared to u on the peruvian shelf the decoupling of v mo and u accumulation is further accentuated by the varying susceptibility to re oxidation of the different authigenic metal phases while authigenic u and v are readily re oxidized and recycled during periods of shelf oxygenation the sequestration of mo by authigenic pyrite is favored by the transient occurrence of oxidizing conditions our findings reveal that redox sensitive trace metals respond in specific manner to short term oxygen fluctuations in the water column the relative enrichment patterns identified might be useful for the reconstruction of past omz extension and large scale redox oscillations in the geological record

organic matter degradation in sediments of the york river estuary effects of biological vs physical mixing abstract we investigated the influence of biological and physical seabed disturbance on the degradation of bulk organic matter and source specific lipid biomarker compounds by measuring downcore changes in bulk elemental composition bulk stable isotopic 13c and 15n signatures and lipid biomarker compounds in sediment cores collected from two sites in the york river a subestuary of the chesapeake bay usa one site ly is influenced by biological mixing bioturbation restricted to the upper 15 20 cm while the other site pod experiences intense episodic physical mixing events that penetrate 50 100 cm into the sediment we utilized a suite of auxiliary measurements to constrain the sources of organic matter depositional environments and general ages of the cores diagenetic modeling of total organic carbon and total nitrogen in sediments yielded higher apparent rate constants for pod than ly suggesting that the physical mixing regime promotes enhanced degradation of bulk organic matter apparent rate constants for select lipids representing distinct sources of organic matter were also higher at pod than ly for all but the most labile i e diatom derived fatty acids biomarkers differences in stanol stenol ratios also supported enhanced diagenesis of stenols at pod the source specific biomarkers while useful in qualitatively identifying the sources of sedimentary organic matter likely do not represent the full spectrum of its reactivity however based on our results we hypothesize that the intense sediment disturbance at pod promotes degradation of more recalcitrant organic material due to prolonged exposure to oxygen and other electron acceptors e g no3 mn and fe oxides in contrast the degradation of more labile constituents is equally facilitated by biological and physical disturbance

chlorophyll production degradation and sedimentation implications for paleolimnology1 chlorophyll a production degradation and sedimentation were studied simultaneously during summer stratification in three lakes with contrasting plankton communities pigment budgets showed that chlorophyll production and pigment resuspension were both major sources of water column pigments photodegradation rates were rapid and indicated that detritus particles that remained in the epilimnion for periods longer than about 3 days lost nearly all detectable pigments therefore only rapidly sinking detrital particles or those produced in deep layers at low light intensity could make appreciable contributions to sedimentary chlorophyll degradation products pheophorbide a a grazing indicator was the dominant chlorophyll a degradation product found in sediment traps pigment sedimentation increased significantly with mean size of cladocerans and omnivorous copepods in contrast sedimentation rates of chlorophyll degradation products did not increase with primary production in these lakes the deposition of chlorophyll degradation products in sediments depended primarily on the size and biomass of grazers

critical state for overconsolidated unsaturated silty soil the critical state concepts have been investigated for an overconsolidated unsaturated silty soil through a comprehensive set of controlled suction triaxial laboratory experiments the experimental

temporal variability of 210pb fluxes and bioturbation in shelf sediments beneath the high primary production area off concepcion central southern chile 36 s abstract we estimated monthly fluxes of 210 pb in shelf sediments beneath a high productivity area off central southern chile 36 s during 1 year september 2002 august 2003 sediment cores were obtained using a multiple corer and were analyzed mainly for 210 pb total pigments and macrofauna abundance the 210 pb inventories and fluxes were estimated for surface sediments 0 5 cm and bioturbation coefficients were inferred using chlorophyll a reactive profiles in general 210 pb content was inversely correlated with phytodetritus fluxes high photosynthetic pigment contents in surface sediments were consistently associated with lower 210 pb contents macrofaunal activity responded to oxygen and organic matter supplies at the sediment surface generally concentrated in the first centimeters but particularly so during months of high organic matter fluxes and deficient bottom water oxygen conditions at this study site several processes involved in the 210 pb surface distribution make it difficult to accurately estimate ages at the surface we postulate that the organic fluxes promote changes in the faunal activity which in combination with sediment resuspension and water circulation over the shelf produce seasonal variations in the 210 pb inventories

mechanical behaviour of unsaturated kaolin with isotropic and anisotropic stress history part 1 wetting and compression behaviour over the last 40 years considerable progress has been made in understanding the complex behaviour of unsaturated soils research using constitutive modelling has extended the critical state framework and the concept of yielding in saturated soils to encompass unsaturated soils experiencing suction however validation testing of the framework for unsaturated soils has shown disagreement with the basic propositions the main reason for this disparity is the anisotropic properties of the soil specimens tested as a result of preparation using one dimensional compaction the paper describes the detailed testing carried out to justify this statement as part of the work presented samples of unsaturated kaolin were prepared using isotropic compression the suctions in these samples were reduced to predefined values by wetting under low isotropic loading the pore size distributions the pressure volume relationships and yielding under subsequent isotropic loading are compared with tests on samples prepared by

deposition rates mixing intensity and organic content in two contrasting submarine canyons the hydrographically different conditions characterising the western iberian margin ne atlantic and the gulf of lions mediterranean may play an important role in determining the biogeochemical characteristics of the sediments to investigate this we compared the nazare and cap de creus canyons and their respective adjacent open slopes in terms of the organic carbon corg contents chlorophyll a chl a concentrations c n and chl a phaeopigment ratios and also in terms of modelled mixing intensities chl a and 210pb deposition and background concentrations in sediments chlorophyll a and 210pb profiles were fitted simultaneously with a reactive transport model to estimate mixing intensity deposition and background concentrations further to account for the possibility that the decay of chl a may be lower in the deep sea than in shallow areas we estimated the model parameters with two models in one approach model 1 the temperature dependent decay rate of chl a as given by sun et al sun m y lee c aller r c 1993 laboratory studies of oxic and anoxic degradation of chlorophyll a in long island sound sediments geochimica et cosmochimica acta 57 147 157 for estuaries was used in the other approach model 2 an extra parameter was estimated to derive the chlorophyll a degradation rate an f test taking into account the different number of parameters in the models was used to single out the model that significantly fitted the data best in most cases the model parameters were best explained with model 1 indicating the empirical relationship by sun et al 1993 is a valid means to estimate the chlorophyll a degradation rate in deep sea sediments to assess the robustness with which the model parameters were estimated we provide a first application of bayesian analysis in the modelling of tracers in sediments bayesian analysis allows calculating the mean and standard deviation for each model parameter and correlations among parameters the model parameters for stations for which 210pb and chlorophyll a profiles were available were robustly fitted as evidenced by an average coefficient of variation of 0 22 corg contents chl a concentrations chl a phaeo ratios mixing intensities depositions and background concentrations of chl a and 210pb indicated that the cap de creus canyon and adjacent slope were less active in terms of organic matter accumulation and burial than the nazare canyon and respective open slope

downward propagating temperature anomalies in the preconditioned polar stratosphere abstract dynamical links of the northern hemisphere stratosphere and troposphere are studied with an emphasis on whether stratospheric changes have a direct effect on tropospheric weather and climate in particular downward propagation of stratospheric anomalies of polar temperature in the winter spring season is examined based upon 22 years of ncep ncar reanalysis data it is found that the polar stratosphere is sometimes preconditioned which allows a warm anomaly to propagate from the upper stratosphere to the troposphere and sometimes it prohibits downward propagation the arctic oscillation ao is more clearly seen in the former case to understand what dynamical conditions dictate the stratospheric property of downward propagation the upper stratospheric warming episodes with very large anomalies such as stratospheric sudden warming are selected and divided into two categories according to their downward propagating features eliassen palm e p diagnostics and wave propagation theories are u

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

40 70 day meridional propagation of global circulation anomalies 1 this paper reports a diagnostic study of circulation anomalies in a semi lagrangian pvlat coordinate by following contours of the daily potential vorticity pv field on isentropic surfaces using the ncep ncar reanalysis ii data set from 1979 to 2003 the leading eof mode which explains about 69 of the total variance of daily northern hemisphere pv anomalies in the pvlat coordinate and is highly correlated with the stratosphere northern annular mode nam index is used to construct a composite life cycle of the nam variability composite circulation anomalies of both signs propagate poleward in the stratosphere and equatorward in the troposphere with an average time of about 44 days for warm anomalies and 72 days for cold anomalies to travel from the equator to the pole accompanying the meridional propagation there exist a simultaneous downward propagation of stratospheric circulation anomalies in both the tropics and extratropics a global mass circulation paradigm is proposed to explain the simultaneous meridional and vertical propagation of global circulation anomalies that appears responsible for the annular mode variability

experimental observations of the stress regime in unsaturated compacted clay when laterally confined construction processes often involve reformation of the landscape which will inevitably encompass compaction of artificially placed soils a common application of fill materials is their use as backfill in many engineering applications for example behind a retaining wall the post construction behaviour of clay fills is complex with respect to stresses and deformation when the fills become saturated over time heavily compacted fills swells significantly more than the lightly compacted fills this will produce enhanced lateral stresses if the fill is laterally restrained the work presented in this paper examines how the stress regime in unsaturated clay fills changes with wetting under laterally restrained conditions specimens of compacted kaolin with different initial conditions were wetted to various values of suction under zero lateral strain at constant net overburden pressure which allowed the concept of k0 the ratio between the net horizontal stress and the net vertical stress to be examined

climate variability and land ocean interactions in the indo pacific warm pool a 460 ka palynological and organic geochemical record from the timor sea climatic conditions in the western timor sea and the adjacent northwestern part of australia are reconstructed for the last 460 ka based oil geochemical and palynological proxy records of paleoproductivity and land vegetation precipitation from images core md01 2378 reduced precipitation and elevated productivity characterize glacial stages whereas enhanced precipitation and reduced productivity are typical of interglacial stages a long term reduction in precipitation over the last 320 ka occurred in two steps at approximately 300 ka and 180 ka bp that are clearly recognizable in the pollen record variations in paleoproductivity and paleoclimate in the timor sea and adjacent landmasses appear to be driven by similar mechanisms that are related to the precession control led australian monsoon system c 2005 elsevier b v all rights reserved

the unusual midwinter warming in the southern hemisphere stratosphere 2002 a comparison to northern hemisphere phenomena a strong midwinter warming occurred in the southern hemisphere sh stratosphere in september 2002 based on experiences from the northern hemisphere nh this event can be defined as a major warming with a breakdown of the polar vortex in midwinter which has never been detected so far in the sh since observations began at the earliest in the 1940s minor midwinter warmings occasionally occurred in the sh but a strong interannual variability as is present in winter and spring in the nh has been explicitly associated with the spring reversals a detailed analysis of this winter reveals the dominant role of eastward traveling waves and their interaction with quasi stationary planetary waves forced in the troposphere such wave forcing finally leading to the sudden breakdown of the vortex is a familiar feature of the northern winter stratosphere therefore the unusual development of this antarctic winter is described in the context of more than 50 arctic winters concentrating on winters with similar wave perturbations the relevance of preconditioning of major warmings by traveling and quasi stationary planetary waves is discussed for both hemispheres

effect of oxygen on degradation rate of refractory and labile organic matter in continental margin sediments in order to study the effect of oxygen on degradation rate of bulk sedimentary organic matter we developed a new incubation method in contrast to most previous experiments 1 all of the sediment undergoing decomposition was maintained under oxygenated or oxygen free conditions and 2 organic matter of varying lability was studied the production of co2 during incubations of sediment in glass test tubes corrected for dissolution precipitation of calcium carbonates was used as a measure of degradation rates the laboratory experiments using surficial and buried continental shelf and slope sediment from the open skagerrak northeastern north sea demonstrated that the effect of oxygen on the degradation rate of sedimentary organic matter is a function of the lability of the decomposing material fresh material was degraded with little difference in rates in the presence or absence of oxygen whereas old material was decomposed significantly up to 3 6 times faster with oxygen than without oxygen an implication of these findings is that bioturbation by exposing old buried material to oxygen may enhance integrated organic carbon oxidation in marine sediments this constitutes a previously unexplored mechanism by which faunal reworking may stimulate carbon degradation the anoxic decomposition rates of organic material buried at 20 cm depth in sediment were the lowest measured we found however that the extent of oxidation of this buried old sediment was considerably larger than that of surficial sediment under oxygenated conditions which indicated that the oxic anoxic oxic redox transitions deposition under oxic conditions burial under anoxia and reexposure to oxygen promoted degradation our results therefore also suggest that the extent of long term decomposition of sedimentary organic material is smaller under oxygenated or anoxic conditions alone than when the material is exposed to the repeated activities of both oxic and anoxic microorganisms