the evolution of oceanic and atmospheric anomalies in the northeast pacific during the el nino and la nina events of 1995 2001 abstract from late 1995 through early 2001 three major interannual climate events occurred in the tropical pacific the 1995 97 la nina ln 1997 98 el nino en and 1998 2001 ln we analyze atmospheric and upper oceanic anomalies in the northeast pacific nep during these events and compare them to anomalies both elsewhere in the north and tropical pacific and to typical en and ln anomaly patterns the atmospheric and oceanic anomalies varied strongly on intraseasonal and interannual scales during the 1995 97 ln and 1997 98 en the northeast pacific was dominated by negative slp and cyclonic wind anomalies and by upper ocean temperature and sea surface height ssh anomalies the latter were positive along the north american west coast and in the nep thermal anomaly pool between hawaii vancouver island and baja california and negative in the central north pacific this atmospheric oceanic anomaly pattern is typical of en an eastward shift in the atmospheric teleconnection from east asia created en like anomalies in the nep during the 1995 97 ln well before the 1997 98 en had begun the persistence of negative sea level pressure slp and cyclonic wind anomalies in the nep during the 1997 98 en intensified pre existing upper oceanic anomalies atmospheric anomalies were shifted eastward during late 1996 early 1998 leading to a similar onshore shift of oceanic anomalies this produced exceptionally strong positive upper ocean temperature and ssh anomalies along the west coast during the 1997 98 en and explains the unusual coastal occurrences of several species of large pelagic warm water fishes the growth and eastward shift of these pre existing anomalies does not appear to have been linked to tropical pacific en anomalies until late 1997 when a clear atmospheric teleconnection between the two regions developed prior to this remote atmospheric impacts on the nep were primarily from east asia as the 1998 2001 ln developed nep anomalies began reversing toward the typical ln pattern this led to predominantly negative slp and cyclonic wind anomalies in the nep and upper ocean temperature and ssh anomalies that were mainly negative along the west coast and positive in the central north pacific the persistence of these anomalies into mid 2001 and a number of concurrent biological changes in the nep suggest that a decadal climate shift may have occurred in late 1998 during 1995 2001 nep oceanic anomalies tracked the overlying atmospheric anomalies as indicated by the maintenance of a characteristic spatial relationship between these anomalies in particular wind stress curl and ssh anomalies in the nep maintained an inverse relationship that strengthened and shifted eastward toward the west coast during late 1996 early 1998 this consistent relationship indicates that anomalous ekman transport driven by regional atmospheric forcing was an important contributor to temperature and ssh anomalies in the nep and ccs during the 1997 98 en other studies have shown that coastal propagations originating from the tropical pacific also may have contributed to coastal nep anomalies during this en our results indicate that at least some of this coastal anomaly signal may have been generated by regional atmospheric forcing within the nep

penetration of atlantic westerly winds into central and east asia abstract the geographical position of the convergence zone where the western atlantic climate system meets the asian winter monsoonal system depends on their relative strength these individual strengths are determined by the intensities of the air pressure gradients over the north atlantic and the siberian high pressure cell respectively since the factors that forced those gradients varied throughout glacial interglacial cycles the location of the convergence zone should have moved accordingly both the grain size characteristics of wind blown sediments and climate modelling prove that the atlantic influence extended remarkably far eastward at times the northeastern tibetan plateau was at the cross road of western and monsoonal influences during the last glacial this region was dominated by an atlantic signal with millennial scale climatic oscillations that are similar to the north atlantic marine and greenland ice core records in contrast that same region was only under monsoonal influence during the last interglacial it implies that the atlantic winds penetrated more vigorously eastward in full glacial conditions than in interglacial conditions

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

ductile fractures and magma migration from source mechanisms proposed to explain effi cient melt transport away from hot ductile source regions are problematic brittle elastic fracturing is a well known mechanism that allows fast magma migration as dikes through cold crust ductile fractures have been propo sed as an alternative for ductile environments where brittle elastic diking is inhibited ductile fracturing results from rock creep and growth of microscale voids that become interconnected leading to rock failure in this paper we present observations and numerical models supporting the hypothesis that ductile fracture controls early steps in magma migration we postulate that once developed ductile fracture dikes may reach a critical length where magma stresses at dike tips overcome fracture toughness and lead to brittle elastic diking which subsequently controls magma migration

extreme climatic conditions recorded in santa barbara basin laminated sediments the 1835 1840macoma event abstract the santa barbara basin sbb record of laminated sediment well known for its excellent time resolution shows the presence of an unusual once in a millenium event in the period 1835 1840 at a depth of 55 57 cm below the surface of the seafloor this macoma event is the brief flourishing of a macrofaunal community in the deep center of the sbb from which large organisms are normally excluded by the lack of oxygen shells of the pelecypodmacoma leptonoidea dall and associated fossils which congregate in a thin layer dated at 1840 provide evidence for a sudden local extinction of macrobenthos by suffocation various stratigraphic evidence suggests thatm leptonoidea colonized the basin floor for a few years prior to 1840 as a result of temporarily decreased productivity and increased oxygen content in the water spilling over the sill into the basin historical eyewitness reports indicate unusually severe winter storms from southeasterly directions during the 1830s in the sbb we suggest that coastal upwelling was severely reduced during 1835 1839 with the effect of reducing the intensity of the oxygen minimum layer themacoma event apparently is one manifestation of large scale climatic anomalies felt throughout north america and which were possibly linked to the major volcanic eruption of cosiguina nicaragua in 1835

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

association between atmospheric circulation patterns and firn ice core records from the inilchek glacierized area central tien shan asia 1 glacioclimatological research in the central tien shan was performed in the summers of 1998 and 1999 on the south inilchek glacier at 5100 5460 m a 14 36 m firn ice core and snow samples were collected and used for stratigraphic isotopic and chemical analyses the firn ice core and snow records were related to snow pit measurements at an event scale and to meteorological data and synoptic indices of atmospheric circulation at annual and seasonal scales linear relationships between the seasonal air temperature and seasonal isotopic composition in accumulated precipitation were established changes in the 18o air temperature relationship in major ion concentration and in the ratios between chemical species were used to identify different sources of moisture and investigate changes in atmospheric circulation patterns precipitation over the central tien shan is characterized by the lowest ionic content among the tien shan glaciers and indicates its mainly marine origin in seasons of minimum precipitation autumn and winter water vapor was derived from the arid and semiarid regions in central eurasia and contributed annual maximal solute content to snow accumulation in tien shan the lowest content of major ions was observed in spring and summer layers which represent maximum seasonal accumulation when moisture originates over the atlantic ocean and mediterranean and black seas

transient dike propagation and arrest near the level of neutral buoyancy abstract we present a finite difference perturbation method to investigate transient dike propagation from a magma chamber 1 2 km below the level of neutral buoyancy in oceanic crust and explore the role of density gradation in dike propagation arrest the dike is modeled as a magma filled blade crack and the host rock is assumed to be a linear elastic medium with graded mass density an integral equation approach is used to obtain the dike propagation velocity and stress intensity factor at the propagating dike tip the finite difference perturbation method is applicable generally to mafic dikes with v less than 50 pa m where is the magma viscosity and v the dike propagation velocity numerical results show that dike propagation velocity initially increases with dike length reaches a peak value when the dike tip reaches a position well above the level of neutral buoyancy and then rapidly decreases to zero after the dike propagates further into the region above the level of neutral buoyancy which indicates that density gradation is an effective mechanism for dike arrest the effects of host rock fracture toughness and magma chamber depth relative to the level of neutral buoyancy are also discussed

annual record of particle fluxes geochemistry and diatoms in effingham inlet british columbia canada and the impact of the 1999 la nina event abstract sediment traps were deployed inside the anoxic inner basin of effingham inlet and at the oxygenated mouth of the inlet from may 1999 to september 2000 in a pilot study to determine the annual depositional cycle and impact of the 1999 la nina event within a western canadian inlet facing the open pacific ocean total mass flux geochemical parameters carbon nitrogen opal major and minor element contents and stable isotope ratios and diatom assemblages were determined and compared with meteorological and oceanographic data deposition was seasonal with coarser grained terrestrial components and benthic diatoms settling in the autumn and winter coincident with the rainy season marine sedimentary components and abundant pelagic diatoms were coincident with coastal upwelling in the spring and summer despite the seasonal differences in deposition the typical temperate zone thalassiosira skeletonema chaetoceros bloom succession was muted a july 1999 total mass flux peak and an increase in biogenous components coincided with a rare bottom water oxygen renewal event in the inlet likewise there were cooler than average sea surface temperatures ssts just outside the inlet and unusually high abundances of a previously undescribed cool water marine diatom fragilariopsis pacifica sp nov within the inlet each of these occurrences likely reflects a response to the strong la nina that followed the year after the strongest ever recorded el nino event of 1997 1998 by the autumn of 1999 ssts had returned to average and f pacifica had all but disappeared from the remaining trap record indicating that oceanographic conditions had returned to normal oxygenation events were not witnessed in the inlet in the years before or after 1999 suggesting that a rare oceanographic and climatic event was captured by this sediment trap time series the data from this record can therefore be used as a benchmark for identifying anomalous environmental conditions on this coast

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

dynamics of advection driven upwelling over a shelf break submarine canyon 1 the response over a submarine canyon to a several day upwelling event can be separated into three phases an initial transient response a later much longer steady advection driven response and a final relaxation phase for the advection driven phase over realistically steep deep and narrow canyons with near uniform flow and stratification at rim depth we have derived scale estimates for four key quantities observations from 5 real world canyon studies and 3 laboratory studies are used to validate the scaling and estimate the scalar constant for each scale based on 4 geometric parameters of the canyon the background stratification the coriolis parameter and the incoming current we can estimate 1 the depth of upwelling in the canyon to within 15 m 2 the deep vorticity to within 15 and 3 the presence absence of a rim depth eddy can be determined based on laboratory data 4 the total upwelling flux can also be estimated the scaling analysis shows the importance of a rossby number based on the radius of curvature of isobaths at the upstream mouth of the canyon this rossby number determines the ability of the flow to cross the canyon isobaths and generate the pressure gradient that drives upwelling in the canyon other important scales are a rossby number based on the length of the canyon which measures the ability of the flow to lift isopycnals and a burger number based on the width of the canyon that determines the likelihood of an eddy at rim depth generally long canyons with sharply turning upstream isobaths strong incoming flow small coriolis parameter and weak stratification have the strongest upwelling response

laminated sediments in the bay of la paz gulf of california a depositional cycle regulated by pluvial flux core bap96 cp sampled from the deepest part of the bay of la paz gulf of california has been analysed sedimentologically taking into account regional climate and oceanography laminated sediments at the bottom of the bay are essentially not bioturbated by benthic fauna a subanoxic condition o 2 0 2 ml l 1 inhibits the proliferation of benthic fauna within the bay the relative abundances of terrigenous and biogenic inputs change periodically the terrigenous input is greater than the biogenic input and apparently experiences larger fluctuations the terrigenous input dominates in dark laminae whereas the biogenic input mostly occurs in light laminae thus it is assumed that down the core the alternation of dark and light laminae represents cycles in the extent of dilution of the biogenic input by terrigenous input the terrigenous input into the bay of la paz is mostly regulated by pluvial runoff thus its temporal fluctuation follows the periods shown by the regional pluvial regime particularly the 11 2 year period this is equal to the frequency of sunspot cycles

spectral characteristics of sea level variability along the west coast of north america during the 1982 83 and 1997 98 el nino events abstract we use hourly sea level records from southern california to the aleutian islands to examine low frequency variability in the northeast pacific during the 1982 83 and 1997 98 el nino events comparison between events is facilitated by long term records for yakutat tofino neah bay and san francisco which appear to be representative of distinct coastal oceanic regimes residual tide removed time series reveal that the anomalously high sea levels of the 1997 98 el nino persisted from the spring of 1997 to the spring of 1998 and this event was more protracted than the 1982 83 el nino during both major events the annual sa semiannual ssa and synoptic scale sea level constituents were amplified relative to non el nino years with synoptic fluctuations in sea level height and sea level pressure for mid latitude sites tofino and neah bay strongly correlated through the inverted barometer response the spectral anomaly coefficient sjr rj 1 rj 1 where r j s j s j is the spectral ratio between the el nino spectrum sj and the time averaged non el nino spectrum s j for tide gauge site j indicates that both events gave rise to enhanced sea level variability at periods of days to weeks because of passing atmospheric systems however the 1982 83 el nino generated greater signal variance at seasonal scales periods of months while the 1997 98 el nino generated greater variance at synoptic scales periods of days findings further indicate that poleward oceanic propagation of the 1982 83 and 1997 98 events terminated near central california and that much of the enhanced sea level variability observed at mid to high latitudes was associated with atmospheric teleconnection responses that gave rise to amplified variations in coastal sea level pressure and or surface wind stress

analysis of a microcrack model and constitutive equations for time dependent dilatancy of rocks summary based on experimental observations and theoretical analyses the author introduces an ideal microcrack model in which an array of cracks with the same shape and initial size is distributed evenly in rocks the mechanism of creep dilatancy for rocks is analysed theoretically initiation propagation and linkage of pre existing microcracks during creep are well described also the relationship between the velocity of microcrack growth and the duration of the creep process is derived numerically the relationship agrees well with the character of typical experimental creep curves and includes three stages of creep then the damage constitutive equations and damage evolution equations which describe the dilatant behaviour of rocks are presented because the dilatant estimated value is taken as the damage variable the relationship between the microscopic model and the macroscopic constitutive equations is established in this way the mechanical behaviour of rocks can be predicted

source regions and formation of the loess sediments on the high mountain regions of northwestern china loess on the high mountains of northwestern china is largely controlled by the topographic features distributed mainly on the northern slopes of the tianshan and kunlun mountains as well as in the ili valley between the northern and central tianshan ranges loess distributed in different regions has different ages with the oldest early pleistocene loess occurring in the ili valley geochemical mineralogical and granulometric analyses demonstrate that the loess in the three different regions has different provenance the loess on the northern tianshan and kunlun mountains is mainly derived from the junggar and taklimakan deserts respectively whereas the loess in the ili valley is derived mainly from the sary ishikotrau desert located in the republic of kazakhstan however these deserts serve mostly as holding areas for the silts rather than original source regions the production of the silt sized particles is mainly associated with glacial abrasion and tectonic induced rock denudation thus the loess in the studied regions can be described as mountainous loess rather than simply glacial loess or desert loess it is unlikely that the mechanisms of loess formation are the same in different regions given their dependence on specific geomorphological conditions and associated processes

moisture dynamics in central asia for the last 15 kyr new evidence from yili valley xinjiang nw china based on high resolution palynological investigations and ams 14 c dating the continuous lacustrine sediments contained in yili valley xinjiang provide an opportunity to reconstruct the effective moisture changes for the last 15 kyr in central asia the relatively warm and humid climate of the bolling allerod 15 12 9 cal kyr bp is a generalization but it seems to show some fluctuations the time of the younger dryas yd interrupted the increasing trend of effective moisture in the study region the climate was cold and relatively dry in the early yd period 12 9 12 0 cal kyr bp whereas the desert vegetation community appeared around 11 8 cal kyr bp almost the driest time since the 15 cal kyr br a sharp increase in effective moisture marked the beginning of the holocene in the yili valley the early holocene 10 6 7 6 cal kyr bp was the wettest time with a developed temperate steppe a dry climate with desert vegetation arose in the early mid holocene 7 6 6 5 cal kyr bp spanning 1100 years a second humid phase emerged between 6 5 and 5 2 cal kyr bp whose vegetation community was represented by temperate steppe moisture was reduced again and the climate became drier between 5 2 and 3 3 cal kyr bp when vegetation was dominated by desert steppe in the yili valley regional comparisons indicate that the moisture changes in yili valley were mainly influenced by the north atlantic ocean ssts through the westerlies the mean position of the siberian high pressure cell probably made a great contribution to the drought between 7 6 and 6 5 cal kyr bp the climate changes were generally consistent between the westerly dominant central asia and asian monsoon regions since the last deglaciation possibly forced by summer insolation conditions in the northern hemisphere c 2011 elsevier ltd all rights reserved

effects of productivity glaciation and ventilation on late quaternary sedimentary redox and trace element accumulation on the vancouver island margin western canada variations in chalcophile and redox sensitive trace elements are examined at high resolution intervals from a 50 kyr long sediment core md02 2496 from the vancouver island margin enrichments of ag cd re u and mo above lithogenous levels signifying sedimentary suboxia and anoxia occurred during the early holocene and bolling allerod and during warm interstadial events of marine isotope stage mis 3 down core trace element profiles co vary with productivity proxy records opal caco3 and marine organic carbon and with sedimentary nitrogen isotope ratios which reflect variably enriched nitrate upwelled from intermediate waters that were transported northward from the eastern tropical north pacific the similarity of the md02 2496 record with records from the southern portion of the california current system ccs and to the greenland ice core oxygen isotope record during warm climate intervals suggests that sedimentary redox conditions along the california current responded to local productivity to north atlantic climate change and to tropical pacific surface water processes via long distance teleconnections concentrations of trace elements and productivity proxies were relatively depleted during the younger dryas cool stadial events of mis 3 and in two episodes of glaciomarine sedimentation from 14 7 to 30 5 kyr bp last glacial maximum lgm and from 44 to 50 4 kyr bp cordilleran ice sheet advancement onto the vancouver island continental shelf during the lgm led to intervals of increased terrigenous sedimentation and greatly reduced productivity not seen in the southern portion of the ccs and along with ventilation of north pacific intermediate waters resulted in brief sedimentary oxic conditions

catastrophic caldera forming eruptions thermomechanics and implications for eruption triggering and maximum caldera dimensions on earth abstract approximately every 100 000 years the earth experiences catastrophic caldera forming supereruptions that are considered to be one of the most hazardous natural events on earth utilizing new temperature dependent viscoelastic numerical models that incorporate a mohr coulomb failure criterion we find that eruptive failure of the largest magma chambers is a function of the geometry of the overlying roof and the location of the brittle ductile transition in particular the ductile halo created around the hot magma chamber buffers increasing overpressures and prevents pressure relief via magmatic injection from the magma chamber the numerical results indicate that as chamber volume increases the higher temperatures in the host rock and the decrease in the roof aspect ratio cause a shift from reservoir triggered eruption to an external roof triggered mechanism specifically as overpressure increases within the largest magma chambers extensive uplift in the overlying roof promotes the development of through going faults that may trigger eruption and caldera collapse from above we find that for magma chamber volumes 103 km3 and roof aspect ratios depth width

the fall dump a new perspective on the role of a shade flora in the annual cycle of diatom production and export flux investigations of diatom fluxes recorded in laminated sediments using scanning electron microscope techniques together with evidence from sediment trap studies have contributed to a reappraisal of the annual cycle of diatom production and export flux we propose that where there is a strong seasonal thermocline and nutricline a number of diatoms hitherto regarded as typical sparse summer flora characteristic of oligotrophic waters are able to generate substantial production at depth these species including rhizosolenia spp stephanopyxis palmeriana thalassiothrix spp and some coscinodiscus spp may represent a shade flora that have adapted to grow in low light conditions and or to regulate their buoyancy to move between a deep nutrient source and the euphotic zone although rates of growth and primary production are substantially lower than species characteristic of spring bloom or upwelling conditions the total primary production integrated over the several month period of summer stratification may be as significant as the spring bloom or greater the term fall or autumn bloom as a counterpart of the spring bloom is therefore a misnomer whereas the spring bloom involves a rapid burst of reproduction and sedimentation the fall dump is the sedimentation of a long lived episode of production lasting the duration of the seasonal thermocline and triggered by the fall winter mixing that breaks down stratification the fall dump may produce as much or in some cases more export production than the spring bloom the results of this study suggest that a reorientation of thinking on diatom ecology and palaeoecology may be required

zooplankton community composition along the inner portion of line p during the 1997 1998 el nino event the 1996 1999 zooplankton samples from oceanic waters off southern british columbia provide time series descrip tions of biomass and community composition before during and immediately after the 1997 1998 el nino event our most frequent sampling every month in 1998 and three to four times per year in other years was off southern van couver island and extended seaward from the shelf break to approximately 200 km offshore along and adjacent to the inner third of the long term line p station p section 48 30 49 n 126 130 40w el nino associated changes in the zooplankton community were most apparent over the shelf break and slope and weaker further offshore at the nearshore portion of this line p03 p06 the 1997 1998 differences from long term seasonal averages included both lower total biomass and shifts in community composition reduced abundance of endemic boreal temperate species increased abundance of mid california neritic and oceanic species toward the seaward end of the section p08 p12 changes of zooplankton species composition were much less apparent and the main signal associated with the 1997 1998 event was an early and narrow spring peak of neocalanus spp although most extreme in 1998 both the nearshore and offshore sets of anomalies were continuations of trends that had developed progressively off british columbia through the 1990s a few taxa normally endemic to southern parts of california current and previously absent or very rare off british columbia appeared in our samples in 1997 1998 and persisted through summer of 1998 and at some locations into 1999 the changes observed over the continental slope of vancouver island were very similar to the observations of 1970s versus late 1990s differences in the zooplankton of the central oregon coast continental shelf pices sci rep 10 1999 45 prog oceangr 2002 suggesting that there was alongshore continuity of both oceanic forcing and zooplankton response crown copyright 2002 published by elsevier science ltd all rights reserved

siliceous microfossil record of late holocene oceanography and climate along the west coast of vancouver island british columbia canada diatoms silicoflagellates and biogenic silica bsi were analyzed from two piston cores recovered from effingham inlet british columbia relatively productive marine conditions from 4850 to 4000 cal yr bp were followed by a transition to the modern ocean climate regime marked by a decreased siliceous microfossil production since 2800 cal yr bp this change in the northeast pacific climate was characterized by an apparent cooling associated with higher rainfall and lower light levels the reduced abundance of most spring summer bloom diatom taxa skeletonema thalassiosira chaetoceros was coupled with a decreased abundance of diatoms normally associated with incursions of offshore water into coastal inlets this pattern reflected a weaker summer upwelling along vancouver island associated with the insolation related increase in the strength of the aleutian low and a weakened north pacific high after ca 2800 cal yr bp diatom assemblages also indicated more frequent periods of relatively low spring summer surface water salinity and a disruption of the typical bloom sequence indicative of increased climatic variability a period of warmer and drier climate conditions and possibly increased coastal upwelling offshore occurred ca 1450 1050 cal yr bp the most recent 500 yr are marked by reduced diatom production and the appearance of three distinct diatom biomarkers in the stratigraphic record rhizosolenia setigera ca ad 1940 minidiscus chilensis ca ad 1860 thalassionema nitzschioides morphotype a ca ad 1550 the oceanographic changes recorded in effingham inlet are correlative with other marine and terrestrial paleoenvironmental records in the northeast pacific ocean

increasing effective moisture during the holocene in the semiarid regions of the yili basin central asia evidence from loess sections abstract the evolution of holocene moisture in semiarid and arid regions of central asia is key to understanding changes in current and future water resources and has been a hotly debated topic in the past few decades central asian loess deposits have shown potential as records of past moisture changes particularly during the holocene here the variations in effective moisture during the holocene in the semiarid regions of the yili basin central asia are obtained from three loess sections reliable chronologies were constructed using 26 quartz optically stimulated luminescence osl ages the strengthening pedogenesis steady increases in magnetic susceptibility and continuous decreases in mean grain size in the three loess sections all suggest that effective moisture continuously increased throughout the holocene indicating a dry early holocene a moderately humid middle holocene and a wet late holocene rainfall carried by the asian summer monsoon and the westerlies contributes to the moisture changes in central asia however considering the dominance of evaporation over rainfall in controlling aridity humidity shifts in this region the continuous weakening of evaporation caused by a decrease in northern hemisphere summer insolation and associated atmospheric temperatures is primarily responsible for the wetting trend throughout the holocene in the semiarid regions of the yili basin

influence of the pacific decadal oscillation el nino southern oscillation and solar forcing on climate and primary productivity changes in the northeast pacific evidence of 11 year schwabe solar sunspot cycles el nino southern oscillation enso and the pacific decadal oscillation pdo were detected in an annual record of diatomaceous laminated sediments from anoxic effingham inlet vancouver island british columbia radiometric dating and counting of annual varves dates the sediments from ad 1947e1993 intact sediment slabs were x rayed for sediment structure lamina thickness and composition based on gray scale and subsamples were examined for diatom abundances and for grain size wavelet analysis reveals the presence of w2e3 w4 5 w 7a ndw9e12 year cycles in the diatom record and an w11e13 year record in the sedimentary varve thickness record these cycle lengths suggest that both enso and the sunspot cycle had an influence on primary productivity and sedimentation patterns sediment grain size could not be correlated to the sunspot cycle although a peak in the grain size data centered around the mid1970s may be related to the 1976e1977 pacific climate shift which occurred when the pdo index shifted from negative cool conditions to positive warm conditions additional evidence of the pdo regime shift is found in wavelet and cross wavelet results for skeletonema costatum a weakly silicified variant of s costatum annual precipitation and april to june precipitation higher spring april may values of the north pacific high pressure index during sunspot minima suggest that during this time increased cloud cover and concomitant suppression of the aleutian low al pressure system led to strengthened coastal upwelling and enhanced diatom production earlier in the year these results suggest that the 11 year solar cycle amplified by cloud cover and upwelling changes as well as enso exert significant influence on marine primary productivity in the northeast pacific the expression of these cyclic phenomena in the sedimentary record were in turn modulated by the phase of pdo as indicated by the change in period of enso and suppression of the solar signal in the record after the 1976e1977 regime shift

integrating satellite observations and modern climate measurements with the recent sedimentary record an example from southeast alaska 1 assessments of climate change over time scales that exceed the last 100 years require robust integration of high quality instrument records with high resolution paleoclimate proxy data in this study we show that the recent biogenic sediments accumulating in two temperate ice free fjords in southeast alaska preserve evidence of north pacific ocean climate variability as recorded by both instrument networks and satellite observations multicore samples ew0408 32mc and ew0408 43mc were investigated with 137cs and excess 210pb geochronometry three dimensional computed tomography high resolution scanning xrf geochemistry and organic stable isotope analyses ew0408 32mc 57 162 n 135 357 w 146 m depth is a moderately bioturbated continuous record that spans ad 1930 2004 ew0408 43mc 56 965 n 135 268 w 91 m depth is composed of laminated diatom oozes a turbidite and a hypopycnal plume river flood deposit a discontinuous event based varve chronology indicates 43mc spans ad 1940 1981 decadal scale fluctuations in sedimentary br cl ratios accurately reflect changes in marine organic matter accumulation that display the same temporal pattern as that of the pacific decadal oscillation an estimated sitka summer productivity parameter calibrated using seawifs satellite observations support these relationships the correlation of north pacific climate regime states primary productivity and sediment geochemistry indicate the accumulation of biogenic sediment in southeast alaska temperate fjords can be used as a sensitive recorder of past productivity variability and by inference past climate conditions in the high latitude gulf of alaska

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

mineral magnetic investigation of the talede loess palaeosol sequence since the last interglacial in the yili basin in the asian interior summary the loess palaeosol deposit in the asian interior is sensitive to the evolution of the westerlies thus providing a good opportunity to investigate regional palaeoenvironmental evolution and its relationship with global climatic changes multiparameter mineral magnetic investigations have been conducted on the talede section in the yili basin asian interior our study finds that 1 loess samples have higher concentration magnetic minerals than palaeosols though the magnetic mineral composition is similar ferrimagnetic magnetite antiferromagnetic hematite and lepidocrocite 2 large pseudo single domain psd and multidomain md like grains dominate both in loess and palaeosols however magnetic mineral grains in loess are much coarser than those in the palaeosols 3 palaeosols contain approx 30 per cent more amount of hematite than the loess samples the frequency dependent susceptibility of both loess and palaeosols is very low indicating the small amount of super paramagnetic grains and the higher fd per cent values of palaeosols also reveal that palaeosols have more amounts of ultrafine magnetic grains than loess the magnetic variations in part 1 and 2 can be well explained by the wind vigour model but the observed enrichment of hematite and ultrafine magnetic grains in palaeosols also reveals the first onset of pedogenic enhancement therefore the talede section could be seen as an end member of the classic chinese loess plateau clp magnetic enhancement model

chemical accumulation variations under the peru current during the past 130 000 years the titanium to aluminum ratio in core v19 29 is correlated with aluminosilicate accumulation rates this correlation may be due to pleistocene eolian transport fluctuations which alter the mean grain size of sedimented eolian material the relation between aluminum accumulation rate and ti al established from accumulation rates integrated over 11 000 50 000 year intervals can be inverted to compute a high resolution record of aluminosilicate and calcium carbonate accumulation rates over the past 130 000 years carbonate accumulation rates are closely related to the oxygen isotope record in the core with a phase lag and damping constant that is compatible with the response time shown to be only 6000 years of calcium carbonate in the ocean carbonate sedimentation at this site responds to several processes independently correlated with climatic change the relative importance of these processes for carbonate sedimentation at this site can be constrained by the record in this core and other lines of evidence 15 of the increased carbonate deposition at this site during glacial periods may be due to diminished nadw north atlantic deep water formation 10 is due to carbonate productivity decreases in the north atlantic 25 may be due to a diminished shallow sea carbonate sink and the residual 50 must be due to a local productivity increase these assignments are consistent with observations on carbonate paleoceanography in the north atlantic aluminosilicate accumulation rate variations correlate with the record of eolian quartz deposition near northwest africa and in a general way with the climatic record but in detail the record differs substantially from the oxygen isotope record and may provide independent evidence on the nature of climate dynamics

geochemical and diatom signatures of bottom water renewal events in effingham inlet british columbia canada abstract sediments from effingham inlet vancouver island british columbia hold a valuable high resolution holocene record of paleoclimatic and paleoceanographic conditions in the northeast pacific ocean accurate interpretation of this record requires that the depositional environment be well understood in order to assess deposition within the fjord over the last 1500 years two cores a soutar box core and a kasten core were analyzed for fossil diatoms and biogeochemical properties the cores contain varved sequences intercalated with homogeneous mud layers and a seismite we show that homogeneous mud units related to periods of bottom water renewal are geochemically distinct from the seismite and that these bottom renewal events are favored when brackish rather than marine surface water conditions are present the seismite deposited in ad 1946 has lower opal and higher organic carbon concentrations and higher organic carbon nitrogen ratios reflecting greater terrestrial material input in contrast homogeneous mud units are marked by a lower organic c n and more isotopically heavy 13 c values suggesting a stronger marine influence major metals and trace element data also confirm that the source material of these units differs from that of the ad 1946 seismite fossil diatom assemblages within the homogeneous mud units are characterized by a decreased abundance of typical marine spring bloom taxa skeletonema costatum chaetoceros spp thalassiosira spp coupled with an increased abundance of the brackish water taxon cyclotella choctawhatcheeana reduced surface salinity enhances stratification of the water column which in turn favors an intensified two layer estuarine exchange across the shallow sills and associated bottom water renewal the homogeneous mud units are produced through transport of sediment into the fjord coupled with a reworking of the upper layers of the sediment column therefore these units represent a recorder of past changes in regional oceanography and climate

multidisciplinary approach for paleoenvironmental reconstruction in loess paleosol studies of the darai kalon section southern tajikistan the available data on the loess paleosol formation in south tajikistan illustrate the completeness of climatostratigraphic records however studies with a multidisciplinary approach have not been practically used for paleoenvironmental reconstructions this study partially corrects the lack of data on paleolandscape evolution in the loess area of pamir and tien shan piedmonts darai kalon serves as a key section embracing the upper part of the matuyama chron and the entire brunhes chron high resolution magnetic susceptibility record shows that during the brunhes epoch the climate cycles reflected by the central asian loess paleosol succession can be correlated to the deep sea oxygen isotope curve the combination of pedological and palynological material is particularly useful for mutual interpretation lithological and mineralogical data essentially extend our understanding of pedogenetic and paleoclimatic dynamics the tendency of soil and paleoenvironmental evolution recorded in the darai kalon section can be associated with subtropical semi humid forest and forest steppe landscapes the variation of paleoclimatic parameters and paleovegetation type are characteristic of the contemporary vertical zone of cinnamon soils

a process based model of pre eruption seismicity patterns and its use for eruption forecasting at dormant stratovolcanoes abstract using long term data sets the eruptive size timing and style can typically be successfully forecast for dormant volcanoes using current monitoring data and knowledge of precursory eruptive patterns the usaid usgs volcano disaster assistance program vdap utilizes seismic data over multiple eruption cycles and across volcano types to successfully forecast eruption size style and onset times as well as changes within ongoing eruptions from millions of seismic event observations we show that seismic data a proxy for rate dependent strain changes in the magmatic system combined with a process based conceptual geologic model enables eruption forecasting especially for stratovolcanoes dormant 20 years we show that this model often works for some open systems ones that sufficiently reseal to plug the conduit and also where a deep intrusion occurs after phreatic or phreatomagmatic explosions have begun this model is divided into four seismicity and geologic stages we describe each of the four stages of seismicity in detail and how they relate to the ongoing geologic process of that stage stage 1 deep intrusion and seismicity occurring at 10 to 40 km depth below the volcanic edifice stage 2 distal vt seismicity induced at distances from 2 to 30 km laterally from the summit by magma intruding into and inflating the upper crustal magma storage region stage 3 vent clearing seismicity associated with the initial vent creation and clearing phase of eruptive activity stage 4 repetitive event seismicity associated with the final ascent of magma from 2 km to the surface we present 36 examples of this seismic progression from 26 volcanoes we believe that this progression generally correlates with the magma flux and the eventual explosivity and is invaluable for forecasting eruptions

stratigraphies and chronologies of late quaternary loess paleosol sequences in the core area of the central asian arid zone abstract the sporadic distribution of the quaternary loess in central asia makes it hard to establish a regional pedostratigraphy through visual tracing of marker strata the pedostratigraphic correlation presented here is thus completely based on the radiocarbon chronologies of the four studied sections the first noticeable feature is that poorly drained conditions predominated in the period between 48 000 and 30 000 14 c bp during which three entisols developed at 45 000 14 c bp 40 000 14 c bp and 35 000 14 c bp after a period of loess deposition between 30 000 and 18 000 14 c bp under poorly drained conditions an entisol at the westernmost site valikhanov south central kazakhstan developed between 18 000 and 10 000 14 c bp also under poorly drained conditions the time equivalent deposits at romantic and zeketai sections to the east do not exhibit any soil forming characteristics although poorly drained conditions are also imprinted in the time equivalent loess the holocene sequences in the central asian domain consist of an early holocene loess unit deposited between 10 000 and 5 000 14 c bp and a late holocene soil formed during the past 5000 years in comparison the climate was also wet between 48 000 and 20 000 14 c bp during which three mollisols developed under well drained conditions in the chinese loess plateau of the east asian domain the loess deposited between 23 000 and 10 000 14 c bp in the chinese loess plateau has neither observable marks of soil formation nor imprints of poorly drained conditions the holocene sequence in the east asian domain exhibits an out of phase relationship with that in the central asian domain consisting of an early holocene soil formed between 9000 and 4000 14 c bp and a late holocene loess unit deposited during the past 4000 years

magma driven subcritical crack growth and implications for dike initiation from a magma chamber 1 the purpose of this paper is to explore a viscoelastic energy dissipation theory for subcritical dike growth from a magma chamber the theoretical relationship between the dike growth velocity and dike length is established using the viscoelastic subcritical crack growth theory proposed by the first author and the solutions of stress intensity factor at the crack tip derived by a perturbation method effects of magma chamber over pressure buoyancy and viscoelastic properties of the host rock on the subcritical growth rate are included in the model the numerical results indicate that the viscous energy dissipation of the host rock could allow a short dike to slowly grow on the order of 10 7 10 5 m s under modest over pressure and to accelerate when the stress intensity factor increases close to the fracture toughness followed by the unstable dike propagation the proposed theory provides a reasonable understanding of dike initiation process from a magma chamber

fault creep growth model and its relationship with occurrence of earthquakes summary a fault model is used to analyse creep growth process of microcracks in damage zone near the tips of fault by means of the rheology fracture mechanics when microcracks in the zone link each other and their deformation quickly intensifies it means that an earthquake is taking place to a certain degree the relationships among some key parameters that are correlated to the growth of microcracks are analysed theoretically these parameters include failure time of fault number of microcracks in unit area stresses field yield strength and rheological properties of medium the results indicate that the model proposed here is reasonable to describe the pregnant process of an earthquake in the meantime this research shows that with the results of in situ surveys and lab experiments it is possible to estimate the time span for a fault expanding

postglacial evolution of a pacific coastal fjord in british columbia canada interactions of sea level change crustal response and environmental fluctuations results from mona core md02 2494this article is one of a series of papers published in this special issue on the theme polar climate stability network the sedimentary record in a 40 9 m giant calypso piston core md02 2494 raised from the inner basin within effingham inlet british columbia canada during the 2002 marges ouest nord americaines mona campaign spans from 14 360 14 c years bp 17 300 calibrated calendar cal years bp to about nine centuries before present the core ar chives changes in sedimentation and sea level immediately following deglaciation of the late wisconsin fraser glaciation which peaked about 15 000 14 c years bp the presence of the mazama ash in the core anchors a detailed chronology based on 49 radiocarbon dates and seven pleistocene paleomagnetic secular variation correlations diatom assemblages identify a marine freshwater marine transition in the basin which occurred 11 630 14 c years bp 13 500 cal years bp at this time a bedrock sill presently at 46 m depth was briefly exposed as sea level fell and then rose again during iso static crustal adjustments these data constrain a new sea level curve for the outer coast of vancouver island covering the past 12 000 14 c years bp 14 000 cal years bp providing new information on the nature of deglaciation along the west coast of canada and informing interpretations of regional paleoceanographic records and mantle viscosity models

variation in biogenic and detrital fluxes and formation of laminae in late quaternary sediments from the peruvian coastal upwelling zone abstract studies of laminated sediments from the peru margin using back scattered electron imagery bsei provide a high resolution record of variation in detrital and biogenic fluxes and highlight the uncertainty involved in preserving a record of surface processes in bottom sediments intermittently laminated sediments which predominate in the peru forearc basins record episodic major diatom bloom events from which there was adequate flux to counteract water column processes of dissolution and comminution a distinctive sub millimetre lamination with a limited occurrence during isotope stage 5 comprises a regular alternation between silt rich and clay rich couplets which may represent annual deposition with irregularly interlaminated diatom ooze containing near monospecific bloom assemblages the absence of diatom ooze layers between silt clay couplets may be controlled by variation of either the intensity of upwelling and or the nutrient content of upwelled waters macroscopically obvious 0 5 3 cm thick pelleted or homogeneous zones which occur throughout the sub millimetre laminated sequence represent periods of increased oxygenation with a probable 8 16 year duration occurring at irregular intervals of a few years to a few hundred years a slight but pervasive microscopic bioturbation is common within laminated intervals which would macroscopically be described as anaerobic sediments

sediment carbon nitrogen and phosphorus cycling in an anoxic fjord effingham inlet british columbia sediment geochemistry as well as benthic exchange of nutrients was investigated in effingham inlet a fjord located on the west coast of vancouver island in barkley sound the effect of bottom water oxygenation on sediment carbon nitrogen and phosphorus cycling was compared at sites overlain by oxic and anoxic bottom waters the sites separated by only 3 kilometers were similar in terms of key diagenetic parameters including mass accumulation rate and bulk sediment organic carbon content thus allowing a focus on diagenetic effects attributable to depositional oxygen availability benthic flux chamber incubations sulfate reduction rate measurements measurements of solid phase and pore water chemical profiles were compared for the sites these comparisons reveal that diagenetic processes in the site overlain by oxic waters act to retain more phosphorus in the sediment relative to the anoxic site differences in phosphorus benthic fluxes and burial between the two sites most likely result from differences in organic matter cycling under aerobic versus anaerobic conditions and are not strongly influenced by cycling of p associated with metal oxide phases

climate shift at 4400 years bp evidence from high resolution diatom stratigraphy effingham inlet british columbia canada abstract diatom paleoecology and climatic interpretations were assessed from a 15 cm long laminated sediment slab extracted from an anoxic fjord in southwest british columbia the slab spans at least 62 years of deposition determined from counting varves and is dated at approximately 4400 years bp the slab shows a sedimentation pattern where thick diatom rich varves at the bottom become thinner and more silty toward the top thin section analysis reveals that the thicker varves contain a distinct succession of diatoms representing seasonal deposition throughout each year annual scale subsampling shows that the abundance of coastal marine diatoms namely a weakly silicified form of skeletonema costatum decreased over the 62 year period while benthic and brackish water diatoms such as planothidium delicatulum and achnanthes minutissima increased with the concomitant increase in silt the increase in such benthic species and silt along with the presence of 1 cm thick nonlaminated intervals is interpreted to represent deposition during progressively increasing precipitation over time these sedimentation patterns and changes in diatom assemblages may signify a change in the relative intensities of the aleutian low al and north pacific high nph atmospheric pressure systems thicker diatomaceous varves at the bottom of the slab reflect a stronger nph system with associated coastal upwelling and enhanced diatom production the thinner silty varves at the top of the slab suggest that the al system was prevalent resulting in greater amounts of precipitation and reduced upwelling the findings of this study show that significant natural environmental change can occur within a twenty year time frame and can provide a basis for the study of modern change in the ocean atmosphere system over the northeast pacific ocean

effects of volcano loading on dike propagation in an elastic half space we use laboratory experiments and numerical models to examine the effects of volcano loading on the propagation of buoyant dikes in a two dimensional elastic half space in laboratory experiments we simulate the propagation of buoyant dikes in an isotropic regional stress field by injecting air into tanks of solidified gelatin a weight resting on the surface of the gelatin represents a volcanic load a numerical model is used to simulate these experiments both experiments and numerical simulations show that as a dike ascends it begins to curve toward the load in response to the local stress field imposed by the load the lateral distance over which dikes curve to the load increases with the ratio of average pressure at the base of the load to the dike driving pressure for realistic volcano and dike dimensions this pressure ratio is going to be large suggesting that dikes can converge to a volcano over lateral distances several times the load width numerical calculations involving an anisotropic regional stress field however predict that the lateral extent of dike attraction shrinks as the regional horizontal compressive stress decreases relative to the vertical compressive stress dike focusing will be substantial if the regional differential stresses are less than the average pressure at the base of the load if this is the case then our models predict a positive feedback between the size of volcanoes and the area of dike attraction this feedback may promote the development of large discrete volcanoes and also predicts a positive correlation between the spacing and sizes of adjacent volcanoes to test this prediction we examine nearest neighbor pairs of the 21 largest volcanoes in the cascade range the 14 pairs examined show a large range in volcano spacing 6 115 km and a statistically significant correlation between spacing and average volcano height this result is consistent with our model results and suggests that the local compressive stress induced by these volcanoes may be an important factor in controlling magma transport in the lithosphere

determining the post glacial evolution of a northeast pacific coastal fjord using a multiproxy geochemical approachthis article is one of a series of papers published in this special issue on the theme polar climate stability network a 40 32 m piston core recovered from effingham inlet on the west coast of vancouver island provides the basis for a high resolution geochemical study of the last deglaciation and the holocene glacial retreat basin isolation sea level rise and productivity variations are determined using proxies for sediment composition k al fe al mg al grain size ti al zr al sedimentary redox conditions mo al u al and productivity wt organic carbon wt opal as local ice retreated and marine waters inundated the basin coarse grained glacimarine sediments were replaced by finer grained laminated opal rich sediments during meltwater pulse 1a the dominance of local crustal rise over eustatic sea level rise resulted in the progressive restriction of ocean circulation in effingham inlet and the formation of a temporary freshwater lake the transition into stable holocene conditions was initiated at 12 700 bp which corresponds to the onset of the younger dryas as identified by the greenland ice

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

subcritical dyke propagation in a host rock with temperature dependent viscoelastic properties summary in this paper we examine the effects of temperature dependent viscoelastic properties of the host rock on the subcritical growth of a dyke from a magma chamber a theoretical relationship between the velocity of subcritical dyke growth and dyke length is established using a perturbation solution of stress intensity factor at the dyke tip and a viscoelastic crack growth theory in which the temperature dependent creep properties are taken into account the temperature field around the dyke is calculated using an analytic solution the numerical results for a dyke subcritically propagating from a magma chamber indicate that while the general dyke growth characteristics are similar to those with constant creep properties the subcritical dyke growth velocity is increased by an order of magnitude by considering the temperature dependence of the creep properties hence the subcritical growth duration before the dyke reaches the unstable growth state is significantly shortened

estuarine versus transient flow regimes in juan de fuca strait 1 residual currents in juan de fuca strait are observed to switch between two fundamental states estuarine and transient the estuarine regime which prevails roughly 90 of the time in summer and 55 of the time in winter has a fortnightly modulated three layer structure characterized by strong 50 cm s 1 outflow above 60 15 m depth moderate 25 cm s 1 inflow between 60 and 125 m depth and weak 10 cm s 1 inflow below 125 10 m depth rotation increases the upper layer depth by 40 m on the northern side of the channel and upwelling favorable coastal winds augment inflow in the bottom layer by as much as 5 cm s 1 rotation combined with modulation of the estuarine currents by tidal mixing in the eastern strait leads to fortnightly variability in the along channel velocity and cross channel positioning of the core flow regions transient flows which occur roughly 10 of the time in summer and 45 of the time in winter are rapidly evolving horizontally and vertically sheared reversals in the estuarine circulation generated during poleward wind events along the outer coast major events can persist for several weeks force a net inward transport and give rise to an o 10 km wide surface intensified o 100 cm s 1 inflow along the southern olympic peninsula boundary of the strait this olympic peninsula countercurrent is typically accompanied by an abrupt decrease in salinity indicating that it is a buoyancy flow originating with low density water on the northern washington shelf

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

a new high resolution radiocarbon bayesian age model of the holocene and late pleistocene from core md02 2494 and others effingham inlet british columbia canada with an application to the paleoseismic event chronology of the cascadia subduction zone annually laminated sediments from the anoxic inner basin of effingham inlet pacific coast of vancouver island british columbia canada yield a high resolution 42 m paleoenvironmental record from the present to about 14 ka 14c bp 17 ka cal bp a new age model based on 68 radiocarbon dates from twigs and small plant material from the 40 m core md02 2494 and 2 m freeze cores from the surface is anchored by the mazama ash and varve counting a poisson process sedimentation model is used applying a new method to determine the poisson k value giving a realistic age model compatible with the multi proxy core data twenty one seismites which are lithofacies in the effingham cores that may be representative of seismically triggered mass wasting events are identified and dated precisely then compared with the chronology of the deep sea turbidite record farther south in the cascadia subduction zone csz to determine if regional sediment disturbances can be identified with 16 proposed correlations

a 2100 year bp record of the pacific decadal oscillation el nino southern oscillation and quasi biennial oscillation in marine production and fluvial input from saanich inlet british columbia exceptional varved sediments of 2100 years bp recovered from saanich inlet have been analysed using high resolution scanning electron microscopy and spectral analysis techniques each varve may contain up to 22 well defined individual laminae which can be attributed to seasonal scale processes sediment flux comprises alternating diatom ooze diatomaceous mud deposited during spring through autumn and a silty clay deposited during winter the latter may be sporadically punctuated by clay rich laminae identification of some 2000 individual consecutive laminae based on fabric and diatom assemblage has allowed the construction of time series data for spectral analysis laminae types analysed include early spring thalassiosira spp late spring early summer skeletonema costatum multiple summer autumn chaetoceros spp diatom oozes and sporadically present clay rich winter flood deposits sub decadal periods have been identified and linked to the quasi biennial oscillation qbo and el nino southern oscillation enso and decadal periods to the pacific decadal oscillation pdo comparison of spectral analysis results with modern analogues suggests associations may exist between early spring thalassiosira spp laminae and stronger la nina events late spring early summer s costatum laminae and el nino events summer autumn chaetoceros spp multiple laminae and negative pacific northwest index pni regimes and sporadically present winter clay rich laminae and pni regimes the average period for an enso cycle was 3 6 years qbo 2 5 years and pdo 14 8 years spectral analysis of the more recent pni record shows similar significant periods of 13 2 3 7 and 2 6 years multi decadal periods recorded include 42 2 and 31 3 years which might suggest multiples of pdo

the geochemical record of the last 17 000 years in the guaymas basin gulf of california abstract sediments deposited on the western slope of the guaymas basin in the central gulf of california are composed predominantly of detrital clastic material and biogenic silica biopal with minor organic material average of 2 8 organic carbon and calcium carbonate the caco 3 is derived from calcareous plankton and is highly variable ranging from 0 to 16 in general the caco 3 content of the sediments varies inversely with the biopal content reflecting the relative abundance of calcareous and siliceous plankton in the photic zone siliceous plankton dominate when winds are predominantly out of the northwest producing strong upwelling calcareous plankton indicates weak southeasterly winds that bring warm tropical pacific surface water into the gulf based mainly on relative abundances of biopal and caco 3 the sediments deposited over the last 17 000 years in the western guaymas basin can be divided into five intervals in general the sediments in the intervals with high biopal and low caco 3 are laminated but this is not always true unlike most other continental margins of the world with well developed oxygen minimum zones where highest concentrations of organic carbon and redox sensitive trace metals occur in laminated sediments the laminated sediments on the anoxic slope of the western guaymas basin do not always have the highest concentrations of organic carbon and trace metals such as mo and cd

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

climatic and atmospheric circulation pattern variability from ice core isotope geochemistry records altai tien shan and tibet several firn ice cores were recovered from the siberian altai belukha plateau central tien shan inilchek glacier and the tibetan plateau zuoqiupu glacier bomi from 1998 to 2003 the comparison analyses of stable isotope geochemistry records obtained from these firn ice cores identified the physical links controlling the climate related signals at the seasonal scale variability the core data related to physical stratigraphy meteorology and synoptic atmospheric dynamics were the basis for calibration validation and clustering of the relationships between the firn ice core isotope geochemistry and snow accumulation air temperature and precipitation origin the mean annual accumulation in water equivalent was 106 g cm 2 a 1 at inilchek glacier 69 g cm 2 a 1 at belukha and 196 gc m 2 a 1 at zuoqiupu the slopes in regression lines between the d 18 o ice core records and air temperature were found to be positive for the tien shan and altai glaciers and negative for southeastern tibet where heavy amounts of isotopically depleted precipitation occur during summer monsoons the technique of coupling synoptic climatology and meteorological data with d 18 o and d excess in firn core records was developed to determine climate related signals and to identify the origin of moisture in altai two thirds of accumulation from 1984 to 2001 was formed from oceanic precipitation and the rest of the precipitation was recycled over aral caspian sources in the tien shan 87 of snow accumulation forms by precipitation originating from the aral caspian closed basin the eastern mediterranean and black seas and 13 from the north atlantic

a basin scale oceanic instability event in the gulf of alaska a composite noaa 14 satellite advanced very high resolution radiometer image of the gulf of alaska for early march 1995 reveals a sequence of six anticyclonic oceanic eddies spanning more than 1500 km of the continental margin of north america from central british columbia to central alaska although isolated mesoscale eddies have previously been documented for this eastern boundary region the composite image provides the first evidence that trains of such eddies can develop simultaneously along the entire coast the 80 km radius and 250 km spacing of these warm core eddies are consistent with a baroclinic instability event in the poleward coastal current that prevails along the northwest continental margin of north america in winter roughly october through march wind data from offshore meteorological buoys combined with partial cloud free thermal images for january and february suggest that the event was triggered in mid january by an abrupt coast wide reversal in the prevailing poleward wind the instability event disrupted the alongshore transport of relatively warm high salinity water and presumably resulted in a greatly enhanced cross shore flux of brackish nutrient rich coastal water into the open ocean on the basis of its basin scale extent and more than 2 month duration it is feasible that the event had a major impact on the early spring recruitment and survival of zooplankton and pelagic fish within the highly productive fishery zones of coastal british columbia and alaska less extensive eddy sequences found in several earlier satellite images for the region suggest that these instability events are fairly common if so this indicates that the poleward current that forms over the eastern pacific continental slope in late fall herein the northeast pacific coastal current is marginally stable and likely to deform into a series of mesoscale eddies following abrupt basin scale reversals in the seasonally dominant wind provided these wind events occur early enough in the season the coastal current could reform with the onset of poleward winter winds

the 2011 tohoku tsunami generated major environmental changes in a distal canadian fjord 1 tsunamis triggered by powerful earthquakes cause extensive damage and loss of life within many regions of the world ocean although coastal inundation from major tsunamis is becoming increasingly well understood we know little about the broader aspects of such events on distal marine systems here we use time series from moored oceanic sensors to show that the tohoku tsunami generated by the magnitude 9 0 earthquake off eastern japan in march 2011 caused days of surge like currents and turbulent mixing in the inner basin of an anoxic canadian fjord located over 7000 km from the seafloor rupture zone mixing combined with the inflow of more oxygen rich water from the adjoining outer basin led to abrupt changes in the hydrodynamics bottom sedimentation and zooplankton behavior in the basin these findings help define mechanisms by which major transoceanic tsunamis can significantly alter coastal marine environments located far from the source area

nitrogen isotope and productivity variations along the northeast pacific margin over the last 120 kyr surface and subsurface paleoceanography 1 glacial interglacial changes in sedimentary 15n over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical north pacific etnp where subsurface denitrification is active to the oregon margin where no denitrification occurs today low 15n values 4 6 generally characterize glacial stages 2 and 4 and higher 15n values 7 10 are representative of the holocene millennial scale periods within stage 3 and stage 5 the inferred synchroneity of 15n variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen poor subsurface waters in the etnp is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone similar to 15n primary production indicators percent corg ba al and percent opal show glacial interglacial as well as millennial scale variations along the ne pacific margin with higher primary production during warm periods however the relative phasing between 15n and paleoproduction tracers within individual records changes latitudinally whereas 15n and primary production vary approximately synchronously in the midlatitudes production lags 15n in the etnp by several kiloyears this lag calls for a new understanding of the processes driving denitrification in the etnp we suggest that oxygen input by the equatorial undercurrent as well as local organic matter flux controls denitrification rates in the etnp moreover the differences in relative timing point to a time transgressive development of upwelling favorable winds along the ne pacific margin after the last glaciation with those in the north developing several kiloyears earlier

hydrological and climatic changes in deserts of china since the late pleistocene article i nfo article history large areas in western china were wetlands or less arid between 40 and 30 ka corresponding to the greatest lake period on the adjacent tibetan plateau during the last glacial maximum some of these western chinese deserts again experienced wetter conditions however at the same time the sandy lands in the eastern chinese desert belt experienced an activation of aeolian dunes while interpretations of the mid holocene environment in the deserts of china are controversial it is quite likely that it was more humid not only in the eastern areas influenced by monsoon climate systems but also in the western deserts where moisture is currently associated with westerlies evaluation of lacustrine records in the lakes recharged by dryland rivers and the complex interactions of these systems as well as other paleoenvironmental proxies such as the artemisia chenopodiaceae ratio should be interpreted with greater caution facing the highlighted uncertainties in our understanding of climate changes in chinese deserts it is hoped that this special issue will improve our knowledge considerably

the propagation of a dyke driven by gas saturated magma summary a new mathematical and numerical model is presented for the propagation of a pressure and buoyancy driven dyke filled with volatile saturated magma and a gas cap at its upper part the model accounts for coupling between conduit flow of a bubbly magma gas filtration through the magma gas accumulation in a gas cap and elastic deformation and fracturing of the host rock all these processes allow studying different regimes of dyke propagation the rate of propagation of dykes is controlled by the rate of the fracturing at the tip and by the flow rate of magma inside the dyke when high energy is needed to fracture the host rock and magma viscosity is low the rate of propagation is controlled by the rate of fracturing fracturecontrolled regime when the energy to fracture the host rock is low propagation is controlled by the magma flow rate magma controlled regime we study the transition between these regimes for the case of a constant magma vesicularity and constant mass of gas in the cap under these conditions the propagation of the dyke is self similar in the fracture controlled regime the propagation rate only weakly depends on the amount of the gas in the gas cap whereas at the magma controlled regime it is significantly enhanced with increase the mass of gas at the cap the gas pressure in the cap opens the dyke in front of the magma and allows magma flow rates that are significantly higher than predicted by models that ignore the gas cap the maximum propagation rate is obtained at the transition between the fracture and magma controlled regimes if the gas mass in the gas cap is high enough a gas pocket can separate from the magma as a distinct unconnected pocket and propagate as a gas filled crack at a constant velocity pressure decreases during ascent leads to higher vesicularity and faster gas filtration through the magma and into a gas cap gradual increase of the mass of gas in the cap is important in accelerating the propagation rate of dykes

hydrothermal plume particles and dissolved phosphate over the superfast spreading southern east pacific rise abstract the distribution and elemental composition of hydrothermal plume particles were mapped along the superfast spreading southern east pacific rise from the garret transform fault to 19 s hydrographic and optical data were obtained using a series of seven tow yos and thirty vertical casts employing a rosette sampler with 19 l pvc bottles for collecting discrete samples of various dissolved and particulate hydrothermal species the extent of hydrothermal plume coverage over the southern east pacific rise between 13 33 and 18 40 s is significantly greater than in other ridgecrest systems the region south of 17 20 s is characterized by significant enrichments of volatile gases resulting from magmatic input of fresh lava at the seafloor between 17 20 and 18 40 s the ratio of s fe in the plume particles is highly correlated with the dissolved gases in the neutrally buoyant hydrothermal plumes plume inventories of fe and s over this portion of the southern east pacific rise are 6 150 times higher than what has been observed over other vent fields because the total abundance of plumes is much greater in addition significant depletions 100 nmol l of dissolved phosphate over the ridge axis were observed at the depth of the hydrothermal plumes these results provide clear evidence that this section of the southern east pacific rise maintains the most extensive complex of hydrothermal plumes observed thus far on the global ridgecrest system

holocene moisture evolution across the mongolian plateau and its surrounding areas a synthesis of climatic records abstract based on the review of 26 high standard holocene climatic reconstructions mainly pollen based from the mongolian plateau and its surrounding areas temporal and spatial patterns of the holocene moisture evolution are synthesized the regionally averaged moisture history from the summer monsoon influenced semiarid belt in china i e region a demonstrates that the moisture index curve is broadly in agreement with the synthesized east asian monsoon strength curve both following the general trend of the west tropical pacific sst that is in turn the delayed response to the northern hemispheric summer solar insolation the regionally averaged moisture indices from the winter monsoon dominated southern siberia including lake baikal area and the altai mountains i e region b exhibit a general declining trends since 10 6 9 6 cal kyr bp being largely consistent with the trends of the annual precipitation and the warm season temperature in the russian plain the consistency might be attributable to the holocene declining trend of the warm season temperature in north atlantic region the predominant feature of the regionally averaged moisture index from the westerlies affected northern xinjiang i e region c is a persistent increasing trend since 8 cal kyr bp the wetting trend of northern xinjiang during the past 8000 years might be attributable to the increasing trend of winter insolation and to the associated increasing trend of cold season temperature in northwestern europe the chronological correspondences between dry phases and warm intervals in the arid areas of the mongolian plateau i e northern mongolian plateau within mongolia and southern mongolian plateau within china region d lend a support to the proposal that the mid holocene dry phase was most likely the result of mid holocene high warm season temperature

causes of early holocene desertification in arid central asia paleoclimate records of effective moisture precipitation minus evaporation or p e show a dry low effective moisture period in mid latitude arid semi arid central asia during the early holocene 11 000 8 000 years ago relative to the middle and late holocene in contrast to evidence for greater than present precipitation at the same time in the south and east asian monsoonal areas to investigate the spatial differences in climate response over mid latitude central asia and monsoonal asia we conducted a series of simulations with the community climate system model version 3 coupled climate model for the early middle and late holocene the simulations test the climatic impact of all important forcings for the early holocene including changes in orbital parameters the presence of the remnant laurentide ice sheet and deglacial freshening of the north atlantic model results clearly show the early holocene patterns indicated by proxy records including both the decreased effective moisture in arid central asia which occurs in the model primarily during the winter months and the increase in summer monsoon precipitation in south and east asia the model results suggest that dry conditions in the early holocene in central asia are closely related to decreased water vapor advection due to reduced westerly wind speed and less evaporation upstream from the mediterranean black and caspian seas in boreal winter as an extra forcing to the early holocene climate system the laurentide ice sheet and meltwater fluxes have a substantial cooling effect over high latitudes especially just over and downstream of the ice sheets but contribute only to a small degree to the early holocene aridity in central asia instead most of the effective moisture signal can be explained by orbital forcing decreasing the early holocene latitudinal temperature gradient and wintertime surface temperature we find little evidence for regional subsidence related to a stronger summer asian monsoon in forcing early holocene aridity in central asia as has been previously hypothesized

late quaternary environmental changes in the taklamakan desert western china inferred from osl dated lacustrine and aeolian deposits sediment records from the tarim basin of western china are of great importance for understanding late quaternary climatic variability in central asia a chronology of aeolian and lacustrine deposits from the centre and southern margin of the taklamakan desert central tarim basin has been established using optical dating methods distinct variations in humidity during the last 40 000 a in this extremely arid inland basin have been identified lacustrine sediments were deposited in the centre of the taklamakan during two periods of wetter than present day conditions at around 2000 and 30 000 a ago another humid period is recorded between 40 000 and 30 000 a ago aeolian processes the development of large migrating dune fields dominated during periods of more arid conditions sand wedges at the southern margin of the taklamakan are dated at ca 40 000 a and ca 18 000 a and imply a significant temperature decrease in that area sedimentological evidence for a late holocene humid period are consistent with records in ancient chinese literature wetter environmental conditions in the past within the taklamakan as indicated by the presence of lacustrine deposits are also supported by data from adjacent regions it is assumed that changes of global westerlies and of the mobile polar high triggered the fluctuations of precipitation in the study area however variations in temperature in the taklamakan desert are presumed to be mainly controlled by the intensity of the winter monsoon

distribution of diatom surface sediment assemblages within effingham inlet a temperate fjord on the west coast of vancouver island canada abstract twenty nine surface sediment samples from effingham inlet a small fjord on the west coast of vancouver island british columbia were analyzed for diatoms this fjord has been selected for paleoceanographic investigation due to the presence of laminated sediments resulting from the dysoxic to anoxic bottom water conditions in the inner and outer basins of the inlet distributional patterns of the diatom microflora reflected proximity to littoral regions phytoplankton production and marine influence from outside the fjord principal components and cluster analyses of the microflora established four diatom assemblages with a clear separation between the inner and outer basin diatom floras inner basin stations were characterized by elevated absolute abundance with assemblages dominated by spring early summer bloom taxa including skeletonema costatum thalassiosira nordenskioeldii and thalassiosira pacifica chaetoceros spp resting spores were abundant throughout effingham inlet with the exception of the stations closest to the fjord head stations located in the outer basin and towards the fjord mouth had relatively lower absolute abundance yet showed a higher relative and absolute abundance of thalassionema nitzschioides rhizosolenia setigera coscinodiscus radiatus ditylum brightwellii odontella longicruris and paralia sulcata in relation to the inner basin many of these latter taxa are often associated with late summer and autumn conditions in fjords along coastal british columbia oceanographic data for effingham inlet suggest that increased offshore penetration is more likely to occur from summer to early fall with a more restricted offshore influence in the inner basin diatom surface sediment assemblages in effingham inlet appear to reflect incursions of offshore waters into the fjord absolute abundance estimates and the preservation of lightly silicified taxa suggest excellent preservation of fossil material in the sediments of the predominantly anoxic inner basin preservation in the outer basin is reduced reflecting more frequent recharge by oxygenated waters spilling over the outer sill into the basin our findings suggest the inner basin should be an optimal site for reconstruction of diatom production with records from the outer basin providing more consistent information about offshore influence and coastal upwelling conditions over the holocene estimates of diatom abundance within the inner basin sediment may serve as a good proxy of production although proxy tracers of bottom water conditions and sedimentological analyses must be coupled to the diatom record to ensure depositional conditions were not influencing valve preservation or abundance our results suggest that fjords can serve as good environments for paleoceanographic reconstructions of both inshore and offshore conditions although careful site selection and understanding of processes affecting the microfossil record are essential

modern to late holocene deposition in an anoxic fjord on the west coast of canada implications for regional oceanography climate and paleoseismic history laminated sediments preserved in the anoxic inner basin of effingham inlet on the pacific coast of vancouver island british columbia canada yield a high resolution sediment deposition record spanning about 6000 yr the varying thickness of diatom terrigenous mud varves in sediment cores from the basin can be interpreted in terms of annual changes in surface productivity and freshwater input within the inlet similarly the occurrence of unlaminated mud units homogenites intercalated amongst the laminated sediments can be interpreted in terms of oceanic and climatic changes these units appear to be associated with coastal upwelling events that result infrequently in highly oxygenated oceanic water penetrating to the bottom of the inner and outer basins of the inlet the sedimentary record also contains massive and graded mud units considered to arise from debris flows and turbidity currents some of which were probably initiated by seismic events including a major event about 4500 14 c yr bp which may be earthquake related a total of seventeen oceanographic surveys of the inlet beginning in 1995 characterize the modern seasonal coastal upwelling regime and a unique bottom water oxygenation event which was

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

pelagic diatom assemblages are good indicators of mixed water intrusions into saanich inlet a stratified fjord in vancouver island abstract we assessed the potential importance of tidally driven intrusions of autochthonous protistan plankton into saanich inlet a fjord in vancouver island as potential sources of fossils in the fine intra annual sediment laminations of odp cores we determined the structure of protistan assemblages throughout the inlet during july 1995 at times of successive neap and spring tides results were compared to a concurrent physical study of tidal flows and nutrient advection into and out of the inlet which allowed us to identify protistan species indicative of mixed satellite channel and stratified saanich inlet waters these identifications were either confirmed or rejected by temporal analyses of protistan assemblages based on weekly sampling at two fixed positions one in saanich inlet and one in sidney channel from may through october 1997 results of both studies supported the hypothesis that the presence of a suite of diatom species including most chaetoceros spp a large celled variant of skeletonema costatum and thalassiosira rotula indicates the intrusion of water with elevated levels of dissolved inorganic nitrogen into saanich inlet from the strait of georgia this indicator group of species contained additional species but not all were observed in large numbers in 1997 many of these species are important components of the laminated sediments of saanich inlet whose presence is probably indicative of paleo environmental conditions in the southern strait of georgia rather than saanich inlet effects of tidal cycles on dinoflagellate and other flagellated cells exclusive of mastigophorans were inconclusive and additional studies are required to elucidate details of their ecology in waters of the southern strait of georgia

anomalous enrichments of iron monosulfide in euxinic marine sediments and the role of h 2 s in iron sulfide transformations examples from effingham inlet orca basin and the black sea it is well documented that sedimentary pyrite formation proceeds through an iron monosulfide fes precursor laboratory studies have tradition ally indicated that intermediate s species such as elemental sulfur s 0 or polysul fides sx 2 are responsible for the transformation of fes to pyrite fes2 recent experimental work however has suggested that h2s may also be responsible for the transformation the present study extrapolates reaction pathways respon sible for pyrite formation in the laboratory to two fundamentally different modern anoxic marine systems we hypothesize that on decadal timescales h2s or hs is responsible for transformations of fes into fes2 in natural systems where intermediate s species are isolated from fes production the possibility of prolonged coexistence of high levels of h2s and fes however challenges recent experimental predictions of extremely rapid transformations that is timescales of hours or less of fes to fes2 via the h2s pathway sediments of effingham inlet a fjord on vancouver island and the orca basin an intraslope brine pool in the northern gulf of mexico are both charac terized by atypically high concentrations of fes but contrasting levels of h2s and fes2 production in both systems fes formation is spatially decoupled from intermediate s species as a consequence of either rapid deposition burial or extreme water column stratification within settings that promote this separa tion h2s may be the principal species responsible for pyrite formation fes to fes2 transformations are favored by the high concentrations of h2s in sediments of effingham inlet additional results from the margin of the anoxic black sea corroborate the effingham model for iron sulfide transformation h2s concentrations are controlled by the amount of bacterial sulfate reduc tion and the availability of reactive fe h2s concentrations will be buffered to low levels via the production of fes in systems with appreciable amounts of reactive fe and therefore be unavailable to transform fes to fes2 under conditions where h2s is the only species available for fes to fes2 transformations some degree of fe limitation may promote pyrite formation by allowing h2 st o accumulate in the pore waters ultimately this balance between h2s production and reactive fe availability may strongly influence the amount of pyrite formed in anoxic systems

a global marine fixed nitrogen isotopic budget implications for holocene nitrogen cycling 1 a nitrogen stable isotopic model was constructed in order to constrain the holocene marine fixed nitrogen budget the primary sources and sinks considered were riverine and atmospheric sources nitrogen fixation sedimentary and water column denitrification and sediment burial the source budget was found to be insensitive to changes in nitrogen fixation rates and thus could not be used to constrain this term however the isotopic value of fixed nitrogen losses was very sensitive to the amount of sedimentary denitrification if the isotopic value of marine fixed nitrogen has not changed during the holocene as supported by sedimentary records then in order to balance the isotopic value of sinks and sources approximately 280 tg n yr 1 of sedimentary denitrification is required if such a high rate of denitrification has been sustained throughout the holocene it implies that present day estimates of marine nitrogen fixation are grossly underestimated it also implies that the marine nitrogen budget has a residence time of less than 2000 years