topographically induced baroclinic eddies near a coastline with application to he northeast pacific abstract a mathematical model is developed to describe the interaction between variable bottom topography and a steady horizontally sheared baroclinic coastal current the topography modeled in this study consists of an offshore seamount and a seaward protrusion of the continental slope the fluid motions are assumed to conserve potential vorticity on the f plane and expressions for the pressure density velocity and mass transport fields are obtained using a normal mode analysis and the appropriate green s function for the horizontal problem the theory is applied to the northeast pacific ocean in an attempt to model the anticyclonic eddy which has been observed by tabata west of sitka alaska the numerical calculations of the model and the observed location dimensions velocities and transports of the sitka eddy are in good agreement the axial velocities and dimensions of the calculated eddy field are largest for upstream surface and bottom currents of approximately 5 7 and 1 2 cm s 1 respectivel

strong and highly variable push of ocean waves on southern ocean sea ice sea ice in the southern ocean has expanded over most of the past 20 y but the decline in sea ice since 2016 has taken experts by surprise this recent evolution highlights the poor performance of numerical models for predicting extent and thickness which is due to our poor understanding of ice dynamics ocean waves are known to play an important role in ice break up and formation in addition as ocean waves decay they cause a stress that pushes the ice in the direction of wave propagation this wave stress could not previously be quantified due to insufficient observations at large scales sentinel 1 synthetic aperture radars sars provide high resolution imagery from which wave height is measured year round encompassing antarctica since 2014 our estimates give an average wave stress that is comparable to the average wind stress acting over 50 km of sea ice we further reveal highly variable half decay distances ranging from 400 m to 700 km and wave stresses from 0 01 to 1 pa we expect that this variability is related to ice properties and possibly different floe sizes and ice thicknesses a strong feedback of waves on sea ice via break up and rafting may be the cause of highly variable sea ice properties

rossby waves and the variability of the north pacific current during 2002 03 abstracta numerical model the parallel ocean program pop with 0 25 horizontal spatial resolution and 28 vertical levels is used to simulate the circulation of the north pacific ocean for the time period 1960 2006 spectral nudging is used so that model drift of the mean state over the 46 yr time period of the simulation is prevented while allowing for the prognostic evolution of the circulation at time scales that are not nudged the simulation successfully reproduces a southward shift in the north pacific current in 2002 03 as calculated from scalar observations it is suggested that this calculated shift may not be solely due to meridional current drift but also a consequence of the shifting intensity of two eastward moving current bands separated by 300 500 km a distance consistent with the rhines scale the scale at which the 2d turbulence cascade tends to be arrested which implies an influence from rossby waves that are heavily affected by nonlinearities the simulation suggests that the nort

elemental carbon record of paleofire history on the chinese loess plateau during the last 420 ka and its response to environmental and climate changes an elemental carbon ec record covering the last 420 ka was reconstructed using chemical oxidation method on a loess and paleosol sequence from the lingtai section on the chinese loess plateau the ec record reveals the paleofire history and its relationship with climate and vegetation changes on the chinese loess plateau our results show that the ec abundance is generally higher in the paleosols than in the loess layers showing a glacial interglacial pattern which is coincident with biomass changes this variation pattern indicates that paleofires were intensified when biomass accumulated and climate changed abruptly especially from wet to dry conditions the ec abundance increases sharply at similar to 130 kab p indicating a dramatic change in the vegetation and climate variation patterns the occurrence of a peak value with the highest average ec abundance in the holocene may reflect the occurrence of a major climate event at similar to 6 kab p and may also be partly due to more frequent anthropogenic fire usages c 2007 elsevier b v all rights reserved

heat and fresh water transport by eddies into the gulf of alaska abstract anticyclonic mesoscale eddies form in winter along the continental margin of canada and southeast alaska between the latitudes of 51n and 60n and drift westward into the gulf of alaska carrying warmer fresher water away from the continental margin detailed measurements of temperature and salinity between 1995 and 2001 were examined to determine the amount of heat and fresh water transported seaward by several eddies that formed west of the queen charlotte islands eddies formed in a typical winter carry about 30 10 18 j of heat into the gulf which is about 35 to 60 of the heat transported northward each winter along the continental margin toward this region the observed range of eddy heat transport is 10 19 to 10 20 j largest observed eddy heat transport coincided with increased northward heat flow along the continental margin during the el nino winter of 1997 1998 fresh water volume was determined by evaluating the amount of fresh water required to reduce the salinity from a reference level to that observed in eddies this volume varied from 0 to 70 km 3 and was largest during the 1997 1998 el nino winter eddies formed in a typical winter transport 50 km 3 of fresh water seaward which is about 15 of the estimated fresh water input to the continental margin in winter between the columbia river and 54n attributed to local runoff plus direct rainfall and flow in major rivers

late quaternary aeolian activity in the mu us and otindag dune fields north china and lagged response to insolation forcing 1 dune fields in parts of northern china contain important stratigraphic records of late quaternary change in the east asian monsoon in this study 33 new optically stimulated luminescence osl ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet dry climate variation in the mu us and otindag dune fields of north china the results indicate dune activity and dry climate in the last few hundred years 14 ka to about 7 8 ka and 50 ka to 60 ka the dunes were mainly stable implying a wetter climate between about 7 8 ka and 2 4 ka these results imply a lag of several thousand years between peak summer insolation at 10 11 ka and high summer monsoon rainfall after 7 8 ka in the investigated regions the monsoon climate may not respond directly to orbital forcing over millennial time scales land surface feedbacks may account for lagged dune field response

holocene climate changes over the desert loess transition of north central china a 2 m trench section at the desert loess transition of north central china was analyzed at 2 cm intervals for grain size distribution md m and total organic carbon toc ams 14c time series of the md and toc records provides direct information on variations of the east asian monsoon climate during the last 10 000 yr md is considered to represent the wind strength and high md reflects strong winter monsoon winds toc denotes the degree of vegetation cover a function of the intensity of summer monsoon circulations from ca 10 000 to 7000 cal yr bp the climate was dominated by a strong winter monsoon and a very weak summer monsoon as indicated by high md and low toc values subsequently climatic conditions became warmer gradually from ca 7000 to 5500 cal yr bp the period between ca 5500 and 2700 cal yr bp displayed the highest toc and lowest md values over the last 10 000 yr marking a stable state of a warm humid climate i e the holocene climatic optimum of china during the interval of ca 2700 1500 cal yr bp the expansion and intensification of agrarian activities could have led to desertification and acceleration of deposition of coarse grained particles resulting in a decreased organic carbon accumulation rate however the toc during this interval still has values as high as during the episode of ca 7000 5500 cal yr bp reflecting a relatively stronger summer monsoon circulation since ca 1500 cal yr ago high amplitude fluctuations of toc that fluctuate in phase with the clay size fraction imply that the climate experienced three major oscillations with a prominent peak of enhanced summer monsoon circulation at ca 1300 cal yr ago and with two intervals of increased winter monsoon strength occurring around ca 1000 and 300 cal yr ago the md and toc records over the past 5000 yr demonstrate a good correlation with the archaeological phenological and historical records of china climate changes in the east asian monsoon region were not only related to the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but were also controlled by the pattern and intensity of the atmospheric circulation

seasonal variability in meanders of the california current system off vancouver island satellite infrared images taken over the past few years reveal seasonal variations in the meanders of the california current system ccs off vancouver island the ccs exhibits meanders with wavelength between 120 and 150 km in both winter and spring when the upper ocean current all flows northwestward or southeastward respectively in summer the ccs includes the california undercurrent which flows northwestward beneath the southeastward surface current and has shorter wavelength 75 80 km meanders around the end of august these shorter scale meanders are engulfed by the longer 150 km meanders finally in the fall eddies are detached from the offshore extensions of the longer meanders a linear stability theory using a four layer model of the ccs successfully predicts the wavelengths in the winter and spring but not in the summer and fall the meander evolution observed in summer and fall is instead simulated by using a nonlinear numerical model in a domain with topographic obstacles selected to match the alongshore variations in the continental slope the topographic features with a spatial periodicity of 75 km act as a trigger to initiate the short wavelength 75 km meanders following this these 75 km meanders grow because of baroclinic instability the 75 km meanders which have grown to large amplitudes are replaced by longer 150 km meanders because of nonlinear interactions between these two scales of meanders cyclonic eddies are finally shed from the longer meanders

multiple expansions of c4 plant biomass in east asia since 7 ma coupled with strengthened monsoon circulation the expansion of plants using the c4 photosynthetic pathway is one of the most prominent changes in the global ecosystem during the cenozoic era a significant late miocene expansion is well documented however the existence and cause of subsequent expansions are still not clear owing in part to the lack of long continuous climate vegetation records here we present two high resolution carbon isotope time series covering the past 7 m y derived from eolian deposits on the chinese loess plateau the data indicate three intervals of significant c4 plant expansions within the semiarid monsoonal region of east asia ca 2 9 2 7 ma 1 3 0 9 ma and 0 6 ma present these expansions covary with strengthened east asian summer monsoon circulation we conclude that in east asia large scale late miocene c4 c3 vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation

changes in fire regimes on the chinese loess plateau since the last glacial maximum and implications for linkages to paleoclimate and past human activity abstract a high resolution black carbon bc record from 27 5 kyr bp to present was reconstructed using a chemical oxidation method on loess and paleosol samples from the lijiayuan section of the chinese loess plateau the black carbon mass sedimentation rates bcmsr and carbon isotopic record reveal a paleofire history and its relationship with climate and vegetation changes at the study site the bcmsr record was decomposed into two components background bcmsr and the bcmsr peaks the background bcmsr represents regional fires and shows high fire activities occurred contemporaneous with the younger dryas older dryas heinrich events and greenland stadials as registered in the loess grain size record this suggests a rapid response of regional fires on the loess plateau to abrupt climate changes spectral analysis of background bcmsr showed two meaningful periodicities of 1620 and 1040 years close to the cyclicity of the east asian monsoon as recorded in the stalagmite 18o record in central china this indicates a tight control of millennial scale wet dry changes in the monsoonal climate on regional fires on the loess plateau by contrast the bcmsr peaks are considered to reflect local fire episodes the occurrences of local fires were more frequent during the last glacial period with a maximum frequency of 6 episodes 1000 years during the last glacial maximum lgm 22 3 to 14 6 kyr bp when the climate was drier and more continuous grassy fuels existed on the landscape during the last glacial interglacial transition lgit period 14 6 to 11 0 kyr bp fire frequency was largely reduced due to an increase in precipitation and more woody vegetation if the lgit period is taken as an analog for the projected near future then future global warming alone may not produce large wildfires in northwestern china wildfires remained infrequent during the early to middle holocene biomass burning increased after 4 0 kyr bp when the climate became drier and land use was more intensive bc carbon isotope ratios may well reflect changes in the vegetation being burnt i e grasses versus trees yielding results consistent with the associated pollen data in the region

multi year meanders and eddies in the alaskan stream as observed by topex poseidon altimeter the birth life and decay of long lived anticyclonic eddies or meanders in the alaskan stream are observed from topex poseidon t p satellite their surface height anomalies approach 72 cm average diameter is about 160km and they live for 1 to 3 years propagating along the stream with mean speed of 2 5 km d 1 of the six observed the last three were formed after the first t p observations in september 1992 of these two evolved from eddies near alaskan panhandle in winter drifting across the northern gulf of alaska before entering the alaskan stream while another formed in the stream west of shelikof strait

measurements of enhanced near surface turbulence under windrows abstractobservations of waves winds turbulence and the geometry and circulation of windrows were made in a shallow bay in the winter of 2018 outside of rimouski quebec water velocities measure

tracing the provenance of fine grained dust deposited on the central chinese loess plateau eolian dust deposits in north china provide an excellent means of determining past variations in continental paleoclimate and atmospheric circulation however debate still exists on which deserts in east asia are the dominant sources of chinese loess and whether the dust provenance has shifted significantly at different time scales here we present new constraints on the provenance of fine grained dust deposited on the central chinese loess plateau clp by combining electron spin resonance signal intensity and crystallinity index of fine grained quartz contained in samples from two loess paleosol sequences our results show that the fine grained dust deposits on the clp originate mainly from the gobi desert in southern mongolia and the sandy deserts in northern china primarily the badain juran and tengger deserts rather than from the taklimakan desert in western china at least during the last climatic cycle the dominant source of fine grained dust varied significantly from southern mongolia during cold periods to northern china during warm periods the glacial interglacial provenance fluctuations are strongly coupled with changes in the intensity of the near surface northwesterly winter monsoon

swell and sea in the emerging arctic ocean ocean surface waves sea and swell are generated by winds blowing over a distance fetch for a duration of time in the arctic ocean fetch varies seasonally from essentially zero in winter to hundreds of kilometers in recent summers using in situ observations of waves in the central beaufort sea combined with a numerical wave model and satellite sea ice observations we show that wave energy scales with fetch throughout the seasonal ice cycle furthermore we show that the increased open water of 2012 allowed waves to develop beyond pure wind seas and evolve into swells the swells remain tied to the available fetch however because fetch is a proxy for the basin size in which the wave evolution occurs thus both sea and swell depend on the open water fetch in the arctic because the swell is regionally driven this suggests that further reductions in seasonal ice cover in the future will result in larger waves which in turn provide a mechanism to break up sea ice and accelerate ice retreat

comparison of quantification methods to measure fire derived black elemental carbon in soils and sediments using reference materials from soil water sediment and the atmosphere black carbon bc the product of incomplete combustion of fossil fuels and biomass called elemental carbon ec in atmospheric sciences was quantified in 12 different materials by 17 laboratories from different disciplines using seven different methods the materials were divided into three classes 1 potentially interfering materials 2 laboratory produced bc rich materials and 3 bc containing environmental matrices from soil water sediment and atmosphere this is the first comprehensive intercomparison of this type multimethod multilab and multisample focusing mainly on methods used for soil and sediment bc studies results for the potentially interfering materials which by definition contained no fire derived organic carbon highlighted situations where individual methods may overestimate bc concentrations results for the bc rich materials one soot and two chars showed that some of the methods identified most of the carbon in all three materials as bc whereas other methods identified only soot carbon as bc the different methods also gave widely different bc contents for the environmental matrices however these variations could be understood in the light of the findings for the other two groups of materials i e that some methods incorrectly identify non bc carbon as bc and that the detection efficiency of each technique varies across the bc continuum we found that atmospheric bc quantification methods are not ideal for soil and sediment studies as in their methodology these incorporate the definition of bc as light absorbing material irrespective of its origin leading to biases when applied to terrestrial and sedimentary materials this study shows that any attempt to merge data generated via different methods must consider the different operationally defined analytical windows of the bc continuum detected by each technique as well as the limitations and potential biases of each technique a major goal of this ring trial was to provide a basis on which to choose between the different bc quantification methods in soil and sediment studies in this paper we summarize the advantages and disadvantages of each method in future studies we strongly recommend the evaluation of all methods analyzing for bc in soils and sediments against the set of bc reference materials analyzed here

coherent changes in relative c4 plant productivity and climate during the late quaternary in the north american great plains evolution of the mixed and shortgrass prairie of the north american great plains is poorly understood because of limited proxies available for environmental interpretations buried soils in the great plains provide a solution to the problem because they are widespread both spatially and temporally with their organic reservoirs serving as a link to the plants than once grew on them through stable carbon isotopic analysis of soil organic carbon d

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

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

drift and deformation of oil slicks due to surface waves we present a theoretical model for the wave induced drift and horizontal deformation of an oil slick the waves and the mean flow are coupled through the influence of the mean flow on the concentration of slick material which in turn determines the damping rate of the waves and hence the transfer of momentum from the waves to the mean flow we also briefly discuss a simplified version of the model that can be used when remote sensing data are available with this simpler model the wave induced forcing of the mean flow is obtained directly from observations of the wave field hence knowledge of any specific slick properties is not required

compression of floating ice fields the compression of ice fields made up of thin floes is central to the processes of ice jam formation in northern rivers pressure ridge formation in northern seas and the dynamics of ice fields in arctic and antarctic marginal seas this work describes the results of computer simulations in which a floating layer of circular floes confined in a rectangular channel is compressed by a pusher plate moving at a constant speed the accuracy of the simulations is assessed by comparison with a series of similar physical experiments performed in a refrigerated basin following this comparison the computer model is used to perform an extensive series of simulations to explore the effect of variations in channel length and width the ratio of floe diameter to thickness floe on floe friction coefficients and the distribution of floe diameters on the force required to compress the floes the results show that reducing the aspect ratio of the floes or increasing the friction coefficient increases the force needed to compress the floes both changes increase the force by changing the dominant failure mechanism in the layer of floes from rafting to underturning increasing channel width reduced the compressive force per unit channel width by reducing the relative importance of frictional drag at the channel edges last the results of a simulation using a distribution of floe diameters was indistinguishable from those of a simulation using floes with a single diameter equal to the average diameter of the distribution

a cyclonic eddy over the continental margin of vancouver island evidence for baroclinic instability abstract this paper describes the circulation water properties and energetics of an observed cyclonic eddy that formed over the continental margin of vancouver island between late july and early september 1980 the eddy was characterized by a depth scale of 1 km a radius of 50 km and a maximum near surface geostrophic flow of 50 cm s 1 within the middepth core of the eddy isopycnal surfaces were domed upward by 50 m and were comprised of relatively warm saline and low dissolved oxygen water that appeared to originate with the california undercurrent the eddy is shown to have been generated through dynamic instability of the seasonal mean flow along vancouver island the appearance in late july of the undercurrent over the slope may have been an important factor in the amplification of the mesoscale meander that eventually deformed into the eddy calculation of each of the terms in the integrated energy balance reveals that both barotropic and baroclinic instability contributed to the amplification

recharge to the inter dune lakes and holocene climatic changes in the badain jaran desert western china we present new estimates on evaporation and groundwater recharge in the badain jaran desert western inner mongolia of northwestern china based on a modified penman equation suitable for lakes in china geochemical data and water balance calculations suggest that local rainfall makes a significant contribution to groundwater recharge and that past lake level variations in this desert environment should reflect palaeoclimatic changes the chronology of lake level change established by radiocarbon and u series disequilibrium dating methods indicates high lake levels and a wetter climate beginning at ca 10 ka and lasting until the late mid holocene in the badain jaran desert the greatest extension of lakes in the inter dune depressions indicates that the water availability was greatest during the mid holocene relicts of neolithic tools and pottery of qijia culture 2400 1900 bc suggest relatively intensive human activity in the badain jaran desert during the early and middle holocene supporting our interpretation of a less harsh environment wetter climates during the holocene were likely triggered by an intensified east asian summer monsoon associated with strong insolation

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

modeling events of sea surface variability using spectral nudging in an eddy permitting model of the northeast pacific ocean 1 eddies are an important part of the current system that hugs the coasts of british columbia and alaska the ability of spectral nudging to improve the eddy statistics determined from model simulations of this current system is investigated spectral nudging differs from standard nudging in that only specified frequency and wave number bands of the simulated potential temperature and salinity fields are nudged toward the observed climatology therefore the simulated eddy field can develop and evolve with time while the model is prevented from drifting far from the observed climatology the parallel ocean program pop is used to do the simulations with 0 25 horizontal resolution and 23 vertical levels the simulated standard deviation and skewness fields for the sea surface height are compared with those estimated from ten years of topex poseidon altimetry observations this comparison shows that spectral nudging allows the model to simulate the eddy statistics of the current system with significantly more accuracy than when the nudging is not used

stable carbon isotope of black carbon in lake sediments as an indicator of terrestrial environmental changes an evaluation on paleorecord from daihai lake inner mongolia china abstract we measured the carbon isotope ratio of black carbon bc from the daihai lake sediment core dh99a in north central china with an objective to examine the effectiveness and sensitivity of the 13c values of bc 13cbc as a potential indicator of terrestrial environmental changes we first performed a statistical study on the available data regarding carbon isotope fractionation cif during the conversion of c3 and c4 vegetation to bc and observed that the mean cif for bc produced from c3 plants is 0 3 whereas that for bc from c4 plants is 1 7 this result provides a solid reference for reconstructing vegetation and environmental changes using the 13cbc values the 13cbc record in the dh99a sediment core spanning the last ca 10 000 years displayed large variations from 23 7 to 29 2 which suggests that c3 plants dominantly occupied the daihai lake region during the holocene the most negative 13cbc peaks coincided with high values of tree percentages and grain sizes which occurred under relatively wetter climatic conditions during the middle holocene ca 6500 3200 cal yr bp and an interval between 1700 and 1350 cal yr bp in contrast the least negative 13cbc values corresponded to low values of tree percentages and grain sizes during relatively drier phases of the early and late holocene the generally negative correlation of the 13cbc values with the tree percentages and grain sizes was thought to reflect a negative correlation of the 13cbc values with the monsoon precipitation this correlation is consistent with the response of carbon isotope in modern c3 plants to precipitation in north china therefore we developed a computational model to reconstruct the changes in annual precipitation over the daihai lake region using the 13cbc values the results indicated that the annual precipitation was highly variable ranging from 170 mm lower to 310 mm higher than that at present during the middle holocene whereas the annual precipitation was generally 70 mm lower than that at present during the early and late holocene the general features of the inferred precipitation changes using the 13cbc values are generally consistent with those reconstructed using pollen data of the same sediment core meanwhile the 13cbc values tend to register some extreme variations of monsoon precipitation which were not reflected in the pollen assemblages we conclude that the 13cbc values in the daihai lake sediments may serve as a sensitive and reliable proxy for monitoring monsoon precipitation

currents in haida eddies abstract measurements by a variety of sensors provided details of flow in haida eddies which are anticyclonic mesoscale features that move slowly westward through the eastern gulf of alaska these measurements provided the best comparison and analysis to date of mesoscale eddy currents by various ship and satellite based sensors the relative contribution of barotropic currents to the total eddy orbital motion at ocean surface was found to be up to 16 based on comparison of total sea surface height anomalies measured by satellite altimetry and baroclinic elevation of the ocean surface detected by ship based measurements of density through the eddies acoustic doppler current meters on a ship transiting two haida eddies found that the observed currents were considerably different from the expected orbital motion perhaps due to inertial currents or to previously undetected barotropic structure lagrangian drifters drogued near the ocean surface in two eddies revealed that inertial currents in late spring and summer were similar in magnitude to eddy orbital motion and larger than eddy currents following periods of strong winds drifter tracks also provided evidence that the eddy rotated as a solid body constant vorticity within 30 40 km of the eddy center and that material could remain in these central waters for at least 2 months in summer for most of the 2 month period during which the drifters were tracked they steadily moved away from the center of the eddy implying a gradual uplift of the pycnocline within the eddy core due to slow decay of the eddy or to its uplift as it moved westward into denser ambient waters

drift of pancake ice floes in the winter antarctic marginal ice zone during polar cyclones high temporal resolution in situ measurements of pancake ice drift are presented from a pair of buoys deployed on floes in the antarctic marginal ice zone during the winter sea ice expansion over 9 days in which the region was impacted by four polar cyclones concomitant measurements of wave in ice activity from the buoys are used to infer that the ice remained unconsolidated and pancake ice conditions were maintained over at least the first 7 days analysis of the data shows i the fastest reported ice drift speeds in the southern ocean ii high correlation of drift velocities with the surface wind velocities indicating absence of internal ice stresses 100 km from the ice edge where remotely sensed ice concentration is 100 and iii presence of a strong inertial signature with a 13 hr period a lagrangian free drift model is developed including a term for geostrophic currents that reproduce the 13 hr period signature in the ice motion the calibrated model provides accurate predictions of the ice drift for up to 2 days and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions

response of surface processes to climatic change in the dunefields and loess plateau of north china during the late quaternary this paper draws on recent optically stimulated luminescence osl dating to evaluate the long held assumption that dust accumulation rates in the loess plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time because both are controlled by the strength of the asian monsoons and also possibly because the dunefields are proximal loess sources the results show there is little evidence that high rates of loess accumulation coincided with well dated episodes of extensive dune activity in the mu us otindag and horqin dunefields at 11 8 ka and 1 0 ka explanations for the apparent lack of coupling include local variation in the trapping of dust and post depositional preservation of the loess and dune sediments in response to varying local environmental conditions in addition a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields the results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale the dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale but the timing of late quaternary dune activity along with a variety of other evidence indicates that moisture changes in many of the drylands of northern china may not be in phase with precipitation in core regions of the asian monsoons copyright 2011 john wiley sons ltd

linkage between c4 vegetation expansion and dune stabilization in the deserts of ne china during the late quaternary abstract knowledge of the role of c4 vegetation expansion in regulating dune stabilization during the late quaternary is important for understanding the evolution of the environment and climate in the climatically sensitive margin of the east asian summer monsoon however due to the lack of both reliable vegetation records and chronological control during episodes of dune activity the relationship between c4 vegetation expansion and dune stabilization in the deserts of ne china during the late quaternary remains unclear here we present a new regional compilation of late quaternary stable carbon isotopic data from organic matter together with dated records from sub aerial sedimentary deposits in the region our compilation of vegetation development and dune activity in these deserts suggests that c4 vegetation expansion with a main contribution from chenopodiaceae and a secondary contribution from poaceae and cyperaceae may have played a critical role in dune semi stabilization with a northwestward trend from 13 to 9 ka and dune stabilization throughout the entire study region from 9 to 5 ka in addition during the late holocene intensified millet cultivation or overgrazing and or climatic deterioration at 1 5 ka likely caused an increase in c4 vegetation abundance in the deserts of ne china which is associated with a dune mobilization episode in contrast after 2 5 ka decreased vegetation cover and dune mobilization in the mu us and hobq deserts were likely caused by poor land use practices and historically documented droughts overall c4 vegetation expansion was the main cause of dune stabilization in these deserts during the late quaternary

marginal ice zone thickness and extent due to wave radiation stress abstractocean surface wave radiation stress represents the flux of momentum due to the waves when waves are dissipated or reflected by sea ice that momentum is absorbed or reflected resulting in

the attenuation rates of ocean waves in the marginal ice zone during field operations in the greenland and bering seas in 1978 1979 and 1983 a number of experiments were carried out in which wave energy was measured along a line of stations running from the open sea deep into an icefield wave buoys in the water and accelerometer packages on floes were the instruments employed with airborne vertical photography to supply information on floe size distribution it was found that the decay of waves is exponential with a decay coefficient which generally increases with frequency except for a roll over at the highest frequencies the observations can be fitted reasonably well to a theory of one dimensional scattering

observation and modeling of satellite sensed meanders and eddies off vancouver island abstract a long time series of satellite infrared images spanning the period 21 july 8 october 1980 reveals the evolution of long 160 km and short 80 km wavelength meanders of the california current system off vancouver island midway in the series strong interactions occurred between the two meander scales although the shorter meanders were initially more energetic they were eventually dominated by the longer meanders near the end of the time series detached mesoscale eddies were formed from the longer meanders current meter data from the period before meander growth clearly indicates the presence of a strong vertical shear near 150 m which consists of a southeastward surface current and a northwestward undercurrent it is argued in this paper that the observed shear flow is the energy source for the meanders and eddies seen in the satellite images a four layer quasi geostrophic model is used to represent the california current system off vancouver island the two upper layers represent the

modelling the generation of haida eddies abstract a numerical model forced with average annual cycles of climatological winds surface heat flux and temperature and salinity along the open boundaries is used to demonstrate that haida eddies are typically generated each winter off cape st james at the southern tip of the queen charlotte islands of western canada annual cycles of sea surface elevation measured at coastal tide gauges and topex poseidon crossover locations are reproduced with reasonable accuracy model sensitivity studies show that haida eddies are baroclinic in nature and are generated by the merging of several smaller eddies that have been formed to the west of cape st james the generation mechanism does not require the existence of instability processes and is associated with the mean advection of warmer and fresher water masses around the cape from hecate strait and from the southeast these advected water masses generate plumes of buoyant flow which intensify and sustain small patches of anticyclonic circulation immediately to the northwest of the cape when the flow is stronger several of these smaller eddies can merge to generate a larger eddy the haida eddy similar to observations a typical generation shedding cycle for larger haida eddies in the model is 3 4 months consistent with previous in situ water property measurements these experiments show that the eddies are generally comprised of mixed layer water from hecate strait queen charlotte sound and the continental shelves off northern vancouver island their vertical extent during the mature stage is roughly 1000 m

organic stable carbon isotopic composition reveals late quaternary vegetation changes in the dune fields of northern china abstract vegetation changes during the late quaternary in the dune fields of northern china are not well understood we investigated organic carbon stable isotopic composition of surface soils related mainly to the ratio of c3 and c4 plants across a range of arid to subhumid climates in this region isotopic composition is weakly related to both temperature and moisture multiple r2 0 53 with the highest 13c greatest c4 abundance in the warm subhumid horqin dune field in late quaternary eolian stratigraphic sections of the mu us and horqin dune fields but not in the much colder otindag dune field 13c is higher in organic carbon from paleosols than in eolian sands this contrast most evident for paleosols recording a major early to middle holocene phase of dune stabilization is interpreted as evidence for expansion of c4 plants due to increased effective moisture high temperature because of high insolation and decreased disturbance related to eolian erosion and deposition

air ice ocean momentum exchange part ii ice drift a model was constructed to estimate ice floe trajectories the model considers the balance of atmosphere and ocean drag forces on ice floes including skin and body drag forces from wind waves and currents discussion of air ice and water ice skin stresses water ice form stress and wave radiation stress is presented estimates are presented for the ice drift in a variety of hypothetical situations i as a function of ice floe diameter thickness and concentration ii in wave and no wave situations and iii in constant wind forcing and time varying wind forcing situations the model is shown to be consistent with wave and ice observations collected during the labrador ice margin experiment 1987 on the grand banks during relatively high wind situations combining this model with the wave scattering model of part i allows estimation of 1 the effect of wave scattering attenuation on ice floe trajectories and the ice edge and 2 the effect of ice floe drift on the wave spectra thus an enhanced modeling of wave and ice dynamics is achieved

baroclinic instability in drake passage abstract a linearized baroclinic instability model is applied to the drake passage area the predictions of the model are found to be in good agreement with observations temporal and spatial scales are predicted accurately and the vertical structure of the most unstable wave is consistent with observations results indicate that the observed release of potential energy from the mean state in this area is made possible by the presence of a negative gradient of mean potential vorticity at and near the lower boundary further it is found that the model results are stable with respect to variations of the mean velocity field which might be incurred by errors in the data explanations for this insensitivity are given

evidence for wildfire in the meishan section and implications for permian triassic events polynuclear aromatic hydrocarbons pahs and black carbon bc in sediments are powerful tools in the identification of the combustion process throughout geologic history in this study combustion derived pahs and bc were carefully investigated in sediments from the global stratotype section and point of the permian triassic p tr boundary in meishan china quantitative analyses of combustion derived pahs and bc demonstrate anomalously high concentrations in the boundary event beds that coincide with the mass extinction horizon the prevalence of parent polynuclear aromatics e g phenanthrene in pahs together with non metric multidimensional scaling analysis confirms that the pahs are mainly derived from vegetation burning instead of having a coal and or oil origin bc detected in sediment occurs in various forms from large irregular charcoal particles to fine aciniform soot with an equivalent reflectance of up to 3 5 the results strongly suggest that a wildfire occurred during the p tr boundary which served as one of the possible triggers of mass extinction on land the wildfire occurrence indicates that the o2 concentration of the atmosphere during or before the p tr mass extinction was probably 17 the temporal coincidence of the mass extinction with intensive volcanic eruption marine anoxia and wildfire events in the region of the meishan section provides new insight into the mechanisms of the p tr biotic crisis our results show that wildfires could have played an important role in the collapse of the ecosystem in the meishan p tr events

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

airborne remote sensing of ocean wave directional wavenumber spectra in the marginal ice zone interactions between surface waves and sea ice are thought to be an important but poorly understood physical process in the atmosphere ice ocean system in this work airborne scanning lidar was used to observe ocean waves propagating into the marginal ice zone miz these represent the first direct spatial measurements of the surface wave field in the polar miz data were compared against two attenuation models one based on viscous dissipation and one based on scattering both models were capable of reproducing the measured wave energy the observed wavenumber dependence of attenuation was found to be consistent with viscous processes while the spectral spreading of higher wavenumbers suggested a scattering mechanism both models reproduced a change in peak direction due to preferential directional filtering floe sizes were recorded using co located visible imagery and their distribution was found to be consistent with ice breakup by the wave field

summer monsoon intensity controls c4 c3 plant abundance during the last 35 ka in the chinese loess plateau carbon isotope evidence from bulk organic matter and individual leaf waxes the natural abundance of c3 and c4 plants is affected by multiple environmental factors including temperature moisture balance and atmospheric pco2 the relative importance of these factors is a subject of considerable debate and may vary in different natural ecosystems previous studies generally focus on single loess sequences in the chinese loess plateau and conflicting conclusions on c4 c3 have been reached when studying carbon isotope ratios in carbonate and organic matter in this paper we report a comprehensive carbon isotopic characterization of total organic carbon toc and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the chinese loess plateau clp the five coring sites encompass large gradients of annual mean temperature 9 2 13 9 c and precipitation 402 673 mm allowing us to assess the controlling mechanisms on c4 c3 plant ratios glacial interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility our results demonstrate that increased c4 c3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites we conclude c4 abundance increases from the last glacial to the holocene in response to greater monsoon activity and that the c4 expression is suppressed in the cold and drier intervals

black carbon in soils and sediments analysis distribution implications and current challenges this review highlights the ubiquity of black carbon bc produced by incomplete combustion of plant material and fossil fuels in peats soils and lacustrine and marine sediments we examine various definitions and analytical approaches and seek to provide a common language bc represents a continuum from partly charred material to graphite and soot particles with no general agreement on clear cut boundaries formation of bc can occur in two fundamentally different ways volatiles recondense to highly graphitized soot bc whereas the solid residues form char bc both forms of bc are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport we summarize chronologically the ubiquity of bc in soils and sediments since devonian times differentiating between bc from vegetation fires and from fossil fuel combustion bc has important implications for various biological geochemical and environmental processes as examples bc may represent a significant sink in the global carbon cycle affect the earth s radiative heat balance be a useful tracer for earth s fire history build up a significant fraction of carbon buried in soils and sediments and carry organic pollutants on land bc seems to be abundant in dark colored soils affected by frequent vegetation burning and fossil fuel combustion thus probably contributing to the highly stable aromatic components of soil organic matter we discuss challenges for future research despite the great importance of bc only limited progress has been made in calibrating analytical techniques progress in the quantification of bc is likely to come from systematic intercomparison using bcs from different sources and in different natural matrices bc identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels the key to estimating bc stocks in soils and sediments is an understanding of the processes involved in bc degradation on a molecular level a promising approach would be the combination of short term laboratory experiments and long term field trials

a mechanism for the formation of ice edge bands we propose a mechanism for the formation of multiple bands at an ice edge that is subjected to an off ice wind the wind moves the outermost floes seaward faster than the interior ice dilating the marginal ice zone and opening up random polynyas in the largest of the polynyas the off ice wind generates a significant fetch limited wave spectrum which produces a wave radiation pressure on floes at the downwind end of the polynya increasing their velocity they are herded against their downwind neighbors creating a band of high ice concentration the band is stabilized by an internal compacting stress due to the exponential decay of the wind wave spectrum across the band and to a slower decay of swell incident from seaward the band s growth terminates when it encounters a second downwind polynya of sufficiently large size we show how an array of immature bands generated in this way matures by selective mergers into larger regularly spaced bands of approximately equal width

air ice ocean momentum exchange part 1 energy transfer between waves and ice floes abstract the energy exchange between ocean surface waves and ice floes in the marginal ice zone miz involves the scattering and attenuation of wave energy and the excitation of oscillation modes of the ice floes as open ocean waves propagate into the miz heave pitch and roll modes of oscillation are linked to estimation of wave scattering and attenuation a model is presented for wave attenuation and compared to measurements from the marginal ice zone experiments in the greenland sea as reported by wadhams et al

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

climatic dependency of soil organic carbon isotopic composition along the s n transect from 34 n to 52 n in central east asia abstract we explored the relationships between surface soil 1 20 cm organic carbon isotopic signatures and associated climatic factors in central east asia in an attempt to develop transfer functions that can be used to retrieve the paleoclimatic information stored in the thick eolian paleosol sequences within the area our analysis shows that the negative correlation between the surface soil organic 13c values and the mean annual precipitation is robust r2 0 453 n 196 p

wave rafting and the equilibrium pancake ice cover thickness 1 pancake ice the circular floes formed during ice growth in a wave field forms in many polar and subpolar seas vertical thin sections of cores taken from the ice cover in these regions show distinct layering structure these observations suggest wave rafting could play a significant role in defining the ice cover thickness much more so than thermodynamic growth although wave rafting is intuitively apparent no previous study relating the resulting ice cover to wave characteristics has been conducted in this study we utilize both laboratory experiments and numerical simulations to determine the rafting process we propose a theory that predicts a final equilibrium thickness provided that the incoming wave is kept constant the equilibrium thickness from the theory is proportional to the square of the wave amplitude and the square of the floe diameter and is inversely proportional to the cube of the wavelength this theory relates the final ice cover thickness to the wave characteristics and the size and surface properties of the pancake ice floes this theory also provides a way to calculate the speed with which the boundary between the single layer pancake ice floes and the equilibrium rafted ice cover propagates we conduct laboratory experiments with plastic model pancake ice to create rafting we perform computer simulations with a three dimensional discrete element model that simulates the movement of disc shaped floes in the wave field we compare the theoretical result with the laboratory experiments and a numerically simulated rafting process both the laboratory and the computer simulation results compare favorably with the theory

stable carbon isotopic composition of black carbon in surface soil as a proxy for reconstructing vegetation on the chinese loess plateau abstract black carbon bc is a continuum of carbon produced by incomplete combustion whether its stable carbon isotopic composition expressed as 13 c bc values can be used directly for paleovegetation reconstruction is still in debate in the present study we investigated surface soil from the chinese loess plateau and collected samples from the following three transects the ruicheng jingbian lantian huanxian and qin an dingxi from east to west the 13 c bc values for surface soil ranged from 27 9 to 21 9 the stable carbon isotopic composition of soil organic carbon expressed as 13 c soc values ranged from 26 8 to 20 9 a strong positive correlation was observed between 13 bc and 13 c soc r 0 88 p 0 000 13 bc and 13 c soc 13 soc bc values ranged from 1 5 to 1 3 with an average of 0 2 the characteristics of vegetation on the chinese loess plateau and its variation indicated by 13 bc and 13 c soc values were consistent with those of modern plants it suggests that 13 bc values for surface soil are controlled mainly by surface plants and that therefore 13 bc can indicate the vegetation effectively within a precision range of 1 5

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

sources of eddy energy simulated by a model of the northeast pacific ocean abstract this paper examines the energy sources for eddy variability in the gulf of alaska using a numerical model and a novel form of data assimilation referred to as spectral nudging spectral nudging is distinguished from conventional nudging by its ability to operate only on specified frequency and wavenumber bands in the present case only the subannual variability is nudged and only on spatial scales of 100 km or more by using this approach the broad brush aspects of the model s mean state are constrained to remain near the mean climatological conditions while the simulated eddy field is determined by the model dynamics simulations of the north pacific ocean with a 0 25 horizontal resolution and spectral nudging have been previously shown to produce eddy fields that are significantly more energetic and more realistic than those produced by prognostic i e not nudged simulations the analysis of the spectrally nudged model results undertaken here reveals the tendency of the circulation to b

determination of black carbon by chemical oxidation and thermal treatment in recent marine and lake sediments and cretaceous tertiary clays abstract several sample treatments and analytical methods for the measurement of black carbon in a wide variety of sediments were considered in which the removal of organic carbon is a critical step in the procedure a comparison between chemical oxidation and thermal treatment was conducted and the latter was shown to be inappropriate due to the polymerisation of organic matter using acid dichromate oxidation reactive kerogen was separated from black carbon in a variety of lake and marine and recent and ancient sediments with relatively small and quantifiable losses 1 6 of black carbon under carefully controlled reaction conditions

a relationship between the aerodynamic and physical roughness of winter sea ice a bulk flux algorithm predicts the turbulent surface fluxes of momentum and sensible and latent heat from mean measured or modelled meteorological variables the bulk flux algorithm resulting from data collected over winter sea ice during sheba the experiment to study the surface heat budget of the arctic ocean failed however in its first trial to predict the turbulent momentum flux over sea ice in the antarctic this result suggests that the main parameter for predicting the momentum flux the aerodynamics roughness length z0 does not respond just to the friction velocity as in the sheba algorithm but is closely related to the physical roughness of snow covered sea ice and may need to be site specific i investigate this idea with simultaneous measurements of z0 and the physical roughness of the surface at ice station weddell the metric derives from surveys of surface elevation and is related to but always less than the standard deviation in surface elevation on combining the z0 pairs from ice station weddell with similar data obtained over arctic sea ice i show that the arctic and antarctic z0 data lie along a continuum such that measuring could provide a means for estimating a site specific z0 for any global sea ice surface backscatter data from satellite borne synthetic aperture radar might provide a remotely sensed estimate of copyright 2011 royal meteorological society

black carbon concentration and isotopic composition of surface sand from deserts and dune fields in northern china abstract black carbon bc is a continuum of incomplete combustion products of vegetation and fossil fuels it can be used as a proxy for wildfires and paleovegetation reconstruction nevertheless bc can be transported by wind and water via atmospheric and fluvial transport to research the characteristics of bc in deserts and dune fields that are directly connected with the chinese loess plateau clp in northern china and to evaluate the possibility that bc in deserts and dune fields occurs as exogenous bc in the clp we investigated surface sand from the mu us dune field the tengger desert and the badain jaran desert and analyzed the stable carbon concentration and carbon isotopes of organic carbon soc 13 c soc and bc bc 13 c bc the 13 c soc 13 c bc values ranged from 27 4 to 22 5 and 28 2 to 23 0 respectively which mainly reflected 13 c changes in surface c 3 grasses a positive correlation was observed between 13 c bc and 13 c soc suggesting that local vegetation mainly controls 13 c bc the difference between 13 c bc and 13 c soc ranged from 0 2 to 3 5 and the difference is likely to be due to carbon isotope discrimination occurring during burning and soc decomposition the soc and bc in these deserts and dune fields are very small averaging 0 048 and 0 011 the bc of surface sand in these areas is about 5 5 of bc in the clp surface soils and the 13 bc value between surface sand in deserts and surface soils in clp ranged from 0 3 to 6 3 so the change of 13 bc in the clp surface soils deduced by exogenous bc from deserts is less than 0 35 all these findings suggest that bc in deserts has a limited impact on bc in the clp and is unlikely to affect interpretations of the bc record of wildfires and paleovegetation information in the clp

black carbon records in chinese loess plateau over the last two glacial cycles and implications for paleofires abstract to study the temporal and spatial changes in paleofires over the chinese loess plateau black carbon concentrations were analyzed on the loess paleosol samples from three sections along a north south transect using the orbitally tuned time scales of the sections the black carbon mass sedimentation rates bcmsr were calculated results show that in the last two glacial cycles the bcmsr values in glacial periods are 2 3 times higher than in interglacial periods and the bcmsr variability has a relatively strong precession associated 23 ky period suggesting that the glacial cold dry climate conditions were apt to induce natural fires over the loess plateau comparison of the bcmsr records among the three loess sections demonstrates that natural fire occurrence was much more intensive and frequent in the northern loess plateau than in the southern part coinciding with the previous conclusion that the northern plateau has experienced a drier climate regime in both glacial and interglacial periods the substantial increase in bcmsr of the upper s0 relative to the lower s0 at lingtai and weinan indicates that human activities have exerted a significant influence on fire regimes in the middle and southern loess plateau during late holocene due to the relatively intensive agricultural usage of land

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