arctic ocean sea ice response to northern annular mode like wind forcing the response of the arctic ocean sea ice system to northern annular mode like wind forcing has been investigated using an ocean sea ice general circulation model coupled to an atmospheric boundary layer model a series of idealized experiments was performed to investigate the arctic ocean s response to idealized winter wind anomalies on interannual to multi decadal time scales the sea ice response of the model consists of a rapid change of ice movements leading to widespread variation in sea ice thickness and concentration in most areas the response is largely independent of the forcing frequency with only a slight increase towards longer periods only the greenland sea exhibited a change in sign of sea ice concentration anomalies at about 20 years period which appears to be caused by slow adjustment of the oceanic circulation

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

wind control of storm triggered shallow landslides 1 heavy rainstorms are a major control of shallow landsliding in mountainous areas the influence of three dimensional 3 d variability of precipitation is analyzed by coupling a fine resolution atmospheric model rams with a fine resolution topographic model dem to represent the 3 d precipitation flux generating the catastrophic flood that occurred in versilia central italy on 19 june 1996 matching of this flux with the observed scars and debris shows that 92 of the mass movements occurred where the normalized precipitation flux exceeds 0 80 and less then 2 where this is null these results give an insight of the detected role of exposure in explaining the spatial variability of observed landslides as emerging from multivariate statistical analysis the interaction of the wind driven precipitation field with topography is an important control of shallow landslides triggered by convective storms in upland catchments

the response of the coupled arctic sea ice atmosphere system to orbital forcing and ice motion at 6 kyr and 115 kyr bp abstract a coupled atmosphere mixed layer ocean gcm genesis2 is forced with altered orbital boundary conditions for paleoclimates warmer than modern 6 kyr bp and colder than modern 115 kyr bp in the high latitude northern hemisphere a pair of experiments is run for each paleoclimate one with sea ice dynamics and one without to determine the climatic effect of ice motion and to estimate the climatic changes at these times at 6 kyr bp the central arctic ice pack thins by about 0 5 m and the atmosphere warms by 0 7 k in the experiment with dynamic ice at 115 kyr bp the central arctic sea ice in the dynamical version thickens by 2 3 m accompanied by a 2 k cooling the magnitude of these mean annual simulated changes is smaller than that implied by paleoenvironmental evidence suggesting that changes in other earth system components are needed to produce realistic simulations contrary to previous simulations without atmospheric feedbacks the sign of the dynamic sea ice feedback is complicated and

lava flow identification and aging by means of lidar intensity mount etna case 1 an application of light detection and ranging lidar intensity for the identification and mapping of different lava flows from the mount etna italy active volcano is described in september 2004 an airborne lidar survey was flown over summit sectors of mount etna the information derived from lidar intensity values was used to compare the lava flows with respect to their age of emplacement analyzed lava flows vary in age between those dating prior to a d 1610 and those active during the survey 2004 2005 eruptions the target emitter distance as well as surface roughness and texture at the lidar footprint scale is the main parameter controlling the intensity response of lava flows variations in the roughness and texture of surfaces at a meter scale result from two main processes initial lava cooling and subsequent surface weathering both lead to variations in the original surface roughness of the flow in summary 1 initially from the time of emplacement the lidar intensity of lava flow surfaces decreases and 2 about 6 years after emplacement the lidar intensity of lava surfaces starts to increase with the age of flows lidar capability in terms of geometric accuracy of 1 m in plan position and less than 1 m in elevation and spectral lidar intensity depends on surface reflection at 1 064 m information can thus be effectively used to map lava flows and to define a relative chronology of lava emplacement

past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

arctic sea ice variability in the context of recent atmospheric circulation trends abstract forty years 1958 97 of reanalysis products and corresponding sea ice concentration data are used to document arctic sea ice variability and its association with surface air temperature sat and sea level pressure slp throughout the northern hemisphere extratropics the dominant mode of winter january march sea ice variability exhibits out of phase fluctuations between the western and eastern north atlantic together with a weaker dipole in the north pacific the time series of this mode has a high winter to winter autocorrelation 0 69 and is dominated by decadal scale variations and a longer term trend of diminishing ice cover east of greenland and increasing ice cover west of greenland associated with the dominant pattern of winter sea ice variability are large scale changes in sat and slp that closely resemble the north atlantic oscillation the associated sat and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr

laser ablation coupled with icp ms applied to u pb zircon geochronology a review of recent advances abstract improvements in the technology of laser ablation and icp ms instruments make la mc icpms a rapid precise and accurate method for u pb zircon geochronology in this review we describe the main stages of the evolution of this in situ approach from the early 1990s to the present time some key points have been progressively improved the crater size has been reduced to achieve real in situ measurements the laser wavelength has been reduced as well as the duration of each pulse in order to lower inter element fractionation the blank from the gas has to be lowered as far as possible double focusing instruments and magnetic field sectors allow flat topped peaks required for precise isotope ratio measurement to be obtained the use of a multi ion counting system significantly improves the sensitivity of the method and the static mode of integration favours the precision of measurement of the transient signal originating from a noisy laser ablated particle beam combining the use of a 213 nm uv laser and a mc icpms equipped with a multi ion counting system operating in static mode the common precisions achieved for the key ratios 207 pb 206 pb and 206 pb 238 u are better than 1 and 3 2 respectively including error propagation associated with standard normalization until now the use of a zircon standard has remained necessary to ensure the accuracy of the calculated age a strategy for common pb correction is proposed according to the age of the zircon and according to the th u ratio of the grains after recording sixteen to twenty spot analyses the precision usually achieved on the age is about 1 and even significantly better for proterozoic samples in order to show the performance achieved by modern la mc icpms geochronology we tested four zircon samples covering a wide age range from 290 to 2440 ma these new age determinations can be compared in term of precision and accuracy since they have already been dated by reference methods id tims and shrimp further developments in the technology of ion counters equipping modern mc icpms and in laser systems will certainly be applied to a large field of geochronology studies in the near future as an alternative to sims for in situ age determination

nonuniform response of the major surface currents in the nordic seas to insolation forcing implications for the holocene climate variability 1 high resolution sediment cores from the voring plateau the north iceland shelf and the east greenland shelf have been studied to investigate the stability of major surface currents in the nordic seas during the holocene results from diatom assemblages and reconstructed sea surface temperatures ssts indicate a division of the holocene into three periods the holocene climate optimum 9500 6500 calendar cal years bp the holocene transition period 6500 3000 cal years bp and the cool late holocene period 3000 0 cal years bp the overall climate development is in step with the decreasing insolation on the northern hemisphere but regional differences occur regarding both timing and magnitude of sst changes sites under the direct influence of the norwegian atlantic current and the irminger current indicate sst cooling of 4 5 c from early holocene to present compared to 2 c recorded under the east greenland current superimposed on the general holocene cooling trend there is a high frequency sst variability which is in the order of 1 1 5 c for the voring plateau and the east greenland shelf and 2 5 3 c on the north iceland shelf

arctic sea ice variability on a timescale of weeks and its relation to atmospheric forcing abstract northern hemisphere sea ice concentration 500 hpa height sea level pressure and 1000 500 hpa thickness at 7 day intervals are examined for the period 1972 1989 with emphasis on the winter season the temporal variability of sea ice concentration is largest along the climatological mean ice edge where its frequency distribution is strongly bimodal with ice free and ice covered conditions being observed much more frequently than partial ice cover these results confirm impressions based on visual inspection of satellite imagery that most of the variability in these regions is associated with the advance and retreat of the ice edge relationships between large scale patterns of atmospheric variability and sea ice variability are investigated making use of singular value decomposition of the temporal covariance matrix the analysis is conducted separately for the atlantic and pacific sectors in agreement with earlier studies based upon monthly mean data on sea ice concentration the strongest

multicentennial scale hydrological changes in the black sea and northern red sea during the holocene and the arctic north atlantic oscillation 1 paleoenvironmental proxy data for ocean properties eolian sediment input and continental rainfall based on high resolution analyses of sediment cores from the southwestern black sea and the northernmost gulf of aqaba were used to infer hydroclimatic changes in northern anatolia and the northern red sea region during the last 7500 years pronounced and coherent multicentennial variations in these records reveal patterns that strongly resemble modern temperature and rainfall anomalies related to the arctic oscillation north atlantic oscillation ao nao these patterns suggest a prominent role of ao nao like atmospheric variability during the holocene beyond interannual to interdecadal timescales most likely originating from solar output changes

dinocyst based reconstructions of sea ice cover concentration during the holocene in the arctic ocean the northern north atlantic ocean and its adjacent seas abstract sea ice cover extent expressed in terms of mean annual concentration was reconstructed from the application of the modern analogue technique to dinocyst assemblages the use of an updated database which includes 1492 sites and 66 taxa yields sea ice concentration estimates with an accuracy of 1 1 10 holocene reconstructions of sea ice cover were made from dinocyst counts in 35 cores of the northern north atlantic and arctic seas in the canadian arctic the results show high sea ice concentration 7 10 with little variations throughout the interval in contrast in arctic areas such as the chukchi sea and the barents sea the reconstructions show large amplitude variations of sea ice cover suggesting millennial type oscillations with a pacing almost opposite in western vs eastern arctic other records show tenuous changes with some regionalism either in trends or sea ice cover variability during the mid holocene and notably at 6 0 5 ka minimum sea ice concentration is recorded in the eastern fram strait northern baffin bay and labrador sea however this minimum cannot be extrapolated at the scale of the arctic and circum arctic the comparison of recent observations and reconstructions suggests larger variations in the arctic sea ice cover during the last decades than throughout the holocene

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

shrimp zircon u pb geochronological and whole rock geochemical evidence for an early neoproterozoic sibaoan magmatic arc along the southeastern margin of the yangtze block abstract it has been generally accepted that the south china block was formed through amalgamation of the yangtze and cathaysia blocks during the proterozoic sibaoan orogenesis but the timing and kinematics of the sibao orogeny are still not well constrained we report here shrimp u pb zircon geochronological and geochemical data for the taohong and xiqiu tonalite granodiorite stocks from northeastern zhejiang southeastern margin of the yangtze block our data demonstrate that these rocks dated at 913 15 ma and 905 14 ma are typical amphibole rich calc alkaline granitoids formed in an active continental margin combined with previously reported isotopic dates for the 1 0 ga ophiolites and 0 97 ga adakitic rocks from northeastern jiangxi the timing of the sibao orogenesis is thus believed to be between 1 0 and 0 9 ga in its eastern segment it is noted that the sibao orogeny in south china is in general contemporaneous with some other early neoproterozoic 1 0 0 9 ga orogenic belts such as the eastern ghats belt of india and the rayner province in east antarctica indicating that the assembly of rodinia was not finally completed until 0 9 ga

collision between the north and south china blocks a crustal detachment model for suturing in the region east of the tanlu fault a crustal detachment model based on the interpretation of linear aeromagnetic anomalies surface geological observations and deep seismic profiles is proposed for the continent continent collision between the north and south china blocks east of the tanlu fault the model suggests that during the mid mesozoic collision between the two continental blocks the upper crust of the south china block in the subei yellow sea region was detached from the lower crust and thrust over the north china block for 400 km whereas the lower part of the lithosphere was subducted under the north china block along a subsurface suture running east from nanjing the sinistral offset of the qinling suture by the tanlu fault is only 110 120 km in the deep crust much less than previously suggested

sensitivity of the northern hemisphere climate system to extreme changes in holocene arctic sea ice the extent of seasonal and perennial sea ice changed dramatically through the late quaternary and these changes influenced both the ocean and atmosphere by controlling the exchange of energy moisture and gases between them and by altering the planetary albedo reconstructing the changing patterns of sea ice distribution in the recent past remains one of the outstanding challenges to the paleo community to evaluate the importance of these reconstructions we performed sensitivity tests using ncar s community climate model ccm3 and a series of prescribed sea ice extents designed to capture the full range of arctic sea ice variability under interglacial holocene and full glacial last glacial maximum boundary conditions our simulations indicate that surface temperatures and sea level pressures in winter djf are most sensitive to changes in sea ice and that these changes are propagated over the surrounding land masses in the north atlantic but that equivalent changes in sea ice produce smaller corresponding changes in temperature or sea level pressure in the north pacific region a comparison between climap map chart series mc 36 geological society of america boulder co 1981 and a more realistic assessment of lgm sea ice yields dramatic changes in winter temperatures and precipitation patterns across eurasia these differences forced only by changed sea ice conditions reinforce the need to develop accurate maps of past sea ice to correctly simulate late quaternary environments such reconstructions also will be essential to validate the next generation of sea ice models

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

the decline in arctic sea ice thickness separating the spatial annual and interannual variability in a quarter century of submarine data 1 naval submarines have collected operational data of sea ice draft 93 of thickness in the arctic ocean since 1958 data from 34 u s cruises are publicly archived they span the years 1975 to 2000 are equally distributed in spring and autumn and cover roughly half the arctic ocean the data set is strong we use 2203 values of mean draft each value averaged over a nominal length of 50 km these values range from 0 to 6 m with a standard deviation of 0 99 m multiple regression is used to separate the interannual change the annual cycle and the spatial field the solution gives a climatology for ice draft as a function of space and time the residuals of the regression have a standard deviation of 0 46 m slightly more than the observational error standard deviation of 0 38 m the overall mean of the solution is 2 97 m annual mean ice draft declined from a peak of 3 42 m in 1980 to a minimum of 2 29 m in 2000 a decrease of 1 13 m 1 25 m in thickness the steepest rate of decrease is 0 08 meters per year m a in 1990 the rate slows to 0 007 m a at the end of the record the annual cycle has a maximum on 30 april and a peak to trough amplitude of 1 06 m 1 12 m in thickness the spatial contour map of the temporal mean draft varies from a minimum draft of 2 2 m near alaska to a maximum just over 4 m at the edge of the data release area 200 miles north of ellesmere island

holocene sea surface conditions in the western north atlantic spatial and temporal heterogeneities 1 holocene records of sea surface conditions in the western nordic seas were obtained from quantitative reconstructions based on dinoflagellate cyst assemblages two sediment cores from the east greenland and the north iceland shelves provide a detailed account of the long and short term dynamics of the opposing flows of arctic versus atlantic waters both marker species and quantitative reconstructions depict an overall trend toward warmer winter temperatures saltier surface waters and decreased sea ice extent the latter is supported by a close relationship between relative abundances of an atlantic dinocyst species nematosphaeropsis labyrinthus and ice rafted debris ird records we propose that the late holocene increased ird delivery in the denmark strait region was primarily induced by a combination of less extensive sea ice cover under increased atlantic water inflow and sustained iceberg calving tied to the readvance of the greenland ice sheet our records thus suggest diminishing polar water supplies throughout the holocene although the timing of regime changes differs between the western and eastern sides of the denmark strait finally comparison of our records with a core from southern greenland points to very heterogeneous sea surface conditions in the western north atlantic which could be explained by the decoupled dynamics of the two irminger current branches similarities between the southern greenland marine record and a continental record nearby suggest a close coupling with atmospheric processes reminiscent of a north atlantic oscillation like climate pattern

recent changes in arctic sea ice the interplay between ice dynamics and thermodynamics abstract it is well established that periods of high north atlantic oscillation nao index are characterized by a weakening of the surface high pressure and surface anticyclone in the beaufort sea and the intensification of the cyclonic circulation in the eastern arctic ocean the response of arctic sea ice to these atmospheric changes has been studied with a thickness distribution sea ice model coupled to an ocean model during a period of high nao 1989 96 the model shows a substantial reduction of ice advection into the eastern arctic from the canada basin and an increase of ice export through fram strait both of which tend to deplete thick ice in the eastern arctic ocean and enhance it in the western arctic in an uneven dipolar pattern we call the east west arctic anomaly pattern ewaap from the period 1979 88 with a lower nao index to the period 1988 96 with a high nao index the simulated ice volume in the eastern arctic drops by about a quarter while that in the western arctic increases by

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

holocene fluctuations in arctic sea ice cover dinocyst based reconstructions for the eastern chukchi sea cores from site hly0501 05 on the alaskan margin in the eastern chukchi sea were analyzed for their geochemical organic carbon 13corg corg n and caco3 and palynological dinocyst pollen and spores content to document oceanographic changes during the holocene the chronology of the cores was established from 210pb dating of near surface sediments and 14c dating of bivalve shells the sediments span the last 9000 years possibly more but with a gap between the base of the trigger core and top of the piston core sedimentation rates are very high 156 cm ka allowing analyses with a decadal to centennial resolution the data suggest a shift from a dominantly terrigenous to marine input from the early to late holocene dinocyst assemblages are characterized by relatively high concentrations 600 7200 cysts cm3 and high species diversity allowing the use of the modern analogue technique for the reconstruction of sea ice cover summer temperature and salinity results indicate a decrease in sea i

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

size dependent isotopic composition of planktic foraminifers from chukchi sea vs nw atlantic sediments implications for the holocene paleoceanography of the western arctic abstract in arctic and sub arctic seas shell growth and or secondary calcite overgrowth of neogloboquadrina pachyderma left coiled npl occur along the pycnocline and their 13c and 18o values are size and weight dependent however whereas the npl 18o data from the nw atlantic indicate near equilibrium conditions with ambient waters and a positive relationship between shell weight and 18o content assemblages from box cored sediments of the chukchi sea western arctic are depleted by 2 with respect to equilibrium values with modern conditions and depict a negative relationship between shell weight and its 18o value 0 15 0 03 g on vpdb scale a similar feature is also depicted by the dextral form of n pachyderma npd we associate the reverse shell size or weight vs 18o relationship to the reverse temperature gradient observed along the thermocline between the surface cold and dilute water layer and the underlying near 3 c warmer saline north atlantic water mass the analysis of two late to post glacial sedimentary sequences from the chukchi sea indicates that such a water mass stratification with a reverse thermocline persisted throughout the holocene thus reflecting an early onset of the modern like linkage between the arctic ocean and the north atlantic moreover lower 18o values in both npl and npd together with larger 18o gradients between the different shell sizes at ca 9 7 ka bp suggest 3 c higher temperatures in the upper north atlantic water mass in comparison with the present approximately 1 c at the study site thus likely a higher inflow rate of this water mass during the early holocene

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

modeling sea ice as a granular material including the dilatancy effect abstract a dynamic sea ice model based on granular material rheology is presented the sea ice model is coupled to both a mixed layer ocean model and a one layer thermodynamic atmospheric model which allows for an ice albedo feedback land is represented by a 6 m thick layer with a constant base temperature a 10 year integration including both thermodynamic and dynamic effects and incorporating prescribed climatological wind stress and ocean current data was performed in order for the model to reach a stable periodic seasonal cycle the commonly observed lead complexes along which sliding and opening of adjacent ice floes occur in the arctic sea ice cover are well reproduced in this simulation in particular shear lines extending from the western canadian archipelago toward the central arctic often observed in winter satellite images are present the ice edge is well positioned both in winter and summer using this thermodynamically coupled ocean ice atmosphere model the results also yield a sea ic

simulation of the interannual variability of the wind driven arctic sea ice cover during 1958 1998 a thermodynamic dynamic sea ice model based on a granular material rheology developed by tremblay and mysak is used to study the interannual variability of the arctic sea ice cover during the 41 year period 1958 98 monthly wind stress forcing derived from the national centers for environmental prediction ncep reanalysis data is used to produce the year to year variations in the sea ice circulation and thickness we focus on analyzing the variability of the sea ice volume in the arctic basin and the subsequent changes in sea ice export into the greenland sea via fram strait the relative contributions of the fram strait sea ice thickness and velocity anomalies to the sea ice export anomalies are first investigated and the former is shown to be particularly important during several large export events the sea ice export anomalies for these events are next linked to prior sea ice volume anomalies in the arctic basin the origin and evolution of the sea ice volume anomalies are then related to the sea ice circulation and atmospheric forcing patterns in the arctic large sea ice export anomalies are generally preceded by large volume anomalies formed along the east siberian coast due to anomalous winds which occur when the arctic high is centered closer than usual to this coastal area when the center of this high relocates over the beaufort sea and the icelandic low extends far into the arctic basin the ice volume anomalies are transported to the fram strait region via the transpolar drift stream finally the link between the sea ice export and the north atlantic oscillation nao index is briefly discussed the overall results from this study show that the arctic basin and its ice volume anomalies must be considered in order to fully understand the export through fram strait

holocene history of the bering sea bowhead whale balaena mysticetus in its beaufort sea summer grounds off southwestern victoria island western canadian arctic abstract the fossil remains of 43 bowhead whales were mapped on the raised beaches of western wollaston peninsula victoria island canadian arctic near the historic summer range limit of the bering sea stock in the beaufort sea the elevations and radiocarbon ages of the remains demonstrate that the bowhead ranged commonly into the region following the submergence of bering strait at ca 10 000 14c yr b p until ca 8500 14c yr b p during the same interval bowheads ranged widely from the beaufort sea to baffin bay subsequently no whales reached wollaston peninsula until ca 1500 14c yr b p late holocene populations evidently were small or occupations were brief in comparison to those of the early holocene although the late holocene recurrence may relate to the expansion of pioneering thule whalers eastward from alaska there are few thule sites and limited evidence of thule whaling in the area surveyed to support this suggestion

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

the lower changjiang yangzi yangtze river metallogenic belt east central china intrusion and wall rock hosted cu fe au mo zn pb ag deposits abstract the lower valley of changjiang from wuhan of the hubei province in the west to zhenjiang of the jiangsu province in the east contains more than 200 polymetallic cu fe au mo zn pb ag deposits and is one of the most important metallogenic belts in china this metallogenic belt situated at the northern margin of the yangzi craton and bordered by the dabieshan ultrahigh pressure metamorphic belt to the north consists mainly of cambrian triassic marine clastic sedimentary rocks and carbonate and evaporite rocks which overlay a precambrian basement and are intruded by yanshanian 205 to 64 ma granitoid intrusions and subvolcanic complexes repeated tectonism from late proterozoic to triassic resulted in extensively developed networks of faults and folds involving the cambrian triassic sedimentary strata and the precambrian basement the yanshanian granitoid intrusions and subvolcanic complexes in the lower changjiang metallogenic belt are characterized by whole rock 18 o of 8 to 10 initial 87 sr 86 sr of 0 704 to 0 708 and ndt from 10 to 17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials also the yanshanian granitoids exhibit eastward younging and increase in alkalinity i e from older calc alkaline in the west to younger subalkaline alkaline in the east which are related to oblique collision between the yangzi and sino korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes most polymetallic deposits in the lower changjiang metallogenic belt are clustered in seven districts where the yanshanian magmatism is particularly extensive from west to east edong jiurui anqing guichi luzhong tongling ningwu and ningzhen mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits orebodies in yanshanian granitoid intrusions skarn orebodies at the contact zones between the yanshanian intrusions and late paleozoic early mesozoic sedimentary rocks and stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata the most important host sedimentary strata are the middle carboniferous huanglong formation lower permian and lower middle triassic carbonate and evaporite rocks the intrusion hosted and skarn orebodies exhibit well developed zonation in alteration assemblages metal contents and isotopic compositions within individual deposits and apparently formed from hydrothermal activities related to the yanshanian magmatism the stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano sedimentary exhalative processes in shallow marine environments however extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization on the basis of geological relationships and isotope geochemical characteristics we propose a carbonate hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies this model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the yanshanian intrusions with carbonate and evaporite wall rocks mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion hosted orebodies the stratabound massive sulfide deposits of the lower changjiang metallogenic belt share many features with the well studied high temperature carbonate hosted replacement deposits of northern mexico and western united states particularly with respect to association with small shallow granitoid complexes structural and stratigraphic controls on mineralization alteration assemblages geometry of orebodies metal association metal zonation and isotopic systematics

arctic north atlantic oscillation signature in holocene sea surface temperature trends as obtained from alkenone data 1 the variability in alkenone derived sea surface temperatures ssts in the north atlantic realm shows that a continuous sst decrease in the northeast atlantic from the early to the late holocene was accompanied by a persistent warming over the western subtropical atlantic the eastern mediterranean sea and the northern red sea based on the analysis of the instrumental data and of atmospheric general circulation model experiments we show that this variation in ssts during the holocene can be attributed to a continuous weakening of a northern hemisphere atmospheric circulation pattern similar to that of the arctic north atlantic oscillation

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

new insights on arctic quaternary climate variability from palaeo records and numerical modelling terrestrial and marine geological archives in the arctic contain information on environmental change through quaternary interglacial glacial cycles the arctic palaeoclimate and its extremes apex scientific network aims to better understand the magnitude and frequency of past arctic climate variability with focus on the extreme versus the normal conditions of the climate system one important motivation for studying the amplitude of past natural environmental changes in the arctic is to better understand the role of this region in a global perspective and provide base line conditions against which to explore potential future changes in arctic climate under scenarios of global warming in this review we identify several areas that are distinct to the present programme and highlight some recent advances presented in this special issue concerning arctic palaeo records and natural variability including spatial and temporal variability of the greenland ice sheet arctic ocean sediment stratigraphy past ice shelves and marginal marine ice sheets and the cenozoic history of arctic ocean sea ice in general and holocene oscillations in sea ice concentrations in particular the combined sea ice data suggest that the seasonal arctic sea ice cover was strongly reduced during most of the early holocene and there appear to have been periods of ice free summers in the central arctic ocean this has important consequences for our understanding of the recent trend of declining sea ice and calls for further research on causal links between arctic climate and sea ice

drivers of declining sea ice in the arctic winter a tale of two seas 1 while the summer perennial arctic sea ice has declined markedly in recent decades the maximum extent of the winter ice cover had decreased only slightly until the past few years when it also receded dramatically this investigation reveals that the timing of maximum extent varies greatly and the drivers of ice edge location differ strikingly between two of the areas where it varies most the bering and barents seas between 1979 and 2005 in the bering sea the ice edge is influenced mainly by anomalies in easterly winds associated with the aleutian low which was particularly strong during the 1980s the barents sea ice edge in contrast is driven primarily by two factors anomalies in sea surface temperature particularly close in time to the maximum extent and by southerly wind from the south anomalies integrated back to mid and early winter the hemispheric mean decline in winter ice extent is due in large part to increasing sea surface temperatures in the barents sea and adjoining waters which are consistent with increased concentrations of greenhouse gases

arctic sea ice cover from the early holocene the role of atmospheric circulation patterns abstract proxy evidence suggests that a mean atmospheric state reminiscent of the positive phase of the north atlantic arctic oscillation nao persisted throughout the early holocene and resulted in a dipole pattern in sea ice concentration between the north eastern and north western north atlantic a dynamic thermodynamic coupled sea ice ocean model is used to simulate the sea ice concentration and thickness in the arctic during the early holocene it is forced with winds ocean currents and surface air temperatures sat from recent years with a positive phase of the nao in conjunction with altered long and shortwave radiation and surface air ocean temperatures the simulation reproduces an east west dipole in sea ice cover of the arctic and is compatible with reconstructed sea ice conditions in the chukchi sea inferred from dinoflagellate cyst analysis of ocean sediment cores sensitivity studies were performed to investigate the individual effects of radiation ocean forcing sat and winds on sea ice cover results show that in the east siberian sea sat is the dominant forcing for changes in sea ice thickness whereas winds and sat are the dominant factors in sea ice concentration anomalies in the barents sea sea ice anomalies are influenced by air and sea surface temperatures and ocean currents

a holocene record of changing arctic ocean ice drift analogous to the effects of the arctic oscillation 1 the arctic oscillation ao controls the configuration of the transpolar drift tpd if thicker ice from the beaufort gyre were exported the volume of fresh water sea ice in the nordic seas would significantly increase decreasing the formation of north atlantic deep water this would cool large parts of the northern hemisphere and affect global climate therefore in order to understand how the global climate system functions it is imperative to know how the tpd changed over the last millennium or more the provenance of grains in a sediment core located near the confluence of the tpd and the beaufort gyre provides a direct proxy for changes in seaice drift owing to these circulation systems the core has more than 200 cm of holocene sediment with intervals dominated by grains from the russian shelves alternating with intervals of abundant grains from north american sources grains matched to russian shelves indicate that the tpd was shifted toward north america similar to what occurs during a more positive phase of the ao this condition alternated with intervals where few grains matched to russian sources presumably because the tpd was restricted to the russian half of the arctic far from the core site during the last 1300 years increased influx of russian grains occurred approximately every 50 150 years this fluctuation might represent the long term oscillation of the ao which modulates the same tpd shift today

tracking the arctic s shrinking ice cover another extreme september minimum in 2004 1 satellite passive microwave observations document an overall downward trend in arctic sea ice extent and area since 1978 while the record minimum observed in september 2002 strongly reinforced this downward trend extreme ice minima were again observed in 2003 and 2004 although having three extreme minimum years in a row is unprecedented in the satellite record attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind temperature and oceanic forcings

one more step toward a warmer arctic this study was motivated by a strong warming signal seen in mooring based and oceanographic survey data collected in 2004 in the eurasian basin of the arctic ocean the source of this and earlier arctic ocean changes lies in interactions between polar and sub polar basins evidence suggests such changes are abrupt or pulse like taking the form of propagating anomalies that can be traced to higher latitudes for example an anomaly found in 2004 in the eastern eurasian basin took 1 5 years to propagate from the norwegian sea to the fram strait region and additional 4 5 5 years to reach the laptev sea slope while the causes of the observed changes will require further investigation our conclusions are consistent with prevailing ideas suggesting the arctic ocean is in transition towards a new warmer state

late mesozoic magmatism of the jiurui mineralization district in the middle lower yangtze river metallogenic belt eastern china precise u pb ages and geodynamic implications abstract the middle lower yangtze river metallogenic belt mlyrmb extending from daye in hubei province in the west to zhenjiang in jiangsu province in the east hosts a number of large polymetallic cu au mo fe zn pb and ag deposits and constitutes one of the most important metallogenic belts in china the cu au mo deposits in the jiurui district are an important component of the mlyrmb in this study we carried out precise and detailed zircon u pb dating for all types of magmatic rocks from the wushan ore deposit in the jiurui district three samples of cu au mo related porphyries from different ore belts at wushan were analyzed and yielded zircon u pb ages of 148 0 1 0 ma 145 4 0 9 ma and 147 3 0 9 ma respectively a series of dykes were emplaced immediately following the cu au mo related porphyries at wushan a dark colored basic dyke which intruded into the granodiorite porphyry at wujia gold deposit near wushan was dated at 144 5 1 2 ma two lamprophyre dykes taken from the north ore belt at wushan underground mining stops were dated at 143 6 0 9 ma and 144 3 0 9 ma respectively a late stage dyke which was also taken from the wushan north ore belt yielded an age of 142 6 1 0 ma and might represent the end of magmatism in the wushan ore deposit these new geochronological data demonstrate that the time range of magmatism in the wushan ore deposit is approximately between 148 ma and 143 ma showing that the magmatic activity at wushan was rapid and intensive the ages of cu au mo related porphyries from other areas in the jiurui district such as the dongleiwan yangjishan and chengmenba ore deposits were also measured and yielded zircon u pb ages of 141 5 1 7 ma 143 4 1 4 ma and 146 6 1 0 ma respectively combined with those previously reported zircon u pb age results from the jiurui district the present age data set demonstrates that extensive magmatism in the jiurui district was coeval and intensive marked by a magmatic activity in the age range of 148 to 138 ma and peaked between 148 ma and 142 ma according to the statistics of all those precise zircon u pb ages the cu au mo related porphyries in the edong and tongling districts in the mlyrmb show similar ages and they have a slightly younger peak age and a longer duration than that of the jiurui district the geographic shape of the mlyrmb in the cretaceous shows an arcuate structure the jiurui district is located at the transitional point of the arcuate structure and the edong and tongling districts are situated on both sides of the arcuate structure considering that the jiurui district has a slightly older peak age and a shorter duration of magmatic activity than that in the edong and tongling districts it seems that the arcuate structure of the mlyrmb played an important role in the formation of these cu au mo related porphyries consequently we suggest that the genesis of the late mesozoic magmatic rocks along the mlyrmb may have been due to a tectonic activity developed from southeast to northwest which probably has a close relationship with the subduction of the paleo pacific plate beneath the eurasian plate in mesozoic times

a data model intercomparison study of arctic sea ice variability the dynamic thermodynamic granular rheology sea ice model of tremblay and mysak is validated against 40 years of observed sea ice concentration sic data subsequently the mechanisms responsible for producing sic anomalies in the model are evaluated by studying the coupled variance using the singular value decomposition method svd between the simulated sic anomalies and the ice speed and air temperature anomalies to execute this validation a 49 year 1949 97 simulation including a 9 year spin up period of the arctic and peripheral sea ice cover using daily varying winds and monthly mean air temperatures is produced in general the simulated sic variations for 1958 97 in the east siberian chukchi and beaufort seas are in agreement with observations while larger discrepancies occur in the laptev and kara seas moreover the sensitivity of the model to southerly wind anomalies in creating summer sic anomalies compares well with the observed sensitivity however the model s sensitivity to summer air temperature anomalies is weaker than observed the summer sic anomalies over an entire sea are not influenced by variations in the level of river runoff results from the svd analysis show that the main source of variability in the peripheral seas is associated with the variation in the strength of the arctic high in the east siberian and laptev seas the strengthening and weakening of the transpolar drift stream also play an important role over the entire arctic domain surface air temperature anomalies are negatively correlated with sea ice anomalies finally the observed downward trend in total sea ice cover in the last two decades as well as record minima in the east siberian sea are well reproduced in the simulation

glacial shortcut of arctic sea ice transport due to the lack of data the extent thickness and drift patterns of sea ice and icebergs in the glacial arctic remains poorly constrained earlier studies are contradictory proposing either a cessation of the marine cryosphere or an ice drift system operating like present day here we examine the marine arctic cryosphere during the last glacial maximum lgm using a high resolution regional ocean sea ice model whereas modern sea ice in the western arctic basin can circulate in the beaufort gyre for decades our model studies present an extreme shortcut of glacial ice drift in more detail our results show a clockwise sea ice drift in the western arctic basin that merges into a direct trans arctic path towards fram strait this is consistent with dated ice plow marks on the seafloor which show the orientation of iceberg drift in this direction also ice transported iron oxide grains deposited in fram strait can be matched by their chemical composition to similar grains found in potential sources from the entire circum arctic the model results indicate that the pattern of arctic sea ice drift during the lgm is established by wind fields and seems to be a general feature of the glacial ocean our model results do not indicate a cessation in ice drift during the lgm