influence of sea ice on the thermohaline circulation in the arctic north atlantic ocean a fully prognostic coupled ocean ice model is used to study the sensitivity of the overturning cell of the arctic north atlantic system to sea ice forcing the strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the arctic to the greenland sea and further to the subpolar gyre the model produces a 2 3 sv increase of the meridional circulation cell at 25n at the simulation year 15 corresponding to a decrease of 800 km in the sea ice export from the arctic previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic implying that sea ice induced variability in the overturning cell can reach 5 6 sv from peak to peak

the shallow plumbing system of rabaul caldera a partially intruded ring fault the floor of rabaul caldera experiences complex deformation as revealed both in the geological and historical record as well as through recent systematic monitoring the observed deformation pattern has been modelled previously as being caused by tumescent strain above one or more point sources at shallow levels within the caldera block or as a response of the caldera structure to deeper sources of deformation here two dimensional finite element modelling is used to re interpret the pre 1994 eruption deformation data demonstrating that the observed pattern may have been caused by dykes located in sectors of the ring fault system as delimited by seismicity both a pressurised ring structure and a pair of arcuate sources are modelled maximum compressional stress results in a central position within the encompassed block and a moat like feature forms offset outwards from the intersection of the azimuth of the modelled deformation sources and the free surface the modelled deformation generally fits well with the observed movements that the shallow ring dyke appears not to be complete existing as two discrete arcuate dykes helps to explain observed changes in the indicated tilt directions through time changing areas of relative down warping offset outwards from the seismically active ring structure and north south oriented structural up doming south of matupit the distribution of thermal anomalies and the lack of evidence for shallow central caldera intrusions can also be explained by this scenario associated normal faulting above these dykes and or the stress regime generated by simultaneous intrusions into opposite sides of the ring fault are proposed to explain the apparent inward dip of the intrusions at very shallow levels leading to the eruptive sites being offset outwards from the seismic zone a conceptual model is proposed to try to explain the general behaviour of the caldera between 1971 and the eruption of 1994

influence of tidal effects on the periodicity of earthquake activity in diverse geological settings with particular emphasis on submarine hydrothermal systems abstract hydrothermal earthquakes may be defined as earthquakes caused by the hydrofracturing of the oceanic crust by submarine hydrothermal fluids it is suggested that they correspond to the cracking of the ocean crust at the brittle ductile transition that marks the downward limit of seawater circulation into the ocean crust semi diurnal variations in submarine hydrothermal discharge in backarc settings and at the crests of mid ocean ridges have been detected by hydrophone but no influence of tidal effects on the periodicity of microearthquakes around submarine hydrothermal vents has been observed so far although tidal stresses are too small to initiate earthquakes themselves they may trigger earthquake activity when imposed on slowly increasing tectonic stress these effects therefore tend to be observed in geologically active regions where stress levels in the earth s crust are high the influence of tides on the periodicity of microearthquakes tends to be complex because the effects of ocean and earth tides are not uniform at the surface of the earth and because the microearthquakes occur in a wide variety of geological settings earth tides cause compression and dilatation of the oceanic crust which may be the most significant factor in initiating changes in fluid flow rate and microseismicity in submarine hydrothermal systems much of the information now available on the tidal periodicity of microearthquakes is based on relatively short term monitoring which lacks statistical validity the development and installation of deep sea monitoring stations will permit rigorous long term monitoring programmes to be carried out which will lead to a better understanding of the nature and periodicity of microearthquakes around submarine hydrothermal vents

upper ocean variability between iceland and newfoundland 1993 1998 we investigate the variability of upper ocean temperature and surface salinity between iceland and newfoundland along world ocean circulation experiment line ax2 in 1993 1998 north of 54 n as well as close to newfoundland deviations from the seasonal cycle indicate upper ocean warming from 1994 to 1998 with largest anomalous warming during late 1995 early 1996 and during the winter 1997 1998 north of 54 n surface salinity increases after mid 1996 the winter of 1995 1996 is the first winter of weak westerlies after more than 20 years of strong westerly conditions in the subarctic gyre and the ocean loses less heat during that winter than during a normal year the magnitude of upper ocean heat content change is at least twice as large as what results from the change in air sea fluxes which indicates a complementary contribution to heat content change by advection altimetric sea level data indicate also an increase of sea level of the order of 6 5 cm during that year out of which more than 4 cm is contributed by the steric change associated with the temperature increase a principal component analysis of the sea level data suggests that the increase sensed along line ax2 west of the reykjanes ridge is found in most of the subpolar gyre although to a lesser extent in most other areas

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

a remarkable pulse of large scale volcanism on new britain island papua new guinea new studies of the deposits from the latest caldera forming eruption the dk event at dakataua volcano new britain island papua new guinea help identify an intense space time concentration of large scale volcanism during the 7th century ad on new britain radiocarbon dating of charcoal from the dk deposits yields an age of 1 383 28 bp calibration of this result gives an age in the range ad 635 670 at 1 s d at about the same time two other volcanoes on new britain rabaul and witori also produced very large eruptions very high acidity levels in ice cores from antarctica and greenland at ad 639 and ad 640 respectively may be linked to either or both of the dakataua and rabaul eruptions another ice core high acidity level at ad 692 may be associated with the witori eruption significant volcanic risk within the new britain region is indicated by its late cenozoic history of relatively frequent large scale eruptions from as many as 8 caldera systems within an arc parallel zone about 380 km long over the last 20 ka the return period for major vei 5 eruptions in this region was about 1 0 ka and individually high frequencies of major eruptive activity were experienced at witori and rabaul the relatively short return period for major eruptions in the region would tend to increase the chance that such events could cluster in time

towards radiocarbon calibration beyond 28 ka using speleothems from the bahamas we present a new speleothem record of atmospheric 14c between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period the record is based on a comprehensive suite of ams 14c ages using new low blank protocols and u th ages using high precision mc icpms procedures atmospheric 14c was calculated by correcting 14c ages with a constant dead carbon fraction dcf of 22 7 5 9 based on a comparison of stalagmite 14c ages with the intcal04 reimer et al 2004 calibration curve between 15 and 11 ka the new 14c speleothem record shows similar structure and amplitude to that derived from cariaco basin foraminifera hughen et al 2004 2006 and the match is further improved if the latter is tied to the most recent greenland ice core chronology svensson et al 2008 these data are however in conflict with a previously published 14c data set for a stalagmite record from the bahamas gb 89 24 1 beck et al 2001 which likely suffered from 14c analytical blank subtraction issues in the older part of the record the new bahamas speleothem 14c data do not show the extreme shifts between 44 and 40 ka reported in the previous study beck et al 2001 causes for the observed structure in derived atmospheric 14c variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity data model comparison indicates that major fluctuations in atmospheric 14c during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity although ocean atmosphere system reorganisation also played a supporting role

quasi decadal salinity fluctuations in the labrador sea abstract the quasi decadal salinity fluctuations in the upper 300 m of the labrador sea are investigated by partitioning all available salinity station data since 1948 by region and bottom depth there are major freshwater anomalies in the early 1970s the great salinity anomaly mid 1980s and early 1990s these vary in amplitude throughout the region being least on the shelf and greatest over the slope region near the labrador current the labrador sea cannot be considered a simple conduit for freshwater anomalies originating in the east greenland current there is evidence that local processes modulate the anomaly the freshwater anomalies in the labrador current are approximately twice as large as those in the east greenland current the baffin island current flowing southward through the western davis strait is the only local source of freshwater with sufficient volume to account for this increase the propagation speed 2 3 cm s 1 of the anomaly along the labrador sea margin is much less than the

a high resolution record of holocene climate change in speleothem calcite from cold water cave northeast iowa high precision uranium thorium mass spectrometric chronology and 18o 13c isotopic analysis of speleothem calcite from cold water cave in northeast iowa have been used to chart mid holocene climate change significant shifts in 18o and 13c isotopic values coincide with well documented holocene vegetation changes temperature estimates based on 18o 16o ratios suggest that the climate warmed rapidly by about 3 c at 5900 years before present and then cooled by 4 c at 3600 years before present initiation of a gradual increase in 13c at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present

multi and quasi decadal variations of sea surface temperature in the north atlantic abstract the multi and quasi decadal variabilities of the sea surface temperature sst anomaly over the north atlantic are investigated by means of two dimensional propagating ceof forty six years of the coads sst dataset from 1947 to 1992 are used after removing the monthly climatology and four year low pass filtering the sst anomaly is submitted to ceof the total variance of the three largest modes accounts for 87 0 of the total variance mode 1 is a very slow oscillation with an approximate 42 yr period and has basinwide spatial evolution with alternate warm and cold anomalies appearing off newfoundland and migrating northward until they disappear south of greenland the center of action of the anomalies both occur in the vicinity of the labrador sea newfoundland and south of greenland where deep water formation takes place mode 2 3 is a quasi decadal fluctuation with an approximate 14 yr period mode 2 3 contains quasi decadal timescales with alternating warm and cold anomalies propagati

sequences and clusterings of significant volcanic eruptions in convergent plate margins during 1900 1980 abstract magmatic eruptions which lasted at least 15 days and had a volcanic explosivity index 1 are defined as significant volcanic eruptions data concerning significant eruptions which occurred from 1900 to 1980 show that in seventeen regions of plate convergence which were examined there is a similar time evolution pattern of the volcanism namely periods of frequent volcanic activity with significant eruptions in at least one volcano usually lasting less than 15 years alternating with intervals of quiescence lasting from 4 5 to 20 years empirical criteria have been applied to classify ordinary periods sequences and clusterings of significant eruptions taking into account the date of the first eruption on all the volcanoes of a given period of frequent volcanic activity then in seven sequences or clusterings occurring in several regions one may observe a systematic migration of the volcanism along the arc e g in lesser sunda banda sea islands during 1963 1974 a clear positive correlation between the delay time of the eruptions and the distance of the corresponding volcanoes from the first erupted volcano has been found it is suggested that large scale long term physical processes in the earth s interior may be responsible for the volcanic activity volcanic quiescence pattern in plate convergence regions

the δ18o and δ13c records in an aragonite stalagmite from furong cave chongqing china a 2000 year record of monsoonal climate abstract a 7 cm long aragonite stalagmite fr0510 1 from furong cave chongqing was dated by 210pb and 230th methods revealing a 2000 year record of climate history under the influence of the east asian monsoon the fr0510 1 record resembles dongge cave da record on 10 100 year scales but quite different from the wanxiang cave wx42b record indicating that while stalagmite 18o record represents local regional moisture change spatial variability of the monsoonal rainfall over eastern china must take into account during the past 2000 years climate in chongqing was relatively wet in the intervals of 50 bc ad 250 ad 1150 1450 and ad 1600 1950 and relatively dry during the periods of ad 250 1150 and ad 1450 1600 dry conditions were prevailing over the medieval warm period whereas wet climates were dominant during the most time of the little ice age in chongqing area

ams 14c dating of the hominin archaeological site chuandong cave in guizhou province southwestern china abstract this study presents detailed ams 14c dating of charcoals burned and unburned bones and teeth from the hominin archaeological site chuandong cave located in puding county guizhou province southwestern china the charcoal samples were pretreated with either the acid base acid aba or orau xr method the unburned bone and teeth samples with aba collagen pretreatment and the burned bone samples with the orau cb method the ams 14c ages of the charcoal samples provide the most reliable results in this study the ams 14c dates of the bone samples are generally younger possibly due to posterior amino acid contamination based on the ams 14c ages we propose the following chronology for the site layers 3 to 5 formed between 11 5 12 5 ka bp all 14c ages reported in this study are calibrated ages unless stated otherwise a bp years before 1950 ce a period corresponding to the younger dryas layers 6 to 7 formed between 14 24 ka bp a period including the last glacial maximum lgm and layers 8 9 likely formed before 34 ka bp corresponding to the late pleistocene according to the above chronology the chuandong humans modern homo sapiens were present at 12 ka bp i e the late pleistocene this conclusion differs from the previous estimate at 9 ka bp i e the early holocene furthermore the chuandong culture likely began as early as 34 ka bp and survived in the region throughout the cold and dry lgm detailed studies on the hominin archaeological sites in guizhou including chuandong cave and maomaodong cave are warranted to better understand hominin evolution in asia

the timing of caldera collapse at mount katmai in response to magma withdrawal toward novarupta several thin layers of nonjuvenile lithic rich tephra from mount katmai are intercalated with 1912 plinian pumice fall deposits that originated at novarupta 10 km away demonstrating that caldera collapse at katmai and eruption at novarupta were synchronous emplaced by phreatic explosions and avalanche generated dustclouds each katmai derived layer is thickest and coarsest at the caldera rim and pinches out within 5 8 km in contrast thicknesses and clast sizes of plinian layers a g decrease radially away from novarupta the first katmai derived layer lies between novarupta derived layers b2 and b3 indicating that collapse began after release of 6 9 km of magma at novarupta the first major earthquake ms 6 5 at 2356 h on 6 june 11 hours after the eruption began may have marked the onset of collapse the katmai river landslide and several debris flow deposits are also sandwiched within the plinian deposits indicating that they too were emplaced during the eruption

high precision and high resolution carbonate 230th dating by mc icp ms with sem protocols abstract to facilitate the measurement of u th isotopic compositions suitable for high precision and high resolution 230th dating of coral and speleothem carbonates secondary electron multiplier sem protocol techniques for multicollector inductively coupled plasma mass spectrometry mc icp ms have been developed the instrumental sensitivities are 1 2 with a precision of 1 2 2 for abundance determination of 50 200 fg 234u 1 4 ng 238u or 230th this method features chemistry refinements improvements to procedural and instrumental blanks spectral inference reductions and careful consideration of non linear sem behavior measurement consistency of this mc icp ms combined with previous mass spectrometric results on u th standards and a variety of carbonates demonstrates the validity of the sem protocol method for fossil corals a routine u th isotopic determination at permil level precision requires only 10 50 mg of carbonate as little as 200 mg of young coral with an age of less than 20 yr can be dated with a precision of 0 3 0 8 yr about 20 200 mg speleothem samples with sub ppm to ppm u are required to earn a 5 precision on ages from 5 to 100 kyr requirement of small sample size 10 100s mg carbonate can permit high temporal resolution to date speleothems with slow growth rates i e 1 10 mm kyr this high precision 230th chronology is critical to accurately establish age models date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography the u th isotopic determination techniques described here can also be applied to different environmental samples such as waters rocks and sediments

anomalous stress diffusion in earthquake triggering correlation length time dependence and directionality 1 it has been recently suggested that moderate and large earthquakes can be triggered by similarly sized events at very long range here we study the main characteristics of earthquake triggering by determining its correlation length time dependence and directionality the problem is examined at a global level by using the harvard centroid moment tensor catalogue our results show that the correlation lengths depend only weakly on the magnitude thresholds involved no significant systematic triggering is observed for distances greater than the lithospheric thickness 100 150 km and the correlation length magnitude is similar to the seismogenic thickness 10 20 km the mean triggering distance and correlation length both increase with time very slowly compared with what would be expected from a normal diffusion process this is consistent with a clock advance on the failure time based on the constitutive rules for subcritical crack growth following a transient change in the loading stress the power law scaling disappears after a few months a functional form for the probability of triggering as a function of time and distance is proposed on the basis of the properties of near critical point systems the model fits the data well and could be used to calculate conditional probabilities for time dependent seismic hazard due to earthquake triggering an apparent directionality effect that was observed in the data set can be attributed to an artefact of poor depth determination these results do not preclude individual long range triggering with a potential directionality effect but they do rule out a statistical correlation at distances much greater than the thickness of the lithosphere

topographic preconditioning of open ocean deep convection abstract evidence for oceanic convection over maud rise in the weddell sea suggests that bottom topography may select the location and scale of deep convecting oceanic chimneys forced by seasonal large scale atmospheric cooling in this paper the role of bottom topography in open mean deep convection is studied using an idealized three dimensional primitive equation model a barotropic mean flow impinges on a gaussian shaped seamount in a stratified domain generating a taylor cap a region of topographically trapped fluid uniform surface cooling is applied throughout the domain when the taylor cap is tall enough to interact with the surface mixed layer the local isolation from the advection of heat by the mean flow forms a conduit into the deep water convection within this region is significantly enhanced relative to ambient levels away from the seamount and to similar numerical simulations performed without bottom topography given uniform background stratification domed isopycnals are not importa

subsurface quasi decadal fluctuations in the north atlantic abstract analysis of hydrographic time series data at ocean station 5 panulirus and along the labrador continental margin is used to investigate the subsurface structure associated with the north atlantic quasi decadal sst fluctuation quasi decadal fluctuations of both temperature and salinity are confined to the upper water column that is ventilated by the seasonal cycle in the subtropical gyre they are independent of the variations of the gyre baroclinic transport on the labrador continental margin the quasi decadal fluctuations are confined to the upper portion of the labrador current the quasi decadal fluctuation appears to be surface forced in the subtropical gyre this is predominantly by latent heat flux in the subpolar gyre latent and sensible heat flux alone cannot account for the in phase variation of temperature and salinity instead the variation involves upper ocean convective mixing whose strength is modulated by the density of the winter cooled surface water it has been noted t

triggering of volcanic eruptions although earthquakes and volcanic eruptions are each manifestations of large scale tectonic plate and mantle motions it is usually thought that the occurrences of these events are not directly related there have been some studies however in which triggering of volcanic eruptions by earthquakes remote from the volcano has been proposed1 2 the 1992 landers southern california earthquake caused triggered seismicity at very large distances3 including the magmatically active4 long valley caldera region which also experienced a significant coincident deformation transient5 motivated by this demonstration of the ability of a distant earthquake to disturb a volcanic system and the earlier studies of specific cases of eruption triggering we examine here the historical record of eruptions and earthquakes to see if there are indeed significantly more eruptions immediately following large earthquakes we find that within a day or two of large earthquakes there are many more eruptions within a range of 750 km than would otherwise be expected additionally it is well known6 that volcanoes separated by hundreds of kilometres frequently erupt in unison the characteristics of such eruption pairs are also consistent with the hypothesis that the second eruption is triggered by earthquakes associated with the first

mechanisms behind the temporary shutdown of deep convection in the labrador sea lessons from the great salinity anomaly years 1968 71 abstractfrom 1969 to 1971 convection in the labrador sea shut down thus interrupting the formation of the intermediate dense water masses the shutdown has been attributed to the surface freshening induced by the great salinity anomaly gsa a freshwater anomaly in the subpolar north atlantic the abrupt resumption of convection in 1972 in contrast is attributed to the extreme atmospheric forcing of that winter here oceanic and atmospheric data collected in the labrador sea at ocean weather station bravo and a one dimensional mixed layer model are used to examine the causes of the shutdown and resumption of convection in detail these results highlight the tight coupling of the ocean and atmosphere in convection regions and the need to resolve both components to correctly represent convective processes in the ocean they are also relevant to present day conditions given the increased ice melt in the arctic ocean and from the greenland ice sheet the analysis herein shows that the shutdown was initiat

representation of convective plumes by vertical adjustment open ocean deep water formation involves the interplay of two dynamical processes plumes 1 km wide driven by upright convection and geostrophic eddies 5 km wide driven by baroclinic instability numerical twin experiments are used to address two questions about the plumes can they be represented by a simple mixing process in large scale models if so is it important that the mixing occurs over a finite time tmix or would instantaneous mixing produce the same effect on large scale properties in numerical simulations which resolve the geostrophic eddies we represent the plumes with a slow convective adjustment algorithm which is broadly equivalent to an enhanced vertical diffusivity of density in statically unstable regions the diffusivity depends on tmix the mixing timescale the fidelity of the plume parameterization is then evaluated by comparison with plume resolving simulations of open ocean deep convection integral properties of the plumes such as the temperature census of the convected water and the strength of the rim current that encircles the convecting region are all accurately reproduced by the slow adjustment scheme the importance of choosing an appropriate finite value for tmix is explored by setting tmix 12 hours in some experiments in accordance with scaling considerations and tmix 0 in others corresponding to instantaneous adjustment the conventional assumption in the case of convection into a moderately or strongly stratified ocean the behavior does not significantly depend on tmix however in neutral conditions the slow adjustment does improve the parametric representation our experiments confirm the picture of plumes homogenizing the water column over a time tmix

variability of the simulated meridional heat transport in the north atlantic for the period 1951 1993 a 43 year ocean model simulation for the period 1951 1993 is analyzed with a focus on the meridional heat transport mht as a proxy for the strength of meridional overturning cell moc at 25 n the surface heat flux forcing associated with the north atlantic oscillation nao pattern is related to the variability in mht both on interannual and longer timescales the manifestation of the interannual and decadal oceanic response to nao is nonlocal as evidenced by the concentrated heat content and sea level variability at the gulf stream and north atlantic current regions and shown by the comparison of the model sea level variability to the altimeter data between low mht years in mid 1980s and high mht years in early 1990s the same area is singled out by empirical orthogonal function analysis in the leading mode of the sea level mht and time series of the leading sea level mode are highly correlated which reflects the importance of the moc in determining the variability of the heat content of the whole basin also the model suggests that the mht moc has entered a very strong phase since the mid 1980s and this trend has continued up to the end of 1993 this behavior follows the general trend in the nao index

preservation of13c 12c original ratio and14c dating of the mineral fraction of human bones from saharan tombs niger abstract the remains of 40 skeletons from the necropolises of iwelen and adrar bous situated in the massif of air southern sahara niger have been investigated for their mineral content carbon isotope ratio and 14 c activity the impermeability of the graves allowed for a good preservation of the bones which are in fact devoid of secondary calcite furthermore the necropolis of iwelen gave the opportunity to study tombs which cover a time interval of about four thousand years which is rather exceptional for sub saharan africa the good state of preservation of the material enabled the study of the geochemical evolution of bone carbonate hydroxylapatite through time with a significant statistical resolution all analytical data allow us to conclude that the initial 13 c 12 c isotopic ratio of the carbonate hydroxylapatite albeit accompanied by a change in the crystallinity index has been preserved given the described local conditions the increase in the crystallinity index cannot be linked to exchanges with the environment but clearly reflects the decrease of co 3 radicals in the bone material a correlation is suggested between the crystallinity index and the residual content of organic matter the 14 c dates obtained for the carbonate hydroxylapatite are identical to those of the material of comparison leather charcoal and associated collagen samples we can therefore conclude that the potential carbon isotopic exchanges either by adsorption of by substitution between the carbonate hydroxylapatite on the one hand and the total dissolved inorganic carbon tdic on the other are too insignificant to be detectable through analysis these results can be explained by the combining of two favourable factors the waterproof nature of the graves and the arid climate the dating of carbonate hydroxylapatite in the restricted conditions already described opens new prospects for establishing a chronology of the principal funerary monuments of the sahara

the seasonality of convective events in the labrador sea abstractmodeling deep convection is a key challenge for climate science here two simulations of the labrador sea circulation obtained with the regional ocean modeling system roms run at a horizontal resolution of 7 5 km are used to characterize the response of convection to atmospheric forcing and its seasonal variability over the period 1980 2009 the integrations compare well with the sparse observations available the modeled convection varies in three key aspects over the 30 years considered first its magnitude changes greatly at decadal scales this aspect is supported by the in situ observations second the initiation and peak of convection i e initiation and maximum shift by 2 3 weeks between strong and weak convective years third the duration of convection varies by approximately one month between strong and weak years the last two changes are associated with the variability of the time integrated surface heat fluxes over the labrador sea during winter and spring while the first resu

δ18o δ13c elemental content and depositional features of a stalagmite from yelang cave reflecting climate and vegetation changes since late pleistocene in central guizhou china abstract a 13 5 cm long stalagmite from yelang cave in central guizhou provides another example of ams 14 c dating on stalagmites which are not suitable for 230 th u dating due to very low u content and low 230 th 232 th ratio this record duplicates the published stalagmite record of 20120824 13 from the same cave zhao et al 2015 not only on 18 o and 13 c records but also on major growth hiatuses facilitating speleothem 18 o and 13 c as climate and vegetation proxies respectively based on the two stalagmite records climate and vegetation conditions can be deciphered as follow relatively cool and dry climates with c4 dominated plants during 33 4 36 ka very cold and dry climates with poor vegetation coverage during the last glacial maximum cold and dry climates with poor vegetation during younger dryas warming and very wet climates with the best vegetation mainly c3 plants coverage during 9 11 5 ka bp corresponding to a maximum insolation drying climate and decreased vegetation intensity from 9 ka to 8 ka relatively good vegetation coverage during 5 6 ka the summer monsoon strength decreased from 5 ka to 1 5 ka bp but increased during the medieval warm period to produce wet climates and abundant vegetation and strongly decadal variations in moisture budget and strong deforestation due to human impact during the past 600 years high fe mn and al contents from detritus caused dark bands near the hiatuses strong positive correlation of mg and sr with high mg sr values 23 in this study reflects source control on the mg and sr variations so that mg sr is not a function of cave temperature in such a case for pure calcite without detrital influence mg sr may register changes in cave temperature with higher mg sr indicating warmer temperature this study calls for the attention to find out climatic conditions in central guizhou during the bolling allerod warming and the middle holocene 6 8 ka intervals because of lacking deposition during these intervals in yelang cave using stalagmite 18 o alone to decipher climatic conditions on decadal to millennial scales needs to consider multiple factors such as amount source and temperature effects on the 18 o

multiyear variability in the near surface temperature structure of the midlatitude western north atlantic ocean between 1966 and 1995 subsurface temperature data have been collected in the western north atlantic ocean using expendable bathythermographs data coverage is sparse in both time and space but evidence for decadal variability in the upper 400 m of the water column is found the data were averaged by month onto a 2 of latitude by 4 of longitude grid thirty one quadrangles in the region bounded by 17 n and 43 n and 78 w and 66 w have sufficient data to provide consistent results anomaly time series at 0 100 200 300 and 400 m were estimated by subtracting a mean monthly climatology the individual records were detrended and filtered to highlight the longer period signals the analysis resulted in 25 year records 1969 1993 for study within the thermocline of the subtropical gyre and the gulf stream at 100 and 200 m periods of predominately positive temperature anomaly end in 1971 1982 and 1990 while periods of negative anomaly end in 1976 and 1985 only the events ending in 1971 1976 and 1990 are in the majority of the records at 300 and 400 m most of the events also appear in the sea surface temperature sst records but are somewhat masked by significant noise at the surface meridional vertical temperature sections through the subtropical gyre show that transitions from negative to positive anomaly events are characterized by a deepening of the isotherms throughout the section and transitions from positive to negative events by a rising of the isotherms significant lateral migration of the axis of the gulf stream although possibly masked by the 2 averaging is not necessary to explain either type of event the transitions in the sst and 100 m temperature time series occur at essentially the same time as the transitions in an index of the north atlantic oscillation nao that has also been detrended i e 1971 1976 1980 1984 1988 the 1971 1976 and 1988 nao events are also observed at 300 and 400 m as described earlier periods of positive subsurface temperature anomaly are coincidental with periods of positive nao index and periods of negative subsurface temperature anomaly are coincidental with periods of negative nao index thus earlier results showing connections between the nao and western atlantic sst at decadal timescales are now extended to at least 400 m in the water column trends were computed from the individual 25 year records the trends at all depths are predominately negative north of 38 n and positive south of 38 n inferences from the horizontal distribution of the trends and results from earlier studies suggest that the 1969 1993 period may be a phase of a 30 to 50 year signal observed in the northern atlantic since the beginning of the century

convective activity in the labrador sea preconditioning associated with decadal variability in subsurface ocean stratification 1 the decadal variability of the convective activity in the labrador sea is investigated using 43 years of model output from a prognostic coupled ice ocean model that simulates both the arctic and the north atlantic oceans the fields of the surface density and the mixed layer depth indicate that the center of the convective activity is located in western labrador sea the decadal variations of the convective depth are controlled to large extent by the oceanic preconditioning associated with changes in subsurface stratification the intensity of the convective mixing varies from year to year depending upon how strong the isopycnal doming is at the preconditioning stage at the center of the convective region the variations of the subsurface stratification seem to be related to the subsurface temperature changes

the formation of labrador sea water part ii mesoscale and smaller scale processes abstract in a previous paper clarke and gascard argued that the formation of labrador sea water was taking place in a cyclonic gyre set up each winter in the western labrador sea within the gyre and at its boundaries a number of different scales of organization are believed to be important in the formation processes the longest of these scales is the mesoscale 50 km which appears to be related to topographic rossby waves generated in the labrador current and propagating offshore the next smaller scale is an eddy scale 20 km believed to arise because the mesoscale is baroclinically unstable as shown by applying a two layer model of tang this instability is believed to promote mixing by generating frontal structures and vertical motions along them thus bringing subsurface t s maxima nearer the surface then within the mesoscale and eddy scale structures intense vertical convective cells take place at scales which are probably of the order of 1 km in three dimensions these events are short liv

comparisons of localized convection due to localized forcing and to preconditioning although observations indicate that localization of deep convection results from oceanic preconditioning and only to a lesser extent from the gradients in the atmospheric forcing most laboratory and numerical simulations of oceanic deep convection localize convection via the buoyancy forcing it is as yet unclear to what extent the localized forcing simplification is representative of realistic preconditioned convection and whether conclusions drawn from analyzing the former scenario can be applied to the latter comparison between these two localized convection scenarios is the focus of this study the analysis is conducted using a high resolution nonhydrostatic numerical model that assumes no variations in the latitudinal direction although this model cannot represent baroclinic instability it represents well the violent mixing phase of chimney formation that precedes baroclinic instability because of the inherently different initial and boundary conditions there is no single comparison to be made between the two scenarios all of the comparisons however show that a localized forcing tends to enhance the frontal structures at the edge of the convected water mass the authors explain these results by means of some simple analytical calculations that indicate that convection as a result of a localized forcing induces a continuous increase in the horizontal density gradient while convection in a surface intensified cyclonic gyre results in a decrease in the horizontal gradient the authors conclude that the two scenarios are not equivalent and discuss how some of the conclusions valid for localized forcing do not necessarily apply to the preconditioned scenario in particular the equilibrium state observed in localized forcing simulations in which the lateral fluxes due to the baroclinic eddies balance the surface buoyancy loss may not have an analog for the case of preconditioned convection

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

hydrography of the labrador sea during active convection the hydrographic structure of the labrador sea during wintertime convection is described the cruise part of the deep convection experiment took place in february march 1997 amidst an extended period of strong forcing in an otherwise moderate winter because the water column was preconditioned by previous strong winters the limited forcing was enough to cause convection to approximately 1500 m the change in heat storage along a transbasin section relative to an occupation done the previous october gives an average heat loss that is consistent with calibrated national centers for environmental prediction surface heat fluxes over that time period 200 wm 22 deep overturning was observed both seaward of the western continental slope which was expected as well as within the western boundary current itself something that had not been directly observed previously these two geographical regions separated by roughly the 3000 m isobath produce separate water mass products the offshore water mass is the familiar cold fresh dense classical labrador sea water lsw the boundary current water mass is a somewhat warmer saltier lighter vintage of classical lsw though in the far field it would be difficult to distinguish these products the offshore product was formed within the cyclonic recirculating gyre measured by lavender et al in a region that is limited to the north most likely by an eddy flux of buoyant water from the eastern boundary current the velocity measurements taken during the cruise provide a transport estimate of the boundary current throughput and offshore recirculation finally the overall trends in stratification of the observed mixed layers are described

changes in climate and vegetation of central guizhou in southwest china since the last glacial reflected by stalagmite records from yelang cave abstract two stalagmites 6 cm and 18 cm long from yelang cave 26 2 28 n 105 44 11 e in central guizhou of china have been dated by icp ms 230th u 210pb and ams 14c dating methods low u but high th contents in the young stalagmites were difficult to apply 230th u dating instead ams 14c dating solved the chronological problem of these stalagmites both stalagmites had fast growth rates during holocene optimum and the last 600 years but absent growth between 4 and 8 ka the 18o record of stalagmite 20120824 13 agrees well with the dongge 18o records on centennial or longer scales showing dry climates during the last glacial maximum lgm and younger dryas and wet climates during holocene optimum following the solar insolation trend the summer monsoon strength decreased from 4 12 ka to 1 5 ka but increased during the medieval warm period to produce wet climates and abundant vegetation in the study area the 18o record during the last 600 years exhibits strongly decadal variations twelve light 18o excursions on decadal scales during the last 600 years can be identified agreeing with the local dry wet index record the pacific decadal oscillation pdo strongly affects decadal variability of the moisture budget in the study area with cold pdo la nina condition in favor of stronger easm and wet climates the 13c record indicates that natural vegetation in the study area was strongly destroyed by human activity after the reign of emperor yong zheng ad 1722 1735 of qing dynasty since then the karst desertification in central guizhou has been strongly developed due to rapidly increased population and land use

hominin distribution and density patterns in pleistocene china climatic influences abstract at the broad early middle late pleistocene level the chinese hominin fossil site distribution data may inform on hominin mobility behavioral interaction strategies hominins during the early pleistocene and well into the middle pleistocene appear to be more restricted to central and southern china by the advent of the late middle pleistocene hominins are found regularly in northern china and by the late pleistocene hominin fossils are found in all latitudes and longitudes encompassing modern day china and beginning some time during marine isotope stage 3 appear in higher altitudinal regions e g qinghai tibetan plateau as well during the middle pleistocene a number of sites are found well away from major riverways suggesting an ability to transport potable water or perhaps an ability to be able to locate smaller bodies of fresh water given the paucity of evidence for storage containers until relatively recently in time it is perhaps not that surprising that many of the middle pleistocene open air sites are reportedly found in or near lacustrine environments hominins had a more restricted range due to climatic variation during the early and early middle pleistocene but were able to more successfully adapt to changing climes beginning during the late middle pleistocene in part this is due to a range of behavioral changes that hominins developed during the pleistocene

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

on the space time distribution of major explosive volcanic eruptions on earth 1 explosive volcanic activity on earth is typically discontinuous in space and time the occurrence of spatial temporal eruption clusters due to mutual cause and effect relationships or external triggers e g tectonic and or tidal forcing is still debated to detect possible clustering of major explosive eruptions we test the distribution of eruptions with volcanic explosivity index vei 4 from 1750 to present the 143 documented vei 4 events display a markedly non uniform frequency distribution with the highest relative probability of eruption recurrence within 500 km distance from the preceding event the analogous frequency pattern obtained from randomized data series of the same catalogue suggests that the observed eruption pattern is primarily imparted by the geodynamic distribution of volcanoes mostly located along tectonically active linear belts with no evidence of mutual or external influence our results highlight a counter intuitive array of major eruption loci as a consequence of the intrinsic worldwide asymmetry of explosive volcanism with implications on hazard assessment

climatic fluctuations during the lia and post lia in the kumaun lesser himalaya india evidence from a 400 y old stalagmite record this paper presents the first stable isotope delta o 18 and delta c 13 data of a similar to 400 years 1590 2006 ad long annual to decadal resolution speleothem record collected from the indian lesser himalaya the data show a variation from 2 7 to 5 9 parts per thousand in delta o 18 and 5 3 to 8 8 parts per thousand in delta c 13 the isotopic analyses indicate that the climate during this period can be divided into two stages a wet phase during the little ice age lia 1590 1850 ad and comparatively dry phase during the post lia after 1850 ad however the record also documents the minor dry events during the lia and a wet episode after the lia within the age uncertainty the dry spells during the lia are linked with the historical drought events in the indian subcontinent and similar latitudes the isotopic record is consistent with a number of previous studies in the areas influenced by the westerlies but appears to be conflicting to the regions dominated by the indian summer monsoon ism this may be due to the possible changes in the strength of westerlies in the study area and added by negative anomaly of north atlantic oscillation nao during the lia c 2012 elsevier ltd and inqua all rights reserved

decadal variability of hydrography in the upper northern north atlantic in 1948 1990 we investigate the variability of the north atlantic subarctic gyre in recent decades from time series of station temperature and salinity decadal variability stronger at the surface is identified which exhibits vertical coherence over a layer deeper than the late winter mixed layer in the northwestern atlantic it corresponds to the layer with a component of water from the arctic ocean or from the canadian arctic the spatial coherence of the signal is investigated an empirical orthogonal function decomposition of lagged time series indicates that a single pattern explains 70 of the variance in upper ocean salt content corresponding to a propagating signal from the west to the northeast in the subarctic gyre the most likely interpretation is that the salinity signal originates in the slope currents of the labrador sea and is diffused advected eastward of the grand banks over the near western atlantic in the northwestern atlantic temperature fluctuations are strongly correlated to salinity fluctuations and are aligned along the average t s characteristics this signal suggests large variations in the outflow of fresh cold water in the slope current and is strongly correlated with ice cover a basin scale atmospheric circulation of weakened westerlies at 55 n weaker northwesterlies west of greenland and weaker southerlies over the central and eastern north atlantic is associated with the high salinity and warm water phase of the first principal component this circulation pattern leads fluctuations in the northeast atlantic and lags those in the northwestern part of the basin the wind indices also suggest that the fluctuations of the fresh water outflow occur during intervals of anomalously northerly winds either east of greenland 1965 1968 1969 or off the canadian archipelago 1983 1984

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

east asian summer monsoon variations in the past 12 5 ka high resolution delta o 18 record from a precisely dated aragonite stalagmite in central china due to possible aragonite to calcite transformation resulting in alteration in isotopic signatures and a bias in age dating aragonite speleothems are often excluded from paleoclimatic archives however aragonite stalagmites contain ppm level uranium content making them much easier to date achieving higher age dating precisions than calcite stalagmites in this regard provided aragonite to calcite transformation did not occur aragonite stalagmites are potentially well suited for holocene climate research given their climate proxies can be placed into a better constrained chronological framework in this paper we present high precision u th dates and o isotopic time series for a 82 cm long continuous growth aragonite stalagmite lh2 from lianhua cave hunan province china and discuss east asian summer monsoon easm variability for the last 12 5 ka bp before present the u th dated delta o 18 sequence with a mean 16 year resolution and the growth rate pattern of lh2 show that easm experienced a strengthening stage a strong stage and a weakening stage during the last 12 5 ka during the yd 12 5 11 5 ka bp heavy delta o 18 values and low growth rate indicate a weak monsoon period during the preboreal from similar to 11 5 to 10 6 ka bp delta o 18 values decreased dramatically similar to 1 94 parts per thousand reflecting abrupt strengthening of the monsoon from 10 6 to 4 2 ka bp the record is characterized by the lightest delta o 18 values and high growth rates suggesting a strong monsoon period the summer monsoon weakened substantially after 4 2 ka bp as inferred from gradually increasing delta o 18 values and decreasing growth rate overall the intensity of the easm is regulated by summer insolation at 30 degrees n during the last 12 5 ka although oxygen isotope fractionation is different between aragonite h2o and calcite h2o because of rayleigh fractionation law the overall temporal pattern of delta o 18 values from aragonite stalagmite lh2 is concordant with other high resolution holocene calcite stalagmite records from south china the comparison among these records shows that the holocene optimum was synchronous across asian continental region influenced by the easm and indian summer monsoon ism lasting from similar to 10 6 to 4 2 ka bp as reflected by consistently lighter delta 18 ovalues among all these records regardless of their latitudinal difference these records do not support previously reported asynchronism between easm and ism in details the long term delta o 18 trend in lh2 is punctuated by a number of centennial fluctuations for instance two weak monsoon events occurred at 9232 57 yr bp and 8137 21 yr bp correlating in time with cooling events in greenland ice cores the latest weak monsoon event centered at 302 8 yr bp which is related to the little ice age lia in addition the monsoon intensity derived from our record also shows a strong connection with latitudinal migration of the inter tropical convergence zone itcz as recorded in the cariaco basin sediments spectral analysis of delta o 18 values shows that significant peaks match with solar periodicities of 208 yr de vries cycle 86 yr gleissberg cycle or related to delta c 14 production suggesting shorter term monsoon variations are forced by solar radiation overall our study suggests that the delta o 18 record in the aragonite stalagmite is highly consistent with those derived from calcite stalagmites suggesting that aragonite stalagmites are suitable for palaeoclimate reconstruction especially for the holocene period as aragonite calcite transformation has not occurred c 2013 elsevier ltd all rights reserved

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

mesoscale eddies in the labrador sea and their contribution to convection and restratification abstract the cycle of open ocean deep convection in the labrador sea is studied in a realistic high resolution 4 km regional model embedded in a coarser north atlantic setup this configuration allows the simultaneous generation and evolution of three different eddy types that are distinguished by their source region generation mechanism and dynamics very energetic irminger rings irs are generated by barotropic instability of the west greenland and irminger currents wgc ic off cape desolation and are characterized by a warm salty subsurface core they densely populate the basin north of 58 n where their eddy kinetic energy eke matches the signal observed by satellite altimetry significant levels of eke are also found offshore of the west greenland and labrador coasts where boundary current eddies bces are spawned by weakly energetic instabilities all along the boundary current system bcs baroclinic instability of the steep isopycnal slopes that result from a deep convective over

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

search of a worldwide catalog for earthquakes triggered at intermediate distances abstract an anomalous increase of seismicity was recorded at intermediate distances from the landers california earthquake of 28 june 1992 m 7 3 several authors have suggested that enhanced activity was triggered at distances of up to 17 fault lengths we test a 90 year catalog of shallow world earthquakes m 7 for evidence of this effect it is found that triggering is present even at these high magnitude levels the pattern of enhanced activity comprises two concentric regions a the aftershock region and b the region of triggered seismicity at distances of 300 to 1000 km the two regions are activated together they are separated by a ring shaped gap at a distance of around 300 km this mexican hat pattern is attributed to recovery flows generated by the stress drop of the earthquake in a steady state convecting system

earth s spin and volcanic eruptions evidence for mutual cause and effect interactions the angular velocity of earth s rotation shows decadal oscillations due to the lunisolar gravitational torque as well as inter or intra annual changes arising from the angular momentum exchange between the atmosphere and the solid earth the energies involved in the length of day lod variations may affect the crustal deformation rate and seismic energy release on a global scale we found significant correlation between the occurrences of major volcanic eruptions and the lod pattern since ad 1750 on a multiyear scale eruption frequency worldwide increases with lod changes moreover the injection of sulphur gases into the atmosphere during major eruptions is accompanied by significant inter annual lod variations this provides evidence of complex mutual cause and effect interactions stress changes induced by multiyear variations in earth s spin may affect climactic volcanic activity also the atmosphere s dynamic response to volcanic plumes may result in global changes of wind circulation and climate with consequent lod variations

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo