insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

grain boundary contact effects during faulting of quartzite an sem ebsd analysis abstract during low temperature faulting of cambrian quartzite assynt nw scotland stress concentrations develop at grain contacts either at the onset of deformation prior to the establishment of a through going fault plane or within the damage zone remote from the main displacement segment such concentrations contribute to the development of intragranular microfractures cataclastic microstructures and fault rocks this contribution considers the progressive deformation sequence that precedes microfracturing and cataclasis the complexity of this deformation is revealed by scanning electron microscope sem electron backscattered diffraction ebsd dauphine twinning is a widespread feature associated with grain contact stress concentration and forms distinctive ebsd microstructures automatic sem ebsd analysis reveals that whilst initial indentation causes dauphine twinning of many grains continued indentation results in the formation of an arcuate array of subgrains via low temperature plasticity and or microcracking which overprint the dauphine twins these observations are consistent with transmission electron microscopic analysis of quartz crystals used for microhardness indentation tests which reveal that indentation causes an intensely deformed region to develop comprising a high density of microfractures and a submicron scale blocky microstructure that accommodates any plastic deformation deformation mechanisms and associated microstructures develop sequentially with progressive indentation and may provide sites of microfracture nucleation via low temperature ductile fracture the new microstructures assist diffusive mass transfer dmt processes by the formation of a cellular or subgrain array that represents a reduction of several orders of magnitude in apparent grain size and hence in diffusion path length concomitantly associated microfracturing perturbs local thermodynamic equilibrium leading to enhanced dmt crack healing and cementation overgrowths together these processes form the aseismic creep and sealing components of fault zone development

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

age of the crowfoot advance in the canadian rocky mountains a glacial event coeval with the younger dryas oscillation a suite of sediment core samples was recovered from two lakes crowfoot and bow lakes that are adjacent to the crowfoot moraine type locality to identify and radiocarbon date sediments related to the crowfoot advance the crowfoot moraine system widely recognized throughout northwestern north america represents a glacial advance that is post wisconsin and pre mazama tephra in age an interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca 11 330 and 10 100 sup 14 c yr b p is associated with the crowfoot moraine the crowfoot advance is therefore approximately synchronous with the european younger dryas cold event ca 11 000 10 000 sup 14 c yr b p furthermore the termination of the crowfoot advance also appears to have been abrupt these findings illustrate that the climatic change responsible for the european younger dryas event extended beyond the northern atlantic basin and western europe equilibrium line altitude ela depressions associated with the crowfoot advance are similar to those determined for the little ice age advance whereas younger dryas ela depressions in europe significantly exceed little ice age ela depressions 26 refs 3 figs 1 tab

comparison between instrumental observational and high resolution proxy sedimentary records of late holocene climatic change a discussion of possibilities abstract variability of the north atlantic region is a key factor in the workings of global climate changes related to orbital factors and to the thermohaline circulation thc occur on timescales ranging from 1000 to 100 000 years whereas subdecadal decadal and multidecadal trends are associated with changes in atmospheric circulation sea surface temperature sst and salinity long term changes are known only from proxies whereas shorter periodicities are identified in instrumental and other observational data between lies a range of less well known centennial periodicities too long to be recorded observationally and too short for all but the highest resolution proxy records such as tree rings atmospheric 14c and varved lake sediments numerous investigations of such periodicities involve comparisons between the proxy and the observational record however results depend on the length of the datasets being analysed the relative strength of the periodicities present whether data are stationary or non stationary the degree to which they have been smoothed in order to remove particular fluctuations and the methods of analysis employed ideally comparisons should be between datasets of equal length and of similar properties but these criteria are not always easy to fulfill a search for periodicities in a range of well known multidecadal datasets reveals that whilst some frequencies previously identified in the central england temperature cet record and in the koch sea ice index are statistically significant those found by several authors in the index of the north atlantic oscillation nao are not as the index approximates to white noise instead decadal periodicity of the nao described by several authors appears to be result of smoothing of the raw data periodicities of 6 1 33 9 and 213 years identified in a proxy record from laminated sediments from loch ness scotland appear respectively to be related to a subdecadal variations in sst and salinity in the north atlantic ocean b multidecadal interactions between the nao and the north atlantic thc and c a well known centennial solar periodicity

late holocene lake sedimentology and climate change in southern alberta canada abstract climatic changes in southern alberta canada for the past 4000 yr are reflected in a high resolution record of lake sediment grain size the proposed mechanism for this response is that outflow discharge removes fine grained sediments but increasingly fine sediments are retained and deposited as streamflow declines at the same time coarse sediments are brought in by high discharge entering the lake the net effect of these two processes is to leave coarse clay deficient sediments during times of high streamflow and clay rich sediments during times of low flow the grain size record from pine lake reflects historic climate fluctuations as well as prehistoric fluctuations including the little ice age and the medieval warm period grain size at this site provides a simple economical and nonbiologically mediated paleoclimate proxy

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

late holocene 1500 yr climatic periodicities and their implications fourier and nonlinear regression analysis of a 4000 yr paleoclimate proxy record in western canada shows strong periodicities of 1500 yr and several weaker century to millenial scale periodicities in conjunction with the 23 708 yr milankovitch periodicity these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid latitudes these results suggest that postglacial climatic anomalies such as the little ice age and the younger dryas were at least in part periodic phenomena rather than the result of unique aperiodic events projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing a natural warming trend will continue until ca a d 2400

the last 18 kyr fluctuations in norwegian sea surface conditions and implications for the magnitude of climatic change evidence from the north sea a combined record of three cores spanning the last 18 kyr from the northern north sea is investigated for content of benthic and planktonic foraminifera and stable oxygen isotopes the paleoenvironmental development through this time period shows an early deglaciation 18 14 4 ka and the younger dryas 12 7 11 5 ka characterized by arctic polar conditions and increased ice rafting in the norwegian channel during the bolling allerod period warm sea surface temperature 9 c conditions similar to present conditions are inferred while bottom waters stayed cold 0 1 c with normal salinity the bolling allerod period is interrupted twice at 13 9 13 6 ka older dryas and at 13 0 12 8 ka inter allerod cooling period by reductions in sea surface temperatures and increased sea ice cover the beginning of the holocene period is marked by increases in surface and bottom water temperature superimposed on the broad climatic changes through the holocene a series of short lived oscillations in the ocean circulation are recorded the amplitude of these holocene events appears larger in the early holocene prior to 8 ka than compared with the remaining part of the holocene this amplification can possibly be attributed to a general increased freshwater budget in the north atlantic at this time during the final stages of the deglaciation of the laurentide and scandinavian ice sheets

persistent suborbital climate variability in marine isotope stage 5 and termination ii new surface water records from two high sedimentation rate sites located in the western subtropical north atlantic near the axis of the gulf stream provide clear evidence of suborbital climate variations through marine isotope stage mis 5 persisting even into the warm peak of the interglaciation substage 5e we found that the amplitude of suborbital climate oscillations did not vary significantly for the whole of mis 5 implying that ice volume has little or no influence on the amplitude of suborbital climate variability in this region although some records suggest that longer suborbital variations 4 10 kyr during mis 5 are linked to deepwater changes none of the existing records is of sufficient resolution to assess if a linkage occurred for oscillations shorter than 4 kyr however when examined in conjunction with published data from the norwegian sea new evidence from the subpolar north atlantic suggests that coupled surface deepwater oscillations occurred during the penultimate deglaciation this supports the hypothesis that during glacial and deglacial times ocean ice interactions and deepwater variability amplify suborbital climate change at higher latitudes we suggest that during the penultimate deglaciation the north atlantic deepwater source varied between nordic sea and open north atlantic locations in parallel with surface temperature oscillations

estuarine processes and their stratigraphic record paleosalinity and sedimentation changes in the hudson estuary north america paleosalinity estimates and rates of sedimentation inferred from core samples from the hudson estuary for the interval between 6 4 and 1 3 ka indicate a possible role for the estuarine turbidity maximum etm in influencing patterns of estuarine sedimentation at centennial to millennial time scales currently in the estuary sedimentation is localized via sediment trapping particularly in the vicinity of the etm 13 26 km upstream from battery park fbp at the southern tip of manhattan in water depths greater than 4 m and on the western side of the estuary data presented in this paper are from cores located within the segment of the estuary 29 50 km fbp age constraints are provided by c 14 dating paleoenvironmental interpretations are based upon paleosalinity estimates grain size variability and sedimentary structures paleosalinity was inferred on the basis of foraminiferal biofacies analysis and a new method for estimating summertime paleosalinity using oxygen isotope measurements in bivalve shell material the isotopic analysis of a narrow size fraction 1 0 1 7 mm representing summer growth of a single bivalve species gemma gemma reduces the uncertainty related to annual changes in temperature data from f45 km fbp indicate a gradual decrease in summertime paleosalinity between 6 4 and 2 0 ka from 25 20x to 15 10x the latter is similar to present day values these results are consistent with the conclusion of an earlier low resolution study sedimentation rates are generally low and are similar to the rate of sea level rise in the hudson river lowest sedimentation rates are noted in short 2 3 to f1 3 ka we hypothesize that the observed pattern in sediment accumulation relates to a location for the etm some 20 km upstream of its present position at 3 ka downstream migration of the etm since 3 ka is ascribed to shoaling of the estuary effectively squeezing the marine saltwater wedge in the same direction and off marginal flats into the channel such shoaling would have enhanced the role of waves in mixing marine and fresher surface water and reduced the effect of the etm in

a late holocene deep seated landslide in the northern french pyrenees abstract a very large deep seated landslide dsl in the northern pyrenees with over 1 4 10 9 m 3 was mapped and dated based on sedimentation rates and 10 be terrestrial cosmogenic radionuclide surface exposure cre dating our analysis on the landslide reveals the role of inherited structures in the landslide process and highlighted typical gravitational morpho structures and a small lake trapped at the toe of the landslide head scarp the rate of lake sedimentation 0 86 0 57 mm yr 1 also provided us with the approximate age of the landslide 1106 540 yr the cre dating result highlights two main slope destabilization phases then we discussed the history of dsl activity and its controlling factors information related to historic markers and the absence of particular climate markers and changes during the medieval dark ages point to a single event in ad 1380 due to a major seismic event lavedan earthquake

temporal geographical meltwater influences on the north atlantic conveyor implications for the younger dryas the temporal and geographical roles of meltwater discharge from the laurentide ice sheet on north atlantic deep water nadw production are investigated utilizing a global realistic geometry coupled climate model which does not require the use of flux adjustments model results suggest that preconditioning by meltwater discharge to the mississippi prior to the younger dryas yd is capable of pushing nadw beyond the limit of its sustainability the diversion of meltwater to the st lawrence then merely serves to completely inhibit nadw production the modeled change in surface air temperature generally agrees with the global pattern and magnitude of temperature change seen in paleoclimatic reconstructions of the yd and is intimately linked to changes in nadw formation the global thermohaline circulation provides an interhemispheric teleconnection with the southern oceans while changes in the atmospheric heat transport reacting to a global redistribution of oceanic heat transport provide a mechanism for interbasin teleconnection although the primary thermodynamic and hydrological cycle feedback processes are included within the atmospheric model in the absence of additional feedbacks an equilibrium without the presence of nadw is possible the inclusion of the wind stress speed feedback is found to significantly contribute to the resumption of nadw production as suggested by previous studies contrary to these same studies however the coupled model indicates an advective spin up timescale is required for resumption of nadw production and hence the termination of the modeled yd like climate event as opposed to a decadal century timescale the reason for the discrepancy is unclear but may be associated with the use of fixed salt flux fields applied in previous studies or the duration strength and geographical location of the imposed meltwater applied

reduced solar activity as a trigger for the start of the younger dryas it is generally assumed that changes in ocean circulation forced the abrupt climate changes during the late pleistocene including the younger dryas event recently however it was proposed that variations in solar irradiance could have played a much more prominent role in forcing pleistocene climate changes furthermore two physical mechanisms were recently published that explain how relatively small changes in solar irradiance could have had a strong impact on the climate system we discuss the possibility that an abrupt reduction in solar irradiance triggered the start of the younger dryas and we argue that this is indeed supported by three observations 1 the abrupt and strong increase in residual c 14 at the start of the younger dryas that seems to be too sharp to be caused by ocean circulation changes alone 2 the younger dryas being part of an similar to 2500 year quasi cycle also found in the c 14 record that is supposedly of solar origin 3 the registration of the younger dryas in geological records in the tropics and the mid latitudes of the southern hemisphere moreover the proposed two physical mechanisms could possibly explain how the north atlantic thermohaline circulation was perturbed through an increase in precipitation together with iceberg influxes in addition the full magnitude of the younger dryas cooling as evidenced by terrestrial records in europe could be explained we conclude that a solar triggering of the younger dryas is a valid option that should be studied in detail with climate models c 2000 elsevier science ltd and inqua all rights reserved

estimating rates of decompression from textures of erupted ash particles produced by 1999 2006 eruptions of tungurahua volcano ecuador persistent low to moderate level eruptive activity of andesitic volcanoes is difficult to monitor because small changes in magma supply rates may cause abrupt transitions in eruptive style as direct measurement of magma supply is not possible robust techniques for indirect measurements must be developed here we demonstrate that crystal textures of ash particles from 1999 to 2006 vulcanian and strombolian eruptions of tungurahua volcano ecuador provide quantitative information about the dynamics of magma ascent and eruption that is difficult to obtain from other monitoring approaches we show that the crystallinity of erupted ash particles is controlled by the magma supply rate msr ash erupted during periods of high magma supply is substantially less crystalline than during periods of low magma supply this correlation is most easily explained by efficient degassing at very low pressures 50 mpa and degassing driven crystallization controlled by the time available prior to eruption our data also suggest that the observed transition from intermittent vulcanian explosions at low msr to more continuous periods of strombolian eruptions and lava fountains at high msr can be explained by the rise of bubbles through strombolian or trapping of bubbles beneath vulcanian vent capping variably viscous and crystalline magma

the lacustrine sedimentary sequence in sygneskardvatnet western norway a continuous high resolution record of the jostedalsbreen ice cap during the holocene abstract two lacustrine sediment cores from sygneskardvatnet sunndalen confirm that at least the northern part of the jostedalsbreen ice cap melted away during the atlantic chronozone between 6475 and 5300 14 c yr bp 7340 and 6150 cal bp possibly interrupted for short intervals of glacier activity around 6000 and 5800 14 c yr bp 6900 and 6700 cal bp prior to this periods of glacier expansion culminated at ca 8500 8400 8200 7750 7600 and 7400 cal bp the 8400 8200 cal bp advances are correlated with the widespread 8200 event finse event recorded in greenland ice cores lacustrine and proglacial sites and marine sediments during the early part of the holocene periods of glacier contraction culminated at ca 8450 8300 7900 7500 and 6250 cal bp of which the last represents climatic optimum conditions lowest supply of minerogenic sediments and or highest organic production the sedimentary record also shows that the ice cap has existed continuously since 5300 14 c yr bp 6150 cal bp neoglaciation involved three main phases 1 6150 4500 cal bp 2 4500 2700 cal bp 3 2700 cal bp to the present and a series of low amplitude glacier advances which occurred at 6000 5800 5700 5600 5500 5200 5100 4900 4800 4700 4550 4450 4300 4200 4150 4050 4000 3900 3800 3550 3300 2550 2450 2350 2250 2150 2000 1800 1700 1600 1400 1300 1150 1050 and the 1000 cal bp including the little ice age loss on ignition analyses indicate however that episodes of less glacier activity occurred during the mid and late holocene at around 5900 5800 5550 5450 5300 5050 4850 4750 4500 4400 4100 3950 3700 3450 3100 2650 2500 2400 2300 2200 1850 1700 1550 1350 1250 1050 1000 cal bp and during the twentieth century altogether the lacustrine record from sygneskardvatnet indicates that the holocene has been interrupted by 41 periods of increased glacier activity mean return period of ca 150 years and by 36 events of glacier contraction mean return period of 210 years spectral analysis of the loi data show peaks at periods of about 50 85 110 250 285 500 and 2000 calendar years the mean time resolution in core sygneskardvatnet 2 is ca 20 yr cm 1 while the mean sedimentation rate is 0 5 mm yr 1

millennial scale dynamics of the east asian winter monsoon during the last 200 000 years the primary productivity dynamics of the last 200 000 years in the sulu sea was reconstructed using the abundance of the coccolithophore florisphaera profunda in the images md97 2141 core we find that primary productivity was enhanced during glacial periods which we suggest is due to a stronger east asian winter monsoon during the last 80 kyr eight significant increases in primary productivity pp in the sulu sea are similar to east asian winter monsoon changes recorded in chinese loess the pp maxima are not linked with heinrich events he in the north atlantic although four pp peaks are synchronous with he the pp oscillations have frequencies near those of the dansgaard oeschger cycles in northern hemisphere ice records and indicate a teleconnection of the east asian winter monsoon with greenland climate in this sulu sea record the east asian winter monsoon oscillates with periodicities of6 4 2 3 4 2 3 and 1 5 kyr in particular the 1 5 kyr cycle exhibits a strong and pervasive signal from stage 6 to the holocene without any ice volume modulation this stationarity suggests that the 1 5 kyr cycle is not driven by some high latitude forcing

7000 year record of lake level change on the northern great plains a high resolution proxy of past climate mineralogical and paleobotanical characteristics of the sedimentary fill in a shallow saline lake in southeastern alberta indicate that drought intervals are aperiodic and that climatic extremes unprecedented in historic time occurred earlier during the holocene when century long intervals of repeated intense droughts alternated with long periods when droughts were rare low water intervals signifying periods of drought are recorded by carbonate rich laminae containing abundant plant fossils indicative of hypersalinity in contrast highstands of relatively fresh water outlining moist periods are represented by massive silicate rich sediment with lower numbers of halophytic indicators

holocene environmental change inferred from a high resolution pollen record lake zhuyeze arid china a high resolution pollen record c 50 yr sample from terminal lake sediments in the shiyang river drainage basin on the present margin of the summer monsoon was used to reconstruct vegetation and climate history during the holocene forest trees from mountainous areas of the drainage including sabina picea and pinus dominated pollen assemblages in the early holocene 11 6 7 1 cal ka in the mid holocene 7 1 3 8 cal ka desert and steppe shrubs and herbs around the lake including nitraria poaceae compositae and artemisia were dominant the late holocene 3 8 0 cal ka was again dominated by alternation of pinus sabina tree pollen and desert steppe pollen the early holocene forest expansion in the mountains and subsequent increase in the river transport of tree pollen corresponds with maximum precipitation during the east asian summer monsoon maximum the timing of these changes in our record from arid china is different from that of east china where the holocene monsoon maximum appeared in

millennial scale rhythms in peatlands in the western interior of canada and in the global carbon cycle abstract anatural 1450 yr global holocene climate periodicity underlies a portion of the present global warming trend calibrated basal radiocarbon dates from 71 paludified peatlands across the western interior of canada demonstrate that this periodicity regulated western canadian peatland initiation peatlands the largest terrestrial carbon pool and their carbon budgets are sensitive to hydrological fluctuations the global atmospheric carbon budget experienced corresponding fluctuations as recorded in the holocene atmospheric co 2 record from taylor dome antarctica while the climate changes following this 1450 yr periodicity were sufficient to affect the global carbon budget the resultant atmospheric co 2 fluctuations did not cause a runaway climate co 2 feedback loop this demonstrates that global carbon budgets are sensitive to small climatic fluctuations thus international agreements on greenhouse gasses need to take into account the natural carbon budget imbalance of regions with large climatically sensitive carbon pools