repeated short term bioproductivity changes in a coastal lake on store koldewey northeast greenland an indicator of varying sea ice coverage a lacustrine sediment core from store koldewey northeast greenland was biogeochemically biologically and sedimentologically investigated in order to reconstruct long and short term climatic and environmental variability the chronology of the uppermost 189 cm of the record is based on ten 14c ams age determinations of aquatic mosses the record covers almost the entire holocene and revealed changes on multidecadal to centennial scales dating of the oldest mosses shows that lacustrine biogenic productivity already began at around 11 cal kyr bp this age pre dates the onset of biogenic productivity in other lakes on store koldewey by about 2 kyr in spite of the early onset of biogenic production organic matter accumulation remained low and minerogenic sedimentation dominated at about 9 5 cal kyr bp moss sulphur organic carbon and biogenic silica content started to increase indicating that the environment stabilized and the biogenic production in the lake adjusted to more preferable conditions s

dating sequences of buried horizons of podzols developed in wind blown sand at ulfborg western jutland abstract the ulfborg project is investigating the interactions of natural and anthropogenic influences on a typical west jutland landscape through the holocene with emphasis on the last millennium pollen analysis and ams 14c dates of buried podzols were used to date periods of blown sand transport and the development of man made calluna vulgaris heath hydrochloric acid extractable carbon expected to represent the most mobile fraction of carbon derived from the youngest soil was a non negligible fraction of the total carbon in the buried soils the age of the humic acid fraction in the bs horizons seems to indicate the start of podzolisation whereas the fulvic acid fraction in the mor layer indicates the time of burial dates for the three alkali extracted fractions within the individual mor layers were similar they agree with the results of pollen analyses which indicate that the original forest was transformed into pure calluna heath and kept as such by burning and cutting thus preventing continuous accumulation of organic matter the first large scale sand movement event was dated to about 6000 bc covering soils on which forest had earlier established the vegetational disturbance and sand movement were probably triggered by a climatic change to cooler conditions in contrast later sand movement seems to be connected with human activity in soils covered by sand at 800 600 bc the pollen record shows that the change from forest to pure calluna vulgaris heath had already taken place together with evidence from lacustrine pollen records the pollen assemblages from all younger mor layers indicate that the area was kept as pure calluna heath until the 19th century 14c dates of the lower bs horizons indicate that podzolisation started soon after the sand was deposited so some parent materials had been leached before deposition

holocene environmental reconstruction from deltaic deposits in northeast greenland terraces of different age in the zackenberg delta located at 74 n in northeast greenland have provided the opportunity for an interdisciplinary approach to the investigation of holocene glacial periglacial pedological biological and archaeological conditions that existed during and after delta deposition the raised zackenberg delta accumulated mainly during the holocene climatic optimum starting slightly prior to 9500 cal yr bp 30 m a s l and continued until at least 6300 cal yr bp 0 5 m a s l evidence of sea level change is based on conventional 14c dates of shells from the marine delta bottomsets 14c ams dating of macroscopic plant material from the foresets and of fluvial deposits arthropod and plant remains from 7960 cal yr bp in the delta foresets include the oldest evidence of the arctic hare in greenland and evidence of a rich herb flora slightly different from the modern flora empetrum nigrum and salix herbacea remains indicate a summer temperature at least as high as today during delta deposition post depositional nivation activity dated by luminescence lichenometry and schmidt hammer measurements indicate mainly late holocene activity at least since 2900 yr bp including little ice age lia avalanche activity pedological analyses of fossil podsols in the zackenberg delta including 14c ams dating of selected organic rich b horizons show continued podsol development during the holocene climatic optimum and into the subsequent colder period of the late holocene until 3000 2400 yr bp a neo eskimo house ruin found on the lower part of the delta presently being eroded by the sea is dated to ad 1800 it presumably was abandoned prior to ad 1869 and suggests that some of the last eskimos that lived in northeast greenland might have occupied the zackenberg delta copyright 2002 john wiley sons ltd

scandinavian glacial and climatic fluctuations during the holocene abstract historical documents and lichenometric studies give a detailed picture of the little ice age in scandinavia there was a large advance in norway which has been dated at a few places to 1750 small readvances during the retreat occurred around a d 1780 1810 1840 1850 1850 1870 1890 1910 and 1930 in sweden most of these advances have been recognized and in addition extensive advances are dated by lichenometry to around a d 1600 1650 and 1700 1720 soils buried beneath moraines often yield radiocarbon dates that are much too old methods dependent on these must therefore be used with care evidence for pre little ice age advances are often considered equivocal the most reliable information is probably provided by studies of lacustrine sediments combining information from all sources the most significant pre little ice age glacier advances most likely occurred in 7 5 5 1 4 5 3 2 2 8 2 2 1 9 and 1 5 1 1 radiocarbon ka bp advances that were less extensive or for which there is less evidence occurred around 6300 5600 2500 940 600 560 and 380 bp

radial cracks around α quartz inclusions in almandine constraints on the metamorphic history of the oman mountains radiating tensional cracks around quartz inclusions in almandine have been observed in metapelite samples from the southeastern saih hatat tectonic window northeastern oman mountains these almandines show an inclusion rich glaucophane epidote and strongly deformed core with inclusions of different mineral phases the rim of the same almandines is inclusion poor and shows only quartz apatite zircon rutile and baal phosphates as inclusions quartz and apatite inclusions in the rim are single crystals often surrounded by radial cracks these radial cracks developed during uplift by the dilation of quartz 4 5 vol without a phase transformation subsequently these cracks were filled with kaolinite phengite si content 3 4 per formula unit p f u chlorite and fe oxides we calculated the appearance of radial cracks without phase transformation using the mathematical procedure of van der molen and van roermund 1 this calculation involves terms for thermal expansion isothermal compressibility and shear modulus for the example of quartz and almandine for the same p and t interval during a retrograde path published geothermobarometric estimates give pressures of between 1 0 and 2 0 gpa and temperatures of between 450 and 600 c for the peak conditions for these rocks of the saih hatat tectonic window on the basis of these p t data we calculated different retrograde p t paths in the quartz domain initiation of garnet fracturing is dependent on the p t starting conditions and the component of isothermal compression of the retrograde path the calculations yield a set of smooth monotonic curves whose exact position on the p t plane between 0 1 and 0 6 gpa and 40 and 500 c depends on the initial p t conditions and the component of isothermal compressibility of the retrograde p t paths this model can be used in general terms to estimate pressure and temperature for the following cases 1 if independent evidence such as petrological data allow the determination of the final pressure at which radial cracks appeared the initial inclusion pressure can be recalculated 2 if the initial inclusion pressure is known e g from petrological data the conditions of radial cracking can be calculated and the pair initial pressure final pressure leads to an estimate of the shape of the retrograde p t path as a function of its component of isothermal decompression in the example from the northeastern saih hatat tectonic window the late syntectonic growth of albite phengite kaolinite suggests that the final pressure for fracturing ranged between 0 4 gpa and 0 5 gpa at temperatures of 300 c these values correspond to high initial pressures of at least 2 0 gpa at a temperature of 550 c the following geodynamic model is suggested a regionally extended metamorphism led to the growth of inclusion rich garnets in the rocks from the northeastern saih hatat tectonic window at depths of about 30 km 0 1 gpa about 450 c continuing prograde metamorphism at a depth of more than 60 km with p 2 0 gpa and t 550 c affected a metapelite unit that is only exposed immediately south of as sifah village in this area clear rims of almandine grew around the older garnets and entrapped mainly quartz and apatite during uplift along a retrograde p t path with a large component of isothermal decompression radial cracks around quartz inclusions developed in the rims of almandines at a depth of about 12 km 0 4 0 5 gpa 300 c

little ice age nivation activity in northeast greenland during the little ice age lia the periglacial landscape in northeast greenland responded rela tively quickly to the climatic deterioration with increased nivation activity resulting nivation landforms and associated sediment basins are used as palaeoclimatic archives documenting the significant geomorphological effect of nivation during the lia period in the zackenberg area a nival basin studied in detail showed the onset and dominance of niveo fluvial sedimentation in the period ad 1250 1420 followed by increasing niveo aeolian sedimentation between ad 1420 1500 1580 finally very rapid niveo aeolian sedimentation prevailed during the period ad 1500 1580 1690 in the same period some large nival fans accumulated in the zackenberg lowland as a result of increased niveo fluvial activity and niveo fluvial sediments were also deposited in pre existing fluvial valleys demonstrating the large areal extension of the nivation activity the chronology is based on nine ams 14c determinations the inte

a technique for the analysis of refold structures abstract when folds of multiple episodes interact complex interference patterns or refolds result simple patterns may be directly interpreted by the structural geologist but more complex ones are often ambiguous and undecipherable a technique to analyze many refolds is presented which does not directly require any field measurements of structural data instead it requires a series of parallel views through the refold as can be obtained in mines or from a slabbed rock sample individual folds are identified on the level maps and hinge trends and plunges are calculated stereonet plots and cross sections yield the fold orientations and shapes assumptions inherent to this technique are 1 the first folds were cylindrical and 2 the second folding motions were approximately those of similar shear type folds the above technique was applied to a small scale example from the kootenay arc washington analysis showed nearly coaxial folds of complex en echelon non cylindrical and non similar type characterizing both generations this example demonstrates that the technique is applicable to refolds that do not meet the idealized assumptions about folds this technique should prove valuable to geologists working in other refold areas and is particularly applicable to mining problems for which the necessary three dimensional data are available

geomorphological and cryostratigraphical analyses of the zackenberg valley ne greenland and significance of holocene alluvial fans abstract in high arctic northern greenland future responses to climatic changes are poorly understood on a landscape scale here we present a study of the geomorphology and cryostratigraphy in the zackenberg valley in ne greenland 74 n containing a geomorphological map and a simplified geocryological map combined with analyses of 13 permafrost cores and two exposures cores from a solifluction sheet alluvial fans and an emerged delta were studied with regards to cryostructures ice and total carbon contents grain size distribution and pore water electrical conductivity and the samples were ams 14c dated the near surface permafrost on slopes and alluvial fans is ice rich as opposed to the ice poor epigenetic permafrost in the emerged delta ground ice and carbon distribution are closely linked to sediment transport processes which largely depend on lithology and topography holocene alluvial fans on the lowermost hillslopes covering 12 of the study area represent paleoenvironmental archives during the contrasting climates of the holocene the alluvial fans continued to aggrade through the warmer early holocene optimum the colder late holocene and the following climate warming and by 0 45 mm a 1 on average this is caused by three factors sedimentation ground ice aggradation and vegetation growth and is reflected by ams 14c dating and continuously alternating cryostructures highly variable sedimentation rates in space and time at the alluvial fans have been detected this is also reflected by alternating lenticular and microlenticular cryostructures indicating syngenetic permafrost aggradation during sedimentation with suspended and organic matrix cryostructures indicating quasi syngenetic permafrost aggradation in response to vegetation growth in periods with reduced or no sedimentation over time this causes organic matter to become buried indicating that alluvial fans represent effective carbon sinks that have previously been overlooked

eclogite facies shear zones deep crustal reflectors strongly foliated eclogite facies rocks in 30 150 m thick shear zones of caledonian age occur within a grenvillian garnet granulite facies gabbro anorthosite terrain in the bergen arcs of norway the predominant eclogite facies mineral assemblages in the shear zones are omphacite garnet zoisite kyanite in gabbroic anorthosite and omphacite garnet in gabbro eclogite facies rocks in shear zones are generally fine grained alternating omphacite garnet and kyanite clinozoisite rich layers define gneissic layering a strong shape preferred orientation of omphacite kyanite and white mica phengitic muscovite and or paragonite define the foliation the anorthositic eclogites show omphacite b axis maxima approximately normal to the foliation and c axis girdles within the foliation plane p wave velocities v determined at confining pressures to 600 mpa for samples from eciogite facies shear zones range from 8 3 to 8 5 km s l and anisotropy ranges from 1 to 7 the few samples with more pronounced anisotropy tend to be approximately transversely isotropic with minimum velocities for propagation directions normal to foliation and maximum velocities for propagation directions parallel to foliation the fast propagation direction lies within the c axis girdles parallel to foliation and the slow propagation direction is parallel to the b axis concentration normal to foliation in samples for which omphacite crystallographic preferred orientation was determined v for the granulite facies protoliths average about 7 5 km s high calculated reflection coefficients for these shear zones 0 04 0 14 indicate that they are excellent candidates for deep crustal reflectors in portions of crust that experienced high pressure conditions but escaped thermal reactivation

mineralogy and composition of the upper mantle seismic velocities are calculated for two petrological models of the upper mantle an olivine rich assemblage pyrolite and a garnet clinopyroxene rich olivine bearing assemblage piclogite these are compared with recent seismic profiles for various tectonic provinces the shield data is most consistent with a cold olivine and orthopyroxene rich lid the seismic lithosphere extending to 150 km followed by a high temperature gradient and or a change in mineralogy that serves to decrease the velocity from 200 to 400 km the velocities follow a 1400 c adiabat the rise tectonic mantle is much slower presumably hotter and is likely to be above the solidus to depths of at least 300 km the high v p v s ratio of the lower oceanic lithosphere in the western pacific is most consistent with eclogite

the impact of north atlantic storminess on western european coasts a review abstract instrumental and documentary records of storminess along the atlantic coast of western europe show that storm activity exhibits strong spatial and temporal variability at annual and decadal scales there is evidence of periods of increased storminess during the little ice age lia ad 1570 1990 and archival records show that these periods are also associated with sand movement in coastal areas independent evidence of sand movement during the lia is derived from dating the coastal sand deposits using luminescence or radiocarbon methods the holocene record of sand drift in western europe includes episodes corresponding to periods of northern hemisphere cooling particularly at 8 2 ka and provides the additional evidence that these periods like the lia were also stormy

holocene sea level reconstruction in the young sound region northeast greenland a relative sea level curve over the holocene is constructed for the young sound region in northeastern greenland the reconstruction is derived by dating the heights of raised beach ridges in coastal plains using optically stimulated luminiscence osl and by dating palaeoterrestrial surface levels now buried beneath the intertidal frame using the 14 c technique the relative sea level curve reveals a rapid fall of at least 10 mm a 1 from ca 9500 to 7500 a ago which slowed to 2 mm a 1 until it reached the present sea level ca 3000 a ago this part of the curve is based on the raised beach ridge data thereafter relative sea level continued to fall to reach a minimum level at about 0 5 m below the present sea level ca 2300 a ago since then relative sea level has experienced a slow rise of about 0 2 mm a 1 this part of the curve uses the data from the palaeoterrestrial surfaces the study supplements other estimates of holocene relative sea level changes and supports the observations of a decreasing trend in the timing of the cross point and in minimum relative sea level from south to north greenland copyright 2011 john wiley sons ltd

elasticity of glaucophane seismic velocities and anisotropy of the subducted oceanic crust abstract upon subduction the oceanic crust transforms to blueschists and eclogites with seismic properties that gradually become similar to those of the surrounding mantle in order to evaluate the anisotropy of blueschists and glaucophane bearing eclogites the elastic constants of glaucophane single crystal plates from the sesia lanzo zone aosta valley western alps were measured using brillouin spectroscopy at ambient conditions the mean p and s wave velocities are 7 8 and 4 6 km s 1 respectively and the anisotropy is high 38 1 av p and 27 3 av s glaucophane develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 110 poles concentrated sub perpendicular to the foliation in both blueschist and eclogite rocks the measured lpo is in good agreement with viscoplastic self consistent numerical models seismic properties of glaucophane bearing blueschist and eclogite are calculated by combining measured lpo and the single crystal elastic moduli of glaucophane with the other main mineral constituents of the rock mostly epidote for blueschist and omphacite and garnet for eclogite blueschists present stronger anisotropies av p 16 1 and av s 10 3 than eclogites av p 2 9 and av s 1 7 the shear wave splitting and resulting delay times for a 7 km thick layer of eclogite or blueschist are low for the eclogite

late quaternary sedimentation in the western north atlantic stratigraphy and paleoceanography abstract a detailed analysis of stratigraphic indices was undertaken to study paleoclimatic change in the western north atlantic three stratigraphic indicators carbonate content globorotalia menardii and uvigerina peregrina were tested in ten radiocarbon dated cores from the north american continental margin of these carbonate content appears to be most accurate carbonate content exhibits two major increases from late glacial time to the present estimated ages of the average of the mid point of these increase are 13 200 b p and 8600 b p an absolute chronology was established down fifteen cores using these stratigraphic indicators and the radiocarbon dates sea surface temperature sst estimates derived from planktonic foraminifera were mapped at 2000 yr intervals from 2000 b p to 14 000 b p sst warms rapidly from 12 000 to 8000 b p reaches a maximum between 8000 and 6000 b p and gradually cools after 6000 b p bottom waters were monitored with uvigerina peregrina and dissolution indices the disappearance of uvigerina suggests that the water type it lives in low o 2 started to thin from both the top and bottom by 13 000 b p and by 7300 b p had disappeared fragmentation of planktonic foraminifera was used as an index of dissolution in most cores dissolution was intense during late glacial time lessened during early postglacial time and resumed in the late postglacial

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

holocene climate history of geographical society o east greenland evidence from lake sediments abstract sediment cores from two lakes in the outer coastal region of east greenland were investigated for chronology lithology palynology and biogeochemistry a 10 m long sequence recovered in basaltso comprises the entire lake history following the last glaciation of the area probably during the preboreal oscillation this is indicated by a succession from glacial via glaciolimnic to limnic sediments deglaciation of the area was associated with a high sedimentation rate mirrored also in the basal part of a 2 6 m long core from a smaller lake b1 about 1 km south of basaltso limnic sedimentation without glacial influence commenced about 10 000 cal yr bp according to radiocarbon dated terrestrial plant remains biogeochemical and palynological data indicate an early holocene climatic optimum from 9000 to 6500 cal yr bp a climatic deterioration began at 6500 cal yr bp with an increase in snow accumulation documented by a change in the pollen assemblage and a coinciding change in the grain size distribution at least since 5000 cal yr bp a decrease in the biogeochemical parameters in both lake sediment successions indicates a temperature decline this deterioration culminated at about 3000 1000 cal yr bp when the climate was cold and dry a slight warming is indicated in the pollen assemblage between ca 1000 and 800 cal yr bp following a subsequent rise in precipitation cooling during the little ice age is mirrored in lowest dwarf shrub pollen percentages and in low contents of organic components

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

procedures used for luminescence dating of sediments abstract an account of the procedures for thermoluminescence tl and optically stimulated luminescence osl dating of sediments used at the nordic laboratory for luminescence dating is given the topics discussed include sampling sample preparation separation of quartz and feldspars using heavy liquids dose rate estimation and methods for estimating the equivalent dose special attention is paid to the partial bleach tl technique of mejdahl 1988 which appears to give reliable results for partially bleached sediments optically stimulated luminescence dating using stimulation by infra red ir and green light has been taken up and especially added dose methods using stimulation by ir or green light have been tried with some success some sources of error are discussed including the adverse effect of shallow traps

patterns of fold interference influence of early fold shapes abstract model experiments were specifically designed to test the effect of different profile shapes of early folds on refolding patterns comparison of natural examples with experimental results and analogy with engineering information on buckling of fold shapes suggest that when layers are mechanically active during refolding the profile shape of the early folds markedly affects the patterns of fold interference open rounded folds tend to refold to form dome and basin patterns of interference whereas isoclinal folds tend to refold by folding their axial plane forming type 2 patterns of interference hence the dimensions and shape of the profile of the early folds control the preferred buckling mode during refolding

a 9000 year old ash bed on the faroe islands abstract radiocarbon datings of the saksunarvatn ash bed on the faroe islands indicate an age of 9000 9100 yr b p the saksunarvatn ash bed differs geochemically from both ash zone 1 in the north atlantic and the vedde ash bed of norway and the norwegian sea all mentioned ashes are assumed to originate from iceland the vedde ash has been dated at 10 600 60 yr b p consequently the saksunarvatn and vedde ash beds provide an opportunity for precise dating of events around the pleistocene holocene boundary in marine cores especially from the region where the two plumes overlap

a quantitative study of hinge thickness of natural folds some implications for fold development abstract a quantitative analysis of some natural folds showing thickened hinges designated here as t folds has been carried out two parameters of a fold have been recognized here a the axial angle is the angle for a given trace or arc as subtended at its apex hinge and b the thickness ratio t is the ratio between the hinge th and limb tl thicknesses the t plots for a variety of natural folds yield a very typical curve that not only reflects interdependence of hinge thickening and axial angle but also bears significant implications for fold development assuming the initiation of folding due to buckling it appears that under a system of compressive forces the naturally deformed buckled folds may retain their parallel fold geometry down to the axial angle of about 130 thereafter i e between 130 and 70 the hinge thickening appears to be a rather slow process with more enhanced deformation i e between 70 and 30 when elevated temperatures also appear to play their part the folds develop great mechanical instability and undergo marked flowage and mass transfer towards the hinge zone flattening at

elasticity of a grossular pyrope almandine garnet the single crystal elastic properties of a natural grossular rich garnet solid solution have been measured at ambient conditions using brillouin spectroscopy this garnet sample is unusual for a grossular in that it contains appreciable pyrope and almandine components with a composition of gr48 4py27 6alm23 4sp0 6 it is thus suitable for investigating the variation of elastic properties with composition in ca rich garnet solid solutions that are stable only at high pressure the values obtained for the bulk modulus k 170 4 6 and for the shear modulus 101 6 3 of the garnet examined in this study vary by less than 1 from those obtained from a weighted sum of the end member moduli this suggests that any composition in the grossular pyrope almandine system which comprise the majority of upper mantle garnets is accurately estimated with this simple approach more complex elasticity composition variations observed for the grossular andradite garnets may be specific to garnet solid solutions where the cation substitutions occur at six coordinated crystallographic sites

luminescence dating of archaeological materials using a new technique based on single aliquot measurements abstract a dating method based on single aliquot luminescence dose determination was applied to quartz and feldspars from heated archaeological materials the problem of changes of sensitivity to radiation resulting from signal erasure in regeneration measurements was studied in some detail and a new method based on single aliquot regeneration measurements within an added dose framework which appears to eliminate the problem of sensitivity change is proposed preliminary dating results mainly using quartz obtained with the new method are presented

paleoceanography of the last interglacial glacial cycle in the polar north atlantic abstract using to its position close to the sites of waxing and waning of the major northern hemisphere ice sheets during the late quaternary climatic cycles the polar north atlantic plays a key role in driving global change therefore analyzing the present day sedimentation processes and reconstructing the late quaternary paleoceanography in this region has been a focus of major scientific interest through the last fifteen years this paper aims to combine the vast amount of new results about modern sediment fluxes surface sediment distribution and the paleoceanographic record and to present a comprehensive overview of the paleoceanography in the polar north atlantic through the last 200 000 years which is based on the basinwide analysis of carbonate and ice rafted detritus records during the last fifteen years the climap paleoceanographic view of the glacial polar north atlantic as an almost permanently isolated sea covered by heavy sea ice throughout the year has been shifted to a much more dynamic view of the environmental conditions a meridional current system similar to the present day conditions secured the exchange of water ice and heat between the polar north atlantic and the alantic and arctic oceans although affected by variations in strength and intensity this meridional current pattern resulted in an almost permanent presence of at least some seasonally ice free areas with all the consequences for e g marine life and deep water formation in addition the development of the continental ice sheets namely the fennoscandian and the barents sea ice sheets is closely related to this dynamic circulation pattern during the so called nordway events the pronounced inflow of temperate waters from the south provided moisture for the growth of the ice sheets the most prominent of these events stage 6 stage 4 and substage 3 1 2 ended in major glaciations reflected in the terrestrial sequences and in the deep sea ird records

stratigraphy and thermoluminescence dating of late glacial cover sand in denmark in western jutland deposits with a texture and structure similar to dutch cover sands have been found investigations have been carried out on the lithology and the lithostratigraphic sequences pollen analysis is used for biostratigraphic correlation and ages have been obtained by the radiocarbon method as well as by thermoluminescence techniques using both quartz and eldspar the five sites are presented separately and the data are integrated into a general stratigraphic outline of the late glacial cover sand sequence in jutland during the latest part of the upper pleniglacial and the earliest late glacial older cover sand type was deposited locally this sediment was also deposited during the later parts of the late glacial younger cover sand type was deposited primarily during the early dryas and late dryas but some sand of this type was also laid down during the allerod and the earliest holocene the palaeobotanical records are discontinuous but plant growth was probably present throughout the late glacial only during the altered did the deposition of sand decrease long enough to allow a relatively stable vegetational development the investigation shows that the sequence of events in jutland is similar to the dutch record

the schmidt hammer as a relative age dating tool and its potential for calibrated age dating in holocene glaciated environments the schmidt hammer is a relatively cheap portable sturdy instrument with proven value over the last two decades or so in rapidly dating coarse inorganic deposits of diverse origins early views were that its dating role was limited to distinguishing recently exposed from much older typically either a few sites of possibly different ages or occasional older surfaces amongst many young sites were studied more recently calibration curves based on individual r value means from small numbers 2 4 of sites of known ages have been used to estimate the ages of undated sites we present schmidt hammer rebound r values from 28 little ice age and younger 23 preboreal and 7 younger dryas glaciated surfaces in southern norway in order first to test rigorously the robustness of the instrument as a relative age dating tool despite being obtained from different surfaces moraines glaciofluvial deposits and bedrock and varied metamorphic lithologies the r value overall means and 95 confidence intervals for the little ice age preboreal and younger dryas age categories respectively 60 0 1 6 41 6 1 4 and 34 2 2 0 are statistically significantly different only two outlying sites in the two younger age categories have overlapping confidence intervals demonstrating remarkable robustness in differentiating early and late holocene surfaces the distinction between preboreal and younger dryas sites with terminal dates 2000 years apart is less clear but still statistically significant though possibly partly because of enhanced weathering conditions at the predominantly well vegetated younger dryas sites second we examine the feasibility and desirability of controlling non age related factors including some previously considered critical instrument wear operator bias initial rock surface texture which emerge either as less important than previously argued or as relatively unimportant together with others previously unreported e g long term changes in lichen soil snow and vegetation covers third we investigate the potential for calibrated age dating by applying exploratory linear rates of r value decline to selected combinations of sites the results suggest that error limits of ca 700 to 1600 years should be achievable over the holocene timescale this improved dating capability however will require adequate numbers of site means not only for each age category used to define these curves but also for each set of test surfaces of the same ages recommendations are made for a suitable sampling protocol for developing further the schmidt hammer as a calibrated age dating tool

p and s wave velocities of the lowermost crustal rocks from the kohistan arc implications for seismic moho discontinuity attributed to abundant garnet abstract p vp and s wave vs velocities of garnet free two pyroxene granulite and garnet bearing garnet granulite and garnet pyroxenite lowermost crustal rocks collected from the kohistan arc northern pakistan were measured at 0 1 1 0 gpa and 25 400 c garnet granulite had higher vp 0 31 km s and vs 0 27 km s than two pyroxene granulite although vp and vs increased with increasing volume percent of garnet plagioclase free garnet pyroxenite showed significantly higher vp and vs than plagioclase rich garnet granulite mainly due to the low vp and vs of plagioclase in contrast we observed two quasi linear relationships between vp vs and sio2 content for the garnet bearing and garnet free rocks the garnet bearing rocks had relatively higher vp and vs and stronger sio2 dependences than the garnet free rocks the stronger sio2 dependences of vp and vs in the garnet bearing rocks suggest that the garnet formation in mafic to ultramafic rocks e g pyroxenite and hornblendite having relatively lower sio2 leads to more pronounced increases in vp and vs than that of relatively felsic rocks e g felsic to mafic granulite indeed the vp and vs of the garnet pyroxenite were significantly higher than those of garnet granulite but comparable to those of dunite the significantly high vp and vs of the garnet pyroxenite yielded high reflection coefficients between the garnet granulite and garnet pyroxenite of up to 0 13 for p waves and 0 14 for s waves comparable to values expected for moho reflection thus the lithological boundary between plagioclase rich garnet granulite and plagioclase free garnet pyroxenite in the lowermost crust of the kohistan arc corresponds to the seismic moho discontinuity

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

a simple model of the 1982 83 californian el nino steric height steric height anomaly sea level and sea level anomaly show that the 1940 41 and the 1982 83 californian el nino events were resonant responses of the california current to the expansion and intensification of the aleutian low and decrease in strength of the north pacific high in both cases the subsurface anomalies were dynamically produced by onshore transport of subarctic water and a downward tilt of the inshore thermocline sea surface temperature anomalies however resulted from thermodynamic as well as dynamic processes most previous californian el nino or anti el nino events probably were resonant or anti resonant responses of the seasonal cycle of the california current to anomalous large scale atmospheric forcing

shear and compressional mode measurements with ghz ultrasonic interferometry and velocity composition systematics for the pyrope almandine solid solution series abstract successful fabrication of a high frequency up to 600 mhz shear transducer enables us to determine the complete sets of sound velocities for single crystal samples using ghz ultrasonic interferometry sound velocities for a natural pyrope and a natural almandine were measured re examining the existing database we found that velocities for the pyrope almandine solid solution series can be modeled quantitatively with linear relationships v p 100 0 0067 x alm 9 08 km s 1 v s 100 0 0041 x alm 5 08 km s 1 v p 110 0 0074 x alm 9 10 km s 1 where x alm is the fe mg fe ratio in the garnet samples maximum deviation of the measurement data from these linear relationships is 1 for every 10 increase in the fe mg fe ratio almandine the velocities decrease by about 1 published density data for this garnet solid solution series fit to a straight line with a maximum deviation of 1 thus the velocities follow linear laws with the density and such velocity density systematics acquire the form of the birch s law using these relationships velocities of an arbitrary composition in this garnet solid solution series can be predicted at present measurement precision of existing data does not warrant an examination of whether bulk modulus is linear with composition the suggested values for the p and s velocities for the pyrope end member and the almandine end member are km s 1 v p 100 v s 100 v p 110 pyrope mg 3 al 2 si 3 o 12 9 08 5 08 9 10 almandine fe 3 al 2 si 3 o 12 8 42 4 68 8 34 the technique used in monitoring the thickness of the linbo 3 crystal during the fabrication of the shear transducer illustrates the feasibility of using samples as thin as a few micrometers in the ghz ultrasonic interferometric measurements

history of a stable ice margin east greenland during the middle and upper pleistocene abstract the east greenland record of glaciation and environmental change is based on a combination of onshore and offshore studies glaciological work on contemporary outlet glaciers provides background for interpreting the glaciation styles of the past the scoresby sund fjord system the single largest outlet of the inland ice in east greenland and the adjacent continental shelf and slope were the main working areas the regionality of these results was tested with onshore and offshore work on sites further to the north in the east greenland fjord zone the record spans the period since isotope stage 7 ca 240 ka the most extensive glaciation phases were the lollandselv and scoresby sund glaciations isotope stages 7 and 6 the langelandselv interglaciation isotope substage 5e comprises shallow marine sediments at more than 20 sites onshore and cibicides wuellerstorfii carrying sediments on the continental slope summer temperatures were 2 3 warmer than the holocene optimum and there was vigorous advection of warm atlantic water into the fjords the warm period seems to be accompanied by a eustatic sea level rise of ca 20 m during the weichselian there were three major glacier advances the aucellaelv jyllandselv and flakkerhuk stades isotope substages 5d 5b and stages 3 2 all three advances mark a shift from one topographically determined stable position to another in each phase the glaciers occupied almost the same space in the fjord basins and had their fronts on the inner shelf but the glacial regime and duration was different the aucellaelv stade lasted ca 10 ka and the regime resembled that of present day outlet glaciers 600 km further to the north the flakkerhuk stade lasted for ca 50 ka but left only thin and sporadic till as well as glaciolacustrine sediments in ice dammed river valleys the regime was polar similar to present day glaciers in antarctica its culmination the last glacial maximum in the period between 22 and 14 ka is shown by a maximum in ird deposition on the continental slope after 12 ka and before 10 ka the outer fjord basins in the southern fjord zone had been abandoned by the glaciers and at ca 9 5 ka the last resurgence the milne land stade had ended

two dimensional refold interference patterns abstract when a rock undergoes two generations of folding complex three dimensional refolded structures result if such a structure is then sectioned two dimensional interference patterns result these patterns have been discussed before but the incredible variety and complexities of these patterns can be shown only with a large number of diagrams using a computer simulation various refolded structures have been sliced at every unique 30 combination of strike and dip thirty sections per structure the characteristics of the patterns observed are discussed and recurring recognizable patterns are identified

a regional 8200 cal yr bp cooling event in northwest europe induced by final stages of the laurentide ice sheet deglaciation the most notable change in 18o in greenland ice cores during the holocene occurs at 8200 cal yr bp here we present a new high resolution marine record from the northern north sea along with tree ring data from germany which contain evidence of a pronounced temperature drop 2 c contemporaneous with that of the greenland ice core records the synchronous timing of the cooling event in the greenland ice cores marine record and tree ring data from northwest europe reflects a regional influence on the north atlantic ocean atmospheric system suggesting a prominent role of the north atlantic thermohaline circulation the operation of the north atlantic ocean circulation is sensitive to variation in the freshwater budget implying that any change in freshwater flux is capable of altering the north atlantic circulation system we hypothesise minor but long term freshwater fluxes in the final stages of the deglaciation of the laurentide ice sheet as a forcing mechanism 1998 john wiley sons ltd

physical models of regional fold superposition the role of competence contrast abstract physical models of superposed folds demonstrate that rheologic contrast strongly controls the style of fold interference rheologic contrast affects strain partitioning between layer parallel shortening and buckling and affects the development of structural anisotropies parallel to first generation folds laminates with insignificant competence contrast are characterized by circular to elliptical domes and basins type 1 interference in addition to folding the layers accommodate shortening by layer parallel thickening preferentially in the fold culminations laminates with significant competence contrast are characterized by buckled fold hingelines and axial surfaces type 2 interference the less competent layers thicken in the hinges the more competent layers maintain their initial thickness in plan view the f 1 hingelines are refolded in a lobate cuspate to box style whose axial traces form conjugate pairs the models are dynamically scaled to represent folds with km scale wavelengths the evolution of surface structures map patterns at different depths and equal area projections synthesized from structure contour maps were used for analysis comparable to regional analysis common to field studies gravitational body forces effectively damp the vertical amplitudes of both the first and second generation folds thereby enhancing the formation of type 2 interference

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

composition of the upper mantle geophysical tests of two petrological models the elastic properties of candidate mantle phases are used to test the viability of olivine rich pyrolitic and cao al 2o 3 rich eclogitic assemblages for the mantle high temperature adiabats for each phase of interest are constructed and compared to mantle seismic properties both pyrolitic and eclogitic assemblages satisfy the seismic properties between 200 and 400 km between 400 and 670 km depth an eclogitic assemblage yields a superior match to velocities and velocity gradients the 400 km seismic discontinuity may represent a chemical boundary between pyrolite and picritic eclogite piclogite or phase transformations in the olivine orthopyroxene components of a piclogitic assemblage containing about 16 olivine high velocity gradients in the transition zone may be explained by the transformation of ca rich cpx to majorite garnet seismic properties at the top of the lower mantle are consistent with pyrolite piclogite or perovskite implying that the 670 km discontinuity may be a chemical boundary

nivation forms and processes in unconsolidated sediments ne greenland in the periglacial unconsolidated sediment landscape of zackenberg in high arctic ne greenland perennial and seasonal snowpatches dominate the geomorphological development in large areas and control the distribution of the vegetation the existence and distribution of snowpatches and their associated landforms are mainly controlled by the dominating winter wind direction and the amount of snow precipitation with aspect exerting much less influence this makes them an important source of information on past environmental change and knowledge of the combination of geomorphological processes and forms that result from their existence is thus essential the main nivation processes are backwall failure sliding and flow niveo aeolian sediment transport supra and ennival sediment flows niveo fluvial erosion development of pronival stone pavements accumulation of alluvial fans and basins and pronival solifluction the importance of failure sliding and flow in the continuous retrogressive extension of nivation hollows and niches is emphasized under the term backwall failure a morphological assemblage of landforms clearly demonstrates the direct nival sediment transfer link between the eroded nivation hollows their associated meltwater eroded channels and the pronival alluvial fans or basins all landform elements and their formative processes are integrated into a comprehensive model 1998 john wiley sons ltd

a younger dryas ash bed in western norway and its possible correlations with tephra in cores from the norwegian sea and the north atlantic abstract a bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western norway it is formally mamed the vedde ash bed and its age is approximately 10 600 yr b p i e mid younger dryas the bed consits of pure glass having a bimodal basaltic and rhyolitic somposition the geochemistry of the glass shards suggests an icelandic source by means of stratigraphic position and geochemistry the ash is correlated with ash zones found in cores from the continental shelf the norwegian sea and the north atlatic

deglaciation chronology sea level changes and environmental changes from holocene lake sediments of germania havn so sabine o northeast greenland abstract germania havn so is located at the outermost coast of northeastern greenland according to radiocarbon dating the lake basin was deglaciated in the early holocene around 11 000 cal yr bp at that time the lake was a marine bay but the lake was isolated soon after deglaciation at 10 600 cal yr bp the marine fauna was species poor indicating harsh conditions with a high sedimentation rate and lowered salinity due to glacial meltwater supply the pioneer vegetation around the lake was dominated by mosses and herbs deposition of relatively coarse sediments during the early holocene indicates erosion of the newly deglaciated terrain remains of the first woody plant salix herbacea appear at 7600 cal yr bp and remains of other woody plants salix arctica dryas octopetala cassiope tetragona and empetrum nigrum appear around one millennium later declining concentrations of d octopetala and the caddis fly apatania zonella in the late holocene probably imply falling summer temperatures only moderate changes in the granulometric and geochemical record during the holocene indicate relatively stable environmental settings in the lake which can probably be explained by its location at the outer coast and the buffering effect of the neighboring ocean

response of the high latitude northern hemisphere to orbital climate forcing evidence from the nordic seas sediment cores from the nordic greenland iceland and norwegian seas provide evidence that this area acts as an initial responder to the forcing effect of orbitally driven changes in insolation on the climate system as postulated by j imbrie et al the 18 o record of the cores documents a widespread initial deglacial signal in the area between 15 and 13 ka 1000 yr before other deglacial signals from other parts of the northern hemisphere an even earlier meltwater event has been dated to 16 090 185 yr b p north of iceland at the initial rise of northern hemisphere insolation after the last glacial maximum during the period with lowered surface salinities the nordic seas were still cold reconstructions of the surface water conditions of the area show that as the summer insolation values of the northern hemisphere reached half of maximum values a sea ice free corridor opened along norway at 13 4 ka nearly contemporaneous fluctuations of the polar front and the sea surface temperatures with the insolation changes indicate that the nordic seas are very sensitive to insolation forcing especially in regions close to the sea ice margin a decrease in sea surface temperature and an increase in the areal extent of sea ice cover since 7 ka indicate that the area is currently on the way to glacial conditions supporting the predictions made earlier by j imbrie et al

the schmidt hammer as a holocene calibrated age dating technique testing the form of the r value age relationship and defining the predicted age errors most recent developments of schmidt hammer exposure age dating shd as a calibrated age dating tool have been limited by the use of locations at two age control points this has necessitated 1 making assumptions about a linear r value age relationship and 2 basing predictions of age errors only on r value variance at the two age control points this paper analyses 9900 r values obtained from multiple age control points on a sequence of glacio isostatically raised shorelines with well constrained ages skuleskogen high coast world heritage site and environs gulf of bothnia northern sweden ranging from modern to 10 5 ka in age the sampling design involved 30 measurements on granite beach boulders from 30 sites at 11 age control points the r value age relationship is best described by a linear function ordinary least squares ols with an r 2 of 0 89 p 0 0001 predicted age errors are calculated using two approaches 1 ols regression which takes account of the uncertainties associated with the regression line and the age control points and 2 weighted total least squares wtls regression which in addition takes account of possible shoreline age errors and the heteroscedasticity of r value residuals with increasing age with both approaches 95 predicted age errors are relatively modest 355 455 years and 300 515 years respectively with larger r value variance and hence uncertainty for older surfaces and the possibility of further improvement from a more selective field sampling scheme that differentiates between age related and non age related rock surface variability our results also indicate that for certain lithologies and weathering environments it is possible to construct reliable calibrated age curves from relatively few age control points

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

sound velocities of morb and absence of a basaltic layer in the mantle transition region 1 compressional vp and shear vs wave velocities of mid ocean ridge basalt morb was investigated atin situ high pressure and high temperature conditions of the mantle transition region by using a combination of ultrasonic and in situx ray measurements both vp and vs of morb are lower than the previously predicted velocities of the major mantle mineral phases we found that the vp and vs of morb along a typical geotherm are lower by about 2 and 5 respectively than those of seismological models and do not match any global and regional seismological models in the deeper parts of the mantle transition region thus the existence of a basaltic layer in this region is unlikely suggesting that the oceanic crust materials are transported into the lower mantle

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

geometric models of folding at loch monar scotland using computer simulation abstract small scale hand specimens were collected at loch monar scotland one of the classic areas of fold interference patterns from the analysis of these the geometries of the f 1 and f 2 folds were derived by computer simulation the complex three dimensional form of the fold interference shapes can then be reproduced very closely f 2 fold shapes and motion directions derived from the small scale structures along with those derived from field observations of f 1 lineations deformed about f 2 folds were then applied to an extrapolated pre f 2 shape of the loch monar synform this generated a map pattern strikingly similar to that mapped by ramsay 1958 the geometric models provide useful information for mechanical hypotheses of the folding observed at loch monar the simulation reveals an interesting problem that whereas many small scale interference patterns reflect the map pattern of the major structure there are exposures of interference patterns that do not these are dome and basin type 1 patterns found in an area where a major f 2 fold hinge crosses an f 1 fold hinge zone by examining the deformed l 1 lineation patterns found in this area along with the computed d 2 strain orientations and the field observations of f 2 fold geometries we suggest that those patterns formed due to local variations in the displacement directions during the f 2 folding perhaps due to the mechanical influence of relatively competent pegmatite veins on the small scale f 2 folds the very high d 2 strain has then amplified the dome and basin elements to very elongate cone and cylinder forms this creates local type 1 patterns within a regional type 2 interference pattern structure

a model of greenland ice sheet deglaciation constrained by observations of relative sea level and ice extent an ice sheet model was constrained to reconstruct the evolution of the greenland ice sheet gris from the last glacial maximum lgm to present to improve our understanding of its response to climate change the study involved applying a glaciological model in series with a glacial isostatic adjustment and relative sea level rsl model the model reconstruction builds upon the work of simpson et al 2009 through four main extensions 1 a larger constraint database consisting of rsl and ice extent data model improvements to the 2 climate and 3 sea level forcing components 4 accounting for uncertainties in non greenland ice the research was conducted primarily to address data model misfits and to quantify inherent model uncertainties with the earth structure and non greenland ice our new model termed huy3 fits the majority of observations and is characterised by a number of defining features during the lgm the ice sheet had an excess of 4 7 m ice equivalent sea level iesl which reached a maximum volume of 5 1 m iesl at 16 5 cal ka bp modelled retreat of ice from the continental shelf progressed at different rates and timings in different sectors southwest and southeast greenland began to retreat from the continental shelf by 16 to 14 cal ka bp thus responding in part to the bolling allerod warm event c 14 5 cal ka bp subsequently ice at the southern tip of greenland readvanced during the younger dryas cold event in northern greenland the ice retreated rapidly from the continental shelf upon the climatic recovery out of the younger dryas to present day conditions upon entering the holocene 11 7 cal ka bp the ice sheet soon became land based during the holocene thermal maximum htm 9 5 cal ka bp air temperatures across greenland were marginally higher than those at present and the gris margin retreated inland of its present day southwest position by 40 60 km at 4 cal ka bp which produced a deficit volume of 0 16 m iesl relative to present in response to the htm warmth our optimal model reconstruction lost mass at a maximum centennial rate of c 103 4 gt yr our results suggest that remaining data model discrepancies are affiliated with missing physics and sub grid processes of the glaciological model uncertainties in the climate forcing lateral earth structure and non greenland ice particularly the north american component finally applying the huy3 greenland reconstruction with our optimal earth model we generate present day uplift rates across greenland due to past changes in the ocean and ice loads with explicit error bars due to uncertainties in the earth structure present day uplift rates due to past changes are spatially variable and range from 3 5 to 7 mm a including earth model uncertainty

ultradeep ultramafic mantle xenoliths transmission electron microscopy preliminary results abstract the defect microstructure of ultradeep garnets from the jagersfontein kimberlite pipe south africa was investigated by transmission electron microscopy these crystals exhibit a high density of dislocations most of which form well organized and regularly spaced subgrain boundaries free dislocations are also detected most of them have a burgers vector 1 2 111 shortest lattice repeat but a few 100 burgers vectors are also characterized especially in junctions small needle shaped pyroxene exsolutions are also detected they exsolved from the si rich garnets during assent to the earth s surface their nucleation and growth required bulk diffusion and this process may have affected the original dislocation microstructure it is believed however that the observed dislocation pattern still reflects the original deformation regime of garnets at very high pressure and temperature and this dislocation pattern strongly suggests that garnets were highly ductile finally a number of precipitates of a dense amorphous phase of pure carbon are also detected they might result from the amorphization of small diamonds exsolved from the garnet as the pressure was progressively released

the position of the gulf stream during quaternary glaciations ocean general circulation theories predict that the position of the boundary between subtropical and subpolar gyres and therefore the position of the gulf stream north atlantic current system and the subpolar subtropical front is set by the line of zero ekman pumping where there is no convergence or divergence of water in the directly wind forced surface layer of the ocean in the present day north atlantic ocean this line runs southwest to northeast from off the carolinas to off ireland however during the last ice age 18 000 years ago the subpolar subtropical boundary ran more zonally directly toward gibraltar a numerical atmospheric general circulation model indicates that the field of ekman pumping 18 000 years ago was modified by the presence of a continental ice cap more than 3 kilometers thick such that the line of zero ekman pumping overlaid the paleogyre boundary these results demonstrate that the presence of a thick continental ice sheet could have caused changes in sea surface temperatures in the north atlantic during quaternary glaciations by altering wind patterns

glacier contraction during the middle holocene in the western italian alps evidence and implications radiocarbon dates of peat from the top and base of a bog exposed by recent retreat of rutor glacier show that the glacier front terminated upvalley from the bog from 8400 until at least 6000 b p the evidence is consistent with botanical data that point to a high tree line during the interval and to reconstructed mean july temperatures at least 4 c warmer than present temperatures if the mass balance history of the glacier is typical of other glaciers in this region it is likely that average equilibrium line altitudes during the interval of contraction remained above those of the present and well above those of subsequent neoglacial ice advances

a diatom maximum horizon in upper quaternary deposits diatom maxima have been observed in three sediment cores two from the skagerrak norwegian sea area and one from the fram strait the maxima occur between 11 000 b p and 9 000 b p in the skagerrak norwegian sea and between about 9 000 b p and 4 500 b p in the fram strait it is thus likely that high diatom productivity as reflected by the diatom maximum horizons are time transgressive and follow the movements of the oceanic polar front the occurrence of diatom maximum horizons can therefore be used as a signal indicating the presence of the polar front at the time of deposition in both the skagerrak and norwegian sea cores the maximum consist of two distinct peaks the oldest characterized by cold water species thalassiosira antarctica the youngest characterized by temperate species reflecting the present diatom flora

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate

variations in surface water mass conditions in the norwegian sea evidence from holocene coccolith and dinoflagellate cyst assemblages coccolith and dinoflagellate cyst assemblages have been investigated in five sediment cores from the norwegian sea and fram strait both fossil groups are characterized by similar patterns of composition the assemblages contain high proportions of single species the coccolith flora is of low diversity and consists almost entirely of coccolithus pelagicus and emiliania huxleyi the dinoflagellate cysts are generally dominated by operculodinium centrocarpum and nematosphaeropsis labyrinthus other species especially bitectatodinium tepikiense peridinium faeroense and impagidinium pallidum sometimes contribute considerably to the assemblages based on the abundance of the assemblages and the ratio change between the dominating species it has been possible to establish three intervals of distinct major changes in surface water mass conditions sparse occurrences of coccoliths and dinoflagellate cysts have been observed before 10 000 yrs b p indicating harsh environmental conditions with a distinct influence of meltwater and temporarily very slight inflow of atlantic water the modern surface water circulation pattern was reinitiated during termination ib the assemblages suggest slightly cooler and probably less saline surface water conditions than are present today until 7500 yrs b p solar insolation may have caused a first temperature peak which is responsible for the early holocene productivity maximum a considerable change in the composition of dinocyst and coccolith assemblages occurs corresponding approximately to the onset of the holocene climatic optimum this change was most probably linked to an almost synchronous reorganization of the hydrographic properties in the entire north atlantic realm after the ice sheets had vanished since 6000 yrs b p the norwegian current with its modern oceanographic and ecological properties has been fully established