space geodetic observations of nazca south america convergence across the central andes space geodetic data recorded rates and directions of motion across the convergent boundary zone between the oceanic nazca and continental south american plates in peru and bolivia roughly half of the overall convergence about 30 to 40 millimeters per year accumulated on the locked plate interface and can be released in future earthquakes about 10 to 15 millimeters per year of crustal shortening occurred inland at the sub andean foreland fold and thrust belt indicating that the andes are continuing to build little 5 to 10 millimeters per year along trench motion of coastal forearc slivers was observed despite the oblique convergence

the sediments of lake logurinn a unique proxy record of holocene glacial meltwater variability in eastern iceland the full holocene development of the large 8100 km 2 vatnajokull ice cap in iceland with its many outlet glaciers is poorly known the idea of an early deglaciation leading to a glacier free period in mid holocene followed by the neoglaciation is still the main concept for the glacial history in the north atlantic region including iceland we have examined a continuous sediment record from the glacier fed lake logurinn in eastern iceland to infer holocene meltwater variability of eyjabakkajokull which is a surge type outlet glacier of the vatnajokull ice cap we focus on the early and mid holocene and our data show that eyjabakkajokull receded rapidly during the final phase of the last deglaciation and did not deliver glacial meltwater to lake logurinn by 9000 years bp suggesting that eyjabakkajokull was significantly smaller than today at that time the return of glacial meltwater transport to lake logurinn and thus a return of eyjabakkajokull is dated to ca 4400 years bp suggesting an almost 5000 years long glacier free period during early and mid holocene during this time period we infer that the 8 2 ka cold event did not cause a significant expansion of eyjabakkajokull however we note a marked decrease in the aquatic productivity in lake logurinn which is suggested to be the result of shorter ice free seasons of lake logurinn the holocene thermal maximum is inferred by a period of maximum holocene aquatic productivity and dated to ca 7900 7000 years bp following the re formation of eyjabakkajokull ca 4400 years bp we suggest that the glacier reached stable conditions ca 1700 years bp and remained fairly stable until the later part of the little ice age when eyjabakkajokull reached its maximum holocene extent c 2012 elsevier ltd all rights reserved less

holocene glacier variability and neoglacial hydroclimate at alfotbreen western norway abstract glaciers and small ice caps respond rapidly to climate perturbations mainly winter precipitation and summer temperature and the mass balance of glaciers located in western norway is governed mainly by winter precipitation pw records of past pw can offer important insight into long term changes in atmospheric circulation but few proxies are able to accurately capture winter climate variations in scandinavia reconstructions of equilibrium line altitude ela variations from glaciers that are sensitive to changes in pw therefore provide a unique opportunity to quantify past winter climate in this region here we present a new holocene glacier activity reconstruction for the maritime ice cap alfotbreen in western norway based on investigations of distal glacier fed lake sediments and modern mass balance measurements 1963 2010 several lake sediment cores have been subject to a suite of laboratory analyses including measurements of physical parameters such as dry bulk density dbd and loss on ignition loi geochemistry xrf surface magnetic susceptibility ms and grain size distribution to identify glacial sedimentation in the lake both radiocarbon ams 14 c and 210 pb dating were applied to establish age depth relationships in the sediment cores a novel approach was used to calibrate the sedimentary record against a simple ela model which allowed reconstruction of continuous ela changes for alfotbreen during the neoglacial when alfotbreen was present i e the last 1400 years furthermore the resulting ela variations were combined with an independent summer temperature record to calculate neoglacial pw using the liestol equation the resulting pw record is of higher resolution than previous reconstructions from glaciers in norway and shows the potential of glacier records to provide high resolution data reflecting past variations in hydroclimate complete deglaciation of the alfotbreen occurred 9700 cal yr bp and the ice cap was subsequently absent or very small until a short lived glacier event is seen in the lake sediments 8200 cal yr bp the ice cap was most likely completely melted until a new glacier event occurred around 5300 cal yr bp coeval with the onset of the neoglacial at several other glaciers in southwestern norway alfotbreen was thereafter absent or very small until the onset of the neoglacial period 1400 cal yr bp the little ice age lia 650 50 cal yr bp was the largest glacier advance of alfotbreen since deglaciation with a maximum extent at 400 200 cal yr bp when the ela was lowered approximately 200 m relative to today the late onset of the neoglacial at alfotbreen is suggested to be a result of its low altitude relative to the regional ela a synthesis of neoglacial ela fluctuations along the coast of norway indicates a time transgressive trend in the maximum extent of the lia which apparently seems to have occurred progressively later as we move northwards we suggest that this trend is likely due to regional winter precipitation differences along the coast of norway

strong contrast in mass and energy balance between a coastal mountain glacier and the greenland ice sheet we show a strong difference in surface mass and energy balance of a mountain glacier and two sites on the ice sheet at 64 n in west greenland using stake and automated weather station observations net surface mass balance is on average 2 2 m w e less negative at the coast compared with the ice sheet in the same elevation we find a larger energy turnover at the ice sheet margin on qamanarssup sermia than measured on the coastal mountain glacier qassigiannguit with both energy input and output being of larger absolute value more cloudiness and a thicker snow cover at the relatively humid coastal glacier result in smaller gains in net shortwave radiation and smaller losses in net longwave radiation and a less negative mass balance lower wind speeds at the coastal glacier result in weaker turbulent heat exchange between atmosphere and ice surface on annual average 17 w m 2 more energy is available for melt at the ice sheet margin compared with the coastal glacier in the same elevation

asynchronous little ice age glacier fluctuations in iceland and european alps linked to shifts in subpolar north atlantic circulation abstract records of past glacier fluctuations are an important source of paleoclimate data and provide context for future changes in global ice volume in the north atlantic region glacier chronologies can be used to track the response of terrestrial environments to variations in marine conditions including circulation patterns and sea ice cover however the majority of glacier records are discontinuous and temporally restricted owing in part to the extensive advance of northern hemisphere glaciers during the little ice age lia the most recent and severe climate anomaly of the neoglacial period here we combine an absolutely dated and continuous record of langjokull ice marginal fluctuations with new reconstructions of sediment flux through the past 1 2 ka using varved sediments from hvitarvatn a proglacial lake in iceland s central highlands large spatial and temporal variations in sediment flux related to changing ice cap dimensions are reconstructed from six sediment cores and seismic reflection profiles sediment data reveal two discrete phases of ice expansion occurring ca 1400 to 1550 ad and ca 1680 to 1890 ad these advances are separated by a persistent interval of ice retreat suggesting that a substantial period of warming interrupted lia cold the pattern of icelandic glacier activity contrasts with that of european glaciers but shows strong similarities to reconstructed changes in north atlantic oceanographic conditions indicating differing regional responses to coupled ocean atmosphere sea ice variations our data suggest that subpolar north atlantic circulation dynamics may have led to coherent asynchronous glacier fluctuations during the mid lia and highlight the importance of circulation variability in triggering and transmitting multidecadal scale climate changes to nearby terrestrial environments

episodic neoglacial snowline descent and glacier expansion on svalbard reconstructed from the 14c ages of ice entombed plants abstract the response of the northern hemisphere cryosphere to the monotonic decline in summer insolation and variable radiative forcing during the holocene has been one of irregular expansion culminating in the little ice age when most glaciers attained their maximum late holocene dimensions although periods of intervening still stand or ice retreat can be reconstructed by direct dating of ice recessional features defining times of neoglacial ice growth has been limited to indirect proxies preserved in distal archives here we report 45 precise radiocarbon dates on in situ plants emerging from beneath receding glaciers on svalbard that directly date the onset of snowline descent and glacier expansion entombing the plants persistent snowline lowering occurred between 4 0 and 3 4 ka but with little additional persistent lowering until early in the first millennium ad populations of individual 14 c calendar age results and their aggregate calendar age probabilities define discrete episodes of vegetation kill and snowline lowering 240 340 ad 410 540 ad and 670 750 ad each with a lower snowline than the preceding episode followed by additional snowline lowering between 1000 and 1220 ad and between 1300 and 1450 ad snowline changes after 1450 ad including the maximum ice extent of the little ice age are not resolved by our collections although snowlines remained lower than their 1450 ad level until the onset of modern warming a time distance diagram derived from a 250 m long transect of dated ice killed plants documents ice margin advances 750 1100 and after 1500 ad concordant with distributed vegetation kill ages seen in the aggregate data set supporting our central thesis that vegetation kill ages provide direct evidence of snowline lowering and cryospheric expansion the mid to late holocene history of snowline lowering on svalbard is similar to ela reconstructions of norwegian and svalbard cirque glaciers and consistent with a cryospheric response to the secular decline of regional summertime insolation and stepped changes in nearby surface ocean environments the widespread exposure of entombed plants dating from the first millennium ad suggests that svalbard s average summer temperatures of the past century now exceed those of any century since at least 700 ad including medieval times

late holocene expansion of istorvet ice cap liverpool land east greenland abstract the greenland ice sheet is undergoing dynamic changes that will have global implications if they continue into the future in this regard an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior small independent ice caps adjacent to the greenland ice sheet hereinafter called local ice caps are sensitive indicators of the response of greenland ice marginal zones to climate change therefore we reconstructed late holocene ice marginal fluctuations of the local istorvet ice cap in east greenland using radiocarbon dates of subfossil plants 10 be dates of surface boulders and analyses of sediment cores from both threshold and control lakes during the last termination the istorvet ice cap had retreated close to its maximum holocene position by 11 730 cal yr bp radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the istorvet cap was smaller than at present from ad 200 to ad 1025 sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its holocene maximum position by ad 1150 thereafter the ice cap remained at or close to this position until at least ad 1660 the timing of this the most extensive of the holocene expansion is similar to that recorded at some glaciers in the alps and in southern alaska however in contrast to these other regions the expansion in east greenland at ad 1150 appears to have been very close to if not at a maximum holocene value comparison of the istorvet ice cap fluctuations with holocene glacier extents in southern hemisphere middle to high latitude locations on the antarctic peninsula and in the andes and the southern alps suggests an out of phase relationship if correct this pattern supports the hypothesis that a bipolar see saw of oceanic and or atmospheric circulation during the holocene produced asynchronous glacier response at some localities in the two polar hemispheres

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

seismicity and shape of the subducted nazca plate an updated compilation of earthquake locations and focal mechanism solutions from the international seismological centre and preliminary determination of earthquakes is the basis of a comprehensive study of the geometry of the wadati benioff zone beneath western south america the new data support previous mapping of a sharp flexure rather than a tear in the subducted nazca plate beneath southern peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with 30 dip at latitude 33 s in contrast the transition from 30 slab dip beneath bolivia to a nearly horizontal dip in the region between 28 s 32 s is more gradual occurring over several hundred kilometers of along strike distance between 20 s and 32 s this southward flattening corresponds to a broadening of a horizontal benchlike part of the subducted plate formed between 100 and 125 km depth the transition in continental tectonic style near 27 s 28 s from a wide volcanically active plateau to a narrow nonvolcanic cordillera appears not to be associated with the main slab flattening which begins to the north of these latitudes but with a more abrupt change in curvature of the subducted slab from convex upward to concave upward immediately below the plate boundary interface the concept of gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the south american plate we hypothesize that the polarity of vertical curvature in the subducting slab is governed by the orientation of lateral curvature of the plate margin focal mechanism solutions for intermediate and deep earthquakes are grouped by geographic region and inverted for the orientation and relative magnitudes of the principal stresses results of the inversion indicate that downdip extension dominates in the slab above 350 km while downdip compression dominates at greater depths

high level surfaces plateau uplift and foreland development bolivian central andes newly dated tertiary strata in the bolivian central andean plateau and synthesis of the tertiary record in the adjacent subandean fold thrust belt constrain the age of deformation in both regions age of deformation within the plateau is determined by dated crosscutting relations associated with a regionally extensive high level surface known as the san juan del oro surface new 40 ar 39 ar dates on undeformed strata above the high level surface preclude significant upper crustal shortening within the eastern cordillera after 10 ma tertiary strata within the adjacent subandean region demonstrate that formation of the fold thrust belt occurred after 10 ma on the basis of these data we propose a two stage model of late cenozoic andean growth that links plateau uplift to the development of the fold thrust belt in the first stage early plateau uplift occurred in response to widespread compressional deformation of the plateau eastern cordillera and altiplano during the second stage beginning after 10 ma upper crustal deformation within the plateau terminated and the subandean fold thrust belt developed crustal scale eastward thrusting along the eastern margin of the eastern cordillera drove subandean folding and thrusting the eastern cordillera served as the bulldozer for the deforming subandean wedge

global variability in subduction thrust zone forearc systems deviations of slip vector azimuths of interplate thrust earthquakes from expected plate convergence directions at oblique subduction zones provide kinematic information about the deformation of forearcs and indirect evidence on the dynamics of the plate boundary a global survey of slip vectors at major trenches of the world reveals a large variability in the kinematic response of forearcs to shear produced by oblique convergence the variability in forearc deformation inferred from slip vector deflections is suggested to be caused by variations in forearc rheology rather than in the stresses acting on subduction zone thrust faults estimated apparent macroscopic rheologies range from elastic to perfectly plastic or viscous forearc rheologies inferred from slip vectors do not correlate with age of the subducting lithosphere but continental forearcs or old arcs appear to deform less than oceanic or young arcs the inferred absence of forearc deformation at continental arcs from this study is counter to inferences drawn from compiled geologic information on forearc faults correlations of the apparent forearc rheology with backarc spreading convergence rate slab dip arc curvature and downdip length of the thrust contact are poor however great subduction zone earthquakes occur where forearcs are apparently more elastic i e less deformed by oblique convergence which suggests that the mechanical properties of forearcs rather than stress magnitude on thrust faults control both the kinematic behavior of forearcs and where great subduction zone earthquakes occur

a new jurassic recent apparent polar wander path for south america and a review of central andean tectonic models abstract the jurassic to recent palaeomagnetic data from the stable cratonic areas of south america and africa are reviewed and evaluated from the combined data set seven mean reference pole positions are calculated for the early middle and late jurassic early and late cretaceous palaeogene and neogene most of these new palaeopoles are well defined and indicate a complex course of apparent polar wander for the south american plate comparison of the palaeomagnetic data from the andean margin with the reference poles indicates vertical axis rotations defining a broad pattern of anticlockwise rotations north of the arica deflection at approximately 19 s and clockwise rotations to the south further analysis indicates however that the distribution and magnitude of rotations is more complicated than this broad division tectonic models proposed to explain the pattern of rotations and the possible origins of the arica deflection are discussed it is suggested that the rotations probably result from localised in situ rotations controlled by strike slip fault systems or thrust sheets rather than large scale rotation mechanisms the broad rotation pattern may result from the influence of pre existing structures in the margin or variations in the flexural rigidity of the brazilian shield behind the deformation zone

glacier fluctuations equilibrium line altitudes and palaeoclimate in lyngen northern norway during the lateglacial and holocene based on lacustrine and morpho stratigraphical evidence from lyngen in troms northern norway 13 marginal moraines have been mapped in front of lenangsbreene in strupskardet moraines m1 m13 are inferred to represent glacier halts or advance readvance taking place during the lateglacial and holocene the presence of collapse depressions suggests that some of them were ice cored m1 m3 a chronological framework taking into account a combination of former shorelines and related glacier meltwater channels lichenometry and ams radiocarbon dated lacustrine sediments spanning the last 20 000 cal yr bp has been established the distal glacier fed lake aspvatnet was isolated from the sea c 10 300 cal yr bp and the lacustrine sediments have been investigated by use of loss on ignition loi magnetic susceptibility water content wet and dry bulk density dbd and the magnetic parameters anhysteretic remanent magnetization arm and saturation remanent magnetization sirm there is in general good agr

holocene climate change in arctic canada and greenland abstract this synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the holocene in arctic canada and greenland our synthesis includes 47 records from a recently published database of highly resolved holocene paleoclimate time series from the arctic sundqvist et al 2014 we analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records mostly from datasets that did not fit the selection criteria for the arctic holocene database combined we review evidence from a variety of proxy archives including glaciers ice cores and glacial geomorphology lake sediments peat sequences and coastal and deep marine sediments the temperature sensitive records indicate more consistent and earlier holocene warmth in the north and east and a more diffuse and later holocene thermal maximum in the south and west principal components analysis reveals two dominant holocene trends one with early holocene warmth followed by cooling in the middle holocene the other with a broader period of warmth in the middle holocene followed by cooling in the late holocene the temperature decrease from the warmest to the coolest portions of the holocene is 3 0 1 0 c on average n 11 sites the greenland ice sheet retracted to its minimum extent between 5 and 3 ka consistent with many sites from around greenland depicting a switch from warm to cool conditions around that time the spatial pattern of temperature change through the holocene was likely driven by the decrease in northern latitude summer insolation through the holocene the varied influence of waning ice sheets in the early holocene and the variable influx of atlantic water into the study region

abrupt holocene climate change as an important factor for human migration in west greenland west greenland has had multiple episodes of human colonization and cultural transitions over the past 4 500 y however the explanations for these large scale human migrations are varied including climatic factors resistance to adaptation economic marginalization mercantile exploration and hostile neighborhood interactions evaluating the potential role of climate change is complicated by the lack of quantitative paleoclimate reconstructions near settlement areas and by the relative stability of holocene temperature derived from ice cores atop the greenland ice sheet here we present high resolution records of temperature over the past 5 600 y based on alkenone unsaturation in sediments of two lakes in west greenland we find that major temperature changes in the past 4 500 y occurred abruptly within decades and were coeval in timing with the archaeological records of settlement and abandonment of the saqqaq dorset and norse cultures which suggests that abrupt temperature changes profoundly impacted human civilization in the region temperature variations in west greenland display an antiphased relationship to temperature changes in ireland over centennial to millennial timescales resembling the interannual to multidecadal temperature seesaw associated with the north atlantic oscillation

contrasting evidence of holocene ice margin retreat south western greenland constraining the greenland ice sheet s gris response to holocene climate change provides calibrations for ice sheet models that hindcast past ice margin fluctuations ice sheet models predict enhanced ice retreat in south western greenland during the middle holocene however few geological observations corroborating the extensive retreat are available we present new data from lake sediment cores from the isua region south western greenland which provide constraints on holocene fluctuations of the gris margins our data indicate that the main gris margin was 30 km west of its present day extent by 5 7k cal a bp and had retreated to within 3 km of its present day margin by 4 6k cal a bp with subsequent re advances by 1 8 and at 1 7 1 3 and 0 5k cal a bp times of ice retreat are coeval with increasing temperatures in western greenland suggesting that temperature was a dominant factor in ice retreat the late retreat at isua is in contrast to the early retreat observed in the godthabsfjord area and is probably related to the lack of fjords extending to the present isua ice margin our data are not consistent with current ice sheet models that overestimate the middle holocene ice retreat in the isua region of south western greenland

topography and subduction geometry in the central andes clues to the mechanics of a noncollisional orogen the central andean orogen between 12 and 32 s latitude exhibits a high degree of spatial order principally an extraordinary bilateral symmetry that is common to the earth s surface the underlying wadati benioff zone and the nazca south america plate kinematics which has been stable since the mid tertiary this spatial order must reflect the physical mechanisms of mountain building in this noncollisional orogen the shapes of the topography and subduction zone can be reduced to symmetric and antisymmeric components relative to any vertical symmetry plane the particular plane which minimizes the antisymmetry and maximizes the symmetry is well resolved and is essentially coincident with the stable euler equator of nazca south america relative motion since the mid tertiary that the topography subduction geometry and persistent mid tertiary plate kinematics share common spatial and geometric elements suggests that the distribution of topography in this orogen depends strongly on the dynamics of subduction other factors that might affect the topography and underlying tectonics such as climate and inherited structural fabric which have different spatial characteristics must be of less significance at a continental scale furthermore the small components of asymmetry among the various elements of the orogen appear to be mutually related in a simple way it is possible that this coupled asymmetry is associated with a late tertiary change in plate kinematics these observations suggest that there is a close connection between plate tectonics and the form of the earth s surface in this noncollisional setting it follows that the distribution of topography near convergent plate boundaries may provide a powerful constraint for understanding the dynamics of subduction

latest pleistocene and holocene glaciation of baffin island arctic canada key patterns and chronologies abstract melting glaciers and ice caps on baffin island contribute roughly half of the sea level rise from all ice in arctic canada although they comprise only one fourth of the total ice in the region the uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change we review the key patterns and chronologies of latest pleistocene and holocene glaciation on baffin island the deglaciation by the laurentide ice sheet occurred generally slowly and steadily throughout the holocene to its present margin barnes ice cap except for two periods of rapid retreat an early interval 12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds and a later interval 7 ka when ice over foxe basin collapsed in coastal settings alpine glaciers were smaller during the younger dryas period than during the little ice age at least some alpine glaciers apparently survived the early holocene thermal maximum which was several degrees warmer than today although data on glacier extent during the early holocene is extremely sparse following the early holocene thermal maximum glaciers advanced during neoglaciation beginning in some places as early as 6 ka although most sites do not record near little ice age positions until 3 5 to 2 5 ka alpine glaciers reached their largest holocene extents during the little ice age when temperatures were 1 1 5 c cooler than during the late 20th century synchronous advances across baffin island throughout neoglaciation indicate sub milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability future work should further elucidate the state of glaciers and ice caps during the early holocene thermal maximum and glacier response to climate forcing mechanisms

early to middle holocene valley glaciations on northernmost greenland abstract this paper presents the glacial stratigraphy and palaeoenvironmental evolution around constable bugt johannes v jensen land located on the north coast of greenland this is a land of extreme climate polar desert conditions and a coast bound by a permanent sea ice cover our data covers the period from the last glacial maximum lgm 18 22 cal ka bp into the holocene it records the history of a shelf based glaciation with ice flowing eastward along the coast as well as two local valley glacier advances from the south during the holocene with ice on the coastal plain during the lgm glaciolacustrine basins formed in marginal positions and in ice dammed valleys to the south into the mountainous area of peary land with the break up of shelf based ice there was a gradual marine inundation at which the marine limit formed at 45 m a s l this initial early holocene ice advance from the south formed prominent valley mouth moraines especially in sifs valley here both glaciolacustrine and marine sediments were remoulded and or dislocated as thrust blocks into a moraine ridge spanning more than 1 km in width and 60 m in height radiocarbon ages of sediments incorporated in this moraine as well as from on lapping sediments suggest that the moraine formed between 9 6 and 6 3 cal ka bp based on 14 c dating results the youngest ice advance phase can be narrowed down to 14 c ages between 5 5 5 0 cal ka bp the recorded ice advances took place during the holocene thermal maximum htm for north greenland the last one close to the beginning of the neoglacial cooling during the htm we have recorded a period of 2500 years during which the north coast of greenland as opposed to today experienced an absence to very restricted occurrence of land fast or multi year sea ice this observation can be explained by the altitudinal and temporal distribution of beach ridge complexes that must have formed by wave action and thus requiring at least partial open water conditions with a moisture source at hand we propose that this lead to enhanced precipitation in the near coastal areas which coupled to documented htm cold reversals caused a lowered glaciation limit and led to a positive mass balance and subsequent ice advance

cenozoic plate kinematics subduction and magmatism south american andes revised plate reconstructions and enlarged isotopic age data sets strongly support three mechanisms for controlling the configuration and associated volcanism and tectonism of the andean subduction zone these include age of subducted plate convergence rate and interaction with hotspot traces from 50 to 25 ma in the andes the age of oceanic plate subducted progressively decreased apparently resulting in a9gradual decrease in subduction angle and consequent eastward shift in the loci of magmatic activity a major reorganization of plate motions at 25 ma resulted in an increased convergence rate normal to the chilean andes and was accompanied by subsequent broadening of the locus of magmatic activity into adjacent portions of bolivia and argentina convergence rates changed only slightly across the peruvian margin and no clear effect on subsequent magmatism is indicated interaction of the andean subduction zone with the juan fernandez and easter nazca hotspot traces apparently resulted in lower angle subduction and consequent gaps in magmatic activity as predicted continuations of the traces correspond with regions lacking dated volcanic rocks the current gaps in igneous activity correspond with contemporary subduction of the two traces and this association apparently occurred in the past as well

greenland surface mass balance observations from the ice sheet ablation area and local glaciers glacier surface mass balance measurements on greenland started more than a century ago but no compilation exists of the observations from the ablation area of the ice sheet and local glaciers such data could be used in the evaluation of modelled surface mass balance or to document changes in glacier melt independently from model output here we present a comprehensive database of greenland glacier surface mass balance observations from the ablation area of the ice sheet and local glaciers the database spans the 123 a from 1892 to 2015 contains a total of 3000 measurements from 46 sites and is openly accessible through the promice web portal http www promice dk for each measurement we provide x y and z coordinates starting and ending dates as well as quality flags we give sources for each entry and for all metadata two thirds of the data were collected from grey literature and unpublished archive documents roughly 60 of the measurements were performed by the geological survey of denmark and greenland geus previously ggu the data cover all regions of greenland except for the southernmost part of the east coast but also emphasize the importance of long term time series of which there are only two exceeding 20 a we use the data to analyse uncertainties in point measurements of surface mass balance as well as to estimate surface mass balance profiles for most regions of greenland

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

10be dating of the narsarsuaq moraine in southernmost greenland evidence for a late holocene ice advance exceeding the little ice age maximum in southernmost greenland near narsarsuaq the terminal narsarsuaq moraine was deposited well outside of a historical little ice age lia moraine adjacent to the modern ice margin using 10be surface exposure dating we determine narsarsuaq moraine abandonment at 1 51 0 11 ka a second set of 10be ages from a more ice proximal position shows that ice has been within or at its historical i e lia extent since 1 34 0 15 ka notably narsarsuaq moraine abandonment was coincident with climate amelioration in southern greenland southern greenland warming at 1 5 ka was also concurrent with the end of the roman warm period as climate along the northern north atlantic sector of europe cooled into the dark ages the warming of southern greenland and retreat of ice from the narsarsuaq moraine is consistent with studies suggesting possible anti phase centennial scale climate variability between northwestern europe and southern greenland other southernmost greenland ice margin records do not preclude a pre lia ice margin maximum potentially concurrent with a narsarsuaq advance prior to 1 51 ka but also lack sufficient ice margin control to confirm such a correlation we conclude that there is a clear need to further determine whether a late holocene pre lia maximum was a local phenomenon or a regional southern greenland ice maximum and if this advance and retreat reflects a regional fluctuation in climate

fluctuations of local glaciers in greenland during latest pleistocene and holocene time abstract this paper is the first to summarize research on fluctuations of local glaciers in greenland e g ice caps and mountain glaciers independent of the greenland ice sheet during latest pleistocene and holocene time in contrast to the extensive data available for fluctuations of the greenland ice sheet surprisingly little data exist to constrain local glacier extents much of the available research was conducted prior to wide spread use of ams radiocarbon dating and the advent of surface exposure and luminescence dating although there is a paucity of data generally similar patterns of local glacier fluctuations are observed in all regions of greenland and likely reflect changes in paleoclimate which must have influenced at least the margins of the inland ice absolute age data for late glacial and early holocene advances of local glaciers are reported from only two locations disko island and the scoresby sund region subsequent to late glacial or early holocene time most local glaciers were smaller than at present or may have disappeared completely during the holocene thermal maximum in general local glacier advances that occurred during historical time 1200 1940 ad are the most extensive since late glacial or early holocene time historical documents and more recent aerial photographs provide useful information about local glacier fluctuations during the last 100 yrs in all but one area north greenland local glaciers are currently receding from historical extents

holocene temperature history of northwest greenland with new ice cap constraints and chironomid assemblages from deltaso abstract arctic temperature shifts drive changes in carbon cycling sea ice extent and greenland ice sheet mass balance all of which have global ramifications paleoclimate data from past warm periods provide a unique means for assessing the sensitivity of these systems to warming climate but the magnitude and timing of past temperature changes in many parts of the arctic are poorly known here we assess orbital scale holocene temperature change in northwest greenland near the margin of the ice sheet using subfossil insect assemblages from lake deltaso based upon sedimentation history in this currently proglacial lake we also place constraints on holocene extents of the adjacent north ice cap a large independent ice cap reconstructed summer temperatures were warmer than present at the onset of lacustrine sedimentation following regional deglaciation by the greenland ice sheet sometime between 10 8 and 10 1 ka bp deltaso experienced the warmest summer temperatures of the holocene between 10 and 6 2 ka bp followed by progressive cooling that continued through the late holocene as summer insolation declined culminating in the lowest temperatures during the pre industrial last millennium deltaso chironomids indicate peak early holocene summer temperatures at least 2 5 3 c warmer than modern and at least 3 5 4 c warmer than the pre industrial last millennium we infer based upon lake sediment organic and biogenic content that in response to declining temperatures north ice cap reached its present day size 1850 ad having been smaller than present through most of the preceding holocene our synthesis of paleoclimate evidence from northwest greenland ellesmere island and northern baffin bay supports the timing of temperature trends inferred at deltaso and suggests that quantitative temperature reconstructions from deltaso may represent a minimum bound on regional early holocene warming collectively records from the region indicate 4 c summer cooling through the holocene intense early holocene warmth around northwest greenland argues against delayed onset of warmer than present conditions due to the influence of the nearby waning laurentide ice sheet and has implications for understanding the greenland ice sheet s sensitivity to climate change

accelerated volume loss in glacier ablation zones of ne greenland little ice age to present mountain glaciers at the periphery of the greenland ice sheet are a crucial freshwater and sediment source to the north atlantic and strongly impact arctic terrestrial fjord and coastal biogeochemical cycles in this study we mapped the extent of 1 848 mountain glaciers in ne greenland at the little ice age we determined area and volume changes for the time periods little ice age to 1980s and 1980s to 2014 and equilibrium line altitudes there was at least 172 76 34 55 km3 volume lost between 1910 and 1980s that is a rate of 2 61 0 52 km3 year between 1980s and 2014 the volume lost was 90 55 18 11 km3 that is a rate of 3 22 0 64 km3 year implying an increase of 23 in the rate of ice volume loss overall at least 7 of mass loss from greenland mountain glaciers and ice caps has come from the ne sector

local glaciers record delayed peak holocene warmth in south greenland abstract local glaciers and ice caps gics respond sensitively and quickly on the scale of decades to centuries to climate variations continuous records of past fluctuations in gic size provide information on the timing and magnitude of holocene climate shifts and a longer term perspective on 21st century glacier retreat although there is broad scale agreement on millennial scale trends in holocene climate variability and fluctuations in local gics in greenland regional variations are only loosely constrained here we present three holocene proglacial lake sediment records from south greenland an area with abundant local glaciers but few holocene length paleoclimate records in addition we use geospatial analysis to model past equilibrium line altitudes elas and thereby constrain the magnitude of ablation season temperature change during the warmest and coolest periods of the holocene physical and geochemical sedimentary characteristics show that two of the proglacial lakes continued to receive glacial meltwater input until 7 3 and 7 1 ka bp the survival of local glaciers implies that south greenland remained relatively cool and that summer temperatures gradually warmed but did not warm well beyond 1 2 c above present in the early holocene in the mid holocene from 7 1 to 5 5 ka bp organic sedimentation at these two sites indicates that local glaciers became very small or more likely melted away completely the glaciers within the third lake s catchment melted away prior to 5 2 ka bp as sediments deposited earlier in the holocene could not be dated at this site we estimate that summer temperatures increased by at least 1 2 1 8 c above present by 7 3 7 1 ka bp our results are consistent with other observations that suggest a north to south gradient in the timing of holocene thermal maximum conditions with southern greenland experiencing a delayed warming relative to other regions in greenland as summer temperatures cooled in the neoglacial our records show that sustained glacier regrowth began 3 1 ka bp with glaciers in the southernmost catchment which at present receive the most precipitation in the other two catchments which host smaller glaciers in a drier environment regrowth began at 1 3 and 1 2 ka bp the timing of which is in agreement with other glacial records from the arctic atlantic region local glaciers reached their maximum late holocene extents during a cooler second phase of the little ice age lia 0 2 0 1 ka bp that we estimate was at least 0 4 0 9 c cooler than present overall these findings improve understanding of the spatio temporal dynamics of holocene glacier and climate change in greenland potentially yielding valuable information about their future response

erratum to holocene thermal maximum in the western arctic 0 180 w quaternary science reviews 23 2003 529 560

was common era glacier expansion in the arctic atlantic region triggered by unforced atmospheric cooling abstract the timing and causes of common era ce glacier growth in the arctic atlantic region remain elusive there is mounting evidence of advances that predate the little ice age 1250 1850 ce this challenges the view that 13th century volcanic eruptions triggered change by spurring sea ice expansion recent climate model simulations indicate this response does not require external forcing under contemporaneous pre industrial boundary conditions here we try to reconcile these new insights by combining regional proxy evidence of glacier and sea ice change with a climate model experiment collated recently published reconstructions demonstrate that regional climate shifted towards a colder mean state around 650 950 ce a period marked by low radiative forcing unforced model simulations reproduce the time transgressive evolution of this response which emerged east of greenland and progressed towards svalbard the inferred pattern is associated with sea ice feedbacks triggered by stochastic atmospheric cooling we argue that this mechanism may explain the timing and pattern of ce glacier growth in the region

plate reconstructions aseismic ridges and low angle subduction beneath the andes low angle subduction segments beneath peru and chile are believed to represent interaction of the subduction zone with the aseismic nazca and juan fernandez ridges on the basis of symmetric sea floor spreading models and plate hotspot reconstructions predicted continuations of the relatively buoyant ridges correspond well with the limits of the low angle subduction segments further the history of interaction of the aseismic ridges with the subduction zone as predicted by plate reconstructions is not inconsistent with available information on volcanic episodes of the andes if the contemporary correlation of volcanic gaps and low angle subduction is also applicable to the rest of the late cenozoic the occurrence of deep seismicity beneath the eastern flanks of the andes is also believed to reflect the effects of low angle subduction the deep seismic segments are adjacent to segments which are presently or were recently experiencing low angle subduction thus the deep seismicity is interpreted as representative of remnants of normal oceanic lithosphere subducted before interaction of aseismic ridges with the subduction zone other geologic phenomena are associated with low angle subduction beneath south america including landward shift in loci of tectonism surficial subsidence and laramide style deformation the aseismic ridge buoyancy hypothesis appears to be a valuable predictive tool for the interpretation of such geologic effects

rapid early holocene ice retreat in west greenland abstract the possible demise of the greenland ice sheet and its effect on global sea level rank among the most serious climate threats to society to improve our knowledge about the future behaviour of the ice margin we studied the ice sheet s response to early holocene warming in west greenland using 47 cosmogenic 10 be exposure ages 26 optically stimulated luminescence ages as well as 15 new and 28 previously published radiocarbon ages paired bedrock and boulder ages show that the entire area was covered by warm based ice during the last glacial maximum lgm although glacial erosion was insufficient to completely remove the upper rock surface containing 10 be inherited from a previous period of exposure in bedrock samples above an elevation of 800 m our compilation of 10 be and 14 c ages demonstrates that the ice sheet retreated from the outer coast to the present ice margin between c 11 4 and 10 4 cal ka bp in the godthabsfjord system and between 10 7 0 6 and 10 1 0 4 ka ago in buksefjord whereas the coast at sermilik became ice free at c 10 5 cal ka bp we find no significant changes in the retreat rates between the deep godthabsfjord system and the buksefjord sermilik region which is characterized by only a few narrow and shallow fjords however deglaciation was initiated c 700 900 years earlier in the godthabsfjord system indicating that the deep fjords probably triggered land based deglaciation by dynamic ice loss leading to an overall rapid early holocene ice retreat and drawdown of the ice sheet in west greenland these results demonstrate that even if there was a topographic control on the onset of deglaciation fast ice retreat is not restricted to deep fjord systems but may occur independently of the topographic setting

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

a complete record of holocene glacier variability at austre okstindbreen northern norway an integrated approach arctic glaciers are currently undergoing major changes but accurate knowledge about how they varied during the entire holocene is still scarce here we present a new complete glacier record from austre okstindbreen in nordland northern norway this reconstruction is based on a number of short and long cores retrieved from several downstream basins which have been analyzed by a suite of methods including geochemical elements xrf rock magnetic properties dry bulk density dbd and loss on ignition loi lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar gpr independently lichen dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210pb dated lake sediment chronology this integrated approach reveals that austre okstindbreen is the first known glacier in scandinavia to possibly have survived the holocene thermal optimum it also brackets the four largest glacier advances to c 7400 7000 1400 1200 900 700 and 300 150 years before ad 2000 b2k in contrast to most reconstructed glaciers in scandinavia the largest glacier advance was not associated with the little ice age but rather to an earlier period centred at 1300 b2k both the moraine chronology and the lacustrine records document this neoglacial advance compared to other glacier reconstructions from the northern hemisphere we identify near synchronous glacier advances occurring roughly at 4000 b2k 2700 b2k 1300 b2k and during the little ice age these correlative advances across the northern hemisphere suggest that these observed centennial scale events are a shared feature regardless of the large geographical distances separating them some minor discrepancies between different geographical areas may be caused by lack of precise dating but local climatic conditions may play a role as well

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

using proglacial threshold lakes to constrain fluctuations of the jakobshavn isbrae ice margin western greenland during the holocene abstract the future response of the greenland ice sheet gis and its potential contribution to sea level rise are uncertain rapid changes of greenland s outlet glaciers over the past decade have made it difficult to extrapolate ice sheet change into the future this significant short term variability highlights the need for longer term geologic e g holocene records of ice margin fluctuations however a major challenge with reconstructing the gis during the holocene stems from it having been smaller than it is at present thus traditional glacial geologic approaches are not suitable we use radiocarbon dated sediment sequences from seven proglacial threshold lakes spanning 50 km of the western gis margin near jakobshavn isbrae to constrain the timing of early holocene deglaciation the duration that this sector of the western gis was smaller than its present configuration and the timing of its advance during neoglaciation our reconstructions suggest deglaciation 7300 cal yr bp minimum ice extent 6000 5000 cal yr bp and smaller than present ice configuration until at least 2300 cal yr bp for the ice margin south of jakobshavn isbrae and until 400 cal yr bp for the ice margin north of jakobshavn isbrae one relatively large proglacial lake that became briefly ice free during the middle holocene lies in a catchment that likely extends 10s of km inland beneath the gis suggesting significant middle holocene retreat of this portion of the gis the overall pattern of ice sheet change is inconsistent with existing ice sheet model reconstructions for this region but is consistent with numerous paleoclimate proxy and relative sea level data these continuous lacustrine records corroborate but provide closer age control than existing non continuous records of radiocarbon dated reworked bivalves from historical moraines in the region reconstructing ice margin change from proglacial threshold lakes is one of few approaches with the potential to constrain smaller than present ice sheet extent

hydrography and climate of the last 4400 years in a sw greenland fjord implications for labrador sea palaeoceanography a multiproxy record including benthic foraminifera diatoms and xrf data of a marine sedi ment core from a sw greenland fjord provides a detailed reconstruction of the oceanographic and cli matic variations of the region during the last 4400 cal years the lower part of our record represents the final termination of the holocene thermal maximum after the onset of the neoglaciation at approxi mately 3 2 ka cal bp the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the labrador sea and the north atlantic region our data show that increased advection of atlantic water irminger sea water from the west greenland current into the labrador sea was a typical feature of northeast atlantic cool ing episodes such as the little ice age and the european dark ages while the advection of irminger sea water decreased significantly during warm episodes such as the mediaeval warm period and the roman warm period whereas the mediaeval warm period was characterized by relatively cool climate as suggested by low meltwater production the preceding dark ages display higher meltwater runoff and consequently warmer climate when compared with european climate these regional climate anomalies indicate persisting patterns of advection of colder respectively warmer air masses in the study region dur ing these periods and thus a long term seesaw climate pattern between west greenland and europe

the drangajokull ice cap northwest iceland persisted into the early mid holocene abstract most glaciers and ice caps in iceland experienced rapid deglaciation in the early holocene reaching a minimum extent during the holocene thermal maximum here we present evidence of the holocene glacial history from lake sediment cores retrieved from seven threshold lakes around the drangajokull ice cap in the vestfir ir peninsula nw iceland the sediment cores show on off signals of glacial meltwater activity as minerogenic material deposited from glacial meltwater alternates with organic rich material gyttja deposited without glacial meltwater we base the chronology of the sediment cores on 14c ages and geochemical identification of key tephra layers with known ages a 25 cm thick layer of the saksunarvatn tephra in lake skorarvatn indicates that the northern part of the ice cap had reached a similar size as today or was smaller already by 10 2 cal kyr bp however 14c ages of lake sediment cores from the highlands southeast of drangajokull suggest that this part of the ice cap was larger than today until 7 8 7 2 cal kyr bp even today the drangajokull ice cap has a different behavior than the main ice caps in iceland characterized by a very low glaciation limit because palaeoclimatic proxies show an early mid holocene temperature optimum in this part of iceland we suggest that the persistence of drangajokull into the early holocene and possibly also the entire holocene was due to high winter precipitation

rapid last deglacial thinning and retreat of the marine terminating southwestern greenland ice sheet abstract marine terminating outlet glaciers are a major source of modern ice loss from the greenland ice sheet gris but their role in gris retreat during the last deglaciation is not well constrained here we develop deglacial outlet glacier retreat chronologies for four regions in southwest and south greenland to improve understanding of spatial variations in centennial to millennial scale ice loss under a warming climate we calculate 10be surface exposure ages of boulders located in fjords near the towns of qaqortoq paamiut nuuk and sisimiut our northernmost study site sisimiut deglaciated earliest at 18 ka to 15 ka with an average thinning rate of 0 1 0 3 m yr 1 inland retreat from sisimiut to the modern ice margin took 7 ka at an average retreat rate of 15 20 m yr 1 a 10be dated moraine 25 km from the modern gris margin deposited at 8 ka suggests a possible ice margin still stand but this does not change overall retreat rates after retreat from the small coastal sisimiut fjords the gris margin was mainly land terminating in this region in contrast earliest exposure occurred at 12 ka near qaqortoq and 11 10 ka near nuuk and paamiut with ice thinning at rates of 0 2 0 3 m yr 1 to instantaneous within measurement uncertainty ice retreat inland through the extensive nuuk paamiut and qaqortoq fjord systems to near modern ice margins occurred in

holocene temperature history at the western greenland ice sheet margin reconstructed from lake sediments abstract predicting the response of the greenland ice sheet to future climate change presents a major challenge to climate science paleoclimate data from greenland can provide empirical constraints on past cryospheric responses to climate change complementing insights from contemporary observations and from modeling here we examine sedimentary records from five lakes near jakobshavn isbrae in central west greenland to investigate the timing and magnitude of major holocene climate changes for comparison with glacial geologic reconstructions from the region a primary objective of this study is to constrain the timing and magnitude of maximum warmth during the early to middle holocene positive anomaly in summer insolation temperature reconstructions from subfossil insect chironomid assemblages suggest that summer temperatures were warmer than present by at least 7 1 ka the beginning of the north lake record ka thousands of years before present and that the warmest millennia of the holocene occurred in the study area between 6 and 4 ka previous studies in the jakobshavn region have found that the local greenland ice sheet margin was most retracted behind its present position between 6 and 5 ka and here we use chironomids to estimate that local summer temperatures were 2 3 c warmer than present during that time of minimum ice sheet extent as summer insolation declined through the late holocene summer temperatures cooled and the local ice sheet margin expanded gradual insolation driven millennial scale temperature trends in the study area were punctuated by several abrupt climate changes including a major transient event recorded in all five lakes between 4 3 and 3 2 ka which overlaps in timing with abrupt climate changes previously documented around the north atlantic region and farther afield at 4 2 ka

an updated radiocarbon based ice margin chronology for the last deglaciation of the north american ice sheet complex abstract the north american ice sheet complex naisc consisting of the laurentide cordilleran and innuitian ice sheets was the largest ice mass to repeatedly grow and decay in the northern hemisphere during the quaternary understanding its pattern of retreat following the last glacial maximum is critical for studying many facets of the late quaternary including ice sheet behaviour the evolution of holocene landscapes sea level atmospheric circulation and the peopling of the americas currently the most up to date and authoritative margin chronology for the entire ice sheet complex is featured in two publications geological survey of canada open file 1574 dyke et al 2003 quaternary glaciations extent and chronology part ii dyke 2004 these often cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka all ages in uncalibrated radiocarbon years using a combination of geomorphology stratigraphy and radiocarbon dating however by virtue of being over 15 years old the ice margin chronology requires updating to reflect new work and important revisions this paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies we also update the original radiocarbon dataset from the 2003 2004 papers with 1541 new ages to reflect work up to and including 2018 a major revision is made to the 18 ka ice margin where banks and eglinton islands once considered to be glacial refugia are now shown to be fully glaciated our updated 18 ka ice sheet increased in areal extent from 17 81 to 18 37 million km2 which is an increase of 3 1 in spatial coverage of the naisc at that time elsewhere we also summarize region by region significant changes to the deglaciation sequence this paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of dyke et al 2003 and dyke 2004 where new information is lacking this is a pragmatic solution to satisfy the needs of a quaternary research community that requires up to date knowledge of the pattern of ice margin recession of what was once the world s largest ice mass the 36 updated isochrones are available in pdf and shapefile format together with a spreadsheet of the expanded radiocarbon dataset n 5195 ages and estimates of uncertainty for each interval

holocene glacier and ice cap fluctuations in southwest greenland inferred from two lake records abstract glaciers and ice caps gics respond rapidly to changes in temperature and precipitation thus records of their past fluctuations yield valuable information on past climate however relatively little is known about the long term holocene history of greenland s local gics peripheral to the greenland ice sheet here we report sediment records of holocene glacier activity from two distally fed glacial lakes near buksefjord southwest greenland the two lakes watersheds host modern gics of contrasting size the pers lake informal name watershed drains part 3 km2 of a single small ice cap in contrast nearby lake t3 s informal name watershed drains numerous gics totaling 100 km2 at the time it emerged from the sea 8 6 ka bp pers lake was receiving no glacial meltwater input sediment physical and geochemical properties indicate persistent meltwater input and regrowth of the ice cap within the pers lake catchment beginning at 1 4 ka bp after almost 3000 years of sporadic meltwater input beginning 4 3 ka bp the ice cap above pers lake reached a maximum late holocene extent during the final phase of the little ice age lia 0 1 ka bp the complementary lake t3 sediment record suggests continued meltwater input from the larger suite of upstream gics from the time of the lake s isolation from the sea 8 4 7 5 ka bp through to the present this indicates that some gics here probably survived the holocene thermal maximum htm although were significantly reduced in size for an extended period of unknown age and duration combined with evidence from pers lake and prior studies that show gics at low and intermediate elevations in this region melted away completely during the htm and evidence for gic presence at lake t3 we provide lower and upper bounds on regional htm equilibrium line altitudes elas we estimate that regional elas were between 1370 and 1470 m above sea level in the early to middle holocene from the middle to late holocene our results along with other regional gic studies indicate progressive lowering of regional glacier elas in response to neoglacial summer cooling of 2 7 c assuming no change in precipitation

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

mass loss of greenland s glaciers and ice caps 2003 2008 revealed from icesat laser altimetry data 1 the recently finalized inventory of greenland s glaciers and ice caps gic allows for the first time to determine the mass changes of the gic separately from the ice sheet using space borne laser altimetry data corrections for firn compaction and density that are based on climatic conditions are applied for the conversion from volume to mass changes the gic which are clearly separable from the icesheet i e have a distinct ice divide or no connection lost 27 9 10 7 gt a 1 or 0 08 0 03 mm a 1 sea level equivalent sle between october 2003 and march 2008 all gic including those with strong but hydrologically separable connections lost 40 9 16 5 gt a 1 0 12 0 05 mm a 1 sle this is a significant fraction 14 or 20 of the reported overall mass loss of greenland and up to 10 of the estimated contribution from the world s gic to sea level rise the loss was highest in southeastern and lowest in northern greenland

high arctic climate conditions for the last 7000 years inferred from multi proxy analysis of the bliss lake record north greenland the arctic is more vulnerable to climate change than are mid latitudes therefore palaeolimnological studies from the high arctic are important in providing insights into the dynamics of the climate system here we present a multi proxy study from one of the world s northernmost lakes bliss lake peary land greenland the early holocene 10 850 10 480 cal a bp is characterized by increased erosion and gradually more marine conditions full marine conditions developed from 10 480 cal a bp until the lake was isolated at 7220 cal a bp from its marine isolation at 7220 cal a bp bliss lake becomes a lacustrine environment evidence from geochemical proxies delta c 13 and total organic carbon suggests that warmer conditions prevailed between 7220 and 6500 cal a bp corresponding to the holocene thermal maximum and from 3300 until 910 cal a bp from 850 to 500 cal a bp colder climate conditions persisted the transition from warmer to colder climate conditions taking place around 850 cal a bp may be associated with the transition from the medieval warm period to the little ice age copyright c 2011 john wiley sons ltd

extracting a climate signal from 169 glacier records i constructed a temperature history for different parts of the world from 169 glacier length records using a first order theory of glacier dynamics i related changes in glacier length to changes in temperature the derived temperature histories are fully independent of proxy and instrumental data used in earlier reconstructions moderate global warming started in the middle of the 19th century the reconstructed warming in the first half of the 20th century is 0 5 kelvin this warming was notably coherent over the globe the warming signals from glaciers at low and high elevations appear to be very similar

strong altitudinal control on the response of local glaciers to holocene climate change in southwest greenland abstract accelerating ice loss during recent years has made the greenland ice sheet one of the largest single contributors to global sea level rise accounting for 0 5 of the total 3 2 mm yr 1 this loss is predicted to continue and will most likely increase in the future as a consequence of global warming however the sensitivity of glaciers and ice caps gics in greenland to prolonged warm periods is less well constrained and geological records documenting the long term glacial history are needed to put recent observations into a broader perspective here we report the results from three proglacial lakes where fluctuations in local glaciers located at different altitudes in kobbefjord southwest greenland have been recorded our results show that the lakes received meltwater from the initial deglaciation of the area 9 2 cal ka bp until 8 7 7 9 cal ka bp when the meltwater input ceased as the glaciers most likely disappeared regrowth of glaciers began again at 5 5 cal ka bp at 1370 m a s l 3 6 cal ka at 1170 m a s l and 1 6 cal ka bp at 1000 m a s l clearly reflecting strong altitudinal control of the gic response to neoglacial cooling our results highlight that gics in kobbefjord southwest greenland are primarily influenced by changes in summer air temperatures and winter precipitation and that they are facing a rapid decay that most likely will result in their disappearance within the next centuries as a consequence of global warming if current 21st century retreat rates continue the gics in the study area will be completely gone in 30 90 years with the smallest gics disappearing first

gps derived deformation of the central andes including the 1995 antofagasta mw 8 0 earthquake in order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the andes a 215 site gps network covering chile and the western part of argentina was selected monumented and observed in 1993 and 1994 a dense part of the network in northern chile and northwest argentina comprising some 70 sites was re observed after two years in october november 1995 the m w 8 0 antofagasta north chile earthquake of 30th july 1995 took place between the two observations the city of antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench three different deformation processes have been considered for modeling the measured displacements 1 interseismic accumulation of elastic strain due to subduction coupling 2 coseismic strain release during the antofagasta earthquake and 3 crustal shortening in the sub andes eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation assuming a uniform slip model of interseismic coupling the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km the geodetically derived fault plane parameters of the antofagasta earthquake are consistent with results derived from wave form modeling of seismolog ical data the coseismic slip predicted by the variable slip model reaches values of 3 2 m in the dip slip and 1 4 m in the strike slip directions the derived rake is 66 our geodetic results suggest that the oblique nazca south american plate convergence is accommodated by oblique earthquake slip with no slip partitioning the observed displacements in the back arc indicate a present day crustal shortening rate of 3 4 mm year which is significantly slower than the average of 10 mm year experienced during the evolution of the andean plateau

a major increase in winter snowfall during the middle holocene on western greenland caused by reduced sea ice in baffin bay and the labrador sea precipitation is predicted to increase in the arctic as temperature increases and sea ice retreats yet the mechanisms controlling precipitation in the arctic are poorly understood and quantified only by the short sparse instrumental record we use hydrogen isotope ratios 2h of lipid biomarkers in lake sediments from western greenland to reconstruct precipitation seasonality and summer temperature during the past 8 kyr aquatic biomarker 2h was 100 more negative from 6 to 4 ka than during the early and late holocene which we interpret to reflect increased winter snowfall the middle holocene also had high summer air temperature decreased early winter sea ice in baffin bay and the labrador sea and a strong warm west greenland current these results corroborate model predictions of winter snowfall increases caused by sea ice retreat and furthermore suggest that warm currents advecting more heat into the polar seas may enhance arctic evaporation and snowfall

latest pleistocene and holocene glacier variations in the european alps in the alps climatic conditions reflected in glacier and rock glacier activity in the earliest holocene show a strong affinity to conditions in the latest pleistocene younger dryas glacier advances in the alps related to younger dryas cooling led to the deposition of egesen stadial moraines egesen stadial moraines can be divided into three or in some cases even more phases sub stadials moraines of the earliest and most extended advance the egesen maximum stabilized at 12 2 1 0 ka based on 10be exposure dating at the schonferwall tyrol austria and the julier pass outer moraine switzerland final stabilization of moraines at the end of the egesen stadial was at 11 3 0 9 ka as shown by 10be data from four sites across the alps from west to east the sites are piano del praiet northwestern italy grosser aletschgletscher central switzerland julier pass inner moraine eastern switzerland and val viola northeastern italy there is excellent agreement of the 10be ages from the four sites in the earliest holocene glaciers in the northernmost mountain ranges advanced at around 10 8 1 1 ka as shown by 10be data from the kartell site northern tyrol austria in more sheltered drier regions rock glacier activity dominated as shown for example at julier pass and larstig valley tyrol austria new 10be dates presented here for two rock glaciers in larstig valley indicate final stabilization no later than 10 5 0 8 ka based on this data we conclude the earliest holocene between 11 6 and about 10 5 ka was still strongly affected by the cold climatic conditions of the younger dryas and the preboreal oscillation with the intervening warming phase having had the effect of rapid downwasting of egesen glaciers at or slightly before 10 5 ka rapid shrinkage of glaciers to a size smaller than their late 20th century size reflects markedly warmer and possibly also drier climate between about 10 5 ka and 3 3 ka conditions in the alps were not conducive to significant glacier expansion except possibly during rare brief intervals past tree line data from kaunertal tyrol austria in concert with radiocarbon and dendrochronologically dated wood fragments found recently in the glacier forefields in both the swiss and austrian alps points to long periods during the holocene when glaciers were smaller than they were during the late 20th century equilibrium line altitudes ela were about 200 m higher than they are today and about 300 m higher in comparison to little ice age lia elas the larstig rock glacier site we dated with 10be is the type area for a postulated mid holocene cold period called the larstig oscillation presumed age about 7 0 ka our data point to final stabilization of those rock glaciers in the earliest holocene and not in the middle holocene the combined data indicate there was no time window in the middle holocene long enough for rock glaciers of the size and at the elevation of the larstig site to have formed during the short infrequent cold oscillations between 10 5 and 3 3 ka small glaciers less than several km2 may have advanced to close to their lia dimensions overall the cold periods were just too short for large glaciers to advance after 3 3 ka climate conditions became generally colder and warm periods were brief and less frequent large glaciers for example grosser aletschgletscher advanced markedly at 3 0 2 6 ka around 600 ad and during the lia glaciers in the alps attained their lia maximum extents in the 14th 17th and 19th centuries with most reaching their greatest lia extent in the final 1850 1860 ad advance

lower bound on the amount of crustal shortening in the central bolivian andes balanced cross sections across the cordillera oriental and subandean zone of the central bolivian andes indicate that crustal shortening probably has played the dominant role in orogeny in this convergent margin setting a minimum amount of shortening 210 km is documented which can account for two thirds of the present day crustal cross sectional area along a transect spanning the entire mountain range substantial crustal shortening may also require loss of the lower lithosphere to the asthenosphere a large minimum amount of crustal shortening in the bolivian andes shows contrary to common assumptions about orogeny that 1 magmatic addition may be volumetrically less important in orogeny in andean type margins and 2 crustal shortening is not uniquely associated with continental or island arc collision

crustal motion north and south of the arica deflection comparing recent geodetic results from the central andes 1 an intercomparison of recent velocity solutions for the global positioning system gps networks constructed by the south american nazca plate project snapp based in bolivia and peru and our central andes gps project cap based in chile and argentina indicates a velocity discontinuity of order 10 mm yr near the boundary between these networks we suggest that this velocity jump manifests measurement bias in the snapp velocity field our results indicate that no major slip partioning occurs within the forearc of northern chile in response to the obliquity of subduction but that nazca south america plate convergence is partitioned between the forearc and the backarc regions the present rate of shortening across the southern part of the sub andean belt in argentina is 8 9 1 6 mm yr

multiple independent records of local glacier variability on nuussuaq west greenland during the holocene abstract the sensitivity of mountain glaciers to small scale climate fluctuations makes records of their past extent among the best proxies for identifying spatio temporal climate variability here we build on the few existing holocene records of local glacier change in greenland by using three independent geochronological methods proglacial lake sediment analysis cosmogenic 10be surface exposure dating and in situ 14c burial modeling to reconstruct continuous records of holocene glacier variability on nuussuaq west greenland 10be ages of perched boulders indicate eastern nuussuaq was deglaciated between 11 0 and 10 5 ka radiocarbon dated sediments from two lakes on nuussuaq contain mineral rich layers between 9 6 and 9 0 and 8 7 8 0 cal ka bp that may be correlative with nearby ice sheet moraines deposited in the early holocene multiple proxies for glacier size indicate frequent high amplitude glacier fluctuations superimposed on net glacier growth during the late holocene with significant ice expansion phases at 3 7 ka 2 8 ka and throughout the past 2 ka mean 10be ages from five nested moraine crests confirm that local glacier extents on nuussuaq culminated during both the little ice age 1470 c e n 3 and 1750 c e n 3 and the preceding centuries 520 1320 c e n 11 results reveal that local glaciers on nuussuaq episodically advanced and retreated at centennial timescales throughout the holocene most likely in response to regional climate changes in west greenland superimposed on the progressive insolation driven cooling trend in the northern hemisphere our new 10be moraine chronologies coupled with other glacier size proxies corroborate an emerging pattern of significant summer cooling and glacier expansion in the centuries prior to the little ice age in the arctic

holocene mountain glacier history in the sukkertoppen iskappe area southwest greenland abstract mountain glaciers and ice caps gic independent of the greenland ice sheet respond rapidly to climate variations and records of their past extent provide information on the natural envelope of climate variability here we use a multi proxy approach that combines proglacial lake sediment analysis cosmogenic nuclide surface exposure dating in situ 10be and 14c and radiocarbon dating of recently ice entombed moss to generate a centennial scale record of holocene gic fluctuations in southwestern greenland following local deglaciation 10 9 ka sediments from proglacial crash lake record a glacier advance at 9 ka that is indistinguishable from nearby ice sheet moraines implying a synchronous response of gic and the greenland ice sheet to a centennial scale climate event following this local glacier advance gic experienced net recession until 4 6 ka radiocarbon ages of in situ moss n 29 and crash lake sediments reveal intervals of glacier expansion at 1 8 1 2 and 0 7 ka that are superimposed on an overall trend of net glacier expansion throughout the late holocene in situ 14c concentrations from bedrock adjacent to radiocarbon dated moss samples further constrain the duration of ice cover through the holocene in this region we find that our glacier size proxy records during the past 4 ka are broadly consistent with relatively lower temperatures recorded in gisp2 and occur during or following intervals of volcanic perturbations thus we speculate that volcanic activity although less frequent and intense than in the early holocene and during the little ice age may have led to centennial scale variability imprinted on net glacier expansion due to decreasing summer insolation through the late holocene

restricted impact of holocene climate variations on the southern greenland ice sheet abstract we use an ice marginal threshold lake lower nordboso in southern greenland to record episodes when the southern greenland ice sheet sgis was close to the present extent represented by beds of clastic sediments whereas gyttja deposition reflects periods when the glacier was behind the threshold and no glacial meltwater input the results show that the sedimentation was initiated at c 10 6 cal ka bp when the ice margin had reached the present extent following the deglaciation after this the ice margin remained close to the present extent until c 6 9 cal ka bp when it retreated behind the threshold and first reappeared with a clear glacial signal at c 3 0 2 8 cal ka bp and from c 0 5 cal ka bp until the present an overall good correlation between clastic input into lower nordboso and ird events from narsaq sound suggests that they represent a general glacial proximity signal of the sgis our data demonstrates that the sgis behaved less vigorously to holocene climate changes compared to previous reconstructions the ice sheet only retreated behind the present ice extent from c 6 9 to 3 0 cal ka bp and c 2 8 to 0 5 cal ka bp in the mountainous southern greenland whereas the more sensitive low lying qassimiut lobe was behind its present margin from c 9 ka until the little ice age accordingly the ice marginal behavior in southern greenland is not only governed by climate changes but also strongly influenced by the local topographic setting

ams c 14 dating of deglacial events in the irish sea basin and other sectors of the british irish ice sheet sedimentary sequences deposited by the decaying marine margin of the british irish ice sheet biis record isostatic depression and successive ice sheet retreat towards centres of ice dispersion radiocarbon dating by accelerator mass spectrometry ams of in situ marine microfaunas that are commonly associated with these sequences constrain the timing of glacial and sea level fluctuations during the last deglaciation enabling us to evaluate the dynamics of the bus and its response to north atlantic climate change here we use our radiocarbon dated stratigraphy to define six major glacial and sea level events since the last glacial maximum 1 initial deglaciation may have occurred 18 3 kyr c 14 bp along the northwestern irish coast in agreement with a deglacial age of similar to 22 cl 36 kyr bp for southwestern ireland ice retreated to inland centres and areas of transverse moraine began to form across the north irish lowlands 2 channels cut into glaciomarine deglacial sediments along the western irish sea coast are graded to below present sea level identifying a fall of relative sea level rsl in response to isostatic emergence of the coast 3 marine mud that rapidly infilled these channels records an abrupt rise in global sea level of 10 15 m similar to 16 7 c 14 kyr bp that flooded the irish sea coast and may have triggered deglaciation of a marine based margin in donegal bay 4 intertidal boulder pavements in dundalk bay indicate that rsl similar to 15 0 c 14 kyr bp was similar to present 5 a major readvance of all sectors of the biis occurred between 14 and 15 kyr 14 c bp which overprinted subglacial transverse moraines and delivered a substantial sediment flux to tidewater ice sheet margins this event the killard point stadial indicates that the bus participated in heinrich event 1 6 subsequent deposition of marine muds on drumlins 12 7 c 14 kyr bp indicates isostatic depression and attendant high rsl resulting from the killard point readvance these events identify a dynamic biis during the last deglaciation as well as significant changes in rsl that reflect a combination of isostatic loading and eustatic changes in global sea level c 2005 elsevier ltd all rights reserved

on the mechanism of crustal block rotations in the central andes abstract the results of 62 paleomagnetic studies of jurassic and younger rock units from the andes of argentina bolivia chile and peru are examined for indications of the timing and mechanism of crustal block rotations rotations and their 95 confidence intervals are recalculated in pole space using a new south american reference apw path as observed by many investigators the arica deflection the change in topographic and tectonic trends located near arica northernmost chile divides the data into a counterclockwise rotated set north of the deflection and a clockwise rotated set to the south rotations range from 75 counterclockwise to nearly 50 clockwise and show substantial differences between neighboring crustal blocks south of arica there is a weak indication of a decrease in amount of rotation with distance from the plate margin but no such correlation is observed north of arica rotation increases with age both north and south of arica for rock units of 90 ma for older rock units no correlation between age and amount of rotation exists unlike the western margin of north america no significant margin parallel displacements accompany the rotations several models for rotation are examined it is concluded that a combination of late cenozoic oroclinal bending and post mid cretaceous local block rotations in response to shear driven sub crustal ductile flow can explain most of the paleomagnetic and geologic observations

current rates of convergence across the central andes estimates from continuous gps observations we present velocity solutions for 16 continuous gps cgps stations located in south america in a geodetic reference frame that nominally fixes the craton or stable core of this continent the rms horizontal velocity of 8 stations located within the craton is 1 3 mm yr three cgps stations located in chile between about 33 s and 20 s have velocities in the range 19 24 mm yr these motions manifest current rates of convergence across the southern limb of the central andes the igs station in arequipa peru at 16 5 s in the northern limb of the orocline however has a velocity of just 10 mm yr

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

early deglacial onset of southwestern greenland ice sheet retreat on the continental shelf abstract the greenland ice sheet gris advanced onto the continental shelf during the last glacial period while deglacial records for when the gris withdrew onto the modern coastline are relatively abundant the timing of early gris retreat on the shelf is poorly constrained here we use planktic foraminiferal 18 o sediment grain size sedimentation rates and 14 c ages in southeastern davis strait core hu87033 008 to develop an early deglaciation chronology of the southwestern gris while on the continental shelf sedimentation rates and especially silt and clay fractions are high between 20 5 and 17 1 ka suggesting that the southwestern gris margin was near or at the shelf break where it released subglacially derived sediment laden meltwater a peak in sedimentation rates of 110 cm ka 1 between 19 3 ka and 18 6 ka combined with an initial decrease in planktic 18 o of 0 5 per mil suggests an early deglacial pull back of the gris margin from the shelf break with a concurrent increase in surface ocean meltwater discharge a subsequent planktic 18 o decrease of 1 0 per mil combined with a drop in silt and clay sedimentation rates at 18 17 ka likely record further gris retreat inland from the shelf break terrestrial 10 be surface exposure ages indicate that the gris margin remained on the continental shelf until 11 ka yet the cause of this subsequent ice margin stability on the inner shelf is not known our new records provide the first evidence that the southwestern gris margin may have begun to deglaciate at the same time as other northern hemisphere ice sheets as labrador sea water temperatures likely remained near glacial values until 15 ka we suggest that initial southwestern gris retreat was in response to rising global sea level from retreat of other ice sheets and or the initial deglacial rise in boreal summer insolation

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

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

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

neoglacial ice expansion and late holocene cold based ice cap dynamics on cumberland peninsula baffin island arctic canada abstract radiocarbon dating of fossil flora and fauna collected along receding cold based ice caps and cold based sections of polythermal glaciers on cumberland peninsula reveal insights into neoglacial ice expansion and late holocene ice dynamics the taphonomic advantages of subfossilized moss were exploited to precisely document regional expansions of ice caps through the late holocene when compared with climate proxies and records of volcanic eruptions the moss radiocarbon age distributions indicate i onset of neoglaciation shortly after 5 ka concomitant with increased sea ice cover ii intensification of ice expansion between 1 9 and 1 1 ka followed by halt of ice growth or ice recession during the medieval warm period and iii renewed ice expansion after 0 8 ka in response to cooling related to a combination of large volcanic eruptions and low solar activity overall the observations support a model of near instantaneous glacial response to regional climate controls and that these responses were synchronous throughout eastern canadian arctic and possibly eastern greenland

holocene temperature and landscape history of southwest greenland inferred from isotope and geochemical lake sediment proxies abstract terrestrial temperature reconstructions from the ice free margins of greenland are critical for constraining the sensitivity of the greenland ice sheet to past climate change numerous investigations have clarified the glacial history of southwest greenland in recent decades however very few local quantitative temperature reconstructions exist as context for changes in the cryosphere we examine sedimentary records from two lakes south of nuuk greenland informally named lakes t1 and t2 and investigate millennial scale holocene climate change using a multi proxy approach changes in x ray fluorescence spectroscopy xrf 15n 13c and biogenic silica concentrations of bulk lake sediments mark the transition from a marine environment to isolated lakes as relative sea level fell in the early holocene 18o values of subfossil insects chironomids from lakes t1 and t2 decreased by 2 3 from c 8 8 ka bp minimum limiting age for the onset of lacustrine sediment deposition in lake t2 ka bp thousands of years before 1950 to 1 ka bp existing isotope independent temperature reconstructions from the west coast of greenland suggest that these changes in 18o values accompanied gradual cooling of 2 4 c concomitant with decreasing summer insolation there is widespread regional evidence that this cooling resulted in progressive regrowth of local glaciers and of the ice sheet the regional consensus on the magnitude of this temperature change indicates that the local modern modeled temperature precipitation 18o relationship cannot be used to quantify millennial scale temperature changes at these sites through the holocene this reinforces that studies utilizing 18o based proxies to infer temperature change should carefully assess local isotope temperature relationships over space and time

holocene relative sea level changes in the inner bredefjord area southern greenland in this paper we present new relative sea level data from southern greenland a key area for understanding the greenland ice sheet gis response to climate change within fourteen lakes and marine lagoons from the inner part of bredefjord nordre sermilik in southern greenland isolations revealed by stratigraphic and palaeoecological analyses are dated and relative sea levels reconstructed due to coastal emergence caused by the gis retreat within the area the relative sea level fell rapidly in the early holocene between at least c 9600 and c 7300 cal yrs bp attaining a rate of 2 cm per year between 9600 and 8000 cal yrs bp spatial variability in relative sea level changes is show for southern greenland from a comparison with the nanortalik and the qagortoq areas the regression occurred about 2000 years later in the inner bredefjord area compared to the nanortalik area and about 1000 years later compared to the qaqortoq area this is a consequence of earlier deglaciation in areas located at the outer coast between c 8000 cal yrs bp and the present day relative sea level was lower than today the lowest relative sea level in the inner bredefjord area of between 5 4 and 15 m a h a t above highest astronomical tide was reached between 7000 and 1000 cal yrs bp the neoglacial readvance together with the collapse of the laurentide peripheral bulge is probably responsible for the transgression in the inner bredefjord area as has been indicated from the nearby sites qagortoq and nanortalik our relative sea level reconstructions showing spatial variability within southern greenland have implications for glacial isostatic adjustment gia modelling and the understanding of the gis ice sheet dynamics the early holocene regression is consistent with the recession of the southern sector of the gis from the shelf edge at c 22 000 cal yrs bp reaching inland of the present day outer coast by c 12 000 cal yrs bp and its present margin by c 10 500 cal yrs bp c 2013 elsevier ltd all rights reserved

reconstructing hydro climatic events and glacier fluctuations over the past millennium from annually laminated sediments of cheakamus lake southern coast mountains british columbia canada abstract we recovered sediment cores from cheakamus lake in the southern coast mountains southwest british columbia to reconstruct late holocene environmental conditions in the watershed the cored sediments are inorganic rhythmically laminated clayey silt radiocarbon ages and correlation of lamina thickness with the magnitude of the annual flood recorded at a nearby gauging station indicate that the laminae are varves we discriminate seven types of varves on the basis of couplet thickness and internal structure and compare them to annual hydrographs over the period of record the seven varve types record summer snowmelt floods autumn floods mid season floods years with two major floods years with three major floods years with more than three major floods and periods of sustained glacier runoff varves attributed to autumn storms and glacier runoff are dominant exhibit serial dependence and are most common during six periods ad 1300 1320 1380 1410 1470 1500 1710 1730 1880 1906 and 1916 1945 in contrast varves attributed to summer snowmelt floods are randomly distributed through time thickest varves occur during the decades ad 1090 1110 1120 1170 1210 1250 1310 1330 1390 1450 1720 1780 1860 1900 and 1920 1945 the relation between little ice age glacier activity and lake sedimentation is complex but the thickest varves coincide with times of rapid glacier retreat and periods when air temperatures were warmer than average the results confirm the importance of sediment transfers during the summer and autumn runoff season in the british columbia coast mountains

local glaciation in west greenland linked to north atlantic ocean circulation during the holocene recent observations indicate that ice ocean interaction drives much of the recent increase in mass loss from the greenland ice sheet however the role of ocean forcing in driving past glacier change is poorly understood to extend the observational record and our understanding of the ocean cryosphere link we used a multi proxy approach that combines new data from proglacial lake sediments 14 c dated in situ moss that recently emerged from beneath cold based ice caps and 10 be ages to reconstruct centennial scale records of mountain glacier activity for the past 10 k y in west greenland proglacial lake sediment records and 14 c dating of moss indicate the onset of neoglaciation in west greenland at ca 5 ka with substantial snowline lowering and glacier expansion at ca 3 7 ka followed by additional ice expansion phases at ca 2 9 ca 1 7 and ca 1 4 ka and during the little ice age we find that widespread glacier growth at ca 3 7 ka in west greenland coincides with marked cooling and reduced strength of the west greenland current in disko bugt the transition to cooler ocean conditions at ca 3 7 ka identified in disko bugt is registered by marine proxy data farther afield in east greenland and on the northwestern icelandic shelf implying large scale paleoceanographic changes across the north atlantic during this interval the similarity between glacier change on west greenland and multiple marine and terrestrial records across the north atlantic suggests that glaciers are strongly influenced by changes in ocean circulation and consequently implies that the ocean cryosphere teleconnection is a persistent feature of the arctic system

holocene fluctuations of bregne ice cap scoresby sund east greenland a proxy for climate along the greenland ice sheet margin abstract the greenland ice sheet is a major component of the arctic cryosphere and the magnitude of its response to future climate changes remains uncertain longer term records of climate near the ice sheet margin provide information about natural climate variability and can be used to understand the causes of past changes in the greenland ice sheet as a proxy for holocene climate near the ice sheet margin we reconstruct the fluctuations of bregne ice cap in the scoresby sund region of central east greenland bregne is a small ice cap 2 5 km 2 in area and responds sensitively to summer temperatures we employ a multi proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping 10 be ages of boulders and bedrock and lake sediment records past extents of bregne ice cap are marked by moraines and registered by sediments in downvalley lakes 10 be ages of bedrock and boulders outboard of the moraines indicate that bregne ice cap was within 250 m of its present day limit by at least 10 7 ka multi proxy data from sediments in two move lake located downvalley from bregne ice cap indicate that the ice cap likely completely disappeared during early and middle holocene time increasing magnetic susceptibility and percent clastic material from 6 5 to 1 9 cal ka bp in two move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake laminated silt deposited at 2 6 cal ka bp and 1 9 cal ka bp to present registers the onset and persistence of bregne ice cap during the late holocene 10 be ages of boulders on an unweathered unvegetated moraine in the bregne ice cap forefield range from 0 74 to 9 60 ka the youngest 10 be age 0 74 ka likely represents the age of the moraine whereas older ages may be due to 10 be inherited from prior periods of exposure this late holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the end of the last ice age the oldest moraine in the forefield dates to 2 6 cal ka bp the fluctuations of bregne ice cap were likely influenced by northern hemisphere summer insolation throughout the holocene and abrupt late holocene cold events

tectonic control of the subducting juan fernandez ridge on the andean margin near valparaiso chile near the latitude of valparaiso chile a fundamental change in configuration of the benioff zone volcanic arc activity and the structure of the continental margin occurs opposite the subducting juan fernandez ridge upper plate tectonics related to subduction of the ridge were studied by an international group of geoscientists in the two degree segment offshore valparaiso extending from the shelf edge seaward across the eastern end of juan fernandez ridge near the o higgins group of seamounts the juan fernandez ridge strikes northeast rather than continuing its east west trend across the pacific basin the ridge uplifts the upper plate and sediments of the valparaiso basin are deformed against its southern flank this deformation is consistent with the southward migration required by an oblique trending ridge and the nearly trench normal vector of plate convergence in the trench axis the ridge forms a basement barrier behind which sediments 2 5 km deep have ponded the lower slope over the ridge appears eroded whereas the margin not yet affected by ridge subduction is fronted by an accretionary prism about 25 km wide nazca plate relief clearly influences tectonism of the margin where it subducts beneath thin continental crust its relation to deeper processes segmenting the andean orogen appears to involve prior tectonic events

high resolution x ray fluorescence core scanning analysis of les echets france sedimentary sequence new insights from chemical proxies the les echets sediment sequence has recently been the subject of a high resolution multi proxy study which revealed shifts in lake productivity linked to greenland stadials and interstadials over the last 40 ka wohlfarth et al 2008 rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka geology 36 407 410 here we present new elemental data for this sequence as acquired using an x ray fluorescence core scanning system which provides in situ high resolution continuous multi element analyses it was found that the strength of associations between the studied elements ti rb k zr si ca sr mn and fe varied over time with changes in lake status which are ultimately driven by changes in climate increases in fine grained detrital input as indicated by ti rb k and zr rb overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions several of these arid periods are coincident with low diatom concentrations and the timing of heinrich events h4 h3 and h2 the duration of the environmental impacts linked to the h events varied by proxy with elemental data ti and zr rb estimating shorter events than the diatom data periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity the elemental data provide new insights into hydrological changes and related sediment processes within the catchment and highlight the need for multi element and multi proxy approaches when reconstructing climate change using lacustrine sediment sequences copyright 2011 john wiley sons ltd

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

a 3000 year varved record of glacier activity and climate change from the proglacial lake hvitarvatn iceland a suite of environmental proxies in annually laminated sediments from hvitarvatn a proglacial lake in the central highlands of iceland are used to reconstruct regional climate variability and glacial activity for the past 3000 years sedimentological analysis is supported by tephrostratigraphy to confirm the continuous annual nature of the laminae and a master varve chronology places proxies from multiple lake cores in a secure geochronology varve thickness is controlled by the rate of glacial erosion and efficiency of subglacial discharge from the adjacent langjokull ice cap the continuous presence of glacially derived clastic varves in the sediment fill confirms that the ice cap has occupied the lake catchment for the duration of the record varve thickness varve thickness variance ice rafted debris total organic carbon mass flux and bulk concentration and c n of sedimentary organic matter reveal a dynamic late holocene climate with abrupt and large scale changes in ice cap size and landscape stability a first order trend toward cooler summers and ice cap expansion is punctuated by notable periods of rapid ice cap growth and or landscape instability at ca 1000 bc 600 bc 550 ad and 1250 ad the largest perturbation began ca 1250 ad signaling the onset of the little ice age and the termination of three centuries of relative warmth during medieval times consistent deposition of ice rafted debris in hvitarvatn is restricted to the last 250 years demonstrating that langjokull only advanced into hvitarvatn during the coldest centuries of the little ice age beginning in the mid eighteenth century this advance represents the glacial maximum for at least the last 3 ka and likely since regional deglaciation 10 ka the multi centennial response of biological proxies to the hekla 3 tephra deposition illustrates the significant impact of large explosive eruptions on local environments and catchment sensitivity to perturbations

an aerial view of 80 years of climate related glacier fluctuations in southeast greenland both marine and land terminating glaciers in southeast greenland have experienced dramatic recent retreat an 80 year record of historical aerial photographs and satellite imagery shows that many land terminating glaciers in this region retreated more rapidly in the 1930s than today whereas marine terminating glaciers have retreated faster in the 2000s