exploring the use of zircon geochronology as an indicator of laurentide ice sheet till provenance indiana usa a pilot study was designed to evaluate the potential of zircon geochronology as a provenance indicator of till from the lake michigan saginaw and huron erie lobes of the laurentide ice sheet based on existing ice flow path models we hypothesized that till from each lobe would have different zircon age population distributions because the lobes originated from regions of the canadian shield with different bedrock ages after correcting for zircon fertility the majority of grains in all till samples are 1600 950 ma with 30 of ages 2500 ma this similarity means that till from the three lobes cannot be clearly differentiated based on their zircon populations the dominant ages found and the homogeneity of distributions in the till indicates a non shield source and instead reflect an origin from some combination of underlying till and sedimentary bedrock in the great lakes region even though the datasets are small the tills have similarities to zircon distributions in michigan basin rocks this implies that a substantial fraction of zircon in till was not transported long distances from the canadian shield although zircon ages are not distinct between tills the method provides a novel application to understand laurentide ice sheet glacial erosion and transport

increased aridity during the early holocene in west greenland inferred from stable isotopes in laminated lake sediments abstract palaeoclimatic inferences from the greenland ice cores suggest that holocene climate was relatively uniform the ice core records primarily reflect hemispheric temperature related climate processes whereas lakes tend to reflect regional scale climatic variability stable isotopes in closed basin lakes are sensitive to changes in effective precipitation here we report stable isotope evidence 18 o and 13 c records from authigenic calcite in laminated lake sediments from two oligosaline closed basin lakes in southern west greenland sondre stromfjord the stable isotope profiles indicate a dynamic early to mid holocene climate as a strongly negative precipitation evaporation balance from 7000 to 5600 cal yr bp lowered lake levels throughout the region this interpretation of the stable isotope data is supported by a survey of modern lake water isotopic composition and fossil shorelines around many closed basin saline lakes which indicate higher lake levels in the past the increased aridity during the early holocene resulted from a shift in regional circulation patterns in the davis straits baffin bay area enhanced stability of the west greenland depression and the situation of a regional trough over the sondre stromfjord area caused weakened westerly airflow and strengthened outflow i e winds blowing off the ice sheet resulting in reduced precipitation in the region decreased precipitation coupled with higher insolation probably caused the negative precipitation evaporation balance

reply to discussion by p j barnett on generation of heavy mineral glacial indicator dispersal trains from a diabase sill nipigon region northwestern ontario larson and mooers 1753 barnett 2006 poses a number of questions regarding some of the field observations and assumptions we used in our interpretation of a heavy mineral dispersal train derived from an isolated eastern outlier of diabase of the nipigon sills in northwestern ontario larson and mooers 2005b he also brings attention to some details of the regional glacial geologic setting we did not address in our analysis and interpretation of the dispersal train and highlights new field data barnett and dyer 2005 relevant to interpretation of past glacial processes acting in the broader nipigon region we thank barnett for his comments and feel they serve in part to highlight the variety of problems regarding glacial erosion and entrainment and transport to which we believe our conceptual model of glacial indicator dispersal larson and mooers 2004 is able to contribute barnett 2006 brings attention to the fact that tills exposed at surface in the beardmore geraldton region contain a wide range 1 up to 23 in carbonate content thorleifson and kristjansson 1993 high carbonate contents in these tills are a clear signal of long distance transport of carbonate bearing debris from the hudson bay lowlands the occurrence of high carbonate tills in patches of thick streamlined drift has been interpreted by hicock 1988 and hicock and others 1989 to mean that all surface tills in this region were deposited at the base of a fastflowing ice stream however the ice stream model does not explain the widely disparate values in till carbonate occurring over distances of only a few kilometres we believe a different interpretation explains the same data larson and mooers 2005a tills sampled in our limited study area contained virtually none of the paleozoic carbonate and proterozoic greywacke clasts characteristic of high carbonate tills found in the region we believe this observation is inconsistent with an origin of the till forming material by longdistance transport of debris from the hudson bay lowlands by an ice stream and rather that it reflects local erosion and entrainment and short distance transport however the origin of the tills we sampled in our study area is not relevant to the interpretations we presented determining whether the till in our study area was generated by erosion and entrainment into the englacial basal debris layer of the ice sheet by erosion and entrainment in a subglacial deforming debris layer or by another process was beyond the scope of our study we deliberately made no explicit assertion regarding the processes by which diabase was eroded and entrained and transported we did however attempt to document the rates at which the erosion and entrainment process worked the only explicit assumptions we incorporated into our interpretations were of the debris mass per unit bed area m and of the velocity at which the basal debris layer was transported u these values were used to estimate the erosivity e recorded in the till sheet and indirectly the absolute erosion and entrainment rate e of diabase into the basal debris layer examination of the equations presented in larson and mooers 2004 and the modified equations presented in larson and mooers 2005b shows that increasing the estimated m results in increased estimates of the values of e and e increasing u likewise results in increased estimates of e however estimates of the erosion length scale and the relative rates of erosion of the diabase and greenstone are unaffected by varying these quantities we feel that the m and u estimates that we incorporated into our interpretation of the heavy mineral dispersal data represent reasonable values for an ice sheet and that the resulting e estimates are likewise reasonable it is important to note that the absolute values of erosion and entrainment we have estimated for diabase and greenstone lithologies lie within the range documented for modern glacial systems cf hallet et al 1996 barnett 2006 questions our conclusion that the diabase sill in our study area was significantly more resistant to glacial erosion and entrainment than the archean greenstones into which it was intruded notwithstanding the higher susceptibility of gabbro diabase to physical and chemical

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

generation of a heavy mineral glacial indicator dispersal train from a diabase sill nipigon region northwestern ontario the heavy clinopyroxene mineral pigeonite forms a glacial indicator dispersal train originating from diabase intrusions in the nipigon region of northwestern ontario analysis and interpretation of the pigeonite dispersal pattern adjacent to the up ice portion of the diabase provides a number of insights into the nature of glacial erosion of bedrock and the generation of heavy mineral dispersal trains bedrock erosion and entrainment rates at the time of pigeonite dispersal train formation were high 3 14 mm a 1 suggesting that bedrock erosion was rapid yet spatially and temporally restricted contrasting erosion rates between the diabase and surrounding greenstone lithologies suggests that modern shield topography is not an assemblage of equilibrium bedforms with respect to the ice sheet this agrees with hypothesized low total erosion of shield bedrock during the pleistocene pigeonite grain size coarsens over the diabase source indicating that most of the pigeonite was quarried from outcrops as coar

little ice age clearly recorded in northern greenland ice cores four ice cores drilled in the little investigated area of northern and northeastern greenland were evaluated for their isotopic 18o and chemical content from these rather uniform records a stable isotope temperature time series covering the last 500 years has been deduced which reveals distinct climate cooling during the 17th and the first half of the 19th century timing of the preindustrial temperature deviations agrees well with other northern hemisphere temperature reconstructions however their extent 1 c significantly exceeds both continental records as well as previous southern and central greenland ice core time series a 20 30 increase in the sea salt aerosol load during these periods supports accompanying circulation changes over the north atlantic comparison with records of potential natural climate driving forces points to an important role of the long term solar influence but to only episodically relevant cooling during years directly following major volcano eruptions

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

holocene sea ice variations in greenland onshore evidence the oldest dated driftwood log from northern greenland is c 9300 cal years old which is about 2000 years younger than the beginning of the last deglaciation and 2000 years younger than the oldes

centennial scale benthic foraminiferal record of late holocene oceanographic variability in disko bugt west greenland a new centennial scale benthic foraminiferal record of late holocene climate variability and oceanographic changes off west greenland disko bugt highlights substantial subsurface water mass changes e g temperature and salinity of the west greenland current wgc over the past 3 6 ka bp benthic foraminifera reveal a long term late holocene cooling trend which may be attributed to increased advection of cold low salinity water masses derived from the east greenland current egc cooling becomes most pronounced from c 1 7 ka bp onwards at this point the calcareous atlantic benthic foraminiferal fauna decrease significantly and is replaced by an agglutinated arctic fauna superimposed on this cooling trend centennial scale variability in the wgc reveals a marked cold phase at c 2 5 ka bp which may correspond to the 2 7 ka bp cooling event recorded in marine and terrestrial archives elsewhere in the north atlantic region a warm phase recognized at c 1 8 ka bp is likely to correspond to the roman warm period and represents the warmest bottom water conditions during the time period of the medieval climate anomaly we observe only a slight warming of the wgc a progressively more dominant cold water contribution from the egc on the wgc is documented by the prominent rise in abundance of agglutinated arctic water species from 0 9 ka bp onwards this cooling event culminates at c 0 3 ka bp and represents the coldest episode of the little ice age gradually increased influence of cold low salinity water masses derived from the egc may be linked to enhanced advection of polar and arctic water by the egc these changes are possibly associated with a reported shift in the large scale north atlantic oscillation atmospheric circulation pattern towards a more frequent negative north atlantic oscillation mode during the late holocene

crustal growth by magmatic overplating in the galapagos the isotopic compositions of xenoliths hosted in lavas from floreana island indicate that they formed from magmas unlike those at present day floreana instead the xenoliths are geochemically more similar to magmas now erupting from sierra negra and cerro azul volcanoes at the leading edge of the galapagos hotspot this is the first evidence for compositional evolution at a galapagos volcano and indicates increasing contributions from an iso topically enriched source with time as the volcano is carried away from the focus of the hot spot clinopyroxenes in many of the xenoliths exhibit positive anomalies of sr and eu which are attributed to the breakdown of plagioclase the growth of clinopyroxene at the expense of plagio clase results from compression as the crust cools compression is caused by growth mostly from above as shallow intrusions and lavas load the middle and upper oceanic crust

early holocene history of the west greenland ice sheet and the gh 8 2 event abstract the margin of the greenland ice sheet retreated rapidly during the first few thousand years of the holocene during this period of relative warmth known as the holocene thermal maximum ice core records identify a significant short lived cooling event at approximately 8 4 8 0 ka cal yr bp the gh 8 2 event associated with a 5 7 c fall in mean annual air temperature over the centre of the ice sheet in this paper we constrain the history of the ice sheet margin in disko bugt west greenland and that of a major ice stream jakobshavns isbrae during the early holocene which incorporates the interval of the gh 8 2 event our work is based on a new relative sea level curve and minimum age estimates for the timing of deglaciation from two field sites combined with a review of previously published research from the study area we identify important differences in the chronology of ice margin recession during the early holocene most noticeably the margin of jakobshavns isbrae retreated well inland of the adjacent ice sheet at this time we conclude that the early holocene fjord stade moraines in disko bugt do not record a uniform ice sheet margin response to the gh 8 2 event rather these moraines are diachronous and formed between c 10 8 ka cal yr bp their age varying as a function of the interplay between topography and ice sheet ice stream dynamics we hypothesise that one cause for the lack of an identifiable response to the gh 8 2 event is because topographic controls dominated ice sheet behaviour at this time in lowland areas any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin

the climate of scotland over the last 5000 years inferred from multiproxy peatland records inter site correlations and regional variability the mid to late holocene climates of most of scotland have been reconstructed from seven peat bogs located across north south and east west geographical and climatological gradients the main techniques used for palaeoclimatic reconstruction were plant macrofossil colorimetric humification and testate amoebae analyses which were supported by a radiocarbon based chronology aided by markers such as tephra isochrons and recent rises in pine pollen and in spheroidal carbonaceous particles scps field stratigraphy was undertaken at each site in order to show that the changes detected within the peat profiles were replicable proxy climate records were reconstructed using detrended correspondence analysis dca of the plant macrofossil data and a mean water table depth transfer function on the testate amoebae data these reconstructions coupled with the humification data were standardised for each site and used to produce a composite record of bog surface wetness bsw from each site the results show coherent wet and dry phases over the last 5000 years and suggest regional differences in climate across scotland specifically between northern and southern scotland distinct climatic cycles are identified all of which record a millennial scale periodicity which can be correlated with previously identified marine and ice core holocene cycles the key role of the macrofossil remains of sphagnum imbricatum a taxon now extinct on many sites is discussed in relation to the identified climatic shifts

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

the application of heavy indicator mineralogy in mineral exploration with emphasis on base metal indicators in glaciated metamorphic and plutonic terrains abstract indicator mineralogy is used to explore for a wide variety of mineral commodities the method utilizes minerals which are sufficiently heavy to be readily concentrated in the laboratory often colourful and possess other useful physical and chemical properties the minerals also must be source specific some indicator minerals are true resistate minerals the others although less resistant are stable in oxidized glacial drift and many non glacial sediments a few such as gold grains are silt sized but most are coarse grained grain size has a major impact on indicator mineral dispersal patterns in glacial drift the coarse grained indicator minerals are of two main types 1 kimberlite indicator minerals kims and 2 metamorphosed or magmatic massive sulphide indicator minerals mmsims kims are enriched in mg and cr and most mmsims are enriched in mg mn al or cr these indicator elements cannot be diagnosed geochemically in anomalous heavy mineral concentrates because the concentrates contain other more plentiful non indicator minerals containing the same elements in the same chemical form chalcopyrite is also a very useful mmsim but the number of surviving grains in a dispersal train is too low for detection by selective geochemical analysis mmsims are derived from three main types of base metal deposits and their associated alteration or reaction zones 1 volcanosedimentary massive sulphides encompassing volcanogenic sedex and mississippi valley subtypes in medium to high grade regional metamorphic terrains 2 skarn and greisen deposits and 3 magmatic ni cu sulphides the variety of mmsims associated with ni cu deposits is astonishing apparently reflecting mineral hybridization related to assimilation of sulphurous sedimentary rocks by ultramafic magmas cr diopside is one of the best indicators of fertile ni cu environments although not necessarily of the actual ni cu deposits heavy indicator mineralogy is much more sensitive than heavy mineral geochemical analysis and offers many exploration benefits in regional exploration programs including 1 sampling efficiencies 2 enlargement of both the bedrock target and dispersal train 3 coverage of a wider range of mineral commodities 4 undiminished sensitivity in areas of overabundant non indicator heavy minerals 5 visual evidence of points of origin of dispersal trains and 6 indications of the economic potential of the source mineralization it is most effective as a reconnaissance exploration tool and is particularly well suited for testing gneissic volcanosedimentary and plutonic terranes where base and precious metal deposits are highly modified and difficult to recognize by other prospecting methods

quaternary glaciations of northern europe this paper presents the outcome of a workshop held in berlin in february 2009 concerned with current research on the glacial history of northern europe including the british isles the methodologies presently used to resolve this topic are outlined particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea bed key new stratigraphic sections higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating the relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences an outline of a most likely glacial history of the scandinavian and british and irish ice sheets is presented along with possible links to global climate change as represented by the marine isotope mis record tentative evidence for glaciation is identified in mis 22 16 12 10 8 6 4 and 2 and correlations of phases within the last glaciation are also explored for both the scandinavian and british and irish ice sheets the results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence

postglacial chironomid assemblage succession in northernmost ungava peninsula canada sediment cores spanning the postglacial period were recovered from two coastal freshwater basins located 300 km apart in northernmost ungava nunavik canada a basal date from the sequence recovered near wakeham bay suggests that the region was ice free by as early as 9600 cal a bp the initial development of both investigated lacustrine ecosystems was characterised by chironomid assemblages strongly dominated by the subtribe tanytarsina these early postglacial assemblages showed greatly reduced diversity but much greater abundance than during subsequent periods of lake evolution an abrupt and distinct turnover in sedimentary chironomid assemblage composition and productivity marked by a switch to a dominance of orthocladiinae occurred around 6 ka bp this turnover likely corresponds with a significant disturbance in the regional environment which could be linked to the final disappearance of the last remnants of the laurentide ice sheet these findings based on the first palaeolimnological investigations undertaken in northernmost ungava provide new insights into lateglacial and postglacial faunal recolonisation patterns in aquatic ecosystems of the eastern canadian arctic copyright 2009 john wiley sons ltd

a chironomid based reconstruction of summer temperatures in nw iceland since ad 1650 few studies currently exist that aim to validate a proxy chironomid temperature reconstruction with instrumental temperature measurements we used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since ad 1650 for nw iceland through a transfer function approach and validated the record against instrumental temperature measurements from stykkisholmur in western iceland the core was dated through pb 210 cs 137 and tephra analyses hekla 1693 which produced a well constrained dating model across the whole study period little catchment disturbance as shown through geochemical itrax and loss on ignition data throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within lake variables particularly cold phases were identified between ad 1683 1710 ad 1765 1780 and ad 1890 1917 with relative drops in summer temperatures in the order of 1 5 2 c the timing of these cold phases agree well with other evidence of cooler temperatures notably increased extent of little ice age lia glaciers our evidence suggests that the magnitude of summer temperature cooling 1 5 2 c was enough to force lia icelandic glaciers into their maximum holocene extent which is in accordance with previous modelling experiments for an icelandic ice cap langjokull

understanding glacier flow in changing times subannual lurches of the greenland and antarctic ice sheets may reduce uncertainties about climate change effects on sea level rise

anomalously mild younger dryas summer conditions in southern greenland the first late glacial lake sediments found in greenland were analyzed with respect to a variety of environmental variables the analyzed sequence covers the time span between 14400 and 10500 calendar yr b p and the data imply that the conditions in southernmost greenland during the younger dryas stadial 12800 11550 calendar yr b p were characterized by an arid climate with cold winters and mild summers preceded by humid conditions with cooler summers climate models imply that such an anomaly may be explained by local climatic phenomenon caused by high insolation and fohn effects it shows that regional and local variations of younger dryas summer conditions in the north atlantic region may have been larger than previously found from proxy data and modeling experiments

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

response of a marine terminating greenland outlet glacier to abrupt cooling 8200 and 9300 years ago greenland s largest outlet glacier using 10 be surface exposure ages and 14 c dated lake sediments our chronology of ice margin change demonstrates that jakobshavn isbrae advanced to deposit moraines in response to abrupt cooling recorded in central greenland ice cores ca 8 200 and 9 300 years ago while the rapid dynamically aided retreat of many greenland outlet glaciers in response to warming is well documented these results indicate that marine terminating outlet glaciers are also able to respond quickly to cooling we suggest that short lag times of high ice flux margins enable a greater magnitude response of marine terminating outlets to abrupt

interglacial and holocene temperature reconstructions based on midge remains in sediments of two lakes from baffin island nunavut arctic canada abstract midge remains insecta diptera chironomidae and chaoboridae from two upland lake basins on the cumberland peninsula of baffin island were analyzed and the results used in a transfer function to reconstruct paleotemperatures this upland region remained ice free throughout the last glacial cycle and the two lake basins retain sediments deposited during the previous interglacial period as well as during the holocene period but they did not accumulate sediment during most of the glacial period midge remains are abundant and well preserved at both sites midge inferred summer surface water temperatures and mean july air temperatures were estimated using an inference model built on modern samples spanning a geographic range extending from devon island canada to maine usa data from twenty nine new surface samples from baffin island were added to an existing inference model the new weighted averaging wa model for summer surface water temperature yields r 2 jack 0 88 and rmsep 2 22 c for summer water temperatures and r 2 jack 0 88 and rmsep 1 53 c for mean july air temperatures reconstructions at both sites indicate that summer temperatures during the last interglacial were higher than at any time in the holocene and 5 to 10 c higher than present peak holocene temperatures occurred in the first half of the period and have decreased since about the mid holocene

discussion of generation of heavy mineral glacial indicator dispersal trains from a diabase sill nipigon region northwestern ontario the paper by phillip larson and howard mooers 2005 is an interesting attempt to document the glacial dispersal of one heavy mineral and then try to relate the mineral s dispersal to their mathematical model for glacial indicator dispersal larson and mooers 2004 the model then allows them to make conclusions about conditions at the base of the glacier the erosion rates and entrainment and deposition processes that occurred beneath the glacier there is however information not apparently considered by the authors that could significantly alter several of the assumptions made and therefore some of the conclusions that were made in this paper a few of my concerns based in part on field observations in the area of nipigon sills to the west of their study area are mentioned as follows for their consideration firstly the study area is located to the east of lake nipigon surrounded by areas that contain thick deposits of carbonate rich till thorleifson and kristjansson 1993 several previous workers in this area have suggested that fast flowing glacial ice an ice stream deposited this material hicock 1988 hicock et al 1989 thorleifson and kristjansson 1993 these workers hicock 1988 hicock et al 1989 thorleifson and kristjansson 1993 argued that the carbonate rich till formed a low resistance stratum for overriding ice streams either by deforming and or supporting high subglacial water pressures hicock et al 1989 p 2249 they

a mid holocene shift in arctic sea ice variability on the east greenland shelf records of iceberg rafting and palaeohydrography from two east greenland shelf cores jm96 1206 1 gc and jm96 1207 1 gc are reported benthic foraminifera stable isotopes and ird e uxes indicate a shift toward colder lower salinity polar conditions c 5 cal ka a new proxy of iceberg rafting on the east greenland shelf is the e ux of calcium carbonate tic thought to be derived from glacial erosion of cretaceous calcareous mudstones a change in the regularity and spacing of carbonate e ux peaks at c 4 7 cal ka in jm96 1207 coincides with the onset of neoglacial cooling in the renland ice core d 18 o record we propose that the carbonate e ux peaks between 4 7 and 0 4 cal ka are related to sea surface coolings associated with increased e ux of polar water and sea ice in the east greenland current these peaks are synchronous with sea surface coolings interpreted from north atlantic deep sea cores but additional peaks centred around 2 4 and 3 8 cal ka in jm96 1207 suggest that the shelf site captures higher frequency events the data indicate that severe arctic sea ice events began in the neoglacial interval and that earlier holocene cool events in deep sea records are associated with other processes such as release of meltwater from residual glacier ice and glacial lakes

varve and radiocarbon dating support the rapid advance of jakobshavn isbrae during the little ice age abstract large outlet glaciers draining the greenland ice sheet significantly influence overall ice sheet mass balance considerable short term years to decades retreat and fluctuations in velocity of jakobshavn isbrae western greenland illustrate the complex nature by which large outlet glaciers respond to climate change making predictions of future ice sheet change challenging to provide a longer term view centuries we investigate the geological record of jakobshavn isbrae change we use continuous sediment records from lakes that were influenced by the recent advance of jakobshavn isbrae which took place during the little ice age in particular we explore the use of annually laminated lake sediments varves to precisely constrain the advance of the ice margin as it approached its late holocene maximum extent we find that the ice margin advanced recently at least after 1650 to 1700 ad and more likely 1800 ad we suggest that during this period jakobshavn isbrae advanced at a rate that was similar to its historically documented average retreat since 1850 ad our results indicate that jakobshavn isbrae and presumably other large marine calving glaciers have the ability to advance quickly in response to climate forcing

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

paleoecological evidence for abrupt cold reversals during peak holocene warmth on baffin island arctic canada a continuous record of insect chironomidae remains preserved in lake sediments is used to infer temperature changes at a small lake in arctic canada through the holocene early holocene summers at the study site were characterized by more thermophilous assemblages and warmer inferred temperatures than today presumably in response to the positive anomaly in northern hemisphere summer insolation peak early holocene warmth was interrupted by two cold reversals between 9 5 and 8 cal ka bp during which multiple cold stenothermous chironomid taxa appeared in the lake the earlier reversal appears to correlate with widespread climate anomalies around 9 2 cal ka bp the age of the younger reversal is equivocal but it may correlate with the 8 2 cal ka bp cold event documented elsewhere widespread abrupt climate shifts in the early holocene illustrate the susceptibility of the climate system to perturbations even during periods of enhanced warmth in the northern hemisphere

a 10 000 year record of arctic ocean sea ice variability view from the beach we present a sea ice record from northern greenland covering the past 10 000 years multiyear sea ice reached a minimum between 8500 and 6000 years ago when the limit of year round sea ice at the coast of greenland was located 1000 kilometers to the north of its present position the subsequent increase in multiyear sea ice culminated during the past 2500 years and is linked to an increase in ice export from the western arctic and higher variability of ice drift routes when the ice was at its minimum in northern greenland it greatly increased at ellesmere island to the west the lack of uniformity in past sea ice changes which is probably related to large scale atmospheric anomalies such as the arctic oscillation is not well reproduced in models this needs to be further explored as it is likely to have an impact on predictions of future sea ice distribution

genesis of dispersal plumes in till in regions formerly covered by continental ice till sheets may contain distinctive clastic particles derived from local bedrock sources such as ore bodies such particles especially in thicker tills may be distributed in three dimensional dispersal trains or plumes developments in our understanding of glacial erosion entrainment and deposition over the past two or three decades help clarify formation of these plumes much of the debris in the basal ice of ice sheets is likely incorporated at places where water is freezing onto the base of the ice sheet this water largely a product of melting of basal ice further upglacier has migrated downglacier under the influence of a gradient in the hydraulic potential controlled primarily by the ice surface slope and secondarily by basal topography and thermal regime refreezing occurs over a substantial distance along flow so as the ice moves away from an ore body material eroded from the body is later elevated above the bed by refreezing of more meltwate

a long term perspective on glacial erosion a rough estimate of glacial erosion in the precambrian basement is related to the total denudation of bedrock since its formation in the proterozoic the basis for the calculations is reference to surfaces of different age glacial erosion is responsible for merely polishing the northern shields major denudation occurred during the proterozoic and amounted to tens of kilometres during long periods the basement was protected by palaeozoic cover rocks it was re exposed successively during the mesozoic and tertiary with denudation amounting to 600 m at the most glacial erosion can generally be counted in tens of metres though with great variations 1997 by john wiley sons ltd

till geochemical and indicator mineral methods in mineral exploration abstract this paper summarizes advances since 1987 in the application of glacial sediment sampling to mineral exploration drift prospecting in areas affected by continental or alpine glaciation in these exploration programs clastic glacial sediments are tested by geochemical or mineralogical methods to detect dispersal trains of mineral deposit indicators that have been glacially transported from source by mechanical processes in glaciated terrain the key sampling medium till is produced by abrasion crushing and blending of rock debris and recycled sediment followed by down ice dispersal ranging from a few metres to many kilometres as a consequence of the mid 1980s boom in gold exploration the majority of case studies and regional till geochemical surveys published in the past decade deal with this commodity approximately 30 of canada and virtually all of fennoscandia have been covered by regional till geochemical surveys that aid mineral exploration and provide baseline data for environmental agricultural and landuse planning the most profound event in drift prospecting in the last decade however has been the early 1990s explosion in diamond exploration which has dramatically increased the profile of glacial geology and glacial sediment sampling and stimulated changes in sampling and analytical methods

early holocene climate variability and the timing and extent of the holocene thermal maximum htm in northern iceland the magnitude and timing of holocene maximum warmth in the arctic and sub arctic has been the subject of considerable recent interest particularly in the context of future climate change although lying at a crucial location in the north atlantic close to significant atmospheric and oceanic boundaries terrestrial holocene climatic data from iceland are few and predominantly derive from glacial and palaeoecological evidence here we present new datasets from trollaskagi based on chironomid inferred temperatures ci t using sub fossil chironomids from the same lake sediments supplemented by pollen data july air temperatures have been derived using an icelandic training set and the data suggest optimal temperatures at sea level up to 1 5 c above current levels around 8 k cal yr bp a time when birch woodland was well developed in trollaskagi but when woodland had still not fully developed in the more isolated nw peninsula our data thus suggest that optimal summer warmth did not occur in iceland until 8 kcal yr bp at the earliest possibly lasting until 6 7 kcal yr bp the amount of warming for july was therefore at least 1 5 c but possibly up to 2 3 c higher than the 1961 1990 average on the basis of the tree line data comparison with data from elsewhere in adjacent arctic regions greenland and eastern arctic canada show peak warmth to be later in iceland and less pronounced it also appears that there were enhanced temperature gradients during the first half of the holocene between the two study areas trollaskagi and the nw peninsula and that they influenced patterns of vegetation colonisation with current spatial temperature patterns only developing as holocene climate deteriorated after around 6 kcal yr bp

spatial and temporal variability of holocene temperature in the north atlantic region the early holocene climate of the north atlantic region was influenced by two boundary conditions that were fundamentally different from the present the presence of the decaying laurentide ice sheet lis and higher than present summer solar insolation in order to assess spatial and temporal patterns of holocene climate evolution across this region we collated quantitative paleotemperature records at sub millennial resolution and synthesized their temporal variability using principal components analysis pca the analysis reveals considerable spatial variability most notably in the time transgressive expression of the holocene thermal maximum htm most of the region but especially areas peripheral to the labrador sea and hence closest to the locus of lis disintegration experienced maximum holocene temperatures that lagged peak summer insolation by 1000 3000 years many sites from the northeastern north atlantic sector including the nordic seas and scandinavia either warmed in phase with maximum summer insolation 11 000 9000 years ago or were less strongly lagged than the baffin bay labrador sea region these spatially complex patterns of holocene climate development which are defined by the pca resulted from the interplay between final decay of the lis and solar insolation forcing

the significance of rock structure lithology and pre glacial deep weathering for the shape of intermediate scale glacial erosional landforms the main landforms within the glacially scoured precambrian rocks of the swedish west coast are closely connected to the principal structural pattern and have lately been explained as mainly a result of etch processes probably during the mesozoic and with a possible second period of etching during the neogene to explore the effect of multiple glacial erosion on the rock surfaces an island with two different lithologies and with striae from different directions was selected for a detailed study focusing on the shape of roches moutonnees air photo interpretation of bedrock lineaments and roches moutonnees combined with detailed field mapping and striae measurements are used to interpret the structural and lithological control on the resulting shape the study reveals a significant difference in shape between roches moutonnees in augen granite and orthogneiss low elongated and streamlined roches moutonnees occur in the gneiss area striated by a late weichselian ice flow from the ne this ice flow is subparallel with both the local dominant trend of topographically well expressed joints and the schistosity of the gneiss frequently there are no signs of quarrying on the lee sides of the gneiss roches moutonnees and hence they resemble the shape of whalebacks or ruwares as typically associated with the exposed basal weathering surface found in tropical areas the granite roches moutonnees were formed by an older ice flow from the ese which closely followed the etched wnw ese joint system of the granite late weichselian ice flow from the ne caused only minor changes of the landforms on the contrary marks of the early ese ice flow are poorly preserved in the gneiss area where it probably never had any large effect as the flow was perpendicular to both schistosity and structures and accordingly also to the pre glacial relief the study demonstrates that coincidence between ice flow direction and pre glacially etched structures is most likely to determine the effects of glacial erosion copyright 2002 john wiley sons ltd

processes of debris comminution in the glacial environment and implications for quarts sand grain micromorphology abstract studies of till composition rock crushing and abrasion experiments and detailed consideration of the mechanics of the comminution processes which occur in the subglacial environment suggest that monomineral quartz sand grains are mostly produced by the brittle fracture of larger particles abrasive wear is an inefficient mechanism for producing and modifying quartz sand grains because of the relatively great hardness of quartz viewed under the scanning electron microscope surface textures of subglacially derived quartz sand grains are typically those associated with brittle fracture of quartz since the release of quartz sand grains from bedrock by mechanical weathering may also involve brittle fracture grains which have been passively transported through a glacier may exhibit similar textures to those actively produced in the glacial environment hence the examination of the surface textures of quartz sand grains under the scanning electron microscope is unlikely to be a satisfactory technique for the discrimination of active and passive transport paths through glaciers

preservation of landforms under ice sheets and ice caps abstract this article addresses the question of whether or not distinct glacial and non glacial landforms can survive beneath ice sheets and ice caps with little or no morphological alteration a review of recent work documents the existence of pre last stadial landforms and landscapes in areas covered by the fennoscandian and laurentide ice sheets a substantial number of independent works indicate that landforms such as eskers drainage channels and boulder fields have escaped destruction despite complete ice overriding during several tens of millenia full preservation of former ground surfaces or delicate landforms probably is linked to areas where the ice sheet base was continuously frozen to its bed larger robust landforms such as large drumlins appear to have been preserved even under wet based conditions in glaciated areas patches preserved under dry cold based conditions provide important windows towards the past showing landscapes that were destroyed in surrounding areas affected by wet based and eroding ice some consequences for the research fields of non glacial geomorphology archaeology and botany include the possibility of subglacial museums and refugia a time space model describes geomorphological access to information from older events in glaciated areas

isolation basin stratigraphy and holocene relative sea level change on arveprinsen ejland disko bugt west greenland this paper presents the results of an investigation into holocene relative sea level rsl change isostatic rebound and ice sheet dynamics in disko bugt west greenland data collected from nine isolation basins on arveprinsen ejland east disko bugt show that mean sea level fell continuously from ca 70 m at 9 9 ka cal yr bp 8 9 ka 14c yr bp to reach a minimum of ca 5 m at 2 8 ka cal yr bp 2 5 ka 14c yr bp before rising to the present day a west east gradient in isostatic uplift across disko bugt is confirmed with reduced rebound observed in east disko bugt however rsl differences up to 20 m at 7 8 ka to 6 8 ka cal yr bp 7 ka to 6 ka 14c yr bp also exist within east disko bugt suggesting a significant north south component to the area s isostatic history the observed magnitude and timing of late holocene rsl rise is not compatible with regional forebulge collapse instead rsl rise began first in the eastern part of the bay as might be expected under a scenario of crustal subsidence caused by neoglacial ice sheet readvance the results of this study demonstrate the potential of isolation basin data for local and regional rsl studies in greenland and the importance of avoiding data compilations from areas where the isobase orientation is uncertain copyright 1999 john wiley sons ltd

midges and palaeotemperature reconstruction the north american experience abstract the development of midge based palaeoclimatology in north america is reviewed with a focus on lateglacial and holocene climatic change although relatively few sites have been studied midge inferred palaeotemperatures reveal detailed records of lateglacial climate oscillations and more subtle holocene temperature changes holocene climate changes are often at or near the detection limit using current palaeotemperature inference models interference from other environmental variables including water depth and oxygen concentration changes are discussed as well as the challenges inherent to developing better models the isotopic signature of chitin preserved in midge head capsules has opened new avenues for midge palaeotemperature inference through coordinated research efforts national and international collaborations will provide opportunities to reconstruct holocene palaeoclimate at continental and hemispheric scales

mid to late holocene hydrological and climatic variability in disko bugt central west greenland diatom and lithological analyses were carried out on two sediment cores from disko bugt and the adjacent kangersuneq fjord west greenland in order to investigate mid to late holocene 6 9 0 7 kyr bp hydrographic and climatic variability while the disko bugt record is found to reflect mainly west greenland current wgc fluctuations that can be linked to north atlantic circulation variability the fjord record appears to be more representative of local climate conditions the records demonstrate that the period of investigation was marked by a late holocene thermal maximum beginning at c 4 8 kyr and ending between 3 5 and 3 1 kyr bp encompassing a colder period between c 4 0 and 3 8 kyr bp an episode of higher surface water temperature is also indicated in disko bugt between 2 2 and 1 5 kyr bp in contrast the record from kangersuneq fjord suggests persisting cooler summer surface waters for this interval interpreted to be attributable to increased meltwater outflow the warming episode recogni