late quaternary glacial interglacial changes in sediment composition at the east greenland continental margin and their paleoceanographic implications stable isotope records and sedimentological and organic geochemical investigations of marine sediments from the east greenland sea at 70 n provide important information about glacial interglacial variations of paleoenvironments through the last 225 kyr the oxygen isotope records established on the planktonic foraminifer n pachyderma sin show some excursions from the global climate pattern probably due to local regional overprint by meltwater supply the cold low saline east greenland current and fluctuations in sea ice covering were a crucial element controlling the carbonate production in the subsurface surface water column in the east greenland sea over the last 225 kyr the beginning of termination ia is ams 14c dated at about 15 8 kyr b p and interpreted as a greenland ice sheet meltwater signal the stage 2 3 boundary is dated at about 25 kyr b p the timing of the onset of the last deglacial meltwater event is about 800 years earlier than that of the barents shelf ice sheet meltwater signal recorded in the fram strait several major pulses of increased supply of coarse grained terrigenous material by glacio marine processes occurred during the last 225 kyr the supply of coarse grained ice rafted debris at the east greenland continental slope reached maximum values during the last glacial maximum stage 2 weichselian 15 19 kyr b p the drastic climatic change and the gradual retreat of continental ice masses glaciers during the last deglaciation termination i are clearly documented in the marine sedimentary sequences from shelf and upper slope environments this process resulted in distinctly decreased supply and deposition of ice rafted debris in the open shelf upper slope environments during termination i the sea ice cover also decreased causing an increase in surface water productivity indicated by increased organic carbon and biogenic opal deposition

complex zoning in apatite from the idaho batholith a record of magma mixing and intracrystalline trace element diffusion apatite crystals in a sample of biotite granodiorite from the idaho batholith display complex chemical zoning characterized by abrupt changes in ree y si content more subtle variations in s na la yb and mn contents and petrographic evidence for multiple episodes of partial resorption the zoning is attributed to changes in melt composition resulting from magma mixing and differentiation although the possibility that some rounded cores may be inherited cannot be disproved high s contents in apatite cores and the presence of an included anhydrite grain indicate crystallization from an oxidized host magma divalent cations that occupy the apatite ca sites sr mn fe show evidence of having been redistributed between zones by intracrystalline diffusion whereas cations that participate in coupled substitutions involving the tetrahedral site si y ree na s were not readily redistributed the main ree substitution in this case is ree super 3 si super 4 ca super 2 p super 5 and ree diffusion is rate limited by slow si diffusion however exchange of lree e g lasm sub 1 on the ca sites does not involve si and proceeds more rapidly resulting in homogenization of la sm between zones within individual crystals relative diffusion rates inferred from zoning profiles in this study are mn sr fe and lasm sub 1 are faster than na s and layb sub 1 which are faster than si these data imply that ree patterns can be decoupled from ree abundances during diffusion and that even apatite zones or cores that appear sharply bounded in backscattered electron images may not retain their original chemical or sr nd isotopic traits

magmatic graphite inclusions in mn fe rich fluorapatite of perphosphorus granites the belvis pluton variscan iberian belt three mn fe rich fluorapatite types have been found in the highly evolved peraluminous and perphosphorous granites of the belvis pluton one of these apatite types includes abundant graphite microinclusions suggestive of a magmatic origin for the graphite the belvis pluton is a reversely zoned massif composed by four highly fractionated granite units showing a varied accessory phosphate phases u rich monazite u rich xenotime u rich fluorapatite and late eosphorite childrenite the strong peraluminous character of the granites determines an earlier monazite and xenotime crystallization so the three types of fluorapatite record late stages of phosphate crystallization the earlier type 1 apatite is mostly euhedral small and clear type 2 apatite is dusty large 2800 m and mostly anhedral with strong interlobates interfaces with the main granite minerals more abundant in the less fractionated units and absent in the most evolved unit type 3 is subeuhedral to anhedral shows feathery aggregate texture and only appears in the most evolved unit apatite composition was acquired by electron microprobe analyses laser ablation inductively coupled plasma mass spectrometry and electron energy loss spectroscopy type 1 and type 2 apatite display similar broad compositional ranges showing high mno up to 4 30 wt and feo up to 2 88 wt contents without traces of carbon in apatite structure type 2 differs from type 1 by having slightly higher lree and sr contents ree spectra also differ with type 1 displaying both variable lree slope and negative eu anomaly whereas type 2 shows constant lree slope and higher negative eu anomaly although both display similar hree slope type 3 apatite displays higher feo contents up to 5 09 wt positively correlated with higher cl na li be b zn contents and extremely low y ree contents when compared to the other apatite types cation substitution indicates that part of the fe content is as fe graphite has been found exclusively as abundant microinclusions in type 2 apatite parallel or randomly distributed and heterogeneously grouped in clusters within the crystals high resolution electronic images show that graphite occurs with unusual habits filaments of stacked hexagonal flakes up to 15 m length and up to 0 5 m width textural and chemical features suggest a highly crystallized melt which favor compartmentalizing in compositional microdomains where the apatite types would have crystallized the cocrystallization of type 2 apatite and graphite suggests a c f p rich melt sufficiently saturated to acquire an immiscible character with the highly evolved silicate melt in late magmatic stages as type 2 differs from type 1 apatite by higher lree and sr contents we interpret that fluxing components were favorably concentrated in those residual less depleted lree sr fraction melts once monazite and zircon and xenotime would have crystallized type 3 apatite records a change in the ultimate melt stage an increase of the oxygen fugacity coupled with high undercooling by volatile lost of highly fractionated residual cl richer melts the presence of biogenic carbon in granite peraluminous melts derived from metasedimentary sources and its later crystallization as graphite filaments opens a discussion on the carbon behavior during magma evolution especially in highly polymerized melt framework

a high resolution14c dated sediment sequence from southwest sweden age comparisons between different components of the sediment a macrofossil rich glaciomarine marine lacustrine sediment from a soft water lake in southwestern sweden has provided an opportunity to 14c date different components of its sediments bulk sediment dates are 100 to 500 yr older than fragile terrestrial macrofossils of corresponding levels with a mean age difference of ca 300 yr this is explained by the presence of old and reworked organic material in the sediment five age comparisons between terrestrial macrofossils and periostraca of marine bivalves probably arctica islandica of allerod age give a mean age difference of 380 yr i e slightly greater than the present reservoir age of 340 30 yr for the swedish west coast this difference is roughly the same as for the marine macroalga desmarestia aculeata a date from shell carbonate fragments of mytilus edulis yields an age that is more than 1000 yr older than corresponding periostraca and terrestrial macrofossils and 500 1000 yr older than the age of the supposed deglaciation of the site altogether this indicates a larger marine reservoir effect during the allerod than at present 1998 john wiley sons ltd

sea surface conditions in northernmost baffin bay during the holocene palynological evidence the analysis of cores collected in northernmost baffin bay from within the area of the north water polynya permits definition of a composite sedimentary sequence ca 12 m thick spanning the last 10 000 14 c yr with only a few discontinuities palynological analyses were performed in order to reconstruct changes in surface water conditions and biogenic production transfer functions using dinocyst assemblages were applied to estimate sea surface temperature sst and salinity as well as the seasonal duration of sea ice cover at the base of the record prior to 9300 14 c yr bp dinocysts and organic linings of benthic foraminifers are sparse indicating harsh conditions and low productivity after ca 9300 14 c yr bp the increased concentration of benthic foraminifers up to 10 3 linings cm 3 and dinocyst fluxes 10 2 10 3 cysts cm 2 yr 1 reveals high biological productivity related to open water conditions the early to middle holocene from ca 9000 to ca 3600 14 c yr bp is marked by relatively high species diversity in dinocyst assemblages and the significant occurrence of autotrophic taxa such as spiniferites elongatus pentapharsodinium dalei and impagidinium pallidum this assemblage suggests conditions at least as warm as at present from ca 6400 to ca 3600 14 c yr bp transfer functions indicate warmer conditions than at present with sst in august fluctuating up to 5 5 c after 3600 14 c yr bp the dinocyst record suggests a trend of decreasing temperature toward modern values marked by recurrent cooling events copyright 2001 john wiley sons ltd

last glacial maximum and deglaciation of devon island arctic canada support for an innuitian ice sheet abstract the extent and origin of quarternary glaciers in the queen elizabeth islands of arctic canada especially during the last glacial maximum lgm has been debated for well over a century no consensus has yet emerged and the spectrum of interpretations within the last decade is the broadest ever the glacial geology of devon island strongly supports the late wisconsinan innuitian ice sheet hypothesis during lgm the southeastern part of the queen elizabeth islands was covered by an ice sheet flowing from a centre or a divide centrally located in the archipelago another ice divide extended from the centre across devon island flow from the innuitian centre and convergent flow from devon island and probably also from cornwallis and bathurst islands sustained an ice stream in wellington channel ice was locally advancing to its lgm limit about 23 ka bp recession in the vicinity of the present coastline was underway by 10 ka bp and final ice remnants west of the present devon ice cap vanished about 8 ka bp the island bears the same two part landscape zonation as do other islands and peninsulas in the region these reflect a cold based core and warm based periphery at lgm

origin of leucite rich and sanidine rich flow layers in the leucite hills volcanic field wyoming two types of orendite sanidine phlogopite lamproite and wyomingite leucite phlogopite lamproite intraflow layering are present in the ultrapotassic leucite hills volcanic field wyoming in large scale layering wyomingites are confined to the base of the flow while in centimeter scale layering orendite and wyomingite alternate throughout the flow the mineralogy of the orendites and wyomingites are the same only the relative amount of each mineral vary substantially the chemical compositions of adjacent layers of wyomingite and orendite are almost identical except for water the centimeter scale flow layering probably represents fossil streamlines of the lava and therefore defines the path of circulation of the viscous melt toward the front of the flow the layers are commonly folded structures present which are indicative that the flows may have possessed a yield strength are limb shears boudinage and slumping phlogopite phenocrysts are poorly aligned in the orendite layers while they are often in subparallel alignment in the wyomingite layers and they are used as a measure of shearing intensity during emplacement of the flow vesicle volumes are concentrated in the orendite layers in the large scale layering a discontinuous base rubble zone of autobreccia is overlain by a thin platy zone followed by a massive zone which composes more than the upper 75 of the flow consequently we feel that the origin of the layering may be related to shearing two extremes in the geometry of shearing are proposed closely spaced thin densely sheared layers separated by discrete intervals throughout a lava flow as in the centimeter scale layering and classical plug flow where all the shearing is confined to the base as in the large scale layering a mechanism is proposed which causes thixotropic behavior and localizes shearing the driving force is the breakdown of molecular water to form t oh bonds which establishes a chemical potential gradient for water in the melt the higher activity of water in the nonsheared regions allows sandine to crystallize whereas the lower activity of water in the areas of active shearing causes leucite to crystallize

palaeoecological studies of holocene lake sediments from west greenland abstract colonisation by plants and animals and subsequent biotic development in west greenland was studied by analyses of macrofossils in four holocene lake sequences one of the lake basins located near the outer coast was deglaciated shortly after the transition from the last glacial stage to the holocene and a basal date of 12 100 11 300 cal years bp was obtained two of the lake basins located near the margin of the greenland ice sheet were deglaciated several millennia later the oldest sediments contain low diversity floras and faunas some of the first immigrants were chironomidae and daphnia pulex soon followed by other insects crustaceans and other invertebrates water mosses ranunculus confervoides hippuris vulgaris and potamogeton filiformis were among the first plants that colonised the lakes the earliest holocene terrestrial flora in west greenland was probably entirely herbaceous with salix herbacea and empetrum nigrum being some of the first woody plants to arrive a number of invertebrates are new to the fossil fauna of greenland and the ostracod ilyocypris bradyi that was found in one sequence from 7000 to 6500 cal years bp has not been recorded from greenland before

spatial and temporal patterns of iceberg rafting ird along the east greenland margin ca 68 n over the last 14 cal ka twelve 1 2 m 10 cm diameter gravity cores collected in 1988 and 1991 from the continental shelf and fjords of east greenland near kangerlussuaq fjord trough ca 68 n 32 w have distinct changes in lithofacies and in the quantity of iceberg rafted ird sediments these changes are readily observed in x radiographs of the split cores we quantify the ird contribution through grain size analyses and counting the number of clasts 2 mm from the x radiographs chronological control is provided by acclerated mass spectroscopy 14c dates on foraminifera during deglaciation after 14 cal ka there was one interval of ird accumulation ca 12 13 cal ka followed by a brief return to ird conditions centred at 9 cal ka thereafter a prominent feature of most cores on the shelf is an increase in ird accumulation that started ca 5 6 cal ka and which has increased toward the present indicators of iceberg rafting such as the net sand flux and numbers of clasts 2 mm ka 1 follow a power law distribution when graphed against distance from the present east greenland coast a measure of the position of the glacier margins the form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf these relationships are used to estimate changes in the location of the ice margin during the late quaternary based on a site on the east greenland slope denmark strait and to discuss factors that can negate such a simple transfer function 1997 by john wiley sons ltd

the late quaternary history of hall land northwest greenland reply the last ice limit on hall land northwest greenland is marked by the newman and petermann moraines which were deposited 40 60 km beyond the present ice margins in newman bay and petermann fiord respectively these moraines flank the eastern and western coasts of hall land but do not extend into its intervening central plain as a result of glacioisostatic depression at this time a full glacial sea transgressed the entire central plain via a narrow estuary located between the newman moraine and the northern plateau of hall land the limit of this full glacial sea is isostatically tilted from 116 m asl on the adjacent coast of ellesmere island to 150 m asl on the southwest extremity of the central plain where it reaches its apex pervasive marine silts cover the central plain and laterally thicken towards the newman and petermann moraines because of the height of the full glacial sea these moraines were deposited in a submarine environment and mark the grounded margins of ice shelves floating in hal

isostatic adjustments in a full glacial sea during the last glaciation an ice free corridor existed between the northeast ellesmere island and northwest greenland ice sheets this corridor constituted a peripheral depression in which the marine limit marks the uppermost extent of a full glacial sea the full glacial sea is characterized by 1 14c dates on in situ marine shells that predate initial emergence unloading followed by 2 synchronous emergence from the marine limit throughout the peripheral depression relative sea level curves from the full glacial sea confirm previous morphostratigraphic and glacioisostatic evidence for limited ice extent during the last glaciation these curves also document the history of glacial unloading and the form of the relative sea level curve that one would theoretically expect in the peripheral depression the form of the curves presented here is unlike any other published emergence curves from arctic canada or from fennoscandia the relative sea level curves for northeast ellesmere island show three segme

the east greenland continental margin 65 n since the last deglaciation changes in seafloor properties and ocean circulation nine gravity cores collected on the east greenland continental margin off kangerdlugssuaq fjord reveal a drastic decrease in average sedimentation rates from the cross shelf through the continental slope from 43 2 cm kyrs to 2 2 cm kyrs respectively since the last deglaciation beginning at 2g cm2kyrs at 4000 yrs b p both caco3 and non caco3 accumulation rates became high g cm2kyrs since 3000 yrs b p these rates distinctly decreased melting of glaciers and current activity which drastically changed in space and time controlled the terrigenous sediment input and thus the grain size distribution and the physical properties of sediments across the shelf these observations suggest that current winnowing on sediments is one of the dominant processes at present this is seen in the acoustic reflectivity and in the acoustically hard seafloor particularly at the upper continental slope in addition icebergs transported southward along the continental margin have scoured the sediment surface in water depths 350m

glacier dynamics and paleoclimatic change during the last glaciation of eastern ellesmere island canada a 300 km transect along the east coast of ellesmere island fills a major gap in the late quaternary data base of the canadian high arctic the last glacial maximum lgm is marked by prominent moraines and meltwater channels that terminate within 30 km of modern ice margins shells in glaciomarine deposits collected beyond the lgm indicate deglaciation by more extensive ice prior to 35 ka bp more than 60 14c dates from glaciomarine sediments provide a chronology for past ice dynamics during the lgm to the north while many areas remained ice free due to severe aridity several glaciers remained in contact with the sea until 7 1 ka bp farther south most glaciers reached the coast and significantly infilled several fiords this southward increase in glacier extent is due to larger glacial catchment basins and increased precipitation towards storm tracks in northern baffin bay the earliest dates on deglaciation along the transect range from 8 1 to 7 7 ka bp initial retreat was controlled by the exten

mineralogy and petrogenesis of a ba ti zr rich peralkaline dyke from sebkovice czech republic recognition of the most lamproitic variscan intrusion abstract a peralkaline ultrapotassic dyke found at sebkovice t ebic district western moravia is a mineralogically extreme member of a dyke swarm occurring along the south eastern border of the moldanubian region of the bohemian massif the dyke shows a simple zoning with a very fine grained marginal zone grading into a medium grained central zone it has a primary mineral assemblage of microcline and potassic amphiboles with accessory apatite and altered phlogopite the microcline exhibits an unusual red luminescence colour and pronounced substitution of fe3 for al with measured contents of fe2o3 up to 8 5 wt 0 31 apfu fe3 amphiboles have very high k up to 0 99 apfu and si contents their compositions follow an alkaline fractionation trend from potassic richterite to potassic magnesio arfvedsonite characterized by an increase of na k and a decrease of ca mg fe2 and ti via heterovalent substitutions b ca c mg fe2 b na c fe3 and ti mg 2fe3 the most evolved apatite is significantly enriched in sro up to 9 7 wt 0 49 apfu sr the core of the dyke and late veinlets contain unique late to post magmatic ba ti zr bearing mineral assemblages of baotite henrymeyerite titanite rutile benitoite and bazirite anhedral baotite fills interstices distributed inhomogeneously in the dyke centre it is locally replaced by a ba bearing titanite henrymeyerite rutile quartz assemblage henrymeyerite the second record in a lamproite shows variable fe ti ratios and represents a solid solution of the hepta and hexatitanate components euhedral crystals of benitoite and bazirite are enclosed in the late stage quartz titanite apatite veinlets in the fine grained margin of the intrusion in terms of a mineralogical genetic classification the sebkovice dyke can be considered as a new high silica 57 wt sio2 variety of lamproite variety sebkovice and represents a unique expression of post collisional potassic magmatism on the south eastern border of the bohemian massif the peralkaline dykes from this area show mineralogical and geochemical features similar to those of silica rich orogenic lamproites emplaced at destructive plate margins in terms of the modern classification of lamproites the sebkovice dyke is the first lamproite recognised in the variscan orogenic belt

quaternary glacial and marine environmental history of northwest greenland a review and reappraisal new information on middle and late quaternary deposits of the thule region northwest greenland necessitates the revision of the chronostratigraphy of the area and allows fuller understanding of the marine environmental changes in ba n bay the stratigraphic record is interpreted as the product of three marine events saunders qarmat and nuna in decreasing age during which marine sedimentation occurred on coastal areas now land and three or four glacial events of decreasing age and ice cover agpat narsaarsuk and kap abernathy wolstenholme fjord to which the marine events were glacio isostatically related subarctic atlantic water reached this northern part of ba n bay during all three marine events but the warmest conditions warmer than the present occurred in the qarmat event correlated with the deep sea oxygen isotope stage 5e the question of late stage 5 events is considered the nuna event dates to latest stage 2 and the holocene whilst the saunders event is of uncertain age but at least stage 6 a number of glacial events with advances confined to the fjords are dated to stage 2 wolstenholme fjord and late stage 6 narsaarsuk and an intermediate advance kap abernathy is undated in the range of stage 2 5 extension of glaciation to the shelf edge is dated to stage 6 agpat event 1999 elsevier science ltd all rights reserved

holocene emergence at cape herschel east central ellesmere island arctic canada implications for ice sheet configuration twenty five radiocarbon age determinations on marine molluscs basal organic pond sediments charred remains in archeological sites and a variety of other materials have allowed the construction of an emergence curve for cape herschel east central ellesmere island 78 35 n 74 40 w only a narrow fringe of land is present between the prince of wales icefield and smith sound yet emergence of the order of 135 m has taken place during the last 8500 8700 radiocarbon years the highest in situ shells were collected at an elevation of 107 5 m and ages of 8470 100 bp gsc 3314 and 8230 70 bp to 230 were obtained on this material the spectacular and fresh appearing glacial sculpture along both sides of smith sound coupled with the rapid emergence in holocene time and the fact that the oldest dates on marine shells at the fiord heads to the west are 3000 4000 years younger than those at cape herschel provides convincing evidence that an ice stream filled smith sound 500 m deep during the late wis

cosmogenic 10be and 26al ages for the last glacial maximum eastern baffin island arctic canada a chronology for the last glacial maximum based on cosmogenic exposure dating in the pangnirtung fjord area eastern baffin island arctic canada is at odds with many decades of land based glacial stratigraphic research most previous chronologies focused primarily on relative weathering criteria and suggested that ice extent was restricted during the late wisconsinan ca 24 8 ka in contrast by directly dating glacial features we conclude that late wisconsinan ice was far more extensive than previously believed there are 36 gneissic boulders and 8 samples of ice molded gneissic bedrock that yield late wisconsinan 10 be and 26 al exposure ages for the last glaciation of pangnirtung fjord the prominent duval moraines which were previously interpreted to represent a significant early wisconsinan 100 60 ka ice advance on southern cumberland peninsula were actually deposited between 24 and 9 ka two boulders from a raised glaciomarine delta stratigraphically related to the duval moraines date to about 10 ka two recessional moraines and striated bedrock along pangnirtung fjord as well as erratics on the floor of the kolik river valley a tributary to pangnirtung fjord indicate that deglaciation began between 12 and 9 ka in situ produced 10 be and 26 al abundances indicate that ice filled pangnirtung fjord for about 15 k y either continuously or intermittently prior to 10 ka which is compatible with 14 c chronologies for adjacent cumberland sound thus our data support other recent studies that suggest the northern and southern margins of the laurentide ice sheet were generally in phase during the latest wisconsinan contrary to earlier interpretations

the mineralogy of the kokchetav lamproite implications for the magma evolution abstract kokchetav lamproite occurs in the east end of kokchetav massif and consists of phenocryst mainly clinopyroxene and matrix mainly feldspar the compositions of clinopyroxene magnetite and biotite phenocryst were determined using wavelength dispersive spectrometry on a jeol super probe 8900 electron microprobe for the purpose of revealing the process of magma evolution analyses revealed a core rim variation which is consistent with three stages of magmatic evolution mg rich clinopyroxene cores diopside and biotite cores phlogopite crystallized in a deep magma chamber stage i fe rich clinopyroxene rim salite and biotite rim crystallized at low pressure in a shallow magma chamber stage ii magnetite phenocryst core also crystallized in a shallow magma chamber and co exists with fe rich clinopyroxene rim and biotite rim the magnetite rims probably formed during magma eruption at the same time when groundmass crystallized stage iii the calculated temperatures for ilmenite magnetite pair range from 679 to 887 c log f o 2 values range from 11 1 to 14 9 log units these values represent the latest conditions of magma as ilmenite exsolution in magnetite probably occurred during magma eruption from the shallow chamber to surface

chronology of the last recession of the greenland ice sheet a new deglaciation chronology for the ice free parts of greenland the continental shelf and eastern ellesmere island canada is proposed the chronology is based on a new compilation of all published radiocarbon dates from greenland and includes crucial new material from southern northeastern and northwestern greenland although each date provides only a minimum age for the local deglaciation some of the dates come from species that indicate ice proximal glaciomarine conditions and thus may be connected with the actual ice recession in addition to shell dates dates from marine algae lake sediments peat terrestrial plants and driftwood also are included only offshore and in the far south have secure late glacial sediments been found other previous reports of late glacial sediments older than 11 5 cal kyr bp from onshore parts of greenland need to be confirmed most of the present ice free parts of greenland and nares strait between greenland and ellesmere island were not deglaciated until the early holocene copyright c 2002 john wiley sons ltd less

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

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

unblocking of the nares strait by greenland and ellesmere ice sheet retreat 10 000 years ago the extent of glaciation at the northern margin of the canadian greenland high latitude arctic region over the past 30 000 years is uncertain geological arguments have been made for greenland and ellesmere island ice sheets that coalesced to block the nares strait1 and for restricted ice sheets on the two islands2 leaving the strait open as it is today3 distinguishing between these two possibilities would provide significant constraints on present understanding of the past circulation between the arctic and atlantic oceans4 5 on estimates of past ice volume6 and on the response of the greenland ice sheet to climate change7 radiocarbon analyses provide dates for the deglaciation of the islands coasts but do not yield information on whether ice filled the strait here we present measurements of cosmogenic 36cl that has accumulated in situ in erratics and glacially polished bedrock on islands within the nares strait these data allow us to determine the time for which the rocks have been recently exposed to the atmosphere and thus the age of the final deglaciation of the strait we show that greenland and ellesmere ice sheets retreated from the nares strait about 10 000 years ago the strait was filled with ice during the last glaciation blocking this connection between the arctic and atlantic oceans and supporting the model of extensive and long lasting ice on land and sea in this region8 9 10 11

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

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

naturally occurring ferric iron sanidine from the leucite hills lamproite sanidine crystals precipitating from lamproitic magmas characteristically contain appreciable amounts of feh sanidine grains from the leucite hills lamproites wyoming have compositions in which up to 70 mol of the kaisi30gmolecule is replaced by kfehsi30g thus constituting a new natural feldspar component sanidine is among the last phases to crystallize in the groundmass of leucite hills lamproites and rarely exceeds 150 lmin length nearly all grains are zoned in fe ranging from 2 5 wt fez03in the cores to 19 6 wt fez03at rims adjacent to quenched glass the fe rich rims are relatively narrow on 010 crystal faces in comparison with 001 faces maximum width 10 lm probably reflecting faster 001 and slower growing 010 crystallographic directions a near perfect correlation is obtained by combining ti mg and excess si cations with feh in tetrahedral substitution for ai insufficient numbers of r2 cations exist to balance the high concentrations of mg through an r2 mg2 r r substitution suggestingthe exchangemg2 si4 ai i in 2kalsi30g analogousto that found in synthetic leucite and kalsilite selected area electron diffraction and convergent beam electron diffraction show that the fe rich sanidine rims have a c2 m structure with cell dimensions of a 8 68 t 0 15 b 13 14 t 0 23 c 7 31 t 0 15 a ex 90 0 t 0 54 j 116 0 t 0 46 y 90 0 t 0 33 and a calculated cell volume of 747 t 21 a3 these crystallographic data are in very close agreement to those obtained previously for synthetic kfehsi30g the unusually high concentrations of feh ti and mg in the sanidine rims are likely the consequence of rapid crystallization during quenching of an unusually siand k rich yet ai deficient residual magma

preglacial surface remnants and quaternary glacial regimes in northwestern sweden abstract we present a detailed map of the distribution of preglacial surface remnants in the kebnekaise region of northwestern sweden in this mountain area we discern four important large scale geomorphological units each representing a specific set of erosional agents and formative conditions these are i intact preglacial surface remnants characterized by gentle slopes round summits wide shallow valleys and an absence of rock basins ii preglacial surface remnants showing signs of minor glacial erosion and deposition iii glacially scoured surfaces including glacial troughs iv deep fluvial valleys cut into the preglacial surface the pattern of glacial erosion is explained as the result of three specific modes of glaciation known to have existed during the last 120 000 years and inferred to have repeatedly prevailed during the last 2 75 million years cirque glaciation mountain ice sheets and fennoscandian ice sheets a deep ocean oxygen isotope record of foraminifera from the north atlantic dsdp 607 was used to infer the temporal extent of these modes of glaciation during the last 2 75 million years we interpret the preglacial landscape preservation and the pattern of glacial erosion in terms of the configuration the basal thermal regime and the duration of such glaciation events the average subglacial thermal regime of both ice sheet types was frozen on the uplands and melting in the main valleys where outlet glaciers and ice streams formed the pre glacial landscape is best preserved at intermediate elevations low enough not to have been covered by cirque glaciers and apparently high enough not to have experienced melted bed conditions and subglacial erosion during ice sheet overriding events in a narrow high relief zone along the elevation axis interglacial fluvial erosion was morphologically important the absence of glacial erosion on uplands in this zone allowed fluvial erosion to commence on the same locations during each ice free interval in contrast no persistent fluvial valley pattern could develop in zones subjected to repeated glacial scouring and hence derangement of fluvial patterns

deglaciation of a major palaeo ice stream in disko trough west greenland recent work has confirmed that grounded ice reached the shelf break in central west greenland during the last glacial maximum lgm here we use a combination of marine sediment core data including glacimarine lithofacies and ird proxy records and geomorphological and acoustic facies evidence to examine the nature of and controls on the retreat of a major outlet of the western sector of the greenland ice sheet gris across the shelf retreat of this outlet which contained the ancestral jakobshavns isbrae ice stream from the outer shelf in disko trough was rapid and progressed predominantly through iceberg calving however minor pauses in retreat tens of years occurred on the middle shelf at a trough narrowing forming subtle grounding zone wedges by 12 1 cal kyr bp ice had retreated to a basalt escarpment and shallow banks on the inner continental shelf where it was pinned and stabilised for at least 100 years during this time the ice margin appears to have formed a calving bay over the trough and melting became an important mechanism of ice mass loss fine grained sediments muds were deposited alternately with ird rich sediments diamictons forming a characteristic deglacial lithofacies that may be related to seasonal climatic cycles high influxes of subglacial meltwater emanating from the nearby ice margins deposited muddy sediments during the warmer summer months whereas winters were dominated by iceberg calving leading to the deposition of the diamictons this is the first example of this glacimarine lithofacies from a continental shelf setting and we suggest that the calving bay configuration of the ice margin plus the switching between calving and melting as ablation mechanisms facilitated its deposition by channelling meltwater and icebergs through the inner trough the occurrence of a major stillstand on the inner shelf in disko trough demonstrates that the ice dynamical response to local topography was a crucial control on the behaviour of a major outlet in this sector of the gris during retreat

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

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

coalescent greenland and innuitian ice during the last glacial maximum revising the quaternary of the canadian high arctic abstract this paper constitutes a fundamental revision of the author s earlier research and resolves a long standing debate concerning the late quaternary history of the canadian high arctic supporting its inundation by glaciers during the last glacial maximum lgm a transect along east ellesmere island demonstrates that ice advanced northward and southward along the axis of nares strait during the late wisconsinan debouching from a central saddle in kane basin the configuration of ellesmere island and greenland ice is based on moraines meltwater channels and erratics the youngest ams 14c date obtained on shelly till suggests ice buildup after 19 ka bp whereas many other dates are younger than 30 ka bp furthermore the lowest youngest detectable amino acid ratios on shells from till postdate the robeson aminozone 70 ka bp and are separated from holocene ratios by a narrow gap wholly consistent with the occupation of the strait by late wisconsinan ice re entry of the sea throughout nares strait is shown by a series of paleogeographic maps based on geomorphic evidence and radiocarbon dates on shells associated with marine limit deglaciation at the north end of the strait occurred by 10 1 ka bp and at the south end by 9 0 ka bp nares strait may still have been blocked by ice north of kane basin at 8 ka bp however by 7 5 ka bp it provided an unobstructed seaway from the arctic ocean to baffin bay the prominent ice margins within the fiords of eastern ellesmere island previously considered to mark the last ice limit record regional stabilization of land based ice after breakup of preceding marine based margins other implications of this study are that ice buildup occurred post 30 ka bp and possibly post 19 ka bp during an interval widely assumed to be constrained by severe aridity in the high arctic and that coalescent greenland and ellesmere island ice during the lgm promoted thickening of the eastern ellesmere island ice divide causing enhanced westward flow across the island to eureka sound sizeable postglacial emergence 80 120 m on eastern ellesmere island is associated with the retreat of thick ice 1 km from the strait greater emergence in eureka sound which extends southward into the central arctic islands confirms the previously proposed axis of the innuitian ice sheet further clarification of the extent geometry and retreat of the innuitian ice sheet will provide new opportunities for glaciological and geophysical modelling and help to identify late quaternary sediment sources for the arctic ocean and baffin bay

estimates of south greenland late glacial ice limits from a new relative sea level curve abstract marine lacustrine isolation contacts from seven basins in the nanortalik area south greenland have been analysed and dated the basins were isolated from the sea as a consequence of isostatic rebound following deglaciation the isolation contacts were identified with litho and biostratigraphical analyses especially sedimentary changes grey scale analyses and analyses of macroscopical remains of plants and animals dating was performed by analytical mass spectroscopy radiocarbon dating of macrofossils and bulk sediment samples a slow initial relative sea level fall that begins at 13 8 cal ka bp changes to a rapid relative sea level fall before the sea level fell below the present day sea level just prior to 10 cal ka bp the emergence curve goes further back in time than any previous emergence curve constructed from greenland which reflects the early deglaciation of the studied region the glacio isostatic crustal rebound following deglaciation was around 110 m the sea level history indicates that the margin of the greenland ice sheet probably extended out to the shelf margin during the last glacial maximum and that the ice thickness must have been at least 1500 m over the outer coast thus the highest coastal mountains would have been ice covered which is surprising given their alpine character in addition the major part of the recession of the ice must have occurred relatively late and quickly maybe from 14 to 12 cal ka bp the late holocene transgression may at least in part be due to increased isostatic loading as a consequence of advancing glaciers during the neoglaciation

ice sheet and ocean interactions margin of the east greenland ice sheet 14 ka to present diatom evidence seven marine sediment cores were collected from the kangerdlugssuaq trough off the southeast coast of greenland the trough cuts across the continental shelf from the fjord mouth to the upper slope in denmark strait and provides a sedimentary environment sheltered from the east greenland current flowing along the shelf the cores have been 14c dated accelerator mass spectroscopy dates and analyzed for diatom accumulation rates and changes in floral composition it was found that the shelf probably was not glaciated by grounded ice but occupied by an ice shelf and or permanent sea ice between 14 000 years b p and the present average retreat rates of glacial permanent sea ice were circa 60 m yr between circa 13 500 and 11 000 years b p the retreat rates increased to about 150 m yr between 11 000 to 10 000 years b p the increase is unexpected because this correlates with fairbanks 1989 projected low glacial meltwater discharge for the same time which is coeval with the younger dryas several events of sea surface warming cooling took place on the outer shelf from 12 000 to 9000 years b p followed by cooling to the present with a possible warming between 3000 4000 years bp on the inner shelf pulses of warm cool surface water occurred from 9000 to 6000 years b p which was succeeded by surface water cooling until present