deep sea carbonates reading the carbon isotope signal the carbon isotope signal in deep sea sediments reflects a mix of 1 global changes in the rates of exchange of the ocean s carbon reservoir with biosphere soil and sediments 2 global and regional changes in surface water productivity 3 internal shifts in water mass structure and circulation basin basin fractionation oxygen minimum development and 4 organism specific fractionation effects due to changes in micro habitat and or ontogenic fractionation vital effects additional complications arise from differential preservation it is impossible to entirely isolate these various factors as a rule of thumb long period signals that are parallel for planktonic and benthic data reflect external global fractionation patterns whilst short period signals are more likely tied to internal patterns water mass fractionation the various approaches to interpretation are illustrated with three case studies the glacial holocene transition the messinian carbon shift and the miocene monterey excursion

past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

central arctic surface ocean environment during the past 80 000 years stable oxygen and carbon isotope and sedimentological paleontological investigations supported by accelerator mass spectrometry 14 c datings were carried out on cores from north of 85 degrees n in the eastern central arctic ocean significant changes in accumulation rates provenance of ice rafted debris ird and planktic productivity over the past 80 000 years are documented during peak glacials i e oxygen isotope stages 4 and 2 the arctic ocean was covered by sea ice with decreased seasonal variation limiting planktic productivity and bulk sedimentation rates in early stage 3 and during termination i major deglaciations of the circum arctic regions caused lowered salinities and poor oxygenation of central arctic surface waters a meltwater spike and an associated ird peak dated to similar to 14 12 14 c ka can be traced over the southern eurasian basin of the arctic ocean this event was associated with the early and rapid deglaciation of the marine based barents sea ice sheet a separate termination ib meltwater event is most conspicuous in the central arctic and is associated with characteristic dolomitic carbonate ird this lithology suggests an origin of glacial ice from northern canada and northern greenland where lower paleozoic platform carbonates crop extensively out

ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

late wisconsinan glaciation and postglacial relative sea level change on western banks island canadian arctic archipelago abstract the study revises the maximum extent of the northwest laurentide ice sheet lis in the western canadian arctic archipelago caa during the last glaciation and documents subsequent ice sheet retreat and glacioisostatic adjustments across western banks island new geomorphological mapping and maximum limiting radiocarbon ages indicate that the northwest lis inundated western banks island after 31 14 c ka bp and reached a terminal ice margin west of the present coastline the onset of deglaciation and the age of the marine limit 22 40 m asl are unresolved ice sheet retreat across western banks island was characterized by the withdrawal of a thin cold based ice margin that reached the central interior of the island by 14 cal ka bp the elevation of the marine limit is greater than previously recognized and consistent with greater glacioisostatic crustal unloading by a more expansive lis these results complement emerging bathymetric observations from the arctic ocean which indicate glacial erosion during the last glacial maximum lgm to depths of up to 450 m

geochemical constraints on the laurentide ice sheet contribution to meltwater pulse 1a planktonic and benthic d 18 o records adjacent to the runoff outlets of the laurentide ice sheet lis indicate that the lis contributed to the abrupt w20 m rise in sea level w14 6 ka meltwater pulse 1a mwp 1a however the magnitude of the lis contribution still remains unresolved here i use a freshwater runoff ocean mixing model to calculate the lis meltwater required to explain the decreases in planktonic and benthic d 18 o observed during mwp 1a at the southern eastern and northern runoff

rapid climatic shifts during isotope stages 2 4 in the polar north atlantic sediment cores from the polar north atlantic provide evidence of six periods of sea ice breakup during isotope stages 4 3 and 2 probably caused by inflow of north atlantic surface water into the polar north atlantic these periods are characterized by having a high number of foraminifera g they last from 2000 to 10000 yr and constitute 50 of the total time span these periods of sea ice breakup correlate temporarily to the heinrich events and the early temperature maximum in the bond cycles of the north atlantic and greenland ice record our hypothesis is that massive iceberg discharges that flooded the north atlantic during each heinrich event probably triggered an oceanographic regime that gave a much more vigorous surface circulation pattern in the polar north atlantic which contributed to the breakup of the sea ice cover open water conditions in the polar north atlantic are inversely related to terrestrial interstadials of coastal norway suggesting ice sheet starvation during the cold periods and ice sheet growth when an open water surface circulation existed in the polar north atlantic our data document synchronous variations on a october 1900 yr time scale between arctic oceanic climate northern hemisphere ice sheet dynamics and ocean atmosphere temperature changes

effects of ice coverage and ice rafted material on sedimentation in the fram strait as little is known about pelagic sedimentation processes in arctic environments1 the interpretation of biological and chemical processes as well as the reconstruction of ancient conditions including those in the glacial north atlantic is difficult here we provide sediment trap results which show that the position of the sea ice boundary significantly influences the particle flux the seasonal variability of the particle flux differed markedly in the various sediment trap sites in fram strait depending on the behaviour of the sea ice under complete ice cover sedimentation is very low whereas maximum sedimentation is found at the ice margin the highest particle flux observed showing a large lithogenic component was observed at the ice edge where the water was warmer 2 c we find that high biogenic opal fluxes are characteristic of the summer ice margin indicating that the sedimentary record of opal fluxes may allow the position of ice margins in the past to be reconstructed

the younger dryas from whence the fresh water 1 oxygen isotopic records of meltwater outflow and records of sea level change do not support the idea that fresh waters derived solely from the melting of northern hemisphere ice sheets was likely to have stabilized the upper layers of the north atlantic ocean and prevented deep convection during the younger dryas yet there are paleoceanographic indicators that point to a pause in the formation of north atlantic deep water during the younger dryas this apparent conflict in evidence may be resolved by the existence of large relatively thick tabular icebergs that spilled out of the arctic and into the norwegian greenland sea and north atlantic the melting of large icebergs would have no impact on sea level but combined with meltwater runoff would provide enough fresh water to cap the north atlantic the timing of the start and the end of the younger dryas however may not have been directly related to freshwater supply

the younger dryas and the sea of ancient ice we propose that prior to the younger dryas period the arctic ocean supported extremely thick multi year fast ice overlain by superimposed ice and firn we re introduce the historical term paleocrystic ice to describe this the ice was independent of continental glacier ice and formed a massive floating body trapped within the almost closed arctic basin when sea level was lower during the last glacial maximum as sea level rose and the barents sea shelf became deglaciated the volume of warm atlantic water entering the arctic ocean increased as did the corresponding egress driving the paleocrystic ice towards fram strait new evidence shows that bering strait was resubmerged around the same time providing further dynamical forcing of the ice as the transpolar drift became established additional freshwater entered the arctic basin from siberia and north america from proglacial lakes and meltwater derived from the laurentide ice sheet collectively these forces drove large volumes of thick paleocrystic ice and relatively fresh water from the arctic ocean into the greenland sea shutting down deepwater formation and creating conditions conducive for extensive sea ice to form and persist as far south as 60 n we propose that the forcing responsible for the younger dryas cold episode was thus the result of extremely thick sea ice being driven from the arctic ocean dampening or shutting off the thermohaline circulation as sea level rose and atlantic and pacific waters entered the arctic basin this hypothesis focuses attention on the potential role of arctic sea ice in causing the younger dryas episode but does not preclude other factors that may also have played a role

regional variations in provenance and abundance of ice rafted clasts in arctic ocean sediments implications for the configuration of late quaternary oceanic and atmospheric circulation in the arctic abstract the composition and distribution of ice rafted glacial erratics in late quaternary sediments define the major current systems of the arctic ocean and identify two distinct continental sources for the erratics in the southern amerasia basin up to 70 of the erratics are dolostones and limestones the amerasia suite that originated in the carbonate rich paleozoic terranes of the canadian arctic islands these clasts reached the arctic ocean in glaciers and were ice rafted to the core sites in the clockwise beaufort gyre the concentration of erratics decreases northward by 98 along the trend of the gyre from southeastern canada basin to makarov basin the concentration of erratics then triples across the makarov basin flank of lomonosov ridge and siltstone sandstone and siliceous clasts become dominant in cores from the ridge and the eurasia basin the eurasia suite the bedrock source for the siltstone and sandstone clasts is uncertain but bedrock distribution and the distribution of glaciation in northern eurasia suggest the taymyr peninsula kara sea regions the pattern of clast distribution in the arctic ocean sediments and the sharp northward decrease in concentration of clasts of canadian arctic island provenance in the amerasia basin support the conclusion that the modern circulation pattern of the arctic ocean with the beaufort gyre dominant in the amerasia basin and the transpolar drift dominant in the eurasia basin has controlled both sea ice and glacial iceberg drift in the arctic ocean during interglacial intervals since at least the late pleistocene the abruptness of the change in both clast composition and concentration on the makarov basin flank of lomonosov ridge also suggests that the boundary between the beaufort gyre and the transpolar drift has been relatively stable during interglacials since that time because the beaufort gyre is wind driven our data in conjunction with the westerly directed orientation of sand dunes that formed during the last glacial maximum on the north slope of alaska suggests that atmospheric circulation in the western arctic during late quaternary was similar to that of the present

ba ca in neogloboquadrina pachyderma as an indicator of deglacial meltwater discharge into the western arctic ocean 1 down core samples of the planktonic foraminifer neogloboquadrina pachyderma sinistral from the mendeleyev ridge in the western arctic ocean have been analyzed for ba ca and 18o the apparent distribution coefficient for n pachyderma sin is estimated at dba 0 22 0 02 a meltwater event is identified at around 11 8 14c kyr bp and is coincident with elevated ba ca ratios the barium enrichment is believed to be the result of enhanced weathering and erosion following glaciation additionally barium may have desorbed from shelf sediments as sea level rose changes in ba ca correlate with the retreat of the laurentide ice sheet and the evolution of the mackenzie river drainage basin therefore maximum ba ca in arctic surface waters at 11 8 ka may be indicative of an increase in the export of freshwater from the arctic to the north atlantic potentially contributing to the onset of the younger dryas this work suggests that ba ca in planktonic foraminifera may be a useful indicator of the timing and processes associated with deglaciation

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

stratigraphic constraints on late pleistocene glacial erosion and deglaciation of the chukchi margin arctic ocean at least two episodes of glacial erosion of the chukchi margin at water depths to 450 m and 750 m have been indicated by geophysical seafloor data we examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock the diamictons are estimated to form during the last glacial maximum lgm and an earlier glacial event possibly between ois 4 to 5d both erosional events were presumably caused by the grounding of ice shelves originating from the laurentide ice sheet broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor postglacial sedimentation evolved from iceberg dominated environments to those controlled by sea ice rafting and marine processes in the holocene a prominent minimum in planktonic foraminiferal 18 o is identified in deglacial sediments at an estimated age near 13 000 cal yr bp this 18 o minimum also reported elsewhere in the amerasia basin is probably related to a major laurentide meltwater pulse at the younger dryas onset the bering strait opening is also marked in the composition of late deglacial chukchi sediments

late quaternary coccoliths at the north pole evidence of ice free conditions and rapid sedimentation in the central arctic ocean calcareous nannofossils from approximately the past 7000 yr of the holocene and from oxygen isotope stage 5 are present at 39 analyzed sites in the central arctic ocean this indicates partly ice free conditions during at least some summers the depth of holocene sediments in the nansen basin is about 20 cm or more where influenced by turbidites on the gakkel ridge calcite preservation is excellent and holocene strata are consistently documented to be at least 4 to 20 cm thick in the amundsen basin preservation of nannofossils is sometimes poor holocene specimens are commonly only found at the surface although at one site they extend down to 26 cm the holocene assemblage is consistently recorded in the upper 5 to 20 cm of sediment on the lomonosov ridge and down to 15 cm depth in the makarov basin this implies that linear sedimentation rates for the holocene in all investigated areas are centimetres per thousand years sediments from the last glacial period oxygen isotope stages 2 4 are relatively thin suggesting significantly reduced sedimentation millimetres per thousand years during this time

erratum superimposed low grade metamorphism in the mount fisher area southeastern british columbia implications for the east kootenay orogeny middle proterozoic 1500 1350 ma belt purcell strata exposed in the purcell and southwestern rocky mountains were affected by at least three distinct episodes of deformation and regional metamorphism the oldest episode 1300 1350 ma apparently terminated belt purcell sedimentation and involved foiding regional metamorphism and granitic intrusion the second episode 800 900 ma occurred during deposition of the windermere supergroup and involved uplift block faulting and low grade regional metamorphism mesozoic cenozoic metamorphism deformation and plutonism overprinted the results of the earlier deformation and metamorphism illite crystallinity and muscovite polymorph ratios indicate that purcell strata in the mount fisher area are in the lower greenschist to prehnite pumpellyite facies of regional metamorphism in the steeples and fisher blocks this metamorphism is related to structures that formed during the late cretaceous paleocene deformation however in the sand creek block the regional metamorphism is related to the development of a spaced cleavage that is folded by a late cretaceous pdeocene nappe regional considerations suggest that this cleavage formed during the 1300 1350 ma episode of deformation and metamorphism the east kootenay orogeny as currently defined embraces the two older episodes of tectonism it is proposed that the term east kootenay orogeny be restricted to designate the 1300 1350 ma episode and that the term goat river orogeny designate the 800 900 ma episode of tectonism the east kootenay and goat rivet orogenies appearto be correlative with the racklan and hayhook orogenies recognized in the northern canadian cordillera

surmounting luminescence age overestimation in alaska margin arctic ocean sediments by use of micro hole quartz dating abstract because of several difficulties with the application of radiocarbon 14c dating to arctic ocean sediments numeric dating techniques are needed that can complement supplant and reach beyond the 14c method however large age overestimates often 7 kyr for near sediment water interface horizons from arctic ocean cores have been almost universal when luminescence dating has been applied to multigrain aliquots of fine silt 4 11 m quartz and feldspar grains here micro hole quartz grain photon stimulated luminescence psl dating is applied to the 0 5 2 0 cm horizons of multicores from high sedimentation rate sites spanning depths from 87 m to 1140 m at the alaska margin of the arctic ocean expected near zero ages 0 200 a result when grains larger than 11 m are used demonstrating that fine silt age overestimations here and perhaps elsewhere in the arctic ocean are a function of grain and aliquot size at the 87 m site the micro hole psl approach revealed no significant gradient in age estimates over the 1 26 cm horizon range implying that bioturbation reached to at least 26 cm micro hole psl dating of 25 62 m quartz grains from trans ocean sea ice sediment also produced expected near zero ages in contrast to earlier reported long bleach multigrain psl results from 4 11 m fractions of the same samples the micro hole psl approach thus surmounts the age overestimation problem associated with the use of multigrain silt fractions and overcomes limitations of the 14c method in this region finally results unexpectedly suggest the potential of micro hole quartz psl for use in provenance studies of arctic ocean sea ice sediment

the last deglaciation event in the eastern central arctic ocean oxygen isotope records of cores from the central arctic ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15 7 thousand years ago 16 650 calendar years b c the almost parallel trends of the isotope records from the arctic ocean the fram strait and the east greenland continental margin suggest contemporaneous variations of the eurasian arctic and greenland laurentide ice sheets or increased export of low saline waters from the arctic within the east greenland current during the last deglaciation on the basis of isotope and carbon data the modern surface and deep water characteristics and seasonally open ice conditions with increased surface water productivity were established in the central arctic at the end of termination lb about 7 2 thousand years ago or 6 000 calendar years b c

quaternary dinoflagellate cysts in the arctic ocean potential and limitations for stratigraphy and paleoenvironmental reconstructions abstract the arctic ocean is a siliciclastic depositional environment which lacks any rock forming biogenic calcareous and siliceous components during large parts of its quaternary history these hemipelagic sediments are nevertheless suitable for the study of organic walled microfossils of which the fossil remains of dinoflagellates dinoflagellate cysts are the most important group dinoflagellate cysts have become an important tool in paleoceanography of the high northern latitudes but their potential for quaternary biostratigraphy has remained largely unexplored dinoflagellate cysts are the dominant marine palynomorph group which is more continuously present in the marginal seas e g barents sea bering sea than in the arctic ocean itself throughout the quaternary most species have long stratigraphic ranges are temporary absent and show abundance variations on glacial interglacial timescales of the more than 30 taxa recorded only habibacysta tectata and filisphaera filifera became extinct in the pleistocene the highest persistent occurrence of h tectata at ca 2 0 ma and the top of f filifera acme at ca 1 8 ma can be used for supra regional stratigraphic correlation between the arctic ocean and adjacent basins these events corroborate a slow sedimentation rate model for the quaternary section on the central lomonosov ridge but a combination of different methods will have to be applied to provide a detailed chronostratigraphy the occurrence of cysts of phototrophic dinoflagellates in certain stratigraphic intervals on lomonosov ridge supports published evidence of episodic opening of the multiyear arctic sea ice cover during the quaternary probably related to a stronger inflow of atlantic water this contradicts the hypothesis of a permanently ice covered central arctic ocean in the quaternary

origins of mineral deposits belt purcell basin united states and canada an introduction the fill of the mesoproterozoic belt purcell basin which straddles the united states canada border within the rocky mountains of western north america fig 1 consists of marine and nonmarine clastic and carbonate strata 15 to 20 km thick three giant metal producing ore deposits or districts account for the bulk of the known metal endowment within the bounds of the belt purcell basin 1 the syndepositional sullivan pb zn ag deposit in southern british columbia total production pb 8 4 million tonnes mt zn 7 9 mt ag 0 0093 mt lydon 2000 2 the mesothermal pb zn ag veins of the coeur d alene district in northern idaho total production pb 7 5 mt zn 3 0 mt ag 0 052 mt long 1998 post 1997 data from usgs annual minerals yearbooks and 3 the cretaceous porphyry copper deposit and associated polymetallic veins in the butte district in montana total resource cu 35 mt zn 4 6 mt ag 0 044 mt long et al 1998 the sullivan mine closed in 2001 after more than 92 years of production mining of 26 major vein deposits in the coeur d alene district began in the 1880s and peaked about 1950 production in the coeur d alene district continues today from the galena and lucky friday mines the latter closed for 2012 to refurbish the mile deep vertical access shaft mining at butte began in 1875 with copper production peaking in 1917 mining continues today in the eastern upfaulted portion of the butte porphyry copper deposit at the continental mine fig 1 locations of major ore deposits within the belt purcell basin area along with other ore deposits and mineralized trends that are discussed in this issue deposit locations are plotted on a geologic map showing the distribution of five stratigraphic units within the belt purcell basin in the united states and canada lower belt formations include the prichard altyn appekunny chamberlain newland lahood

freshwater and atlantic water inflows to the deep northern barents and kara seas since ca 13 14 c ka foraminifera and stable isotopes foraminiferal stable isotopes and assemblages from franz victoria and st anna troughs provide a valuable record of freshwater and atlantic water flows to the northern barents and kara seas from deglaciation to present the d 18 o and d 13 c of planktonic neogloboquadrina pachyderma s and benthic elphidium excavatum were up to1 4 lower than present at ca 13 11 5 and 10 14 c ka global sea level corrected mostly reflecting substantial freshwater inputs coincident with glacial marine sediment deposition cassidulina teretis exceeded 40 of benthic foraminifera ca 13 and 10 14 c ka indicating subsurface penetrations of atlantic water the transition to postglacial marine conditions is marked by a 1 rise in foraminiferal d 18 o and a sharp fall in c teretis soon after 10 14 c ka these changes imply reduced inputs of freshwater and atlantic water subsequent isotopic and foraminiferal assemblage variations reflect changing atlantic water conditions upstream in the nordic seas and shifts between the warm fram strait and cold barents sea branches of atlantic water we hypothesize that glacial isostatically induced deepening by up to 150 m influenced atlantic water inflows to the northern barents sea during deglaciation and the holocene thus effects of isostatic recovery have to be factored into paleoceanographic reconstructions 2001 elsevier science ltd all rights reserved

bathozonal tilt corrections to paleomagnetic data from mid cretaceous plutonic rocks examples from the omineca belt british columbia the skelly creek batholith 49 4 n 116 6 w 94 99ma and summit stock 49 1 n 117 0 w 102 ma are intruded into the southern omineca belt of southeastern british columbia bathozonal mineral assemblages from contact aureoles of these plutons and others of the same age indicate that post emplacement tilting of the purcell anticlinorium has probably not exceeded about 5 whereas the summit stock has been tilted 24 down to the west the skelly creek batholith has a mean direction of magnetization d i with respect to present horizontal 349 74 13 sites k 53 95 6 the mean direction of magnetization of the summit stock is 48 72 nine sites k 290 95 3 and after correction for a westerly dip of 24 the mean direction becomes 318 74 directions of the skelly creek batholith and tilt corrected direction from the summit stock are in agreement with the reference field for cratonic north america evidently this part of the eastern omineca belt was close to the margin of ancestral north america in mid cretaceous time essentially where it is today

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

glacial freshwater discharge events recorded by authigenic neodymium isotopes in sediments from the mendeleev ridge western arctic ocean the freshwater budget of the arctic ocean is a key component governing the deep water formation in the north atlantic and the global climate system we analyzed the isotopic composition of neodymium end in authigenic phases of marine sediments on the mendeleev ridge in the western arctic ocean spanning an estimated time interval from present to about 75 ka bp this continuous record was used to reconstruct the end of the polar deep water pdw and changes in freshwater sources to the pdw through time three deviations in end from a long term average of 10 2 were identified at estimated 46 51 35 39 and 13 21 ka bp the estimated 46 51 ka bp event can be traced to bursting of ice dammed lakes accompanying the collapse of the barents kara ice sheet which would have released radiogenic nd to the eastern arctic ocean the cyclonic surface circulation in the eastern arctic ocean must have been stronger than at present for the event to be recorded on the mendeleev ridge for the 35 39 and 13 21 ka bp events it is likely that the laurentide ice sheet lis supplied the unradiogenic freshwater the configuration of the anticyclonic circulation in the western arctic was probably similar to today or expanded eastward our simple mass balance calculations suggest that large amounts of freshwater were released but due to significant deep water formation within the arctic ocean the effect on the formation of nadw was probably minor

time constraints from 230th and 231pa data in late quaternary low sedimentation rate sequences from the arctic ocean an example from the northern mendeleev ridge abstract due to the lack of conventional oxygen isotope stratigraphies the setting of unquestionable time frames in late quaternary records from low sedimentation rate settings of the arctic ocean often encounters difficulties here we use hotrax cores raised from the mendeleev ridge multicore hly0503 12 1600 m water depth multicore and trigger weight core hly0503 11 2500 m water depth to demonstrate that u series data may supply reliable time constraints and sedimentation rate estimates grain size mineralogical geochemical corg cinorg and isotopic 210pb 238u 234u 232th 230th 231pa measurements were made on ground bulk sediment whereas isotopic 13c 14c 18o measurements were performed on planktonic foraminifers when present the two multicores present remarkably similar profiles despite their 1 km bathymetric difference both show three majors units the top 0 8 cm and bottom 26 38 cm units have high clay and carbonate contents whereas the intermediate unit 8 26 cm shows high sand and low clay and inorganic carbon contents an apparently short event with higher clay and inorganic content is recorded at 17 cm 230th excess and 231pa excess are observed down to 35 and 27 cm respectively thus locking minimum ages of 340 ka and 140 ka at these depths age model estimates allowed us to assign the top unit to the marine isotopic stages mis 1 3 interval and the bottom unit to the termination iii mis 7 interval the intermediate unit would represent the last two glacial cycles interrupted by a short termination ii mis 5e excursion data from the twc allow this stratigraphy to be extended to mis 13 glacial units correspond to very low sedimentation rates essentially linked to ice rafting deposition as indicated by their high sand content this study suggests a mean sedimentation rate of about 1 5 mm ka 1 for this sector of the mendeleev ridge which supports the very low sedimentation rate suggested by 10be data in a nearby site from other studies

the aitik cu au ag deposit in northern sweden a product of high salinity fluids the aitik cu au ag deposit is located in northern sweden and is hosted by strongly deformed 1 9 ga svecofennian volcano sedimentary rocks the main copper mineralization which occurs as disseminations and veinlets is hosted by garnet biotite schist subeconomic mineralization in the footwall to the ore is hosted by feldspar biotite amphibole gneiss and porphyritic quartz monzodiorite the deposit has been affected by post mineralization metamorphic and igneous activity fluid inclusions in six samples of copper mineralized quartz veins record the presence of three different fluid populations the main ore was deposited from an aqueous highly saline 31 37 eq wt nacl cacl2 fluid this fluid was trapped in inclusions intimately associated with the main chalcopyrite mineralization later bornite deposition took place from a less saline 18 27 eq wt nacl cacl2 aqueous fluid a third fluid composed of almost pure co2 interacted with the copper rich system during a post ore event the aitik cu au ag deposit shares some features with both porphyry type and fe oxide cu au deposits a high calcium content of the ore fluids similar to other cu au deposits in northern scandinavia suggests a contribution to the salinity of the mainly magmatic hydrothermal fluids from evaporitic rocks in stratigraphically lower units

geochemical and isotopic tracers of arctic sea ice sources and export with special attention to the younger dryas interval radiogenic isotopes sr nd in ice rafted debris ird sediments from the lomonosov ridge and fram strait arctic areas are used to document changes in arctic sea ice sources and trajectories since the last glacial maximum lgm the two records provide evidence for enhanced sea ice production in the beaufort sea and its subsequent export through fram strait during the younger dryas yd interval this pattern exclusive to the yd followed an lgmebollingeallerod interval when multiyear and or reduced sea ice mobility resulted in sedimentary hiatuses in the central arctic meanwhile ird from svalbardebarents ice sheet margin source were still deposited in the fram strait area the isotopic excursion of the yd points to enhanced sea ice production in the beaufort sea which we link to the lake agassiz laurentide ice sheet drainage event through the mackenzie route following this event the holocene depicts a 5 fold reduction in ird rates with a shift towards prominent sea ice production along russian shelves from a methodological viewpoint we demonstrate that radiogenic isotopes must be used in a multi proxy approach to better constrain ird and sea ice sources and routes from a paleoceanographic perspective we conclude that an arctic freshwater sea ice export route should now be seen as the most likely mechanism for an amoc reduction during the yd in accordance with more recent improved model experiment

support for the innuitian ice sheet in the canadian high arctic during the last glacial maximum the extent of glacier ice in the canadian high arctic during the last glacial maximum lgm has been debated for decades one school proposed a regional innuitian ice sheet whereas another proposed a smaller non contiguous franklin ice complex research throughout western nares strait supports coalescent innuitian and greenland ice during the lgm based on widespread glacial and marine deposits dated by 14c and amino acid analyses this coalescence likely promoted a vigorous regional ice flow westward across ellesmere island to eureka sound post glacial emergence in eureka sound suggests a former ice thickness at least as great as that in nares strait 1 km recently independent field studies elsewhere in the high arctic also support an innuitian ice sheet during the lgm collectively these studies resolve a long standing debate and initiate new opportunities concerning the reconstruction of high latitude palaeoenvironmental and palaeoclimatic change 1998 john wiley sons ltd

stable oxygen and carbon isotopes in planktic foraminifers from arctic ocean surface sediments reflection of the low salinity surface water layer planktic foraminifers neogloboquadrina pachyderma sin from 87 eastern and central arctic ocean surface sediment samples were analyzed for stable oxygen and carbon isotope composition additional results from 52 stations were taken from the literature the lateral distribution of 18o full size image 33 atlantic waters entering the arctic ocean through the fram strait 18o values decrease both to the barents shelf and to the north pole in accordance with the decreasing salinities of the halocline waters in the nansen basin a strong n s 18o gradient is in contrast with a relatively low salinity change and suggests contributions from different freshwater sources i e salinity reduction from sea ice meltwater in the south and from light isotope waters meteoric precipitation and river runoff in the northern part of the basin north of the gakkel ridge 18o and salinity gradients are in good accordance and suggest less influence of sea ice melting processes the 13c full size image 1 k values of n pachyderma sin from arctic ocean surface sediment samples are generally high 0 75 0 95 lower values in the southern eurasian basin appear to be related to the intrusion of atlantic waters the high 13c values are evidence for well ventilated surface waters because the perennial arctic sea ice cover largely prevents atmosphere ocean gas exchange ventilation on the seasonally open shelves must be of major importance lack of 13c gradients along the main routes of the ice drift from the siberian shelves to the fram strait suggests that primary production i e co2 consumption does probably not change the co2 budget of the arctic ocean significantly

geochronology and tectonic implications of magmatism and metamorphism southern kootenay arc and neighbouring regions southeastern british columbia part ii mid cretaceous to eocene a north south trending belt of amphibolite facies regional metamorphism parallels the purcell trench transects the kootenay arc and is in part fault bounded towards the axis of this belt progressively higher pressure metamorphic mineral assemblages are exposed in the contact aureoles of post kinematic mid cretaceous 100 ma plutons and in metapelites contours of k ar biotite dates for plutonic rocks 55 95 ma are regular are broadly conformable with metamorphic isograds appear to cross internal intrusive contacts of post kinematic plutons and young towards the highest pressure and temperature regional metamorphic zones within the sillimanite zone most micas yield k ar dates between 40 and 55 ma rb sr muscovite dates for deformed and undeformed pegmatites and for muscovite bearing monzogranite and granodiorite fall between 53 and 84 ma u pb zircon dates for the kaniksu batholith and nearby gneiss of uncertain origin yield a lower concordia intercept of 94 ma micas from mid jurassic and mid

quaternary paleoceanography of the central arctic based on integrated ocean drilling program arctic coring expedition 302 foraminiferal assemblages the integrated ocean drilling program iodp arctic coring expedition acex hole 4c from the lomonosov ridge in the central arctic ocean recovered a continuous 18 m record of quaternary foraminifera yielding evidence for seasonally ice free interglacials during the matuyama progressive development of large glacials during the mid pleistocene transition mpt 1 2 0 9 ma and the onset of high amplitude 100 ka orbital cycles 500 ka foraminiferal preservation in sediments from the arctic is influenced by primary sea ice organic input and other environmental conditions and secondary factors syndepositional long term pore water dissolution taking these into account the acex 4c record shows distinct maxima in agglutinated foraminiferal abundance corresponding to several interglacials and deglacials between marine isotope stages mis 13 37 and although less precise dating is available for older sediments these trends appear to continue through the matuyama the mpt is characterized by nearly barren intervals during major glacials mis 12 16 and 22 24 and faunal turnover mis 12 24 abundant calcareous planktonic mainly neogloboquadrina pachyderma sin and benthic foraminifers occur mainly in interglacial intervals during the brunhes and very rarely in the matuyama a distinct faunal transition from calcareous to agglutinated foraminifers 200 300 ka in acex 4c is comparable to that found in arctic sediments from the lomonosov alpha and northwind ridges and the morris jesup rise down core disappearance of calcareous taxa is probably related to either reduced sea ice cover prior to the last few 100 ka cycles pore water dissolution or both

quaternary arctic ocean sea ice variations and radiocarbon reservoir age corrections a short sediment core from a local depression forming an intra basin on the lomonosov ridge was retrieved during the healy oden trans arctic expedition 2005 hotrax it contains a record of the marine isotope stages mis 1 3 showing exceptionally high abundances of calcareous microfossils during parts of mis 3 based on radiocarbon dating linear sedimentation rates of 7 9 cm ka persist during the last deglaciation the last glacial maximum lgm is partly characterized by a hiatus planktic foraminiferal abundance variations of neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in arctic ocean summer sea ice coverage and probably inflow of subpolar north atlantic water calibration of the radiocarbon ages using modeled reservoir corrections from previous studies and the microfossil abundance record of the studied core results in marine reservoir ages of 1400 years or more at least during the last deglaciation paired benthic planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the lateglacial to the holocene suggesting circulation and ventilation changes c 2010 elsevier ltd all rights reserved

extent and basal characteristics of the m clintock channel ice stream abstract the m clintock channel palaeo ice stream drained the northwestern margin victoria island arctic canada of the laurentide ice sheet functioning for 200 years prior to 10 ka bp from its bed imprint it is reconstructed as 720 140 km with a cross sectional area of 100 km2 comparable in size to the hudson strait ice stream it drained an estimated 80 000 km3 of ice enough to significantly affect the shrinking ice sheet and drive the keewatin ice divide south eastwards such discharges likely produced heinrich events and influenced the temperature and salinity of the western arctic ocean ice stream location was controlled by a topographic trough but glaciological regulation rather than properties of the bed controlled margin locations and hence ice stream width the ice stream eroded into pre existing unconsolidated sediments and left a pattern of subglacially produced landforms recording a snapshot view of the bed prior to shutdown frictional shutdown occurred once downcutting through sediments reached bedrock in places high sediment availability appears critical for ice stream functioning with a drift thickness of 50 m required to sustain its 200 year lifespan debris discharge was exceptionally high 73 000 m3 a 1 m 1 this ice stream demonstrates non steady response of ice sheets to climate change and their large impact on mass balance and stability of ice sheets

size dependent isotopic composition of planktic foraminifers from chukchi sea vs nw atlantic sediments implications for the holocene paleoceanography of the western arctic abstract in arctic and sub arctic seas shell growth and or secondary calcite overgrowth of neogloboquadrina pachyderma left coiled npl occur along the pycnocline and their 13c and 18o values are size and weight dependent however whereas the npl 18o data from the nw atlantic indicate near equilibrium conditions with ambient waters and a positive relationship between shell weight and 18o content assemblages from box cored sediments of the chukchi sea western arctic are depleted by 2 with respect to equilibrium values with modern conditions and depict a negative relationship between shell weight and its 18o value 0 15 0 03 g on vpdb scale a similar feature is also depicted by the dextral form of n pachyderma npd we associate the reverse shell size or weight vs 18o relationship to the reverse temperature gradient observed along the thermocline between the surface cold and dilute water layer and the underlying near 3 c warmer saline north atlantic water mass the analysis of two late to post glacial sedimentary sequences from the chukchi sea indicates that such a water mass stratification with a reverse thermocline persisted throughout the holocene thus reflecting an early onset of the modern like linkage between the arctic ocean and the north atlantic moreover lower 18o values in both npl and npd together with larger 18o gradients between the different shell sizes at ca 9 7 ka bp suggest 3 c higher temperatures in the upper north atlantic water mass in comparison with the present approximately 1 c at the study site thus likely a higher inflow rate of this water mass during the early holocene

freshwater forcing from the greenland ice sheet during the younger dryas evidence from southeastern greenland shelf cores abstract we present evidence for freshwater forcing from the greenland ice sheet during the last deglaciation explore its potential involvement in the younger dryas cooling and investigate the role of atlantic intermediate water in the retreat of the greenland ice sheet paleoceanographic conditions and ice sheet retreat history are interpreted from ird stable isotopes and foraminiferal assemblages in sediment cores retrieved along the length of the kangerlussuaq trough a cross shelf trough on the southeast greenland shelf the vedde ash 11 980 cal yr bp which is a marker bed within the younger dryas and the saksunarvatn tephra 10 180 cal yr bp an early holocene marker horizon have been located in these cores the tephra markers and calibrated 14c dates on foraminifers and molluscs provide the basis for the age models in the cores the stable isotope records indicate a 0 5 depletion of the 18o between 13 4 and 12 8 cal ka bp a pronounced light isotope event exceeding 1 5 on the inner shelf and 0 8 on the outer shelf occurs at the beginning of the younger dryas cold period 12 8 cal ka bp and ends by 12 cal ka bp immediately before deposition of the vedde ash the light isotope spikes are interpreted as glacial meltwater spikes associated with retreat of the adjacent greenland ice sheet associated with the light isotope events are episodic high percentages of the atlantic intermediate water benthic foraminiferal species cassidulina neoteretis which continue from the bolling allerod into the younger dryas high percentages of this species suggest that atlantic intermediate water entered the kangerlussuaq trough during the allerod and the younger dryas via the irminger current as it does today we conclude that advection of atlantic intermediate water into the kangerlussuaq trough south of the denmark strait promoted melting and retreat of the marine portions of the greenland ice sheet explaining the observed glacial meltwater spikes

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

origin of rare earth element enriched hematite breccias at the olympic dam cu u au ag deposit roxby downs south australia hematite breccias the host rocks to cu u au ag ore at the olympic dam deposit occur as steeply dipping northwest striking dikelike bodies within fractured granite the breccia complex has a strike length of over 5 km and extends to depths greater than 1 km both the deposit as a whole and the individual breccia bodies are zoned from weakly brecciated sericitized and hematized granite on the margins through heterolithic breccias to hematite quartz microbreccia at the center hematite occurs as euhedral laths and fine grained aggregates in the matrices of all breccia types in veins and fragments as pseudomorphs after feldspar and rarely as pseudomorphs after siderite and magnetite relict magnetite is rare and most iron oxide was deposited as hematite heterolithic breccias include fragments of earlier breccia and veins minor sedimentary rocks including bedded hematite and laminated barite also are present as clast components in the upper portion of the deposit volcaniclastic conglomerate and siltstone occur in a fault bounded block approximately 500 x 500 m in plan view copper iron sulfides occur as interstitial grains most common microveinlets and rare clasts they are most abundant in heterolithic breccias and are zoned laterally from chalcocitebornitc to chalcopyrite pyrite zonal boundaries are subparallel to steep breccia contacts copper iron sulfides commonly are intergrown with fluorite and locally rim corroded quartz grains the breccias are highly enriched in light lree and heavy rare earth elements hree avg approximately 5 000 ppm ree in hematite rich rocks total lree content and la lu ratios are correlated with hematite abundance maximum la values 10 000 x chondrite occur in hematite quartz microbreccias from the geographic center of the deposit five hydrothermal ree phases have been identified bastnaesite florencite monazite xenotime and britholite they occur in all breccia types and in a variety of habits disseminated in quartz sericite matrices of granite breccia in quartz sericite veins interstitial to hematite laths intergrown with barite in laminated sedimentary rocks and as inclusions in hematite and in sulfide grains the hematite breccias formed by progressive hydrothermal brecciation and iron metasomatism of the granite host minor sedimentary components preserved as blocks and fragments within the upper portion of the deposit point to a near surface environment for the breccia complex textural relations indicate that most of the copper was introduced late relative to hematization and brecciation based on spatial relations between barren zones oxidized sulfide grains and high grade chalcocite ore some supergene redistribution of copper probably occurred the abundance of ree in hydrothermal phases ree enrichment of altered relative to unaltered wall rock concentration of ree in the center of the system and variable slopes of chondrite normalized patterns combined with the lack of evidence of intrusion of unusual magmas at the present level of exposure attest to extensive transport and deposition of ree by hydrothermal fluids responsible for hematization and breccia formation this study demonstrates hydrothermal ree mobility on a scale previously undocumented and suggests that ree may be particularly mobile in f rich hydrothermal systems

principal component analysis of magnetite composition from volcanogenic massive sulfide deposits case studies from the izok lake nunavut canada and halfmile lake new brunswick canada deposits abstract magnetite grains from the izok lake nunavut canada and the halfmile lake new brunswick canada volcanogenic massive sulfide deposits and from till covering the nearby areas were investigated using the scanning electron microscopy sem electron probe micro analyzer epma laser ablation inductively coupled plasma mass spectrometry la icp ms and optical microscopy the method of robust estimation for compositional data rob composition was applied to censored geochemical data and the results were analyzed by principal component analysis pca textural relationships and mineral association of magnetite reveal the history of formation and contribute to the explanation of characteristic compositional differences of magnetite from different geological settings the integration of petrography and mineral chemistry allows discriminating magmatic metamorphic and hydrothermal magnetite grains in the vms deposits bedrock samples magmatic magnetite is found in izok lake gabbro and halfmile lake syenite felsic ash tuff and gossan samples whereas magnetite in izok lake massive sulfides gahnite rich dacite and iron formations formed during the amphibolite facies metamorphism in halfmile lake andesite magnetite recrystallized during greenschist facies metamorphism in the magnetite alteration zone associated to the halfmile lake deposit hydrothermal magnetite has been overprinted by metamorphic magnetite halfmile lake massive sulfides in chloritic argillite contain hydrothermal magnetite pca identifies discriminator elements and their contributions to magnetite composition from different izok lake lake and halfmile lake bedrock samples the results suggest that si ca zr al ga mn mg ti zn co ni and cr are discriminator elements for vms deposits and their host bedrocks the distinct chemical signatures for magnetite from various bedrock lithologies demonstrate that magnetite grains of the same origin share more similarities in chemistry as high ti indicates magmatic sources for magnetite whereas high si ca and mg are indicative of hydrothermal settings variable compositions of metamorphic magnetite suggest that the chemistry of this type of magnetite is controlled by the composition of host rocks the grade of metamorphism and oxygen fugacity pca of epma and la icp ms data of magnetite from the izok lake and halfmile lake bedrock samples yield discrimination models for classification of magnetite grains from till decreases in the proportion of magnetite grains with the chemical signature of the izok lake massive sulfides and gahnite rich dacite down ice from the izok lake deposit show the use of magnetite chemistry in geochemical exploration in the halfmile lake area till magnetite grains with the signature of vms mineralization make a glacial dispersal train more than 2 km down ice from the deposit

stable isotope evidence for glacial lake drainage through the st lawrence estuary eastern canada 13 1 12 9 ka abstract postglacial varved and rhythmically laminated clays deposited during the transition from glacial lake vermont lv to the champlain sea cs record hydrological changes in the champlain st lawrence valley cslv at the onset of the younger dryas 13 1 12 9 ka linked to glacial lake drainage events oxygen isotope 18o records of three species of benthic foraminifera cassidulina reniforme haynesina orbiculare islandiella helenae from six sediment cores and the freshwater ostracode candona from one core were studied results show six large isotope excursions 0 5 to 2 in c reniforme 18o values five excursions in h orbiculare

central arctic paleoceanography for the last 50 kyr based on ostracode faunal assemblages abstract the paleoceanography of the central arctic ocean was reconstructed for the last 50 kyr marine isotope stages mis 1 3 based on ostracode assemblages from 21 14c dated sediment cores from the mendeleev lomonosov and gakkel ridges arctic sediments deposited during the holocene interglacial period mis 1 the bolling allerod and larger interstadial dansgaard oeschger do events 3 4 8 and 12 contain abundant cytheropteron spp henryhowella asperrima and krithe spp at intermediate deep depths 1000 to 3000 m these assemblages suggest a ventilated deep arctic ocean water mass similar to the modern arctic ocean deep water aodw during these time periods in contrast sediment deposited during stadial events corresponding to heinrich events 1 2 3 and 4 also possibly the younger dryas yd contain abundant polycope spp 60 80 suggesting a greater influence of the atlantic layer al on the arctic intermediate water aiw and aodw reduced sea ice during the early holocene the last deglacial and mis 3 interstadials is indicated by the reoccurrence of acetabulastoma arcticum an epipelagic species that is parasitic on sea ice dwelling amphipods one hypothesis to explain these oceanographic changes during longer stadial events particularly within the last glacial period mis 2 involves sluggish ocean circulation thicker sea ice cover and a deeper halocline with ocean exchange between greenland sea and arctic ocean deep water through the fram strait

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

subglacial bedform evidence for a major palaeo ice stream and its retreat phases in amundsen gulf canadian arctic archipelago ascertaining the location of palaeo ice streams is crucial in order to produce accurate reconstructions of palaeo ice sheets and examine interactions with the ocean climate system this paper reports evidence for a major ice stream in amundsen gulf canadian arctic archipelago mapping from satellite imagery landsat etm and digital elevation models including bathymetric data is used to reconstruct flow patterns on southwestern victoria island and the adjacent mainland nunavut and northwest territories several flow sets indicative of ice streaming are found feeding into the marine trough and cross cutting relationships between these flow sets and utilising previously published radiocarbon dates reveal several phases of ice stream activity centred in amundsen gulf and dolphin and union strait a large erosional footprint on the continental shelf indicates that the ice stream ca 1000 km long and ca 150 km wide filled amundsen gulf probably at the last glacial maximum subsequent to this the ice stream reorganised as the margin retreated back along the marine trough eventually splitting into two separate low gradient lobes in prince albert sound and dolphin and union strait the location of this major ice stream holds important implications for ice sheet ocean interactions and specifically the development of arctic ocean ice shelves and the delivery of icebergs into the western arctic ocean during the late pleistocene copyright c 2006 john wiley sons ltd

dating late quaternary planktonic foraminifer neogloboquadrina pachyderma from the arctic ocean using amino acid racemization the long term rate of racemization for amino acids preserved in planktonic foraminifera was determined by using independently dated sediment cores from the arctic ocean the racemization rates for aspartic acid asp and glutamic acid glu in the common taxon neogloboquadrina pachyderma were calibrated for the last 150 ka using 14c ages and the emerging quaternary chronostratigraphy of arctic ocean sediments an analysis of errors indicates realistic age uncertainties of about 12 for asp and 17 for glu fifty individual tests are sufficient to analyze multiple subsamples identify outliers and derive robust sample mean values the new age equation can be applied to verify and refine age models for sediment cores elsewhere in the arctic ocean a critical region for understanding the dynamics of global climate change

modeling the surface mass balance response of the laurentide ice sheet to bolling warming and its contribution to meltwater pulse 1a meltwater pulse mwp 1a occurred 14 5 14 ka and is the largest abrupt rise in sea level 10 20 m of sea level rise of the last deglaciation the timing of mwp 1a is coincident with or shortly follows the abrupt warming of the north atlantic region into the bolling warm period which could have triggered a large laurentide ice sheet lis contribution to mwp 1a given that outside of the arctic lis iceberg discharge probably did not increase during the bolling much of the lis mwp 1a contribution likely occurred through surface ablation here we test the response of lis surface mass balance to bolling warming by forcing a lis energy mass balance model with climate from an atmosphere ocean general circulation model our modeling approach neglects changes in lis mass from dynamics and iceberg calving allowing us to isolate the surface mass balance response model results suggest that lis surface ablation can explain much of the sea level rise just prior to mwp 1a lis surface mass balance becomes more negative in response to the bolling warming contributing an additional 2 9 1 0 m of sea level rise in 500 yr in addition to the background contribution of 4 0 0 8 m the modeled lis mwp 1a contribution is less than previous assumptions but agrees with geochemical runoff and lis area volume estimates the fraction of mwp 1a attributable to other ice sheets particularly antarctica depends on the total sea level rise that occurred during this mwp

iron oxide cu au deposits in the iron range purcell basin southeastern british columbia the iron range iron oxide cu au deposits in southeastern british columbia comprise massive lenses and veins of hematite and martite with lesser magnetite in the iron range fault zone which crosscuts the proterozoic aldridge formation and moyie sills the mineralized zones are flanked by albite quartz iron oxide breccia within sedimentary rocks and by chlorite altered iron oxide breccia where they are in contact with moyie sills oxygen isotope analyses indicate 340 to 400 c precipitation temperatures for the albite quartz magnetite assemblages in the mineralized zones magnetite trace element compositions closely compare with those in iron oxide copper gold iocg to porphyry type mineralization worldwide paleomagnetic studies show consistent paleopole orientations concordant with cretaceous poles and support links to a porphyry type genesis associated with phases of the nearby 80 to 105 ma magnetite bearing bayonne suite plutonic rocks the iron range iron oxide mineralized zones share many characteristics of major iocg deposits with the exception of economic cu au concentrations in the exposed rocks however recent drilling intersected minor chalcopyrite pyrite and gold

high resolution paleoproductivity fluctuations during the past 24 kyr as indicated by benthic foraminifera in the marginal arctic ocean abstract analyses of benthic foraminifera in sediment cores taken at about 1000 m water depth at the yermak plateau and the barents sea slope adjacent to the position of the ice sheet edge during the last glacial maximum show that paleoproductivity was reduced to about a third of its present level during peak glacial stadials these reduced values are still higher than values for modern permanently ice covered regions suggesting that the core locations were at least partially ice free even during stadials paleoproductivity at the core locations was higher than or equal to that of today during initial deglaciations and warm substages peak paleoproductivity occurred in samples with low salinity surface waters as indicated by oxygen isotope values of planktonic foraminifera and slightly after increased abundance of atlantic species suggesting that enhanced advection of warmer waters from the atlantic supported the initial ice sheet retreat during the holocene climatic optimum productivity was much less than at present on the yermak plateau high at the barents sea site perhaps because of increased advection of atlantic water to the latter site and heavier ice coverage at the former after this optimum paleoproductivity at both sites was similar with slightly lower values during cold periods such as the little ice age

contrasting glacial interglacial regimes in the western arctic ocean as exemplified by a sedimentary record from the mendeleev ridge distinct cyclicity in lithology and microfaunal distribution in sediment cores from the mendeleev ridge in the western arctic ocean water depths ca 1 5 km reflects contrasting glacial interglacial sedimentary patterns we conclude that during major glaciations extremely thick pack ice or ice shelves covered the western arctic ocean and its circulation was restricted in comparison with interglacial modern type conditions glacier collapse events are marked in sediment cores by increased contents of ice rafted debris notably by spikes of detrital carbonates and iron oxide grains from the canadian arctic archipelago composition of foraminiferal calcite n 18 o and n 13 c also shows strong cyclicity indicating changes in freshwater balance and or ventilation rates of the arctic ocean light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca 12 14 c kyr bp the prolonged period with low n 18 o and n 13 c values and elevated contents of iron oxide grains from the canadian archipelago in the lower part of the mendeleev ridge record is interpreted to signify the pooling of freshwater in the amerasia basin possibly in relation to an extended glaciation in arctic north america unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the mendeleev ridge and other mid depth locations throughout the arctic ocean such as the northwind and lomonosov ridges this correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for arctic ocean sediments 2003 elsevier b v all rights reserved

multiple meltwater discharge and ice rafting events recorded in the deglacial sediments along the beaufort margin arctic ocean abstract the first regional model for the deglacial history of the beaufort margin slope in the western arctic is presented the conceptual model was developed using new high resolution chirp seismic reflection multibeam bathymetry and sediment core data acquired along the margin this synthesis provides important constraints on sediment source and dispersal patterns for the last deglaciation the continental slope from barrow canyon to the mackenzie trough is characterized by thick holocene sediments mostly sourced from barrow canyon and continental discharge this acoustically transparent fine grained unit overlies acoustically laminated sediments sourced from the mackenzie river and ice rafting the deglacial history of the margin from mackenzie trough to the amundsen gulf is characterized by many ice rafting and meltwater discharge events ice rafted debris layers were deposited around 14 6 ka and 14 1 ka and likely document enhanced ice shedding events from the amundsen and m clure ice streams as they retreated there are three inferred meltwater discharge events all sourced from the mackenzie region the oldest discharge event had two phases one sometime between 14 5 ka and 14 2 ka and another between 14 0 ka and 13 0 ka this discharge deposited finely laminated sediments more than 7 m thick sourced from proglacial lakes in the area following this was a flood event starting at 12 94 ka which generated high amplitude reflectors deposited coarse debris and caused a lowering in the 18o record this is possibly a major outburst flood from glacial lake agassiz with an additional component of agassiz meltwater that was diverted from its southern drainage pathway down the mississippi to the gulf of mexico finally a third discharge event was initiated by 11 3 ka which deposited coarse laminated sediments focused in the mackenzie trough timing of these second and third events correlates with the onset of the younger dryas cold period and the preboreal oscillation event respectively suggesting that fresh water discharge may have reached a tipping point leading to those climate events

late pleistocene and holocene meltwater events in the western arctic ocean accelerator mass spectrometer 14 c dated stable isotope data from neogloboquadrina pachyerma in cores raised from the mendeleyev ridge and slope provide evidence for significant influx of meltwater to the western arctic ocean during the early part of marine oxygen isotope stage 1 ois 1 and during several intervals within ois 3 the strongest ois 3 meltwater event occurred before ca 45 ka conventional radiocarbon age and was probably related to the deglaciation at the beginning of ois 3 major meltwater input to the western arctic ocean during the last deglaciation coincides closely with the maximum rate of global sea level rise as determined from the barbados sea level record demonstrating a strong link between the global record and changes in the central arctic ocean ois 2 which includes the last glacial maximum is very condensed or absent in the cores abundance and 13 c values for n pachyderma in the middle part of ois 3 are similar to modern values indicating high productivity and seasonal ice free areas along the arctic margin at that time these records indicate that the arctic ocean was a source of heat and moisture to the northern polar atmosphere during parts of ois 3

data for enhanced deposition of coal fragments at the chukchi margin western arctic ocean implications for deglacial drainage history from the laurentide ice sheet abstract distribution and composition of coarse particles 250 m were investigated in 13 sediment cores from the chukchi margin western arctic ocean petrographic clast identification is supplemented by xrf core scanning eds analysis of coal fragments and ams 14c dating of planktic foraminifera for age control coal debris distribution is also investigated in surface sediments of the study region for provenance interpretation the sediment core study focuses on the interval between the last glacial maximum and the holocene for constraining provenance and timing of the deglacial discharge we find that this interval is characterized by a distinct enrichment in sedimentary rock fragments including coal comparison with longer stratigraphic records indicates that this composition is unique for the time interval since at least maine isotope stage 5 based on the timing interpreted provenance and geographic distribution of the coal enrichment we conclude that the most likely primary source was the deglacial discharge from the mackenzie drainage basin of the laurentide ice sheet lis the identified coal bearing layer also expressed in the xrf sulfur record can be thus used as a stratigraphic marker for the lis discharge to the arctic ocean during the last deglaciation

freshwater input and abrupt deglacial climate change in the north atlantic greenland ice core records indicate that the last deglaciation 7 21 ka was punctuated by numerous abrupt climate reversals involving temperature changes of up to 5 10oc within decades however the cause behind many of these events is uncertain a likely candidate may have been the input of deglacial meltwater from the laurentide ice sheet lis to the high latitude north atlantic which disrupted ocean circulation and triggered cooling yet the direct evidence of meltwater input for many of these event has so far remained undetected in this study we use the geochemistry paired mg ca 18 o of planktonic foraminifera from a sediment core south of iceland to reconstruct the input of freshwater to the northern north atlantic during abrupt deglacial climate change our record can be placed on the same timescale as ice cores and therefore provides a direct comparison between the timing of freshwater input and climate variability meltwater events coincide with the onset of numerous cold intervals including the older dryas 14 0 ka two events during the allerod at 13 1 and 13 6 ka the younger dryas 12 9 ka and the 8 2 ka event supporting a causal link between these abrupt climate changes and meltwater input during the bolling allerod warm interval we find that periods of warming are associated with an increased meltwater flux to the northern north atlantic which in turn induces abrupt cooling a cessation in meltwater input and eventual climate recovery this implies that feedback between climate and meltwater input produced a highly variable climate a comparison to published data sets suggests that this feedback likely included fluctuations in the southern margin of the lis causing rerouting of lis meltwater between southern and eastern drainage outlets as proposed by clark et al science 2001 v293 283 287

quaternary sea ice history in the arctic ocean based on a new ostracode sea ice proxy paleo sea ice history in the arctic ocean was reconstructed using the sea ice dwelling ostracode acetabulastoma arcticum from late quaternary sediments from the mendeleyev lomonosov and gakkel ridges the morris jesup rise and the yermak plateau results suggest intermittently high levels of perennial sea ice in the central arctic ocean during marine isotope stage mis 3 25 45 ka minimal sea ice during the last deglacial 16 11 ka and early holocene thermal maximum 11 5 ka and increasing sea ice during the mid to late holocene 5 0 ka sediment core records from the iceland and rockall plateaus show that perennial sea ice existed in these regions only during glacial intervals mis 2 4 and 6 these results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon

major changes in ice stream dynamics during deglaciation of the north western margin of the laurentide ice sheet abstract victoria island lies at the north western limit of the former north american laurentide ice sheet in the canadian arctic archipelago and displays numerous cross cutting glacial lineations previous work suggests that several ice streams operated in this region during the last wisconsinan glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the arctic ocean this paper produces the first detailed synthesis of their behaviour from the last glacial maximum through to deglaciation 21 9 5 cal ka bp based on new mapping and a previously published radiocarbon constrained ice sheet margin chronology over 70 discrete ice flow events flow sets are fitted to the ice margin configuration to allow identification of several ice streams ranging in size from large and long lived thousands of years to much smaller and short lived hundreds of years the reconstruction depicts major ice streams in m clure strait and amundsen gulf which underwent relatively rapid retreat from the continental shelf edge at some time between 15 2 and 14 1 cal ka bp a period which encompasses climatic warming and rapid sea level rise meltwater pulse 1a following this overall retreat was slower and the ice streams exhibited asynchronous behaviour the amundsen gulf ice stream continued to operate during ice margin retreat whereas the m clure strait ice stream ceased operating and was replaced by an ice divide within 1000 years this ice divide was subsequently obliterated by another short lived phase of ice streaming in m clintock channel 13 cal ka bp the timing of this large ice discharge event coincides with the onset of the younger dryas subsequently a minor ice divide developed once again in m clintock channel before final deglaciation of the island shortly after 9 5 cal ka bp it is concluded that large ice streams at the nw margin of the laurentide ice sheet equivalent in size to the hudson strait ice stream underwent major changes during deglaciation resulting in punctuated delivery of icebergs into the arctic ocean published radiocarbon dates constrain this punctuated delivery as far as is possible within the limits imposed by their precision and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores

a 600 ka arctic sea ice record from mendeleev ridge based on ostracodes arctic paleoceanography and sea ice history were reconstructed from epipelagic and benthic ostracodes from a sediment core hly0503 06jpc 800 m water depth located on the mendeleev ridge western arctic ocean the calcareous microfaunal record ostracodes and foraminifers covers several glacial interglacial cycles back to estimated marine isotope stage 13 mis 13 500 ka with an average sedimentation rate of 0 5 cm ka for most of the stratigraphy mis 5 13 results based on ostracode assemblages and an unusual planktic foraminiferal assemblage in mis 11 dominated by a temperate water species turborotalita egelida show that extreme interglacial warmth high surface ocean productivity and possibly open ocean convection characterized mis 11 and mis 13 400 and 500 ka respectively a major shift in western arctic ocean environments toward perennial sea ice occurred after mis 11 based on the distribution of an ice dwelling ostracode acetabulastoma arcticum spectral analyses of the ostracode assemblages indicate sea ice and mid depth ocean circulation in western arctic ocean varied primarily at precessional 22 ka and obliquity 40 ka frequencies

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

atlantic meridional overturning and climate response to arctic ocean freshening 1 the global deglaciation event that followed last glacial maximum was punctuated by a sequence of rapid climate changes this began with the laurentide ice sheet derived calving event called heinrich event 1 continued with the bolling allerod warming that occurred synchronously with meltwater pulse 1a and was in turn followed by the younger dryas abrupt return to cold conditions although it has long been believed that these events are consequences of the response of atlantic meridional overturning circulation to freshwater inputs it has always been assumed that these inputs were applied directly to the atlantic ocean itself we address the question of how the atlantic meridional overturning circulation would have responded to the recently hypothesized addition of freshwater into the arctic ocean at the time of onset of the younger dryas and thereby demonstrate that this response is essentially identical to the response to north atlantic freshening

radiocarbon chronology of depositional regimes in the western arctic ocean abstract the foraminiferal abundance and percentage of coarse ice rafted detritus ird define glacial deglacial and interglacial depositional regimes in ams radiocarbon dated box cores from the western arctic ocean sediment deposition rates are generally less than 0 5 cm ka for glacial regimes greater than this for deglacial regimes and greater than 1 2 cm ka for interglacial regimes these differences in deposition rates might account for the much lower average sedimentation rates for the last 780 ka of 1 3 mm ka in cores from the central arctic ocean if glacial regimes dominated this interval foraminiferal abundances are less than 500 g during glacial maxima and mostly higher than 2000 g during deglacial and interglacial regimes slightly higher coarse ird percentages occur in deglacial intervals 5 10 up to 30 compared with interglacial intervals mostly 5 which characterize the last 10 12 ka in the western arctic ocean glacial regimes occurred from about 40 to 11 ka except for a brief interglacial or deglacial interval around 24 28 ka in the central arctic ocean the coarsest deglacial events occurred prior to 45 ka the late wisconsin deglaciation sediments approximately 9 16 ka are difficult to detect in the central arctic ocean sediments because they are only slightly coarser than the holocene and in some box cores less coarse than the holocene a previously unrecognized coarse ird event occurred near the core tops 0 3 cm between 1500 and 3500 radiocarbon years ago in the western arctic ocean only sediment older than 40 ka is coarser than this recent ird event which might correspond to a neoglaciation recognized in the north atlantic and elsewhere

trans arctic ocean tests of fine silt luminescence sediment dating provide a basis for an additional geochronometer for this region abstract new geochronometers are needed for sediments of the arctic ocean spanning at least the last half million years largely because oxygen isotope stratigraphy is relatively ineffective in this ocean and because other dating techniques require significant assumptions about sedimentation rates multi aliquot luminescence sediment dating procedures were applied to polymineral fine silt samples from 9 core top and 37 deeper samples from 20 cores representing 19 sites across the arctic ocean most samples have independent age assignments and other known properties e g coarse fraction carbonate u th isotopes thick source alpha particle counting indicates that for most regions the contribution of measured unsupported 230 th and 231 pa to calculated dose rates is 14 c range from other sites produce large long bleach age overestimates indicating the variable effects of ice rafting and other depositional and bottom current reworking re suspension processes during glacial stages short bleach dating tests provide ir psl age estimates for core tops that appear to penetrate the reworking veil of inherited ages and not only suggest a procedure to greatly reduce long bleach inherited ages but also have implications for the 14 c reservoir correction this study identifies the most promising regions for future luminescence dating and suggests that for several regions of the arctic ocean interglacial stage foram rich sediments from ridge tops are preferred for the fine grain luminescence dating methods

arctic ocean during the last glacial maximum atlantic and polar domains of surface water mass distribution and ice cover on the basis of 52 sediment cores analyzed and dated at high resolution the paleoceanography and climate of the last glacial maximum lgm were reconstructed in detail for the fram strait and the eastern and central arctic ocean sediment composition and stable isotope data suggest three distinct paleoenvironments 1 a productive region in the eastern to central fram strait and along the northern barents sea continental margin characterized by atlantic water advection frequent open water conditions and occasional local meltwater supply and iceberg calving from the barents sea ice sheet 2 an intermediate region in the southwestern eurasian basin up to 84 85 n and the western fram strait characterized by subsurface atlantic water advection and recirculation a moderately high planktic productivity and a perennial ice cover that breaks up only occasionally and 3 a central arctic region north of 85 n in the eurasian basin characterized by a low salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates although the total inflow of atlantic water into the arctic ocean may have been reduced during the lgm its impact on ice coverage and halocline structure in the fram strait and southwestern eurasian basin was strong

new constraints on arctic ocean mn stratigraphy from radiocarbon dating on planktonic foraminifera abstract variations in the abundance of manganese mn in arctic ocean sediments are used as a tool to identify glacial and interglacial periods this study aims to provide new insight into the applicability of mn as a stratigraphic tool in the topmost sediment and to investigate the occurrence of mn peaks in sediments within the range of radiocarbon dating in combination with variations in ice rafted debris ird radiocarbon dating is used to better constrain the stratigraphic occurrence of mn peaks and the synchroneity between multiple records especially during the late glacial and the holocene we find that a hiatus spanning mis 2 is widely observed in most of our cores resulting in a merging of mn peaks of holocene age and the later part of mis 3 the holocene mn peak is usually high amplitude but short while the mis 3 mn peak has a lower amplitude and is protracted where preserved mis 2 sediments form a 2 3 cm thick layer characterized by a light color low mn content sparse ird and low foraminiferal abundance ird variations provide a powerful tool to identify the boundary of the holocene and late mis 3 in cores with a mis 2 hiatus because the ird content displays a general increment from the start of mis 3 and both the holocene and mis 2 show small ird variations the end of mis 3 can be pinpointed to the point of decrease in ird the hiatus of mis 2 is widely observed in our cores suggesting extensive persistent sea ice coverage during the peak of the last glacial cycle with sharply reduced sedimentation throughout the arctic ocean identifying similar events during previous glacial periods may be an important step towards constructing longer and more accurate chronologies for arctic ocean sediments

quaternary history of axel heiberg island bordering nansen sound northwest territories emphasizing the last glacial maximum the landscape of northeastern axel heiberg island records an erosional history since the neogene whereas the glacial and sea level history relate to late wisconsinan glaciation during the last glacial maximum northeastern axel heiberg island was covered by glaciers emanating from local and regional sources local ice caps expanded from highlands on axel heiberg island across the coastal slope a trunk glacier flowed northward out of eureka and flat sounds into nansen sound and reached northernmost axel heiberg island radiocarbon ages on marine shells suggest that the last glacial maximum was attained along the coast after 29 ka bp and extensive deglaciation was taking place by 10 3 ka bp the postglacial marine limit rises continuously from 78 m above sea level near the entrance to nansen sound to 158 m above sea level at the mouth of eureka sound showing greatest glacioisostatic loading to the south

a holocene record of changing arctic ocean ice drift analogous to the effects of the arctic oscillation 1 the arctic oscillation ao controls the configuration of the transpolar drift tpd if thicker ice from the beaufort gyre were exported the volume of fresh water sea ice in the nordic seas would significantly increase decreasing the formation of north atlantic deep water this would cool large parts of the northern hemisphere and affect global climate therefore in order to understand how the global climate system functions it is imperative to know how the tpd changed over the last millennium or more the provenance of grains in a sediment core located near the confluence of the tpd and the beaufort gyre provides a direct proxy for changes in seaice drift owing to these circulation systems the core has more than 200 cm of holocene sediment with intervals dominated by grains from the russian shelves alternating with intervals of abundant grains from north american sources grains matched to russian shelves indicate that the tpd was shifted toward north america similar to what occurs during a more positive phase of the ao this condition alternated with intervals where few grains matched to russian sources presumably because the tpd was restricted to the russian half of the arctic far from the core site during the last 1300 years increased influx of russian grains occurred approximately every 50 150 years this fluctuation might represent the long term oscillation of the ao which modulates the same tpd shift today

the westphalian stephanian macrofloral record from the south wales coalfield uk the south wales coalfield has the most complete westphalian macrofloral record anywhere on the variscan foreland or adjacent basins with 135 biodiversity meaningful morphospecies having been recognized all of the standard macrofloral biozones of the westphalian stage have been recognized although a detailed comparison with the central pennines coalfields has indicated some discrepancies in the relative positions of the biozonal boundaries total species richness progressively increases through the langsettian substage and then remains relatively stable through most of the duckmantian and bolsovian substages there is a distinct reduction in total species richness towards the top of the bolsovian substage but this partially recovers in the middle asturian substage with the appearance of a range of marattialean ferns and medullosalean and callistophytaleans pteridosperms there is no evidence of any significant drop in total species richness towards the top of the succession indicating that conditions at this time were relatively stable the change from coastal floodplain to alluvial braidplain conditions in middle bolsovian times correlates with a marked increase in the proportion of medullosalean remains being preserved in the adpression record reflecting an expansion of the clastic substrate habitats

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr