late quaternary marine sediment accumulation in fiord shelf deep sea transects baffin island to baffin bay abstract piston cores from fiords shelf troughs and the deep sea off eastern baffin island n w t canada have been sampled for texture and detrital carbonate in the 2 ka over the last ca 10 ka three sets of two cores each lie on a fiord shelf transect and thus define variations in sediment accumulation gradients these continental margin data are compared with cruder estimates of holocene sediment accumulation at three sites farther offshore in baffin bay davis strait and the northern labrador sea minimum accumulation in a 2 ka interval was 200 kg m 2 with a maximum estimate of 8 800 kg m 2 detrital carbonate accumulation varies between 0 and 1 300 kg m 2 median accumulation for a typical fiord shelf deep sea transect over the last 10 ka have been 10 340 3493 and 820 kg m 2 at dsdp leg site 645 in central baffin bay the sedimentation rate ranged between 40 and 130 m ma ca 400 and 1200 kg m 2 2ka that is comparable with the late quaternary input into baffin bay

accelerator mass spectrometer ages for the younger dryas event in atlantic canada abstract in atlantic canada bulk sediment dates for the onset of a late glacial cooling widely regarded as the younger dryas event are highly variable ranging from 14 300 270 to 10 800 100 yr b p we present the first accelerator mass spectrometer ams 14c dates from atlantic canada at or close to the boundaries of this event from six sites in new brunswick and nova scotia the mean of five dates places the onset of this cooling at ca 10 770 yr b p the inclusion of a sixth perhaps anomalously old date changes the mean to 10 880 yr b p the termination averages three dates ca 10 000 yr b p these dates place the timing of the younger dryas event in atlantic canada closer in line with the traditional chronozone boundaries of 11 000 and 10 000 yr b p in northwest europe

temporal offsets between surface temperature ice rafting and bottom flow speed proxies in the glacial mis 3 northern north atlantic rapid climatic switches during marine isotope stage 3 29 59 ka bp are often attributed to ocean circulation changes caused by freshwater input into the north atlantic through the melting of large amounts of icebergs and sea ice however recent studies have questioned this direct coupling between factors influencing the ocean climate system by combining multiple proxies from two mid depth northern north atlantic sediment cores we assess temporal offsets and links between freshwater input and response of the near bottom flow as well as between near bottom flow and sea surface temperatures changes grain size mineralogical and magnetic proxies for ice rafting and near bottom flow speed interpreted as indicators of freshwater input and deep circulation strength consistently indicate a delay in the recovery of the deep circulation after freshwater perturbations sea surface temperature variability is inferred from foraminiferal assemblages and mg ca and 18o of neogloboquadrina pachyderma s the records show rapid switches towards higher temperatures following the ice rafting events interestingly near sea surface temperatures increased and decreased again during periods of accelerating bottom flow speed likely reflecting the sudden release of heat from deeper in the water column rather than circulation changes our data thus confirm the impact of freshwater forcing on the atlantic deep circulation but suggest that temperature variability at the surface was not directly linked to these circulation changes

historical ecology in beringia the south land bridge coast at st paul island a 14 m core of lake sediments from st paul island yields a long environmental history of the south coast of the bering land bridge tritium assay demonstrates that sands in the bottom 8 m of deposit are injected with modern water suggesting that a radiocarbon anomaly is the result of modern carbon introduced in groundwater the remaining radiocarbon chronology coupled with a time stratigraphic pollen zone boundary suggests that the record penetrates to the mid wisconsin interstadial pollen percentage data picea pollen influx and pollen species lists allow reconstruction of the land bridge vegetation which was tundra without shrubs or trees with bare ground and comparable to bering land bridge tundras found further north there was no coastal mild or wet strip plant associations comparable to those of the modern aleutians or pribilofs probably did not exist along the land bridge coast and the region was probably not suitable for breeding by fur seals and other marine mammals a cold dry continental air mass system reached to the coast itself the south land bridge coast did not offer an environment to aboriginal human populations that was significantly milder than that of the land bridge plains to the north at about 11 000 yr b p the wisconsin dry climate was replaced by a regimen comparable to that at the modern tree line of the interior and this climate in turn was replaced with the modern system at about 9500 yr b p climatic change was independent of fluctuating sea level

geomorphological evidence of holocene climatic change from northwest ellesmere island canadian high arctic proxy data from the northern coast of ellesmere island are used to reconstruct holocene palaeoclimate and appear to corroborate the ice core record from the canadian and greenland high arctic despite some regional variation geomorphological evidence indicates that deglaciation was associated with a marked climatic amelioration in the late pleistocene early holocene 10 ka bp this contrasts with glaciers on the south side of grant land mountains which started to retreat at 7 5 ka bp perhaps due to significant differences in glacioclimatic regime and the influence of the arctic ocean indicators of sea ice conditions on northern ellesmere island suggest that the early holocene was a period of considerable open water radiocarbon dates on driftwood collected from behind the north coast ice shelves suggest that the ice shelves formed during a mid holocene climatic deterioration geomorphic evidence shows that the ice shelves are presently breaking up and melting in response to recent warming glaciers hav

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

the source of benguela ninos in the south atlantic ocean 1 the intermittent occurrence of anomalous warm events in the upwelling regions of the pacific el ninos has been intensively studied pacific ninos have striking effects on the local ecosystem hence on the fisheries and on rainfall similar dramatic events have been observed in the south atlantic off the coasts of angola and namibia and named benguela ninos they tend not to occur in unison with their pacific counterpart and may thus have unrelated forcing mechanisms using an ocean general circulation model forced by real winds and verified with satellite data it is shown that benguela ninos are generated by specific wind stress events in the west central equatorial atlantic and progress from there as subsurface temperature anomalies that eventually outcropped only at the south west african coast these results suggest that it now may be possible to predict the occurrence of these disruptive events with a lead time of 2 months

holocene glacimarine sedimentation and macrofossil palaeoecology in the canadian high arctic environmental controls abstract raised glacimarine sediments adjacent to strand bay axel heiberg island and on fosheim peninsula ellesmere island record sedimentation in environments proximal to tidewater glaciers and glacimarine deltas the different styles of sedimentation during early holocene deglaciation ca 8 10 ka bp of these regions are of particular interest in strand fiord axel heiberg island coarse grained sediments deposited from high density turbidity currents generated along the margin of tidewater glaciers are overlain by laminated fine grained sediments deposited by suspension settling in a shallow ice proximal environment the fining upward sequence records the reduction in sediment supply as tidewater glaciers retreated onto land in contrast on fosheim peninsula ellesmere island laminated to massive fine grained sediments were deposited from low density turbidity currents and by suspension settling in a deep prodeltaic environment several kilometres from upland ice caps sediment texture coarsens upward reflecting increasing proximity to sediment sources as deltas prograded during early holocene marine regression two macrofossil faunas a portlandia arctica assemblage and a hiatella arctica mya truncata assemblage occur in association with early holocene sediments mid holocene sedimentation ca 4 8 ka bp in both regions was characterized by the accumulation of laminated or massive fine grained sediments deposited from low density turbidity currents and by suspension settling in prodeltaic environments several macrofossil faunas are recorded in these sediments a portlandia arctica assemblage and an astarte borealis mya truncata assemblage associated with laminated muds deposited in shallow water and a deep water portlandia arctica assemblage associated with massive muds variations in sedimentation rates can be correlated with the summer melt layer record of the agassiz ice cap on ellesmere island early holocene deglaciation coincided with a period of increased summer ablation ca 8 5 11 5 ka bp that contributed to the massive influx of sediment into marine environments the mid holocene ice core record indicates a sharp decline in summer ablation ca 6 0 9 5 ka bp resulting in the reduction of sediment flux to marine environments

interlaminated ice proximal glacimarine sediments in muir inlet alaska muir inlet in glacier bay alaska is a glacial fjord receiving a tremendous volume of sediment annually the rate of sediment accumulation is greatest proximal to muir glacier about 9 m yr 1 and decreases away from the glacier the primary sediment sources are meltwater streams discharging at subglacial and ice marginal positions to form overflows interflows and underflows continuous turbidity currents overflows and interflows interact with diurnal tidal currents and their volume and sediment concentration varies diurnally and annually with meltwater discharge these effects produce cyclic deposits of a thin fine grained sand or silt lamina that grades normally to a thicker poorly to very poorly sorted mud lamina this lamina couplet is termed a cyclopel underflows are suggested to occur in this glacimarine environment because of conditions unique to subglacial fluvial systems underflow deposits occur only in proximal positions 0 5 km from glacier face and are coarse grained reverse to normal graded and exhibit an increase in sorting and sand content up layer ice rafted debris identified as particles 177 m is ubiquitous though low 5 by weight and occurs as isolated particles frozen pellets or as lenses that in cores may have a lamina appearance proximally ice rafted debris is difficult to identify because proximal sediment is often as coarse grained deposited sediment may be reworked by tidal currents and sediment gravity flows depositional processes operating in muir inlet produce interlaminated sand silt clay that characterizes sediment proximal to a glacier and fines seaward to mud sediment is classified into one of three sediment types 1 1 type i sediment is very fine grained mean 8 65 7 17 o low in sand 0 1 11 2 and very poorly to poorly sorted it is the dominant sediment type in muir inlet and is transported by plumes and deposited by suspension settling 2 2 type ii sediment is fine to coarse grained mean 6 70 3 12 o low to high in sand 5 1 86 6 and very poorly to moderately sorted it represents reworked sediment proximal plume deposits or coarse grained laminae of cyclopels 3 3 type iii sediment is coarse grained mean 3 89 2 38 o high in sand 58 0 100 0 and poorly to well sorted it is deposited by sediment gravity flows or underflows

arctic ice shelves and ice islands origin growth and disintegration physical characteristics structural stratigraphic variability and dynamics ice shelves are thick floating ice masses most often associated with antarctica where they are seaward extensions of the grounded antarctic ice sheet and sources of many icebergs however there are also ice shelves in the arctic primarily located along the north coast of ellesmere island in the canadian high arctic the only ice shelves in north america and the most extensive in the north polar region the ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands the tabular icebergs of the arctic ocean the present state of knowledge and understanding of these ice features is summarized in this paper it includes historical background to the discovery and early study of ice shelves and ice islands including the use of ice islands as floating laboratories for polar geophysical research growth mechanisms and age the former extent and the twentieth century disintegration of the ellesmere ice shelves and the processes and mechanisms of ice island calving are summarized surface features thickness thermal regime and the size shape and numbers of ice islands are discussed the structural stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described large scale and small scale dynamics of ice islands are described and the results of modeling their drift and recurrence intervals are presented the conclusion identifies some unanswered questions and future research opportunities and needs

a multiproxy based reconstruction of the mid to late holocene paleoenvironment in the laptev sea off the lena river delta siberian arctic abstract land shelf interactions and related environmental changes were reconstructed for the past 6 cal kyrs interpreting multiproxy records from the two ams14c dated sediment cores from the sites located to the north and northeast of the lena river delta proxies used include terrestrial and aquatic palynomorphs benthic planktic foraminifers and ostracods paired with benthic 18o and 13c records of haynesina orbiculare the study focused on unravelling the relation between river runoff and the regional climate changes on the one hand and its imprint on the shelf sea environment on timescales beyond the instrumental records on the other the palynomorph records show that the lena river outflow largely determined the composition of species associations and the magnitude of terrestrial matter influx from land pollen assemblages of the inner laptev sea shelf reflect complex pollen contribution of the arctic tundra and remote taiga zones drained by the lena river and indicate a vegetation response to warmer than present climatic conditions between 6 0 and 4 5 cal ka and a subsequent gradual cooling fluvial influence in the records is manifested by 1 increases in sedimentation rates 2 high influxes of pollen spores and freshwater chlorophycean algae wood and plant remains 3 negative 13c excursions due to the introduction of dissolved inorganic carbon dic from river water episodes of enhanced freshwater influence in the surface water layers fluvial events correlate with positive benthic 18o excursions and increasing representation of river distal species among benthics altogether this points to an estuarine like reversed north to south bottom current activity along the submarine paleovalleys on the shelf the most pronounced fluvial events are recognized at 5 3 5 9 1 5 and

an origin for laminated glacimarine sediments through sea ice build up and suppressed iceberg rafting laminated glacimarine sediments are observed in visual core logs and x radiographs from scoresby sund and nansen fjord east greenland they are mostly underlain and overlain by massive or stratified glacimarine diamicton dmm or dms which is a product of iceberg delivery of heterogeneous debris and in scoresby sund reworking by deep drafted iceberg keels the laminated sediments are ams radiocarbon dated to two cold periods since the last late weichselian deglaciation the younger dryas stadial milne land stadial in east greenland and the little ice age during cold climatic events multiyear shorefast sea ice sikussak formed in these fjords and trapped the icebergs fine grained laminated muds fl were deposited in scoresby sund when the flux of icebergs was suppressed but turbid meltwater continued to provide some sediment flux to the fjord systems varying through time to produce laminations in nansen fjord thinner and often massive mud layers fm resulted from shorter intervals of sea ice cover with no ice rafting stratified diamicton layers dms which alternate with mud deposition to produce a laminated unit probably represent intervening times of more open conditions with iceberg rafting in scoresby sund foraminifera are either absent from the laminated unit or begin to appear towards the end of its deposition the absence of both benthic and planktonic foraminifera also suggests that multiyear sea ice was covering the core sites there is no evidence of macrofaunal activity and bioturbation is absent from the laminated sediments satellite data show that multiyear shorefast sea ice is present in several areas of the high arctic today and this traps icebergs calved from interior ice cap drainage basins thus the process of laminated glacimarine sediment formation is likely to be applicable to a number of areas of the modern and quaternary arctic

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

holocene environmental history of a peatland in the lena river valley siberia a 3 86 m core of peat and organic lake mud from a polygonal peatland in the lena river valley of siberia was radiocarbon dated and analyzed for pollen plant macrofossils chrysophyte stomatocysts stable isotopes and charcoal at around 7200 bp a shallow lake or open water wetland supported diverse aquatic macrophytes the site had transformed initially into a richer fen with carex comarum palustris and drepanocladus and later a poorer fen with sphagnum which persisted until around 3000 bp fire may have been responsible for silt being blown onto the peatland which changed the hydrological and geochemical conditions for development of the poor fen ice accretion led to an increase in the height of the centre of the polygon and expansion of sphagnum peatland 18 o values become progressively more enriched which reflects more direct input of summer precipitation waters and less groundwater during this period finally the peatland surface was elevated sufficiently to limit water and nutrient supply thereby allowing ericaceae and betula to grow at the coring site fire burned the peatland surface and may have exaggerated the extremely slow rate of peat accumulation fire may also be a factor in maintaining the open larix dahurica forest in the region today while climate may be contributing to reducing postfire regeneration fire and climate together may be controlling the character and composition of forests near tree line in the lena river valley of this part of siberia resume une carotte de tourbe et de boue organique lacustre diune longueur de 3 86 m prolevoe dans une tourbire polygonale dans la valloe de la rivire lena en siborie a oto datoe au radiocarbone et analysoe pour les pollens plantes

shallow plio pleistocene contourites on the hebrides slope northwest u k continental margin abstract british geological survey borehole 88 7 was drilled on the continental margin of the northeast rockall trough in a water depth of 560 m with the intention of coring an unbroken plio pleistocene succession the borehole penetrated 102 m of pleistocene and tertiary sediments with 60 recovery the majority of the plio pleistocene succession is composed of bioturbated muds and sandy muds with rare dropstones in most of the core bioturbation has obscured any primary sedimentary structures although in places the muds are laminated and graded on a centimetric scale subtly different trace fossil assemblages in the homogeneous and laminated core indicate that the preservation of laminae is not simply the result of a decrease in burrowing activity x radiographs of the apparently homogeneous sections of core indicate that both coarsening and fining upward sequences between 5 and 50 cm in thickness are present particle size analysis has identified larger variations in grain size over several metres sands in the plio pleistocene are not common and comprise under 8 of the total succession most of which directly overlie older tertiary sediments the mineralogy of the plio pleistocene sands implies reworking of the lower beds and their base is marked by a conglomeratic lag deposit the change between homogeneous and laminated muds appears to be the result of variations in the style of sediment deposition at times deposition rate was relatively rapid and formed a laminated sediment with a trace fossil assemblage containing bedding parallel forms this more rapid sedimentation rate may be the result of greater down slope transport of material to the north or south of 88 7 giving rise to the lateral redistribution of fine sediment which was laid down in laminated beds similar in form to distal turbidites when this lateral source was not present the background sedimentation of ice rafted and ice margin derived material gave rise to a poorly sorted deposit which was reworked into both coarsening and fining upward units which have similarities with muddy contourites all the plio pleistocene muds have been influenced by along slope currents during deposition

sedimentary processes of canadian arctic fjords abstract conceptual models of circulation and sedimentation in arctic fjords are presented to illustrate the current understanding of these environments circulation is a vigorous process in these fjords and is enhanced by the loss of the freshwater cap during the long winter period of near zero inflow the process of brine rejection during the formation of sea ice and the role of glaciers and icebergs injecting freshwater at depth on the other hand the presence of sea ice blocks reduces the mixing action of wind which may otherwise represent the largest input of energy to fjord circulation it also provides a freshwater layer on melting and may in some circumstances damp the amplitude of tides during summer large loads of glacial sediment entering arctic fjords are separated into streams of overflowing suspended load and bed load in the presence of salt water as the concentrations of suspended load in the freshwater are normally much less than required to overcome the density of the salt water deposition occurs throughout the fjord by rapid settling of flocculated particles from the overflowing brackish water and from grain flows in the proximal environment created as the fluvial traction carpet moves over the delta foreset slope after sediment has been deposited it may be remobilized by slides which in turn may develop into fully turbulent flows as they move down the fjord floor a range of deposits from slump debris to minor turbidites are postulated to occur with the flocculated muds although not all have yet been examined in the arctic fjord stratigraphic record sea ice is an important sedimentological agent in arctic fjords it passively carries fluvial aeolian and colluvial material which is subsequently released from the ice during the stage of puddle draining at break up sea ice also actively incorporates fine and coarse sediments up to large boulders during freezing along the shores in winter and by wave and tidal current washing controlled by the presence of the ice during break up

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

sediments of the lomonosov ridge and makarov basin a pleistocene stratigraphy for the north pole sediments of 16 short cores taken as part of the lomonosov ridge experiment lorex can be organized into the first pleistocene stratigraphy for the north polar region this stratigraphy can be correlated with stratigraphic units described from the alpha chukchi areas 300 km distant the lorex cores include at least 12 sedimentary subunits differentiated by texture color and carbonate content the units are silty and arenaceous lutites and are principally glacial marine benthic and planktonic foraminifera degree of bioturbation and fe mn micro nodule abundance generally are positively correlated foraminifera in core b 8 from 3 956 m in the makarov basin may have been affected by ccd fluctuations that did not affect fossils in core b 24 from 1 600 m on the crest of the lomonosov ridge the 12 stratigraphic units were deposited during the late pleistocene and represent the same major sedimentary events as those of stratigraphic units k l and m of the amerasian basin this correlation is excellent evidence for the remarkable and widespread uniform depositional style of glacial marine sediment times of major glacial ice transport reflect deglaciation events in the central arctic ocean surface currents during deglaciation transport glacial ice in a more or less uniform pattern over at least 50 of the arctic ocean even thin sedimentary units deposited during relatively long time intervals are correlated over 500 000 km 2

late wisconsinan glaciation of southern eureka sound evidence for extensive innuitian ice in the canadian high arctic during the last glacial maximum abstract southern eureka sound was originally proposed as the centre of an innuitian ice sheet in the canadian high arctic at the last glacial maximum lgm based largely on the pattern of holocene emergence this paper focuses on the glacial geological evidence for such an ice sheet in the region granite dispersal trains and ice moulded bedrock record regional westward flow of warm based ice into eureka sound from se ellesmere island regional ice was coalescent with local ice domes on inter fiord peninsulas marine limit in the form of raised deltas beaches and washing limits formed during deglaciation of the regional ice throughout southern eureka sound marine limit dates 9 2 ka bp indicating that ice commenced retreat during the early holocene ice divides were located along the highlands of central ellesmere and axel heiberg islands from which ice inundated eureka sound flowing north and south along the channel regional radiocarbon dates on marine limit show that deglaciation occurred in two steps initial break up and radial retreat of ice from eureka sound to the inner fiords was rapid and preceded stabilisation along adjacent coastlines and at fiord heads two step deglaciation is also reflected in differences in glacial geomorphology between the inner and outer parts of many fiords a prominent belt of fiord head glaciogenic landforms long proposed to mark the last glacial limit is re interpreted to record initial stabilisation of ice margins due predominantly to bathymetric control

vegetation history of pleasant island southeastern alaska since 13 000 yr b p abstract a 13 000 year history of late quaternary vegetational and climatic change has been derived from lacustrine sediments from pleasant island in the glacier bay region of southeastern alaska early arrival of lodgepole pine and mountain hemlock indicated by the presence of pollen and conifer stomata suggests expansion from refugia in the alexander archipelago a short term climatic reversal possibly correlated with the european younger dryas is inferred from the expansion of tundra elements and deposition of inorganic sediments between 10 600 and 9900 14 c yr b p two peat cores from the lake catchment verify holocene vegetation changes and aid in the separation of biogenic from climatic forces affecting vegetation history differences in pollen representation among the three cores illustrate the variation among pollen collecting substrates as well as the spatial heterogeneity of peatland development and its dependence on local hydrology initial peat accumulation and soil paludification occasioned by increases in temperature and precipitation in the early holocene allowed western and mountain hemlock to replace sitka spruce 8500 8000 yr b p open muskeg became widespread about 7000 yr b p and allowed lodgepole pine to reinvade the region after a 2000 yr absence the extensive replacement of fen elements by bog taxa at 3400 yr b p suggests increased paludification due to changing hydrologic conditions its correlation with the upland expansion of tsuga heterophylla suggests the onset of a cooler wetter neoglacial climate in southeastern alaska

evolution of interannual warm and cold events in the southeast atlantic ocean extreme warm episodes in the southeast atlantic ocean known as benguela ninos have devastating envi ronmental impacts and have been shown to be remotely forced to place these extreme events into perspective the investigation is here extended to minor warm events as well as to cold episodes to this end different sets of observations have been combined with outputs from a numerical simulation of the tropical atlantic for the period 1982 99 it is shown that both warm and cold surface events develop regularly in the same specific region along the coast of angola and namibia some cold events compete in magnitude with major warm episodes local sea air heat flux exchanges do not seem to precondition the sea surface in the angola benguela region prior to the arrival of an event most warm and cold episodes are large scale events despite their limited surface signature they appear to be generated by wind anomalies in the western and central equatorial atlantic in the same way as benguela ninos seasonal fluctuations of the depth and shape of the tropical thermocline seem partly to control the way subsurface anomalies eventually impact the surface during austral summer surface anomalies create an identifiable pool centered near 158s whereas in winter they show an elongated pattern along the coast stretching toward the equator local upwelling or downwelling favorable wind regimes as well as local net heat fluxes may modulate the surface expression of events

latest pleistocene increase in wind intensity recorded in eolian sediments from central alaska abstract a brief increase in wind intensity between ca 11 100 and 10 700 yr b p is recorded by a sharp increase in sediment grain size at eolian sections along the nenana river in central alaska this occurred at the same time as the younger dryas climatic reversal in northern europe and an increase in the vigor of atmospheric circulation recorded by greenland ice cores climatic fluctuations in high latitude areas during younger dryas time may reflect variations in the co2 content of the atmosphere

rainstorm induced event sedimentation at the tidewater front of a temperate glacier runoff from a late summer storm drained rapidly to a subglacial stream of mcbride glacier southeast alaska the stream transported large volumes of sediment that discharged from the glacier s tidewater front directly into fjord water at 40 m depth measurements of salinity temperature and suspended sediment concentration indicate that the sediment was transported by interflows within brackish fjord water sedimentation rates were exceptionally high up to five times normal laminated fine sand accumulated in proximal sediment traps and silty mud accumulated in distal traps the low frequency of large storms late in the melt season indicates that the sedimentary products would be rare but significant marker horizons in temperate glaciomarine sequences

postglacial to holocene history of the laptev sea continental margin palaeoenvironmental implications of benthic assemblages abstract bivalves ostracods and foraminifers were studied in four ams 14 c dated sediment cores from the laptev sea one from the upper continental slope with a date of 15 8 cal ka in its basal part and three from river palaeovalleys on the outer middle shelf aging back to 12 7 11 2 cal ka at the continental margin high relative proportions of cassidulina neoteretis planktic foraminifers and ostracods with north atlantic affinities provide evidence on past inflows of atlantic derived waters whereas freshwater inputs downslope sediment movements and ice rafting are documented by the presence of euryhaline brackish water and freshwater ostracods and low planktic benthic ratio atlantic derived subsurface waters reached the studied site by ca 16 cal ka i e prior to the establishment of the pathway across the barents sea shelf further west the strongest atlantic influence occurred prior to 12 cal ka and after 3 cal ka a cold low nutrient marine environment with a coastal polynya setting is reconstructed for the time 16 14 cal ka whereas between 12 7 and 11 2 cal ka freshwater influence reached its maximum during a time when the outer shelf was flooded and brackish water assemblages inhabited the estuarine parts of palaeovalleys following the temporal and spatial pattern of sea level rise these fluvially affected assemblages rapidly transformed into shallow marine faunas after ca 3 5 3 cal ka well pronounced changes in the benthic communities indicate a general climate cooling characterized by a more intensified surface and bottom water circulation regime

holocene glacimarine sedimentary environments in fiords of disko bugt west greenland abstract acoustic and sedimentary properties of three fiord systems were examined in the region of disko bugt west greenland to understand variability in the processes rates and sources of sediment delivery during the late glacial and holocene kangerluk and kangersooq of western disko are dominated by meltwater inputs of sediment from local ice fields of the island interior modern sediments are delivered primarily via overflow currents rainout occasional bottom currents and small amounts of iceberg rafting where exposure to baffin bay allows penetration of the west greenland current 14 c and acoustic derived accumulation rates for the last 1 2 ka vary from about 1 mm a 1 in distal fiord settings to more than 5 mm a 1 in proximal sites adjacent to actively building deltas these rates are generally larger than has been observed in other greenland and baffin bay fiords the tidewater terminus of inland ice at ikerasak is also meltwater dominated but produces lower than expected sediment accumulation due to low gradients of the outlet ice and resistant substrates these high latitude west greenland fiords are subarctic in character and contrast significantly with colder polar type fiords at similar latitudes in east greenland sediment deposition which was focused in the outer disko fiords during the late glacial and early holocene is due to one of two possible mechanisms standstill of local ice or enhanced rafting of sediment from disko bugt icebergs this study contributes to the debate on the extent of glaciation and holocene spatial variability in fiord processes of west greenland

a holocene palynological record from the northeastern laptev sea and its implications for palaeoenvironmental research a 844 cm long core ps51 118 3 77 53 54 n 132 11 92 e recovered from the upper slope 122 m water depth of the laptev sea russian arctic has been studied for pollen spores and aquatic palynomorphs including freshwater green algae and cysts of marine dinoflagellates the age model was established on the basis of radiocarbon dates obtained on marine bivalve mollusk shells the available dates suggest that the analyzed sediment was accumulated during the last ca 10 8 cal ka and reveal two intervals with markedly different sedimentation rates reflecting the sedimentary regime changes of the laptev sea shelf during postglacial sea level rise very high sedimentation rates ca 4 7 mm per year in the lower part of the core 120 866 cm between ca 9 2 and 10 8 cal ka bp reflect lower than present sea levels high erosion activity and much closer position of the palaeo shoreline with the lena and yana river mouths to the core site dramatic decrease in sedimentation rates ca 0 1 mm per year during the middle and late holocene interval reflects high sea level and decreased amount of suspended material transported to the outer shelf by rivers despite the location of the core site at the continental slope and far away from the modern coastline pollen spores and fresh water algae constitute a major part of the microfossils throughout the whole record indicating great impact of the lena and yana rivers and possibly prevalent wind regime on the pollen and non pollen palynomorph npp assemblages although a number of short term decadal to multi century oscillations deviate from the mean holocene values pollen taxa percentages and pollen based numerical biome reconstructions do not show very clear trends the latter is likely a result of the mixed environmental signal and complex pollen contribution of several large environmental regions and vegetation zones of siberia drained by the lena and yana rivers the greater pollen contribution of the forested regions to the ps51 118 3 record reflects higher pollen production of the boreal trees and shrubs over the low productive arctic vegetation the intervals of the relative increase in the tundra biome scores in the ps51 118 3 record reflect decreased arboreal pollen production or and increased landscape openness within the pollen source area and can be correlated within the uncertainty of the age models with the cold episodes observed in the greenland ice and north atlantic sediment records

the glacimarine sedimentary environment of expedition fiord canadian high arctic abstract expedition fiord is a small shallow inlet on the west coast of axel heiberg island near 80 n latitude it receives runoff and sediment at its head from a 1079 km 2 drainage basin 72 of which is glacier covered subbottom acoustic survey and cores from the fiord floor were used to assess the sedimentary environment most of the sediment is deposited within 3 km of the inflow from suspension in the overflowing cap and by gravity flows on the foreset beds of the delta occasionally weak turbidity currents reach the mid fiord where they deposit fine grained sediments icebergs from a large calving glacier in an adjacent fiord raft additional sediment especially to the outer part of the fiord they also scour the seafloor although the persistent ice cover and slow currents in the fiord restrict this process except near the inflow the total sediment accumulation since deglaciation is less than 20 m and the rates of 0 5 1 mm yr have not varied significantly to the present a thicker deposit in the outer fiord is probably related to an early holocene glacier margin near that location

glaciomarine sedimentation in disraeli fiord high arctic canada abstract disraeli fiord represents a glaciomarine environment unique to the north coast of ellesmere island featuring floating glacier tongues multi year landfast sea ice and a strongly stratified water body which results from enclosure of the fiord by ward hunt ice shelf it is a very low energy depositional environment even at sites proximal to glaciers sediment enters the fiord by interflow and is deposited through suspension settling ice rafting is precluded by the year round sea ice cover sedimentation rates in the inner fiord since about 7000 yrs b p are estimated to be 5 10 cm ka a reflection of the limited sediment influx from the cold based glaciers which contact the fiord changes in sediment structure through the holocene reflect changes in the rate and process of sediment input as well as changes in fiord circulation all of which relate to regional climate during deglaciation early holocene sedimentation rates were orders of magnitude greater than at present subglacial meltwater was the dominant source of inflow with sediment transported in turbid plumes as over or interflow and deposited through suspension settling this is supportive of other studies indicating that a pronounced climatic amelioration led to warm based glaciers at this time

marine sedimentation at a calving glacier margin a 2 month study at a subpolar tidewater glacier was conducted at anvers island antarctic peninsula lat 64 s to improve understanding of sedimentary processes and associated deposits in glacial marine settings data collected in the ice proximal environment were 1 brash ice size distribution and melt rates to assess sediment source and transport mechanisms 2 conductivity temperature turbidity depth cttd profiles water samples and sediment trap catches to study processes and patterns of sediment dispersal 3 bottom cores and grabs to document recent glacial marine sedimentation and 4 remotely operated vehicle video surveys of the ice terminus and sea bottom to obtain images of physical and biological processes the water column is stratified and a halocline occurs at 20 30 m water temperature ranged from 1 to 1 6 c salinity was 32 34 and suspended solids were 3 5 mg l well above the bottom ephemeral turbid horizons contain 8 15 mg l suspended solids rare surface plumes and a quasipermanent turbid layer produced by resuspension during calving events reach 25 35 mg l meltwater drains from the glacier surface but no subglacial meltwater was detected directly entering the sea the most important sources of sediment appear to be the direct melting of the submerged ice front and melting of calved glacial ice most fragments of floating ice melt within 1 km of the ice front some sediment may be contributed as low density 1 1 g cm 3 algae bound sediment pellets by meltwater streams draining the ablating ice surface sediment enters the stratified water column and is moved by tidal and wind driven circulation marine sedimentation rates are low 3 mm yr relative to depth of bioturbation resulting in unstratified sandy mud with dispersed clasts

a late wisconsin and holocene vegetation history from the central brooks range implications for alaskan palaeoecology abstract five pollen diagrams reveal late wisconsin and holocene vegetation changes in the walker lake alatna valley region of the central brooks range approximately 100 km west of the area studied by d a livingstone 1955 ecology 36 587 600 new insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate picea glauca and p mariana pollen three major pollen zones are identified 1 a basal herb zone characterized by high percentages of cyperaceae gramineae salix and artemisia and low total pollen influx 2 a shrub betula zone with increased total pollen influx and very high percentages of betula pollen predominantly in the size range of b nana and b glandulosa and 3 and alnus zone dominated by alnus pollen lakes currently within the boreal forest or near tree line show relatively high percentages of picea pollen in the alnus zone several striking vegetation changes occurred between ca 10 000 and 7000 yr b p between ca 11 000 and 10 000 yr b p populus balsamifera pollen percentages as great as 30 indicate that this species was present at low elevation sites near walker lake these populations declined abruptly ca 10 000 yr ago and have never regained prominence about 8500 yr b p picea glauca pollen reached 10 15 indicating the arrival of p glauca in or near the study area p glauca populations evidently decreased ca 8000 yr ago when picea pollen percentages and influx fell to low values about 7000 yr b p alnus pollen percentages and influx rose sharply as alder shrubs became established widely picea once more expanded ca 5000 yr ago but these populations were dominated by p mariana rather than p glauca which increased slowly at this time and may still be advancing northward some vegetation changes have been remarkably synchronous over wide areas of interior alaska and probably reflect responses of in situ vegetation to environmental changes but others may reflect the lagged responses of species migrating into new areas

reprint of benthic and planktic community changes at the north siberian margin in response to atlantic water mass variability since last deglacial times abstract the eastward penetration of atlantic derived water adw into the eurasian basin of the arctic ocean was investigated at the western laptev sea continental margin for the time since c 17 6 ka using a high resolution investigation of the lithology geochemistry planktic and benthic foraminifers and ostracods on a sediment core from 270 m water depth major steps in the environmental evolution of the region are recognized in general adw was continuously present in the study area between 17 6 and 15 4 ka adw manifested itself through open water polynyas and associated upwelling events comparison between the laptev sea and northern svalbard shelf using cassidulina neoteretis allows assuming an unmodified subsurface inflow of adw within its northern branch between 15 4 and 13 2 which was strongest after 14 7 ka and in line with the overall climate amelioration a local freshwater event at 13 ka followed by shelf flooding and the establishment of a freshened shelf water mass resulted in an off shelf displacement of adw from the studied site as suggested by the disappearance of c neoteretis between 12 and 7 ka as evidenced by an abundance peak in nonion labradoricum the sea ice marginal zone was located at the site around 12 11 ka but then shifted northward during the early holocene warming enhanced adw inflow since 7 ka correlated with climate cooling and southward retreat of the seasonal drift ice margin the inflow of adw during mid late holocene differed from deglacial times because of the combined influence of northern and eastern adw branches

comparative radiocarbon dating of terrestrial plant macrofossils and aquatic moss from the ice free corridor of western canada in order to assess the reliability of aquatic moss for radiocarbon dating sup 14 c analyses were performed on a stratigraphic series of terrestrial plant macrofossils and samples of drepanocladus crassicostatus from a small hard water lake ph 8 2 in the ice free corridor of alberta all sup 14 c dating was done by using accelerator mass spectrometry mazama ash provided an independent chronological control the aquatic bryophyte samples consistently produced sup 14 c ages significantly older than the terrestrial macrofossils the relation between the radiocarbon dates from the macrofossils and the moss was not linear and age differences ranged from approximately 1400 to 6400 yr the sup 14 c content of d crassicostatus growing in the lake at present was less than 85 modern despite the apparent inability to take up sup 14 c deficient carbon by the direct incorporation of bicarbonate the bryophytes clearly do not provide reliable material sup 14 c dating the sup 14 c deficiency of aquatic mosses may be explained by the generation of sup 14 c deficient co sub 2 through isotopic exchange the formation of co sub 2 from bicarbonate by chemical processes and metabolic co sub 2 production these results demonstrate the potential unreliability of sup 14 c dates from aquatic mosses and raise serious concernsmore about the deglaciation dates from the ice free corridor that were obtained from aquatic drepanocladus less

benthic and planktic community changes at the north siberian margin in response to atlantic water mass variability since last deglacial times the eastward penetration of atlantic derived water adw into the eurasian basin of the arctic ocean was investigated at the western laptev sea continental margin for the time since c 17 6 ka using a high resolution investigation of the lithology geochemistry planktic and benthic foraminifers and ostracods on a sediment core from 270 m water depth major steps in the environmental evolution of the region are recognized in general adw was continuously present in the study area between 17 6 and 15 4 ka adw manifested itself through open water polynyas and associated upwelling events comparison between the laptev sea and northern svalbard shelf using cassidulina neoteretis allows assuming an unmodified subsurface inflow of adw within its northern branch between 15 4 and 13 2 which was strongest after 14 7 ka and in line with the overall climate amelioration a local freshwater event at 13 ka followed by shelf flooding and the establishment of a freshened shelf water mass resulted in an off shelf displacement of adw from the studied site as suggested by the disappearance of c neoteretis between 12 and 7 ka as evidenced by an abundance peak in nonion labradoricum the sea ice marginal zone was located at the site around 12 11 ka but then shifted northward during the early holocene warming enhanced adw inflow since 7 ka correlated with climate cooling and southward retreat of the seasonal drift ice margin the inflow of adw during mid late holocene differed from deglacial times because of the combined influence of northern and eastern adw branches

geomorphic and sedimentary signatures of early holocene deglaciation in high arctic fiords ellesmere island canada implications for deglacial ice dynamics and thermal regime integrated studies of glacial geomorphology sedimentology marine limit elevations and radiocarbon dating in two adjacent fiords on southwestern ellesmere island indicate that early holocene regional deglaciation was characterized by a two step retreat pattern where initial rapid breakup of marine based ice preceded slower terrestrial retreat these data also indicate interfiord variations in early holocene deglacial thermal regime and illustrate the role of fiord topography as a control on glacier retreat in starfish bay deglacial landform sediment associations are preferentially located at fiord side topographic irregularities and record ice proximal glaciomarine sedimentation during stillstands at pinning points abundant fine grained subaquatic outwash indicates that the retreating trunk glacier was characterized by a warm based thermal regime the discrete location of these deposits and associated radiocarbon dates suggest rapid early holocene deglaciation of the outer and middle fiord inter

climatic control of sedimentation in bays and fjords of the northern antarctic peninsula abstract the northern antarctic peninsula is dominated by strong climatic gradients which are locally enhanced by subsidiary orographic and topographic effects these gradients are reflected in the sediments of the bays and fjords of the region the climate of the south shetland islands is relatively warm with high levels of precipitation this leads to a temperate glacial setting in which many glaciers terminate on land and bay waters which are turbid with terrigenous debris sediments which consist of terrigenous muds and sands with a low ice rafted debris ird content are relatively thick 70 m and have now filled in and almost completely mask the underlying basement topography the palmer archipelago is colder than the south shetland islands and is the wettest area of the antarctic it is heavily glaciated and all major glaciers are grounded below sea level only rarely have sediment plumes been seen the sediments which are primarily terrigenous muds and sands with a variable ird component are thin maximum 40 m but are ponding in every available bathymetric depression the pristine nature of the ice visible above sea level indicates that terrigenous debris is entering the bays from below sea level sediment gravity flows are important in redistributing sediment the danco coast lies within the precipitation shadow of the graham land plateau its climate is slightly colder and is the driest in the study area with less than half of the precipitation of the palmer archipelago nevertheless it is also heavily glaciated with few exceptions sediments here are diatomaceous muds and oozes they are very thin and drape across the rugged basement topography rather than ponding in lows sediment gravity flow deposits are rare these observations indicate a lower rate of production of terrigenous sediment here a consequence of the drier climatic setting

high resolution lacustrine record of the late glacial holocene transition in central europe abstract in this paper we present the high resolution record of proxy climatic data in central europe during the final stages of the last deglaciation derived from the annually laminated sediments of lake go ciaz central poland the isotopic palynological and other microfossil data confirm sudden changes of climate at the onset and termination of the younger dryas completed within 150 and 70 years respectively in close agreement with the previous estimates derived from the polar ice cores and marine sediments in the upper yd some amelioration of climate took place already about 600 years before the main yd preboreal transition counting of annual varves in the lake sediments allows a direct estimate of the duration of the younger sdryas in central europe it lasted approximately 1640 years substantially longer than suggested by previous estimates derived from laminated lake sediments and glacial varves but agreeing with the radiocarbon calibration data obtained for barbados corals the calendar ages of the boundaries of the yd 12 920 and 11 280 cal bp are tentatively set

early to middle holocene pollen record from the laptev sea arctic siberia on the basis of pollen and spore assemblages in sediment core from the eastern laptev sea shelf climatic fluctuations and related changes in vegetation on the adjacent land can be recognized for the time from 11 3 cal ka bp to 5 3 cal ka bp around 11 3 cal ka bp climate was warmer than now and southern shrubby tundra was widely distributed on the coast until 10 3 cal ka bp shrub tundra dominated and climate was milder than today the time interval 10 3e9 0 cal ka bp was marked by increased abundance of arboreal plants climate became more humid and warmer in the interval of 9 3e8 0 cal ka bp climate was increasingly humid and warm and forest tundra vegetation occupied more favorable locations in the region the increased abundance of arboreal pollen in the shelf zone can be interpreted as a response to the northward displacement of the treeline after 9 0 cal ka bp from approximately 7 6 to nearly 5 3 cal ka bp southern shrub tundra was renewed and climatic conditions were warmer than now

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

clay mineralogy of late cenozoic sediments in the cesar cores alpha ridge central arctic ocean the clay sized 2 m fraction of the silty and arenaceous lutites constituting cesar cores 14 and 103 alpha ridge central arctic ocean is composed predominantly of mica 40 60 with subequal percentages 10 20 of kaolinite and chlorite and lesser amounts 5 of smectite quartz plagioclase and potassium feldspar calcite and dolomite also occur but only intermittently in the upper 1 2 m dissolution is probably responsible for their absence in other units the silty lutites have a constant mineralogy throughout the 4 5 m long 4 25 ma section whereas some of the arenaceous intervals in the upper 2 1 m have markedly higher amounts of kaolinite calcite dolomite and to a lesser extent smectite the silty lutites were most likely derived from the beaufort sea shelf during nonglacial periods whereas the distinctive components in the sandy layers suggest that they were transported from the canadian arctic islands and greenland by glacial ice the absence of kaolinite peaks in the lower

contrasting glacimarine sedimentary environments of two arctic fiords on disko west greenland abstract two fiords kangerluk and akulliit on the island of disko central west greenland have very different sedimentary regimes caused by differences in the characteristics of their drainage basins and in the exposure of their waters to the open sea of baffin bay their insular location also results in much lower input of water and sediment than in nearby fiords on the mainland of greenland that are affected by glaciers from the greenland ice cap akulliit has a small drainage basin and low input of water and sediment it is directly exposed to the higher energy wave environment of baffin bay as a consequence the mean thickness of holocene glacimarine sediment assessed in acoustic records is less than 6 m in the inner and middle reaches of the fiord mean holocene accumulation 0 4 mm a and about 11 m 1 mm a near the mouth dated core sediment indicates that rates are less than 0 5 mm a in the outer fiord in the last 2 ka the larger more glacier covered drainage basin of kangerluk contributes much larger loads of sediment to a fiord environment protected from the open sea as a result holocene glacimarine sediment is more than 80 m thick in the inner fiord mean holocene accumulation up to 5 mm a decreasing to 10 40 m about 1 mm a in the middle reaches accumulation rates in kangerluk are within the range of arctic fiords including those of baffin island but those in akulliit are near the lower limit the decrease in thickness distally in kangerluk is typical of arctic fiords but the opposite trend in akulliit is probably due to erosion and re distribution of sediment in the higher energy environment there

canadian geomorphology 2000 geomorphology has a distinguished history in canada as old as the country itself initially the science of geomorphology of canada drew on rich british and french scientific traditions but later it developed its own character strongly influenced by the richness and diversity of the canadian landscape the strong imprint of glaciation and the importance of periglacial processes permafrost and sea ice canada is the second largest country in the world its coastline is longer and more varied than that of any other country nearly one third of canada is underlain by permafrost some up to 700 m thick the country s physiography ranges from nearly flat coastal and interior plains to the glacierised mountains of baffin and ellesmere islands british columbia and the yukon its climate and vegetation are equally diverse ranging from the cold semiarid tundra of the high arctic to the temperate rainforest of the pacific coast given this diversity it is not surprising that canada is active in many areas of geomorphic research an incredible spectrum of landforms and geomorphic processes has fostered world class research in canada both by canadians and by scientists from other countries much of this research is field based and empirical rooted in field observation in recent decades however there have been important advances in inductive laboratory and

past environmental and climatic changes related to tree line shifts inferred from fossil diatoms from a lake near the lena river delta siberia changes in diatom assemblages in a sediment core taken from a tundra lake near the lena river delta northeastern siberia reflect climatic and environmental changes throughout the holocene significant limnological changes occurred at the same time as trees advanced into the region c 9100 cal yr bp 8500 radiocarbon yr bp and subsequently retreated c 3800 cal yr bp 3500 radiocarbon yr bp prior to this tree line shift diatom assemblages were dominated by small benthic fragilaria species and diatom inferred alka linity values were high suggesting that climatic conditions were cool and relatively dry and that lake pro ductivity was probably low coincident with tree line advance into the region c 9100 cal yr bp inferred alkalinity decreased and remained low throughout the forested period reflecting soil development and increased organic runoff associated with the shift in catchment vegetation the establishment of a larch forest in the catchment corresponded with an initial period of limnolo

late quaternary glacial and sea level events clements markham inlet northern ellesmere island arctic canada clements markham inlet cuts into the grant land mountains of the northernmost coast of ellesmere island the head of the inlet is bounded on three sides by mountain ice caps that surround lowlands mantled by extensive raised marine deposits fieldwork and mapping of late quaternary sediments were used to determine the limits of past glaciations and the nature of ice retreat from the inlet head forty five radiocarbon dates on driftwood and marine shells provide a deglacial chronology and document related sea level adjustments high level ice marginal meltwater channels and mountain summit erratics indicate that ice once inundated all of clements markham inlet during at least one of these undated glaciations ice flowed unconstrained by the local topography in contrast the most recent glaciation involved confluent trunk glaciers which terminated near the head of the inlet beyond this terminus smaller glaciers entering the sides of the inlet debouched into a glacioisostatically depressed sea full glac

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

holocene sedimentation in glacial tasikutaaq lake baffin island tasikutaaq lake on cumberland peninsula baffin island receives inflow and fine sediment from a 448 km2 drainage basin 21 of which is glacier covered during the summer of 1983 the lake remained essentially isothermal between about 4 and 6 c the suspended sediment concentration of inflow never exceeded 100 mg l 1 with overflow and homopycnal flow dominant surface sediments are clearly laminated although varves are not apparent the sediments are very fine with less than 3 sand in all but the most proximal sites average sedimentation rates between 1976 and 1983 ranged from about 4 mm a 1 to 0 25 mm a 1 down lake from the point of inflow the absence of varves is a function of the low rates of sediment accumulation and the long residence time of the fine sediments in the water column three sediment cores up to 135 cm in length reveal marked changes in sediment characteristics and diatom assemblages through the holocene during the late foxe glaciation it is likely that glacier ice contacted the la

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

a reconstruction of sea surface warming in the northern north atlantic during mis 3 ice rafting events marine isotope stage 3 29 59 kyr bp is characterised by rapid shifts from cold stadial to warm interstadial periods which may be linked to changes in the vigour of the atlantic meridional overturning circulation due to variable freshwater input by melting ice here we present two northern north atlantic multi proxy records of sea surface conditions that indicate warm near sea surface conditions during such ice rafting events we infer near surface temperature from planktonic foraminiferal counts mg ca and oxygen isotopes of left coiling neogloboquadrina pachyderma and from calcite content temperatures increased during ice rafting and rose rapidly to interstadial values after ice rafting ceased this pattern is clearest during heinrich event 4 but also present throughout the other millennial scale ice rafting events it indicates that stadials in the greenland ice cores are concurrent with a near surface warming in the north atlantic which was probably restricted to the summer as winter temperatures must have remained low for sediment laden ice to reach the site as similar warming during ice rafting events is seen regionally in the northern north atlantic it cannot be explained by a rerouting of the north atlantic current rather we attribute it to a shoaling of a warm subsurface water mass that was formed as a result of decreased ventilation of the upper waters and a continued northward subsurface flow of warm water planktonic carbon isotopes support this suggestion showing coincident decreased ventilation during deposition of ice rafted detritus ird the absence of a clear meltwater spike in the 18o records during ird input suggests that besides glacial freshwater sea ice may have been responsible for the ventilation decrease and associated near surface heat built up the proposed scenario is in agreement with modelling studies that require the release of heat trapped below the surface to restart the overturning circulation

paleogeography and geochronology in the russian eastern arctic during the second half of the quaternary abstract during the conclusion of the middle pleistocene continental glaciation was initiated in the western part of northern eurasia while alpine glaciers developed in the mountain ranges in the east small ice caps developed on wrangel and delong islands and most of the chukchi peninsula was glaciated the continental shelves of the laptev and east siberian seas remained ice free and subaerially exposed as indicated by cryogenic and aeolian sediments xerophytic herbaceous palynological assemblages and remains of mammuthus primigenius the initiation of the late pleistocene was marked by a major marine transgression over the eastern part of the arctic ocean shelf correlative with the pelukian transgression of alaska and the sangamonian interglacial isotope stage 5e of north america sea levels exceeded present values by approximately 10 15 m a subsequent regression marked the onset of sartanian glaciation ca 25 000 bp climate warming began ca 14 000 bp reaching an optimum ca 8000 bp and was accompanied by renewed marine transgression climate fluctuations persisted throughout the holocene as indicated by alternating tundra shrub tundra and taiga palynomorph assemblages

environmental assessment from the sedimentary record of high latitude fiords the sedimentary record of fiords at high latitude where global change may be occurring earliest and will be greatest has the potential for assessment of environmental change at both low resolution the scale of millennia and high resolution decadal to less than daily unlike the lacustrine record which has been used very successfully in these studies the sedimentary processes and thus the sedimentary deposits of fiords differ 1 in the role of salt water in inhibiting mixing and promoting flocculation and through the role of sea ice 2 in the exchange of mass and energy with the much larger ocean beyond and 3 in the role of benthic biota in the sedimentary environment the work reviewed in this paper shows that fiord sediments are being used to assess sedimentary and oceanic processes as well as glacial periglacial and geomorphic history and that they are important proxies for long term climate and hydrology recommendations for advancing this work include long term monitoring of conditions in fiords and their drainage basins so that the transfer relations can be more solidly constructed from the proxy of fiord sediment integration of results from fiords in opposite polar latitudes and among proxies especially from lacustrine and ice core records will produce valuable insights assessment of the range of conditions in fiords from the most polar to temperate regions is important to building models of their processes and understanding of the paleoenvironmental signals that can be interpreted from each type

analysis of the atlantic meridional mode using linear inverse modeling seasonality and regional influences abstractpredictability and variability of the tropical atlantic meridional mode amm is investigated using linear inverse modeling lim analysis of the lim using an energy norm identifies two optimal structures that experience some transient growth one related to el nino southern oscillation enso and the other to the atlantic multidecadal oscillation amo amm patterns analysis of the lim using an amm norm identifies an amm optimal with similar structure to the second energy optima opt2 both the amm optimal and opt2 exhibit two bands of sst anomalies in the mid to high latitude atlantic the amm optimal also contains some elements of the first energy optimal enso indicating that the lim captures the well known relationship between enso and the amm seasonal correlations of lim predictions with the observed amm show enhanced amm predictability during boreal spring and for long lead around 11 15 months forecasts initialized around september regional lims were constructed to determine the

atlantic sst gradient and the influence of enso 1 the relationship between the boreal winter el nino sst anomaly and boreal spring tropical atlantic sst gradient north atlantic minus south atlantic is investigated using a long detrended sst record for both el nino and la nina concordant cases same sign for nino3 index and atlantic sst gradient slightly dominate over discordant ones reflecting the fact that the nino3 index correlates more strongly with the north atlantic than the south atlantic sst anomaly the ratio of the numbers of concordant and discordant cases is 4 3 overall indicating strong non enso influences on the atlantic sst gradient the composite of the concordant cases shows an sst anomaly in the north atlantic with the same sign as nino3 and an opposite signed anomaly off the southwest coast of africa resembling benguela nino that of the discordant cases is dominated by a pre existing sst anomaly with the same sign as nino3 in the south central south atlantic

continental slope sedimentation adjacent to an ice margin iii the upper labrador slope abstract the upper labrador slope is the key area for sediment transfer from the northeastern margin of the pleistocene laurentide ice sheets lis to the deep basin it is subdivided from north to south into 8 sectors based on relief differences and echo character on 750 line km of continuous sleeve gun and 3 5 khz seismic profiles high to moderate relief sectors 2 and 4 and in part 6 and 8 are seismically transparent and well stratified with continuous individual high amplitude reflections and deep penetration low relief sectors 1 3 5 and 7 show strong bottom reflections and with the exception of sector 1 low seismic penetration poor stratification and low amplitude if any subbottom reflections the lateral distribution of these alternating high to moderate and low relief sectors reflects fundamental differences in the sediment transfer mechanisms through outlets from the lis onto the slope low relief slope sectors represent debrite and turbidite slopes and are located in front of ice outlets on the slope and adjacent regions to the north they originate from mass wasting on the upper slope of glacial detritus with a significant coarse component originally delivered as englacial or subglacial material and deposited in end moraines or as bedload by subglacial or supraglacial rivers high to moderate relief sectors originate from fall out of suspended sediment from turbid surface plumes tsp and preferentially occur off the southern half of outlets and south of major outlets as exemplified by sector 2 south of the hudson strait outlet this asymmetry is caused by the south flowing labrador current which entrains the buoyantly rising turbid meltwater plumes at the glacier front the present high relief topography which shows a dendritic pattern of upslope canyon branching is the result of retrograde headward canyon erosion by mass wasting processes of an originally much smoother mud blanket surface the sediment is remobilized by slumping and entrained in debris flows and turbidity currents the occurrence of tsp deposits on the high to moderate relief upper slope sectors requires a summer sea surface not frozen over during major parts of the pleistocene including glacial maxima tps deposition on the upper slope ice rafting and a plethora of ice margin depositional phenomena many of which give rise to mass wasting and mass flow phenomena are the main features that make high latitude continental slopes adjacent to continental ice sheets different from their lower latitude counterparts

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

a model for sedimentation by tidewater glaciers sampling of sediment from the fjord floor in front of tidewater glaciers in glacier bay alaska has provided information about processes in this restricted glacimarine dreimanis 1979 setting sediment sampling in conjunction with oceanographic and glacial dynamics data has also enabled the discrimination of sediment types and their facies associations deposits are strongly controlled by sea water characteristics position and sediment discharge of melt water streams iceberg calving and rate of glacierfront retreat five distinct facies associations have been found to reflect glacier fjord regimes the facies associations and ice fjord conditions responsible for them form the basis for constructing a preliminary model for glacimarine sedimentation by tidewater glaciers the model can be used to predict i rapid retreat of an actively calving ice front ii slow retreat or stabilization of a calving ice front at a channel constriction iii stabilization of a melting very rarely calving ice front when the glacier base is near tidewater elevation and iv large outwash delta progradation into a fjord when the ice front retreats onto land this model can be used to interpret facies associations found in a stratigraphic record

the last glaciation of marvin peninsula northern ellesmere island high arctic canada the limit of the last glaciation on marvin peninsula northernmost ellesmere island is recorded by extensive ice marginal landforms and early holocene glaciomarine sediments while glaciers occupied most valleys on the peninsula other areas remained ice free as did most of the adjacent fiords beyond the ice limit sparse erratics and degraded meltwater channels within weathered bedrock are evidence of older more extensive glaciation s shorelines and marine shells 50 m above the limit of the holocene sea along the north coast relate to these older glacial events thirty four new radiocarbon dates provide a chronology of ice buildup and retreat glaciers reached their limit after 23 ka and locally as late as 11 ka this was achieved by both expansion of existing glaciers and accumulation on plateau and lowland sites which are presently ice free late wisconsinan climate was characterized by cold and extreme aridity five dates ranging from 11 to 31 ka bp on subfossil bryophytes suggest that ice free

sedimentology of an ice contact glaciomarine fan complex nastapoka hills eastern hudson bay northern quebec abstract emerged holocene coalescing glaciomarine fans are exposed along the nastapoka hills eastern hudson bay the fans form part of a regional stratified drift belt associated with terrestrial and submarine frontal moraines and other grounding lines deposits these thick extensive and in many cases coalescent sediment bodies were deposited during a stillstand of the quebec labrador sector qls of the laurentide ice sheet lis that pinned on the hills during eastward retreat from hudson bay the fans are composed of basal interbedded and interlaminated sand silt and silty clay facies association i fa i deposited by suspension settling from overflow plumes sediment gravity flows and ice rafting towards the ice contact zone fa i interfingers with diamict layers fa ii deposited by gravity flows and ice rafting these two sedimentary units are overlain by interbedded sand and gravel fa iii formed by reworking during subsequent emergence parts of fa i and fa ii were remobilized by submarine gravity flows which prevailed long after ice retreat the sedimentology of the nastapoka hills provides information on the processes operating near the grounding line of a temperate ice sheet reaching tidewater

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

south atlantic variability arising from air sea coupling local mechanisms and tropical subtropical interactions abstract interannual variability in the southern and equatorial atlantic is investigated using an atmospheric general circulation model agcm coupled to a slab ocean model som in the atlantic in order to isolate features of air sea interactions particular to this basin simulated covariability between sea surface temperatures ssts and atmosphere is very similar to the observed non enso related covariations in both spatial structures and time scales the leading simulated empirical coupled mode resembles the zonal mode in the tropical atlantic despite the lack of ocean dynamics and is associated with baroclinic atmospheric anomalies in the tropics and a rossby wave train extending to the extratropics suggesting an atmospheric response to tropical sst forcing the second non enso mode is the subtropical dipole in the sst with a mainly equivalent barotropic atmospheric anomaly centered on the subtropical high and associated with a midlatitude wave train consistent with atmospheric forcing of the sub

weichselian sediments at foss eikeland jaeren southwest norway sea level changes and glaciation history the jaeren area in southwestern norway has experienced great changes in sea levels and sedimentary environments during the weichselian and some of these changes are recorded at foss eikeland four diamictons interbedded with glaciomarine and glaciofluvial sediments are exposed in a large gravel pit situated above the post glacial marine limit the interpretation of these sediments has implications for the history of both the inland ice and the norwegian channel ice stream during a middle weichselian interstadial a large glaciofluvial delta prograded into a shallow marine environment along the coast of jaeren a minor glacial advance deposited a gravelly diamicton and a glaciomarine diamicton was deposited during a following marine transgression this subsequently was reworked by grounded ice forming a well defined boulder pavement the boulder pavement is followed by glaciomarine clay with a lower laminated part and an upper part of sandy clay the laminated clay probably was deposited under sea ice whereas more open glaciomarine conditions prevailed during deposition of the upper part the clay is intersected by clastic dykes protruding from the overlying late weichselian till preconsolidation values from the marine clay suggest an ice thickness of at least 500 m during the last glacial phase the large variations in sea level probably are a combined effect of eustasy and glacio isostatic changes caused by an inland ice sheet and an ice stream in the norwegian channel copyright 2002 john wiley sons ltd

glacial geology and quaternary marine stratigraphy of the robeson channel area northeastern ellesmere island northwest territories glacial and marine deposits associated with two phases of glaciation are exposed along a 60 km corridor on ellesmere island that borders robeson channel the oldest sediments tentatively dated at 70 000 bp were deposited during a major advance of the northwest greenland ice sheet across robeson channel during subsequent retreat of this ice mass glaciomarine sediments containing a high arctic macro and microfauna were deposited in the isostatic downwarp on ellesmere island this marine unit was radiocarbon dated at 31 300 900 and 32 000 bp mean aile ile ratios are 0 218 0 03 for the free fraction and 0 063 0 011 for the total acid hydrolysate the last ice advance late wisconsin early holocene did not extend into the field area from either interior ellesmere island or northwest greenland the ice marginal sea transgressed to the marine limit 116 m and overlapped the deposits of the previous maximum greenland advance local plateau ice caps did however spill over into one major valle

composition and flux of holocene sediments on the eastern laptev sea shelf arctic siberia a 467 cm long core from the inner shelf of the eastern laptev sea provides a depositional history since 9400 cal yr b p the history involves temporal changes in the fluvial runoff as well as postglacial sea level rise and southward retreat of the coastline although the core contains marine fossils back to 8900 cal yr b p abundant pf ant debris in a sandy facies low in the core shows that a river influenced the study site until similar to 8100 cal yr b p as sea level rose and the distance to the coast increased this riverine influence diminished gradually and the sediment type changed by 7400 cal yr b p from sandy silt to clayey silt although total sediment input decreased in a step like fashion from 7600 to 4000 cal yr b p this interval had the highest average sedimentation rates and the greatest fluxes in most sedimentary components while this maximum probably resulted from middle holocene climate warming the low input of sand to the site after 7400 cal yr b p probably resulted from further southward retreat of the coastline and river mouth since about 4000 cat yr b p total sediment flux has remained rather constant in this part of the laptev sea shelf due to a gradual stabilization of the depositional regime after completion of the holocene sea level rise

late quaternary vegetational change in the kotzebue sound area northwestern alaska abstract two sediment cores from kaiyak and squirrel lakes in northwestern alaska yielded pollen records that date to ca 39 000 and 27 000 yr b p respectively between 39 000 and 14 000 yr b p the vegetation around these lakes was dominated by gramineae and cyperaceae with some salix and possibly betula nana glandulosa forming a local shrub component of the vegetation betula pollen percentages increased about 14 000 yr b p indicating the presence of a birchdominated shrub tundra alnus pollen appeared at both sites between 9000 and 8000yr b p and picea pollen mostly p mariana arrived at squirrel lake about 5000 yr b p the current foresttundra mosaic around squirrel lake was established at this time whereas shrub tundra existed near kaiyak lake throughout the holocene when compared to other pollen records from north western north america these cores 1 represent a meadow component of lowland beringian tundra between 39 000 and 14 000 yr b p 2 demonstrate an early holocene arrival of alnus in northwestern alaska that predates most other alnus horizons in northern alaska or northwestern canada and 3 show an east to west migration of picea across northern alaska from 9000 to 5000 yr b p

the lateglacial and postglacial vegetation history of the northwestern limits of beringia based on pollen stomate and tree stump evidence abstract in order to reconstruct the late and postglacial vegetation history of the northwestern edge of beringia a sediment core was collected from a lake north of the present treeline along the lower lena river of northeastern siberia and analysed for fossil pollen and stomates in addition fossil tree stumps were collected in the vicinity of the lake eight radiocarbon dates indicate that the lake sediment record spans at least the past 12 300 yr bp the early vegetation at this site was dominated by herb and shrub tundra possible evidence of younger dryas cooling consisting of a decrease in shrub birch and increases in grass and herbaceous plants occurs between 11 000 and 10 000 yr bp forests dominated by larix dahurica and including picea obovata extended northward to the site between 8500 and 3500 yr bp there is an agreement between the pollen stomate and tree stump evidence for this advance the modern vegetation of shrub tundra was established after 3500 yr bp

terrestrial and aquatic palynomorphs in holocene sediments from the chukchi alaskan margin western arctic ocean implications for the history of marine circulation and climatic environments two sediment cores from the chukchi sea margin north of alaska were analyzed for palynological composition including terrestrial and aquatic palynomorphs based on 13 radiocarbon ages the investig

what determines the position and intensity of the south atlantic anticyclone in austral winter an agcm study abstract the south atlantic anticyclone is a major feature of the austral winter climatology an atmospheric general circulation model agcm is used to study the dynamics of the south atlantic anticyclone by means of control simulations and experiments to investigate sensitivity to prescribed orography sea surface temperatures and soil wetness the south atlantic anticyclone in the first control simulation is unrealistically zonally elongated and centered too far west errors typical of coupled ocean atmosphere gcms results of the sensitivity experiments suggest that these deficiencies are associated with another family of systematic model errors the overprediction of convection over the tropical land surfaces particularly over eastern tropical africa and india and the concurrent large scale westward shift in the divergence center at upper levels and the convergence center at lower levels the results also confirm the important role of south american and african orography in localizing the south atl

late quaternary lacustrine pollen records from southwestern beringia sediment cores from three lakes in the upper kolyma region northeast russia provide the first well dated continuous record of late quaternary vegetation change from far southwestern beringia the oldest pollen zone tentatively assigned to the karginsk mid wisconsinan interstade indicates an artemisia shrub tundra with pinus pumila betula and alnus at mid to low elevations with the onset of the sartan late wisconsinan stade pinus disappeared probably indicating severely cold dry winters and cool summers as conditions deteriorated further an artemisia gramineae tundra developed selaginella rupestris and minor herb taxa indicate the presence of poor soils and disturbed ground this herb tundra was replaced by a short lived 1000 yr betula alnus shrub tundra followed by the rapid establishment of a larix dahurica forest with a betula exilis ericales lichen understory populus suaveolens and chosenia may have formed limited hardwood gallery forests at this time modern vegetation associations probably developed during the early holocene with the arrival of pinus pumila ca 9000 yr b p this shrub became important in the forest understory and with b exilis formed a belt of shrub tundra beyond altitudinal treeline comparison of the upper kolyma and alaskan pollen records indicates that important differences in vegetation types and timing of vegetation change occurred across beringia during the late quaternary

provenance of sediment in the labrador current a record of hinterland glaciation over the past 125 ka the labrador current flows southward along the continental margin off eastern canada and is the principal source of sediment to the outer continental margin areas where ice sheets did not cross the continental shelf we present multi proxy mineralogical and geochemical records based principally on x ray diffraction and x ray fluorescence for core 2011031 059 from northern flemish cap to determine changes in supply and hence to reconstruct provenance evolution during the last glacial cycle the calcite to dolomite ratios in heinrich layers ranged from 2 to 4 suggesting carbonate layers derived from hudson strait as early as marine isotope stage mis 5a d mineral abundance shows three time dependent predominant sediment sources other than in heinrich layers i baffin bay shelves and adjacent land in mis 5 and 1 with high ca sr kaolinite and feldspars and low clay minerals and calcite dolomite ratios ii labrador in mis 3 with low clays and grey color and iii north east newfoundland shelf in mis 2 and 4 with higher concentrations of clay minerals red sandstones and transition elements these results allow a reconstruction of principal ice streams supplying the north west atlantic over the last full glacial cycle

glaciation and the evolution of the canadian high arctic landscape the canadian arctic islands represent a tertiary fluvial landscape developed on a contiguous landmass subsequently fractured by block faulting nonetheless some theoretical models invoke pervasive high latitude ice sheets and continue to misattribute the faulted landscape to glacially scoured river valleys quaternary fieldwork on northern ellesmere island suggests that these models are inappropriate for high latitude ice sheets and should be abandoned if there was ever a regional ice sheet over arctic canada it likely occurred on a prefaulted contiguous landmass that had a more temperate climate than at present possibly during the late tertiary after block faulting the marine channels permanently prevented the ice from inundating the landscape it once crossed tectonics and not climate have led to a fundamental change in glacial style this block faulting also may have played a role in terminating the late tertiary boreal forest to 80 n by establishing cold marine channels that diminished the continentality of the once contiguous landmass for a thorough understanding of the canadian arctic landscape future research should determine the continuity between the tertiary and quaternary paleoenvironments the unknown ages of the fiords and interisland channels are of primary importance

holocene treeline history and climate change across northern eurasia radiocarbon dated macrofossils are used to document holocene treeline history across northern russia including siberia boreal forest development in this region commenced by 10 000 yr b p over most of russia forest advanced to or near the current arctic coastline between 9000 and 7000 yr b p and retreated to its present position by between 4000 and 3000 yr b p forest establishment and retreat was roughly synchronous across most of northern russia treeline advance on the kola peninsula however appears to have occurred later than in other regions during the period of maximum forest extension the mean july temperatures along the northern coastline of russia may have been 2 5 to 7 0 c warmer than modern the development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions including heightened summer insolation the demise of eurasian ice sheets reduced sea ice cover greater continentality with eustatically lower sea level and extreme arctic penetration of warm north atlantic waters the late holocene retreat of eurasian treeline coincides with declining summer insolation cooling arctic waters and neoglaciation

marine controls on modern sedimentation on the antarctic continental shelf abstract the extreme depth and rugged topography of the antarctic continental shelf its seasonal to perennial sea ice cover and its large slowly calving ice shelves exert major influences on the adjacent ocean and sediments regionally variable exchanges of heat and momentum between the atmosphere and ocean result in net off shelf transport of sea ice and net downward salt flux this buoyancy partitioning drives a vertical convection that is followed by westward and northward flows of ventilated dense water across the continental shelves shelf waters meet mix with and modify circumpolar deep water at a dynamic slope front near the continental shelf break locally or periodically forming antarctic bottom water nutrient rich deep water upwells along this front regionally intruding onto the continental shelf in long thermally attenuated filaments these intrusions are frequently linked to mass balance processes at the base of ice tongues and ice shelves melting freezing and tidal currents beneath glacial ice are related to the larger scale circulation and to the fate of basal debris in the ice sheet the ocean circulation near ice fronts and decadal variability in ice front positions may account for several features of the sediment record time series 1 yr current measurements in the ross and weddell seas have revealed moderate to strong currents that are seasonally variable vertically coherent and dominated by the diurnal tide and longer term events few long term current measurements exist in the shelf and slope bottom boundary layers that are most important to sediment deposition and erosion icebergs may frequent certain routes e g in association with currents and fronts near the edge of the continental shelf and are capable of scouring and resuspending sediments down to shelf break depths sea ice plays a role in shelf sedimentation by rafting eolian and bottom debris away from the nearshore regions in addition generally offshore winds produce numerous leads and polynyas along the coastline and within the sea ice fields higher biological productivity in these polynyas may be linked to higher local sedimentation rates biogenic marine sediments apparently comprise a major percentage of the regionally variable modern shelf deposits despite the impressive glacial setting and polar environment

direct land sea correlations in the last interglacial complex isotopic and pollen analyses of an eastern atlantic core permit the first direct correlation of substages 5e and 5c of the marine climatostratigraphical system with the eemian and st germain i respectively of the classical grande pile pollen sequence north east france the vegetational sequences during the warm intervals of the last interglacial complex 125 000 75 000 yr bp indicate that climatic deterioration occurred late on the mid european continent after the initiation of glaciation over continental masses in high latitudes

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime