last deglacial sea surface temperature evolution in the southeast pacific compared to climate changes on the south american continent abstract applying the alkenone method we estimated sea surface temperatures ssts for the past 33 kyr in two marine sediment cores recovered from the continental slope off mid latitude chile the sst record shows an increase of 6 7 c from the last ice age lia to the holocene climatic optimum while the temperature contrast between lia and modern temperatures is only about 3 4 c the timing and magnitude of the last deglacial warming in the ocean correspond to those observed in south american continental records according to our sst record the existence of a younger dryas equivalent cooling in the southeast pacific is much more uncertain than for the continental climate changes a warming step of about 2 5 c observed between 8 and 7 5 cal kyr bp may have been linked to the early to mid holocene climatic transition 8 2 7 8 cal kyr bp also described from equatorial africa and antarctica in principal variations in the latitudinal position of the southern pacific westerlies are considered to be responsible for sst changes in the peru chile current off mid latitude chile

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 last glaciation in central magellan strait southernmost chile abstract glacial landforms and drift stratigraphy in central magellan strait southernmost chile document repeated fluctuations during the last glacial cycle of outlet lobes from an ice cap centered over the southern andes the lobes developed comparatively low gradient profiles because of low basal shear stresses over soft deformable beds and this made them sensitive to even small scale changes in the mass balance such low profiles and rapid calving in deep proglacial lakes during deglaciation may have made the magellan ice lobe particularly responsive to climatic fluctuations during the last glacial cycle and to advance and retreat over considerable distances study of the glacial landforms and drift stratigraphy has led to the identification of at least five glacier advances to limits at and south of the segunda angostura fragments of mollusc shells contained in basal till indicate marine incursions between some advances thus documenting extensive deglaciation a partial chronology based on amino acid studies and radiocarbon dating suggests that five of these advances occurred during the last glacial cycle the most extensive advances may have culminated during substages of marine isotope stage 5 substage 5b or 5d and or during stage 4 slightly less extensive advances occurred between ca 28 000 and 14 000 yr b p

late quaternary vegetation and climate of southern tierra del fuego vegetation and climate over approximately the past 13 000 yr are reconstructed from fossil pollen in a 9 4 m mire section at caleta robalo on beagle channel isla navarino 54 56 s 67 38 w southern tierra del fuego fifty surface samples reflecting modern pollen dispersal serve to interpret the record chronologically controlled by nine radiocarbon dates fossil pollen assemblages are empetrum gramineae gunnera tubuliflorae zone 3b 13 000 11 850 yr b p gramineae empetrum assorted minor taxa zone 3a 11 850 10 000 yr b p nothofagus gramineae tubuliflorae polypodiaceae zone 2 10 000 5000 yr b p nothofagus empetrum zone 1b 5000 3000 yr b p and empetrum nothofagus zone 1a 3000 0 yr b p assemblages show tundra under a cold dry climate zone 3 followed by open woodland zone 2 as conditions became warmer and less dry and later with greater humidity and lower temperatures by closed forest and the spread of mires zone 1 comparisons drawn with records from antarctica new zealand tasmania and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar southern hemisphere the influences of continental and maritime antarctic air masses were apparently considerable in tierra del fuego during cold late glacial time whereas holocene climate was largely regulated by interplay between maritime polar and maritime tropical air

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

three late quaternary pollen diagrams from southern patagonia and their palaeoecological implications abstract diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late glacial and holocene vegetation and palaeoclimate in southern patagonia sites are mires located along the estrecho de magallanes at punta arenas 53 09 s 70 57 w and puerto del hambre 53 36 s 70 55 w and an intermittent lake some 300 km to the north at torres del paine 50 59 s 72 40 w chronostratigraphy is controlled by 20 radiocarbon dates the oldest site puerto del hambre covering close to 16 000 years charcoal from the sites and carbonate torres del paine as well as tephra layers and an instance of marine incursion puerto del hambre supply additional data of interpretive value accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities late glacial vegetation during deglaciation consisted mostly of tundra dominated by communities of empetrum acaena gunnera and tubuliflorae compositae under a relatively cold dry climate nothofagus although present in numbers initially at puerto del hambre did not expand until the close of the late glacial at punta arenas expansion of nothofagus was episodic occurring during apparent warmer intervals of the last three millennia of steppe tundra holocene vegetation is depicted at first as a patchwork of nothofagus woodland and steppe subject to climate of relative warmth and limited moisture except at torres del paine where moisture levels were apparently higher than at sites to the south closed nothofagus forest communities subsequently are best developed in the late holocene under a climate with generally cooler wetter parameters fire believed to be caused mostly by palaeoindians has had an important role in shaping vegetation sequences in the holocene formidable however in the development of vegetation are the latitudinal displacements variable intensities of atmospheric conditions caused by shifting storm tracks of the southern westerlies

full glacial late glacial palaeoclimate of the southern andes evidence from pollen beetle and glacial records palaeoecological studies carried out in the chilean lake district and chilotan archipelago 41 43 s record full glacial and late glacial pollen assemblages beginning just after 21000 and beetle assemblages after 18000 both sets extending until 10000 14c yr bp pollen records indicate that subantarctic parkland the vegetation of the early millennia of record changed after about 14000 yr bp to become open woodland and later north patagonian evergreen forest assemblages of plants and beetles responding more or less in unison to a strong rise in temperature 6 c behaved in accord at around 14000 until 13000 12500 yr bp the beetle fauna displaying a marked increase in obligate forest types during full glacial conditions 17400 16100 and 15300 and 14400 yr bp and in the late glacial interval after about 13000 yr bp however climate evidently coerced populations dissimilarly the pollen sequence showing an increase in plant taxa indicative of colder climate whereas the beetle fauna underwent little or no variation contrasting climate modes implied by plants and beetles may be attributed to differential responses to apparent low order temperature changes 2 3 c

glacier modeling and the climate of patagonia during the last glacial maximum ice cap modeling constrained by empirical studies provides an effective way of reconstructing past climates the former patagonian ice sheet is in a climatically significant location since it lies athwart the southern hemisphere westerlies and responds to the latitudinal migration of climatic belts during glacial cycles a numerical model of the patagonian ice cap for the last glacial maximum lgm is developed which is time dependent and driven by changing the mass balance altitude relationship it relies on a vertically integrated continuity model of ice mass solved over a finite difference grid the model is relatively insensitive to ice flow parameters but highly sensitive to mass balance the climatic input is adjusted to produce the best fit with the known limits of the ice cap at the lgm the ice cap extends 1800 km along the andes and has a volume of 440 000 km3 during the lgm the equilibrium line altitude ela was lower than at present by at least 560 m near latitude 40 s 160 m near latitude 50 s and 360 m near latitude 56 s the latitudinal variation in ela depression can be explained by an overall fall in temperature of about 3 0 c and the northward migration of precipitation belts by about 5 latitude annual precipitation totals may have decreased by about 0 7 m at latitude 50 s and increased by about 0 7 m at latitude 40 s the ela rises steeply by up to 4 m per kilometer from west to east as the westerlies cross the andes and this prevents ice growth to the east the limited decrease in temperature during the lgm could be related to the modest migration of the antarctic convergence between south america and the antarctic peninsula

millennial band climate spectrum resolved and linked to centennial scale solar cycles abstract spectral comparison of the hulu cave grip and gisp2 18o records suggests that the single dominant period centered on 1470 yr in the gisp2 spectrum the so called 1500 yr cycle is an artifact of the age model the 230th dated hulu cave record indicates a millennial band spectrum with a weak spectral peak near this period flanked by two stronger peaks centered on 1667 and 1190 yr similar to the grip 18o record all three millennial band cycles may derive from heterodynes of centennial band solar cycles as observed in the holocene record of atmospheric 14c production this suggests a link between centennial scale solar variability and abrupt climate change at the millennial time scale

glacial and tectonic control on fjord morphology and sediment deposition in the magellan region 53 s chile in the patagonian andes erosion by temperate pleistocene glaciers has produced a deeply incised fjord system in which glacial and non glacial sedimentswere deposited since the late glacial glacier retreat so far fjord bathymetry and structures in the sediment infill were widely unexplored here we report the results of an investigation of morphology and sediment characteristics of a 250 km long fjord transect across the southernmost andes 53 s using multibeam and parametric echosounder data and sediment cores subaquatic morphology reveals continuity of on land tectonic lineaments mapped using field and remote sensing data our results indicate that glacial erosion and fjord orientation are strongly controlled by three major strike slip fault zones furthermore erosion is partly controlled by older and or reactivated fracture zones as well as by differential resistance of the basement units to denudation basement morphology is regionally superimposed by late glacial and holocene subaquatic moraines which are associated to known glacier advances the moraines preferentially occur on basement highs which constrained the glacier flows this suggests that the extent of glacier advances was also controlled by basement morphology subaquatic mass flows fluid vent sites as well as distinct late glacial and holocene sediment infills have furthermore modified fjord bathymetry in the western fjord system close to the strait of magellan subaquatic terraces occur in 20 to 30 m water depth providing an important tag for proglacial lake level during the late glacial

glacial cirque formation in northern scandinavia passglaciaren is a small cirque glacier in the kebnekaise massif northern sweden it is frozen to its bed over more than 70 of its area and under present climatic conditions has little effect on cirque formation more favourable conditions for cirque glacier erosion during the holocene are of short duration assuming similar conditions during previous interglacials it is suggested that forms such as the passglaciaren cirque developed mainly during the initial phases of glacials when they were part of networks of large valley glaciers or of a small warm based mountain centred ice sheet passglaciaren has been examined in order to evaluate its erosive capacity and its association with the subglacial cirque morphology the methods used are radar surveys and direct ice temperature measurements erosion is restricted to a small section of the glacier bed at present resulting in only partial deepening of the cirque and erosion of the backwall in cold arid regions with extensive permafrost small cirque glaciers are largely frozen to the bed and therefore cannot contribute significantly to cirque formation in such regions glacial erosion by larger temperate glaciers is more likely to be the major cause of cirque excavation

dynamics of former ice lobes of the southernmost patagonian ice sheet based on a glacial landsystems approach reconstructions of former ice masses from glacial geomorphology help to constrain the nature and timing of glaciation in relation to climatic forcing this paper presents a new reconstruction of the glacial history of five ice lobes in southernmost south america the bahia inutil san sebastian magellan otway skyring and rio gallegos ice lobes we use previous geomorphological mapping of glacial landforms to reconstruct former glacial limits and proglacial lakes demarcate flow sets from the distribution of glacial lineations and evaluate glacial landsystem signatures and their palaeoglaciological implications evidence suggests that the ice lobes predominantly reflect active temperate glacial landsystems which may have switched to polythermal systems when periods of cold based ice developed ephemerally this complex landsystem signature implies that the ice lobes were sensitive to regional climate variability with active re advances during overall retreat of the ice margins there is also evidence for periods of fast ice flow and possible surge like activity in the region followed by the rapid retreat or even collapse of some of the ice lobes in association with proglacial lakes constraining our new reconstruction with published chronological information suggests that at least some of the ice lobes advanced before the global last glacial maximum glgm ca 26 5 19 ka during the last glacial cycle our new reconstruction demonstrates a more complex picture of ice dynamics than has previously been portrayed and one in which the advance and retreat of the ice lobes was likely to have been primarily driven by changes in climate as such ice advances before the glgm in the southernmost part of the patagonian ice sheet are likely to indicate a wider climatic forcing at this time

the sedimentary and structural evolution of a recent push moraine complex holmstrombreen spitsbergen abstract the glacier holmstrombreen in spitsbergen surged into the ice contact scarp of a proglacial outwash sequence at some time during its neoglacial maximum the outwash sediments were pushed along a decollement to produce a moraine in which deformation extended for 1 5 km beyond the furthest extent of the glacier front the style of folding and faulting and the nature of the pre syn and post tectonic sedimentary sequence across the whole push moraine is described from a continuously exposed section of the push moraine which extends from its proximal to distal extremities the precise extent of incremental compressive shortening of the pushed sediments of some 900 m is established the depth to the underlying decollement is inferred to be an average of about 30 m indicating that stresses and movement were transmitted through a thin nappe with an aspect ratio of about 1 in 30 it is suggested that this nappe was frozen and that an artesian water pressure head of 60 m immediately beneath it reduced friction along its base to a very low value it is calculated that a glacially generated force of about 1 5 10 7 kn was responsible for pushing the sediment nappe the nature of the glacially controlled groundwater flow system rather than the magnitude of longitudinal forces generated by the glacier is the principle determinant of large scale push moraine characteristics the changing ice topography produced by the pushing event during the surge and in the post surge decay had a major influence on the evolution of the meltwater drainage system and the style of fluvial sedimentation the structure sedimentary architecture and evolution of the whole glacitectonic fluvial complex can best be understood by considering the impact of the surge on a complete outwash system it is suggested that the setting and processes which produced the holmstrombreen push moraine could account for many broad multi ridge and fold push moraines which formed proglacially and that the thickness of original sediments above the decollement can be a guide to the thickness of contemporary permafrost

characteristics of the bed of the lower columbia glacier alaska an unplanned but unique experiment has given an in situ measurement of the strength of deforming subglacial till under the central region of a major valley glacier we report on both planned and unplanned borehole investigations of the subglacial shear zone of columbia glacier southeast alaska basal samples coring and down hole water samples show that the fiord filling lower reach of the glacier is underlain by a thin 7 cm veneer of rock debris fluidized debris intruded at least a meter up the borehole at a higher site 13 km from the terminus and above the fiord probing samples and the bending of a drill stem which was stuck in the basal zone for 5 days showed that the basal till layer was 65 cm thick horizontal velocity of the till decreased monotonically downward from the ice till interface till at the interface moved with the ice velocity plastic deformation of the drill stem gave an estimate of the strength of the basal till which is normally described as a viscoplastic material if the till is assumed to be either perfectly plastic or newtonian viscous then the strengths are as follows the plastic yield strength of the till was 5 5 10 3 pa 0 055 bar with an upper bound of 1 3 10 4 pa 0 13 bar while the nominal viscosity was of the order of 2 10 8 pa s 2 10 9 poise with an upper bound of 5 10 8 pa s in neither case is the till strength enough to supply the bulk basal shear stress to resist the glacier flow

winter currents and hydrographic conditions on the northern central bering sea shelf current observations obtained from the northern bering shelf region in winter 1984 1985 indicate that midwinter circulation patterns differed from those during the rest of the year annual mean circulation in this region is dominated by vigorous northward currents from 10 cm s in shpanberg strait to more than 50 cm s in bering strait these northward currents are accompanied by a weak northwestward coastal flow south of st lawrence island in february april 1985 however flow was weakly 0 5 cm s southward through shpanberg strait and southeastward south of st lawrence island while remaining northward through anadyr and bering straits comparison with current data obtained from previous years suggests that midwinter reversal of flow in shpanberg strait is a recurrent winter feature it generally occurs at about the same time that the winter ice cover undergoes its major advance and it is associated with strong northerly winds northward flow through anadyr strait persists conversely through the winter and is the northward extension of a western intensified northward flow over the bering shelf its source is bering sea water farther south rather than water from the northern central shelf the resultant trapping of shelf water on the northern central shelf coupled with intensive regional ice formation during the same period as the flow reversal led in 1985 to significant about 1 5 brine enrichment this salinity increase agrees qualitatively with historical data which suggest that the northern central bering shelf is the site both of sluggish winter circulation and of elevated salinities due to brine enrichment from ice formation

late glacial ice advances in the strait of magellan southern chile abstract during the last glacial cycle low gradient glaciers repeatedly drained north eastward into the strait of magellan and dammed extensive proglacial lakes in the central section of the strait this paper focuses on the two most recent glacial advances in the strait culminating over 150 and 80 km from the present ice limits the timing of the first of the two advances has up to now been ambiguous and depended on the interpretation of anomously older dates of 16 590 15 800 yr bp for deglaciation at puerto del hambre here we show there is evidence from seismic data and truncated shorelines that the puerto del hambre basin has been tectonically displaced and that the dates do not represent minimums for deglaciation several other dates show that the advance occurred sometime before 14 260 yr bp the timing of the second advance has been investigated using a refined tephrochronology for the region which has also enabled a palaeoshoreline and glaciolacustrine sediments to be linked to a moraine limit 14c dating of peat and a key tephra layer above and below the glaciolacustrine deposits respectively suggest that the advance culminated in the strait of magellan between 12 010 and 10 050 yr bp

early summer water mass transformation in the eastern chukchi sea abstract pacific water entering the chukchi sea through bering strait can be modified by physical processes such as surface heating and cooling and internal mixing here we document the existence of a previously unobserved water mass in the eastern chukchi sea during the early summer using hydrographic and velocity data from the june july 2010 icescape survey the water mass in question is as salty as pacific winter water pww but is much warmer with temperatures typical of summer waters we label the water mass dense chukchi summer water dcsw which is dense enough to ventilate the upper halocline of the western arctic ocean normally ventilated by the much colder pww satellite sea surface temperature data long term mooring data from bering strait and the beaufort shelfbreak and atmospheric reanalysis fields are used to characterize the spatial and temporal variability of the dcsw and explore potential forcing scenarios that can lead to its formation in 2010 the dcsw did not enter the chukchi sea through bering strait hence it had to be formed locally on the shelf two distinct forcing mechanisms are considered 1 mixing of very warm alaskan coastal water with the cold pww when the two water masses come in contact in the energetic alaskan coastal current and 2 warming of pww when it experiences solar heating within the coastal polynya in the northeastern chukchi sea during the spring melt season finally we explore the conditions under which the springtime polynya has formed over the past three decades as it relates to the formation of dcsw

concertina eskers bruarjokull iceland an indicator of surge type glacier behaviour abstract bruarjokull is a surging outlet lobe of vatnajokull in se iceland geological evidence indicates that during quiescent phases water drainage takes place in ice walled and ice roofed channels as the glacier retreats the courses of these channels are represented by eskers eskers which were englacial prior to surges become deformed during a surge the deformation of eskers reflects strong longitudinal compression of the ice in the terminal zone the wavelength of one of the compressed eskers indicates that ice in a 4 km wide margin was compressed by 50 of its original length compressed or concertina eskers date from the 1963 1964 and the 1890 surges of bruarjokull they have not been found from the 1810 surge indicating that they may not survive if overrun by subsequent surges

fossil beetle evidence for climatic change 18 000 10 000 years b p in south central chile abstract cold adapted beetles colonized the lowlands of the lake region of south central chile following the retreat of glaciers from their maximum extent at about 19 500 yr b p the beetle fauna from 18 000 to 14 000 yr b p was characterized by species of moorland habitats this fauna was species poor compared to later faunas of the postglacial interval by 14 000 yr b p arboreal species were replacing species of open habitats reflecting a change toward a warmer climate by about 12 500 yr b p fossil beetle assemblages consisted entirely of rain forest species the fauna of the postglacial interval was about five times as species rich as that of the glacial interval the change in species composition and greater diversity of the beetle fauna was produced by an increase in mean annual temperature estimated to be about 4 5 c this was the last major climatic change to affect profoundly the biota of the middle latitudes of south america the fossil beetle assemblages do not imply a reversal to a colder climate at the time of the european younger dryas interval between 11 000 and 10 000 yr b p

younger dryas glacial landsystems in north west scotland an assessment of modern analogues and palaeoclimatic implications abstract by explicitly linking process to form landsystem models developed in modern environments provide powerful tools for the reconstruction of past environments from the sedimentological and geomorphological record some landform characteristics however may originate by more than one process equifinality so although a particular depositional model may fit the data it is not necessarily the correct one here we critically examine the use of modern analogues to interpret glacial landforms focusing on hummocky moraine a distinctive landform association consisting of numerous sharp crested moraine mounds and ridge fragments which occurs on many valley floors in upland britain detailed studies of examples of younger dryas age in the north west highlands of scotland show that they represent ice contact fans which have been affected to varying degrees by ice push and subglacial deformation and that they formed at active oscillating ice margins the sedimentological data are inconsistent with an origin by englacial thrusting as has been proposed for similar moraines elsewhere in upland britain on the basis of morphological criteria comparison with modern glacial landsystems shows that although aspects of hummocky moraines in the study area have close modern counterparts none provides an exact analogue in all respects this may reflect the distinctive climate of western scotland during the younger dryas estimates of mean july temperatures in the younger dryas in scotland based on chironomid assemblages are c 8 c at sea level when combined with reconstructed equilibrium line altitudes for contemporaneous glaciers these estimates indicate mean annual precipitation totals in the range of 2358 337 mm yr 1 at sea level in nw scotland c 26 higher than present day values the implied heavy snowfall suggests that glaciers in western scotland during the younger dryas were of high activity type unlike modern glaciers in svalbard for example high glacier velocities and high winter precipitation would suppress permafrost development despite low mean annual temperatures the climatic environment also favoured rapid oscillations of glacier margins during both glacier build up and retreat phases climatic factors combined with the availability of large quantities of subglacial debris led to the development of distinctive glacial landsystems which may have no direct modern analogue

till beneath ice stream b 3 till deformation evidence and implications most of the velocity of ice stream b near the upstream b camp upb west antarctica appears to arise from deformation of a seismically detected subglacial till layer that averages 6 m thick available evidence indicates that the entire thickness of this till layer is deforming and is eroding subjacent bedrock into flutes parallel to ice flow and hundreds of meters across the resulting till flux beneath upb is equivalent to an average erosion rate of about 0 4 mm yr 1 in the catchment area and suggests that till deltas tens of kilometers long have been deposited at the grounding line during the holocene such deltas should be characterized by partial ice till decoupling across a water film and by a small ice air surface slope they may have been discovered by recent geophysical work

circulation and water mass transformation in a model of the chukchi sea 1 the circulation and water mass transformation in a regional ocean ice model of the chukchi sea are discussed the model has horizontal resolution of o 4 km is forced by fluxes derived from daily ncep reanalysis fields and has seasonally varying transport temperature and salinity imposed at bering strait many of the observed characteristics of the mean circulation and seasonal cycle in the chukchi sea are reproduced the discussion focuses on the branching of the inflow transport into pathways following herald canyon central channel and the alaskan coast the pattern of ice melt and the water mass transformation and formation of winter water and hypersaline water the ice melt pattern and timing is strongly influenced by advection through bering strait high frequency forcing results in a larger region of ice melt particularly over the shoals and in the northern chukchi sea compared to monthly mean forcing in the model the seasonal cycle of salinity in the southern and central chukchi sea is dominated by advection through bering strait while local atmospheric forcing and brine rejection are more important north of herald and hanna shoals and in barrow canyon however since the residence time in the chukchi sea is generally less than 1 year interannual variability in the bering strait salinity will be reflected in the salinity across the chukchi sea and at barrow canyon

rheological nonlinearity and flow instability in the deforming bed mechanism of ice stream motion contrary to what has recently been assumed in modeling the proposed deforming bed mechanism for the rapid motion of antarctic ice streams the rheology of water saturated till is probably highly nonlinear according to information from soil mechanics and preliminary experiments on till from the base of ice stream b the equivalent flow law exponent n is probably as high as 100 and the nonlinearities of the shear stress and effective pressure dependences are closely linked the high nonlinearity has important consequences for the deforming bed mechanism a flow system operating by this mechanism can be unstable as a result of feedback from the generation of basal water by shear heating of basal till the short term feedback effect is analyzed for a perturbation in a model ice stream in which the basal meltwater is transported through a distributed system of narrow gap conduits at the ice till interface although the analysis is approximate and some of the system parameters are poorly known the results suggest that the deforming bed mechanism is unstable for n 20 the apparent lack of such an instability in the currently active ice streams implies that their motion is controlled not by the deforming bed mechanism but by some other as yet unidentified mechanism

varieties of shallow temperature maximum waters in the western canadian basin of the arctic ocean the properties and spreading pathways of shallow temperature maximum waters stms in the western canadian basin are investigated using ctd and mooring data obtained in 1997 98 as part of the sheba surface heat budget of the arctic ocean drift experiment and available historical data three distinct varieties of stm are recognized on the basis of salinity range 1 surface mixed layer water smlw with s 32 psu these stms carry sufficient heat within the upper layers of the ocean to significantly affect the rates of ice cover and decay for example during the winter of 1997 98 anomalously warm stm 0 c originating from ecsw was observed to spread northwards along the northwind ridge and chukchi plateau where the maximum reduction of the ice covers was subsequently observed in late summer 1998 maslanik et al 1999 regional climate variability and ice cover in the western canadian basin are thus affected not only by anomalous atmospheric circulation patterns but also by the circulation of upper ocean water masses

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

genesis of an imbricate push moraine hofdabrekkujokull iceland observations on a push moraine now being formed at the margin of the advancing glacier hofdabrekkujokull in iceland provide a background for interpreting the geomorphic and paleoclimatic significance of pleistocene push moraines this moraine up to 10 m high consists partly of unfrozen thrust slabs of glaciofluvial sand and partly of debris derived from the glacier surface during the present advance 10 to 12 m yr 1982 thrust planes intersect the glacier foreland and recurrent thrusting produces an imbricate structure as the moraine grows in height folds and faults are produced as the first formed slabs are rotated slowly backward up the glacier front and the whole moraine deforms under its own weight simultaneously the moraine receives a cover of supraglacial debris from the glacier surface above during the summer of 1982 the push moraine moved forward at a rate averaging about 4 cm day

the western arctic boundary current at 152 w structure variability and transport abstract from august 2002 to september 2004 a high resolution mooring array was maintained across the western arctic boundary current in the beaufort sea north of alaska the array consisted of profiling instrumentation providing a timeseries of vertical sections of the current here we present the first year velocity measurements with emphasis on the pacific water component of the current the mean flow is characterized as a bottom intensified jet of o 15 cm s 1 directed to the east trapped to the shelfbreak near 100 m depth its width scale is only 10 15 km seasonally the flow has distinct configurations during summer it becomes surface intensified as it advects buoyant alaskan coastal water in fall and winter the current often reverses flows westward under upwelling favorable winds between the storms as the eastward flow re establishes the current develops a deep extension to depths exceeding 700 m in spring the bottom trapped flow advects winter transformed pacific water emanating from the chukchi sea the year long mean volume transport of pacific water is 0 13 0 08 sv to the east which is less than 20 of the long term mean bering strait inflow this implies that most of the pacific water entering the arctic goes elsewhere contrary to expected dynamics and previous modeling results possible reasons for this are discussed the mean atlantic water transport to 800 m depth is 0 047 0 026 sv also smaller than anticipated

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

phytoplankton blooms beneath the sea ice in the chukchi sea in the arctic ocean phytoplankton blooms on continental shelves are often limited by light availability and are therefore thought to be restricted to waters free of sea ice during july 2011 in the chukchi sea a large phytoplankton bloom was observed beneath fully consolidated pack ice and extended from the ice edge to 4100 km into the pack the bloom was composed primarily of diatoms with biomass reaching 1291 mg chlorophyll a m 2 and rates of carbon fixation as high as 3 7 g c m 2 d 1 although the sea ice where the bloom was observed was near 100 concentration and 0 8 1 2 m thick 30 40 of its surface was covered by melt ponds that transmitted 4 fold more light than adjacent areas of bare ice providing sufficient light for phytoplankton to bloom phytoplankton growth rates associated with the under ice bloom averaged 0 9 d 1

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

mechanical and hydrologic basis for the rapid motion of a large tidewater glacier 1 observations the data presented in part 1 of this paper meier et al this issue are here used to assess the role of water input output water storage and basal water pressure in the rapid movement of columbia glacier alaska consistently high basal water pressures mostly in the range from 300 kpa below to 100 kpa above the ice overburden pressure are responsible in an overall way for the high glacier flow velocities 3 5 9 m d 1 which are due mainly to rapid basal sliding caused by the high water pressure diurnal fluctuation in basal water pressure is accompanied by fluctuation in sliding velocity in what appears to be a direct causal relation at the upglacier observation site the water pressure fluctuation tracks the time integrated water input less a steady withdrawal as expected for the diurnally fluctuating storage of water in the glacier far from the terminus at the downglacier site the situation is more complex diurnal peaks in water level which are directly related to intraglacial water storage as well as to basal water pressure are shifted forward in time by 4 hours probably as a result of the effect of diurnal fluctuation in water output from the glacier which affects the local water storage fluctuations near the terminus because of the forward shift in the basal water pressure peaks which at the downglacier site lead the velocity peaks by 6 hours a mechanical connection between water pressure and sliding there would have to involve a 6 hour quarter period delay however the nearly identical nature of the diurnal fluctuations in velocity at the two sites argues for a single consistent control mechanism at both sites the velocity variations in nondiurnal speed up events caused by extra input of water on the longer timescale of several days are only obscurely if at all correlated with variations in basal water pressure but correlate well with water storage in the glacier it appears that small variations in water pressure 100 kpa sufficient to produce the observed velocity variations 15 30 are mostly masked by pressure fluctuations caused by spontaneous local reorganizations of the basal water conduit system on a spatial scale much smaller than the longitudinal coupling length over which basal water pressure is effectively averaged in determining the sliding velocity at the achieved level of observation the clearest though not complication free control variable for the sliding velocity variations is basal water storage by cavitation at the glacier bed

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

pleistocene glacitectonic landforms and sediments around central magellan strait southernmost chile evidence for fast outlet glaciers with cold based margins abstract proglacial and subglacial glacitectonic sediments and landforms around the margins of the strait of magellan southernmost chile record the advance and retreat of outlet glaciers of the patagonian ice cap during the last glacial cycle the spatial arrangement of glacitectonic landforms in the area is inferred to have resulted from the advance of ice lobes with cold based margins and wet based interiors as the ice advanced subglacial basins were excavated beneath the glacier margins and the eroded material was pushed up into thrust moraines probably because frozen bed conditions formed a thermal dam against the free drainage of subglacial meltwater these ice marginal glacitectonic landforms were then overridden and streamlined into drumlins and flutes as thicker wet based ice passed over the area evidence for permafrost near sea level in patagonia during the last glaciation suggests that mean annual temperatures were several degrees lower than indicated by recent modelling studies the results indicate that future modelling experiments should incorporate more realistic basal boundary conditions particularly the presence of a weak deforming layer at the glacier bed to improve climatic reconstructions of southern south america

evolution and dynamics of the flow through herald canyon in the western chukchi sea abstract the flow of summer and winter pacific water masses through herald canyon is investigated using data from a high resolution hydrographic velocity survey conducted in summer 2004 the survey was part of the russian american long term census of the arctic rusalca program and consisted of four cross canyon transects occupied over a 2 day period at the time of the survey dense winter water was entering the western side of the canyon from the chukchi sea flowing alongside a poleward jet of summer water on the canyon s eastern flank as the dense water progressed northward it switched sides of the canyon and underwent a sudden increase in layer thickness this coincided with vertical mixing near the interface of the winter and summer water producing a new water mass mode exiting the canyon all of these features are consistent with the notion of hydraulic activity occurring in the canyon a three layer hydraulic theory is applied to the flow which suggests that it is supercritical and that hydraulic control is likely a lock exchange formulation accurately predicts the northward transport of the winter water the origin of the winter water and the manner in which it drains into the canyon is investigated using satellite ice concentration data atmospheric re analysis fields historical in situ data and a simple circulation model finally the fate of the pacific water exiting the canyon and its connection to the chukchi shelfbreak current is discussed

glacial sediment landform associations and paleoclimate during the last glaciation strait of magellan chile abstract glacial sediments and landforms preserved beside the strait of magellan record repeated advances of an outlet of the patagonian icefield during and following the last glacial maximum lgm 25 000 14 000 14c yr b p ice marginal landform assemblages consist of thrust moraine complexes kame and kettle topography and lateral meltwater channels very similar to those found at the margins of modern subpolar glaciers taken together with other forms of paleoenvironmental evidence the landform assemblages show that during the lgm and late glacial time permafrost occurred near sea level in southernmost south america this finding implies that mean annual temperatures were 7 8 c lower than at present somewhat lower than those reconstructed by current glacier climatic models comparison with precipitation temperature relationships for modern glaciers suggests in addition that precipitation levels were lower than today reduced glacial age precipitation may have resulted from a precipitation shadow induced by the patagonian icefield an equatorward migration of the average position of westerly cyclonic storm tracks in the southern midlatitudes or both these factors

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

two configurations of the western arctic shelfbreak current in summer abstractdata from a closely spaced array of moorings situated across the beaufort sea shelfbreak at 152 w are used to study the western arctic shelfbreak current with emphasis on its configuration during the summer season two dynamically distinct states of the current are revealed in the absence of wind with each lasting approximately one month the first is a surface intensified shelfbreak jet transporting warm and buoyant alaskan coastal water in late summer this is the eastward continuation of the alaskan coastal current it is both baroclinically and barotropically unstable and hence capable of forming the surface intensified warm core eddies observed in the southern beaufort sea the second configuration present during early summer is a bottom intensified shelfbreak current advecting weakly stratified chukchi summer water it is baroclinically unstable and likely forms the middepth warm core eddies present in the interior basin the mesoscale instabilities extract energy from the mean flow such

englacial and proglacial glaciotectonic processes at the snout of a thermally complex glacier in svalbard many glaciers in svalbard which tend to be thermally complex with both warm and cold ice produced complex push moraines or thrust moraine complexes at the time of their maximum neoglacial advance and during their subsequent recession uv rsbreen which nearly reaches the coast of northwest spitsbergen has a push moraine 50 m high comprising gravel and sand of fluvial origin and diamicton derived from basal ice as well as thrust masses of dead ice the push moraine is almost entirely a product of the tectonic processes especially thrusting that occurred in the snout of the glacier and in the frozen sediments immediately in journal of quaternary science front thrusting is probably initiated where the glacier switches from a sliding mode to a state of being frozen to the bed thrusting in the foreland is an extension of the same processes that occur within the ice itself and a sole thrust probably extends from the frozen sediment that underlies the base of the glacier near its snout thrusting results in subglacial sediment being uplifted to a high level within the glacier or even to the surface subsidiary near horizontal thrusts parallel to the bedding plane link thrusts dipping up glacier and result in local thickening of individual subglacial sedimentary units gravels incorporated in this way retain their integrity but sands are folded whereas uplifted debris rich basal ice is intensely folded the distinctive tectonic style of low dip bedding in gravels truncated by high angle 30 40 thrusts and only localised folding in less competent material differs from most descriptions of such ridges but may be typical of many push moraines composed principally of fluvial material

a 10 000 yr b p extensive ice shelf over viscount melville sound arctic canada abstract late wisconsinan age glacial landforms and deposits indicate that an ice shelf of at least 60 000 km 2 flowed northwestward into viscount melville sound probably from the m clintock dome of the laurentide ice sheet the ice shelf overlapped coastal areas and laid winter harbour till up to 125 m above present sea level on the southern coast of melville island to 135 m on byam martin island to possibly 90 m on the northeast tip of banks island and to 150 m on the north coast of victoria island the contemporary sea level was 50 to 100 m higher than present it now rises eastward a maximum age of 10 340 150 yr b p for the till and thus the ice shelf advance is provided by shells in marine sediments which underlie it whereas a minimum age of 9880 150 yr b p is provided by overlying shells that postdate the ice advance the major advance of shelf ice into viscount melville sound may be the result of the rapid disintegration of the m clintock dome while the climate ameliorated in the western arctic

late holocene sea surface temperature and precipitation variability in northern patagonia chile jacaf fjord 44 s abstract a high resolution multi proxy study including the elemental and isotopic composition of bulk organic matter land plant derived biomarkers and alkenone based sea surface temperature sst from a marine sedimentary record obtained from the jacaf fjord in northern chilean patagonia 44 20 s provided a detailed reconstruction of continental runoff precipitation and summer sst spanning the last 1750 yr we observed two different regimes of climate variability in our record a relatively dry warm period before 900 cal yr bp lower runoff and average sst 1 c warmer than present day and a wet cold period after 750 cal yr bp higher runoff and average sst 1 c colder than present day relatively colder ssts were found during 750 600 and 450 250 cal yr bp where the latter period roughly corresponds to the interval defined for the little ice age lia similar climatic swings have been observed previously in continental and marine archives of the last two millennia from central and southern chile suggesting a strong latitudinal sensitivity to changes in the southern westerly winds the main source of precipitation in southern chile and validating the regional nature of the lia our results reveal the importance of the chilean fjord system for recording climate changes of regional and global significance

expansion of magellanic moorland during the late pleistocene palynological evidence from northern isla de chiloe chile the late quaternary vegetation of northern isla de chiloe is inferred from palynological analysis of a section in the rio negro drainage 42 03 s 73 50 w at ca 30 500 yr b p maxima of astelia and donatia occurred suggesting wetland development from that time until ca 27 000 yr b p steppe indicators such as compositae gramineae dominated suggesting drier conditions after 27 000 yr b p the moorland shrub dacrydium gradually increased reaching a maximum by 18 000 yr b p at this time astelia increased again suggesting development of cushion bog during cold and wet conditions the glacial postglacial transition is characterized by a marked change from peaty sediments to clays a decrease in the cushion bog flora and the prevalence of gramineae compositae and swamp taxa this vegetation prevailed until ca 7000 yr b p when forest taxa became dominant the floristic pattern inferred from the pollen spectra of the rio negro section suggests that the late pleistocene vegetation of chiloe resembled modern magellanic moorland vegetation 52 56 lat s based on climatic conditions presently associated with magellanic moorland its occurrence in chiloe at low elevations during the late pleistocene implies a decrease in average temperature of at least 4 c and an increase in annual precipitation of at least 1500 mm

asymmetrical drumlins in patagonia chile abstract drumlins in south america are described and discussed in some detail for the first time they occur in the chilean part of southern patagonia close to the magellan straits here the majority of drumlins are spindle shaped and have asymmetric cross profiles with the steeper slopes consistently on the same side southeast elongated enclosed hollows are commonly associated with the steeper slopes till with blade shaped clasts showing preferred alignment roughly parallel with the drumlin long axes composes at least the outer 2 m and up to 6 m of the stoss end of some drumlins thick sequences of glaciofluvial and glaciolacustrine sediments may underlie much of the main drumlin field the subglacial deformation of earlier quaternary sediments may explain the spatial pattern and morphological characteristics of drumlins in patagonia

summertime circulation in the eastern chukchi sea abstract the transport of pacific origin water across the eastern chukchi sea during summer is studied using shipboard hydrographic and acoustic doppler current profiler data from multiple surveys the study identifies two major transport pathways in this region the well known alaskan coastal current acc flows poleward along the alaska coast while a more recently discovered and slower current flows northward through the central channel between herald and hanna shoals the two currents separate past point hope and appear to merge again in barrow canyon via previously unresolved pathways flowing west to east across the chukchi sea the collective flow that transports pacific water from bering strait to barrow canyon is termed the bering to barrow current system bbcs the coastal branch of the bbcs which encompasses the acc is a weakly baroclinic flow with a maximum speed in excess of 80 cm s inside barrow canyon the central channel branch of the bbcs is considerably weaker with a maximum flow speed under 20 cm s a portion of the pacific water that flows towards herald canyon to the west may also contribute to the bbcs the amount but the amount is within the margin of error of our data the difference in the advective time scales of the various branches allows water masses of different seasonal characteristics to be transported simultaneously by the bbcs summer water masses occupy most of the southern and central chukchi sea while winter water masses occupy hanna shoal and shelfbreak regions in the northern chukchi sea during summer the total bbcs volume transport in summer is measured at four different locations in the eastern chukchi sea and found to be generally consistent the overall mean transport is 0 86 sv compared to the summer bering strait transport of 1 08 sv this study suggests that the bbcs is the main transport pathway delivering pacific water masses into the western arctic basin

sedimentology of a debris rich perhumid valley glacier margin in the rakaia valley south island new zealand the sedimentology and stratigraphy of a multi phase glaciation sequence dating to marine isotope stage 6 in the rakaia valley south island new zealand is presented this outcrop presents an example of the depositional signature of an end member of temperate valley glaciation where voluminous sediment supply in a tectonically active setting combines with high annual temperatures and low seasonality to generate significant year round glacifluvial activity such glacial systems produce geological climatic units that are dominated by thick sequences of aggradational gravels and proglacial lake sediments trapped behind outwash heads during deglaciation at bayfields cliff outwash sequences record an oscillating glacier margin marked by a sequence of glacier fed gilbert type deltas the deltas are cut by numerous small scale syndepositional normal faults indicating both loss of glacier support and melt out of buried ice a larger scale thrust fault system reflects late stage ice overrun braid plain gravels and chaotic disturbed glacial lake sediments are also recorded a notable feature of these systems is the virtual absence of till in an environment with much other evidence for proximal ice cumulatively we regard these sediment landform associations as diagnostic of debris laden perhumid temperate valley glacier systems

divergent patterns of recent sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region abstract over the past three decades of the observed satellite record there have been significant changes in sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region par satellite data reveal that patterns in sea ice cover have been spatially heterogeneous with significant declines in the chukchi and beaufort seas yet more complex multi year variability in the bering sea south of st lawrence island these patterns in the chukchi and beaufort seas have intensified since 2000 indicating a regime shift in sea ice cover across the northern portion of the par in particular satellite data over 1979 2012 reveal localized decreases in sea ice presence of up to 1 64 days year canada basin and 1 24 days year beaufort sea which accelerated to up to 6 57 days year canada basin and 12 84 days year beaufort sea over the 2000 2012 time period in contrast sea ice in the bering sea shows more complex multi year variability with localized increases in sea ice presence of up to 8 41 days year since 2000 the observed increases in sea ice cover since 2000 in the southern bering sea shelf region are observed in wintertime whereas sea ice losses in the canada basin and beaufort sea have occurred during summer we further compare sea ice variability across the region with the national centers for environmental prediction ncep north american regional reanalysis narr wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs wind driven processes results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover those in the beaufort sea are primarily wind driven those offshore in the canada basin are primarily thermally driven and those in the bering sea are influenced by elements of both sea ice variability and its drivers across the par provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels

the effect of possible taylor columns on the summer ice retreat in the chukchi sea the chukchi sea topography consists of a broad flat 50 m deep plain with two prominent shoals herald and hanna which have horizontal dimensions of about 100 km and rise to depths of about 30 m herald shoal in particular is a prominent isolated seamount which because of the warm water flux in summer through bering strait has a warm 0 1 m s 1 flow incident upon it examination of active and passive microwave imagery of the region for 1992 1994 shows that as the general ice cover recedes the ice remains preferentially over herald shoal for 3 4 weeks after the surrounding ice has melted a scale analysis suggests that the cause of the ice persistence is the formation of a taylor column over the shoal which traps cold water and ice above it a similar trapping of ice occurs over hanna shoal and on its eastern slope but the response is complicated by a very different topography and the northward flow down barrow canyon

late quaternary climatic history of the chilean channels based on fossil pollen and beetle analyses with an analysis of the modern vegetation and pollen rain fossil beetles and pollen were examined from an intermorainal bog at puerto eden isla wellington chile latitude 49 08 s longitude 74 25 w wood from near the base of the section has an age of 12 960 150 yr bp occurrence of flightless beetle species in the basal peat sample is evidence that some members of the biota survived the last glacial maximum in refugia the assumption that the chilean channels were entirely ice covered is incorrect plants and insects that invaded the deglaciated terrain were those of an empetrum heathland in which patches of nothofagus forest were restricted to sheltered locations the climate supporting the heathland is inferred to have been windier and probably drier than that of the present day from 13 000 yr bp to 9500 yr bp nothofagus forest expanded possibly in response to less windiness and more available moisture neither the fossil beetle nor pollen data support a return to significantly colder conditions between 11 000 and 10 000 yr bp at the time of the younger dryas stade from 9500 to 5500 yr bp the climate was as wet as that of the present day based on an increased representation of the pollen of moorland plants and of aquatic beetle species from 5500 to 3000 yr bp the climate was drier as indicated by the expansion of empetrum heath and the reduction in mesic habitats from 3000 yr bp to the present day mesic habitats dominated as the climate returned to a wetter mode the alternatively wetter and drier episodes are attributed to latitudinal shifts in the position of storm tracks in the belt of southern westerlies

the tekapo glacier new zealand during the last glacial maximum an active temperate glacier influenced by intermittent surge activity abstract quaternary glaciations have created impressive landform assemblages that can be used to understand palaeo glacier extent character and behaviour and hence past global and local glacier forcings however in the southern hemisphere and especially in new zealand the quaternary glacial landform record is relatively poorly investigated with regard to glaciological properties in this study a 1 m digital elevation model dem was generated from airborne lidar data and supplemented with aerial imagery and field observations to analyse the exceptionally well preserved glacial geomorphology surrounding lake tekapo new zealand we describe a rich suite of last glacial maximum lgm and recessional ice marginal subglacial supraglacial glaciofluvial and glaciolacustrine landform assemblages these represent two landsystems comprising i fluted till surfaces with low relief push moraine ridges and ii crevasse squeeze ridges zig zag eskers and attenuated lineations the former landsystem records the behaviour of an active temperate glacier and the latter landsystem which is superimposed upon and inset within the former strongly suggests intermittent surge phases the two landsystem signatures indicate a sequential change in ice marginal dynamics during recession that was likely to have been partially non climatically driven overall we present the first evidence of surge type glacier behaviour in new zealand

glacial dynamics in southernmost south america during marine isotope stage 5e to the younger dryas chron a brief review with a focus on cosmogenic nuclide measurements the timing of major glacial changes between marine isotope stage mis 5e and the younger dryas chron yd in southern south america is reviewed focus is placed on studies that use cosmogenic nuclide measurements however other dated records and modelling results are also discussed to provide the broader glacial geological context limits on the state of glacial geologic knowledge are examined and suggestions are made as to how some of these can be addressed in future studies studies show that on the east side of the andes at lago buenos aires 45 s there is evidence indicating that following a mis 6 glaciation ice was less extensive during mis 4 than mis 2 in contrast on the west side of the andes in the chilean lake district area mis 4 ice may have been more extensive than during mis 2 although patagonia experienced an mis 2 glaciation broadly in phase with that in other areas around the globe there are differences in glacial histories between areas on millennial timescales climate reversals are evident in many records between ca 17 and 10 ka the timing of such lateglacial activity which included less extensive advances than during the local last glacial maximum lgm varies somewhat between areas this could be due to the relative influence of middle to high latitude climatic regimes at present chronological uncertainties prevent confident assignment of cosmogenic ages for glacial events at the millennial timescale and defining associated climate variability between different study areas copyright 2008 john wiley sons ltd

the glaciogenic origin of the pleistocene calcareous dust in argentina on the basis of field mineralogical textural and geochemical analyses calcareous dust occurs in argentina as layers and pockets closely associated with pleistocene deposits and periglacial features from southernmost patagonia to at least the mendoza precordillera and has been traditionally interpreted as a soil horizon resulting from postdepositional pedogenesis during interglacials detailed field and microscopic observations and sedimentological and geochemical analyses of more than 100 samples collected from lower to upper pleistocene deposits between 51 s and 33 s and from near sea level to 2800 m asl allow us to interpret the dust as synchronous with the host sediment all observations and analyses lead us to conclude that 1 the cryogenic morphology and the chemical signatures of the calcite component show that the dust is glaciogenic 2 the dust was carried by southeasterly antarctic winds and 3 it was deposited over most of southern and central argentina field observations geomorphic evidence and radiocarbon dates suggest that the dust was deposited during several pleistocene glacial episodes