propagation of signals in basin scale ocean bottom pressure from a barotropic model 1 the exchange of atmospheric plus oceanic mass between ocean basins is investigated using a global barotropic ocean model we find two particular cases of exchange between two basins at periods of 4 6 days the exchange is between the atlantic and pacific basins and represents a known oscillation forced by atmospheric pressure this mode represents a failure of the inverse barometer relationship due to the large scale and high frequency of atmospheric forcing and the presence of continents significant exchange between atlantic and pacific also occurs at longer periods the second case is most prominent at periods longer than 30 days strongest at periods longer than 100 days and represents a mass exchange between the southern ocean and the pacific the southern ocean part of this exchange is clearly related to the southern mode of fluctuations in antarctic circumpolar transport forced by southern ocean wind stress the reason for the exchange being with the pacific rather than other basins is explored and is found to be related to the balance of wind stress by form stress in drake passage exchange with the atlantic and indian oceans becomes dominant if drake passage topography is removed while recognizing the limitations of a barotropic model we contend that it is necessary to understand the barotropic adjustment process in order to make sense of longer timescale processes accordingly we end with speculation on the possible importance of the barotropic results for global sea level and tropical dynamics

past ice sheet flow east of svalbard inferred from streamlined subglacial landforms the pattern of late weichselian ca 20 ka ice flow in the northern barents sea is not well known due mainly to a lack of marine data east of svalbard several years with little summer sea ice have allowed acquisition of swath bathymetric imagery of well preserved subglacial landforms characterizing late weichselian ice flow directions over 150 000 km2 of the northwestern barents sea we show that a major ice dome was located on easternmost spitsbergen or southern hinlopen strait at least 500 km west of its previously inferred position in the northern barents sea this dome controlled the regional flow pattern ice flowed eastward around kong karls land into franz victoria trough and north through hinlopen strait an ice dome west of kong karls land is required to explain the observed ice flow pattern but does not preclude an additional ice dome to the southeast discrepancies with earlier ice sheet reconstructions reflect the lack of previous seafloor observations with evidence limited mainly to past ice loading and postglacial rebound the new pattern of ice flow directions shows predominantly eastward rather than northward flow with franz victoria trough a major drainage pathway with a full glacial balance flux of 40 km3 yr 1

baroclinic transport time series of the antarctic circumpolar current measured in drake passage abstractthe first multiyear continuous time series of antarctic circumpolar current acc baroclinic transport through drake passage measured by moored observations is presented from 2007 to 2011 19 current and pressure recording inverted echo sounders and 3 current meter moorings were deployed in drake passage to monitor the transport during the cdrake experiment full depth acc baroclinic transport relative to the bottom has a mean strength of 127 7 1 0 sverdrups sv 1 sv 106 m3 s 1 with a standard deviation of 8 1 sv mean annual baroclinic transport is remarkably steady about 65 of the baroclinic transport variance is associated with time periods shorter than 60 days with peaks at 20 and 55 days nearly 28 of apparent energy in the spectrum computed from transport subsampled at the 10 day repeat cycle of the jason altimeter results from aliasing of high frequency signals approximately 80 of the total baroclinic transport is carried by the subantarctic front and the polar front partition

on the transport of the antarctic circumpolar current through drake passage and its relation to wind a time series of net transport during 1979 of the antarctic circumpolar current acc through the upper 2500 m of drake passage was obtained as part of the international southern ocean studies program by whit worth 1983 and was presented in a revised form by whitworth and peterson 1985 spectral analyses are performed on records comprising the revised series to determine the major sources of transport variability multiyear records from bottom pressure gauges at each side of the passage are then compared with fields of wind stress over the southern ocean the net transport series is dominated in the subseasonal time scales by the lunar fortnightly and monthly tides and by baroclinic activity in the northern passage processes that are independent of wind for seasonal time scales transport variability appears to be mainly barotropic thus being well represented by bottom pressure records from each side of the passage comparisons of multiyear bottom pressure records with time series of the zonally averaged curl of wind stress in narrow bands along the perimeters of the acc suggest that seasonal fluctuations in the strengths of the subtropical and subpolar atmospheric pressure systems flanking the acc induce changes in the slope of the sea surface across the current the dominant annual cycle in curl associated with the subtropical highs appears to influence sea level across the entire acc whereas the effects of the strong semiannual cycle in curl associated with the subpolar lows are confined to the southern portions of the current

assemblages of submarine landforms produced by tidewater glaciers in svalbard 1 high resolution swath bathymetry from the marine margins of several svalbard tidewater glaciers shows an assemblage of submarine landforms that is probably linked to glacier surging these landforms are essentially unmodified since their initial deposition over the past hundred years or so because they have not been subjected to subaerial erosion or periglacial activity swath images comprise an assemblage of superimposed landforms allowing reconstruction of relative age of deposition 1 large transverse ridges interpreted as recessional moraines overridden by a subsequent ice advance 2 a series of curvilinear streamlined bedforms orientated parallel to former ice flow interpreted as lineations formed subglacially during rapid advance 3 large terminal ridges marking the farthest extent of ice at the last advance with flow lobes immediately beyond interpreted as submarine debris flows 4 a series of interconnected rhombohedral ridges interpreted as a product of soft sediment squeezing into crevasses formed at the glacier bed probably formed during immediate post surge stagnation and 5 a series of fairly evenly spaced small transverse ridges interpreted as push moraines produced annually at tidewater glacier termini during retreat a simple descriptive landsystem model for tidewater glaciers of probable surge type is derived from these observations we also show that megascale glacial lineations can form not only beneath large ice streams but are also produced beneath surging tidewater glaciers lying on deforming sedimentary beds

two full depth velocity sections in the drake passage in 2006 transport estimates abstract in january february 2006 a hydrographic section under jason track 104 across drake passage dp was performed twice within 3 weeks on board of the r v polarstern two ladcps mounted on the ctd rosette provided the most comprehensive synoptic top to bottom observations of directly measured velocity available in the drake passage to date with an estimated error of less than 3 cm s 1 geostrophic velocities computed from the hydrographic data were referenced to ladcp velocities the velocity structure of the antarctic circumpolar current acc along the track and its evolution within 3 weeks reflect the frontal branches presented by barre et al 2011 and provost et al 2011 the repeated section offers two independent transport estimates computed from the ladcp velocities 145 8 8 and 137 9 10 5 sv respectively and from the adjusted geostrophic velocities 136 6 7 and 129 7 sv respectively error bars of the transport estimates are small contributions of the fronts and eddies to the total transport are modified within 3 weeks but tend to compensate each other the total transport is reduced by about 10 15 17 sv between the southward and northward journey total transport estimations are compared to previous results in particular the isos international southern ocean study data from which the canonical value of 134 sv has been estimated within the uncertainties due to uneven data distribution no trend is discernible neither in the baroclinic nor total transports from 1975 to 2006

submarine landforms characteristic of glacier surges in two spitsbergen fjords abstract well preserved submarine landforms all less than 100 years old are imaged on high resolution swath bathymetry obtained from van keulenfjorden and rindersbukta inner van mijenfjorden spitsbergen svalbard several tidewater glaciers in these fjords have surged in the last few hundred years streamlined landforms found within the limits of known surges are interpreted as mega scale glacial lineations msgl formed subglacially beneath actively surging ice large transverse ridges are terminal moraines formed by thrusting at the maximum position of glacier surges sediment lobes at the distal margins of terminal moraines are interpreted as glacigenic debris flows formed either by failure of the frontal slopes of thrust moraines or from deforming sediment extruded from beneath the glacier sinuous ridges are eskers formed after surge termination by the sedimentary infilling of subglacial conduits concordant ridges parallel to former ice margins are interpreted as minor push moraines probably formed annually during winter glacier readvance discordant ridges oblique to former ice margins are interpreted as crevasse squeeze ridges forming when soft subglacial sediments are injected into basal crevasses these submarine landforms have been deposited in the following sequence based on cross cutting relationships between them linked to stages of the surge cycle 1 msgl 2a terminal moraines and 2b lobe shaped debris flows 3 isolated areas of crevasse fill ridges 4 eskers and 5 annual retreat ridges a descriptive landsystem model for tidewater surge type glaciers has been developed whose wider applicability is emphasised by comparison with two areas in isfjorden spitsbergen the model also has a number of features in common with landsystem models for terrestrial surge type glaciers but is likely to be more complete since submarine landforms are particularly well preserved the landforms discussed here may be produced and preserved in different proportions in the varied environmental settings where surging glaciers are found

comparisons of sea level and bottom pressure measurements at drake passage tide gauge and atmospheric sea level pressure measurements from each side of drake passage are compared with multiyear time series of bottom pressure at 500 m depth synthetic subsurface pressure ssp smoothed with a 40 hour low pass filter derived from tidal and sea level pressure records from the british antarctic survey base faraday is coherent with bottom pressure from southern drake passage for periods of 6 to 600 days but it is about 60 out of phase at the annual period the difference between the two series for periods longer than 60 days is mainly annual and is as large as or larger than the seasonal variability of bottom pressure itself annual variations in open ocean mixed layer density near antarctica are too small to account for the difference the faraday ssp series spans 21 years slightly longer than the 18 6 year lunar nodal tide which appears to exist in the record at the northern side of drake passage ssp from puerto williams chile does not compare well with nearby bottom pressure for any band of periods apparently due to local winds for periods under 100 days and to annual cycles in upper layer density barotropic changes in transport of the antarctic circumpolar current cannot be directly estimated using these surface observations even though over seasonal periods they are an order of magnitude larger than the baroclinic changes due to variations in upper layer density

establishment of modern circulation pattern at c 6000 cal a bp in disko bugt central west greenland opening of the vaigat strait variations in the holocene circulation of the west greenland current wgc in the disko bugt region have been reconstructed from a suite of sediment cores palaeoceanographic proxies include magnetic susceptibility ms and x ray fluorescence titanium counts which document a major shift in circulation at c 6000 cal a bp before this date sediments in southern disko bugt were characterized by high terrigeneous and basaltic input suggesting widespread influence of meltwater plumes our data show that the wgc re circulated in the southern disko bugt area because a potential northern pathway the narrow vaigat strait was blocked by icebergs that calved from marine outlet glaciers in eastern disko bugt sediments in southern disko bugt deposited after c 6000 cal a bp have significantly lower terrestrial and basaltic sediment input which coincides with minimum holocene ice sheet extent the reduced meltwater and iceberg discharge to the embayment caused the vaigat strait to become free of blocking icebergs and terrigenous input was partly diverted to the outer shelf thus the modern circulation pattern of the wgc was established in the disko bugt region through the opening of the vaigat strait c 6000 cal a bp

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

particle interaction in fjord suspended sediment abstract glacial flour enters the surface layer of howe sound a fjord in southwestern british columbia as a sediment plume which moves quickly down inlet while gradually mixing with the sea water flocculation occurs in the lower brackish waters of the surface layer although mixing and diffusion are the dominant processes for sediment to enter the marine water once in the underlying marine water zooplankton pelletization and biologic agglomeration of inorganic floccules predominate this generates a response in the order of days between the two layers in terms of sedimentation of particulate matter most particles settling in the fjord environment fall as 1 sand and silt grains containing attached clay particles 2 clay clasts possibly related to river mudballs 3 mineral bearing fecal pellets from pelagic zooplankton 4 large grain inorganic and colloidal floccules and 5 inorganic biogenic agglomerates analysis of sediment trap data has led to the following conclusions 1 water turbidity cannot be used to infer the downward flux of particles 2 size distributions of sediment deposited on the sea bed are a function of non lognormal size distributions from particles composing sub laminae

interaction between subsurface ocean waters and calving of the jakobshavn isbrae during the late holocene a marine sediment core from vaigat in disko bugt west greenland has been analysed in terms of lithology dinoflagellate cysts and foraminifera in order to evaluate the influence of oceanographic variability on west greenland glacier stability the data show that during the past 5200 years the atlantic foraminiferal abundance in the subsurface waters of the west greenland current wgc episodically increased indicating periods of increases in the inflow of subsurface warm atlantic water at 2000 1500 cal yr bp and 1300 cal yr bp as well as periods of less pronounced increased bottom water temperatures around 4700 4000 cal yr bp 3100 2800 2600 1000 800 500 400 and at 200 cal yr the sedimentological and dinoflagellate cyst data indicate that these episodes with enhanced advection of irminger sea derived waters are accompanied by increased iceberg rafting which we link to increased iceberg calving in relation to destabilization of the jakobshavn isbrae the long term trend in the data documents the end of a late holocene thermal maximum between 5200 and 4300 cal yr bp and a final onset of the neoglaciation at 3500 cal yr bp increased responses of the iceberg rafting after 3500 cal yr bp reflects a westward seaward advance of the glacier margin in relation to onset of neoglaciation and a development of the glacier into a floating tongue after 2000 cal yr bp a comparison of our record with a record from the eastern north atlantic indicates that a nao like anomaly pattern between subsurface waters in west greenland and atmospheric temperature in the eastern north atlantic may have been operating during most of the late holocene however during the past 1000 years the nao signal may have weakened as some other mode of climate variability overprints the anti phase climate signal in this region

seafloor geomorphology and glacimarine sedimentation associated with fast flowing ice sheet outlet glaciers in disko bay west greenland fast flowing outlet glaciers currently drain the greenland ice sheet gis delivering ice meltwater and debris to the fjords around greenland although such glaciers strongly affect the ice sheet s mass balance their glacimarine processes and associated products are still poorly understood this study provides a detailed analysis of lithological and geophysical data from disko bay and the vaigat strait in central west greenland disko bay is strongly influenced by jakobshavn isbrae greenland s fastest flowing glacier which currently drains 7 of the ice sheet streamlined glacial landforms record the former flow of an expanded jakobshavn isbrae and adjacent gis outlets through disko bay and the vaigat strait towards the continental shelf thirteen vibrocores contain a complex set of lithofacies including diamict stratified mud interbedded mud and sand and bioturbated mud deposited by 1 suspension settling from meltwater plumes and the water column 2 sediment gravity flows and 3 iceberg rafting and ploughing the importance of meltwater related processes to glacimarine sedimentation in west greenland fjords and bays is emphasised by the abundance of mud preserved in the cores radiocarbon dates constrain the position of the ice margin during deglaciation and suggest that jakobshavn isbrae had retreated into central disko bay before 10 6 cal ka bp and to beyond isfjeldsbanken by 7 6 7 1 cal ka bp sediment accumulation rates were up to 1 7 cm a 1 for ice proximal glacimarine mud and 0 007 0 05 cm a 1 for overlying distal sediments in addition to elucidating the deglacial retreat history of jakobshavn isbrae our findings show that the glacimarine sedimentary processes in west greenland are similar to those in east greenland and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime

antarctic circumpolar current transport variability during 2003 05 from grace abstract gravity recovery and climate experiment grace gravity data spanning january 2003 november 2005 are used as proxies for ocean bottom pressure bp averaged over 1 month spherical gaussian caps 500 km in radius and along paths bracketing the antarctic circumpolar current s various fronts the grace bp signals are compared with those derived from the estimating the circulation and climate of the ocean ecco ocean modeling assimilation system and to a non boussinesq version of the regional ocean model system roms the discrepancy found between grace and the models is 1 7 cmh2o 1 cmh2o 1 hpa slightly lower than the 1 9 cmh2o estimated by the authors independently from propagation of grace errors the northern signals are weak and uncorrelated among basins the southern signals are strong with a common seasonality the seasonal cycle grace data observed in the pacific and indian ocean sectors of the acc are consistent with annual and semiannual amplitudes of 3 6 and 0 6 cmh2o 1 1 and 0

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

on the wind forcing of bottom pressure variability at amsterdam and kerguelen islands southern indian ocean 1 bottom pressure records from amsterdam and kerguelen islands southern indian ocean were collected between 1986 and 1989 and interpreted previously in terms of volume transport fluctuations between the islands vassie et al 1994 since a substantial portion of the mean transport of the antarctic circumpolar current acc flows between the islands it was assumed that acc transport variability was the predominant signal being measured and comparisons with acc variability at other longitudes were made here we examine the relationship between atmospheric forcing and observed bottom pressure variability we find that kerguelen bottom pressure is forced predominantly by wind stress curl over the kerguelen plateau for periods between around 5 days and 1 year a weaker correlation with circumpolar eastward winds is observed but is seen not to be causal amsterdam pressure shows a similar local response to curl for high frequencies 5 10 days but at longer periods is sensitive to curl over the sub basin between kerguelen plateau the southeast indian ridge and antarctica this is the region of long wavelength sea level variability observed by chao and fu 1995 and interpreted in terms of a geostrophic resonance by webb and de cuevas 2002a altimetric studies confirm the usefulness of the amsterdam location in monitoring this mode we conclude that the amsterdam kerguelen pressure difference is not a useful measure of acc transport variability and that previous agreement found between variability observed here and other locations is largely fortuitous instead the series separately reflect different important dynamical modes in the southern indian ocean

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

ice stream retreat and ice shelf history in marguerite trough antarctic peninsula sedimentological and foraminiferal signatures the timing nature and causes of grounded ice sheet retreat following the last glacial maximum lgm in marguerite trough west antarctic peninsula and subsequent early holocene ice shelf decay are presented in this paper we use sedimentological foraminiferal geotechnical and accelerator mass spectrometer ams radiocarbon data from marine cores from the mid continental shelf together with previously published ams dates to establish a sedimentological and chronological model initial ice sheet retreat through the outer and mid shelf sectors of marguerite trough was under way by ca 14 ka b p was rapid and coincided with the sea level rise of meltwater pulse 1a an ice shelf formed during this retreat and fine grained laminated muds reflecting meltwater derived suspension settling and or tidal pumping were deposited during this time the ice sheet remained grounded on the inner shelf ice shelf breakup and retreat of the calving front from ca 13 2 to 12 5 ka b p was slow 100 m a 1 across the outer and mid shelf with calving bay conditions remaining for at least 3 5 ka we interpret this ice shelf decay to have been driven by an incursion of weddell sea transitional water onto the shelf in contrast grounding line and ice shelf retreat in the inner bay occurred from ca 9 3 ka b p and was driven by circumpolar warm deep water encroaching onto the continental shelf at this time the mid shelf was an open marine environment characterized by hemipelagic deposition these findings highlight the importance of oceanographic controls in the breakup of antarctic peninsula ice shelves during the holocene

the evolution of a submarine landform record following recent and multiple surges of tunabreen glacier svalbard this study focuses on the glacial landform record associated with recent surge events of tunabreen a calving tidewater glacier in tempelfjorden spitsbergen submarine geomorphology and recent te

dynamics of the wind driven sea level variation around antarctica coastal sea level variation around antarctica is characterized by a coherent circumpolarly in phase fluctuation correlated with the antarctic oscillation aao this study addresses the dynamics of the winddriven sea level variation around antarctica a realistic barotropic numerical model reproduced well the observed sea level around antarctica from numerical model experiments the authors demonstrate that the forcing responsible for the coastal sea level is the wind stress at the coastal boundary both the dominant coherent signal and westward propagating signals are identified in the model and these signals are trapped over the shelf and slope around antarctica as a mechanism of these trapped signals the authors consider analytical solutions of the oceanic response to alongshore wind stress over the shelf and slope in the circumpolar domain in these solutions besides the shelf wave mode a wavenumber zero mode appears and characterizes the coastal dynamics around antarctica at periods from 10 to 200 days the coherent sea level can be explained quantitatively by the solution of this wavenumber zero mode with a 5 10 day damping time scale the spectral peaks of the westward propagating signals can be explained by the resonance of the shelf wave mode the wavenumber zero mode can respond to the wavenumber zero forcing at any frequency and the degree of response increases with decreasing frequency in addition the wavenumber zero component of wind stress corresponding to the aao variation is a dominant forcing therefore the coherent sea level variation around antarctica is preferably generated and becomes a dominant feature in the circumpolar domain particularly at lower frequencies

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

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

lithofacies and seismic reflection interpretation of temperate glacimarine sedimentation in tarr inlet glacier bay alaska abstract high resolution seismic reflection profiles of sediment fill within tarr inlet of glacier bay alaska show seismic facies changes with increasing distance from the glacial termini five types of seismic facies are recognized from analysis of huntec and minisparker records and seven lithofacies are determined from detailed sedimentologic study of gravity vibro and box cores and bottom grab samples lithofacies and seismic facies associations and fjordfloor morphology allow us to divide the fjord into three sedimentary environments ice proximal iceberg zone and ice distal the ice proximal environment characterized by a morainal bank depositional system can be subdivided into bank back bank core and bank front subenvironments each of which is characterized by a different depositional subsystem a bank back subsystem shows chaotic seismic facies with a mounded surface which we infer consists mainly of unsorted diamicton and poorly sorted coarse grained sediments a bank core depositional subsystem is a mixture of diamicton rubble gravel sand and mud seismic reflection records of this subsystem are characterized by chaotic seismic facies with abundant hyperbolic diffractions and a hummocky surface a bank front depositional subsystem consists of mainly stratified and massive sand and is characterized by internal hummocky facies on seismic reflection records with significant surface relief and sediment gravity flow channels the depositional system formed in the iceberg zone environment consists of rhythmically laminated mud interbedded with thin beds of weakly stratified diamicton and stratified or massive sand and silt on seismic reflection profiles this depositional system is characterized by discontinuously stratified facies with multiple channels on the surface in the proximal zone and a single channel on the largely flat sediment surface in the distal zone the depositional system formed in the ice distal environment consists of interbedded homogeneous or laminated mud and massive or stratified sand and coarse silt this depositional system shows continuously stratified seismic facies with smooth and flat surfaces on minisparker records and continuously stratified seismic facies which are interlayered with thin weakly stratified facies on huntec records

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

coherence of antarctic sea levels southern hemisphere annular mode and flow through drake passage 1 it is known from small sets of tide gauges that sub surface pressure sea level corrected for the inverse barometer effect around antarctica varies coherently around about half of the continent and that this coherent signal is related to atmospheric forcing in the form of the antarctic oscillation or southern hemisphere annular mode we here confirm that this coherence extends to a more extensive network of tide gauges and to parts of the continental shelf far from the shore as measured by bottom pressure gauges we use time series from an eddy permitting ocean model with realistic forcing to relate the coherent mode to fluctuations in transport through drake passage and confirm using a 1 resolution barotropic model that the fluctuations are predominantly due to barotropic dynamics although baroclinic dynamics are expected to play an increasing role at interannual timescales

surficial glaciology of jakobshavns isbrae west greenland part i surface morphology jakobshavns isbrae is a large fast moving ice stream outlet glacier in west greenland which ends at a floating calving front it drains about 6 5 of the area of the greenland ice sheet studies of its surface morphology are described in this paper the surface is relatively steep 0 01 0 03 and the thickness is large up to 2600 m along the center line clarke and echelmeyer 1989 indicating very high driving stresses 200 300 kpa the ice stream is about 6 km wide and 85 90 km long all of which is in an area of surface melting the base of the ice stream and of much of the drainage area is below sea level marginal crevasse zones have a width on the order of the width of the ice stream itself unique surficial features are ice blisters and lakes the latter have a sequence of ogive like features on their floating ice cover which can be used to determine velocity there is a pinning point near the terminus which may act as a stabilizing influence possibly playing a role in halting at least temporarily a recent retreat of the terminus ice thickness estimates at the terminus lead to a flux which is less than previously assumed by others e g bindschadler 1984 pelto and others 1989 when estimating jakobshavns isbrae s drainage basin to be nearly in balance the driving stresses on jakobshavns isbrae are an order of magnitude higher than those of the ice streams of west antarctica its crevasse patterns are much less localized its relatively unconfined terminus is more comparable to that of relatively unbuttressed ice streams such as pine island and thwaites glaciers than it is to other west antarctic ice streams which terminate in large confined ice shelves

theory and observations of ekman flux in the chlorophyll distribution downstream of south georgia 1 a large phytoplankton bloom occurs downstream of south georgia an island on the northern edge of the scotia sea atlantic sector of the southern ocean this is due to natural iron fertilisation being advected downstream in the antarctic circumpolar current mapping of seawifs chl a in dynamic height longitude space reveals the trajectory of surface water under the dual influences of geostrophic flow and ekman flux a theoretical estimate of the trajectory shows good agreement with observations the trajectory is dependent on the wind stress mixed layer depth ratio but independent of the latitudinal separation of dynamic height contours the chl a distribution suggests that iron reaches 20 w below the mixed layer away from the effects of ekman flux but beyond the iron is confined to the surface layer chl a reduces monotonically east of south georgia with the signal detectable to 15 e over 3500 km downstream indicating the basin scale biogeochemical influence of the iron supply

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

sediment thicknesses and holocene glacial marine sedimentation rates in three east greenland fjords ca 68 n we compared measured and estimated sediment budgets in heavily glaciated fjords in east greenland mass balance calculations and regional glacio climatic conditions suggest that the sediment flux to the seafloor in kangerdlugssuaq and nansen fjords should be dominated by iceberg rafting and not by the rain out of suspended particulates in meltwater as the glacier calving flux is estimated at 15 and 2 km 3 yr compared to meltwater volumes of 4 4 and 1 7 km 3 yr respectively gravity cores in the three fjords indicate that the uppermost 1 2 5 m of sediment consists of diamictons or fine grained laminated muds ams radiocarbon dates on calcareous foramininfera or shells 16 total indicate sedimentation rates of 110 to 340 cm ka within the fjords over the last 1 ka and 10 20 cm ka during the holecene on the inner and middle shelf annual sediment discharge is around 0 67 times 10 6 tonnes yr within the kangerdlugssuaq fjord and trough system which translates into an average basin wide rate

jakobshavns glacier drainage basin a balance assessment maximum and minimum estimates are made of the drainage basin feeding the jakobshavns glacier by using surface elevation maps derived from seasat altimetry benson s 1962 net balance measurements are used to calculate the balance flow within the basin comparisons of the balance flux at the terminus with estimates of actual flux suggest the basin is in overall equilibrium or slightly thickening this agrees with measurements along the nearby egig traverse balance velocities accelerate rapidly within 100 km of the coast farther upstream balance velocities are consistent with both measured velocities along the egig traverse and calculated deformation velocities it is estimated that jakobshavns glacier discharges between 4 8 and 7 6 of the annual net balance over greenland and drains between 3 7 and 5 8 of the ice sheet area

possible triggering of heinrich events by ice load induced earthquakes north atlantic sediments dating from the last ice age contain layers of rock fragments from northeastern canada so called heinrich layers 1 like modern iceberg borne sediments from greenland these layers have been attributed to ice rafting episodes1 2 3 six heinrich layers have been documented and correlated with climate changes4 5 6 7 8 the layers which are several centimetres thick contain negligible amounts of foraminifera which accumulate at a few millimetres per century implying that they were deposited over just a few years these ice rafting heinrich events are separated by progressively shorter intervals from about 40 to 6 kyr ref 9 and it has been suggested10 that they are related to the milankovitch cycles in the earth s orbital parameters11 alternatively they may be generated by forcing mechanisms arising from the internal dynamics of the laurentide ice sheet12 here we suggest the possibility that the heinrich events were precipitated by ice load induced earthquakes analogous to those produced by reservoir water loads13 we suggest that near its edge the laurentide ice sheet sheared the earth s crust inducing repeated failure that released the ice rafts this region along canada s northeastern seaboard shows evidence of both current14 15 and past seismic activity owing to postglacial rebound our model accounts for the intervals between both the heinrich events and the evidence of palaeoseismicity and can be tested by studying local sedimentary relationships

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

holocene sedimentary environment of cambridge fiord baffin island northwest territories the holocene sedimentary environment of cambridge fiord in northeastern baffin island is interpreted from six piston cores distinct sediment types represent three sedimentary processes 1 muds deposited from suspension from fluvial sources at the fiord head and glacial sources near the mouth are the dominant components of the sediments the rate of accumulation in mid fiord based on a radiocarbon date on dispersed organic material indicates an average rate of sedimentation of 1 24 mm a since about 5800 bp upper portions of the cores are bioturbated although bands of well preserved fine rhythmites indicate the sudden loss of the benthos perhaps caused by oxygen depletion associated with reduced circulation rhythmites near the sediment surface have a mean thickness similar to the calculated annual accumulation indicating that they probably are varves those at depth average 8 1 mm thick fine sediment at depth in several cores was not bioturbated for long periods indicating reduced effectiveness of

ocean dynamics associated with rapid j2 fluctuations importance of circumpolar modes and identification of a coherent arctic mode 1 fluctuations of the earth s dynamic oblateness j2 are a measure of global redistributions of mass between equatorial and polar regions sensitive to the component which is symmetric about the equator cox and chao recently published a time series of monthly values of j2 based on satellite orbit determination which showed rapid fluctuations from month to month as well as a large change in j2 in 1997 1998 we here investigate the ocean dynamics associated with these rapid fluctuations using a barotropic ocean model forced by atmospheric wind stress and pressure we find that the model has significant skill in reproducing the observations though not the change in 1997 1998 much of the model variability is related to coherent circumpolar fluctuations in arctic and antarctic bottom pressure which despite their apparent symmetry are forced by quite different mechanisms the antarctic mode is forced by circumpolar winds whereas the arctic mode is forced by northward winds over the entrances to the polar sea comparison with in situ observations shows that the model has skill in reproducing the polar modes arctic tide gauge records confirm the presence of a coherent mode at short periods and at long periods over at least the eurasian arctic shelf if barotropic and representative of the whole arctic this would be large enough to make a major contribution to measured j2 fluctuations but does not account for the 1997 1998 event

a 100 yr record of ocean temperature control on the stability of jakobshavn isbrae west greenland an understanding of the interaction between ice sheet dynamics and forcing mechanisms such as oceanic and atmospheric circulation is important because of the potential contribution of these processes to constraining models that seek to predict future rates of sea level change here we report new benthic foraminiferal data from disko bugt west greenland showing a close correlation between subsurface ocean temperature changes and the ice margin position of the glacier jakobshavn isbrae over the past 100 yr in particular our faunal data show that warm ocean currents entered a bay disko bugt during the retreat phases of jakobshavn isbrae from a d 1920 to 1950 and since 1998 we also show a link between west greenland ocean temperature and the atlantic multidecadal oscillation a key climate indicator in the north atlantic ocean the close coupling between the oceans and the cryosphere identified here should be assessed in future projections of sea level change

variability of antarctic circumpolar transport and the southern annular mode associated with the madden julian oscillation 1 the variability of oceanic antarctic circumpolar transport and the atmospheric southern annular mode sam on intraseasonal 30 70 day timescales is shown to be related to the tropical atmospheric madden julian oscillation mjo during southern winter approximately 7 days after anomalous mjo convection in the equatorial indian ocean peaks an atmospheric extratropical response is set up with anomalous surface westerlies around almost the entire latitude circle at 60 s this pattern projects strongly onto the sam and leads to an acceleration of the eastward circumpolar transport around antarctica as measured by tide gauges and bottom pressure recorders this ocean response is confirmed by a global ocean model which shows a maximum in the transport through drake passage 3 days after the atmospheric extratropical response

new detection of tremor triggered in hokkaido northern japan by the 2004 sumatra andaman earthquake 1 the transient stress change caused by the passage of surface waves resulting from the 26 december 2004 sumatra andaman earthquake triggered seismic tremor in two regions in hokkaido in the northernmost part of the japanese islands where tectonic tremor associated with the subducting plate has not previously been detected the amplitude pattern of the tremor envelope in both regions is characterized by a periodic enhancement at an interval of about 20 s which correlates with the surface wave one tremor that was triggered in central hokkaido at a depth of around 10 20 km coincides with active seismicity linked to previously known deep low frequency microearthquakes related to volcanic activity another tremor occurred in northernmost hokkaido where there are no known active faults volcanoes or microearthquake seismicity if the source of the northern tremor is located near the ground surface it would be possible that the tremor is related to fluid pressure change because the periodic enhancement of tremor amplitude is in phase with the largest compressional strain caused by surface waves

hydrography and climate of the last 4400 years in a sw greenland fjord implications for labrador sea palaeoceanography a multiproxy record including benthic foraminifera diatoms and xrf data of a marine sedi ment core from a sw greenland fjord provides a detailed reconstruction of the oceanographic and cli matic variations of the region during the last 4400 cal years the lower part of our record represents the final termination of the holocene thermal maximum after the onset of the neoglaciation at approxi mately 3 2 ka cal bp the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the labrador sea and the north atlantic region our data show that increased advection of atlantic water irminger sea water from the west greenland current into the labrador sea was a typical feature of northeast atlantic cool ing episodes such as the little ice age and the european dark ages while the advection of irminger sea water decreased significantly during warm episodes such as the mediaeval warm period and the roman warm period whereas the mediaeval warm period was characterized by relatively cool climate as suggested by low meltwater production the preceding dark ages display higher meltwater runoff and consequently warmer climate when compared with european climate these regional climate anomalies indicate persisting patterns of advection of colder respectively warmer air masses in the study region dur ing these periods and thus a long term seesaw climate pattern between west greenland and europe

low frequency currents and continental shelf waves in the southern weddell sea abstract the salient features of low frequency current fluctuations obtained from an analysis of eight current meter records from the continental shelf and slope of the southern weddell sea are compared to baroclinic and barotropic theories a simple baroclinic theory of internal waves is used successfully to predict high frequency spectral cutoff values from low frequency velocity ellipse calculations made from the continental slope mooring data the success of this theory indicates that the higher spectral energy levels observed over the slope compared to the shelf are probably due to baroclinic motions a barotropic model of free continental shelf waves probably by saint guily 1976 is adapted for the local topography and the predictions of the model compared to observations coherences and phases between moorings separated by 10 and 160 km in the along shelf direction provide substantial evidence of the existence of shelf waves as predicted by the theory for periods of 3 60 days and for the lowest

coherent sea level fluctuations along the global continental slope signals in sea level or more properly sub surface pressure ssp sea level corrected for the inverse barometer effect are expected to propagate rapidly along the continental slope due to the effect of sloping topography on wave modes resulting in strongly correlated ssp over long distances observations of such correlations around the arctic and antarctic are briefly reviewed and then extended using satellite altimetry to the rest of the global continental slope it is shown that such long distance correlations are common especially in extra tropical regions simple correlations from altimetry cannot however establish the wave speed or whether waves are responsible for the correlations as opposed to large scale coherence in the forcing a case study around south america is used to highlight some of the complications and is found to strengthen the case for the importance of wave modes in such long distance ssp coherence although more detailed in situ data are required to resolve the cause of the correlations

coherent sea level response to the antarctic oscillation 1 large scale sea level variations around antarctica were studied and their relationship with atmospheric variations was investigated tide gauge data at five coastal stations were used coherent sea level variations were clearly detected for all stations on intraseasonal time scales the coherent variations had significant negative correlations with an index of the atmospheric annular mode variation antarctic oscillation coherence was significant for periods from 10 to 100 days with negligible time lag the negative correlation is consistent with the mechanism that a high low westerly anomaly leads to a stronger weaker northward ekman drift and causes divergence convergence around antarctica

age of the fjord stade moraines in the disko bugt region western greenland and the 9 3 and 8 2 ka cooling events abstract retreat of the western greenland ice sheet during the early holocene was interrupted by deposition of the fjord stade moraine system the fjord stade moraine system spans several hundred kilometers of western greenland s ice free fringe and represents an important period in the western greenland ice sheet s deglaciation history but the origin and timing of moraine deposition remain uncertain here we combine new and previously published 10 be and 14 c ages from disko bugt western greenland to constrain the timing of fjord stade moraine deposition at two locations 60 km apart at jakobshavn isfjord the northern of two study sites we show that jakobshavn isbrae advanced to deposit moraines ca 9 2 and 8 2 8 0 ka in southeastern disko bugt the ice sheet deposited moraines ca 9 4 9 0 and 8 5 8 1 ka our ice margin chronology indicates that the greenland ice sheet in two distant regions responded in unison to early holocene abrupt cooling 9 3 and 8 2 ka as recorded in central greenland ice cores although the timing of fjord stade moraine deposition was synchronous in jakobshavn isfjord and southeastern disko bugt within uncertainties we suggest that jakobshavn isbrae advanced while the southeastern disko bugt ice margin experienced stillstands during the 9 3 and 8 2 ka events based on regional geomorphology and the distribution of 10 be ages at each location the contrasting style of ice margin response was likely regulated by site specific ice flow characteristics jakobshavn isbrae s high ice flux results in an amplified ice margin response to a climate perturbation both warming and cooling whereas the comparatively low flux sector of the ice sheet in southeastern disko bugt experiences a more subdued response to climate perturbations our chronology indicates that the western greenland ice sheet advanced and retreated in concert with early holocene temperature variations and the 9 3 and 8 2 ka events although brief were of sufficient duration to elicit a significant response of the western greenland ice sheet

adjustment of the southern ocean to wind forcing on synoptic time scales abstract this study addresses the response of the southern ocean to high frequency wind forcing focusing on the impact of several barotropic modes on the circumpolar transport a suite of experiments is performed with an unstratified model of the southern ocean forced with a stochastic wind stress that contains a large range of frequencies with synoptic time scales the southern ocean adjustment displays a different character for frequencies below and above 0 2 cpd the low frequency range is dominated by an almost free mode response in the region where contours of f h are obstructed by only a few bathymetric features the truly free mode only plays a minor role topographic form stress rather than friction is the dominant decay mechanism of the southern mode it leads to a spindown time scale on the order of 3 days for the high frequency range the circumpolar transport is dominated by the resonant excitation of oscillatory modes the active response of the ocean leads to strong changes and eve

an extensive and dynamic ice sheet on the west greenland shelf during the last glacial cycle considerable uncertainty surrounds the extent and timing of the advance and retreat of the greenland ice sheet gis on the continental shelf bordering baffin bay during the last glacial cycle here we use marine geophysical and geological data to show that fast flowing ice sheet outlets including the ancestral jakobshavn isbrae expanded several hundred kilometers to the shelf edge during the last glaciation ca 20 ka retreat of these outlets was asynchronous initial retreat from the shelf edge was underway by 14 880 calibrated cal yr b p in uummannaq trough radiocarbon dates from the adjacent disko trough and adjoining trough mouth fan imply later deglaciation of jakobshavn isbrae and significantly an extensive readvance and rapid retreat of this outlet during the younger dryas stadial yd this is notable because it is the first evidence of a major advance of the gis during the yd on the west greenland shelf although the short duration suggests that it may have been out of phase with yd temperatures

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

sediment characteristics in iceberg dominated fjords kangerlussuaq region east greenland abstract sediment cores from three east greenland fjords contain sediment lithofacies and depositional processes in an iceberg dominated glacial marine setting three major lithofacies diamicton fine grained mud and sand are deposited by two processes sediment rain out and sediment gravity flows the sediments in kangerlussuaq fjord are predominately fine grained muds deposited by rain out from icebergs and glacier meltwater with sediment gravity flows acting as secondary agents of deposition miki fjord records rain out of fine grained muds from a river plume emanating from a proglacial delta at the fjord head alternating units of diamicton and fine grained mud in nansen fjord are deposited by sediment rain out from icebergs particle size is governed by the oceanographic conditions in the fjord at the time of deposition despite their proximity to each other each fjord is distinguished by a distinct sedimentological signature kangerlussuaq fjord has low total organic carbon contact miki fjord has high mass magnetic susceptibility and nansen fjord has high amounts of ice rafted debris comparison of the east greenland iceberg dominated and alaska glacial meltwater dominated environments indicates few major differences between sediments deposited in these two settings this similarity raises doubt as to how well glacial marine sedimentary sequences can be used to interpret and reconstruct differences between glacial marine environments in the past without knowledge of sediment accumulation rates environmental conditions at the time of sediment deposition and comparable sedimentological data between studies

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

early holocene palaeoceanography and deglacial chronology of disko bugt west greenland two new cores from disko bugt a large marine embayment in west greenland are used to assess the deglacial chronology and palaeoceanography of the area during the early holocene deglaciation of the main part of disko bugt is directly dated for the first time to a minimum of ca 10 2 ka cal bp by this time the jakobshavn isbrae ice stream had retreated to the eastern margins of disko bugt initial deglaciation took place before the relatively warm west greenland current wgc was initiated a strengthening in the wgc is identified from ca 9 2 ka cal bp accompanied by retreat of the ice stream to a shallow bank immediately west of the present day jakobshavn isfjord while in this position the calving and melting ice stream produced large volumes of sediment and meltwater the large volumes of meltwater prevented the relatively warm waters of the wgc reaching the eastern margins of disko bugt the ice stream remained grounded on this bank for over a thousand years until ca 7 9 ka cal bp when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system

glacimarine sedimentary processes and facies on the polar north atlantic margins abstract major contrasts in the glaciological oceanic and atmospheric parameters affecting the polar north atlantic both over space between its eastern and western margins and through time from full glacial to interglacial conditions have lead to the deposition of a wide variety of sedimentary facies in these ice influenced seas the dynamics of the glaciers and ice sheets on the hinterlands surrounding the polar north atlantic have exterted a major influence on the processes rates and patterns of sedimentation on the continental margins of the norwegian and greenland seas over the late cenozoic the western margin is influenced by the cold east greenland current and the svalbard margin by the northernmost extent of the warm north atlantic drift and the passage of relatively warm cyclonic air masses in the fjords of spitsbergen and the northwestern barents sea glacial meltwater is dominant in delivering sediments in the fjords of east greenland the large numbers of icebergs produced from fast flowing outlets of the greenland ice sheet play a more significant role in sedimentation during full glacials sediments are delivered to the shelf break from fast flowing ice streams which drain huge basins within the parent ice sheet large prograding fans located on the continental slope offshore of these ice streams are made up of stacked debris flows large scale mass failures turbidity currents and gas escape structures also rework debris in continental slope and shelf settings even during interglacials both the margins and the deep ocean basins beyond them retain a glacimarine overprint derived from debris in far travelled icebergs and sea ice under full glacial conditions the glacier influence is correspondingly stronger and this is reflected in the glacial and glacimarine facies deposited at these times

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

current variability under landfast sea ice in lutzow holm bay antarctica current measurements were made under landfast sea ice in lutzow holm bay antarctica in 1991 in spite of no direct wind forcing and negligible thermohaline forcing currents with a magnitude of 0 1 0 3 m s 1 were observed it is suggested that current variability strongly depends on the extent of the landfast ice on the eastward continental shelf before the fast ice edge extends to the shelf break the current at ongul strait located near the continental coast is highly coherent with the wind with a time lag of 1 1 5 days and somewhat coherent with the adjusted sea level with no time lag at periods of 6 8 days after the fast ice edge is stably located along the shelf break the current is not at all coherent with the wind or sea level we infer that the variability at periods of 6 8 days is mainly due to the first mode shelf wave excited by the wind stress over the eastward continental shelf the direction of the prevailing current at ongul strait changed drastically from southward the same direction of the wind to northward in may although the prevailing wind direction did not change this change in timing coincides with the rapid development period of the fast ice extent

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

bottom pressure changes around antarctica and wind driven meridional flows 1 spatially averaged bottom pressure anomalies near antarctica south of 60 s calculated from grace data are well correlated with those produced by the ecco project using least squares optimization methods to fit an ocean model to most available data both grace and ecco results indicate mass exchange primarily between the southern ocean and the pacific and the importance of zonal wind stress to this exchange the ecco flow fields show that the near surface meridional ekman transport directly driven by the zonal wind stress is nearly balanced by return flows below the shallowest topography at 60 s 1300 m at this drake passage latitude with the return transport being slightly lagged in time relative to the ekman transport such time lags which may result from geostrophic adjustment at depth cause the small associated net transport across 60 s to be 90 out of phase with the wind this in turn can explain why zonal wind stress and bottom pressure anomalies around antarctica tend to be anticorrelated in both grace and ecco results

changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode 1 we present the first direct evidence that interannual changes in ocean transport through drake passage are forced by variability in the southern annular mode sam this evidence is derived from two decades 1980s and 1990s of subsurface pressure measurements from the tide gauge at faraday station western antarctic peninsula combined with the output of an ocean general circulation model in recent decades the sam has moved toward a higher index state stronger circumpolar winds this trend is not simply monotonic but is the product of a long term change in the seasonality of the sam whilst we cannot address directly the effect of the long term trend on circumpolar transport bottom pressure data from drake passage during the 1990s demonstrate that ocean transport showed the same changes in seasonality as did the sam this offers a mechanism for atmospheric climate change to influence directly the largescale ocean circulation indexterms 4207 oceanography general arctic and antarctic oceanography 4215 oceanography general climate and interannual variability 3309 4532 oceanography physical general circulation 1635 global change oceans 4203 4556 oceanography physical sea level variations citation meredith m p p l woodworth c w hughes and v stepanov 2004 changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode geophys res lett 31 l21305 doi 10 1029 2004gl021169

late quaternary ice flow in a west greenland fjord and cross shelf trough system submarine landforms from rink isbrae to uummannaq shelf and slope sea floor landforms and acoustic stratigraphic records allow interpretation of the past form and flow of a westward draining ice stream of the greenland ice sheet rink isbrae the late pliocene pleistocene glacial package is several hundred metres thick and down laps onto an upper miocene horizon several acoustic facies are mapped from sub bottom profiler records of the 400 km long uummannaq fjord shelf slope system an acoustically stratified facies covers much of the fjord and trough floor interpreted as glacimarine sediment from rain out of fine grained debris in turbid meltwater beneath this facies is a semi transparent deformation till unit which includes buried streamlined landforms landform distribution in the uummannaq system is used to reconstruct past ice extent and flow directions the presence of streamlined landforms mega scale glacial lineations drumlins crag and tails shows that an ice stream advanced through the fjord system to fill uummannaq trough reaching the shelf edge at the last glacial maximum beyond the trough there is a major fan built mainly of glacigenic debris flows turbidity current channels were not observed on uummannaq fan contrasting with well developed channels on disko fan 300 km to the south ice retreat had begun by 14 8 cal ka ago grounding zone wedges gzw in uummannaq trough imply that retreat was episodic punctuated by several still stands ice retreat between gzws may have been relatively rapid there is little sedimentary evidence for still stands in the inner fjords except for a major moraine ridge marking a little ice age maximum position on the shallow banks either side of uummannaq trough iceberg ploughing has reworked any morphological evidence of earlier ice sheet activity

quasi biennial modulation of the southern ocean coherent mode empirical orthogonal function eof analysis of two independent southernocean sea level datasets for the period 1992 2002 shows that the coherent oceanicmode a zonally symmetric counterpart to the atmospheric southern annular mode sam consistently emerges as the predominant mode of variability and is revealedto be a reliable proxy for circumpolar transport upon subannual to interannualtime scales cross validation of the coherent mode from each dataset and that ofa global barotropic model demonstrates a high degree of correspondence betweensea level observations and model estimations and also indicates that the coherentoceanic mode is largely barotropically driven upon subannual time scales whilstbaroclinic oceanic effects predominate at longer periods both the coherent modeand transport are shown to be modi ed by the stratospheric quasi biennial oscilla tion qbo and a mechanism is described by which qbo dependent planetary waveactivity may be guided from the stratosphere towards the surface by high latitudeeasterly and westerly jets inducing wind anomalies that force sea level variabilitythrough equatorward ekman transport a longer 18 year tide gauge record fromthe vernadsky faraday station and a 22 year time series of sea level estimationsfrom an ocean general circulation model are used to show that qbo inducedsea level and transport variability may be modulated upon longer time scales by aquasi decadalcycleofsolaractivity copyright c 2010royalmeteorologicalsociety

late holocene environment and climatic changes in ameralik fjord southwest greenland evidence from the sedimentary record sedimentological and geochemical xrf data together with information from diatom and benthic foraminiferal records of a 3 5 m long gravity core from ameralik fjord southern west greenland is used for reconstructing late holocene environmental changes in this area the changes are linked to large scale north atlantic ocean and climate variability ams 14c dating of benthic foraminifera indicates that the sediment core records the last 4400 years and covers the termination of the holocene thermal maximum htm the late htm 4 4 3 2 ka bp is characterized by high accumulation rates of fine silty sediments related to strong meltwater discharge from the inland ice the htm benthic foraminiferal fauna demonstrates the presence of well ventilated saline bottom water originating from inflow of subsurface west greenland current water of atlantic irminger sea origin the hydrographic conditions were further characterized by limited sea ice probably related to a mild and relatively windy winter climate af

kelvin waves around antarctica abstractthe southern ocean allows circumpolar structure and the antarctic coastline plays a role as a waveguide for oceanic kelvin waves under the cyclic conditions the horizontal wavenumbers and frequencies for circumpolarly propagating waves are quantized with horizontal wavenumbers 1 2 and 3 corresponding to periods of about 32 16 and 11 h respectively at these frequencies westward propagating signals are detected in sea level variation observed at antarctic coastal stations the occurrence frequency of westward propagating signals far exceeds the statistical significance and the phase speed of the observed signal agrees well with the theoretical phase speed of external kelvin waves therefore this study concludes that the observed westward propagating sea level variability is a signal of the external kelvin waves of wavenumbers 1 2 and 3 around antarctica a series of numerical model experiments confirms that kelvin waves around antarctica are driven by surface air pressure and that th

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

glacimarine sedimentary processes and depositional environments in an embayment fed by west greenland ice streams abstract the extent and behaviour of the central west greenland sector of the greenland ice sheet gis during the last glacial maximum lgm and the following deglaciation remains poorly constrained to investigate deglacial marine environments and sedimentary processes in an area fed by several lgm ice streams we now report findings from a 3 5 khz sub bottom profiler survey acquired in and around disko bay in 2009 sediment thicknesses and volumes in three glaciated areas disko bay southern vaigat and egedesminde dyb are fully constrained for the first time acoustic facies types and distributions were also mapped the largest sediment thicknesses 256 m and widest variation in acoustic character was observed in disko bay adjacent to the mouth of jakobshavns isfjord significant sediment thicknesses were also observed in isolated basins in the egedesminde dyb trough and in a trough in southern vaigat strait up to 110 m given low modern sedimentation rates these thick sediment packages are inferred to record the retreat of glaciers from the middle shelf through disko bay and into both the jakobshavns and torssukatak fjord systems in central west greenland our results highlight similarities in deglacial sedimentary processes across the study area when the margins of retreating glaciers supplied large volumes of sediment to the marine environment from sediment laden meltwater plumes and melting icebergs we estimate the sediment flux for the palaeo jakobshavn ice stream while the ice margin was stable at a fjord entrance sill to be 1 6 3 6 10 7 m 3 a 1 assuming a flux at the upper end of our range for the torssukatak fjord system requires the grounded ice margin to be stable for about 450 years during retreat the sediment fluxes we estimate are within the range of previously calculated fluxes for other arctic and antarctic ice streams and suggest that large volumes of meltwater and sediment were available at the base of the outlet glaciers during deglaciation even during periods of quasi stability retreat of the ice margins into the fjord systems is characterised by a rapid transition to ice distal sedimentation by rainout of iceberg rafted detritus ird and hemipelagic material accumulation rates drop to 2 mm a 1 this study demonstrates the variability in glacimarine processes and environments on high latitude continental margins and highlights the importance of local factors such as bedrock morphology as well as glacio dynamic factors on sedimentation

late holocene relative sea levels near palmer station northern antarctic peninsula strongly controlled by late holocene ice mass changes abstract many studies of holocene relative sea level rsl changes across antarctica assume that their reconstructions record uplift from glacial isostatic adjustment caused by the demise of the last glacial maximum lgm ice sheets however recent analysis of gps observations suggests that mantle viscosity beneath the antarctic peninsula is weaker than previously thought which would imply that solid earth motion is not controlled by post lgm ice sheet retreat but instead by late holocene ice mass changes if this hypothesis is correct one might expect to find holocene rsl records that do not reflect a monotonic decrease in the rate of rsl fall but show variations in the rate of rsl change through the holocene we present a new record of late holocene rsl change from torgersen island near palmer station in the western antarctic peninsula that shows an increase in the rate of relative sea level fall from 3 0 1 2 mm yr to 5 1 1 8 mm yr during the late holocene independent studies of the glacial history of the region provide evidence of ice sheet changes over similar time scales that may be driving this change when our rsl records are corrected for sea surface height changes associated with glacial isostatic adjustment gia the rate of post 0 79 ka land uplift at torgersen island 5 3 1 8 mm yr is much higher than the rate of uplift recorded at a nearby gps site at palmer station prior to the larsen b breakup in 2002 ad 1998 2002 ad

variability of the ross gyre southern ocean drivers and responses revealed by satellite altimetry year round variability in the ross gyre rg antarctica during 2011 2015 is derived using radar altimetry the rg is characterized by a bounded recirculating component and a westward throughflow to the south two modes of variability of the sea surface height and ocean surface stress curl are revealed the first represents a large scale sea surface height change forced by the antarctic oscillation the second represents semiannual variability in gyre area and strength driven by fluctuations in sea level pressure associated with the amundsen sea low variability in the throughflow is also linked to the amundsen sea low an adequate description of the oceanic circulation is achieved only when sea ice drag is accounted for in the ocean surface stress the drivers of rg variability elucidated here have significant implications for our understanding of the oceanic forcing of antarctic ice sheet melting and for the downstream propagation of its ocean freshening footprint

monitoring the transport of the antarctic circumpolar current at drake passage abstract data from an extensive moored instrument array and three hydrographic cruises are used to calculate a time series of the net transport through the upper 2500 m of the drake passage the baroclinic geostrophic transport was monitored with heavily instrumented moorings at each side of the passage pressure gauge measurements at the northern and southern ends of the passage provided a reference speed at 500 m to adjust the relative transport the net transport of the upper 2500 m for the 370 day record ending in january 1980 averaged 121 106 m3 s 1 the total transport through the entire cross sectional area of drake passage is probably between 118 and 146 106 m3 s 1 fluctuations in the relative transport are related to changes in latitude of the northernmost front in the passage the subantarctic front variability of the net transport is coherent with the zonally averaged eastward wind stress

changes in ice front position on greenland s outlet glaciers from 1992 to 2007 1 previous studies in greenland show that retreat of tidewater glaciers may be linked to recent increases in ice loss raising greenland s contribution to sea level rise we examined ice front changes of 203 tidewater glaciers land terminating glaciers and glaciers terminating with ice shelves to understand greenland glacier behavior over three periods 1992 2000 2000 2006 and 2006 2007 we observed synchronous ice sheet wide increases in tidewater retreat during 2000 2006 relative to 1992 2000 coinciding with a 1 1 c increase in mean summer temperature at coastal weather stations rates of retreat for the southeast and east slowed during 2006 2007 when temperatures were slightly cooler than the 2000 2006 average our work suggests that regional greenland tidewater retreat responds strongly to climate change with higher temperatures corresponding to increasing retreat and helps confirm a link between ice thickness velocity and ice front position

circumpolar response of southern ocean eddy activity to a change in the southern annular mode 1 analysis of satellite altimeter data reveals anomalously high eddy kinetic energy eke in the antarctic circumpolar current acc during the period 2000 2002 around 2 3 years earlier 1998 the circumpolar eastward wind stress as quantified by the southern annular mode sam showed a significant positive peak and we have shown previously that the acc peaked around 1998 in response an eddy resolving ocean model is used to investigate the delay between wind forcing and the eddy response and demonstrates that the lag is due to the time taken to influence the deep circulation of the acc winds over the southern ocean have shown a strong climatic increase over the past few decades if this increase in winds is also reflected as an increase in eddy activity as our analysis suggests it might then the increased poleward heat flux may have played a significant role in the observed warming of the southern ocean citation meredith m p and a m hogg 2006 circumpolar response of southern ocean eddy activity to a change in the southern annular mode geophys res lett 33 l16608 doi 10 1029 2006gl026499

preliminary 10be chronology for the last deglaciation of the western margin of the greenland ice sheet the now acknowledged thinning of the greenland ice sheet raises concerns about its potential contribution to future sea level rise in order to appreciate the full extent of its contribution to sea level rise reconstruction of the ice sheet s most recent last deglaciation could provide key information on the timing and the height of the ice sheet at a time of rapid climate readjustment we measured 10be concentrations in 12 samples collected along longitudinal and altitudinal transects from sisimiut to within 10 km of the isunguata sermia glacier ice margin on the western coast of greenland along the longitudinal transect we collected three perched boulders and two bedrocks in addition we sampled seven perched boulders along a vertical transect in a valley within 10 km of the isunguata sermia glacier ice margin our pilot dataset constrains the height of the ice sheet during the last glacial maximum lgm between 500 m and 840 m including the 120 m relative sea level depression at the time of the lgm 21 ka bp from the transect we estimate the thinning of the ice sheet at the end of the deglaciation between 12 3 1 5 10be ka n 2 and 8 3 1 2 10be ka n 3 to be 6 cm a 1 over this time period direct dating of the retreat of the western margin of the greenland ice sheet has the potential to better constrain the retreat rate of the ice margin the thickness of the former ice sheet as well as its response to climate change copyright 2008 john wiley sons ltd

wind induced sea surface slopes on the west florida shelf abstract tidal and meteorological records at stations in the eastern gulf of mexico have been studied the sea level response is a maximum for winds along the coast and varies symmetrically with angle the coherence is maximum at periods of 4 10 days the horizontal coherence of sea level is high out to 500 km for 4 10 day periods the horizontal coherence for wind measured at coastal stations is high out to at least 500 km the amplitude of the response of sea level to winds is larger by a factor of 4 here on a broad shelf than on the oregon coast which is more narrow by about the same ratio a response of 16 cm is induced by 4 m s 1 wind this response or transfer function is uniform over the spectral range 4 100 days the sea level response to the longshore wind stress is not linear but to the power 0 8 0 1 and is attributed to the relatively low tidal currents in this region the large horizontal coherences of wind and sea level imply broad longshore flows extending 500 km or more along

acoustic mapping of the ilulissat ice fjord mouth west greenland a ship based acoustic mapping campaign was conducted at the exit of ilulissat ice fjord of west greenland and in the sedimentary basin of disko bay west of the fjord mouth submarine landscape and sediment distribution patterns represented by five acoustic facies types represent glaciomarine sediment facies types that are related to variations in the past position and relative motion of the glacier front asymmetric ridges on the shelf that form a curved entity and a large sill at the fjord mouth represent moraines that depict at least two relatively stable positions of the ice front in the disko bay and at the fjord mouth comparable ice end features are not observed seaward of the east greenland kangerdlugssuaq glacier although both glaciers are comparable in their latitudinal position present size and present role for the ice discharge from the inland ice sheet apparently the retreat of the greenland inland ice after the last maximum expansion was a more discontinuous process on the west greenland shelf than on the east greenland shelf the iceberg bank a prominent sill at the fjord exit appears to play an important role for the sedimentation after the retreat of the ice front from the shelf was completed the retreat of the glacier behind the iceberg bank into the inner fjord is marked by a reorganization of sediment delivery in disko bay as most of the till is now deposited within the fjord two linear clusters of pockmarks in the center of the sedimentary basin seem to be linked to methane release due to dissociation of gas hydrates a process driven by fast crustal uplift of the greenland shelf the orientation of these clusters appears to reflect a migration path that is defined by a buried structure which we could not resolve

the last glaciation of germania land and adjacent areas northeast greenland a profile across the unglaciated coast of northeast greenland at 77 n was studied with regard to the quaternary stratigraphy and glacial history the germania land peninsula is characterised by till covered lower ground which contrasts sharply with the blockfields and extensive gelifluction deposits of its higher altitudes two glaciations are distinguished the older one extended over the entire area and had its margin on the continental shelf the younger one of late weichselian age reached the present coastline and several mountains and high plateaus on western germania land formed nunataks the late weichselian glaciation was more extensive and occurred later on the germania land peninsula than on the coast further south radiocarbon dates suggest that the glacier margin rested to the east of the present coastline until ca 10 000 yr bp this correlates with the late weichselian milne land stage which is found as a late glacial readvance along the coast of east greenland a series of recessional moraines formed during the deglaciation were probably caused by glacier dynamics as opposed to being of climatic origin

causes of large scale sea level variations in the southern ocean analyses of sea level and a barotropic model 1 we analyze a decade of sea surface height ssh measurements in the southern ocean from the topex poseidon and ers altimeters with a focus on the variability at timescales 2 years among the different processes contributing to large scale ssh variations the barotropic response to the winds dominates poleward of 50 s while thermosteric processes dominate equatorward except for resonant basins for the barotropic modes and regions of intense eddy activity a finite element barotropic model has been developed to analyze the vorticity budget the ssh from the model agrees well with observations the leading barotropic mode which is annular and is confined near antarctica is responsible for most of the barotropic circumpolar transport it is coherent with the zonally integrated eastward wind stress consistent with a free mode response although previously evidenced in bottom pressure data this mode is only partially seen in altimeter data because of ice coverage it nevertheless distinctly appears above the pacific ridges where it expands meridionally up to midlatitudes in the rest of the domain several regions coherent with the local wind stress curl are found these are regions isolated by f h contours mostly deep basins an analysis of the vorticity budget shows that generally topographic sverdrup balance is the leading process for periods 50 days but in some regions resonant basins diffusive and nonstationary terms are important a model experiment shows that transients redistribute energy along f h waveguides contributing to drain resonant regions as was hypothesized in previous works

antarctic circumpolar current frontal system in the south atlantic monitoring using merged argo and animal borne sensor data 1 we describe large scale features of the antarctic circumpolar current acc in the atlantic part of the southern ocean by merging argo data and data obtained by novel animal borne ctd sensors twenty one of these ctd satellite relay data loggers ctd srdls were attached to southern elephant seals mirounga leonina on south georgia the merged data yield unified gridded hydrogaphic fields with high temporal and spatial resolution enabling the determination of features absent in each of the data sets separately the structure and variability of the frontal field revealed by this data set were compared with those in daily quarter degree optimally interpolated sea surface temperature fields and fields of weekly gridded sea level anomaly in general the frontal positions derived using our data set are in agreement with previous work especially where the pathways are constrained by topography e g at the north scotia ridge and the south scotia ridge however with the improved temporal and spacial resolution provided by the ctd srdls we were able to observe some novel features all frontal positions are more variable than previously indicated across the scotia sea and west of the mid atlantic ridge on seasonal time scales the merged data set shows the temporal variability of the southern acc front saccf north of south georgia and in its position east of the island where the saccf lies further north than has been suggested in previous work in addition the subantarctic front crosses the mid atlantic ridge about 400 km further north when compared to previous work

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