underwater passive acoustic localization of pacific walruses in the northeastern chukchi sea this paper develops and applies a linearized bayesian localization algorithm based on acoustic arrival times of marine mammal vocalizations at spatially separated receivers which provides three dimensional 3d location estimates with rigorous uncertainty analysis to properly account for uncertainty in receiver parameters 3d hydrophone locations and synchronization times and environmental parameters water depth and sound speed correction these quantities are treated as unknowns constrained by prior estimates and prior uncertainties unknown scaling factors on both the prior and arrival time uncertainties are estimated by minimizing akaike s bayesian information criterion a maximum entropy condition maximum a posteriori estimates for sound source locations and times receiver parameters and environmental parameters are calculated simultaneously using measurements of arrival times for direct and interface reflected acoustic paths posterior uncertainties for all unknowns incorporate both arrival time and prior uncertainties monte carlo simulation results demonstrate that for the cases considered here linearization errors are small and the lack of an accurate sound speed profile does not cause significant biases in the estimated locations a sequence of pacific walrus vocalizations recorded in the chukchi sea northwest of alaska is localized using this technique yielding a track estimate and uncertainties with an estimated speed comparable to normal walrus swim speeds

influence of the great lakes on the dynamics of the southern laurentide ice sheet numerical experiments a time dependent flow line ice sheet model is used to explore interactions between last glacial climate the laurentide ice sheet and the great lakes we seek to understand perturbations in the ice flow field that caused three neighboring lobes to leave different geomorphic and sedimentary records driven by reconstructed air temperature variations from 65 to 18 ka the simulated lobe dynamics are consistent with constraints from loess and till chronologies till stratigraphy and ice surface profiles contrasts in lobe dynamics are best explained by the geometry of lakes along each flow line as ice entered these lakes calving influenced glacier mass balance in particular deep water in lake superior likely delayed ice advance into northern wisconsin by promoting large calving losses whereas lobes to the east that encountered shallower water were less affected by calving the driftless area of wisconsin may thus owe its existence at least in part to the presence of lake superior our results suggest that morainal bank evolution should be treated in ice sheet models in lacustrine and shallow marine settings determining the sediment flux to the morainal bank remains a difficult task for example ice advance across central lake superior was probably sediment flux limited otherwise the driftless area would have been glaciated

passive acoustic localization of the atlantic bottlenose dolphin using whistles and echolocation clicks a method for localization and tracking of calling marine mammals was tested under realistic field conditions that include noise multipath and arbitrarily located sensors experiments were performed in two locations using four and six hydrophones with captive atlantic bottlenose dolphins tursiops truncatus acoustic signals from the animals were collected in the field using a digital acoustic data acquisition system the data were then processed off line to determine relative hydrophone positions and the animal locations accurate hydrophone position estimates are achieved by pinging sequentially from each hydrophone to all the others a two step least squares algorithm is then used to determine sensor locations from the calibration data animal locations are determined by estimating the time differences of arrival of the dolphin signals at the different sensors the peak of a matched filter output or the first cycle of the observed waveform is used to determine arrival time of an echolocation click cross correlation between hydrophones is used to determine inter sensor time delays of whistles calculation of source location using the time difference of arrival measurements is done using a least squares solution to minimize error these preliminary experimental results based on a small set of data show that realistic trajectories for moving animals may be generated from consecutive location estimates

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

glacial geomorphic features in the northern barents sea direct evidence for grounded ice and implications for the pattern of deglaciation and late glacial sedimentation

lift off moraines markers of last ice flow directions on the scotian shelf lift off moraines are acoustically incoherent subparallel ridges observed on sidescan sonograms and high resolution reflection seismic profiles on the southeastern continental margin of canada they are up to 3 m high 20 80 m wide and are commonly overlain by stratified proglacial sediments although little is known about them detailed study of high resolution seismic profiles from the emerald basin and the lahave basin on the scotian shelf show that their height width ratio varies with the sounder seabed separation suggesting that the ridges may be narrower than they appear their morphology is similar to degeer moraines or cross valley moraines which form perpendicular to ice flow direction as their orientations can be estimated at the intersection of seismic lines they can be used to estimate ice flow directions since proglacial sediments are draped directly over top of them they are assumed to record the direction of last ice flow this directional data suggests that ice retreated not only

asynchronous little ice age glacier fluctuations in iceland and european alps linked to shifts in subpolar north atlantic circulation abstract records of past glacier fluctuations are an important source of paleoclimate data and provide context for future changes in global ice volume in the north atlantic region glacier chronologies can be used to track the response of terrestrial environments to variations in marine conditions including circulation patterns and sea ice cover however the majority of glacier records are discontinuous and temporally restricted owing in part to the extensive advance of northern hemisphere glaciers during the little ice age lia the most recent and severe climate anomaly of the neoglacial period here we combine an absolutely dated and continuous record of langjokull ice marginal fluctuations with new reconstructions of sediment flux through the past 1 2 ka using varved sediments from hvitarvatn a proglacial lake in iceland s central highlands large spatial and temporal variations in sediment flux related to changing ice cap dimensions are reconstructed from six sediment cores and seismic reflection profiles sediment data reveal two discrete phases of ice expansion occurring ca 1400 to 1550 ad and ca 1680 to 1890 ad these advances are separated by a persistent interval of ice retreat suggesting that a substantial period of warming interrupted lia cold the pattern of icelandic glacier activity contrasts with that of european glaciers but shows strong similarities to reconstructed changes in north atlantic oceanographic conditions indicating differing regional responses to coupled ocean atmosphere sea ice variations our data suggest that subpolar north atlantic circulation dynamics may have led to coherent asynchronous glacier fluctuations during the mid lia and highlight the importance of circulation variability in triggering and transmitting multidecadal scale climate changes to nearby terrestrial environments

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

deglaciation of the central barents sea abstract the marine based barents sea ice sheet covered the polar continental shelf north of norway and western russia during the last glacial maximum initial ice sheet retreat along the western margin is well established while the retreat pattern in the interior parts of the ice sheet remains poorly known here we present new geological data from the central barents sea the results are based on analysis of several marine geophysical datasets including geomorphological mapping of multibeam swath bathymetry data and analysis of seismic and acoustic stratigraphy the new results provide insights into the configuration and dynamics of the ice sheet during its retreat across the central barents sea in particular they show clear changes in the location of the main ice divides and domes with ice flow becoming gradually more topographically controlled as deglaciation progressed major troughs were characterised by episodic retreat and reoccurring cycles of fast and slow ice flow sometimes leading to stagnation and ice shelf formation meanwhile adjacent bank areas were covered by comparatively slowly retreating ice although evidence of streaming ice is also seen locally

proglacial lakes character behaviour and geological importance proglacial lakes are ubiquitous within the quaternary record and can provide exceptional breadth and depth of palaeoenvironmental information present deglaciation is increasing the number and size of proglacial lakes around the world this study provides a synthesis of knowledge on proglacial lake character and behaviour and critically evaluates the importance of proglacial lakes from a geological perspective we show how ice marginal or ice contact lakes and other distal proglacial lakes can be distinguished from each other by geomorphological sedimentological chemical and biological characteristics the key controls on proglacial lake geomorphology and sedimentology are outlined and discussed proglacial lakes can exacerbate mountain glacier and ice sheet margin ablation via mechanical and thermal stresses but very large lakes can moderate summer air temperatures and relatively retard summer ice ablation proglacial lakes interrupt meltwater flux and are very efficient sediment traps hydrological routing and consequent geomorphological activity can be radically modified by sudden drainage of proglacial lakes and resultant glacial lake outburst floods exceptionally large proglacial lake drainages affected global ocean circulation and global climate during the quaternary overall analyses of proglacial lakes can provide a valuable insight into i patterns character and behaviour of mountain glaciers ice sheets and glaciations and ii the impacts of past present and future deglaciation

one hydrophone method of estimating distance and depth of phonating dolphins in shallow water previous attempts at localizing cetaceans have generally used multiple hydrophone arrays and multichannel recording systems in this paper a low budget localization technique using only one hydrophone is described the time delays of the signals traveling via the surface and bottom reflection paths to the hydrophone relative to the direct signal are used to calculate the distance and the depth of a phonating animal only two additional measures the depth of the bottom and hydrophone have to be taken the method requires relatively shallow waters and a flat bottom surface echolocating and burst pulsing hawaiian spinner dolphins stenella longirostris at the waianae coast of oahu hawaii were localized over different bottom substrates a tracking range of up to 100 m was achieved the accuracy of the method is estimated by the total error differential technique the relative distance estimation error is below 35 and the absolute depth error below 0 7 m so that the location method is sufficiently precise for examining source levels in our study area because of its simplicity the method ideally complements sound recordings and visual sightings of marine mammals and could lead to a better understanding of the nature and use of click trains by dolphins

ice velocity measurements of langjokull iceland from interferometric synthetic aperture radar insar we have computed the velocity of langjokull ice cap lic iceland using insar data acquired by the european remote sensing satellite in 1994 and an ice surface elevation model derived from a gps survey conducted in 1997 the velocity map covers 68 of the 925 km 2 of lic eight principal outlet glaciers were identified along which ice velocities increased from zero at the ice divide to a maximum of 75 m a 1 when the insar velocity dataset is compared with surface gps measurements of ice flow determined in summer 2001 there is generally good agreement suggesting interannual and seasonal stability for much of the ice cap during this period however non zero ice velocities at the termini of four of the eight glaciers surveyed suggest that these glaciers were advancing in 1994 comparison of our gps and insar velocities suggests that sudurjokull experienced elevated velocity in late february 1994 which when other studies are considered appears to be consistent with a glacier surge

ranging bowhead whale calls in a shallow water dispersive waveguide this paper presents the performance of three methods for estimating the range of broadband 50 500 hz bowhead whale calls in a nominally 55 m deep waveguide conventional mode filtering cmf synthetic time reversal str and triangulation the first two methods use a linear vertical array to exploit dispersive propagation effects in the underwater sound channel the triangulation technique used here while requiring no knowledge about the propagation environment relies on a distributed array of directional autonomous seafloor acoustics recorders dasars arranged in triangular grid with 7 km spacing this study uses simulations and acoustic data collected in 2010 from coastal waters near kaktovik alaska at that time a 12 element vertical array spanning the bottom 63 of the water column was deployed alongside a distributed array of seven dasars the estimated call location to array ranges determined from cmf and str are compared with dasar triangulation results for 19 whale calls the vertical array ranging results are generally within 10 of the dasar results with the str results providing slightly better agreement the results also indicate that the vertical array can range calls over larger ranges and with greater precision than the particular distributed array discussed here whenever the call locations are beyond the distributed array boundaries

retreat patterns and dynamics of the sentralbankrenna glacial system central barents sea accepted manuscript version published version available at https doi org 10 1016 j quascirev 2017 06 004 accepted manuscript version licensed cc by nc nd 4 0

glacier fluctuation and inferred climatology of langjokull ice cap through the little ice age abstract emerging paleoclimate records from proglacial lake hvitarvatn central iceland suggest that langjokull ice cap attained its maximum holocene extent within the last 400 years with the aim of constructing glaciological models and appropriate model inputs for holocene simulations of langjokull we begin by simulating the evolution of langjokull through the little ice age to present a period for which we have some constraint on ice cap geometry using modern measured mass balance distributions 1997 2003 and meteorological data from nearby hveravellir we derive a reference precipitation field for the period 1961 1990 over the ice cap our simulations suggest langjokull attained its maximum little ice age volume around 1840 with a second local maximum around 1890 the two outlet glaciers terminating in hvitarvatn nor urjokull and su urjokull advance slowly into the lake occupying their maximum lake area in the late 19th century and retreat comparatively rapidly in the mid to late 20th century simulations of nor urjokull are much more faithful to the geomorphic evidence than are simulations of su urjokull potentially suggesting a difference in dynamics between these two glaciers while only 35 of the hvitarvatn catchment area is ice covered meltwater from langjokull comprises 70 of the water input to the lake two thirds of this input from the ice cap is transported as groundwater simulated glacier derived discharge to the lake through the little ice age suggests that a sediment concentration of 1 5 kg m 3 would have resulted in the transport of 1 5 10 11 kg of material to the lake over the last 300 years comparable to the estimated mass of sediment in the most recently deposited sedimentary unit in the lake

geomorphic and shallow acoustic investigation of an antarctic peninsula fjord system using high resolution rov and shipboard geophysical observations ice dynamics and behaviour since the last glacial maximum detailed bathymetric and sub bottom acoustic observations in bourgeois fjord marguerite bay antarctic peninsula provide evidence on sedimentary processes and glacier dynamics during the last glacial cycle submarine landforms observed in the 50 km long fjord from the margins of modern tidewater glaciers to the now ice distal marguerite bay are described and interpreted the landforms are grouped into four morpho sedimentary systems i glacial advance and full glacial ii subglacial and ice marginal meltwater iii glacial retreat and neoglaciation and iv holocene mass wasting these morpho sedimentary systems have been integrated with morphological studies of the marguerite bay continental shelf and analysed in terms of the specific sedimentary processes and or stages of the glacial cycle they demonstrate the action of an ice sheet outlet glacier that produced drumlins and crag and tail features in the main and outer fjord meltwater processes eroded bedrock channels and ponds infilled by fine grained sediments following the last deglaciation of the fjord at about 9000 yr bp subsequent holocene neoglacial activity involved minor readvances of a tidewater glacier terminus in blind bay recent stillstands and or minor readvances are inferred from the presence of a major transverse moraine that indicates grounded ice stabilization probably during the little ice age and a series of smaller landforms that reveal intermittent minor readvances mass wasting processes also affected the walls of the fjord and produced scars and fan shaped deposits during the holocene glacier terminus changes during the last six decades derived from satellite images and aerial photographs reveal variable behaviour of adjacent tidewater glaciers the smaller glaciers show the most marked recent retreat influenced by regional physiography and catchment area size

holocene glacier and climate variations in vestfirðir iceland from the modeling of drangajokull ice cap abstract drangajokull is a maritime ice cap located in northwest vestfir ir iceland drangajokull s evolution is therefore closely linked to atmospheric and ocean variability in order to better constrain the holocene climate and glacier history of vestfir ir we model the past evolution of drangajokull ice cap simulations from 10 ka to present are forced by general circulation model output ice core based temperature reconstructions and sea surface temperature reconstructions based on these 10 thousand year simulations drangajokull did not persist through the holocene we estimate that air temperatures were 2 5 3 0 c higher during the holocene thermal maximum than the local 1960 1990 average simulations support drangajokull s late holocene inception between 2 and 1 ka though intermittent ice likely occupied cirques as early as 2 6 ka drangajokull is primarily a little ice age ice cap it expanded between 1300 and 1750 ce with the most rapid growth occurring between 1600 and 1750 ce the maximum holocene extent of drangajokull occurred between 1700 and 1925 ce despite the lowest late holocene temperatures occurring between 1650 and 1720 ce between 1700 and 1925 ce temperatures were likely 0 6 0 8 c lower than the 1950 2015 reference temperature the modern equilibrium line altitude ela is bracketed by topographic thresholds a 1 c temperature increase from the modern ela would eliminate the ice cap s accumulation area while a reduction of 0 5 c would lead to the rapid expansion of the ice cap across vestfir ir the proximity of drangajokull to topographic thresholds may explain its late inception and rapid expansion during the little ice age

the geomorphic imprint of glacier surges into open marine waters examples from eastern svalbard abstract seafloor morphology beyond nine tidewater glaciers terminating in open marine settings in eastern svalbard has been investigated using multibeam swath bathymetry historical information on tidewater glacier fluctuations over the past century or so shows that the seafloor offshore has been exposed only recently most glaciers have been observed to surge or have looped surface moraines indicating past surges during these ice advances and subsequent retreat a well preserved submarine landform assemblage has been produced a subglacial landforms include overridden moraine ridges mega scale glacial lineations msgls other streamlined lineations elongate drumlins and medial moraines small ridges forming a complex boxwork or rhombohedral pattern and meltwater related eskers and channels b ice marginal landforms include large terminal moraines with debris flow lobes on their outer flanks and indentations on their inner sides small transverse retreat moraines and crater like kettle holes c glacimarine features include iceberg ploughmarks and an otherwise relatively smooth sedimentary seafloor produced by fine grained debris rain out a schematic plan view landform assemblage model for tidewater glaciers advancing into open marine settings is developed arcuate terminal moraines marking the ice advance limit provide a distinctive component submarine basin s exposed inside these moraine ridges when ice retreats contain suites of individual landforms produced subglacially and ice marginally with a consistent order of timing of deposition and stratigraphic superposition the new schematic model is compared with earlier models based on submarine landforms associated with surges in the more topographically constrained setting of spitsbergen fjords differences include i the overall arcuate shape of the open marine assemblage ii the indented ice proximal sides of terminal moraine ridges iii the fan shaped pattern of streamlined lineations iv crater like kettle holes at the inner lateral margins of many submarine basins v prominent systems of eskers and channels modern glaciological analogues from ongoing surges of ice caps in eastern svalbard and severnaya zemlya provide contemporary observations of ice advance into open marine settings including heavily crevassed ice lobes with finger like termini

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

long range acoustic detection and localization of blue whale calls in the northeast pacific ocean analysis of acoustic signals recorded from the u s navy s sound surveillance system sosus was used to detect and locate blue whale balaenoptera musculus calls offshore in the northeast pacific the long low frequency components of these calls are characteristic of calls recorded in the presence of blue whales elsewhere in the world mean values for frequency and time characteristics from field recorded blue whale calls were used to develop a simple matched filter for detecting such calls in noisy time series the matched filter was applied to signals from three different sosus arrays off the coast of the pacific northwest to detect and associate individual calls from the same animal on the different arrays a u s navy maritime patrol aircraft was directed to an area where blue whale calls had been detected on sosus using these methods and the presence of a vocalizing blue whale was confirmed at the site with field recordings from sonobuoys

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

evolution of nao and amo strength and cyclicity derived from a 3 ka varve thickness record from iceland abstract a 3000 year varve thickness record from hvitarvatn a glacier dominated lake in central iceland preserves inter annual variations in the delivery of glacially eroded sediment to the lake the first order low frequency trend in varve thickness reflects increased glacial erosion through the late holocene reaching a peak during the little ice age lia superimposed on this trend are large inter annual to decadal fluctuations in varve thickness that we suggest reflect variability in climate parameters that determine the efficiency of the fluvial transport system to deliver glacially eroded sediment to the lake each year we use spectral analysis to test whether regular high frequency cyclicity in varve thickness exists in the 3 ka record after removing the low frequency variability spectral analyses from three sediment cores recovered from the lake show essentially the same periods of 2 8 3 4 13 35 40 and 85 93 for the overlapping 900 year period additionally cycles of 55 130 and 290 years are found in the spectrum for the 3000 year record that do not show up in the spectra for the shorter cores some of these cycles show similar variability to those of the north atlantic oscillation nao and atlantic multidecadal oscillation amo this relationship is supported by a significant correlation between varve thickness and both the nao precipitation and amo summer temperature indices over the 180 year instrumental period nao cyclicities 2 15 years are weakly expressed in the first half of the record increase between 600 and 1000 ad decrease in strength during medieval time and are most strongly expressed between 1300 ad and the early 20th century amo cyclicities 50 to 130 years are also relatively weak in the first half of the record becoming quite strong between 600 and 1000 ad and again between 1100 and 1500 ad but are essentially absent through the peak of the lia between 1500 and 1900 ad a time when strong cyclicities of about 35 years appear

stabilization of glaciers terminating in closed water bodies evidence and broader implications 1 the behavior of glaciers terminating in deep water is determined by the interaction of buoyancy iceberg production and the sensitivity of ice flow to subtle changes in resistance at the glacier bed modeling efforts assume rapid evacuation of icebergs but some glaciers terminate in closed basins where icebergs may accumulate multibeam bathymetric survey of a glacial lake in iceland that received outlet glaciers during the little ice age document near parallel flow of narrow ice fingers that extended up to 1 km beyond the grounding line these previously unseen features apparently occurred when iceberg production exceeded iceberg melt resulting in iceberg buttressing of the ice margin similar stabilization of ice flow may resolve long standing debates about past continental ice sheet behavior including the rapid readvance of the laurentide ice sheet into lake superior ca 11 ka and the genesis of glacial flutes observed in the central arctic ocean basin

dynamic jamming of iceberg choked fjords we investigate the dynamics of ice melange by analyzing rapid motion recorded by a time lapse camera and terrestrial radar during several calving events that occurred at jakobshavn isbrae greenland during calving events 1 the kinetic energy of the ice melange is 2 orders of magnitude smaller than the total energy released during the events 2 a jamming front propagates through the ice melange at a rate that is an order of magnitude faster than the motion of individual icebergs 3 the ice melange undergoes initial compaction followed by slow relaxation and extension and 4 motion of the ice melange gradually decays before coming to an abrupt halt these observations indicate that the ice melange experiences widespread jamming during calving events and is always close to being in a jammed state during periods of terminus quiescence we therefore suspect that local jamming influences longer timescale ice melange dynamics and stress transmission

scales and rates of glacial sediment removal a 20 km long 300 m deep trench created beneath breiðamerkurjokull during the little ice age

age verification of the lake gribben forest bed and the younger dryas advance of the laurentide ice sheet analysis of nine wood samples from the lake gribben forest bed near lake gribben michigan yielded a combined age of 10 025 100 14c years bp which confirms and refines prior age estimates for the bed the stratigraphic position of these samples below a prograding ice contact fan indicates the time that a glacial margin reached the southern edge of the lake superior basin geomorphic tracing and correlation of associated deposits indicate that a contemporaneous margin extended almost 1000 km from duluth minnesota across the lake superior basin to north bay ontario along the southern shore of lake superior ice margin expansion began during and ended at the close of the younger dryas a surging glacier system would not produce a nearly linear moraine system across both a major basin lake superior and a major upland abitibi upland therefore we attribute this advance of the laurentide ice sheet to climatic forcing of the younger dryas event

sea floor engineering geomorphology recent achievements and future directions abstract new mapping technology is providing perspectives of the sea floor as if there were no ocean revealing that ocean floors exhibit a wide variety of relief sediment properties and active geologic processes such as erosion faulting fluid expulsion and landslides the development of coastal and offshore resources such as oil and gas and minerals involves sea floor engineering in remote complex and sometimes hazardous environments optimum engineering design and construction practice require detailed surveys of sea floor geomorphology geologic conditions on the sea bed and to various depths beneath it combined with geotechnical properties of the sediments and oceanographic information integrated site survey models attempt to predict conditions and process frequencies and magnitudes relevant to the engineering design lifetimes of sea floor installations such as cables pipelines production platforms as well as supporting coastal infrastructure such as jetties wharves bridges and harbors recent use of deep water areas for oil and gas production pipelines and cable routes are also showing that the world s greatest slopes beyond the continental shelves contain exciting exotic and enigmatic geomorphological features and processes safe and cost effective engineering use of these regions depends upon exciting new technical and conceptual advances for understanding sea floor geomorphology a task which has barely begun

quantifying flow and stress in ice melange the world s largest granular material tidewater glacier fjords are often filled with a collection of calved icebergs brash ice and sea ice for glaciers with high calving rates this melange of ice can be jam packed so that the flow of ice fragments is mostly determined by granular interactions in the jammed state ice melange has been hypothesized to influence iceberg calving and capsize dispersion and attenuation of ocean waves injection of freshwater into fjords and fjord circulation however detailed measurements of ice melange are lacking due to difficulties in instrumenting remote ice choked fjords here we characterize the flow and associated stress in ice melange using a combination of terrestrial radar data laboratory experiments and numerical simulations we find that during periods of terminus quiescence ice melange experiences laminar flow over timescales of hours to days the uniform flow fields are bounded by shear margins along fjord walls where force chains between granular icebergs terminate in addition the average force per unit width that is transmitted to the glacier terminus which can exceed 107 n m increases exponentially with the melange length to width ratio these buttressing forces are sufficiently high to inhibit the initiation of large scale calving events supporting the notion that ice melange can be viewed as a weak granular ice shelf that transmits stresses from fjord walls back to glacier termini

morphology volcanism and mass wasting in crater lake oregon crater lake was surveyed nearly to its shoreline by high resolution multibeam echo sounding in order to define its geologic history and provide an accurate base map for research and monitoring surveys the bathymetry and acoustic backscatter reveal the character of landforms and lead to a chronology for the concurrent filling of the lake and volcanism within the ca 7700 calibrated yr b p caldera the andesitic wizard island and central platform volcanoes are composed of sequences of lava deltas that record former lake levels and demonstrate simultaneous activity at the two vents wizard island eruptions ceased when the lake was 80 m lower than at present lava streams from prominent channels on the surface of the central platform descended to feed extensive subaqueous flow fields on the caldera floor the wizard island and central platform volcanoes andesitic merriam cone and a newly discovered probable lava flow on the eastern floor of the lake apparently date from within a few hundred years of caldera collapse whereas a small rhyodacite dome was emplaced on the flank of wizard island at ca 4800 cal yr b p bedrock outcrops on the submerged caldera walls are shown in detail and in some cases can be correlated with exposed geologic units of mount mazama fragmental debris making up the walls elsewhere consists of narrow talus cones forming a dendritic pattern that leads to fewer wider ridges downslope hummocky topography and scattered blocks up to 280 m long below many of the embayments in the caldera wall mark debris avalanche deposits that probably formed in single events and commonly are affected by secondary failures the flat floored deep basins contain relatively fine grained sediment transported from the debris aprons by sheet flow turbidity currents crater lake apparently filled rapidly ca 400 750 yr until reaching a permeable layer above glaciated lava identified by the new survey in the northeast caldera wall at 1845 m elevation thereafter a gradual climatically modulated rise in lake level to the present 1883 m produced a series of beaches culminating in a modern wave cut platform commonly 40 m wide where suitable material is present the new survey reveals landforms that result from intermediate composition volcanism in rising water delineates mass wasting and sediment transport into a restricted basin and yields a more accurate postcaldera history leading to improved assessment of volcanic hazards

tracking of pacific walruses in the chukchi sea using a single hydrophone the vocal repertoire of pacific walruses includes underwater sound pulses referred to as knocks and bell like calls an extended acoustic monitoring program was performed in summer 2007 over a large region of the eastern chukchi sea using autonomous seabed mounted acoustic recorders walrus knocks were identified in many of the recordings and most of these sounds included multiple bottom and surface reflected signals this paper investigates the use of a localization technique based on relative multipath arrival times rmats for potential behavior studies first knocks are detected using a semi automated kurtosis based algorithm then rmats are matched to values predicted by a ray tracing model walrus tracks with vertical and horizontal movements were obtained the tracks included repeated dives between 4 0 m and 15 5 m depth and a deep dive to the sea bottom 53 m depths at which bell like sounds are produced average knock production rate and source levels estimates of the knocks were determined bell sounds were produced at all depths throughout the dives average knock production rates varied from 59 to 75 knocks min average source level of the knocks was estimated to 177 6 7 5 db re 1 pa peak 1 m

recurrent mesolithic neolithic occupation at sise western latvia and shoreline displacement in the baltic sea basin a major assemblage of mesolithic and neolithic wooden artefacts has been recovered from the bed of the river u ava at sise in the coastal belt of western latvia new archaeological investigation h

quaternary geology and surficial sediment processes browns bank scotian shelf based on multibeam bathymetry abstract browns bank is located on the glaciated continental shelf off southern nova scotia geological mapping of browns bank is based on interpretation of multibeam bathymetric and backscatter data in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms sea floor sediment samples and bottom photographs the fundian moraine part of the previously identified end moraine system on the continental shelf off nova scotia is a prominent west east flat topped multi lobate ridge identifiable in the multibeam bathymetric data and in geophysical records the fundian moraine was subjected to erosion in the surf zone during sea level rise in depths less than 100 m a series of north south roughly parallel till ridges continuous in the subsurface with the fundian moraine is interpreted as interlobate moraines suggesting formation by a tidewater glacier the browns bank moraine connected to the fundian moraine is evidence of a newly identified grounded ice position farther seaward than the latter bedforms including obstacle marks comet marks sand waves and megaripples are evidence of a vigorous anticyclonic current pattern on browns bank the combination of multibeam bathymetric imagery with high resolution geoscientific information represents a powerful technique for sea floor geological investigations

a preliminary survey of relict shoreface attached sand ridges in western lake superior abstract high resolution multibeam and seismic reflection surveying in western lake superior near the outflow of the amnicon river wisconsin has shown that the nearshore lake floor appears to consist of till with no recent sediment cover this surface is partially obscured 3 km offshore by a series of low relief elongate sand ridges that are arranged in an en echelon pattern at an oblique angle to the present day shoreline they are extensively gullied suggesting that they are not presently active two sets of elongate features can be identified the features in first group group i are over 0 5 km wide rise 3 5 m above the surrounding lake floor and are over 2 km long the features belonging to the second set group ii are not as well developed and are typically smaller than those in group i group ii features are typically 0 2 0 3 km wide 0 4 1 6 km long and rise 1 3 m above the surrounding lake floor the most striking difference between the groups is the difference in their orientation with respect to the shoreline the group i features run ne sw while the group ii features are directed approximately n s the shoreline runs approximately ene wsw so the features in both cases open northeast the group i features are believed to be relict drowned shoreface attached sand ridges that formed when the lake level lay over 10 m below its present day level these sand ridges formed as the result of currents associated with strong northeasterly gales moving the abundant sediment eroded off the shore the smaller group ii features are believed to be sub aqueous sand dunes that developed transverse to bottom currents produced by the northeasterly gales no dates have been obtained for the sand ridges based upon their depth and the lake level history curve for lake superior we suggest that the ridges formed either 6500 6000 bp prior to the nipissing highstand

non linear holocene climate evolution in the north atlantic a high resolution multi proxy record of glacier activity and environmental change from hvitarvatn central iceland abstract iceland is well situated to monitor north atlantic holocene climate variability terrestrial sites there offer the potential for well dated high resolution continuous records of environmental change and or glacier activity laminated sediments from the proglacial lake hvitarvatn provide a continuous record of environmental change and the development of the adjacent langjokull ice cap for the past 10 2 ka replicate lake sediment cores collected from multiple locations in the basin are placed in a secure geochronology by splicing a varve chronology for the past 3 ka with a tephra constrained paleomagnetic secular variation derived chronology for older sediments multiple proxies including sedimentation rate bulk density ice rafted debris sediment organic matter biogenic silica and diatom abundance allow annual to multi decadal resolution and reveal a dynamic holocene terrestrial climate following regional deglaciation of the main iceland ice sheet summer temperatures were high enough that mountain ice caps had already melted or were contributing insignificant sediment to the lake pronounced increases in sedimentation rate sediment density and the influx of terrestrial organic matter between 8 7 and 7 9 ka suggest early holocene warmth was interrupted by two distinct pulses of cold summers leading to widespread landscape destabilization and possibly glacier growth the holocene thermal maximum htm 7 9 to 5 5 ka was characterized by high within lake productivity and ice free conditions in the watershed neoglaciation is recorded as a non linear transition toward cooler summers landscape destabilization and the inception and expansion of langjokull beginning ca 5 5 ka with notable increases in ice cap size and landscape instability at 4 2 and 3 0 ka the past two millennia are characterized by the abrupt onset of sustained cold periods at ca 550 and 1250 ad separated by an interval of relative warmth from ca 950 to 1150 ad the greatest holocene extent of langjokull occurred in the nineteenth century and is coincident with peak landscape instability followed by ice recession throughout the twentieth century

evolution of glacier dammed lakes through space and time brady glacier alaska usa abstract glacier dammed lakes and their associated jokulhlaups cause severe flooding in downstream areas and substantially influence glacier dynamics brady glacier in southeast alaska is well suited for a study of these phenomena because it presently dams 10 large 1 km 2 lakes our objectives are to demonstrate how brady glacier and its lakes have co evolved in the past and to apply this knowledge to predict how the glacier and its lakes will likely evolve in the future to accomplish these objectives we georeferenced a variety of maps airphotos and optical satellite imagery to characterize the evolution of the glacier and lakes we also collected bathymetry data and created bathymetric maps of select lakes despite small advances and retreats the main terminus of brady glacier has changed little since 1880 however it downwasted at rates of 2 3 m y between 1948 and 2000 more than the regional average the most dramatic retreat 2 km and downwasting 120 m have occurred adjacent to glacier dammed lakes and are primarily the result of calving brady glacier is a former tidewater glacier with continued downwasting brady glacier may return to a tidewater regime and enter into a phase of catastrophic retreat the situation at brady glacier is not unique and the lessons learned here can be applied elsewhere to identify future glacier dammed lakes jokulhlaups and glacier instability

multibeam bathymetric and sediment profiler evidence for ice grounding on the chukchi borderland arctic ocean multibeam bathymetry and 3 5 khz sub bottom profiler data collected from the us icebreaker healy in 2003 provide convincing evidence for grounded ice on the chukchi borderland off the northern alaskan margin arctic ocean the data show parallel glacially induced seafloor scours or grooves and intervening ridges that reach widths of 1000 m rim to rim and as much as 40 m relief following previous authors we refer to these features as bmegascale glacial lineations msgls q additional support for ice grounding is apparent from stratigraphic unconformities interpreted to have been caused by ice induced erosion most likely the observed sea floor features represent evidence for massive ice shelf grounding the general ese wnw direction of the msgls together with sediment evidently bulldozed off the chukchi plateau that is mapped on the western siberian side of the plateau suggests ice flow from the canada basin side of chukchi borderland two separate generations of glacially derived msgls are identified on the chukchi borderland from the healy geophysical data the deepest and oldest extensive msgls appear to be draped by sediments less than 5 m thick whereas no sediment drape can be distinguished within the resolution of the sub bottom profiles on the younger generation d 2005 university of washington all rights reserved

iceberg scours pits and pockmarks in the north falkland basin abstract glaciation in the southern hemisphere is limited by the availability of land from which to seed ice sheets the extents of the antarctic patagonian and new zealand ice sheets at the last glacial maximum lgm are relatively well known although the rates and styles of their retreat after the lgm are poorly constrained particularly in antarctica offshore records of glaciation are relatively sparse in the southern hemisphere despite the potential ocean climate insights that can be gained from records of glaciation that are preserved offshore in this study we document the occurrence of iceberg scours and accompanying pits within the north falkland basin c 50 s and discuss their origin the cross sectional shapes of scours are u to v shaped and occur in present day water depths of 280 to 460 m individual scours are up to 38 km long 1 km wide and up to 10 m deep the scours are observed as erosional linear to curvilinear depressions showing only one point of contact between the iceberg and seafloor often with raised berms composed of excavated material identified either side of the main depression undulating width of scours is interpreted as an effect of rotation of the iceberg keel during scour excavation the elongate morphology of the scours differentiates them from asymmetrical pits interpreted to represent iceberg impact pits and symmetrical pockmarks interpreted to form due to fluid expulsion in cross section the differentiation is highly interpretative but the 3d bathymetric expression is unequivocal the sinusoidal character of the scours suggests the interaction between local tidal currents and the east falkland malvinas currents in the north falkland basin at the time of formation offshore and onshore landscape analysis is used to determine potential sources of icebergs and suggests that they were most likely sourced from the antarctic peninsula these results inform our understanding of southern hemisphere ocean climate interactions during the last glacial cycle and suggest that the east falklands malvinas current a key current in the southern hemisphere bringing cold low salinity antarctic derived waters into the south atlantic was in operation during the last glacial cycle the accumulation of icebergs west of the falkland islands would also result in further cooling from fresh meltwater perturbations enhancing the development of a potential ice bridge along the argentinian coast

matched field processing geoacoustic inversion and source signature recovery of blue whale vocalizations matched field processing mfp and global inversion techniques have been applied to vocalizations from four whales recorded on a 48 element tilted vertical array off the channel islands in 1996 global inversions from selected whale calls using as few as eight elements extracted information about the surrounding ocean bottom composition array shape and the animal s position these inversion results were then used to conduct straightforward mfp on other calls the sediment sound speed inversion estimates are consistent with those derived from sediment samples collected in the area in general most animals swam from the east to west but one animal remained within 500 m of its original position over 45 min all whales vocalized between 10 and 40 m depth three acoustic sequences are discussed in detail the first illustrating a match between an acoustic track and visual sighting the second tracking two whales to ranges out to 8 km and the final sequence demonstrating high resolution dive profiles from

precise chronology of little ice age expansion and repetitive surges of langjokull central iceland the nonlinear and complex behavior of glacier dynamic processes e g surging and ice calving presents major challenges for future estimates of runoff and sea level change because direct observations are temporally limited reconstructions of past fluctuations from glaciers that undergo dynamic advance and or retreat are valuable we constructed a 300 yr annually resolved record of surges and terminus fluctuations of langjokull ice cap central iceland using a novel combination of varve counting multibeam bathymetry seismic imagery and multiple sediment cores from targeted sites in hvitarvatn a large proglacial lake langjokull achieved its maximum neoglacial extent between ca a d 1700 and ca 1930 when two outlet glaciers nor urjokull and su urjokull advanced into the lake and maintained active calving margins nor urjokull advanced into the basin ca 1720 and remained at or near its maximum extension for most of the 19 th century whereas su urjokull underwent a quasi periodic series of 8 surges between 1828 and 1930 with a recurrence interval of 14 4 yr each surge event resulted in fragmentation of the glacier terminus during advances of up to 1 6 km that occurred in 2 yr collapse of the expanded ice iceberg melting and reestablishment of the ice front at a nearshore grounding line occurred within 1 3 yr of the surge surges converted glacier ice to runoff at 10 the non surging rate our precise estimates of the timing duration and magnitude of su urjokull surges provide ideal targets for the next generation of glacier surge models

temperature and precipitation history of the arctic as the planet cooled from peak warmth in the early cenozoic extensive northern hemisphere ice sheets developed by 2 6 ma ago leading to changes in the circulation of both the atmosphere and oceans from not vert similar2 6 to not vert similar1 0 ma ago ice sheets came and went about every 41 ka in pace with cycles in the tilt of earth s axis but for the past 700 ka glacial cycles have been longer lasting not vert similar100 ka separated by brief warm interglaciations when sea level and ice volumes were close to present the cause of the shift from 41 ka to 100 ka glacial cycles is still debated during the penultimate interglaciation not vert similar130 to not vert similar120 ka ago solar energy in summer in the arctic was greater than at any time subsequently as a consequence arctic summers were not vert similar5 c warmer than at present and almost all glaciers melted completely except for the greenland ice sheet and even it was reduced in size substantially from its present extent with the loss of land ice sea level was about 5 m higher than present with the extra melt coming from both greenland and antarctica as well as small glaciers the last glacial maximum lgm peaked not vert similar21 ka ago when mean annual temperatures over parts of the arctic were as much as 20 c lower than at present ice recession was well underway 16 ka ago and most of the northern hemisphere ice sheets had melted by 6 ka ago solar energy reached a summer maximum 9 higher than at present not vert similar11 ka ago and has been decreasing since then primarily in response to the precession of the equinoxes the extra energy elevated early holocene summer temperatures throughout the arctic 1 3 c above 20th century averages enough to completely melt many small glaciers throughout the arctic although the greenland ice sheet was only slightly smaller than at present early holocene summer sea ice limits were substantially smaller than their 20th century average and the flow of atlantic water into the arctic ocean was substantially greater as summer solar energy decreased in the second half of the holocene glaciers re established or advanced sea ice expanded and the flow of warm atlantic water into the arctic ocean diminished late holocene cooling reached its nadir during the little ice age about 1250 1850 ad when sun blocking volcanic eruptions and perhaps other causes added to the orbital cooling allowing most arctic glaciers to reach their maximum holocene extent during the warming of the past century glaciers have receded throughout the arctic terrestrial ecosystems have advanced northward and perennial arctic ocean sea ice has diminished here we review the proxies that allow reconstruction of quaternary climates and the feedbacks that amplify climate change across the arctic we provide an overview of the evolution of climate from the hot house of the early cenozoic through its transition to the ice house of the quaternary with special emphasis on the anomalous warmth of the middle pliocene early quaternary warm times the mid pleistocene transition warm interglaciations of marine isotope stages 11 5e and 1 the stage 3 interstadial and the peak cold of the last glacial maximum

glacier fluctuations during the past 2000 years abstract a global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions excluding antarctica highlights the nature of glacier fluctuations during the late holocene the dataset includes 275 time series of glacier fluctuations based on historical tree ring lake sediment radiocarbon and terrestrial cosmogenic nuclide data the most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and when available winter precipitation reconstructions the most important parameters for glacier mass balance in many cases major glacier advances correlate with multi decadal periods of decreased summer temperature in a few cases such as in arctic alaska and western canada some glacier advances occurred during relatively warm wet times the timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region however the number of glacier advances shows a clear pattern for the high mid and low latitudes and hence points to common forcing factors acting at the global scale globally during the first millennium ce glaciers were smaller than between the advances in 13th to early 20th centuries ce the precise extent of glacier retreat in the first millennium is not well defined however the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th early 21st centuries other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the european alps in the 3rd 6th and 9th centuries in norway during the 10th 13th centuries in southern alaska and in the 18th century in spitsbergen however no single period of common global glacier retreat of centennial duration except for the past century has yet been identified in contrast the view that the little ice age was a period of global glacier expansion beginning in the 13th century or earlier and reaching a maximum in 17th 19th centuries is supported by our data the pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales the number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia although the resolution of most glacier chronologies is not enough for robust statistical correlations glacier retreat in the past 100 150 years corresponds to the anthropogenic global temperature increase many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain

submarine landforms and the reconstruction of fast flowing ice streams within a large quaternary ice sheet the 2500 km long norwegian svalbard margin 57 80 n morphological interpretation of regional and detailed bathymetric data sets on the 2500 km long norwegian shelf from the north sea 57 n to svalbard 80 n has revealed a dynamic ice flow pattern along the western marginof the scandinavian and barents svalbard ice sheets about 20 cross shelf troughs with megascale glacial lineations msgl elongate ridges and grooves oriented parallel to trough long axes are interpreted as former pathways for fast flowing ice streams studies of large scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross shelf troughs less dynamic ice probably existed on shallower banks the two largest paleo ice streams were the norwegian channel ice stream and bear island trough ice stream each 150 200 km wide at the mouth the lengths of individual msgl vary from hundreds of meters to several tens of kilometers and the distance between ridges varies from 0 1 to 3 km msgl amplitudes reach 15 m but are commonly 10 m the onset of msgl and hence fast ice flow is generally close to the outer coast at the border zone between crystalline rocks and softer sedimentary rocks transverse submarine ridges on various scales commonly parallel to the shelf edge reflect either the maximum ice sheet position or the recessional pattern of the ice sheet lateral ice stream moraines several tens of kilometers long have also been mapped along the sides of several cross shelf troughs identifying the border zone between fast ice flow and stagnant or slow flowing ice on intervening banks

late quaternary glacial to postglacial sedimentation in three adjacent fjord lakes of the quebec north shore eastern canadian shield abstract high resolution swath bathymetry imagery allowed mapping in great detail the sublacustrine geomorphology of lakes pentecote walker and pasteur three deep adjacent fjord lakes of the quebec north shore eastern canada these sedimentary basins have been glacio isostatically uplifted to form deep steep sided elongated lakes their key geographical position and limnogeological characteristics typical of fjords suggest exceptional potential for long term high resolution paleoenvironmental reconstitutions acoustic subbottom profiles acquired using a bi frequency chirp echosounder 3 5 12 khz together with cm and m long sediment core data reveal the presence of four acoustic stratigraphic units the acoustic basement unit 1 represents the structural bedrock and or the ice contact sediments of the laurentide ice sheet and reveals v shaped bedrock valleys at the bottom of the lakes occupied by ice loaded sediments in a basin fill geometry unit 2 moraines observed at the bottom of lakes and in their structural valleys indicate a deglaciation punctuated by short term ice margin stabilizations following ice retreat and their isolation the fjord lakes were filled by a thick draping sequence of rhythmically laminated silts and clays unit 3 deposited during glaciomarine and or glaciolacustrine settings these sediments were episodically disturbed by mass movements during deglaciation due to glacial isostatic rebound ams 14c dating reveal that the transition between deglaciation of the lakes pentecote and walker watersheds and the development of para and post glacial conditions occurred around 8000 cal bp the development of the lake head river delta plain during the holocene provided a constant source of fluvial sediment supply to the lakes and the formation of turbidity current bedforms on the sublacustrine delta slopes the upper sediment succession i e 4 6 5 m consists of a continuous para to post glacial sediment drape unit 4 that contains laminated and massive sediment and series of rapidly deposited layers these results allow establishing a conceptual model of how a glaciated coastal fjord evolves during and after deglaciation in a context of rapid glacio isostatically induced forced regression

laurentide ice sheet dynamics in the bay of fundy canada revealed through multibeam sonar mapping of glacial landsystems abstract recent multibeam sonar data collected in the bay of fundy canada interpreted in conjunction with geophysical profiling and sediment sampling reveal in unprecedented detail a suite of glacial landforms associated with the southwest margin of the laurentide ice sheet these landforms constitute four glacial landsystems 1 subglacial landsystem i in southwestern bay of fundy the elongated grand manan basin contains ice contact sediments of possible mid wisconsinan age overlain by late wisconsinan ice contact sediments strongly imprinted by iceberg furrows and pits in places possible mid wisconsinan glaciomarine sediments have been eroded by late wisconsinan ice creating streamlined landforms eroded bedrock and megafluted ice contact sediment on the flanks of grand manan basin indicate the southwest direction of topographically steered ice 2 subglacial landsystem ii along the southern margin of the bay of fundy an array of drumlins with superimposed esker complexes was formed by glacial ice that emanated northwest from the interior of nova scotia and was deflected to the southwest by the ice flowing out of the bay of fundy to the gulf of maine the esker complexes formed later when the nova scotia ice sheet stagnated and meltwater escaped northwest via topographic gaps 3 ice marginal landsystem i in northern bay of fundy both small de geer moraines and larger basin bounding moraines were created when retreating late wisconsinan ice became grounded in relatively shallow water new radiocarbon ages show that the owen basin moraine in this landsystem was abandoned prior to c 14 600 14 c yr bp cal bp 17 015 17 270 0 7 17 286 17 405 0 3 4 ice marginal landsystem ii this distinctive landsystem consists of numerous arcuate moraines commonly superimposed on one another this landsystem was formed by thin 170 m lightly grounded ice that retreated northeast into the bay of fundy the splayed pattern of the ice margin was a response to a large accommodation space and velocity variations within the ice the isle haute moraine is a large lobate moraine its age is poorly constrained by shells from glaciomarine sediments 13 750 60 14 c yr bp cal bp 15 970 15 996 0 03 16 047 16 665 0 97 but the moraine may be coeval with the onset of a terrestrial ice margin established at the head of the bay of fundy by c 14 300 14 c yr bp cal bp 16 824 17 013

abrupt drainage cycles of the fennoscandian ice sheet continental ice sheets are a key component of the earth s climate system but their internal dynamics need to be further studied since the last deglaciation the northern eurasian fennoscandian ice sheet fis has been connected to the black sea bs watershed making this basin a suitable location to investigate former ice sheet dynamics here from a core retrieved in the bs we combine the use of neodymium isotopes high resolution elemental analysis and biomarkers to trace changes in sediment provenance and river runoff we reveal cyclic releases of meltwater originating from lake disna a proglacial lake linked to the fis during heinrich stadial 1 regional interactions within the climate lake fis system linked to changes in the availability of subglacial water led to abrupt drainage cycles of the fis into the bs watershed this phenomenon raised the bs water level by 100 m until the sill of the bosphorus strait was reached flooding the vast northwestern bs shelf and deeply affecting the hydrology and circulation of the bs and probably of the marmara and aegean seas

morphology and processes in lake tahoe california nevada lake tahoe was surveyed using a state of the art high resolution multibeam mapping system to provide an accurate base map for the myriad of ongoing environmental studies in and around the lake the newly defined basin morphology shows steep basin margins on the northern eastern and western sides and a gentle margin on the southern side two large flat plateaus several kilometers wide extend from the shore to about 40 m water depth in the northern and northwestern sections of the basin a series of ridges in the west and north are presumed traces of faults some of which border the lake basin and some of which traverse across the northern section of the lake and converge in mckinney bay mckinney bay is a large reentrant in the western margin that was created by a failure of the western margin that occurred about 300 ka the failure generated a major debris avalanche that carried large blocks some more than 1000 m long and 80 m high across the basin apparently the debris avalanche was deflected by the eastern margin of the basin and flowed to the north and south small debris flows and slides have continued to occur in this area small debris aprons occur along the northern western and eastern margins some apparently the remnants of collapsed terminal moraines formed in the basin from the 160 ka tahoe glaciation which reached the edge of the basin eroded plateaus and ridges occur on a glacial outwash plain that covers the gentle southern margin the plateaus and ridges are inferred to be remnants of another large terminal moraine of the tahoe glaciation

a 3000 year varved record of glacier activity and climate change from the proglacial lake hvitarvatn iceland a suite of environmental proxies in annually laminated sediments from hvitarvatn a proglacial lake in the central highlands of iceland are used to reconstruct regional climate variability and glacial activity for the past 3000 years sedimentological analysis is supported by tephrostratigraphy to confirm the continuous annual nature of the laminae and a master varve chronology places proxies from multiple lake cores in a secure geochronology varve thickness is controlled by the rate of glacial erosion and efficiency of subglacial discharge from the adjacent langjokull ice cap the continuous presence of glacially derived clastic varves in the sediment fill confirms that the ice cap has occupied the lake catchment for the duration of the record varve thickness varve thickness variance ice rafted debris total organic carbon mass flux and bulk concentration and c n of sedimentary organic matter reveal a dynamic late holocene climate with abrupt and large scale changes in ice cap size and landscape stability a first order trend toward cooler summers and ice cap expansion is punctuated by notable periods of rapid ice cap growth and or landscape instability at ca 1000 bc 600 bc 550 ad and 1250 ad the largest perturbation began ca 1250 ad signaling the onset of the little ice age and the termination of three centuries of relative warmth during medieval times consistent deposition of ice rafted debris in hvitarvatn is restricted to the last 250 years demonstrating that langjokull only advanced into hvitarvatn during the coldest centuries of the little ice age beginning in the mid eighteenth century this advance represents the glacial maximum for at least the last 3 ka and likely since regional deglaciation 10 ka the multi centennial response of biological proxies to the hekla 3 tephra deposition illustrates the significant impact of large explosive eruptions on local environments and catchment sensitivity to perturbations

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet