implications of till deformation on glacier dynamics the dynamics of glacier motion are governed to a large extent by the properties of the basal interface in this paper we address the interaction of a glacier with a layer of till at its bed in an attempt to test whether our physical understanding of till is sufficient to explain general features of the observed flow field and changes in geometry of black rapids glacier alaska u s a we also investigate whether or not a till layer has a clear surface observable signature in the dynamics of the glacier towards this end we use a finite element ice flow model with a coulomb failure criterion within the basal till layer we find that simple till physics can be used to describe decadal seasonal and short term hours to days velocity variations and possibly uplift events mechanisms for each of these variations involve an increase in the extent of till at failure a transfer of shear stress across the bed and a consequent increase in ice deformation effective shape factors are calculated that permit a simple incorporation of this boundary condition into glacier response models our analyses however have not resulted in the identification of a clear and unique signature of a till layer in the surface dynamics of a glacier

automated detection of unstable glacier flow and a spectrum of speedup behavior in the alaska range surge type glaciers are loosely defined as glaciers that experience periodic alterations between slow and fast flow regimes glaciers from a variety of mountain ranges around the world have been classified as surge type yet consensus of what defines a glacier as surge type has not always been met a common source of dispute is the lack of a succinct and globally applicable delimiter between a surging and nonsurging glacier the attempt is often a boolean classification however glacier speedup events can vary significantly with respect to event magnitude duration and the fraction of the glacier that participates in the speedup for this study we first updated the inventory of glaciers that show flow instabilities in the alaska range and then quantified the spectrum of speedup behavior we developed a new method that automatically detects glaciers with flow instabilities our automated results show a 91 success rate when compared to direct observations of speedup events and glaciers that are suspected to display unstable flow based on surface features through a combination of observations from the landsat archive and previously published data our inventory now contains 36 glaciers that encompass at least one branch exhibiting unstable flow and we document 53 speedup events that occurred between 1936 and 2014 we then present a universal method for comparing glacier speedup events based on a normalized event magnitude metric this method provides a consistent way to include and quantify the full spectrum of speedup events and allows for comparisons with glaciers that exhibit clear surge characteristics yet have no observed surge event to date our results show a continuous spectrum of speedup magnitudes from steady flow to clearly surge type which suggests that qualitative classifications such as surge type or pulse type behavior might be too simplistic and should be accompanied by a standardized magnitude metric

the response of black rapids glacier alaska to the denali earthquake rock avalanches 1 we describe the impact of three simultaneous earthquake triggered rock avalanches on the dynamics of black rapids glacier alaska by using spaceborne radar imagery and numerical modeling we determined the velocities of the glacier before and after landslide deposition in 2002 by using a combination of ers 1 ers 2 tandem radarsat 1 and alos palsar synthetic aperture radar data ice velocity above the debris covered area of the glacier increased up to 14 after the earthquake but then decreased 20 by 2005 within the area of the debris sheets mean glacier surface velocity increased 44 within 2 years of the landslides at the downglacier end of the lowest landslide where strong differential ablation produced a steep ice cliff velocities increased by 109 over the same period by 2007 ice velocity throughout the debris area had become more uniform consistent with a constant ice flux resulting from drastically reduced ablation at the base of the debris without further analysis we cannot prove that these changes resulted from the landslides because black rapids glacier displays large seasonal and interannual variations in velocity however a full stokes numerical ice flow model of a simplified glacier geometry produced a reversal of the velocity gradient from compressional to extensional flow after 5 years which supports our interpretation that the recent changes in the velocity field of the glacier are related to landslide induced mass balance changes

long chain alkenones and alkyl alkenoates as palaeotemperature indicators their production flux and early sedimentary diagenesis in the eastern north atlantic the production and fate of long chain alkenones and alkenoates was examined with regard to their use as palaeotemperature indicators alkenoate abundances were higher than previously reported for other regions and more strongly correlated with temperature than was alkenone unsaturation u37k suggesting biogeographical variability in alkenone and alkenoate production in surface waters we define the aa36 ratio to parameterize alkenoate abundance and present an empirical temperature calibration derived from our euphotic zone samples for use in the north atlantic t 17 35 25 12 u37k 26 73 aa36 93 90 u37k aa36 significant diagenetic losses of alkenones and alkenoates were found within the water column and near surface sediments in spite of diagenetic losses the temperature signal recorded by these compounds in the sediments remains largely unaltered and corresponds to the euphotic zone water temperature during the springtime period of maximum coccolithophorid production and flux rather than the average annual sea surface temperature

anomalous change in atmospheric radon concentration sourced from broad crustal deformation a case study of the 1995 kobe earthquake abstract before the kobe earthquake an anomalous increase in atmospheric rn concentration was observed by separating the measured concentration of atmospheric rn into three components according to the distance from the monitoring station the variation of rn exhalation rate can be estimated for the respective area using the daily minimum and maximum concentrations the mean rate of rn exhalation gradually increased in an area of 20 km around the monitoring station becoming five times higher than normal in the period between october 1994 and the date of the earthquake this area had a large co seismic displacement of up to 30 cm which roughly corresponds to the crustal strain of 10 6 order and it is considered the main source for the atmospheric rn prior to the kobe earthquake analyses revealed that the pre seismic change in the atmospheric rn concentration exhibited an anomalous pattern which would yield information on the spatial distribution of the mechanical response of the ground

an organic geochemical assessment of oceanographic conditions at manop site c over the past 26 000 years eleven sediment samples taken downcore and representing the past 26 kyr of deposition at manop site c 0 57 2 n 138 57 3 w were analyzed for lipid biomarker composition biomarkers of both terrestrial and marine sources of organic carbon were identified in general concentration profiles for these biomarkers and for total organic carbon toc displayed three common stratigraphic features in the time series 1 a maximum within the surface sediment mixed layer 4 ka 2 a broad minimum extending throughout the interglacial deposit and 3 a deep pronounced maximum within the glacial deposit using the biomarker records a simple binary mixing model is described that assesses the proportion of terrestrial to marine toc in these sediments best estimates from this model suggest that 20 of the toc is land derived introduced by long range eolian transport and the remainder is derived from marine productivity the direct correlation between the records for terrestrial and marine toc with depth in this core fits an interpretation that primary productivity at site c has been controlled by wind driven upwelling at least over the last glacial interglacial cycle the biomarker records place the greatest wind strength and highest primary productivity within the time frame of 18 to 22 kyr b p diagenetic effects limit our ability to ascertain directly from the biomarker records the absolute magnitude that different types of primary productivity have changed at this ocean location over the past 26 kyr

kuannersuit glacier revisited constraining ice dynamics landform formations and glaciomorphological changes in the early quiescent phase following the 1995 98 surge event abstract kuannersuit glacier in west greenland experienced a major surge in 1995 1998 where the glacier advanced 10 5 km down valley in this paper we examine how the quiescent phase has progressed until 2015 with respect to ice dynamics landform formations and glaciomorphological changes in the initial quiescent phase 2001 2005 ice velocities along the center flowline were 37 55 higher than ice velocities 6 3 9 0 m yr 1 in 2005 2015 and a linear relationship between ice velocity and distance from the glacier front which existed during the initial quiescent phase had disappeared in 2005 2015 between 2001 and 2015 the post surge glacier tongue thinned by 84 0 6 3 m equal to 6 0 0 5 m yr 1 the 30 m high terminal moraine detached from the active glacier along the uppermost thrust band between 2005 and 2015 after which the glacier front receded 1 5 km between the terminal moraine and the glacier front observations suggested that a proximal outwash plain was forming on top of glacier ice and that glacier naled icing aufeis was incorporated into the outwash plain in less dynamic areas with gently sloping topography along the lateral glacier margins crevasse squeeze ridges were melting out the most prominent glaciomorphological feature in 2015 was a c 1 km long gorge with c 30 40 m high ice cliffs this gorge had formed into the glacier front following the collapse of a series of chasms above the main subglacial channel roof collapse processes above subglacial channels had a significant impact on the glacier s mass loss and on the glaciomorphology during the quiescent phase earlier observations from 1913 suggest that the formation of this gorge is a reoccurring phenomenon during the quiescent phase a lower pothole field on the glacier tongue that existed during the initial quiescent phase had completely disappeared in 2015 while a larger upper pothole field in the reservoir area prevailed during the initial quiescent phase the subglacial drainage system developed into a stable channelized network although a jokulhlaup from a large ice dammed lake occurred this single event was dated to have occurred between 11 and 13 august 2006 and the lake did not refill the spatiotemporal association and evolution of glacial and glaciomorphological landforms at kuannersuit glacier are likely similar to processes at many other surging and rapidly receding glaciers of similar size

observations on the distribution and characteristics of potholes on surging glaciers potholes are depressions often water filled 10 100 m across found on the surfaces of glaciers most fields of potholes are found on surging glaciers suggesting that potholes form as a result of surging a photographic inventory of hundreds of glaciers in alaska and yukon territory allowed this hypothesis to be tested out of 26 pothole fields observed 19 were on known surging glaciers two on probable surging glaciers and the rest in areas where surging glaciers are common the majority of pothole fields were found near the equilibrium line photographs show that potholes formed within several years following the 1937 surge of the black rapids glacier in a zone where there had been intense crevassing between 1949 and 1986 the total number of potholes on the glacier decreased from approximately 700 to less than 200 while their mean size increased from 20 to 30 m some of these potholes have been observed to drain englacially the movement of these potholes were measured photogrammetrically to be less than 10 m yr the majority of the motion resulting from ice flow intense crevassing resulting from surging appears to be necessary for the formation of potholes but not sufficient as only 21 out of 256 surging glaciers contain potholes

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

stress gradient coupling in glacier flow i longitudinal averaging of the influence of ice thickness and surface slope for a glacier flowing over a bed of longitudinally varying slope the influence of longitudinal stress gradients on the flow is analyzed by means of a longitudinal flow coupling equation derived from the vertically cross sectionally integrated longitudinal stress equilibrium equation by an extension of an approach originally developed by budd 1968 linearization of the flow coupling equation by treating the flow velocity u vertically averaged ice thickness h and surface slope in terms of small deviations u h and a from overall average datum values u 0 h 0 and 0 results in a differential equation that can be solved by green s function methods giving u x as a function of h x and x x being the longitudinal coordinate the result has the form of a longitudinal averaging integral of the influence of local h x and x on the flow u x u x u0 2l l 0 ln n nh n l exp x x l dx where the integration is over the length l of the glacier the operator specified deviations from the datum state and the term on which it operates which is a function of the integration variable x represents the influence of local h x x and channel shape factor x at longitudinal coordinate x on the flow u at coordinate x the influence being weighted by the influence transfer function exp x x l in the integral the quantity l that appears as the scale length in the exponential weighting function is called the longitudinal coupling length it is determined by rheological parameters via the relationship l 2h n n 3n where n is the flowlaw exponent n the effective longitudinal viscosity and n the effective shear viscosity of the ice profile n is an average of the local effective viscosity n over the ice cross section and n 1 is an average of n 1 that gives strongly increased weight to values near the base theoretically the coupling length l is generally in the range one to three times the ice thickness for valley glaciers and four to ten times for ice sheets for a glacier in surge it is even longer l 12h it is distinctly longer for non linear n 3 than for linear rheology so that the flow coupling effects of longitudinal stress gradients are markedly greater for non linear flow the averaging integral indicates that the longitudinal variations in flow that occur under the influence of sinusoidal longitudinal variations in h or with wavelength are attenuated by the factor 1 1 2 l 2 relative to what they would be without longitudinal coupling the short intermediate and long scales of glacier motion raymond 1980 over which the longitudinal flow variations are strongly partially and little attenuated are for 2l 2l 20l and 20l for practical glacier flow calculations the exponential weighting function can be approximated by a symmetrical triangular averaging window of length 4l called the longitudinal averaging length the traditional rectangular window is a poor approximation because of the exponential weighting the local surface slope has an appreciable though muted effect on the local flow which is clearly seen in field examples contrary to what would result from a rectangular averaging window tested with field data for variegated glacier alaska and blue glacier washington the longitudinal averaging theory is able to account semi quantitatively for the observed longitudinal variations in flow of these glaciers and for the representation of flow in terms of effective surface slope values exceptions occur where the flow is augmented by large contributions from basal sliding in the ice fall and terminal zone of blue glacier and in the reach of surge initiation in variegated glacier the averaging length 4l that gives the best agreement between calculated and observed flow pattern is 2 5 km for variegated glacier and 1 8 km for blue glacier corresponding to l h 2 in both cases if l varies with x but not too rapidly the exponential weighting function remains a fairly good approximation to the exact green s function of the differential equation for longitudinal flow coupling in this approximation l in the averaging integral is l x but is not a function of x effects of longitudinal variation of l are probably important near the glacier terminus and head and near ice falls the longitudinal averaging formulation can also be used to express the local basal shear stress in terms of longitudinal variations in the local stope stress with the mediation of longitudinal stress gradients

biomarker temperature estimates for modern and last glacial surface waters of the california current system between 33 and 42 n sea surface temperature sst estimates were made using data for c37 39 alkenones analyzed in modern and glacial age intervals of sediment cores collected along an east west 42 n from 125 to 132 w and a north south 41 33 n transect of the california current system ccs the prymnesiophyte biomarker results suggest that surface waters warmed significantly throughout this region since the last glacial maximum lgm but the magnitude of warming varied spatially stratigraphic profiles from four sediment cores along the north south transect indicate the warming period was confined to the glacial interglacial transition 15 10 ka with sst reaching a maximum value at 10 ka and maintaining a uniformly high value throughout the holocene comparison of estimates derived from analysis of modern and lgm sediment intervals indicates the magnitude of the sst change was minimal for locations south of about 36 n 1 2 c and increased significantly 3 5 c north of this latitude using a simple heat balance model we calculate from the latitudinal gradient in sst that southward flow in the california current system during the lgm was about 60 of that measured today at 36 n our findings support the conclusion of others based on pollen data that coastal upwelling in the region of the northeast pacific off northern california was significantly reduced or even completely shutdown during the lgm

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

glacier motion dominated by processes deep in underlying till black rapids glacier is a 40 km long surge type glacier in the central alaska range in spring 1997 a wireline drill rig was set up at a location where the measured surface velocities are high and seasonal and annual velocity variations are large the drilling revealed a layer of subglacial till up to 7 m thick that is believed to be water saturated at one location a string of instruments containing three dual axis tiltmeters and one piezometer was successfully introduced into the till the tiltmeters monitored the inclination of the borehole at the ice till interface and at 1 and 2 m into the till for 410 days they showed that no significant deformation occurred in the upper 2 m of the till layer and no significant amount of the basal motion was due to sliding of the ice over the till the measured surface velocity at the drill site is about 60 m a 1 of which 20 30 m a can be accounted for by ice deformation almost the entire amount of basal motion 30 40 m a 1 was taken up at a depth of 2 m in the till possibly in discrete shear layers or as sliding of till over the underlying bedrock we propose that the large scale mobilization of such till layers is a key factor in initiating glacier surges

long chain alkenones and alkyl alkenoates and the fossil coccolith record of marine sediments long chain n c37 c39 alkenones and alkyl alkenoates are biological markers for sediment inputs of algae from the class prymnesiophyceae which includes the coccolithophorids these compounds have been recognized in many recent and ancient marine sediments but in only a few living algal species notably the ubiquitous coccolithophorid emiliania huxleyi the proven value of long chain alkenones in palaeotemperature assessment prompts an evaluation of their sedimentary record especially their correspondence with coccolithophorid fossils in ancient marine sediments synthesis of available micropalaeontological and molecular data suggests that morphologically related species of the genera crenalithus dictyococcites emiliania gephyrocapsa pseudoemiliania and reticulofenestra all belonging to the family gephyrocapsaceae were potential biological sources of alkenones and alkyl alkenoates in marine sediments deposited since the eocene 45 ma the occurrence of alkenones in cenomanian and albian sediments devoid of nannofossils may be presumed to reflect contributions from ancestors of the gephyrocapsaceae although an investigation of cretaceous samples containing both coccoliths and alkenones would provide further evidence of this proposed correspondence the combination of palaeontological and molecular chemotaxonomic information offers a novel approach to the evaluation of the phylogenetic lineages that link living and extinct algae

pleistocene water cycle and eastern boundary current processes along the california continental margin 1 coastal marine sediments contain mixtures of terrestrial and marine paleoclimate proxies that record how the coastal water cycle has behaved over long time frames we explore a 600 kyr marine record from odp site 1018 located due west of santa cruz california to identify coastal wet and dry periods and to associate them with oceanographic processes wet periods in central california identified by increased tree pollen relative to pollen from grasslands and scrublands are found on every major deglaciation in the last 600 kyr sea surface temperature sst data were collected for the last two deglaciations wet periods are associated with a rapid rise in sst off central california sst gradients along the california margin and changes in biogenic deposition show that wet periods in central california are associated with a weakening of the california current and weakened coastal upwelling high carbonate production suggests that there was significant curl of wind stress upwelling offshore we propose that wet periods in central california are associated with a meteorological connection to the tropical pacific and weakened southward flow in the california current that shunted temperate pacific water northward into the alaska gyre we do not observe evidence for a south shifted westerly storm track at the last glacial maximum but find that wet periods are diachronous along the california margin the wettest period around the santa barbara basin peaked at 16 ka preceding the wet peak in central and northern california by 4 kyr

the organic geochemistry of peru margin surface sediments i a comparison of the c37 alkenone and historical el nino records abstract the alkenone u k 37 paleothermometer has potential as a sedimentary marker for el nino southern oscillation enso events in the peru upwelling regime we assessed this potential by comparing the historical enso record with detailed u k 37 profiles for 210 pb dated cores from the peru margin oxygen minimum zone omz sediments with the greatest potential for holding a sedimentary u k 37 record of el nino events are sediments from the center of the omz sectioned at intervals the yearly sedimentation rate the u k 37 signals of individual el nino events were substantially attenuated in the sediments we examined and periods of frequent enso activity e g 1870 1891 were more readily identified than isolated enso events in periods of less frequent enso activity detailed depth profiles of the c 37 alkenones in a core from 253 m o 2 k 37 values for the five 2 mm sections from 0 1 cm suggests that the u k 37 may be unaffected by the alkenone loss correlation between the c 37 alkenone concentration profiles in two cores from 15 s collected nine years apart are consistent with the use of these compounds for molecular stratigraphy

elevation changes 1949 1995 of black rapids glacier alaska derived from a multi baseline insar dem and historical maps we have constructed a new digital elevation model dem of the 1995 surface of black rapids glacier a surge type glacier in the central alaska range using ers 1 2 repeat pass interferometry we isolated the topographic phase from three interferograms with contrasting perpendicular baselines numerous phase unwrapping errors caused by areas of poor coherence were corrected in all three interferograms using a novel iterative semi automated approach that capitalizes on the multi baseline nature of the dataset comparison of our dem with a 1949 us geological survey dem and with 1973 95 ground survey data shows the gradual return of black rapids glacier to a pre surge hypsometry following a surge in 1936 37 maximum elevation changes along the glacier center line in the ablation and accumulation areas are respectively 249 and 63 m 5 4 and 1 4 m a 1 maximum elevation changes of survey points at nearby locations are 4 9 m a 1 1975 84 and 0 5 ma 1 1975 85 center line thickening of 62 m between 1949 and 1995 1 4 m a 1 just above the loket tributary in the upper part of the ablation zone indicates dynamic thickening following the 1936 37 surge

mass balance in the glacier bay area of alaska usa and british columbia canada 1995 2011 using airborne laser altimetry the glacier bay region of southeast alaska usa and british columbia canada has undergone major glacier retreat since the little ice age lia we used airborne laser altimetry elevation data acquired between 1995 and 2011 to estimate the mass loss of the glacier bay region over four time periods 1995 2000 2000 05 2005 09 2009 11 for each glacier we extrapolated from center line profiles to the entire glacier to estimate glacier wide mass balance and then averaged these results over the entire region using three difference methods normalized elevation area weighted method and simple average we found that there was large interannual variability of the mass loss since 1995 compared with the long term post lia average for the full period 1995 2011 the average mass loss was 3 93 0 89 gt a 1 0 6 0 1 m w e a 1 compared with 17 8 gt a 1 for the post lia 1770 1948 rate our mass loss rate is consistent with grace gravity signal changes for the 2003 10 period our results also show that there is a lower bias due to center line profiling than was previously found by a digital elevation model difference method

in situ measurements of till deformation and water pressure a newly developed hammer was used to insert two autonomous probes 0 8 m and 2 1 m into clast rich subglacial till under black rapids glacier alaska usa both probes were instrumented with a dual axis tilt sensor and a pore water pressure transducer the data are compared to a 75 day record of surface velocities till deformation at depth was found to be highly seasonal it is significant during an early season speed up event but during long periods thereafter measured till deformation rates are negligible both tilt records show rotation around the probe axis which indicates a change in tilt direction of about 30 the tilt records are very similar suggesting spatial homogeneity on the scale of the probe separation 4 m horizontal and 3 3 m vertical there is evidence that during much of the year sliding of ice over till or deformation of a thin till layer 20 cm accounts for at least two thirds of total basal motion basal motion accounts for 50 70 of the total surface motion the inferred amount of ice till sliding is larger than that found at the same location in a previous study when surface velocities were about 10 lower we suggest that variations in ice till coupling account for the observed variations in mean annual speed

hydrological discharges and motion of fels and black rapids glaciers alaska u s a implications for the structure of their drainage systems characteristics of the hydrology and motion of black rapids and fels glaciers alaska were observed from 1986 to 1989 hydrological measurements included stage electrical conductivity and suspended sediment concentration in the discharge stream of each glacier and were made at 0 5 1 h intervals continuously through most of the melt seasons variations in the glacier speed were monitored through the full year at a number of locations along the length of each glacier using time lapse photography 1 d time resolution strain meters 0 5 1 h resolution and seismometers set up to count acoustic emissions both glaciers show similar seasonal diurnal and short term event changes in hydrological discharges and ice speed the hydrological behavior is analyzed in terms of a fast sub system composed of surface streams moulins and large tunnels with discharge that responds rapidly and a slow sub system composed of heterogeneous small passageways through the ice and distributed over the bed that maintain approximately uniform discharge over a day the timing and amplitude of water discharge in the diurnal cycle indicate that roughly 10 40 of the water is routed directly into the fast system the remaining 90 60 of the water enters the slow system dilution of the solute discharged from the slow system by the variable discharge in the fast system results in changes in water discharge and solute concentration that are approximately equal in relative amplitude and inversely related a small time lag from discharge maximum minimum to solute minimum maximum suggests that the fast system is confined to roughly the lowermost 30 40 of the full glacier length the residence time of water in the fast system is short compared to 1 d the slow system contains both short and long residence time passages characteristics of the diurnal cycles are somewhat variable through the melt season but no systematic evolutionary patterns were discerned even though large changes in the mean discharges of water and solutes occur which suggests parallel evolution of the variables that control the response of the fast system events were characterized by contemporaneous increases in suspended sediment concentration in the discharge water and distinct changes in straining on the glaciers events caused by increases in melt or precipitation related to weather and events related to release from reservoirs internal to the glaciers could be distinguished based on the changes in electrical conductivity of the discharge water the correlated changes in sediment discharge and motion of the glaciers indicate that the events were associated with temporary modifications of the slow passages distributed over the bed that allowed enhanced sliding and access of basal water flow to erosion products hydrological differences between black rapids and fels glaciers can be explained by differences in the size of the glaciers if there is a difference in bed structure that explains the difference in dynamics surge black rapids glacier versus non surge fels glacier it does not affect the hydrological parameters that were observed

assessment of sea surface temperature at 42 n in the california current over the last 30 000 years assessment of changes in surface ocean conditions in particular sea surface temperature sst is essential to understand long term changes in climate especially in regions where continental climate is strongly influenced by oceanographic processes to evaluate changes in sst in the northeast pacific we have analyzed long chain alkenones of prymnesiophyte origin at 38 depths in a piston and associated trigger core collected beneath the contemporary core of the california current system at 42 n 270 km off the coast of oregon california the samples span 30 000 years of deposition at this location unsaturation patterns u37k in the alkenone series display a statistically significant difference p 0 001 between interglacial 0 44 0 02 n 11 and glacial 0 29 0 04 n 20 intervals of the cores detailed examination of other compositional features of the c37 c38 c39 alkenone series and a related c36 alkenoate series measured downcore suggests the published u37k temperature calibration u37k 0 034 t 0 039 defined for cultures of a strain of emiliania huxleyi isolated from the subarctic pacific provides best estimates of winter sst at our study site this inference is purely statistical and does not imply however that the phytoplankton source of these biomarkers is most productive in winter or at the ocean surface the temperature record for u37k implies 1 an 4 c shift occurred in winter sst from 7 5 1 1 c at the last glacial maximum to 11 7 0 7 c in the present interglacial period and 2 this warming trend was confined to the time frame 14 10 ka within the glacial to interglacial transition period these conclusions are corroborated entirely by results from an independent sst transformation of radiolarian species assemblage data obtained from the same core materials

spatial patterns of summer speedup on south central alaska glaciers seasonal changes in glacier basal motion are attributable to variations in subglacial hydrology and cause variations in both ice discharge and glacier erosion we develop a novel workflow based upon landsat 8 feature tracking to document differences between spatial patterns of summer and winter glacier surface speed which reflect changes in the distribution of basal motion we identify and characterize summer speedups on 13 of 19 land terminating glaciers in alaska s wrangell st elias ranges the speedups are relatively uniform over much of the ablation zones and the speedup magnitudes vary by only a factor of 2 between glaciers whose velocities span an order of magnitude summer speedups extend up to 30 km up glacier from termini and often end at the bases of icefalls these data provide systematic observation of the spatial pattern of enhanced summer glacier basal motion and suggest the possibility of its parameterization in glacier models

multi model photogrammetric analysis of the 1990s surge of sortebrae east greenland sortebrae is a surge type tidewater glacier complex draining southeastward from the geikie plateau east greenland sortebrae s main flow unit surged around 1950 and again between 1992 and 1995 the 1990s surge affected the lower 50 km of sorte brae over an area of approximately 335 km2 over a period of 5 km surge velocities in the order of kilometres per annum are about 100 fold the quiescent velocities multi model photogrammetric analysis shows a thinning of the reservoir zone of up to 219 m and thickening of the receiving zone of up to 74 m the surge transported approximately 18 6 km 3 of ice down glacier the total calving volume as a result of the surge amounted to 11 7 km 3 equivalent to a calving flux of 3 9 7 3 km a 1 the surge characteristics and environmental setting suggest that the surge mechanism involves a switch in the subglacial drainage this surge of sortebrae is more similar to the fast short alaskan type surges than to the sluggish long svalbard type surges

evolution of variegated glacier alaska u s a prior to its surge on presente l evolution saison apres saison des changements dans la geometrie et la vitesse du glacier et on tente de rattacher ces variations a la deformation de la glace et au glissement basal

growth and collapse of the distributed subglacial hydrologic system of kennicott glacier alaska usa and its effects on basal motion nearly 100 days of hourly glacier motion hydrology and hydrochemistry measurements on kennicott glacier alaska usa demonstrate the complicated relationship between water and motion at the glacier bed our observations capture the transient glacier response to seasonal and daily melt cycles and to a jokulhlaup that prompts a sixfold increase in glacier speed sliding is promoted whenever the water inputs to the glacier exceed the capacity of the subglacial hydrologic system to transmit the water sensitivity of sliding to daily meltwater inputs varies strongly through the season implying that the state of the hydrologic system governs the sensitivity of basal sliding a numerical model constructed to explore these relationships reveals the roles of the effective pressure the exponent to which this is taken in the sliding law 0 1 0 6 glacier macroporosity 2 and the cavity generating capacity of the glacier bed which encapsulates the sizes and spacing of bed roughness elements temporal changes in the effective pressure associated with evolution of both water inputs and subglacial water transmission capacity can explain the varying strength of diurnal velocity fluctuations of kennicott glacier spatial patterns of glacier macroporosity and of basal roughness govern variation in sensitivity of sliding to water inputs

record negative glacier balances and low velocities during the 2004 heatwave in alaska usa implications for the interpretation of observations by zwally and others in greenland

flow and structure in a dendritic glacier with bedrock steps sherpa romeo green journal open access article creative commons attribution 4 0 international cc by 4 0 applies

quiescent phase evolution of a surge type glacier black rapids glacier alaska u s a black rapids glacier a surge type glacier in the alaska range most recently surged in 1936 37 and is currently in its quiescent phase mass balance ice velocity and thickness change have been measured at three to ten sites from 1972 to 1994 the annual speed has undergone cyclical fluctuations of as much as 45 about the mean speed ice thickness and surface slope did not change enough to cause the speed fluctuations through changes in ice deformation which indicates that they are being driven by changes in basal motion the behavior of black rapids glacier during this quiescent phase is significantly different from that variegated glacier another well studied surge type glacier in alaska the present medial moraine configuration of black rapids glacier indicates that a surge could occur at any time however ice velocity data indicate that the next surge may not be imminent we believe that there is little chance that the next surge will cross and dam the delta river

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

coseismic deformation of the 2002 denali fault earthquake insights from gps measurements 1 we estimate coseismic displacements from the 2002 m w 7 9 denali fault earthquake at 232 gps sites in alaska and canada displacements along a n s profile crossing the fault indicate right lateral slip on a near vertical fault with a significant component of vertical motion north side up we invert both gps displacements and geologic surface offsets for slip on a three dimensional 3 d fault model in an elastic half space we restrict the motion to right lateral slip and north side up dip slip allowing for oblique slip along the denali and totschunda faults improves the model fit to the gps data by about 30 we see mostly right lateral strike slip motion on the denali and totschunda faults but in a few areas we see a significant component of dip slip the slip model shows increasing slip from west to east along the denali fault with four localized higher slip patches three near the trans alaska pipeline crossing and a large slip patch corresponding to a m w 7 5 subevent about 40 ion west of the denali totschunda junction slip of 1 3 m was estimated along the totschunda fault with the majority of slip being at shallower than 9 km depth we have limited resolution on the susitna glacier fault but the estimated slip along the fault is consistent with a m w 7 2 thrust subevent total estimated moment in the denali fault earthquake is equivalent to m w 7 89 the estimated slip distribution along the surface is in very good agreement with geological surface offsets but we find that surface offsets measured on glaciers are biased toward lower values

airborne surface profiling of glaciers a case study in alaska a relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested the aircraft position is determined by kinematic global positioning system gps methods the distance to the glacier surface is determined with a laser ranger the accuracy is about 0 3 m sufficient to permit future changes to be observed over short time intervals long term changes can be estimated by comparison of profiles with existing maps elevation profiles obtained in 1993 94 from three glaciers in central and south central alaska are compared with maps made about 1950 the resulting area averaged seasonally corrected thickness changes during the interval are gulkana glacier central alaska range 11 m worthington glacier central chugach mountains 7 m and bear lake glacier kenai mountains 12 m all three glaciers retreated during the interval of comparison the estimated uncertainty in the average thickness change is 5 m which is mainly due to errors in the existing maps constraints on the accuracy of the maps are obtained by profiling in proglacial areas

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

1 4 ghz radar penetration and evidence of drainage structures in temperate ice black rapids glacier alaska u s a we have tested the ability of a 1 12 1 76 ghz bandwidth airborne frequency modulation continuous wave fm cw radar with an effective pulse duration of 3 ns to penetrate temperate ice of the ablation zone of black rapids glacier central alaska u s a we used high gain horn antennas to suppress clutter and tested over cold and nearly ideal surface conditions englacial horizons dipping to at least 60 m depth were found along three sections of one axial profile more narrow band 1 21 1 29 ghz low resolution 24 ns pulse duration profiles from a fourth section detected events at about 100 150 m depth comparative profiles recorded with a 100 mhz short pulse type radar reproduce the horizons of two of the sections and verify the penetration in all cases all horizons are composed of diffractions we interpret voids from the phase of the 100 mhz diffractions within one of the horizons the diffraction nature of the horizons the void interpretation and the proximity to a nearby and up glacier pothole field lead us to conclude that the horizons within two of the sections are meandering drainage channels a more complex branching structure with near surface horizons profiled within the third section much farther down glacier may also be a complex drainage system fed by near surface melting the fm cw signal to clutter noise ratios of some of the targets predict that they could be detected at 200 m depth in the 1 2 ghz range significant performance improvements at maximum vertical resolution could be achieved with higher gain antennas

the galloping glacier trots decadal scale speed oscillations within the quiescent phase a 28 year record of annual surface speeds has revealed oscillations with a period of roughly 12 years during the quiescent phase of black rapids glacier alaska u s a the original galloping glacier these oscillations are hypothesized to be the manifestation of slowly propagating waves of till failure and till healing with at least the second cycle being initiated by the anomalous advance of a tributary glacier observations support the idea that such dynamics may have occurred but are not conclusive in the conceptual model describing the mechanisms of till failure and healing temporal variations in longitudinal stress gradients are proposed to be more important in causing till failure than temporal variations in effective pressure

analysis of the 1993 95 bering glacier alaska surge using differential sar interferometry differential spaceborne radar interferometry observations of west bagley icefield are used to measure surface velocity and topography bagley icefield is the accumulation area fur bering glacier which surged in two phases from spring 1993 through summer 1905 the observations presented are based on data collected during the winter of 1992 prior to the surge and during winter 1994 while the surge was in full progress both observation intervals correspond to 3 day repeat orbit phases of the ers i c band sar this paper gives an overview of the algorithms used to derive surface velocity vector fields and topography for valley glaciers from sar images the resulting high resolution velocity data clearly show west bagley icefield accelerating from its quiescent pre surge velocity by a factor of 2 7 in response to the bering glacier surge persistence of lnterfero metric phase coherence and the relatively moderate degree of acceleration on the western arm of bagley icefield suggest that the velocity increase may have been caused by increased longitudinal stress gradients resulting from coupling to the surging main trunk of bering glacier

insar observations of the 1993 95 bering glacier alaska u s a surge and a surge hypothesis time varying accelerations were observed on bagley icefield during the 1993 95 surge of bering glacier alaska u s a using repeat pass synthetic aperture radar interferometry observations were from datasets acquired during winter 1991 92 pre surge winter 1993 94 during the surge and winter 1995 96 post surge the surge is shown to have extended 110 km up the icefield from bering glacier to within 15 km or less of the flow divide acceleration and step like velocity profiles are strongly associated with an along glacier series of central phase bull s eyes with diameters of 0 5 4 km these bull s eyes are interpreted to represent glacier surface rise fall events of 3 30 cm during 1 3 day observation intervals and indicate possible migrating pockets of subglacial water we present a surge hypothesis that relates late summer climate to englacial water storage and thence to the subglacial water dynamics pressurization hydraulic jacking depressurization and migration suggested by our observations

geodetic mass balance of surge type black rapids glacier alaska 1980 2001 2010 including role of rockslide deposition and earthquake displacement we determine the geodetic mass balance of surge type black rapids glacier alaska for the time periods 1980 2001 and 2001 2010 by combining modern interferometric synthetic aperture radar insar derived digital elevation models dems dems derived from archival aerial imagery laser altimetry data and in situ surface elevation measurements our analysis accounts for both the large rockslides and terrain displacements caused by the 2002 m7 9 earthquake on the denali fault which runs through black rapids glacier to estimate uncertainties we apply monte carlo simulations for the earthquake triggered rockslides we find a volume of 56 62 2 86 106 m3 equivalent to an average debris thickness of 4 44 0 24 m across the 11 7 km2 deposit area on the glacier terrain displacement due to the earthquake corresponds to an apparent glacier volume change of 53 1 106 m3 which would cause an apparent specific mass balance of 0 19 meter water equivalent mwe if not taken into account the geodetic mass balance of black rapids glacier is 0 48 0 07 mwe a 1 for the entire 30 year period but more negative for the period 2001 2010 0 64 0 11 mwe a 1 than the period 1980 2001 0 42 0 11 mwe a 1 in agreement with trends indicated by in situ mass balance measurements elevation data indicate no net thickening of the surge reservoir between 1980 and 2010 in contrast to what is expected during the quiescent phase a surge of black rapids glacier in the near future is thus considered unlikely

time dependent basal stress conditions beneath black rapids glacier alaska usa inferred from measurements of ice deformation and surface motion observations of surface motion and ice deformation from 2002 03 were used to infer mean stress fields in a cross section of black rapids glacier alaska usa over seasonal timescales basal shear stresses in a well defined zone north of the center line orographic left were approximately 7 and 16 lower in spring and summer respectively than in winter correspondingly higher stresses were found near the margins these changes in the basal shear stress distribution were sufficiently large to cause mean surface velocities to be 1 2 and 1 5 times larger in spring and summer than in winter these results were inferred with a simple inverse finite element flow model that can successfully reproduce bulk surface velocities and tiltmeter data stress redistribution between the well defined zone and the margins may also occur over much shorter time periods as a result of rapidly changing basal conditions ice bed decoupling or enhanced till deformation thereby causing large variations in surface velocity and strongly influencing the glacier s net motion during summer

subglacial drilling at black rapids glacier alaska u s a drilling method and sample descriptions we employed a commercial wireline drill rig to investigate the subglacial conditions of black rapids glacier a well studied surge type glacier in the central alaska range the four main goals were to assess the capabilities of the commercial drilling industry for sampling subglacial material to investigate the basal morphology to determine the subglacial geology and to emplace borehole instruments the drilling was done in an area where seasonal and secular variations in speed are large and where seismic studies suggested the presence of a till layer four holes were drilled at three locations to a maximum depth of 620 m three holes yielded samples of basal ice and till although recovery of the latter was generally poor bedrock was sampled in one or possibly two of the holes in the area sampled the glacier is underlain by a till layer some 4 7 m thick confirming the seismic interpretation it consists ofa sandy matrix at least 20 30 of which comprises larger clasts limited samples ofthe matrix indicate that near the top ofthe till the porosity is 40 and that some of the pore water is frozen geologic studies suggest that the drilling area lies to the north of the denali fault a major tectonic boundary followed by the glacier and that most of the till is locally derived with transport distances of 2 km

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

seismic detection of transient changes beneath black rapids glacier alaska u s a i techniques and observations to gain new insight into the mechanisms of basal motion we have demonstrated the feasibility of an active seismic technique to measure temporal changes in basal conditions on sub hourly time scales one region of the bed of black rapids glacier alaska u s a was monitored for a period of 45 days using seismic reflections the majority ofthese reflections were nearly identical however three significant anomalies were recorded several days apart these corresponded with the englacial drainage of two ice marginal lakes and one supraglacial pothole each up glacier of the study site as well as dramatic increases in basal motion two of these seismic anomalies revealed identical changes over 1 km 2 of the bed despite the fact that their drainage events occurred at different locations further these two seismic anomalies were followed by records identical to the non anomalous state showing that the seismic changes were reversible in one of these events two records taken 36 min apart revealed that the transition between the anomalous and normal states occurred completely within this short interval

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

assessment of mass balance variations within a sparse stake network qamanârssup sermia west greenland les fluctuations du bilan moyen d un glacier est calcule a partir d un reseau limite de balises si on peut appliquer le modele lineaire de lliboutry l ecart standard du residu est de 0 34 m d eau l incertitude sur le bilan annuel 0 23 m la fluctuation sur 4 ans 0 52 m d eau

spatiotemporal variations in surface velocity of the gangotri glacier garhwal himalaya india study using synthetic aperture radar data the gangotri glacier is the largest in the garhwal himalaya india and its melt water forms the main source stream of the ganga river yet its dynamics are poorly understood its long record of terminus retreat measurements 1800 present shows multi decadal oscillations and more recently a slowing down of the retreat its complex dynamics are also indicated by studies of proglacial melt water at the terminus however there have been no systematic measurements of its surface velocity or how it changes seasonally or over longer term time scales here i have characterized the spatiotemporal variations of surface velocity of the gangotri glacier using synthetic aperture radar sar data spanning nearly two decades 1991 2011 the main findings are as follows 1 the glacier undergoes seasonal fluctuations in surface velocities there was a clear summer speedup of similar to 57 126 compared to winter velocities between 0 and 12 6 km from the terminus with peak summer speeds of 63 1 5 4 m yr in 1992 66 6 6 0 m yr in 1999 58 2 4 5 m yr in 2004 and 42 8 4 2 m yr in 2007 whereas winter speeds were relatively stable 25 30 m yr during the same period this summer speedup is indicative of increased basal sliding known to occur when melt waters penetrate to the glacier bed resulting in reduced friction 2 these summer velocities exhibited an inter annual reduction which was manifest as a reduction in summer speed up from 120 in 2004 to 60 in 2007 this pattern continued into 2011 despite the availability of abundant melt water during those years this inter annual reduction indicates the formation of increasingly efficient melt water channels year on year resulting in lesser lubrication at the glacier bed interface my results show that the gangotri glacier is dynamic throughout its length with systematic spatiotemporal variations in surface velocity that elucidate its subglacial processes based on my results and other evidence in the literature i propose that the subglacial drainage system of the gangotri glacier is subject to seasonal and inter annual hydrodynamic coupling between winters and melt seasons akin to other glaciers c 2016 elsevier inc all rights reserved

paleoproductivity and carbon burial across the california current the multitracers transect 42 n the multitracers experiment studied a transect of water column sediment trap and sediment data taken across the california current to develop quantitative methods for hindcasting paleoproductivity the experiment used three sediment trap moorings located 120 km 270 km and 630 km from shore at the oregon california border in north america we report here about the sedimentation and burial of particulate organic carbon corg and caco3 in order to observe how the integrated caco3 and corg burial across the transect has changed since the last glacial maximum we have correlated core from the three sites using time scales constrained by both radiocarbon and oxygen isotopes by comparing surface sediments to a two and a half year sediment trap record we have also defined the modern preservation rates for many of the labile sedimentary materials our analysis of the corg data indicates that significant amounts 20 40 of the total corg being buried today in surface sediments is terrestrial at the last glacial maximum the terrestrial corg fraction within 300 km of the coast was about twice as large such large fluxes of terrestrial corg obscure the marine corg record which can be interpreted as productivity when we corrected for the terrestrial organic matter we found that the mass accumulation rate of marine corg roughly doubled from the glacial maximum to the present because preservation rates of organic carbon are high in the high sedimentation rate cores corrections for degradation are straightforward and we can be confident that organic carbon rain rate new productivity also doubled as confirmation the highest burial fluxes of other biogenic components opal and ba also occur in the holocene productivity off oregon has thus increased dramatically since the last glacial maximum caco3 fluxes also changed radically through the deglaciation however they are linked not to caco3 production but rather to changes in deepwater carbonate chemistry between 18 ka and now

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd