discharge of debris from ice at the margin of the greenland ice sheet sediment production at a terrestrial section of the ice sheet margin in west greenland is dominated by debris released through the basal ice layer the debris flux through the basal ice at the margin is estimated to be 12 45 m 3 m 1 a 1 this is three orders of magnitude higher than that previously reported for east antarctica an order of magnitude higher than sites reported from in norway iceland and switzerland but an order of magnitude lower than values previously reported from tidewater glaciers in alaska and other high rate environments such as surging glaciers at our site only negligible amounts of debris are released through englacial supraglacial or subglacial sediment transfer glaciofluvial sediment production is highly localized and long sections of the ice sheet margin receive no sediment from glaciofluvial sources these findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin these data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the greenland ice sheet

late wisconsinan stratigraphy and chronology of southern st george s bay newfoundland a re appraisal reply brookes identifies two points of difference in his discussion of our re appraisal of the late wisconsinan stratigraphy and chronology of southern st george s bay newfoundland i the applicability of our sedimentological model and ii the relation of sediments to late glacial sea level the latter point is the subject of a manuscript submitted for review to this journal incorporating 91 radiocarbon dates from onshore and offshore marine records 19 of which are reported for the first time we therefore restrict our rebuttal to what we believe are the critical disagreements in field observations and interpretations that underpin the two points of difference and invite readers to visit the contentious coastal sections to compare published accounts access to these sites is described in several field guides to southern st george s bay liverman and batterson 1995 liverman et al 2001 in our paper we explicitly state that for 80 of the 39 km long coastal exposure our non ridge sections p 866 our observations broadly confirm earlier interpretations by brookes 1969 1974 1977 and macclintock and twenhofel 1940 with the one important exception that we found no evidence for glacial readvance following initial deglaciation and marine submergence of the present coastline in almost 100 logged sections through non ridge exposures we did not encounter an upper till or ice contact gravels robinsons head drift indicative of a glacial readvance instead we described laterally continuous moderately to well sorted planar bedded and trough cross bedded fine gravel capping sections which we interpreted as glaciofluvial outwash p 859 figs 4 5 c consequently our deglacial depositional model for a large part of the coast of southern st george s bay is neither compatible with nor applicable to published sedimentary sequences in the remaining 20 of coastal exposure our ridge sections p 866 our mapping revealed complex sedimentary sequences of interbedded diamicton gravel and mud above

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

a simple model for the influence of push morainal banks on the calving and stability of glacial tidewater termini push morainal banks at the grounding lines of tidewater termini of temperate glaciers are the source of two types of restraining forces operating at the glacier terminus horizontal normal forces derive from the lateral support and transport of the bank of sediment at the terminus whereas a horizontal shear force operates along the base of a bank pushed in front of an advancing glacier the simple model we present suggests that bank related restraining forces are significantly larger than the restraining force derived from the hydrostatic pressure of water adjacent to the submerged terminus of a glacier during glacier advance restraining forces continually increase resulting in decreasing flow rates glacier thickening and the eventual cessation of advance during retreat restraining forces continually decrease resulting in increasing flow rates glacier thinning and the potential for unstable rapid sustained retreat the normal seasonal oscillatory advance retreat cycle of a glacier is moderated by restraining forces associated with push moraines unstable retreat is likely initiated when bank related restraining forces fall below some threshold value during the seasonal retreat cycle calving is not a primary cause of glacier retreat but is more likely a short term response to increased flow rates increased flow rates result in glacier thinning and an approach toward buoyancy both of which fluctuate seasonally in accordance with bank related restraining forces

multicentennial scale hydrological changes in the black sea and northern red sea during the holocene and the arctic north atlantic oscillation 1 paleoenvironmental proxy data for ocean properties eolian sediment input and continental rainfall based on high resolution analyses of sediment cores from the southwestern black sea and the northernmost gulf of aqaba were used to infer hydroclimatic changes in northern anatolia and the northern red sea region during the last 7500 years pronounced and coherent multicentennial variations in these records reveal patterns that strongly resemble modern temperature and rainfall anomalies related to the arctic oscillation north atlantic oscillation ao nao these patterns suggest a prominent role of ao nao like atmospheric variability during the holocene beyond interannual to interdecadal timescales most likely originating from solar output changes

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

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

glacial outburst flood sediments within disenchantment bay alaska implications of recognizing marine jokulhlaup deposits in the stratigraphic record abstract glacial outburst floods have been observed or inferred in most glaciated regions of the world outburst flooding events along past ice sheet margins have been discussed as possible causes for changes in ocean circulation while subglacial lake drainage under ice sheets may influence ice sheet stability the recognition of these geologically instantaneous events in the marine sediment or rock record is critical in order to characterize the magnitude and frequency of past outburst events as well as to predict the likelihood of future occurrences in this paper we characterize outburst lithofacies and infer depositional processes from two outburst floods within disenchantment bay alaska and compare these deposits to other recognized outburst deposits within marine depositional settings here we show that the outburst deposits are lithologically similar and are composed of stratified mud sand and diamicton we interpret these facies to have been formed by sediment gravity flows and hypopycnal plume sedimentation these results show that the volume of sediment lithofacies and inferred depositional processes cannot be easily distinguished from normal sediment accumulation within the proximal temperate glacimarine depositional environment the paucity of fluvial subglacial discharge in polar glacimarine environments suggests the potential for recognition of such deposits in the antarctic

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

recent changes in deep water formation and spreading in the eastern mediterranean sea a review abstract observations of the last decade testify that the characteristics of the deep thermohaline circulation in the eastern mediterranean sea have changed thoroughly the source of the most dense waters of the basin has moved from the adriatic to the aegean sea this new source has proved to be very efficient since the estimated formation rate for the period 1989 95 was more than 1 sv about three times more than the dense water formation rate of the adriatic sea these new waters with hydrological characteristics that are warmer and more saline have replaced almost 20 of the older deep waters of the basin and have uplifted the deep isopycnals by about 500 m this major event can be attributed to important meteorological anomalies in the eastern mediterranean and to changes of circulation patterns the extended dry period of 1988 93 and the exceptionally cold winters of 1987 and 1992 93 created favorable conditions for increased formation of dense water in the aegean furthermore changes in the circulation patterns in the intermediate water range levantine intermediate water liw and cretan intermediate water themselves possibly linked to meteorological anomalies appear to have played an important role in the redistribution of salt as a result of an interruption to exchanges between the ionian and levantine basin the salinities in the latter started to rise high salinity waters were diverted into the aegean malanotte rizzoli p manca b b ribera dacala m theocharis a 1998 the eastern mediterranean in the 80s and in the 90s the big transition emerged from the poem bc observational evidence rapport du commission international de la mer medittanee 35 174 175 and the westward transport of liw was reduced an additional effect of the deep water discharge from the aegean and the resulting uplifting of mid depth waters was to lower salinities in the liw layer this effect is most strongly felt in the ionian sea a 3 d primitive equation numerical model for the eastern mediterranean with a 20 km grid size is used to simulate the observed changes and understand the basic mechanisms which caused them under appropriate atmospheric forcing the model successfully reproduces the main characteristics of the transient these results indicate that the observed changes can be at least partially explained as a response of the eastern mediterranean and more specifically of the aegean to atmospheric forcing variability

sediment glaciohydraulic supercooling and fast glacier flow glaciers often advance over proglacial sediments which then may enhance basal motion forglaciers with abundant meltwater thermodynamic considera tions indicate that the sediment ice contact in the direction of ice flow tends toward an angle opposed to and somewhat steeper than the surface slope by slightly more than 50 a simple model basedonthis hypothesisyieldstheextentof over ridden sediments as a function of sediment thickness and strength a result that may be useful in guiding additional fieldwork forhypothesistesting sediment floored as wellasrock floored over deepenings are common features along glacier flow paths and are expected based on theories of glacier erosion entrainment transport and deposition

marginal formation of de geer moraines and their implications to the dynamics of grounding line recession de geer moraine ridges occur in abundance in the coastal zone of northern sweden preferentially in areas with proglacial water depths in excess of 150 m at deglaciation from detailed sedimentological and structural investigations in machine dug trenches across de geer ridges it is concluded that the moraines formed due to subglacial sediment advection to the ice margin during temporary halts in grounding line retreat forming gradually thickening sediment wedges the proximal part of the moraines were built up in submarginal position as stacked sequences of deforming bed diamictons intercalated with glaciofluvial canal infill sediments whereas the distal parts were built up from the grounding line by prograding sediment gravity flow deposits distally interfingering with glaciolacustrine sediments the rapid grounding line retreat ca 400 m yr 1 was driven by rapid calving in turn enhanced by fast iceflow and marginal thinning of ice due to deforming bed conditions the spatial distribution of the moraine ridges indicates stepwise retreat of the grounding line it is suggested that this is due to slab and flake calving of the ice cliff above the waterline forming a gradually widening subaqueous ice ledge which eventually breaks off to a new grounding line followed by regained sediment delivery and ridge build up less

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

analysis of the seasonal and interannual variability of the sea surface temperature field in the adriatic sea from avhrr data 1984 1992 seasonal and interannual variability of the sea surface temperature field in the adriatic sea is analyzed from the low resolution advanced very high resolution radiometer data the spatial resolution of 18 km allowed analysis of only basin and subbasin scale features average monthly and seasonal sea surface temperature fields for the entire studied period 1984 1992 are discussed the analysis shows the absence of any permanent sea surface thermal features in the adriatic sea the south adriatic sea surface temperature minimum presumably associated to the cyclonic gyre previously considered as one of the permanent features appears to be recurrent being prominent only in late autumn and early winter i e in the preconditioning and a deepwater formation phases the major ionian water inflow is documented in autumn while the thermal signature of the western surface outflow of adriatic water appears most prominent in winter the variability of the basin wide thermal pattern in the adriatic reveals four distinct seasons which is different from both the eastern and western mediterranean where only two major patterns are recognized a prominent interannual signal occurs in a northward extension of the warm water plume along the eastern coast which in some years reaches the northernmost corner of the adriatic while in other situations it remains trapped in the south adriatic cyclonic gyre the surface thermal signature of the south adriatic gyre also varies on an interannual timescale and it was weak or completely absent during the period 1984 1986 while it was rather prominent in the period 1987 1992 a constant trend of sea surface temperature decrease in the center of the south adriatic gyre and in the northernmost corner of the adriatic was evidenced over the studied period

neogene fjordal sedimentation on the western margin of the lambert graben east antarctica neogene glacial sedimentation east antarctica

debris in icebergs and rates of glaci marine sedimentation observations from spitsbergen and a simple model debris distribution and content in spitsbergen icebergs varies but basal debris rich layers often 1 m thick are the most important sources of iceberg rafted material angular iceberg rafted clasts in the glaci marine record imply the presence of nunataks or valley walls rather than unbroken ice sheet surfaces indicating paleo ice mass configuration calculated iceberg melt rates imply that most iceberg rafted debris is released within spitsbergen fjords sedimentation from icebergs is calculated as 1 mm a 1 for inner mollerfjorden and 8 mm a 1 for inner kongsfjorden an order of magnitude lower than total sediment inputs turbid subglacial meltwater is a more important debris source a simple model is proposed to calculate the flux of basal debris in icebergs and iceberg sedimentation rates

modeling the mediterranean sea interannual variability during 1961 2000 focus on the eastern mediterranean transient 1 this work is dedicated to the study of the climate variability of the mediterranean sea in particular the study of the eastern mediterranean transient emt which occurred in the early 1990s simulations of the 1961 2000 period have been carried out with an eddy permitting ocean general circulation model of the mediterranean sea driven by realistic interannual high resolution air sea fluxes using different databases for the river runoff black sea inflow and atlantic thermohaline characteristics at climatological or interannual scales we assess the effects of the non atmospheric hydrological forcings on the simulation of the interannual variations of the mediterranean circulation the evolution of the basin scale heat content is in very good agreement with the observations especially in the surface and intermediate layers while the agreement is lower for the evolution of the salt content convection events in the aegean sea are noticed in the simulations between 1972 and 1976 in the late 1980s and around the emt period the formation rates of cretan deep water cdw are different during these periods allowing or preventing the spreading of cdw into the eastern mediterranean the sequence of the emt events is well reproduced the high winter oceanic surface cooling and net evaporation over the aegean sea in the early 1990s the high amount of dense cdw formed during these winters and then the overflow and the spreading of this cdw in the eastern mediterranean among the preconditioning processes suggested in the literature we find that changes in the levantine surface circulation possibly induced by the presence in the cretan passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern mediterranean lead to an increase of the salt content of the aegean sea changes in the black sea freshwater inflow or in the characteristic of the atlantic water entering at the gibraltar strait also modify the thermohaline state of the aegean sea before the emt but as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the aegean sea we conclude that concerning the emt the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991 1992 and 1992 1993

transient eastern mediterranean deep waters in response to the massive dense water output of the aegean sea in the 1990s abstract we present a detailed account of the changing hydrography and the large scale circulation of the deep waters of the eastern mediterranean emed that resulted from the unique high volume influx of dense waters from the aegean sea during the 1990s and of the changes within the aegean that initiated the event the so called eastern mediterranean transient emt the analysis uses repeated hydrographic and transient tracer surveys of the emed in 1987 1991 1995 1999 and 2001 2002 hydrographic time series in the southern aegean and southern adriatic seas and further scattered data aegean outflow averaged nearly 3 10 6 m 3 s 1 between mid 1992 and late 1994 and was largest during 1993 when south and west of crete aegean influenced deep waters extended upwards to 400 m depth emt related aegean outflow prior to 1992 confined to the region around crete and to 1800 m depth wise amounted to about 3 of the total outflow outflow after 1994 up to 2001 2002 derived from the increasing inventory of the tracer cfc 12 contributed 20 to the total of 2 8 10 14 m 3 densities in the southern aegean sea deep waters rose by 0 2 kg m 3 between 1987 and 1993 and decreased more slowly thereafter the aegean waters delivered via the principal exit pathway in kasos strait east of crete propagated westward along the cretan slope such that in 1995 the highest densities were observed in the hellenic trench west of crete aegean influenced waters also crossed the east mediterranean ridge south of crete and from there expanded eastward into the southeastern levantine sea transfer into the ionian mostly followed the hellenic trench largely up to the trench s northern end at about 37 n from there the waters spread further west while mixing with the resident waters additional transfer occurred through the herodotus trough in the south levantine waters after 1994 consistently showed temperature salinity t s inversions in roughly 1000 1700 m depth with amplitudes decreasing in time the t s distributions in the ionian sea were more diverse one cause being added aegean outflow of relatively lower density through the antikithira strait west of crete spreading of the aegean influenced waters was quite swift such that by early 1995 the entire emed was affected and strong mixing is indicated by near linear t s relationships observed in various places referenced to 2000 and 3000 dbar the highest aegean generated densities observed during the event equaled those generated by adriatic sea outflow in the northern ionian sea prior to the emt a precarious balance between the two dense water source areas is thus indicated a feedback is proposed which helped triggering the change from a dominating adriatic source to the aegean source but at the same time supported the previous long year dominance of the adriatic the emed deep waters will remain transient for decades to come

flow dynamics of tidewater glaciers a numerical modelling approach the dynamics of grounded tidewater glaciers is investigated with a time dependent numerical flow model which solves the full equations for the stress and velocity fields and includes a water pressure dependent sliding law the calving criterion implemented in the model shifts the calving front at each time step to the position where the frontal ice thickness exceeds flotation height by a prescribed value with this model the linear relation between calving rate and water depth proposed on empirical grounds is qualitatively reproduced for the situation of a slowly retreating or advancing terminus but not for situations of rapid changes length changes of tidewater glaciers i e especially rapid changes are dominantly controlled by the bed topography and are to a minor degree a direct reaction to a mass balance change thus accurate information on the near terminus bed topography is required for reliable prediction of the terminus changes due to climate changes the results also confirm the suggested cycles of slow advance and rapid retreat through a basal depression rapid changes in terminus positions preferably occur in places where the bed slopes upwards in the ice flow direction

toward an understanding of deep water renewal in the eastern mediterranean abstract this paper presents a scenario for understanding the unexpectedly large changes of deep waters and thermohaline circulation in the eastern mediterranean during the past decade it is demonstrated as a possible deep water renewal mechanism in the eastern mediterranean in a numerical simulation with a high resolution model which has successfully reproduced the observed 1987 and 1995 regimes as shown by the two meteor cruises a budget study of the model simulation has shown that more than 75 of the salt added to the deep layers of the eastern mediterranean could have come from the top 1000 m by a salinity redistribution process triggered by intensive cooling over the aegean sea a water transformation process analysis is carried out in the model simulation to reveal how colder and fresher dense deep water formed in the aegean is turned into the eastern mediterranean deep water emdw as observed surface heat and freshwater fluxes are diagnosed to show the roles of each component during the trans

eastern mediterranean transient studied with lagrangian diagnostics applied to a mediterranean ogcm forced by satellite sst and ecmwf wind stress for the years 1988 1993 1 in this work we estimate deep and intermediate water mass dispersal in the different phases of the eastern mediterranean transient by means of the lagrangian analysis of a mediterranean ocean general circulation model ogcm run forced by daily european centre for medium range weather forecasts ecmwf wind stress and satellite sea surface temperature sst over the years from 1988 to 1993 while in a first phase 1989 1991 major modifications of the intermediate salty waters path are observed during 1992 and 1993 the general mechanism of the transient is reproduced in the deep ionian basin where the cretan overflow replaces adriatic deep water that uplifting of several hundred meters freshens in the intermediate layers analysis of the water mass formation rates shows that dense water production during 1993 is twice the climatological values in the eastern subbasins of the mediterranean and that the densest water is formed in the cretan sea from 1988 to 1993 about 1 3 1014 m3 of water flows over the cretan arcs see the caption of figure 1 for a definition of the cretan arcs to sink deeper than 600 m in the eastern mediterranean which is roughly half of the value estimated by roether et al 1996 about 60 of this deep outflow 0 8 1014 m3 occurs in a few months during the cold winters of 1992 and 1993 when the overflow of cretan dense water in the antikithera strait reaches 1 5 sv and rapidly propagates in the deep ionian basin developing very energetic coherent structures we study the characteristic times of the relaxation of the system toward the climatology and finally we estimate the rate and the geographical distribution of the upwelling in the intermediate and subsurface layers

lateglacial and holocene climate and environmental change in the northeastern mediterranean region diatom evidence from lake dojran republic of macedonia greece abstract the juncture between the west east and north south contrasting holocene climatic domains across the mediterranean is complex and poorly understood diatom analysis of lake dojran republic of macedonia greece provides a new insight into lake levels and trophic status during the lateglacial and holocene periods in the northeastern mediterranean following a very shallow or even desiccated state at the core base at ca 12 500 cal yr bp indicated by sedimentological and hydro acoustic data diatoms indicate lake infilling from a shallow state with abundant benthos to a plankton dominated relatively high lake level and eutrophic state thereafter diatom inferred shallowing between ca 12 400 12 000 cal yr bp and a very low lake level and eutrophic oligosaline state between ca 12 000 11 500 cal yr bp provide strong evidence for younger dryas aridity the earliest holocene ca 11 500 10 700 cal yr bp was characterised by a high lake level followed by a lake level reduction and increased trophic level between ca 10 700 8 500 cal yr bp the lake was relatively deep and exhibited peak holocene trophic level between ca 8 500 3 000 cal yr bp becoming shallow thereafter the diatom data provide more robust evidence and strengthen previous lake level interpretation based on sedimentological and geochemical data during the earliest mid and late holocene and also clarify previous uncertainty in interpretation of lateglacial and early holocene lake level change our results are also important in disentangling regional climate effects from local catchment dynamics during the holocene and to this end we exploit extant regional palynological evidence for vegetation change in the highlands and lowlands the importance of seasonality in driving holocene climate change is assessed by reference to the summer and winter latitudinal temperature gradient ltg model of davis and brewer 2009 we suggest that increased precipitation drove the high lake level during the earliest holocene the early holocene low lake level and relatively high trophic state may result climatically from high seasonality of precipitation and locally from limited nutrient rich catchment runoff we argue that the mid holocene relatively deep and eutrophic state was driven mainly by local vegetation succession and associated changes in catchment processes rather than showing a close relationship to climate change the late holocene shallow state may have been influenced by a temperature induced increase in evaporative concentration but was coupled with clear evidence for intensified human impact this study improves understanding of lateglacial and holocene climate change in the northeastern mediterranean suggests the important role of the ltg on moisture availability during the holocene and clarifies the influence of catchment processes on palaeohydrology

controls on advance of tidewater glaciers results from numerical modeling applied to columbia glacier 1 a one dimensional numerical ice flow model is used to study the advance of a tidewater glacier into deep water starting with ice free conditions the model simulates glacier growth at higher elevations followed by advance on land to the head of the fjord once the terminus reaches a bed below sea level calving is initiated a series of simulations was carried out with various boundary conditions and parameterizations of the annual mass balance the results suggest that irrespective of the calving criterion and accumulation rate in the catchment area it is impossible for the glacier terminus to advance into deeper water 300 m water depth unless sedimentation at the glacier front is included the advance of columbia glacier alaska is reproduced by the model by including conveyor belt recycling of subglacial sediment and the formation of a sediment bank at the glacier terminus results indicate slow advance through the deep fjord and faster advance in shallow waters approaching the terminal moraine shoal and the mouth of the fjord

morainal bank progradation and sediment accumulation in disenchantment bay alaska response to advancing hubbard glacier 1 morainal banks are primary features at the margins of advancing and stable to quasi stable temperate tidewater glaciers yet their roles in glacier dynamics and terminus stability are poorly defined by submarine observations analysis of new and archival multibeam data and landsat images of the advancing hubbard glacier southeast alaska reveal that between 1978 and 2010 the ice face and morainal bank advanced together at an average rate of 34 m yr varying spatially and temporally between 14 and 80 m yr morphological features including gullies and a boulder lag suggest cyclical deposition and gravitational erosion on the proximal slope of the morainal bank 15 18 and possible ice pushing in an area without recent sedimentation in contrast the morainal bank of the nearby quasi stable surging turner glacier advanced steadily since 1978 by proximal sedimentation on the steep fjord wall below its hanging valley sedimentation in the deep 220 m basin of disenchantment bay increased from 0 88 m yr spanning 1978 to 1999 to 1 22 m yr thereafter this change appears to be a combined response to glacier advance and sediment dispersal farther down fjord and to an increase in sediment yield from other glacial and non glacial sources analysis of hubbard glacier illustrates the direct correlation between movement of the terminus and morainal bank in advancing the grounding line of a marine terminating glacier and that morainal banks provide a fundamental stabilizing role for advance into a deep water fjord compensating for changes in water depth at the grounding line

ice foot development at temperate tidewater margins in alaska the presence of an ice foot at the base of temperate tidewater ice cliffs has been debated for nearly 100 years this paper presents evidence demonstrating ice feet at tidewater margins in glacier bay alaska ice feet are likely sources of many submarine icebergs originating at the ice margin the cause of ice foot development is unclear but may represent a change in fracture behavior near the bed where higher debris concentrations affect fracture propagation and calving ice foot formation can be favored by englacial discharge and sediment ramps along the glacier margin that can cause differential melting of the ice cliff the presence of ice feet is important to understanding ice proximal sediment dynamics because they are a primary source of debris rich icebergs and their calving affects sediment redistribution patterns

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

the role of the cryosphere in source to sink systems abstract glacial erosion and sediment production are of interest to diverse scientific communities concerned with the interaction of climatic tectonic and surface processes that influence the evolution of orogens and with the climatic signals archived in glacigenic strata we review the current state of knowledge on the generation transfer and accumulation of glacigenic sediment from land to sea we draw from geomorphology marine geology geochronology numerical modeling of surface processes and landscape evolution and experimental and field observations of glacier erosion and deposition and the interaction of ice with its bed and the ocean boundary our primary goal is to examine glacial systems using a holistic source to sink approach with a focus on describing a how glacial motion produces sediment b how the sediments sink record the dynamic nature of glacial systems under different climatic thermal regimes c the challenges in using the sedimentary record to interpret these dynamics in space and time and d the approaches still needed to further our understanding of how ice and associated sediment fluxes respond to climatic and other perturbations the dynamic state of ice i e the ice flux and ice extent is defined differently between the source and sink communities reflecting the challenges of establishing a stratigraphic signal that volumetrically constrains glacigenic sediment production as a function of the ice response to climate advances in marine geophysics have greatly assisted our understanding of mass transfer pathways and of former ice extents as a measure of ice dynamics and have identified the primary depocenters and key lithofacies of glacial sinks sediment fluxes associated with the dynamic state of the ice are best constrained where sediment volumes derived from key lithofacies and seismic reflection isopachs can be temporally partitioned of which there are few examples rather than from discrete point measures of sediment flux that are subject to sediment transfer biases forward numerical modeling of sediment fluxes as a function of ice dynamics agree with observational data at the continental margin scale but finer time space scale ice dynamic models do not yet recreate observed ice extent or flowpaths future source to sink work in glaciated systems should focus on refining empirical relationships between ice velocity and sediment production and expand the application of existing methods to develop sediment volumes and fluxes in known depocenters of former and modern ice streams

kinematics of the pacific equatorial undercurrent an eulerian and lagrangian approach from gcm results abstract three dimensional monthly velocity fields from an ocean general circulation model are used to study the annual mean mass balance of the pacific equatorial undercurrent euc eulerian diagnostics are used to evaluate the various meridional vertical and zonal mass fluxes related to the euc there are several distinct regimes along the equator showing clear asymmetries between the western and eastern parts of the basin and between the northern and southern edges of the euc meridional fluxes are decomposed into pure ekman divergence and geostrophic convergence and it is shown that the asymmetries are mainly related to the spatial structure of the ekman divergence and thus to that of the trade winds lagrangian calculations are used to evaluate accurately the mass transfers between various sections of the euc and between the euc domain and the tropics the authors show that geostrophic convergence only ventilates the upper layers of the euc and that the euc really is a tongue of water flowing

glacimarine sedimentation processes at kronebreen and kongsvegen svalbard tidewater glaciers deposit sediment at their terminus thereby reducing the relative water depth reduced water depth can lead to increased glacier stability through decreased rates of iceberg calving glacier thinning and submarine melting here we investigate sedimentation processes at the termini of kronebreen and kongsvegen svalbard we mapped the fjord floor bathymetry in august 2009 and calculate sedimentation rates based on our bathymetry and that from a similar study in 2005 a grounding line fan is developing near the current position of the subglacial stream an older abandoned grounding line fan that likely formed between 1987 and 2001 is degrading near the middle of the ice front our findings indicate that sediment gravity flows reduce the height of the sediment mound forming at the glacier terminus the future impact of glacimarine sedimentation processes on glacier stability will depend on the net balance between the observed gravity flows and sediment deposition

outburst flooding and the initiation of ice stream surges in response to climatic cooling a hypothesis abstract outburst flooding from subglacial reservoirs and associated surging of ice streams are caused by processes following climatic cooling that produce ice shelf grounding on proglacial sills trapping subglacial water according to an hypothesis presented here glaciers often advance into proglacial water bodies cooling may allow ice shelf formation and advance causing grounding on a proglacial sill trapping subglacial water ice shelf freeze on to the sill and development of a local reversal in ice air surface slope over the sill then are likely allowing ice thickening and water overpressurization if basal thawing then occurs as is likely an outburst flood and a surge may be triggered these processes may have been involved in heinrich events generation of antarctic subglacial lakes and meltwater scouring of some regions

the general circulation of the mediterranean sea from a 100 year simulation results from a 120 year simulation of the mediterranean sea with a 1 4 19 level eddy permitting cox model with monthly varying wind and buoyancy forcing are presented mean and seasonal currents are examined along with water distributions on isopycnals detailed equilibrated thermohaline water pathways broadly consistent with observed hydrographic data are determined the most important factor permitting a long model run is low vertical mixing which maintains levantine intermediate water liw above the level of the sicily sill so that it can reach the western basin a new feature is tyrrhenian deep water which is formed after 40 years by deep water transfer from the balearic basin south of sardinia a water mass analysis reveals the modification of water properties in t s space through the mixing processes that take place at straits and through the action of mesoscale eddies the surface heat and freshwater fluxes derived a posteriori are in very good agreement with observations showing that basin average fluxes are closely tied to the generation of a realistic thermohaline circulation a complete analysis of surface and strait fluxes demonstrates that equilibrium conditions have been reached a study of the heat budget in the intermediate water layer at 280 m depth reveals that the dominant diabatic terms are at localized convection sites suggesting that at this depth the thermocline is under advective rather than diffusive control the eddy and mean flow heat transports balance to a large degree away from these sites with a negligible role for diffusion

meltwater and tidal currents controls on circulation in a small glacial fjord mcbride inlet is a small glacial fjord that receives freshwater from a submarine tunnel at the base of a tidewater glacier at its head the upwelling buoyant plume mixes with basin water lowering the salinity throughout the ice proximal basin freshwater also upwells from the melting ice face but the effects are only important in winter when discharge is low deep water renewal occurs in summer because the water mass crossing the sill inward is denser than the deep basin water the thick low velocity surface layer is affected by tides and wind producing a slow moving gyre near the glacier meltwater discharge from a submarine position and the resultant circulation in mcbride inlet result in extremely high ice proximal sedimentation rates

bedload component of glacially discharged sediment insights from the matanuska glacier alaska the flux of glacially derived bedload and the proportions of the suspended and bedload components carried by proglacial streams are highly debated published data indicate a large range from 30 to 75 in the bedload percentage of the total load two vents where supercooled subglacial meltwater and sediment are discharged were sam pled over the course of an entire melt season in order to quantify the flux of glacially delivered bedload at the matanuska glacier alaska the bedload component contributed by these vents for the one melt season monitored is negligible furthermore the bedload fluxes appear to be strongly supply limited as shown by the poorly correlated discharge bedload flux magnitude and grain size caliber thus in this case any attempt to employ a predictive quantitative expression for coarse sediment production based on discharge alone would be inaccurate a nonglaciated basin proximal to the matanuska glacier ter minus yielded higher bedload sediment fluxes and larger clast sizes than delivered by the two monitored vents such nonglaciated basins should not be overlooked as potentially major sources of coarse bedload that is reworked and incorporated into valley outwash usually subequal although bedload may range from 30 to 75 of the total clastic load establishing portable relationships between suspended load bedload and discharge would enhance our understanding of how and when glaciers erode for the melt season studied we show that bedload is 1 of the total clastic load and does not have any obvious correla tion to discharge at two of the main vents at the terminus of the matanuska glacier alas ka these observations coupled with high measured bedload component of adjacent non glaciated valleys inspire several working hy potheses for the observed origin of coarse bedload in the matanuska river downstream of the ice margin

late wisconsinan stratigraphy and chronology at highlands southern st george s bay southwest newfoundland abstract this paper provides detailed sedimentological and chronological data of coastal exposures at highlands in southern st george s bay southwest newfoundland the highlands section shows a coarsening upward sequence from mud to sand and gravel and diamicton and represents an ice distal to ice proximal glaciomarine environment where sediment was introduced via a subglacial meltwater jet and deposited by underflow current flow debris flow and overflow on a grounding line fan diamicton forms a continuous unit along the top of the section grading laterally from structureless to stratified and has characteristics of subglacial sediment gravity flow and rainout depositional processes at one site a fossiliferous diamicton is interpreted to be deposited by rainout through a combination of suspension settling from meltwater plumes and ice rafting with subsequent modification by sediment gravity flow on the fan slope a radiocarbon date of 13 680 90 bp beta 120124 on paired shells from this diamicton is interpreted to represent the date of its emplacement this date lies within the range of all other dates 13 1 14 ka bp on marine organisms from sediments along the coast of southern st george s bay and suggests that deposition of the diamicton was contemporaneous with sedimentation in all areas along the coast evidence to support a previously interpreted late glacial readvance at 12 6 ka bp was not found

climatic changes in the aegean sea influence the eastern mediterranean thermohaline circulation 1986 1997 recent changes of water mass characteristics in the south aegean sea have considerably influenced the eastern mediterranean thermohaline circulation a combination of salinity increase 1987 92 and temperature drop 1992 94 caused massive dense water formation and strong outflow towards the deep and bottom parts of the eastern mediterranean this climatic shift the most important since the existence of observations in the basin is a combined effect of extreme meteorological events superimposed on large scale trends it has initiated a series of modifications in the hydrology and dynamics of the entire eastern mediterranean with possible influence on the mediterranean outflow in the north atlantic ocean