occurrence of rocky and sedimentary glacier beds in the swiss alps as estimated from glacier inventory data the occurrence of rocky and sedimentary glacier beds in the swiss alps was investigated using two approaches 1 a detailed and systematic classification of glacier forefields in the completely revised swiss glacier inventory and 2 the application of an algorithm for estimating bed characteristics from glacier inventory data the algorithm is based on the assumption that the sediment balance of a glacierized catchment i e the ratio between debris input from the surrounding rock walls and debris evacuation by the meltwater stream determines the occurrence of rocky sedimentary or mixed beds the processes which govern the sediment balance within a glacierized catchment cannot be easily observed or measured in the field however the main factors reflecting them can be organized in the form of an erosion sedimentation index this index discriminates between glaciers eroding into bedrock and those building up thick sediment beds and thus allows for rough assessments concerning bed characteristics sedimentary and mixed sedimentary rocky glacier beds clearly predominate in the swiss alps but more detailed spatial analysis is required for better predictions

cryogenic carbonates in cave environments a review abstract cryogenic cave carbonate ccc represents a specific type of speleothem its precipitation proceeds at the freezing point and is triggered by freezing induced concentration of solutes compared to classical speleothems stalagmites flowstones ccc occurs as accumulations of loose uncemented aggregates the grain sizes range from less than 1 m to over 1 cm in diameter karst groundwater chemistry and its freezing rate upon entering the cave are responsible for highly variable grain morphology rapid freezing of water results in the formation of ccc powders with grain size typically below 50 m slow freezing of water in caves usually in systems where the co2 escape is partly restricted e g ice covered water pools results in the formation of large mineral grains with sizes from less than 1 mm to about 20 mm the range of carbon and oxygen stable isotope compositions of ccc is larger than for a typical carbonate speleothem rapid freezing of water accompanied by a quick kinetic co2 degassing results in large ranges of 13c of the ccc powders between 10 and 18 pdb slow freezing of water with a restricted co2 escape results in gradual increase of 13c values from 9 to 6 pdb data ranges in individual caves are usually much more restricted accompanied by a 18o decrease of the precipitated carbonate overall range from 10 to 24 pdb these unusual trends of the carbonate 18o evolution reflect incorporation of the heavier 18o isotope into the formed ice new isotope data on ccc from three romanian ice caves allow better understanding of the carbon and oxygen isotope fingerprint in carbonates precipitated from freezing of bulk water cccs are proposed as a new genetic group of speleothems

influence of the icelandic low latitude on the frequency of greenland tip jet events implications for irminger sea convection 1 the occurrence of greenland tip jet events has been reported as the dominant factor controlling the formation of intermediate water in the irminger sea it has been suggested that the frequency of these events is correlated with the north atlantic oscillation to examine this process in more detail we separate the north atlantic oscillation into icelandic low and azores high components and carry out a regression fit of the frequency of tip jet events between 1961 and 2005 our findings suggest that the frequency of greenland tip jet events is highly dependent on the latitude of the icelandic low and the 2 year time lagged february icelandic low latitude with r 2 0 48 we find that the winds near the southern tip of greenland are predominately westerly during years when the iceland low is located above 63n latitude these conditions also correspond to colder air temperatures in the labrador and irminger seas implying larger oceanic heat losses due to the greenland tip jet events and hence stronger convective overturning in the irminger sea

cryogenic cave calcite from several central european caves age carbon and oxygen isotopes and a genetic model abstract cryogenic cave calcite ccc formed by segregation of solutes during water freezing was found in three central european caves this calcite type forms accumulations of loose calcite grains on cave floor the calcite grains are of highly variable crystal morphology and of sizes ranging from less than 1 mm to over 1 cm the most typical feature is their accumulation as loose uncemented crystals u series dating indicates the formation of ccc in the studied caves during several climatic oscillations of the weichselian between 61 and 36 ka bp in the chelsiowa jama jaskinia jaworznicka cave system in poland between 34 and 26 ka bp in the buml cave in the czech republic and between 26 and 21 ka bp in the stratenska jasky a cave system slovakia at the time of ccc formation the studied caves were lying in a periglacial zone detailed c and o stable isotope study of ccc samples revealed that slow water freezing under isotope equilibrium was the dominant formational process in the studied polish and czech caves significantly higher 13 c values of ccc in the stratenska jasky a cave indicate either water freezing in a more opened system with continuous co 2 escape rayleigh fractional separation or participation of another co 2 source the model of slow water freezing under isotope equilibrium is supported by isolated character of the caves having limited ventilation in contrast modern cryogenic cave calcite powders sampled directly on the ice surface of two recently iced caves in slovakia with high ventilation showed much higher 18 o and 13 c data similar to cryogenic calcites obtained in experimental rapid water freezing

impact of the atlantic meridional mode on gulf stream north wall position abstractthe path of the gulf stream as it leaves the continental shelf near cape hatteras is marked by a sharp gradient in ocean temperature known as the north wall previous work in the literature

patterning mechanisms in subglacial carbonate dissolution and deposition deglaciated bedrock surfaces in limestone areas often exhibit extensive patterning by solutional furrows and carbonate deposits that occur in close association with undulations in the bed topography these features clearly result from subglacial dissolution and precipitation of calcite on the bed induced for instance by melting and freezing in a regelation water film but little is known about the observed morphology in particular it is intriguing that i the solutional furrows whose formation requires explanation are collectively organized into arcuate patterns with characteristic spacing and ii a fluted or spiculed surface texture is ubiquitous on the calcite deposits herein we propose specific mechanisms for such patterning based on a theory where chemical processes in the water film are coupled to regelation physics solutional furrows reflect locally enhanced dissolution along stoss surfaces where co 2 rich bubbles advected in the ice from up glacier come into contact with the bed the bubbles form as co 2 is exsolved from freezing film water at the lee of bed bumps the flutings on the deposit are inherently the manifestation of a spatial instability at the interface where calcite precipitation occurs complex interactions underlie some of the striking glacier bed features shaped by subglacial chemical processes

on the drivers of decadal variability of the gulf stream north wall abstractthe gulf stream is bounded to the north by a strong temperature front known as the north wall the north wall is subject to variability on a wide range of temporal and spatial scales on int

subglacially precipitated carbonates record geochemical interactions and pollen preservation at the base of the laurentide ice sheet on central baffin island eastern canadian arctic the mineralogy and isotopic compositions of subglacially precipitated carbonate crusts spccs provide information on conditions and processes beneath former glaciers and ice sheets here we describe spccs formed on gneissic bedrock at the bed of the laurentide ice sheet lis during the last glacial maximum on central baffin island geochemical data indicate that the ca in the crusts was likely derived from the subglacial chemical weathering ca bearing minerals in the local bedrock c and sr isotopic analyses reveal that the c in the calcite was derived predominantly from older plant debris the 18o values of the spccs suggest that these crusts formed in isotopic equilibrium with basal ice lis preserved in the barnes ice cap bic columnar crystal fabric and the predominance of sparite over micrite in the spccs are indicative of carbonate precipitation under open system conditions however the mean 18o value of the calcite crusts is 10 higher than those of primary lis ice preserved in the bic demonstrating that spccs record the isotopic composition of only basal ice palynomorph assemblages preserved within the calcite and basal bic ice include species last endemic to the arctic in the early tertiary the source of these palynomorphs remains enigmatic

a test of the parsons veronis hypothesis on the separation of the gulf stream abstract the parsons veronis model based on a two layer wind driven ocean predicts the latitude at which the western boundary current separates from the western boundary it has been tested on the gulf stream using both satellite and in situ observations the hypothesis attributes the difference in the thermocline depth from the eastern to the western side of the ocean and the corresponding northward geostrophic transport with closed northern end to the southward ekman transport integrated across the basin twelve years 1977 88 of satellite sea surface temperature data and wind data from the fleet numerical oceanography center fnoc wind database have been used for this study the satellite derived gulf stream northern edges were used to determine the latitudes of separation i e crossing the 2000 m isobath into deep water parsons model is sensitive to two free parameters namely the reduced gravity and the thermocline depth on the eastern side of the basin based on available ctd data an

the role of dissolution kinetics in the development of karst aquifers in limestone a model simulation of karst evolution to model the development of karst aquifers from primary fissures in limestone rock a numerical model of solutional widening of such fractures by calcite agressive water is suggested the geological setting determines relevant geometrical parameters i e length of the fracture its initial width and the hydraulic gradient driving water from the input to the output to simulate the solutional widening as it proceeds in time the solution rates must be known as a function of concentration c of dissolved calcite they are given as a first order kinetic rate law for c leq k cdot c eq as f 1 alpha 0 c c eq for c k cdot c eq close to equilibrium a fourth order rate law becomes dominant f 4 beta cdot c c eq 4 the parameters alpha 0 beta and k depend on the chemistry of the carbonate system and rock chemistry the saturation concentration c eq with respect to calcite depends on the initial co 2 concentration of the inflowing solution

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

a model of variations in the north atlantic oscillation 1 the major source of interannual variability in the atmospheric circulation over the north atlantic ocean is the north atlantic oscillation nao which is associated with the strength of the winter surface westerly winds over the ocean during the last century the nao has shown pronounced multi annual and multi decadal variations fluctuations that have been accompanied by changes in the marine and terrestrial ecosystems of the north atlantic region this paper presents a simple model which reproduces the major trends in the nao index from 1866 to 2004 the model is based on climatic resonators that are forced by the global mean temperature and the southern oscillation of the pacific ocean so the ocean component of the model shows similar variations to time series from the north atlantic

bedrock surface roughness and the distribution of subglacially precipitated carbonate deposits implications for formation at glacier de tsanfleuron switzerland two carbonate deposits are identified on the exposed bedrock surface in the forefield of glacier de tsanfleuron switzerland macrocrystalline sparite and microcrystalline micrite comparison of the distributions of these forms with lee side slope facets identified by high pass filtering of a flow parallel bedrock profile at a range of frequencies reveals two significant results first while the distribution of sparite is consistent with formation in the lee side of subglacial bedrock hummocks that of micrite is not this contrasts with previous investigations in which both sparite and micrite have been considered to form by mineral concentration and precipitation during the refreezing of regelation related basal meltwaters in the lee side of bedrock hummocks alternative mechanisms of micrite formation involving carbonate deposition and or precipitation within subglacial bedrock hollows are proposed second the distribution of sparite is most strongly correlated with the distribution of lee side slope facets identified by filtering at a frequency equivalent to a hummock wavelength of c 0 1 m this correspondence indicates empirically that pressure related melting and refreezing regelation operates most effectively around bedrock hummocks that are shorter than c 0 1 m 1998 john wiley sons ltd

wind induced interannual variability of sea level slope along shelf flow and surface salinity on the northwest atlantic shelf in this study we examine the importance of regional wind forcing in modulating advective processes and hydrographic properties along the northwest atlantic shelf with a focus on the nova scotian shelf nss gulf of maine gom region long term observational data of alongshore wind stress sea level slope and along shelf flow are analyzed to quantify the relationship between wind forcing and hydrodynamic responses on interannual time scales additionally a simplified momentum balance model is used to examine the underlying mechanisms our results show significant correlation among the observed interannual variability of sea level slope along shelf flow and alongshore wind stress in the nss gom region a mechanism is suggested to elucidate the role of wind in modulating the sea level slope and along shelf flow stronger southwesterly northeastward winds tend to weaken the prevailing southwestward flow over the shelf building sea level in the upstream newfoundland shelf region whereas weaker southwesterly winds allow stronger southwestward flow to develop raising sea level in the gom region the wind induced flow variability can influence the transport of low salinity water from the gulf of st lawrence to the gom explaining interannual variations in surface salinity distributions within the region hence our results offer a viable mechanism besides the freshening of remote upstream sources to explain interannual patterns of freshening in the gom

southeast greenland winter precipitation strongly linked to the icelandic low position abstractgreenland s largest precipitation flux occurs in its southeast se region during the winter controlled primarily by easterly winds and frequent cyclogenesis in the north atlantic several

the icelandic low as a predictor of the gulf stream north wall position abstractthe gulf stream s north wall east of cape hatteras marks the abrupt change in velocity and water properties between the slope sea to the north and the gulf stream itself an index of the north wall position constructed by taylor and stephens called gulf stream north wall gsnw is analyzed in terms of interannual changes in the icelandic low il pressure anomaly and longitudinal displacement sea surface temperature sst composites suggest that when il pressure is anomalously low there are lower temperatures in the labrador sea and south of the grand banks two years later warm sst anomalies are seen over the northern recirculation gyre and a northward shift in the gsnw occurs similar changes in ssts occur during winters in which the il is anomalously west resulting in a northward displacement of the gsnw 3 years later although time lags of 2 and 3 years between the il and the gsnw are used in the calculations it is shown that lags with respect to each atmospheric variable are statistica

experimental investigations of the weathering of suspended sediment by alpine glacial meltwater the magnitude and processes of solute acquisition by dilute meltwater in contact with suspended sediment in the channelized component of the hydroglacial system have been investigated through a suite of controlled laboratory experiments constrained by field data from haut glacier d arolla valais switzerland the effects of the water to rock ratio particle size crushing repeated wetting and the availability of protons on the rate of solute acquisition are demonstrated these free drift experiments suggest that the rock flour is extremely geochemically reactive and that dilute quickflow waters are certain to acquire solute from suspended sediment these data have important implications for hydrological interpretations based on the solute content of glacial meltwater mixing model calculations geochemical denudation rates and solute provenance studies

meridional gulf stream shifts can influence wintertime variability in the north atlantic storm track and greenland blocking author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 46 3 2019 1702 1708 doi 10 1029 2018gl081087

control of saharan mineral dust transport to barbados in winter by the intertropical convergence zone over west africa 1 the reasons for the inter annual variability of dust transport from the sahara across the atlantic are not well understood here we address this issue by defining three new climate indices that capture the position and intensity of the zone of near surface convergence over west africa a part of the global intertropical convergence zone itcz we then relate these indices to a 38 year record of mineral dust concentrations at barbados focusing on the winter season the results show that the latitudinal displacement of the itcz over west africa and the dust load in barbados are statistically significantly correlated with a correlation coefficient of r 0 69 a southward movement of the itcz corresponds to an increased dust load at barbados this correlation represents an improvement upon previous results which focused on traditional teleconnection indices such as the north atlantic oscillation or the el nino southern oscillation from analyzing composites of wind and precipitation we conclude that for the winter season the inter annual variability of the barbados dust load is related to changes in near surface northeasterly winds in semi arid regions in north africa coincident with the movement of the itcz changes in precipitation appear to only play a minor role citation doherty o m n riemer and s hameed 2012 control of saharan mineral dust transport to barbados in winter by the intertropical convergence zone over west africa j geophys res 117 d19117 doi 10 1029 2012jd017767

two modes of gulf stream variability revealed in the last two decades of satellite altimeter data monthly mapped sea level anomalies mslas of the nw atlantic in the region immediately downstream ofthegulfstream gs separationpointrevealaleadingmodeinwhichthepathshiftsapproximately 100km meridionally about a nominal latitude of 398n producing coherent sea level anomaly sla variability from 728 to 508w this mode can be captured by use of a simple 16 point index based on sla data taken along the maximum of the observed variability in the region 338 468n and 458 758w the gs shifts between 2010 and 2012 are the largest of the last decade and equal to the largest of the entire record the second group of eof modesofvariabilitydescribesgsmeanders whichpropagatemainlywestwardinterruptedbybriefperiodsof eastwardorstationarymeanders thesemeandershavewavelengthsofapproximately400kmandcanbeseen in standard eofs by spatial phase shifting of a standing meander pattern in the sla data the spectral properties of these modes indicate strong variability at interannual and longer periods for the first mode and periods of a few to several months for the meanders while the former is quite similar to a previous use of the altimeter for gs path the simple index is a useful measure of the large scale shifts in the gs path that is quickly estimatedand updatedwithoutchangesin previous estimates thetime scaleseparationallows alowpass filtered 16 point index to be reflective of large scale coherent shifts in the gs path

slow variations in mean path of the gulf stream east of cape hatteras the gulf stream between cape hatteras and the new england seamounts varies in position over a wide range of time scales we present evidence that interannual path changes may be governed by a time varying outflow of waters from the labrador shelf region when the shelf and slope waters south of new england turn cold and fresh the stream frequently assumes a more southerly track and conversely when the waters are warm and saline these changes in path and surface water properties most likely result from large variations in shelf transport and thus greater or less dilution of the warm saline gulf stream waters that continually leak from the current into the slope sea these observations point to a thermohaline rather than winddriven mechanism for governing the path of the gulf stream after it leaves the coast

sea level on the u s east coast decadal variability caused by open ocean wind curl forcing one of the puzzling features of sea level on the east coast of the united states is the decedal scale variability the fluctuations are 10 15 cm peak to peak at periods longer than a few years the authors find that this variability in the frequency band treated with the model is largely caused by a deep sea signal generated by the wind stress curl over the north atlantic a simple forced long rossby wave model of the response of the thermocline to wind forcing is used computing long wave speeds from observed hydrographic data the authors model the response of the ocean at periods longer than 3 years for the full width of the atlantic and for the north south extent of the main anticyclonic gyre 188 388n the model output in deep water shows remarkably good agreement with tide gauges both at bermuda 328n and puerto rico 188n as well as with dynamic height fluctuations of 20 cm peak to peak once these fluctuations reach the western side of the ocean the authors estimate coastal sea level by constructing a complementary coastal model the coastal model is geostrophic and conserves mass within a nearshore region that encompasses the gulf stream by extending this nearshore region as far south as 148 188n and using only the oceanic fluctuations to force the variability in the stream between 80 and 90 of the variance of sea level at coastal tide gauges can be explained sea level along the coast is used to test the model assumptions the basic results however seem important because they are constrained only by open ocean wind forcing and not by input boundary conditions

gulf stream excursions and sectional detachments generate the decadal pulses in the atlantic multidecadal oscillation abstractdecadal pulses within the lower frequency atlantic multidecadal oscillation amo are a prominent but underappreciated amo feature representing decadal variability of the subpolar gyre e g the great salinity anomaly of the 1970s and wielding notable influence on the hydroclimate of the african and american continents here clues are sought into their origin in the spatiotemporal development of the gulf stream s gs meridional excursions and sectional detachments apparent in the 1954 2012 record of ocean surface and subsurface salinity and temperature observations the gs excursions are tracked via meridional displacement of the 15 c isotherm at 200 m depth the gs index whereas the amo s decadal pulses are targeted through the amo tendency which implicitly highlights the shorter time scales of the amo index the gs s northward shift is shown to be preceded by the positive phase of the low frequency north atlantic oscillation lf nao and followed by a positive amo tendency by 1 25 and 2 5 yea

subglacial carbonate deposition an isotopic study of a present day case abstract different types of calcite deposits may be formed in the subglacial environment patchy coatings on polished and striated bedrock pavements occur on outcrops recently exposed by retreating temperature glaciers coated pebbles and thin limestone crusts in fissures are present in recent basal till exposures freezing of meltwater is the main process susceptible to explain most of these carbonate deposits partial freezing is accompanied by a rejection of ions from the growing ice and a concentration increase in the residual water eventually until saturation is reached glacier sliding over a protuberance by pressure melting on the stoss side and refreezing on the lee side is likely to be responsible for subglacial carbonate deposition a fixed bedrock protuberance will give rise to fluted and furrowed coatings on its lee side a mobile protuberance like a pebble at the ice bedrock interface because it is susceptible to rotate while in traction will have a coating on most of its surface a present day case in the swiss alps is studied by a comparison of the isotopic composition of calcite deposits ice and meltwater from the glacier this study indicates that melting of the basal ice layer not of glacier ice is at the origin of the initial water giving rise to the precipitate since the basal ice layer is formed in the marginal zone of the glacier subglacial carbonate deposition is a marginal feature in this case

sea level changes in iceland and the influence of the north atlantic oscillation during the last half millennium abstract we present a new diatom based sea level reconstruction for iceland spanning the last 500 years and investigate the possible mechanisms driving the sea level changes a sea level reconstruction from near the icelandic low pressure system is important as it can improve understanding of ocean atmosphere forcing on north atlantic sea level variability over multi decadal to centennial timescales our reconstruction is from vi arholmi salt marsh in snaefellsnes in western iceland a site from where we previously obtained a 2000 yr record based upon less precise sea level indicators salt marsh foraminifera the 20th century part of our record is corroborated by tide gauge data from reykjavik overall the new reconstruction shows ca 0 6 m rise of relative sea level during the last four centuries of which ca 0 2 m occurred during the 20th century low amplitude and high frequency sea level variability is super imposed on the pre industrial long term rising trend of 0 65 m per 1000 years most of the relative sea level rise occurred in three distinct periods ad 1620 1650 ad 1780 1850 and ad 1950 2000 with maximum rates of 3 2 mm yr during the latter two of these periods maximum rates were achieved at the end of large shifts from negative to positive of the winter north atlantic oscillation nao index as reconstructed from proxy data instrumental data demonstrate that a strong and sustained positive nao a deep icelandic low generates setup on the west coast of iceland resulting in rising sea levels there is no strong evidence that the periods of rapid sea level rise were caused by ocean mass changes glacial isostatic adjustment or regional steric change we suggest that wind forcing plays an important role in causing regional scale coastal sea level variability in the north atlantic not only on multi annual timescales but also on multi decadal to centennial timescales

the dominant influence of the icelandic low on the position of the gulf stream northwall 1 the location where the gulf stream separates from the american coast and turns eastward is called its northwall the interannual fluctuations of the northwall are significantly correlated with the north atlantic oscillation with a lag of two years when the azores high and the icelandic low pressures are taken as independent variables the latter dominates the relationship with the northwall and the influence of the azores high pressure is insignificant this is consistent with the hypothesis that the major oceanic control of the northwall is in the southward flow of labrador sea water into the slope sea the alternative mechanism that the interaction of westward propagating rossby waves with the american coast is responsible for northwall fluctuations is considered less likely because its initiation requires perturbations of the eastward winds in the mid atlantic region and they are very likely dependent on the azores high the analysis suggests that the time lag between perturbations of the icelandic low and the northwall varies between one and three years