recent progress in snow and ice research a review of snow and ice research in 1987 1990 is presented focusing on the effects of layers in seasonal snow covers ice mechanics on fresh water and sea ice and remote sensig of polar ice sheets these topics provide useful examples of general needs in snow and ice research applicable to most areas such as better representation in models of detailed processes controlled laboratory experiments to quantify processes and field studies to provide the appropriate context for interpretation of processes from remote sensing

meltwater floods into the black and caspian seas during heinrich stadial 1 abstract deglaciation of the eurasian ice sheet dispensed vast amounts of meltwater laden with red brown clay into black and caspian sea s freshwater lakes between 16 350 and 15 400 calendar years bp the arriving sediment had a mineral composition and strontium neodymium isotope signatures 87sr 86sr and end consistent with the crystalline bedrock that lay beneath the ice sheet as opposed to sources from landscapes crossed by the rivers that carried meltwater to the lakes the magnitude and rapidity of the shifts of 87sr 86sr and 18o in shells of ostracods and mollusks an eight fold increase in sediment accumulation rate and a plunge of 1250 14c years in the radiocarbon reservoir age indicate a volume of meltwater sufficient to have replaced most or all of the pre existing lake water if the release of 25 000 km3 of water from the caspian into the black sea s new euxine lake was abrupt by judging the magnitude of erosion in the floor of the manych strait spillway this event qualifies as a megaflood deeply scoured furrows channel floor bars and swaths of mounds 5 20 km in length and 5 20 m in height are reminiscent of scabland landscapes the meltwater is coincident with heinrich stadial 1 when the alpine and eurasian ice sheets re advanced and temperatures of the black sea s lake surface remained cold sand grains within the red brown clay indicate they were transported by lake surface ice

relationships between interannual variability of glacier mass balance and climate the interannual variability of glacier mass balance is expressed by the standard deviation of net balance which varies from about 0 1 to 1 4 m a for a sample of 115 glaciers with at least 5 years of record the standard deviation of net balance is strongly correlated with the mass balance amplitude half the difference between winter and summer balances for 60 glaciers so the amplitude can be estimated from net balance standard deviation for the other 55 glaciers where winter and summer balances are unavailable the observed and calculated mass balance amplitudes for the 115 glaciers show contrasts between the arctic and lower latitudes and between maritime and continental regions the interannual variability of mass balance means that balances must be measured for at least a few years to determine a statistically reliable mean balance for any glacier the net balance of the greenland ice sheet is still not accurately known but its standard deviation is here estimated to be about 0 24 m a 1 in agreement with other arctic glaciers mass balance variability of this magnitude implies that the ice sheet can thicken or thin by several metres over 20 30 years without giving statistically significant evidence of non zero balance under present climate

the mass balance of circum arctic glaciers and recent climate change the sum of winter accumulation and summer losses of mass from glaciers and ice sheets net surface mass balance varies with changing climate in the arctic glaciers and ice caps excluding the greenland ice sheet cover about 275 000 km2of both the widely glacierized archipelagos of the canadian norwegian and russian high arctic and the area north of about 60 n in alaska iceland and scandinavia since the 1940s surface mass balance time series of varying length have been acquired from more than 40 arctic ice caps and glaciers most arctic glaciers have experienced predominantly negative net surface mass balance over the past few decades there is no uniform recent trend in mass balance for the entire arctic although some regional trends occur examples are the increasingly negative mass balances for northern alaska due to higher summer temperatures and increasingly positive mass balances for maritime scandinavia and iceland due to increased winter precipitation the negative mass balance of most arctic glaciers may be a response to a step like warming in the early twentieth century at the termination of the cold little ice age arctic ice masses outside greenland are at present contributing about 0 13 mm yr 1to global sea level rise

growth of the greenland ice sheet a performance assessment of altimeter retracking algorithms the authors compare the performance of different altimeter retracking algorithms for measuring ice sheet elevations and growth rates the results show that the threshold esa and s v retracking algorithms produce growth rates that are 30 55 smaller than those produced by the nasa algorithm based upon a comparison of crossover point standard deviations the analysis indicates that the surface elevation estimates produced by these algorithms are more repeatable than the nasa surface elevations an analysis of the nasa algorithm shows that a mixing of its 5 and 9 parameter functional fits on the crossover point altimeter waveforms occurs in over 70 of the crossover data the mixing of the functional fits is shown to reduce the repeatability of the nasa elevations and this may be responsible for the larger estimates of ice sheet growth produced by the nasa retracking algorithm the extremely close agreement between the standard deviations and the growth rate estimates from the threshold esa and s v retracking algorithms lead the authors to conclude that 0 10 m yr is a more accurate estimate of the growth of the greenland ice sheet from 1978 1987 south of 72 spl deg n

sea level rise a review of recent past and near future trends global mean sea level is a potentially sensitive indicator of climate change global warming will contribute to worldwide sea level rise slr from thermal expansion of ocean water melting of mountain glaciers and polar ice sheets a number of studies mostly using tide gauge data from the permanent service for mean sea level bidston observatory england have obtained rates of global slr within the last 100 years that range between 0 3 and 3 mm yr 1 with most values concentrated between 1 and 2 mm yr 1 however the reliability of these results has been questioned because of problems with data quality and physical processes that introduce a high level of spatial and temporal variability sources of uncertainty in the sea level data include variations in winds ocean currents river runoff vertical earth movements and geographically uneven distribution of long term records crustal motions introduce a major source of error to a large extent these can be filtered by employing palaeo sea level proxies and geophysical modelling to remove glacio isostatic changes ultimately satellite geodesy will help resolve the inherent ambiguity between the land and ocean level changes recorded by tide gauges future sea level is expected to rise by 1 m with a best guess value of 48 cm by the year 2100 such rates represent an acceleration of four to seven times over present rates local land subsidence could substantially increase the apparent slr for example louisiana is currently experiencing slr trends nearly 10 times the global mean rate these recently reduced slr estimates are based on climate models that predict a zero to negative contribution to slr from antarctica most global climate models gcms indicate an ice accumulation over antarctica because in a warmer world precipitation will exceed ablation snow melt however the impacts of attritional processes such as thinning of the ice shelves have been downplayed according to some experts furthermore not all climate models are in agreement opposite conclusions may be drawn from the results of other gcms in addition the west antarctic ice sheet is potentially subject to dynamic and volcanic instabilities that are difficult to predict because of the great uncertainty in slr projections careful monitoring of future sea level trends by upgraded tide gauge networks and satellite geodesy will become essential finally because of the high spatial variability in crustal subsidence rates wave climates and tidal regimes it will be the set of local conditions especially the relative sea level rise rather than a single global mean sea level trend that will determine each locality s vulnerability to future slr

tectonic versus climatic control on the evolution of a loess paleosol sequence at beremend hungary an integrated approach based on paleoecological clay mineralogical and geochemical data the role of two major factors climate and tectonism in controlling loess paleosol evolution has been evaluated in the present study based on a multi proxy dataset comprising mollusc bulk and clay mineralogical and geochemical data a recent trend has been to use chemical indices such as the chemical index of alteration cia for paleoclimate reconstructions in loess paleosol sequences spanning several hundreds of thousands of years but without any tectonic interpretation possible effects of geodynamic factors on physical erosion chemical weathering and consequently weathering proxies are discussed clearly the relative rates of physical erosion and chemical weathering in a sedimentary environment could be significantly influenced by geodynamic factors and governed not just by climate intensifying tectonic uplift gives rise to enhanced physical erosion leading to increased supply of fresh mineral surfaces having less time to react with weathering agents in theory this process may point towards decreasing chemical weathering in a sequence without any real changes of climate in the studied loess paleosol sequence at beremend hungary a trend of decreasing chemical weathering has been observed which can be explained by a global climate deterioration and accelerating uplift in and around the sedimentary basin increasing dust sedimentation could theoretically also contribute to this process as a result of increasing aridification and wind strength reflecting climate change in weathering records following a non linear amplification the findings refer to the fact that the impact of tectonism should also be taken into consideration in tracing past chemical weathering trends on timescales of hundreds of thousands or millions of years this is because tectonic effects may impose on the cia signal and distort it suggesting a potential bias in reconstructing paleoclimate change based only on this proxy from certain loess sequences associated with young orogenic belts

kaolinite smectite mixed layer clays in the jiujiang red soils and their climate significance abstract clay mineralogy of the jiujiang soils classified as red earth on summit and slope were investigated using x ray diffraction xrd cation exchange capacity cec determination and high resolution transmission electron microscopy hrtem the xrd results show that the soils included kaolinite illite vermiculite and mixed layer i s and k s as clay minerals in xrd patterns of clay separates the low angle shoulder on the kaolinite 001 peak shifted to 8 a on glycolation indicating the presence of mixed layer k s clays in the soils kaolinite content in the interstratified kaolinite smectites was estimated to be 95 for samples of the middle to lower soil profile and 60 for that of the upper portion respectively a broad reflection for 10 14 a disappeared and an 18 7 a peak occurred in the xrd patterns after formamide treatment the 10 a peak became much more intense on heating to 400 c indicating that the 10 14 a peak was expandable and easily contractible and thus originated from mixed layer illite smectite i s clays after heating to 550 c the 7 a peak disappeared while the 10 a peak became more intense and showed a low angle tail indicating the interstratified smectite component was hydroxy interlayered the higher cec values of the jiujiang clay separates 22 2 27 3 cmol kg also pointed to the occurrence of smectite in the soils hrtem analysis showed different lattice fringes for clay particles in the samples a great majority of layer spacings were in the range 10 20 a with a minority of 7 and 25 a particles with 7 a fringes showed a lateral transition of two 7 a kaolinite layers merging into one 12 a smectite layer this can be interpreted as the partial intercalation of one smectite layer in kaolinite there was no long range order in the stacking sequence of k s layers and the interstratification was of a random nature in the uniform soil horizon of the upper profile there was more vermiculite and illite but less i s and k s while in the net like soil horizon of the middle lower profile there was more kaolinite i s and k s with only a trace of vermiculite the occurrence of k s clays confirmed that the jiujiang red earth was derived from syndepositional pedogenesis and the climates changed from warm and seasonally dry to warm and more humid conditions during the soil forming period

geomorphological impacts of high latitude storm waves on low latitude reef islands observations of the december 2008 event on nukutoa takuu papua new guinea abstract low latitude reefs and reef islands usually experience relatively benign climatic and hydrodynamic conditions due to their location near to the equator outside of the major storm belts and they typically exhibit geomorphological traits that reflect the prevailing low energy conditions for example algal ridges are poorly developed reef flat boulder zones are modest or lacking rubble banks are rare and reef islands tend to be low and dominated by sand nukutoa is a low lying triangular shaped reef island of 6 ha located on the eastern rim of takuu atoll 4 45 s 157 2 e papua new guinea approximately 300 km northeast of bougainville the approximately 450 residents of takuu all live on nukutoa in december 2008 takuu was struck by several days of very high water levels and waves which washed completely over approximately 50 of nukutoa gps shoreline mapping and topographic surveys of the island were undertaken in the days immediately prior to the event and were repeated immediately after homes and village infrastructure were damaged during this event which eroded around 60 of the shoreline and deposited a sand sheet averaging around 50 mm thick over approximately 13 of the island this event was generated by two distant storms one located 6000 km away near 50 n and affected a wide area of the western pacific oral histories record at least five similar events since the 1940s in this paper we document the geomorphic impacts of the december 2008 event and discuss the possible significance of similar events in the past and in the future

the european space agency s earth explorer mission cryosat measuring variability in the cryosphere cryosat is currently being prepared for a 2005 launch as the first european space agency earth explorer opportunity mission it is a dedicated cryospheric mission equipped with a ku band siral sar interferometric radar altimeter whose primary objectives are to measure the variability and trends in the mass of the arctic sea ice cover and large terrestrial ice sheets in this paper an overview is provided of the mission and of the measurement characteristics of the new siral instrument examples of data acquired on recent preparatory campaigns are presented illustrating the operating characteristics of the key siral modes preparatory plans for calibration and validation of cryosat data are described

clay mineral composition and palaeoclimatic interpretation of the pleistocene deposits of ukraine abstract the pleistocene deposits on the plains regions of ukraine are subaerial and subaqueous formations of diverse types loesses and fossil soils represent 16 climatic stages 8 warm and 8 cold of the pleistocene and environmental changes are reflected in their clay mineral composition clay fractions

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

late quaternary caspian sea environment late khazarian and early khvalynian transgressions from the lower reaches of the volga river abstract this magnetic clay minerals and palynological study provides a record of two late pleistocene transgressions late khazarian and early khvalynian in the caspian sea through the analysis of present day lower volga terraces the results allow the clarification of some points about the caspian sea evolution during the considered periods early diagenetic iron sulphides greigite and pyrite are present in sediments of the lower part of the late khazarian and reflect restricted water circulation in the basin the change in iron sulphide mineralogy is most probably related to the change of the water level and its salinity low magnetic mineral contents with magnetite if any recorded in the upper part of the late khazarian atelian and early khvalynian reflect a well oxygenated basin and detrital material sources poor in magnetic minerals smectite is the dominant clay mineral in the late khazarian reflecting chemical weathering in its source area due to the wet and warm climate the upper part of this transgression is nevertheless marked by a stepwise relative decrease of smectite and an increase of illite attributed to a cooling climate during the atelian and early khvalynian periods phases of sandy deposits are characterised by equal proportions of illite and smectite similar to ukrainian loess chocolate clays are clearly dominated by illite both clay mineralogies are attributed to cool climate which favours physical weathering in the catchment area the conditions of chocolate clays deposition are unclear the recorded cooling during the last phase of the late khazarian and the 14c age on a well preserved bivalve shell suggest that it is probably much younger than the eemian interglacial and could correspond to the girkan transgression the 14c age for the early khvalynian sample suggests approximately a last glacial maximum age for this transgression

modeled variations of precipitation over the greenland ice sheet abstract a parameterization of the synoptic activity at 500 hpa and a simple orographic scheme are used to model the spatial and temporal variations of precipitation over the greenland ice sheet for 1963 88 from analyzed geopotential height fields produced by the national meteorological center nmc model coefficients are fitted to observed accumulation data primarily from the summit area of the ice sheet all major spatial characteristics of the observed accumulation distribution are reproduced apart from the orographic accumulation maximum over the northwestern coastal slopes the modeled time averaged total precipitation amount over greenland is within the range of values determined by other investigators from surface based observations a realistic degree of interannual variability in precipitation is also simulated a downward trend in simulated ice sheet precipitation over the 26 years is found this is supported by a number of lines of evidence it matches the accumulation trends during this peri

wave driven sea level anomalies at the midway tide gauge as an index of north pacific storminess over the past 60 years 1 sixty years of sea level data collected in the interior lagoon of midway atoll in the northern hawaiian islands are used to examine short term 2 days high amplitude up to 1 m sea level anomaly sla events that occur during the winter months a combination of wind and wave model hindcasts satellite altimetry product and in situ water level data confirms that these high sla events are driven primarily by the arrival of energetic swell waves generated by storms in the north pacific as breaking waves on the northwest side of the atoll lead to the setup of the lagoon the number of high sla events recorded in midway during each winter season correlates well with the storminess in the central north pacific defined as the mean seasonal wave height this leads us to conclude that the seasonal number of high sla events measured at this specific tide gauge in midway can be used as an index of storminess in the central north pacific over climatic time scales our midway based index of storminess correlates well with the pacific decadal oscillation pdo index and its observed increase over the past 60 years is attributed to variability associated with the pdo rather than a long term trend

improved elevation change measurement of the southern greenland ice sheet from satellite radar altimetry a new analysis of seasat and geosat satellite radar altimeter measurements over the greenland ice sheet was performed to determine surface elevation change the new analysis includes twice as many measurements and has 50 greater spatial coverage than the authors previous study in addition a precise global ocean reference network created from four years of topex poseidon altimeter data is used to obtain improved estimates of altimeter orbit errors and measurement system biases the results show that the average elevation change of the southern greenland ice sheet above 2000 m from 1978 to 1988 is not significantly different than zero this contradicts earlier and even more recent studies that reported positive ice sheet growth rates and suggested increased precipitation due to a warmer polar climate

elevation change of the southern greenland ice sheet from 1978 to 1988 interpretation the spatial pattern of elevation change estimates derived from satellite radar altimeter data for the period from 1978 to 1988 for the southern greenland ice sheet is examined as reported previously the results from 12 ice cores widely distributed in the study area indicate that much of the spatial variability in the elevation change estimates can be explained by temporal variations in accumulation most notably the areas of largest thickening and thinning east and west of the ice divide around 66 n recently experienced substantial decadal fluctuations in accumulation sufficient to explain the observed elevation change rates that span the range of 24 cm yr 1 elevation change estimates in the nw of the study area around the 2000 m elevation contour were found to be inconsistent with both short and long term changes in accumulation fluctuations examination of stratigraphy in several shallow ice cores in the nw indicates that significant melting took place in 1977 and 1978 and this was followed by many years of very little melt activity this likely resulted in a significant downward bias in the 1978 1988 elevation change estimates in the nw comparison of measured surface velocities with those calculated assuming steady state balance show very good agreement overall but there are many instances in the southeast where the steady state velocities are significantly smaller than measured surface velocities we cannot rule out the possibility that increased ice flow in lower elevation outlet glaciers has migrated farther upstream thereby causing negative long term mass imbalance in southeast greenland

climate control on the palaeo lake evolution in the southern datong basin north china evidence from 800 ka core records integrated sedimentological and clay mineral analyses of a 300 m depth core reveal the history of the palaeo lake and palaeoclimatic evolution of the southern datong basin over the past 800 ka the sedimentary facies including deep lake shallow lake alternation of lakeside and shallow lake and the river environment are identified based on the general characteristics of the grain size analysis two episodes of warm humid events are responsible for the palaeo lake expansion during the period of 800 480 ka corresponding to the presence of s7 s6 and s5 in the loess plateau a stepwise cooling and drying trend since approximately 480 ka is strongly linked to the gradual shrinkage and extinction of the palaeo lake our results demonstrated that climate change has played an essential role on the palaeo lake expansion shrinkage during the middle pleistocene breaching of shixia gorge by active neotectonic movement since the middle late pleistocene enhanced the shrinkage and extinction of the palaeo lake coupled with a cold dry climate in the last glacial the climatic changes documented by clay minerals and grain size parameters in the datong basin are consistent with the loess paleosol sequences in the loess plateau and fluvio lacustrine sediments in the nihewan basin mainly controlled by the east asian monsoon in response to the regional global change since the mid late pleistocene

global sea level change determination and interpretation the notion of sea level rise brings to the popular mind the specter of deep inundation of coastal regions one pictures skyscrapers emerging from the waters like so many sleeping flamingos standing in the shallows of a lake of course if all of the world s ice sheets suddenly melted or collapsed this vision would apply to new york city and its coastal counterparts but there is a general consensus that such a calamity is not an immediate threat houghton et al 1990 the actual situation for the recent historical past and near future appears to be more benign but with nonetheless extremely significant even devastating impacts due to erosion and flooding of coastal areas

elevation change of the greenland ice sheet and its measurement with satellite radar altimetry satellite radar altimetry is presently the only method that has provided the spatial coverage and density of observations needed to reduce the present uncertainty in the mass balance of the greenland ice sheet and its contribution to change in eustatic sea level the only such measurement reported however estimated that southern greenland was thickening at 23 6 cm a 1 which is larger than was thought hitherto this value is reconsidered given more recent information concerning the errors in the measurement a survey of measurements of specific mass balance of the greenland ice sheet is given together with estimates of its sensitivity to temperature change the expected behaviour is described of errors in the satellite position and errors in the range measurement to the ice sheet surface the treatment of biases and the number of independent observations of random errors is described it is found in particular that a higher degree of independence was given to the random errors than should have been the case the total error is recalculated with this accounted for and is found to remain dominated by the bias estimate and therefore largely unaffected by this change the estimate is 23 7 cm a 1 it is concluded that the observation does support a recent thickening of the southern greenland ice sheet

variability of the winter wind waves and swell in the north atlantic and north pacific as revealed by the voluntary observing ship data this paper analyses secular changes and interannual variability in the wind wave swell and significant wave height swh characteristics over the north atlantic and north pacific on the basis of wind wave climatology derived from the visual wave observations of voluntary observing ship vos officers these data are available from the international comprehensive ocean atmosphere data set icoads collection of surface meteorological observations for 1958 2002 but require much more complicated preprocessing than standard meteorological variables such as sea level pressure temperature and wind visual vos data allow for separate analysis of changes in wind sea and swell as well as in significant wave height which has been derived from wind sea and swell estimates in both north atlantic and north pacific midlatitudes winter significant wave height shows a secular increase from 10 to 40 cm decade 1 during the last 45 yr however in the north atlantic the patterns of trend changes for wind sea and swell are quite different from each other showing opposite signs of changes in the northeast atlantic trend patterns of wind sea swell and swh in the north pacific are more consistent with each other qualitatively the same conclusions hold for the analysis of interannual variability whose leading modes demonstrate noticeable differences for wind sea and swell statistical analysis shows that variability in wind sea is closely associated with the local wind speed while swell changes can be driven by the variations in the cyclone counts implying the importance of forcing frequency for the resulting changes in significant wave height this mechanism of differences in variability patterns of wind sea and swell is likely more realistic than the northeastward propagation of swells from the regions from which the wind sea signal originates

wave driven flow over shallow reefs long term 1 month observations of waves and currents over a natural reef are presented which show a strong correlation between offshore rms incident wave height and cross reef currents at subtidal frequencies the energy spectrum of the cross reef currents shows a significant peak at twice the semidiurnal tidal frequency while the spectrum of sea surface elevation over the reef flat shows no corresponding peak furthermore experimental results reported by gourlay 1993 show setup over the reef occurs in the absence of a beach and the cross reef transport decreases with an increase in the sea surface slope across the reef flat due to an increase in setup at the top of the reef face analytic solutions for flow forced by wave breaking over an idealized reef explain the above features of cross reef flows in the absence of a beach through the surf zone on the reef face the cross reef gradient in the radiation stress due to wave breaking is partitioned between balancing an offshore pressure gradient associated with setup over the reef and forcing a mean flow across the reef over the reef flat where the depth is constant there is no forcing due to wave breaking and the flow is driven by a pressure gradient which results from the setup through the surf zone the magnitude of the setup through the surf zone is such that the transport across the reef flat matches the transport through the surf zone which is forced by the gradient in the radiation stress solutions are presented for general reef geometry defined by the reef width and slope of the seaward reef face and incident wave forcing defined by the depth at the breakpoint and the depth of water over the reef as the depth over the reef goes to zero the solutions converge to the plane beach solutions described by longuet higgins and stewart 1964 wave setup is maximized and the cross reef transport is zero in other cases the relative magnitudes of the setup and the cross reef transport depend on the geometry of the reef and the incident wave forcing

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

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

rates and causes of recent global sea level rise inferred from long tide gauge data records abstract tide gauge data at seven sites of the permanent service for mean sea level psmsl with information for relative sea level during the past 140 200 yr were analyzed to examine the rates and causes of the global sea level rise gslr during the twentieth century by subtracting linear trends for relative sea level rise during the past 100 yr from the observed data we get the apparent gslrs of 1 mm yr 1 for five sites around the baltic sea and brest the rate for san francisco is significantly larger than this with an optimum value 2 mm yr 1 the spatial difference of 1 mm yr 1 between these sites is reasonably explained by the recent melting of the greenland ice sheet with an equivalent sea level rise of 1 mm yr 1 the predicted relative sea level change for this melting scenario is 0 5 mm yr 1 at sites around the baltic sea and brest and 1 5 mm yr 1 for san francisco the residuals between observations and predictions 0 5 mm yr 1 at all sites may be contributed by thermal expansion of seawater and or other melting sources these results suggest the rate of twentieth century gslr to be 1 5 mm yr 1

present day secular variations in the zonal harmonics of earth s geopotential we develop a new formalism for the prediction of secular variations in the gravitational potential field of a spherically symmetric self gravitating maxwell viscoelastic planetary model subjected to an arbitrary surface load which may include a gravitationally self consistent ocean loading component the theory is applied to generate the most accurate predictions to date of the present day secular variations in the zonal harmonics of the geopotential the so called for degree arising as a consequence of the late pleistocene glacial cycles in this respect we use the very recent ice 3g reconstruction of the last late pleistocene deglaciation event tushingham and peltier 1991 a comparison of these predictions with those generated using simplified disk models of the ice sheets which have been used in all previous studies of the harmonics 2 indicates that the disk model approximation introduces unacceptably large errors at all spherical harmonic degrees except perhaps 2 predictions have also been made using a eustatic loading approximation also used in previous studies in place of a gravitationally self consistent ocean loading component and we have found that the resulting discrepancy is largest at degrees 2 8 and 10 in the case of the magnitude of the error incurred using the eustatic approximation can be as large as order 10 15 of the predicted value we have attributed this discrepancy to the present day net flux of water away from the equatorial regions arising from the remnant present day adjustment associated with the late pleistocene glacial cycles the effect represents a heretofore unrecognized contribution to the harmonics or alternatively the nontidal acceleration of earth s axial rate of rotation in terms of the latter the maximum anomaly in the length of day is approximately 1 7 s yr we also consider the sensitivity of the data to variations in the radial mantle viscosity profile by using a suite of forward calculations and an examination of frechet kernels the theory required for the computation of those kernels is described herein we find that the radial variation in sensitivity can be a strong function of the viscosity model used in the calculations for models with a uniform upper mantle viscosity um of 1021 pa s forward predictions of the harmonics exhibit a pronounced peak when a wide enough range of lower mantle viscosities lm are considered we denote the lm value at this peak as at the lowest degrees 4 frechet kernels computed for a series of increasing lm values 1021 pa s lm 1023 pa s indicate a migration of the dominant sensitivity of the data to variations in viscosity from regions below approximately 1200 km depth for to regions above this depth in the lower mantle for the sensitivity of the data to variations in the viscosity profile in the shallowest parts of the lower mantle for the case is also reflected in a set of forward calculations described herein as an example predictions made using earth models in which the viscosity above 1200 km depth is constrained to be 1021 pa s do not exhibit the multiple solutions characteristic of the um 1021 pa s calculations the same is true of earth models in which the upper mantle viscosity is weakened an order of magnitude to 1020 pa s the theory described herein is also applied to compute the signal 10 arising from the retreat of small ice sheets and glaciers described by meier 1984 and also from any potential variations in the mass of the antarctic and greenland ice sheets the present day signal due to the late pleistocene glacial cycles dominates the signal from meier s sources at all degrees except 3 in contrast the signal arising from mass variations in the antarctic and greenland ice sheets is potentially comparable to the former a comparison of observational constraints on the data with predictions of the postglacial rebound signal described in this paper in order to infer mantle rheology cannot proceed until constraints are placed on the present day mass flux of these large polar ice sheets we show that the constraints required are weakest at degrees 2 and 4 finally we outline a potentially important procedure for incorporating predictions of the signal due to the late pleistocene glacial cycles and meier s sources with an observational constraint on the datum to yield bounds on the present day net mass flux from the antarctic and greenland ice sheets a rigorous application of this procedure must wait until observational constraints on are reestablished in the literature

climate of the last 500 years high resolution ice core records precipitation accumulating on the earth s ice sheets and ice caps records a variety of physical and chemical information about the atmosphere and in some cases provides unique insight to both the history and the mechanics of the earth s environmental system high resolution well dated dust records from both polar ice sheets suggest a linkage between increased atmospheric dust and cooler temperatures over antarctica but a similar relationship is not observed in ice cores from either greenland or china net accumulation histories for the last 490 years reveal no discemible global pattern although interesting regional differences and similarities exist excess non sea salt sulfate profiles provide

earthquakes and sea level space and terrestrial metrology on a changing planet the complacency with which man inhabits continent ocean margins or plate boundaries is based on the assumption that sea level rise and periodic seismicity are acceptable risks the forecast of future sea level or future seismicity is essential for informed assessment of these risks the historical data from which forecasts may be derived are in each case of limited antiquity and uneven spatial distribution developments in space geodesy and crustal deformation metrology in the past two decades offer the means to acquire a homogeneous global data set for monitoring relative vertical and horizontal motions of the earth s surface to within several millimeters these new tools are reviewed in terms of their application to forecasting trends in sea level rise and forecasting damaging earthquakes

greenland ice sheet thickness changes measured by laser altimetry precise airborne laser altimetry surveys at locations on the greenland ice sheet that had been accurately surveyed in 1980 and 1981 reveal a thickening in western greenland of up to two meters between 1980 and 1993 we cannot yet state whether this represents a long term trend or the cumulative effects of interannual variability of snow accumulation rates nevertheless the information presented here provides an indication of ice thickness changes across southern greenland in unprecedented detail laser altimetery surveys have now been made over all the major ice sheet drainage basins and will be repeated at regular intervals to provide detailed estimates of ice thickening thinning rates over the entire ice sheet

perturbations of the earth s rotation and their implications for the present day mass balance of both polar ice caps summary the present day perturbations of the earth s rotation are sensitive to the glacial isostatic adjustment gia arising from the late pleistocene glacial cycles and also to the recent mass balance of polar ice caps in this study we evaluate the polar wander and the change of degreetwo harmonic of the earth s geopotential j 2 proportional to the rotation rate for four late pleistocene ice models we examine these perturbations as a function of lower and uppermantle viscosities and lithospheric thickness and rheology elastic or viscoelastic in which a compressible earth model with elasticity and density given by the seismological model prem is used by considering the observations and predictions including the gia process arising from the late pleistocene ice and recent mass balance of polar ice caps we discuss the recent mass balance of the antarctic and greenland ice sheets we also examine the effects of internal processes and the melting of mountain glaciers although this work is only preliminary the results shown below seem to be supported even if these effects are included two solutions are obtained for source areas of the recent antarctic melting we denote an equivalent sea level esl rise mm yr 1 from the greenland and antarctic ice sheets as gl and