historical reconstruction of monthly oceanic precipitation 1900 2006 1 an oceanic precipitation reconstruction is developed and evaluated for periods extending back to as early as 1900 large scale monthly oceanic precipitation is reconstructed using the available network of historical gauge data fit to a set of large scale covariance spatial modes based on modern analysis the modern analysis is based on satellite microwave estimates merged with atmospheric reanalysis estimates for 1900 2006 a monthly and 5 spatial product is developed for reconstructing climate scale large scale spatial and inter seasonal and longer timescales variation in pre satellite periods advantages of this study include the use of a homogeneous satellite analysis for computing reconstruction statistics and improved tuning of the reconstruction methods cross validation testing is used to show how much historical variance can be reconstructed with the available sampling in addition reconstructions are performed using several different gauge data sets to evaluate differences due to the choice of gauge data testing shows that that these improved methods produce reconstructions with useful skill in the tropics and northern hemisphere midlatitudes in the southern hemisphere midlatitudes and in polar latitudes in both hemispheres sampling is too sparse to yield much skill the reconstruction is able to resolve large scale modes of variation useful for some diagnostic studies of the 20th century reconstruction efforts will continue as improved satellite and atmospheric reanalyses become available

salinity change in the subtropical atlantic secular increase and teleconnections to the north atlantic oscillation 1 recent studies comparing shipboard data between the 1950 s and the 1990 s have shown significant heterogeneous adjustments of the temperature salinity structure of the n atlantic ocean here we present proxy records of temperature and salinity from aragonite sclerosponge skeletons extending existing records of the salinity maximum waters smw of the n atlantic back to 1890 these proxy records show secular temperature increases of 1 6 2 0 c higher than published global averages and salinity increases of 0 35 0 5 psu smaller than short term secular trends recently measured salinity reconstructions vary more significantly on the decadal scale showing changes that are related to low frequency variations of the north atlantic oscillation nao on both secular and decadal time scales the records indicate significant thermohaline changes in the smw either via forcing at the surface or increasing depths of density surfaces in the bahamas

validation of the ice 3g model of wurm wisconsin deglaciation using a global data base of relative sea level histories a global data base consisting of radiocarbon controlled relative sea level rsl histories from 392 different geographic locations has been compiled for use in analyses of the glacial isostatic adjustment process these data may be employed to constrain both the spatiotemporal characteristics of the last deglaciation event of the current ice age and the rheological structure of the planetary interior in a previous paper in this series tushingham and peltier 1991 we employed the rsl data in this set from sites that were once ice covered to refine the apriori model of deglaciation that had been delivered by past research in the area of pleistocene geomorphology peltier and andrews 1976 wu and peltier 1983 to produce a new global model of this event that we have called ice 3g in the present paper following a description of the full data base and of the methods used to compile it we employ data from the sites that were not ice covered 200 time series to verify the plausibility of this refined model of deglaciation and to test the extent to which the totality of the observations constrain the radial viscoelastic structure of the planet the analysis of solutions to the forward problem presented here reinforce previous inferences of a preference for a thick lithosphere by rsl data from sites along the u s east coast and a preference by data from most near field sites for an increase in viscosity across the 670 km discontinuity in the mantle by a factor of approximately 2 when the viscosity of the upper mantle is fixed to the value of 1021 pa s originally deduced by haskel 1935 on the basis of his analysis of the data from fennoscandia

density segregation of minerals during high velocity transport over a rough bed implications for the formation of placers preferential accumulation of minerals with high densities forming placer deposits in longitudinal bars of braided rivers relies on the segregation of this denser material from the quartz and feldspar sands dominating sediment in transport flume experimentation conducted on mixtures of quartz pyroxene magnetite and lead sand transported over rough cobble beds demonstrated that the sand distribution was more uniform above the bed than theory predicted the deviation from theory was inversely proportional to the density of the mineral fall velocity was not a good predictor of the amount of a mineral species carried in suspension as coarse grained quartz dominated the suspension population in the flume runs where lead was a major constituent in the traction population even though the quartz had a greater fall velocity applying these results to placer deposits indicates that during flood events even the smaller dense minerals and especially the super dense minerals will be transported with the gravel and cobble load whereas the quartz and feldspar will be spatially segregated during transport and temporally and spatially segregated during deposition this mechanism of placer formation is capable of creating the types of deposits present in orebodies and showings such as the uraniferous paleoplacers at elliot lake canada and the gold bearing longitudinal bars in the witwatersrand

the north atlantic oscillation and oceanic precipitation variability global north atlantic oscillation nao oceanic precipitation features in the latter half of the twentieth century are documented based on the intercomparison of multiple state of the art precipitation datasets and the analysis of the nao atmospheric circulation and sst anomalies most prominent precipitation anomalies occur over the ocean in the north atlantic where in winter a quadrupole like pattern is found with centers in the western tropical atlantic sub tropical atlantic high latitude eastern atlantic and over the labrador sea the extent of the sub tropical and high latitude center and the amount of explained variance over 50 are quite remarkable however the tropical atlantic center is probably the most intriguing feature of this pattern apparently linking the nao with itcz variability in summer the pattern is tripole like with centers in the eastern mediterranean sea the north sea baltic sea and in the sub polar atlantic in the eastern indian ocean the correlation is positive in winter and negative in summer with some link to enso variability the sensitivity of these patterns to the choice of the nao index is minor in winter while quite important in summer interannual nao precipitation anomalies have driven similar fresh water variations in these key regions in the sub tropical and high latitude atlantic in winter precipitation anomalies have been roughly 15 and 10 of climatology per unit change of the nao respectively decadal changes of the nao during the last 50 years have also influenced precipitation and fresh water flux at these time scales with values lower higher than usual in the high latitude eastern north atlantic labrador sea in the 1960s and the late 1970s and an opposite situation since the early 1980s in summer the north sea baltic region has been drier than usual during the period 1965 1975 when the nao was generally positive

sedimentological and stable isotope evolution of lakes in the vestfold hills antarctica the sedimentological chemical and isotopic characteristics of sediment cores from three slightly saline to hypersaline lakes highway ace and organic lakes and two marine inlets ellis fjord and taynaya bay in the vestfold hills antarctica have been examined sections of the cores deposited in marine environments are characterized by uniform regularly laminated fine grained organic rich sediments with uniform organic 13c values 18 0 to 19 4 vs pdb and sulfur contents in contrast sediments deposited in lacustrine environments are extremely heterogeneous varying from finely laminated mat like sequences to poorly sorted clastic rich sediments authigenic monohydrocalcite and aragonite occur in some lake sediments the 13c values of organic matter in the lacustrine sediments exhibit an extremely wide range 10 5 to 25 3 that can be related to variations in physico chemical conditions in the lake waters strongly negative organic 13c values coupled with high sulfur contents are indicative of an anoxic zone in the overlying lake waters whereas less negative organic 13c values coupled with low sulfur contents are indicative of well mixed oxic conditions particularly high organic 13c values result during high levels of microbial activity in the lakes due to high rates of photosynthetic co2 fixation the large shifts in organic 13c are not necessarily accompanied by any change in macroscopic sedimentological characteristics illustrating the utility of isotopic investigations in these environments the 13c composition of authigenic carbonate in hypersaline organic lake sediments provides a record of changes in palaeoproductivity while the 18o of the carbonate provides information on rates of meltwater input and evaporation in the lake 14c dating suggests that highway lake was isolated from the sea by isostatic uplift at least 4600 yr before present b p whereas organic lake was isolated at approximately 2700 yr b p apparent emergence rates calculated from the 14c ages range from 1 0 to 2 1 mm yr 1 the reservoir effect in the lacustrine and marine environments is variable but probably does not exceed 1000 yr in any of the lakes examined

fossil rotifers and the early colonization of an antarctic lake abstract early holocene sediments from a continental antarctic lake ace lake vestfold hills east antarctica contained abundant fossil rotifers of the genus notholca the fossil is similar to specimens of notholca sp present in modern day ace lake and other fresh and brackish lakes of the vestfold hills cyanobacteria and protists chrysophyte cysts dinoflagellate cysts and rhizopod tests were also recovered from the core samples these sediments were deposited early in the freshwater phase of ace lake soon after deglaciation of the area the occurrence of this trophically diverse assemblage of organisms at an early stage in the evolution of the lake suggests either that they were part of an endemic antarctic flora and fauna which pre dated the last glacial maximum and survived in glacial refugia or that efficient intercontinental dispersal had occurred

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

the deglaciation of atlantic canada as reconstructed from the postglacial relative sea level record the post wisconsinan relative sea level record from atlantic canada is used to reconstruct the morphology of late wisconsinan age ice cover during its retreat from the atlantic region the proposed reconstruction has little or no grounded ice in the southern gulf of st lawrence an ice dome over the north shore of the st lawrence and thin ice often less than 1 km thick over much of the rest of the area a sensitivity analysis shows that the proposed reconstruction is not unique in its ability to account for the relative sea level record but that the thickness of ice in any individual area of the reconstruction is unlikely to be in error by more than a factor of two the exact position of the ice margin in some areas is not well constrained by the model an example is in southeastern newfoundland the numerical model used to relate ice morphology to postglacial relative sea level assumes that the ice sheets are isostatically equilibrated at the glacial maximum and therefore that load changes associat

reconstruction of historical sea surface temperatures using empirical orthogonal functions abstract studies of climate variability often rely on high quality sea surface temperature sst anomalies although the high resolution national centers for environmental prediction formerly the national meteorological center optimum interpolation oi sst analysis is satisfactory for these studies the oi resolution cannot be maintained before november 1931 due to the lack of satellite data longer periods of ssts have come from traditional analyses of in situ ship and buoy sst observations alone a new interpolation method is developed using spatial patterns from empirical orthogonal functions e0fs that is a principal component analysis to improve analyses of sst anomalies from 1950 to 1981 the method uses the more accurate oi analyses from 1982 to 1993 to produce the spatial eofs the dominant eof modes which correspond to the largest variance are used as basis functions and are fit in a least squares sense to the in situ data to determine the time dependence of each mode a complete field

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

interannual to interdecadal variability of sea surface salinity in the atlantic and its link to the atmosphere in a coupled model 1 the interannual to interdecadal variability of sea surface salinity sss in the atlantic is investigated using 200 years of a control simulation of the bergen climate model after verifying that the model behaves realistically we show that most centers of sss variability are located near the mouths of the main rivers of the basin this variability is due primarily to anomalous runoff except in the st lawrence area and to anomalous ekman and geostrophic currents while fluctuations in the freshwater flux play a somewhat lesser role away from the coast sss variability is strong in the northern tropics due largely to anomalous advection and freshwater exchanges regression analysis and a lagrangian technique show that the sss anomalies are advected by the mean oceanic circulation and can be followed along the gyres for several years the link between sss anomalies and the dominant modes of variability of the atmosphere is also investigated the sss response to the north atlantic oscillation nao is dominated by relatively small scales that are forced by anomalous ekman currents but the relative influence of the large scale freshwater fluxes increases at long timescales the nao induced sss anomalies are also strongly advected and distorted by the mean currents so that their pattern at the interannual timescale only reflects in part that of the atmospheric forcing the link between sss anomalies and the east atlantic pattern is similar

a diatom based palaeosalinity history of ace lake vestfold hills antarctica a comprehensive diatom stratigraphy is used to calculate a palaeosalinity history for an antarctic lake via an established diatom salinity transfer function for the vestfold hills antarctica a sediment core taken from ace lake in 1995 shows three distinct changes in diatom assemblage constituents initial benthic hyposaline freshwater taxa are replaced by marine planktonic and sea ice taxa with these taxa in turn replaced by the benthic hypersaline taxa dominant in the lake today these changes in assemblage composition enable the lakewater salinity of each stage to be determined and the holocene evolution of the lake to be refined deglaciation of the vestfold hills at the beginning of the holocene exposed ace lake basin following this fresh lacustrine diatoms were deposited from 11 380 to 8110 corrected 14c yr bp relative sea level rise after this time led to the progressive marine inundation of the lake and the deposition of marine diatom taxa marine taxa were dominant in the sediment for mo

laterally extensive modified placer gold deposits in the paleoproterozoic mississagi formation clement and pardo townships ontario local gold concentrations are found in laterally extensive pyrite bearing framework supported cobble and boulder conglomerates in the basal 30 m of the mississagi formation in the south eastern part of the huronian outcrop belt these were deposited as part of a valley fill succession in shallow gravel bed braided rivers with local hyperconcentrated flows the basal contact with underlying archean psammites is typically highly irregular and shows no obvious sign of weathering suggesting that deposition took place soon after retreat of the glaciers responsible for deposition of the ramsey lake formation highest gold concentrations are associated with moderately well sorted medium to large pebble conglomerate that show some signs of reworking during low flow events depositional elements are typically lenticular and of limited lateral extent unlike the older pyritic quartz pebble conglomerates at the base of the matinenda formation in the elliot lake and blind river areas these conglomerates contain no uraninite and are polymict with material derived from a highly restricted catchment area with marked local and regional topographic relief porous detrital allogenic pyrite and euhedral post depositional pyrite have overlapping generally positive delta 34 s values indicating a closed system during diagenesis and metamorphism the presence of biotite enriched rims on many of the metavolcanic and metasedimentary clasts in the conglomerates suggests that gold was partly leached from the allogenic pyrite grains at the peak of the penokean orogeny at 1 85 1 5 ga the potential source of the au bearing detrital allogenic pyrite appears to be an as yet undiscovered archean volcanic hosted massive sulfide vhms deposit located 1 to 8 km north of the deposit

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

recent variability of the north atlantic thermohaline circulation inferred from surface heat and freshwater fluxes abstract an annual mean surface forced component of the north atlantic thermohaline circulation thc in density space surf is diagnosed from observed surface heat and freshwater fluxes the climatological mean of surf over 1980 97 indicates steady overturning rates for those water masses that are principally formed through surface buoyancy forcing 8 sv of greenland sea deep water gsdw 4 sv of labrador sea water lsw and 4 sv of 18 water stmw obtained for each year over 1980 97 surf reveals interannual to decadal variability in the renewal and overturning of these water masses the total surface forced overturning rate varies in the range 10 20 sv reaching peak values in 1989 90 and generally decreasing over the period 1990 97 more dramatic changes are apparent in the overturning of different water masses the overturning of stmw exhibits large amplitude interannual variability a background positive trend over 1980 97 is dominated by variance of 13 4 sv by contrast the overtur

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

placer formation during progradational fluvial degradation the late archean middelvlei gold placer witwatersrand south africa previous workers have established experimentally that geomorphologic conditions of degradation are favorable for the transport and concentration of heavy minerals and should therefore be conducive to the formation of placers this principle may apply generally to the late archean gold uranium placers of south africa most of which rest on erosion surfaces the middelvlei gold placer a quartz pebble conglomerate which occurs near the base of the central rand group of the witwatersrand supergroup is mined selectively in a gold field known as the west wits line situated west of johannesburg the placer is considered part of a depositional system which overlies a regional mudstone marker the green bar member and comprises three members the footwall member the middelvlei placer and the hanging wall member the footwall member consists predominantly of trough crossbedded quartz wackes with lag conglomerates and massive mudstone as subordinate lithofacies thickness of this member varies from about 35 to more than 100 m and is generally smaller in the eastern parts of the gold field where it is overlain by a large pebble type middelvlei placer paleocurrent distributions of the footwall member are unimodal in all parts of the gold field with mean directions toward the southeast in the eastern regions and toward the south southeast in the western parts directional variances are typically smaller than 1 600 the middelvlei placer overlies the footwall member unconformably in most parts of the gold field but in some southern parts of the western region no sedimentary break between these two members is evident the placer comprises interbeds of quartz pebble conglomerate mostly massive cross and horizontally bedded quartz wacke and thin massive mudstone maximum pebble size is about 6 0 phi and sizes are generally greater in the eastern parts of the gold field paleocurrent distributions are also unimodal and in any particular area the means are not significantly different from those of the underlying footwall member directional variances are typically smaller than 2 000 the hanging wall member consists mainly of trough crossbedded quartz wackes and subordinate lag conglomerates for the western regions of the gold field information on paleo currents is sparse but in the eastern region the distribution is unimodal with a mean not significantly different from that of the underlying middelvlei placer the middelvlei depositional system is thought to be fluvial in origin and was probably deposited in braided streams the footwall member and the middelvlei placer constitute a coarsening upward megacycle and are thought to represent a prograding braid plain in most areas the transport of coarse grained gravel during progradation was accompanied by erosion of the underlying footwall member gold concentrations are generally higher in areas of severe degradation of the footwall member than in regions where little or no basal erosion by the placer has taken place and where a conformable relationship between the two members exists statistical analyses revealed that the gold rich facies of the placer is a single relatively thin bed of massive clast supported conglomerate with large pebbles

an ocean model s response to north atlantic oscillation like wind forcing the response of the atlantic ocean to north atlantic oscillation nao like wind forcing was investigated using an ocean only general circulation model coupled to an atmospheric boundary layer model a series of idealized experiments was performed to investigate the interannual to multi decadal frequency response of the ocean to a winter wind anomaly pattern overall the strength of the sst response increased slightly with longer forcing periods in the subpolar gyre however the model showed a broad response maximum in the decadal band 12 16 years

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

the ventersdorp contact placer a gold pyrite placer of stream and debris flow origins from the archaean witwatersrand basin of south africa five local varieties of the ventersdorp contact placer at the east driefontein gold mine carletonville are distinguished by clast type assemblage reflecting discrete provenances the placer further comprises six lithofacies which are not restricted to specific provenance varieties the six lithofacies are massive matrix supported conglomerate facies gms massive or crudely bedded clast supported conglomerate facies gm channel based conglomerate facies gt single clast layers facies glag horizontally stratified sandstone facies sh and trough cross stratified sandstone facies st facies gms represents debris flow deposits whereas the other facies are stream deposits lithofacies and provenance varieties are complexly interrelated in local environments which are themselves complexly related to geomorphic elements of a degradation surface the maximum thickness of the placer is 7 m the placer was deposited on a hard i e non alluvial bedrock surface suggesting that it is a pediment mantle it owes its preservation to a capping of conformably overlying basalts economic gold mineralization is present in all the conglomerate facies and all the provenance varieties gold concentrations are high in gravel bar deposits and channel fills but are not restricted to these environments a major feature of gold concentration is its variability between provenance controlled varieties the gold concentration of a specific primary source is interpreted to be a major control on gold concentration in the final deposit the origin of the placer as a pediment mantle and its subsequent preservation by lava flows suggests that there was little potential for selective reworking of heavy minerals nevertheless the ventersdorp contact placer on the carletonville goldfield is one of the richest gold placers in the witwatersrand basin

seasonality of the north atlantic oscillation abstract monthly sea level pressure slp data from the national centers for environmental prediction reanalysis for 1948 99 are used to develop a seasonally and geographically varying mobile index of the north atlantic oscillation naom naom is defined as the difference between normalized slp anomalies at the locations of maximum negative correlation between the subtropical and subpolar north atlantic slp the subtropical nodal point migrates westward and slightly northward into the central north atlantic from winter to summer the naom index is robust across datasets and correlates more highly than eof coefficients with historical measures of westerly wind intensity across north atlantic midlatitudes as measured by this mobile index the nao s nodes maintain their correlation from winter to summer to a greater degree than traditional nao indices based on fixed stations in the eastern north atlantic azores lisbon iceland when the naom index is extended back to 1873 its annual values during

holocene deglaciation sea level change and the emergence of the windmill islands budd coast antarctica a holocene deglaciation sequence for the windmill islands was determined from the 14c age of raised marine shorelines lakebottom sediments and adelie penguin remains found in abandoned rookeries a north south gradient in the elevation of the upper marine limit was observed with the highest marine limit 31 32 m observed on browning peninsula and hull island at the southern edge of the islands correspondingly the southern islands were found to have been deglaciated by 8000 corr yr b p while the northern islands were deglaciated by 5500 corr yr b p isostatic uplift rates were calculated as 0 5 to 0 6 m 100 yr with an estimated total uplift of around 53 m which indicates late pleistocene ice sheet thicknesses of 200 and 400 m over the islands and adjacent petersen bank respectively the margin of the late pleistocene grounded ice sheet extended an estimated 8 15 km offshore which coincides with the location of the 200 m isobath

antarctic ice volume and contribution to sea level fall at 20 000 yr bp from raised beaches the contribution of the antarctic ice sheets to global sea level fall at the last glacial maximum lgm depends largely on how the extent and thickness of peripheral ice changed model studies1 3 suggest that there was widespread thickening from 500 m to more than 1 000 m of the ice sheet margins sufficient to induce a drop in sea level of at least 25 m geological evidence4 5 on the other hand indicates only limited ice expansion and a sea level fall of just 8 m here we use recent data on the altitudes and ages of raised beaches from the ross embayment and east antarctica to investigate the timing and extent of antarctic deglaciation these indicate that the ice margin during the lgm was thinner and less extensive than has been formerly thought and that its contribution to the drop in sea level was only 0 5 2 5 m deglaciation was well advanced by 10 kyr bp and was complete by 6 kyr bp these findings imply either that sea level during the lgm fell less than present estimates suggest or that an ice volume considerably greater than currently accepted must have been present in the northern hemisphere

how enso impacts precipitation in southwest central asia 1 a linkage between enso and the hydroclimatic variability of the southwest central asia region swca is established through observational analysis of precipitation moisture flux and sea level pressure data with further support from an atmospheric model of intermediate complexity enhanced precipitation in swca during warm enso events results from an anomalous southwesterly moisture flux coming from the arabian sea and tropical africa which is generated along the northwestern flank of the high pressure anomaly over the indian and western pacific oceans part of the canonical enso sea saw pressure anomalies the enso impact on swca precipitation is found to be greatest in the transition seasons of autumn and spring but the dynamical impact on pressure and circulation persists throughout the year this connection was particularly strong in recent decades model sensitivity experiments further show that this is driven primarily by tropical pacific sst anomalies and associated large scale sea level pressure changes while the indian ocean sst has opposite effects

recent changes in the surface salinity of the north atlantic subpolar gyre sea surface salinity sss was measured since 1896 along 60 n between greenland and the north sea and since 1993 between iceland and newfoundland along 60 n away from the shelves and north of 53 n the amplitude of the seasonal cycle is comparable to or less than interannual variability in these parts of the north atlantic subpolar gyre large scale deviations from the seasonal cycle correlate from one season to the next this suggests that in these regions summer and autumn surface data are useful for monitoring changes in upper ocean salinity best diagnosed from less common winter surface data further south near the subarctic front the labrador current or near shelves where seasonal variability is strong this is not the case along 60 n the multiannual low frequency variability is well correlated across the basin and exhibits fresher surface water since the mid 1970s than in the late 1920s to 1960s sss in the irminger sea along 60 n lags by 1 year sss farther east in the iceland basin variability between iceland and newfoundland within the irminger sea north of 54 n presents similar characteristics to what is observed along 60 n variability near the northwest corner of the north atlantic current 52 n 45 w is larger and is not correlated to what is found further north maps of sss were constructed for a few recent seasons between july 1996 and june 2000 which illustrate the fresh conditions found usually during that period across the whole north atlantic subpolar gyre although this includes an episode of higher salinity the sss anomaly maps have large uncertainties but suggest that the highest sss occurred before the spring of 1998 in the iceland basin and after that in the irminger sea this is followed by fresher conditions first in the labrador and iceland basin reaching recently the irminger sea

sedimentology of the lower huronian supergroup early proterozoic elliot lake area ontario canada abstract the early proterozoic huronian supergroup is a slightly metamorphosed sedimentary succession locally 10 km thick exposed to the north of lake huron ontario canada the lower part of the supergroup comprising the matinenda mckim ramsay lake and pecors formations was studied in the quirke syncline area elliot lake and regions immediately to the west and south thirteen lithofacies are present trough and planar cross stratified sandstone quartz pebble conglomerate clay rich sandstone lenticular bedded sandstone siltstone mudstone laminated sandstone siltstone mudstone massive sandstone massive pebbly sandstone massive diamictite stratified matrix supported diamictite stratified clast supported diamictite graded diamictite and massive siltstone the lithofacies may be grouped into associations which correspond approximately to the mapped formations the crossbedded sandstones and conglomerates comprise a fluvial association matinenda formation which was formed mainly in shallow braided channels clay rich sandstone and the lenticular and laminated lithofacies constituting portions of the mckim and pecors formations were deposited on the strand and offshore areas of braid deltas interfingering laterally and vertically with the matinenda fluvial deposits four glacigenic subassociations are present in the ramsay lake formation an ice proximal subassociation i consists of massive pebbly sandstone and diamictite which progressively truncates the matinenda and mckim formations to the north the massive sandstone may be an ice override deposit formed by erosion and reworking of the underlying matinenda formation or a sub ice shelf rain out accumulation of locally eroded glacial debris subassociations ii and iii consist mainly of subaqueous sediment gravity flow and ice rain out deposits subassociation iv is interpreted as an ice proximal fluvial outwash deposit containing resedimented blocks of moraine material stratigraphic and paleocurrent data indicate a south dipping paleoslope that tilted southeast during the deposition of the fluvial and deltaic units a trough of relatively deep water extended nw se across the region transverse to the e w divergent continental margin hinge line that is assumed to have existed to the south of the project area analogies are suggested to mesozoic recent basins on the atlantic margin of canada where transverse paleogeographic trends reflect either landward extension of active oceanic fracture zones or reactivation of earlier structural lineaments

chironomid evidence for late glacial climatic reversals in maine previously published pollen studies from maine have not identified any late glacial reversals despite evidence for them from adjacent areas the distribution and abundance of midge flies are strongly correlated with summer surface water temperatures we analyzed fossils of larval midge flies from the sediments of two ponds trout and tilley from maine each site reveals a major and a minor oscillation during which inferred summer surface water temperatures fell by 7 13 c and 2 1 2 6 c respectively we tentatively correlate these events with the younger dryas cooling and killarney oscillation reported from adjacent maritime canada where they have been ams 14c dated at 10 770 10 000 and 11 160 10 910 yr b p respectively a third oscillation occurs at the northernmost site tilley pond and may represent the effects of a local ice advance in northern maine

on the interannual variability of surface salinity in the atlantic the mechanisms controlling the interannual variability of sea surface salinity sss in the atlantic are investigated using a simulation with the echam4 opa8 coupled model and for comparison the ncep reanalysis and an observed sss climatology anomalous ekman advection is found to be as important as the freshwater flux in generating sss anomalies in contrast to sea surface temperature sst anomalies which are primarily caused by surface heat flux fluctuations since the surface heat flux feedback does not damp the sss anomalies but generally damps existing sst anomalies sss anomalies have a larger characteristic time scale as a result they are more influenced by the mean currents and the geostrophic variability which dominate the sss changes at low frequency over much of the basin the link between sss anomalies and the dominant patterns of atmospheric variability in the north atlantic sector is also discussed it is shown that the north atlantic oscillation generates sss anomalies much more by ekman advection than by freshwater exchanges at least in the coupled model there is little one to one correspondence between the main atmospheric and sss anomaly patterns unlike what is found for sst anomalies

glacial rebound and relative sea level variations a new appraisal summary late pleistocene and holocene changes in sea level at technically stable shorelines contain information on the melting history of the ice sheets and on the response of the earth to changes in surface loads on time scales of 104yr some separation of parameters defining the ice loads and the earth s response can be achieved by examining sea level change at different sites around the world and at different epochs this paper examines the mathematical requirements for obtaining satisfactory solutions for the sea level equation rather than emphasizing results for the earth s response to the surface loads an examination of the equation expressing the sea level variation on a viscoelastic earth indicates that careful consideration needs to be given to both the definition of the ice load and the geometry of the redistributed water load if geophysically significant earth response parameters are to be deduced from observations of relative sea level the spectrum of the 5 x 5 area mean description of the ice load widely used in glacial rebound studies contains significant power at high degrees n 30 and can result in substantial spatial variations in sea level unless a thick lithosphere is introduced in the earth s response function a smoothed 1 1 description of the ice model avoids these high degree oscillations in relative sea level and produces satisfactory sea level results without requiring a thick lithosphere at far field sites the holocene sea levels are sensitive to the earth s response to the meltwater loading in the vicinity of the site and a high degree spatial resolution of coastline geometry is required to model the mantle flow driven by the differential loading about the site at some sites convergence of the solution to the sea level equation is not obtained even when the solution is expanded to degree 180 convergent solutions at lower degrees can be achieved by introducing earth models with a moderately thick lithosphere if high resolution ice and meltwater load models are not used then the tendency will be to overestimate the effective elastic thickness of the lithosphere estimates of mantle viscosity are also of questionable value if these high resolution models are not used a preliminary examination of sea levels at sites in both the near and far field places an upper limit of about 50 80 km on the effective lithospheric thickness these sea level observations are also consistent with an upper mantle viscosity of about 1021 pas with a lower mantle viscosity in the range of 1021 1023pa s

faunal microfossils indicators of holocene ecological change in a saline antarctic lake abstract the sediment record of the fauna of ace lake a saline meromictic lake in the vestfold hills antarctica consists of copepod eggs spermatophores and exoskeletal fragments rotifer and tintinnid loricae and foraminiferal and folliculinid tests the relative abundance of these remains along with other characteristics of the core allows the development of a coherent picture of the progress of ace lake from a species poor freshwater lake early in the holocene to a biodiverse marine basin following a marine transgression subsequent sea level fall reformed ace lake as a saline lake and productivity initially increased after isolation after a major event possibly associated with overturn of the meromictic lake biodiversity and productivity decreased and have continued to do so until the present

in situ trace element and sulfur isotope analysis of pyrite in a paleoproterozoic gold placer deposit pardo and clement townships ontario canada extensive pyrite bearing auriferous cobble and boulder conglomerates are present in the basal 30 in of the mississagi formation in pardo and clement townships ontario canada the sedimentology of the conglomerates combined with regional geology indicates limited fluvial transport in a gravel bed braided river with local hyperconcentrated flows with material derived from a highly restricted catchment area postdepositional overprinting of the conglomerates is related to the penokean orogeny at 1 85 to 1 5 ga and alkali metasomatism at similar to 1 7 ga several pyrite varieties including detrital and postdepositional recrystallized and altered grains are present in the conglomerates detailed in situ laser ablation inductively coupled plasma mass spectrometry la icpms analysis of pyrite revealed that the gold in the deposit is intimately associated to large detrital pyrite grains as invisible au with lesser amounts of free gold postdepositional pyrite and pyrite overgrowths have very low au content elements such as pb bi sb te ag and hg together with au were mobilized during hydrothermal alteration and dissolution of detrital pyrite grains small scale transport and reprecipitation formed part of the postdepositional pyrite and free gold in immediate contact with postdepositional grains in contrast ni co and as were not mobilized external fluid infiltration is negligible and is indicated only by minor compositionally distinct late sulfide veinlets crosscutting the conglomerates sulfur isotope analysis of detrital pyrite yields generally positive delta 34 s values 0 97 9 26 0 the delta 34 s sulfur isotope composition of pyrite overgrowths and postdepositional grains overlaps the isotopic range of the detrital grains suggesting a near closed s system during postd epositional processes however the detrital pyrite tends to have slightly negative delta 33 s while the postdepositional and overgrowth pyrite are either neutral or slightly positive the s isotope composition of the detrital pyrite is compatible with an origin of s as dissolved sulfate in an ocean under a low oxygen atmosphere the potential source of the au bearing detrital pyrite appears to have been an as yet undiscovered archean deposit located within 1 to 8 kin of the placer deposit

holocene development of the fauna of lake boeckella northern antarctic peninsula the origins of the freshwater fauna that inhabits antarctic lakes are poorly known the species present today could be relict species that have survived quaternary glaciations on the continent or holocene migrants from more temperate regions one approach to investigating these questions is to study faunal microfossils in lake sediment this approach was applied to a 293 cm sediment core from lake boeckella located at the northern tip of the antarctic peninsula the microfossils indicated that most of the metazoan species that occur in the lake today have been present since soon after the lake s formation c 5 5 ka ago in particular the centropagid copepod boeckella poppei mra zek has been present throughout the lake s history suggesting a local source for this species the development of biodiversity in the lake with time was in general more consistent with local antarctic rather than distant south american sources though an alternative explanation is that dispersal to antarctica was more efficient in the mid holocene evidence of dispersal from extra continental sites comes from the scattered occurrence throughout the core of eubosmina chilensis daday a south american species that does not reach the antarctic or the sub antarctic islands at present and which failed to establish a permanent population in the lake

the north atlantic oscillation and its imprint on precipitation and ice accumulation in greenland interannual to decadal fluctuations in net precipitation and ice accumulation are examined over greenland it is shown that in western greenland these fluctuations are correlated with the north atlantic oscillation the analysis is based on two complementary data sources a highly resolved net precipitation and accumulation history over 15 years derived form the reanalysis data of the european centre for medium range weather forecasts and a composite ice accumulation record representative for the western part of central greenland it is suggested that western greenland snow accumulation is a good proxy for the nao index with the potential for the reconstruction of a long time series

combined dna and lipid analyses of sediments reveal changes in holocene haptophyte and diatom populations in an antarctic lake preserved ribosomal dna of planktonic phototrophic algae was recovered from holocene anoxic sediments of ace lake antarctica and the ancient community members were identified based on comparative sequence analysis the similar concentration profiles of dna of haptophytes and their traditional lipid biomarkers alkenones and alkenoates revealed that fossil rdna also served as quantitative biomarkers in this environment the dna data clearly revealed the presence of six novel phylotypes related to known alkenone and alkenoate biosynthesizing haptophytes with isochrysis galbana uio 102 as their closest relative the relative abundance of these phylotypes changed as the lake chemistry particularly salinity evolved over time changes in the alkenone distributions reflect these population changes rather than a physiological response to salinity by a single haptophyte using this novel paleo ecological approach of combining data from lipid biomarkers and preserved dna we showed that the post glacial development of ace lake from freshwater basin to marine inlet and the present day lacustrine saline system caused major qualitative and quantitative changes in the biodiversity of the planktonic populations over time

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

occurrence and formation of water laid placers a placer is a deposit of residual or detrital mineral grains in which a valuable mineral has been concentrated by a mechanical agent the agent is usually running water and the valuable mineral is usually denser than quartz for example gold diamond cassiterite ilmenite or chromite it is difficult to overemphasize the importance of placers as sources of mineral wealth the witwatersrand south africa paleoplacers discovered in 1886 alone have provided over half of all the gold ever mined in the world pretorius 1976 and alluvial placer deposits of cassiterite in southeast asia presently are the world s major source of tin toh 1978 the earliest evidence of placer mining comes from stone carvings in egypt dated at 2500 b c macdonald 1983 and as early as 7 b c strabo pointed out that in turdetania spain more gold was procured from washing sand in the rivers than by digging in the mines given the economic importance of water laid placers and the long history oftheir exploitation it is remarkable that they have received so little attention in sedimentary research mining and exploration practices for the most part have been guided by empirical rules of thumb that are locally useful but lack any firm physical basis of understanding see bateman

holocene sea level change and ice sheet history in the vestfold hills east antarctica abstract a new holocene sea level record from the vestfold hills antarctica has been obtained by dating the lacustrine marine and marine lacustrine transitions that occur in sediment cores from lakes which were formerly connected to the sea from an elevation of 7 5 m 8000 yr ago relative sea level rose to a maximum 9 m above present sea level 6200 yr ago since then sea level has fallen monotonically until the present the precision of the new record makes it suitable for constraining the recent history of the ice sheet in that region using numerical models of glacio hydro isostasy simplified regional models suggest that the ice sheet margin has retreated 30 40 km since the last glacial maximum with 600 700 m of thinning occurring at the present coastline

diamondiferous neoarchean fan delta deposits western superior province canada sedimentology and provenance abstract most fluvial diamond placers occur in non aggrading braided systems where the diamonds are preferentially trapped by very rough substrates the recognition that some of the neoarchean diamond bearing breccias near wawa ontario canada are actually fluvial conglomerates deposited by a mixture of traction current and mass flow processes provided the opportunity to add information on aggradational diamond placer systems the 454 m thick leadbetter conglomerate was studied to ascertain the depositional processes that led to the development and provenance of the placer the conglomerate is composed of a series of weakly sheared and highly viscous debris flows interbedded with boulder to pebble conglomerates representing longitudinal bars and channels pebble conglomerate and sandstone channels become more dominant upwards with a decrease in mass flow processes an abrupt marine transgression flooded this fan delta assemblage ending deposition of the coarse grained lithofacies the lowest 100 m of the conglomerate is composed of clasts derived solely from the underlying mafic volcanic assemblage above this zone the clast types become more diverse and felsic volcanic clasts become progressively more important upwards whole rock geochemistry performed on coarse grained sandstone samples indicates that major sediment contributions came from mafic rocks and nearby diamondiferous lamprophyres and related breccias though the possible existence of a localized kimberlitic source cannot be excluded geochemistry also indicates that minor enrichments of heavy minerals formed on the alluvial fan delta surface but the primary cause of the conglomerate s diamondiferous nature was a nearby diamond bearing source rock

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

constraints on the late weichselian ice sheet over the barents sea from observations of raised shorelines abstract direct evidence for late weichselian grounded glacier ice over extensive areas of the barents sea is based largely on indirect observations including elevations of old shorelines on svalbard and arguments of isostatic rebound such isostatic models are discussed here for two cases representing maximum and minimum ice sheet reconstructions in the former model the ice extends over the kara sea whereas in the latter the ice is limited to the barents sea and island archipelagos comparisons of predictions with observations from a number of areas including spitsbergen nordaustlandet edgeoya kong karls land franz josef land novaya zemlya and finnmark support arguments for the existence of a large ice sheet over the region at the time of the last glacial maximum this ice sheet is likely to have had the following characteristics conclusions that are independent of assumptions made about the earth s rheological parameters i the maximum thickness of this ice was about 1500 2000 m with the centre of the load occurring to the south and east of kong karls land ii the ice sheet extended out to the western edge of the continental shelf and its maximum thickness over western spitsbergen was about 800 m iii to the north of svalberg and frans josef land the ice sheet extended out to the northern shelf edge iv retreat of the grounded ice across the southern barents sea occurred relatively early such that this region was largely ice free by about 15 000 bp v by 12 000 bp the grounded ice had retreated to the northern archipelagos and was largely gone by 10 000 bp vi the ice sheet may have extended to the kara sea but ice thicknesses were only a fraction of those proposed in those reconstructions where the maximum ice thickness is centered on novaya zemlya models for the palaeobathymetry for the barents sea at the time of the last glacial maximum indicate that large parts of the barents sea were either very shallow or above sea level providing the opportunity for ice growth on the emerged plateaux as well as on the islands but only towards the end of the period of fennoscandian ice sheet build up

role of hydraulic sorting in the origin of fluvial placers a necessary condition for placer development is selective sorting at the grain scale by size and density the effects of differential entrainment suspension and transport on an initial distribution composed of medium size quartz and 10 fine size magnetite were modeled by solving the einstein bedload function for specific grain friction velocities u super in the range 3 63 cm sec super 1 and bed roughnesses of 0 55 2 5 and 10 mm for any value of u super and for both mineral densities the transport rate for all sizes in the initial distribution decreases with increasing roughness the decrease being greatest in the finer sizes the concentration of magnetite transported in the flow increases with increasing u super for each roughness and decreases with increasing roughness for each u super the settling velocity ratio of magnetite to quartz in transport decreases with increasing u super for any value of roughness for any value of u super the ratio first decreases then increases with increasing roughness ranging from 1 36 at low u super and roughness to 0 76 at high u super and intermediate roughness these results are due to variations in the reactive angles of grains and the extent to which grains hide in the lower inner zone of the boundary layer concentrations of heavy minerals at the bed bar and system scales are explained using these results

downstream lightening and upward heavying experiments with sediments differing in density sorting and selective transport of particles by material density is important for understanding a wide range of processes including the formation of mineral placers deposition of mine tailings and routing of tracers and contaminants this article describes an experimental study of the transport of mixtures of particles of differing density in a sediment feed flume during the runs a downstream prograding wedge shaped deposit was formed results show two sorting processes i longitudinal sorting characterized by preferential deposition of heavy particles in the upstream part of the deposit downstream lightening and ii vertical sorting with less dense particles preferentially deposited in the lowermost portion of the migrating front upward heavying downstream lightening is the analogue of the well known downstream fining observed in the more studied case of mixtures of heterogeneous size with the same density in both cases the lighter particles are carried further downstream than the heavier particles upward heavying is unexpected when compared with deposits of heterogeneous size and same density particles where the heaviest i e coarsest particles are deposited in the lowermost part of the front the physical mechanism underlying this upward heavying might be related to the physics of gravity driven granular flows the front of the deposit acts like a dense granular flow down an inclined plane in this case the denser particles settle away from the free surface and at the top of the heap while the lighter particles flow to the bottom as the front of the deposit advances this progressively gives rise to an upward heavying pattern the application of classical surface based fractional bedload transport models suggests that equal mobility is not approached in the case of mixtures of particles with uniform size and different densities this study hypothesizes that other mechanics related to the physics of the segregation processes in these systems contribute to these results

a 3 d model for the antarctic ice sheet a sensitivity study on the glacial interglacial contrast on the longer climatic time scales changes in the elevation and extent of the antarctic ice sheet have an important role in modulating global atmospheric and oceanographic processes and contribute significantly to world wide sea levels in this paper a 3 d time dependent thermomechanical model for the entire ice sheet is presented that is subsequently used to examine the effects of glacial interglacial shifts in environmental boundary conditions on its geometry the model takes into account a coupled ice shelf grounding line dynamics basal sliding and isostatic bed adjustment and considers the fully coupled velocity and temperature fields ice flow is calculated on a fine mesh 40 km horizontal grid size and 10 layers in the vertical for grounded and floating ice and a stress transition zone in between at the grounding line where all stress components contribute in the effective stress in the flow law there is free interaction between ice sheet and ice shelf so that the entire geometry is internally generated a simulation of the present ice sheet reveals that the model is able to yield realistic results a series of sensitivity experiments are then performed in which lower temperatures reduced accumulation rates and lower global sea level stands are imposed either singly or in combination by comparing results of pairs of experiments the effects of each of these environmental changes can be determined in agreement with glacial geological evidence we found that the most pronounced changes show up in the west antarctic ice sheet configuration they appear to be essentially controlled by variations in eustatic sea level whereas typical glacial interglacial changes in temperature and ice deposition rates tend to balance one another these findings support the hypothesis that the antarctic ice sheet basically follows glacial episodes in the northern hemisphere by means of sea level teleconnections grounding occurs more readily in the weddell sea than in the ross sea and long time scales appear to be involved it may take up to 30 40000 years for these continental shelf areas to become completely grounded after an initial stepwise perturbation in boundary conditions according to these reconstructions a steady state antarctic ice sheet may contribute some 16 m to global sea level lowering at maximum glaciation

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

palaeohydrological modelling of ace lake vestfold hills antarctica the major influences on the salinity and water level of an antarctic lake are parameterized and a palaeohydrological model linking the palaeosalinity of an antarctic lake to the palaeohydrology of the lake is developed climatic change in this lake is recorded in the evaporative loss trend reconstructed from water level and lakewater salinity estimates a decrease in salinity between 700 and 200 years bp corresponds with c 5 m increase in water level over the same time period both water level and lakewater salinity then stabilize in the last 200 years bp the palaeohydrological model derived from the changes inferred in salinity and water level shows that there is no significant change in evaporation for the last 700 years but that a lower evaporation period is evident at 150 200 years bp suggestive of a mild little ice age event in the vestfold hills

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

methods of computation of suspended load from bed materials and flow parameters computation of the grain size distribution of the suspended load above a sand bed must take into consideration 1 sorting processes from the bed to the bed layer and 2 sorting between the bed layer and suspension grain size distributions of the bed layers above sand beds of three different types have been computed in this work both by the einstein and the gessler methods using these as references suspended load distributions have been obtained in each case by the rouse suspension equation a new formula has also been developed in partial modification of hunt s method for direct computation of bed load and suspended load from a bed s grain size distribution and flow parameters comparison of the computed data with actual observations in laboratory flumes show that no one method is particularly superior to the others but the present method is advantageous because it affords direct computation of the suspended load from a bed s grain size distribution without going through an intermediate stage bed load the possible sources of error in each of the methods have been discussed

glacial rebound of the british isles ii a high resolution high precision model summary observations of ice movements across the british isles and of sea level changes around the shorelines during late devensian time after about 25 000 yr bp have been used to establish a high spatial and temporal resolution model for the rebound of great britain and associated sea level change the sea level observations include sites within the margins of the former ice sheet as well as observations outside the glaciated regions such that it has been possible to separate unknown earth model parameters from some ice sheet model parameters in the inversion of the glaciohydro isostatic equations the mantle viscosity profile is approximated by a number of radially symmetric layers representing the lithosphere the upper mantle as two layers from the base of the lithosphere to the phase transition boundary at 400 km the transition zone down to 670 km depth and the lower mantle no evidence is found to support a strong layering in viscosity above 670 km other than the high viscosity lithospheric layer models with a low viscosity zone in the upper mantle or models with a marked higher viscosity in the transition zone are less satisfactory than models in which the viscosity is constant from the base of the lithosphere to the 670 km boundary in contrast a marked increase in viscosity is required across this latter boundary the optimum effective parameters for the mantle beneath great britain are a lithospheric thickness of about 65 km a mantle viscosity above 670 km of about 4 5 lo2 pa s and a viscosity below 670 km greater than 4 x lo2 pas

the evolution of watts lake vestfold hills east antarctica from marine inlet to freshwater lake abstract watts lake is a 0 38 km2 freshwater lake in the vestfold hills east antarctica 68 35 s 78 00 e that was formerly a marine embayment the water level of the lake is currently rising it is now at 5 8 m altitude the lake currently has a maximum salinity of 2 4 g 1 1 and no outlet abundant holocene marine fossil molluscs polychaetes and algae dated at 4700 8000 14c yr b p indicate that the lake was one basin of a complex marine inlet during the early to mid holocene a prominent terrace formed in the tide zone during this period processes involved in terrace formation are discussed using watts lake as an example other basins of this inlet have now become saline or hypersaline isostatic uplift isolated the whole inlet from the sea and allowed the basins to become separate lakes from 3000 4000 14c yr b p copious volumes of freshwater from nearby stagnant ice and possibly from a major river system poured into watts lake displacing the salt water over a sill at the eastern end within 2000 yr the lake was fresh freshwater inflow declined and the lake level began to fall from evaporation cyanobacterial stromatolites formed from 2800 to 1700 14c yr b p at the eastern end of the lake at least two other lakes in the hills have similar histories

the variability of the atlantic meridional overturning circulation the north atlantic oscillation and the el nino southern oscillation in the bergen climate model abstract the link between the interannual to interdecadal variability of the atlantic meridional overturning circulation amoc and the atmospheric forcing is investigated using 200 yr of a control simulation of the bergen climate model where the mean circulation cell is rather realistic as is also the location of deep convection in the northern north atlantic the amoc variability has a slightly red frequency spectrum and is primarily forced by the atmosphere the maximum value of the amoc is mostly sensitive to the deep convection in the irminger sea which it lags by about 5 yr the latter is mostly forced by a succession of atmospheric patterns that induce anomalous northerly winds over the area the impact of the north atlantic oscillation on deep convection in the labrador and greenland seas is represented realistically but its influence on the amoc is limited to the interannual time scale and is primarily associated with wind forcing the tropical pacific shows a strong variability in the model

precipitation over greenland and its relation to the north atlantic oscillation the equation method based on an equivalent isobaric geopotential height in coordinates has been used to retrieve the precipitation over greenland this approach is designed to accurately represent the topographic effects of the greenland ice sheet on atmospheric motion and precipitation the 11 year mean precipitation from 1985 to 1996 over all of greenland is 376 mm yr 1 which is close to the long term mean precipitation of 346 mm yr 1 estimated from glaciological data the precipitation over all of greenland shows that the largest value in 1986 is 472 mm yr 1 and the smallest value in 1995 is 309 mm yr 1 the major interannual variability of the atmospheric circulation in the north atlantic can be represented by the variation of the north atlantic oscillation nao index which is most pronounced during winter it is found that if the nao index increases the total precipitation over greenland decreases and vice versa the correlation coefficient between these two series for 1985 1995 is 0 75 the mean precipitation over southern greenland where the majority of precipitation falls is more closely related to the nao index in winter and their correlation coefficient is 0 80 this relationship can be understood from the composite maps of sea level pressure and greenland precipitation for the high and low index months during months of high nao index values the icelandic low is strong during months of low nao index values the monthly mean low is located to the southwest of greenland over the labrador sea precipitation amounts over the southeast coast of greenland are about 100 mm larger during the low nao index months than the high nao index months precipitation over all of greenland during the low nao index months is higher there are significant downward trends in annual precipitation from 1985 1995 for all of greenland and its southern and central west coastal regions amounting to about 3 per year

the evolution of ace lake antarctica determined from sedimentary diatom assemblages abstract the sediments in ace lake in the vestfold hills east antarctica contain a continuous sequence of diatom frustules that record the lake s history since its formation during the retreat of continental ice more than 9200 years ago frustules from six indicator groups pinnularia microstauron nitzschia cylindrus nitzschia curta eucampia antarctica a freshwater stauroneis species and several centric species in a sediment core were used to determine the sequence of the lake s evolution the history of the lake falls into five stages ace lake began as a marine inlet influenced by dynamic mixing of ocean and meltwater inputs as the ice sheet retreated isostatic uplift isolated the lake allowing it to be flushed by meltwater input from the retreating ice sheet over the course of 800 years 9200 8400 14c yr b p the lake became meromictic supporting a freshwater diatom assemblage approximately 6700 years ago coinciding with antarctic sea level maxima diatom assemblages indicate that seawater flooded over the sill into ace lake disturbing the freshwater meromixis the sediments in this period were laminated and contained elemental sulphur suggesting that the marine input was limited in extent and energy approximately 5500 years ago this marine input ceased and the lake again became a meromictic basin which stabilised over 1700 years to become the lake that it is today and has been with little change for about the past 4000 years