evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

easterly denitrification signal and nitrogen fixation feedback documented in the western pacific sediments 1 a sedimentary 15n record in the equatorial western pacific wp shows glacial interglacial variability from 6 2 to 11 2 during the last two climatic cycles similar to the denitrification record in the eastern tropical pacific etp contrastively a record in the south china sea scs exhibits less changes from 4 4 to 6 4 and is quite alike previously published results in marginal seas in the wp by ruling out several possible causes for the 15n variability the 15n record in the equatorial wp is interpreted as the source nitrate 15n signals advected from the etp comparison of several 15n records for the last 25 ka distributed in the wp brings out a pattern of northward decrease in 15n values and variability from the equator to off mindano and then to marginal seas supposed to be caused by the northward increase of local n2fixation therefore the less glacial interglacial changes in some 15n records in the wp could imply that the glacial decrease in subsurface 15n due to less denitrification in source waters from the etp would have been isotopically compensated by a synchronous decrease in local n2 fixation

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

climatic influence in nrm and 10be derived geomagnetic paleointensity data abstract one can determine geomagnetic paleointensities from natural remanent magnetizations nrm and by inverting production rates of cosmogenic isotopes such as 10 be and 14 c recently two independently derived 200 kyr stacks y guyodo j p valet relative variations in geomagnetic intensity from sedimentary records the past 200 000 years earth planet sci lett 143 1996 23 36 m frank b schwarz s baumann p w kubik m suter a mangini a 200 kyr record of cosmogenic radionuclide production rate and geomagnetic field intensity from 10 be in globally stacked deep sea sediments earth planet sci lett 149 1997 121 129 were compared and the good agreement was suggested to validate the use of sedimentary cores for studies both compilations use mainly the astronomically forced and climatically controlled oxygen isotope stratigraphy to date and synchronize the sedimentary records while this very curve has several coherent features with the supposedly pure geomagnetic records an nrm relative paleointensity record which was included in the conventional paleointensity stack shows correspondence with climatic features which is explained by an inadequacy in the normalization technique therefore it is possible that the extraction of the pure paleointensity signal from marine sediments has not always been accomplished

variations in solar magnetic activity during the last 200 000 years is there a sun climate connection abstract the production of 10be in the earth s atmosphere depends on the galactic cosmic ray influx that in turn is affected by the solar surface magnetic activity and the geomagnetic dipole strength using the estimated changes in 10be production rate and the geomagnetic field intensity variations in solar activity are calculated for the last 200 ka large variations in the solar activity are evident with the sun experiencing periods of normal enhanced and suppressed activity the marine 18o record and solar modulation are strongly correlated at the 100 ka timescale it is proposed that variations in solar activity control the 100 ka glacial interglacial cycles however the 10be production rate variations may have been under estimated during the interval between 115 ka and 125 ka and may have biased the results future tests of the hypothesis are discussed

astronomical theory of the pleistocene ice ages a brief historical review abstract this paper traces the evolution of the astronomical theory of the pleistocene ice ages from its origin in the work of adhemar and croll through its quantitative transformation in the hands of milankovitch to its current renaissance emphasis is given to the interplay between climatic theory and geologic observation from 1941 when milankovitch published his final version of the theory until the early 1970s most attempts to test the theory empirically were carried out in the time domain by comparing the geologic record of climate with predicted climate curves these attempts ran into serious difficulties particularly the inaccuracy of the geologic time scale and the ambiguity of climate predictions early attempts to evaluate the theory with simple radiation balance models appeared to indicate that the climatic response to secular changes in the orbit would be too small to be observed geologically but by the mid 1970s the advent of an improved time scale for pleistocene marine deposits and the availability of long closely sampled records made it possible to arrange generalized but unambiguous tests of the theory in the frequency domain by comparing orbital and climatic spectra these results decisively confirmed the idea that orbital variations significantly influenced the earth s climate during the pleistocene but they did not tell us how this influence was exercised the emphasis of current work has therefore shifted to the identification and quantitative modeling of physical mechanisms by which the climate system responds so dramatically to the predicted rather subtle changes in radiative boundary conditions

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

a comparative study of accumulation rates derived by he and th isotope analysis of marine sediments abstract we present a detailed down core analysis of helium isotope ratios and concentrations for bulk sediments from the central equatorial pacific that span the last two glacial interglacial cycles measured 3 he 4 he ratios range from 1 0 10 5 to 2 1 10 4 or 7 4 to 149 times the atmospheric ratio the 3he from interplanetary dust particles idps constitutes virtually all of the 3he measured within the sediment because carbonate accumulation rates are high in the equatorial pacific the measured 3he concentrations are lower than have been measured elsewhere and range from 4 7 10 13 to 3 0 10 12 cm3stp g 1 if the cosmic dust 3he flux is constant with time sediment mass accumulation rates can be determined from the 3he concentration in sediments the excess 230th technique is an entirely independent method for calculating sediment mass accumulation rates because its source is in situ decay of 234u in seawater to first order initial excess 230th activities correlate with 3he concentrations within this core based on the 230th results we estimate the 3he flux to the earth s surface as 9 6 2 0 10 16 cm3stp cm 2 a 1 if this flux has remained constant over extended periods of time it can be used to determine sediment accumulation rates beyond the 230th range 300 000 yr

extraterrestrial 3 he as a tracer of marine sediment transport and accumulation the deposition rate of deep sea sediments and their focused redeposition by deep sea currents can be evaluated from analyses of sedimentary 230th with a temporal resolution limited only by bioturbation6 7 10 11 230th is produced uniformly throughout the ocean by radioactive decay of dissolved 234u and is removed sufficiently fast by sorption onto sinking particles to act as a constant flux tracer of sedimentation rates but the half life of 230th 75 kyr limits its use for this purpose to the past 200 250 kyr here we explore the use of extraterrestrial 3he from interplanetary dust particles1 4 idps as a constant flux proxy that is free from this limitation a comparison of 3he with 230th in two cores from the equatorial pacific ocean indicates that the variability in the mean flux of idps over the past 200 kyr is less than 75 but in contrast to this relatively constant rate of supply of 3he to the deep sea the local burial rates of 3he and 230th have varied by a factor of five over the past 450 and 200 kyr respect ively we interpret this variability as reflecting sediment focusing with a temporal pattern that suggests regular cycles of climate driven reorganization of near bottom currents in the deep pacific ocean

the 100 kyr ice age cycle internal oscillation or inclinational forcing the ice age hypothesis of muller and macdonald 1995 1997a 1997b has two parts a the 100 kyr cycle does not owe its existence to milankovitch forcing and b variations in inclination of earth s orbit i e the orbit s angle with the solar system invariable plane provide the mechanism sought in support of the first proposition muller and macdonald point to the paradox that the spectrum of oxygen isotope series from deep sea sediments contains no power for two prominent eccentricity cycles 125 and 400 kyr in support of the second proposition they offer a match between the specmap record imbrie et al 1984 and a plot of the amplitude of orbital inclination shifted by 33 kyr the hypothesis of muller and macdonald is rejected in both parts although an influence of inclination forcing is not precluded entirely the paradox of the missing eccentricity cycles 125 and 400 kyr is explained by suppression of the two longer cycles and enhancement of the one near 96 kyr as a result of internal oscillation a muller macdonald machine for making the 100 kyr ice age cycles however conceived would have to have a memory near 30 kyr to provide for phase shift between input and output precisely this amount of memory is sufficient to produce the needed oscillation in milankovitch machine here applied thus there is no advantage from the point of view of either necessity or simplicity in replacing milankovitch forcing with its precise phasing despite the fuzzy physics with inclination forcing and with its severe problems in phasing and thus far no physics at all

an experimental evaluation of the reaction of granite with streamwater seawater and nacl solutions at 200 c abstract experiments reacting granite with streamwater seawater and nacl solutions have been conducted at 200 c 50 mpa under batch conditions using direct sampling autoclaves for durations up to 80 days granite streamwater experiments at 10 1 and 2 1 water rock ratios produced fluids of low tds the reaction of granite with seawater produced a fluid of low ph 3 5 and principal changes in the fluid chemistry as follows a gain of sio2 and losses of sulphate magnesium and calcium appreciable mobilisation of heavy metals into the fluid phase such as fe up to 15 mg l and mn up to 2 mg l were noted solid precipitates consisted of anhydrite caminite magnesium hydroxide sulphate hydrate and a mixed layer smectite chlorite clay the low ph of the evolved fluid is attributed to the precipitation of the hydroxyl consuming mineral phases caminite and the smectite chlorite clay the reaction of granite with nacl solutions 0 008 and 0 028 m produced fluids which were similar to those of the streamwater experiments however ph was lower in the nacl experiments 7 4 7 8 so that the steady state concentrations of a number of the cationic constituents of the fluids were slightly greater in these experiments compared with the streamwater experiments the dominant constituent of the product fluids excepting nacl was sio2 the concentration of which was buffered by quartz solubility the sole secondary solid product identified was a sparsely developed illitic clay the injection of a li rb cs na cl fluid into the experiments after 1000 hours demonstrated that the concentrations of the rare alkalis in the fluids were controlled by non equilibrium processes other chemical components perturbed by dilution returned to the steady states developed prior to the injection process demonstrating buffering by metastable reactions with the rock the steady state composition of the fluids was adequately predicted using an assumption of chemical equilibrium between the principal minerals of the granite and thermodynamic data for pure mineral compositions

absolute paleointensity from hawaiian lavas younger than 35 ka abstract paleointensity studies have been conducted in air and in argon atmosphere on nine lava flows with radiocarbon ages distributed between 3 3 and 28 2 ka from the mauna loa volcano in the big island of hawaii determinations of paleointensity obtained at eight sites depict the same overall pattern as the previous results for the same period in hawaii although the overall average field intensity appears to be lower since the present results were determined at higher temperatures than in the previous studies this discrepancy raises questions regarding the selection of low versus high temperature segments that are usually made for absolute paleointensity the virtual dipole moments are similar to those displayed by the worldwide data set obtained from dated lava flows when averaged within finite time intervals the worldwide values match nicely the variations of the sint 200 synthetic record of relative paleointensity and confirm the overall decrease of the dipole field intensity during most of this period the convergence between the existing records at hawaii and the rest of the world does not favour the presence of persistent strong non dipole components beneath hawaii for this period

10be in a deep sea core implications regarding10be production changes over the past 420 ka abstract the influx of 10 be into a globigerinid ooze core ch72 02 from the eastern north atlantic has been studied this core contains a depositional record of the first 11 18 o stages covering the last 423 ka it is shown that the marine deposition of 10 be is strongly influenced by the sedimentation of clays clay particles appear 10 times more efficient than the carbonate component as a carrier in bringing 10 be to the bottom sediments in core ch72 02 the deposition rates of 10 be averaged over each oxygen isotope stage for the past 11 stages show a scatter of 40 about the mean value of 6 6 10 8 atoms cm 2 ka 1 however after correction for changes in lithology the data show that the production rate of 10 be over the same period has varied no more than 25 and the variations are not systematic in that high or low 10 be production appear to be associated with either cold or warm climates on the time scale of this investigation intervals of ca 50 ka over the last 420 ka with resolutions as fine as 10 ka for portions of the record it is unlikely that the shielding effect of the solar wind has deviated by more than 25 or the geomagnetic field intensity has deviated by more than a factor of 1 6 from their long term averages

response of beryllium and radiogenic isotope ratios in northern atlantic deep water to the onset of northern hemisphere glaciation we present time corrected ratios of cosmogenic 10 be to continent sourced 9 be from two fe mn crusts located in the northwest atlantic in the vicinity of the origins of northern atlantic deep water nadw these initial 10 be 9 be ratios represent those of the ambient seawater at the time of crust deposition and are constant through the last 7 ma previously published isotope records of radiogenic nd and pb isotopes in these crusts show a decrease in e nd and an increase in 206 pb 204 pb over the last 5 ma these changes are consistent with a gradual increase in the strength of nadw production an increase in the labrador sea component of nadw or an increased erosional input into the labrador sea since the residence time and thus the advective length scales of dissolved be in deep water lie between those of nd and pb records of 10 be 9 be should contrary to what has been observed vary in phase with those of nd and pb if these variations are accounted for by changes in paleo circulation the observed variations in radiogenic nd and pb isotopes are therefore most likely to be explained with an increase in the flux of terrigenous matter in the area of the labrador sea which was possibly associated with ice rafting and selective leaching of pb isotopes an increase of the labrador sea component that contributes to nadw is also a possibility but based on the 10 be 9 be data presented here large scale changes in the thermohaline circulation can be discounted as cause for the radiogenic tracer variations

paleointensity of the geomagnetic field during the last 80 000 years high resolution records of the relative paleointensity of the geomagnetic field have been obtained from five marine cores three duplicate records were used to estimate the regional coherency of the data within a single area tyrrhrenian sea while the two others document the field variations in the eastern mediterranean and the southern indian ocean careful investigations of distinct rock magnetic parameters have established the downcore uniformity of the sediments in terms of magnetic mineralogy and grain sizes the time depth control was provided by oxygen isotopes and small scale variations in the deposition rates were constrained by means of tephrachronology the synthetic curve calculated from the mediterranean records provides a continuous record of the intensity variations during the last 80 000 years 80 kyr which correlates well with the sparse volcanic data available for the period 0 40 kyr the fact that identical behavior is seen in both data sets and that they also compare quite well with results from a core collected in the pacific ocean establishes the truly dipolar character of these variations the dipole field moment is characterized by large scale changes as shown by the existence of pronounced drops at 39 and 60 kyr alternating with periods of higher intensity the record suggests a periodic nature for these intensity variations however the period studied is not sufficiently long to state this conclusively these results demonstrate the potential of sediments for such studies and constitute a first step towards obtaining a global paleointensity record over a long period of time

the intensity of the time averaged geomagnetic field the last 5 myr the existing database for paleointensity estimates of the ancient geomagnetic field contains more than 1500 data points collected through decades of effort despite the huge amount of work put into obtaining these data there remains a strong bias in the age and global distribution of the data toward very young results from a few locations also few of the data meet strict criteria for reliability and most are of unknown quality in order to improve the age and spatial distribution of the paleointensity database we have carried out paleointensity experiments on submarine basaltic glasses from a number of dsdp sites of particular interest are the sites that provide paleointensity data spanning the time period 0 3 5 ma a time of relatively few high quality published data points our new data are concordant with contemporaneous data from the published literature that meet minimum acceptance criteria and the combined data set yields an average dipole moment of 5 49 2 36u10 22 am 2 this average value is comparable to the average paleofield for the period 5 160 ma 4 2 2 3u10 22 am 2 t juarez l tauxe j s gee and t pick 1998 nature 394 878 881 and is substantially less than the value of approximately 8u10 22 am 2 often quoted for the last 5 myr e g mcfadden

the 14c record in bristlecone pine wood of the past 8000 years based on the dendrochronology of the late c w ferguson when in 1950 willard libby and his coworkers obtained their first radiocarbon 14 c dates c w ferguson at the university of arizona tree ring laboratory was working on establishing a continuous tree ring series for the newly discovered bristlecone pine pinus aristata before his untimely death in 1986 he had extended the series nearly 8000 years into the past from the ferguson series i obtained for 14 c determinations wood samples grown at various times also two other laboratories obtained such samples for b c times in particular our measured 14 c values that deviated consistently from those calculated from tree rings and the deviations increased with age this general trend was observed by other laboratories but the presence of deviations from these trends of the so called wiggles was questioned by other workers to me these wiggles indicated the existence of a most interesting geophysical parameter valid for the whole terrestrial atmosphere fourier spectra obtained at my request by kruse in 1972 and by neftel demonstrated the consistency of the results and supported my contention that the secular variations of 14 c in atmospheric co 2 are related to variations of solar activity

analysis of 11 myr of geomagnetic intensity variation we have conducted a detailed exploratory analysis of an 11 million year long almost continuous record of relative geomagnetic paleointensity from a sediment core acquired on deep sea drilling project leg 73 at site 522 in the south atlantic we assess the quality of the paleointensity record using spectral methods and conclude that the relative intensity record is minimally influenced by climate variations isothermal remanence is shown to be the most effective normalizer for these data although both susceptibility and anhysteretic remanence are also adequate statistical analysis shows that the paleointensity variations follow a gamma distribution and are compatible with predictions from modified paleosccular variation models and global absolute paleointensity data when subdivided by polarity interval the variability in paleointensity is proportional to the average and further the average is weakly correlated with interval length spectral estimates for times from 28 77 until 22 74 ma when the reversal rate is about 4 myr 1 are compatible with a poisson model in which the spectrum of intensity variations is dominated by the reversal process in the frequency range 1 50 myr 1 in contrast between 34 7 and 29 4 ma when the reversal rate is about 1 6 myr 1 the spectra indicate a different secular variation regime the magnetic field is stronger and more variable and a strong peak in the spectrum occurs at about 8 myr 1 this peak may be a reflection of the same signal as recorded by the small variations known as tiny wiggles seen in marine magnetic anomaly profiles

increased production of cosmogenic 10be during the last glacial maximum beryllium 10 half life 1 5 myr is produced by spallation of nitrogen and oxygen atoms by cosmic rays in the upper atmosphere its production rate is proportional to the flux of cosmic rays which is modulated by solar activity and the strength of the earth s magnetic field1 2 weakening of the magnetic field allows more cosmic rays to impinge on the earth s atmosphere thereby increasing 10be production here we report that the ocean wide average accumulation rate of 10be in pacific sediments which reflects the global average production rate of 10be ref 3 was at least 25 greater during the height of the most recent ice age 24 000 16 000 yr ago than during the holocene the past 10 000 yr the higher production rate of 10be records the lower intensity of the geomagnetic field during that period and is consistent with the hypothesis developed to explain the younger 14c ages of fossil corals compared with ages obtained by u th dating4 these results also point to a more general need to consider variations in production rate in geochronological studies using other cosmogenic nuclides

solar modulation of cosmogenic nuclide production over the last millennium comparison between 14c and 10be records for about the last 30 years it has been recognized that the high frequency component of the tree rings 14c 12c record is dominated by the modulation of the cosmic ray flux by the solar wind in particular it has been demonstrated that the three most recent periods of low sunspot occurrence were characterized by high values of atmospheric 14c 12c during the last millennium other periods of high 14c 12c values were observed but their solar origin is still debatable in the present work we compare these fluctuations with an independent record of cosmogenic 10be measured in ice from the south pole to check the solar origin of the observed 14c 12c variations in order to compare quantitatively the results obtained on 10be and 14c it is necessary to take into account the different behaviour of these two cosmogenic isotopes and especially the damping effect of the carbon cycle in the case of 14c as an input to a 12 box numerical model we used the relative fluctuations of the 10be concentrations record measured in south pole ice and converted it into a synthetic 14c record we took into account the fact that 10be modulation is enhanced in polar regions due to the orientation of the geomagnetic field as expected the fluctuations of the modelled 14c record are much smaller a factor of 20 than those observed for the raw 10be record in addition the variations are smoother and shifted in time by a few decades the 10be based 14c variations closely resemble the 14c measurements obtained on tree rings r 0 81 in particular it is easy to identify periods of maximal 14c 12c which correspond to solar activity minima centred at about 1060 1320 wolf 1500 sporer 1690 maunder and 1820 dalton yr a d cross correlation calculations suggest that there is no significant lag between the 10be based 14c and the tree ring 14c records our study strongly suggests the dominance of the solar modulation on the cosmonuclide production variations during the last millennium

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

glacial cycles and astronomical forcing narrow spectral features in ocean sediment records offer strong evidence that the cycles of glaciation were driven by astronomical forces two million years ago the cycles match the 41 000 year period of earth s obliquity this supports the croll milankovitch theory which attributes the cycles to variations in insolation but for the past million years the spectrum is dominated by a single 100 000 year feature and is a poor match to the predictions of insolation models the spectrum can be accounted for by a theory that derives the cycles of glaciation from variations in the inclination of earth s orbital plane

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence