eemian cooling in the norwegian sea and north atlantic ocean preceding continental ice sheet growth changing conditions in the north atlantic region may drive global climate changes1 2 according to previous reconstructions of the last interglacial the eemian north atlantic sea surface tempera tures ssts were similar to present day values3 in the norwegian sea even warmer conditions appeared as a single pulse of short duration4 5 whereas the greenland ice record suggests that the warm interglacial air temperatures were interrupted by several cold periods6 here we use faunal and stable isotope analyses of foraminifera in two sediment cores from the north atlantic ocean and norwegian sea to reconstruct high resolution records of sst and sea surface salinity sss during the eemian interglacial our results which differ significantly from the greenland record6 show a sharp decrease in sst and sss of the norwegian sea associated with a more moderate cooling and freshening of the north atlantic at the middle of isotope substage 5e several millennia before the beginning of continental ice sheet growth changes in the norweg ian sea surface conditions appear to have represented an important climate change affecting global atmospheric and thermohaline circulations

the meridional temperature gradient in the eastern north atlantic during mis 11 and its link to the ocean atmosphere system temporal and spatial patterns in eastern north atlantic sea surface temperatures sst were reconstructed for marine isotope stage mis 11c using a submeridional transect of five sediment cores the sst reconstructions are based on planktic foraminiferal abundances and alkenone indices and are supported by benthic and planktic stable isotope measurements as well as by ice rafted debris content in polar and middle latitudes additionally the larger scale dynamics of the precipitation regime over northern africa and the western mediterranean region was evaluated from iron concentrations in marine sediments off nw africa and planktic 13c in combination with analysis of planktic foraminiferal abundances down to the species level in the mediterranean sea compared to the modern situation it is revealed that during entire mis 11c sensu stricto ss i e between 420 and 398 ka according to our age models a cold sst anomaly in the nordic seas co existed with a warm sst anomaly in the middle latitudes and the subtropics resulting in steeper meridional sst gradients than during the holocene such a sst pattern correlates well with a prevalence of a negative mode of the modern north atlantic oscillation we suggest that our scenario might partly explain the longer duration of wet conditions in the northern africa during mis 11c compared to the holocene

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

european contribution of ice rafted sand to heinrich layers h3 and h4 abstract this paper reports the sr nd isotopic composition of the carbonate free sand 63 m 1 mm fraction of heinrich layers 3 and 4 from about 17 cores from the northern atlantic ocean 38 n to 68 n the results indicate that the transporting icebergs were calved from many ice sheets from around the north atlantic at least the fennoscandian icelandic and laurentide our isotopic data show a more distinctly european origin for ice rafted debris ird deposited during the atypical heinrich event h3 than for background ird in contrast heinrich layer h4 a representative of typical heinrich events h1 h2 h4 and h5 presents a clear dominant laurentide signal this result confirms that these typical heinrich events are associated with a massive discharge of icebergs from the laurentide ice sheet however the theory that the laurentide ice sheet set the events into motion alley r b macayeal d r 1993 ice rafted debris associated with binge purge oscillations of the laurentide ice sheet paleoceanography 9 4 503 511 cannot explain the fact that a european signal of an early h4 sample has been observed prior to the laurentide signature of a late h4 sample in the same core along the european margin this observation indicates that the european ice sheets may have surged before the north american ones and suggests that the laurentide ice sheet was not the sole motor behind the heinrich events moreover in the norwegian sea ird has a scandinavian origin in both h3 and h4

suborbital scale surface and deep water records in the subtropical north atlantic implications on thermohaline overturn abstract we reconstruct millennial scale variations in sea surface hydrography and deep water flow in the northwestern subtropical atlantic ocean drilling program leg 172 sites 1056 and 1063 with a focus on marine isotope stage mis 9 together with published records from this region the new data also afford a longer term perspective on millennial scale changes in meridional overturning circulation spanning two full interglacial intervals mis 9 and 11 as well as two full glacial intervals mis 10 and 12 planktic foraminiferal 18o values indicate relatively stable conditions during the peak warmth of mis 9 but three large cold excursions disrupt the otherwise smooth transition toward glacial mis 8 there is no unique response in the site 1063 benthic foraminiferal 13c values that would suggest a concomitant decrease in the relative flux of nadw during these events similarly there is no persistent correlation between millennial scale variations in surface and deep water hydrography over the entire mis 8 13 interval while millennial scale variations at the sea surface are most pronounced during glacial intervals and the transitions toward glacial intervals millennial scale variations in the deep water hydrography tend to be largest during the warm periods this observation supports that rapid changes in thermohaline circulation are sensitive to driving forces other than those directly related to ice sheet size time series analysis shows that spectral power in the benthic foraminiferal 13c record contains periodicities related to the second 10 kyr and fourth harmonics 5 kyr of precession in this record 20 kyr pointing to the importance of tropical processes

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

dynamics of atlantic water advection to the norwegian greenland sea a time slice record of carbonate distribution in the last 300 ky abstract short term variability in volume and configuration of atlantic water advection to the norwegian greenland sea ngs has recently been identified as a new and significant element for northern hemisphere glacial interglacial climatic fluctuations the amount of salt heat and moisture transferred by atlantic waters to the high arctic effectively influences northern hemisphere climates and is critical for the overall oceanic turnover rate in particular determining the extent and duration of atlantic water intrusions in the ngs is essential because of 1 its effect on the climate of the nordic continents and 2 its trigger function on the stability of the ice sheets with a weak inflows of atlantic water during glacials promoting an increase in ice volume by moisture supply to polar areas and b positive feed back mechanisms of atlantic water intrusions during ice sheet decay in this study the dynamics of surface water mass regimes in the ngs have been reconstructed for the past 300 ky by means of time slice compilations of calcium carbonate distribution and micropaleontologic proxies in addition carbonate preservation records are used to quantify deep water ventilation and production rates in contrast to the climap scenario but in accordance with many recent publications results of this study indicate that atlantic water advection was also a common feature during most glacial periods but varied strongly in volume and configuration significant modes recognized are 1 the full interglacial mode with a wide inflow of warm atlantic waters covering a broad area in the eastern sector of the ngs and extending far north combined with excellent carbonate preservation and very efficient deep water formation stages 1 and 5 5 1 2 the moderate interglacial mode with a rather small extension of atlantic waters along a narrow corridor in the southeastern sector of the ngs but still very efficient deep water exchange stages 9 isotopic events 7 5 7 3 7 1 5 3 and 5 1 3 pronounced cool phases during interglacials with only a very narrow inflow of atlantic waters into the southeastern ngs while the coastal areas off norway were still affected by iceberg drift substages 7 4 and 5 2 carbonate preservation records indicate ongoing deep water formation in the ngs 4 the normal glacial mode characterized by a variable but persistent inflow of cool temperate atlantic water lower stage 8 repetitively during stages 6 4 3 1 and 2 carbonate preservation records indicate ongoing deep water formation in the ngs 5 short glacial and deglacial periods characterized by episodic high inputs of ird evidenced by a wide coverage of diamicton deposition and strong carbonate dissolution e g episodically within stages 10 6 and 2 the 6 5 4 3 and 2 1 transitions some of these ngs diamicton layers correlate with heinrich layers in the north atlantic but generally ngs diamicton layers occur more frequently than heinrich layers the role of atlantic water influence during these events remains enigmatic but atlantic water influence is frequently found just above and below these sections a scenario with rapid ice sheet disintegration induced by atlantic water advection via increase of the thermal regime along the ice margin possibly triggered by small scale sea level rise might be envisaged more obviously the short term cessation of deep water formation in the ngs as evidenced by the dissolution spikes may be correlated with contemporaneous ventilation minima in the north atlantic

hydrological variability in florida straits during marine isotope stage 5 cold events modeling and proxy studies indicate that a reduction of atlantic meridional overturning circulation amoc strength profoundly impacts temperatures and salinities in the sub tropical atlantic especially on subsurface levels while previous studies focused on prominent periods of amoc reduction during the last deglaciation we aim to test whether similar reconfigurations of the subtropical hydrography occurred during the moderate climatic alterations punctuating the last interglacial marine isotope stage mis 5 here we present temperature and salinity records from a florida straits core by combining d18o and mg ca analyses on surface globigerinoides ruber white and deep dwelling globorotalia crassaformis foraminifera covering mis 5 in high resolution the data reveal increasing salinities at intermediate depths during interglacial cooling episodes decoupled from relatively stable surface conditions this probably indicates the spatial expansion of saline subtropical gyre waters due to enhanced ekman downwelling and might also point to a changed density structure and altered geostrophic balance in florida straits notably these oceanographic alterations are not consistently occurring during periods of amoc reduction the data suggest that the expansion of gyre waters into florida straits was impeded by the increasing influence of antarctic intermediate water aaiw from mis 5 5 to 107 kyr bp afterward increasingly positive benthic d13c values imply a recession of aaiw allowing the temporary expansion of gyre waters into florida straits we argue that the inferred transient subtropical salt accumulation and warm pool expansion might have played a pivotal role in reinvigorating meridional overturning and dampen the severity of interglacial cold phases

comparison of changes in vegetation in northeast greece with records of climate variability on orbital and suborbital frequencies over the last 450 000 years abstract a new direct pollen orbital tuning procedure based on a correspondence between changes in certain vegetation elements and march and june perihelion configurations is applied to the tenaghi philippon record northeast greece the development of a refined chronological scheme allows comparisons to be made with records of climate variability from the north atlantic as well as of global sea level ice volume and atmospheric co2 content on orbital frequencies the comparison reveals a close correspondence between relative ice volume extent and tree population size during glacial intervals during interglacial and interstadial periods the degree of forest development is more closely associated with high latitude insolation and related climate regimes rather than extent of residual ice volume on suborbital frequencies the greek record shows similar repeat times in peaks of steppe vegetation with north atlantic ice rafting events but the amplitude of this variability in the two records is not always proportional overall what emerges is that the major shifts in the relative abundance of forest v open vegetation communities at tenaghi philippon on orbital and suborbital frequencies over the last 450 000 years are coherent with high latitude changes affecting atmospheric and oceanic circulation glacial decreases in atmospheric co2 content contributed to the elimination of tree populations by exacerbating water stress conditions during arid intervals but do not appear to be the primary driver of the observed vegetation changes at this latitude variations in co2 levels in the order of 40 ppmv between different interglacial interstadials periods with adequate moisture availability appear to have had a limited effect on the nature and size of tree populations

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

north atlantic sea surface temperatures for the last 1 1 million years summary a 1 2 ma time series of north east atlantic sea surface temperature sst has been assembled from the spliced record of piston core k 708 7 0 68 0 ma and hydraulic piston cores taken in nearby dsdp hole 552a 1 2 0 68 ma a no analogue fauna precludes making credible sst estimates in the interval 1 2 1 1 ma but the record above 1 1 ma is suitable for sst estimates and related time series analysis the amplitude of sst variation is considerably higher in the brunhes than in the upper matuyama this is due both to colder glacial sst minima after 0 85 ma and to increasingly warm interglacial sst maxima from 0 7 to 0 4 ma the dominant periodicity in the sst signal is centred near 95 000 years it increases in amplitude by a factor of four from the bottom of the record to the top with the largest increase occurring between 0 7 and 0 4 ma this suggests a relatively gradual evolution of 100 000 year power over half a million years of the late quaternary rather than a single abrupt change at 0 9 ma significant but progressively smaller spectral peaks occur at periods of 54 000 41 000 31 000 23 000 and 19 000 years both the 54 000 year and 31 000 year signals may be a response to insolation forcing by minor obliquity terms long term 18 o records show small responses by the ice sheets at or near these two periods indicating the probable initial response of the climate system to these insolation rhythms in phase relationships between 18 o and sst at these periods suggest that the ice sheets then impose these rhythms on the ocean with no lag the mechanism by which such small insolation and ice volume signals become enhanced in the sst record is not clear

timing of massive fleuve manche discharges over the last 350 kyr insights into the european ice sheet oscillations and the european drainage network from mis 10 to 2 continuous high resolution mass accumulation rates mar and x ray fluorescence xrf measurements from marine sediment records in the bay of biscay ne atlantic have allowed the determination of the timing and the amplitude of the fleuve manche channel river discharges during glacial stages mis 10 mis 8 mis 6 and mis 4 2 these results have yielded detailed insight into the middle and late pleistocene glaciations in europe and the drainage network of the western and central european rivers over the last 350 kyr this study provides clear evidence that the fleuve manche connected the southern north sea basin with the bay of biscay during each glacial period and reveals that fleuve manche activity during the glaciations mis 10 and mis 8 was significantly less than during mis 6 and mis 2 we correlate the significant fleuve manche activity detected during mis 6 and mis 2 with the extensive saalian drenthe substage and the weichselian glaciations respectively confirming that the major elsterian glaciation precedes the glacial mis 10 in detail massive fleuve manche discharges occurred at ca 155 ka mid mis 6 and during termination i while no significant discharges are found during termination ii it is assumed that a substantial retreat of the european ice sheet at ca 155 kyr followed by the formation of ice free conditions between the british isles and scandinavia until termination ii allowed meltwater to flow northwards through the north sea basin during the second part of the mis 6 we assume that this glacial pattern corresponds to the warthe substage glacial maximum therefore indicating that the data presented here equates to the drenthe and the warthe glacial advances at ca 175 160 ka and ca 150 140 ka respectively finally the correlation of our records with odp site 980 reveals that massive fleuve manche discharges related to partial or complete melting of the european ice masses were synchronous with strong decreases in both the rate of deep water formation and the strength of the atlantic thermohaline circulation fleuve manche discharges over the last 350 kyr probably participated with other meltwater sources in the collapse of the thermohaline circulation by freshening the northern atlantic surface water

modelling rates of sedimentation from icebergs abstract icebergs transport debris from ice masses into the glacimarine environment but iceberg production debris content and sedimentation rate will vary with glacier dynamics and the nature of marine waters a model incorporating glaciological and oceanographic parameters calculates the flux of debris calved in icebergs iceberg melt rates and sedimentation rates with distance from calving tidewater ice fronts the flux of basal debris calved through a 1 m width of tidewater margin is h d c 100 v c where h d and c are basal debris rich ice thickness and sediment content and v c is iceberg calving rate iceberg basal melting for any horizontal interval d x away from the calving glacier is dy m b d x v b where m b is iceberg melt rate and v b is horizontal iceberg velocity sediment release for any x increment depends on iceberg debris concentration and previous berg melt history model parameters vary with the nature of climatic conditions on a continuum from cold polar environments e g high canadian arctic antarctic peninsula through sub polar environments e g baffin island svalbard to more temperate environments e g se alaska these parameters include glacier flow velocity glacier thermal regime basal debris rich ice thickness and marine water temperature model results suggest that iceberg sedimentation rates are lowest for high polar settings and most rapid in warm maritime and some sub polar areas however icebergs in cold waters transport debris to significantly greater distances from the parent glacier the model provides calculations of order of magnitude rates of iceberg sedimentation in varying glacimarine settings

phase relationship and surface water mass change in the northeast atlantic during marine isotope stage 11 mis 11 planktic foraminiferal census data faunal sea surface temperatures ssts and oxygen isotopic and lithic records from a site in the northeast atlantic were analyzed to study the interglacial dynamics of marine isotope stage mis 11 a period thought to closely resemble the holocene on the basis of orbital forcing interglacial conditions during mis 11 persisted for approximately 26 ka after the main deglacial meltwater processes ceased a 10 to 12 ka long transitional period marked by significant water mass circulation changes occurred before surface waters finally reached their thermal maximum this sst peak occurred between 400 and 397 ka inferred from the abundance of the most thermophilic foraminiferal species and was coincident with lowest sea level according to benthic isotope values the ensuing stepwise sst decrease characterizes the overall climate deterioration preceding the increase in global ice volume by 3 ka this cooling trend was followed by a more pronounced cold event that began at 388 ka and that terminated in the recurrence of icebergs at the site around 382 ka because the water mass configuration of early mis 11 evolved quite differently from that of the early holocene there is little evidence that mis 11 can serve as an appropriate analogue for a future holocene climate despite the similarity in some orbital parameters

recession of the southern part of barnes ice cap baffin island canada between 1961 and 1993 determined from digital mapping of landsat tm changes along the margin of the southern half of the 5900 km 2 barnes ice cap have been assessed using 1993 landsat tm imagery in comparison with digitized 1 50 000 nts maps based on 1961 photogrammetry the average recession over the 183 km long southern perimeter was found to be at least 4 m a 1 with no significant difference between the southeast and southwest sectors viewed in conjunction with the sustained retreat previously reported for the northwest margin these results indicate that a general reduction in the size of barnes ice cap is occurring the present retreat phase began under a regional climate warming in the late 19th to early 20th century period and continues while the record of the ablation season temperature since the midcentury has not shown any significant trend

glacial interglacial instabilities of the western boundary under current during the last 365 kyr from sm nd ratios of the sedimentary clay size fractions at odp site 646 labrador sea we present 40 sm nd isotope measurements of the clay size 2 m fractions of sediments from the sout hern greenland rise odp 646 that span the last 365 kyr these data track changes in the relative supply o f fine particles carried into the deep labrador sea by the western boundary under current wbuc back to the fourth glacial interglacial cycles earlier studies reveal ed three general sources of particles to the core s ite i precambrian crustal material from canada greenland and or scandinavia north american shield nas ii palaeozoic or younger crustal material from east gr eenland nw europe and or western scandinavia young crust yc and iii volcanic material from iceland and the mid atlantic ridge mar clay size fractions from glacial sediments have the lowest nd isotopic ratios supplies of young crustal particles were si milar during glacial oxygen isotope stages ois 2 6 and 10 i n contrast the mean volcanic contributions decrease d relative to old craton material from ois 10 to ois 6 and the n from ois 6 to ois 2 the glacial ois 8 interval d isplays a mean sm nd ratio similar to those of interglacials ois 1 5 and 9 compared with other interglacials ois 7 was marked by a higher yc contribution but a similar 3 0 mar supply the overall nas contribution dropped by a factor of 2 during each glacial interglacial tran sition with the mar contribution broadly replacing it during interglacials to decipher between higher supplies and or dilution particle fluxes from each end memb er were estimated glacial nas fluxes were systematically h igher than interglacial fluxes during the time int erval examined fine particle supplies to the labrador se a were strongly controlled by proximal ice margin e rosion and thus echoed the glacial stage intensity in con trast the wbuc carried mar supplies from the eastern basins did not change significantly throughout the last 36 5 kyr except for a marked increase in surface sedi ments that suggests unique modern conditions distal wbuc controlled inputs from the northern and ne north atlant ic seem to have been less variable than proximal suppl ies linked with glacial erosion rate

modeling the effect of freshwater pulses on the early holocene climate the influence of high frequency climate variability freshwater 4 67 10 14 m 3 into the labrador sea at three different constant rates 1 5 sv 1 sv 1 10 6 m 3 s 1 i n 10 years 0 75 sv in 20 years and 0 3 sv in 50 years for each rate five ensemble experiments have been performed varying in initial conditions the freshwater pulses produce a weakening of the thermohaline circulation the perturbed state is in agreement with proxy evidence for the 8 2 ka event two types of recovery of the thermohaline circulation occurred differing in time scale 1 200 years and 2 200 years in the experiments with 10 year and 20 year pulses both types of recovery were observed this suggests that the model response is unpredictable in the range of parameters studied here it is hypothesized that the unpredictability is associated with annual to decadal climate variability our results demonstrate that several types of recovery may exist with the same kind of perturbation the interpretation of events observed in proxy data may be thus more complex than realized until now since the magnitude and duration of climatic events caused by freshwater pulses is likely to depend strongly on nonlinear dynamics inside the coupled atmosphere sea ice ocean system index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4255 oceanography general numerical modeling 4532 oceanography physical general circulation 4215 oceanography general climate and interannual variability 3309 9325 information related to geographic region atlantic ocean keywords holocene thermohaline circulation predictability meltwater coupled climate model

insights into north atlantic deep water formation during the peak interglacial interval of marine isotope stage 9 mis 9 foraminifera abundance and stable isotope records from odp site 984 61 25 n 24 04 w 1648 m in the north atlantic are used to reconstruct surface circulation variations and the relative strength of the north atlantic deep water nadw formation over the period spanning the peak warmth of marine interglacial stage mis 9e 324 336 ka this interval includes the preceding deglaciation termination 4 t4 and the subsequent glacial inception of mis 9d the records indicate a greatly reduced contribution of nadw during t4 as observed in more recent deglaciations in contrast with the most recent deglaciation the lack of a significant nadw signal extended from t4 well into the peak interglacial mis 9e and persisted nearly until the transition to the subsequent glacial stage mis 9d although nadw formation resumed during mis 9e only depths greater than 2000 m appear to have been ventilated the poorly ventilated intermediate depth of site 984 2000 m may have resulted on one hand from a general reduction of deep water ventilation by nadw during the study interval or on the other hand from different pathways of the spread of newly formed nadw that bypassed the study location the intermediate depths may have also been invaded by southern sourced waters as the formation of intermediate depth nadw weakened the absence of any significant nadw signal at the water depth of site 984 during the climatic optimum contrasts sharply with subsequent interglacial peaks mis 5e and the holocene despite the perturbed intermediate depth circulation oceanic heat transport northeastward was not interrupted and may have contributed to the relatively mild interglacial conditions of mis 9e

interglacials of the last 800 000 years interglacials including the present holocene period are warm low land ice extent high sea level end members of glacial cycles based on a sea level definition we identify eleven interglacials in the last 800 000 years a result that is robust to alternative definitions data compilations suggest that despite spatial heterogeneity marine isotope stages mis 5e last interglacial and 11c 400 ka ago were globally strong warm while mis 13a 500 ka ago was cool at many locations a step change in strength of interglacials at 450 ka is apparent only in atmospheric co2 and in antarctic and deep ocean temperature the onset of an interglacial glacial termination seems to require a reducing precession parameter increasing northern hemisphere summer insolation but this condition alone is insufficient terminations involve rapid nonlinear reactions of ice volume co2 and temperature to external astronomical forcing the precise timing of events may be modulated by millennial scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere a variety of temporal trends is observed such that maxima in the main records are observed either early or late in different interglacials the end of an interglacial glacial inception is a slower process involving a global sequence of changes interglacials have been typically 10 30 ka long the combination of minimal reduction in northern summer insolation over the next few orbital cycles owing to low eccentricity and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future

changes in the vertical structure of the north atlantic ocean between glacial and modern times the distribution of planktic foraminiferal 18o over the north atlantic ocean has been interpreted by duplessy et al 1991 1992 in terms of the distribution of surface water salinity during the last glacial maximum lgm and the younger dryas yd we present here the implications of this surface salinity distribution for changes in deep convection during these periods temperature salinity density diagrams of the water column have been constructed using the plancktic and benthic foraminifera 18o values together with sea surface temperature estimates obtained by using micropaleontological transfer functions the precision of these reconstructions is limited by the remaining uncertainties in the two basic assumptions upon which the methods are based the sea surface temperature reconstruction by climap are valid within the statistical uncertainties the water salinity 18o relationship is well constrained for surface and intermediate ocean waters a significant difference between the modern and the reconstructed glacial water structure is observed during the lgm the modern relatively warm and salty norwegian sea surface water and the north atlantic deep water nadw were replaced by low salinity surface water in the northern atlantic ocean and the norwegian sea and cold deep water 0 1 c however surface water salinity in the central north atlantic ocean 52 54 n 25 40 w was sufficiently high to permit deep water convection as a source of north atlantic intermediate and deep waters open ocean convection at the northern limit of the subtropical surface waters around 40 n may have contributed to the ventilation of the intermediate waters the waters deeper than 2000 m were the result of mixing between poorly oxygenated southern waters and well ventilated north atlantic deep waters a similar reconstruction for the cold yd period indicates that the modern type of circulation with warm and ventilated nadw was largely in operation and that the hydrologic pattern was different from that prevailing during the lgm

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

microfabric and mineralogical studies on the stabilization of an expansive soil using cement by pass dust and some types of slags this paper describes the microfabric and mineralogical aspects of the expansive soil of al khod northern oman treated with cement by pass dust cbpd copper slag slag cement and granulated blast furnace slag gbfs first the engineering properties and chemical and mineralogical composition of the untreated soil were determined the soil was then mixed with the additives at 3 6 and 9 of the dry weight of the soil the microfabric and mineralogical characteristics of the treated soil were determined the high amounts of calcium ions and calcium oxide which produces calcium ions react with the clay particles through a cation exchange process resulting in the formation of aggregations and reduction of the swell potential of the soil mineralogical tests on the treated samples indicated a general reduction in all clay minerals peak intensities particularly in the case of cbpd treated samples the fabric of the untreated soil is composed of dense clay matrices with no appearance of aggregations or

analysis of the railway heave induced by soil swelling at a site in southern france in order to better understand the heave observed on the railway roadbed of the french high speed train tgv at chabrillan in southern france the swelling behaviour of the involved expansive clayey marl taken from the site by coring was investigated the aim the study is to analyse the part of heave induced by the soil swelling first the swell potential was determined by flooding the soil specimen in an oedometer under its in situ overburden stress on the other hand in order to assess the swell induced by the excavation undertaken during the construction of the railway a second method was applied the soil was first loaded to its in situ overburden stress existing before the excavation it was then flooded and unloaded to its current overburden stress after the excavation the swell induced by this unloading was considered finally the experimental results obtained were analyzed together with the results from other laboratory tests performed previously and the data collected from the field monitoring this study allowed estimating the heave induced by soil swelling subsequently the part of the heave due to landslide could be estimated which corresponds to the difference between the monitored heave and the swelling heave

were the north atlantic heinrich events triggered by the behavior of the european ice sheets theories explaining the origin and distribution of heinrich layers abrupt massive discharges of ice rafted detritus generally attribute these layers to the laurentide ice sheet however doubt has been cast by the discovery that sediments also originated from european ice sheets here we present isotopic sr nd fingerprints of heinrich layers obtained in cores from the european margin they reveal that for most of the heinrich layers the icebergs were calved first from the european ice sheets predating the laurentide surges accelerator mass spectrometry 14c ages reveal that the oceanic heinrich events were synchronous with their dust equivalents in the greenland ice cores implying a direct ocean atmosphere link the typical laurentide surge seems to have occurred over a short time span after about 1 5 k y of iceberg release from the european ice sheets this suggests that the laurentide ice sheet responded to a stimulus created by events in the european sector

simulation of abrupt climate change induced by freshwater input to the north atlantic ocean temperature records from greenland ice cores1 2 suggest that large and abrupt changes of north atlantic climate occurred frequently during both glacial and postglacial periods one example is the younger dryas cold event broecker3 speculated that these changes result from rapid changes in the thermohaline circulation of the atlantic ocean which were caused by the release of large amounts of melt water from continental ice sheets here we describe an attempt to explore this intriguing phenomenon using a coupled ocean atmosphere model in response to a massive surface flux of fresh water to the northern north atlantic of the model the thermohaline circulation weakens abruptly intensifies and weakens again followed by a gradual recovery generating episodes that resemble the abrupt changes of the ocean atmosphere system recorded in ice and deep sea cores4 the associated change of surface air temperature is particularly large in the northern north atlantic ocean and its neighbourhood but is relatively small in the rest of the world

remote sensing science and technology for studying glacier processes in high asia a large number of multispectral and stereo image data are expected to become available as part of the global land ice measurements from space project we investigate digital elevation model extraction anisotropic reflectance correction and selected glacier analysis tasks that must be developed to achieve full utility of these new data results indicate that glaciers in the karakoram and nanga parbat himalaya northern pakistan exhibit unique spectral spatial and geomorphometric patterns that can be exploited by various models and algorithms to produce accurate information regarding glacier extent supraglacial features and glacier geomorphology the integration of spectral spatial and geomorphometric features coupled with approaches for advanced pattern recognition can help geoscientists study glacier mass balance glacier erosion sediment transfer efficiency and landscape evolution

monitoring termination ii at high latitude anomalies in the planktic foraminiferal record microfaunal studies of planktic foraminifera carried out on 21 sediment cores from the norwegian greenland sea ngs reveal the spatial and lateral distribution as well as meltwater implication of today s non polar subpolar species beella megastoma earland previous findings are verified in that this foraminifera is characteristic only of the deglaciation phases of termination ii iii and vi and not the ensuing interglacial optima thus rendering this species a meltwater indicator its distribution is restricted to cores from the central i e more pelagic part of the ngs covering an area as far north as 77 latitude a detailed investigation of termination ii indicates that b megastoma first appeared in the southwest of the ngs at 131 ka and then about 6 kyr later in the eastern and northern parts of the ngs for the entire duration b megastoma always coincided with the deposition of distinct ice rafted detritus ird suggesting the presence of drifting icebergs during this period two different oceanographic models each with a two stepped evolution of the post saalian surface water circulation are proposed to account for this time transgressive character the mechanism of brine formation as possible oceanic phenomenon forcing atlantic water northwards is suggested for being responsible for the occurrence of b megastoma in the ngs during early termination ii the presence of b megastoma always ceased with the culmination of the interglacial optimum oxygen isotopic substage 5 51 eemian when the subpolar foraminiferal fauna reached highest abundances and a general lack of ird is observed

the new remote sensing derived swiss glacier inventory ii first results complete swiss glacier inventories are available for 1850 reconstructed and 1973 from aerial photography connected to the global land ice measurements from space project a new swiss glacier inventory for approximately the year 2000 sgi 2000 is compiled mainly based on satellite imagery the developed and applied remotesensing and geographical information system gis methods are described in part i of the contribution in part ii the inventory design first result analyses and comparisons with former glacial conditions are presented as basic entries sgi 2000 contains the individual glacier identification planimetric glacier boundaries as derived from image analysis digitized central flowlines and polygonal glacier basin maps all other parameters are automatically deduced from the above entries and a digital elevation model within a gis here we analyze a set of small bernese and valais glaciers of area 2 these glaciers lost about 21 of area from 1973 to 1998 in addition to about 80 during 1850 1973 both with respect to the 1973 area in order to track the latest trend in more detail anintermediate glacier condition has been compiled from satellite imagery of 1985 this analysis gave an increasing speed of area loss 19 for 1985 98

asynchronous deposition of ice rafted layers in the nordic seas and north atlantic ocean instabilities in ice stream flow within the north american laurentide ice sheet leading to the periodic release of armadas of icebergs into the north atlantic ocean over the past 60 000 years have produced extensive layers of coarse grained iceberg rafted debris heinrich layers in north atlantic sediments1 2 correlation of these layers with iceberg discharge events from the ice sheets on greenland iceland and scandinavia suggested in previous studies for some heinrich layers and in some areas3 4 5 would imply that ice sheet instability had been synchronous across the north atlantic presumably in response to a common environmental cause here we show a lack of widespread systematic correlations both between ice rafted debris layers in different sediment cores from the nordic seas and between the nordic layers and the north atlantic heinrich layers this suggests that the full glacial nordic ice sheets did not exhibit unstable behaviour coincident with iceberg discharge from the vast hudson bay drainage basin of the laurentide ice sheet6 7 off the hudson strait significant ice sheet discharge of melt water is indicated by size sorted sandy and muddy turbidite sediments different from the poorly sorted debris flows which dominate sedimentation on the margins of the nordic seas8 9 10 together these results suggest that the dynamics of quaternary ice sheets surrounding the nordic seas were different from the outlet glacier draining the hudson bay basin and they provide evidence against a common circum north atlantic mechanism driving the discharge of icebergs

towards an understanding of the response of southern european vegetation to orbital and suborbital climate variability abstract in recent years the generation of high resolution terrestrial and marine long pollen sequences with improved chronological control has provided new insights into the vegetation response in southern europe to orbital and suborbital climate variability here a synthesis of our current understanding of the phase and amplitude relationships between climate forcing and vegetation changes is presented what emerges is that on orbital frequencies the timing of interglacial forest expansion is closely linked to the summer insolation maximum but does not have a fixed lag relative to the mid point of the deglaciation which may vary from one termination to another for the closing phases of interglacials the available evidence suggests that forest in southern europe usually extends into the interval of ice growth however suborbital variability may override the diachronous relationship between glacial inception and forest decline leading to a premature ending of forest periods during glacial intervals there is a close correspondence between tree population size and ice volume extent while during temperate intervals the extent of forest development is closely related to the amplitude of insolation and associated climate regimes but may diverge from the extent of residual ice volume on suborbital frequencies changes in tree population size are in phase with climate forcing while the amplitude of these changes is modulated by geographical position and local factors finally orbital mean state can lead to the modulation of the amplitude of suborbital scale variability examination of additional climatic cycles and increased resolution better than 200 years are needed to test further these preliminary conclusions

spatial variability of glacier elevation changes in the swiss alps obtained from two digital elevation models 1 massive glacier thinning in the alps during the past 20 years is documented by direct mass balance measurements on nine regularly observed glaciers how representative this limited sample of glaciers is for the entire alps however remained uncertain the near global digital terrain model from the srtm enables a closer analysis of this question which is of fundamental importance to assess overall glacier volume change here we present elevation changes from 1985 to 1999 for about 1050 glaciers in the swiss alps the analysis reveals extreme thickness losses 80 m for flat low lying glacier tongues and a strong overall surface lowering the mean cumulative mass balance of the nine glaciers with direct measurements 10 8 m w e agrees well with the mean change of the entire region from dem differencing 11 m w e and can thus be considered to be representative mean thickness change of individual glaciers is correlated with their size elevation and exposure to solar irradiation this implies that mass losses of large glaciers can be underestimated when they are directly inferred from values measured at much smaller glaciers

the mis 11 paradox and ocean circulation role of millennial scale events the role of millennial scale climate variability in supplementing the astronomical forcing of glacial interglacial transitions remains a major unresolved question here we compare the occurrence and character of terminal ice rafting events in both the north and south atlantic during the last deglaciation termination i ti and during the transition between marine isotope stages mis 12 and 11 or termination v tv we show that tv experienced a massive terminal ice rafting event in the north atlantic that was more intense and longer lasting than heinrich event 1 h1 of the last deglaciation this massive ice rafting event was linked to cold stadial conditions and reduced deep water formation in the north atlantic in parallel with warming at high southern latitudes similar to the bipolar seesaw pattern exhibited during h1 over the last deglaciation we propose that the particular intensity and duration of the tv ice rafting event resulted from the especially large volume of northern hemisphere ice sheets during mis12 in turn the unusually long duration and large amplitude of tv likely resulted from the exceptionally prolonged collapse of the amoc during the tv heinrich stadia and from a subsequent transient amoc overshoot with respect to later mis11 interglacial circulation furthermore we suggest that the intense heinrich stadial of tv contributed to the deglaciation primarily via meridional heat transport anomalies that would have enhanced the incipient warming arising from relatively weak insolation forcing and only secondarily via co2 release

geological and engineering characteristics of expansive soils and rocks in northern oman the geology and former climate of northern oman favoured the formation of smectite clay minerals in certain materials which are implicated in ground heave problems investigations have shown that the smectite content of these expansive materials was developed in oligocene miocene and pliocene times no evidence of a significant content of smectite was found in pre eocene strata or in quaternary strata except for desert fill it is shown that the main types of expansive materials in northern oman are bentonitic mudstones marls and silty mudstones argillaceous dolomitic limestone altered conglomerates and the desert fill derived from these these swelling materials exist as impersistent bands within the bedrock tertiary conglomerates and limestones a geotechnical testing program was carried out on undisturbed samples from sultan qaboos university staff housing areas where building damage had occurred to evaluate mineralogical composition cation content and swelling characteristics the test results characterized these soils rocks as highly expansive type with na smectite as the dominant clay mineral

late quaternary deep sea ostracodes in the polar and subpolar north atlantic paleoecological and paleoenvironmental implications two sediment cores from the northern north atlantic one from the iceland plateau and one from the rockall plateau were investigated in order to examine the response of deep sea benthic ostracodes to climate related environmental changes since marine isotope stage mis 7 ostracode fauna was divided into three factor assemblages by using q mode factor analyses and diversity was calculated using the shannon wiener index the iceland plateau revealed an interglacial assemblage dominated by henryhowella a transitional assemblage dominated by eucythere and a background assemblage that consists of the common taxa krithe and cytheropteron the presence of henryhowella is linked to conditions that prevailed during the peak interglacial periods mis 5e and 1 characterized by increased food supply well oxygenated bottom water and lateral advection the presence of eucythere mainly during the interstadial periods appears to be related to slightly increased food supply whereas the background assemblage is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times on the rockall plateau the opportunistic background assemblage consisting mainly of krithe argilloecia and cytheropteron shows no obvious relation to climate changes the interglacial assemblage consists of several taxa dominated by pelecocythere but as on the iceland plateau it also contains henryhowella the third assemblage is the glacial assemblage that consists of a variety of taxa several of which are known from the modern arctic ocean and the greenland sea shelf thus this assemblage indicates glacial conditions on the rockall plateau that are comparable to those found in the present day arctic ocean diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg rafted debris ird in the rockall plateau core both cores reveal lower surface water productivity during the glacial compared to the interglacial periods and particularly low productivity during the ird events as inferred from carbonate contents we assume therefore that ostracode diversity in the study areas is negatively correlated with food flux

species composition and glacial interglacial variations in the ostracode fauna of the northeast atlantic during the past 200 000 years sediment core m23414 from the rockall plateau north atlantic covering the last two climatic cycles marine isotope stages mis 7 to 1 was investigated for glacial interglacial variations in the deep sea benthic ostracode fauna a highly diversified ostracode fauna including 98 species was found two climate related assemblages were identified associated with interglacial and peak glacial periods respectively the interglacial group occurs during the end of mis 7 5 and 1 and is composed of the genera henryhowella pelecocythere echinocythereis cytherella bradleya aversovalva and eucytherura the glacial group consists of the genera acetabulastoma which is known as sea ice indicator in the modern arctic ocean polycope bythoceratina rhombobythere and some species possibly belonging to the genus pseudocythere and is found during mis 6 4 and 2 these longer term variations within the ostracode fauna seem related to the particular glacial and interglacial climate conditions that affected both deep water production as well as primary production in the surface waters however a detailed comparison of ostracode abundances with the occurrence of events marked by increased ice rafted debris reveals also much shorter term climate related changes in the ostracode fauna thus the temporal fluctuations within ostracode assemblages reflect long and short term alterations of the deep sea environment that are clearly linked to climate changes

a 1 0 myr record of glacial north atlantic intermediate water variability from odp site 982 in the northeast atlantic changes in the intermediate water structure of the north atlantic were reconstructed using benthic foraminiferal 13c at ocean drilling program odp site 982 for the past 1 0 myr during most terminations of the late pleistocene melting of icebergs and low salinity surface waters caused production of glacial north atlantic intermediate water to cease resulting in decreased ventilation of the middepth north atlantic poor ventilation of intermediate water masses lasted well into some interglacial stages until upper north atlantic deep water nadw production resumed under full interglacial conditions the magnitude of benthic 13c minima and ice rafted debris maxima at terminations at site 982 generally match the degree of glacial suppression of nadw inferred from site 607 these processes may be related and controlled by the spatial and seasonal extent of sea ice cover during glaciations in the nordic seas

interannual variability of planktic foraminiferal populations and test flux in the eastern north atlantic ocean jgofs planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties between water masses and after periodical changes and episodic events e g reproduction storms distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data in this paper we discuss the short term impacts on interannual flux rates based on data from opening closing net hauls obtained between the ocean surface and 500 m water depth data were recorded during april may june and august at around 47 n 20 w biotrans in 1988 1989 1990 1992 1993 and during may 1989 and 1992 at 57 n 20 22 w species assemblages closely resemble each other when comparing the mixed layer fauna with the fauna of the upper 100 m and the upper 500 m of the water column in addition species assemblages 100 m are almost indistinguishable from assemblages that are 125 m in test size the standing stock of planktic foraminifers at biotrans can vary by more than one order of magnitude over different years however species assemblages may be similar when comparing corresponding seasons early summer assemblages june are distinctly different from late summer assemblages august significant variations in the species composition during spring april may are independent of the mixed layer depth spring assemblages are characterized by high numbers of globigerinita glutinata in particular day to day variations of the number of specimens and in species composition may have the same order of magnitude as interannual variations this appears to be independent of the reproduction cycle species assemblages at 47 n and 57 n are similar during spring although surface water temperatures and salinities differ by up to 10 c and 0 7 psu we suggest that the main factors controlling the planktic foraminiferal fauna are the trophic properties in the upper ocean productive layer planktic foraminiferal carbonate flux as calculated from assemblages reveals large seasonal variations a quasi annual periodicity in flux levels and substantial differences in timing and magnitude of peak fluxes at the biotrans station the average annual planktic foraminiferal caco 3 fluxes at 100 and 500 m depth are estimated to be 22 4 and 10 0 g m 2 yr 1 respectively

variable sequence of events during the past seven terminations in two deep sea cores from the southern ocean the relationships among internally consistent records of summer sea surface temperature ssst winter sea ice wsi and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from odp sites 1093 and 1094 the sequence of events at both sites indicates that ssst and wsi changes led the carbon and nitrogen isotopic changes in three terminations ti tii and tvi and followed them in the other four terminations tiii tiv tv and tvii in both tiii and tiv the leads and lags between the proxies were related to weak glacial mode while in tv and tvii they were due to the influence of the mid pleistocene transition we show that the sequence of events is not unique and does not follow the same pattern across terminations implying that the processes that initiated climate change in the southern ocean has varied through time

photogrammetric reconstruction of glacier mass balance using a kinematic ice flow model a 20 year time series on grubengletscher swiss alps the kinematic boundary condition at the glacier surface can be used to provide glacier mass balance at individual points if changes in surface elevation horizontal and vertical surface velocities and surface slope are known vertical ice velocity can in turn be estimated from basal slope basal ice velocity and surface strain this relation is applied to reconstruct a 20 year mass balance curve of grubengletscher swiss alps largely using repeated aerial photogrammetry but only a minimum of field work for individual years the mass balance distribution on the glacier tongue was modelled with an accuracy of about 0 9 m a 1 ice mechanical assumptions and errors in glacier bed geometry markedly affect discrete mass balance patterns but are eliminated to a major extent when calculating year to year mass balance changes the resulting curve for the grubengletscher tongue 1973 1992 shows reasonable consistency with meteorological data and other glaciologically derived mass balance series large changes in measured ice speed on the glacier tongue 50 significantly governed the long term variability of ice thickness over the observational period

interglacial responses of the southern greenland ice sheet over the last 430 000 years determined using particle size specific magnetic and isotopic tracers abstract the past behavior of the greenland ice sheet can provide important insight into climatic thresholds that may initiate and drive major ice sheet retreat particle size specific magnetic and sr nd pb isotope records from eirik ridge sediments south of greenland track southern greenland ice sheet sgis erosional signatures over the past 430 ka by discriminating changes in sediment source and transport over the eirik ridge ground truthed magnetic and isotopic compositions of subglacial silt from south greenland s precambrian bedrock terranes constrain independent magnetic and isotopic estimates of eirik ridge silt provenance which in turn indicate that the southern greenland ice sheet sgis retreated within its present margin during three of the four previous interglaciations over the past 430 ka retreat of the sgis was extensive during the marine isotope stage mis 5e 9 and 11 interglaciations continuing unabated despite declining insolation during mis 5e and 9 with near complete deglaciation in mis 11 retreat of the sgis during mis 7 was minimal notwithstanding strong insolation forcing while holocene retreat slowed shortly after peak insolation the reconstruction of sgis retreat during the last five deglacial and interglacial periods suggests that a threshold for extensive sgis retreat exists between the insolation and co 2 states of the holocene and the mis 5e and 9 interglaciations with co 2 exerting a stronger control on sgis retreat than insolation our results also suggest that the extent and stability of the sgis in the holocene is anomalous in the context of late quaternary interglaciations

the climate influence on the mid depth northeast atlantic gyres viewed by cold water corals 1 the neodymium nd isotopic composition expressed in epsilon units nd of reef framework forming cold water corals provides unique measures of water mass provenance and mixing within the northeast atlantic today and in the past a reconstruction of near thermocline water nd from cold water corals of the gulf of cadiz and porcupine seabight spanning over the past 300 000 years now revealed that climate cooling during marine isotope stages mis 7 2 and mis 8 9 led to a retraction of the mid depth subpolar gyre mspg to the west conversely northern hemisphere warming and increasing fresh water fluxes to the northwest labrador sea favor a stronger eastward extension of the mspg blocking the northward flow of temperate atlantic water as observed during the early mis 1 and the early stage mis 5 5 these changes are likely the result of large scale south north displacement of the westerlies similar to present day observations that the north atlantic oscillation nao is linked with mid depth ocean circulation based on these observations we hypothesize that further climate warming will also strengthen the mspg leading to a salt and temperature decrease in the northeast atlantic whereas salinity and temperature will increase in the temperate atlantic however the amplitude of such changes on north atlantic overturning remains to be tested

surface and deep water changes in the subpolar north atlantic during termination ii and the last interglaciation to reconstruct the history of water mass exchange between the ne atlantic and the nordic seas sediment cores from 2 km water depth were studied across termination ii tii and through the last interglaciation mis5e during early tii the sudden appearance of the low latitude planktonic foraminifera beella megastoma is noted in both regions along with a steep decrease in benthic foraminiferal 18o since other proxies indicate that surface waters were cold and stratified because of meltwater conditions which prevented near surface thermohaline circulation and vertical convection in the nordic seas water mass exchange between the two areas occurred at the subsurface during later tii surface conditions changed and this subsurface circulation style was eventually replaced by vertical convection in the nordic seas b megastoma vanished from the record together with ice rafted debris ird at the end of tii while subpolar foraminiferal abundance rose peak interglacial conditions with intensive vertical convection now fully developed generating a bottom water temperature gradient of 4 c between the two areas however surface water temperatures deteriorated in the nordic seas already notably before ird recurred and 18o increased at the end of mis5e

comparison of glacial and interglacial conditions between the polar and subpolar north atlantic region over the last five climatic cycles a multiparameter based interpretation of sediment records from the northeast atlantic and the western nordic seas suggests that during the last 500 000 years only in marine isotopes stage mis 11 5e and 1 were there somewhat comparable interglacial boundary conditions in both regions i e strongly reduced occurrence of iceberg rafted debris ird and high carbonate bioproductivity although the northeast atlantic experienced such conditions during all peak interglaciations with the exception of mis 7 planktic foraminiferal 18o from this region would still indicate that significantly colder sea surface temperatures sst prevailed during mis 11 than during mis 9 5e and 1 this assumption is corroborated by a continuous input of ird into the western nordic seas during mis 11 implying a much steeper sst gradient between the polar and subpolar region and an overall reduced thermohaline activity in the polar latitudes the iceberg proxy also reveals that maximum ird discharge always happened during the final phase of glaciation and into early deglaciation terminations as these ird records from the two regions are characterized by a high time coherency it is concluded that short term variability is a persistent feature of the glacial climate system

nutrient regime at the siliceous belt of the atlantic sector of the southern ocean during the past 660 ka 1 sediment cores from ocean drilling program sites 1094 and 1093 hold the most extensive and most detailed records of carbon and nitrogen isotopes of diatom bound organic matter in the atlantic sector of the southern ocean over the past 660 ka these records were combined with summer sea surface temperatures and winter sea ice that were deduced from diatom transfer functions to reconstruct the nutrient regime at the northern and southern boundaries of the siliceous belt at latitudes 53 s and 50 s respectively the strong coupling between carbon and nitrogen isotope records at site 1093 suggests that the diatom productivity was influenced mainly by changes in nutrient availability the anticorrelation between the carbon and nitrogen isotopes at site 1094 suggests that the diatom productivity was closely linked to global temperature changes sea ice coverage and dissolved co2 concentration a detailed comparison of the nitrogen isotope records between the two sites shows three time intervals that represent different nutrient regimes the nutrients at site 1093 which is close to the polar front were dominated by eddies and meanders that sustained relatively high productivity at times of stratification or reduced ventilation whereas at site 1094 the nutrients were influenced by ventilation processes

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

evidence for a steeper eemian than holocene sea surface temperature gradient between arctic and sub arctic regions sediment proxy data from the norwegian greenland and iceland seas nordic seas are presented to evaluate surface water temperature sst differences between holocene and eemian times and to deduce from these data the particular mode of surface water circulation records from planktic foraminiferal assemblages caco3 content oxygen isotopes of foraminifera and iceberg rafted debris form the main basis of interpretation all results indicate for the eemian comparatively cooler northern nordic seas than for the holocene due to a reduction in the northwardly flow of atlantic surface water towards fram strait and the arctic ocean therefore the cold polar water flow from the arctic ocean was less influencial in the southwestern nordic seas during this time as can be further deduced from the eemian data slightly higher eemian ssts are interpreted for the western iceland sea compared to the norwegian sea ca south of 70 n this eemian situation is in contrast to the holocene when the main mass of warmest atlantic surface water flows along the norwegian continental margin northwards and into the arctic ocean thus a moderate northwardly decrease in sst is observed in the eastern nordic seas for this time causing a meridional transfer in ocean heat due to this distribution in ssts the holocene is dominated by a meridional circulation pattern the interpretation of the eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in ssts

dating late quaternary planktonic foraminifer neogloboquadrina pachyderma from the arctic ocean using amino acid racemization the long term rate of racemization for amino acids preserved in planktonic foraminifera was determined by using independently dated sediment cores from the arctic ocean the racemization rates for aspartic acid asp and glutamic acid glu in the common taxon neogloboquadrina pachyderma were calibrated for the last 150 ka using 14c ages and the emerging quaternary chronostratigraphy of arctic ocean sediments an analysis of errors indicates realistic age uncertainties of about 12 for asp and 17 for glu fifty individual tests are sufficient to analyze multiple subsamples identify outliers and derive robust sample mean values the new age equation can be applied to verify and refine age models for sediment cores elsewhere in the arctic ocean a critical region for understanding the dynamics of global climate change

the new remote sensing derived swiss glacier inventory i methods a new swiss glacier inventory is to be compiled from satellite data for the year 2000 the study presented here describes two major tasks 1 an accuracy assessment of different methods for glacier classification with landsat thematic mapper tm data and a digital elevation model dem 2 the geographical information system gis based methods for automatic extraction of individual glaciers from classified satellite data and the computation of three dimensional glacier parameters such as minimum maximum and median elevation or slope and orientation by fusion with a dem first results obtained by these methods are presented in part ii of this paper kaab and others 2002 thresholding of a ratio image from tm4 and tm5 reveals the best suited glacier map the computation of glacier parameters in a gis environment is efficient and suitable for worldwide application the methods developed contribute to the u s geological survey led global land ice measurements from space glims project which is currently compiling a global inventory of land ice masses within the framework of global glacier monitoring haeberli and others 2000

radiometrically determined sedimentary fluxes in the sub polar north atlantic during the last 140 000 years abstract we have examined the record of sediment input during the last 140 000 years in a deep sea core from 49 27 n 22 16 w in the eastern north atlantic using uranium series disequilibria to constrain time we have calculated mass fluxes of total sediment as well as mass and particle fluxes of major sedimentary components sediment accumulation rates were generally lower and relatively constant during broadly defined interglacial intervals driven primarily by the burial of biogenic material accumulation rates were higher and more variable during glacial intervals and were influenced primarily by terrigenous material peaks in bulk mass fluxes were associated with particular episodes heinrich events within the last glacial and during each of the last two deglaciations the flux of ice rafted debris as uniquely identified by coarse detrital fragments was higher during layers representing each of the glacial heinrich events with modest increases during events h3 and h6 and dramatic increases during the others confirming the widespread interpretation of these layers as episodes of enhanced iceberg delivery the burial flux of foraminifera was markedly lower during each of the glacial heinrich events also confirming the original identification of these layers as barren intervals ice rafting events within marine isotope stage 5 left neither a large detrital nor biogenic flux imprint at our study site variations in the burial rates of non carbonate sediments were largely responsible for overall changes in sediment accumulation throughout the last climate cycle ice rafting was apparently an important delivery mechanism for this terrigenous material the instantaneous chronometer established here for the last 140 000 years in the subpolar north atlantic allows the transformation of existing and subsequent data from relative values to absolute burial fluxes

temperature and precipitation history of the arctic as the planet cooled from peak warmth in the early cenozoic extensive northern hemisphere ice sheets developed by 2 6 ma ago leading to changes in the circulation of both the atmosphere and oceans from not vert similar2 6 to not vert similar1 0 ma ago ice sheets came and went about every 41 ka in pace with cycles in the tilt of earth s axis but for the past 700 ka glacial cycles have been longer lasting not vert similar100 ka separated by brief warm interglaciations when sea level and ice volumes were close to present the cause of the shift from 41 ka to 100 ka glacial cycles is still debated during the penultimate interglaciation not vert similar130 to not vert similar120 ka ago solar energy in summer in the arctic was greater than at any time subsequently as a consequence arctic summers were not vert similar5 c warmer than at present and almost all glaciers melted completely except for the greenland ice sheet and even it was reduced in size substantially from its present extent with the loss of land ice sea level was about 5 m higher than present with the extra melt coming from both greenland and antarctica as well as small glaciers the last glacial maximum lgm peaked not vert similar21 ka ago when mean annual temperatures over parts of the arctic were as much as 20 c lower than at present ice recession was well underway 16 ka ago and most of the northern hemisphere ice sheets had melted by 6 ka ago solar energy reached a summer maximum 9 higher than at present not vert similar11 ka ago and has been decreasing since then primarily in response to the precession of the equinoxes the extra energy elevated early holocene summer temperatures throughout the arctic 1 3 c above 20th century averages enough to completely melt many small glaciers throughout the arctic although the greenland ice sheet was only slightly smaller than at present early holocene summer sea ice limits were substantially smaller than their 20th century average and the flow of atlantic water into the arctic ocean was substantially greater as summer solar energy decreased in the second half of the holocene glaciers re established or advanced sea ice expanded and the flow of warm atlantic water into the arctic ocean diminished late holocene cooling reached its nadir during the little ice age about 1250 1850 ad when sun blocking volcanic eruptions and perhaps other causes added to the orbital cooling allowing most arctic glaciers to reach their maximum holocene extent during the warming of the past century glaciers have receded throughout the arctic terrestrial ecosystems have advanced northward and perennial arctic ocean sea ice has diminished here we review the proxies that allow reconstruction of quaternary climates and the feedbacks that amplify climate change across the arctic we provide an overview of the evolution of climate from the hot house of the early cenozoic through its transition to the ice house of the quaternary with special emphasis on the anomalous warmth of the middle pliocene early quaternary warm times the mid pleistocene transition warm interglaciations of marine isotope stages 11 5e and 1 the stage 3 interstadial and the peak cold of the last glacial maximum

paleoenvironmental conditions at core kc01b ionian sea through mis 13 9 evidence from calcareous nannofossil assemblages quantitative analyses on calcareous nannofossil assemblages on high temporal resolution 600e800 years have been carried out from core kc01b in the ionian sea eastern mediterranean throughout marine isotope stage mis 13e9 between 500 and 300 ka this is an interval of considerable climate changes known as the mid brunhes event which includes mis 11 considered as a possible analogue for future interglacial conditions in the mediterranean core the interval is characterized by the dominance of gephyrocapsaspp as also known fromocean records calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity water stratification and temperature specifically the increase in abundance of gephyrocapsa caribbeanica and small gephyrocapsa coupled with decreases of florisphaera profunda syracosphaera spp and rhabdosphaera spp suggests enhanced primary productivity mixed surface waters during interglacial stages and at the terminations which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation on the other hand distributions of calciosolenia spp oolithotus spp and umbilicosphaera sibogae which are inphase with d 18 o curve showing higher abundances at the lighter values of the marine

south greenland ice sheet collapse during marine isotope stage 11 varying levels of boreal summer insolation and associated earth system feedbacks led to differing climate and ice sheet states during late quaternary interglaciations in particular marine isotope stage mis 11 was an exceptionally long interglaciation and potentially had a global mean sea level 6 to 13 metres above the present level around 410 000 to 400 000 years ago implying substantial mass loss from the greenland ice sheet gis there are however no model simulations and only limited proxy data to constrain the magnitude of the gis response to climate change during this super interglacial thus confounding efforts to assess climate ice sheet threshold behaviour and associated sea level rise here we show that the south gis was drastically smaller during mis 11 than it is now with only a small residual ice dome over southernmost greenland we use the strontium neodymium lead isotopic composition of proglacial sediment discharged from south greenland to constrain the provenance of terrigenous silt deposited on the eirik drift a sedimentary deposit off the south greenland margin we identify a major reduction in sediment input derived from south greenland s precambrian bedrock terranes probably reflecting the cessation of subglacial erosion and sediment transport as a result of near complete deglaciation of south greenland comparison with ice sheet configurations from numerical models suggests that the gis lost about 4 5 to 6 metres of sea level equivalent volume during mis 11 this is evidence for late quaternary gis collapse after it crossed a climate ice sheet stability threshold that may have been no more than several degrees above pre industrial temperatures

interglacial climates and the atlantic meridional overturning circulation is there an arctic controversy arctic palaeorecords are important to understand the natural range of forcing and feedback mechanisms within the context of past and present climate change in this temperature sensitive region a wide array of methods and archives now provide a robust understanding of the holocene climate evolution by comparison rather little is still known about older interglacials and in particular on the effects of the northward propagation of heat transfer via the atlantic meridional ocean circulation amoc into the arctic terrestrial records from this area often indicate a warmer and moister climate during past interglacials than in the holocene implying a more vigorous amoc activity this is in conflict with marine data although recognized as very prominent interglacials in antarctic ice cores cross latitudinal surface ocean temperature reconstructions show that little of the surface ocean warmth still identified in the northeast atlantic during older interglacial peaks e g mis5e 9 11 was further conveyed into the polar latitudes and that each interglacial developed its own specific palaeoclimate features interactive processes between water mass overturning and the hydrological system of the arctic and how both developed together out of a glacial period with its particular ice sheet configuration and relative sea level history determined the efficiency of an evolving interglacial amoc because of that glacial terminations developed some very specific water mass characteristics which also affected the climate evolution of the ensuing interglacial periods moreover the observed contrasts in the arctic directed meridional ocean heat flux between past interglacials have implications for the palaeoclimatic evaluation of this polar region crucial environmental factors of the arctic climate system such as the highly dynamical interactions between deep water mass flow surface ocean temperature salinity sea ice and atmosphere exert strong feedbacks on interglacial climate regionality that goes well beyond the arctic a sound interpretation of such processes from palaeoarchives requires a good understanding of the applied proxies fossils in particular are often key to the reconstruction of past conditions but the tremendously flexible adaptation strategies of biota sometimes hampers further in depth interpretations especially when considering their palaeoenvironmental meaning in the context of rapid palaeoclimatic changes and long term pleistocene evolution

maastrichtian to early tertiary stratigraphy and palaeogeography of the central and northern oman mountains abstract maastrichtian to tertiary sedimentary rocks outcrop extensively around the periphery of the oman mountains they form part of a geologically distinct suite of strata deposited after obduction of the semail ophiolite and thrusting of the hawasina and sumeini imbricates onto the eastern edge of the arabian plate the lithostratigraphy of maastrichtian and early tertiary rocks of the central and northern oman mountains is revised and a number of new formations are erected the proto oman mountains were emergent in the early maastrichtian and were subject to subaerial erosion and weathering nw and w of the mountains gradual subsidence followed during the maastrichtian allowing for formation of a transgressive onlapping sequence represented by the qahlah fluviatile to shallow marine terrigenous clastics and simsima shallow shelf carbonate formations more rapid subsidence ne of the mountains produced fan delta and submarine debris flow turbidite apron sequences comprising the al khawd and thaqab formations respectively a low angle unconformity separates tertiary strata from older units during the palaeogene basinal and slope facies with debris flows and turbidite sequences were deposited directly upon the unconformity surface in rapidly subsiding basins nw muthaymimah formation and nne ruwaydah formation of the oman mountains elsewhere shallow carbonate shelf facies were extensively developed in less rapidly subsiding areas during the palaeogene the palaeocene and early eocene is represented by the jafnayn limestone formation this is succeeded and overlapped by a variety of later eocene units ene and e of the mountains early eocene regression is marked by restricted facies of the rusayl formation overlying the rusayl formation are shallow open shelf limestones of the seeb formation which is rich in alveolinid and nummulitic foraminifera on the arabian side of the mountains the rusayl formation is not developed and the jafnayn formation is succeeded either by the seeb formation or fine grained faunally restricted limestones and marls of the fahud beds which represent intra shelf facies

eemian and early weichselian 140 60 ka paleoceanography and paleoclimate in the nordic seas with comparisons to holocene conditions paleoceanographic and paleoclimatic time series were extracted from norwegian iceland and greenland sea the nordic seas sediment sequences covering the time intervals 60 140 ka and 0 15 ka on the basis of stable isotope stratigraphy planktonic foraminiferal faunas and sedimentological methods the proxy temperature records from the norwegian iceland sea display a number of high frequency and high amplitude variations within the last interglacial the eemian indicating marked changes in heat flux at high northern latitudes eemian holocene comparisons document that the climate of the norwegian iceland sea in the last interglacial was less stable than that of the present interglacial and that the distribution of surface water masses in the eemian differed from that of the holocene within the greenland sea uniform cold conditions prevailed throughout both interglacials cooling of the nordic seas as well as the initial growth of the surrounding ice sheets began within the eemian interval before the main increase in global ice volume heat flux to the nordic seas was significantly higher during the interglacials than at any time during the early weichselian 60 113 ka and no marked stadial interstadial changes in sea surface temperature and deep water ventilation are documented in the early weichselian records contrary to the pattern found in north atlantic sediment records however fluctuations in planktonic foraminiferal content planktonic 13c and ice rafting on suborbital timescales mostly comparable in number and age to the stadial interstadial fluctuations in the greenland ice cores are demonstrated in our records the ice rafted detritus records provide a more detailed account of ice sheet variability than previously known for the early weichselian period and demonstrate that glaciers advanced to sea level somewhere around the nordic seas several times during this interval

glacial interglacial records of the reflectance of sediments from the norwegian greenland iceland sea nordic seas the reflectance of sediments gray level were measured on 11 sediment cores from the norwegian greenland iceland sea nordic seas the analyzed time interval covers the past five glacial interglacial cycles although the results demonstrate that the gray level method has a potential for stratigraphic purposes it is indicated that gray level changes in the nordic seas are not necessarily driven by variations in the content of biogenic calcite a detailed comparison of gray level values with contents of total caco3 carbonate and total organic carbon toc reveals no overall causal link between these proxies however specific glacial core sections with layers containing organic rich sediment clasts as a consequence of iceberg rafting seem to correlate well with law gray level values of those cores which show relatively high and comparable carbonate values in the last three main interglacial intervals stages 11 5 5 and 1 stage 11 is always marked by the highest gray level values a close inspection of the surface structure of the foraminiferal tests as well as the conduction of reflectance measurements on these tests leads to the conclusion that enhanced carbonate corrosion occurred during stage 11 the test corrosion not only affected the reflectance of the tests by making them appear whiter it also seems responsible for the comparatively high gray level values of the total sediment in stage 11 in contrast the relatively low gray level values found in stages 5 5 and 1 are not associated with enhanced test corrosion this observation implies that variable degrees of carbonate corrosion can have a profound effect on total sediment reflectance

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

multiproxy fossil comparison reveals contrasting surface ocean conditions in the western iceland sea for the last two interglacials abstract dinoflagellate cyst dinocyst coccolith and planktic foraminiferal assemblages from a core in the western iceland sea were used to reconstruct and compare the surface ocean developments of the holocene and the last interglacial marine isotopic stage or mis 5e while increasing subpolar planktic foraminifers from 10 ka indicate subsurface warming peaking around 7 5 ka the dinocyst data suggest that the uppermost ocean remained dominated by cold waters until 6 5 ka a reduced advection of cold polar waters through the east greenland east icelandic current thereafter entailed warmest and most saline holocene conditions between 6 5 and 5 ka in turn followed by a general cooling trend by contrast both planktic foraminifers and dinocysts show an increased presence of atlantic type waters from 122 ka onward resulting in a mis 5e thermal optimum around 120 5 ka nonetheless occasional freshwater input from melting drift ice created stratified but also seasonally variable conditions during this first half of mis 5e this stratification signature disappeared at 120 ka when a marked repositioning of the oceanographic fronts occurred slightly colder conditions are indicated by both phyto and zooplankton from there on until the end of mis 5e around 117 ka a late mis 5e cooling at the iceland plateau is opposite to a late mis 5e optimum observed in the eastern nordic seas this regional difference is likely explained by various feedback mechanisms following the major reorganisation of the oceanic fronts at 120 ka the holocene and mis 5e interglacial variability is not reflected in the quasi monospecific coccolith assemblages and illustrates the low sensitivity of living coccolithophore communities to subtle temperature changes in the low temperature regions of the nordic seas overall quite different surface water properties appear to have characterised both interglacial intervals with a higher share of warm atlantic elements in the planktic communities during mis 5e this suggests a higher contribution of atlantic waters in the southwestern nordic seas probably due to a more northward expansion of the irminger current under weakened polar east greenland east icelandic currents such a reduced influence of polar waters in the southwestern nordic seas may thus explain other evidence for relatively warm conditions in mis 5e all around southern greenland

abrupt climate events 500 000 to 340 000 years ago evidence from subpolar north atlantic sediments subpolar north atlantic proxy records document millennial scale climate variations 500 000 to 340 000 years ago the cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle these findings suggest that such climate variations are inherent to the late pleistocene regardless of glacial state sea surface temperature during the warm peak of marine isotope stage 11 mis 11 varied by 0 5 to 1 c less than the 4 to 4 5 c estimated during times of ice growth and the 3 c estimated for glacial maxima coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

reflectances of glaciers as calculated using landsat 5 thematic mapper data landsat 5 thematic mapper tm data have been used in previous work in order to locate zones of similar spectral reflectance on glaciers in austria and alaska and to relate these zones to the glacier facies which are indicative of glacier mass balance in this paper landsat 5 digital numbers dns have been used to compute the at satellite planetary reflectances p on spectrally similar zones on the meares and schwanda glaciers in alaska and the grossglockner glacier group in austria the patterns of tm derived reflectances in the ablation areas of the grossglockner glacier group and the meares glacier compare favorably with published reflectance curves measured on the surface of glacier ice though the surface reflectance of snow covered ice is higher than the landsat derived reflectance for the glaciers studied the accuracy of the at satellite planetary reflectances is shown to be affected by topographic and atmospheric effects and by the anisotropic nature of snow reflectance use of reflectance values for analysis of snow and ice facilitates scene to scene comparisons of glaciers

time scale for adjustment of glaciers to changes in mass balance the length of time tm over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models we show the following tm may in general be estimated by a volume time scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states the factor f in the classical estimate of m l u where i is glacier length and u is terminus velocity has a simple geometrical interpretation ft is the ratio of thickness change averaged over the full length i to the change at the terminus although both u and f relate to dynamic processes local to the terminus zone the ratio f u and therefore tm are insensitive to details of the terminus dynamics in contrast to conclusions derived from some simplified kinematic wave models a more robust estimate of tm independent of terminus dynamics is given by tm h b where h is a thickness scale for the glacier and b is the mass balance rate negative at the terminus we suggest that tm for mountain glaciers can be substantially less than the 1o2 103 years commonly considered to be theoretically expected

rapid changes in ocean circulation and heat flux in the nordic seas during the last interglacial period the apparent similarity of climate variability in the north atlantic region in the last interglacial period1 5 and the present interglacial holocene has recently been challenged by the rapid oscillations in climate conditions indicated by some marine6 7 and terrestrial climate records8 10 for the last interglacial ocean circulation in the northern north atlantic seems to be intimately coupled to the processes of climate change on various time scales11 12 so that climate variability and the associated mechanisms of change should be well recorded by sediments from these high latitudes previous studies in this region5 13 have indeed indicated an apparently less stable last interglacial climate than at middle latitudes of the north atlantic ocean4 here we present detailed records from marine sediments in the nordic seas of oceanographic conditions during the last interglacial the records show three large sea surface temperature fluctuations a weakening of the east west sea surface temperature gradient with time and changes in deep water properties in contrast similar analyses of a core from the same region indicate that sea surface temperature during the holocene has been relatively stable our data along with those from the labrador sea7 indicate rapid changes in ocean circulation and oceanic heat fluxes at high northern latitudes during the last interglacial which may have been associated with marked temperature changes on adjacent continents

central mediterranean mid pleistocene paleoclimatic variability and its association with global climate abstract planktonic foraminiferal assemblages were studied at high resolution in core kc01b from the ionian sea quantitative analysis allowed us to distinguish the main climatic features and associated paleoceanographic changes that occurred between marine isotopic stages mis 13 and 9 500 300 ka mis 12 and mis 10 are characterized by relatively temperate conditions and an oligotrophic oceanographic regime in the early part and by colder conditions and nutrient supply in the sub surface water masses in the upper part during these intervals small but distinct peaks of neogloboquadrina pachyderma sinistral sin are detected at times of extremely negative values of the planktonic foraminifera paleoclimatic curve their co occurrence with similar episodes in the atlantic suggests that the climate in the central mediterranean was associated with north atlantic millennial scale climate instability mis 11 and mis 9 are dominated by surficial warm water taxa the climate optimum is reached in the middle part of each of these stages as denoted by the presence of globigerinoides sacculifer and persists for approximately 20 and 6 ka during mis 11 and mis 9 respectively this warming is not constant but is characterized by three distinct intervals with elevated winter temperatures and or weak winter mixing distribution of globigerina bulloides turborotalita quinqueloba and n pachyderma dextral dex indicates that significant environmental changes occur across the transitions from glacial to interglacial mis 12 mis 11 termination v and mis 10 mis 9 termination iv the studied record documents a close linkage between mediterranean climate evolution and higher and lower latitude climate change throughout mis 13 9