sedimentology and stratigraphy in the cave hamnsundhelleren western norway the stratigraphy in hamnsundhelleren is as follows a basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the laschamp excursion 43 47 000 yr bp angular blocks bones and clay above this are 14c dated to the alesund interstadial 28 38 000 yr bp another stadial laminated clay following the alesund interstadial includes a palaeomagnetic excursion correlated with lake mungo 28 000 yr bp the newly discovered hamnsund interstadial above this consists of frost weathered clay and scattered angular blocks it is 14c dated to 24 500 yr bp on bones mixed into the alesund interstadial the hamnsund interstadial is succeeded by another stadial laminated clay and then a late glacial holocene mixture of bones and blocks in hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice free ice covered cycle have been identified i ice free phase deposition of bones and frost weathered blocks ii subaerial ice dammed lake phase sand or silt deposited in a lateral glacial lake iii subglacial ice dammed lake phase cave closed by ice deposition of till debris flows and laminated clay d ice plugged phase cave is plugged by frozen lake water and or glacial ice no deposition

changes in meridional temperature and salinity gradients in the north atlantic ocean 30 72 n during the last interglacial period eight deep sea sediment cores from the north atlantic ocean ranging from 31 to 72 n are studied to reconstruct the meridional gradients in surface hydrographic conditions during the interval of minimum ice volume within the last interglacial period using benthic foraminiferal 18o measurements and estimates of sea surface temperature sst and sea surface salinity sss we show that summer ssts and ssss decreased gradually during the interval of minimum ice volume at high latitude sites 52 72 n whereas they were stable or increased during the same time period at low latitude sites 31 41 n this increase in meridional gradients of ssts and ssss may have been due to changes in the latitudinal distribution of summer and annual average insolation and associated oceanic and atmospheric feedbacks these trends documented for the eemian ice volume minimum period are similar to corresponding changes observed during the holocene and may have had a similar origin

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

moisture supply for northern ice sheet growth during the last glacial maximum during the last ice age the barents sea ice sheet began to grow 22 kyr ago1 only 8 kyr before it began to disintegrate2 this implies that the ice must have grown very rapidly from the coast to the edge of the continental shelf such rapid growth of a large ice sheet requires significant amounts of moisture3 but the origin of this moisture has been unclear particularly as the climap climate reconstruction suggests4 5 that the greenland iceland norwegian gin seas were perennially ice covered during this period here we present data from deep sea sediment cores from the fram strait which suggest that relatively warm water from the north atlantic ocean was advected into the gin seas in two short term events 27 22 5 and 19 5 14 5 kyr ago we suggest that the resulting seasonally ice free waters were an important regional moisture source for the barents sea ice sheet and that the gin seas played a much more active role in climate during the last glaciation than has previously been supposed

magnetic petrology of eastern north america diabases i olivine normative dikes from western south carolina abstract the oxide mineralogy and magnetic properties were examined in a suite of fifteen olivine normative diabase dike samples from western south carolina in an attempt to elucidate their magnetic petrology titanomagnetite 1 2 vol is the dominant fe ti oxide mineral ilmenite and secondary magnetite are generally present in very minor amounts chromite constitutes up to 0 5 vol its abundance and composition correlate with bulk rock cr various types of fine scale microstructure are evident in titanomagnetite crystals the most important are patterned anisotropism and the development of trellis type ilmenite lamellae microprobe analyses indicate 1 titanomagnetite compositions x are mostly between 0 4 and 0 55 and 2 low analytical totals are characteristic of most titanomagnetites curie temperatures of the diabases are 500 540 c which are several hundred degrees higher than predicted from the observed titanomagnetite x s 150 300 c we attribute these higher curie temperatures to oxidation of the titanomagnetites which has produced titanomaghemites having visible microstructure and yielding low analyses because they are cation deficient natural remanence magnetization and rem ratio of natural remanence to saturation remanence vary between 4 and 100 10 4 a m2 kg 1 and 0 0019 and 0 032 respectively these properties inversely correlate with cr content and demonstrably contrast cr rich and cr poor samples initial susceptibility saturation magnetization and coercivity values show a two to three fold range variations in initial susceptibility and coercivities appear to be largely related to the type and extent of oxidation induced microstructure in the titanomagnetites

timescales for dust variability in the greenland ice core project grip ice core in the last 100 000 years the calcium representing dust concentration record of the last 100 000 years from the greenland ice core project grip ice core shows a huge dynamic range factor 100 the relationship between dust concentrations and temperature represented by the oxygen isotope ratio is not a simple one as has often been assumed a rapid alternation factor of 5 10 between low concentrations during the dansgaard oeschger interstadial periods and high levels in colder periods is superimposed on a long term trend encompassing a further factor of 5 10 within climate periods there is only a very weak relationship between ca concentration and temperature previous authors biscaye et al 1997 have suggested that the most likely source for the increased dust is eastern asia for the first time we consider each possible cause of both rapid and slow increases from source to deposition we suggest that to account for the size and rapidity of the fast changes significantly higher wind speed in the source area is required although changes in atmospheric residence time could also play a role for the slower long term variability changes in transport speed or possibly route are probably also involved changes in the size of the source area could give some change on longer time periods the probable importance of changes in source area wind speed almost simultaneous with greenland temperature changes confirms that climatic parameters in high and low latitudes were strongly coupled through the atmosphere during glacial climatic changes this adds to evidence that the atmospheric circulation system underwent almost instantaneous large scale changes during the last glacial period

temperature and circulation changes in the eastern north atlantic during the last 150 000 years evidence from the planktonic foraminiferal record during the last 150 000 years the circulation of the subtropical gyre in the eastern north atlantic has changed in response to glacial interglacial variations in climate maps and time series constructed from planktonic foraminifera recovered from 18 piston cores show the nature of this response paleontological chemical and lithologic indices are used to establish a stratigraphy in the cores numerical analysis of the paleontological data yields estimates of the sea surface temperatures sst and salinity maps of these estimates and of the interpreted circulation have been constructed for 18 28 73 93 125 and 150 000 years b p 18o stages 2 3 4 5 b 5 e 6 the analysis yielded six major results 1 1 in the southern sargasso sea faunal abundances and sst have remained essentially constant for the last 150 000 years 2 2 in the northwestern part of the study area between 30 n and 40 n faunal variations were large but sst variations small 2 3 c during the last 150 000 years sst remained stable due to different ecological water types of similar temperature range exchanging dominance downcore 3 3 in the northern part of the study area between 40 45n sst remained warm in the west and decreased to glacial level minima in the east between 120 and 80 000 years b p 18o substages 5 d to 5 a the large west east gradients may have been maintained by a meridional flow of the north atlantic current around the azores plateau 4 4 along the canary current there were generally monotonic decreases in sst during the last climatic cycle 5 5 the advance of ice that culminated in the wisconsin maximum at 18 000 years b p was accompanied by rising sst in both the vicinity of the azores and along the southern part of the canary current 6 6 inferred increases in the velocities of the north atlantic current occurred at approximately the same time as all seven of the major polar advances of the last 150 000 years and are associated with stable or rising temperatures these sst patterns may have resulted from increased north atlantic current velocities advecting warm source waters more rapidly into the mid latitudes the increased velocities may have been due to a combination of reinforcing factors increased wind stress steepening of the thermocline due to increased cooling of 18 c water south of the gulf stream and increased baroclinicity that resulted when the low temperature north atlantic polar front migrated southward toward the stable gyre center

sea level change along the french mediterranean coast for the past 30 000 years abstract observational evidence for sea level change along the french mediterranean coast has been examined and compared with glacio hydro isostatic models to predict the spatial and temporal patterns of change for about the past 30 000 14c years these predictions are pertinent to discussions of changing ocean volumes during this interval the tectonic stability or otherwise of the coastal areas mantle rheology and the timing of possible human occupation of the now submerged coastal plain and caves such as cosquer cave near marseille the principal results from the analysis are i sea levels along this section of the coast have risen continually since the time of the last glacial maximum lgm and at no time during the holocene has the mean sea level been higher than that of today ii the coast has been tectonically stable between marseille and nice as well as further to the west in roussillon western corsica may have experienced a slow tectonic uplift of between 0 15 0 3 mm year for the past 3000 years but northernmost corsica appears to have been stable during this same interval iii during the lgm sea levels along the coast and immediate off shore areas stood at between 105 115 m below present level the range reflecting the importance of the isostatic contributions during oxygen isotope stage 3 sea levels do not appear to have risen locally above about 60 m iv the rebound parameters describing the mantle rheology and ice sheets required to match the limited observational evidence are consistent with the results of similar analyses carried out for other parts of europe because of its distance from the former northern ice sheets the isostatic factors are particularly sensitive to the value of the lower mantle viscosity v the model predictions for sea level change at the cosquer cave site and for its immediate environments indicate that the cave was last readily accessible before about 10 700 500 14c years about 12 500 500 cal years bp and that the cave entrance was completely flooded by 9000 200 radiocarbon years bp between about 9800 and 10 300 calibrated years bp the cave was above sea level throughout the oxygen isotope stage 3

identification of a 15 m wisconsin shoreline on the texas inner continental shelf abstract the maximum sea level position during the middle wisconsin oxygen isotope stage 3 is controversial it being interpreted as anywhere from at or above present day levels to 85 m high resolution seismic lithologic paleontologic and radiocarbon data from the east texas continental shelf were used to map a stage 3 shoreline the shoreline was placed in a regional context with a study of the texas shelf based on seismic profiles core and platform boring descriptions that identifies the stage 3 maximum flooding surface and the stage 2 sequence boundary these surfaces were then traced up dip on the east texas shelf where a shore parallel escarpment was recognized landward of the escarpment the stage 3 maximum flooding surface is amalgamated with the stage 2 sequence boundary therefore the location of the escarpment marks the up dip limit of stage 3 deposits and a stage 3 shoreline lagoonal sediments with in situ brackish water fossils on lap the escarpment seaward of the escarpment remnants of barrier island facies have been preserved as a bank freeport rocks bathymetric high located in 18 m of water the shoreline adjusted for subsidence is located at 15 2 m which is shallower than what oxygen isotope and coral records indicate

ice age initiation by an ocean atmospheric circulation change in the labrador sea abstract the contrast between the large greenland ice sheet and the nearly ice free area of canada to the west exemplifies the critical role of the moisture supply in glaciation the trigger for new ice sheet growth in canada at the end of the last interglacial was probably an increase in the moisture supply rather than regional cooling triggering is attributed to stronger storm activity in the labrador baffin area caused by warming in the labrador sea and cooling in the greenland norwegian sea the key to this temperature and circulation change may have been an increase in the hydrologic deficit of the mediterranean sea a larger hydrologic deficit would have increased mediterranean salinity and consequently the volume of mediterranean overflow water a resulting increased upwelling of mediterranean overflow water from the lower thermocline off scotland would have diverted additional warm north atlantic drift water westward via the irminger current thus warming the labrador sea the underlying cause of the hydrologic deficit increase was diminishing milankovitch summer insolation in lower latitudes this reduced african monsoon intensity and nile river discharge in modern times nearly all nile discharge to the mediterranean has been lost due to irrigation practices culminating with the completion of the aswan high dam in 1968 the total increase in the hydrologic deficit due to nile discharge loss is now 8 in the next 70 100 years the nile loss added to larger evaporative losses due to co 2 warming may increase the deficit as much as 22 above the inferred deficit at the beginning of the last glaciation thus further warming the labrador sea consequently the triggering of major ice sheet growth in canada 100 years from now is possible

millennial scale fluctuations in north atlantic heat flux during the last 150 000 years abstract surface water and deep ocean palaeoclimate records obtained from north atlantic core su90 03 40 n 32 w exhibit pronounced fluctuations at sub orbital time scales surface temperature variability in the mid latitude atlantic over the last 150 kyr is dominated by forcing at precession 21 kyr and semi precession harmonics 11 kyr abrupt changes in sea surface temperatures show that the northward transport of heat by the north atlantic current was curtailed during ice rafting events sea surface temperatures were about 12 c colder than modern values during the most intense cooling episodes associated with major ice rafting events heinrich events 1 4 6 and 11 and 10 c below modern values during the later part of isotope stage 3 40 30 ka during these cold intervals the north atlantic current was displaced to south of 40 n as the cold meltwaters penetrated southwards into what is now the subtropical ocean these changes in surface ocean heat exchange were most probably allied to a latitudinal migration and increase in zonality of atmospheric circulation patterns concurrent shifts in ird concentration sea surface temperatures and benthic 13 c values provide evidence of coupling between sea surface processes and the deep water circulation and suggest that decreases in surface temperature and salinity during ice rafting events culminated in a significant reorganisation of north atlantic deep water production

solution conduits as indicators of late quaternary sea level position abstract solution conduits or caves can provide a measure of glacio eustatic sea level position for the quaternary in high latitudes cave deposits contain artifacts fossils and sediments that reflect surface conditions with respect to climate secondary calcite deposits most notably stalagmites record growth episodes during ice minima and non growth during ice maxima they provide an indirect estimate of areal ice cover at high latitudes and are an indirect measure of sea level in low latitudes stable carbonate platforms contain caves that provide a direct measure of past sea level position solution conduits developing in a fresh water lens will record the position of the lens and therefore sea level as sea level fluctuates fresh water lens horizons and conduit development horizons will shift preserving a record of past sea level position cave wall rock and cave deposits can produce a chronology for given conduit positions secondary calcite deposits notably stalagmites record growth periods during sea level low stands or ice maxima and record growth hiatuses during flooding by sea level high stands or ice minima the inverse of high latitude stalagmites lighthouse cave san salvador island bahamas records a sea level high stand at 1 to 6 m for some time period between 85 000 and 70 000 years ago based on position and timing of conduit development and records sea level at present elevation for some time period between 49 000 and 37 000 years ago based on a stalagmite with a marine overgrowth

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

photosynthetic fractionation of 13c and concentrations of dissolved co2 in the central equatorial pacific during the last 255 000 years carbon isotopically based estimates of co2 levels have been generated from a record of the photosynthetic fractionation of 13c is equivalent to epsilon p in a central equatorial pacific sediment core that spans the last approximately 255 ka contents of 13c in phytoplanktonic biomass were determined by analysis of c37 alkadienones these compounds are exclusive products of prymnesiophyte algae which at present grow most abundantly at depths of 70 90 m in the central equatorial pacific a record of the isotopic composition of dissolved co2 was constructed from isotopic analyses of the planktonic foraminifera neogloboquadrina dutertrei which calcifies at 70 90 m in the same region values of epsilon p derived by comparison of the organic and inorganic delta values were transformed to yield concentrations of dissolved co2 is equivalent to c e based on a new site specific calibration of the relationship between epsilon p and c e the calibration was based on reassessment of existing epsilon p versus c e data which support a physiologically based model in which epsilon p is inversely related to c e values of pco2 the partial pressure of co2 that would be in equilibrium with the estimated concentrations of dissolved co2 were calculated using henry s law and the temperature determined from the alkenone unsaturation index u k 37 uncertainties in these values arise mainly from uncertainties about the appropriateness particularly over time of the site specific relationship between epsilon p and 1 c e these are discussed in detail and it is concluded that the observed record of epsilon p most probably reflects significant variations in delta pco2 the ocean atmosphere disequilibrium which appears to have ranged from approximately 110 microatmospheres during glacial intervals ocean atmosphere to approximately 60 microatmospheres during interglacials fluxes of co2 to the atmosphere would thus have been significantly larger during glacial intervals if this were characteristic of large areas of the equatorial pacific then greater glacial sinks for the equatorially evaded co2 must have existed elsewhere statistical analysis of air sea pco2 differences and other parameters revealed significant p 0 01 inverse correlations of delta pco2 with sea surface temperature and with the mass accumulation rate of opal the former suggests response to the strength of upwelling the latter may indicate either drawdown of co2 by siliceous phytoplankton or variation of co2 si oh 4 ratios in upwelling waters

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

initiation of the last glaciation in northern europe abstract the bio and chronostratigraphy of the eemian interglacial marine isotope substage 5e and an early weichselian glaciation 5d a established from representative and detailed sequences can be correlated with the deep sea oxygen isotope stratigraphy ice core data sea level fluctuations and coupled ice sheet climate models biostratigraphic sequences from fennoscandian key sections are correlated with reference sequences from estonia and from sections located near or beyond the margins of the last glaciation organic sediments previously attributed to early and middle weichselian interstadial periods in finland are argued to be redeposited and mixed older last interglacial material pollen and diatom spectra of the undisturbed materials suggest that the eemian climatic optimum was followed by a continuously cooling climate and a regressive marine level if only undisturbed sequences are considered the major climatic fluctuations of the early weichselian apparent in central and western europe are not apparent in the sequences from the central part of the glaciated terrain instead some sequences are truncated by sediments indicating approaching ice sheets soon after the interglacial this may imply that the ice sheet grew over finland during the first early weichselian stadial the preservation of the interglacial beds and the lack of younger non glacial sediments support the interpretation that the area remained ice covered until the final deglaciation during the early weichselian the norwegian coast was probably occasionally ice free similar to the coastal zone of greenland today the authors interpretation of the fennoscandian organic deposits of the last glaciation may also explain similar observations from the central parts of the laurentide ice sheet

variations of terrestrial input and marine productivity in the southern ocean 48 s during the last two deglaciations various biomarkers n alkanes n alcohols and sterols have been studied in a piston core tsp 2pc taken from the southern ocean to reconstruct the paleoenvironmental changes in the subantarctic region for the last two deglaciations mass accumulation rates of terrestrial higher molecular weight n alkanes and n alcohols and marine dinosterol and brassicasterol biomarkers increased significantly at the last two glacials and stayed low during interglacial peaks early holocene and the eemian these records indicate that the enhanced atmospheric transport of continental materials and the increased marine biological productivity were synchronously linked in the southern ocean at the last two glacials this suggests that increased glacial dust inputs have relieved iron limitation in the subantarctic southern ocean these two processes however were not linked at the cooling phase from the eemian to marine isotope stage mis 5d during this period paleoproductivity may have been influenced by the latitudinal migration of the high production zone associated with the antarctic polar front

paleoceanographic reconstructions from planktonic foraminifera off the iberian margin temperature salinity and heinrich events a quantitative analysis of planktonic foraminifera in a core from the iberian margin allows a reconstruction of the evolution of oceanographic parameters during the last glacial cycle with a resolution of 1000 years a principal component analysis performed on 19 species allows the identification of 11 intervals characterized by increased abundances of the subpolar species the youngest six of these intervals are correlated with the last 6 heinrich events hes the five cold events older than stage 4 are dated at 81 90 110 129 and 140 ka respectively paleotemperatures reconstructed using the modern analog technique indicate 4 c decreases during all even numbered isotopic stages and stage 3 during the hes temperature decreases reach 10 c and seawater 18o anomalies reach 1 temperature and salinity reconstructions indicate that the environment of the iberian margin has been under the combined influence of global factors such as the migration of the polar front and iceberg discharge and of regional factors such as the precipitation evaporation regime on both oceanic and continental area

reflection of scandinavian ice sheet fluctuations in norwegian sea sediments during the past 150 000 years the record of glacier fluctuations in western scandinavia as reconstructed from continental data has been correlated with records of ice rafted detritus ird from well dated sediment cores from the norwegian sea covering the past 150 000 yr b p the input of ird into the ocean is used as a proxy for ice sheet advances onto the shelf and thus for the calibration of a glaciation curve the marine results generally support land based reconstructions of glacier fluctuations and improve the time control on glacial advances the saalian ice sheet decayed very rapidly approximately 125 000 yr b p in the early weichselian a minor but significant ird maximum indicates the presence of icebergs in isotope substage 5b especially between 95 000 and 83 000 yr b p reduced amounts of calcareous nannofossils indicate that surface waters were influenced by meltwater discharges during isotope substages 5d and 5b an extensive build up of inland ice began again during isotope stage 4 but maximum glaciation was reached only in early stage 3 58 000 53 000 yr b p marine sediments have minimum carbonate content indicating strong dilution by lithogenic ice rafted material generally the ird accumulation rate was considerably higher in stages 4 2 than in stage 5 a marked peak in ird accumulation rates from 47 000 to 43 000 yr b p correlates well with a second middle weichselian ice sheet advance dated by the laschamp olby paleomagnetic event minimum ice extent during the alesund interstade 38 500 32 500 yr b p and several glacial oscillations during the late weichselian are also seen in the ird record of several late weichselian glacial oscillations on the shelf at least four correspond to the north atlantic heinrich events ice sheet behavior was either coupled or linked by external forcing during these events whereas internal ice sheet mechanisms may account for the noncoherent fluctuations

initiation and development of the laurentide and cordilleran ice sheets following the last interglaciation abstract fossil records from sites overridden by or adjacent to the laurentide ice sheet indicate that the climate of the last interglaciation oxygen isotope substage 5e ca 130 116 ka was warmer than today following the last interglaciation the laurentide ice sheet first developed during stage 5 over keewatin quebec and baffin island along its northern margin the ice sheet reached its maximum extent of the last glaciation during stage 5 the ice sheet advanced across baffin island onto the continental shelf early during stage 5 5d whereas the advance into the western canadian arctic occurred late during stage 5 5b the ice sheet also may have advanced into the st lawrence lowland during substage 5b although this event may be younger stage 4 the hudson bay lowland became ice free during substage 5a retreat of the ice sheet on baffin island occurred during late stage 5 probably substage 5a the exact timing of retreat from the western canadian arctic is unknown but it occurred before 48 ka the southern sector including the st lawrence lowland was ice free during late stage 5 the hudson bay lowland may have remained ice free through stage 4 and much of stage 3 because of conflicting chronologies however it is more likely that this area was glaciated throughout stage 3 and perhaps stage 4 nevertheless the data demonstrate that the lowland was ice free during part of the last glaciation an independent ice cap developed over the appalachian uplands and advanced across nova scotia during stage 4 perhaps as far as the edge of the continental shelf the ice cap remained active over nova scotia as a setellite to the laurentide ice sheet throughout the remainder of the last glaciation the ice sheet advanced into the st lawrence lowland during stage 4 and subsequently overwhelmed the local ice cap in the appalachian uplands advancing perhaps into northern new england but not farther south the lowland remained covered by the ice sheet until late stage 2 the ice sheet may also have advanced into the lake ontario basin during stage 4 the position of the northern margin of the laurentide ice sheet during stage 4 is not known but it remained an unknown distance behind its maximum position reached during stage 5 cores from baffin bay indicate a substantial decrease in high latitude glaciation during stage 4 following retreat the keewatin sector of the ice sheet may have remained over much of northwestern canada as a quasi stable ice mass until it readvanced during stage 2 similarly the baffin island sector of the ice sheet may have remained largely intact the southern margin of the ice sheet may have advanced into the lake ontario basin and upper mississippi valley during the middle of stage 3 ca 50 ka reaching its maximum extent of the last glaciation during stage 2 ca 18 21 ka advance of the northern margin was younger ca 8 13 ka than that of the southern margin this advance was less extensive than the penultimate advance stage 5 paleoenvironmental records indicate that the last interglaciation in areas covered by and near the cordilleran ice sheet was as warm as or warmer than present the cordilleran ice sheet appears to have developed during stage 5 or 4 at that time it advanced over southern british columbia and into the northern puget lowland there is no record of this event in northern areas that were later covered by the ice sheet the ice sheet disappeared before 59 ka at the beginning of a lengthy nonglacial interval paleoenvironmental records indicate that climate was similar to the present during part of this interval the ice sheet was absent and glaciers probably were confined to mountain areas throughout stage 3 climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka by 14 15 ka the ice sheet had achieved its maximum extent of the last glaciation because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted we consider this synthesis as tentative and subject to significant revision as dating methods improve nevertheless this perspective of the north american ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

olivine normative dolerite dikes from western south carolina mineralogy chemical composition and petrogenesis this investigation describes five mesozoic dolerite dikes which intrude paleozoic metamorphic and igneous rocks of the inner piedmont of western south carolina the dikes are vertical or nearly so and strike approximately n40 w three major northeast trending faults also occur in the study area left lateral displacement of one dolerite is documented at a locality near cleveland south carolina elsewhere several of the dolerite dikes appear to terminate at or near the faults the dolerite dikes have subophitic to microporphyritic textures and consist principally of plagioclase generally an70 80 olivine dominantly fo80 90 and augite with subordinate pigeonite titanomagnetite chromite and brown partly glassy mesostasis in one dike pyroxene compositions trend from augite to ferroaugite in contrast to an augite subcalcic augite pigeonite trend characteristic of the other dolerites the contrasting trends primarily result from differences in sio2 abundance in the dolerite magmas major and trace element analyses indicate the presence of two different olivine normative dolerite magma types the two magma types are not related by near surface crystal fractionation models for genesis of the olivine normative dolerite magmas by partial melting of a plagioclase peridotite upper mantle source region are presented the models require that the source region be enriched in lree and incompatible elements such as rb ba hf and th relative to cl chondritic abundances one magma type appears to represent a primary dolerite magma that ascended from the source region with little subsequent compositional change the second magma type most likely experienced assimilation of clinopyroxene garnet eclogite during ascent thereby acquiring a ree pattern with a less steep negative slope for the lree and a slight positive slope in the hree

the magnitude and proximate cause of ice sheet growth since 35 000 yr b p the magnitude of late wisconsinan post 35 000 yr b p ice sheet growth in the northern hemisphere is not well known ice volume at 35 000 yr b p may have been as little as 20 or as much as 70 of the volume present at the last glacial maximum lgm a conservative evaluation of glacial geologic sea level and benthic 18o data indicates that ice volume at 35 000 yr b p was approximately 50 of that extant at the lgm 20 000 yr b p that is it doubled in about 15 000 yr on the basis of literature for the north atlantic and a sea surface temperature sst data compilation it appears that this rapid growth may have been forced by low to mid latitude sst warming in both the atlantic and pacific oceans with attendant increased moisture transport to high latitudes the sst ice sheet growth notion also explains the apparent synchroneity of late wisconsinan mountain glaciation in both hemispheres

paleomagnetism of upper carboniferous limestones from the carnic alps abstract limestones of stephanian age belonging to the carboniferous permian sedimentary sequence of the auernig group at passo pramollo carnic alps were investigated by a paleomagnetic study these limestones represent the late tectonic molassic stage of the hercynian orogeny in the paleozoic chain of the carnic alps after a preliminary sampling at twenty sites unstable magnetization was found to affect the remanence at eight sites of twelve sites studied in detail about 180 specimens 10 sites had a mean paleomagnetic direction of d 141 8 and i 8 1 and 95 17 8 after cleaning and corrections for bedding attitudes tilted by subsequent mainly alpine tectonics the corresponding virtual mean pole position lies at 243 3 e 36 2 n coincident with data of comparable age from morocco and is located east of the african poles of late carboniferous to permian age in addition the pole from the pramollo limestones is also comparable with the younger permian poles from the southern alps and from most mediterranean crustal blocks showing that the area was also rotated counterclockwise with respect to europe paleogeographically the area of the carnic alps already belonged to the southern alpine domain by upper carboniferous times and was located in the northern hemisphere at that time

simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation according to milankovitch theory the lower summer insolation at high latitudes about 115 000 years ago allowed winter snow to persist throughout summer leading to ice sheet build up and glaciation1 but attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only2 3 4 5 these results point towards the importance of feedback effects for example through changes in vegetation or the ocean circulation for the amplification of solar forcing6 7 8 9 here we present a fully coupled ocean atmosphere model of the last glaciation that produces a build up of perennial snow cover at known locations of ice sheets during this period we show that ocean feedbacks lead to a cooling of the high northern latitudes along with an increase in atmospheric moisture transport from the equator to the poles these changes agree with available geological data10 11 12 13 14 15 and together they lead to an increased delivery of snow to high northern latitudes the mechanism we present explains the onset of glaciation which would be amplified by changes in vegetation in response to weak orbital forcing

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

juxtaposed mesozoic diabase dike sets from the carolinas a preliminary assessment aeromagnetic anomaly maps of the north carolina piedmont provide confirming evidence of juxtaposed mesozoic diabase dike sets dikes in north carolina may be divided into four domains on the basis of dike orientations most dikes are olivine normative but there are apparent systematic differences in chemical compositions that are reflected in different orientations and ages two orientations dominate northwest and north south the northwest trending set dominates in the south carolina piedmont and the north south set extends through much of the central virginia piedmont and under the coastal plain in south carolina the north south dikes are part of a set that converges near charleston and georgetown south carolina and diverges northward into virginia preliminary information suggests that the north south dikes are younger than the more common northwest trending dikes current models proposed for stress regimes associated with the breakup of pangea can accommodate the northwest set but not the north south convergent set this convergent set may be evidence for crustal deformation above a mantle plume centered near charleston and georgetown in middle jurassic time it is possible that presumed mafic plutons under the coastal plain near charleston regional seismicity patterns and orientations of the diabase dikes are all related to an intersection of zones of crustal weakness inherited from mid mesozoic time the western margin of northwest trending dikes may be related to tectonic features inherited from pre mesozoic time

the genesis of zr nb ree mineralisation at khalzan buregte western mongolia reconsidered abstract the sources and formation conditions of unconventional zr nb ree mineralisation ree rare earth elements presently found in increasing number worldwide are still poorly constrained one particular problem is the specific role of magmatic and hydrothermal processes active in various geological settings investigation of zr nb ree mineralisation at khalzan buregte and tsakhir western mongolia enables to evaluate magmatic processes preceding economic mineralisation and in a second step to compare similar ore forming processes developing in host rocks of contrasting rock composition low vs high silica rocks the genesis of the zr nb ree mineralisation is re assessed using field observations whole rock analysis chemical composition quantitative modal analysis by x ray diffraction and by the application of various transmitted light and electron microscopic techniques coarse grained intrusive bodies dikes and volcanic rocks of alkaline silica saturated composition were found to be contemporarily emplaced at subvolcanic to volcanic levels forming four alkaline massifs within the khalzan buregte area the whole rock composition of weakly altered magmatic rocks ranges from syenite to quartz monzonite and alkaline granite alkali feldspar syenite to alkali feldspar granite according to their modal composition magmatic and at least two subsequent hydrothermal processes contributed significantly to the formation of economic concentrations of high field strength elements hfse such as zr hf nb ta ree and y in the khalzan buregte deposit and in the nearby tsakhir prospect mixing of magma from at least three sources and the formation of potassium feldspar cumulates resulted in local enrichment of zr nb and light rare earth elements lree in the rocks up to sub economic levels there was no significant increase in y and heavy rare earth elements hree during magmatism multistage metasomatic alteration resulted in a pronounced chemical and mineralogical heterogeneity of associated alteration assemblages the main hosts of zr and hf in the ores are zircon and other zirconium silicates gittinsite catapleiite ca and elpidite the rare metals nb and ta are mainly contained in various types of pyrochlore khalzan buregte and to a lesser extent in fergusonite and other minerals tsakhir a large variety of ree and y bearing minerals have been identified including oxides fluorocarbonates and silicates early hydrothermal alteration by silica and carbonate rich fluids yielded extreme concentrations of zr nb and lree later alteration resulted in enrichment of y and hree in the latter case fluids were very rich in fluorine our preliminary genetic model assumes a carbonatite related fluid system responsible for the early alteration that occurred late during or postdating the intrusion extrusion of the silica saturated magmas a li f granite type fluid system was active during the late alteration the interplay of all these processes resulted in the formation of a complex economic zr nb ree mineralisation at khalzan buregte

amino acid racemization and radiocarbon dating of interstadial marine strata oxygen isotope stage 3 gulf st vincent south australia abstract concordant results for the extent of racemization of the amino acids aspartic acid leucine and valine and isoleucine epimerization in several mollusc genera support radiocarbon data that indicate an interstadial age oxygen isotope stage 3 45 000 to 30 000 yr b p for a sequence of mollusc rich carbonate muds in gulf st vincent south australia a numeric age of 46 500 9100 yr b p was obtained on marine molluscs from these sediments using a model based on apparent parabolic racemization kinetics in a global context the sequence represents one of the few well documented occurrences of marine strata of this age from a tectonically quiescent setting a sea level as high as 22 m is indicated for this interval amino acid racemization provides an important method for validating conventional finite radiocarbon ages close to the practical limits of radiocarbon dating and in studies of reworking

maximum sea levels for the last glacial period from u series ages of submerged speleothems pleistocene sea levels reflect changes in the surface distribution of land sea and ice which in turn significantly influence the earth s climate1 the most complete record of sea levels for the last glacial cycle has come from raised coral reef terraces of the huon peninsula papua new guinea2 4 but interpretation of this record is hampered by relatively large age uncertainties and the possibility of variation in the rate of tectonic uplift subaerial speleothems stalagmites stalactites and flowstones from submerged caves in tetonically stable areas provide an alternative source of data5 8 as their growth stops when rising sea levels flood the caves previous studies of speleothems have been limited by dating precision5 6 and sample availability5 7 here we present high precision thermal ionization mass spectrometric 230th ages9 11 for a comprehensive suite of speleothem samples from the bahamas our results provide a record of maximum elevation of sea levels for the period from 80 to 10 kyr before the present for much of which sea levels are poorly known we also find that regional palaeoclimatic change can be an important factor in the termination of speleothem growth

new radiocarbon dates from finnish mammoths indicating large ice free areas in fennoscandia during the middle weichselian new radiocarbon dates from finnish subfossil mammoth material mammuthus sp transported by glacial ice range in age from ca 32000 to ca 22500 yr bp these results suggest that there was a larger ice free area in fennoscandia during the middle weichselian than previously assumed in addition two dates are also presented for bones found in clay with a different transport history copyright 1999 john wiley sons ltd

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