paleogene synorogenic sedimentation in the altiplano plateau and implications for initial mountain building in the central andes sedimentologic data and palynological ages from paleogene clastic deposits of the northern and central altiplano plateau suggest foreland basin development in the central andes by mid paleocene time the nonmarine potoco formation 3000 6500 m thick constitutes the majority of cenozoic basin fill the potoco overlies the santa lucia formation 50 300 m thick previously dated as mid paleocene by mammal fossils and magnetostratigraphy new geochronologic data for the potoco formation include late eocene to oligocene palynomorph assemblages recovered throughout lower to upper stratigraphic levels these ages and published 40 ar 39 ar and k ar ages from overlying upper oligocene lower miocene volcaniclastic rocks indicate 1 nondeposition or greatly reduced deposition average sediment accumulation rates 10 m m y from mid paleocene to middle eocene time top santa lucia to lowermost potoco formation followed by 2 rapid deposition average sediment accumulation rates up to 500 m m y throughout late eocene and oligocene time majority of potoco formation lithofacies and paleocurrent data confirm both depositional phases a 20 100 mthick interval of superimposed paleosols in the basal potoco supports reduced sediment accumulation and low rates of subsidence during mid paleocene to middle eocene time the overlying main body of the potoco contains facies assemblages and stratigraphic architecture dominantly nonero

glacial extent and catastrophic meltwater events during the deglaciation of southern iceland abstract reconstruction of the paleoenvironment of south iceland based on lithofacies and chronological studies of the budi morainal complex lacustrine deposits at ofaerugil and a sediment core from lake hestvatn south iceland revealed evidence for repeated catastrophic flood jokulhlaup activities during the late younger dryas yd and the early preboreal pb chronozones during this time thin and lobate outlet glaciers from the retreating iceland ice cap extended from major valleys and calved into the paleobay of southern lowlands of iceland where relative sea level was at least 70 m higher than today a number of ice marginal lakes formed during the stepwise retreat of the south iceland ice sheet at the transition of the yd and pb primary geomorphic and sedimentologic impact of the jokulhlaups was erosion of multiple channels downstream from the most prominent moraines in south iceland and through the coastal sediment accompanied by net aggradation of chaotically stratified sand and silt lenses at the ice distal environment these floods accumulated in the form of recurrent turbidity currents volcanic eruptions supplemented by a catastrophic release of the ice marginal lakes are postulated as the main triggers for the jokulhlaup activity the jokulhlaup events evidenced in this study and subsequent break up of the partly marine based glacier may have contributed to the ice rafting events found in the north atlantic paleoenvironmental record

potential links between surging ice sheets circulation changes and the dansgaard oeschger cycles in the irminger sea 60 18 kyr surface and deepwater paleoclimate records in irminger sea core so82 5 59on 31 ow and icelandic sea core ps2644 68on 22ow exhibit large fluctuations in thermohaline circulation thc from 60 to 18 calendar kyr b p with a dominant periodicity of 1460 years from 46 to 22 calendar kyr b p matching the dansgaard oeschger d o cycles in the greenland ice sheet project 2 gisp2 temperature record grootes and tuiver 1997 during interstadials summer sea surface temperatures sstsu in the irminger sea averaged to 8oc and sea surface salinities sss averaged to 36 5 recording a strong irminger current and atlantic thc during stadials sstsu dropped to 2o 4oc in phase with sss drops by 1 2 they reveal major meltwater injections along with the east greenland current which turned off the north atlantic deepwater convection and hence the heat advection to the north in harmony with various ocean circulation and ice models on the basis of the ird composition icebergs came from iceland east greenland and perhaps svalbard and other northern ice sheets however the southward drifting icebergs were initially jammed in the denmark strait reaching the irminger sea only with a lag of 155 195 years we also conclude that the abrupt stadial terminations the d o warming events were tied to iceberg melt via abundant seasonal sea ice and brine water formation in the meltwater covered northwestern north atlantic in the 1 1460 year frequency band benthic 15 80 brine water spikes led the temperature maxima above greenland and in the irminger sea by as little as 95 years thus abundant brine formation which was induced by seasonal freezing of large parts of the northwestern atlantic may have finally entrained a current of warm surface water from the subtropics and thereby triggered the sudden reactivation of the thc in summary the internal dynamics of the east greenland ice sheet may have formed the ultimate pacemaker of d o cycles

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

shifting paradigms in geomorphology the fate of research ideas in an educational context the acceptance of new ideas into the mainstream of geomorphological education is illustrated from the development of theories dealing with earth history glaciation uniform flow mass movement continental mobility cyclic erosion and drainage networks the lag between the conception of new ideas and their incorporation into mainstream texts has varied from negligible to more than 200 years on one hand despite its then untestable assumptions the davisian cycle of erosion gained rapid favor as the dominant paradigm of the early 20th century before it was found wanting in contrast concepts of uniform flow and slope stability confirmed in the 18th century waited almost 200 years for incorporation into geomorphology texts sensu stricto although they had long been available in books on hydraulics and soil mechanics continental mobilism had a wild ride culminating in the eventual acceptance of the plate tectonics paradigm in the later 20th century explanations for the fate of these and other ideas are varied new ideas are often opposed by establishment conservatism language barriers the perceived surrealism of new concepts and simple ignorance in contrast new ideas may be accepted sooner or later by virtue of simplicity forceful and well connected leadership or the death of opponents although mitigated by the information revolution of recent decades these forces still persist and influence the extension of new ideas into a larger arena

application of tephrochronology to the timing and correlation of palaeoceanographic events recorded in holocene and late glacial shelf sediments off north iceland abstract the north icelandic shelf is partly distinguished by the tjornes fracture zone featuring numerous active basins in a mud dominated shelf environment late glacial and holocene high resolution sedimentary records from this area have been studied with tephrochronology as the main tool for correlation and for exact timing of palaeoceanographic events in the area data from three new piston cores from the shelf demonstrate the importance of tephra markers for the first chronological evaluation and correlation of the cores the correlation is extended with lithological logs and with magnetic susceptibility records a detailed multidisciplinary study including biostratigraphy and tephrochronology of a late holocene record of predominantly muddy sediments at the same location demonstrates that marked variations in the distribution of water masses occurred repeatedly through the last 4500 cal yr of special interest is the exact timing of a marked drop in sea surface temperature in the area indicated by ice rafting debris concentration to about 50 years before the hekla 3 eruption which occurred at 2980 cal yr bp this appears to predate most records of a general cooling event in nw europe by a couple of centuries two different possible age models one based on 14c dates combined with tephra markers and one based on tephra markers alone are discussed in context with the problem of different marine reservoir ages of the water masses in the area

latest pleistocene ice rafting events on the scotian margin eastern canada and their relationship to heinrich events piston cores from the continental margin off nova scotia show up to four discrete intervals of brick red sandy mud which are up to 20 cm thick the ages of these intervals are bracketed by several radiocarbon dates and three fall in the range 12 5 14 1 ka radiocarbon years with 0 4 kyr reservoir correction the youngest dates from 10 4 ka placing it within the younger dryas the distribution of the beds and their petrographic character indicate a source in the gulf of saint lawrence the grain size of these beds suggests that they comprise a coarse component transported by ice rafting that diminishes distally and a fine component that represents suspension fallout from a surface plume and resulting nepheloid layers graded brick red beds in some cores were probably redeposited from turbidity currents the lowermost bed on the laurentian fan and east scotian rise is immediately overlain by a carbonate rich interval that can be identified all around the margin of the grand banks this interval is correlated with detrital carbonate bed dc 1 in the labrador sea and heinrich event h1 in the north atlantic the sequential occurrence of the two beds suggests that they may be a response to the same trigger probably sea level rise but that the gulf of saint lawrence source was more easily destabilized

late quaternary sedimentary processes and ocean circulation changes at the southeast greenland margin a study has been made of late quaternary depositional processes and bottom current activity on the southeast greenland margin using seismic sub bottom profiling and deep tow side scan sonar data as well as sediment core information the seabed data demonstrate the occurrence of strong southerly bottom currents prevailing on the slope and rise well defined longitudinal bedforms indicate maximum mean near bottom current velocities of up to at least 1 0 m s at the depth stratum of labrador sea water 800 1500 m similarly strong currents occur in denmark strait overflow water dsow at the base of the slope whereas more basinward the maximum dsow flow speed is lower iceberg plow marks were found down to about 700 m water depth both at the shelf edge and on the lower slope and rise the seafloor morphology is indicative of downslope sediment transport and mass flow deposition which is concluded to be a typically glacial feature after generally more sluggish deep water circulation during the last glacial maximum dsow basin ventilation was re established shortly before 13 3 ka on the shelf in front of the retreating greenland ice margin permanent or semi permanent sea ice conditions prevailed until about 12 5 ka at that time increased irminger current activity had resulted in warming and east greenland current egc controlled iceberg drift increased no evidence was found for a return to extreme glacial conditions or a ceasing of dsow flow during the younger dryas abundant coarse ird collected at greater water depth from shallow sub seabed strata has a provenance mainly in the northern part of east greenland 68 73 n which demonstrates the existence of a pre holocene egc system initially extending to beyond the shelf edge

enhanced airborne dispersal of silicic tephras during the onset of northern hemisphere glaciations from 6 to 0 ma records of explosive volcanism and climate change in the subpolar north atlantic a 6 m y long composite marine record of explosive silicic volcanism from five ocean drilling program sites in the subpolar north atlantic was compared with several marine records of global and local paleoclimate proxies benthic d 18 o and ice rafted debris records coarsening and high frequency of occurrence of icelandic tephras were recorded in 3 6 3 ma sediments suggesting that these tephras were dispersed farther from the source by enhanced westerly winds over the subpolar north atlantic the 40 ar 39 ar ages were determined by laser probe on k feldspar and biotite phenocrysts of tephras that were erupted from the jan mayen volcanic system compared to the tuned paleomagnetic age model the 40 ar 39 ar dating 0 618 6 0 007 ma to 4 90 6 0 05 ma yields a new age model that postdates by 155 k y the inception of ice rafting on the iceland plateau during the cold marine isotope stage m2 i e 3 3 3 14 ma

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

surface and deep ocean circulation in the subpolar north atlantic during the mid pleistocene revolution 1 we investigated surface and deep ocean variability in the subpolar north atlantic from 1000 to 500 thousand years ago ka based on two ocean drilling program odp sites feni drift site 980 55 29 n 14 42 w and bjorn drift site 984 61 25 n 24 04 w benthic foraminiferal stable isotope data planktic foraminiferal faunas ice rafted debris data and faunally based sea surface temperature estimates help test the hypothesis that oceanographic changes in the north atlantic region were associated with the onset of the 100 kyr world during the mid pleistocene revolution based on percentage of neogloboquadrina pachyderma s records from both sites surface waters during interglacials and glacials were cooler in the mid pleistocene than during marine isotope stages mis 5 and 6 in particular interglaciations at bjorn drift site 984 were significantly cooler faunal evidence suggests that the interglacial arctic front shifted from a position between the two sites to a position northwest of bjorn drift site 984 after ca 610 ka as during the late pleistocene we find faunal evidence for lagging surface warmth at most of the glacial initiations during the mid pleistocene each initiation is associated with high benthic 13c values that are maintained into the succeeding glaciation which we term lagging nadw production these findings indicate that lagging warmth and lagging nadw production are robust features of the regional climate system that persist in the middle to late pleistocene

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

late brunhes polarity excursions mono lake laschamp iceland basin and pringle falls recorded at odp site 919 irminger basin abstract component natural remanent magnetizations derived from u channel and 1 cm3 discrete samples from odp site 919 irminger basin indicate the existence of four intervals of negative inclinations in the upper brunhes chronozone according to the age model based on planktic oxygen isotope data these excursional intervals occur in sediments deposited during the following time intervals 32 34 ka 39 41 ka 180 188 ka and 205 225 ka these time intervals correspond to polarity excursions detected elsewhere known as mono lake laschamp iceland basin and pringle falls the isotope based age model is supported by the normalized remanence paleointensity record that can be correlated to other calibrated paleointensity records for the 0 500 ka interval such as that from odp site 983 for the intervals associated with the mono lake and laschamp excursions virtual geomagnetic poles vgps reach equatorial latitudes and mid southerly latitudes respectively for intervals associated with the iceland basin and pringle falls excursions repeated excursions of vgps to high southerly latitudes indicate rapid directional swings rather than a single short lived polarity reversal the directional instability associated with polarity excursions is not often recorded probably due to smoothing of the sedimentary record by the process of detrital remanence drm acquisition

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

evolution of iceberg melting biological productivity and the record of icelandic volcanism in the irminger basin since 630 ka abstract planktic 18 o and 13 c records and point count records of biogenic volcanic and nonvolcanic terrigenous ice rafted debris ird sediment components from hole 919a in the irminger basin northern north atlantic provide a comprehensive dataset from which a paleoceanographic reconstruction for the last 630 kyr has been developed the paleoceanographic evolution of the irminger basin during this time contains both long term patterns and significant developmental steps one long term pattern observed is the persistent deposition of hematite stained ice rafted debris this record suggests that the modern and late pleistocene discharges of icebergs from northern redbed regions to the irminger sea lie in the low end of the range observed over the last 630 kyr in addition arctic front fluctuations appear to have been the main controlling factor on the long term accumulation patterns of ird and planktic biogenic groups the hole 919a sediment record also contains a long term association between felsic volcanic ash abundances and light 18 o excursions in both interglacial and glacial stages which suggests a causal link between deglaciations and explosive icelandic eruptions a significant developmental step in the paleoceanographic reconstruction based on benthic evidence was for diminished supply of denmark strait overflow water dsow beginning at 380 ka possibly initiated by the influx of meltwater from broad scale iceberg discharges along the east greenland coast there is also planktic evidence of a two step cooling of sea surface conditions in the irminger basin first at 338 309 ka and later at 211 190 ka after which both glacials and interglacials were colder as the arctic front migrated southeast of site 919 in addition to offering these findings this reconstruction provides a longer term geologic context for the interpretation of more recent paleoceanographic events and patterns of deposition from this region

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

changes in deep and intermediate water properties in the western north atlantic during marine isotope stages 11 12 evidence from odp leg 172 abstract the interval of time represented by marine isotope stages 11 and 12 360 470 ka contains what may be the most extreme glacial and interglacial climate conditions of the late pleistocene it has been suggested that sea level rose by 160 m at the termination of glacial stage 12 this is 30 greater than the sea level rise that followed the most recent glacial maximum there have been few detailed studies of the unique conditions that existed during the stage 11 12 time period because of the lack of high quality core material this problem has been addressed by the collection of high deposition rate cores from sediment drifts in the western north atlantic during ocean drilling project leg 172 benthic foraminiferal 13 c data from cores collected between 4600 and 1800 m were used to reconstruct bathymetric gradients in deep and intermediate water properties for selected time slices during this glacial interglacial cycle during glacial stage 12 the deep western north atlantic was filled by a water mass that was more nutrient enriched than modern antarctic bottom water above 2000 m a more nutrient depleted water mass existed during this glacial stage such an intermediate water mass has been described for more recent glacial periods and presumably forms in a more proximate region of the north atlantic interglacial stage 11 water mass properties closely resemble those of the present day western north atlantic a nutrient depleted water mass 13 c of 0 75 1 0 similar to modern north atlantic deep water existed between 3500 and 2000 m this was underlain by a water mass with lower 13 c values 13 c change of 0 95 from stage 12 to stage 11 this is twice the whole ocean 13 c change reported for the transition from the last glacial maximum to the holocene

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

quaternary tephrachronology on the iceland plateau north of iceland four major ash zones recorded in piston cores raised from the iceland plateau north of iceland are shown to be coincident with the last four interglacial isotopic stages their geochemical composition links the ashes to volcanic events on iceland the occurrence of these ash layers which record events orders of magnitude larger than the normal holocene volcanic eruptions can not be explained by changes in sea ice cover and atmospheric circulation alone it is suggested that these events are related to pressure releases in the magma chambers resulting from major deglaciations of the icelandic ice cap

ice rafted evidence of long term north atlantic circulation abstract the absolute and relative rates of deposition of ice rafted volcanic and terrigenous clastic material were determined for the interval from the base of oxygen isotope stage 5 127 000 yrs b p to the lower part of stage 3 50 000 yrs b p in five subpolar north atlantic deep sea cores during this time interval global climate changed from a full interglaciation to nearly a full glaciation for the sediment derived from the continents dominantly quartz and feldspar the eastward decrease in deposition rates during interglacial intervals and eastward increase during glacial intervals is best explained by a southeastward jump in the locus of iceberg melting during climates colder than that of today a similar model may explain the eastward increase in volcanogenic debris during glacial time intervals however the eastward increase of volcanogenic debris during interglacial stage 5 requires a stronger southeastward component of flow from greenland than is evident in the modern circulation

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

arctic front shifts in the subpolar north atlantic during the mid pleistocene 800 400ka and their implications for ocean circulation abstract surface water conditions at the integrated ocean drilling program iodp site u1314 southern gardar drift 56 21 8 n 27 53 3 w 2820 m depth were inferred using planktic foraminifer assemblages between marine isotope stage mis 19 and 11 ca 800 400 ka factor analysis of the planktic foraminifer assemblages suggests that the assemblage was controlled by three factors the first factor which explained 49 of the variance is dominated by transitional and subpolar species and points to warm and salty surface water conditions atlantic water the second factor 37 is dominated by neogloboquadrina pachyderma sin and has been associated with the presence of cold and low saline surface waters arctic water finally the third factor 9 linked to a significant presence of turborotalita quinqueloba reflects the closeness of the arctic front the boundary between atlantic and arctic water the position of the arctic and polar fronts has been estimated across the glacial interglacial cycles studied according to planktic foraminifer abundances from site u1314 and their factor analysis combined with a synthesis of planktic foraminifer and diatom data from other north atlantic sites regarding at the migrations of the arctic front and the surface water masses distribution across each climatic cycle we determined five phases of development furthermore deep ocean circulation changes observed in glacial interglacial cycles have been associated with each phase the high abundance of transitional subpolar foraminifers above 65 at site u1314 during the early interglacial phase indicated that the arctic front position and surface water masses distribution were similar to present conditions during the late interglacial phase n pachyderma sin and t quinqueloba slightly increased indicating that winter sea ice slightly expanded southwestwards whereas the ice volume remained stable or was still decreasing n pachyderma sin increased rapidly above 65 at site u1314 at the first phase of glacial periods indicating the expansion of the arctic waters in the western subpolar north atlantic during the second phase of glacial periods the transitional subpolar assemblage throve again in the central subpolar north atlantic associated with strong warming events that followed ice rafting events the third phase of glacial periods corresponds to full glacial conditions in which n pachyderma sin dominated the assemblage for the whole subpolar north atlantic this division in phases may be applied to the last four climatic cycles

volcanic triggering of late pliocene glaciation evidence from the flux of volcanic glass and ice rafted debris to the north pacific ocean abstract mass accumulation rates mar of different components of north pacific deep sea sediment provide detailed information about the timing of the onset of major northern hemisphere glaciation that occurred at 2 65 ma an increase in explosive volcanism in the kamchatka kurile and aleutian arcs occurred at this same time suggesting a link between volcanism and glaciation sediments recovered by piston coring techniques during odp leg 145 provide a unique opportunity to undertake a detailed test of this possibility here we use volcanic glass as a proxy for explosive volcanism and ice rafted debris ird as a proxy for glaciation the mar of both glass and ird increase markedly at 2 65 ma further the flux of the volcanic glass increased just prior to the flux of ice rafted material suggesting that the cooling resulting from explosive volcanic eruptions may have been the ultimate trigger for the mid pliocene glacial intensification

the last occurrence of proboscia curvirostris in the north atlantic marine isotope stages 9 8 well preserved diatoms are present in high sedimentation rate pleistocene cores retrieved on ocean drilling program odp legs 151 152 162 and images cruises of r v marion dufresne from the north atlantic investigation of the stratigraphic occurrence of diatom species shows that the youngest diatom event observed in the area is the last occurrence lo of proboscia curvirostris jouse jordan and priddle p curvirostris is a robust species that can easily be identified in the sediments and therefore can be a practical biostratigraphic tool we have mapped its areal distribution and found that it stretches from 408 nt o 808n in the north atlantic further we have correlated the lo p curvirostris to the oxygen isotope records of six cores to refine the age of this biostratigraphic event the extinction of p curvirostris is latitudinally diachronous through marine isotope stages mis 9 to 8 within the north atlantic this is closely related to the paleoceanography of the area p curvirostris first disappeared within interglacial mis 9 324 ka from the northern areas that are most sensitive to climatic forcing like the east greenland current and the sea ice margin it survived in mid north atlantic until the conditions of the mis 8 glaciation became too severe 260 ka in the north pacific at odp site 883 the lo p curvirostris falls within mis 8 the observed overlap in age between the north atlantic and the north pacific strongly suggests that the extinction of p curvirostris is synchronous between these oceans q 2001 elsevier science b v all rights reserved

growth dynamics and deglaciation of the last british irish ice sheet the deep sea ice rafted detritus record the evolution and dynamics of the last british irish ice sheet biis have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data this reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary in order to enhance biis reconstruction we present a compilation of new and previously published ice rafted detritus ird flux and concentration data from high resolution sediment cores recovered from the ne atlantic deep sea continental slope adjacent to the last biis these cores are situated adjacent to the full latitudinal extent of the last biis and cover marine isotope stages mis 2 and 3 age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera neogloboquadrina pachyderma sinistral nps to the greenland gisp2 ice core record multiple ird fingerprinting techniques indicate that at the selected locations most ird are sourced from adjacent biis ice streams except in the centre of heinrich h layers in which ird shows a prominent laurentide ice sheet provenance ird flux data are interpreted with reference to a conceptual model explaining the relations between flux north atlantic hydrography and ice dynamics both positive and rapid negative mass balance can cause increases and prominent peaks in ird flux first order interpretation of the ird record indicates the timing of the presence of the biis with an actively calving marine margin the records show a coherent latitudinal but partly phased signal during mis 3 and 2 published data indicate that the last biis initiated during the mis 5 4 cooling transition renewed growth just before h5 46 ka was succeeded by very strong millennial scale variability apparently corresponding with dansgaard oeschger do cycles closely coupled to millennial scale climate variability in the north atlantic region involving latitudinal migration of the north atlantic polar front this indicates that the previously defined precursor events are not uniquely associated with h events but are part of the millennial scale variability major growth of the ice sheet occurred after 29 ka with the barra ice stream attaining a shelf edge position and generating turbiditic flows on the barra donegal fan at 27 ka the ice sheet reached its maximum extent at h2 24 ka earlier than interpreted in previous studies rapid retreat initially characterised by peak ird flux during greenland interstadial 2 23 ka was followed by readvance between 22 and 16 ka readvance during h1 was only characterised by biis ice streams draining central dome s of the ice sheet and was followed by rapid deglaciation and ice exhaustion the evidence for a calving margin and ird supply from the biis during greenland stadial 1 younger dryas event is equivocal the timing of the initiation maximum extent deglacial and readvance phases of the biis interpreted from the ird flux record is strongly supported by recent independent data from both the irish sea and north sea sectors of the ice sheet

persistent suborbital climate variability in marine isotope stage 5 and termination ii new surface water records from two high sedimentation rate sites located in the western subtropical north atlantic near the axis of the gulf stream provide clear evidence of suborbital climate variations through marine isotope stage mis 5 persisting even into the warm peak of the interglaciation substage 5e we found that the amplitude of suborbital climate oscillations did not vary significantly for the whole of mis 5 implying that ice volume has little or no influence on the amplitude of suborbital climate variability in this region although some records suggest that longer suborbital variations 4 10 kyr during mis 5 are linked to deepwater changes none of the existing records is of sufficient resolution to assess if a linkage occurred for oscillations shorter than 4 kyr however when examined in conjunction with published data from the norwegian sea new evidence from the subpolar north atlantic suggests that coupled surface deepwater oscillations occurred during the penultimate deglaciation this supports the hypothesis that during glacial and deglacial times ocean ice interactions and deepwater variability amplify suborbital climate change at higher latitudes we suggest that during the penultimate deglaciation the north atlantic deepwater source varied between nordic sea and open north atlantic locations in parallel with surface temperature oscillations

chemical composition distribution and origin of silicic volcanic ash layers in the greenland iceland norwegian sea explosive volcanism from 10 to 300 ka as recorded in deep sea sediments explosive ocean island volcanism in the greenland iceland norwegian sea gin sea is indicated by marine tephra layers at 10 300 ka peaks of explosive volcanism occurred in oxygen isotope stages 8 7 5 and 1 the depositional age of the tephra was estimated using the oxygen isotope stratigraphy and dating of marine records geochemical analyses of the tephra layers show that all originate from iceland here we report the characteristics of tephra from these major icelandic events in 30 deep sea cores from the gin sea our findings provide constraints on the distribution of tephra from the eruption source for the vedde ash oxygen isotope stage 1 we estimate a minimum fallout area of 2 105 km2 stretching from central greenland in the west and southern sweden in the east to 71 n in the gin sea the magnitude of the eruption and the regional wind conditions controlled the extent and concentrations of these ash fallout events oceanic circulation and differential settling may have affected the distribution and final deposition of ash particles such as bubble wall shards

source and dispersal of jokulhlaup sediments discharged to the sea following the 1996 vatnajokull eruption the october 1996 gjalp eruption beneath vatnajokull glacier led to one of the largest jokulhlaups glacial floods in iceland in the twentieth century a catastrophic discharge of meltwater and sediment swept across the skeidararsandur flood plain to the sea tephra from the eruption consists of vesicular sideromelane shards with a basaltic andesite composition 53 sio 2 3 mgo 0 8 k 2 o after the flood sediment samples were collected from the flood plain and off the southeast coast of iceland where a major sediment plume had been created by the discharge compositions of glass shards from flood plain and seafloor deposits do not match those of the gjalp magma flood plain samples consist primarily of blocky to poorly vesicular sideromelane clasts with compositions that are characteristic of grimsvotn volcanic products 50 sio 2 5 5 mgo 0 4 k 2 o marine samples collected near the jokulhlaup outflow into the sea also consist primarily of blocky to poorly vesicular sideromelane clasts with compositions that are for the most part similar to products of the grimsvotn volcanic center distal marine samples have more vesicular sideromelane clasts with compositions that are similar to products of the katla volcanic center e g 48 sio 2 4 5 mgo 0 8 k 2 o significant deposition to the seafloor was apparently limited to an area just offshore of the skeidararsandur there is no indication that juvenile volcanic material from the gjalp eruption was carried by the 1996 jokulhlaup onto the flood plain or into the ocean instead the jokulhlaup carried primarily older volcaniclastic material eroded by the flood

the marine record of deglaciation from the continental margin off nova scotia continental margin sediments off nova scotia accumulate at high rates up to 360 cm kyr 1 and contain a history of millennial scale environmental changes which are dominated by the proximity of the laurentide ice sheet during the latest quaternary using stable isotope ratios of oxygen accelerator mass spectrometer radiocarbon dating micropaleontology and sedimentology we document these changes in six piston cores ranging in water depth from 450 to 4300 m we find that maximum 18o in n pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by 1000 years between 13 and 14 ka we find a second peak in abundance of n pachyderma minimum 18o and two pulses of ice rafting the sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper paleozoic and mesozoic red beds by 14 ka in southeastern canada so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the st lawrence valley the younger dry as event is recognized as a peak in abundance of n pachyderma and ice rafting dated as 11 3 ka but meltwater discharge to the gulf of st lawrence was either too small or occurred over too long a time to leave a distinct 18o minimum off nova scotia at 7 1 ka in the middle of holocene warming we find a third peak in abundance of n pachyderma and another 18o minimum but no ice rafting we interpret these data as evidence of a late occurring meltwater event which if correct could have originated in the great lakes in the labrador ungava region or in both the final millennial scale phenomenon off nova scotia is the onset of neoglaciation marked by increased ice rafting and increased n pachyderma beginning about 5 kyr ago

rapid deglaciation as an initiator of volcanic activity an hypothesis volcanic activity on sub antarctic marion island is found to have occurred only during the interglacials the present volcano distribution is associated with a radial and peripheral fault system the location of which appears to be related to the former glacier distribution an hypothesis is presented suggesting that the faulting is a result of deglaciation and that the specific location of the faults is due to the differential stresses occurring between ice covered and ice free areas during isostatic uplift the faulting initiates volcanism due to the location of the island within a volcanic region

history of a stable ice margin east greenland during the middle and upper pleistocene abstract the east greenland record of glaciation and environmental change is based on a combination of onshore and offshore studies glaciological work on contemporary outlet glaciers provides background for interpreting the glaciation styles of the past the scoresby sund fjord system the single largest outlet of the inland ice in east greenland and the adjacent continental shelf and slope were the main working areas the regionality of these results was tested with onshore and offshore work on sites further to the north in the east greenland fjord zone the record spans the period since isotope stage 7 ca 240 ka the most extensive glaciation phases were the lollandselv and scoresby sund glaciations isotope stages 7 and 6 the langelandselv interglaciation isotope substage 5e comprises shallow marine sediments at more than 20 sites onshore and cibicides wuellerstorfii carrying sediments on the continental slope summer temperatures were 2 3 warmer than the holocene optimum and there was vigorous advection of warm atlantic water into the fjords the warm period seems to be accompanied by a eustatic sea level rise of ca 20 m during the weichselian there were three major glacier advances the aucellaelv jyllandselv and flakkerhuk stades isotope substages 5d 5b and stages 3 2 all three advances mark a shift from one topographically determined stable position to another in each phase the glaciers occupied almost the same space in the fjord basins and had their fronts on the inner shelf but the glacial regime and duration was different the aucellaelv stade lasted ca 10 ka and the regime resembled that of present day outlet glaciers 600 km further to the north the flakkerhuk stade lasted for ca 50 ka but left only thin and sporadic till as well as glaciolacustrine sediments in ice dammed river valleys the regime was polar similar to present day glaciers in antarctica its culmination the last glacial maximum in the period between 22 and 14 ka is shown by a maximum in ird deposition on the continental slope after 12 ka and before 10 ka the outer fjord basins in the southern fjord zone had been abandoned by the glaciers and at ca 9 5 ka the last resurgence the milne land stade had ended

origin of orbital periods in the sedimentary relative paleointensity records abstract orbital cycles with 100 kyr and or 41 kyr periods detected in some sedimentary normalized remanence relative paleointensity records by power spectral analysis or wavelet analysis have been attributed either to orbital forcing of the geodynamo or to lithologic contamination in this study local wavelet power spectra lwps with significance tests have been calculated for seven relative paleointensity rpi records from different regions of the world the results indicate that orbital periods 100 kyr and or 41 kyr are significant in some rpi records during certain time intervals and are not significant in others time intervals where orbital periods are significant are not consistent among the rpi records implying that orbital periods in these rpi records may not have a common origin such as orbital forcing on the geodynamo cross wavelet power spectra xwt and squared wavelet coherence wtc between rpi records and orbital parameters further indicate that common power exists at orbital periods but is not significantly coherent and exhibits variable phase relationships implying that orbital periods in rpi records are not caused directly by orbital forcing similar analyses for rpi records and benthic oxygen isotope records from the same sites show significant coherence and constant in phase relationships during time intervals where orbital periods were significant in the rpi records indicating that orbital periods in the rpi records are most likely due to climatic contamination although common power exists at orbital periods for rpi records and their normalizers with significant coherence during certain time intervals phase relationships imply that contamination at orbital periods is not directly due to the normalizers orbital periods are also significant in the nrm intensity records and contamination in rpi records can be attributed to incomplete normalization of the nrm records further tests indicate that contamination is apparently not directly related to physical properties such as density or carbonate content or to the grain size proxy arm however wtc between rpi records and the grain size proxy arm irm implies that arm irm does reflect the contamination in some rpi records it appears that orbital periods were introduced into the nrm records and have not been normalized when calculating rpi records through magnetite grain size variations reflected in the arm irm grain size proxy the orbital power in arm irm for some north atlantic sites is probably derived from bottom current velocity variations that are orbitally modulated and are related to the vigor of thermohaline circulation and the production of north atlantic deep water nadw in the case of odp site 983 the orbital power in rpi appears to exhibit a shift from 41 kyr to 100 kyr period at the mid pleistocene climate transition 750 ka reinforcing the climatic origin of these orbital periods rpi records from the atlantic and pacific oceans and rpi records with orbital periods eliminated by band pass filters are highly comparable with each other in the time domain and are coherent and in phase in time frequency space especially at non orbital periods indicating that contamination although present at orbital periods is not debilitating to these rpi records as a global signal that is primarily of geomagnetic origin

rapid onset of glacial conditions in the subarctic north pacific region at 2 67 ma clues to causality north pacific deep sea sediments recovered by ocean drilling leg 145 constrain the timing of the late pliocene major intensification of northern hemisphere continental glaciation a change in sediment character from nonglacial to glacial specifically abrupt increases in the amount of terrigenous clastic sediment and ice rafted debris occurred all across the north pacific at about 2 67 ma this change occurred very rapidly perhaps within 2000 yr too quickly to be a direct response to either tectonic or orbital forcing as the number and thickness of volcanic ash layers increased 10 fold at this same time we suggest that rapid intensification of glaciation may be associated with the widespread episode of explosive volcanism that began then

explosive silicic volcanism in iceland and the jan mayen area during the last 6 ma sources and timing of major eruptions abstract fifty three major explosive eruptions on iceland and jan mayen island were identified in 0 6 ma old sediments of the north atlantic and arctic oceans by the age and the chemical composition of silicic tephra the depositional age of the tephra was estimated using the continuous record in sediment of paleomagnetic reversals for the last 6 ma and paleoclimatic proxies 18 o ice rafted debris for the last 1 ma major element and normative compositions of glasses were used to assign the sources of the tephra to the rift and off rift volcanic zones in iceland and to the jan mayen volcanic system the tholeiitic central volcanoes along the iceland rift zones were steadily active with the longest interruption in activity recorded between 4 and 4 9 ma they were the source of at least 26 eruptions of dominant rhyolitic magma composition including the late pleistocene explosive eruption of krafla volcano of the eastern rift zone at about 201 ka the central volcanoes along the off rift volcanic zones in iceland were the source of at least 19 eruptions of dominant alkali rhyolitic composition with three distinct episodes recorded at 4 6 5 3 3 5 3 6 and 0 1 8 ma the longest and last episode recorded 11 pleistocene major events including the two explosive eruptions of tindfjallajokull volcano thorsmork ca 54 5 ka and katla volcano solheimar ca 11 9 ka of the southeastern transgressive zone eight major explosive eruptions from the jan mayen volcanic system are recorded in terms of the distinctive grain size mineralogy and chemistry of the tephra the tephra contain k rich glasses k 2 o sio 2 0 06 ranging from trachytic to alkali rhyolitic composition their normative trends ab q or and their depleted concentrations of ba eu and heavy ree reflect fractional crystallisation of k feldspar biotite and hornblende in contrast their enrichment in highly incompatible and water mobile trace elements such as rb th nb and ta most likely reflect crustal contamination one late pleistocene tephra from jan mayen was recorded in the marine sequence its age estimated between 617 and 620 ka and its composition support a common source with the borga pumice formation at sor jan in the south of the island

changes in the oceanic 13c 12c ratio during the last 140 000 years high latitude surface water records detailed records of the carbon and oxygen isotopic ratios of neogloboquadrina pachyderma are compared between nine high latitude sediment cores from the northern and southern hemispheres covering the last 140 000 yrs the strong analogies between the 13c records permit to define a 13c stratigraphic scale with three clear cut transitions simultaneous with the oxygen isotopic transitions 65 125 kyrs 54 65 kyrs and 21 13 kyrs the 13c records of n pachyderma in the high latitude cores which follow the changes in 13c of the surface water tco2 near areas of deep water formation present trends similar to the benthic foraminifera 13c records in cores v19 30 and m12 392 although amplitudes of the isotopic shifts are different this implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean the 13c12c ratios of n pachyderma in the north atlantic cores display larger regional variations at 18 kyrs b p than at present to explain these differences we have plotted the 18 kyrs b p 13c values of n pachyderma from 17 cores distributed n of 40 n comparison with published surface water temperature distribution at 18 kyrs b p indicates that a strong divergent cyclonic cell centered approximatively 55 n and 15 w was active during most of the last ice age maximum this hydrology analogous to the present weddell sea explains the published evidences of bottom water formation if located on the northern flank of the gyre and the strong polar front on the southern flank probable location of intermediate water formation

ocean circulation at the last glacial maximum a combined modeling and magnetic proxy based study 1 formation of north atlantic deep water nadw is an important component of the ocean thermohaline circulation but debate exists over the ocean circulation state during glacial stages some geological and modeling studies suggest decreased nadw and increased formation of southern ocean deep water during the last glacial maximum lgm others indicate similar or higher rates of nadw advection here we test three different potential lgm ocean states by comparing the modeled iceberg trajectories each produces with magnetically mapped patterns and sources of lgm ice rafted debris ird the three lgm states are characterized by vigorous nadw formation deepwater production in the southern ocean and a third intermediate state with southern ocean deepwater formation but also some north atlantic intermediate water formation cluster analysis of sediment magnetic properties was used to characterize north atlantic ird patterns and sources which match most closely iceberg trajectories arising from some combination of the southern sinking and intermediate ocean circulation states the magnetic data indicate two major ird sources fennoscandia and greenland iceland and one minor source the st lawrence region the model and magnetic data suggest that the lgm north atlantic circulation was dominated by a cyclonic central north atlantic gyre separated from the north atlantic current which was displaced south of 42 n

identification of a mis 6 age c 180 ka icelandic tephra within ne atlantic sediments a new potential chronostratigraphic marker the incidence of volcanic ash tephra within marine sediments serves as a useful stratigraphic marker and tool for correlation in addition where an independent age estimate exists tephra layers can provide a means of dating the sediments themselves here we present a geochemically characterized size sorted tephra layer within marine isotope stage mis 6 most likely resulting from primary air fall from an icelandic volcanic source this tephra layer is tentatively correlated to the kerlingarfjoll volcanic system using major element geochemistry the ash layer has an interpolated age of 181 6 ka based on the age model for md04 2822 we briefly review the occurrence of silicic tephra in the north atlantic region from mis 7 to mis 5e inclusive and find potential correlatives to the md04 2822 mis 6 ash layer in the norway basin and irminger sea

the relationship of heinrich events and their european precursors over the past 60 ka bp a multi proxy ice rafted debris provenance study in the north east atlantic high resolution multi proxy records of ice rafted debris ird flux and provenance in the ne atlantic detail the development variability and decline of marine margins of the last glacial circum north atlantic ice sheets coupled lithological identification sr and nd isotopic composition and 40ar 39ar ages of individual hornblende grains reduce ambiguity as to ird potential source region allowing clear differentiation between laurentide lis icelandic and british bis ice sheet sources the icelandic and bis are collectively referred to as the nw european ice sheet nweis a step wise increase in the flux of ird to the core site at 26 5 ka bp documents bis advance and glaciation of ireland millennial scale variability of the bis at a 2 ka periodicity is inferred through clusters of pulsed ird fluxes throughout the late glacial 26 5 10 ka bp combination of these european ird events and the 7 ka periodicity of lis instability is thought to account for quasi synchronicity of the nweis and lis ird pulses at heinrich event h 2 and h1 previously suggested to represent the possible involvement of the nweis in the initiation of h events furthermore the lack of extensive nweis marine margin is inferred prior to h3 31 5 ka bp such that no european precursor event is associated with either h5 or h4 this suggests that precursor events were not directly implicated in the collapse of the lis and the persistent instabilities of the bis that are clustered at a 2 ka periodicity are incompatible with the concept that both h events and their precursors are independent responses to a common underlying trigger

coherent patterns of ice rafted debris deposits in the nordic regions during the last glacial 10 60 ka we have synchronized records of ice rafted rock debris deposits of three sediment cores from the norwegian sea and the irminger basin during the last glacial period from 10 to 50 ka by combining the use of radiocarbon dates and adjustments of physical properties our synchronized records indicate that layers rich in ice rafted debris were deposited throughout the nordic regions at times near to synchronous with the major collapses of the laurentide ice sheet during the heinrich events there are also millennial scale coherent and near to synchronous deposits of ice rafted rock debris into the norwegian sea related to repetitive changes of the flux of icebergs from the fenno scandinavian the correlation with the cold phases of the dansgaard oeschger temperature record points to a close coupling between atmospheric temperature oscillations and variations of iceberg fluxes into the norwegian sea during the last glacial variations in atmospheric circulation patterns bringing moisture supply to high latitudes and the distribution of this moisture over the different northern hemisphere coastal ice sheets and ice shelves could be controlling both the timing of ice sheet advances and the flux of iceberg to the open ocean

millennial scale iceberg discharges in the irminger basin during the last glacial period relationship with the heinrich events and environmental settings high resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the irminger basin the last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from iceland and corresponding to millennial scale instabilities of the coastal ice sheets and ice shelves in the nordic area a comparison with midlatitude sediment cores shows that ice rafted material corresponding to the heinrich events was deposited synchronously from 40 to 60 n there are thus two oscillating systems every 5 10 kyr massive iceberg armadas are released from large continental ice caps whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1 2 3 8 kyr at the time of the heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems

dissolved iron anomaly in the deep tropical subtropical pacific evidence for long range transport of hydrothermal iron abstract dissolved iron profiles along a north south transect along 158 w in the tropical pacific show evidence of two deepwater anomalies the first extends from station aloha 22 78 n to the equator at 1000 1500 m and lies below the maximum apparent oxygen utilization and nutrient n p concentrations the feature is not supported by vertical export processes but instead corresponds with the lateral dilution field of 3 he derived from the loihi seamount hawaii though a sediment source associated with the hawaiian island chain cannot be entirely ruled out the second deeper 2000 3000 m anomaly occurs in tropical south pacific waters 7 s and also does not correlate with the depths of maximum nutrient concentrations or apparent oxygen utilization but it does coincide closely with 3 he emanating from the east pacific rise more than 5000 km to the east we hypothesize that these anomalies represent the long range 2000 km transport of hydrothermal iron residuals stabilized against scavenging by complexation with excess organic ligands in the plume source regions such trace leakage of hydrothermal iron to distal plume regions would have been difficult to identify in most hydrothermal vent mapping studies because low analytical detection limits were not needed for the proximal plume regions these findings suggest that hydrothermal activity may represent a major source of dissolved iron throughout the south pacific deep basin today as well as other regions having high mid ocean spreading rates in the geologic past in particular we hypothesize that high spreading rates along the south atlantic and southern ocean mid oceanic ridges combined with the upwelling ventilation of these distal hydrothermal plumes may have increased ocean productivity and carbon export in the southern ocean assessing the magnitude and persistence of dissolved hydrothermal iron in basin scale deep waters will be important for understanding the marine biogeochemistry of iron and potentially on ocean productivity and climate change during the geologic past

recent and pleistocene carbonate dissolution in sediments of the norwegian greenland sea surface sediment samples from the norwegian greenland sea were investigated to reconstruct the spatial distribution of recent carbonate dissolution on the seafloor additionally carbonate dissolution records of ocean drilling program sites 985 and 987 are presented to outline the development of pleistocene carbonate preservation today well preserved carbonate tests can be observed along the inflow of warm atlantic surface water extending as far as into the northernmost norwegian greenland sea increased dissolution is indicated along the continental margins and in the deepest parts of the greenland basin factors favoring carbonate preservation were found to be supersaturation of the water column with respect to calcium carbonate high carbonate rain and probably excess alkalinity of bottom waters supplied by the arctic river discharge supralysoklinal dissolution is most important for recent carbonate dissolution in the norwegian greenland sea whereas the deepest parts of the greenland basin reaches the calcite saturation horizon pleistocene dissolution records show some prominent peaks of extreme carbonate dissolution during the brunhes chron carbonate dissolution maxima can be related to meltwater pulses which probably inhibited deep water formation in the norwegian greenland sea during deglaciation events long term severe carbonate dissolution is evident during the late matuyama chron this can be probably related to low carbonate rain due to a more eastwards located east greenland current and the nearly absence of the not yet polar adapted neogloboquadrina pachyderma sin during that period extreme dissolution events during the late matuyama indicate strongly reduced deep water formation

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

eruptive environment of volcanism on brabant island evidence for thin wet based ice in northern antarctic peninsula during the late quaternary terrestrial volcanism occurred extensively on brabant island northern antarctic peninsula during the late quaternary 200 ka probably entirely late pleistocene two compositionally distinct volcanic sequences formed three large shield volcanoes the volcanoes were constructed in association with a 150 m thick non ice stream glacial cover although it was likely to be thicker few hundred metres where it extended onto the continental shelf the glacial cover on the volcanoes was probably mainly permeable snow firn and fractured crevassed ice it was wet based erosive and sediment forming indicating either a temperate or perhaps more likely sub polar thermal regime and would have been more extensive than that present today such a thin ice sheet would have had a low surface gradient during periods of extension across the continental shelf this is the first direct evidence for the thickness and thermal regime of the terrestrial ice sheet in the antarctic peninsula during any quaternary period prior to the last glacial maximum