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

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

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

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

beaufort shelf break eddies and shelf basin exchange of pacific summer water in the western arctic ocean detected by satellite and modeling analyses 1 mesoscale eddies and shelf basin exchange of pacific summer water in the western arctic ocean are examined using satellite data sets and an eddy resolving coupled sea ice ocean model several surface eddy like features along the beaufort shelf break are detected by the moderate resolution imaging spectroradiometer modis sea surface temperature and the global imager gli radiance image the quikscat sea wind vectors indicate that summertime shelf wide wind is an important factor for interannual variations in the eddy properties a realistic numerical experiment reveals that the origin of shelf break warm eddies and timing of their generation can be classified into three types type i eddies are frequently produced in the vicinity of the barrow canyon throughout the summer season by a combination of outflow of pacific summer water with a low potential vorticity from the barrow canyon and lateral velocity shear of the canyon jet surface wind variability modulates the timing of generation type ii and type iii eddies originate from an eastward current along the beaufort shelf break although origin depth and background hydrographic structure differ between them type ii eddies are spawned from the shelf slope at middepth during early summer type iii eddies are generated from the surface isopycnal front over the shelf break during late summer the shift from type ii eddies to type iii eddies is caused by surface buoyancy input in the upstream region a sensitivity experiment using different atmospheric forcing data suggest that the mechanism controlling pacific water transport from the chukchi shelf to the canada basin differs depending on surface wind fields in the shelf region the mesoscale eddies primarily induce the shelf to basin transport under weak or westerly wind conditions during summer while wind driven ekman transport is a major driver in the easterly wind regime year 2003 2007 corresponds to the former latter case

extreme reduction mantle derived oxide xenoliths from a hydrogen rich environment abstract coarse grained xenoliths of hibonite grossite mg al v spinel from cretaceous pyroclastic rocks on mt carmel n israel and from sierra de comechingones argentina include spherules rods and dense branching structures of native vanadium and v al alloys microstructures suggest that vanadium melts became immiscible with the host ca al mg si o melt and nucleated as droplets on the surfaces of the oxide phases principally hibonite many extended outward as rods or branching structures as the host oxide crystal grew the stability of v0 implies oxygen fugacities 9 log units below the iron wustite buffer suggesting a hydrogen dominated atmosphere this is supported by wt levels of hydrogen in gasses released by crushing by raman spectroscopy and by the presence of vh2 among the vanadium balls the oxide assemblage formed at 1400 1200 c the solution of hydrogen in the metal could lower the melting point of vanadium to these temperatures these assemblages probably resulted from reaction between differentiated mafic melts and mantle derived ch4 h2 fluids near the crust mantle boundary and they record the most reducing magmatic conditions yet documented on earth

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

a pathway connecting the monsoonal heating to the rapid arctic ice melt abstractthis study provides a monsoonal link to the rapid arctic ice melt each year the planetary scale african asian monsoonal outflow near the tropopause carries a large anticyclonic gyre that has a longitudinal spread that occupies nearly half of the entire tropics in recent years the south asian summer monsoon has experienced increased rainfall over northwestern india and pakistan and it has also contributed to more intense local anticyclonic outflows from this region the western lobes of these intense upper high pressure areas carry outflows with large heat fluxes from the monsoon belt toward central asia and eventually to the region of the rapid ice melt of the canadian arctic in this study this spectacular pathway has been defined from airflow trajectories heat content and heat flux anomalies most of these show slow increasing trends in the last 20 years the monsoonal connection to the rapid arctic ice melt is a new contribution of this study this is shown from the passage of a vertical c

role of ice dynamics in anomalous ice conditions in the beaufort sea during 2006 and 2007 1 a new record minimum in summer sea ice extent was set in 2007 and an unusual polynya formed in the beaufort sea ice cover during the summer of 2006 using a combination of visual observations from cruises ice drift and satellite passive microwave sea ice concentration we show that ice dynamics during preceding years included events that preconditioned the beaufort ice pack for the unusual patterns of opening observed in both summers intrusions of first year ice from the chukchi sea to the northern beaufort and increased pole ward ice transport from the western arctic during summer has led to reduced replenishment of multiyear ice older than five years in the western beaufort resulting in a younger thinner ice pack in most of the beaufort we find ice younger than five years melts out completely by the end of summer south of 76n the 2006 unusual polynya was bounded to the south by an ice tongue composed of sea ice older than 5 years and formed when first year and second year ice melted between 76n and the older ice to the south in this paper we demonstrate that a recent shift in ice circulation patterns in the western arctic preconditions the beaufort ice pack for increased seasonal ice zone extent

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

the role of summer surface wind anomalies in the summer arctic sea ice extent in 2010 and 2011 1 strong summertime anticyclonic wind anomalies over the arctic ocean with anomalous flow toward the fram strait during summer months of 2007 contributed to the record low the arctic sea ice extent observed in september of that year had the summer winds over the arctic during the summers of 2010 and 2011 been the same as those in 2007 september sea ice extent would have reached new record lows in those years as well by regulating the flow of ice toward and through the fram strait variations in low level winds over the arctic have contributed to the month to month year to year and decade to decade variability of sea ice extent

propagating atmospheric patterns associated with sea ice motion through the fram strait abstracta novel analysis method involving phase shifted complex hilbert empirical orthogonal functions heofs was used to examine how variations in predominant propagating patterns of arctic surface wind influence daily fram strait sea ice export f during extended winter october april a primary control on arctic sea ice volume northwesterly winds favorable to f were provided by poleward moving anticyclones upstream over the canadian arctic associated with the leading heof of wind and also by eastward moving cyclones downstream over the barents sea associated with the second heof of wind a suite of spatial and statistical analyses indicated that the aggregate of the two propagating patterns largely explains a sea level pressure pattern analyzed in several prior studies as a standing wave oriented east west across the strait

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

summer sea ice motion from the 18 ghz channel of amsr e and the exchange of sea ice between the pacific and atlantic sectors 1 we demonstrate that sea ice motion in summer can be derived reliably from the 18ghz channel of the amsr e instrument on the eos aqua platform the improved spatial resolution of this channel with its lower sensitivity to atmospheric moisture seems to have alleviated various issues that have plagued summer motion retrievals from shorter wavelength observations two spatial filters improve retrieval quality one reduces some of the microwave signatures associated with synoptic scale weather systems and the other removes outliers compared with daily buoy drifts uncertainties in motion are 3 4 km day using the daily motion fields we examine five years of summer ice area exchange between the pacific and atlantic sectors of the arctic ocean with the sea level pressure patterns during the summer of 2006 and 2007 favoring the export of sea ice into the atlantic sector the regional outflow is 21 and 15 of the total sea ice retreat in the pacific sector

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

is the dipole anomaly a major driver to record lows in arctic summer sea ice extent recent record lows of arctic summer sea ice extentare found to be triggered by the arctic atmospheric dipoleanomaly da pattern this local second leading mode ofsea level pressure slp anomaly in the arctic produced astrong meridional wind anomaly that drove more sea ice outof the arctic ocean from the western to the eastern arcticinto the northern atlantic during the summers of 1995 1999 2002 2005 and 2007 in the 2007 summer the daalso enhanced anomalous oceanic heat flux into the arcticoceanviaberingstrait whichacceleratedbottomandlateralmelting of sea ice and amplified the ice albedo feedback acoupled ice ocean model was used to confirm the historicalrecord lows of summer sea ice extent

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

characteristics of the beaufort sea high abstract characteristics of the arctic ocean s beaufort sea high are examined using fields from the ncep ncar reanalysis at a 2 hpa contour interval the beaufort sea high appears as a closed anticyclone in the long term annual mean sea level pressure field and in spring in winter the beaufort sea region is influenced by a pressure ridge at sea level extending from the siberian high to the yukon high over northwestern canada as assessed from 6 hourly surface winds the mean frequency of anticyclonic surface winds over the beaufort sea region is fairly constant through the year while for all seasons a strong closed high can be interpreted as the surface expression of an amplified western north american ridge at 500 hpa there is some suggestion of a split flow where the ridge linked to the surface high is separated from the ridge to the south that lies within the main belt of westerlies the aleutian low in the north pacific tends to be deeper than normal when there is a strong beaufort sea high in

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

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

extreme low sea ice years in the canadian arctic archipelago 1998 versus 2007 1 extreme sea ice minima were observed within the canadian arctic archipelago caa during 1998 and 2007 the september average sea ice area was 2 90 and 2 65 standardized anomalies below the historical 1968 1996 climatology for 1998 and 2007 respectively october sea ice area for 1998 was a staggering 4 45 standardized anomalies below the historical 1968 1996 climatology and 2007 was lower by 3 36 standardized anomalies we examine the role of thermodynamic and dynamic forcing on caa sea ice that was responsible for its extreme loss in 1998 and 2007 thermodynamic forcing on the sea ice was concentrated over 1 month in 2007 facilitating rapid melt contrasted against a long melt season in 1998 this variation was attributed to anomalously warm air temperatures in june september and october for 1998 compared to anomalously warm temperatures in july for 2007 sea ice dynamics contributed to the 1998 minimum by inhibiting replenishment from the arctic ocean but actually facilitated replenishment in 2007 thereby preventing record low conditions replenishment was driven by dissimilarities in sea level pressure patterns over the caa during these extreme years evidence for preconditioned thinning was apparent leading up to 2007 but not strongly apparent for 1998 remarkably at the onset of 1998 melt season multi year ice area within the caa was 11 more than the historical climatology and 48 more than at the start of the 2007 melt season yet an extreme minima was still reached

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

thickness and surface properties of different sea ice regimes within the arctic trans polar drift data from summers 2001 2004 and 2007 1 large scale sea ice thickness and surface property data were obtained in three summers and in three different sea ice regimes in the arctic trans polar drift tpd by means of helicopter electromagnetic sounding distribution functions p of sea ice thickness and of the height spacing and density of sails were analyzed to characterize ice regimes of different ages and deformations results suggest that modal ice thickness is affected by the age of a sea ice regime and that the degree of deformation is represented by the shape of p mean thickness changes with both age and deformation standard error calculations showed that representative mean and modal thickness could be obtained with transect lengths of 15 km and 50 km respectively in less deformed ice regimes such as those around the north pole in heavier deformed ice regimes closer to greenland 100 km transects were necessary for mean thickness determination and a representative modal thickness could not be obtained at all mean sail height did not differ between ice regimes whereas sail density increased with the degree of deformation furthermore the fraction of level ice open melt ponds and open water along the transects were determined although overall ice thickness in the central tpd was 50 thinner in 2007 than in 2001 first year ice fyi was not significantly thinner in 2007 than fyi in 2001 with a decrease of only 0 3 m thinner fyi in 2007 only occurred close to the sea ice edge where open water covered more than 10 of the surface melt pond coverage retrieved from laser measurements was 15 in both the 2004 myi regime and the 2007 fyi regime

a vorticity based analysis of the spatial and temporal characteristics of the beaufort anticyclone 1 the beaufort anticyclone is the dominant pressure feature over the arctic ocean in all seasons and has a large influence on the surface wind regime and sea ice motion sea level pressure slp from the national center for atmospheric research national centers for environmental prediction reanalysis is used to create a vorticity metric to investigate the spatial and temporal characteristics of the beaufort anticyclone from 1948 to 2008 correlations between vorticity averaged over the beaufort anticyclone region and northern hemisphere slp are strongest south of alaska and north of siberia these two areas are also present in slp composite maps based on extremes of the vorticity metric temporal characteristics are investigated using running means and spectral analysis in which the only predominant peak is the annual cycle if 30 year time periods are compared little to no trend in the vorticity metric is found except in october december where the more recent time period has slightly larger vorticity magnitudes the beaufort anticyclone vorticity metric is correlated with teleconnection index values the pacific ocean patterns show a larger influence than the atlantic patterns including the arctic oscillation which has been shown in recent studies to have little correspondence to changes in sea ice in the early 21st century a significant correlation is found with the pacific north american pattern in all seasons except summer the el nino southern oscillation shows a significant correlation with the vorticity metric in winter and the pacific decadal oscillation shows a significant correlation in winter and spring

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

the encoding of wind forcing into the pacific arctic pressure head chukchi sea ice retreat and late summer barrow canyon water masses abstract barrow canyon which incises the northeast corner of the chukchi sea shelf is a major conduit through which pacific origin waters carrying nutrients biota freshwater and heat enter the arctic ocean as such barrow canyon was adopted as a long term monitoring site for the distributed biological observatory dbo in 2010 however annual hydrographic surveys across barrow canyon conducted during late august 2005 2015 along a location near what is the barrow canyon dbo survey line and in support of other research programs extend and complement the dbo hydrographic record these complementary hydrographic surveys show that volumes of pacific origin and melt water masses in barrow canyon are significantly correlated with daily sea ice areas in the eastern chukchi sea for most of the may august ice retreat season year to year differences in the timing and pattern of sea ice retreat across the chukchi sea are also shown to be well correlated with changes in seasonally averaged regional winds particularly as defined by the strength and longitudinal location of the beaufort sea high pressure cell these interdependent wind ice retreat water mass relationships are largely predicated on wind stress curl driven changes to sea level in the east siberian sea northwestern chukchi sea statistically significant correlations among wind forced sea surface heights ice areas and water mass volumes suggest that during the ice retreat season the east siberian sea western chukchi sea region serves as the arctic terminus for the pacific arctic pressure head

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

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

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

intensification of geostrophic currents in the canada basin arctic ocean abstractcontinuous sampling of upper ocean hydrographic data in the canada basin from various sources spanning from 2003 through 2011 provides an unprecedented opportunity to observe changes occurring in a major feature of the arctic ocean in a 112 km radius circle situated near the center of the traditional beaufort gyre geopotential height referenced to 400 dbar increased by about 0 3 gpm from 2003 to 2011 and by the end of the period had increased by about 65 from the climatological value near the edges of the domain considered the anomalies in dynamic height are much smaller indicating steeper gradients a rough dynamic topography constructed from profiles collected between 2008 and 2011 shows the center of the gyre to have shifted south by about 2 in latitude along the 150 w meridian geostrophic currents are much stronger on the periphery of the gyre reaching amplitudes 5 6 times higher than climatological values at grid points just offshore from the beaufort and chukchi shelf slopes esti

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

predictability of large interannual arctic sea ice anomalies in projections of twenty first century climate arctic sea ice declines and at the same time exhibits strong interannual anomalies here we investigate the potential to predict these strong sea ice anomalies under a perfect model assumption using the max planck institute earth system model in the same setup as in the coupled model intercomparison project phase 5 cmip5 we study two cases of strong negative sea ice anomalies a 5 year long anomaly for present day conditions and a 10 year long anomaly for conditions projected for the middle of the twenty first century we treat these anomalies in the cmip5 projections as the truth and use exactly the same model configuration for predictions of this synthetic truth we start ensemble predictions at different times during the anomalies considering lagged perfect and sea ice assimilated initial conditions we find that the onset and amplitude of the interannual anomalies are not predictable however the further deepening of the anomaly can be predicted for typically 1 year lead time if predictions start after the onset but before the maximal amplitude of the anomaly the magnitude of an extremely low summer sea ice minimum is hard to predict the skill of the prediction ensemble is not better than a damped persistence forecast for lead times of more than a few months and is not better than a climatology forecast for lead times of two or more years predictions of the present day anomaly are more skillful than predictions of the mid century anomaly predictions using sea ice assimilated initial conditions are competitive with those using lagged perfect initial conditions for lead times of a year or less but yield degraded skill for longer lead times the results presented here suggest that there is limited prospect of predicting the large interannual sea ice anomalies expected to occur throughout the twenty first century

application of partial least squares regression to the diagnosis of year to year variations in pacific northwest snowpack and atlantic hurricanes 1 application of the method of partial least squares pls regression to geophysical data is illustrated with two cases 1 finding sea level pressure patterns over the north pacific associated with dynamically induced winter to winter variations in snowpack in the cascade mountains of western washington state and 2 finding patterns of sea surface temperature over the tropical oceans that modulate atlantic hurricane activity on a year to year basis in both examples two robust patterns in the predictor field are identified that in combination account for over half the variance in the target time series

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

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

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

on the scaling laws derived from ice beacon trajectories in the southern beaufort sea during the international polar year circumpolar flaw lead study 2007 2008 1 sea ice motion is an important element in mass balance calculations ice thermodynamic modeling ice management plans for industry and ecosystems studies in the historical literature sea ice motion in the beaufort sea was characterized by a predominantly anticyclonic motion during winter months with episodic reversals to cyclonic activity during summer however recent studies have shown an increase in cyclonic activity throughout the annual cycle in this paper we examine circulation in the beaufort sea based on the trajectories of 22 ice beacons launched in the franklin bay area during the international polar year circumpolar flaw lead ipy cfl study during an over wintering experiment in 2007 2008 dispersion characteristics of ice motion show that absolute zonal dispersion follows a t2 scaling law characteristic of advection associated with beaufort gyre circulation whereas absolute meridional dispersion follows a scaling law of t5 4 characteristic of floaters and dispersion in 2 d turbulence temporal autocorrelations of ice velocity fluctuations highlight definitive timescales with values of 1 2 0 7 days in the zonal meridional direction near gaussian behavior is reflected in higher order moments for ice velocity fluctuation probability density functions pdfs non gaussian behavior for absolute displacement pdfs indicates spatial heterogeneity in the ice motion fields atmospheric forcing of sea ice is explored through analysis of daily north american regional reanalysis and in situ wind data where it is shown that ice in the cfl study region travels with an average speed of approximately 0 2 and an average angle of 51 5 to the right of the surface winds during the 2007 2008 winter the results from this analysis further demonstrate seasonality in ice drift to wind ratios and angles that corresponds to stress buoy data indicative of increases in internal ice stress and connectivity due to consolidation of the seasonal ice zone to the coast and perennial ice pack during winter in the beaufort sea region

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

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

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

did unusually sunny skies help drive the record sea ice minimum of 2007 1 we conduct experiments with an ice ocean model to answer the question whether and to what degree unusually clear skies during the summer of 2007 contributed to the record sea ice extent minimum in the arctic ocean during september of 2007 anomalously high pressure over the beaufort sea during summer 2007 appears associated with a strong negative cloud anomaly this anomaly is two standard deviations below the 1980 2007 average established from a combination of two different satellite based records cloud anomalies from the modis sensor are compared with anomalies from the ncep ncar reanalysis and are found in good agreement in spatial patterns and magnitude however these experiments establish that the negative cloud anomaly and increased downwelling shortwave flux from june through august did not contribute substantially to the record sea ice extent minimum this finding eliminates one aspect of the unusual weather that may have contributed to the record minimum

tracking the arctic s shrinking ice cover another extreme september minimum in 2004 1 satellite passive microwave observations document an overall downward trend in arctic sea ice extent and area since 1978 while the record minimum observed in september 2002 strongly reinforced this downward trend extreme ice minima were again observed in 2003 and 2004 although having three extreme minimum years in a row is unprecedented in the satellite record attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind temperature and oceanic forcings

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

summer retreat of arctic sea ice role of summer winds 1 the unprecedented retreat of first year ice during summer 2007 was enhanced by strong poleward drift over the western arctic induced by anomalously high sea level pressure slp over the beaufort sea that persisted throughout much of the summer comparison of the tracks of drifting buoys with monthly mean slp charts shows a substantial ekman drift by means of linear regression analysis it is shown that ekman drift during summer has played an important role in regulating annual minimum arctic sea ice extent in prior years as well in combination the preconditioning by events in prior years as represented by an index of may multi year ice and current atmospheric conditions as represented by an index of july august september slp anomalies over the arctic basin account for 60 of the year to year variance of september sea ice extent since 1979