assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

bay of bengal exhibits warming trend during the younger dryas implications of amoc a sharp decline in temperature during the younger dryas yd preceding the current warmer holocene is well documented in climate archives from the northern hemisphere high latitudes although the magnitude of yd cooling varied spatially the response of yd cooling was well documented in the atlantic and pacific oceans but not in the indian ocean here we investigate whether the modern remote forcing of tropical indian ocean sea surface temperature sst by northern hemisphere climate changes holds true for events such as the yd our sst reconstruction from the western bay of bengal exhibits an overall warming of 1 8 c during the yd we further compared our data with other existing mg ca based sst records from the northern indian ocean and found no significant negative sst anomalies in both the arabian sea and the bay of bengal compared to pre and post yd suggesting that no apparent cooling occurred during the yd in the northern indian ocean in contrast most part of the yd exhibits positive sst anomalies in the northern indian ocean that coincide with the slowdown of the atlantic meridional overturning circulation during this period

subtropical atlantic salinity variability and atlantic meridional circulation during the last deglaciation during the last deglaciation ca 21 10 ka freshening of the north atlantic surface likely caused reductions in atlantic meridional overturning circulation amoc the mechanisms related to amoc recovery remain poorly understood here we present three new deglacial surface temperature and 18oseawater 18osw reconstructions from the western subtropical north and south atlantic similarities to tropical caribbean and western atlantic 18osw records suggest that a salty surface water mass accumulated in the western atlantic from 27 s to 33 n during periods of reduced amoc however 18osw decreases led deep amoc resumption by hundreds of years we suggest that the northward export of salt previously trapped in the western atlantic resulted in the early establishment of a shallow overturning circulation that eventually culminated in deep amoc resumption implying that amoc may constitute a self limiting system

palaeoceanographic implications of genetic variation in living north atlantic neogloboquadrina pachyderma the shells of the planktonic foraminifer neogloboquadrina pachyderma have become a classical tool for reconstructing glacial interglacial climate conditions in the north atlantic ocean1 2 3 palaeoceanographers utilize its left and right coiling variants which exhibit a distinctive reciprocal temperature and water mass related shift in faunal abundance both at present and in late quaternary sediments1 2 4 5 recently discovered cryptic genetic diversity in planktonic foraminifers6 7 8 now poses significant questions for these studies here we report genetic evidence demonstrating that the apparent single species shell based records of right coiling n pachyderma used in palaeoceanographic reconstructions contain an alternation in species as environmental factors change this is reflected in a species dependent incremental shift in right coiling n pachyderma shell calcite 18o between the last glacial maximum and full holocene conditions guided by the percentage dextral coiling ratio our findings enhance the use of 18o records of right coiling n pachyderma for future study they also highlight the need to genetically investigate other important morphospecies to refine their accuracy and reliability as palaeoceanographic proxies

rapid subtropical north atlantic salinity oscillations across dansgaard oeschger cycles geochemical and sedimentological evidence suggest that the rapid climate warming oscillations of the last ice age the dansgaard oeschger cycles were coupled to fluctuations in north atlantic meridional overturning circulation through its regulation of poleward heat flux the balance between cold meltwater from the north and warm salty subtropical gyre waters from the south influenced the strength and location of north atlantic overturning circulation during this period of highly variable climate here we investigate how rapid reorganizations of the ocean atmosphere system across these cycles are linked to salinity changes in the subtropical north atlantic gyre we combine mg ca palaeothermometry and oxygen isotope ratio measurements on planktonic foraminifera across four dansgaard oeschger cycles spanning 45 9 59 2 kyr ago to generate a seawater salinity proxy record from a subtropical gyre deep sea sediment core we show that north atlantic gyre surface salinities oscillated rapidly between saltier stadial conditions and fresher interstadials covarying with inferred shifts in the tropical atlantic hydrologic cycle and north atlantic overturning circulation these salinity oscillations suggest a reduction in precipitation into the north atlantic and or reduced export of deep salty thermohaline waters during stadials we hypothesize that increased stadial salinities preconditioned the north atlantic ocean for a rapid return to deep overturning circulation and high latitude warming by contributing to increased north atlantic surface water density on interstadial transitions

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

evidence from the northeastern atlantic basin for variability in the rate of the meridional overturning circulation through the last deglaciation a first study from the subtropical western atlantic using 231pa 230th ratios as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation however these results warrant confirmation from additional locations and water depths because the interpretation of the sedimentary 231pa 230th ratio in terms of circulation vigor can be biased by variations in particle flux and composition we have measured 231pa 230th in a core from the iberian margin in the northeastern atlantic basin and have compared these new results to the data from the western atlantic basin we find that the reduction in the circulation during h1 and yd and the subsequent increases first recognized in the sediment deposited on bermuda rise are also evident in the eastern basin in a totally different sedimentary regime confirming that sedimentary 231pa 230th ratios record basin wide changes in deep water circulation however some differences between the eastern and western records are also recognized providing preliminary evidence to differentiate between renewal rates in the two north atlantic basins and between shallower and deeper overturning our results suggest the possible existence of two sources of glacial north atlantic intermediate deep water gnaiw one in the south labrador sea and another west of rockall plateau both sources contributed to the meridional overturning but the two had different sensitivity to meltwater from the laurentide and the fennoscandian ice sheets during the deglaciation these results indicate that additional information on the geometry and strength of the ventilation of the deep atlantic can be obtained by contrasting the evolution of sediment 231pa 230th in different sections of the atlantic ocean

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

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

palaeo oceanography deepwater variability in the holocene epoch the conversion of surface water to deep water in the north atlantic results in the release of heat from the ocean to the atmosphere which may have amplified millennial scale climate variability during glacial times1 and could even have contributed to the past 11 700 years of relatively mild climate known as the holocene epoch 2 3 4 here we investigate changes in the carbon isotope composition of benthic foraminifera throughout the holocene and find that deep water production varied on a centennial millennial timescale these variations may be linked to surface and atmospheric events that hint at a contribution to climate change over this period

ground penetrating radar a near face experience from washington county arkansas digital ground penetrating radar gpr is an emerging technology for detecting locating and or mapping features in the shallow subsurface it has application to geology civil engineering environmental science engineering soil science and many other fields this case history describes a high quality gpr survey performed in very close proximity to a vertical limestone rock face at a roadcut site in northwest arkansas the configuration allowed interpretation of the gpr results with the maximum of amount of geologic control the rock face itself our experience suggests that gpr has significant potential as a high resolution tool for mapping shallow structure and stratigraphy in carbonate rocks

advection and scavenging controls of pa th in the northern ne atlantic over the last 2 decades significant advances have been made in reconstructing past rates of ocean circulation using sedimentary proxies for the dynamics of abyssal waters in this study we combine the use of two rate proxies sortable silt grain size and sedimentary 231pa 230th measured on a depth transect of deep sea sediment cores from the northern ne atlantic to investigate ocean circulation changes during the last deglacial we find that at two deep sites the core top 231pa 230th ratios reflect holocene circulation rates while during heinrich stadial 1 the deglacial ratios peaked as the sortable silt grain size decreased reflecting a general circulation slowdown however the peak 231pa 230th significantly exceeded the production ratio in both cores indicating that 231pa 230th was only partially controlled by ocean circulation at these sites this is supported by a record of 231pa 230th from an intermediate water depth site where values also peaked during heinrich stadial 1 but were consistently above the production ratio over the last 24 ka reflecting high scavenging below productive surface waters at our study sites we find that preserved sediment component fluxes cannot be used to distinguish between a scavenging or circulation control although they are consistent with a circulation influence since the core at intermediate depth with the highest 231pa 230th recorded the lowest particle fluxes reconstruction of advection rate using 231pa 230th in this region is complicated by high productivity but the data nevertheless contain important information on past deep ocean circulation

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

effects of temperature on mg ca in neogloboquadrinid shells determined by live culturing 1 new culturing protocols allowed the development of a mg ca temperature calibration equation for neogloboquadrina pachyderma d when cultured between 9 c and 19 2 c mg ca in n pachyderma d shell calcite exhibits a clear dependence on temperature shell calcite mg ca increased exponentially with temperature mg ca 0 51 0 15 0 23 exp 0 10 0 02 t limited data suggest n dutertrei exhibit similar elemental temperature relationships to n pachyderma d we applied the temperature relationship established by culturing to mg ca in neogloboquadrinid shells collected using plankton tows compared to measured sst the calculated temperatures were within 2 c for mg ca 95 ci multiple samples from single tows generally had calculated temperatures that ranged from near surface values to temperatures consistent with calcification depths down to 70 m our work indicates that mg ca temperature calibration equations for temperate and polar foraminiferal species have a similar exponential constant but a higher pre exponential constant than those for surface dwelling tropical species therefore accurate paleotemperature reconstructions from temperate and polar species require the use of an equation distinct from those used for tropical species

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

ground penetrating radar used to assess aggregate in catastrophic flood deposits northeast alberta canada coarse grained aggregate deposited by a catastrophic flood located north of fort mcmurray alberta was examined using ground penetrating radar gpr and lithostratigraphic logging techniques gpr transects were acquired from an upper scoured zone of flood deposits sedimentary structures cross beds and plane beds within the coarse sand and gravel and determinations of depth to bedrock sediment thickness of the aggregate were recognized in the gpr profiles by their varying dielectric properties fine grained conductive underlying oil sand till or glaciolacustrine sediment silt and clay attenuated the radar signal the sedimentary structures mapped from the gpr transects were confirmed in adjacent trench exposures we suggest that gpr is an efficient methodology for determining volumes of aggregate reserves thicknesses of aggregate deposits and mapping sedimentary structures of high energy fluvial sediments key words aggregate ground penetrating radar alberta spillway

systematic change of foraminiferal mg ca ratios across a strong salinity gradient abstract the mg ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures used in conjunction with 18 o of foraminiferal calcite it allows deconvolution of temperature and ice volume signals to infer past ocean temperatures and salinities assuming the relationship between seawater 18 o and salinity is known such work assumes that temperature is the only or at least the dominant environmental controller of foraminiferal mg ca the semi enclosed mediterranean sea where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 c to 8 c provides a relevant setting to test this assumption outside the laboratory in this study planktonic foraminifera o universa g siphonifera g bulloides and g ruber white and pink were picked from 11 box core tops spanning the mediterranean salinity gradient and analysed for their trace element concentrations mg ca ratios are higher for the associated calcification temperatures than in other regions where calibrations have been conducted and correlate poorly with calcification temperature mg ca ratios are particularly high for samples from the eastern mediterranean where salinity is unusually high correlations of mg ca with the calcification salinity are statistically significant with mg ca changing by 15 59 per psu suggesting that salinity may act as a control on mg ca ratios in addition to the dominant temperature control we show that contamination by non carbonate material and diagenetic high mg carbonate overgrowths cannot account for the observed trend of increasing mg ca with salinity a relationship between mg ca and salinity is also suggested by re analysis of calibrations from open ocean settings these new mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the mg ca palaeothermometer should be considered even in open ocean settings particularly where large salinity changes occurred in the past

two phase structure of tropical hydroclimate during heinrich stadial 1 and its global implications abstract previous studies have proposed that the two phase structure of heinrich stadial 1 hs1 is a ubiquitous feature however few studies have focused on the internal structure of hs1 over a tropical domain thus the interhemispheric ocean atmosphere teleconnections during hs1 are poorly defined here we present high resolution sedimentological geochemical and palaeoceanographic records from the core cg2 in the southern south china sea scs off the northern sunda shelf the core continuously spans 9 0 22 0 ky bp the records suggest two episodes of increased monsoon rainfall during the pre hs1 19 0 18 0 ky bp and in the early hs1 17 5 16 1 ky bp along with a weaker monsoon rainfall during the late hs1 16 1 14 7 ky bp in contrast a lower precipitation over the flores sea occurred during the early hs1 off the southern sunda shelf followed by an enhanced precipitation runoff during the late hs1 muller et al 2012 notably these two different precipitation phases characterise a southward intertropical convergence zone itcz shift over the sunda shelf during hs1 these changes are also consistent with other monsoon records as well as other available data from the tropical to high latitudes of both hemispheres supporting the global scope of the twofold hs1 we propose that the two episodes of intense monsoon rainfall over the northern sunda shelf during the pre hs1 and the early hs1 observed in our study are closely linked to two different melting events associated with european ice sheet eis retreat we further propose that the subsequent maximum atlantic meridional overturning circulation amoc reduction and the migration of the itcz to its southernmost position during the late hs1 are tightly connected with the destabilization of the marine terminating ice streams of the laurentide ice sheet lis in the north atlantic tropical positive feedbacks during hs1 in turn should have played an important role in sustaining the amoc reduction and northern hemisphere nh stadial conditions by continuously lowering the salinity of the low latitude currents in the atlantic ocean in addition the tropical itcz appears to have been a key bridge in promoting interhemispheric climate connections by which north atlantic cooling was rapidly linked to increased southern ocean surface westerlies this in turn drove upwelling and co2 ventilation from the southern ocean and thereby facilitated deglacial warming finally these findings show that tropical climate variation is an important component of deglacial climate changes understanding how it responds to millennial events like hs1 may help us better understand global teleconnections

millennial scale surface and subsurface paleothermometry from the northeast atlantic 55 8 ka bp we present high resolution records of upper ocean temperatures derived from mg ca ratios of surface dwelling globigerina bulloides and subsurface dwelling neogloboquadrina pachyderma sinistral and the relative abundance of n pachyderma sinistral for the period 55 8 ka bp from ne atlantic sediment core md01 2461 millennial scale temporal variability and longer term trends in these records enable us to develop a detailed picture of past ocean conditions such as a weakening of thermocline intensity from marine isotope stage 3 mis 3 to the last glacial maximum lgm the correspondence of all temperature proxies and convergence of paired oxygen isotope 18o records from both planktonic species implies a breakdown in the thermocline and year round mixing of the upper water column through the lgm perhaps related to decreasing insolation and additional cooling in association with the expansion of the circum north atlantic ice sheets millennial scale divergence in surface and subsurface temperatures and 18o across the last glacial correspond to meltwater release and the development of a strong halocline associated with both heinrich h events and instabilities of the nw european ice sheet during such episodes g bulloides mg ca appears to record ambient even warming summer sea surface temperatures across h events while the other proxies record maximum cooling

ice sheets and sea level of the last glacial maximum this paper outlines the general issues regarding ice sheets and sea level of the last glacial maximum lgm which formed the basis of an epilog project workshop papers in this special issue of quaternary science reviews provide a comprehensive assessment of these issues from the perspective of geological reconstructions of ice sheet extent records of sea level change ice sheet modelling geophysical models of glacial isostatic adjustment and geochemical proxies of ice volume this new assessment has substantially narrowed the uncertainties in the total changes in ice sheets and sea level and their proxies suggesting a net decrease in eustatic sea level at the lgm ranging from 120 to 135 m r 2001 elsevier science ltd all rights reserved

accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation 1 abrupt decreases of the atlantic meridional overturning circulation moc during the late pleistocene have been directly linked to catastrophic discharges of glacimarine freshwater triggering disruption of northward marine heat transport and causing global climate changes here we provide measurements of excess sedimentary 231 pa 230 th from a high accumulation sediment drift deposit in the ne atlantic that record a sequence of sudden variations in the rate of moc associated deep ocean ventilation and surface ocean climatology the data series reveal a sequential decrease in the moc rate at 18 0 ka bp ago that coincides with only transient and localized freshwater inputs this change represents a substantial though not total cessation in moc that predates the major heinrich h1 meltwater event by at least 1 200 years these results highlight the potential of targeted freshwater perturbations in promoting substantial moc changes without a direct linking with catastrophic freshwater surges citation hall i r s b moran r zahn p c knutz c c shen and r l edwards 2006 accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation geophys res lett 33 l16616 doi 10 1029 2006gl026239

high resolution record of late glacial and deglacial sea ice changes in fram strait corroborates ice ocean interactions during abrupt climate shifts the transition from last glacial to deglacial and subsequently to modern interglacial climate conditions was accompanied by abrupt shifts in the palaeoceanographic setting in the subpolar north atlantic knowledge about the role that sea ice coverage played during these rapid climate reversals is limited since most marine sediment cores from the higher latitudes provide only a coarse temporal resolution and often poorly preserved microfossils here we present a highly resolved reconstruction of sea ice conditions that characterised the eastern fram strait a key area for water mass exchange between the arctic ocean and the north atlantic for the past 30 ka bp this reconstruction is based on the distribution of the sea ice biomarker ip25 and phytoplankton derived biomarkers in a sediment core from the continental slope of western svalbard during the late glacial 30 ka to 19 ka bp recurrent advances and retreats of sea ice characterised the study area and point to a hitherto less considered oceanic and or atmospheric variability a long lasting perennial sea ice coverage in eastern fram strait persisted only at the very end of the last glacial maximum i e from 19 2 to 17 6 ka bp and was abruptly reduced at the onset of heinrich event 1 coincident with or possibly even inducing the collapse of the atlantic meridional overturning circulation amoc further maximum sea ice conditions prevailed during the younger dryas cooling event and support the assumption of an amoc reduction due to increased formation and export of arctic sea ice through fram strait a significant retreat of sea ice and sea surface warming are observed for the early holocene

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

distribution of planktic foraminifera at the ice margin in the arctic fram strait planktic foraminifera were collected in net tows 63 m along two east west transects at 78 and 80 n in the fram strait northern nordic seas at five concurrent depth intervals in the upper 200 m of the water column in the ice free zone absolute abundances in the upper 200 m of the water column up to 500 individuals m3 were obtained along the ice margin the absolute abundances reached up to 1250 ind m3 while in the ice covered areas not more than 50 ind m3 have been found surprisingly these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice free and the ice covered regions neogloboquadrina pachyderma is the dominant species in most samples making up to 60 of the total faunal assemblage globigerina quinqueloba contributes 38 and all other species combined make up only 2 of the total fauna both absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used using smaller mesh sizes provides a wider species spectrum which is of special interest for paleoceanographic reconstructions in the nordic seas where fossil assemblages 150 m often consist of only one species the specific hydrographic conditions in the fram strait with warm atlantic waters underlying cold polar surface waters result in a rather atypical depth distribution of the planktic foraminifera all species seem to prefer the temperate atlantic waters between 50 m and 200 m thus the species composition as well as geochemical tracers do not reflect the surface ocean conditions which again has potentially interesting implications for paleoceanographic reconstructions

neogloboquadrina pachyderma dex and sin mg ca and δ18o records from the norwegian sea magnesium calcium mg ca records based on n pachyderma dex and n pachyderma sin from the last 1200 years have been retrieved from high resolution cores in the norwegian sea comparing temperatures inferred from mg ca and the oxygen isotopic composition of calcite 18oc with instrumental temperature records from ocean weather ship mike suggests that n pachyderma calcifies during the summer season with an offset to oxygen isotope equilibrium of 0 6 in this region summer temperatures below the thermocline are related to the winter season ventilation and breakdown of the seasonal thermocline hence the deeper dwelling n pachyderma sin provides a winter season signal down core n pachyderma dex mg ca temperatures display larger variance than observed in 18oc temperatures record derived from the same morphotype the smaller variance in the 18ocn pachyderma dex temperatures is probably linked to salinity changes in the upper 50 m of the water column the mg ca temperature and 18oc records are used to reconstruct changes in the oxygen isotopic composition of water 18ow during the last 1200 years the reconstructed 18ow records show variation within a realistic range allowing the influence of other water masses than those present at the site today and suggest that the mg ca signal in morphotypes of n pachyderma in the norwegian sea responds to changes in climatic parameters

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

geological modeling for simulation studies reservoir heterogeneity is hierarchical in nature and different levels of reservoir heterogeneity need to be quantified by the reservoir geologist for numerical simulation studies at the largest scale field scale sand body continuity and interconnectedness are the most important parameters at the scale of a reservoir or a genetic sand body areal permeability trends presence and distribution of permeability baffles vertical profiles of permeability and presence of directional permeability within a sand body are the most critical parameters at a smaller scale the influence of cross bedding on displacement processes is shown to be significant and in fact should be assessed to obtain more meaningful results from larger scale simulation models the examples given show some of the effects of the different scales of heterogeneity on fluid flow patterns these examples indicate the degree of detail that must be considered at different scales if simulations are to give meaningful results

geochemical response of the mid depth northeast atlantic ocean to freshwater input during heinrich events 1 to 4 heinrich events are intervals of rapid iceberg sourced freshwater release to the high latitude north atlantic ocean that punctuate late pleistocene glacials delivery of fresh water to the main north atlantic sites of deep water formation during heinrich events may result in major disruption to the atlantic meridional overturning circulation amoc however the simple concept of an amoc shutdown in response to each freshwater input has recently been shown to be overly simplistic here we present a new multi proxy dataset spanning the last 41 000 years that resolves four heinrich events at a classic mid depth north atlantic drill site employing four independent geochemical tracers of water mass properties boron calcium carbon and oxygen isotopes in foraminiferal calcite and neodymium isotopes in multiple substrates we also report rare earth element distributions to investigate the fidelity by which neodymium isotopes record changes in water mass distribution in the northeast north atlantic our data reveal distinct geochemical signatures for each heinrich event suggesting that the sites of fresh water delivery and or rates of input played at least as important a role as the stage of the glacial cycle in which the fresh water was released at no time during the last 41 kyr was the mid depth northeast north atlantic dominantly ventilated by southern sourced water instead we document persistent ventilation by glacial north atlantic intermediate water gnaiw albeit with variable properties signifying changes in supply from multiple contributing northern sources

introduction to the special issue on aquifer sedimentology problems perspectives and modern approaches abstract progress towards a better understanding of groundwater circulation and transport processes in aquifers demands a multidisciplinary approach to a host of unresolved problems although much progress has been made within recent years in interpreting the dynamic character of groundwater systems many key issues remain to be addressed in particular several areas demand attention the role of sedimentological information heterogeneity in groundwater and transport models the scaling up of observations from outcrop scale to larger scales and the integration of geological and geophysical information of different quality into the description of an aquifer structure still nowadays many of the heterogeneities cannot be recognized directly because of the limitation of measurement techniques this is probably one of the reasons for the limited application of aquifer sedimentology and geophysics in practical cases in order to consolidate expand and make a larger number of people aware of the contribution of modern aquifer sedimentology including modelling and ultra high resolution geophysical methods several lines of intervention were identified 1 a better collaboration of the different disciplines on site specific applied problems 2 development of new modelling techniques combining data of different quality 3 development of optimizing tools position and number of wells additional geophysical methods baysian techniques 4 development of a common language among sedimentologists and hydrogeologists to overcome communication problems

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

synchronization of north pacific and greenland climates preceded abrupt deglacial warming some proposed mechanisms for transmission of major climate change events between the north pacific and north atlantic predict opposing patterns of variations others suggest synchronization resolving this conflict has implications for regulation of poleward heat transport and global climate change new multidecadal resolution foraminiferal oxygen isotope records from the gulf of alaska goa reveal sudden shifts between intervals of synchroneity and asynchroneity with the north greenland ice core project ngrip 18 o record over the past 18 000 years synchronization of these regions occurred 15 500 to 11 000 years ago just prior to and throughout the most abrupt climate transitions of the last 20 000 years suggesting that dynamic coupling of north pacific and north atlantic climates may lead to critical transitions in earth s climate system

a numerical three dimensional conditioned unconditioned stochastic facies type model applied to a remediation well system in this study a three dimensional stochastic facies based aquifer model was developed the model can be used to numerically simulate flow and solute transport in heterogeneous groundwater aquifers the stochastic generation process can be conditioned by using available facies information in one vertical plane or two orthogonal vertical ones in this study the information was obtained from a facies interpretation of a vertical georadar profile in a natural gravel formation in switzerland in the domain outside the known profile unconditioned lenses and layers were generated at random according to statistical information on coherent sedimentary structures based on observations in adjacent gravel pits jussel et al 1994a the method was applied to a single extraction well designed to capture an initially block shaped contaminant plume a total of 80 conditioned and unconditioned synthetic aquifers was generated the flow and transport simulations were performed using a finite element flow model and a random walk transport model the results are presented as the ensemble of integral solute mass recovery curves of single realizations one would expect conditioning to reduce the bandwidth of the recovery curves representing the uncertainty but the results show that the bandwidth even increased this effect was attributed to a discrepancy in the mean volumetric fraction of the different facies types in the conditioned and the unconditioned cases moreover a simulation using a homogeneous model with constant equivalent flow and transport parameters overestimated the remediation efficiency the influence of a linear reversible equilibrium sorption on the remediation well efficiency was taken into account by an uncorrelated random field of the retardation factor based on values from the literature however the impact of the variability in hydraulic conductivity clearly exceeded the effect of the variability in the retardation factor

using species specific paleotemperature equations with foraminifera a case study in the southern california bight abstract species specific paleotemperature equations were used to reconstruct a record of temperature from foraminiferal 18 o values over the last 25 kyr in the southern california bight the equations yield similar temperatures for the 18 o values of globigerina bulloides and neogloboquadrina pachyderma in contrast applying a single paleotemperature equation to g bulloides and n pachyderma 18 o yields different temperatures which has been used to suggest that these species record the surface to thermocline temperature gradient in santa barbara basin an isotopically distinct morphotype of g bulloides dominates during glacial intervals and yields temperatures that appear too cold when using a paleotemperature equation calibrated for the morphotype common today when a more appropriate paleotemperature equation is used for glacial g bulloides we obtain more realistic glacial temperatures glacial interglacial temperature differences g i t calculated in the present study indicate significant cooling 8 10 c throughout the southern california bight during the last glacial maximum lgm the magnitude of glacial cooling varies from 8 c near the middle of the southern california bight tanner basin and san nicolas basin to 9 c in the north santa barbara basin and 9 5 10 c in the south velero basin and no name basin our temperature calculations agree well with previous estimates based on the modern analog technique in contrast studies using n pachyderma coiling ratios u k 37 indices and transfer functions estimate considerably warmer lgm temperatures and smaller g i t

northern source for deglacial and holocene deepwater composition changes in the eastern north atlantic basin over the last decades extensive research has been carried out on changes in the atlantic meridional overturning circulation and its role during the last deglacial period at present only a few high resolution data sets from the deep eastern north atlantic exist for this period it therefore remains uncertain whether deepwater changes in the eastern north atlantic basin were governed by alternating contributions of northern and southern deepwater or whether the eastern north atlantic basin reflects changes in the initial composition and source of north atlantic deepwater furthermore it is still debated whether such changes are triggered by northern or southern hemisphere climatic changes in this centennial to decadal scale resolution study we investigate deepwater composition changes in the eastern north atlantic basin over the last 15 ka br we used sediment cores geofar kf16 and md08 3180 37 984 degrees n 31 118 degrees w wd 3050 m 37 999 degrees n 31 134 degrees w wd 3064 m obtained from a small basin at the eastern flank of the mid atlantic ridge south of the azores islands under modern conditions the coring site is situated at the boundary between southern lower deep water and northern eastern north atlantic deep water consisting of iceland scotland overflow water and labrador sea water distinct differences between the three water masses in terms of ventilation state temperature and salinity signatures are ideal for tracking changes in the deglacial north atlantic deepwater distribution using paired benthic foraminiferal stable isotopes delta c 13 delta o 18 and mg ca bottom water temperature reconstructions the results show a close coupling of low bottom water temperature 1 5 degrees c and delta c 13 0 0 5 parts per thousand values during cold heinrich event 1 the younger dryas and the preboreal that were coeval with a major delta o 18 depletion of deepwater the strong similarities between subtropical eastern north atlantic deep water and subpolar north atlantic surface and deepwater changes indicate that deglacial changes in eastern north atlantic deep water distribution were triggered in the north atlantic consequently this would imply that changes in the north atlantic also contributed to deglacial changes in antarctic bottom water composition during the early holocene stepwise increasing delta c 13 values suggest increasing eastern north atlantic deep water production and or increasing eastern north atlantic deep water ventilation with minor but distinct interruptions at 10 8 10 6 9 1 8 4 8 1 and 7 2 ka bp which were most probably also triggered in the subpolar north atlantic c 2015 elsevier b v all rights reserved

hydrographic changes in the eastern subpolar north atlantic during the last deglaciation abstract millennial scale climate fluctuations of the last deglaciation have been tied to abrupt changes in the atlantic meridional overturning circulation moc a key to understanding mechanisms of moc collapse and recovery is the documentation of upper ocean hydrographic changes in the vicinity of north atlantic deep convection sites here we present new high resolution ocean temperature and 18osw records spanning the last deglaciation from an eastern subpolar north atlantic site that lies along the flow path of the north atlantic current approaching deep convection sites in the labrador and greenland iceland norwegian gin seas high resolution temperature and 18osw records from subpolar site 980 help track the movement of the subpolar subtropical front associated with temperature and atlantic moc changes throughout the last deglaciation distinct 18osw minima during heinrich 1 h1 and the younger dryas yd correspond with peaks in ice rafted debris and periods of reduced atlantic moc indicating the presence of melt water in this region that could have contributed to moc reductions during these intervals increased tropical and subtropical 18osw during these periods of apparent freshening in the subpolar north atlantic suggest a buildup of salt at low latitudes that served as a negative feedback on reduced atlantic moc

fragmentation mechanisms associated with explosive lava water interactions in a lacustrine environment rootless cones form when partially outgassed lava interacts explosively with external water the explosions represent an end member system that can elucidate mechanisms of explosive magma water interactions in the absence of magmatic fragmentation induced by outgassing the proportion of finely fragmented ejecta i e ash generated in rootless explosions may contribute significantly to the energy of the explosion even if the ash volume is small relative to coarser ejecta laboratory experiments indicate that the degree of melt water mixing and energy release are proportional to the abundance of blocky grains fragmented by brittle disintegration which effectively contribute thermal energy to the system to constrain the mechanisms and dynamics of rootless explosive activity we assess the nature and modes of fragmentation and ejecta characteristics through morphological textural and density analysis of rootless tephra associated with a p hoehoe lava flow in a lacustrine lake basin environment we observe strong correlations between the mean grain size and the mass percentage of both blocky negative power law trend and fluidal positive logarithmic tephra clasts of all sizes we interpret these trends as scale dependent fragmentation behavior due to the decreasing efficacy of hydrodynamic fragmentation as it occurs over finer scales especially over the ash size range additionally all analyzed beds contain fine ash sized blocky and mossy clasts which are thought to be diagnostic of a high transfer rate of thermal to mechanical energy characteristic of molten fuel coolant interactions these results agree with a recent model of rootless cone formation prior fragmentation theory and scaled laboratory experiments and therefore provide a field based analog for future experimental and modeling efforts

moisture transport across central america as a positive feedback on abrupt climatic changes reconstruction of sea surface salinities in the eastern equatorial pacific ocean over the past 90 000 years detected strong millennial scale fluctuations that are associated with the migration of the tropical atlantic intertropical convergence zone thus millennial scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes modulating the north atlantic freshwater budget and hence north atlantic ocean circulation moisture transport from the atlantic to the pacific ocean across central america leads to relatively high salinities in the north atlantic ocean1 and contributes to the formation of north atlantic deep water2 this deep water formation varied strongly between dansgaard oeschger interstadials and heinrich events millennial scale abrupt warm and cold events respectively during the last glacial period3 increases in the moisture transport across central america have been proposed to coincide with northerly shifts of the intertropical convergence zone and with dansgaard oeschger interstadials with opposite changes for heinrich events4 here we reconstruct sea surface salinities in the eastern equatorial pacific ocean over the past 90 000 years by comparing palaeotemperature estimates from alkenones and mg ca ratios with foraminiferal oxygen isotope ratios that vary with both temperature and salinity we detect millennial scale fluctuations of sea surface salinities in the eastern equatorial pacific ocean of up to two to four practical salinity units high salinities are associated with the southward migration of the tropical atlantic intertropical convergence zone coinciding with heinrich events and with greenland stadials5 the amplitudes of these salinity variations are significantly larger on the pacific side of the panama isthmus as inferred from a comparison of our data with a palaeoclimate record from the caribbean basin6 we conclude that millennial scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes modulating the north atlantic freshwater budget and hence north atlantic deep water formation

the oxygen isotopic composition of seawater during the last glacial maximum high resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep sea sediments from sites in the north and south atlantic the data provide direct measurements of changes in the isotopic composition of bottom waters during the last glacial maximum lgm results from ocean drilling program odp site 981 in the north atlantic currently bathed in north atlantic deep water nadw reproduces previous results from the ceara and bermuda rises constraining the glacial interglacial change in 18 o of the deep atlantic to be 0 7 0 8 results from site 984 which is located north of site 981 and at a shallower water depth yield a similar value 0 8 providing insight into the properties of glacial north atlantic intermediate water gnaiw sites from odp leg 177 in the south atlantic span the modern boundary between northern and southern sources of deep water data from the northern site 1088 yield a similar result to sites in the tropical and north atlantic 0 7 at the southern site 1093 located south of the polar front the change is substantially larger 1 1 representing the change in 18 o of southern source waters since the lgm these results confirm previous estimates that the global average change in 18 o of seawater is 1 0 0 1 hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations giving further support to these results at all sites studied the temperature of the deep ocean during the lgm calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera was within 1 c of the freezing point of seawater

eastern pacific warm pool paleosalinity and climate variability 0 30 kyr multiproxy geologic records of 18o and mg ca in fossil foraminifera from sediments under the eastern pacific warm pool epwp region west of central america document variations in upper ocean temperature pycnocline strength and salinity i e net precipitation over the past 30 kyr although evident in the paleotemperature record there is no glacial interglacial difference in paleosalinity suggesting that tropical hydrologic changes do not respond passively to high latitude ice sheets and oceans millennial variations in paleosalinity with amplitudes as high as 4 practical salinity units occur with a dominant period of 3 5 ky during the glacial deglacial interval and 1 0 1 5 ky during the holocene the amplitude of the epwp paleosalinity changes greatly exceeds that of published caribbean and western tropical pacific paleosalinity records epwp paleosalinity changes correspond to millennial scale climate changes in the surface and deep atlantic and the high northern latitudes with generally higher lower paleosalinity during cold warm events in addition to intertropical convergence zone itcz dynamics which play an important role in tropical hydrologic variability changes in atlantic pacific moisture transport which is closely linked to itcz dynamics may also contribute to hydrologic variations in the epwp calculations of interbasin salinity average and interbasin salinity contrast between the epwp and the caribbean help differentiate long term changes in mean itcz position and atlantic pacific moisture transport respectively

bivalve shell horizons in seafloor pockmarks of the last glacial interglacial transition a thousand years of methane emissions in the arctic ocean we studied discrete bivalve shell horizons in two gravity cores from seafloor pockmarks on the vestnesa ridge 1200 m water depth and western svalbard 79 00 n 06 55 w to provide insight into the temporal and spatial dynamics of seabed methane seeps the shell beds dominated by two genera of the family vesicomyidae phreagena s l and isorropodon sp were 20 30 cm thick and centered at 250 400 cm deep in the cores the carbon isotope composition of inorganic 13c from 13 02 to 2 36 and organic 13c from 29 28 to 21 33 shell material and a two end member mixing model indicate that these taxa derived between 8 and 43 of their nutrition from chemosynthetic bacteria in addition negative 13c values for planktonic foraminifera 6 7 to 3 1 concretions identified as methane derived authigenic carbonates and pyrite encrusted fossil worm tubes at the shell horizons indicate a sustained paleo methane seep environment combining sedimentation rates with 14c ages for bivalve material from the shell horizons we estimate the horizons persisted for about 1000 years between approximately 17 707 and 16 680 years b p corrected the seepage event over a 1000 year time interval was most likely associated with regional stress related faulting and the subsequent release of overpressurized fluids

the north atlantic atmosphere sea surface 14c gradient during the younger dryas climatic event abstract we attempt to quantify the 14c difference between the atmosphere and the north atlantic surface during a prominent climatic period of the last deglaciation the younger dryas event yd our working hypothesis is that the north atlantic may have experienced a measurable change in 14c reservoir age due to large changes of the polar front position and variations in the mode and rate of north atlantic deep water nadw production we dated contemporaneous samples of terrestrial plant remains and sea surface carbonates in order to evaluate the past atmosphere sea surface 14c gradient we selected terrestrial vegetal macrofossils and planktonic foraminifera neogloboquadrina pachyderma left coiling mixed with the same volcanic tephra the vedde ash bed which occurred during the yd and which can be recognized in north european lake sediments and north atlantic deep sea sediments based on ams ages from two norwegian sites we obtained about 10 300 yr bp for the atmospheric 14c age of the volcanic eruption foraminifera from four north atlantic deep sea cores selected for their high sedimentation rates 10 cm kyr 1 were dated by ams 21 samples for each core the raw 14c ages assigned to the ash layer peak is significantly older than the 14c age obtained on land part of this discrepancy is due to bioturbation which is shown by numerical modelling nevertheless after correction of a bioturbation bias the mean 14c age obtained on the planktonic foraminifera is still about 11 000 11 100 yr bp the atmosphere sea surface 14c difference was roughly 700 800 yr during the yd whereas today it is 400 500 yr a reduced advection of surface waters to the north atlantic and the presence of sea ice are identified as potential causes of the high 14c reservoir age during the yd

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

the greenland ice sheet during the last glacial cycle current ice loss and contribution to sea level rise from a palaeoclimatic perspective abstract during the last interglacial lig period between 130 and 116 thousand years before present ka bp the greenland ice sheet gris was considerably reduced in size contributing to a global mean sea level msl rise of 0 5 4 2 m relative to the present this is not sufficient to explain the 6 9 m msl rise estimated for the lig which implies that a significant contribution to the lig highstand came from antarctica following the lig the gris grew and attained its maximum volume of about 12 m global sea level equivalents sles between 18 and 16 ka bp since then the gris margins have retreated on an order of several hundred km following a general pattern of lagged response to changes in high latitude summer insolation and global greenhouse gas concentrations on shorter timescales and over smaller spatial scales the combination of internal ice sheet dynamics and external climate dynamics has often resulted in a more complex and asynchronous behaviour of the ice sheet margin the gris probably reached its minimum holocene extent around 4 ka bp and modelling studies suggest that it contributed to a rise in global msl of less than 0 2 m relative to the present at this time a period of steady growth followed the holocene minimum and in many areas the ice sheet advanced beyond its present limits during the little ice age i e the last few centuries currently the gris occupies an area of 1 7 10 6 km 2 and features a volume of 2 96 10 6 km 3 which amounts to 7 4 m sle observations show that the rate of mass loss from the gris has been accelerating over the past few decades and ice sheet modelling indicates that we have to go back to the last deglaciation around 10 ka bp in order to find sustained melt rates that were higher than those experienced over the last decade the future development of the gris will have a profound influence on sea level both globally and regionally but there are large uncertainties related to how the gris will respond to future global warming based on a range of modelling studies employing different emission scenarios the gris is expected to contribute about 0 1 0 3 m to global msl rise by the end of the 21st century in a longer time perspective modelling suggests that melting of the gris may replace ocean thermal expansion as the most important factor in future sea level rise potentially contributing with 0 7 2 6 m sle within the next 500 years multi millennial simulations show that the entire ice sheet 7 4 m sle might disappear completely within less than three thousand years under high emission scenarios i e with atmospheric co 2 reaching four times preindustrial levels

high resolution evidence for linkages between nw european ice sheet instability and atlantic meridional overturning circulation published studies show that ice rafted debris ird deposition preceding heinrich h events h1 and h2 in the ne atlantic was derived from the nw european ice sheets nweis possibly offering clues about ice sheet sensitivity and stability and the mechanisms that caused periodic collapse of the laurentide ice sheet lis we present detailed lithological and geochemical records including radiogenic isotope fingerprinting of ird deposits from core md01 2461 proximal to the last glacial british ice sheet bis demonstrating persistent instability of the bis with significant destabilisation occurring 1 5 1 9 kyr prior to both h1 and h2 dated at 16 9 and 24 1 kyr bp respectively in the ne atlantic paired mg ca and 18o data from the surface dwelling globigerina bulloides and subsurface dwelling neogloboquadrina pachyderma sinistral are used to determine late glacial variability of temperature salinity and stratification of the upper water column a picture emerges that the bis was in a continuing state of readjustment and never fully reached steady state increased sea surface temperatures appear to have triggered the episode of nweis instability preceding h1 it seems most probable that the so called precursor events were not linked to the h events however if response to a common thermal forcing is considered an increased response time of the lis up to 2 kyr longer than the nweis may be inferred negative salinity excursions of up to 2 6 indicate significant incursions of melt water associated with peaks in nweis instability decreased surface density led to a more stable stratification of the upper water column and is associated with reduced ventilation of intermediate waters recorded in depleted epibenthic 13c cibicidoides wuellerstorfi we suggest that instability and meltwater forcing of the nweis temporarily weakened atlantic meridional overturning circulation allowing transient advance of southern sourced waters to this site prior to h events 1 and 2

response of the subtropical north atlantic surface hydrography on deglacial and holocene amoc changes the north atlantic subtropical gyre stg circulates warm waters between 10 and 40 degrees n and is a potential area of heat storage during periods of reduced north atlantic meridional overturning circulation amoc when warm salt rich waters are retained in the subtropics in this study we investigated multicentennial to millennial scale changes in subtropical north atlantic hydrography in response to amoc changes during the last deglaciation and early holocene using sediment cores md08 3180 and geofar kf16 the coring site 38 degrees n is situated near the boundary between transitional eastern north atlantic waters and stg waters that is formed by the azores front hydrographic changes are reconstructed using new stable isotope data of benthic and subsurface dwelling planktonic foraminifera mg ca measurements on planktonic foraminifera and planktonic foraminifera abundances that are supplemented with published sea surface temperature and stable isotope data these multiproxy data indicate a close coupling between the latitudinal position of the northern stg boundary and deglacial amoc modes during weak amoc phases heinrich event 1 younger dryas yd 8 2ka event northern hemisphere subpolar water reached down to the northern stg boundary displacing the boundary southward during the bolling allerod warm period a strong warming trend of the subtropical region to 19 degrees c is observed a cooling of the sea surface temperature by 6 degrees c during the yd is accompanied by ongoing northward transport of warm subsurface water that might have contributed to the restart of amoc

fine scale sediment structure and geochemical signature between eastern and western north atlantic during heinrich events 1 and 2 abstract heinrich iceberg rafting events 1 and 2 h1 and h2 in the labrador sea are identified by their typical nepheloid flow deposit sedimentary structure high bulk carbonate increase in iceberg rafted detritus ird and depletion of 18o in the surface dwelling foraminifer neogloboquadrina pachyderma s h layers in this region have sedimentological characteristics different than those in the north atlantic and consist of ird interspersed in pelagic sediments high resolution 14c ams dates allowed us to delineate the leads and lags in instability between different ice streams of the former laurentide ice sheet lis our data suggest that the discharge from the hudson strait ice stream was followed by cumberland sound ice sheet during h1 and h2 new radiogenic isotopes from the ice proximal and surficial sediments of the greater hudson strait region and labrador sea h0 h1 and h2 layers suggest that carbonate rich layers were only derived from hudson strait not baffin bay fine scale structure of h1 and h2 intervals in labrador sea slope cores is characterized by two lithic peaks dominated by detrital carbonate grains and a single peak in cores from the central labrador sea a similar pattern in the structure of h1 and h2 is observed along the western european margin these findings contrast with north atlantic h1 and h2 intervals which are characterized by a peak of carbonate rich grains followed by a peak of quartz and volcanic grains this comparison with north atlantic and western european margin cores leads us to suggest that the coupling or lack thereof between the lis and european ice sheet is related to the depositional processes occurring along the margins as well as the distance from the sources and the ability of the oceanic currents to disperse icebergs any significant change in ice sheet dynamics would be recorded close to the ice sheet margin while distal locations would only record extreme events we hypothesize that the discordance between the findings reported in the literature is most likely similar to the difference between the upper slope deep labrador sites and the flemish pass site described in this contribution but requires vigorous testing

movement of deep sea coral populations on climatic timescales during the past 40 000 years global climate has moved into and out of a full glacial period with the deglaciation marked by several millennial scale rapid climate change events here we investigate the ecological response of deep sea coral communities to both glaciation and these rapid climate change events we find that the deep sea coral populations of desmophyllum dianthus in both the north atlantic and the tasmanian seamounts expand at times of rapid climate change however during the more stable last glacial maximum the coral population globally retreats to a more restricted depth range holocene populations show regional patterns that provide some insight into what causes these dramatic changes in population structure the most important factors are likely responses to climatically driven changes in productivity o 2 and co 3 2

radiocarbon variability in the western north atlantic during the last deglaciation we present a detailed history of glacial to holocene radiocarbon in the deep western north atlantic from deep sea corals and paired benthic planktonic foraminifera the deglaciation is marked by switches between radiocarbon enriched and depleted waters leading to large radiocarbon gradients in the water column these changes played an important role in modulating atmospheric radiocarbon the deep ocean record supports the notion of a bipolar seesaw with increased northern source deep water formation linked to northern hemisphere warming and the reverse in contrast the more frequent radiocarbon variations in the intermediate deep ocean are associated with roughly synchronous changes at the poles

changes in sea surface hydrology associated with heinrich event 4 in the north atlantic ocean between 40 and 60 n abstract the changes in distribution of sea surface temperature and salinity in the north atlantic between 40 and 60 n were reconstructed for the time interval between 40 and 30 kyr bp which includes the large iceberg discharge event associated with the deposition of heinrich layer 4 we found that the meltwater input during deposition of heinrich layer 4 resulted in a 1 2 kyr temperature decrease of about 2 c and a salinity decrease in the range of 1 5 3 5 between 40 and 50 n sites above 50 n did not experience significant salinity variations a much larger area was affected by the reduction in sea surface temperature the amplitude of the sea surface temperature shift was however much smaller than the atmospheric temperature changes over greenland at gisp and grip sites

mountain glacier evolution in the iberian peninsula during the younger dryas abstract we review the evolution of glaciers in the iberian mountains during the younger dryas 12 9 11 7 ka following the chronology of greenland stadial 1 gs1 and compare with available environmental and climate data to investigate glacier dynamics during cold stadial episodes the best examples of younger dryas moraines are found in the central pyrenees involving short ice tongues up to 4 km in length in the highest massifs above 3000 m a s l of the southern versant small cirque glaciers and rock glaciers formed during the yd occurred in other pyrenean massifs in the cantabrian range and in the gredos and guadarrama sierras central range as indicated by several rocky polished thresholds that were ice free at the beginning of the holocene although some former rock glaciers were re activated during the younger dryas glacial activity was limited in the southernmost part of the iberian peninsula sierra nevada most iberian records show vegetation changes during the yd characterized by a forest decline and an expansion of shrubs mainly juniperus and steppe herbs although the vegetation response was not homogeneous because of variable resilience among ecosystems available records also document a variable lake response in terms of hydrology and productivity with a decrease in sedimentation rates and organic productivity in most high altitude lakes and increases in salinity and relatively lower lake levels at lower altitudes the impact of the younger dryas on the coastal environment was almost negligible but it was responsible for a brief cessation in sea level rise high resolution analyses of new speleothem records have documented a double structure for the yd with an earlier drier phase followed by a relatively more humid period the review of geomorphological evidence demonstrates a strong latitudinal control of glacial activity during the yd with more intense development in the northern than in the southern regions the increase in humidity during the second phase of the yd in southern latitudes could have been a decisive factor for glacier advance in the northern iberian mountains

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume