readjustment of glacial radiocarbon chronologies by self consistent three dimensional ocean circulation modeling a critical problem in radiocarbon dating is the spatial and temporal variability of marine 14c reservoir ages this is particularly true for the time scale beyond the tree ring calibration range here we propose a method to assess the evolution of marine reservoir ages during the last deglaciation by numerical modeling we apply a self consistent iteration scheme in which existing radiocarbon chronologies can be readjusted by transient three dimensional simulations of marine and atmospheric 14c to estimate the uncertainties regarding the ocean ventilation during the last deglaciation we consider various ocean overturning scenarios which are based on different climatic background states an example readjusting 14c data from the caribbean points to marine reservoir ages varying between 200 and 900 a during the last deglaciation correspondingly the readjustment leads to enhanced variability of atmospheric 14c by 30 and increases the mysterious drop of atmospheric 14c between 17 5 and 14 5 cal ka bp by about 20

ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

multiple stage deglacial retreat of the southern greenland ice sheet linked with irminger current warm water transport 1 there is limited knowledge pertaining to the history of the greenland ice sheet gis during the last glacial interglacial transition as it retreated from the continental margins to an inland position here we use multiproxy data including ice rafted debris ird planktonic isotopes alkenone temperatures and tephra geochemistry from the northern labrador sea off southwest greenland to investigate the deglacial response of the gis and evaluate its implications for the north atlantic deglacial development the results imply that the southern gis retreated in three successive stages 1 early deglaciation of the east greenland margins by tephra rich ird that embrace heinrich event 1 2 progressive retreat during allerod culminating in major meltwater releases 18o depletion of 1 2 at the allerod younger dryas transition 12 8 13 0 kyr b p and 3 a final stage of glacial recession during the early holocene 9 11 kyr b p rather than indicating local temperatures of ambient surface water the alkenones likely were transported to the core site by the irminger current we attribute the timing of gis retreat to the incursion of warm intermediate waters along the base of grounded glaciers and below floating ice shelves on the continental margin the results lend support to the view that gis meltwater presented a forcing factor for the younger dryas cooling

coastal lake records add constraints to the age and magnitude of the younger dryas ice front oscillation along the skagerrak coastline in southern norway

mediterranean sea surface radiocarbon reservoir age changes since the last glacial maximum sea surface reservoir ages must be known to establish a common chronological framework for marine continental and cryospheric paleoproxies and are crucial for understanding ocean continent climatic relationships and the paleoventilation of the ocean radiocarbon dates of planktonic foraminifera and tephra contemporaneously deposited over mediterranean marine and terrestrial regions reveal that the reservoir ages were similar to the modern one 400 years during most of the past 18 000 carbon 14 years however reservoir ages increased by a factor of 2 at the beginning of the last deglaciation this is attributed to changes of the north atlantic thermohaline circulation during the massive ice discharge event heinrich 1

developments in radiocarbon calibration for archaeology this update on radiocarbon calibration results from the 19th international radiocarbon conference at oxford in april 2006 and is essential reading for all archaeologists the way radiocarbon dates and absolute dates relate to each other differs in three periods back to 12400 cal br radiocarbon dates can be calibrated with tree rings and the calibration curve in this form should soon extend back to 18 000 cal bp between 12 400 and 26000 cal br the calibration curves are based on marine records and thus are only a best estimate of atmospheric concentrations beyond 26000 cal br dates have to be based on comparison rather than calibration with a variety of records radical variations are thus possible in this period a highly significant caveat for the dating of middle and lower paleolithic art artefacts and animal and human remains

evidence for sea level and monsoonally driven variations in terrigenous input to the northern east china sea during the last 24 3 ka geochemical and sedimentological analyses of core pc 1 recovered from the northern east china sea ecs provide insights into variations in terrigenous input associated with sea level and climate changes over the past 24 3 ka based on high resolution multiproxy records our results suggest that the competing processes of sea level and monsoonally driven precipitation determined terrigenous input to the northern ecs dominance of terrigenous material along with relatively light globigerinoides ruber 18o indicates that the last glacial maximum lgm lowstand of sea level has occurred during the period 21 5 19 6 ka not suggesting an early slow rise but supporting the conventional lgm age of 21 ka this lgm lowstand was terminated by the rapid sea level rise of 19 ka meltwater pulse mwp which is well expressed by the nearly synchronous decreases in both terrigenous detritus and mean grain size from 19 6 to 18 9 ka mwp 1a is clearly marked in our records by a sharp reduction in terrigenous input and pronounced maxima of g ruber 18o at 15 3 14 8 ka given the considerable age uncertainties of deglacial marine radiocarbon samples a slightly increasing input of terrigenous matter is noted after 13 4 ka potentially pointing to a sea level fall following the inter allerod cooling period which was seldom reported previously although mwp 1b did not leave robust signatures in terrigenous input it is explicitly captured by the heavy 18o of g ruber and decline in mean grain size at 11 5 10 9 ka mwp 1c probably occurred in a broad millennial interval with multiple peaks which are robustly marked by the abrupt variations in terrigenous input and marine organic matter at 9 7 9 3 and 9 1 ka respectively during the late holocene the effect of continuously weakening monsoon precipitation overwhelmed that of stable sea level resulting in a uniform increase in the proportion of marine derived organic matter after 5 5 ka

constant holocene southern ocean 14c reservoir ages and ice shelf flow rates article i nfo southern ocean radiocarbon reservoir ages i e non zero radiocarbon ages in seawater are the highest in the world s surface ocean constraining these reservoir ages at present and in the past is important not only because unknown reservoir ages limit the interpretation of antarctic radiocarbon chronologies but also because reservoir ages provide information about ocean circulation as a recorder of past circulation and as an end member for major deep water masses in today s ocean in this study we use paired u th and 14 c ages of an unusual set of solitary coral samples trapped by fringing ice shelves in the ross sea to provide the first detailed study of holocene reservoir ages for the southern ocean our results indicate a relatively constant marine radiocarbon reservoir age of 1144 120 years for the past 6000 years these results are consistent with extrapolation of the relationship between 14 c and alkalinity seen elsewhere supporting the use of this empirical relationship in high latitudes the results also suggest constant deep ocean circulation and air sea exchange during the holocene and provide a good target for tuning ocean models of modern circulation combining the new ages for corals with their distance from the modern day ice shelf grounding line provides some of the first long term records of ice shelf velocities for any region and indicates constant flow of the mcmurdo ice shelf during the holocene at a rate similar to that observed today

deglaciation of a marine based ice sheet late weichselian palaeo ice dynamics and retreat in the southern barents sea reconstructed from onshore and offshore glacial geomorphology abstract marine and terrestrial datasets swath bathymetry 2d and 3d seismic and remote sensing data are used to map the megascale glacial geomorphology of the southern barents sea seafloor northern fennoscandia and the kola peninsula giving new insights into the dynamics and behaviour of the barents sea ice sheet during retreat the glacial geomorphology indicates clear spatial and temporal variations in ice dynamics with evidence for both active ice streaming and frozen bed conditions at the maximum and during deglaciation a five stage reconstruction of the late weichselian deglaciation is proposed at the late weichselian maximum ice covered the whole of the barents sea shelf and the configuration and dynamics of the ice sheet were controlled by the bjornoyrenna bear island trough ice stream this was fed by source areas in the central and north eastern barents sea and in the fennoscandian mainland deglaciation was initiated along the western continental margin available dating results show that this occurred after 19 cal ka bp the bjornoyrenna ice stream retreated rapidly ice margin retreat rates of 275 m a 1 but was periodically grounded as evidenced by a well developed series of grounding zone wedges this was followed by an advance of two short lived ice streams from the eastern sector of the ice sheet into the south western barents sea these ice streams advanced and retreated very rapidly with no evidence for ice margin standstills correlation to dated cores suggests an age of around 16 000 cal ka bp for this readvance the period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in russia the western barents sea ice margin then retreated onshore with deglaciation continuing at a reduced rate the initiation of deglaciation coincided with rising global eustatic sea level acceleration of calving due to grounding line floatation rapidly opened up a major calving bay in bjornoyrenna encouraging rapid loss of the marine based ice the retreat rate stabilised only once the ice sheet retreated onshore and calving ceased we note that the observed pattern of rapid retreat with high variability in ice streaming for the marine based barents sea ice sheet is similar to that of the marine based sectors of the late weichselian british laurentide and west antarctic ice sheets

accounting for the marine reservoir effect in radiocarbon calibration abstract the radiocarbon dating method is supported by highly refined calibration data empirically obtained from environmental archives nevertheless marine calibration remains problematic due to the spatiotemporally variable marine reservoir effect mre the currently accepted curve for radiocarbon calibration in the ocean is a global curve partly derived by numerical modelling from its atmospheric counterpart as such this curve cannot account for the effects of local phenomena strongly correlated with 14c signatures in seawater e g ocean dynamics and continental input although the radiocarbon community has suggested the use of regional calibration curves that would better represent the heterogeneous ocean reservoir a reasonable method for their construction has not yet been proposed we directly address this longstanding issue in radiocarbon research by exploring the output of a model for the temporal evolution of the mre the limitations of this model are inherited by our method and this hinders the use of the regional curves derived here in many regions of the world ocean nevertheless the approach described in this paper remains valid regardless of the chosen model and our preliminary results show that with the future development of accurate and highly resolved models for the mre this method may be a promising alternative to the use of r values in the process of marine calibration

the younger dryas and the sea of ancient ice we propose that prior to the younger dryas period the arctic ocean supported extremely thick multi year fast ice overlain by superimposed ice and firn we re introduce the historical term paleocrystic ice to describe this the ice was independent of continental glacier ice and formed a massive floating body trapped within the almost closed arctic basin when sea level was lower during the last glacial maximum as sea level rose and the barents sea shelf became deglaciated the volume of warm atlantic water entering the arctic ocean increased as did the corresponding egress driving the paleocrystic ice towards fram strait new evidence shows that bering strait was resubmerged around the same time providing further dynamical forcing of the ice as the transpolar drift became established additional freshwater entered the arctic basin from siberia and north america from proglacial lakes and meltwater derived from the laurentide ice sheet collectively these forces drove large volumes of thick paleocrystic ice and relatively fresh water from the arctic ocean into the greenland sea shutting down deepwater formation and creating conditions conducive for extensive sea ice to form and persist as far south as 60 n we propose that the forcing responsible for the younger dryas cold episode was thus the result of extremely thick sea ice being driven from the arctic ocean dampening or shutting off the thermohaline circulation as sea level rose and atlantic and pacific waters entered the arctic basin this hypothesis focuses attention on the potential role of arctic sea ice in causing the younger dryas episode but does not preclude other factors that may also have played a role

sun ocean nuclear bombs and fossil fuels radiocarbon variations and implications for high resolution dating radiocarbon or 14c is a radiometric dating method ideally suited for providing a chronological framework in archaeology and geosciences for timescales spanning the last 50 000 years 14c is easily detectable in most common natural organic materials and has a half life 5 730 40 years relevant to these timescales 14c produced from large scale detonations of nuclear bombs between the 1950s and the early 1960s can be used for dating modern organic materials formed after the 1950s often these studies demand high resolution chronology to resolve ages within a few decades to less than a few years despite developments in modern high precision 14c analytical methods the applicability of 14c in high resolution chronology is limited by short term variations in atmospheric 14c in the past this article reviews the roles of the principal natural drivers e g solar magnetic activity and ocean circulation and the anthropogenic perturbations e g fossil fuel co2 and 14c from nuclear and thermonuclear bombs

the benthic foraminiferal record of the medieval warm period and the recent warming in the gullmar fjord swedish west coast a high resolution study of benthic foraminiferal assemblages was performed on a ca eight metre long sediment core from gullmar fjord on the west coast of sweden the results of pb 210 and ams c 14 datings show that the record includes the two warmest climatic episodes of the last 1500 years the medieval warm period mwp and the recent warming of the 20th century both periods are known to be anomalously warm and associated with positive nao winter indices benthic foraminiferal successions of both periods are compared in order to find faunal similarities and common denominators corresponding to past climate changes during the mwp adercotryma glomerata cassidulina laevigata and nonionella iridea dominated the assemblages judging from dominance of species sensitive to hypoxia and the highest faunal diversity for the last ca 2400 years the foraminiferal record of the mwp suggests an absence of severe low oxygen events at the same time faunas and delta c 13 values both point to high primary productivity and or increased input of terrestrial organic carbon into the fjord system during the medieval warm period comparison of the mwp and recent warming revealed different trends in the faunal record the thin shelled foraminifer n iridea was characteristic of the mwp but became absent during the second half of the 20th century the recent skagerrak kattegat fauna was rare or absent during the mwp but established in gullmar fjord at the end of the little ice age or in the early 1900s also there are striking differences in the faunal diversity and absolute abundances of foraminifera between both periods changes in primary productivity higher precipitation resulting in intensified land runoff different oxygen regimes or even changes in the fjord s trophic status are discussed as possible causes of these faunal differences c 2011 elsevier b v all rights reserved less

ages of 24 widespread tephras erupted since 30 000 years ago in new zealand with re evaluation of the timing and palaeoclimatic implications of the lateglacial cool episode recorded at kaipo bog abstract tephras are important for the nz intimate project because they link all three records comprising the composite inter regional stratotype developed for the new zealand climate event stratigraphy nz ces here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30 000 calendar cal years ago in new zealand to help facilitate their use as chronostratigraphic dating tools for the nz ces and for other palaeoenvironmental and geological applications the selected tephras comprise 12 rhyolitic tephras from taupo nine rhyolitic tephras from okataina one peralkaline rhyolitic tephra from tuhua and one andesitic tephra each from tongariro and egmont taranaki volcanic centres age models for the tephras were obtained using three methods i 14 c based wiggle match dating of wood from trees killed by volcanic eruptions these dates published previously ii flexible depositional modelling of a high resolution 14 c dated age depth sequence at kaipo bog using two bayesian based modelling programs bacon and oxcal s p sequence function and the intcal09 data set with sh offset correction 44 17 yr and iii calibration of 14 c ages using oxcal s tau boundary function and the shcal04 and intcal09 data sets our preferred dates or calibrated ages for the 24 tephras are as follows youngest to oldest all mid point or mean ages of 95 probability ranges kaharoa ad 1314 12 taupo unit y ad 232 10 mapara unit x 2059 118 cal yr bp whakaipo unit v 2800 60 cal yr bp waimihia unit s 3401 108 cal yr bp stent unit q 4322 112 cal yr bp unit k 5111 210 cal yr bp whakatane 5526 145 cal yr bp tuhua 6577 547 cal yr bp mamaku 7940 257 cal yr bp rotoma 9423 120 cal yr bp opepe unit e 9991 160 cal yr bp poronui unit c 11 170 115 cal yr bp karapiti unit b 11 460 172 cal yr bp okupata 11 767 192 cal yr bp konini bed b 11 880 183 cal yr bp waiohau 14 009 155 cal yr bp rotorua 15 635 412 cal yr bp rerewhakaaitu 17 496 462 cal yr bp okareka 21 858 290 cal yr bp te rere 25 171 964 cal yr bp kawakawa oruanui 25 358 162 cal yr bp poihipi 28 446 670 cal yr bp and okaia 28 621 1428 cal yr bp secondly we have re dated the start and end of the lateglacial cool episode climate event nzce 3 in the nz ces previously referred to as the lateglacial climate reversal as defined at kaipo bog in eastern north island new zealand using both bacon and oxcal p sequence modelling with the intcal09 data set the ca 1200 yr long cool episode indicated by a lithostratigraphic change in the kaipo peat sequence to grey mud with lowered carbon content and a high resolution pollen derived cooling signal began 13 739 125 cal yr bp and ended 12 550 140 cal yr bp mid point ages of the 95 highest posterior density regions bacon modelling the oxcal modelling generating almost identical ages confirmed these ages the lateglacial cool episode ca 13 8 12 6 cal ka bp thus overlaps a large part of the entire antarctic cold reversal chronozone ca 14 1 12 4 cal ka bp or ca 14 6 12 8 cal ka bp and an early part of the greenland stadial 1 younger dryas chronozone ca 12 9 11 7 cal ka bp the timing of the lateglacial cool episode at kaipo is broadly consistent with the latitudinal patterns in the antarctic cold reversal signal suggested for the new zealand archipelago from marine and terrestrial records and with records from southern south america

moisture variations in lacustrine eolian sequence from the hunshandake sandy land associated with the east asian summer monsoon changes since the late pleistocene abstract paleoclimate records currently lack sufficient geographic detail to understand the spatiotemporal evolution of east asian summer monsoon easm rain belt since the late pleistocene in particular there is no consensus on whether the easm rain belt reached its modern northern limit by the early holocene here we present inferred moisture variations from a multi parameter absolute dated lacustrine eolian sequence from northern china that date back to the late pleistocene 14 ka bp or thousand years ago we observed a sharp transition towards wet conditions at the onset of the holocene epoch maximum wet climate occurred here during 11 3 8 5 ka the climate remained predominantly wet until 4 2 ka then it became progressively drier we observed alternating organic rich fine grained lake deposits and organic depleted coarse grained eolian sand layers during 14 7 ka these layers correspond to sedimentation associated with the allerod younger dryas yd post yd warming pre boreal oscillation pbo early holocene and 8 2 ka event we interpreted the orbital scale moisture variation at our study site to the changes in insolation assigning these abrupt and short lived changes during the late pleistocene holocene transition to a persistent teleconnection between the north atlantic and east asian climate zones

radiocarbon constraints on readvances of the british irish ice sheet in the northern irish sea basin during the last deglaciation moraines deposited by the dundalk bay ice lobe record two readvances of the irish ice sheet into the northern irish sea basin during the last deglaciation these readvances overrode and incorporated fossiliferous marine muds from the floor of dundalk bay ams 14c dates from monospecific microfaunas obtained from these muds indicate that the earlier clogher head readvance occurred sometime between 15 0 and 14 2 14c ka bp thus identifying a previously unrecognized ice margin fluctuation in the irish sea basin that is correlative with a readvance in northwest ireland the younger readvance occurred after 14 2 14c ka bp and is equivalent to the killard point readvance identified elsewhere in the irish sea basin these readvances occurred during the oldest dryas cold interval and bracket heinrich event 1 raised marine muds that were deposited between ice readvances require that a substantial ice sheet remained on ireland throughout much of the last deglaciation with attendant isostatic depression of at least 110 m

consistently large marine reservoir ages in the norwegian sea during the last deglaciation with the exception of the gs 1 younger dryas coldperiodmarine reservoir ages for the last deglaciation in the north atlantic norwegian sea are generally assumed to have been around 400 500 radiocarbon years in magnitude earth planet sci lett 126 1994 275 radiocarbon 37 1995 53 quat res 52 1999 104 nature 412 2001 724 by comparing the climate records obtained from the grip ice core nature 359 1992 311 j quat sci 13 4 1998 283 andfrom north atlantic norwegian sea cores quat res 52 1999 104 geology 23 12 1995 1059 nature 356 1991 757 nature 356 1992 757 paleoceanography 3 1 1988 1 nature 343 1990 612 earth planet sci lett 126 1994 275 with radiocarbon dated european continental records we show that marine reservoir ages in the norwegian sea were of the order of 1000 14 c yr including large uncertainties this approach rests on the reasonable assumption that climate changes throughout the ne atlantic andeurope were more or less synchronous at the centennial scale fairly large variations in reservoir ages over time may have been causedby changing atmospheric 14 c content the results indicate that detailed land sea correlations for the north atlantic during the last deglaciation are not feasible using radiocarbon dating alone r 2003 elsevier science ltd all rights reserved

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

palynological evidence of climatic and oceanographic changes in the north sea during the last deglaciation abstract palynological analyses performed on cores from the norwegian channel troll 8903 led to reconstruction of the late glacial variations in sea surface conditions using dinoflagellate cyst data and permitted direct correlation with the vegetation history of northwestern europe derived from pollen assemblages by 15 000 yr b p ice rapidly receded from the norwegian shelf and relatively warm summer conditions prevailed in surface waters a first late glacial cooling marked by extensive seasonal sea ice cover is dated at ca 13 600 13 00014c yr b p which coincides with the oldest dryas interval during the bolling allerod interval a rise in sea surface temperature both in february up to 3 c and august up to 15 c led to the establishment of ice free conditions in the northern north sea while pollen data reveal a densification of the vegetation cover the beginning of the younger dryas interval is marked by an increase in nonarboreal pollen input indicative of the opening of the forest vegetation cover concomitant with a cooling of surface waters during winter and development of sea ice cover however sea surface conditions remained relatively warm in summer until about 10 300 yr b p when extremely cold conditions and extensive sea ice cover developed up to 7 months yr improving conditions are recorded in surface waters by 10 100 yr b p a few hundred years before the development of forest cover onshore as shown by the pollen record such a discrepancy between marine and terrestrial indicators at the end of younger dryas time suggests a delayed response of the vegetation to regional climate warming

early holocene deglaciation of northern hudson bay and foxe channel constrained by new radiocarbon ages and marine reservoir correction abstract radiocarbon ages from southampton island canada provide new chronological control on the deglaciation of foxe channel and northern hudson bay a strategic area for understanding the demise of a marine based portion of the laurentide ice sheet a regional marine reservoir age of 630 45 yr and a reservoir offset r of 263 48 yr were calculated from two early to mid holocene terrestrial marine radiocarbon age pairs these values are consistent with corrections based on early 20th century mollusks suggesting that following deglaciation the oceanic conditions controlling the regional reservoir effect rapidly became similar to those of modern times however our r value is 352 52 yr less than another correction from eastern foxe basin which may be affected by 14 c dilution from carbonate rocks our r value is used to calibrate new marine radiocarbon ages which help further develop the deglaciation history of southampton island especially along the north coast where deglaciation of foxe channel appears to have been completed by 8100 7800 cal yr bp 2 this provides key chronological constraints on the development of a long marine ice margin in southern foxe basin prior to the final breakup of the foxe ice dome

identification of contrasting seasonal sea ice conditions during the younger dryas abstract a palaeo sea ice reconstruction for northern norway for the interval ca 13 8 7 2 cal ka bp has been performed using a combined organic geochemical proxy based study of a marine sediment core jm99 1200 obtained from andfjorden 69 15 95 n 16 25 09 e and the outcomes compared with a series of other palaeoclimate studies carried out previously within this study particular emphasis has been placed on the identification of the sea ice conditions during the younger dryas and the application of different biomarker based proxies to both identify and quantify seasonal sea ice conditions firstly the appearance of the specific sea ice diatom proxy ip 25 at ca 12 9 cal ka bp in the sedimentary record has provided an unambiguous but qualitative measure of seasonal sea ice and thus the onset of the younger dryas stadial the near continuous occurrence of ip 25 for the next ca 1400 yr demonstrates seasonal sea ice during this interval although variable abundances suggest that the recurrent conditions in the early mid younger dryas ca 12 9 11 9 cal ka bp changed significantly from stable to highly variable sea ice conditions at ca 11 9 cal ka bp and this instability in sea ice prevailed for the subsequent ca 400 yr during which an extremely short interval of permanent or near permanent sea ice was observed at ca 11 75 cal ka bp at ca 11 5 cal ka bp ip 25 disappeared from the record indicating ice free conditions that signified the beginning of the holocene the ip 25 concentrations were also combined with those of the open water phytoplankton biomarker brassicasterol to generate p b ip 25 data from which more quantitative measurements of sea ice were determined p b ip 25 data were consistent with consecutively seasonal then infrequent sea ice cover for the early mid and late younger dryas while further comparisons of the p b ip 25 data with the outcomes of previous correlations with modelled sea ice concentrations suggested that these intervals were characterised by ca 60 90 and ca 0 60 sea ice cover respectively both qualitative and quantitative sea ice records were also consistent with sea surface temperature and other palaeoclimate estimates derived previously from various other proxy studies the contrasting seasonal sea ice conditions during the younger dryas were further verified through a comparison of the concentrations of ip 25 with those of another highly branched isoprenoid hbi alkene that is di unsaturated and believed to also be produced by sea ice diatoms the ratio of the hbi diene to ip 25 termed dip 25 is believed to provide a useful indicator of stability or variability in sea ice conditions and complements the outcomes from the ip 25 and p b ip 25 index data the identification of contrasting seasonal sea ice conditions during the younger dryas will likely contribute to the debate regarding the climatic impacts that took place during this intriguing interval

an arctic perspective on dating mid late pleistocene environmental history to better understand pleistocene climatic changes in the arctic integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required not least for correlation to extra arctic records in this paper we discuss from an arctic perspective methods and correlation tools that are commonly used to date arctic pleistocene marine and terrestrial events we review the state of the art of arctic geochronology with focus on factors that affect the possibility and quality of dating and support this overview by examples of application of modern dating methods to arctic terrestrial and marine sequences event stratigraphy and numerical ages are important tools used in the arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes age control is commonly provided by radiocarbon luminescence or cosmogenic exposure ages arctic ocean deep sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition patterns in palaeomagnetic records and increasingly biostratigraphic data many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning recent advances in dating technology calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material i e foraminifera for c 14 and single grain luminescence however for much of the pleistocene there are still limits to the resolution of most dating methods consequently improving the accuracy and precision analytical and geological uncertainty of dating methods through technological advances and better understanding of processes are important tasks for the future another challenge is to better integrate marine and terrestrial records which could be aided by targeting continental shelf and lake records exploring proxies that occur in both settings and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers

a calendar age estimate of the younger dryas holocene boundary at krakenes western norway the younger dryas holocene transition yd h in the sediments of krakenes lake western norway is well marked both lithologically and palaeobiologically at 756 5 cm in the investigated core a ser

downcore variations of sedimentary detrital 238 u 232 th ratio implications on the use of 230 th xs and 231 pa xs to reconstruct sediment flux and ocean circulation excess 231 pa and 230 th 231 pa xs and 230 th xs can be used to reconstruct past oceanic sedimenta tion 230 th normalized flux and circulation changes 231 pa 230 th xs 0 hereafter pa th these quantities are determined by computing the detrital and authigenic contributions from bulk sediment measurement the method relies on the use of a chosen constant value of the detrital 238 u 232 th activity ratio hereafter u th det in this study we have extracted the detrital fraction of the sediments from north atlantic deep sea core su90 08 43803 0 1n 30802 0 5w 3 080 m and determined its u th det value over the last 40 ky we find that u th det varied significantly through time with a minimum value of 0 4 during the holocene and a maximum value of 0 7 during the last glacial maximum lgm the sensitivity of sedimentary 230 th normalized flux and pa th is tested for our study site and for other north atlantic sites we show that the sensitivity is highly dependent on the core location and its terrigenous material supply the 230 th normalized flux and pa th signals are very robust in cores with low detrital contributions whereas they are very sensitive to u th det changes in cores with higher detrital contribution in the latter case changes in 230 th normalized flux and pa th due to the choice of a constant u th det can largely exceed the uncertainty on the 230 th normalized flux and pa th inducing potential biases in the amplitude and temporal variability of reconstructed sedimentation and ocean circulation changes

marine 14c reservoir ages for 19th century whales and molluscs from the north atlantic abstract in order to compare radiocarbon dates on marine and terrestrial samples the former have to be corrected for a reservoir age we present reservoir ages from dating 21 whales collected 1860 1901 and recalculating dates of 23 molluscs collected 1857 1926 most of the whales were caught along the coast of norway but one is from france and one from iceland we assume the former mainly lived in the north and equatorial atlantic and in the norwegian sea whales feed only on pelagic organisms and will provide the reservoir age for the open ocean surface water however they travel long distances and will integrate the reservoir ages of the different water masses along their way molluscs dated from norway spitsbergen and arctic canada are stationary and monitor the sea water passing their dwelling site but some also take up carbon from particulate food or sediment pore water coastal water also often contains some continental carbon we present two different views on how to analyze and interpret the data mangerud recommends to use reservoir ages based on a combination of the whale and mollusc dates i e 380 30 and 360 30 yr relative to intcal04 and british oak respectively and a r value of 20 30 for the surface water in the n atlantic and norwegian sea bondevik and gulliksen maintain that the reservoir age and r along the norwegian coast is latitude dependant with r values increasing from 3 22 in the south to 105 24 at spitsbergen whales reflecting north atlantic open ocean surface water have lower r 7 11 than most molluscs

rapid changes in ocean circulation and atmospheric radiocarbon a latitude depth coupled global ocean ice atmosphere model is extended to include a simple biosphere component a physically reasonable adjustment of runoff into the north atlantic is invoked to achieve a transient response to glacial meltwater perturbations which closely resembles the younger dryas climate event we then investigate the evolution of the isotopic ratio of atmospheric radiocarbon 14c due to the rapid changes of deep ocean circulation when the north atlantic branch of the conveyor belt circulation is interrupted the oceanic uptake of radiocarbon is reduced resulting in an increase of atmospheric 14c by about 35 the reduction of ventilation in the north atlantic is partly compensated by an increase of the 14c ratios of the biosphere the southern ocean and the upper ocean above 1000 m depth a plateau of the 14c year calendar year relation can be generated at the time of the rapid reinitiation of deep ocean ventilation which begins coincident with the major temperature increase and lasts for about 60 years it is hence significantly shorter than that found by analyzing tree rings during the termination of younger dryas longer than 400 years a sensitivity study reveals that the duration of the plateau depends strongly on the transient evolution of the gas exchange rate and can increase to 150 300 years if changes of pco2 or sea ice coverage are taken into account

postglacial uplift and relative sea level changes in finnmark northern norway abstract the outer coast of finnmark in northern norway is where the former fennoscandian and barents sea ice sheets coalesced this key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines but only a few existing radiocarbon dates constrain their chronology here we present three holocene sea level curves based on radiocarbon dated deposits from isolation basins at the outermost coast of finnmark located at the islands soroya and rolvsoya and at the nordkinn peninsula we analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments terrestrial plant fragments from these transitions were then radiocarbon dated radiocarbon dated mollusk shells and marine macroalgae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14 600 cal yr bp we find that the gradients of the shorelines are much lower than elsewhere along the norwegian coast because of substantial uplift of the barents sea also the anomalously high elevation of the marine limit in the region can be attributed to uplift of the adjacent seafloor after the younger dryas the coast emerged 1 6 1 0 cm per year until about 9500 9000 cal yr bp between 9000 and 7000 cal yr bp relative sea level rose 2 4 m and several of the studied lakes became submerged at the outermost locality rolvsoya relative sea level was stable at the transgression highstand for more than 3000 years between ca 8000 and 5000 cal yr bp deposits in five of the studied lakes were disturbed by the storegga tsunami ca 8200 8100 cal yr bp

changes in north atlantic radiocarbon reservoir ages during the allerod and younger dryas estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late quaternary climate we radiocarbon dated marine shells and terrestrial plant remains deposited in two bays on norway s west coast between 11 000 and 14 000 years ago a time of large and abrupt climatic changes that included the younger dryas yd cold episode the radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early yd stabilized for 900 years and dropped by 300 years within a century across the yd holocene transition

the last 18 kyr fluctuations in norwegian sea surface conditions and implications for the magnitude of climatic change evidence from the north sea a combined record of three cores spanning the last 18 kyr from the northern north sea is investigated for content of benthic and planktonic foraminifera and stable oxygen isotopes the paleoenvironmental development through this time period shows an early deglaciation 18 14 4 ka and the younger dryas 12 7 11 5 ka characterized by arctic polar conditions and increased ice rafting in the norwegian channel during the bolling allerod period warm sea surface temperature 9 c conditions similar to present conditions are inferred while bottom waters stayed cold 0 1 c with normal salinity the bolling allerod period is interrupted twice at 13 9 13 6 ka older dryas and at 13 0 12 8 ka inter allerod cooling period by reductions in sea surface temperatures and increased sea ice cover the beginning of the holocene period is marked by increases in surface and bottom water temperature superimposed on the broad climatic changes through the holocene a series of short lived oscillations in the ocean circulation are recorded the amplitude of these holocene events appears larger in the early holocene prior to 8 ka than compared with the remaining part of the holocene this amplification can possibly be attributed to a general increased freshwater budget in the north atlantic at this time during the final stages of the deglaciation of the laurentide and scandinavian ice sheets

radiocarbon reservoir age of high latitude north atlantic surface water during the last deglacial the radiocarbon reservoir age of high latitude north atlantic ocean surface water is essential for linking the continental and marine climate records and is expected to vary according to changes in north atlantic deep water nadw production measurements from this region also provide important input and or tests of oceanic radiocarbon using 3 d global ocean circulation models here we present a surface water radiocarbon reservoir age record of the high latitude western north atlantic for the deglacial period via the use of fossil cold water corals growing in waters that are rapidly exchanged with nearby surface waters the reservoir age of high latitude north atlantic surface waters was computed from the radiocarbon age difference between our radiocarbon calibration record http radiocarbon ldeo columbia edu and our marine radiocarbon data 230th 234u 238u dates provide the absolute coral ages our high latitude north atlantic ocean reservoir age data combined with recalculated reservoir ages based on published coexisting terrestrial and marine material and vedde ash radiocarbon dates from central and eastern north atlantic show modern values 380 140 year n 14 during the bolling and allerod warm period and a 200 year increase in reservoir age 590 130 year n 10 during the entire younger dryas yd cold episode the reservoir age then decreased to 270 20 year n 2 at the preboreal yd transition although the dates are too sparse for us to be confident in this estimate we are not able to resolve the timing of the transition to increased reservoir ages from the mid allerod to the yd due to the relatively small change and correspondingly large uncertainty in the estimates the atmospheric 14c record derived from our atmospheric radiocarbon record displays a 40 per mil increase from 12 900 to 12 650 cal years bp coincident with the shift to high reservoir ages in the early yd cold event intrusion of 14c depleted antarctic intermediate water aaiw to the high latitude north atlantic and reduction of nadw formation are possible causes for the coincident shift to high reservoir ages in the north atlantic surface ocean and increased atmospheric 14c during the beginning of the yd event

late weichselian marine 14c reservoir ages at the western coast of norway abstract a shallow marine late weichselian deposit on the outer coast of western norway contains both terrestrial plant material and articulated marine shells we have 14 c dated both types of material from eight different stratigraphic levels covering the time interval 12 300 to 11 100 14 c yr b p the difference between 14 c dated terrestrial plant material and marine shell material the marine reservoir age ranges from 200 to 525 yr with a weighted average of 380 32 yr this is almost identical to the present reservoir age of 379 20 yr for southern norway in the mid younger dryas yd interval the reservoir age in the north atlantic 55 n 65 n was 700 800 yr considerably greater than the present reservoir age and the age we have measured for the bolling allerod interval the reason for this increase during the yd is probably a combination of reduced inflow of surface waters to the north atlantic and more extensive sea ice cover evidence from marine cores show that the southeastern norwegian sea experienced rapid fluctuations in the inflow of warm atlantic surface water during the period 12 300 to 11 000 yr b p however the reservoir age apparently did not increase during these colder periods older dryas i and ii the reason is probably that in contrast to the yd these colder periods did not last long enough and or were of too limited extent to alter the reservoir age of the ocean a comparison of the obtained 14 c dates with the varve 14 c chronology from lake suigetsu indicates an age of 12 770 cal yr b p for the al yd boundary

devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last british irish ice sheet this contribution documents the process of assessing the quality of data within a compilation of legacy geochronological data relating to the last british irish ice sheet a task undertaken as part of a larger community based project britice chrono that aims to improve understanding of the ice sheet s deglacial evolution as accurate reconstructions depend on the quality of the available data some form of assessment is needed of the reliability and suitability of each given age s in our dataset we outline the background considerations that informed the quality assurance procedures devised given our specific research question we describe criteria that have been used to make an objective assessment of the likelihood that an age is influenced by the technique specific sources of geological uncertainty when these criteria were applied to an existing database of all geochronological data relating to the last british irish ice sheet they resulted in a significant reduction in data considered suitable for synthesis the assessed data set was used to test a bayesian approach to age modelling ice stream retreat and we outline our procedure that allows us to minimise the influence of potentially erroneous data and maximise the accuracy of the resultant age models

atmospheric 14c variations derived from tree rings during the early younger dryas abstract atmospheric radiocarbon variations over the younger dryas interval from 13 000 to 11 600 cal yr bp are of immense scientific interest because they reveal crucial information about the linkages between climate ocean circulation and the carbon cycle however no direct and reliable atmospheric 14c records based on tree rings for the entire younger dryas have been available in this paper we present 1 high precision 14c measurements on the extension of absolute tree ring chronology from 12 400 to 12 560 cal yr bp and 2 high precision high resolution atmospheric 14c record derived from a 617 yr long tree ring chronology of huon pine from tasmania australia spanning the early younger dryas the new tree ring 14c records bridge the current gap in european tree ring radiocarbon chronologies during the early younger dryas linking the floating lateglacial pine record to the absolute tree ring timescale a continuous and reliable atmospheric 14c record for the past 14 000 cal yr bp including the younger dryas is now available the new records indicate that the abrupt rise in atmospheric 14c associated with the younger dryas onset occurs at 12 760 cal yr bp 240 yrs later than that recorded in cariaco varves with a smaller magnitude of 40 followed by several centennial 14c variations of 20 25 comparing the tree ring 14c to marine derived 14c and modelled 14c based on ice core 10be fluxes we conclude that changes in ocean circulation were mainly responsible for the younger dryas onset while a combination of changes in ocean circulation and 14c production rate were responsible for atmospheric 14c variations for the remainder of the younger dryas

late quaternary chronostratigraphic framework of deep baffin bay glaciomarine sediments from high resolution paleomagnetic data 1 the late quaternary baffin bay sediments provide exclusive records of greenland innuitian and laurentide ice sheet margin activities as well as information about the arctic and northern atlantic ocean linkages through the canadian arctic archipelago because of specific oceanographic conditions foraminiferal 18o stratigraphies and radiocarbon ages fail to provide reliable chronologies here we propose an original chronostratigraphy spanning the last glacial cycle based on high resolution paleomagnetic investigations on a 741 cm long core hu2008 029 016pc raised from the deep central baffin bay near odp site 645 two major difficulties were encountered 1 the high frequency occurrence of rapidly deposited layers related to short ice sheet margin events e g ice surges and 2 the magnetic grain size variability physical and magnetic mineralogical properties were used to screen out unreliable magnetic sediment layers the obtained relative paleointensity rpi proxy matches reference paleomagnetic stacks and regional records moreover the resulting record depicts two major excursions which were assigned to the laschamp and the norwegian greenland sea events it has thus been possible to derive a robust 115 ka chronology for the cored sequence we concluded that even under such a dynamic sedimentary regime magnetic properties of the sediments can provide a reliable chronostratigraphy together with information on sedimentary processes

modeling the effect of abrupt ocean circulation change on marine reservoir age abstract radiocarbon surface reservoir age is required for precise dating of marine organisms although often assumed constant changes in atmospheric radiocarbon content ocean circulation and ocean mixing imprint changes on this quantity the spatial and temporal variations of marine surface and bottom reservoir ages in response to a shutdown and subsequent recovery of atlantic meridional overturning circulation moc are analyzed using a cost efficient three dimensional ocean circulation model generally surface reservoir age changes are limited to the atlantic ocean with a reduction of about 100 yr after the moc shutdown followed by a slow increase and a peak at the time of moc resumption parameter sensitivity studies with respect to the roles of gas exchange diffusivity and north atlantic ice cover show that ice cover has the largest effect on the transient evolution of surface reservoir age during the shutdown our model results agree well with a recent reconstruction of surface reservoir age changes during the younger dryas when we reduce the rate of gas exchange in the model and include a parametrization of seasonal ice cover in the north atlantic

brine formation in relation to climate changes and ice retreat during the last 15 000 years in storfjorden svalbard 76 78 n storfjorden svalbard is an area of intense brine formation the brine is cold dense rich in oxygen and co2 and has reduced ph storfjorden is unique because it contains well preserved agglutinated foraminifera dating back to the beginning of the last deglaciation we have investigated the distribution of calcareous and agglutinated benthic foraminifera benthic oxygen and carbon isotopes calcium carbonate total organic carbon and ice rafted debris in five cores from storfjorden comprising the holocene and the deglaciation the purpose of the study is to reconstruct brine formation in the past under different climate scenarios the data indicate that in storfjorden the ratio of agglutinated to calcareous benthic foraminifera can be taken as a measure of the strength of brine formation the foraminiferal data which are supported by stable isotopes degree of fragmentation and geochemical parameters signify that brine formation intensified during cold periods and weakened during warm periods during the deglaciation increased brine flow coincides with the older dryas the intra allerod cold period and the younger dryas brine formation increased from circa 8200 years b p reaching periodic maxima during the last 4000 years b p in response to the unstable climate maximum brine production correlates with the dark ages cold period circa 1500 1100 years b p and the little ice age circa 600 100 years b p lower production correlates with the roman warm period circa 2500 2000 years b p and the medieval warm period circa 1000 700 years b p

the younger dryas in palynological records from the northern northwest atlantic does the terrestrial record lag the marine and air records abstract major changes in both pollen and dinocyst assemblages are recorded during the younger dryas in bay of islands and are associated with large drops in air and sea surface temperatures and sea surface salinity the changes in vegetation are similar with those observed at other sites in newfoundland dinoflagellate cyst assemblages also show similar species succession as nearby sites from the gulf of st lawrence and laurentian channel the amplitude of changes in air temperature a 7 c drop is similar to those recorded in northeastern north america in the sea surface temperature dropped by 7 c salinity by 4 psu and the sea ice cover duration increased by 7 months sea surface and air temperatures started cooling 250 and 110 years before the start of the yd hence there is a 140 years delay between ocean and atmosphere a warming trend is seen in the marine record 310 years before the end of the yd while vegetation and air temperatures started recovering after the end of the event some 370 years later the major lithological and vegetation changes observed during the yd period in eastern north america might actually represent the full impacts of the cooling associated with the yd since the cooling trend actually started before the start of the yd period as defined by radiocarbon dates and pollen zones

re advance of the fennoscandian ice sheet during heinrich event 1 abstract five sediment cores bathymetric and 2d seismic reflection data from vestfjorden northern norway were studied in order to constrain the timing and extent of a major ice stream draining the northwestern fennoscandian ice sheet during the last deglaciation 15 10 14 c ka b p the bathymetric and seismic data indicate that vestfjorden traenadjupet was covered by grounded ice reaching the shelf break during the last glacial maximum lgm after the lgm break up and recession towards outer inner vestfjorden at 13 6 14 c ka b p the ice re advanced towards the outer part of vestfjorden prior to 13 1 14 c ka b p this is inferred from glaciomarine sediments overlain by diamicton at the base of the sediment cores interpreted as basal tills and associated contemporaneous build up of grounding zone wedges in the central vestfjorden this sequence of events is coherent with the late weichselian ice sheet dynamics both along the western norwegian continental shelf and in the barents sea possibly indicating a direct response to meltwater injection and accompanied cooling during disruption of the thermohaline circulation associated with heinrich event 1 enhanced supply of suspension load resulted in deposition of laminated sediments at 13 14 c ka b p reflecting the retreat of the ice stream towards the inner fjord in response to global climate amelioration and increased atlantic water inflow two additional ice re advances towards the norwegian coastline are inferred from distinct input of ice rafted debris ird with a typical mineralogical fingerprint derived from neoproterozoic early silurian calcite and dolomite marbles in the ice sheet catchment area thus the re advances may be concurrent with the older dryas 12 2 14 c ka b p skarpnes and younger dryas 10 7 14 c ka b p tromso lyngen cooling events

north atlantic circulation and reservoir age changes over the past 41 000 years 1 constraints on the timing of atlantic meridional overturning circulation amoc changes during the last deglaciation are fundamental to understanding the climate s rapid response to insolation forcing however uncertainty about high latitude north atlantic hlna radiocarbon reservoir ages has previously precluded robust age model development for this critical region hlna reservoir ages also serve as a proxy for amoc strength we present regionally averaged hlna reservoir ages for 0 to 41 thousand years before the present kyr bp based on over 500 radiocarbon dates from 33 north atlantic cores an early deglacial increase to 1000 14c yr reservoir ages between 18 5 and 16 5 kyr bp suggests reduced amoc before peak heinrich stadial 1 hs1 ice rafted debris ird a rapid decrease in reservoir ages coincident with the ird maximum at 16 kyr bp indicates strong stratification of the upper water column caused by massive freshwater release

a 10be chronology of south western scandinavian ice sheet history during the lateglacial period we present 34 new cosmogenic 10be exposure ages that constrain the lateglacial bolling preboreal history of the scandinavian ice sheet in the lysefjorden region south western norway we find that the classical lysefjorden moraines earlier thought to be entirely of younger dryas age encompass three adjacent moraines attributed to at least two ice sheet advances of distinctly different ages the 10be age of the outermost moraine 14 0 0 6 ka n 4 suggests that the first advance is of older dryas age the innermost moraine is at least 2000 years younger and was deposited near the end of the younger dryas 11 4 0 4 ka n 7 after abandonment of the innermost lysefjorden moraine the ice front receded quickly towards the head of the fjord where recession was interrupted by an advance that deposited the trollgaren moraine at 11 3 0 9 ka n 5 10be ages from the inboard side of the trollgaren moraine suggest final retreat by 10 7 0 3 ka n 7 the late culmination of the younger dryas advance contrasts with other sectors of the scandinavian ice sheet where the margin appears to have culminated earlier during the younger dryas stadial followed by retreat during the middle and late part of the younger dryas

an oceanic origin for the increase of atmospheric radiocarbon during the younger dryas 1 variations in carbon 14 to carbon 12 ratio in the atmosphere 14catm provide a powerful diagnostic for elucidating the timing and nature of geophysical and anthropological change the atlantic marine archive suggests a rapid 14catm increase of 50 at the onset of the younger dryas yd cold reversal 12 9 11 7 kyr bp which has not yet been satisfactorily explained in terms of magnitude or causal mechanism as either a change in ocean ventilation or production rate using earth system model simulations and comparison of marine based radiocarbon records from different ocean basins we demonstrate that the yd 14catm increase is smaller than suggested by the marine archive this is due to changes in reservoir age predominantly caused by reduced ocean ventilation

a new concept for the paleoceanographic evolution of heinrich event 1 in the north atlantic new records of planktonic foraminiferal 18o and lithic and foraminiferal counts from eirik drift are combined with published data from the nordic seas and the ice rafted debris ird belt to portray a sequence of events through heinrich event 1 h1 these events progressed from an onset of meltwater release at not vert similar19 ka bp through the conventional h1 ird deposition phase in the ird belt starting from not vert similar17 5 ka bp to a final phase between 16 5 and not vert similar15 ka bp that was characterised by a pooling of freshwater in the nordic seas which we suggest was hyperpycnally injected into that basin after not vert similar15 ka bp this freshwater was purged from the nordic seas into the north atlantic which preconditioned the nordic seas for convective deep water formation this allowed an abrupt re start of north atlantic deep water nadw formation in the nordic seas at the bolling warming 14 6 ka bp in contrast to previous estimates for the duration of h1 i e 1000 years to only a century or two the total combined composite h1 signal presented here had a duration of over 4000 yrs not vert similar19 14 6 ka bp which spanned the entire period of nadw collapse it appears that deep water formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead the location of meltwater injections may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

radiocarbon content of pre bomb marine mollusks and variations in the 14c reservoir age for coastal areas of the barents and kara seas russia fourteen mollusks collected alive between 1900 and 1945 from the russian barents and kara seas were analyzed by ams 14c dating to evaluate variations in the 14c marine reservoir for arctic coastal sites which is important for correcting ages in paleoenvironmental time series and advancing understanding of the exchange of carbon the 14c ages on the mollusks reveal a range of marine reservoir values r t from 159 14c yr to 764 14c yr the oldest r t values of 764 to 620 14c yr are for the bivalve portlandia arctica which often inhabit cold and low salinity waters and muddy substrates the depleted 14c content for this bivalve reflects possibly the incorporation of old carbon from freshwater inputs and or the consumption of old organic matter from the underlying sediments and pore waters other mollusks with sessile habitats and pelagic food sources gave significantly lower r t values between 159 and 344 14c yr the youngest r t values indicate enrichment in 14c and may partially reflect enhanced transfer of 14c enriched co2 from the atmosphere to the ocean surface with wind generated wave agitation this study underscores that a variety of processes can lead to variable 14c depletion and enrichment of surface waters yielding a ca 600 year age span for contemporaneous arctic mollusks there may be added uncertainty in the 14c reservoir correction for deposit feeder species such as portlandia sp and perhaps for certain benthic foraminifera e g nonion labradoricum because these taxa often incorporate old organic matter from the substrate a reservoir correction of 700 years may be more appropriate for infaunal deposit eater species particularly in glacier dominated environments mollusks and foraminifera with sessile habits and pelagic food sources should be selected preferentially for 14c dating because their shells may more closely reflect the 14c content of the global ocean mixed layer

testing a soil development model against southern norway soil chronosequences abstract the first results of modeling soil development in marine sediments in s norway using the model soilgen are compared to measured properties of two soil chronosequences on the western and eastern side of oslofjord respectively the aim of this work is to test how well soil development under well defined environmental conditions can be modeled such testing reveals to what degree soil forming processes are understood allowing formulation of adequate calculations reflecting these processes the model predicts particle size distribution reasonably well although clay depletion in the upper parts of the soils as a result of clay migration is overestimated the model tends to underestimate contents of organic carbon and cec in the a horizons below modeled cec matches well with measured cec base saturation is overestimated in the upper 40 cm and underestimated below apparently leaching of bases proceeds less rapidly in reality than is predicted by the model due to strong soil structure of the b horizons causing preferential flow and base leaching around the aggregates whereas bases inside the aggregates are only slightly affected by leaching difficulties and possibilities for improvements are identified some related to model input data and some to the model itself input data could be improved by determining the amounts of organic carbon in organic surface horizons and by quantifying effects of bioturbation a big challenge is the implementation of soil structure formation in the model quantitative data on the development of soil structure with time that can be included in a model are required amounts distribution and connectivity of macro pores need to be defined for each stage of soil development and zones of low and high base leaching need to be distinguished in the model for each time step the long term aim of this work is to model soil development with different sets of soil forming factors e g different climatic conditions in order to reliably predict soil development under different climate scenarios and related sets of soil forming factors the results of the first model runs and the identified possible improvements suggest that this aim is generally achievable

atlantic surface water inflow to the nordic seas during the pleistocene holocene transition mid late younger dryas and pre boreal periods 12 450 10 000 a bp the inflow of atlantic water to the nordic seas from mid late younger dryas to earliest holocene 12 450 10 000 a bp is reconstructed on the basis of a high resolution core link14 from 346 m water depth on the east faroe shelf we have analysed the distribution of planktic and benthic foraminifera stable isotopes and ice rafted debris ird and calculated absolute temperatures and salinities by transfer functions during the investigated time period there was almost continuous inflow of atlantic water to the nordic seas deposition of ird during the mid late younger dryas and pre boreal coolings indicates the presence of melting icebergs and that summer sea surface temperatures were low the east west temperature gradient across the faroe shetland channel was much steeper than today the cold conditions around the faroe islands are attributed to stronger east greenland and east icelandic currents than at present the near continuous inflow of atlantic water is consistent with published evidence suggesting that deep convection took place in the nordic seas although the convection sites probably had shifted to a more easterly position than at present around the time of deposition of the saksunarvatn tephra c 10 350 a bp sea surface temperatures increased to the present level

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

variability of sea ice conditions in the fram strait over the past 30 000 years sea ice is a critical component of the climate and oceanographic system in the north atlantic ocean a biomarker record reveals millennial scale and glacial interglacial fluctuations in sea ice coverage in the northernmost atlantic ocean over the past 30 000 years

a major re growth of the scandinavian ice sheet in western norway during allerod younger dryas abstract distinct younger dryas yd moraines are mapped more or less continuously around the scandinavian ice sheet in most areas there is no evidence to suggest that a glacial re advance took place during the yd either because it did not happen or because older deposits have been removed by glacial erosion in contrast we here present 90 radiocarbon dates from 36 different sites that were overrun by a major ice sheet advance in the area between hardangerfjorden and sognefjorden sw norway thus this region is exceptional for examining the glacial response to the climate shifts across allerod yd the re growth of the ice sheet in this sector commenced during the allerod interstadial it expanded along 600 800 m deep fjords reaching a thickness of up to 2000 m we produce time distance diagrams for two lobes for both the outermost coast became ice free close to 15 cal ka bp i e at the onset of the bolling the hardangerfjorden lobe re advanced during the older dryas 14 cal ka bp an event that was not replicated for the herdla lobe farther north both lobes reached their most landward position before re advancing at 13 5 13 0 cal ka and obtained their maximum extent at the very end of the yd 11 5 cal ka the late culmination of the advance is accurately dated and differs from most of the scandinavian ice sheet margin where the maximum was reached during early or middle yd we also present a time distance diagram from the last glacial maximum to the ice divide showing two step retreat fast retreat occurs 21 20 and 11 5 10 cal ka bp separated by a period of almost no net retreat 20 11 5 cal ka bp which contrasts with much more even retreat in other parts of the scandinavian ice sheet

redating the advance of the new zealand franz josef glacier during the last termination evidence for asynchronous climate change abstract dating climatic and environmental records with accuracy and precision is critical if we are to robustly test hypotheses of synchronous change between the hemispheres in the southern hemisphere the advance of the new zealand franz josef glacier to the waiho loop terminal moraine has been used as evidence of synchronous global change during the younger dryas chronozone however radiocarbon ages for wood incorporated into the sediments associated with the advance span an interval of 900 years here we demonstrate that weathered old wood was incorporated into the deposit prior to or during the advance and that this material is highly susceptible to contamination by young carbon resulting in the wide range of age estimates reported previously we have identified material with little evidence of reworking well preserved wood with bark attached that provides a statistically robust mean radiocarbon age of 11 062 30 bp 13 1 ka for the advance of the franz josef glacier the timing of this event falls within the later part of the antarctic cold reversal comparison with local regional and global records suggests that cold conditions in the southern ocean were probably experienced in new zealand at this time driving the glacial advance

preboreal onset of cold water coral growth beyond the arctic circle revealed by coupled radiocarbon and u series dating and neodymium isotopes cold water coral mounds of lophelia pertusa are widespread across the scandinavian shelf which was completely ice covered during the last glacial maximum between 22 to 18 ka bp rapid deglacial meltdown of the fennoscandian inland ice and the retreat of its ice streams freed most of the shelf of ice by 15 ka bp however cold water coral growth commenced only after the pleistocene holocene transition at 11 65 ka bp when modern like climatic patterns and oceanographic conditions were established a tight climatic coupling has been constrained with u series ages coupled 14c ages provide local reservoir ages from various gravity cores in a fjord setting in stjernsund at 70 n and on the open shelf in traenadjupet at 66 n reinvestigation of earlier 14c coral chronologies suggests that coral ecosystems widely established themselves across the entire 3000 km long scandinavian shelf prior to 10 ka bp the earliest occurrence of madrepora oculata at 2 4 ka bp suggests a late holocene colonization of the norwegian shelf which is linked to a prominent mound growth hiatus in traenadjupet 64 n mound growth rates near the northern biogeographic boundary of l pertusa with up to 614 cm ka 1 during certain growth periods are much higher than the previously reported fastest rates of 220 cm ka 1 from the irish margin contemporaneous rapid fjordbasin sedimentation is slower with 63 cm ka 1 matrix 14c ages overlap with coral 14c ages from the same horizon this indicates rapid framework construction and efficient trapping of background sediment hiatuses are frequent in on mound sediments and only short periods of coral growth are recorded coupled 14c and end values indicate a persistent holocene inflow of the north atlantic current in stjernsund but also deglacial meltwater mixing during the early holocene prior to 9 5 ka bp reservoir ages are overall close to the surface marine reservoir age but r is highly localized

coupled response of the late glacial climatic shifts of northwest europe reflected in greenland ice cores evidence from the northern north sea the climatic regimes of the land areas adjacent to the north sea are controlled by the influx of atlantic water north of the british isles and into the north sea a high resolution record from the norwegian channel off western norway covering the past 15 ka 14 c shows that prior to the younger dryas there were three periods of sea surface conditions there similar to those of the present interspersed with arctic conditions these changes corresponding to an increase of approx 5 c in summer sea surface temperatures took place on the scale of

identification and dating of a key late pleistocene stratigraphic unit in the st lawrence estuary and gulf eastern canada abstract a recently acquired 8 m long sediment core along with high resolution seismic reflection and subbottom profiler sections allowed the identification characterization and dating of a widespread seismic unit extending from the head of the laurentian channel lower st lawrence estuary to honguedo strait gulf of st lawrence eastern canada this seismic unit labelled unit 2 is characterized by a series of parallel high amplitude reflections with thicknesses ranging from 68 m near the head of the laurentian channel to 250 m in the st lawrence estuary leaving it very difficult to be reached by conventional coring operations here we reveal how we were able to trace and core this seismic unit in an area where it lays closer to the seafloor near the southern wall of the laurentian channel in the lower st lawrence estuary this seismic unit consists of two sedimentary facies sandy mud including ice rafted debris ird underlying faintly laminated to homogenous and plastic silty clays based on the sedimentary facies we interpret the upper clays as ice distal glaciomarine sediments and the lower sandier sediments as ice proximal glaciomarine sediments this interpretation is further supported by the fact that no seismic nor sediment facies present above seismic unit 2 throughout the estuary and gulf of st lawrence can be linked to glacial i e ice contact sediments such as till moraines esker etc sediments seismic unit 2 is highly disturbed by iceberg scouring in the gulf of st lawrence where it is found at shallower depths indicating that it was deposited during deglaciation the available ams 14c dates obtained in the ice proximal glaciomarine sediments indicate that the lower part of seismic unit 2 was deposited during local re advances or stillstands of the laurentide ice sheet margins in the goldthwait sea that began at or before the younger dryas cold event 11 100 10 000 yr bp and that seismic unit 2 can be used as a chronostratigraphic marker throughout the st lawrence estuary and northwestern gulf of st lawrence

variations in temperature and extent of atlantic water in the northern north atlantic during the holocene we compare six high resolution holocene sediment cores along a s n transect on the norwegian svalbard continental margin from ca 601n to 77 41n northern north atlantic planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties including summer sea surface temperatures sst the cores are located below the axis of the norwegian current and the west spitsbergen current which today transport warm atlantic water to the arctic sediment accumulation rates are generally high at all the core sites allowing for a temporal resolution of 10 10 2 years sst is reconstructed using different types of transfer functions resulting in very similar sst trends with deviations of no more than 71 0 1 51c a transfer function based on the maximum likelihood statistical approach is found to be most relevant the reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the younger dryas preboreal transition the earliest part of the holocene was characterized by large temperature variability including the preboreal oscillations and the 8 2 k event in general the early holocene was characterized by ssts similar to those of today in the south and warmer than today in the north and a smaller s n temperature gradient 0 231c 1n compared to the present temperature gradient 0 461c 1n the southern proxy records 60 691n were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening the northern records 72 77 41n display a millennial scale change associated with reduced insolation and a gradual weakening of the north atlantic thermohaline circulation thc the observed northwards amplification of the early holocene warming is comparable to the pattern of recent global warming and future climate modelling which predicts greater warming at higher latitudes the overall trend during mid and late holocene was a cooling in the north stable or weak warming in the south and a maximum s n sst gradient of ca 0 71c 1n at 5000 cal years bp superimposed on this trend were several abrupt temperature shifts four of these shifts dated to 9000 8000 5500 3000 and 1000 and 400 cal years bp appear to be global as they correlate with periods of global climate change in general there is a good correlation between the northern north atlantic temperature records and climate records from norway and svalbard r 2007 elsevier ltd all rights reserved

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

the marine 14c age of the vedde ash bed along the west coast of norway articulated molluscs sea urchins and barnacle fragments close to the vedde ash bed in a shallow marine deposit on the west coast of norway have been 14c dated the weighted mean of four dates from a sediment slice 8 cm thick centred on the vedde ash bed is 10920 24 14c yr bp the most accurate 14c age of the vedde ash from terrestrial plant macrofossils is 10310 50 yr bp the difference is the 14c reservoir age for coastal water at the west coast of norway during the mid younger dryas and equals 610 55 yr this is 230 yr older than the reservoir age for the bolling allerod and for the present day in this area the result supports earlier conclusions of a higher reservoir age for the younger dryas in the north atlantic and nordic seas although our reservoir age of 610 55 yr is a few hundred years younger this suggests that the 14c reservoir age at vedde ash time may increase from coastal water towards the open north atlantic and nordic seas copyright 2001 john wiley sons ltd

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

early holocene planktic foraminifers record species specific 14c reservoir ages in arctic gateway to trace spatial variations in holocene reservoir ages of surface and subsurface waters we studied narrowly spaced 14c records of planktic foraminifera in three high sedimentation rate cores from the nordic seas the barents sea continental margin and eastern fram strait the two northern cores reveal a distinct early holocene 14c plateau in dates on the subsurface dweller neogloboquadrina pachyderma at 9 3 9 1 14c ka the plateau was tuned to an atmospheric 14c plateau at 9 0 8 7 14c ka that spans 10 2 9 6 calendar ka these two plateau boundaries provide robust age control points to estimate short term changes in sedimentation rate and to correlate paleoceanographic signals over 900 km along the west spitsbergen current the difference between planktic and atmospheric 14c plateau ages suggests local 14c reservoir ages of 370 400 yr planktic foraminifera species that inhabit different water masses document different reservoir ages by comparison the subpolar n incompta reveals a reservoir age of 150 yr probably formed in well mixed atlantic sourced waters during winter the near surface dweller turborotalita quinqueloba shows an age of 290 yr in the fram strait but one of 720 yr at the barents sea continental margin the latter age suggests a calcification within old meltwater enriched arctic surface waters admixed by the east spitsbergen current likewise we assign an elevated reservoir age of 760 yr on mixed species at a norwegian sea site near 71 n to preboreal meltwaters that spread from northern norway far west also documented by the spatial distribution of a coeval 13c minimum of n pachyderma

early deglacial onset of southwestern greenland ice sheet retreat on the continental shelf abstract the greenland ice sheet gris advanced onto the continental shelf during the last glacial period while deglacial records for when the gris withdrew onto the modern coastline are relatively abundant the timing of early gris retreat on the shelf is poorly constrained here we use planktic foraminiferal 18 o sediment grain size sedimentation rates and 14 c ages in southeastern davis strait core hu87033 008 to develop an early deglaciation chronology of the southwestern gris while on the continental shelf sedimentation rates and especially silt and clay fractions are high between 20 5 and 17 1 ka suggesting that the southwestern gris margin was near or at the shelf break where it released subglacially derived sediment laden meltwater a peak in sedimentation rates of 110 cm ka 1 between 19 3 ka and 18 6 ka combined with an initial decrease in planktic 18 o of 0 5 per mil suggests an early deglacial pull back of the gris margin from the shelf break with a concurrent increase in surface ocean meltwater discharge a subsequent planktic 18 o decrease of 1 0 per mil combined with a drop in silt and clay sedimentation rates at 18 17 ka likely record further gris retreat inland from the shelf break terrestrial 10 be surface exposure ages indicate that the gris margin remained on the continental shelf until 11 ka yet the cause of this subsequent ice margin stability on the inner shelf is not known our new records provide the first evidence that the southwestern gris margin may have begun to deglaciate at the same time as other northern hemisphere ice sheets as labrador sea water temperatures likely remained near glacial values until 15 ka we suggest that initial southwestern gris retreat was in response to rising global sea level from retreat of other ice sheets and or the initial deglacial rise in boreal summer insolation

timing of the younger dryas glacial maximum in western norway this study precisely constrains the timing of the younger dryas yd glacial maximum in south western norway by utilizing sediment records from lake basins two of the basins located on the distal side of the mapped herdla halsnoy moraine received meltwater directly from the ice sheet only when the ice margin reached its maximum extent during the yd in the cores the ice maximum is represented by well defined units with meltwater deposits dominantly laminated silt plant macrofossils in the sediment sequences are common and we obtained 18 radiocarbon ages from one of the cores by applying bayesian age depth modelling we obtained a precise date for this meltwater event and thereby also for the timing of the yd glacial maximum we conclude that the ice sheet advance culminated at the halsnoy moraine at 11 760 120 cal a bp and that the ice margin stayed in this position for 170 120 years the subsequent retreat started at 11 590 100 cal a bp i e close to the yd holocene boundary withdrawal was probably triggered by abrupt climatic warming at this time copyright 2011 john wiley sons ltd

temporal variability in the holocene marine radiocarbon reservoir effect for the tropical and south pacific understanding the marine radiocarbon reservoir effect i e marine radiocarbon reservoir age r and or correction r is important for the construction of robust radiocarbon chronologies for marine archives for various research areas including archaeology palaeoecology paleoceanography quaternary research and climate change studies in this study we examined temporal r variability for the south china sea scs and the great barrier reef gbr during the past 8 1 ka based on 14c analysis of 230th dated corals results show large r variations of 410 yr and 490 yr for the scs and the northern gbr for 5 5 8 1 ka and 5 5 7 ka respectively and a smaller r variability of 200 yr for the scs for 2 3 5 ka our data together with those previously published for the tropical and south pacific indicate that variability in ocean upwelling bringing old subsurface waters to the surface and or changes in the sources or 14c level of the upwelled waters are responsible for seeing large r variations in coastal areas along the eastern pacific and the tropical east pacific tep of several hundred to a thousand years mostly during the early to middle holocene r variations in the central and western pacific of several and a couple of hundred years during the middle and late holocene respectively might be due to variability in pacific wide ocean circulation associated with climatic changes controlling the spread of upwelled waters from the tep to the west this mechanism together with local regional effects such as changes in ocean upwelling in the scs resulting from east asian monsoon variability and changes in upwelling and or horizontal advection in the northern gbr associated with variability in the el nino southern oscillation might be responsible for the observed r variations in these areas the results of our study also indicate the need for regional marine radiocarbon calibration curves for improved radiocarbon dating of marine samples as the observed holocene r values for the tropical and south pacific are not fully reproduced by a recent modelling work using a 3d ocean model which takes into account climate change effects ocean circulation changes were included in the model for the period of 11 5 50 cal kyr bp but possibly not considered or not well represented for the holocene which might explain the differences between the observed and modelled r values

large variations in the holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes accurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect this effect for a particular site region is generally assumed constant through time when calibrating marine 14c ages however recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late quaternary and holocene here we report marine radiocarbon reservoir correction r r for heron reef and moreton bay in southwestern sw pacific for the last 8 ka derived from 14c analysis of 230th dated corals most of our r r for the last 5 4 ka agree well with their modern value but large r r variability of 410 yr from trough to peak with possible decadal centennial fluctuations is evident for the period 5 4 8 ka the latter time interval also has significant variations with similar features in previously published r r values for other sites in the pacific including southern peru northern chile in southeastern se pacific the south china sea vanuatu and papua new guinea with the largest magnitude of 920 yr from se pacific the mechanisms for these large r r variations across the pacific during the mid holocene are complex processes involving 1 changes in the quantity and 14c content of upwelled waters in tropical east pacific tep frequency and intensity of ocean upwelling in the tep and contribution of subantarctic mode water to the upwelled waters which is influenced by the intensity and position of southern westerly winds and 2 variations in ocean circulation associated with climate change la nina el nino conditions intensity of easterly trade winds positions of the intertropical convergence zone and the south pacific convergence zone which control the spreading of the older upwelled surface waters in the tep to the western sites our results imply the need for employing temporal changes in r r values instead of constant modern values for age calibration of holocene marine samples not only for the sw pacific sites but also for other tropical and subtropical sites in the pacific

reconstruction of ice sheet retreat after the last glacial maximum in storfjorden southern svalbard abstract storfjorden is a large north south trending sound located in the southern part of svalbard in the northwestern barents sea presently several glaciers drain into the northern and western part of storfjorden our study area covers the southern part of the sound which is divided by a north south striking basement ridge the mid ridge into a narrow western trough little storfjorden and a broader eastern trough storfjorden in the latter three grounding zone wedges gzws were discovered in 2005 showing evidence of former grounded ice here we confirm the existence and map the extent of the gzws and reconstruct the pattern and timing of ice retreat in storfjorden during the deglaciation the study is based on high resolution seismic and shallow acoustic profiles and swath bathymetry combined with information of lithology and radiocarbon dates from sediment cores the results show that the three gzws stretch across the fjord and that all three are located south of higher basement areas that were upstream of the gzws and which acted as pinning points during ice retreat the mid ridge imposed a lateral drag to the ice resulting in an uneven ice retreat across the fjord outside of the gzws only a thin cover of glacial deposits was found the cores were taken in vicinity of the gzws and all reached till deposits overlain by glacimarine or hemipelagic sediments enabling dating of the gzws altogether we find that the fjord and basement topography played an important role in the ice retreat ams 14c dates show that the formation of the three gzws correlate with three well known atmospheric warming phases start of bolling interstadial allerod interstadial and holocene interglacial respectively associated with inflows of warm atlantic water indicating a strong ocean climate control on the deglaciation of storfjorden

sea level fluctuations imply that the younger dryas ice sheet expansion in western norway commenced during the allerod after the first emergence following deglaciation relative sea level rose by 10 m in western norway and culminated late in the younger dryas yd the relative sea level history reconstructed by dating deposits in isolation basins shows a sea level low stand between 13 640 and 13 080 cal yr bp a 10 m sea level rise between 13 080 and 11 790 cal yr bp and a sea level high stand between 11 790 and 11 550 cal yr bp shortly after the yd holocene boundary sea level fell abruptly by 37 m the shorelines formed during the sea level low stand in the mid allerod and during the sea level high stand in the yd have almost parallel tilts with a gradient of 1 3 m km 1 indicating that hardly any isostatic movement has taken place during this period of sea level rise we conclude that the transgression was caused by the major re advance of the scandinavian ice sheet that took place in western norway during the lateglacial the extra ice load halted the isostatic uplift and elevated the geoid due to the increased gravitational attraction on the sea our results show that the crust responded to the increased load well before the yd starting 12 900 cal yr bp with a sea level low stand at 13 640 cal yr bp and the subsequent yd transgression starting at 13 080 cal yr bp thus we conclude that the so called yd ice sheet advance in western norway started during the allerod possibly more than 600 years before the allerod yd transition r 2007 elsevier ltd all rights reserved

akaogiite an ultra dense polymorph of tio2 with the baddeleyite type structure in shocked garnet gneiss from the ries crater germany akaogiite an ultra dense polymorph of tio2 was encountered in heavily shocked garnet cordierite sillimanite gneiss in the suevite breccia of the ries meteorite impact crater in germany the chemical formula of akaogiite is tio2 containing wt tio2 97 6 97 7 nb2o5 0 15 0 20 and feo 0 11 0 14 the empirical formula is ti0 998fe0 002nb0 001o2 akaogiite is optically distinguishable from rutile only in reflected light microscopy through its slightly higher brightness and the intense royal blue color of its internal reflections in crossed nicols the mineral grains consist of countless randomly oriented submicrometer particles in situ micro beam x ray diffraction established akaogiite to be monoclinic with the baddeleyite type structure cell parameters are a 4 606 2 angstrom b 4 896 3 angstrom c 4 933 3 angstrom and beta 99 17 6 degrees space group p2 1 c molar volume 16 82 2 cm 3 mol density 4 72 g cm 3 akaogiite coexists in the shocked gneiss with graphite diamond phase transition assemblage a second dense tio2 polymorph with the scrutinyite type structure tio2 ii liquidus idiomorphic jadeite inclusions in melt pockets in garnet and a new fetio3 polymorph with the li niobate structure the high pressure assemblage constrains the equilibrium peak shock pressure to be 22 gpa and a post shock temperature 500 degrees c thus correcting previous estimates the name was approved by the commission on new minerals nomenclature and classification of the international mineralogical association ima2007 058 the name is for masaki akaogi professor at the department of chemistry gakushuin university in tokyo japan

late glacial holocene clay minerals elucidating glacial history in the sw barents sea abstract detailed investigations of the distribution of clay minerals of late glacial holocene sediments from the sw barents sea provide important new information about the provenance and transport paths of the sediments this information leads to better understanding of the onset of the last deglaciation and subsequent advances retreats of the barents sea and fennoscandian ice sheets the results show interaction and changes in the fennoscandian ice sheet and bjornoyrenna ice stream during the last deglaciation high illite content and maximum kaolinite content 18 700 cal yr b p indicate glacial erosion from both the fennoscandian ice sheet and bjornoyrenna ice stream lgm ii the occurrence of a c reniforme dominated benthic foraminiferal assemblage 18 700 cal yr b p indicates that the northern most cores site in ingoydjupet had already been deglaciated and was probably situated in a glacier distal environment in addition smectite content reaching its highest level concurrent with the presence of neogloboquadrina pachyderma sin dominated planktic foraminifera can be related to the strengthening of the atlantic current the inflow of the atlantic water may have triggered deglaciation of the fennoscandian ice sheet bolling interstadial a rapid increase in illite content reflecting strong melting of the fennoscandian ice sheet 15 000 cal yr b p indicates the onset of deglaciation in a core closer to the continent decrease of illite and ird content together with the deposition of laminated sediments during the older dryas stadial 15 000 14 000 cal yr b p indicates colder conditions and formation of at least seasonal sea ice in addition increased kaolinite content indicates increased glacial erosion of the bjornoyrenna ice stream the highest values of illite content and increased ird content 14 000 13 000 cal yr b p can be related to strong melting of the fennoscandian ice sheet a slight indication of the younger dryas cold period is given by the decrease in illite and ird contents all clay contents are more stable during holocene compared to lgm and the last deglaciation

paleoceanographic development in the sw barents sea during the late weichselian early holocene transition abstract the late weichselian early holocene variability of the north atlantic current has been studied with focus on the zonal component of this meridional transport during the transition from glacial to interglacial conditions the investigated sediment core is from 409 m water depth in the sw barents sea eight accelerator mass spectrometry ams 14c dates show that the core covers the last 20 000 cal yr b p with a centennial scale resolution during late weichselian early holocene planktic foraminiferal assemblages were analyzed using the 100 m size fraction and foraminiferal planktic and benthic 13c and 18o isotopes were measured furthermore a range of physical and chemical analyses has been carried out on the bulk sediment samples four time periods have been identified which represent the varying oceanographic conditions in ingoydjupet a glacial trough located off the north coast of norway in the sw barents sea 1 the late glacial before ca 15 000 cal yr b p influenced by the nearby ice sheets with high amounts of sea ice or iceberg transported detritus 2 the late oldest dryas stadial and the bolling allerod interstadial ca 15 000 12 700 cal yr b p with cold surface water conditions influenced by the collapse of the nearby ice sheets high amounts of sea ice or iceberg transported detritus and melt water and weak subsurface inflow of atlantic water 3 the younger dryas cold stadial 12 700 11 650 cal yr b p with low primary productivity and extensive sea ice cover and 4 the preboreal and early holocene 11 650 6800 cal yr b p cal yr b p with strong influx of atlantic water into the area near absence of ice rafted debris and generally ameliorated conditions in both surface and bottom water masses as seen from a high flux of foraminifera and increased marine primary production

structural and stratigraphic controls on subsurface fluid flow at the veslemoy high sw barents sea abstract subsurface and seafloor fluid flow anomalies are gaining large interest after the finding of five new hydrocarbon discoveries and observation of large gas flares in the sw barents sea in the present study we have analysed structural and stratigraphic controls on fluid flow towards the seafloor using gravity cores selected based on subsurface gas anomalies observed on seismic data from the veslemoy high sw barents sea the subsurface fluid flow at the veslemoy high is observed to be controlled by 1 the morphology and orientation of regional faults structural highs and sedimentary basins 2 the presence of paleocene silica ooze deposits that changes microstructure with temperature thereby controlling fluid flow and 3 the location of regional and local open faults formed by glacial loading and unloading analysis of extractable organic matter in subsurface holocene sediments corroborates the active migration pathways inferred from seismic data micropalaeontological studies on benthic foraminifera reveal methane seep associated assemblages that confirm the interpretation of subsurface gas anomalies in seismic data we ultimately link these new results to the geological evolution history of the region to give a comprehensive model for the fluid flow system within the study area

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation

assessing the ability of the 14c projection age method to constrain the circulation of the past in a 3 d ocean model radiocarbon differences between benthic and planktonic foraminifera b p ages and radiocarbon projection ages are both used to determine changes of the past ocean circulation rate a global 3 d ocean circulation model with a constant modern ocean circulation is used to study which method is less influenced by atmospheric 14c variations three factors cause uncertainties first the long equilibration time of the ocean after atmospheric 14c changes second different mixing processes in the ocean which cause an ocean response of smaller amplitude than the atmospheric forcing and third the unknown source region and corresponding initial surface 14c reservoir age of subsurface waters the model suggests that b p ages and projection ages have lower uncertainties the closer they are to deepwater formation zones in the north atlantic the b p age method is less influenced by atmospheric 14c variations than the projection age method projections ages vary less in the pacific as long as atmospheric 14c decreases linearly a more irregular atmospheric 14c evolution leads to age variations of similar magnitude with both methods on the basis of the model experiment we suggest a potential improvement of the projection age method