a planktic foraminiferal transfer function for the southern south atlantic ocean abstract quantitative analysis of planktic foraminiferal assemblages in 81 surface sediment samples from 20 s subtropical gyre to 55 s antarctic zone in the south atlantic ocean documents a close relationship between species distribution and austral summer surface water temperature a data set including the abundance pattern of 25 taxa and morphotypes was used to establish a transfer function based on the definition of five factors altogether these factors account for 97 of the total variance of the original data and their geographic distribution is closely linked to sea surface temperatures the transfer function f81 25 5 allows reconstruction of late quaternary summer surface water temperatures in the boundary region between the antarctic cold and subtropical warm water realm 0 5 to 26 0 c the statistical error for modern data is 1 3 c

late quaternary variations in calcium carbonate preservation of deep sea sediments in the northern cape basin results from a multiproxy approach in this study we test various parameters in deep sea sediments bulk sediment parameters and changes in microfossil abundances and preservation character which are generally accepted as indicators of calcium carbonate dissolution we investigate sediment material from station geob 1710 3 in the northern cape basin eastern south atlantic 280 km away from the namibian coast well outside today s coastal upwelling as northern benguela upwelling cells were displaced westward and periodically preceded the core location during the past 245 kyr volbers et al submitted geob 1710 3 sediments reflect these changes in upwelling productivity results of the most commonly used calcium carbonate dissolution proxies do not only monitor dissolution within these calcareous sediments but also reflect changes in upwelling intensity accordingly these conventional proxy parameters misrepresent to some extent the extent of calcium carbonate dissolution these results were verified by an independent dissolution proxy the globigerina bulloides dissolution index bdxp volbers and henrich submitted the bdxp is based on scanning electronic microscope ultrastructural investigation of planktonic foraminiferal tests and indicates persistent good carbonate preservation throughout the past 245 kyr with the exception of one pronounced dissolution event at early oxygen isotopic stage ois 6 the early ois 6 is characterized by calcium carbonate contents sand contents and planktonic foraminiferal concentrations all at their lowest levels for the last 245 kyr at the same time the ratio of radiolarian to planktonic foraminiferal abundances and the ratio of benthic to planktonic foraminiferal tests are strongly increased as are the rain ratio the fragmentation index and the bdxp the sedimentary calcite lysocline rose above the core position and geob 1710 3 sediments were heavily altered as attested to by the unusual accumulation of pellets aggregates sponge spicules radiolaria benthic foraminifera and planktonic foraminiferal assemblages solely the early ois 6 dissolution event altered the coarse fraction intensely and is therefore reflected by all conventional calcium carbonate preservation proxies and the bdxp we attribute the more than 1000 m rise of the sedimentary calcite lysocline to the combination of two processes a a prominent change in the deep water mass distribution within the south atlantic and b intense degradation of organic material within the sediment preserved as maximum total organic carbon content creating microenvironments favorable for calcium carbonate

short fluctuations in antarctic isotope records a link with cold events in the north atlantic abstract the recent synchronization of antarctic and greenland ice cores obtained by blunier and colleagues from methane measurements in the 10 15 kyr and 25 45 kyr intervals allows us to investigate leads and lags between climatic changes in the two hemispheres we observe that most of the cold episodes recorded in the greenland ice correspond to peaks in isotope antarctic records once the common timescale derived from methane measurements is adopted these antarctic peaks are commonly interpreted as reflecting warmings in antarctica here we draw attention on a possible alternative explanation those peaks could at least partially correspond to a temporary cooling of the source water providing antarctic precipitation as a result of cold conditions in the north atlantic and of a fast interhemispheric transfer of this cooling via the atmosphere or the ocean this suggestion would be consistent with recent measurements of the deuterium excess in vostok ice antarctica although there are good arguments in favor of the currently accepted interpretation the influence of temperature changes in the source regions of antarctic precipitation on the temperature proxy has to be kept in mind when interpreting the phasing between greenland and antarctic ice core records

climate records covering the last deglaciation the oxygen 18 oxygen 16 ratio of molecular oxygen trapped in ice cores provides a time stratigraphic marker for transferring the absolute chronology for the greenland ice sheet project gisp ii ice core to the vostok and byrd ice cores in antarctica comparison of the climate records from these cores suggests that near the beginning of the last deglaciation warming in antarctica began approximately 3000 years before the onset of the warm bolling period in greenland atmospheric carbon dioxide and methane concentrations began to rise 2000 to 3000 years before the warming began in greenland and must have contributed to deglaciation and warming of temperate and boreal regions in the northern hemisphere

timing of the antarctic cold reversal and the atmospheric co2increase with respect to the younger dryas event the transition from the last glacial to the holocene is a key period for understanding the mechanisms of global climate change ice cores from the large polar ice sheets provide a wealth of information with good time resolution for this period however interactions between the two hemispheres can only be investigated if ice core records from greenland and antarctica can be synchronised accurately and reliably the atmospheric methane concentration shows large and very fast changes during this period these variations are well suited for a synchronisation of the age scales of ice cores from greenland and antarctica here we confirm the proposed lead of the antarctic cold reversal on the younger dryas cold event the antarctic cooling precedes the younger dryas by at least 1 8 kyr this suggests that northern and southern hemispheres were in anti phase during the younger dryas cold event a further result of the synchronisation is that the long term glacial interglacial increase of atmospheric co 2 was not interrupted during the younger dryas event and that atmospheric co 2 changes are not necessarily dominated by changes in the north atlantic circulation

old radiocarbon ages in the southwest pacific ocean during the last glacial period and deglaciation marine radiocarbon 14c dates are widely used for dating oceanic events and as tracers of ocean circulation essential components for understanding ocean climate interactions past ocean ventilation rates have been determined by the difference between radiocarbon ages of deep water and surface water reservoirs but the apparent age of surface waters currently approximately 400 years in the tropics and approximately 1 200 years in antarctic waters might not be constant through time as has been assumed in radiocarbon chronologies and palaeoclimate studies here we present independent estimates of surface water and deep water reservoir ages in the new zealand region since the last glacial period using volcanic ejecta tephras deposited in both marine and terrestrial sediments as stratigraphic markers compared to present day values surface reservoir ages from 11 900 14c years ago were twice as large 800 years and during glacial times were five times as large 2 000 years contradicting the assumption of constant surface age furthermore the ages of glacial deep water reservoirs were much older 3 000 5 000 years the increase in surface to deep water age differences in the glacial southern ocean suggests that there was decreased ocean ventilation during this period

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

a review of the australian new zealand sector of the southern ocean over the last 30ka aus intimate project the australia new zealand region of the southern ocean is influenced by several of the major global water masses of the oceans and is the prime entry point for cold deep waters into the pacific basin during the last glacial there was increased sea ice extent around antarctica as far north as 55 s as well as increased iceberg presence inferred from ice rafted debris evidence from microfossil assemblages suggests that sea surface temperatures sst were up to 7 c cooler consistent with recent estimates of cooling for new zealand derived from glacier modelling and other terrestrial proxies the subtropical front stf subantarctic front saf and polar front pf had migrated north except where the position of the fronts were controlled bathymetrically despite the potential for iron fertilisation by increased dust input into the ocean during the glacial there is limited evidence for higher total biological productivity in the pacific sector of the southern ocean the altered oceanic circulation during the glacial also decreased nutrients in the surface waters and affected the outgassing of co 2 this contributed to an increased storage of co 2 in the deep waters and lowering of the carbonate lysocline during the deglaciation sea ice retreat and sst increased rapidly at 18 ka roughly synchronous with the reinvigoration of deep water circulation in the southern ocean and the release of co 2 stored in the deep waters the gradient in carbon isotopes 13 o benthic between antarctic intermediate water aaiw and lower circumpolar deep water lcdw was greatest at the start of the deglaciation suggesting that the aaiw ventilation preceded lcdw ventilation or there was a significant change in air sea fractionation of 13 o benthic there was a slight enrichment in 18 o planktic decrease in ssts and a reduction in intermediate and deep water circulation between 14 and 12 5 ka bp during the antarctic cold reversal acr coincident with glacier advances in the new zealand southern alps and other terrestrial records of cooling following the acr there was a second more minor release of deep water co 2 most likely related to reinvigoration of north atlantic deep water nadw from 10 ka onwards the modern intermediate and deep water circulation was established air temperatures and ssts reached a maximum in the early holocene with the stf located at its most southerly position and there was a widespread retreat of antarctic ice sheets to their modern position a decline to modern sst and air temperatures in the mid to late holocene followed while millennial cycles overprinted on the sst and 18 o planktic records may be the result of subtle changes in the position and strength of the westerly winds during the holocene

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

climate connections between the hemisphere revealed by deep sea sediment core ice core correlations abstract correlation of southern ocean deep sea sediment core records with ice core records of polar climate delineates with unprecedented detail the relationship between high latitude climate and the ocean s thermohaline circulation over the last 80 000 years our observations suggest that while north atlantic deep water variability manifests itself clearly in southern ocean nutrient proxy records over periods as short as 500 yr this deep water variability did not promote a direct link between climate variability in the high latitudes of the two hemispheres on millennial timescales in particular the proxy records indicate that on average northern hemisphere climate fluctuations lagged those of the southern hemisphere by 1500 yr

planktic foraminifera from the southwestern atlantic 30 60 s species specific patterns in the upper 50 m abstract planktic foraminifers were studied in 96 samples collected in the southwestern atlantic 30 60 s along 53 w in november 1993 mainly from depths between 0 and 50 m very high proportions of juveniles unidentified were present throughout the area especially north of 37 s where they accounted for up to 70 80 of all shells recorded for most species no clear vertical specific stratification was detected in the 0 50 m layer zoogeographic grouping of the 18 species identified allowed the defining of 5 distinct zones along the transect subtropical north of 31 s 80 warm water individuals warm transitional 34 37 s 35 warm water transitional 37 49 s 99 cold water subantarctic 49 55 s 100 cold water and antarctic south of 56 s 100 cold water boundaries between foraminiferal assemblage zones are in good agreement with hydrological fronts described for the area comparison of the present data with planktic collections from the north atlantic show large differences in the proportions of various taxa in the 14 24 c range g bulloides is much more abundant in the northern hemisphere than in the southern one whereas g quinqueloba g inflata and g rubescens show the opposite trend on the other hand temperature related percentage contributions within the 14 24 c range indicate that the preferred thermic regimes of the 9 species considered are remarkably similar in the north and south atlantic collections compared the southernmost planktic distributional ranges of selected warm water taxa are roughly coincident with those established previously on the basis of surface sediments disagreements being chiefly attributable to selective dissolution on the bottom in contrast at the bottom percentages of cold water foraminifers g bulloides g pachyderma are significantly enhanced with respect to their planktic populations and their sedimentary northward limits extend well beyond their maximum ranges in the upper layer plankton it is suggested that submergence of these cold water species and northward displacement at subsurface depths is chiefly responsible for the mismatching patterns observed dissimilar species proportions in both hemispheres and plankton sediment uncoupling can conceivably engender erroneous conclusions when distributional data are used for paleoecologic reconstructions with the aid of numerical analyses such as the imbrie kipp transfer function technique

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

benthic foraminiferal abundance and stable isotope changes in the indian ocean sector of the southern ocean during the last 20kyr paleoceanographic implications abstract benthic foraminiferal faunas and benthic stable isotopes during the last 20 kyr were investigated in core md02 2488 46 28 8 s 88 01 3 e 3420 m water depth from the southeast indian ocean sector of the southern ocean in order to document paleoceanographic changes from the last glacial through deglaciation and into the holocene variations occurred in the accumulation rates species composition diversity and stable isotopes during the last 20 kyr the benthic 18o and 13c records during the last 28 kyr show that no significant deep water circulation changes took place before 15 6 calendar kyr ka the 13c increase at 15 6 ka is interpreted as reflecting the arrival of better ventilated deep waters at the site and is associated with the progressive increase in of miliolids from 15 ka to 0 ka an interval 16 15 ka of low benthic foraminiferal accumulation rates bfars and an increase in the relative abundance of stainforthia complanata deep waters were 2 2 0 4 c colder during the last glacial than at present carbonate dissolution proxies indicate that carbonate dissolution was higher during the last glacial than during the last deglacial and holocene bfars and the percentage of species indicative of high productivity suggest that the flux of organic matter resulting from surface water productivity was generally higher between 20 and 13 ka than between 12 and 0 ka consistent with the observed higher proportion of biosiliceous sediment at 20 14 ka and published records the combined percentages of the two most abundant species alabaminella weddellensis and epistominella exigua phytodetritus species suggest that seasonality of productivity intermittency of primary productivity fluctuated over the last 20 kyr and was higher during the last glacial and deglaciation 20 10 ka compared with the holocene 10 0 ka the relative abundances of a weddellensis and e exigua do not covary over the last 20 kyr an observation also reported from other areas

quantifying carbonate dissolution and calibration of foraminiferal dissolution indices in the somali basin two sediment traps moored off somalia in 1992 1993 collected similar settling fluxes of carbonate and siliceous shells formed by various plankton groups planktic foraminifera showed large seasonal variations with more than 74 of the total planktic foraminifera flux collected during the sw monsoon summer upwelling when globigerina bulloides was dominating along with globigerinita glutinata and neogloboquadrina dutertrei the intermonsoon and ne monsoon assemblages were dominated by globigerinoides ruber we used the trap records as our no dissolution reference for comparison with three boxcore recorders in order to quantify the carbonate dissolution along a depth transect dissolution increases downslope from station 905 to 907 and 915 at depths of 1567 m 2807 m and 4035 m respectively the carbonate fraction of the sediment at station 915 which is located near the ccd is the most affected by dissolution with more than 97 of the planktic foraminifera dissolved here the planktic foraminifera assemblage is strongly modified with thick walled species such as n dutertrei globorotalia tumida and pulleniatina obliquiloculata as the most resistant it is not representative of the settling assemblage the planktic foraminiferal assemblages of the sediment surface at stations 905 and 907 remain similar to the trap assemblages and the foraminifera are well preserved although only 25 of foraminifera are apparently preserved at station 905 and 8 at station 907 those numbers are surprisingly low and infer that only a small fraction of the foraminiferal carbonate production is buried and removed from the carbon cycle this discrepancy between the export and buried flux is partly be due to bio mechanical destruction by benthic processes and to supralysoclinal dissolution due to metabolic co2 generated by the benthic organisms another important factor is the interannual variability of the productivity well known in the arabian sea the calibration of commonly used foraminiferal dissolution indices percentage of foraminiferal fragments percentage of resistant species foraminiferal dissolution index fdx to our data only shows reliable results for high dissolution levels 97 off somalia the most accurate of the proxies is the percentage of foraminiferal fragments compared to the other methods tested i e fdx planktic foraminiferal loss l percentage of radiolarians and diatoms percentage of benthic foraminifera the species assemblage appears to be not significantly modified by dissolution unless the estimated shell loss is high 92 of the arriving shells in our samples this level is expressed in the percentage of fragmentation the percentage of radiolarians and diatoms the percentage of resistant foraminifera species and fdx as 80 35 25 and 1 8 respectively the relative abundance of globigerina bulloides is a valid sw monsoon upwelling proxy only when dissolution is moderate 92 globigerina bulloides and globigerinoides ruber have similar burial efficiencies and susceptibilities to dissolution thus the ratio g bulloides g ruber is a valid proxy for past changes in the intensity of the sw monsoon even in the strongly dissolved samples in our sediment record the ratio g bulloides g ruber indicates that the sw monsoon was stronger in the recent past than in 1992 93

magnitude and geographic variation of the radiocarbon content in antarctic marine life implications for reservoir corrections in radiocarbon dating abstract radiocarbon age estimates on marine derined materials from the antarctic appear old in comparison with the terrestrial radiocarbon timescale as a result of significantly depleted 14 c concentrations in antarctic seas we review measurements of 14 c concentrations in modern antarctic marine life from south georgia the shetland islands and antarctic peninsula and suggest correction factors required to relate radiocarbon measurements on fossil marine materials from these areas to the conventional radiocarbon timescale for dates based on shells seaweeds sealbones and penguin bones the minimum correction factor for south georgia is ca 750 years and for the south shetland islands and antarctic peninsula it may be up to 1250 1300 years for whalebones a minimum correction of 1000 years may apply over a wide geographic area for comparison we also review radiocarbon measurements on marine species and seawater from other sectors of the antarctic in high latitudes correction factors of ca 1400 years are generally applicable to shell seal and penguin samples

carbon isotopes and habitat of polar planktic foraminifera in the okhotsk sea the carbonate ion effect under natural conditions the upper 500 or 1000 m of the water column in the okhotsk sea was sampled for living planktic foraminifera the polar species neogloboquadrina pachyderma sinistral strongly dominates the foraminiferal assemblage the subpolar to temperate species globigerina bulloides accounts for 10 25 other species account for up to 3 only the shell 18o and 13c values of the species n pachyderma sin are compared to water 18o values and 13c values of dissolved inorganic carbon dic the strong gradient in 18o composition and temperature in the upper water column is reflected in the 18o of n pachyderma sin relative to the values expected for inorganic calcite precipitated under equilibrium conditions n pachyderma sin displays a vital effect of about 1 in 18o the 13c composition of n pachyderma sin is about constant with water depth and the reflection of 13cdic in the foraminiferal shell seems to be masked by other effects most foraminifera are found above or slightly below the thermocline and can be assumed to calcify in the upper 200 m of the water column the gradient of 13cdic extends well below this depth therefore the lack of correlation can partly be attributed to this fact the remaining discrepancy between 13c of n pachyderma sin and 13cdic correlates with the carbonate ion concentration in the water column this leads to the conclusion that the carbonate ion effect cie which has been derived from culturing experiments for other species spero et al 1997 nature 390 497 500 is found here under natural conditions when the magnitude of the cie derived for g bulloides is applied to n pachyderma sin cie corrected 13c of n pachyderma sin is a direct reflection of 13cdic in the water column with a constant offset of 1 2

the transition from the last glacial period in inland and near coastal antarctica recent studies suggested that during the transition out of the last glacial period one near coastal site in antarctica showed a response similar to that of greenland and unlike that of central antarctica here we present a new high resolution record of calcium from dome c antarctica changes in flux of calcium an indicator of dust input from other continents should be synchronous across the region and probably the continent using ca to synchronise records we find that the main warming at the near coastal site of taylor dome was slower than suggested previously and similar to that of central antarctica until there is further evidence it is still a reasonable hypothesis that antarctic climate behaved more or less as a single unit during the transition

sea surface temperature estimates from the southwest pacific based on planktonic foraminifera and oxygen isotopes planktonic foraminiferal census data were collected on 34 surficial sediment samples from east of new zealand sea surface temperature estimates were derived from the data using the modern analogue technique mat and compared to data from climap s fa 20 equation they were also computed from oxygen isotope analyses of globigerina bulloides the temperature estimates compared well between the three methods and were found to correlate closely with the appropriate seasonal sea surface temperature as measured by satellite the foraminiferal assemblages and derivative temperatures clearly identify the major watermasses and oceanic fronts in the region and thus can be applied to palaeoceanographic analysis of southwest pacific sediments

a possible record of the younger dryas event in deep sea sediments of the southern ocean pacific sector abstract the oxygen isotope record combined with radiocarbon dating from two deep sea cores collected along a transect between new zealand and the ross sea are used to establish a reliable chronostratigraphy for the last 14 kyr after an integrated geochemical and micropaleontological analysis in this timeframe we detected a cooling interval dated between 12 5 cal kyr bp and 11 4 cal kyr bp the age control suggests that this event started 1 5 kyr after the onset of the antarctic cold reversal previously observed in several antarctic ice cores we infer that the observed cool event corresponds to the younger dryas event defined in northern europe this suggests that climate change recorded in this sector of the southern hemisphere still shows some synchronicity with northern hemisphere variations and that the decoupling of climate change between the two hemispheres likely occurred south of the polar front

the deglaciation of the northern hemisphere a global perspective orbitally induced increase in northern summer insolation after growth of a large ice sheet triggered deglaciation and associated global warming ice albedo sealevel and greenhouse gas feedbacks together with tropical warming from weakening winds in response to polar amplification of warming caused regionalto global near synchronization of deglaciation effects were larger at orbital rather than millennial frequencies because ice sheets and carbon dioxide vary slowly ice sheet linked changes in freshwater delivery to the north atlantic and possibly free oscillations in the climate system forced millennial climate oscillations associated with changes in north atlantic deep water nadw flow the north atlantic typically operates in one of three modes modern glacial and heinrich deglaciation occurred from a glacial mode ocean that in comparison to modern had shallower depth of penetration of nadw formed further south causing strong northern cooling and the widespread cold dry and windy conditions associated with the glacial maximum and the cold phases of the millennial dansgaard oeschger oscillations the glacial mode was punctuated by meltwater forced heinrich conditions that caused only small additional cooling at high northern latitudes but greatly reduced the formation of nadw and triggered an oceanic seesaw that warmed some high latitude southern regions centered in the south atlantic

synchronous climate changes in antarctica and the north atlantic central greenland ice cores provide evidence of abrupt changes in climate over the past 100 000 years many of these changes have also been identified in sedimentary and geochemical signatures in deep sea sediment cores from the north atlantic confirming the link between millennial scale climate variability and ocean thermohaline circulation it is shown here that two of the most prominent north atlantic events the rapid warming that marks the end of the last glacial period and the bolling allerod younger dryas oscillation are also recorded in an ice core from taylor dome in the western ross sea sector of antarctica this result contrasts with evidence from ice cores in other regions of antarctica which show an asynchronous response between the northern and southern hemispheres

development of sediment drifts approaching an active plate margin under the sw pacific deep western boundary current the abyssal pacific ocean is fed by a 1000 km wide deep western boundary current dwbc that flows northward along the continental margin east of new zealand between the passive margin of chatham rise and the subduction zone of kermadec trench a distance of 1200 km the dwbc has formed a suite of sediment drifts over a depth range of 2200 5700 m airgun and 3 5 khz profiles record a variety of drift types that reflect regional variations in bathymetry sediment supply and the tectonic volcanic framework on chatham rise the dwbc has deposited a sinuous linear body along the south flank 3000 m an extensive apronlike drift on the north flank 2200 4500 m and a ridgelike drift about the rise base 4500 5200 m the flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby louisville seamount chain further downcurrent the 250 km long rekohu drift 3600 4190 m has developed northward to 39 s south of this latitude drifts comprise mainly reworked pelagic hemipelagic material and sediment transported from distant southerly sources in contrast drifts north of 39 s have received a major injection of terrigenous sediment from hikurangi channel which runs 1400 km from new zealand eastward across the hikurangi plateau to disgorge on to the abyssal floor at the plateau edge en route turbidity current overspill from the channel has moved north under the influence of the shallow dwbc to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500 4200 m off hikurangi channel mouth a large fan has accumulated the dwbc has extended the fan into a drift running over 250 km along the base of hikurangi plateau 5150 5770 m toward kermadec trench here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area the seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the dwbc in the region with the late oligocene opening of the australian antarctic seaway drift construction commenced during the miocene but was punctuated in the late miocene by another period of erosion that coincided with increased bottom water production in antarctica deposition resumed in plio pleistocene times when large quantities of sediment from the rapidly rising landmass of new zealand were injected into the boundary current the modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of hikurangi plateau and widespread scour zones and sediment wave fields

neogloboquadrina pachyderma sinistral coiling as paleoceanographic tracers in polar oceans evidence from northeast water polynya plankton tows sediment traps and surface sediments the abundance and chemistry of the planktonic foraminifera neogloboquadrina pachyderma sinistral coiling have long been used as tools for monitoring polar surface ocean changes and for correlating these changes to atmospheric and thermohaline circulation fluctuations however due to its remote habitat very little is known about how modern n pachyderma s respond to changing environmental conditions in the polar seas modern samples of n pachyderma s from the northeast water polynya provide a means for studying how environmental conditions affect the vertical distribution and chemistry of this species highest abundances of n pachyderma s were associated with the chlorophyll maximum in the surface 20 80 m where they are exploiting their primary food source evidence suggests that the addition of a calcite crust modifies the calcite tests of some n pachyderma s between 50 and 200 m increasing shell density and modifying shell chemistry the shell mass of encrusted forms is 3 4 times greater than the nonencrusted forms between 50 and 200 m the oxygen isotope composition of n pachyderma s shells increase by 1 5 in response to local water column gradients the 13c values of n pachyderma s are basically invariant with depth in this region are consistently 1 0 depleted in comparison with the 13c for equilibrium calcite and remain basically constant during the shell thickening process mass balance calculations suggest that encrustation occurs at all depths but abundance counts suggest that the process occurs mostly at the depth of the main pycnocline sediment fluxes of n pachyderma s occur during a 2 week bloom event and decrease to almost zero below complete ice cover the decoupling of the processes controlling abundances and shell chemistry explain the discrepancies between transfer function and isotopically derived paleotemperature estimates of surface conditions in some oceanic settings the ability of 18o to record surface ocean conditions will depend on vertical water column gradients as evidenced by the differences in core top calibrations between the north and south atlantic

weathering and vegetation controls on nickel isotope fractionation in surface ultramafic environments albania abstract the dissolved nickel ni isotopic composition of rivers and oceans presents an apparent paradox even though rivers represent a major source of ni in the oceans seawater is more enriched in the heavier isotopes than river water additional sources or processes must therefore be invoked to account for the isotopic budget of dissolved ni in seawater weathering of continental rocks is thought to play a major role in determining the magnitude and sign of isotopic fractionation of metals between a rock and the dissolved product we present a study of ni isotopes in the rock soil plant systems of several ultramafic environments the results reveal key insights into the magnitude and the control of isotopic fractionation during the weathering of continental ultramafic rocks this study introduces new constraints on the influence of vegetation during the weathering process which should be taken into account in interpretations of the variability of ni isotopes in rivers the study area is located in a temperate climate zone within the ophiolitic belt area of albania the serpentinized peridotites sampled present a narrow range of heavy ni isotopic compositions ni 60 0 25 0 16 2sd n 2 at two locations horizons within two soil profiles affected by different degrees of weathering all presented light isotopic compositions compared to the parent rock 60nisoil rock up to 0 63 this suggests that the soil pool takes up the light isotopes while the heavier isotopes remain in the dissolved phase by combining elemental and mineralogical analyses with the isotope compositions determined for the soils the extent of fractionation was found to be controlled by the secondary minerals formed in the soil the types of vegetation growing on ultramafic derived soils are highly adapted and include both ni hyperaccumulating species which can accumulate several percent per weight of ni and non accumulating species whole plant isotopic compositions were found to be isotopically heavier than the soil 60niwhole plant soil up to 0 40 fractions of ni extracted by dtpa diethylenetriaminepentaacetic acid presented isotopically heavy compositions compared to the soil 60nidtpa soil up to 0 89 supporting the hypothesis that the dissolved ni fraction controlled by weathering has a heavy isotope signature the non hyperaccumulators n 2 were inclined to take up and translocate light ni isotopes with a large degree of fractionation 60nileaves roots up to 0 60 for ni hyperaccumulators n 7 significant isotopic fractionation was observed in the plants in their early growth stages while no fractionation occurred during later growth stages when plants are fully loaded with ni this suggests that i the high efficiency translocation process involved in hyperaccumulators does not fractionate ni isotopes and ii the root uptake process mainly controls the isotopic composition of the plant in ultramafic contexts vegetation composed of hyperaccumulators can significantly influence isotopic compositions through its remobilization in the upper soil horizon thereby influencing the isotopic balance of ni exported to rivers

evidence for global teleconnections in a late pleistocene speleothem record of water balance and vegetation change at sudwala cave south africa abstract understanding the global response to millennial scale climatic events is essential to our comprehension of climatic teleconnections and projection of future change however the extent and nature of their expression in areas of the southern hemisphere is often viewed as equivocal here we report uranium thorium dating of speleothem formations sampled at sudwala cave in the north eastern lowveld region of south africa s summer rainfall zone srz the growth intervals of multiple formations alongside a detailed chronology and multi proxy analysis of two periods of growth 40 35 ka and 13 8 12 8 ka in a stalagmite sc1 provide information regarding key fluctuations in the palaeoclimatic and palaeoenvironmental conditions during the late pleistocene high resolution stable isotope trace element and micro raman analysis are used alongside petrographic investigation to provide a detailed assessment of the climatic conditions associated with the onset and termination of growth in sc1 the combined raman and petrographic analysis represents a rare approach enabling the identification of aragonite calcite shifts both within and across growth intervals and diagenetic events potentially significantly influencing the recorded signal and often resulting in the major loss of chemical information consequently the identification of this post depositional chemical alteration could become a crucial prerequisite in speleothem palaeoclimatology particularly in areas prone to aragonite speleothem deposition susceptible to calcite conversion such as cave sites hosted by dolomitic karst systems the multiple proxies used in this study highlight the complex forcing relationships between climatically related environmental change and local cave conditions on speleothem precipitation contesting a common paradigm by associating drier conditions at sudwala with the initiation of speleothem growth the growth interval identified in stalagmite sc1 during the late deglaciation 13 85 12 79 ka coincides convincingly with both the southern hemispherically forced antarctic cold reversal 14 1 12 8 ka and the younger dryas 12 9 11 5 ka of northern hemispheric origin identifying southern africa as a vital location for the investigation of the hemispheric to global expression of the millennial scale fluctuations of the last deglaciation

pre bomb radiocarbon and the reservoir correction for calcareous marine species in the southern ocean four antarctic marine mollusc shells which were collected alive between 1917 and 1940 were analyzed by accelerator mass spectrometry to provide the first pre bomb radiocarbon measurements of biogenic carbonates from the southern ocean after correcting for the impact of fossil fuel combustion suess effect radiocarbon activities of the pre bomb shells averaged 149 8 10 4 in contrast the 14c values for post bomb molluscs echinoderms brachiopods and foraminifera averaged 96 1 25 2 these biogenic carbonate 14c values are nearly identical to pre bomb estimates 148 to 152 and post bomb measurements 98 4 22 0 of the surface waters in the southern ocean average radiocarbon ages of the biogenic carbonates before and after 1950 1303 84 years and 811 205 years respectively along with those from seals and penguins indicate that the antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300 100 years for calcareous marine fossils which are widespread abundant and well preserved organic materials for interpreting ice sheet climate and sea level impacts on the antarctic marine ecosystem during the holocene

an oceanic cold reversal during the last deglaciation a detailed deuterium excess profile measured along the dome c epica european project for ice coring in antarctica core reveals the timing and strength of the sea surface temperature changes at the source regions for dome c precipitation we infer that an oceanic cold reversal took place in the southern indian ocean 800 years after the antarctic cold reversal the temperature gradient between the oceanic moisture source and antarctica is similar to the dome c sodium profile during the deglaciation illustrating the strong link between this gradient and the strength of the atmospheric circulation

evidence against a significant younger dryas cooling event in new zealand pollen records of deglacial sequences from northwest nelson new zealand demonstrate that there was no significant temperature decline associated with the younger dryas in new zealand records of glacial advances at this time were either the product of increased snow accumulation under enhanced precipitation regimes or random variation rather than the result of a regional thermal decline this finding supports those models of younger dryas initiation that require neither enhanced westerly circulation nor significant thermal decline in the southern hemisphere

intercrater plains on mercury insights into unit definition characterization and origin from messenger datasets abstract orbital observations by the mercury surface space environment geochemistry and ranging messenger spacecraft are used to re evaluate the nature and origin of the oldest mapped plains deposits on mercury the intercrater and intermediate plains units defined by mariner 10 investigators despite the large areal extent of these plains which comprise approximately one third of the planetary surface area viewed by mariner 10 their formation mechanism was not well constrained by mariner 10 imaging one hypothesis attributed plains formation to ponding of fluidized impact ejecta to create relatively smooth surfaces another hypothesis was that these plains are of volcanic origin to assess the origin of these older plains and the contribution of early volcanism to resurfacing on mercury we have used messenger data to analyze the morphology spectral properties impact crater statistics and topography of mariner 10 type areas of intercrater and intermediate plains on the basis of new criteria for the identification of intercrater and intermediate plains derived from these observations we have remapped 18 of the surface of mercury we find that the intercrater plains are a highly textured unit with an abundance of secondary craters whereas the intermediate plains are composed of both intercrater and smooth plains we suggest that the term intermediate plains not be used to map the surface of mercury henceforth but rather this unit should be subdivided into its constituent intercrater and smooth plains units we argue that a substantial percentage of the intercrater plains are composed of volcanic materials on the basis of 1 examples of areas where ejecta from a small number of superposed craters have transformed smooth plains deposits of volcanic origin into a unit indistinguishable from intercrater plains 2 the range in ages of intercrater plains deposits as interpreted from crater size frequency distributions and 3 the near global distribution of intercrater plains compared with the uneven distribution of impact basins and their associated ejecta deposits

late quaternary caco3 production and preservation in the southern ocean implications for oceanic and atmospheric carbon cycling recent geochemical models invoke ocean alkalinity changes particularly in the surface southern ocean to explain glacial age pco2 reduction in such models alkalinity increases in glacial periods are driven by reductions in north atlantic deep water nadw supply which lead to increases in deep water nutrients and dissolution of carbonate sediments and to increased alkalinity of circumpolar deep water upwelling in the surface southern ocean we use cores from the southeast indian ridge and from the deep cape basin in the south atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by circumpolar deep water this suggests that deep southern ocean carbonate ion concentrations were lower in glacial stages than in interglacials rather than higher as suggested by the polar alkalinity model broecker and peng 1989 our observations show that changes in southern ocean caco3 preservation are coherent with changes in the relative flux of nadw suggesting that southern ocean carbonate chemistry is closely linked to changes in deepwater circulation the pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrient depleted water nadw to the southern ocean and with an increase of nutrients in deep water masses carbonate mass accumulation rates on the southeast indian ridge 3200 3800 m and in relatively shallow cores 3000 m from the kerguelen plateau and the south pacific were significantly reduced during glacial stages by about 50 the reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in caco3 corg flux ratios acting as another mechanism which would raise the alkalinity of southern ocean surface waters the polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant even if overall productivity in the southern ocean were held constant a decrease in the caco3 corg ratio would result in increased alkalinity and reduced pco2 in southern ocean surface waters during glacials this ecologically driven surface alkalinity change may enhance deepwater mediated changes in alkalinity and amplify rapid changes in pco2

hydrographic changes of the southern ocean southeast indian sector over the last 230 kyr hydrographical changes of the southern indian ocean over the last 230 kyr is reconstructed using a 17 m long sediment core md 88 770 46 01 s 96 28 e 3290m the oxygen and carbon isotopic composition of planktonic n pachyderma sinistra and g bulloides and benthic cibicidoides wuellerstorfi epistominella exigua and melonis barleeanum foraminifera have been analysed changes in sea surface temperatures sst are calculated using diatom and foraminiferal transfer functions a new core top calibration for the southern ocean allows an extension of the method developed in the north atlantic to estimate paleosalinities duplessy et al 1991 the age scale is built using accelerator mass spectrometry ams 14c dating of n pachyderma s for the last 35 kyr and an astronomical age scale beyond changes in surface temperature and salinity clearly lead by 3 to 7 kyr deep water variations thus changes in deep water circulation are not the cause of the early response of the surface southern ocean to climatic changes we suggest that the early warming and cooling of the southern ocean result from at least two processes acting in different orbital bands and latitudes 1 seasonality modulated by obliquity affects the high latitude ocean surface albedo sea ice coverage and heat transfer to and from the atmosphere 2 low latitude insolation modulated by precession influences directly the atmosphere dynamic and related precipitation evaporation changes which may significantly change heat transfer to the high southern latitudes through their control on latitudinal distribution of the major frontal zones and on the conditions of intermediate and deep water formation

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales