temporal variability in snow distribution snow distribution changes during the winter due to spatially variable snowfall and snowmelt events and wind induced redistribution of the snow this influences the spatial distribution of the melting process and thus the dynamics of the spring flood snow course data was collected in the catchments aursunden and atnasjo during the melt season in order to investigate the temporal variability of the snow distribution in alpine and forested terrain a time variant gamma distribution function was fitted to the snow course data

changes in environment over the last 800 000 years from chemical analysis of the epica dome c ice core the epica ice core from dome c extends 3259 m in depth and encompasses 800 ka of datable and sequential ice numerous chemical species have been measured along the length of the cores here we concentrate on interpreting the main low resolution patterns of major ions we extend the published record for non sea salt calcium sea salt sodium and non sea salt sulfate flux to 800 ka the non sea salt calcium record confirms that terrestrial dust originating from south america closely mirrored antarctic climate both at orbital and millennial timescales a major cause of the main trends is most likely climate in southern south america which could be sensitive to subtle changes in atmospheric circulation sea salt sodium also follows temperature but with a threshold at low temperature we re examine the use of sodium as a sea ice proxy concluding that it is probably reflecting extent with high salt concentrations reflecting larger ice extents with this interpretation the sodium flux record indicates low ice extent operating as an amplifier in warm interglacials non sea salt sulfate flux is almost constant along the core confirming the lack of change in marine productivity for sulfur producing organisms in the areas of the southern ocean contributing to the flux at dome c for the first time we also present long records of reversible species such as nitrate and chloride and show that the pattern of post depositional losses described for shallower ice is maintained in older ice it appears possible to use these concentrations to constrain snow accumulation rates in interglacial ice at this site and the results suggest a possible correction to accumulation rates in one early interglacial taken together the chemistry records offer a number of constraints on the way the earth system combined to give the major climate fluctuations of the late quaternary period

southern ocean buoyancy forcing of ocean ventilation and glacial atmospheric co2 ocean circulation and dynamics can alter atmospheric co2 concentrations numerical modelling suggests that shifts in surface buoyancy loss and the location of upwelling can sequester co2 in the southern ocean during glacial periods

atlantic meridional overturning circulation during the last glacial maximum the circulation of the deep atlantic ocean during the height of the last ice age appears to have been quite different from today we review observations implying that atlantic meridional overturning circulation during the last glacial maximum was neither extremely sluggish nor an enhanced version of present day circulation the distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the atlantic only slightly greater than today however evidence from multiple water mass tracers supports a different distribution of deep water properties including density which is dynamically linked to circulation

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

antarctic sea ice and palaeoproductivity variation over the last 156 000 years in the indian sector of southern ocean abstract antarctic sea ice plays a vital role in global climate via its impact on ocean circulation biological productivity and co2 partitioning between the ocean and the atmosphere however very little is known about its past history especially in the southwestern indian sector of the southern ocean so we here provide new quantitative records of winter sea ice concentration wsic and duration wsid sea surface temperatures sst and productivity in sediment core sk 200 33 55 s 45 e from the permanently open ocean zone over the last 156 000 years the new records combined with regional records indicate that the hydrological structures migrated northward by a few degrees of latitude during all glacial periods with the southern antarctic circumpolar current front reaching the core site the antarctic polar front located at 46 s and the winter sea ice wsi probably extending to 49 s in contrast hydrological fronts and wsi edge migrated poleward by a couple of degrees of latitude during the early holocene and last interglacial comparison to sst and wsi records from different sectors of the so suggests higher amplitude variations in wsi in the atlantic sector as compared to the indian and western pacific sectors over the last glacial interglacial cycle which we attribute to the presence of the weddell gyre transporting far to the north the sea ice produced in the weddell sea the new records also suggest a drop in productivity in the pooz during glacial periods probably related to greater wsi extent and reduced growing season

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

last glacial sea surface temperatures and sea ice extent in the southern ocean atlantic indian sector a multiproxy approach 1 on the basis of the quantitative study of diatom radiolarian and planktic foraminiferal assemblages we estimated summer sea surface temperature ssst and sea ice extent at 50 sediment core localities in the atlantic and western indian sector of the southern ocean to reconstruct the last glacial environment at the glamap 18 to 15 ka equal to 21 500 to 18 000 calendar cal years bp and epilog 19 5 to 16 0 ka equal to 23 000 to 19 000 cal years bp time slices stratigraphic identification of the time slices was accomplished by a combination of ams 14c measurements benthic isotope and siliceous microfossil abundance records while the ssst estimates reveal greater surface water cooling than reconstructed by climap 1981 reaching a maximum in the area of the present subantarctic zone the sea ice reconstruction indicates that climap overestimated the expansion of the antarctic sea ice field especially for austral summer during winter the sea ice field was expanded by 60 70 compared to the present last glacial summer sea surface isotherms indicate a northward shift of the zonal bands of the antarctic circumpolar current and a relative expansion of the cold water realm south of the subantarctic front by 5 in latitude this coincides with a northward displacement of the zone of enhanced biogenic silica deposition and iceberg occurrence as a result of northward expansion of antarctic cold waters and a relatively small displacement of the subtropical front thermal gradients were steepened during the last glacial in the area of the present subtropical front the northward displacement of antarctic cold waters and the related deflection of southern ocean waters along the eastern boundary of south america may have resulted in a weakened cold water route across the drake passage in contrast the transport of warm and salty surface water from the indian into the atlantic ocean via the warm water route was not blocked allowing continuous but reduced import of heat into the south atlantic

antarctic sea ice control on ocean circulation in present and glacial climates in the modern climate the ocean below 2 km is mainly filled by waters sinking into the abyss around antarctica and in the north atlantic paleoproxies indicate that waters of north atlantic origin were instead absent below 2 km at the last glacial maximum resulting in an expansion of the volume occupied by antarctic origin waters in this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around antarctica a simple theory further suggests that these deep waters only came to the surface under sea ice which insulated them from atmospheric forcing and were weakly mixed with overlying waters thus being able to store carbon for long times this unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean s role in regulating atmospheric carbon dioxide on glacial interglacial timescales previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide here it is shown that many of these changes are dynamically linked and therefore must co occur

seasonality of southern ocean sea ice the sea ice cover of the southern ocean undergoes a rapid decrease from mid november to mid january the atmosphere to ocean heat flux is insufficient to account for this melting even in the presence of the high percentage of open water characteristic of the southern ocean sea ice it is estimated that sea air heat exchange in the 60 to 70 s zone can account for roughly 50 of the required spring heating the remainder must be supplied by the relatively warm deep water residing below the southern ocean pycnocline deep to surface water heat flux is accomplished by upwelling of the pycnocline due to the regional ekman divergence of the surface layer and by cross pycnocline mixing it is estimated that the required vertical mixing coefficient for the pycnocline is 1 5 cm2 s this value is considered as realistic in view of the relatively weak pycnocline which is a consequence of low levels of fresh water input to the surface layer it is suggested that the magnitude of fresh water input is a major factor in determining the degree of seasonality of southern ocean sea ice

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

on the combined effects of vertical shear and zonal electric field patterns on nonlinear equatorial spread f evolution in order to understand observations of modulated irregularities in a localized region on the bottomside of the equatorial ionosphere without the presence of vertically rising large scale plume events an investigation is carried out by means of a nonlinear numerical simulation model using different background ionospheric conditions the investigation revealed that the development of long wavelength 200 km perturbations can only be confined to the bottomside of the ionosphere in a localized region with the combined effects of shear in the zonal plasma drift and a nighttime westward electric field the variabilities in the occurrence characteristic are shown to depend on the variabilities in the prereversal enhancement in the zonal electric field further the resurgence of a plume event at a later time as seen by the jicamarca radar is explained on the basis of confined preseeded structures subject to a fresh instability source first evidence is presented that a source of fresh instability may actually be a wind and or a temperature disturbance launched hours earlier by a small substorm

potential and limitations of marine and ice core sea ice proxies an example from the indian ocean sector diatom assemblages in marine cores and sea salt deposition fluxes in ice cores have been used as sea ice proxies in the southern hemisphere here a marine and an ice core proxy record for the indian ocean covering the last two glacial cycles are compared in order to illustrate their potential and limitations the marine core was extracted in a location completely ice free under present day conditions and therefore was unable to record changes to the recent sea ice extent similarly no sea ice was recorded at that location during the previous interglacial period during the last glacial period however the site was seasonally covered by sea ice and the diatom assemblages allowed an estimation of average seasonal sea ice presence the ice core data originated from the east antarctic plateau the marine sodium present in the ice core was used as a proxy of the sea ice coverage and on average a larger sea ice surface led to an increased sea salt aerosol flux seen e g at the last glacial inception however the response of the sea salt flux to increasing sea ice extent diminished during peak glacial conditions when only minimal variability was recorded in the ice core record a first order approximation is used to take this non linear response of the ice core sea ice proxy into account based on the ice core proxy record sea ice extent was reduced considerably during the warm episodes of the previous two interglacial periods compared to modern sea ice extent in particular during the peak warmth of the last interglacial the ice core proxy also showed a very strong precessional variability pronounced spectral peak at 23 ka period over the past 240 ka the advantage of combining the two proxy records lies in the complementary nature of their response while the ice core proxy showed limited sensitivity during full glacial conditions the marine proxy recorded the seasonal sea ice coverage once the sea ice retreated south of the location of the marine core the ice core proxy responded to changes in sea ice extent a composite of marine and ice core records may thus provide a data basis for a more detailed reconstruction of sea ice around antarctica over the last few glacial interglacial cycles

the southern ocean surface between marine isotope stages 6 and 5d shape and timing of climate changes summer sea surface temperature ssst and sea ice extent obtained at millennial to centennial resolution are presented for seven cores recovered in the atlantic and western indian antarctic zone from termination ii and the last interglacial s s i e marine isotope substage mis 5e the diatom based ssst estimates show that during the late mis 6 intensified export of cold waters from the weddell sea resulted in sssts close to 0 c in the central and eastern atlantic sector due to northward expansion of the winter sea ice edge by 3 5 latitude the sea ice seasonality was reduced such conditions have great potential for efficient year round reduction in air sea gas exchange and glacial co2 draw down the warming at termination ii started at 132 131 ka marked by rapid retreat of the sea ice edge the ssst increased within a few thousands of years to reach maximum interglacial summer temperatures ranging between 2 5 and 3 5 c in the earliest mis 5e 128 125 ka besides a distinct cold reversal around 129 5 ka the warming was punctuated by short lived temperature rebounds with amplitudes of 1 1 5 c occurring at 200 300 yr frequency thus in the range of the periodicity of solar input increased chaetoceros spp abundance suggests meltwater events as the primary cause of the coolings the ssst optimum characterised by strongly enhanced biogenic sedimentation rates ended at ca 125 ka with the full re establishment of the global conveyor belt and beginning of the northern hemisphere climatic optimum at this time sssts decreased stepwise and stabilised on values slightly warmer than today showing in the following period of mis 5e only low amplitude oscillations during mis 5d a northward expansion of the sea ice field took place but sssts only slightly colder than modern ones and a weakened meridional temperature gradient indicate that the southern ocean did not fall in a true glacial mode the tight correlation between southern ocean ssst and winter sea ice records and vostok atmospheric temperature and co2 records support the idea that the antarctic winter sea ice and southern ocean temperature exert a primary control on the atmospheric ocean co2 exchanges and hence on global climate reduction of the antarctic sea ice field and increase of ssst at the onset of termination ii could have been triggered by precessional changes influencing southern high latitude summer insolation positive feedback mechanisms reduction of surface albedo and release of co2 into the atmosphere and changes in global ocean circulation affected by a collapse or strong reduction in north atlantic deep water nadw production could have induced further reinforcement of the southern ocean warming

late quaternary sea ice history in the indian sector of the southern ocean as recorded by diatom assemblages abstract a modern analog technique mat5201 31 has been applied to fossil diatom assemblages to provide down core estimates of february sea surface temperatures ssts and of sea ice duration over the past 220 000 years at 56 40 s 160 14 e at the core location sea ice progression lagged the sst drop by 1 ka at interglacial glacial transitions and sea ice retreat was almost synchronous to the sst increase at glacial interglacial terminations sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times although ssts were almost constant during glacials this indicates that ssts are the major parameter determining the advance and retreat of sea ice at transitions but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo air temperature and meridional wind stress the strong correlation r 0 75 between sea ice duration at the core location and the vostok co2 record argues for a control of antarctic sea ice extent on atmospheric co2 concentration via the modification of the ocean to atmosphere gas balance

interhemispheric controls on deep ocean circulation and carbon chemistry during the last two glacial cycles changes in ocean circulation structure together with biological cycling have been proposed for trapping carbon in the deep ocean during glacial periods of the late pleistocene but uncertainty remains in the nature and timing of deep ocean circulation changes through glacial cycles in this study we use neodymium nd and carbon isotopes from a deep indian ocean sediment core to reconstruct water mass mixing and carbon cycling in circumpolar deep water over the past 250 thousand years a period encompassing two full glacial cycles and including a range of orbital forcing building on recent studies we use reductive sediment leaching supported by measurements on isolated phases foraminifera and fish teeth in order to obtain a robust seawater nd isotope reconstruction neodymium isotopes record a changing north atlantic deep water nadw component in the deep indian ocean that bears a striking resemblance to northern hemisphere climate records in particular we identify both an approximately in phase link to northern hemisphere summer insolation in the precession band and a longer term reduction of nadw contributions over the course of glacial cycles the orbital timescale changes may record the influence of insolation forcing for example via nadw temperature and or antarctic sea ice extent on deep stratification and mixing in the southern ocean leading to isolation of the global deep oceans from an nadw source during times of low northern hemisphere summer insolation that evidence could support an active role for changing deep ocean circulation in carbon storage during glacial inceptions however mid depth water mass mixing and deep ocean carbon storage were largely decoupled within glacial periods and a return to an interglacial like circulation state during marine isotope stage mis 6 5 was accompanied by only minor changes in atmospheric co2 although a gradual reduction of nadw export through glacial periods may have produced slow climate feedbacks linked to the growth of northern hemisphere ice sheets carbon cycling in the glacial ocean was instead more strongly linked to southern ocean processes

large inert carbon pool in the terrestrial biosphere during the last glacial maximum during each of the late pleistocene glacial interglacial transitions atmospheric carbon dioxide concentrations rose by almost 100 ppm the sources of this carbon are unclear and efforts to identify them are hampered by uncertainties in the magnitude of carbon reservoirs and fluxes under glacial conditions here we use oxygen isotope measurements from air trapped in ice cores and ocean carbon cycle modelling to estimate terrestrial and oceanic gross primary productivity during the last glacial maximum we find that the rate of gross terrestrial primary production during the last glacial maximum was about 40 10 pg c yr 1 half that of the pre industrial holocene despite the low levels of photosynthesis we estimate that the late glacial terrestrial biosphere contained only 330 pg less carbon than pre industrial levels we infer that the area covered by carbon rich but unproductive biomes such as tundra and cold steppes was significantly larger during the last glacial maximum consistent with palaeoecological data our data also indicate the presence of an inert carbon pool of 2 300 pg c about 700 pg larger than the inert carbon locked in permafrost today we suggest that the disappearance of this carbon pool at the end of the last glacial maximum may have contributed to the deglacial rise in atmospheric carbon dioxide concentrations

control of the glacial carbon budget by topographically induced mixing evidence for the oceanic uptake of atmospheric co2 during glaciations suggests that there was less production of southern origin deep water but paradoxically a larger volume of southern origin water than today here we demonstrate using a theoretical box model that the inverse relationship between volume and production rate of this water mass can be explained by invoking mixing rates in the deep ocean that are proportional to topographic outcropping area scaled with ocean floor slope furthermore we show that the resulting profile of a near linear decrease in mixing intensity away from the bottom generates a positive feedback on co2 uptake that can initiate a glacial cycle the results point to the importance of using topography dependent mixing when studying the large scale ocean circulation especially in the paleo intercomparison models that have failed to produce the weaker and more voluminous bottom water of the last glacial maximum

temporal relationships of carbon cycling and ocean circulation at glacial boundaries evidence from high sedimentation rate south atlantic deep sea cores indicates that global and southern ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice sheet growth and retreat respectively no consistent lead lag relationships are observed during abrupt millennial warming events during the last ice age allowing for the possibility that ocean circulation triggered some millenial climate changes at the major glacial interglacial transitions the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets

deep circulation changes in the central south atlantic during the past 145 kyrs reflected in a combined231pa 230th neodymium isotope and benthic δ13c record abstract previous work showed that south atlantic sediments have lower glacial than holocene 231pa 230th which was attributed to a switch in the flow direction of atlantic deep water debate exists however as to the degree to which two processes circulation and scavenging determine sedimentary 231pa 230th making this interpretation contentious here we address this issue using 145 kyr records of paleocirculation proxies benthic foraminiferal c 13 neodymium isotopes end and sedimentary 231pa 230th were all measured in a single sediment core from the south atlantic subtropical gyre this site largely excludes the influence of local productivity changes on 231pa 230th records measured 231pa 230th ranges between 0 041 during glacials and 0 055 during interglacial periods and is consistently lower than the production ratio indicating export of 231pa from the central south atlantic for the entire duration of the record the lower glacial 231pa 230th is regionally consistent suggesting that basin scale oceanographic processes cause the decrease in turn less radiogenic end and lower benthic c 13 confirm the classical picture of an increase in southern component water scw influence in the atlantic during glacial periods and point to a circulation control on the observed 231pa 230th decrease rather than a local productivity change we suggest that associated with this change in water mass distribution the dominant sink for 231pa shifted from the margins of the south atlantic and or the southern ocean during interglacials to the north atlantic during glacial periods indeed elevated 231pa 230th in the deep north atlantic during glacials supports this mechanism of northward transport of 231pa by scw

the southern ocean at the last glacial maximum a strong sink for atmospheric carbon dioxide analysis of satellite ocean color sea surface temperature and sea ice cover data reveals consistent patterns between biological production iron availability and physical forcings in the southern ocean the consistency of these patterns in conjunction with information on physical conditions during the last glacial maximum lgm enables estimates of export production at the lgm the lgm southern ocean experienced increased wind speeds colder sea surface and atmospheric temperatures increased deposition of atmospheric dust and a greatly expanded winter sea ice cover these variations had strong effects on southern ocean ecology and on air sea fluxes of co2 the seasonal ice zone siz was much larger at the lgm 30 million km2 than at present 19 million km2 the antarctic polar front pf likely marked the northern boundary of this expanded siz throughout the southern ocean as it does today in the drake passage region a large northward shift in the position of the pf during glacial times is unlikely due to topographic constraints north of the pf the increased flux of aeolian dust during glacial times altered phytoplankton species composition and increased export production and as a result this region was a stronger sink for atmospheric co2 than in the modern ocean south of the pf interactions between the biota and sea ice strongly influence air sea gas exchange over seasonal timescales the combined influence of melting sea ice and increased aeolian dust flux with its associated iron increased both primary and export production by phytoplankton over daily monthly timescales during austral spring summer resulting in a strong flux of co2 into the ocean heavy ice cover would have minimized air sea gas exchange over much of the rest of the year thus an increased net flux of co2 into the ocean is likely during glacial times even in areas where annual primary production declined we estimate that export production in the southern ocean as a whole was increased by 2 9 3 6 gt c yr 1 at the lgm relative to the modern era altered seasonal sea ice dynamics would further increase the net flux of co2 into the ocean thus the southern ocean was a strong sink for atmospheric co2 and contributed substantially to the lowering of atmospheric co2 levels during the last ice age

new tools for the reconstruction of pleistocene antarctic sea ice abstract based on the quantitative analysis of diatom assemblages preserved in 274 surface sediment samples recovered in the pacific atlantic and western indian sectors of the southern ocean we have defined a new reference database for quantitative estimation of late middle pleistocene antarctic sea ice fields using the transfer function technique the detrended canonical analysis dca of the diatom data set points to a unimodal distribution of the diatom assemblages canonical correspondence analysis cca indicates that not only winter sea ice wsi but also summer sea surface temperature ssst represent the most prominent environmental variables that control the spatial species distribution to test the applicability of transfer functions for sea ice reconstruction in terms of concentration and occurrence probability we applied four different methods the imbrie and kipp method ikm the modern analog technique mat weighted averaging wa and weighted averaging partial least squares wapls using logarithm transformed diatom data and satellite derived 1981 2010 sea ice data as a reference the best performance for ikm results was obtained using a subset of 172 samples with 28 diatom taxa taxa groups quadratic regression and a three factor model ikm d172 28 3q resulting in root mean square errors of prediction rmsep of 7 27 and 11 4 for wsi and summer sea ice ssi concentration respectively mat estimates were calculated with different numbers of analogs 4 6 using a 274 sample 28 taxa reference data set mat d274 28 4an 6an resulting in rmsep ranging from 5 52 4an to 5 91 6an for wsi as well as 8 93 4an to 9 05 6an for ssi wa and wapls performed less well with the d274 data set compared to mat achieving wsi concentration rmsep of 9 91 with wa and 11 29 with wapls recommending the use of ikm and mat the application of ikm and mat to surface sediment data revealed strong relations to the satellite derived winter and summer sea ice field sea ice reconstructions performed on an atlantic and a pacific southern ocean sediment core both documenting sea ice variability over the past 150 000 yr mis 1 mis 6 resulted in similar glacial interglacial trends of ikm and mat based sea ice estimates on the average however ikm estimates display smaller wsi and slightly higher ssi concentration and probability at lower variability in comparison with mat this pattern is a result of different estimation techniques with integration of wsi and ssi signals in one single factor assemblage by applying ikm and selecting specific single samples thus keeping close to the original diatom database and included variability by mat in contrast to the estimation of wsi reconstructions of past ssi variability remain weaker combined with diatom based estimates the abundance and flux pattern of biogenic opal represents an additional indication for the wsi and ssi extent

temporal evolution of mechanisms controlling ocean carbon uptake during the last glacial cycle many mechanisms have been proposed to explain the 85 90 ppm decrease in atmospheric carbon dioxide co2 during the last glacial cycle between 127 000 and 18 000 yrs ago when taken together these mechanisms can in some models account for the full glacial interglacial co2 drawdown most proxy based evaluations focus on the peak of the last glacial maximum 24 000 18 000 yrs ago and little has been done to determine the sequential timing of processes affecting co2 during the last glacial cycle here we use a new compilation of sea surface temperature records together with time sequenced records of carbon and nd isotopes and other proxies to determine when the most commonly proposed mechanisms could have been important for co2 drawdown we find that the initial major drawdown of 35 ppm 115 000 yrs ago was most likely a result of antarctic sea ice expansion importantly changes in deep ocean circulation and mixing did not play a major role until at least 30 000 yrs after the first co2 drawdown the second phase of co2 drawdown occurred 70 000 yrs ago and was also coincident with the first significant influences of enhanced ocean productivity due to dust finally minimum concentrations of atmospheric co2 during the last glacial maximum resulted from the combination of physical and biological factors including the barrier effect of expanded southern ocean sea ice slower ventilation of the deep sea and ocean biological feedbacks

a possible sequence of events for the generalized glacial interglacial cycle 1 there is not yet widespread agreement as to the underlying cause of the 80 100 ppmv roughly 100 kyr duration glacial interglacial cycles in atmospheric pco2 most of the mechanisms which have been proposed to account for the observed pco2 variations appear to in some way violate interpretations of paleo proxy data the inability of a single mechanism to explain the observed cycles in atmospheric co2 which show amazing similarity over the past 430 000 years is perplexing and leads us to consider whether a combination of mechanisms might be consistent with available evidence consistent with previous work we find that physical changes ocean circulation temperature mixing can only explain part of the observed atmospheric pco2 variability changes in ocean chemistry are invoked to explain the remainder in order to account for the initial pco2 drawdown from interglacial to intermediate levels we invoke physical changes in the ocean mixing temperature the transition from intermediate atmospheric pco2 levels to full glacial conditions involves a small increase in mean ocean nutrient levels and mean ocean alkalinity accomplished by falling sea level and subsequent erosion of organic rich shelf sediments the first part of the transition out of full glacial conditions is achieved through increased temperature and increased mixing in the southern ocean the final part of the atmospheric pco2 rise up to full interglacial conditions is accomplished through rising sea level and the subsequent change in mean ocean alkalinity and phosphate and a rise in the northern hemisphere temperature and ocean mixing the proposed sequence of events is consistent with most existing proxy evidence for paleo nutrient levels and changes in export production over the last glacial interglacial cycle furthermore it is consistent with evidence for a whole ocean shift in 13c toward significantly more negative values in the late glacial the proposed scenario is also consistent with ice core based timing constraints as summarized by broecker and henderson 1998 we show that we are able to explain the full magnitude of the glacial interglacial cycle in atmospheric pco2 without the need to invoke iron fertilization in the southern ocean

evidence for northward expansion of antarctic bottom water mass in the southern ocean during the last glacial inception 1 we investigated deep water changes in the southern ocean during the last glacial inception in relationship to surface hydrology and global climatology to better understand the mechanisms of the establishment of a glacial ocean circulation changes in benthic foraminiferal 13c from three high resolution cores are compared and indicate decoupled intermediate and deep water changes in the southern ocean from the comparison with records from the north atlantic south atlantic and the southern ocean we show that the early southern deep water 13c drop observed at the mis 5 5 5 4 transition occurred before any significant reduction of north atlantic deep water ventilation we propose that this drop is linked to the northward expansion of poorly ventilated antarctic bottom water aabw mass in the southern ocean associated with an early cooling in the high southern latitudes the westerly winds and surface oceanic fronts would migrate equatorward thus weakening the upwelling of circumpolar deep waters reduced heat brought to antarctic surface waters would enhance sea ice formation during winters and the deep convection of cold and poorly ventilated aabw

antarctic zone nutrient conditions during the last two glacial cycles in a sediment core from the pacific sector of the antarctic zone az of the southern ocean we report diatom bound n isotope 15ndb records for total recoverable diatoms and two distinct diatom assemblages pennate and centric rich these data indicate tight coupling between the degree of nitrate consumption and antarctic climate across the last two glacial cycles with 15ndb and thus the degree of nitrate consumption increasing at each major antarctic cooling event coupled with evidence from opal and barium based proxies for reduced export production during ice ages the 15ndb increases point to ice age reductions in the supply of deep ocean sourced nitrate to the az surface the two diatom assemblages and species abundance data indicate that the 15ndb changes are not the result of changing species composition the pennate and centric assemblage 15ndb records indicate similar changes but with a significant decline in their difference during peak ice ages a tentative seasonality based interpretation of the centric to pennate 15ndb difference suggests that late summer surface waters became nitrate free during the peak glacials

the impact of precession changes on the arctic climate during the last interglacial glacial transition three sensitivity experiments using an ocean atmosphere general circulation model oagcm are conducted to simulate the climate impact of precession the relative contributions of components of the hydrological cycle including the albedo of arctic sea ice advection of atmospheric water vapor and sea surface temperature to the summer arctic melt process are evaluated timing of the perihelion is varied in each experiment with meteorological spring sp winter wp and autumn ap perihelion corresponding to conditions at 110 115 and 120 ky bp respectively obliquity is unchanged at the 115 ky level which is lower than today the experiments are assessed relative to the present day control which has been shown to simulate current conditions based on observations in the sp experiment top of the atmosphere toa insolation is weaker than today between the summer solstice and autumnal equinox in the ap case representing the interglacial it is less intense between vernal equinox and summer solstice but stronger during the remainder of the year although the incident solar radiation is reduced in summer in the sp experiment increased melting of snow is found primarily as a result of feedbacks from the delayed seasonal cycle of hydrologic components this is in contrast to both the wp and ap cases in which the perennial snow cover is simulated at the time of the last glacial inception 115 ky bp the wp experiment shows lower insolation to the high northern latitudes in late spring and summer mainly as a result of lower obliquity than today dynamical ocean atmosphere interactions in response to precession maintain the reduced sea ice melting in late spring strengthen the annual equator to pole sea surface temperature sst gradient and increase atmospheric moisture convergence in glaciation sensitive regions in both the wp and

application of modern analog technique to marine antarctic diatoms reconstruction of maximum sea ice extent at the last glacial maximum modern analog technique mat applied to antarctic diatoms is a new approach for quantitative sea ice paleoreconstructions in the southern ocean in a first step we show that mat is a better approach than the imbrie and kipp method to reconstruct the modern sea ice pattern we then use this approach to reconstruct sea ice presence in number of months per year during the last glacial maximum lgm at this time sea ice presence was greater than today leading to a shorter diatom growing season the maximum sea ice extent inferred from quantitative values of sea ice presence was located 5 8 north of its actual position leading to double the surface of modern winter sea ice this greater sea ice extent may have played a significant role on atmospheric and surface oceanic circulations and therefore on southern mid latitude and high latitude climates it may also have reduced the amount of heat moisture and co2 from the ocean to the atmosphere thus participating in the lowering of atmospheric co2 during the lgm

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

strong and deep atlantic meridional overturning circulation during the last glacial cycle extreme abrupt northern hemisphere climate oscillations during the last glacial cycle 140 000 years ago to present were modulated by changes in ocean circulation and atmospheric forcing1 however the variability of the atlantic meridional overturning circulation amoc which has a role in controlling heat transport from low to high latitudes and in ocean co2 storage is still poorly constrained beyond the last glacial maximum2 3 4 here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle dominating ocean circulation in the atlantic whereas a shallower glacial mode with southern sourced waters filling the deep western north atlantic prevailed during glacial maxima3 5 our results are based on a reconstruction of both the strength and the direction of the amoc during the last glacial cycle from a highly resolved marine sedimentary record in the deep western north atlantic parallel measurements of two independent chemical water tracers the isotope ratios of 231pa 230th and 143nd 144nd 6 7 8 which are not directly affected by changes in the global cycle reveal consistent responses of the amoc during the last two glacial terminations any significant deviations from this configuration resulting in slowdowns of the amoc were restricted to centennial scale excursions during catastrophic iceberg discharges of the heinrich stadials severe and multicentennial weakening of north atlantic deep water formation occurred only during heinrich stadials close to glacial maxima with increased ice coverage probably as a result of increased fresh water input in contrast the amoc was relatively insensitive to submillennial meltwater pulses during warmer climate states and an active amoc prevailed during dansgaard oeschger interstadials greenland warm periods

increased dust deposition in the pacific southern ocean during glacial periods dust deposition in the southern ocean constitutes a critical modulator of past global climate variability but how it has varied temporally and geographically is underdetermined here we present data sets of glacial interglacial dust supply cycles from the largest southern ocean sector the polar south pacific indicating three times higher dust deposition during glacial periods than during interglacials for the past million years although the most likely dust source for the south pacific is australia and new zealand the glacial interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from antarctica and the south atlantic dominated by patagonian sources these similarities imply large scale common climate forcings such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in new zealand and patagonia

simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation according to milankovitch theory the lower summer insolation at high latitudes about 115 000 years ago allowed winter snow to persist throughout summer leading to ice sheet build up and glaciation1 but attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only2 3 4 5 these results point towards the importance of feedback effects for example through changes in vegetation or the ocean circulation for the amplification of solar forcing6 7 8 9 here we present a fully coupled ocean atmosphere model of the last glaciation that produces a build up of perennial snow cover at known locations of ice sheets during this period we show that ocean feedbacks lead to a cooling of the high northern latitudes along with an increase in atmospheric moisture transport from the equator to the poles these changes agree with available geological data10 11 12 13 14 15 and together they lead to an increased delivery of snow to high northern latitudes the mechanism we present explains the onset of glaciation which would be amplified by changes in vegetation in response to weak orbital forcing

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

reconstruction of sea surface temperatures from assemblages of planktonic foraminifera multi technique approach based on geographically constrained calibration data sets and its application to glacial atlantic and pacific oceans abstract we present a conceptual framework for a new approach to environmental calibration of planktonic foraminifer census counts this approach is based on simultaneous application of a variety of transfer function techniques which are trained on geographically constrained calibration data sets it serves to minimise bias associated with the presence of cryptic species of planktonic foraminifera and provides an objective tool for assessing reliability of environmental estimates in fossil samples allowing identification of adverse effects of no analog faunas and technique specific bias we have compiled new calibration data sets for the north n 862 and south n 321 atlantic and the pacific ocean n 1111 we show evidence that these data sets offer adequate coverage of the sea surface temperature sst and faunal variation range and that they are not affected by the presence of pre holocene samples and or calcite dissolution we have applied four transfer function techniques including artificial neural networks revised analog method and simmax with and without distance weighting on faunal counts in a last glacial maximum lgm data set for the atlantic ocean 748 samples in 167 cores based on the glamap 2000 compilation and a new data set for the pacific ocean 265 samples in 82 cores and show that three of these techniques provide adequate degree of independence for the advantage of a multi technique approach to be realised the application of our new approach to the glacial pacific lends support to the contraction and perhaps even a cooling of the western pacific warm pool and a substantial 3 c cooling of the eastern equatorial pacific and the eastern boundary currents our results do not provide conclusive evidence for lgm warming anywhere in the pacific the atlantic reconstruction shows a number of robust patterns including substantial cooling of eastern boundary currents with considerable advection of subpolar waters into the benguela current a cooling of the equatorial atlantic by 5 c and steep sst gradients in the mid latitude north atlantic the transfer function techniques generally agree that subtropical gyre areas in both hemispheres did not change significantly since the lgm although the ann technique produced glacial sst in the southern gyre 1 2 c warmer than today we have revisited the issue of sea ice occurrence in the nordic seas and using the distribution of subpolar species of planktonic foraminifera in glacial samples we conclude that the norwegian sea must have been ice free during the summer

abyssal atlantic circulation during the last glacial maximum constraining the ratio between transport and vertical mixing transport to vertical diffusivity in the deep atlantic our calculations suggest that the ratio was at least twice as large at the lgm we speculate that the primary cause was reduced mixing between northern and southern component waters associated with movement of this water mass boundary away from the zone of intense mixing near the seafloor the shallower water mass boundary yields an order of magnitude increase in the volume of southern component water suggesting its residence time may have increased substantially our analysis supports the idea that an expanded volume of antarctic bottom water and limited vertical mixing enhanced the abyssal ocean s ability to trap carbon during glacial times

southern hemisphere westerly wind changes during the last glacial maximum paleo data synthesis changes in the strength and position of southern hemisphere westerly winds during the last glacial cycle have been invoked to explain both millennial and glacial interglacial climate fluctuations however neither paleo models nor paleodata agree on the magnitude or even the sign of the change in wind strength and latitude during the most studied glacial period the last glacial maximum lgm compared to the recent past this paper synthesizes paleo environmental data that have been used to infer changes in lgm winds data compilations are provided for changes in terrestrial moisture dust deposition sea surface temperatures and ocean fronts and ocean productivity and existing data on southern hemisphere ocean circulation changes during the lgm are summarized we find that any hypothesis of lgm wind and climate change needs to provide a plausible explanation for increased moisture on the west coast of continents cooler temperatures and higher productivity in the subantarctic zone and reductions in agulhas leakage around southern africa our comparison suggests that an overall strengthening an equatorward displacement or no change at all in winds could all be interpreted as consistent with observations if a single cause related to the southern westerlies is sought for all the evidence presented then an equatorward displacement or strengthening of the winds would be consistent with the largest proportion of the observations however other processes such as weakening or poleward shifts in winds a weakened hydrological cycle extended sea ice cover and changed buoyancy fluxes cannot be ruled out as potential explanations of observed changes in moisture surface temperature and productivity we contend that resolving the position and strength of westerly winds during the lgm remains elusive based on data reconstructions alone however we believe that these data reconstructions of environmental conditions can be used in conjunction with model simulations to identify which processes best represent westerly wind conditions during the lgm

physical mechanisms behind biogeochemical glacial interglacial co2 variations the atmospheric concentration ofco2 has un dergonesignicantandfairlyregularchangesonatimescale of 100 kyr during the at least last four glacial interglacial cycles here we present a novel coupled physical biogeo chemical mechanism for these variations previous studies had to arbitrarily specify the behavior of the physical cli matesysteminordertoinvokeabiogeochemical mechanism for the glacial co2 changes be it an arbitrarily specied changeintheverticaloceanmixing toggweiler 1999 orar bitrarily specied sea ice cover changes stephens and keel ing 2000 instead we present here a new self consistent qualitative physical mechanism for both the vertical mixing and sea ice cover changes in this mechanism the cooling of north atlantic deep water due to northern hemisphere glaciationistransportedsouthwardbythethermohalinecir culation andcoolsthedeepwaterupwellinginthesouthern ocean this in turn aects the southern ocean stratica tion reducesthe rate of vertical mixing of thesurface water with the deep water and increases the sea ice cover we also explain the continuous time evolution between glacial and interglacial states rather than treat them as two steady states and are able to model explicitly for the rst time the amplication of the glacial interglacial variability of the physical climate system by the ocean biogeochemistry

how much did glacial north atlantic water shoal observations of 13c and cd ca from benthic foraminifera have been interpreted to reflect a shoaling of northern source waters by about 1000 m during the last glacial maximum with the degree of shoaling being significant enough for the water mass to be renamed glacial north atlantic intermediate water these nutrient tracers however may not solely reflect changes in water mass distributions to quantify the distribution of glacial north atlantic water we perform a glacial water mass decomposition where the sparsity of data geometrical constraints and nonconservative tracer effects are taken into account and the extrapolation for the unknown water mass end members is guided by the modern day circulation under the assumption that the glacial sources of remineralized material are similar to that of the modern day we find a steady solution consistent with 241 13c 87 cd ca and 174 18o observations and their respective uncertainties the water mass decomposition indicates that the core of glacial north atlantic water shoals and southern source water extends in greater quantities into the abyssal north atlantic as previously inferred the depth of the deep northern southern water mass interface and the volume of north atlantic water however are not grossly different from that of the modern day under this scenario the vertical structure of glacial 13c and cd ca is primarily due to the greater accumulation of nutrients in lower north atlantic water which may be a signal of the hoarding of excess carbon from the atmosphere by the glacial atlantic

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced

ice core evidence for the extent of past atmospheric co2 change due to iron fertilisation 1 an extended high resolution ice core record of dust deposition over the past 60 ka from dome c antarctica is presented the data are in conflict with the idea that changes in aeolian iron input into the southern ocean were the major cause for the 80 ppm glacial interglacial co2 increase during the deglaciation the co2 increase shows a linear relationship with the fall of the logarithm of the nss ca2 flux a proxy for dust deposition however the very large variations in the nss ca2 flux related to the glacial antarctic warm events a1 to a4 were accompanied by small co2 variations only our data based analysis suggests that decreased southern ocean dust deposition caused at most a 20 ppm increase in co2 at the last glacial interglacial transition rapid decreases in dust deposition to the northern pacific could have been responsible for a maximum of 8 ppm in addition

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr