info:doi/10.1038/nature04614 2006-03-23T00:00:00Z 2006-03-23T00:00:00Z E. W. Wolff H. Fischer F. Fundel U. Ruth B. Twarloh G. C. Littot R. Mulvaney R. Röthlisberger M. de Angelis C. F. Boutron M. Hansson U. Jonsell M. A. Hutterli F. Lambert P. Kaufmann B. Stauffer T. F. Stocker J. P. Steffensen M. Bigler M. L. Siggaard-Andersen R. Udisti S. Becagli E. Castellano M. Severi D. Wagenbach C. Barbante P. Gabrielli V. Gaspari &copy; 2006 Nature Publishing Group Nature 440 7083 491 496 0028-0836 1476-4679 Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial–interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO 2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago. Sea ice dust flux increased greatly Southern Ocean during last glacial period. Palaeorecords provide contradictory evidence about marine productivity region, but beyond one glacial cycle, data sparse. Here present continuous chemical proxy data spanning last eight glacial cycles (740,000 years) Dome C Antarctic ice core. These data constrain winter sea-ice extent Indian Ocean, Southern Ocean biogenic productivity Patagonian climatic conditions. found maximum sea-ice extent closely tied Antarctic temperature multi-millennial timescales, but less so shorter timescales. Biological dimethylsulphide emissions south polar front seem have changed little climate, suggesting sulphur compounds not active climate regulation. observe large glacial–interglacial contrasts iron deposition, which infer reflects strongly changing Patagonian conditions. During glacial terminations, changes Patagonia apparently preceded sea-ice reduction, indicating multiple mechanisms may responsible different phases CO 2 increase during glacial terminations. observe no changes internal climatic feedbacks could have caused change amplitude Antarctic temperature variations observed 440,000 years ago. (?-mix:\s+\W+|\W+\s+|\s+|\/) glacial sea-ice Antarctic Ocean data changes conditions last have during temperature climatic Southern Patagonian terminations productivity years ice extent observe but climate timescales These Palaeorecords eight continuous constrain present front multiple caused amplitude biogenic provide feedbacks Dome 2 dimethylsulphide so may region cycles indicating mechanisms regulation shorter changing increased internal one chemical apparently greatly large change evidence found could During less marine sulphur period iron responsible proxy active changed sparse 440,000 no multi-millennial CO not reflects little deposition Here closely maximum observed which winter polar phases flux increase contrasts 740,000 contradictory core compounds tied infer cycle seem glacial–interglacial Biological south suggesting C dust emissions about different beyond reduction preceded variations Sea Patagonia strongly ago. Indian spanning (?-mix:\.\s+(?=[A-Z])) Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO 2 increase during glacial terminations Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales We observe large glacial–interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago. (?-mix:\s+\W+|\W+\s+|\s+|\/) IC Ca m 2 data between samples CFA using Na into sea nssCa terrestrial ratio periods water SO42 Fe used here 580 found calculated agreement glacial part analysis cm interglacial ssNa at material methods but latter affect have most time discrete source measured 5 device contaminated interval results then three Fig shown case measurements ions ice outer field melted 3.4 If 1 any upper ratios present other sources marine weight average cut ultrapure concentrations crustal seen EDC2 averages removal correction rather melt below directly proportion about uncertainty layers core 90 conventional does system salt paper would well use collected derived not good calculate vials occasionally later cold possible acid either could excellent had nor cent nitric 0.038 (but beyond significantly spectrometrically 10 fed points representing chromatography lower sections better sample choice 17 70 Precision averaged long 18 0.25 reasonable different consist marker section presented some accumulation ion element anything problem insoluble may larger 0.1 close melting highly assuming around 0–580 leading before interglacials sector detection flux 2.2 differences which led sulphate passing dominated fraction strip prefer if arise h rates left so comparison Some sea-salt previous dust widely higher actually also per individual detailed traditionally hereafter Major European method—again much acidified even derive conclusions covering often Although washings repeat no inductively few main only reason suitable 27 low 1,038 kyr contrast ICP-SFMS Ice-core measure stand None flow plasma exception subtracting can shape ref spaced more generally paper. aerosols mass falls refs along nss suggested shows remove fast-IC 60 4 slightly 24 crust continuous depth likely smaller timescale analysed lowest coupled fluxes authors substantial therefore owing components 6 cumulative our incomplete inner Na-rich clays variable been after one onto various compared depleted spectrometry averaging 20 sea-ice series figure Samples they 1.1 However devices hotplate first although nssSO decontaminated fact determined surface least increments 1.78 pH described two laboratory Methods than estimated (?-mix:\.\s+(?=[A-Z])) A comparison between the two methods shows excellent agreement, but hereafter conventional IC data are used Although the latter figure could be highly variable between different terrestrial sources, leading to a substantial uncertainty in ssNa, previous authors have suggested that this is the most suitable ratio to use Fe was measured on 1,038 discrete samples using inductively coupled plasma sector field mass spectrometry (ICP-SFMS) For the IC measurements, samples were collected as the cumulative melt or cut from anything between 5 cm to 1.1 m of ice, and in Fig. 1 we present averages of 2.2 m increments However, if the main source of sea salt is actually the sea-ice surface, then this source is depleted in sulphate compared to sea water, with a ratio close to 0.1 (refs 17 , 18 ) Ice-core sections 5 cm long were decontaminated by three repeat washings in ultrapure water to remove 60% of the material, acidified to pH 1 with ultrapure nitric acid, and then left to stand for at least 24 h before analysis If the crustal source material is dominated by marine clays or other Na-rich material the correction would be larger If we had used crustal ratios with Fe as the terrestrial marker element, the correction would have been smaller In any case, no reasonable ratios affect the shape of the derived time series, nor the conclusions of this paper In glacial periods, about 90% of Ca is from terrestrial sources, but the proportion can be much lower in interglacials. nss SO42- was first derived by subtracting the sea-salt part, traditionally calculated by using ssNa, along with the weight ratio of SO42- /Na in sea water (0.25) In the latter case, a 3.4 × 3.4 cm strip of ice was melted onto a hotplate (either in the field or in a European cold laboratory) , and part of the melt from the inner part of the core was led directly to various detection devices (in a continuous flow analysis (CFA) system), or fed into vials for later IC analysis It is for this reason that we prefer to use nssCa for most of the paper Methods Major ions presented here (Na + , Ca 2+ , SO42- ) were measured using IC (ion chromatography), with an estimated uncertainty on individual measurements of better than 5% (but rather higher at the lowest concentrations seen in interglacial periods) None of the three methods described here is likely to measure the insoluble fraction of terrestrial dust Of the components shown here, Na + and Ca 2+ were determined spectrometrically using the CFA system as well as by IC On average we calculate that about 90% of Na is from sea salt, although the proportion occasionally falls below 70% in glacial periods Precision is around 20% for interglacial and 10% for glacial samples SO42- was measured by passing some of the CFA water directly into a fast-IC device , as well as by conventional IC Samples from 0–580 m depth were cut into discrete samples from a section of the core after removal of the contaminated outer layers, melted and analysed; below 580 m, they were collected into sample vials using a melting device Some of the detailed differences between nssCa and Fe arise from the fact that the nssCa data are averaged from samples covering most of the averaging interval, in contrast to the Fe data The discrete samples are rather widely spaced, so that the time averages seen in Fig. 2 often consist of one or more data points representing only a few per cent of the time interval The exception is for Ca 2+ in the upper 580 m, for which the IC data may be slightly contaminated owing to possible incomplete removal of outer layers The results shown here are from IC, but good agreement between methods is generally found The timescale is EDC2 (ref. 6 ), and the accumulation rates used to calculate flux also derive from EDC2 This problem does not affect any other ions, and we found good agreement between IC and CFA Ca 2+ data, even at the low concentrations found in interglacial periods, beyond 580 m We calculated ssNa and nssCa assuming a Ca/Na weight ratio of 0.038 for marine aerosols and 1.78 for the average crust We have therefore used the CFA Ca 2+ data for the upper 580 m (27 kyr) We present nssSO 4 2- fluxes calculated with the latter method—again, our choice does not significantly affect the results of this paper. (?-mix:\s+\W+|\W+\s+|\s+|\/) at flux changes kyr sea source record have change between has been also climate salt DMS SO42 glacial during Antarctica Dome sea-ice Fig Antarctic marine 2 about dust transport not extent periods C but no very snow ice terrestrial increased these production nssCa main our mainly conditions present aerosol Patagonian period LGM data MS concentrations than interglacials Fe Ocean only temperature deposition see Na ssNa maximum constant would although which atmospheric sector shelf evidence recent continental significant CO south concentration therefore interglacial higher seen nss should Patagonia representing last when 440 both deuterium probably part new bp throughout due result biogenic influence S can material iron 740 suggest conclude strength winter timescales related there Southern emissions feedback studies level factors through fertilization pattern compared values occurred use APF each productivity ice-core such their chemical accumulation suggests value later around sources input large sites role similar cold despite strong some continuous low Supplementary over more may fluxes must emission amplitude transition increases South least first reduction relationship Information However could Vostok background 3 changing Methods activity glacial–interglacial summer Indian ocean occurs interpretation shows 1 rate modelling any greater lower close often strongly attributed north most much spikes chemistry past within contrast proxy dominant leading America general core particularly cannot while other single into rather different environmental region almost Termination time parameters reaching profiles had process central representative relevant discussions Marine rates half does significantly measurements termination exposed closely cycles longer few might used There double below found transitions Holocene seems major components biological represented high because sulphate they changed quoted 740-kyr even including small before earlier important cause marker further characterized cyclonic coastal synchronous detail among giving assumed many all terminations estimated moisture note clearly circulation tens Iron cycle suggested isotope calculated variability assessing better annual V sea-salt exposure tied Because proxies dry present-day acid budget 422 model feedbacks MIS16 NssCa producers using Our Ice suitable climatic maxima non-sea-salt assumptions open-water observed point distance providing post-depositional less reflects Recently per case D rest mechanisms where area export derived cores possible methanesulphonic above fact based external approximately aridity its sensitive active volcanic increase coldest location remained Model causes stable remarkably way correspondence profile forcing 42 under peak wind led water meridional several yr expected organisms limited Although multimillennial oxidation surface interpretations play Sea atmosphere then those how implies remaining Fuji continent yet remains Ca example timing 4 implying cent factor good oceanic averaged replicated addition 50 geochemical dealing comparisons climate-dust coupled Phaeocystis Project Australia Such interpreted widely latest 6 55 drilled resolution millennial aspects heavily already Unfortunately decisive precipitation show dynamics showing metals volcanism—the ratios Major attempt If proportion 60 called stage vegetation removing describe anthropogenic derives system 14–12 products three differences LGM–Holocene date seasonally mass unless climate–sea-ice inputs m implied out provide influencing fraction appear amount dimethylsulphide explanation study 06 calibration indicator sodium inland suffers areas According will non-volcanic route Fluxes figures unlikely chromatography remarkable variables order 3,233 overcome nearest 45 travel deglaciation ionic 75 shown exactly removed origin Here residence uplift frost look likely inception argued impact given together late give High Using depleted rule affect rapidly Mechanisms did signature time-resolved particle considerably analogy cloud being self-regulation Estimates dominated element overall continents fills serve transformations situation moved weak sublimation leads challenged Very Climate p.p.m.v discussed considered imply unspecified short-lived determined grounds preferred re-flooded loss extreme internal glacier 18–15 same without define linkage occur 740,000 key insoluble slightly quantitative test nutrient models metres All circumstantial represent high-plateau ref hence fossil sea-level EPICA responsible halves Coring investigate entire Phasing diatom 100 conclusion Deuterium fixation emphasized speed implications one Sodium responded vary followed downward apparently 10 stratosphere mechanism objective need available fractionation 428 seasonal minima positive troposphere question intermittent largest gases plausible events upper 426 westerlies measure showed stages en brine cancel just (nss representing—at modelled varying burden generally intensified enhanced effects 425–422 ten little negligible approximate E primarily Assuming agreement along size remove Both themselves glaciation edge previous snowpits complete Therefore surrounding simply losses evaporative 123 coverage shorter tracer certainly presented obvious nearby knowledge 30 part—changes similarly records make 100,000-year glacials American fortuitously halved understanding ceases curve distinguish variations sheet estimates uncertainty 424 emphasis particular extending intermediate recently depletion 2-kyr indicates polar Methanesulphonate range previously information Nitrate MIS12 product doubled proposed brine-soaked eruptive total MIS15 625–623 I assume SO choice Previously year-round if drawdown specifically latter scavenging method rise European analogous 700 indicate parallel effect become warm more-detailed stratospheric precedes tentative modern deeper altitude 420 nitrate eight limiting allowing station second comes causing front salts highlighted whole threshold entirely diffuse benthic contrasts sulphur volatile Volcanic nuclei came illustrated 428–424 Winter however characteristic though either (2 two temperatures features believed (3 component depend lead sets against arriving identified drier so robust relatively climate. precede condensation fast well Despite 1–3 eventually stays ions slow inconsistent negative noted processes glaciations MIS)18.4 phasing thus parts minimum dominate amplify link neutral Sea-ice 21 preserved early greenhouse glacial-period Part cooler 410 falls Quaternary applies 20 depending non-volatile flooding needed opposite leave reduced oxygen Finally dominance fine acids oxidized analysis decrease nonlinear 629–625 detailed altered short regions instead taken ion average Defining surfaces holds compounds Atlantic flowers Nonetheless indicative adding Flooding suggestion Most 17 magnitude recognize unique calcium (?-mix:\.\s+(?=[A-Z])) A process of sublimation at the Antarctic snow surface was proposed , but this should not lead to fractionation A recent model study suggested that, south of 50° S, the westerlies were intensified at the LGM, and that this was coupled to a reduction in moisture transport to Patagonia from the Atlantic (giving drier conditions) A significant increase in methanesulphonic acid concentrations was attributed to increased marine biological productivity in the Southern Ocean A similar result (with concentrations approximately doubled in peak glacials compared to interglacials, implying little change in flux) would have been found for Vostok or Dome Fuji According to our interpretation, maximum sea-ice extent in the Indian Ocean sector is tied very closely to Antarctic temperature at multimillennial timescales, but they are not synchronous at short timescales Although we recognize that our use of sea salt as a sea-ice proxy remains tentative, we suggest that the ssNa flux curve in Fig. 2 may be taken as a first attempt at a quantitative winter ice extent over the last 740 kyr for use in modelling studies Assuming this applies to the whole record then the order of magnitude changes in dust flux seen at Dome C must result primarily from changes in the source region Because DMS emissions south of the APF apparently remained constant to within a few tens of per cent throughout the last 740 kyr, despite very large climate changes, the sulphur cycle does not appear to have responded to climate change with either a positive or negative feedback Because the products of DMS oxidation, through their role as cloud condensation nuclei, may themselves cause climate feedbacks , the Vostok MS - record is often quoted in discussions about climate self-regulation Both metals are assumed to be representative of terrestrial material, and their concentration profiles look similar to that of insoluble dust mass Climate and chemistry over eight cycles Using only Antarctic ice-core chemical data, we describe the dynamics of three external parts of the climate system over a period of 740 kyr, and provide continuous data sets as inputs for climate modelling DMS production is also quoted as one indicator of productivity, relevant to the drawdown of CO 2 , although it has to be emphasized that DMS producers may not be representative of total biological production Defining the ice-core proxies All chemical concentrations (see Methods) are higher during glacial periods than during interglacial periods ( Fig. 1 ) Despite differences in detail, the good general agreement between nssCa and Fe profiles ( Fig. 2 ) suggests that each is suitable as a terrestrial marker element at Dome C, although Fe might be preferred in discussions about iron fertilization of the ocean Deuterium increases between 428 and 422 kyr Estimates of the annual downward transport from the stratosphere to the troposphere , comparisons of the stratospheric aerosol burden in non-volcanic and volcanic periods, and modelling studies suggest that the volcanic input during background periods is <10% of the deposition of SO42- to the Antarctic ice sheet Finally, although Australia could also be a significant source of dust, models suggest that Patagonia should also be the main source of atmospheric iron to most of the Southern Ocean , and thus our record should serve both as a continuous profile of changes in Patagonian climate, and as a suitable input for assessing the influence of Fe fertilization on atmospheric CO 2 concentration Flooding of the shelf cannot be the main cause of reduced nssCa flux, although the changing exposure of continental shelf could play some part Fluxes are similar in the first and second halves of the record for a given deuterium value ( Fig. 3 ); slightly higher glacial values earlier in the record rest heavily on a few high flux values in MIS12 and MIS16 For Antarctica, both dust (representing terrestrial aerosol) and sodium (representing marine aerosol) data have been presented from the Vostok core, extending 420 kyr into the past For the remaining figures, we therefore calculated sea-salt Na (ssNa) and non-sea-salt Ca (nssCa) concentrations and fluxes (see Methods) Here we present the chemical data only for the main oceanic (sea salt and marine biogenic) and terrestrial (including iron) aerosol components reaching Antarctica However, because of the very low snow accumulation rates at Dome C, the dominant process for aerosol deposition is almost certainly dry deposition However, more-detailed profiles from other sites, along with a better knowledge of transport, deposition and post-depositional processes , have called these interpretations into question However, recent evidence has shown clearly that, under modern conditions at sites with very low snow accumulation rates, MS - concentration falls rapidly in the upper metres of snow; this is also seen in snowpits at Dome C However, we have more continuous data available for calcium (Ca), which is often used to define terrestrial sources, but which also has a marine source Ice cores play a key part in providing an understanding of climate variability during this period because many components of forcing and feedback, including greenhouse gases , are represented in a single core If the main dust source is well south, then it should be enhanced by such changes In Fig. 2 , fluxes have been calculated (using the estimated snow accumulation rate ) and they are used for the later discussions (see also Supplementary Information ) In Termination V, at 424 kyr, when the terrestrial dust change is almost complete, CO 2 has increased by <30 p.p.m.v., adding to evidence that this is a maximum possible impact of iron fertilization In contrast to MS - , the nss SO42- flux is stable, within about 20%, through the entire 740-kyr record ( Fig. 2 ) In deeper ice, these spikes become diffuse, and eventually cannot be identified against the background: as a result there is no objective way to remove their influence In fact, production by these organisms remained approximately constant, despite the large changes in Antarctic environmental conditions and the decrease in overall export production In glacial periods, much more terrestrial material is present in the atmosphere and snow In such a situation, the flux rather than the concentration in ice is expected to be the measure that is indicative of changes in atmospheric concentration In the LGM, when ssNa flux is double the present value, winter sea-ice extent is believed to have been about double that of the present , providing an approximate calibration of our proxy In this termination, the main change in terrestrial material flux (at 428–424 kyr) precedes that in sea salt (425–422 kyr), while the CO 2 change occurs mainly between 426 and 422 kyr bp Iron (Fe) is derived almost entirely from continental terrestrial sources Iron flux and South American climate The nssCa flux, as also does the Fe flux, shows extreme variations, being about a factor of ten higher in glacial maxima than in interglacial periods ( Fig. 2 ) It also has strong implications for the possible causes of CO 2 increases during terminations, because mechanisms related to changing Fe fertilization can only be active in the first half of the termination, unless Fe ceases to be the limiting nutrient at deposition rates only just above those seen in the Holocene It has been argued that the detailed timing of sea-level rise is inconsistent with the timing of the main changes in dust flux during the LGM–Holocene transition It is very likely that climate conditions in Patagonia did change during glacial periods It was previously noted that, at Termination I, the main change in nssCa flux occurred in the first half of the transition (18–15 kyr), while the main change in Na flux occurred later (14–12 kyr) It will also be important for assessing the role of sea-ice mechanisms in CO 2 changes MS - has no other significant source for Antarctica Major glaciations of Patagonia occurred during cold periods in the ice-core record , although it is not obvious how this would affect the dust source Marine diatom evidence suggests that summer sea ice was negligible in this sector even in the LGM , which is among the coldest periods in the Dome C deuterium profile Marine productivity High glacial MS - was used to suggest increased oceanic DMS emissions during the last glacial period Marine proxies have suggested that export production south of the present-day Antarctic polar front (APF) was lower in the LGM than in the Holocene Mechanisms related to changing sea-ice extent , at least in the ocean sector represented in our record, should be active in the later stages of each transition only Methanesulphonate (MS - ) and sulphate ( SO42- ) in Antarctica are both considered to be derived mainly from marine biogenic emission of dimethylsulphide (DMS) , followed by oxidation in the atmosphere Model studies , and previous studies of dust particle size for the more recent part of the record , suggest that changes in the transport strength and atmospheric residence time between South America and Dome C were small, despite the changes in precipitation scavenging and atmospheric circulation that must have occurred Model studies of tracer transport, although mainly dealing with transport from further north than the DMS source regions, suggest a rather small change in transport time for the LGM compared to the present Most of the area of continental shelf south of 45° S that would have been exposed during the LGM would have been re-flooded early in the deglaciation (see Supplementary Information ) Nitrate and, if the analogy holds, MS - , are no longer mainly present as relatively volatile acids, but are instead preserved as non-volatile neutral salts Nonetheless, the nssCa flux had already halved from its LGM maximum by 17 kyr bp , before any significant change in sea level or exposed area, and the nssCa flux reduction clearly leads the flooding of the shelf NssCa flux (and similarly Fe flux) increases significantly only below a threshold (about -410‰ at Dome C) in Antarctic deuterium ( Fig. 3 ) NssCa flux, in some way a record of Patagonian conditions, shows a very close, but nonlinear, link between Patagonian conditions and Antarctic climate throughout the period Our measurements are probably less sensitive to changes in DMS production further north Our result implies that organisms such as Phaeocystis , which leave no fossil record, but which are major DMS producers, also had no increased production south of the APF Part of the concentration contrast seen is therefore simply due to the fact that the snow accumulation rate is estimated to be more than a factor of two higher in warm interglacials than in the coldest part of each glacial Patagonian conditions changed very strongly between glacial and interglacial, leading to a large change in iron input to the Southern Ocean Phasing of changes at climatic transitions Although many aspects of climate throughout the 740-kyr record change together at each termination and inception, this is not the case, at least at millennial resolution, for sea salt (representing sea ice) and terrestrial material (representing Patagonian conditions) Previously, the increased cold period ssNa flux or concentration has been attributed to greater cyclonic activity at the (assumed open-water) source, and to greater meridional transport of sea salt into the continent Recently, this interpretation has been challenged on several grounds Recently, year-round measurements of aerosol concentrations at the high-plateau inland station of Dome Fuji showed SO42- /Na ratios that were often below that expected from sea water, with a pattern exactly as found at the coastal sites SO 42- comes also from sea salt, anthropogenic sources (though these have a very limited influence in Antarctica ), terrestrial dust (also limited), and from volcanism—the latter causing intermittent spikes and a continuous background Sea ice based on sea salt The ssNa (representing sea salt) flux has minima in interglacials, and maxima in glacial periods Sea salt concentrations, even in central Antarctica, peak seasonally when sea ice is at its maximum, and there is no evidence that cyclonic activity has the seasonal contrast needed to overcome the greater travel distance this implies Sea-ice extent was intermediate between recent glacial and interglacial values during most of the weak interglacials before 440 kyr bp Sodium (Na) has a mainly marine source, but some continental dust influence Such changes in South America could result from (1) changes in the strength of the Patagonian source due to changes in temperature, moisture and vegetation, (2) changes in uplift of source material due to changes in wind strength, (3) an increased Patagonian source of fine glacial material due to varying glacier coverage, or (4) the addition of new source areas on exposed continental shelf as sea level changed The amount of nss SO42- reaching Dome C should depend on the production and emission of DMS, on the location of emissions (and hence the transport distance), on transport speed and on transformations en route The chemical signature of both aerosol and snow, showing a characteristic depletion of SO42- /Na compared to sea water, suggests that new sea-ice surfaces are the major source of sea salt to coastal Antarctica The climate of Antarctica over the longer period of 740,000 yr (740 kyr, to marine isotope stage (MIS)18.4) has recently been characterized through a new ice-core record The concentrations of both components are significantly increased in glacial periods compared to interglacials The constant nss SO42- flux could result from all these factors changing between glacial and interglacial (in which case their effects must fortuitously cancel out), or from the dominant factors remaining constant The core, drilled by the European Project for Ice Coring in Antarctica (EPICA) came from Dome C (75° 06′ S, 123° 21′ E, altitude 3,233 m above sea level) The deuterium (temperature proxy) record ( Fig. 1 ) highlighted the change in glacial–interglacial temperature amplitude that occurred around 440 kyr bp (before present); interglacials in the earlier part of the record were much cooler than recent interglacials, despite similar external forcing The evidence for a sea-ice source of sea salt to central Antarctica has been circumstantial The increased exposure of continental shelf may amplify the effect when sea level is particularly low The ionic chemistry in ice cores is mainly representative of aerosol, and has been interpreted as giving information about important environmental features such as sea-ice extent, marine biological productivity of the nearby ocean, aridity of the surrounding continents, and transport strength The late Quaternary period is characterized particularly by strong 100,000-year (100 kyr) cycles The latest evidence suggests that geochemical measurements cannot yet distinguish between a Patagonian and continental shelf source The linkage between Antarctic temperature and sea-ice extent is less strong at shorter timescales; changes in sea salt and deuterium are not synchronous during major climate transitions, as discussed later The low variability in the rest of the record is remarkable, and unique among ice-core chemistry records to date The main origin of dust reaching these sites is South America, specifically Patagonia The maximum values are about double the present-day value, while the minimum 2-kyr average observed is about half the present value The modelled flux of sea salt arriving in Antarctica from an open-water source was found to be much lower in the last glacial maximum (LGM) compared to the present, when the data show the opposite The most plausible explanation is that the aerosol derives from a source depleted in SO42- The new record shows that this is a general rule at terminations, as illustrated in detail for Termination V ( Fig. 4 ) The part of marine biogenic activity in the Southern Ocean that is related to DMS emission south of the APF seems to have been remarkably constant through the period; atmospheric S compounds had no significant role in climate feedback The proportion of DMS that is oxidized to SO42- or to MS - might vary with climate, but nss SO42- probably remains the dominant product under all conditions The relationship between each chemical component and Antarctic deuterium (temperature) stays remarkably constant through the last 740 kyr, with no significant change at the point where the amplitude of interglacials increases strongly (around 440 kyr) The relationship is stable throughout the last 740 kyr, implying that the change in climatic pattern at around 440 kyr is not due to any change in the climate–sea-ice feedback The relevant region (based on model estimates for Vostok) is the Indian Ocean sector, with the largest influence between 55° and 60° S The same pattern is seen also at the earlier changes, where there is a lower amplitude in δ D (the phasing between CO 2 (ref. 42 ) and our parameters has yet to be determined at these transitions): at the transition from MIS16 to MIS15, for example, the reduction in nssCa occurs mainly between 629–625 kyr, and the reduction in ssNa occurs mainly between 625–623 kyr bp The sea-salt source of sulphate can be removed using Na data (see Methods) to give non-sea-salt SO42- (nss SO42- ) The single short-lived increase in flux, depending mainly on a single data point at about 700 kyr seems not to be replicated in a parallel analysis by the fast ion chromatography method (see Methods) The summer sea-ice edge was close to the continent in the sector of Antarctica nearest to Dome C even in the LGM , so that the location of summer DMS emission need not have moved significantly There is a general correspondence between particularly high marine benthic oxygen isotope values , representing—at least in part—changes in sea level, and high nssCa fluxes ( Fig. 2 ); however, there is also a strong correspondence between nssCa flux and other parameters such as Antarctic δ D There is a very close relationship between Na flux and temperature throughout the 740-kyr period, with cold temperatures leading to higher Na flux ( Fig. 3 ) There seems to be no significant change in the climate-dust feedback at 440 kyr Therefore the higher concentrations of both ions in snow from cold periods reflects better fixation (or a different deposition mechanism), and does not indicate the past production of DMS This is probably due to a slow evaporative loss of methanesulphonic acid, in a process analogous to that observed for nitrate This led to the suggestion that the S cycle has been very sensitive to climate change This pattern suggests that the main changes in Patagonia generally precede those in sea-ice extent This was attributed to a range of causes, with a particular emphasis on increased meridional transport This would imply that the sea salt flux at Dome C is related to new sea-ice production in the Indian Ocean sector of Antarctica (see Supplementary Information ), at least on longer timescales Unfortunately, there is no good time-resolved record of any of these factors that we can use to test their influence on the Antarctic dust record Very large glacial–interglacial contrasts in MS - (seen also at Dome C) have been widely quoted in the past as evidence of increased glacial-period marine biogenic activity in the Southern Ocean Volcanic input during eruptive events can dominate the SO42- budget for 1–3 yr, but fills only a small time fraction, representing (for example) only about 6% of the Holocene sulphate budget We also investigate how the relationship between different variables altered when the climate pattern changed around 440 kyr bp We can conclude that annual production and maximum extent are closely related; with our interpretation, ssNa flux indicates winter sea-ice extent We conclude that change in internal feedbacks represented by these parameters was not responsible for the change in amplitude of interglacial climate. We conclude that the sea-ice surface (including frost flowers, brine and brine-soaked snow) is probably the main source of sea salt to central Antarctica for recent winter conditions We have therefore averaged the data without removing the spikes or background, but can assume that the nss SO42- flux is strongly dominated by marine biogenic sources throughout the record We make new interpretations of the environmental changes during several glacial–interglacial cycles that they represent We note that the increased productivity implied by iron fertilization would have to occur north of the APF We note that the use of concentrations rather than fluxes would have led to a different conclusion, but our assumptions about aerosol deposition leading to this choice are robust (see Supplementary Information ) We therefore conclude that the nssCa record probably mainly reflects changes in atmospheric circulation influencing Patagonian wind strength and aridity, although changes in glaciation might also have an unspecified role We therefore conclude that these factors are unlikely to have been decisive: allowing for some changes in these factors, and for uncertainty in our assumptions about the dominance of dry deposition and the snow accumulation rate, DMS emissions in the relevant region must have also been constant to within a few tens of per cent We therefore conclude that, at multimillennial timescales, winter ice extent in this sector is very closely tied to Antarctic temperature ( Fig. 3 ) We therefore use nss SO42- , which suffers no post-depositional losses, as our marker of marine biogenic emissions Winter ice extent has probably been considerably below the present value in recent interglacials Measured concentrations from the EPICA Dome C ice core. Data are on an ice depth scale. δ D are averaged over 3.85-m sections 6 ; chemical concentrations are averaged over 2.2-m sections. Chemical measurements from the EPICA Dome C core, on an age scale. Chemical components (2-kyr averages) and δ D (3-kyr averages) 6 are from the EDC core; oxygen isotope values (1 kyr averages) from the marine benthic stack (on the LR04 timescale and with selected MIS numbers shown) 39 . While nssCa data represent almost continuous averages within each 2-kyr period, Fe data are averages of a few discrete samples. In the deeper ice, many 2-kyr periods have no Fe data, or are based on a single data point representing only a few decades. The obvious timing mismatch between EDC and the benthic stack around MIS14 is not yet resolved 39 . Relationship between chemistry and climate. ssNa and nssCa fluxes plotted against δ D for the entire ice core, using 2-kyr averages. Blue crosses are for the period from 0–440 kyr bp , red squares are for 440–740 kyr bp . Chemistry and CO 2 across Termination V. Chemical fluxes (averaged over 1.1 m depth increments, equivalent to a few hundred years at this depth, except for Fe, which consists of spot values at irregular intervals), and CO 2 concentration 6 , across Termination V, between MIS12 and MIS11. Uncertainty in the alignment of the timescales for the CO 2 and chemical records is caused by the calculation of the gas-age/ice-age difference 6 , and could be several centuries. 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