Aluminium and iron record for the last 28 kyr derived from the Antarctic EDC96 ice core using new CFA methods

AbstractSpectrofluorimetric and spectrophotometric continuous flow analysis (CFA) methods were developed and applied to the determination of aluminium and iron in EPICA Dome C (East Antarctica) ice-core samples (6–585m depth). The methods are able to measure the fraction of Al and Fe which can be detected once the sample is filtered on a 5.0 μm membrane and acidified to pH 2. Both the methods present high sensitivity (detection limit of 10 ng L–1 for Al and 50 ng L–1 for Fe) and reproducibility (5% at sub-ppb level). The Fe and Al profiles show sharp decreases in concentrations in the last glacial/interglacial transition, reflecting the decreasing dust aerosol load. The two elements show a different pattern during the Antarctic Cold Reversal (ACR) climatic change, with high iron concentrations (similar to the glacial period) and low but increasing Al content during the ACR minimum. In order to interpret the Al and Fe data obtained by CFA, a comparison with Al and Fe composition, as measured by inductively coupled plasma sector field mass spectrometry (ICP-SFMS), was performed for Holocene, ACR and glacial periods. The percentage of CFA-Al with respect to ICP-SFMS-Al in the three periods shows a lower variability than CFA-Fe (3% in the glacial period and 64% in the ACR). This pattern may be explained by the different dominant iron sources in the different climatic periods. During the Last Glacial Maximum, Fe is proposed to arise mainly from insoluble continental dust, while a variety of ocean-recycled Fe, mainly distributed in fine particles and as more soluble species, shows a higher contribution in the ACR and, to a lesser extent, in the Holocene

A major glacial-interglacial change in aeolian dust composition inferred from Rare Earth Elements in Antarctic ice

We present the first Rare Earth Elements (REE) concentration record determined in 294 sections of an Antarctic ice core (EPICA Dome C), covering a period from 2.9 to 33.7 kyr BP. REE allow a detailed quantitative evaluation of aeolian dust composition because of the large number of variables (i.e. 14 elements). REE concentrations match the particulate dust concentration profile over this period and show a homogeneous crustal-like composition during the last glacial stage (LGS), with only a slight enrichment in medium REE. This signature is consistent with the persistent fallout of a mixture of dust from heterogeneous sources located in different areas or within the same region (e.g. South America). Starting at ∼15 kyr BP, there was a major change in dust composition, the variable character of which persisted throughout the Holocene. This varying signature may highlight the alternation of single dust contributions from different sources during the Holocene. We observe that the frequent changes in REE composition at the onset of the Holocene (10-13.5 kyr BP) are linked to dust size and in turn to wind strength and/or the path of the atmospheric trajectory. This may indicate that atmospheric circulation dictated the composition of the dust fallout to East Antarctica at that time. Although the dust concentrations remained fairly low, a notable return towards more glacial dust characteristics is recorded between 7.5 and 8.3 kyr BP. This happened concomitantly with a widespread cold event around 8 kyr BP that was 400-600 years long and suggests a moderate reactivation of the dust emission from the same potential source areas of the LGS

Links between iron supply, marine productivity, sea surface temperature and CO2 over the last 1.1 Ma

Paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric CO2 concentrations. However, the mechanisms behind glacial/interglacial (G/IG) variations in atmospheric CO2 concentrations observed in the Antarctic ice cores are still not fully understood. Here we present a new multiproxy data set of sea surface temperatures (SST), dust and iron supply, and marine export productivity, from the marine sediment core PS2489-2/ODP Site 1090 located in the subantarctic Atlantic, that allow us to evaluate various hypotheses on the role of the Southern Ocean (SO) in modulating atmospheric CO2 concentrations back to 1.1 Ma. We show that Antarctic atmospheric temperatures are closely linked to changes in SO surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) records. The close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the G/IG cycles of the last 1.1 Ma. However, our data suggest that marine productivity can only explain a fraction of atmospheric CO2 changes (up to around 40-50 ppmv), ccurring at glacial maxima in each glacial stage. In this sense, the good correlation of our SST record to the EDC temperature reconstruction suggests that the initial glacial CO2 decrease, as well as the change in the amplitude of the CO2 cycles observed around 400 ka, was most likely driven by physical processes, possibly related to changes in Antarctic sea ice extent, surface water stratification, and westerly winds position

Ultrasensitive determination of heavy metals at the sub-picogram per gram level in ultraclean Antarctic snow samples by inductively coupled plasma sector field mass spectrometry

Assessing changes in heavymetals concentrations in Antarcticsnow dated from the last century is of high interest to determine to which extent the most remote regions of our planet are contaminated for these metals, and to have a better understanding into their long-range transport from the different natural and anthropogenic source areas to the Antarctic continent. Such investigations are unfortunately very difficult because the concentrations to be measured are exceedingly low, down to the sub-picogrampergramlevel. They require a strict control of contamination problems from field sampling to laboratory analysis, and the use of ultrasensitive analytical techniques. We present here important advances in the analytical protocols for obtaining reliable data on the occurrence of heavymetals in Antarcticsnow. Utmost precautions were taken to obtain a series of large size ultracleansnow blocks from the wall of a 8.3 m clean hand-dug pit at a remote site in Coats Land, Antarctica. These blocks were then sub-sampled inside a laminar flow clean bench in a cold room, using ultraclean protocols, to provide high-resolution heavymetal times series. V, Cr, Mn, Cu, Ag, Ba, Pb, Bi and U were then determined directly, without any pre-concentration step, by the ultrasensitiveinductivelycoupledplasmasectorfieldmassspectrometry (ICP-SFMS) technique in clean room conditions. Calibration of the instrument was performed using ultralow concentrations standards, and extreme precautions were taken to ensure the cleanliness of the instrument and its introduction system. The results show that it is possible to accurately measure a variety of heavymetals in Antarcticsnow, down to the sub-picogrampergramlevel, using this approach. Examples of the data obtained for the Coats Land site are finally presented. For U, the observed concentrations range from 0.004 to 0.21 pg/g; they are the first data ever obtained for this metal for Antarcticsnow and ice

Short-term variations in the occurrence of heavy metals in Antarctic snow from Coats Land since the 1920s

Short-term variations in heavy metals concentrations in Antarctic snow have been investigated by analysing 13 metals (Al, V, Cr, Mn, Co, Cu, Zn, Ag, Cd, Ba, Pb, Bi and U) in a series of ultraclean samples collected from two snow pits in Coats Land in the Atlantic sector of Antarctica. The samples covered a similar to70 years time period from the 1920s to 1990. They were analysed by inductively coupled plasma sector field mass spectrometry and graphite furnace atomic absorption spectrometry. The results conclusively show that there is a pronounced short-term (intra and inter-annual) variability of heavy metal in Antarctic snow, with the highest concentrations being up to 100 times higher than the lowest ones for metal such as Cr, Mn, Pb and U. Contributions from the different possible natural and anthropogenic sources are found to be extremely variable. This is especially due to the large variability in the transport patterns of heavy metals from Southern America, Southern Africa and Australia to the Antarctic continent. Inputs from several volcanic events were identified in our samples from non-seasalt sulfate concentrations profiles. The only ones that gave clear signals for heavy metals were eruptions at Deception Island the proximity of which allowed for tropospheric transport to Coats Land

Links between iron supply, marine productivity, sea surface temperature and CO2 over the last 1.1 Ma

Paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric CO2 concentrations. However, the mechanisms behind glacial/interglacial (G/IG) variations in atmospheric CO2 concentrations observed in the Antarctic ice cores are still not fully understood. Here we present a new multiproxy data set of sea surface temperatures (SST), dust and iron supply, and marine export productivity, from the marine sediment core PS2489-2/ODP Site 1090 located in the subantarctic Atlantic, that allow us to evaluate various hypotheses on the role of the Southern Ocean (SO) in modulating atmospheric CO2 concentrations back to 1.1 Ma. We show that Antarctic atmospheric temperatures are closely linked to changes in SO surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) records. The close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the G/IG cycles of the last 1.1 Ma. However, our data suggest that marine productivity can only explain a fraction of atmospheric CO2 changes (up to around 40-50 ppmv), ccurring at glacial maxima in each glacial stage. In this sense, the good correlation of our SST record to the EDC temperature reconstruction suggests that the initial glacial CO2 decrease, as well as the change in the amplitude of the CO2 cycles observed around 400 ka, was most likely driven by physical processes, possibly related to changes in Antarctic sea ice extent, surface water stratification, and westerly winds position

Atmospheric iron fluxes over the last deglaciation: Climatic implications

International audienceA decrease in the micronutrient iron supply to the Southern Ocean is widely believed to be involved in the atmospheric CO2 increase during the last deglaciation. Here we report the first record of atmospheric iron fluxes as determined in 166 samples of the Dome C ice core and covering the last glacial-interglacial transition (22–9 kyr B.P.). It reveals a decrease in fallout flux from 24 × 10−2 mg Fe m−2 yr−1 during the Last Glacial Maximum to 0.7 × 10−2 mg Fe m−2 yr−1 at the onset of the Holocene. The acid leachable fraction of iron determined in our samples was the 60% of the total iron mass in glacial samples, about twice the value found for Holocene samples. This emerging difference in iron solubility over different climatic stages provides a new insight for evaluating the iron hypothesis over glacial/interglacial periods

Pb isotope record over one century in snow from Victoria Land, Antarctica

International audiencePb and Ba concentrations and Pb isotopic compositions are reported for firn core and snow pit samples from Victoria Land, Antarctica, dating from 1872 AD to 1994 AD. From variations in Pb/Ba ratios and Pb isotopic compositions, two periods of major Pb enhancements were identified, from 1891 to 1908 AD and from 1948 to 1994 AD. The earlier pollution event is attributed to Pb emissions from non-ferrous metal production and coal combustion in the Southern Hemisphere and is in excellent agreement with coincident pollution inputs reported in firn/ice cores from two other regions of Antarctica, at Coats Land and Law Dome. Using Pb isotopic systematics, it was calculated that 50% of Pb deposited in Victoria Land in 1897 originated from anthropogenic emission sources. The more recent period of Pb enhancements, from 1948 to 1994 AD, corresponds to the introduction and widespread use of gasoline alkyl Pb additives in automobiles in the Southern Hemisphere, with anthropogenic Pb inputs averaging 60% of total Pb but with large uncertainty. Intra- and inter-annual variations in Pb concentrations and isotopic compositions were evaluated in snow pits samples corresponding to the period 1991–1994. Substantial variations in Pb/Ba and 206Pb/207Pb ratios were detected but the absence of a regular seasonal pattern for these parameters suggests that the transport and deposition of aerosols to the Antarctic ice sheet are complex and vary from year to year

Variations in atmospheric trace elements in Dome C (East Antarctica) ice over the last two climatic cycles

International audienceConcentrations of Li, Mg, Cr, Mn, Co, Cu, As, Rb, Cd, Ba and Bi have been determined by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in various sections of the new Dome C EPICA Antarctic ice core, down to the depth of 2193 m, covering a time period of two climatic cycles. The time resolution of these records is at least twice as good as previously published ultra trace elements profiles obtained from the Vostok ice core. During the 217 kyr period spanned by this record, a high variability in concentrations is observed for most elements, with low values during warm periods and high values during cold periods. The highest concentrations are recorded at the times of the last two glacial maxima (20 and 140 kyr BP). The timing and the amplitude of the main concentration peaks match remarkably well the insoluble dust concentration profile. It confirms that dust was the main carrier of atmospheric trace elements to East Antarctica during the cold periods. For Ba, Co, Cu and Rb the crustal contribution was also dominant during warm periods. For other elements the situation is more complex during interglacial periods, when other sources such as volcanic quiescent emissions, became possibly significant for several trace elements such as Cd and Bi. Peculiarly high concentration values are observed for Cd and Bi for a short depth interval dated at 18 kyr BP. It is the same depth interval in which elevated F− values were previously observed. These very high concentrations are attributed to fallout from major local volcanic emissions at that time