XRF-XANES characterization of deep ice core insoluble dust
01 Jan 2012-Journal of Analytical Atomic Spectrometry (The Royal Society of Chemistry)-Vol. 27, Iss: 1, pp 33-37
TL;DR: An analytical protocol based on X-ray spectroscopic measurements (XRF and Fe and Ti K-edges XAS) has been applied to evaluate the mineralogical phase composition of dust trapped in deep ice cores as discussed by the authors.
Abstract: An analytical protocol based on X-ray spectroscopic measurements (XRF and Fe and Ti K-edges XAS) has been applied to evaluate the mineralogical phase composition of dust trapped in deep ice cores. Information on the insoluble dust composition and local and species-selective information as oxidation and coordination states has been obtained to recognize the main mineralogical families of aerosol particles contained in deep ice cores. In this framework we point out the possibility to obtain the mineralogical characterization of dust from deep ice core samples from Antarctica by means of XANES spectroscopy.
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TL;DR: It is suggested that glacial physical weathering increases the proportion of highly bioavailable Fe(II) in dust that reaches the subantarctic Southern Ocean in glacial periods, which represents a positive feedback between glacial activity and cold glacial temperatures.
Abstract: Changes in bioavailable dust-borne iron (Fe) supply to the iron-limited Southern Ocean may influence climate by modulating phytoplankton growth and CO2 fixation into organic matter that is exported to the deep ocean. The chemical form (speciation) of Fe impacts its bioavailability, and glacial weathering produces highly labile and bioavailable Fe minerals in modern dust sources. However, the speciation of dust-borne Fe reaching the iron-limited Southern Ocean on glacial−interglacial timescales is unknown, and its impact on the bioavailable iron supply over geologic time has not been quantified. Here we use X-ray absorption spectroscopy on subantarctic South Atlantic and South Pacific marine sediments to reconstruct dust-borne Fe speciation over the last glacial cycle, and determine the impact of glacial activity and glaciogenic dust sources on bioavailable Fe supply. We show that the Fe(II) content, as a percentage of total dust-borne Fe, increases from ∼5 to 10% in interglacial periods to ∼25 to 45% in glacial periods. Consequently, the highly bioavailable Fe(II) flux increases by a factor of ∼15 to 20 in glacial periods compared with the current interglacial, whereas the total Fe flux increases only by a factor of ∼3 to 5. The change in Fe speciation is dominated by primary Fe(II) silicates characteristic of glaciogenic dust. Our results suggest that glacial physical weathering increases the proportion of highly bioavailable Fe(II) in dust that reaches the subantarctic Southern Ocean in glacial periods, which represents a positive feedback between glacial activity and cold glacial temperatures.
50 citations
Cites background from "XRF-XANES characterization of deep ..."
...The small beam size allows us to probe the speciation of Fe in individual particles in the sediment sample (32), in contrast to bulk XAS, which provides the average Fe speciation and identifies the mix of minerals....
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Journal Article•
TL;DR: In this article, the authors provided evidence supporting the hypothesis that Ocean Station Papa (OSP) received a lateral supply of particulate iron from the continental margin off the Aleutian Islands in the winter, coincident with the observed biological bloom.
Abstract: Heightened biological activity was observed in February 1996 in the high-nutrient low-chlorophyll (HNLC) subarctic North Pacific Ocean, a region that is thought to be iron-limited. Here we provide evidence supporting the hypothesis that Ocean Station Papa (OSP) in the subarctic Pacific received a lateral supply of particulate iron from the continental margin off the Aleutian Islands in the winter, coincident with the observed biological bloom. Synchrotron X-ray analysis was used to describe the physical form, chemistry, and depth distributions of iron in size fractionated particulate matter samples. The analysis reveals that discrete micron-sized iron-rich hotspots are ubiquitous in the upper 200m at OSP, more than 900km from the closest coast. The specifics of the chemistry and depth profiles of the Fe hot spots trace them to the continental margins. We thus hypothesize that iron hotspots are a marker for the delivery of iron from the continental margin. We confirm the delivery of continental margin iron to the open ocean using an ocean general circulation model with an iron-like tracer source at the continental margin. We suggest that iron from the continental margin stimulated a wintertime phytoplankton bloom, partially relieving the HNLC condition.
24 citations
TL;DR: In this article, the authors demonstrate that a conventional source combined with a polycapillary semi-lens can provide a quasi-parallel beam intense enough for desktop TXRF analysis of low concentration samples.
16 citations
28 Aug 2018
TL;DR: In this paper, the application of synchrotron light to microgram-sized atmospheric dust samples extracted from deep ice cores is extremely promising, showing that mineral particles entrapped in the deepest ice layers display altered elemental composition and anomalies concerning iron geochemistry, besides being affected by interparticle aggregation.
Abstract: The possibility of finding a stratigraphically intact ice sequence with a potential basal age exceeding one million years in Antarctica is giving renewed interest to deep ice coring operations But the older and deeper the ice, the more impactful are the post-depositional processes that alter and modify the information entrapped within ice layers Understanding in situ post-depositional processes occurring in the deeper part of ice cores is essential to comprehend how the climatic signals are preserved in deep ice, and consequently how to construct the paleoclimatic records New techniques and new interpretative tools are required for these purposes In this respect, the application of synchrotron light to microgram-sized atmospheric dust samples extracted from deep ice cores is extremely promising We present here preliminary results on two sets of samples retrieved from the Talos Dome Antarctic ice core A first set is composed by samples from the stratigraphically intact upper part of the core, the second by samples retrieved from the deeper part of the core that is still undated Two techniques based on synchrotron light allowed us to characterize the dust samples, showing that mineral particles entrapped in the deepest ice layers display altered elemental composition and anomalies concerning iron geochemistry, besides being affected by inter-particle aggregation
15 citations
TL;DR: In this article, the authors presented synchrotron radiation X-ray fluorescence geochemical data of dust from the TALDICE ice core drilled at Talos Dome, a peripheral ice dome of East Antarctica (Western Ross Sea).
Abstract: Ice cores from inner East Antarctica provided some of the longest and most detailed climatic reconstructions and allowed understanding the relationships between atmospheric mineral dust and climate. In this work we present synchrotron radiation X‐ray Fluorescence geochemical data of dust from the TALDICE ice core drilled at Talos Dome, a peripheral ice dome of East Antarctica (Western Ross Sea). Results highlight a dominant southern South American origin for dust at TALDICE during the Last Glacial Maximum, similarly to other sites located further inland onto the polar plateau. On the contrary, a different scenario concerns Talos Dome during the Holocene if it is compared to more inner sites. The tight connection between high southern latitudes and Antarctica that characterizes cold climate stages becomes weaker since the onset of the last climatic transition and throughout the Holocene. The net effect of this process at Talos Dome is a modification of the atmospheric and environmental settings, owing to local Antarctic sources of Victoria Land to gain importance and become the dominant ones. At the same time in inner East Antarctica the provenance of dust remains remote also during Holocene, revealing an evolution of the homogeneous scenario observed in glacial periods. The enhanced sensitivity of peripheral ice sheet sites to local dust sources makes Talos Dome an ideal site to assess the climatic and atmospheric changes of the peripheral sectors of East Antarctica during the current interglacial period.
14 citations
References
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TL;DR: The early Proterozoic Huronian Supergroup of the north shore of Lake Huron (Fig. 1) is a thick succession of sedimentary and volcanic rocks deposited between about 2,500 and 2,100 Myr ago as discussed by the authors.
Abstract: The early Proterozoic Huronian Supergroup of the north shore of Lake Huron (Fig. 1) is a thick (up to 12,000 m) succession of sedimentary and volcanic rocks deposited between about 2,500 and 2,100 Myr ago1. Here we present a palaeoclimatic interpretation of the Huronian based on approximately 200 major elements analyses of lutites. Most of these are new analyses from the Gowganda and Serpent Formations (Fig. 2). The remainder are from published sources cited in Fig. 4. The composition of lutites from the Huronian Supergroup records an early period of intense, probably tropical, weathering followed by climatic deterioration that culminated in widespread deposition of glaciogenic sediments of the Gowganda Formation. Climatic amelioration followed during deposition of the succeeding Huronian formations. The Huronian succession can be interpreted using a uniformitarian approach in that present day seafloor spreading rates and latitude-related climatic variations are compatible with available geochronological and palaeomagnetic data.
4,822 citations
Versailles Saint-Quentin-en-Yvelines University1, Joseph Fourier University2, Alfred Wegener Institute for Polar and Marine Research3, Reykjavík University4, University of Copenhagen5, University of Bern6, Centre national de la recherche scientifique7, University of Parma8, Université libre de Bruxelles9, University of Trieste10, Max Planck Society11, British Antarctic Survey12
TL;DR: It is suggested that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records.
Abstract: 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.
1,723 citations
01 Jan 2006
TL;DR: A high-resolution deuterium profile is 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.
Abstract: 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.
1,566 citations
TL;DR: It is proposed that the observed ∼25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.
Abstract: Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation; it can also be a source of micronutrients, such as iron, to the ocean. It has been suggested that production, transport and deposition of dust is influenced by climatic changes on glacial-interglacial timescales. Here we present a high-resolution record of aeolian dust from the EPICA Dome C ice core in East Antarctica, which provides an undisturbed climate sequence over the past eight climatic cycles. We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods. Our data suggest that dust flux is increasingly correlated with Antarctic temperature as the climate becomes colder. We interpret this as progressive coupling of the climates of Antarctic and lower latitudes. Limited changes in glacial-interglacial atmospheric transport time suggest that the sources and lifetime of dust are the main factors controlling the high glacial dust input. We propose that the observed approximately 25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.
613 citations
TL;DR: In this paper, a scattering-theoretic interpretation of various features in the experimental spectra, including pre-edge and main-edge peaks, is presented together with an interpretation of the effects of disorder.
Abstract: Experimental Ti $K$-edge x-ray-absorption near-edge structure (XANES) spectra for a variety of Ti(IV)-bearing crystalline oxide model compounds are compared with those calculated using the ab initio multiple-scattering code FEFF7. A scattering-theoretic interpretation of various features in the experimental spectra, including pre-edge and main-edge peaks, is presented together with an interpretation of the effects of disorder. The observed pre-edge features are found to vary in both position (by $\ensuremath{\approx}2\ifmmode\pm\else\textpm\fi{}0.1\mathrm{eV}$) and normalized height (from $\ensuremath{\approx}0.04$ to $1.0\ifmmode\pm\else\textpm\fi{}0.05$) as a function of Ti coordination (4, 5, or 6 oxygen nearest neighbors), in agreement with calculations. In aperiodic oxide compounds where the Ti coordination is unknown (e.g., titanosilicate glasses and melts), pre-edge position and height can be used to derive reliable information on Ti coordination chemistry. For example, one can distinguish between fivefold coordinated Ti (i.e., ${\mathrm{TiO}}_{5}$) and a 50:50 mixture of fourfold- and sixfold-coordinated Ti (i.e., ${\mathrm{TiO}}_{4}$ vs ${\mathrm{TiO}}_{6}$). Finally, it is proposed that the intensity of the main-edge features can be used as a probe of disorder in the short- and medium-range environment of Ti. This is exemplified by Ti XANES studies of the effect of radiation damage on ${\mathrm{CaTiSiO}}_{5}$ and the melting of ${\mathrm{K}}_{2}{\mathrm{TiSi}}_{2}{\mathrm{O}}_{7}$ glass at high temperature.
529 citations