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Martin Frank - One of the best experts on this subject based on the ideXlab platform.

  • The evolution of climatically driven weathering inputs into the western Arctic Ocean since the late Miocene: Radiogenic Isotope evidence
    Earth and Planetary Science Letters, 2015
    Co-Authors: Veit Dausmann, Martin Frank, Christopher Siebert, Marcus Christl, James R. Hein
    Abstract:

    Highlights • Seawater Hf–Nd–Pb isotopic evolution in the deep Arctic Ocean of the past 7 Myr. • Climatically driven changes in weathering inputs since 4 Ma. • North American (Laurentide Ice Sheet) runoff controlled the isotopic budget in the Canada Basin. • More congruent Hf release due to glacial weathering conditions. • Past Arctic Ocean water masses show larger isotopic differences than today. Abstract We present the first continuous records of dissolved Radiogenic neodymium, hafnium, and lead Isotope compositions of deep waters in the western Arctic Ocean, spanning the time from the late Miocene to the present. The data were obtained from three hydrogenetic ferromanganese (Fe–Mn) crusts recovered from seamounts along the northernmost edge of the Northwind Ridge in the Canada Basin from water depths of 2200, 2400, and 3600 m. Dating the crusts using cosmogenic 10Be documents undisturbed present-day growth surfaces and yields growth rates between 27 and 2.2 mm/Myr. The Nd (Hf) Isotope time series of the three crusts show similar evolutions from eNdeNd(eHf)(eHf) of −8.5 (+4) in the oldest parts to −11.5 (−4) at the surfaces and a pronounced trend to less Radiogenic values starting at ∼4 Ma. This coincided with a trend of the Pb Isotope evolution towards more Radiogenic 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb. It is inferred that climatically controlled changes in weathering regime and sediment transport along the North American continent were responsible for the major change of the Radiogenic Isotope composition of the Arctic Deep Water (ADW) in the Canada Basin. Based on these records we conclude that weathering inputs from the North American continent linked to enhanced glacial conditions started to increase and to influence the Radiogenic Isotope composition of ADW ∼4 million years ago and were further intensified at ∼1 Ma. These new time series differ markedly from the Radiogenic Isotope evolution of Arctic Intermediate Water recorded on the Lomonosov Ridge and suggest that much larger isotopic differences between the water masses of the Arctic Ocean than today prevailed in the past.

  • Neoglacial change in deep water exchange and increase of sea-ice transport through eastern Fram Strait: evidence from Radiogenic Isotopes
    Quaternary Science Reviews, 2014
    Co-Authors: Kirstin Werner, Martin Frank, Claudia Teschner, Juliane Müller, Robert F Spielhagen
    Abstract:

    Sediment core MSM5/5-712 from the West Spitsbergen continental margin has been investigated at high resolution for its seawater-derived neodymium (Nd) and lead (Pb) Isotope compositions stored in ferromanganese oxyhydroxide coatings of the sediment particles to reconstruct Holocene changes in the sources and mixing of bottom waters passing the site. The Radiogenic Isotope data are used in combination with a multitude of proxy indicators for the climatic and oceanographic development of the eastern Fram Strait during the past 8500 years. To calibrate the downcore data, seawater and core top samples from the area were analysed for their Radiogenic Isotope compositions. Core top leachates reveal relatively high (more Radiogenic) Nd Isotope compositions between eNd −9.7 and −9.1, which are higher than present-day seawater eNd in eastern Fram Strait (−12.6 to −10.5) and indicate that the seawater values have only been established very recently. The core top data agree well with the downcore signatures within the uppermost 40 cm of the sediment core (eNd −9.1 to −8.8) indicating a reduced inflow of waters from the Nordic Seas, concurrent with cool conditions and a south-eastward shift of the marginal ice zone after ca 2.8 cal ka BP (Late Holocene). High sea-ice abundances in eastern Fram Strait are coeval with the well-known Neoglacial trend in the northern North Atlantic region. In contrast, warmer conditions of the late Early to Mid-Holocene were accompanied by lower (less Radiogenic) eNd signatures of the bottom waters indicating an increased admixture from the Nordic Seas (−10.6 to −10.1). A shift to significantly more Radiogenic eNd signatures of the detrital material also occurred at 3 cal ka BP and was accompanied by a marked increase in supply of fine-grained ice-rafted material (IRF) from the Arctic Ocean to the core site. The most likely source areas for this Radiogenic material are the shallow Arctic shelves, in particular the Kara Sea shelf. The evolution of the Pb Isotope compositions of past seawater was dominated by local signatures characterized by high 208, 207, 206Pb/204Pb values during the warm Early and Mid-Holocene periods related to enhanced chemical weathering on Svalbard and high glacial and riverine input derived from young granitic (more Radiogenic) material to the West Spitsbergen margin. At 3 cal ka BP both detrital and seawater Pb Isotope data changed towards more Kara Sea-like signatures.

  • Contrasting geochemical cycling of hafnium and neodymium in the central Baltic Sea
    Geochimica et Cosmochimica Acta, 2013
    Co-Authors: Tianyu Chen, Martin Frank, Roland Stumpf, Jacek Bełdowski, Michael Staubwasser
    Abstract:

    The central Baltic Sea is a marginal brackish basin which comprises anoxic bottom waters and is surrounded by geological source terrains with a wide variety of compositions and ages. This allows the investigation of water mass mixing using Radiogenic Isotope compositions of Nd and Hf as well as their geochemical cycling across varying redox conditions in the water column. In this study, we present the distribution of Nd and Hf concentrations and their isotopic compositions for 6 depth profiles and 3 surface water sites obtained during a cruise in the central Baltic Sea onboard the RV Oceania as a part of the international GEOTRACES program. The results obtained indicate that Nd Isotopes effectively trace the mixing between more Radiogenic saline waters from the south and unRadiogenic fresh waters from the north, which helps to understand the reliability of Nd Isotopes as water mass tracer in the open ocean. In surface waters, Nd shows higher concentrations and less Radiogenic Isotope compositions at the northern stations, which are progressively diluted and become more Radiogenic to the south, consistent with the counterclockwise circulation pattern of central Baltic Sea surface waters. In contrast to the variable Nd concentrations, Hf shows much less variability. At the Gotland Deep station, the Nd concentrations of the euxinic waters are higher by a factor >10 than those of the overlying oxygen-depleted waters, whereas Hf only shows small concentration variations. This indicates faster removal of Hf from the water column than Nd. Moreover, the dissolved Hf Isotope signatures document great variability but no consistent mixing trends. Our explanation is that Hf has a lower residence time than Nd, and also that the Hf Isotope signatures of the sources are highly heterogeneous, which is attributed to their differing magmatic and tectonic histories as well as incongruent post-glacial weathering around the central Baltic Sea.

  • changes in silicate utilisation and upwelling intensity off peru since the last glacial maximum insights from silicon and neodymium Isotopes
    Quaternary Science Reviews, 2013
    Co-Authors: Claudia Ehlert, Patricia Grasse, Martin Frank
    Abstract:

    We combine the stable silicon Isotope composition (δ30Si) of diatoms and the Radiogenic neodymium Isotope compositions (eNd) of past seawater extracted from the authigenic fraction of the sediments (Mn–Fe coatings of particles and benthic foraminifers), as well as the Radiogenic Isotope compositions (Nd, Sr) of the detrital material itself to reconstruct silicic acid utilisation, water mass mixing, and upwelling intensity from the same marine sediments in the Peruvian upwelling region during the past 20,000 years. Additionally, the sedimentary signals were compared to the water column Isotope compositions. Along the Peruvian shelf, the dissolved eNd in the water column ranges from −5.7 to +0.6. The corresponding eNd signatures of the coatings and the benthic foraminifers of the surface sediments range from −4.5 to +1.8 and from −2.5 to +2.2, respectively. The detrital eNd (87Sr/86Sr) signatures range from −6.3 to 0 (0.70508–0.71049). All phases show a trend from more Radiogenic eNd values in the north towards less Radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology. The eNd signatures of the coatings extracted from sediment core SO147-106KL located in the present day centre of coastal upwelling near 12°S have been essentially constant (−1.5) throughout the past 20,000 years, while the detrital eNd (87Sr/86Sr) varied between values of −0.7 (0.70620) during the Last Glacial and −4.5 (0.70849) during the late Holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling. The δ30Si signature of both total biogenic opal (δ30Siopal) and of hand-picked diatoms (δ30Sidiatom) ranged from +0.3‰ (Last Glacial) to +1.4‰ (late Holocene) confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms. Our combined bSiO2 MAR, δ30Siopal and detrital Radiogenic Isotope results demonstrate that the strongest El Nino-Southern Oscillation conditions off Peru of the past 20 ka have prevailed during the past 5 ka.

  • Changes in silicate utilisation and upwelling intensity off Peru since the Last Glacial Maximum – insights from silicon and neodymium Isotopes
    Quaternary Science Reviews, 2013
    Co-Authors: Claudia Ehlert, Patricia Grasse, Martin Frank
    Abstract:

    We combine the stable silicon Isotope composition (δ30Si) of diatoms and the Radiogenic neodymium Isotope compositions (eNd) of past seawater extracted from the authigenic fraction of the sediments (Mn–Fe coatings of particles and benthic foraminifers), as well as the Radiogenic Isotope compositions (Nd, Sr) of the detrital material itself to reconstruct silicic acid utilisation, water mass mixing, and upwelling intensity from the same marine sediments in the Peruvian upwelling region during the past 20,000 years. Additionally, the sedimentary signals were compared to the water column Isotope compositions. Along the Peruvian shelf, the dissolved eNd in the water column ranges from −5.7 to +0.6. The corresponding eNd signatures of the coatings and the benthic foraminifers of the surface sediments range from −4.5 to +1.8 and from −2.5 to +2.2, respectively. The detrital eNd (87Sr/86Sr) signatures range from −6.3 to 0 (0.70508–0.71049). All phases show a trend from more Radiogenic eNd values in the north towards less Radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology. The eNd signatures of the coatings extracted from sediment core SO147-106KL located in the present day centre of coastal upwelling near 12°S have been essentially constant (−1.5) throughout the past 20,000 years, while the detrital eNd (87Sr/86Sr) varied between values of −0.7 (0.70620) during the Last Glacial and −4.5 (0.70849) during the late Holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling. The δ30Si signature of both total biogenic opal (δ30Siopal) and of hand-picked diatoms (δ30Sidiatom) ranged from +0.3‰ (Last Glacial) to +1.4‰ (late Holocene) confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms. Our combined bSiO2 MAR, δ30Siopal and detrital Radiogenic Isotope results demonstrate that the strongest El Nino-Southern Oscillation conditions off Peru of the past 20 ka have prevailed during the past 5 ka.

Claudia Ehlert - One of the best experts on this subject based on the ideXlab platform.

  • changes in silicate utilisation and upwelling intensity off peru since the last glacial maximum insights from silicon and neodymium Isotopes
    Quaternary Science Reviews, 2013
    Co-Authors: Claudia Ehlert, Patricia Grasse, Martin Frank
    Abstract:

    We combine the stable silicon Isotope composition (δ30Si) of diatoms and the Radiogenic neodymium Isotope compositions (eNd) of past seawater extracted from the authigenic fraction of the sediments (Mn–Fe coatings of particles and benthic foraminifers), as well as the Radiogenic Isotope compositions (Nd, Sr) of the detrital material itself to reconstruct silicic acid utilisation, water mass mixing, and upwelling intensity from the same marine sediments in the Peruvian upwelling region during the past 20,000 years. Additionally, the sedimentary signals were compared to the water column Isotope compositions. Along the Peruvian shelf, the dissolved eNd in the water column ranges from −5.7 to +0.6. The corresponding eNd signatures of the coatings and the benthic foraminifers of the surface sediments range from −4.5 to +1.8 and from −2.5 to +2.2, respectively. The detrital eNd (87Sr/86Sr) signatures range from −6.3 to 0 (0.70508–0.71049). All phases show a trend from more Radiogenic eNd values in the north towards less Radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology. The eNd signatures of the coatings extracted from sediment core SO147-106KL located in the present day centre of coastal upwelling near 12°S have been essentially constant (−1.5) throughout the past 20,000 years, while the detrital eNd (87Sr/86Sr) varied between values of −0.7 (0.70620) during the Last Glacial and −4.5 (0.70849) during the late Holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling. The δ30Si signature of both total biogenic opal (δ30Siopal) and of hand-picked diatoms (δ30Sidiatom) ranged from +0.3‰ (Last Glacial) to +1.4‰ (late Holocene) confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms. Our combined bSiO2 MAR, δ30Siopal and detrital Radiogenic Isotope results demonstrate that the strongest El Nino-Southern Oscillation conditions off Peru of the past 20 ka have prevailed during the past 5 ka.

  • Changes in silicate utilisation and upwelling intensity off Peru since the Last Glacial Maximum – insights from silicon and neodymium Isotopes
    Quaternary Science Reviews, 2013
    Co-Authors: Claudia Ehlert, Patricia Grasse, Martin Frank
    Abstract:

    We combine the stable silicon Isotope composition (δ30Si) of diatoms and the Radiogenic neodymium Isotope compositions (eNd) of past seawater extracted from the authigenic fraction of the sediments (Mn–Fe coatings of particles and benthic foraminifers), as well as the Radiogenic Isotope compositions (Nd, Sr) of the detrital material itself to reconstruct silicic acid utilisation, water mass mixing, and upwelling intensity from the same marine sediments in the Peruvian upwelling region during the past 20,000 years. Additionally, the sedimentary signals were compared to the water column Isotope compositions. Along the Peruvian shelf, the dissolved eNd in the water column ranges from −5.7 to +0.6. The corresponding eNd signatures of the coatings and the benthic foraminifers of the surface sediments range from −4.5 to +1.8 and from −2.5 to +2.2, respectively. The detrital eNd (87Sr/86Sr) signatures range from −6.3 to 0 (0.70508–0.71049). All phases show a trend from more Radiogenic eNd values in the north towards less Radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology. The eNd signatures of the coatings extracted from sediment core SO147-106KL located in the present day centre of coastal upwelling near 12°S have been essentially constant (−1.5) throughout the past 20,000 years, while the detrital eNd (87Sr/86Sr) varied between values of −0.7 (0.70620) during the Last Glacial and −4.5 (0.70849) during the late Holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling. The δ30Si signature of both total biogenic opal (δ30Siopal) and of hand-picked diatoms (δ30Sidiatom) ranged from +0.3‰ (Last Glacial) to +1.4‰ (late Holocene) confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms. Our combined bSiO2 MAR, δ30Siopal and detrital Radiogenic Isotope results demonstrate that the strongest El Nino-Southern Oscillation conditions off Peru of the past 20 ka have prevailed during the past 5 ka.

  • Current transport versus continental inputs in the eastern Indian Ocean; Radiogenic Isotope signatures of clay size sediments
    Geochemistry Geophysics Geosystems, 2011
    Co-Authors: Claudia Ehlert, Martin Frank, Brian A. Haley, U. Böniger, P. De Deckker, Franz X. Gingele
    Abstract:

    Analyses of Radiogenic neodymium (Nd), strontium (Sr), and lead (Pb) Isotope compositions of clay-sized detrital sediments allow detailed tracing of source areas of sediment supply and present and past transport of particles by water masses in the eastern Indian Ocean. Isotope signatures in surface sediments range from −21.5 (ɛNd), 0.8299 (87Sr/86Sr), and 19.89 (206Pb/204Pb) off northwest Australia to +0.7 (ɛNd), 0.7069 (87Sr/86Sr), and 17.44 (206Pb/204Pb) southwest of Java. The Radiogenic Isotope signatures primarily reflect petrographic characteristics of the surrounding continental bedrocks but are also influenced by weathering-induced grain size effects of Pb and Sr Isotope systems with superimposed features that are caused by current transport of clay-sized particles, as evidenced off Australia where a peculiar isotopic signature characterizes sediments underlying the southward flowing Leeuwin Current and the northward flowing West Australian Current (WAC). Gravity core FR10/95-GC17 off west Australia recorded a major isotopic change from Last Glacial Maximum values of −10 (ɛNd), 0.745 (87Sr/86Sr), and 18.8 (206Pb/204Pb) to Holocene values of −22 (ɛNd), 0.8 (87Sr/86Sr), and 19.3 (206Pb/204Pb), which documents major climatically driven changes of the WAC and in local riverine particle supply from Australia during the past 20 kyr. In contrast, gravity core FR10/95-GC5 located below the present-day pathway of the Indonesian throughflow (ITF) shows a much smaller isotopic variability, indicating a relatively stable ITF hydrography over most of the past 92 kyr. Only the surface sediments differ significantly in their isotopic composition, indicating substantial changes in erosional sources attributed to a change of the current regime during the past 5 kyr.

Thomas F Nagler - One of the best experts on this subject based on the ideXlab platform.

  • weathering versus circulation controlled changes in Radiogenic Isotope tracer composition of the labrador sea and north atlantic deep water
    Paleoceanography, 2001
    Co-Authors: Friedhelm Von Blanckenburg, Thomas F Nagler
    Abstract:

    Geological reconstructions and general circulation models suggest that the onset of both Northern Hemisphere glaciation, 2.7 Myr ago, and convection of Labrador Sea Water (LSW) were caused by the closure of the Panama Gateway ∼ 4.5 Myr ago. Time series data that have been obtained from studies of ferromanganese crusts from the northwestern Atlantic suggest that Radiogenic Isotopes of intermediate ocean residence time (Pb and Nd) can serve as suitable tracers to reconstruct these events. However, it has been unclear until now as to whether the changes that have been observed in Isotope composition at this time are the result of increased thermohaline circulation or due to the effects of increased glacial weathering. In this paper we adopt a box model approach to demonstrate that the shifts in Radiogenic Isotope compositions are unlikely to be due to changes in convection in LSW but can be explained in terms of increases of erosion levels due to the glaciation of Greenland and Canada. Furthermore, we provide experimental evidence for the incongruent release of a labile fraction of strongly Radiogenic Pb and nonRadiogenic Nd from continental detritus eroding into the Labrador Sea. This can be attributed to the glacial weathering of old continents and accounts for the paradox that one of the areas of the world most deficient in Radiogenic Pb should provide such a rich supply of Radiogenic Pb to the oceans. An important general conclusion is that the compositions of Radiogenic Isotopes in seawater are not always a reflection of their continental sources. Perhaps more importantly, the transition from chemical weathering to mechanical erosion is likely to result in significant variations in Radiogenic tracers in seawater.

  • Weathering versus circulation‐controlled changes in Radiogenic Isotope tracer composition of the Labrador Sea and North Atlantic Deep Water
    Paleoceanography, 2001
    Co-Authors: Friedhelm Von Blanckenburg, Thomas F Nagler
    Abstract:

    Geological reconstructions and general circulation models suggest that the onset of both Northern Hemisphere glaciation, 2.7 Myr ago, and convection of Labrador Sea Water (LSW) were caused by the closure of the Panama Gateway ∼ 4.5 Myr ago. Time series data that have been obtained from studies of ferromanganese crusts from the northwestern Atlantic suggest that Radiogenic Isotopes of intermediate ocean residence time (Pb and Nd) can serve as suitable tracers to reconstruct these events. However, it has been unclear until now as to whether the changes that have been observed in Isotope composition at this time are the result of increased thermohaline circulation or due to the effects of increased glacial weathering. In this paper we adopt a box model approach to demonstrate that the shifts in Radiogenic Isotope compositions are unlikely to be due to changes in convection in LSW but can be explained in terms of increases of erosion levels due to the glaciation of Greenland and Canada. Furthermore, we provide experimental evidence for the incongruent release of a labile fraction of strongly Radiogenic Pb and nonRadiogenic Nd from continental detritus eroding into the Labrador Sea. This can be attributed to the glacial weathering of old continents and accounts for the paradox that one of the areas of the world most deficient in Radiogenic Pb should provide such a rich supply of Radiogenic Pb to the oceans. An important general conclusion is that the compositions of Radiogenic Isotopes in seawater are not always a reflection of their continental sources. Perhaps more importantly, the transition from chemical weathering to mechanical erosion is likely to result in significant variations in Radiogenic tracers in seawater.

Wafa Abouchami - One of the best experts on this subject based on the ideXlab platform.

  • Seasonal Radiogenic isotopic variability of the African dust outflow to the tropical Atlantic Ocean and across to the Caribbean
    Earth and Planetary Science Letters, 2018
    Co-Authors: Ashwini Kumar, Wafa Abouchami, Stephen J G Galer, Satinder Singh, K. W. Fomba, Joseph M. Prospero, Meinrat O Andreae
    Abstract:

    Abstract In order to assess the impact of mineral dust on climate and biogeochemistry, it is paramount to identify the sources of dust emission. In this regard, Radiogenic Isotopes have recently been used successfully for tracing North African dust provenance and its transport across the tropical Atlantic to the Caribbean. Here we present two time series of Radiogenic Isotopes (Pb, Sr and Nd) in dusts collected at the Cape Verde Islands and Barbados in order to determine the origin of the dust and examine the seasonality of westerly dust outflow from Northern Africa. Aerosol samples were collected daily during two campaigns – February 2012 (winter) and June–July 2013 (summer) – at the Cape Verde Atmospheric Observatory (CVAO) on the island of Sao Vicente (16.9°N, 24.9°W). A one-year-long time series of aerosols from Barbados (13.16°N, 59.43°W) – a receptor region in the Caribbean – was sampled at a lower, monthly resolution. Our results resolve a seasonal isotopic signal at Cape Verde shown by daily variations, with a larger Radiogenic Isotope variability in winter compared to that in summer. This summer signature is also observed over Barbados, indicating similar dust provenance at both locations, despite different sampling years. This constrains the Isotope fingerprint of Saharan Air Layer (SAL) dust that is well-mixed during its transport. This result provides unequivocal evidence for a permanent, albeit of variable strength, long-range transport of African dust to the Caribbean and is in full agreement with atmospheric models of North African dust emission and transport across the tropical Atlantic in the SAL. The seasonal isotopic variability is related to changes in the dust source areas – mainly the Sahara and Sahel regions – that are active all-year-round, albeit with variable contributions in summer versus the winter months. Our results provide little support for much dust contributed from the Bodele Depression in Chad – the “dustiest” place on Earth – reaching Cape Verde and Barbados during the summer, while contributions during the winter months are likely patchy and minor at most. Importantly, a short-term isotopic excursion is resolved in the Cape Verde winter record during a dust outbreak on 06–08 February 2012. This features a highly Radiogenic Pb and Sr and unRadiogenic Nd signature, marking a clear shift in dust provenance relative to that of normal days. As the dust storm waned, continuous gradual changes are observed, reflecting mixing and progressive dilution with dust typical of normal days. These inferences from Radiogenic Isotope tracers are corroborated by both satellite images (CALIPSO and MODIS) and back-trajectory analyses. The Radiogenic Isotope fingerprinting of these presently-active North African dust sources, and especially the Saharan Air Layer, will prove invaluable in studies of past dust emission from Northern Africa, where imagery and back trajectory analysis are unavailable.

  • a Radiogenic Isotope tracer study of transatlantic dust transport from africa to the caribbean
    Atmospheric Environment, 2014
    Co-Authors: Ashwini Kumar, Wafa Abouchami, Stephen J G Galer, V H Garrison, Earle Williams, Meinrat O Andreae
    Abstract:

    Abstract Many studies have suggested that long-range transport of African desert dusts across the Atlantic Ocean occurs, delivering key nutrients and contributing to fertilization of the Amazon rainforest. Here we utilize Radiogenic Isotope tracers – Sr, Nd and Pb – to derive the provenance, local or remote, and pathways of dust transport from Africa to the Caribbean. Atmospheric total suspended particulate (TSP) matter was collected in 2008 on quartz fibre filters, from both sides of the Atlantic Ocean at three different locations: in Mali (12.6°N, 8.0°W; 555 m a.s.l.), Tobago (11.3°N, 60.5°W; 329 m a.s.l.) and the U.S. Virgin Islands (17.7°N, 64.6°W; 27 m a.s.l.). Both the labile phase, representative of the anthropogenic signal, and the refractory detrital silicate fraction were analysed. Dust deposits and soils from around the sampling sites were measured as well to assess the potential contribution from local sources to the mineral dust collected. The contribution from anthropogenic sources of Pb was predominant in the labile, leachate phase. The overall similarity in Pb Isotope signatures found in the leachates is attributed to a common African source of anthropogenic Pb, with minor inputs from other sources, such as from Central and South America. The Pb, Sr and Nd isotopic compositions in the silicate fraction were found to be systematically more Radiogenic than those in the corresponding labile phases. In contrast, Nd and Sr isotopic compositions from Mali, Tobago, and the Virgin Islands are virtually identical in both leachates and residues. Comparison with existing literature data on Saharan and Sahelian sources constrains the origin of summer dust transported to the Caribbean to mainly originate from the Sahel region, with some contribution from northern Saharan sources. The source regions derived from the Isotope data are consistent with 7-day back-trajectory analyses, demonstrating the usefulness of Radiogenic Isotopes in tracing dust provenance and atmospheric transport.

  • Radiogenic Isotope fingerprint of wilkes land adelie coast bottom water in the circum antarctic ocean
    Geophysical Research Letters, 2006
    Co-Authors: Tina Van De Flierdt, Sidney R. Hemming, Steven L. Goldstein, Wafa Abouchami
    Abstract:

    [1] Wilkes Land–Adelie Coast Bottom Water encompasses the bottom waters formed around the coast of East Antarctica in the area east of Prydz Bay and west of the Ross Sea (90°E–150°E). Here we show that these bottom waters have not only characteristic physical properties, but also carry a distinct Radiogenic Isotope signal that traces their dispersal. The Nd, Hf and Pb isotopic compositions of Circum-Antarctic ferromanganese nodules record the isotopic composition of ambient seawater. Those with the lowest Nd and Hf isotopic ratios and the highest Pb isotopic ratios are from the deep Australian-Antarctic Basin, and they fingerprint Wilkes Land–Adelie Coast Bottom Water. The data illustrate the potential value of these Isotope systems as tracers of present and past deep and bottom waters in the Circum-Antarctic realm and elsewhere.

  • Radiogenic Isotope fingerprint of Wilkes Land–Adélie Coast Bottom Water in the circum-Antarctic Ocean
    Geophysical Research Letters, 2006
    Co-Authors: Tina Van De Flierdt, Sidney R. Hemming, Steven L. Goldstein, Wafa Abouchami
    Abstract:

    [1] Wilkes Land–Adelie Coast Bottom Water encompasses the bottom waters formed around the coast of East Antarctica in the area east of Prydz Bay and west of the Ross Sea (90°E–150°E). Here we show that these bottom waters have not only characteristic physical properties, but also carry a distinct Radiogenic Isotope signal that traces their dispersal. The Nd, Hf and Pb isotopic compositions of Circum-Antarctic ferromanganese nodules record the isotopic composition of ambient seawater. Those with the lowest Nd and Hf isotopic ratios and the highest Pb isotopic ratios are from the deep Australian-Antarctic Basin, and they fingerprint Wilkes Land–Adelie Coast Bottom Water. The data illustrate the potential value of these Isotope systems as tracers of present and past deep and bottom waters in the Circum-Antarctic realm and elsewhere.

Simone Tommasini - One of the best experts on this subject based on the ideXlab platform.

  • Geochemical and Radiogenic Isotope probes of Ischia volcano, Southern Italy: Constraints on magma chamber dynamics and residence time
    American Mineralogist, 2017
    Co-Authors: Martina Casalini, Riccardo Avanzinelli, Arnd Heumann, Sandro De Vita, Fabio Sansivero, Sandro Conticelli, Simone Tommasini
    Abstract:

    The active volcano of Ischia, an island off-shore the city of Naples, Southern Italy, has a discontinuous volcanic activity characterized by caldera-forming paroxysmal eruptions, lava flows, and lava domes, and thus offers the opportunity to study the complexity of magma storage, differentiation, and extraction mechanisms in a long-lived magma reservoir. The overall geochemical composition of erupted magmas varies from shoshonite to latite and trachyte/trachyphonolite. Their Sr and Nd, Isotope composition variation is typical of subduction-related magmas, akin to other potassic magmas of the Neapolitan District, and there is a complete overlap of Radiogenic Isotope composition among shoshonite, latite, and trachyte/trachyphonolite. The lack of systematic Radiogenic Isotope covariation during differentiation suggests that the Radiogenic Isotope variability could be a signature of each magma pulse that subsequently evolved in a closed-system environment. Erupted magmas record a recurrent evolutionary process consisting of two-step fractional crystallization along similar liquid lines of descent for each magma pulse, suggesting near steady-state magma chamber conditions with balanced alternating periods of replenishment, differentiation, and eruption. The dominant role of fractionating feldspars determines a significant depletion of Sr ( 200) in the residual trachyte magma. Several more-evolved trachytes have anomalous Radiogenic 87 Sr/ 86 Sr i (>0.707) coupled with high 87 Rb/ 86 Sr (>50), all other geochemical and isotopic characteristics being similar to normal 87 Sr/ 86 Sr i trachytes at the same degree of evolution. This Radiogenic Sr Isotope signature is not consistent with assimilation of crustal material and demands for a time-related in-growth of 87 Sr during storage within the magma chamber. Rb-Sr isochrons on separated mineral-groundmass pairs provide robust constraints on a prolonged pre-eruptive history ranging from a few tens to hundreds of thousands of years at relatively low temperature (~750 °C). Remarkably, also normal trachytes with high 87 Rb/ 86 Sr (>200) yield a magma residence time from some 4 to 27 kyr, implying that the long-lived history of Ischia magmas is not limited to the anomalous 87 Sr/ 86 Sr i trachytes. This long-lived history could be a characteristic feature of the magma chamber reservoir of this active volcano, which other volcanic products (i.e., shoshonite and latite) cannot disclose due to their lower Rb/Sr (i.e., low 87 Sr in-growth rate) and higher magma storage temperature (>900 °C) (i.e., rapid Sr Isotope homogenization via diffusion). The magma chamber dynamics of the active volcano of Ischia, probed on the basis of geochemical and Radiogenic Isotope tools, is consistent with recent models of complex magma chamber reservoirs made up of multiple discrete melt pockets, isolated by largely crystalline mush portions, maintained in a steady-state thermal flux regime with no mass exchange, and with reactivation shortly before eruption.

  • The Fate of High-Angle Dipping Slabs in the Subduction Factory: an Integrated Trace Element and Radiogenic Isotope (U, Th, Sr, Nd, Pb) Study of Stromboli Volcano, Aeolian Arc, Italy
    Journal of Petrology, 2007
    Co-Authors: Simone Tommasini, Riccardo Avanzinelli, Arnd Heumann, Lorella Francalanci
    Abstract:

    The subaerial part of the Stromboli stratovolcano was built up in the last 100 kyr through six periods of activity; the erupted magmas record the largest compositional variation of all the Aeolian arc volcanoes (calc-alkaline, shoshonitic, and potassic alkaline magma series).The trace element characteristics of the less evolved magmas of each period of activity are coherently correlated with their Radiogenic Isotope (Sr, Nd, Pb) composition, and are typical of volcanic arc rocks. In terms of U-series Isotopes, samples from the different magma series have both U and Th excesses, and this distinctive feature provides additional constraints on source enrichment processes within the mantle wedge and on the mechanism of partial melting. Overall the complete set of data demonstrates that the genesis of the different magma series at Stromboli can be accommodated in a mantle source that experienced two distinct enrichment processes by different parts of the subducting oceanic crust of the Ionian slab.The first was caused by supercritical liquids originating from the basaltic and sedimentary parts of the subducting slab at 45 GPa and 9008C.The second was induced by aqueous fluids, again originating from the basaltic and sedimentary parts of the slab, released from a shallower part of the subducted Ionian slab (55 GPa and 8008C). U^Th disequilibria constrain the timing of the first metasomatic event (Stage I: supercritical liquids) at 4435 ka, whereas the second event (Stage II: aqueous fluids) occurred at 100 ka.The high-angle dip of the Ionian slab ( 708) caused the superimposition of the metasomatizing agents of the two enrichment processes in the same volume of the mantle wedge, explaining the occurrence of such different magma series in a single volcanic edifice. The U^Th disequilibria provide evidence for dynamic melting of the metasomatized mantle wedge combined with an ageing effect resulting from the restoration of secular equilibrium after the perturbation caused by the U-rich aqueous fluids of Stage II.The trace element and Radiogenic Isotope (U,Th, Sr, Nd, Pb) signature of the mantle source of the magmas at Stromboli is thus dependent upon the amount of supercritical liquids and aqueous fluids released by the two components of the subducted slab, whereas the distinctive U and Th excesses of the magmas result from a combination of mantle ageing and time-dependent dynamic melting. The geochemical and Radiogenic Isotope signature of the mantle source beneath Stromboli places important constraints on the isotopic polarity from Southern Latium to the Aeolian arc attributed to the effect of a HIMU mantle component following either lateral inflow of foreland mantle material or upwelling of a mantle plume in the centre of the Tyrrhenian basin. Our geochemical model demonstrates that the high Pb/Pb of the putative ‘HIMU’ mantle component could be equally formed during metasomatism of the pre-existing mantle wedge by either the supercritical liquid (Stage I) or aqueous fluid (Stage II) released by the subducted altered basalt of the Ionian plate.