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Gerold Wefer - One of the best experts on this subject based on the ideXlab platform.

  • Holocene rainfall variability in southern Chile: a Marine Record of latitudinal shifts of the Southern Westerlies
    Earth and Planetary Science Letters, 2001
    Co-Authors: Frank Lamy, Dierk Hebbeln, Ursula Röhl, Gerold Wefer
    Abstract:

    Geochemical and clay mineral parameters of a high accumulation Marine sediment core from the Chilean continental slope (41‡S) provide a 7700 yr Record of rainfall variability in southern Chile related to the position of the Southern Westerlies. We especially use the iron content, measured with a time-resolution of ca. 10 yr on average, of 14 Caccelerator mass spectrometry dated Marine sediments as a proxy for the relative input of iron-poor Coastal Range and iron-rich Andean source rocks. Variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position. Based on these interpretations, we find a pronounced rainfall variability on multicentennial to millennial time-scales, superimposed on generally more arid conditions during the middle Holocene (7700 to 4000 cal yr B.P.) compared to the late Holocene (4000 to present). This variability and thus changes in the position of the Southern Westerlies are first compared to regional terrestrial paleoclimate data-sets from central and southern Chile. In order to derive possible wider implications and forcing mechanisms of the Holocene latitudinal shifts of the Southern Westerlies, we then compare our data to ice-core Records from both tropical South America and coastal Antarctica. These Records show similar bands of variability centered at ca. 900 and 1500 yr. Comparisons of band pass filters suggest a close connection of shifts of the Southern Westerlies to changes within the tropical climate system. The correlation to climate conditions in coastal Antarctica shows a more complicated picture with a phase shift at the beginning of the late Holocene coinciding with the onset of the modern state of El Nin ‹ o-Southern Oscillation system. The presented data provide further evidence that the well known millennial-scale climate variability during the last glacial continued throughout the Holocene. fl 2001 Elsevier Science B.V. All rights reserved.

  • Holocene rainfall variability in southern Chile: a Marine Record of latitudinal shifts of the Southern Westerlies
    Earth and Planetary Science Letters, 2001
    Co-Authors: Frank Lamy, Dierk Hebbeln, Ursula Röhl, Gerold Wefer
    Abstract:

    Radiocarbon age relationships between co-occurring planktic foraminifera, alkenones, and total organic carbon in sediments from the continental margins of southern Chile, northwest Africa, and the South China Sea were compared with published results from the Namibian margin. Age relationships between the sediment components are site-specific and relatively constant over time. Similar to the Namibian slope, where alkenones have been reported to be 1000-4500 years older than co-occurring foraminifera, alkenones were significantly (~1000 years) older than co-occurring foraminifera in the Chilean margin sediments. In contrast, alkenones and foraminifera were of similar age (within 2 sigma error or better) in the NW African and South China Sea sediments. Total organic matter and alkenone ages were similar off Namibia (age difference TOC alkenones: 200-700 years), Chile (100-450 years), and NW Africa (360-770 years), suggesting minor contributions of preaged terrigenous material. In the South China Sea, total organic carbon is significantly (2000-3000 years) older owing to greater inputs of preaged terrigenous material. Age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter. Physical characteristics of the depositional setting, such as seafloor morphology, shelf width, and sediment composition, may control the age of co-occurring sediment components. In particular, offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions. Aging of organic matter is promoted by transport. Age offsets are correlated with organic richness, suggesting that formation of organic aggregates is a key process

  • High-Resolution Marine Record of Climatic Change in Mid-latitude Chile during the Last 28,000 Years Based on Terrigenous Sediment Parameters
    Quaternary Research, 1999
    Co-Authors: Frank Lamy, Dierk Hebbeln, Gerold Wefer
    Abstract:

    AbstractMarine sediment cores from the continental slope off mid-latitude Chile (33°S) were studied with regard to grain-size distributions and clay mineral composition. The data provide a 28,000-yr14C accelerator mass spectrometry-dated Record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland. These variations can be interpreted in terms of the paleoclimatic evolution of mid-latitude Chile and are compared to existing terrestrial Records. Glacial climates (28,000–18,000 cal yr B.P.) were generally cold–humid with a cold–semiarid interval between 26,000 and 22,000 cal yr B.P. The deglaciation was characterized by a trend toward more arid conditions. During the middle Holocene (8000–4000 cal yr B.P.), comparatively stable climatic conditions prevailed with increased aridity in the Coastal Range. The late Holocene (4000–0 cal yr B.P.) was marked by more variable paleoclimates with generally more humid conditions. Variations of rainfall in mid-latitude Chile are most likely controlled by shifts of the latitudinal position of the Southern Westerlies. Compared to the Holocene, the southern westerly wind belt was located significantly farther north during the last glacial maximum. Less important variations of the latitudinal position of the Southern Westerlies also occurred on shorter time scales.

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

  • Holocene rainfall variability in southern Chile: a Marine Record of latitudinal shifts of the Southern Westerlies
    Earth and Planetary Science Letters, 2001
    Co-Authors: Frank Lamy, Dierk Hebbeln, Ursula Röhl, Gerold Wefer
    Abstract:

    Geochemical and clay mineral parameters of a high accumulation Marine sediment core from the Chilean continental slope (41‡S) provide a 7700 yr Record of rainfall variability in southern Chile related to the position of the Southern Westerlies. We especially use the iron content, measured with a time-resolution of ca. 10 yr on average, of 14 Caccelerator mass spectrometry dated Marine sediments as a proxy for the relative input of iron-poor Coastal Range and iron-rich Andean source rocks. Variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position. Based on these interpretations, we find a pronounced rainfall variability on multicentennial to millennial time-scales, superimposed on generally more arid conditions during the middle Holocene (7700 to 4000 cal yr B.P.) compared to the late Holocene (4000 to present). This variability and thus changes in the position of the Southern Westerlies are first compared to regional terrestrial paleoclimate data-sets from central and southern Chile. In order to derive possible wider implications and forcing mechanisms of the Holocene latitudinal shifts of the Southern Westerlies, we then compare our data to ice-core Records from both tropical South America and coastal Antarctica. These Records show similar bands of variability centered at ca. 900 and 1500 yr. Comparisons of band pass filters suggest a close connection of shifts of the Southern Westerlies to changes within the tropical climate system. The correlation to climate conditions in coastal Antarctica shows a more complicated picture with a phase shift at the beginning of the late Holocene coinciding with the onset of the modern state of El Nin ‹ o-Southern Oscillation system. The presented data provide further evidence that the well known millennial-scale climate variability during the last glacial continued throughout the Holocene. fl 2001 Elsevier Science B.V. All rights reserved.

  • Holocene rainfall variability in southern Chile: a Marine Record of latitudinal shifts of the Southern Westerlies
    Earth and Planetary Science Letters, 2001
    Co-Authors: Frank Lamy, Dierk Hebbeln, Ursula Röhl, Gerold Wefer
    Abstract:

    Radiocarbon age relationships between co-occurring planktic foraminifera, alkenones, and total organic carbon in sediments from the continental margins of southern Chile, northwest Africa, and the South China Sea were compared with published results from the Namibian margin. Age relationships between the sediment components are site-specific and relatively constant over time. Similar to the Namibian slope, where alkenones have been reported to be 1000-4500 years older than co-occurring foraminifera, alkenones were significantly (~1000 years) older than co-occurring foraminifera in the Chilean margin sediments. In contrast, alkenones and foraminifera were of similar age (within 2 sigma error or better) in the NW African and South China Sea sediments. Total organic matter and alkenone ages were similar off Namibia (age difference TOC alkenones: 200-700 years), Chile (100-450 years), and NW Africa (360-770 years), suggesting minor contributions of preaged terrigenous material. In the South China Sea, total organic carbon is significantly (2000-3000 years) older owing to greater inputs of preaged terrigenous material. Age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter. Physical characteristics of the depositional setting, such as seafloor morphology, shelf width, and sediment composition, may control the age of co-occurring sediment components. In particular, offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions. Aging of organic matter is promoted by transport. Age offsets are correlated with organic richness, suggesting that formation of organic aggregates is a key process

  • High-Resolution Marine Record of Climatic Change in Mid-latitude Chile during the Last 28,000 Years Based on Terrigenous Sediment Parameters
    Quaternary Research, 1999
    Co-Authors: Frank Lamy, Dierk Hebbeln, Gerold Wefer
    Abstract:

    AbstractMarine sediment cores from the continental slope off mid-latitude Chile (33°S) were studied with regard to grain-size distributions and clay mineral composition. The data provide a 28,000-yr14C accelerator mass spectrometry-dated Record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland. These variations can be interpreted in terms of the paleoclimatic evolution of mid-latitude Chile and are compared to existing terrestrial Records. Glacial climates (28,000–18,000 cal yr B.P.) were generally cold–humid with a cold–semiarid interval between 26,000 and 22,000 cal yr B.P. The deglaciation was characterized by a trend toward more arid conditions. During the middle Holocene (8000–4000 cal yr B.P.), comparatively stable climatic conditions prevailed with increased aridity in the Coastal Range. The late Holocene (4000–0 cal yr B.P.) was marked by more variable paleoclimates with generally more humid conditions. Variations of rainfall in mid-latitude Chile are most likely controlled by shifts of the latitudinal position of the Southern Westerlies. Compared to the Holocene, the southern westerly wind belt was located significantly farther north during the last glacial maximum. Less important variations of the latitudinal position of the Southern Westerlies also occurred on shorter time scales.

Dierk Hebbeln - One of the best experts on this subject based on the ideXlab platform.

  • Holocene rainfall variability in southern Chile: a Marine Record of latitudinal shifts of the Southern Westerlies
    Earth and Planetary Science Letters, 2001
    Co-Authors: Frank Lamy, Dierk Hebbeln, Ursula Röhl, Gerold Wefer
    Abstract:

    Geochemical and clay mineral parameters of a high accumulation Marine sediment core from the Chilean continental slope (41‡S) provide a 7700 yr Record of rainfall variability in southern Chile related to the position of the Southern Westerlies. We especially use the iron content, measured with a time-resolution of ca. 10 yr on average, of 14 Caccelerator mass spectrometry dated Marine sediments as a proxy for the relative input of iron-poor Coastal Range and iron-rich Andean source rocks. Variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position. Based on these interpretations, we find a pronounced rainfall variability on multicentennial to millennial time-scales, superimposed on generally more arid conditions during the middle Holocene (7700 to 4000 cal yr B.P.) compared to the late Holocene (4000 to present). This variability and thus changes in the position of the Southern Westerlies are first compared to regional terrestrial paleoclimate data-sets from central and southern Chile. In order to derive possible wider implications and forcing mechanisms of the Holocene latitudinal shifts of the Southern Westerlies, we then compare our data to ice-core Records from both tropical South America and coastal Antarctica. These Records show similar bands of variability centered at ca. 900 and 1500 yr. Comparisons of band pass filters suggest a close connection of shifts of the Southern Westerlies to changes within the tropical climate system. The correlation to climate conditions in coastal Antarctica shows a more complicated picture with a phase shift at the beginning of the late Holocene coinciding with the onset of the modern state of El Nin ‹ o-Southern Oscillation system. The presented data provide further evidence that the well known millennial-scale climate variability during the last glacial continued throughout the Holocene. fl 2001 Elsevier Science B.V. All rights reserved.

  • Holocene rainfall variability in southern Chile: a Marine Record of latitudinal shifts of the Southern Westerlies
    Earth and Planetary Science Letters, 2001
    Co-Authors: Frank Lamy, Dierk Hebbeln, Ursula Röhl, Gerold Wefer
    Abstract:

    Radiocarbon age relationships between co-occurring planktic foraminifera, alkenones, and total organic carbon in sediments from the continental margins of southern Chile, northwest Africa, and the South China Sea were compared with published results from the Namibian margin. Age relationships between the sediment components are site-specific and relatively constant over time. Similar to the Namibian slope, where alkenones have been reported to be 1000-4500 years older than co-occurring foraminifera, alkenones were significantly (~1000 years) older than co-occurring foraminifera in the Chilean margin sediments. In contrast, alkenones and foraminifera were of similar age (within 2 sigma error or better) in the NW African and South China Sea sediments. Total organic matter and alkenone ages were similar off Namibia (age difference TOC alkenones: 200-700 years), Chile (100-450 years), and NW Africa (360-770 years), suggesting minor contributions of preaged terrigenous material. In the South China Sea, total organic carbon is significantly (2000-3000 years) older owing to greater inputs of preaged terrigenous material. Age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter. Physical characteristics of the depositional setting, such as seafloor morphology, shelf width, and sediment composition, may control the age of co-occurring sediment components. In particular, offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions. Aging of organic matter is promoted by transport. Age offsets are correlated with organic richness, suggesting that formation of organic aggregates is a key process

  • High-Resolution Marine Record of Climatic Change in Mid-latitude Chile during the Last 28,000 Years Based on Terrigenous Sediment Parameters
    Quaternary Research, 1999
    Co-Authors: Frank Lamy, Dierk Hebbeln, Gerold Wefer
    Abstract:

    AbstractMarine sediment cores from the continental slope off mid-latitude Chile (33°S) were studied with regard to grain-size distributions and clay mineral composition. The data provide a 28,000-yr14C accelerator mass spectrometry-dated Record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland. These variations can be interpreted in terms of the paleoclimatic evolution of mid-latitude Chile and are compared to existing terrestrial Records. Glacial climates (28,000–18,000 cal yr B.P.) were generally cold–humid with a cold–semiarid interval between 26,000 and 22,000 cal yr B.P. The deglaciation was characterized by a trend toward more arid conditions. During the middle Holocene (8000–4000 cal yr B.P.), comparatively stable climatic conditions prevailed with increased aridity in the Coastal Range. The late Holocene (4000–0 cal yr B.P.) was marked by more variable paleoclimates with generally more humid conditions. Variations of rainfall in mid-latitude Chile are most likely controlled by shifts of the latitudinal position of the Southern Westerlies. Compared to the Holocene, the southern westerly wind belt was located significantly farther north during the last glacial maximum. Less important variations of the latitudinal position of the Southern Westerlies also occurred on shorter time scales.

Jérôme Chappellaz - One of the best experts on this subject based on the ideXlab platform.

  • Marine Isotope Stage (MIS) 8 millennial variability stratigraphically identical to MIS 3
    Paleoceanography, 2007
    Co-Authors: Mark Siddall, Thomas F. Stocker, Thomas Blunier, Renato Spahni, Jakob Schwander, Jean-marc Barnola, Jérôme Chappellaz
    Abstract:

    International audienceThe Marine Isotope Stage (MIS) 3 stratigraphy is highly robust and was reproduced during another period: MIS 8.6 global ice volume was similar during MIS 8.6 to MIS 3 (60 to 90 m sea level equivalent), but the Milankovitch insolation forcing was different, implying that Earth's predisposition to millennial internal variability is controlled by the configuration of the major ice sheets. The involvement of additional factors cannot be ruled out but by identifying several such periods using new deep ice cores from Dome Concordia and Dome Fuji (Antarctica) as well as the Marine Record we may isolate the factors predisposing Earth to these highly significant modes of climate variability

  • Marine Isotope Stage (MIS) 8 millennial variability stratigraphically identical to MIS 3
    Paleoceanography, 2007
    Co-Authors: Mark Siddall, Thomas Blunier, Renato Spahni, Jakob Schwander, Jean-marc Barnola, Thomas F. Stocker, Jérôme Chappellaz
    Abstract:

    The Marine Isotope Stage (MIS) 3 stratigraphy is highly robust and was reproduced during another period: MIS 8.6 global ice volume was similar during MIS 8.6 to MIS 3 (60 to 90 m sea level equivalent), but the Milankovitch insolation forcing was different, implying that Earth's predisposition to millennial internal variability is controlled by the configuration of the major ice sheets. The involvement of additional factors cannot be ruled out but by identifying several such periods using new deep ice cores from Dome Concordia and Dome Fuji (Antarctica) as well as the Marine Record we may isolate the factors predisposing Earth to these highly significant modes of climate variability.

Francisco J Jiménez-espejo - One of the best experts on this subject based on the ideXlab platform.

  • Radiogenic isotopes for deciphering terrigenous input provenance in the western Mediterranean
    Chemical Geology, 2015
    Co-Authors: Marta Rodrigo-gámiz, Francisca Martínez-ruiz, Massimo Chiaradia, Francisco J Jiménez-espejo, Daniel Ariztegui
    Abstract:

    Abstract Radiogenic isotopic signatures in Marine sediments can be used to trace terrigenous source areas and transport mechanisms, which are in turn related to climate variability. To date, most of the published studies using this approach have been focused on eastern Mediterranean sediments. In contrast, we study here the terrigenous input provenance in the westernmost Mediterranean (Alboran Sea basin) by using radiogenic isotope proxies and Nd model ages in a Marine Record spanning the last 20 ka. Nd, Sr and Pb isotopes, obtained from carbonate-free samples from the

  • Climate forcing and Neanderthal extinction in Southern Iberia: insights from a multiproxy Marine Record
    Quaternary Science Reviews, 2007
    Co-Authors: Francisco J Jiménez-espejo, Francisca Martínez-ruiz, Clive Finlayson, Adina Paytan, Tatsuhiko Sakamoto, Miguel Ortega-huertas, Geraldine Finlayson, Koichi Iijima, David Gallego-torres
    Abstract:

    6 figures, 1 tablePaleoclimate Records from the western Mediterranean have been used to further understand the role of climatic changes in the replacement of archaic human populations inhabiting South Iberia. Marine sediments from the Balearic basin (ODP Site 975) was analysed at high resolution to obtain both geochemical and mineralogical data. These data were compared with climate Records from nearby areas. Baexcces was used to characterize Marine productivity and then related to climatic variability. Since variations in productivity were the consequence of climatic oscillations, climate/productivity events have been established. Sedimentary regime, primary Marine productivity and oxygen conditions at the time of population replacement were reconstructed by means of a multiproxy approach. Climatic/oceanographic variations correlate well with Homo spatial and occupational patterns in Southern Iberia. It was found that low ventilation (U/Th), high river supply (Mg/Al), low aridity (Zr/Al) and low values of Baexcess coefficient of variation, may be linked with Neanderthal hospitable conditions. We attempt to support recent findings which claim that Neanderthals populations continued to inhabit southern Iberia between 30 and 28 ky cal BP and that this persistence was due to the specific characteristics of South Iberian climatic refugia. Comparisons of our data with other Marine and continental Records appear to indicate that conditions in South Iberia were highly inhospitable at 24 ky cal BP. Thus, it is proposed that the final disappearance of Neanderthals in this region could be linked with these extreme conditions.This work was financed by Projects REN2003-09130-CO2-01 and CGL2006-13327-C04-04 (MEC), project RNM 432 and Research Group RNM 179 (Junta de Andalucía). We also thank project CSD2006-00041 (TOPOIBERIA). We would like to thank the ODP Core Repository (Bremen, Germany) for their assistance with sampling, and the university of Bremen for the use of the XRF core scanner. Other geochemical analyses were performed at the “Centro de Instrumentación Científica” (University of Granada), the Department of Mineralogy and Petrology (University of Granada), and the Japan Agency for Marine–Earth and Science Technology (JAMSTEC) laboratories. Our thanks to E. Abarca, E. Holanda, J. Montes, C. Niembro and D. Ortega for their laboratory assistance. Dr. J.S. Carrion and one anonymous reviewer are greatly thanked for constructive comments and reviews. The authors also are grateful to P. González-Sampériz and A. Moreno for their stimulating suggestion. Thorough editing of the original English manuscript was done by M. Bettini.Peer reviewe