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  • 1
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    High-resolution chemostratigraphic record of late Pleistocene lake-level variability, Mono Lake, California (2011)
    Geological Society of America (GSA)
    Details
    Publication Date: 2011-11-01
    Description: The study of abrupt changes in global climate requires high-resolution records for which the connection to the climate system is well understood. Because lake systems are by their nature unique, ground truthing of geochemical measurements against directly observable physical evidence is required. The Mono Lake basin exposes multiple outcrops of lake sediments deposited during the last glacial period, providing the opportunity to reconstruct lake-level changes through stratigraphy-based interpretation of high-resolution records. Here we present a record of bulk-sediment carbonate derived from overlapping sections in three outcrops around the Mono Lake basin. We interpret this record as a reflection of lake-level variation, based on well-exposed stratigraphy and sedimentary facies changes. The co-variation of lake level with Sr isotopes measured in ostracodes is interpreted to reflect increased proportion of water supplied from the eastern basin during wet times. This high carbonate-high lake-level relationship is the opposite of the high carbonate-low lake-level relationship inferred in nearby Owens Lake, a difference attributable to extreme differences in basin geometry affecting the frequency of spilling conditions and resultant lake chemistry.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 2
    Electronic Resource
    Electronic Resource
    Reduced North Atlantic Deep Water flux to the glacial Southern Ocean inferred from neodymium isotope ratios (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 405 (2000), S. 935-938 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The global circulation of the oceans and the atmosphere transports heat around the Earth. Broecker and Denton suggested that changes in the global ocean circulation might have triggered or enhanced the glacial–interglacial cycles. But proxy data for past circulation taken from ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35016049
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  • 3
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    Deep water variability on the Southern Agulhas Plateau over the past 1.5 Ma (2018)
    In:  EPIC3AGU Fall Meeting, Washington, D.C., U.S.A., 2018-12-10-2018-12-14
    Details
    Publication Date: 2018-12-21
    Description: An important element of the global ocean thermohaline circulation is the oceanic connection between the Indian and South Atlantic Oceans off South Africa. Variable amounts of warm, salt-enriched South Indian Ocean waters enter the South Atlantic, the so-called ‘warm water return route’, and provide a source for heat and salt to the Atlantic thermocline that ultimately preconditions the Atlantic meridional overturning circulation for convection in the north, the formation of North Atlantic Deep Water (NADW). This eastward surface return flow is compensated at depth by a westward setting deep flow into the southern Indian Ocean that consists of NADW exiting the South Atlantic and Southern Source Waters (SSW), influenced by the Antarctic Circumpolar Current (ACC). Here we present a high-resolution multi-proxy record of deep water variability from sediment core MD02-2588 (2907 m water depth) and IODP Site U1475 (2669 m water depth) both recovered from the southern flank of the Agulhas Plateau in the southernmost South Atlantic. The location is close to the interface between NADW and SSW in the Southern Ocean enabling the reconstruction of the timing and amplitude of changes in southward advection of NADW and Southern Ocean circulation. We concentrate on identifying the phasing between changes in ice volume, the location of surface ocean fronts, deep ventilation and near-bottom flow speeds over the past 1.5 Ma – across the Middle Pleistocene transition. Our benthic carbon isotope record from MD02-2588/Site U1475 strongly suggest that there was a continued mid-depth northern source water influence over the southern Agulhas Plateau during glacial periods of the past 1.5 Ma. Nonetheless, significantly increased near bottom flow speeds, ~5–10 cm s−1 (3–7 μm coarser), during glacial periods indicates that there must be additional controls on physical ventilation. We suggest that vigor of near bottom currents on the Southern Agulhas Plateau is likely influenced by the orbital scale meridional expansion and contraction of the ACC and its associated surface fronts.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 4
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    XRF core-scanning signal interpretation in Miocene carbonate and siliciclastic contourite deposits (IODP sites U1387 and U1475) (2017)
    In:  EPIC3XRF Core Scanning 2017, National Taiwan University, Taiwan, 2017-03-20-2017-03-24
    Details
    Publication Date: 2017-03-31
    Description: Contourites are deposits formed by along-slope bottom currents and are therefore sensitive to changes in current velocity, sediments supply and paleoceanographic conditions. They are typically associated with high accumulation rates making these archives ideal for paleoenviromental reconstructions. Nevertheless, they are also occasionally affected by winnowing of fine particles and erosion/deposition of allochthonous material, which alters the grain-size and mineralogy. These processes can, as such, promote significant bias in proxy interpretation compared with other pelagic deposits. X-ray fluorescence (XRF) core-scanning is ideal to assess elemental variations in these high accumulation rate sequences. The comparison between lithological changes, Natural Gamma Ray and other parameters with XRF scanning data, along with statistical analysis can provide very useful information to support improved proxy interpretation. Using this approach at Site U1387, (detrital contourite system at Gulf of Cadiz), results indicate that the Zr/Al ratio represents a promising proxy for bottom current speed and show the transition from a hemipelagic to a contouritic system during the Miocene/Pliocene transition. Carbonate content and Ba/Al ratio appear to represent paleo-productivity variations and later to be completely overprinted by current activit y. At Site U1475 (carbonate contourite system at Agulhas Plateau) Zr content is just one artifact associated with high Sr content and the Ca/Sr ratio appears to be a more promising proxy for contourite reconstruction that is influenced by carbonate dissolution by deep corrosive waters. Comparing both locations we can conclude that proxies associated with the continuous background sediment settling over the seafloor (e.g. planktonic foraminifera) do not appear to be severely biased in countourite systems.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 5
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    Glacial-interglacial cycles in detrital sediment supply to the Amundsen Sea: Implications for West Antarctic Ice Sheet dynamics during the Late Pleistocene (2017)
    AGU, abstract #C21E-1161
    In:  EPIC3American Geophysical Union, Fall Meeting 2017, New Orleans, 2017-12-11-2017-12-15AGU, abstract #C21E-1161
    Details
    Publication Date: 2018-08-10
    Description: The West Antarctic Ice Sheet (WAIS) plays a key role in the global climate system and its collapse could contribute up to 4.3 m of sea-level rise. Mass loss of this marine-based ice sheet is largely caused by ocean-driven melting of ice shelves. This is confimed by modern observational data which show significant glacier thinning and retreat of grounding lines, particularly in the Amundsen Sea area. We here apply an integrated approach to determine provenance of marine sediments, which enables us to trace erosion of different bedrock lithologies, ultimately tied to the location of the eroding ice through time. We present provenance analysis on detrital Holocene seafloor sediments from the Amundsen Sea Embayment as well as from two marine cores PS58/254 (69°19´S, 108°27´W) and PC493 (71°09´S, 119°57´W), located on the continental rise of the Amundsen Sea and covering glacial-interglacial cycles of the past 800 kyrs. We use strontium (Sr) and neodymium (Nd) isotopic compositions of fine terrigenous grains (〈63μm), and 40Ar/39Ar ages on ice-rafted (〉150μm) hornblende and biotite grains. Our Holocene mapping results reveal drainage pathways with distinct signatures in the eastern and western Amundsen Sea Embayment. The western embayment records a homogenous provenance signature, pointing to a local source area in the hinterland, while the eastern embayment shows a range of compositions indicating erosion of the eastern coastal margin and a distinct, but unexposed source lithology under Pine Island Glacier and/or its drainage basin. Systematic isotope variations are detected between glacial and interglacial stages in both downcore records. Core PS58/254 exhibits a radiogenic fingerprint throughout the Late Pleistocene and systematic glacial-interglacial fluctuations in the order of three εNd units. They correlate with physical properties of the sediments (i.e. magnetic susceptibility) and trend towards lower values during interglacials, notably during Marine Isotope Stage (MIS) 5 and MIS 7. Core PC493 exhibits similar radiogenic Nd isotope composition, but a slightly reduced magnitude of glacial-interglacial changes. Detailed analysis of our results will offer a framework for interpreting sediment records from the area, including those from a recent MeBo expedition (PS104) and upcoming IODP expedition 379.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 6
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    GEOTRACES intercalibration of neodymium isotopes and rare earth element concentrations in seawater and suspended particles. Part 1: reproducibility of results for the international intercomparison (2012)
    In:  EPIC3Limnology and Oceanography: Methods, 10(4), pp. 234-251, ISSN: 15415856
    Details
    Publication Date: 2018-03-12
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    The Pliocene sedimentary record offshore the Amundsen Sea, West Antarctica: initial results from IODP Expedition 379 (2020)
    In:  EPIC3AGU Fall Meeting, online, 2020-12-01-2020-12-17
    Details
    Publication Date: 2020-12-20
    Description: How greenhouse forcing affects ice sheets and sea level during peak interglacial times is an unresolved question of great societal importance. Here we examine the development of glacial-interglacial sequence motifs in drill cores from the Pacific margin of Antarctica and explore how the West Antarctic Ice Sheet impacted sedimentary systems under different climate states, including during the Pliocene Climatic Optimum (PCO) ~4.5-4.0 Ma. Hundreds of meters of Pliocene sediments were recovered during IODP Expedition 379 in two drill sites within the Resolution Drift. Site U1533 was positioned near a submarine channel originating from the Amundsen Sea continental slope, and Site U1532 was located on the western upper flank of the hemipelagic drift. Abundance and type of sediment transport structures in the cores change gradually in lower Pliocene strata in both drill sites in concert with changes in sedimentation rate. Pliocene strata are characterized with a repetitive facies stacking pattern composed of greenish gray clast-bearing mud with a biosiliceous component, interbedded with dark brownish gray laminated silty clay. The greenish gray clast-bearing muds are tentatively interpreted as “interglacials”, however, many greenish grey units have sharp upward transitions into “glacial” laminated mud and the units are irregularly spaced with depth. Analysis of the red-green channel (a*) in shipboard reflectance spectroscopy and colorimetry (RSC) data for Site U1532 on the shipboard age model demonstrates the variable orbital cyclicity of the facies assemblage. Sequence motifs, which are further explored in half-core magnetic susceptibility and XRF core-scanner data, highlight how ice growth and decay, downslope sediment transport, and the position and intensity of ocean currents affected the depositional systems. The ultimate goal of this work is to combine facies interpretations with the detrital sedimentology and other data sets to assess the behavior of the West Antarctic Ice Sheet in a warmer than present climate scenario.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 8
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    Antarctic icebergs reorganize ocean circulation during Pleistocene glacials (2021)
    Nature Publishing Group
    In:  EPIC3Nature, Nature Publishing Group, 589(7841), pp. 236-241, ISSN: 0028-0836
    Details
    Publication Date: 2021-02-03
    Description: The dominant feature of large-scale mass transfer in the modern ocean is the Atlantic meridional overturning circulation (AMOC). The geometry and vigour of this circulation influences global climate on various timescales. Palaeoceanographic evidence suggests that during glacial periods of the past 1.5 million years the AMOC had markedly different features from today; in the Atlantic basin, deep waters of Southern Ocean origin increased in volume while above them the core of the North Atlantic Deep Water (NADW) shoaled. An absence of evidence on the origin of this phenomenon means that the sequence of events leading to global glacial conditions remains unclear. Here we present multi-proxy evidence showing that northward shifts in Antarctic iceberg melt in the Indian–Atlantic Southern Ocean (0–50°E) systematically preceded deep-water mass reorganizations by one to two thousand years during Pleistocene-era glaciations. With the aid of iceberg-trajectory model experiments, we demonstrate that such a shift in iceberg trajectories during glacial periods can result in a considerable redistribution of freshwater in the Southern Ocean. We suggest that this, in concert with increased sea-ice cover, enabled positive buoyancy anomalies to ‘escape’ into the upper limb of the AMOC, providing a teleconnection between surface Southern Ocean conditions and the formation of NADW. The magnitude and pacing of this mechanism evolved substantially across the mid-Pleistocene transition, and the coeval increase in magnitude of the ‘southern escape’ and deep circulation perturbations implicate this mechanism as a key feedback in the transition to the ‘100-kyr world’, in which glacial–interglacial cycles occur at roughly 100,000-year periods.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 9
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    New Magnetostratigraphic Insights From Iceberg Alley on the Rhythms of Antarctic Climate During the Plio-Pleistocene (2021)
    Wiley
    In:  EPIC3Paleoceanography and Paleoclimatology, Wiley, 36(2), pp. 1-27, ISSN: 0883-8305
    Details
    Publication Date: 2021-02-25
    Description: International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ18O during the 41‐kyr world.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 10
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    A Plio-Pleistocene (c. 0–4 Ma) cyclostratigraphy for IODP Site U1478 (Mozambique Channel, SW Indian Ocean): Exploring an offshore record of paleoclimate and ecosystem variability in SE Africa (2021)
    In:  EPIC3Newsletters on Stratigraphy, 54(2), pp. 159-181, ISSN: 0078-0421
    Details
    Publication Date: 2021-05-07
    Description: The paleoclimate and ecosystem variability in Africa during the Plio/Pleistocene has received considerable attention due to its potential links to hominid evolution. However, the reconstruction of this variability hinges critically upon highly temporally resolved proxy data from continuous, well-dated sediment archives. In light of these requirements we use a new XRF core-scanning record from International Ocean Discovery Program (IODP) Site U1478 off the Limpopo River mouth (Mozambique Channel, SW Indian Ocean) spanning the past c. 4 Ma to identify the climate variability in SE Africa. Our results show that the elemental distribution in the Site U1478 cores is mainly controlled by the rate of terrigenous input and – to a lesser extent – by bottom-current transport and post-depositional processes such as propagation of paleoredox boundaries and diagenesis across some intervals. The log(Ti/Ca) ratio, which is used as a tracer of terrigenous sediment input, shows quasi-cyclical variability across the entire record that closely matches the periods of orbital parameters. However, the cyclical behaviour of the log(Ti/Ca) signal varies through time, with the uppermost 106 m of the sequence (0–1.07 Ma) displaying a mix of precession and obliquity signals, the intervals 106–223 m (1.07–2.80 Ma) and 240–257 m (3.68–4.05 Ma) being dominated by precession, and the interval 223–240 m (2.80–3.68 Ma) being controlled by eccentricity. To refine the available chronology for Site U1478, which is based on shipboard biostratigraphic and paleomagnetic data, we have tuned the log(Ti/Ca) record to the LR04 benthic oxygen isotope record, summer insolation at 25° S, and orbital eccentricity depending on the dominant cyclicities in the XRF dataset across individual time intervals. The resulting chronology enables us to evaluate the XRF data as well as the previously available shipboard sedimentological and geochemical datasets within a regional and global climatic context. This allows the connection of a c. 7-m-thick contourite deposit and a prominent paleoredox boundary to hydroclimate and ocean-circulation changes during the early Pleistocene and across the Mid-Pleistocene Transition, respectively. Moreover, a decoupling of the log(Ti/Ca) and the log(Ti/K) records, with the latter indicating the degree of sediment weathering, from 3.2 to 2.8 Ma points to an increased delivery of highly weathered sediments to Site U1478. We attribute this to temporarily wetter and warmer conditions in the catchment of the Limpopo River and/or a change in the sediment source, perhaps associated with the tectonically driven enlargement of the Zambezi River catchment during the late Pliocene/early Pleistocene.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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