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  • 2020-2024
  • 2015-2019  (36)
  • 2019  (36)
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  • 2020-2024
  • 2015-2019  (36)
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  • 1
    Keywords: Forschungsbericht
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (12 Seiten, 1,48 MB) , Illustrationen
    Language: German
    Note: Förderkennzeichen BMBF 03G0256A , Unterschiede zwischen dem gedruckten Dokument und der elektronischen Ressource können nicht ausgeschlossen werden
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  • 2
    Publication Date: 2019-04-02
    Description: oraminifera are commonly used in paleoclimate reconstructions as they occur throughout the world's oceans and are often abundantly preserved in the sediments. Traditionally, foraminifera‐based proxies like δ18O and Mg/Ca are analyzed on pooled specimens of a single species. Analysis of single specimens of foraminifera allows reconstructing climate variability on timescales related to El Niño‐Southern Oscillation (ENSO) or seasonality. However, quantitative calibrations between the statistics of individual foraminiferal analyses (IFA) and climate variability are still missing. We performed Mg/Ca and δ18O measurements on single specimens from core‐top sediments from different settings to better understand the signal recorded by individual foraminifera. We used three species of planktic foraminifera (G. ruber (s.s.), T. sacculifer, and N. dutertrei) from the Indo‐Pacific Warm Pool (IPWP) and one species (G. ruber (pink)) from the Gulf of Mexico (GoM). Mean values for the different species of Mg/Ca vs calculated δ18O temperatures agree with published calibration equations. IFA statistics (both mean and standard deviation) of Mg/Ca and δ18O between the different sites show a strong relationship indicating that both proxies are influenced by a common factor, most likely temperature variations during calcification. This strongly supports the use of IFA to reconstruct climate variability. However, our combined IFA data for the different species only show a weak relationship to seasonal and interannual temperature changes, especially when seasonal variability increases at a location. This suggests that the season and depth habitat of the foraminifera strongly affect IFA variability, such that ecology needs to be considered when reconstructing past climate variability.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
    Format: application/pdf
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  • 3
    Publication Date: 2020-09-06
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev , info:eu-repo/semantics/conferenceObject
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  • 4
    Publication Date: 2020-09-06
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev , info:eu-repo/semantics/conferenceObject
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  • 5
    Publication Date: 2023-03-31
    Description: Coeval changes in atmospheric CO2 and 14C contents during the last deglaciation are often attributed to ocean circulation changes that released carbon stored in the deep ocean during the Last Glacial Maximum (LGM). Work is being done to generate records that allow for the identification of the exact mechanisms leading to the accumulation and release of carbon from the oceanic reservoir, but these mechanisms are still the subject of debate. Here we present foraminifera 14C data from five cores in a transect across the Chilean continental margin between ~540 and ~3,100 m depth spanning the last 20,000 years. Our data reveal that during the LGM, waters at ~2,000 m were 50% to 80% more depleted in Δ14C than waters at ~1,500 m when compared to modern values, consistent with the hypothesis of a glacial deep ocean carbon reservoir that was isolated from the atmosphere. During the deglaciation, our intermediate water records reveal homogenization in the Δ14C values between ~800 and ~1,500 m from ~16.5–14.5 ka cal BP to ~14–12 ka cal BP, which we interpret as deeper penetration of Antarctic Intermediate Water. While many questions still remain, this process could aid the ventilation of the deep ocean at the beginning of the deglaciation, contributing to the observed ~40 ppm rise in atmospheric pCO2.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
    Format: application/pdf
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  • 6
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    PANGAEA
    In:  Supplement to: Martínez Fontaine, Consuelo; De Pol-Holz, Ricardo; Michel, Elisabeth; Siani, Giuseppe; Reyes-Macaya, Dharma; Martínez Méndez, Gema; DeVries, Tim; Stott, Lowell D; Southon, John; Mohtadi, Mahyar; Hebbeln, Dierk (2019): Ventilation of the deep ocean carbon reservoir during the last deglaciation: results from the southeast pacific. Paleoceanography and Paleoclimatology, 34(12), 2080-2097, https://doi.org/10.1029/2019PA003613
    Publication Date: 2023-03-03
    Description: Supplementary material for Martínez Fontaine et al., 2019 (Table S1), including the radiocarbon ages in benthonic and planktonic foraminifera in six cores in the Chilean margin, beetween ~31°S and ~36°S (Table S3). The age models for the cores are detailed in Martínez Fontaine et al., 2019 and were produced using the information on planktonic δ13C (Table S2). Also included are the Δ14C resulting from the age models.
    Keywords: Center for Marine Environmental Sciences; Deglaciation; MARUM; radiocarbon; Southeast Pacific
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 7
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    PANGAEA
    In:  Supplement to: Cheng, Zhongjing; Weng, Chengyu; Steinke, Stephan; Mohtadi, Mahyar (2018): Anthropogenic modification of vegetated landscapes in southern China from 6,000 years ago. Nature Geoscience, 11, 939-943, https://doi.org/10.1038/s41561-018-0250-1
    Publication Date: 2023-03-03
    Description: Vegetation dynamics during previous warm interglacial periods shed light on the human impacts on natural ecosystems during the Holocene. However, reliable terrestrial records that span such periods are rare and provide little information on regional scale. Here we present a high-resolution marine pollen record from the northern South China Sea, which reveals that during five peak interglacial periods, Marine Isotope Stages 13a, 11c, 9c, 5e and 1 (the Holocene), the vegetation successions in southern China were similar. At the beginning of each interglacial period, tropical rainforest conifers, which include Dacrydium, Dacrycarpus and Podocarpus, and associated broadleaved taxa, such as Altingia, expanded quickly at the expense of the subtropical/temperate montane conifer Pinus. Near the end of the warm periods, Pinus recovered and the tropical taxa retreated. However, the Holocene displays subtle but significant differences in which the species turnover was interrupted and the rainforest conifers did not fully expanded. The Mg/Ca-based sea surface temperature record from the same site reveals that temperature was the major control of the rise and fall of the peak interglacial vegetation. However, exceptionally high charcoal fluxes during the Holocene suggest that human activities through land-use modifications completely, and possibly permanently, altered the natural vegetation trend five to six thousand years ago.
    Keywords: Center for Marine Environmental Sciences; MARUM
    Type: Dataset
    Format: application/zip, 5 datasets
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  • 8
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    PANGAEA
    In:  Supplement to: Contreras-Rosales, Lorena Astrid; Jennerjahn, Tim C; Steinke, Stephan; Mohtadi, Mahyar; Schefuß, Enno (2019): Holocene changes in biome size and tropical cyclone activity around the Northern South China Sea. Quaternary Science Reviews, 215, 45-63, https://doi.org/10.1016/j.quascirev.2019.05.004
    Publication Date: 2023-03-03
    Description: The South China Sea (SCS), characterized by a large continental shelf, is located at the edge of the Asian monsoon domain. In this study, two marine sediment cores from the northern SCS (NSCS) continental slope were investigated to construct composite vegetation and precipitation isotopic composition records based on the δ13C and δD values of plant-wax n-alkanes throughout the Holocene (last 11,200 years; i.e. 11.2 ka). The composite δ13Cwax record indicates an overall predominance of C3 vegetation over the last 11.2 ka. Before 8 ka BP, higher δ13Cwax values are attributed to preferential wax input from grassland and wetland biomes on the exposed continental shelf. After the inundation of the shelf by eustatic sea level rise until ca. 8 ka BP grassland and wetland biomes suffered a major size reduction and arboreal vegetation became better represented in the δ13Cwax record. The composite temperature corrected δDwax-T record suggests that moisture source variability drove precipitation isotopic composition changes during the Holocene. Lower δDwax-T values before 8.3 ka BP are interpreted as a larger moisture contribution by Pacific Ocean tropical cyclones, whereas higher δDwax-T values after 8.5 ka BP are interpreted as a larger moisture contribution from the Indian Ocean summer monsoon. Higher incidence of tropical cyclones in the NSCS during the Early Holocene was related to a temporary westward shift of the Western Pacific Warm Pool and enhanced insolation over the Northern Hemisphere. Both external and internal forcing mechanisms regulated moisture source changes in East Asia during the Holocene.
    Keywords: Center for Marine Environmental Sciences; Leibniz Centre for Tropical Marine Research; MARUM; ZMT
    Type: Dataset
    Format: application/zip, 5 datasets
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  • 9
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    PANGAEA
    In:  Supplement to: Hollstein, Martina; Mohtadi, Mahyar; Rosenthal, Yair; Prange, Matthias; Oppo, Delia W; Martínez Méndez, Gema; Tachikawa, Kazuyo; Moffa-Sanchez, Paola; Steinke, Stephan; Hebbeln, Dierk (2018): Variations in Western Pacific Warm Pool surface and thermocline conditions over the past 110,000 years: Forcing mechanisms and implications for the glacial Walker circulation. Quaternary Science Reviews, 201, 429-445, https://doi.org/10.1016/j.quascirev.2018.10.030
    Publication Date: 2023-03-03
    Description: Surface and thermocline conditions of the Western Pacific Warm Pool (WPWP) reflect changes in regional and basin scale ocean and atmosphere circulations and in turn may affect climate globally. Previous studies suggest that a range of factors influences the WPWP on different timescales, however the precise forcings and mechanisms are unclear. Combining surface and thermocline records from sediment cores offshore Papua New Guinea we explore the influence of local and remote processes on the WPWP in response to astronomical forcing and changing glacial-interglacial boundary conditions over the past 110 kyr. We find that thermocline temperatures change with variations in Earth's obliquity with higher temperatures coinciding with high obliquity, which is attributed to variations in subduction and advection of the South Pacific Tropical Water. In contrast, rainfall variations associated with meridional migrations of the Intertropical Convergence Zone are primarily driven by changes in insolation due to precession. Records of bulk sedimentary Ti/Ca and foraminiferal Nd/Ca indicate an additional influence of obliquity, which, however, cannot unambiguously be related to changes in precipitation. Finally, our results suggest a thermocline deepening during the Last Glacial Maximum (LGM). A compilation of available proxy records illustrates a dipole-like pattern of LGM thermocline depth anomalies with a shoaling (deepening) in the northern (southern) WPWP. A comparison of the proxy compilation with an ensemble of Paleoclimate Model Intercomparison Project (PMIP) climate model simulations reveals that the spatial pattern of LGM thermocline depth anomalies is mainly attributable to a contraction of the Pacific Walker circulation on its western side.
    Keywords: Center for Marine Environmental Sciences; MARUM
    Type: Dataset
    Format: application/zip, 4 datasets
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  • 10
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    PANGAEA
    In:  Supplement to: Moffa-Sanchez, Paola; Rosenthal, Yair; Babila, Tali L; Mohtadi, Mahyar; Zhang, Xu (2019): Temperature Evolution of the Indo‐Pacific Warm Pool Over the Holocene and the Last Deglaciation. Paleoceanography and Paleoclimatology, 34(7), 1107-1123, https://doi.org/10.1029/2018PA003455
    Publication Date: 2023-01-30
    Description: The Indo-Pacific Warm Pool (IPWP) contains the warmest surface ocean waters on our planet. Changes in the extent and position of the IPWP likely impacted the tropical and global climate in the past. To put recent ocean changes into a longer temporal context, we present new paleoceanographic sea surface temperature reconstructions from off Papua New Guinea (RR1313-23PC: 4.4939°S, 145.6703°E, 712 m water depth) which is at the heart of the Western Pacific Warm Pool (WPWP), which is the warmest region within the IPWP, across the last 17,000 years. A new surface temperature dataset from the northeast South China Sea is also presented (ODP1144: 20.053°N, 117.4189°E; water depth 2037 m). In both locations we use Mg/Ca measurements on G.ruber s.s. (white) to calculate sea surface temperatures.
    Keywords: G.ruber; Holocene; Mg/Ca; Western Pacific
    Type: Dataset
    Format: application/zip, 3 datasets
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