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  • 1
    Book
    Book
    Variable c:n ratios of particulate organic matter and their influence on the marine carbon cycle : = Variable C:N-Verhältnisse von partikulärem organischen Material und deren Einfluß auf den marinen Kohlenstoffhaushalt (2003)
    Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung
    Details Availability
    Keywords: Carbon cycle (Biogeochemistry) ; Marine organisms ; Chemical oceanography ; Dissertation ; Hochschulschrift ; Meer ; Partikulärer organischer Stoff ; Meereschemie ; Biogeochemie ; Meer ; Kohlenstoffhaushalt ; Stickstoffhaushalt ; Redfield-Verhältnis ; Meer ; Partikulärer organischer Stoff ; Meereschemie ; Biogeochemie ; Meer ; Kohlenstoffhaushalt ; Stickstoffhaushalt ; Redfield-Verhältnis ; Meer ; Kohlenstoffhaushalt ; Partikulärer organischer Stoff ; Kohlenstoff ; Stickstoff
    Type of Medium: Book
    Pages: VI, 98 S. , Ill., graph. Darst., Kt.
    Series Statement: Berichte zur Polar- und Meeresforschung 437
    URL: http://www.gbv.de/dms/goettingen/360784488.pdf
    URL: http://www.gbv.de/dms/goettingen/360784488.pdf
    URL: http://www.awi-bremerhaven.de/GEO/Publ/PhDs/BSchneider
    DDC: 577/.144
    RVK:
    RY 20075
    Language: English
    Note: Zsfassung in dt. Spr , Zugl.: Bremen, Univ., Diss., 2002
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  • 2
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    East–west contrast of Northeast Asian summer precipitation during the Holocene (2018)
    Elsevier
    In:  Global and Planetary Change, 170 . pp. 190-200.
    Details
    Publication Date: 2021-02-08
    Description: Highlights: • We compare proxy moisture records in Northeast Asia with the results from a transient simulation. • An east–west antiphasing of summer precipitation in Northeast Asia during the Holocene is found. • The East Asian summer monsoon circulation and mid-latitude westerlies caused the zonal precipitation contrast. Abstract: The East Asian summer monsoon (EASM) is a complex system that brings precipitation to East Asia showing considerable spatiotemporal variations. This study explored the zonal differences of summer precipitation in Northeast Asia at orbital timescales during the Holocene by comparing proxy records with simulation results. At orbital timescales, there was generally an east–west antiphasing of summer precipitation in Northeast Asia during the Holocene. Model–proxy comparison revealed that the driest interval occurred during the late Holocene in western Northeast Asia and during the early to middle Holocene in eastern Northeast Asia. Changes of summer precipitation in western Northeast Asia were mainly influenced by precession-driven EASM circulation. On the one hand, a weaker EASM circulation during the late Holocene weakened water vapor transport from the North Pacific Ocean to Northeast Asia, and on the other hand it was associated with anomalous downward motions in western Northeast Asia. Both factors were in favor of a reduction of summer precipitation in western Northeast Asia during the late Holocene. In contrast, anomalous downward motions prevailed in eastern Northeast Asia during the early to middle Holocene, which were probably related to stronger western Pacific subtropical high and weaker westerlies. The effect of the anomalous downward motions overwhelmed the enhanced water vapor transport, leading to a dry climate in this area from the early to middle Holocene. This study suggests that special care should be taken when discussing the meridional shift of the Holocene climatic optimum in the EASM region due to the zonal precipitation contrast.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.gloplacha.2018.08.018
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Millennial-scale fluctuations in Saharan dust supply across the decline of the African Humid Period (2017)
    Elsevier
    In:  Quaternary Science Reviews, 171 . pp. 119-135.
    Details
    Publication Date: 2020-02-06
    Description: The Sahara is the world's largest dust source with significant impacts on trans-Atlantic terrestrial and large-scale marine ecosystems. Contested views about a gradual or abrupt onset of Saharan aridity at the end of the African Humid Period dominate the current scientific debate about the Holocene Saharan desiccation. In this study, we present a 19.63 m sediment core sequence from Lake Sidi Ali (Middle Atlas, Morocco) at the North African desert margin. We reconstruct the interaction between Saharan dust supply and Western Mediterranean hydro-climatic variability during the last 12,000 yr based on analyses of lithogenic grain-sizes, XRF geochemistry and stable isotopes of ostracod shells. A robust chronological model based on AMS 14C dated pollen concentrates supports our multi-proxy study. At orbital-scale there is an overall increase in southern dust supply from the Early Holocene to the Late Holocene, but our Northern Saharan dust record indicates that a gradual Saharan desiccation was interrupted by multiple abrupt dust increases before the ‘southern dust mode‘ was finally established at 4.7 cal ka BP. The Sidi Ali record features millennial peaks in Saharan dust increase at about 11.1, 10.2, 9.4, 8.2, 7.3, 6.6, 6.0, and 5.0 cal ka BP. Early Holocene Saharan dust peaks coincide with Western Mediterranean winter rain minima and North Atlantic cooling events. In contrast, Late Holocene dust peaks correspond mostly with prevailing positive phases of the North Atlantic Oscillation. By comparing with other North African records, we suggest that increases in Northern Saharan dust supply do not solely indicate sub-regional to regional aridity in Mediterranean Northwest Africa but might reflect aridity at a trans-Saharan scale. In particular, our findings support major bimillennial phases of trans-Saharan aridity at 10.2, 8.2, 6.0 and 4.2 cal ka BP. These phases coincide with North Atlantic cooling and a weak African monsoon.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.quascirev.2017.07.010
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  • 4
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    Detecting the relationship between moisture changes in arid central Asia and East Asia during the Holocene by model-proxy comparison (2017)
    Elsevier
    In:  Quaternary Science Reviews, 176 . pp. 36-50.
    Details
    Publication Date: 2020-02-06
    Description: Identifying the relationships between moisture changes in arid central Asia and those in East Asia may help us understand the interplay between the westerlies and the Asian summer monsoon. We combined proxy moisture records with the results from a transient simulation forced by changes in orbital parameters to analyse their relationships during the Holocene (9.5–0 ka BP). The proxy records and simulation results generally agree with a relatively dry early Holocene, the wettest period in the middle Holocene, and a dry late Holocene in East Asia. These periods were not solely controlled by precession-driven East Asian summer monsoon variability, but were significantly influenced by precipitation during the other seasons and by evaporation. However, different proxy records show contrasting results for moisture changes in arid central Asia during the Holocene. To study this, we analysed the climatic signals of the competing proxy records by comparing these proxy records with simulation results. We found that speleothem δ18O was significantly influenced by water vapour sources and evaporation rather than by the amount of precipitation. Thus, the model data reveals a persistent wetting trend throughout the Holocene that was out-of-phase with the trend in East Asia. The wetting trend in arid central Asia was caused by precipitation that increased faster than evaporation during the Holocene. The enhanced water vapour input from South Asia and the Middle East was the main cause of the increase in precipitation in arid central Asia, which in turn gave rise to the intensification of evaporation.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1016/j.quascirev.2017.09.012
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  • 5
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    The spatial-temporal patterns of Asian summer monsoon precipitation in response to Holocene insolation change: a model-data synthesis (2014)
    Elsevier
    In:  Quaternary Science Reviews, 85 . pp. 47-62.
    Details
    Publication Date: 2019-09-23
    Description: Highlights: • Slice and transient simulations of Holocene climate change were performed. • Spatial–temporal patterns of Holocene Asian summer precipitation are investigated. • A tripole pattern of summer precipitation can be seen over monsoonal Asia. • Insolation change is a key factor for Holocene Asian summer monsoon change. • Internal feedbacks are important to Holocene Asian summer precipitation changes. Abstract: Paleoclimate proxy records of precipitation/effective moisture show spatial–temporal inhomogeneous over Asian monsoon and monsoon marginal regions during the Holocene. To investigate the spatial differences and diverging temporal evolution over monsoonal Asia and monsoon marginal regions, we conduct a series of numerical experiments with an atmosphere–ocean–sea ice coupled climate model, the Kiel Climate Model (KCM), for the period of Holocene from 9.5 ka BP to present (0 ka BP). The simulations include two time-slice equilibrium experiments for early Holocene (9.5 ka BP) and present-day (0 ka BP), respectively and one transient simulation (HT) using a scheme for model acceleration regarding to the Earth's orbitally driven insolation forcing for the whole period of Holocene (from 9.5 to 0 ka BP). The simulated summer precipitation in the equilibrium experiments shows a tripole pattern over monsoonal Asia as depicted by the first modes of empirical orthogonal function (EOF1) of H0K and H9K. The transient simulation HT exhibits a wave train pattern in the summer precipitation across the Asian monsoon region associated with a gradually decreased trend in the strength of Asian summer monsoon, as a result of the response of Asian summer monsoon system to the Holocene orbitally-forced insolation change. Both the synthesis of multi-proxy records and model experiments confirm the regional dissimilarity of the Holocene optimum precipitation/effective moisture over the East Asian summer monsoon region, monsoon marginal region, and the westerly-dominated areas, suggesting the complex response of the regional climate systems to Holocene insolation change in association with the internal feedbacks within climate system, such as the air-sea interactions associated with the El Nino/Southern Oscillation (ENSO) and shift of the Intertropical Convergence Zone (ITCZ) in the evolution of Asian summer monsoon during the Holocene.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.quascirev.2013.11.004
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  • 6
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    Pliocene aridification of Australia caused by tectonically induced weakening of the Indonesian throughflow (2011)
    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 309 (1-2). pp. 111-117.
    Details
    Publication Date: 2019-09-23
    Description: Tectonic changes of the Early to Mid-Pliocene largely modified the Indonesian Passages by constricting and uplifting the passages between today's New Guinea and Sulawesi. The associated changes in strength and water mass properties of the Indonesian throughflow (ITF) might have influenced the amount of heat transported from the Pacific to the Indian Ocean and thus contributed to Pliocene climate change of the Indo-Pacific. We study the climate response to changes in the geometry of the Indonesian Passages in an atmosphere–ocean general circulation model (AOGCM). We compare climate simulations with present-day topography and with a topography resembling the Early Pliocene situation in the Indo-Pacific, i.e. passages East of Sulawesi deepened and widened to the South. We find that transport through the Indonesian Archipelago is weakened in the constricted passage by 1.7 Sv and in the unchanged Makassar Strait West of Sulawesi by 3.5 Sv, while transport weighted temperature of the outflow into the Indian Ocean increases by 1 °C. Consistent with recent proxy evidence the reduction in ITF transport causes a decrease in subsurface temperatures in the Indian Ocean while surface waters of the equatorial Pacific exhibit an increase by up to 0.9 °C centred in the warm pool. As a local response to the sea surface temperature anomalies, we observe an anomalous precipitation dipole across the Indonesian passages with increased rainfall over the Pacific warm pool and decreased precipitation in the eastern Indian Ocean. The Australian continent experiences a pronounced aridification with mean annual precipitation rates dropping by 30% over most parts of the continent. Using an uncoupled vegetation model, we demonstrate that the simulated climate change might partly explain the observed Late Pliocene desertification of Australia.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.palaeo.2011.06.002
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  • 7
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    Changes in equatorial Pacific thermocline depth in response to Panamanian seaway closure: Insights from a multi-model study (2012)
    Elsevier
    In:  Earth and Planetary Science Letters, 317-318 . pp. 76-84.
    Details
    Publication Date: 2019-09-23
    Description: The early Pliocene warm phase was characterized by high sea surface temperatures and a deep thermocline in the eastern equatorial Pacific. A new hypothesis suggests that the progressive closure of the Panamanian seaway contributed substantially to the termination of this zonally symmetric state in the equatorial Pacific. According to this hypothesis, intensification of the Atlantic meridional overturning circulation (AMOC) – induced by the closure of the gateway – was the principal cause of equatorial Pacific thermocline shoaling during the Pliocene. In this study, twelve Panama seaway sensitivity experiments from eight ocean/climate models of different complexity are analyzed to examine the effect of an open gateway on AMOC strength and thermocline depth. All models show an eastward Panamanian net throughflow, leading to a reduction in AMOC strength compared to the corresponding closed-Panama case. In those models that do not include a dynamic atmosphere, deepening of the equatorial Pacific thermocline appears to scale almost linearly with the throughflow-induced reduction in AMOC strength. Models with dynamic atmosphere do not follow this simple relation. There are indications that in four out of five models equatorial wind-stress anomalies amplify the tropical Pacific thermocline deepening. In summary, the models provide strong support for the hypothesized relationship between Panama closure and equatorial Pacific thermocline shoaling. Highlights: ► We study the effect of the Panama seaway on Pacific equatorial thermocline depth. ► Results from twelve model experiments are examined. ► Eastward net throughflow leads to a reduction in Atlantic overturning. ► We find a relationship between Panama closure and Pacific thermocline depth.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.epsl.2011.11.028
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  • 8
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    Holocene thermokarst dynamics in Central Yakutia – A multi-core and robust grain-size endmember modeling approach (2019)
    Elsevier
    In:  EPIC3Quaternary Science Reviews, Elsevier, 218, pp. 10-33, ISSN: 0277-3791
    Details
    Publication Date: 2022-07-04
    Description: Differentiating thermokarst basin sediments with respect to the involved processes and environmental conditions is an important tool to understand permafrost landscape dynamics and scenarios and future trajectories in a warming Arctic and Subarctic. Thermokarst basin deposits have complex sedimentary structures due to the variability of Yedoma source sediments, reworking during the Late Glacial to Holocene climate changes, and different stages of thermokarst history. Here we reconstruct the dynamic growth of thermokarst lakes and basins and related changes of depositional conditions preserved in sediment sequences using a combination of biogeochemical data and robust grain-size endmember analysis (rEMMA). This multi-proxy approach is used on 10 sediment cores (each 300–400 cm deep) from two key thermokarst sites to distinguish four time slices that describe the Holocene thermokarst (lake) basin evolution in Central Yakutia (CY). Biogeochemical proxies and rEMMA reveal fine-grained sedimentation with rather high lake levels and/or reducing conditions, and coarse-grained sedimentation with rather shallow lake levels and/or oxidizing (i.e. terrestrial) conditions in relation to distal and proximal depositional and post-sedimentary conditions. Statistical analysis suggests that the biogeochemical parameters are almost independent of thermokarst deposit sedimentology. Thus, the biogeochemical parameters are considered as signals of secondary (post-sedimentary) reworking. The rEMMA results are clearly reflecting grain-size variations and depositional conditions. This indicates small-scale varying depositional environments, frequently changing lake levels, and predominantly lateral expansion at the edges of rapidly growing small thermokarst lakes and basins. These small bodies finally coalesced, forming the large thermokarst basins we see today in CY. Considering previous paleoenvironmental reconstructions in Siberia, we show the initiation of thaw and subsidence during the Late Glacial to Holocene transition between about 11 and 9 cal kyrs BP, intensive and extensive thermokarst activity for the Holocene Thermal Maximum (HTM) at about 7 to 5 cal kyrs BP, severely fluctuating water levels and further lateral basin growth between 3.5 cal kyrs BP and 1.5 cal kyrs BP, and the cessation of thermokarst activity and extensive frost-induced processes (i.e. permafrost aggradation) after about 1.5 cal kyrs BP. However, gradual permafrost warming over recent decades, in addition to human impacts, has led to renewed high rates of subsidence and abrupt, rapid CY thermokarst processes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Format: application/pdf
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