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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.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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    Early Holocene aeolian sediments in southwestern Crete−preliminary results (2021)
    Springer International Publishing
    Details
    Publication Date: 2023-09-13
    Description: The soilscapes along the southern and western coast of Crete (Greece) are dominated by coarse-grained reddish-brown slope sediments whose natural (pre-anthropogenic) configuration and properties are difficult to reconstruct due to the long history of intense land use. As a consequence, datable terrestrial sediment archives of pre-anthropogenic genesis are scarce. We present preliminary results of a study performed on an accumulation within an alluvial fan south of Stomio Bay in southwestern Crete. The studied profile is located in a small depression and is composed of a sequence of sandy to silty yellowish-brown calcareous sediments overlying coarse-grained slope sediments, including a fossil topsoil horizon. Based on macroscopic, micromorphological, geochemical, geophysical and mineralogical analysis, we interpret the fine-grained sediments to have a local aeolian origin. OSL dating indicates a final deposition phase during the early Holocene. Considering the scarcity of early Holocene terrestrial archives in Crete, the analysed profile provides valuable data for the reconstruction of landscape dynamics and paleoecological conditions as well as soil-sediment configurations during this time period. Additional research is needed to address the specific source area(s) as well as the ages of the deposition of slope sediments and formation of the fossil topsoil.
    Description: Freie Universität Berlin (1008)
    Keywords: ddc:551.3 ; Aeolian sediments ; Fossil soil ; Early Holocene ; Crete ; Eastern Mediterranean
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 3
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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
  • 4
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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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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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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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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Influence of seaway changes during the Pliocene on tropical Pacific climate in the Kiel climate model: mean state, annual cycle, ENSO, and their interactions (2017)
    Springer
    In:  Climate Dynamics, 48 (11-12). pp. 3725-3740.
    Details
    Publication Date: 2020-02-06
    Description: The El Niño/Southern Oscillation (ENSO) is the leading mode of tropical Pacific interannual variability in the present-day climate. Available proxy evidence suggests that ENSO also existed during past climates, for example during the Pliocene extending from about 5.3 million to about 2.6 million years BP. Here we investigate the influences of the Panama Seaway closing and Indonesian Passages narrowing, and also of atmospheric carbon dioxide (CO2) on the tropical Pacific mean climate and annual cycle, and their combined impact on ENSO during the Pliocene. To this end the Kiel Climate Model), a global climate model, is employed to study the influences of the changing geometry and CO2-concentration. We find that ENSO is sensitive to the closing of the Panama Seaway, with ENSO amplitude being reduced by about 15–20 %. The narrowing of the Indonesian Passages enhances ENSO strength but only by about 6 %. ENSO period changes are modest and the spectral ENSO peak stays rather broad. Annual cycle changes are more prominent. An intensification of the annual cycle by about 50 % is simulated in response to the closing of the Panama Seaway, which is largely attributed to the strengthening of meridional wind stress. In comparison to the closing of the Panama Seaway, the narrowing of the Indonesian Passages only drives relatively weak changes in the annual cycle. A robust relationship is found such that ENSO amplitude strengthens when the annual cycle amplitude weakens.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00382-016-3298-x
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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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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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Seychelles coral record of changes in sea surface temperature bimodality in the western Indian Ocean from the Mid-Holocene to the present (2014)
    Springer
    In:  Climate Dynamics, 43 (3-4). pp. 689-708.
    Details
    Publication Date: 2019-09-23
    Description: We report fossil coral records from the Seychelles comprising individual time slices of 14–20 sclerochronological years between 2 and 6.2 kyr BP to reconstruct changes in the seasonal cycle of western Indian Ocean sea surface temperature (SST) compared to the present (1990–2003). These reconstructions allowed us to link changes in the SST bimodality to orbital changes, which were causing a reorganization of the seasonal insolation pattern. Our results reveal the lowest seasonal SST range in the Mid-Holocene (6.2–5.2 kyr BP) and around 2 kyr BP, while the highest range is observed around 4.6 kyr BP and between 1990 and 2003. The season of maximum temperature shifts from austral spring (September to November) to austral autumn (March to May), following changes in seasonal insolation over the past 6 kyr. However, the changes in SST bimodality do not linearly follow the insolation seasonality. For example, the 5.2 and 6.2 kyr BP corals show only subtle SST differences in austral spring and autumn. We use paleoclimate simulations of a fully coupled atmosphere–ocean general circulation model to compare with proxy data for the Mid-Holocene around 6 kyr BP. The model results show that in the Mid-Holocene the austral winter and spring seasons in the western Indian Ocean were warmer while austral summer was cooler. This is qualitatively consistent with the coral data from 6.2 to 5.2 kyr BP, which shows a similar reduction in the seasonal amplitude compared to the present day. However, the pattern of the seasonal SST cycle in the model appears to follow the changes in insolation more directly than indicated by the corals. Our results highlight the importance of ocean–atmosphere interactions for Indian Ocean SST seasonality throughout the Holocene. In order to understand Holocene climate variability in the countries surrounding the Indian Ocean, we need a much more comprehensive analysis of seasonally resolved archives from the tropical Indian Ocean. Insolation data alone only provides an incomplete picture.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00382-014-2082-z
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Impact of ENSO on East Asian winter monsoon during interglacial periods: effect of orbital forcing (2017)
    Springer
    In:  Climate Dynamics, 49 (9-10). pp. 3209-3219.
    Details
    Publication Date: 2020-02-06
    Description: Orbital forcing influences climate phenomena by changing incoming solar radiation in season and latitude. Here, changes in the El Niño-Southern Oscillation (ENSO)’s impact on the East Asian winter monsoon (EAWM) due to orbital forcing, especially for three selected time periods in each of two interglacial periods, the Eemian (126, 122, 115 ka) and Holocene (9, 6, 0 ka), are investigated. There was a high negative correlation between ENSO and EAWM when the obliquity was low, the processional angle was large, and especially when accompanied by large eccentricity, which corresponds to a weaker monsoon period. The correlation was also high when ENSO variability was high, which interestingly corresponded to lower obliquity and higher-degree precession periods. Therefore, as both lower obliquity and higher-degree precession, such as during 115 ka and 0 ka, cause the EAWM to be weakened through higher winter insolation over Northern hemisphere, and the ENSO to be enhanced through an intensified zonal contrast of the equatorial sea surface temperature, the relationship between the ENSO and EAWM becomes tighter. The opposite case (i.e., during 126 and 9 ka) is also true dynamically. Furthermore, the sensitivity of boreal winter precipitation against sea surface temperature (SST) anomaly over the tropical Pacific, which depends on mean SST, was positively correlated to the strength of the ENSO-EAWM correlation, implying that the warmer mean ocean surface causes the strong response of atmosphere to change in the SST anomaly, thereby enhancing the impact of ENSO on EAWM. Warmer wintertime tropical SST is attributed to higher insolation over the tropics, especially during 115 and 0 ka, while cooler SSTs occurred during 126 and 9 ka.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00382-016-3506-8
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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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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    OceanRep: Article in a Scientific Journal - peer-reviewed
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