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Palaeogeography, Palaeoclimatology, Palaeoecology
Elsevier
Palaeogeography, Palaeoclimatology, Palaeoecology

Elsevier

0031-0182

Palaeogeography, Palaeoclimatology, Palaeoecology/Journal Palaeogeography, Palaeoclimatology, Palaeoecology
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    A quantitative reconstruction of Holocene annual precipitation in the marginal zone of the East Asian summer monsoon

    Lu, HuayuWang, YuchenHan, ZhiyongZhou, Yuwen...
    12页
    查看更多>>摘要：There is great controversy regarding variations in the East Asian summer monsoon (EASM) during the Holocene. Simulations and modern observations have revealed that a strengthened EASM results in more precipitation in the monsoon marginal zone. Therefore, quantitative reconstruction of precipitation in this region is the key to revealing monsoon variability. Here, two closed-basin lakes, namely, Angulinao Lake and Dali Lake, with similar weather conditions on the southeastern margin of the Mongolian Plateau are studied. The Angulinao paleolake level is established by optically stimulated luminescence (OSL) dating of 17 beach ridges. The annual precipitation (AP) is calculated for Angulinao and Dali Lakes using a hydrological and energy balance model. A composite precipitation curve is obtained, which shows that the AP increased with time during the early Holocene, reached its maximum 9.2 ka, was generally high in the middle Holocene with two events of decreasing AP 7.7 ka and 5.2 ka, and decreased abruptly beginning 4.4-4.2 ka, followed by a continuous reduction to the lowest level observed at present. These results suggest that the oxygen isotopes of speleothems are proxies for EASM (circulation) intensity, the simulated AP does not underestimate the Holocene peak precipitation, and the pollen-based AP in neighboring lakes underestimates the early Holocene precipitation and fails to capture the precipitation peak 9.2 ka.
      原文链接:
    • NSTL
    • Elsevier

    Spatially calibrating polycyclic aromatic hydrocarbons (PAHs) as proxies of area burned by vegetation fires: Insights from comparisons of historical data and sedimentary PAH fluxes

    Vachula, Richard S.Karp, Allison T.Denis, Elizabeth H.Balascio, Nicholas L....
    11页
    查看更多>>摘要：Many regions worldwide have experienced increasing wildfire activity in recent years and climate changes are predicted to result in more frequent and severe fires. Reconstruction of past fire activity offers paleoenvironmental context for modern and future burning. Pyrogenic polycyclic aromatic hydrocarbons (PAHs) have been increasingly used as a molecular biomarker for fire occurrence in the paleorecord and offer opportunity for nuanced reconstructions of fire characteristics. A suite of PAHs is produced during combustion, and the emission amount and assemblage is influenced by many variables including fuel type, fire temperature, and oxygen availability. Despite recent advances in understanding the controls and taphonomy of these biomass burning markers, the spatial scale of this proxy is unknown. In this paper, measurements of PAH fluxes preserved in a lake sediment archive from the Sierra Nevada, California were compared with a historical geographic information system (GIS) dataset of area burned up to 150 km distance from the lake to determine the spatial scales for which these biomarkers are reliable proxies of biomass burning. The PAH fluxes in the Swamp Lake sediments record a change in the relative anthropogenic and pyrogenic sourcing of PAHs. Anthropogenic pollution sources could explain why some PAHs (fluoranthene (Fl), pyrene (Py), benz[a]anthracene (BaA), retene (Ret), benzo[a]pyrene (BaP), dibenzo[a,h]anthracene (DA) and ideno[1,2,3-cd]pyrene (IP)) did not correlate with area burned within 150 km. This indicates that individual PAHs may have different efficacies in recording area burned and be more susceptible to masking of fire signals by pollution sources. Despite these complications, we find that the PAHs naphthalene (Na), acenaphthene (Ace), fluorene (F), and anthracene (An) are reliable local proxies of area burned (within 40 km), whereas the PAHs phenanthrene (Phe), chrysene (Ch), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), and benzo[g,h,i]perylene (Bghi) are both reliable local (within 36 km) as well as more regional (as much as 75 km for phenanthrene (Phe), chrysene (Ch), and benzo[g,h,i]perylene (Bghi) or 150 km for benzo[b]fluoranthene (BbF) and benzo[k]fluoranthene (BkF)) area burned proxies. Comparisons of PAH fluxes with charcoal accumulation rates in the same sediments suggest that pyrogenic particulate transport modulates low to mid-molecular weight PAHs via adsorption. Overall, the results show that PAH records integrate a combination of spatial signals of area burned and measurement of individual PAHs may enable cross-scale paleofire reconstructions.
      原文链接:
    • NSTL
    • Elsevier

    Astronomically forced cycles in Middle Permian fluvial sediments from Karoo Basin (South Africa)

    Lanci, L.Galeotti, S.Ratcliffe, K.Tohver, E....
    12页
    查看更多>>摘要：We report evidence for Milankovitch cycles discovered in Middle Permian strata of the fluvial Abrahamskraal formation, lower Beaufort Group, in Karoo Basin of the Northern Cape Province, South Africa. Statistical analyses of ranked lithologies and of major element oxides have been used to obtain clusters of elements that capture lithological variations and reflect changes of the sedimentary environment through time. Spectral analysis of these elemental statistical groups reveal significant meter-scale sedimentary cycles of 67 m, 17.5 m, 5.9 m and 3.5-2.8 m, which can be interpreted as the sedimentary expression of astronomical forcing, based on the available estimate of sedimentation rate. The identified periods of short-eccentricity, precession and obliquity show a good match with those predicted for Middle Permian times, providing a data-based validation of the astronomical theory. Cycle counting integrated with available U-Pb dating, provides a cyclochronological calibration for Wordian normal magnetozones and, combined with radiometric ages, indicates an age of 266.5 +/- 0.26 Ma for the end of Kiaman superchron. Recognition of the orbitally driven sedimentation in Gondwana supercontinent suggest a global extension of astronomical influence of Permian climate and confirms empirical knowledge of Earth's astronomical parameters before 260 million years ago. The new data demonstrate a rare case of astronomically paced cyclicity in fluvial deposits and a unique cyclostratigraphic record of the Middle Permian Gondwana supercontinent whose sedimentation reflects orbitally-paced precipitation changes.
      原文链接:
    • NSTL
    • Elsevier