Journal of Quaternary Science最新文献

This research documents the paleoenvironmental evolution of Eighteen Mile Swamp on North Stradbroke Island (Minjerribah), Australia, from oscillating coastal lagoon into stable freshwater swamp over the last ca. 1600 years. We analyzed multiple sediment cores via physical description, acid sulfate soil assays, particle size analysis, diatom and pollen assemblages, photosynthetic pigment content, and Itrax XRF spectrometry, alongside ground-penetrating radar cross-sections. This provided a detailed ecological, geochemical and chronological framework, derived from radiocarbon, Pu and ²¹⁰Pb dating, for the wetland's evolution. Results indicate spatial complexity in the timing of a pronounced shift in sedimentary conditions between ca. 300 and 1000 years ago, from estuarine mud to freshwater peat, marked by abrupt chemical and ecological changes. Unexpectedly, there were at least three and potentially many periods of dominant freshwater influence within the primarily estuarine phase, suggesting episodic estuarine closure and freshening by groundwater influx. Results provide critical insights into the complex response of subtropical wetland systems to environmental change, emphasizing the importance of interdisciplinary approaches in understanding both sedimentologic and geomorphic responses in coastal wetlands, and their potential vulnerability to future climate change. The study of Eighteen Mile Swamp is significant as it provides a detailed paleoenvironmental reconstruction that documents the wetland's evolving nature over the past two millennia. This research highlights the importance of understanding historical responses of wetlands to environmental changes, which helps inform their current and future management, conservation and restoration efforts, particularly in the context of climate change and human impacts. This study also serves as a tribute to the late Lynda Petherick, acknowledging her contributions in this field.

Paleoflood slackwater deposits have recently been investigated in small to moderately sized rivers. However, our understanding of the characteristics of paleoflood slackwater deposits in large rivers remains limited, which poses a notable obstacle to accurately predicting the magnitude, frequency and force of extraordinary floods. To address this research gap, this study compares the characteristics of paleoflood slackwater deposits in the middle Yarlung Zangbo River (YZR) and the upper Hanjiang River in China. Paleoflood slackwater deposits and aeolian deposits (e.g. loess, paleosol S₀ and aeolian sand) were investigated and sampled from these locations. For the paleoflood slackwater deposits and aeolian deposits, sedimentology (e.g. grain size distribution, magnetic susceptibility and geochemical elements) was analyzed in the laboratory. The macroscopic features of the paleoflood slackwater deposits in the middle YZR valley are very similar to those of the upper Hanjiang River valley. The paleoflood slackwater deposits were dominated by sand and silt in the middle YZR and by silt and sand in the upper Hanjiang River; this implied that the paleoflood slackwater deposits were suspended sediments of floodwater from different source regions. Compared with the paleoflood slackwater deposits in the upper Hanjiang River and other large rivers in China (e.g. the Yellow and Yangtze Rivers), the paleoflood slackwater deposits contained more coarse particles in the middle YZR; this result may be closely related to the particular hydrogeologic and geomorphic conditions (e.g. rich sandy sediment, high riverbed slope and narrow valley) in the southeastern Tibetan Plateau. Compared with the paleoflood slackwater deposits in the upper Hanjiang River, the paleoflood slackwater deposits presented considerably worse sorting in the middle YZR; this may be closely related to the short transport distance in the middle YZR. The magnetic susceptibility values of the paleoflood slackwater deposits were relatively higher in the middle YZR and the upper Hanjiang River, suggesting that these slackwater deposits with minimal pedogenesis may contain a relatively high ferromagnetic mineral content because of the formation process of slackwater deposits. The sediment provenance of the paleoflood slackwater deposits may be closely related to that of the loess in the middle YZR valley, which implies that the sediment provenance of deposits of different genetic types may be greatly affected by the particular hydrologic–climatic and geomorphic conditions in the southeastern Tibetan Plateau.

The SiO₂/Al₂O₃ and SiO₂/TiO₂ ratios of loess–paleosol sequences in the Chinese Loess Plateau have been proposed as indicators recording changes of the East Asian winter monsoon. However, interference from silicon (Si) leaching induced by chemical weathering raises concerns about their applications to paleoclimate reconstruction. Silicon isotopes can serve as an effective tool for monitoring Si leaching, as the release of Si can lead to a decrease in δ³⁰Si values of soils. Here we use Si isotopes to evaluate previously published SiO₂/Al₂O₃ and SiO₂/TiO₂ ratios in loess–paleosol sequences from the Yimaguan profile, Gansu Province, Northwest China, and examine the potential alteration caused by chemical weathering. The SiO₂/Al₂O₃ and SiO₂/TiO₂ ratios show opposite trends to that of the frequency-dependent magnetic susceptibility (χ_fd) and the chemical index of alteration (CIA). However, the whole profile exhibits limited Si isotopic variation, with δ³⁰Si values ranging from −0.28‰ to −0.16‰. The homogeneous Si isotopic signature indicates that Si is not significantly leached during pedogenesis. Therefore, the SiO₂/Al₂O₃ and SiO₂/TiO₂ ratios are not modified by Si leaching due to chemical weathering; instead, they are mainly affected by the grain size sorting effect, which is controlled by the change of winter monsoon intensity. This suggests that SiO₂/Al₂O₃ and SiO₂/TiO₂ can serve as reliable indicators of paleoclimate changes, with an increase in the ratios reflecting the strengthening of the East Asian winter monsoon. Based on our observation of the Yimaguan loess–paleosol samples and the global loess data previously published, we also constrained the average Si isotopic composition of the upper continental crust (UCC) to be −0.22 ± 0.06‰ (2 s.d.).

The iconic sand dune systems of Minjerribah (North Stradbroke Island), in southeastern Queensland, Australia, host numerous lakes and swamps containing organic-rich sediment deposits that record changes in climate, fire and surrounding vegetation. Palaeoenvironmental reconstructions from individual locations can provide insights into changes in the environment, but determining the regional extent of these changes is seldom possible from a single site. Multi-site compilations help elucidate the geographical nature of environmental changes and determine if they are driven by local or regional forces. Here, a synthesis of palynological records from six Minjerribah wetlands using a muti-tiered Monte Carlo empirical orthogonal function (EOF) analysis allows island-wide patterns of vegetation change to be identified. Coherent changes in vegetation were recorded, with first-order changes (EOF1) indicating a long-term shift in vegetation composition from closed forests towards woodland and heath vegetation. A compilation of macroscopic and microscopic charcoal from the same sites shares coherent patterns of change with a rainfall record from the island, suggesting that regional fire occurrence between 7000 and 2000 cal a bp was driven primarily by long-term variations in rainfall and its influence on biomass. Comparison with fire activity, rainfall, sedimentary carbon, nitrogen and dust records from Minjerribah suggests that regional vegetation changes occur primarily in response to long-term changes in nutrients and increasing rainfall variability. This analysis highlights the multi-millennial connection between vegetation composition, climate, nutrients and fire occurrence across the Holocene in subtropical environments.

The present landscapes that define the tropical African region have evolved through the intricate interplay of climate and human interventions across various spatial and temporal scales. The late Holocene period is a valuable window for investigating how the environment responded to human influence. This study examined paleoenvironmental changes in the African tropics over the past 3500 years using proxy data, encompassing pollen, fungal spores, loss-on-ignition and microscopic charcoal extracted from core SS4 collected from Saiwa Swamp in western Kenya. The results show that Afromontane forests, represented by Podocarpus, Olea, Celtis and Juniperus, persisted in the region for much of the late Holocene despite prevailing conditions that favored the expansion of open savanna-like vegetation and drought-adapted taxa. The charcoal record reveals continuous fire occurrences throughout the sequence, raising questions about human-induced fires and their potential role in shaping the landscape. The emergence of Sordaria fungal spores in the record between approximately 925 bce and 970 ce points to early human settlements engaging in livestock farming. Yet, these initial anthropogenic impacts did not trigger extensive forest clearing, hinting at a nuanced interplay between human activities and the environment during that era. The study emphasizes the importance of considering natural and human factors when interpreting environmental changes. It highlights the complex interplay of climatic, ecological and anthropogenic factors in shaping the landscape and vegetation dynamics over time.