Journal of Quaternary Science最新文献

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.

The upper water column (UWC) is involved in the worldwide distribution of heat and nutrients. However, global warming is expected to alter the UWC structure due to temperature- and precipitation-induced stratification. This impact of global warming is comparatively more pronounced in the Indian Ocean. Therefore, to understand the fate of the UWC structure in the future, it is important to comprehend its past variability in the Indian Ocean. To achieve this, we have reconstructed sub-centennial scale variations in the UWC structure of the tropical central Indian Ocean by using the isotopic composition (δ¹⁸O and δ¹³C) of surface-dwelling planktic foraminifera Globigerinoides ruber and subsurface-dwelling Neogloboquadrina dutertrei. The difference in the isotopic composition of the surface- and subsurface-dwelling species (Δδ¹⁸O_r-d and Δδ¹³C_r-d) was used to understand the UWC structure variability in the tropical central Indian Ocean. We report a deeper mixed layer and thermocline during the last glacial period, followed by a shoaling of the thermocline during the glacial–interglacial transition. The thermocline also deepened during intense boreal summer monsoon events such as in the Bølling–Allerød and early Holocene. Our findings suggest that the tropical Indian Ocean UWC is influenced primarily by the intensity of the monsoon winds. From the comparison of our record with those of the eastern and western Indian Ocean, it is evident that a similar climatic forcing governed the central and eastern regions during the last glacial–interglacial period.

The study of fire and charcoal production in tropical mesophytic ecosystems provides valuable insights into the ecological and climatic history of these systems. The diverse vegetation produces charcoal in various forms and sizes, which influences its dispersion and provides key information about fire dynamics. In this study, we used an approximately 850-year sedimentary charcoal record extracted from Lake Atezca in east-central Mexico to reconstruct the history of fire activity, including frequency and intensity. We present innovative information on charcoal morphotypes to interpret fire regimes, identify the types of vegetation burned and analyze human impact. The results reveal a shift in fire regimes during the Spanish Conquest, transitioning from local-scale burning associated with intensive wood burning for indigenous agriculture to regional-scale burning characterized by the burning of herbs and grasses linked to the expansion of extensive livestock grazing. This transition is reflected in the decrease of wood charcoal and the increase of smaller particles, as well as in the rise in titanium in the sediments, indicating greater landscape alteration. The evolution of fire regimes in Lake Atezca was driven primarily by human activities since pre-Hispanic times, although climatic factors, such as severe droughts, may have also influenced fire activity.

The first ¹⁴C dates for representatives of the Late Pleistocene – Early Holocene megafauna are reported from sites in Kaliningrad Province, Russia. The dates for woolly mammoth and cave lion are older than ca. 45 000 bp, and could have corresponded to the Middle Weichselian interglacial (Marine Isotope Stage 3). The age of reindeer is ca. 10 000 bp, and of aurochs ca. 7000 bp. This shows that megafauna existed in this part of the Eastern Baltic region prior to the Last Glacial Maximum (LGM). After the LGM, Kaliningrad Province was recolonized by reindeer.

Subtropical zones are crucial for understanding climate dynamics, as they strongly control the subtropical anticyclone system and serve as a bridge between the tropical and temperate regions of the planet. Therefore, understanding the long-term dynamics of these areas is vital on a hemispheric scale. A continuous late Pleistocene climate record based on sedimentological proxies was reconstructed using a lacustrine core from the Chilean Subtropical Andes (~33°S). Since the late Pleistocene, high lake levels subjected to cold and wet conditions prevailed between ~15.4 and 14k cal a bp, followed by glacier retreat between 14 and 13.7k cal a bp. The Pleistocene–Holocene transition is marked by increasing sedimentological parameter values and organic matter content, recording a significant shift in the environmental conditions. Decreased lake levels and high-energy events predominated until ~8.5k cal a bp, followed by warm and arid conditions with high-energy/runoff events from 8.5 to 5.2k cal a bp, with the driest period occurring ~6.4k cal a bp. Turbiditic flows appear between 5.2 and 2.6k cal a bp, and cold conditions between 2.6 and 2.3k cal a bp. From 1720 to 960 cal a bp, cold and wet conditions predominated. Warm and wet conditions prevailed to the present, with a brief return to cold and dry conditions at 720 cal a bp. Important widely represented events such as the Last Glacial termination, early to mid-Holocene Transition and Little Ice Age are present in the core record.

In this study, we provide an ~47.0-kyr mercury (Hg) deposition record derived from a lacustrine sedimentary sequence in Dahu swamp in the eastern Nanling Mountains, China. The results indicate that organic matter (OM) input played a role in Hg accumulation, whereas the contribution of inorganic weathering detritus had a negligible impact. On the other hand, evolution of the plant community and wildfire events were also important factors affecting Hg accumulation. Compared to arboreal plants, lower (herbs and ferns) plants had stronger absorption and enrichment ability for Hg thus favoring enhanced Hg accumulation in the sediments. We therefore infer that Hg deposition in Dahu sediments was greatly controlled by changes in climatic conditions. Relatively dry and cold climatic conditions, which resulted in reduced arboreal plant communities and increased lower plants, would favor an increased Hg accumulation rate; furthermore, dry conditions may cause more wildfire events thus leading to enhanced release of Hg into the environment and increased contribution of Hg to the sediments, whereas relatively wet and warm conditions would result in the opposite situation. The record of Hg deposition demonstrates a synchronous orbital-scale variation trend with the intensity of the East Asian summer monsoon. Period analysis reveals several millennial- and centennial-scale cycles similar to solar insolation, together with several millennial events of increased Hg concentration and accumulation rate, which coincided with the corresponding Heinrich events, suggesting joint impacts of solar irradiation and the action of melting water as well as changes in zonal atmospheric circulation on Hg accumulation in Dahu sediments.