Quaternary Research最新文献

This research was carried out in north-central Poland, which was occupied by the ice sheet of the Saalian (Marine Isotope Stage [MIS] 6) and Upper Stadial of the Weichselian (MIS 2) glaciation. The application of the anisotropy of magnetic susceptibility (AMS) method supported by a digital elevation model (DEM) analysis of the orientation of glacial landforms allowed for the reconstruction of ice-sheet extent and ice movement directions of these two Pleistocene glaciations. The research used an innovative method of collecting AMS till samples from the glacial plateau areas. Based on the research, it was found that during the general recession of the ice sheet of the Saalian glaciation, a previously undescribed glacial transgression occurred, characterized by a different direction of ice-sheet movement. On the basis of detailed geomorphological studies of the area of terminal moraines, previously described in fragments, the maximum extent of the ice sheet during the Weichselian glaciation was clarified. The recession of the ice sheet of the Weichselian glaciation from the area of north-central Poland took place in four regressive or transgressive–regressive stages with variable directions of ice-sheet movement. The results obtained indicate the great potential of the AMS method in paleoenvironmental studies of glaciated areas.

Mining operations in the Enmynveem valley, northeastern Siberia, exposed a well-preserved right hind leg of Mammuthus primigenius (woolly mammoth), dated to ca. 37,500 cal yr BP. The leg had a fracture that crosscut the midsections of the tibia and fibula. Additional skeletal and soft tissue remains, including two mummified adults (Berezovka, ca. 47,200 cal yr BP; Bolshoi Lyakhovsky, ca. 37,000 cal yr BP), document the presence of mammoths in interior mountain valleys and across both northern and southern coasts of far northeastern Siberia during Marine Isotope Stage (MIS) 3. A mosaic of herb-dominated tundra communities characterized the vegetation of the Enmynveem site during late to middle MIS 3 and MIS 2 (ca. 37,000–17,000 cal yr BP). Shrubs were limited to Salix during the late Pleistocene, whereas Betula also may have been present in sheltered sites during MIS 3. Herb communities remained dominant during the late Pleistocene–Early Holocene transition, although shrub Betula increased during this interval. By ca. 10,200 cal yr BP, the vegetation was Betula–Alnus shrub tundra. Larix and Pinus pumila were established in the valley by ca. 8700 cal yr BP and ca. 5700 cal yr BP, respectively.

Recent research has shown the potential of speleothem δ13C to record a range of environmental processes. Here, we report on 230Th-dated stalagmite δ13C records for southwest Sulawesi, Indonesia, over the last 40,000 yr to investigate the relationship between tropical vegetation productivity and atmospheric methane concentrations. We demonstrate that the Sulawesi stalagmite δ13C record is driven by changes in vegetation productivity and soil respiration and explore the link between soil respiration and tropical methane emissions using HadCM3 and the Sheffield Dynamic Global Vegetation Model. The model indicates that changes in soil respiration are primarily driven by changes in temperature and CO2, in line with our interpretation of stalagmite δ13C. In turn, modelled methane emissions are driven by soil respiration, providing a mechanism that links methane to stalagmite δ13C. This relationship is particularly strong during the last glaciation, indicating a key role for the tropics in controlling atmospheric methane when emissions from high-latitude boreal wetlands were suppressed. With further investigation, the link between δ13C in stalagmites and tropical methane could provide a low-latitude proxy complementary to polar ice core records to improve our understanding of the glacial–interglacial methane budget.

Loess paleoenvironmental reconstructions on regional to supra-regional scales have recently gained much attention. Geochemistry comparisons in relation to reference datasets, such as the Upper Continental Crust (UCC) data, have furthered our understanding of the climatic and geomorphological conditions under which terrestrial sites have developed. However, UCC data differs from loess, thereby obscuring important features, and the existing “average loess” datasets also are not sufficient for modern investigations.

In this study, we examine the youngest Polish loess (L1LL1 = MIS 2, ca. 26–15 ka) for its suitability as a new, loess-focused reference dataset. Eighty-nine samples from seven sites were analyzed, using inductively coupled plasma spectrometry. The loess had assumedly been homogenized during transportation and/or sedimentary recycling (LaN/SmN = 3.34–4.06, median 3.78; Eu/Eu* = 0.46–0.66, median 0.55; GdN/YbN = 1.08–1.49, median 1.26), and weakly affected by pre- or post-depositional weathering (CIA = 53.64–69.12, median 57.69). The statistically significant differences between sites in elemental medians were mostly conditioned by variations in grain size and in the “fresh” to “re-deposited” sediment ratio. Nonetheless, the overall geochemical composition homogeneity provided a basis for the estimation of Polish Median Loess (PML) data, as determined for 41 chemical elements. When used, PML data highlight differences between loess regions in Europe, thereby providing a tool for cross-continental comparisons.

We examined a Late Holocene sea-level stillstand using phreatic overgrowths on speleothems (POS) recovered from Medvjeđa Špilja [Bear Cave] (northern Adriatic Sea) from −1.28 ± 0.15 m below present mean sea level. Different mineralogical analyses were performed to characterize the POS and better understand the mechanisms of their formation. Results reveal that the fibrous overgrowth is formed of calcite and that both the supporting soda straw and the overgrowth have very similar trace element compositions. This suggests that the drip-water and groundwater pool from which the POS formed have similar chemical compositions. Four subsamples were dated by means of uranium-series. We found that ca. 2800 years ago, the relative sea level was stable for about 300 years at a depth of approximately −1.28 ± 0.15 m below the current mean sea level. This finding roughly corresponds with the end of a relatively stable sea-level period, between 3250 and 2800 cal yr BP, previously noted in the southern Adriatic. Our research confirms the presence of POS in the Adriatic region and establishes the Medvjeđa Špilja pool as a conducive environment for calcite POS formation, which encourages further investigations at this study site.