Quaternary International最新文献

Understanding the depositional processes on the inner shelf of Antarctica is a significant challenge. This difficulty arises from the heterogeneity of sediment sources, their poor preservation potential due to the advance and retreat cycles of ice bodies, and the impact of relatively strong bottom currents generated by high density contrasts in the water column. These factors contribute to the overall complexity of the glacio-influenced marine environment, particularly below present-day floating ice shelves in correspondence of areas draped in sediments related to Late Pleistocene-Holocene glacial variations. These locations provide crucial information for reconstructing past glacial dynamics driven by global changes.

In this study, we present an analysis of glaciomarine deposits collected from the Western Ross Sea, offshore Mario Zucchelli Station, in a protected indentation of the Victoria Land Coast that hosts the Terra Nova Bay polynya. We conducted multi-proxy analyses on three sediment cores sampled from selected seafloor morphological units associated with fluctuations of the grounded ice, which preserve sedimentary facies representative of this distinctive depositional environment.

We identified and described six depositional facies, characterized by diagnostic sedimentological, textural and geochemical patterns. Direct observations were integrated with high-resolution geophysical data and geomorphological seafloor analysis. Our findings highlight a Late Pleistocene-Holocene depositional sequence linked to fluctuations in grounded ice, with unconformities and sedimentary patterns potentially related to climatic variations driving ice advances and retreats.

The present work describes the taxonomic and paleobiogeographic study of two fossil woods related to extant Aspidosperma. The silicified specimens come from the fossil localities of Santa Ana (30°54′S, 57°55′W) and Concordia (31°19′S, 57°59′W), Entre Ríos Province, Argentina, belonging to the El Palmar Formation (Late Pleistocene). This unit represents the sedimentary body of the upper fluvial terrace generated by the Uruguay River in its middle basin in eastern Argentina. The anatomical features that distinguish the woods are growth rings delimited by axial parenchyma and fibers, semi-ring to-diffuse-porous woods; mainly solitary vessels; simple perforation plates; alternate, bordered, and vestured intervessel pits; scarce paratracheal and diffuse apotracheal axial parenchyma; homocellular, and uniseriate to-triseriate rays; non-septate fibers. Climate reconstruction modelled at the regional scale (Ecological Niche Modeling) revealed variations in macroecological diversity patterns of the nearest living relatives (Aspidosperma australe and A. polyneuron) over the last ca. 130,000 years. Optically stimulated luminescence dating of sediments from the upper part of the El Palmar Formation in the type area reveals that the unit spans from the Last Interglacial period (warm substage, MIS marine isotope stage 5a), to the penultimate interglacial (MIS 7). This period was characterized by warmer and wetter conditions than those observed today. The eco-anatomical characteristics of the fossil record reflect this type of environment. The modern analogues of the fossils studied here are now part of the forests that integrate the Atlantic forest and Araucaria forest biogeographic provinces in South America.

Ciénegas are desert wetlands that are strongly correlated with the stability of the hydrologic cycle in arid landscapes. However, these environments are particularly vulnerable to climate change, drought, water diversion, and fire suppression which all have contributed to the degradation of ciénegas along the U.S.-Mexican borderlands. Therefore, identifying the timing of precipitation patterns in this region is of particular interest because of its relationship to many ecological responses of the landscape such as groundwater recharge and fire. Here, we present the first-ever fire paleoenvironmental record from Ciénega Chimeneas, a ciénega complex in the Sierra de Juárez of Baja California. We explore how changes in the amount and seasonality of moisture affected ciénega complexes and fire activity from across the southwestern North American region over the past 45,000 years. Our record suggests that during the late glacial period, 41,000–21,000 cal yr BP, the increase of Larrea and Quercus indicate an increase in summer precipitation. Subsequently, when summer precipitation increased, pollen preservation and pollen accumulation rates (PAR) also increased. Increased vegetation allowed for increased fire activity during the late glacial period. Regionally, most of the comparison sites also indicated wet conditions during the full glacial period. However, around 21,000 cal yr BP, effective moisture decreased resulting in a dramatic change in the vegetation assemblage. Specifically, the summer wet taxa disappeared, while pollen preservation and PAR decreased, suggesting a dry period until ∼14,000 cal yr BP. Little fire activity is recorded after 21,000 cal yr BP, likely due to the absence of fuels. At ∼14,000 cal yr BP, Larrea and Quercus reappear suggesting increased summer precipitation. However, the appearance of Cyperaceae and increases in grasses suggest increased winter precipitation. We suggest that the combination of summer wet and winterwet taxa ∼14,000 cal yr BP represents an increase in ENSO conditions, while the summer moisture controls remained relatively constant.

As one of the most important terrestrial sediments, Chinese loess provides valuable information on regional and global climatic and environmental changes and holds great potential for studying on nonlinear behaviors of the East Asian monsoon system. Utilizing objective and quantitative methods to identify tipping points and climate transitions in paleoclimatic records can help us understand the climatic change in the Chinese Loess Plateau (CLP). This study explores critical tipping points and nonlinear climate transitions within the CLP using the Chiloparts record, a comprehensive 2600-ka paleoclimate dataset. We pinpointed potential tipping points using recurrence quantification analysis and the augmented Kolmogorov-Smirnov test, ultimately leading to 15 critical tipping points. We argued that these 15 tipping points represent some of the most significant climatic changes recorded in the Chinese loess paleoclimate record. Employing recurrence quantification analysis, recurrence networks, and visibility graphs, we also identified several climate transitions and provided some nonlinear information, including the Mid-Pleistocene Transition (MPT) as well as the Mid-Brunhes Transition (MBT). We particularly highlight a significant climatic regime transition around 500 ka that may reflect a nonlinear response to variations in the Atlantic Meridional Overturning Circulation (AMOC). Our research also contributes to the understanding of the complex interplay between loess deposition, environmental change, and tectonic activity, emphasizing the need for further investigations to elucidate the mechanisms driving these transitions.

Worldwide, Quaternary loess-paleosol sequences archive terrestrial paleoenvironmental information. The Palouse loess in the northwestern USA is one such deposit representing at least a million years of sediment accumulation. Loess paleosol sequences are often studied via the magnetic susceptibility of sediments and the changes in susceptibility with depth. However, since variations in magnetic susceptibility can have different underlying causes, the interpretation of the magnetic susceptibility of loess depends on factors specific to each major loess region. We measured the magnetic susceptibility of sediments along depth profiles in a well-studied exposure of the Palouse loess in eastern Washington, USA (the “CLY-2 site,” 46.3131° N, 118.4874° W, WGS84). Our measurements show that the magnetic susceptibility of sediments in the Palouse loess varies systematically and predictably with depth and can be correlated with other magnetic susceptibility profiles at the outcrop scale and at the regional scale. We also measured changes in grain size, elemental abundance, mineralogy, and other magnetic properties to determine the most likely cause of the magnetic susceptibility signal. Based on these results, variations in magnetic susceptibility in the Palouse are likely driven mostly by changes in coarse sediment supply and accumulation of tephra rather than changes in weathering. Magnetic susceptibility is useful as an inexpensive, non-destructive tool for stratigraphic correlation of Quaternary loess deposits in the Palouse, especially in combination with paleosol stratigraphic markers and known tephra deposits.

An investigation of Lake Vransko, located on the island of Cres in the Adriatic Sea, was performed in order to reconstruct the palaeoenvironmental changes that occurred during the late Holocene, based on diatoms. Fluctuations in the lake level were mostly driven by the intensification of climatic oscillations (wet periods during North Atlantic Oscillation intervals and summer drought during Azores High intervals) and anthropogenic influences (e.g. the extraction of drinking water). The anthropogenic impact of local deforestation is encountered, associated with a peak in phosphorous in the deeper parts of the lake cores. As a consequence of these impacts ten diatom abundance zones (DZs) and the water/sediment interface (WSI) were recorded from the deeper core (CS-51) and two from the shallower (CS-52) core, along with the WSI, based on which an abrupt fluctuation in the level of the lake was interpreted. A dominance of Epithemia adnata in the deeper core, and Gomphonema pumilum in the CS-51, and in the CS-52 indicated a shallow phase connected with the summer drought recorded in the lake. A dominance of Amphora inariensis, Pseudostaurosira spp., Cyclotella spp. and Pantocsekiella ocellata in the rest of the cores indicated deeper, more alkaline lake conditions during the wet periods. The DZs accord with depth variations in Adriatic coastal lakes that are key sites of more extreme recent changes in the local climate.

In this paper, sedimentological and geochemical data from six cores are presented and discussed in order to better understand the Holocene palaeoenvironmental evolution of the coastal plains of the Pecora and Cornia Rivers (southern Tuscany, Italy). Overall, the stratigraphies show a general upward trend in the evolution of the sedimentary succession of lagoonal environments (low Zr/Rb, high EC values) connected or partially connected to the sea (low EC values), to a seaward progradation of marshy-swampy environments (Mn/Ti, high TOC values) and finally to continental environments with the progradation of distal alluvial plains (high Zr/Rb, low EC values) influenced by runoff phenomena or local water stagnation. This trend is closely related to the increasing input of sediments from inland due to soil erosion processes and, especially in the last two centuries, land reclamation works. In the Cornia coastal plain, the chronologies indicate that lagoonal environments were already present before ca. 8.2ka BC and started receding seaward at around 3.7ka BC. On the other hand, chronologies from ca. 0.5ka BC to ca. 0.6ka AD point to a persistence of lagoonal environments only in areas very close to those already identified as such in historical cartography. In the Pecora coastal plain, the chronologies show that the lagoon environments had already disappeared before ca. 3.3ka BC, whilst the peripheral environments were characterised by abundant vegetation. The latter gradually degraded in favour of the development of shallow to very deep, unvegetated marshlands, which persisted until ca. 1ka AD.

Coastal sediment stratigraphies, their physical properties and microfossil assemblages are commonly used to reconstruct sea-level change. However, coastal sediments are affected by tidal, wave, aeolian, and overwashing processes at a range of elevations both within and above the tidal frame which means that their sea-level signatures may not always be clearly identified. Saltmarsh is a common coastal sedimentary environment along the Atlantic-facing coastline of northwest Ireland where bedrock headlands and an archipelago of small offshore islands have provided accommodation space for aggradational Holocene sediment sequences. A 2.85 m-long sediment sequence was investigated at Cloughglass, northwest Ireland. This shows weathered granite bedrock overlain by glacigenic cobbles and then in situ Pinus stumps within humified peat that is exposed in the upper foreshore. Above this, organic-rich and laminated saltmarsh sediments are arranged in packages (20–80 cm thick) bounded by undulating erosional surfaces. The saltmarsh sediments are unconformably overlain by a palaeosol (30 cm thick) and 1.5 m of recent dune sand. Sediment samples were removed at 5 cm intervals through the entire logged section and analysed for grain size properties, combustible organic content, CaCO₃ content, and microfossil assemblages. Five samples were dated by the AMS ¹⁴C method. Results show organic sediment accumulated around the pine tree stumps at ∼4400 cal yr BP but that later sedimentation was episodic, as evidenced by erosional surfaces throughout the saltmarsh part of the succession that may correspond to episodic storms or flood events. Three microfossil biostratigraphic zones are identified which broadly correspond to the sediment stratigraphy. The lowermost zone has poor preservation. The middle zone contains several halophytic species in low abundance but is dominated by the ubiquitous diatom Achnanthidium minutissimum. The uppermost zone is less diverse, with low but consistent abundance of predominately freshwater species and those that can tolerate brackish conditions. Integrating these results suggests that late Holocene coastal erosion and sea-level rise brought the coastline closer to the site over time, with a concomitant increase in wave and tidal influence as recorded in both sedimentary structures and biofacies. Subsequently, the land surface became stabilized with development of a dune palaeosol and decreased abundance of A. minutissimum. This evolutionary history reflects changing patterns of wave exposure and sediment supply as a result of changes in sand accumulation around the surrounding bedrock islands. Thus, the coastal stratigraphy more strongly reflects local sediment dynamics and accommodation space rather than regional sea-level change in the late Holocene.

Sandy deserts/lands along the western edge of the Asian summer monsoon domain are regarded as the major dust source of the East Asia and Pacific Ocean. However, the climatic background of aeolian sand accumulation in sandy deserts/lands and the potential provenance linkage between sand accumulation in sandy deserts/lands and aeolian dusts in the Chinese Loess Plateau (CLP) remains controversial. Based on age data compiled from published studies, we analyze the climatic background of aeolian sand accumulation in the proximal sandy deserts/lands, and the potential linkage between aeolian sand accumulation and the synchronous aeolian dusts in the CLP. The following conclusions are achieved: 1) Aeolian sand accumulation is almost synchronous with the development of loess/palaeosol/lacustrine sediments within the proximal sandy deserts/lands, supporting the idea that in the proximal sandy deserts/lands the aeolian sand accumulated at the high regional effective moisture condition. 2) Coupled with climatic background in neighboring areas, the inconsistent changes during the latest ∼20 ka in accumulation rate between aeolian sands in sandy deserts/lands and loess in the CLP support the idea that the contribution from the proximal sandy deserts/lands to loess in the downwind CLP is limited.

Mountain forests are sensitive ecosystems. This is why in recent years the dynamics of these forest ecotones have been researched from several different approaches. One of these has been the paleoecological perspective, which is particularly interesting in the mountainous areas of the Mediterranean region, where interactions between climate, vegetation and anthropic activities have been documented for millennia. This is the case of the Sierra de las Nieves Natural Park (southwestern Baetic Cordillera), a mountainous area that constitutes an important refuge for flora in southern Iberian Peninsula. At present, endemic trees such as Abies pinsapo and Quercus faginea subs. alpestris are found. However, its strategic geographical location may also have served in the past as a refuge for other tree taxa. In order to reconstruct the vegetation history in this protected natural area, this research aims to use pedoanthracological analysis in an unexplored area of this mountainous system. The results obtained have allowed to identify a new paleopopulation of Abies, a finding that provides new keys on the paleobiogeography of this species. This is the oldest evidence of this genus and at the highest altitude of those found to date in the southwestern Baetic Cordillera, which would confirm that this fir tree was present in high elevations of the Sierra de las Nieves during the Pleistocene-Holocene transition. Likewise, the first anthracological evidence of Pinus nigra/sylvestris type in the southwestern end of the Baetic Cordillera has been obtained. Forest fires could have been one of the main factors which would be determined the shaping and evolution of the vegetation landscape, as suggested by the fire events identified from the soil analysis. This information can be useful for the conservation and adaptive management of the most threatened forests and their habitats in the face of global change.