Journal of Paleolimnology最新文献

At the margin of the Pingorsuit Glacier in North-West Greenland, an organic-rich deposit that has recently emerged from the retreating ice cap was discovered in 2019 at an elevation of 480 m above sea level. Here we report on cladoceran and diatom analyses of this freshwater deposit from three samples of detritus gyttja, which occurred beneath a thin cover of till and glaciofluvial deposits. The cladoceran fauna comprises many non-Greenlandic, non-Arctic taxa, in accordance with previous studies of Coleoptera, Trichoptera and vascular plants. The fossil assemblages from the Pingorsuit beds resemble other fossil assemblages from Greenland that have been assigned an Early Pleistocene age, and a similar age has been suggested for the sediments found at the margin of the Pingorsuit Glacier. The fossil cladoceran and diatom species indicate a shallow lake with oligo- and dystrophic, circumneutral to slightly acidic waters. Their assemblages are more diverse compared to Holocene assemblages from northern Greenland, further indicating warmer summers than present.

Varved lake sediments offer valuable insight into past environmental conditions with high temporal resolution and precise chronological control. A combination of diatom and geochemical analyses of the recently deposited sediments of Odensjön, a small dimictic lake in southern Sweden, shows alternating light and dark laminae composed of greater amounts of biogenic silica and organic matter, respectively. As confirmed by independent radiometric dating and Pb pollution data, and supported by scanning electron microscopy of individual laminae, these features represent ongoing deposition of biogenic varves. Corresponding diatom and geochemical data obtained from a 92-cm long freeze core provide evidence of substantial lake-ecosystem dynamics during the last six centuries, related mainly to variations in light penetration and wind shear driven by human-induced changes in catchment vegetation. The diatom assemblage of Odensjön’s varved sediments is dominated by planktonic species, primarily Asterionella formosa, Fragilaria saxoplanktonica and Discostella lacuskarluki during periods of forest cover, while increased catchment openness from the mid-1500s to the late 1800s led to increased abundance of Lindavia comensis. Long-term variations in climate and land use, mediated through changing length of the ice-cover season and nutrient input, respectively, probably contributed to the observed trends, as well as to variations in the appearance and visibility of the varve record across the sampled sediment sequence. Odensjön represents the southernmost varved sediment record in Fennoscandia documented to date, offering potential to study the effects of various types of external forcing on its sensitive lacustrine ecosystem since the Late Weichselian deglaciation. In the present study, we investigated the possibility of assessing the local impacts of two major, historically documented volcanic events, Laki 1783–84 and Tambora 1815, which are known to have affected European societies. Although the mildly alkaline waters of the lake are well buffered and hence relatively resilient to volcanic acid deposition, a minor response to the Laki eruption may be recorded in the diatom stratigraphy.

Heavy minerals offer significant potential in elucidating sediment provenance in a variety of depositional systems. Nevertheless, source identification through heavy minerals remains a relatively understudied aspect, particularly for small floodplain lakes. Located in the North China Plain, Dongping Lake represents an exceptional site for validating the efficacy of this methodology. In this study, we collected 31 samples from Dongping Lake and surrounding floodplains and used analyses of heavy mineral compositions to establish the spatial distribution and characteristics of source regions and modern sediments of Dongping Lake. The heavy mineral assemblages demonstrate significant variations for sediments of the Yellow River and the Dawen River. The Yellow River floodplain samples are dominated by hornblende, epidote, limonite, and actinolite, with minor garnet, sphene, clinozoisite, etc. Samples from the Dawen River are dominated by epidote, hornblende, and actinolite, with minor sphene, clinozoisite, limonite, apatite, etc. Our data show that modern sediments of Dongping Lake exhibit significant variations in heavy mineral assemblages. The mineralogical composition at most sites except for the southeastern part of Dongping Lake is similar to that of sediments in the Yellow River, but differs markedly from that in the Dawen River. This variation indicates that the Yellow River contributes significant volumes of sediment to modern sediments of Dongping Lake. The results are also confirmed by the grain-size end-member unmixing analysis in modern sediments of the lake. Specifically, materials derived from the Yellow River exhibit a widespread dispersion across the lake, whilst those originated from the Dawen River are primarily concentrated in the river mouth. In addition, proximally eroded materials from the west shore of the lake also have some extent of influence, but are mainly distributed in the western region of the lake.

The global research community is concerned about the potential impact of Lake Outburst Floods (LOFs) worldwide due to glacier retreat and permafrost melting as a consequence of global climate change. These conditions have led to the formation of new potentially dangerous lakes. Extreme climatic conditions, high topography, and active tectonics highlight the vulnerability of the Andean region. Additionally, the region is exposed to increasing urbanization pressures in mountainous areas. This review presents an updated inventory of LOF events in the Argentinean Andes (31–51° S) as a complete catalog is currently lacking. The main characteristics and hydrodynamic parameters were compiled from the collected historical LOFs, while missing data were estimated in this study. These findings provide insight into the dynamics and outreach of this type of threatening phenomena in the Andean region. Possible triggering mechanisms were investigated to better understand the main causes of LOFs in the Andes. This understanding is crucial for the development of effective prevention and mitigation measures against regional lake-related hazards.

Lake Zminje Jezero (1535 m a.s.l.) in Montenegro was studied for chironomid and other aquatic invertebrate remains in a sediment sequence dating back to 12,000 calibrated ¹⁴C years before present (cal yr BP), providing, to our knowledge, the first lake-sediment record studied for chironomids and other associated chitinous aquatic invertebrate remains in the Dinaric Alps. Changes in chironomid and other invertebrate remains along the record make it possible to constrain changes of relevant environmental variables for aquatic invertebrates in the lake including temperature, oxygen availability, trophic status and water depth. The results suggest moderate changes in trophic conditions with chironomid assemblages indicating meso- to eutrophic conditions during the analysed interval. Invertebrate assemblages were typical for lakes with relatively high oxygen availability with a minor trend during the middle to late Holocene to conditions observed in lakes that are more hypoxic. A change in temperature is suggested in the earlier part of the record when the share of chironomid taxa adapted to warmer conditions increased, at the Younger Dryas to Holocene transition, whereas later no particularly pronounced shifts in temperature-sensitive taxa were observed. July air temperatures were estimated based on chironomid assemblages using a transfer function based on calibration data consisting of 117 lakes sampled in the Swiss Alps and northern Switzerland. The results suggest that temperatures rapidly increased by 5 °C at the onset of the Holocene (11,500 cal yr BP) leading to a relatively warm early to mid-Holocene and thereafter slightly decreased during the late Holocene. Reconstructed temperatures are discussed together with a previously published pollen record for our study site and are broadly consistent with other chironomid-based temperature reconstructions from Central, Eastern and Southern Europe. From ca. 3000 cal yr BP sedimentation rates increased and from ca. 500 cal yr BP onwards pollen data suggest that the vegetation and lake catchment were affected by human activities, possibly influencing chironomid and other invertebrate assemblages in the lake and thereby also reconstructed temperatures. Overall, our results show that combining analyses of chironomid and other invertebrate assemblages can provide valuable insights into long-term environmental changes and can provide temperature reconstructions for small mountain lakes in the Balkans, such as Zminje Jezero.

Lake Pavin, a maar lake was formed approximately 7000 years ago by a phreatomagmatic explosion, leaving a deep central crater with shallow steep side slopes. PAV12 core, collected from the center of the lake, displayed two diatomite layers, separated by a 4-m thick unit of reworked sediments. Diatom diversity and zonation analyses registered six zones documenting the lake evolution. Asterionella formosa, Pantocsekiella ocellata and Discostella pseudostelligera (including f. diminuta) along with fragilariod taxa composed the basal unit (L-1, ~ 6900 to 6570 cal a BP). With increased mineralization of the lake waters, Stephanodiscus taxa became the major species (L-2, 6190–3800 cal a BP). A transition zone was noted between Zone L-2 and L-3 (3950–3700 BP) and related to a major change in diatom composition. Asterionella formosa and Nitzschia paleacea dominated Zone L-3 (3760–1470 cal a BP) with a large decrease in Stephanodiscus taxa. This major change has been related to soil erosion and the possible development of meromixis. Stephanodiscus parvus and Asterionella formosa dominated the upper diatomite zone L-4 (640–400 cal a BP) while zone L-5 (290–160 cal a BP) is dominated by Aulacoseira subarctica (including f. recta) and may be caused by the Little Ice Age. Zone L-6 (subrecent) saw a return to similar conditions as in zone L-4. The gradual opening of the diversified forest and appearance of regional agriculture appears to be related to the development of meromixis. Changes in the upper diatomite zone are related to agricultural activity, changes in incomplete overturn and climate. This study examines relationships between diatom changes and pollen and geochemical changes observed within the lake.

Paleoenvironmental analyses have been widely used to infer the fluctuations in past environmental conditions of lakes and reservoirs due to either anthropogenic and/or climatic influences. The Siete Lomas shallow lake (37° 08′ S, 57° 38′ W) is located in an area with a long history of anthropogenic impacts in the Pampa plain, southeastern Argentina. Our aim was to reconstruct the paleoenvironmental history of the Siete Lomas shallow lake and to identify the main forcings of change during the last 1000 years. A multi-proxy analysis was performed including pollen and non-pollen palynomorphs, diatoms, fossil pigments, plant macrofossils and the associated fauna, Total Phosphorus (TP) and organic matter. Two main environmental stages (the latter including two substages) throughout the history of the Siete Lomas lake were recognized as a result of the action of natural variability and anthropogenic drivers. Stage I (1100–1880/1900 AD) recorded a pre-agricultural period when human impacts were negligible, and was considered as reference conditions. In this stage, a temporary, brackish and oligotrophic lake was inferred. Stage II was composed by two substages. Substage II-1 (1900–1945 AD) suggested the establishment of a permanent freshwater lake with higher pelagic primary production and an incipient eutrophication process, associated to increased anthropogenic activity and higher precipitation. Nutrient load and eutrophication processes controlled Substage II-2 (1945–2021), as a productive lake subject to increased eutrophication as a consequence of nutrient loadings from the surrounding catchment was identified. In particular, a highly productive, turbid-hypereutrophic and permanent lake related to the increase in agricultural activities was recognized for the period 2005–2021 AD. Overall, during the early period of the lake history, changes in dominant communities were mainly controlled by climate whereas after 1900 AD anthropogenic and natural forcing synergistically promoted the generalized degradation of the water quality of the Siete Lomas shallow lake.

Patagonia is a unique area for climate studies, exposed to the strong Southern Hemisphere Westerly Winds (SWW) and modulated by the Southern Annular Mode (SAM). Patagonia is also affected by volcanic eruptions of the Andean Mountain Range, and is rich in lacustrine environments, which are ideal for paleocological and paleoclimatological reconstructions. Sediments of Patagonian lakes provide an excellent opportunity to study the responses of aquatic communities to major climatic and environmental events in still pristine freshwater ecosystems. Here, we present a high-resolution paleolimnological reconstruction using testate amoebae and chironomid assemblages and compare it with organic and inorganic sediment geochemistry (Ca, K, Ti, N, TOC, TOC/N, δ¹⁵N, δ¹³C) from a sediment core of Laguna Polo (49°S, Santa Cruz, Argentina) covering the last ca. 1300 years. Our results imply a warm-dry and productive environment from around 1300–1400 CE, a cold and less productive environment from ca. 1400–1700 CE, broadly corresponding to the Little Ice Age (LIA). The latter period is followed by high volcanic activity between ca. 1700 and 1960 CE. The tephra layers are known from other records in the vicinity and are preliminarily attributed to the eruptions of the adjacent Lautaro Volcano. A warm-stenothermic chironomid assemblage indicates a progressive increase in temperature in the most recent time after the last eruption, attributed to Lautaro Volcano in 1960 CE.