Explore the vast range of titles available.

Sedimentary archives provide long-term records of heavy metal pollution crucial for making an efficient pollution control policy to protect humans and our ecosystem. In this study, we present V, Cr, Ni, Cu, Co, Sn, Zn, Cd, and Pb concentrations measured in a 38 cm long sediment core from the Upper Lake (wetland protected under Ramsar convention 2002) in Bhopal to provide the last century records of heavy metal pollution in Central India. Few riverine sediments and free-fall atmospheric dust samples collected from the lake periphery were also analyzed. Principal component analysis and heavy metal abundance patterns in the lake sediments and the likely endmembers suggest atmospheric deposition as the major cause of heavy metal influx into the lake. The geochemical background upper limits of heavy metals as determined using modal analysis were used to calculate the metal-specific enrichment factor (EF) and the overall heavy metal pollution load index (PLI). The overall metal pollution has remained insignificant (PLI ~ 1) throughout the core history, while minor pollution of Zn, Cd, and Pb (EF > 1–2) emerged in the early-1980s. This study highlights that the emergence of Zn, Cd, and Pb pollution in Central India is contemporaneous to that seen in multiple lacustrine sediment records from China but it does not yet show any modern phasing-out trend as seen in China and elsewhere.

Wuhan area located middle Yangtze River Basin, is dominated by East Asian Monsoon. Widely developed Holocene flu-lacustrine sediments are ideal materials for the reconstruction of paleoclimate change and geo-environment evolution, for which the chronology is a key issue. In this study, 20 luminescence dating samples were collected from a flu-lacustrine sequence and the reliability of the quartz OSL dating to these samples were checked by using luminescence characteristics of dose recovery test and thermos transfer test. Our results indicate that different grain size fraction of 4∼11 μm, 38∼63 μm, and 90∼125 μm were well-bleached before burial. Dating results show that all these ages range from 0.8 ± 0.1 to 7. 9 ± 0.7 ka between 4.25 and 38.55 m, and most of them follow the stratigraphic sequence and other climatic recorder within the normal range of error. Disordered OSL ages may be caused by complicated transport-deposit processes. As a consequence, OSL dating method of SAR-SGC protocol could provide a significant chronology for Holocene flu-lacustrine sediment in large river depo-system.

Low-altitude lakes in eastern Africa have long been investigated and have provided valuable information about the Late Quaternary paleohydrological evolution, such as the African Humid Period. However, records often suffer from poor age control, resolution, and/or ambiguous proxy interpretation, and only little focus has been put on high-altitude regions despite their sensitivity to global, regional, and local climate change phenomena. Here we report on Last Glacial environmental fluctuations at about 4000 m asl on the Sanetti Plateau in the Bale Mountains (SE Ethiopia), based on biogeochemical and palynological analyses of laminated lacustrine sediments. After deglaciation at about 18 cal kyr BP, a steppe-like herb-rich grassland with maximum Chenopodiaceae/Amaranthaceae and Plantago existed. Between 16.6 and 15.7 cal kyr BP, conditions were dry with a desiccation layer at ~ 16.3 cal kyr BP, documenting a temporary phase of maximum aridity on the plateau. While that local event lasted for only a few decades, concentrations of various elements (e.g. Zr, HF, Nb, Nd, and Na) started to increase and reached a maximum at ~ 15.8–15.7 cal kyr BP. We interpret those elements to reflect allochthonous, aeolian dust input via dry northerly winds and increasingly arid conditions in the lowlands. We suggest an abrupt versus delayed response at high and low altitudes, respectively, in response to Northern Hemispheric cooling events (the Heinrich Event 1). The delayed response at low altitudes might be caused by slow negative vegetation and monsoon feedbacks that make the ecosystem somewhat resilient. At ~ 15.7 cal kyr BP, our record shows an abrupt onset of the African Humid Period, almost 1000 years before the onset of the Bølling–Allerød warming in the North-Atlantic region, and about 300 years earlier than in the Lake Tana region. Erica pollen increased significantly between 14.4 and 13.6 cal kyr BP in agreement with periodically wet and regionally warm conditions. Similarly, intense fire events, documented by increased black carbon, correlate with wet and warm environmental conditions that promote the growth of Erica shrubs. This allows to conclude that biomass and thus fuel availability is one important factor controlling fire events in the Bale Mountains.

The ICDP “PaleoVan” drilling campaign at Lake Van, Turkey, provided a long (>100 m) record of lacustrine subsurface sedimentary microbial cell abundance. After the ICDP campaign at Potrok Aike, Argentina, this is only the second time deep lacustrine cell counts have been documented. Two sites were cored and revealed a strikingly similar cell distribution despite differences in organic matter content and microbial activity. Although shifted towards higher values, cell counts from Lake Potrok Aike, Argentina, reveal very similar distribution patterns with depth. The lacustrine cell count data are significantly different from published marine records; the most probable cause is differences in sedimentary organic matter composition with marine sediments containing a higher fraction of labile organic matter. Previous studies showed that microbial activity and abundance increase centimetres to metres around geologic interfaces. The finely laminated Lake Van sediment allowed studying this phenomenon on the microscale. We sampled at the scale of individual laminae, and in some depth intervals, we found large differences in microbial abundance between the different laminae. This small-scale heterogeneity is normally overlooked due to much larger sampling intervals that integrate over several centimetres. However, not all laminated intervals exhibit such large differences in microbial abundance, and some non-laminated horizons show large variability on the millimetre scale as well. The reasons for such contrasting observations remain elusive, but indicate that heterogeneity of microbial abundance in subsurface sediments has not been taken into account sufficiently. These findings have implications not just for microbiological studies but for geochemistry as well, as the large differences in microbial abundance clearly show that there are distinct microhabitats that deviate considerably from the surrounding layers.

The Mars 2020 mission will seek the signs of ancient life on Mars and will identify, prepare, document, and cache a set of samples for possible return to Earth by a follow-on mission. Mars 2020 and its Perseverance rover thus link and further two long-held goals in planetary science: a deep search for evidence of life in a habitable extraterrestrial environment, and the return of martian samples to Earth for analysis in terrestrial laboratories. The Mars 2020 spacecraft is based on the design of the highly successful Mars Science Laboratory and its Curiosity rover, but outfitted with a sophisticated suite of new science instruments. Ground-penetrating radar will illuminate geologic structures in the shallow subsurface, while a multi-faceted weather station will document martian environmental conditions. Several instruments can be used individually or in tandem to map the color, texture, chemistry, and mineralogy of rocks and regolith at the meter scale and at the submillimeter scale. The science instruments will be used to interpret the geology of the landing site, to identify habitable paleoenvironments, to seek ancient textural, elemental, mineralogical and organic biosignatures, and to locate and characterize the most promising samples for Earth return. Once selected, ∼35 samples of rock and regolith weighing about 15 grams each will be drilled directly into ultraclean and sterile sample tubes. Perseverance will also collect blank sample tubes to monitor the evolving rover contamination environment. In addition to its scientific instruments, Perseverance hosts technology demonstrations designed to facilitate future Mars exploration. These include a device to generate oxygen gas by electrolytic decomposition of atmospheric carbon dioxide, and a small helicopter to assess performance of a rotorcraft in the thin martian atmosphere. Mars 2020 entry, descent, and landing (EDL) will use the same approach that successfully delivered Curiosity to the martian surface, but with several new features that enable the spacecraft to land at previously inaccessible landing sites. A suite of cameras and a microphone will for the first time capture the sights and sounds of EDL. Mars 2020’s landing site was chosen to maximize scientific return of the mission for astrobiology and sample return. Several billion years ago Jezero crater held a 40 km diameter, few hundred-meter-deep lake, with both an inflow and an outflow channel. A prominent delta, fine-grained lacustrine sediments, and carbonate-bearing rocks offer attractive targets for habitability and for biosignature preservation potential. In addition, a possible volcanic unit in the crater and impact megabreccia in the crater rim, along with fluvially-deposited clasts derived from the large and lithologically diverse headwaters terrain, contribute substantially to the science value of the sample cache for investigations of the history of Mars and the Solar System. Even greater diversity, including very ancient aqueously altered rocks, is accessible in a notional rover traverse that ascends out of Jezero crater and explores the surrounding Nili Planum. Mars 2020 is conceived as the first element of a multi-mission Mars Sample Return campaign. After Mars 2020 has cached the samples, a follow-on mission consisting of a fetch rover and a rocket could retrieve and package them, and then launch the package into orbit. A third mission could capture the orbiting package and return it to Earth. To facilitate the sample handoff, Perseverance could deposit its collection of filled sample tubes in one or more locations, called depots, on the planet’s surface. Alternatively, if Perseverance remains functional, it could carry some or all the samples directly to the retrieval spacecraft. The Mars 2020 mission and its Perseverance rover launched from the Eastern Range at Cape Canaveral Air Force Station, Florida, on July 30, 2020. Landing at Jezero Crater will occur on Feb 18, 2021 at about 12:30 PM Pacific Time.

Lacustrine sediments are often used for paleoclimate reconstructions as continuous archives of several physical and biological proxies. The relation between autochthonous and allochthonous sedimentation in alpine lakes is a complex system that may cause difficulties when interpreting biological and physical parameters. Results from previous studies of alpine lakes in northern Sweden have demonstrated that non-glacial processes produce minerogenic lake deposits with similar physical characteristics (density, LOI, magnetic susceptibility, grain-size) as those that have been associated with glacier fluctuations in proglacial lakes. In this study of two consecutive proglacial alpine lakes we show that fluvial redeposition of alluvial fan deposits significantly affects the Holocene lake sedimentation. Depending on the geomorphological setting, such fluvial redeposition signals may actually overprint a glaciofluvial signal. We also show that minerogenic laminations of fluvial origin are impossible to separate from the type of laminations usually used to infer glacier activity using the most common lithological sediment parameters. This emphasizes the complexity of sediment transport system in proglacial (paraglacial) settings where redeposition of older glacial sediment is of major importance. Our results highlight the need for thorough understanding of the geomorphological setting before inferences are made about climate variations from sedimentation in alpine lakes. Both lakes in this study contain sediment sequences with both episodic (turbidites) and continuously deposited sediments. Unfortunately we have too few radiocarbon dates to exactly date the turbidites but it is clear that turbidite layers in any case should be excluded from age model constructions since episodic sedimentation significantly influences the sediment age—depth relationship. In our age-model turbidites cause a potential dating error of several hundred, up to a thousand, years.

Sediment grain size is a conventional proxy of climatic changes. Larger sediment grain size is often interpreted to indicate dry climate during lower lake level while smaller sediment grain size implies wet climate during higher lake level. Through detailed study on sediment grain sizes in Lake Erhai and Lake Chenghai, this paper reveals the different indication significances of sediment grain sizes in different time scales, different resolution investigations. For long time-scale and low resolution (102a or 103a) studies, larger sediment grain size indicates lower lake level, smaller lake area and drier climate while smaller sediment grain size indicates higher lake level, larger lake area and wetter climate. For short time-scale and high resolution (a or 10a) studies, larger sediment grain size reflects more rainfall and wetter climate while smaller sediment grain size reflects less rainfall and drier climate. Environmental information revealed by lacustrine sediment records is often different in different time scales because of the variance of sedimentation resolution, sampling resolution and dating precision. Therefore, paleoclimate implications of environmental proxies in long time-scale and low resolution investigations could not be mechanically applied to short time-scale and high resolution studies. Only after synthetically analyzing the influence manner and extent of all factors on the sediment records in different time scales, can credible conclusions be obtained.

The Curiosity rover has documented lacustrine sediments at Gale Crater, but how liquid water became physically stable on the early Martian surface is a matter of significant debate. To constrain the composition of the early Martian atmosphere during sediment deposition, we experimentally investigated the nucleation and growth kinetics of authigenic Fe-minerals in Gale Crater mudstones. Experiments show that pH variations within anoxic basaltic waters trigger a series of mineral transformations that rapidly generate magnetite and H2(aq). Magnetite continues to form through this mechanism despite high partial pressure of carbon dioxide (pCO2) and supersaturation with respect to Fe-carbonate minerals. Reactive transport simulations that incorporate these experimental data show that groundwater infiltration into a lake equilibrated with a CO2-rich atmosphere can trigger the production of both magnetite and H2(aq) in the mudstones. H2(aq), generated at concentrations that would readily exsolve from solution, is capable of increasing annual mean surface temperatures above freezing in CO2-dominated atmospheres. We therefore suggest that magnetite authigenesis could have provided a short-term feedback for stabilizing liquid water, as well as a principal feedstock for biologically relevant chemical reactions, at the early Martian surface.

Lacustrine groundwater discharge (LGD) is an important water and nutrient source for lakes. Despite its importance, high‐resolution quantifying the spatial variability of LGD remains challenging. Particularly, little studies have explored the impact of the interaction zone structure between lakes and aquifers on this variability. Present study presents a high‐resolution quantitative estimation of LGD spatial patterns in an oxbow lake by combining thermal remote sensing with a 222Rn mass balance model. The vertical distribution characteristics of various parameters including lake water temperature, 222Rn concentration, electrical conductivity, and δ18O were examined to elucidate the influence of groundwater on the distribution pattern of lake surface temperature (LST). Regression equations were formulated to correlate LST with lake water 222Rn concentration across different water depth zones, enabling the inverse calculation of the 222Rn concentration in the water of the entire lake. Utilizing a 222Rn mass balance model across all grid points, the LGD rate was determined to vary from 0 to 330.96 mm/d, with an average of 55.02 ± 19.61 mm/d. In shallow water zones, the accumulation of lacustrine sediments has resulted in isolation from confined aquifers, causing LGD to primarily occur as springs in nearshore lake areas. Conversely, the direct connection between the deepwater zone of the lake and the water‐rich confined aquifer has resulted in a higher LGD rate in the lake interior. Present study not only offers a novel approach for quantifying the spatial patterns of LGD but also provides valuable insights for LGD studies conducted in lakes globally. Plain Language Summary Lacustrine Groundwater Discharge (LGD) is a crucial water and nutrient source for lakes, but accurately quantifying its spatial variability is challenging. Little research has explored the impact of interaction zone structures between lakes and aquifers on this variability. This study combines thermal remote sensing with a 222Rn model to estimate LGD spatial patterns in a central Yangtze River basin oxbow lake. Various parameters' vertical distributions were examined to elucidate groundwater's influence on lake surface temperature (LST) distribution. Regression equations correlated LST with lake water 222Rn concentration across different depth zones, enabling inverse calculation of 222Rn concentration in the entire lake. Utilizing a 222Rn mass balance model, LGD rates varied from 0 to 330.96 mm/d. Shallow water zones, isolated from underlying confined aquifers due to lacustrine sediment accumulation, primarily exhibited LGD as nearshore springs. Conversely, direct connections between the lake's deepwater zone and water‐rich confined aquifers led to higher LGD rates in the lake interior. Key Points Novel approach coupling thermal infrared remote sensing and 222Rn model was used for gridded estimation of Lacustrine groundwater discharge (LGD) The spatial distribution patterns of LGD in deep water and shallow water areas are opposite Groundwater‐lake interaction zone structure controls the spatial distribution of LGD

The Paleocene‐Eocene Thermal Maximum (PETM; ∼56 Ma)–a geologically rapid carbon‐release event similar to anthropogenic carbon emissions–is ideal for investigating weathering responses to rapid carbon release and associated climate change. Here, for the first time, we present high‐resolution lacustrine lithium isotope data that reflect basin‐scale silicate weathering across the PETM in the Nanyang Basin, eastern China. Our results reveal an ∼100% increase in regional silicate weathering intensity through the PETM relative to the pre‐PETM level. Synchronous variations between carbon isotope values and weathering intensity demonstrate a strong coupling between carbon cycle, climate, and chemical weathering on millennial timescales. These findings argue that strong negative weathering feedback and massive removal of CO2 maintained Earth's climate within a habitable range during the PETM. Plain Language Summary The chemical breakdown of silicate minerals on continents is a major regulator of climate via atmospheric CO2 removal on million‐year timescales; however, on shorter timescales of greater relevance to understanding the fate of anthropogenic CO2, the link between silicate weathering and climate remains unclear. The Paleocene‐Eocene Thermal Maximum (PETM; ∼56 Ma)–a geologically rapid carbon‐release event similar to anthropogenic carbon emissions–represents an ideal interval for investigating weathering responses to rapid carbon release and climate change. Here, we measured the chemistry of lacustrine sediments that span the PETM in the Nanyang Basin, eastern China to reveal the link between silicate weathering and rapid carbon release. We find that regional silicate weathering increased by ∼100% through the PETM. Our results also demonstrate that carbon release, climate change, and silicate chemical weathering were closely coupled over millennial time scales. Strong negative silicate weathering feedback and massive removal of CO2 maintained Earth's climate within a habitable range across the PETM. Key Points First lacustrine Li isotope measurements during the Paleocene‐Eocene Thermal Maximum (PETM) Lacustrine Li isotope compositions reflect regional silicate weathering processes across the PETM Carbon release, climate, and weathering were tightly coupled on millennial timescales