Description: Chondrules in chondritic meteorites are unique witnesses of nebular and asteroidal processes that preceded large-scale planetary accretion. Together with refractory calcium-aluminium-rich inclusions (CAIs), they are the sources of our knowledge of the initial evolution of the early Solar System. We have investigated a single very large (〉10 mm in longer dimension) chondrule, hereafter, the mega-chondrule A25-2, extracted from the Allende CV3 chondrite. We characterised texture, mineralogy and mineral chemistry of this chondrule, and studied its Al-Mg, U-Pb and U-isotope systematics. We also studied the distribution of U, Th and Pb, and measured Pb isotopic composition in individual minerals of A25-2 by secondary ion mass-spectrometry (SIMS). The main difficulty in absolute age determination was the presence of pervasive and resilient non-radiogenic Pb. In the search for the best way to separate radiogenic Pb from non-radiogenic Pb components of terrestrial and asteroidal origins, we used various protocols of multi-step leaching and assessed their efficiency in generating data suitable for the construction of an isochron. Testing the data filtering procedure led us to explore the behaviour of the stepwise leaching method in the presence of pervasive and resilient non-radiogenic Pb. The model age patterns observed in the final HF partial dissolution steps were probably induced by isotopic fractionation. Although step leaching did not yield fractions with highly radiogenic Pb, a Pb-Pb isochron age corrected for measured 238U/235U was obtained by: (1) data filtering process based on strict analytical and geochemical criteria to include in the Pb-Pb isochron only leaching steps free from terrestrial contamination and (2) arithmetically recombined analyses to cancel the effects of leaching-induced isotopic fractionation. This extensive data processing yielded the age of 4568.5±3.0 Ma, which we consider reliable within its uncertainty limits, although it is not as precise as, and more model dependent than, the age that could have been obtained if Pb isotopic compositions were more radiogenic. The 238U/235U ratio of the mega-chondrule is 137.764±0.016, which is similar to the ratios obtained from single chondrules yet slightly different from small pooled Allende chondrules. The initial 27Al/26Al ratio inferred from internal isochron obtained from SIMS Al-Mg isotope measurements is (5.4±6.5)×10–6, which corresponds to 4565.0 +0.8/-∞ Ma, assuming homogeneous distribution of 26Al throughout the protoplanetary disk at the canonical level (∼5.2×10−5). This age is 3.5±3.1 Ma younger than the Pb-isotopic age. Calculation of 26Al-26Mg age assuming initial (27Al/26Al)0 of (1.36±0.72)×10–5 in the chondrule-forming region yields the age of 4566.4+0.8/-∞, which is consistent with the Pb-isotopic age.

Description: The problem of black and malodorous water bodies has been a pressing concern for urban administrators, and the utilization of submerged macrophytes for ecological restoration has been demonstrated as a potent technique for the abatement of these issues. This study investigated the use of Vallisneria natans, Ceratophyllum demersum, and Potamogeton malainus for the remediation of black and malodorous water bodies. The optimization of the planting structure of the submerged macrophytes was based on the efficacy of removal of chemical oxygen demand (COD), total phosphorus (TP), ammonia nitrogen (NH4+-N), and total nitrogen (TN). High-throughput DNA sequencing was also employed to analyze the bacterial communities adhered to the submerged macrophytes. The results of the study indicated that a combination of Vallisneria natans and Potamogeton malainus was the most effective planting structure for water restoration. The DNA sequencing analysis revealed that the dominant bacterial phyla in the selected submerged macrophytes were Proteobacteria, Actinobacteria, Bacteroidetes, and Cyanobacteria. Among the monotype submerged macrophytes, Vallisneria natans demonstrated the highest water purification capacity, with the highest relative abundance of functional bacteria. Furthermore, the abundance of Pseudomonas in nitrogen and phosphorus removal bacteria was found to be absolutely dominant (65.4%, 23.7%) in two of the samples. Given that the abundance of Pseudomonas in the best planting structure was relatively low, it is hypothesized that other functional bacteria may play a more significant role in nitrogen and phosphorus removal.

Description: Understanding the sea ice variability and the mechanisms involved during warm periods of the Earth is essential for a better understanding of the sea ice changes at the present and in the future. Based on simulations with the model LOVECLIM, this study investigates the sea ice variations during the last nine interglacials and focuses on the inter-comparison between interglacials as well as their differences from the present and future. The results show that the annual mean Arctic sea ice variation is primarily controlled by local summer insolation, while the annual mean Southern Ocean sea ice variation is more influenced by the CO〈sub〉2〈/sub〉 concentration but the effect of local summer insolation can’t be ignored. As compared to the present, the last nine interglacials all have much less sea ice in the Arctic annually and seasonally due to high summer insolation. They also have much less Arctic sea ice in summer than the double CO〈sub〉2〈/sub〉 experiment, which makes to some degree the interglacials possible analogues for the future in terms of the changes of sea ice. However, compared to the double CO〈sub〉2〈/sub〉 experiment, the interglacials all have much more sea ice in the Southern Ocean due to their much lower CO〈sub〉2〈/sub〉 concentration, which suggests the inappropriateness of considering the interglacials as analogues for the future in the Southern Ocean. Our results suggest that in the search for potential analogues of the present and future climate, the seasonal and regional climate variations should be considered.

Description: Various paleoclimate records show that the end of interglacials of the late Pleistocene was marked by abrupt cooling events. Strong abrupt cooling occurring when climate was still in a warm interglacial condition is puzzling. Our transient climate simulations for the eleven interglacial (sub)stages of the past 800,000 years show that, when summer insolation in the Northern Hemisphere (NH) high latitudes decreases to a critical value (a threshold), it triggers a strong, abrupt weakening of the Atlantic meridional overturning circulation and consequently an abrupt cooling in the NH. The mechanism involves sea ice-ocean feedbacks in the Northern Nordic Sea and the Labrador Sea (Yin et al., 2021, doi: 10.1126/science.abg1737). The insolation-induced abrupt cooling is accompanied by abrupt changes in precipitation, vegetation from low to high latitudes and in particular by abrupt snow accumulation in polar regions. The timing of the simulated abrupt events at the end of interglacials is highly consistent with those observed in marine and terrestrial records, especially with those observed in high-resolution, absolutely-dated speleothem records in Asia and Europe, which validates the model results and reveals that the astronomically-induced slow variations of insolation could trigger abrupt climate events. Our results show that the insolation threshold occurred at the end of each interglacial of the past 800,000 years, suggesting its fundamental role in terminating the warm climate conditions of the interglacials. The next insolation threshold will occur in 50,000 years, implying an exceptionally long interglacial ahead.

Description: Archaeological records document a significant expansion of populations from the Last Glacial Maximum (LGM, ~23-19 ka) to the early Holocene (EH, ~9 ka) in Eurasia, which is often attributed to the influence of orbital-scale climate changes. Yet, information remains limited concerning the climatic factor(s) which were responsible for conditioning demographic patterns. Here, we present results from an improved Minimalist Terrestrial Resource Model (MTRM), forced by a transient climate simulation from the LGM to the EH. Simulated potential hunter-gatherer population densities and spatial distributions across Eurasia are supported by observed archaeological sites in Europe and China. In the low latitudes, potential population size change was predominantly controlled by precipitation and its strong influence on plant and animal resources. In the middle-high latitudes, temperature was the dominant driver in influencing potential population size change and animal resource availability. Different regional responses of potential populations to climate change across Eurasia - owing to variations in available food resources between the LGM and EH - provide a better understanding of human dispersal during the Late Pleistocene.

Description: The Asian-Australian monsoon (AAM) system distinctly influences global climate. However, the linkage between ENSO (El Ni~noeSouthern Oscillation) and AAM is still poorly understood over the last millennium. Here, we combined stalagmite d18O (d18Os) records with exceptionally high-resolution and high-precision chronologies to demonstrate a tight remote coupling between AAM and tropical ocean hydrology on the multi-year, decadal, and centennial timescales. Our results reveal that (1) There is a significant negative correlation between the multi-year weighted average precipitation d18O (d18Oaw) from the AAM and Southern Oscillation Index (SOI), providing a modern analogous coupling for linking stalagmite d18O (d18Os) and ENSO over the past 100 years. (2) Over the last millennium, the integrated d18Os record exhibit positive excursions during the Little Ice Age (LIA), marked by a tendency for more El Ni~no-like state conditions in the tropical Pacific, which is consistent in SST-gradient ENSO reconstruction but different to precipitation reconstruction. (3) Wavelet and power spectrum analysis for the integrated d18Os record in the AAM region show that there is a significant multi-year periodicity (2.2, 2.8, 3.5, 4.6 yr), conceding with the ENSO cycle (2e7 yr), whereas, some multi-decadal and centennial cycles (10.1, 17, 28.6, 52.7, 143 yr) are significant too. We provide evidence from instrumental and paleocliamte datasets (GNIP and NOAA) and propose a possible “circulation effect” mechanism responsible for variations of d18Os in the East Asian Monsoon (EAM) and Australian Monsoon (AM) region over the last millennium.