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Geothermal heat flow (GHF), which contains integrated information on geothermal gradient, thermal conductivity, and heat productivity of rocks as well as crustal/mantle heat flow, is a crucial parameter in many studies including the evaluation of geothermal resources in a region and the prediction of ice sheet mass loss. The GHF measurements in the Bohai Bay Basin are insufficient and unevenly distributed, and no model has been developed to predict the GHF distribution. In this paper, using eight geological features as input data and output GHF predictions, four different machine learning algorithms were evaluated and implemented to predict the GHF data in this area: (1) a generalized linear model (GLM), (2) a deep neural network (DNN), (3) a gradient boosted regression tree (GBRT), and (4) a support vector machine (SVM). The DNN model, in which the number of neurons is a multiple of the number of features, tended to perform better than the others. Both the SVM and DNN algorithms demonstrated better accuracy, with average relative prediction errors of 13.3 and 12.7%, respectively. The accuracy improved when using a hybrid SVM and DNN approach, with an average relative prediction error of 12.2%. Based on the above models, we produced three new GHF maps of the Bohai Bay Basin. They showed similar local anomaly features but with different ranges and degrees. The new GHF maps are more detailed and rational than the map produced by kriging interpolation. The predicted GHF had much higher accuracy, which is more consistent with the measured geothermal gradient in the related areas. Finally, we reclassified the basin into four different levels of geothermal exploration target areas based on the new GHF maps. [ABSTRACT FROM AUTHOR]

The Holocene hydrological regime on the Heixiazi Island is critical for understanding the evolution of the East Asian summer monsoon (EASM) for the island's climate-sensitive location on the northern fringe of the EASM domain. In this paper, a marsh depression on the central island was selected to reconstruct the locally hydrological variation and to discuss its indications for the Holocene EASM evolution. This work is based on multi-proxy (magnetic susceptibility, grain size, loss-on-ignition, and carbonate content) analyses of 22 modern sedimentary samples with a water-level gradient of 0–66 cm and 100 cored sedimentary samples covering last ~ 9.0 ka BP. The proxies' hydrological significance was previously interpreted by the 22 modern samples using linear regression equations to construct their relationships to water-level changes. Among these proxies, the magnetic susceptibility, carbonate content, as well as the Md and sand fraction of grain size exhibit high-level relationships against the water-level changes with R2 > 0.6. Thus, these four proxies' linear-regression equations were selected and used on the 100 cored samples, and the Holocene water-level changes in the studied depression were quantitatively reconstructed. It shows that two relatively high water-level stages with strengthened EASM occurred during 8.0–4.5 ka BP and 3.0–1.4 ka BP, which were alternated by three low water-level stages with declined EASM during ~ 9.0–8.0 ka BP, 4.5–3.0 ka BP, and 1.4–0 ka BP, respectively. Among these fluctuations, the highest water-level stage with most strengthened EASM which is defined as the Holocene Monsoon Maximum occurred during 6.4–4.5 ka BP. Such a new evolution pattern of the EASM can be further supported by a large variety of records from monsoon-margin regions. We suggest the Holocene EASM evolution was generally associated with the thermal conditions in both the inner Eurasia landmass and the West Pacific Ocean, with an exception of the weak EASM before 8.0 ka BP due to the enhanced Siberia High with the dominance of the Eurasia ice sheet in the early Holocene. [ABSTRACT FROM AUTHOR]

Nanopore metagenomic sequencing enables rapid annotating microbiological ecosystems, and the previous glacier-related sequencing applications (e.g., targeted ice sheets, ice lake, and cryoconite holes) inspire us to explore high-altitude glacier meltwater at Qilian Mountain, China (3000 to 4000 m above sea level, MASL). Our findings suggest that (1) despite only several hundred meters apart, the microbial communities and functionalities are quite different among vertical alpine distributions; (2) the high-altitude Qilian meltwater microbiome serve several main metabolic functions, including sulfur oxidation, selenite decomposing, photosynthesis, energy production, enzymic, and UV tolerant activities. Meanwhile, our Nanopore metagenomic results indicate that the microbial classifications and functionalities (e.g., chaperones, cold-shock, specific tRNA species, oxidative stress, and resistance to toxic compounds) of Qilian meltwater are highly consistent with the other glacial microbiome, emphasizing that only certain microbial species can survive in the cold environment and the molecular adaptions and lifestyles remain stable all over the world. Besides, we have shown Nanopore metagenomic sequencing can provide reliable prokaryotic classifications within or among studies, which therefore can encourage more applications in the field given faster turnaround time. However, we recommend accumulating at least 400 ng nucleic acids (after extraction) and maximizing Nanopore library preparation efficiency before on-site sequencing to obtain better resolutions. [ABSTRACT FROM AUTHOR]

The Holocene hydroclimate evolution and underlying mechanisms modulating the East Asian summer monsoon (EASM) remains controversial, especially in south eastern China. Here we present a multiproxy peat record of monsoon evolution from southeastern China covering the last 14 ka. Our new records show a relatively weaker EASM but wetter hydroclimate during the early (10 to 8 ka) and late Holocene (after 5.4 ka), while a stronger EASM and overall drier climate during the mid-Holocene (8 to 5.4 ka). In line with nearby speleothem records, our results reveal a dominant control of the northern-latitude ice-sheet meltwater forcing on millennial-scale East Asian hydroclimate variability during the last deglaciation and early Holocene. This dominant influence, however, likely waned once the global sea level had stabilized during the mid-to-late Holocene, giving way to other drivers of the monsoon and hydroclimate, including a combination of summer insolation and teleconnection patterns associated with vegetation-dust feedbacks. [ABSTRACT FROM AUTHOR]

The rainfall changes in East Asian summer monsoon (EASM) regions on the orbital timescale remain controversial due to the lack of reliable rainfall records. Here, we present new multiproxy records (δ18O, δ13C, Sr/Ca and Mg/Ca) of a 230Th-dated stalagmite from Hulu Cave in central eastern China. Multiproxy records reconstruct a regional hydroclimate history from 340 to 261 kyr BP (thousand years before present), approximately covering the antepenultimate glacial period. The δ18O record is dominated by the precessional cycles, suggesting that EASM responds to changes in Northern Hemisphere summer insolation (NHSI) on the orbital timescale. Significant correlations amongst the δ13C, Sr/Ca and Mg/Ca suggest that a common factor, i.e., the local hydrological cycle, controlled their variability, and their leading principal component can be used as a proxy linked to regional rainfall. This composite record bears a good similarity to those from the Chinese Loess Plateau, showing a gradually decreasing rainfall during the antepenultimate glacial period, consistent with changes in global ice volume. Superimposed on the long-term trend, three relative wetter intervals were responding to the higher NHSI periods, suggesting that EASM rainfall variability was induced by integrated effects of global ice volume and NHSI. The increased ice sheets and lower NHSI resulted in an increased meridional temperature gradient and southward shift of the westerlies, which shortened the duration of Meiyu and midsummer rainfall. The differences between the rainfall record and the stalagmite δ18O record indicate that the latter represents the overall EASM intensity linked to monsoon circulation, but does not directly reflect the rainfall changes at the cave sites. [ABSTRACT FROM AUTHOR]