Stalagmite is one kind of secondary carbonates formed in limestone caves (speleothem). After cave water droplets containing Ca2+ and $$\rm{HCO}_3^-$$
 drip onto floor, carbonate in the water might become supersaturated due to CO2 degassing under certain conditions, resulting in the formation of stalagmite in a process year after year. Stalagmite is one of important geological archives for paleoclimate research. The advantages include wide spatial distribution, suitable for U-Th and U-Pb dating, enriched in climate proxies, continuity, long time span, comparability and lower sampling cost etc. These factors have propelled stalagmite paleoclimate research to the forefront of global paleoclimatology with an irreplaceable role. The stalagmite paleoclimate study started in the western countries, mainly in Europe and America in 1960s–1970s, while the relevant research in China was progressively developed in the 1980s–1990s after the Reform and Opening up. Although there was a huge gap between the overall research level in China and western countries, a solid research foundation, as well as a number of talent teams were established during the period. In the 21st century, starting from the publication of stalagmite records from Hulu Cave in Nanjing in 2001, the stalagmite paleoclimate research in China has ushered in a flourishing development and a real leap on the basis of international cooperation, resulting in significant international impacts. The landmark achievements, including establishment of the world’s longest (640000 years) East Asian monsoon stalagmite record, as well as the longest Indian monsoon (280000 years), South American monsoon (250000 years), North American westerly climate (330000 years), Central Asian westerly climate (135000 years), and northwestern China westerly climate (500000 years), have laid a milestone in the paleoclimate study in these climate domains. Importantly, these stalagmite records have revealed the relationship of Asian monsoon variations with solar insolation climate change in polar regions, and the South American monsoon changes on orbital-suborbital timescales, which have provided new geological observations for the development of orbital-suborbital climate theory; elaborated coupling and differentiation relationships between the Asian monsoon and the westerly climate; reconstructed the history of Asian monsoon changes in the Holocene in detail, and thus the hydrological and climate variances behind Chinese and Indian civilization-cultural evolutions. Furthermore, a large number of high-resolution stalagmite records over the past 2000 years have been reconstructed, which are important for understanding short-term climate variability and magnitude, events, cycles, and thus the future climate projection. The achievements have also involved the improvements of a number of important techniques, such as U-Th dating method, the establishments of various hydroclimatic proxies, as well as the contributions to the reconstruction of the atmosphere 14C variation history over the past ∼54000 years. On the perspective of the future, the Chinese stalagmite community should continue to develop key techniques, further clarify the hydroclimatic significance of stalagmite proxies, impel the integration of related disciplines, and concentrate on key scientific issues in global climate change and major social demands.

Chinese stalagmite paleoclimate researches: A review and perspective

Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude-to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies.

Synchronous timing of abrupt climate changes during the last glacial period.

. Stable isotope
records from speleothems provide information on past climate changes, most
particularly information that can be used to reconstruct past changes in
precipitation and atmospheric circulation. These records are increasingly
being used to provide “out-of-sample” evaluations of isotope-enabled
climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an
international working group of the Past Global Changes (PAGES) project. The
working group aims to provide a comprehensive compilation of speleothem
isotope records for climate reconstruction and model evaluation. The SISAL
database contains data for individual speleothems, grouped by cave system.
Stable isotopes of oxygen and carbon ( δ18 O, δ13 C)
measurements are referenced by distance from the top or bottom of the speleothem. Additional
tables provide information on dating, including information on the dates used
to construct the original age model and sufficient information to assess the
quality of each data set and to erect a standardized chronology across
different speleothems. The metadata table provides location information,
information on the full range of measurements carried out on each speleothem
and information on the cave system that is relevant to the interpretation of
the records, as well as citations for both publications and archived data.
The compiled data are available at https://doi.org/10.17864/1947.147 .

/pdf/the-sisal-database-a-global-resource-to-document-oxygen-and-4nnq9c9vi6.pdf

The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems

Geochemical characteristics of cave drip water respond to ENSO based on a 6-year monitoring work in Yangkou Cave, Southwest China

Variation of the Asian summer monsoon since the last glacial-interglacial recorded in a stalagmite from southwest China

Potential influence of temperature changes in the Southern Hemisphere on the evolution of the Asian summer monsoon during the last glacial period

The excessive extraction and recharge of groundwater lead to long-time seasonal land subsidence in Los Angeles, USA, and especially in the Santa Ana basin. The rate of land subsidence in the Santa Ana basin has been rising, which could pose a danger to infrastructure and human lives. However, the most recent research on land surface deformation in the area was conducted using the traditional parameter estimation method, resulting in little understanding of the regional spatiotemporal characteristics. The parametric method consists of a least square linear inversion, using the pre-defined mathematical geometric or geophysical theoretical models to describe groundwater deformation, and it requires precise external environmental variables and accurate geophysical parameters, which are more difficult to implement. In this study, multitemporal InSAR-derived deformation time series are analyzed by using 69 descending C-band Sentinel-1A SAR scenes acquired from 2015 to 2018. A method based on independent component analysis (ICA) is applied to characterize the spatial pattern and temporal evolution of land subsidence in the Santa Ana basin. The results reveal two different spatial and temporal deformation patterns in the basin. First, a widespread seasonal deformation is identified by the first component, related to annual seasonal groundwater level changes, and the overall deformation shows a concentrated spatial pattern. The second component captures a long-term signal with a large-scale spatial pattern. For quantitative assessment, the obtained deformation time series are compared with the GNSS data, validating an accuracy of millimeters. We further calculate the cross-correlation coefficient and the elastic skeletal storage coefficient from the ICA-derived seasonal deformation and groundwater level, which reveals that the deformation responds quickly (i.e., a lag of 8 days) to the change in groundwater and the Santa Ana aquifer retains almost the same elasticity for at least 15 years. Quantifying the spatiotemporal characteristics of the deformation in the Santa Ana basin can provide a reference for the monitoring and managing of groundwater.

https://www.mdpi.com/2072-4292/14/11/2624/pdf?version=1654076354

Characterizing Spatiotemporal Patterns of Land Deformation in the Santa Ana Basin, Los Angeles, from InSAR Time Series and Independent Component Analysis

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Potential influence of temperature changes in the Southern Hemisphere on the evolution of the Asian summer monsoon during the last glacial period

Characterizing Spatiotemporal Patterns of Land Deformation in the Santa Ana Basin, Los Angeles, from InSAR Time Series and Independent Component Analysis