In situ measurement of seasonal δ18O variations and analysis of isotopic trends in a modern speleothem from southwest Australia
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Speleothem
Stalagmite
δ18O
Seasonality
Ice core
Global warming and climate anomalies have attracted worldwide attention. The study of global climate change has received increasing attention from all countries and fields worldwide. Paleoclimate research is an important way to understand past global change and environmental evolution and to simulate and predict future climate development. A stalagmite ND3 collected in Naduo Cave was used to reconstruct the history of local climate and environmental changes from 0.55 to 5.07 ka BP based on the data of 13 230Th ages and 642 groups of oxygen and carbon stable isotopes. First, according to correlation analysis, δ18O and δ13C were significantly correlated (correlation coefficient r = 0.308, n = 318, ) during the 5.07–2.00 ka BP period. However, during the period of 2–0.55 ka BP, there was no significant correlation . The δ18O and δ13C data indicate that the climatic environment changed asynchronously during the period of 2.00–0.55 ka BP. During the period of 5.07–2.00 ka BP, the influence of human activities was weak, and δ18O and δ13C indicate similar climatic and environmental conditions, both of which changed in the same direction (positive correlation). In other words, when δ18O was positive, it indicated weak summer monsoons and lower precipitation, which led to declines in vegetation, weakened biological activity, and decreased soil CO2 and positive δ13C. The reverse patterns were also true. Since 2.0 ka BP, the intensity of human activities and the transformation and influence of surface vegetation have increased, and native vegetation has been destroyed in large quantities. Therefore, the climatic and environmental significance indicated by δ13C and δ18O has been well demonstrated. Second, the δ18O records showed that stalagmite ND3 responded to the weak monsoon drought events of 4.2 ka BP and 2.8 ka BP in the Holocene in a discontinuous deposition manner, which brings up new directions for future research.
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TIMS U-Th dating and high-resolution oxygen isotopic composition measurements were conducted on a stalagmite SI3 collected from Shizi cave, Nuoshuihe, northeastern Sichuan, Central China. The stalagmite SI3 was developed between 54-46 ka. Its δ18O record displays a high similarity with those of stalagmites MSL and MSD from Hulu cave, East China and D4 from Dongge cave, Southwest China, respectively. The trend of the δ18O record of SI3 also parallels with those of ice core GISP2 from polar area and of speleothem in Israel. These suggest that the δ18O record of SI3 is closely related with summer monsoon variation in East Asia. However, some evidences seem to suggest that carbonates in SI3 are more 18O enriched than those deposited under oxygen isotopic equilibrium condition. There was probably kinetic fractionation when SI3 was developed. This may be explained by the locus of SI3 that was collected near the entrance of Shizi cave. The possible mechanism between the δ18O record of SI3 and the variation in East Asian summer monsoon was speculated. It is suggested that in the East Asian summer monsoon domain, the δ18O record of some speleothem deposited even under nonequilibrium condition is still a potential proxy for summer monsoon variation.
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Here we use the δ 18 O time‐series of three stalagmites from the high alpine Spannagel cave (Austria) which grew in small distance from each other to construct a precisely dated, continuous δ 18 O curve for the last 9 kyr (COMNISPA). This speleothem record is not influenced by effects of kinetic isotope fractionation due to the low temperatures in the cave. Thus, the variations in δ 18 O can be interpreted in terms of past climate change. COMNISPA exhibits several oscillations within the Holocene, and their timing and duration is in agreement with that documented by other alpine archives.
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Abstract Fluid inclusion water isotope measurements in speleothems have great potential for paleoclimate studies as they enable the reconstruction of precipitation dynamics and land temperatures. Several previous observations, however, suggest that inclusion waters do not always reflect the isotopic composition of surface precipitation. In such cases, dripwaters are thought to be modified by evaporation in the cave environment that results in more positive δ 2 H and δ 18 O values and shallow δ 2 H/δ 18 O slopes. Although evaporation can occur in cave systems, water can also be lost to evaporation during analysis but before water extraction. Here, we examine the likelihood of this possibility with a stalagmite from Borneo. We demonstrate that many samples lose water, and that water loss is controlled by the type and size of inclusions. With multiple replicate measurements of coeval samples, we calculate an evaporative δ 2 H/δ 18 O slope of 1.0 ± 0.6 (2SE). This value is consistent with model predictions of evaporative fractionation at high analytical temperature and low humidity. Finally, we propose a method to correct for this effect. We find that fluid–calcite δ 18 O paleotemperatures calculated with corrected δ 18 O data show excellent agreement with recent microthermometry temperature estimates for Borneo, supporting the validity of our approach and implying limited stalagmite δ 18 O disequilibrium variations. Corrected fluid inclusion δ 18 O and δ 2 H values follow the expected hydroclimate response of Borneo to periods of reduced Atlantic Ocean meridional overturning circulation. Our results suggest that careful petrographic examination and multiple replicate measurements are necessary for reliable paleoclimate reconstructions with speleothem fluid inclusion water isotopes.
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