ALBERT

Description: The Greenland Interstadial 21 (GIS 21), one of the longest warm events during the last glacial, occurred in conjunction with the transition from marine isotope stages (MIS) 5a to 4. Precise determination of the timing and duration of this event can improve our understanding of hydroclimatic connection between low and high latitudes over this MIS boundary. Facilitated by a robust chronology with closely spaced U-Th ages, replicated sub-decadal-resolved δ18O records of two stalagmites from Sanxing Cave, Southwest China, express Asian Summer Monsoon (ASM) history from 79.0 ± 0.2 to 75.7 ± 0.2 thousand years before present (kyr BP, before AD 1950) to reveal detailed structure of MIS 5a/4 transition and Chinese Interstadial (CIS) 21. The composited Sanxing record is characterized with three centennial-scale strong monsoon peaks and a 700-yr-long weak monsoon period within the CIS 21 rebound-type event, concurrent with its counterpart of Greenland Interstadial 21 (GIS 21). This strong resemblance suggests a rapid atmospheric teleconnection between the North Atlantic and the ASM regions. The transition at the termination of the Chinese Interstadial (CIS) 21 is determined to be from 77.0 ± 0.2 to 76.6 ± 0.2 kyr BP with a mid-point at 76.8 ± 0.2 kyr BP, which is 0.5–1.0 kyr younger than the correspondent of the end of GIS 21 on GICC05modelext and AICC2012 timescales. Given its high accuracy, our Sanxing Cave chronology can become one of the potential references for chronological refinement for ice-core records.

Description: Stalagmite ky1, with a length of 75 mm and the upper part (from top to 42.769 mm depth) consisting of 678 laminae, was collected from Kaiyuan Cave in the coastal area of Shandong Peninsula, northern China, located in a warm temperate zone in the East Asia monsoon area. Based on high-precision dating with the U–230Th technique and continuous counting of laminae, the 1st and 678th laminae have been confirmed to be AD 1894 ± 20 and 1217 ± 20 from top to bottom, respectively. By the measurement of laminae thickness and δ18O ratios, we haved obtained the time series data of thickness of laminae and δ18O ratios from AD 1217 ± 20 to 1894 ± 20, analyzed the climatic–environmental meaning of variations in the thickness of laminae, which have a good correspondence with the cumulative departure curve of the drought–waterlog index in the historical period. The results show that, in the  ∼  678 years from AD 1217 ± 20 to 1894 ± 20, both the thickness of the laminae and the degree of fluctuation in the thickness of the laminae of stalagmite ky1 have obvious stages of variation and are completely synchronized with the contemporaneous intensity of the summer monsoons and precipitation as time changed. There is a negative correlation between the thickness of the laminae and the summer monsoon intensity and precipitation. There is a positive correlation between the degree of fluctuation in the thickness of the laminae and both the intensity of the summer monsoons and the precipitation. Therefore, for the Kaiyuan Cave in the coastal area of both the warm temperate zone and the East Asia monsoon area, the variations in the thickness of the laminae are not only related to the change in the climatic factors themselves but also related to the degree of climatic stability. In the coastal area belonging to the warm temperate zone and the East Asia monsoon area, the climate change between the LIA (Little Ice Age) and the MWP (Medieval Warm Period), in addition to less precipitation and low temperatures (a type of dry and cold climate), also shows an obviously decreasing trend in the degree of climatic stability.

Description: The oxygen and hydrogen isotopic compositions of water in fluid inclusions in speleothems are important hydroclimate proxies because they provide information on the isotopic compositions of rainwater in the past. Moreover, because isotopic differences between fluid inclusion water and the host calcite provide information on the past isotopic fractionation factor, they are also useful for quantitative estimation of past temperature changes. The oxygen isotope ratio of inclusion water (δ18Ofi), however, may be affected by isotopic exchange between the water and the host carbonate. Thus, it is necessary to estimate the bias caused by this postdepositional effect for precise reconstruction of paleotemperatures. Here, we evaluate the isotopic exchange reaction between inclusion water and host calcite based on a laboratory experiment involving a natural stalagmite. Multiple stalagmite samples cut from the same depth interval were heated at 105 ∘C in the laboratory from 0 to 80 h. Then, the isotopic compositions of the inclusion water were measured. In the 105 ∘C heating experiments, the δ18Ofi values increased from the initial value by 0.7 ‰ and then remained stable after ca. 20 h. The hydrogen isotope ratio of water showed no trend in response to the heating experiments, suggesting that the hydrogen isotopic composition of fluid inclusion water effectively reflects the composition of past drip water. We then evaluated the process behind the observed isotopic variations using a partial equilibration model. The experimental results are best explained by the assumption that a thin CaCO3 layer surrounding the inclusion reacted with the water. The amount of CaCO3 that reacted with the water is equivalent to 2 % of the water inclusions in molar terms. These results suggest that the magnitude of the isotopic exchange effect has a minor influence on paleotemperature estimates for Quaternary climate reconstructions.

Description: Recent Southern Hemisphere (SH) atmospheric circulation, predominantly driven by stratospheric ozone depletion over Antarctica, has caused changes in climate across the extratropics. Here, we present evidence that the Brazilian coast (southwestern Atlantic) may have been impacted from both wind and sea-surface temperature changes derived from this process. Skeleton analysis of massive coral species living in shallow waters off Brazil are very sensitive to air–sea interactions, and seem to record this impact. Growth rates of Brazilian corals show a trend reversal that fits the ozone depletion evolution, confirming that ozone impacts are far reaching and potentially affect coastal ecosystems in tropical environments.