| 1. |
- Buntgen, U., et al.
(författare)
-
Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE
- 2018
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.
|
|
| 2. |
- Feng, X. Y., et al.
(författare)
-
Tree-ring cellulose oxygen isotopes indicate atmospheric aridity in the western Kunlun Mountains
- 2022
-
Ingår i: Ecological Indicators. - : Elsevier BV. - 1470-160X. ; 137
-
Tidskriftsartikel (refereegranskat)abstract
- As an important indicator of atmospheric aridity, the vapor pressure deficit (VPD) is being paid increasing attention in global change researches during recent decades. However, available proxy data with the capability to represent VPD is still scarce in the globe. Herein we demonstrated a "hidden " frequency-dependent indication of tree-ring cellulose oxygen isotope (delta(OTRC)-O-18) to atmospheric aridity in the western Kunlun Mountains, Central Asia. In applying correlation and partial correlation analysis, frequency-dependent climatic drivers triggering the delta(OTRC)-O-18 values were detected. For the raw data with inter-decadal variability, delta(OTRC)-O-18 variations mainly indicated May-August precipitation (Local: r = -0.59, p < 0.001; Moisture source: r = -0.53, p < 0.001), evapotranspiration (ET) (Local: r = -0.57, p < 0.001; Moisture source: r = -0.51, p < 0.001). After a 5-year high-pass filter, the delta(OTRC)-O-18 series revealed highly significant correlation with May-August VPD (Local: r = 0.82, p < 0.001; Moisture source: r = 0.80, p < 0.001). The partial correlation further confirmed the strong linkages with high-frequency VPD when the impact of any additional eco-climatological variable (precipitation, temperature, ET, soil moisture 0-40 cm) was excluded. In contrast, if the effect of May-August VPD was excluded, relationships between delta(OTRC)-O-18 and other variables turned insignificant. Collectively, it was concluded that delta 18OTRC from the western Kunlun Mountains may indicate VPD at timescales < 5 years. Our results suggest that frequency dependent climatic significances should be considered when interpreting multi-process determined delta(OTRC)-O-18 as a climate-proxy.
|
|
| 3. |
- Wang, L., et al.
(författare)
-
Enhanced Variability and Declining Trend of Soil Moisture Since the 1880s on the Southeastern Tibetan Plateau
- 2023
-
Ingår i: Water Resources Research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 59:3
-
Tidskriftsartikel (refereegranskat)abstract
- Historical soil moisture (SM) variations, trends, and their driving factors remain scarce for the area of Tibetan Plateau (TP), which hinders putting a sensible assessment of the current and future ecological drought risk into perspective. Here, we report the first three century-long regional summer (July-August) SM reconstruction for the southeastern TP during 1691-2007 CE using a paleoclimate proxy, that is, tree-ring delta O-18. The SM reconstruction, which explained 60.9% of the actual variance, revealed that an abrupt wet-to-dry change occurred in 1884. After 1884, SM exhibited a decreasing trend and enhanced variability, and dry summers occurred more frequently. In particular, the variability in SM reached an unprecedented level after the 1950s relative to that during the past three centuries. A structural equation model and running correlation analysis revealed that SM variation was mainly controlled by precipitation rather than temperature. This indicates that the anthropogenic-related weakening of the Indian summer monsoon played a more dominant role in SM changes after 1884 than the increase in temperature. If the SM variability is to be further increased in the future, it may undermine ecosystem stability and forest health. The results of this study are significant for predicting ecological drought in ecologically vulnerable regions such as the High Asia.
|
|
| 4. |
- Wang, L., et al.
(författare)
-
The 1820s Marks a Shift to Hotter-Drier Summers in Western Europe Since 1360
- 2022
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:15
-
Tidskriftsartikel (refereegranskat)abstract
- Recent soil moisture (SM) reconstructions revealed plunging trends and enhanced SM-temperature couplings over the last two decades in dry regions. However, how SM changed and whether the land-atmosphere interaction was intensified over time in humid regions remained unknown. Here we reported the first six-century-long regional summer SM reconstruction (1360-2000 CE) in western Europe (WE) using three individual tree-ring delta O-18 chronologies in England and France. A sharp wet-to-dry change occurred around 1820, earlier than 1850-1900 CE, the commonly used historical baseline of anthropogenic climate changes. Enhanced coupling of SM-temperature followed, with stronger summer sea level pressure anomalies in dry years after the 1820s. Our results reveal that the hotter-drier regime has also become more frequent in humid WE under global warming.
|
|
