Quantification of Holocene temperatures in the eastern Hunshandake Sandy Land using δ13C of loess organic matter.

The soil organic carbon isotope indicator (δ13C org) is widely used in paleoecology and paleoclimate reconstruction due to its ability to record the history of paleovegetation change. Although it has been used as a proxy for precipitation reconstruction, increasing evidence suggests that temperature has played a crucial role in influencing the relative abundance of C 3 /C 4 plants in the mid-latitudes during the interglacial period. This opens up the possibility of reconstructing Holocene temperature using δ13C org. In this study, the variation of δ13C org values in a Holocene loess profile (GLH profile), located in the eastern Hunshandake Sandy Land, China, was investigated. And we analyzed the correlation between δ13C org values and modern temperatures for a total of 792 surface soil samples from mid-latitudes of the Northern Hemisphere, which had thermal conditions comparable to the GLH profile. Strong positive correlations were found between δ13C org values of surface soil samples and both summer temperatures (r = 0.672, p < 0.001) and growing season temperatures (r = 0.669, p < 0.001). Additionally, δ13C org values showed significant positive correlations with accumulated temperatures above 10 °C (r = 0.641, p < 0.001) and above 0 °C (r = 0.527, p < 0.001). However, the correlation with mean annual temperature was weak (r = 0.280, p < 0.001). The δ13C org variation in the GLH profile recorded a mixed C 3 /C 4 vegetation composition, with C 4 plants comprising between 23.40% and 1.70% of the total abundance during the Holocene. The combined evidence from modern processes and profile variations confirms that warm-season temperature was the main factor driving variations in the δ13C org values in the GLH profile. Therefore, we used δ13C org –temperature conversion equations to quantify Holocene seasonal and accumulated temperatures based on the GLH profile. The reconstructed summer temperatures peaked at 9.3 ka, followed by a fluctuating downward trend during the mid- and late-Holocene, which is consistent with variations in summer solar insolation. Mean summer temperatures were relatively high at 23.3 °C and 22.5 °C in the early and mid-Holocene, respectively, while the lowest mean summer temperature of 20.5 °C occurred in the late Holocene. Accumulated temperatures above 10 °C and above 0 °C in the early Holocene were 3722 °C·d and 4641 °C·d, respectively, similar to modern observations in the Beijing area, indicating a southward shift of the temperature zone by nearly three degrees of latitude since the early Holocene. These reconstruction results are supported by modern observations, TraCE21 simulations, and other studies. This study is significant for extending the application of the δ13C org indicator for quantitative paleoclimate reconstructions. It verifies its effectiveness in quantifying Holocene temperatures in the marginal zone of the East Asian summer monsoon. • Attempt to reconstruct paleotemperatures quantitatively using the δ13C org indicator. • Conversion equations established between δ13C org - temperature in mid-latitude regions. • Holocene summer temperature and accumulated temperature (T ≥ 0 °C, T ≥ 10 °C) obtained. • Holocene summer temperature peaked at 9.3 ka and was controlled by solar insolation forcing. • Temperature zone shifted nearly three latitudes southward since early Holocene. [ABSTRACT FROM AUTHOR]