Large variations of <scp>δ¹³C</scp> values in stalagmites from southeastern <scp>C</scp>hina during historical times: implications for anthropogenic deforestation

<jats:p>Variations in speleothem <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> values can reflect changes in overlying surface vegetation, which, over historical time scales, may represent the influence of human activities. Here, we examined <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> variations in two stalagmites growing for the last 2200 years in <jats:styled-content style="fixed-case">S</jats:styled-content>hennong <jats:styled-content style="fixed-case">C</jats:styled-content>ave, <jats:styled-content style="fixed-case">J</jats:styled-content>iangxi <jats:styled-content style="fixed-case">P</jats:styled-content>rovince, <jats:styled-content style="fixed-case">SE C</jats:styled-content>hina. The two <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> records corroborate well one another and show a prominent 6‰ enrichment of the <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> values from <jats:styled-content style="fixed-case">AD</jats:styled-content> 700 to 1100. The isotopic equilibrium for modern calcite and negative correlation between <jats:styled-content style="fixed-case">δ<jats:sup>18</jats:sup>O</jats:styled-content> and <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> values along the growth axis suggest that the influences of kinetic fractionation are negligible. Varied correlations between <jats:styled-content style="fixed-case"><jats:roman>Mg</jats:roman></jats:styled-content>/<jats:styled-content style="fixed-case"><jats:roman>Ca</jats:roman></jats:styled-content> and <jats:styled-content style="fixed-case"><jats:roman>Sr</jats:roman></jats:styled-content>/<jats:styled-content style="fixed-case"><jats:roman>Ca</jats:roman></jats:styled-content> ratios and divergent changes between <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> values and <jats:styled-content style="fixed-case"><jats:roman>Mg</jats:roman></jats:styled-content>/<jats:styled-content style="fixed-case"><jats:roman>Ca</jats:roman></jats:styled-content> and <jats:styled-content style="fixed-case"><jats:roman>Sr</jats:roman></jats:styled-content>/<jats:styled-content style="fixed-case"><jats:roman>Ca</jats:roman></jats:styled-content> ratios from <jats:styled-content style="fixed-case">AD</jats:styled-content> 700 to 1100 reveal that the prior calcite precipitation (<jats:styled-content style="fixed-case">PCP</jats:styled-content>) and water–rock interaction did not dominate the increase of <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> values. It is plausible that the obvious <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> variation was largely influenced by the changes in vegetation cover overlying the cave. Our <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> results, together with the records of climate and human activity from historical documentary records, suggest that: (i) prior to <jats:styled-content style="fixed-case">AD</jats:styled-content> 700, small fluctuations in relatively light <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> values reflect the presence of lush forest coverage above the cave, which was minimally disturbed by human activities; (ii) during <jats:styled-content style="fixed-case">AD</jats:styled-content> 700–1100, the drastic increase in <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> values indicates persistent and massive deforestation associated with large‐scale immigration into northern <jats:styled-content style="fixed-case">J</jats:styled-content>iangxi after the <jats:italic><jats:styled-content style="fixed-case">R</jats:styled-content>ebellion of <jats:styled-content style="fixed-case">A</jats:styled-content>n & <jats:styled-content style="fixed-case">S</jats:styled-content>hi</jats:italic> (<jats:styled-content style="fixed-case">AD</jats:styled-content> 755–763) in the <jats:styled-content style="fixed-case">T</jats:styled-content>ang <jats:styled-content style="fixed-case">D</jats:styled-content>ynasty and the subsequent development of agriculture and economic activity; and (iii) since <jats:styled-content style="fixed-case">AD</jats:styled-content> 1100, fluctuations in relatively high <jats:styled-content style="fixed-case">δ<jats:sup>13</jats:sup>C</jats:styled-content> values suggest that local vegetation during the last millennium has been sparse. Since the <jats:italic><jats:styled-content style="fixed-case">R</jats:styled-content>ebellion of <jats:styled-content style="fixed-case">A</jats:styled-content>n & <jats:styled-content style="fixed-case">S</jats:styled-content>hi</jats:italic>, southeastern <jats:styled-content style="fixed-case">C</jats:st ...