第六届青年地学论坛

1873 / 2019-08-30 10:47:05

Paleo-pH reconstruction in a subtropical peat deposit based on the distribution of long-chain n-alkan-2-ones

peatland; pH; n-alkan-2-ones; acidification; drought.

2、地球化学 > 专题8：微生物有机地球化学

Peatlands are important repositories of organic carbon and recorders of paleoenvironment on continents. Peat pH values are sensitive to the nutrient status, vegetation assemblages, and ecosystem types of peatlands, and these factors are essential to influencing plant growth dynamics and establishing peat carbon stocks. However, few proxies currently exist that could accurately quantify past peat pH changes. Here we evaluate the pH significance of n-alkan-2-ones, which occur widely in peat deposits, and then apply the n-alkan-2-one derived pH-proxies to reconstruct peat pH changes for last 13 kyr in a subtropical peat core in central China. By comparisons to modern peat settings with different pH gradients, we found the distribution of n-alkan-2-ones was significantly different between acid and alkaline conditions. This difference can be explained by the pH control on the conversion of n-alkan-2-one precursor compounds. Based on this, transfer functions between pH and n-alkan-2-one proxies are established by applying linear and logarithmic regression models. Then we reconstruct variations of paleo-pH in the Dajiuhu peat sequence to identify the history of peatland acidification since the late deglacial that includes an abrupt decrease of pH from 11.6 to 10.6 ka. This acidification pattern is associated with times of regionally moderately dry climate. The drought-induced peat acidification is further evidenced by modern monitoring in the Dajiuhu peatland. We propose that n-alkan-2-ones in peats have potential value as a proxy to reconstruct paleo-pH changes, but one that still has limitations and constraints when applied to different peatlands and succession stages.