Carbon burial records during the last ~40,000 years in sediments of the Liaohe Delta wetland, China

Abstract

Delta wetland sediments constitute a long-term natural carbon sink and play a critical role in the global carbon cycle. In this study, borehole core ZK3 (36.7-m long), drilled in 2012 in the Liaohe Delta wetland, was investigated to assess the rate of carbon sequestration and the factors influencing carbon burial since the Late Pleistocene. Here we report the results of integrated analyses of the core, including its sedimentary lithology, grain size, foraminiferal abundance, chemical elements, and accelerator mass spectrometry (AMS)14C and optically stimulated luminescence (OSL) dates. The sedimentary environment has evolved from a fluvial-deposit, limnetic-deposit, littoral-deposit, shallow sea–deposit, and finally to a delta-deposit environment since 40,000 cal yr BP. Environmentally induced differences in apparent mass accumulation rates (AMARs) of organic carbon (OC) have been significant; they have ranged between 3.73 and 30.77 g/(m2·yr). The fact that the highest rates were associated with the delta-deposit environment indicates that the rate of carbon sequestration was greater in the sediments of estuarine wetlands than sediments of the continental shelf. The chemical index of alteration (CIA) proxy responded to several cold events, and there was a positive correlation between the CIA and OC-AMAR. Climate may therefore have regulated the excursions of ecosystem productions and in turn impacted the dynamics of carbon burial.