Black carbon concentration and isotopic composition of surface sand from deserts and dune fields in Northern China

摘要

Black carbon (BC) is a continuum of incomplete combustion products of vegetation and fossil fuels. It can be used as a proxy for wildfires and paleovegetation reconstruction. Nevertheless, BC can be transported by wind and water via atmospheric and fluvial transport. To research the characteristics of BC in deserts and dune fields that are directly connected with the Chinese Loess Plateau (CLP) in Northern China, and to evaluate the possibility that BC in deserts and dune fields occurs as exogenous BC in the CLP, we investigated surface sand from the Mu Us dune field, the Tengger Desert, and the Badain Jaran Desert, and analyzed the stable carbon concentration and carbon isotopes of organic carbon (SOC%, delta C-13(SOC)) and BC (BC%, delta C-13(BC)). The delta C-13(SOC), delta C-13(BC) values ranged from -27.4 parts per thousand to 22.5 parts per thousand, and 28.2%a to 23.0 parts per thousand, respectively, which mainly reflected delta C-13 changes in surface C-3 grasses. A positive correlation was observed between delta C-13(BC) and delta C-13(SOC), suggesting that local vegetation mainly controls delta C-13(BC). The difference between delta C-13(BC) and delta C-13(SOC) ranged from -0.2 parts per thousand to +3.5 parts per thousand, and the difference is likely to be due to carbon isotope discrimination occurring during burning and SOC decomposition. The SOC% and BC% in these deserts and dune fields are very small (averaging 0.048% and 0.011%). The BC% of surface sand in these areas is about 5.5% of BC% in the CLP surface soils, and the Delta-delta C-13(BC) value between surface sand in deserts and surface soils in CLP ranged from 03L to 63L, so the change of delta C-13(BC) in the CLP surface soils, deduced by exogenous BC from deserts, is less than 035 parts per thousand. All these findings suggest that BC in deserts has a limited impact on BC in the CLP and is unlikely to affect interpretations of the BC record of wildfires and paleovegetation (C) 2015 Elsevier B.V. All rights reserved.