Application of black carbon in sediments in paleoenvironment and paleoclimate studies

Black carbon refers to a series of continuum of carbonaceous substances from incomplete combustion of biomass or fossil fuels or weathering of rocks. Its unique physical and chemical properties have significant impacts on the global climate and environment, such as exacerbating the greenhouse effect, affecting hydrological cycling and carbon sequestration. Due to its relatively stable chemical properties and small carbon isotope fractionation before and after combustion, black carbon has been used as a reliable proxy for the reconstruction of geological time-scale fire history and vegetation evolution. We reviewed the characteristics, sources, cycles, extraction methods in sediments, and their applications in paleoenvironmental reconstruction on different time scales of black carbon, and raised some issues in the current application of black carbon records for paleoenvironmental reconstruction. For example, the impact of the degradation and transformation of black carbon on black carbon deposition, as well as the lag in black carbon age, the complexity in black carbon origination and deposition, and the role of black carbon in carbon cycling at geological time scales, are still unclear. In addition, prospects for future research are presented: Unlike terrestrial soil, lakes, rivers, glaciers, and other carriers, black carbon in marine sediments are poorly studied. For more than half a century, international and national ocean drilling expeditions have obtained a large number of high-quality sedimentary cores in the global oceans, providing a possibility of using black carbon to study the interaction among tectonics, climate, vegetation, fire, and even human activities since the Cenozoic.