More Than Half of Emitted Black Carbon Is Missing in Marine Sediments

Marine sediments are the ultimate reservoir for black carbon (BC) preservation, and BC burial in sediment/soils is an efficient method for carbon sequestration to mitigate CO2 emissions. A portion of soil charcoal and atmospheric BC is dissolved in inland and oceanic water, but the amount of BC in the ocean remains unclear. We analyzed multi-sediment cores from the northwestern Pacific Ocean and lakes in China and reconstructed the timeline of BC deposition from 1860 to similar to 2012. The lacustrine sediment cores showed an increase in BC deposition by a factor of 4-7 during the industrialization period in China compared to the years 1860-1950 (reference level). Such increasing trends in BC have also been reproduced by ten global climate model simulations. However, the marine sediment cores did not retain these significant increases in BC deposition. Meanwhile, the model simulations predicted increased trends compared to the observed flat trends of BC deposition in marine sediments. The discrepancy suggests a large amount of BC, i.e., 65 (+/- 11)%, is missing in marine sediment sinks. Thus, since more than half of emitted BC has dissolved into oceanic water, the dissolved BC and carbon cycle should be reconsidered in the global carbon budget.