Black carbon (BC), a highly refractory fraction of organic carbon produced by the incomplete combustion of biomass and fossil fuels, represents an important long-term carbon sink in marine sediments. Hadal trenches are recognized as efficient depocenters for organic carbon burial because of their unique topography and high sediment accumulation efficiency. However, most previous studies have focused on low- and mid-latitude trenches, while the distribution, sources, and burial of BC in high-latitude trench systems remain poorly understood. The South Sandwich Trench, located at the margin of the Southern Ocean, provides an ideal natural laboratory for investigating the fate of refractory organic carbon under the combined influence of Antarctic ocean circulation and long-range atmospheric transport.

In this study, we investigated the spatial distribution, source characteristics, and burial potential of black carbon, together with its relationship to sedimentary organic carbon, in surface sediments from the South Sandwich Trench and adjacent areas. By integrating bulk geochemical, molecular, and isotopic evidence, we found pronounced spatial heterogeneity in both organic carbon and BC across the trench system. Higher BC contents generally occurred in regions affected by stronger material input, while BC still represented an important fraction of the organic carbon pool in offshore sediments with relatively low organic carbon backgrounds. Molecular and isotopic signatures suggest that highly condensed BC is mainly derived from fossil fuel combustion, with additional contributions from biomass burning. Variations among different geomorphic settings further indicate that ocean circulation, long-range atmospheric transport, particle transport, and sediment focusing jointly regulate the delivery and preservation of BC in this region. These findings improve our understanding of refractory organic carbon cycling in the Southern Ocean and highlight the role of high-latitude hadal trenches as important sinks in the global carbon cycle.

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