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Distribution, Source and Burial of Black Carbon in the Aleutian Trench: Local Effects and Global Implication.

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Title: Distribution, Source and Burial of Black Carbon in the Aleutian Trench: Local Effects and Global Implication.
Authors: Zhu, Linghua1 (AUTHOR), Xiao, Wenjie2 (AUTHOR), Wang, Yasong1 (AUTHOR), Liu, Liang1 (AUTHOR), Sindlev, Marco Benkhettab2 (AUTHOR), Glud, Ronnie N.2,3 (AUTHOR), Xu, Yunping1 (AUTHOR) ypxu@shou.edu.cn
Source: Journal of Geophysical Research. Biogeosciences. May2026, Vol. 131 Issue 5, p1-18. 18p.
Subject Terms: *Carbon-black, *Fossil fuels, Hadal zone, Submarine trenches, Sediment sampling, Deep-sea exploration, Carbon isotopes
Abstract: Recent studies of low‐ and mid‐latitude trench systems have identified the hadal zone, the deepest region of the ocean, as a significant sink for black carbon (BC). However, the BC in high‐latitude trenches remains largely unexplored. In this study, we employed the chemothermal oxidation method (CTO‐375), benzene polycarboxylic acid (BPCA) analysis, and carbon isotope (δ13C) to quantify the content and composition of BC in 11 sediment cores collected from the Aleutian Trench, the northernmost hadal trench. The BCCTO content ranged from 0.08% to 0.27%, with higher concentrations observed in the eastern and central sections compared to the western section. The mean BC to total organic carbon ratio was 0.30 ± 0.06, significantly higher than the value reported for low‐ and mid‐latitude trenches (0.12 ± 0.04). The mixing stable isotope analysis in R (MixSIA) based on δ13CBC indicated that fossil fuel combustion is the primary regional source of BC, accounting for 72%–78%. The estimated accumulation rate of BC in the Aleutian Trench was 0.9 ± 0.1 g m−2 yr−1, which is twice the previously reported average for low‐ and mid‐latitude trench regions. When scaled to the hadal region of the Aleutian Trench, this corresponds to a burial rate of 0.08 ± 0.03 Tg per year. Our findings underscore the distinctive nature of the Aleutian Trench regarding carbon transport and burial. Although significant spatial variability may occur at both inter‐ and intra‐trench scales, our study supports the importance of hadal environments as sinks for BC. Plain Language Summary: Black carbon (BC) is recognized as a slow‐cycling component of organic carbon that can be transported from terrestrial ecosystems to the deep ocean. Recent research suggests that the hadal zone, the deepest region of the ocean characterized by depths exceeding 6,000 m, functions as a significant sink for BC; however, data from high‐latitude trenches remain insufficient. In this study, we employed multiple methodologies to examine sedimentary BC in the Aleutian Trench, the northernmost hadal trench located between 46° and 58°N. Our results indicate that BC concentrations varied from 0.08% to 0.27%, averaging 30 ± 6% of the total organic carbon content. Carbon isotope analysis demonstrates that the primary source of BC is fossil fuel combustion, which accounts for 72%–78% of the total BC. The total burial flux of BC in the Aleutian Trench is estimated to be approximately 80,000 tons. On a per unit area (m2) basis, the annual accumulation rate of BC in the Aleutian Trench is 0.9 ± 0.1 g, which is 30 times greater than the global ocean average. These findings underscore the potential significance of hadal environments as important BC sinks. Key Points: Black carbon (BC)/total organic carbon ratio in the Aleutian Trench is significantly higher than that observed in low‐to mid‐latitude trenchesδ¹³CBC and B5CA/B6CA indicate variability in sources and degradation of BC from northern slope, through hadal, and to southern slopeThe BC accumulation rate in the Aleutian Trench is 0.91 g m⁻² yr⁻¹, corresponding to a burial flux of 80,000 tons per year [ABSTRACT FROM AUTHOR]
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Abstract:Recent studies of low‐ and mid‐latitude trench systems have identified the hadal zone, the deepest region of the ocean, as a significant sink for black carbon (BC). However, the BC in high‐latitude trenches remains largely unexplored. In this study, we employed the chemothermal oxidation method (CTO‐375), benzene polycarboxylic acid (BPCA) analysis, and carbon isotope (δ13C) to quantify the content and composition of BC in 11 sediment cores collected from the Aleutian Trench, the northernmost hadal trench. The BCCTO content ranged from 0.08% to 0.27%, with higher concentrations observed in the eastern and central sections compared to the western section. The mean BC to total organic carbon ratio was 0.30 ± 0.06, significantly higher than the value reported for low‐ and mid‐latitude trenches (0.12 ± 0.04). The mixing stable isotope analysis in R (MixSIA) based on δ13CBC indicated that fossil fuel combustion is the primary regional source of BC, accounting for 72%–78%. The estimated accumulation rate of BC in the Aleutian Trench was 0.9 ± 0.1 g m−2 yr−1, which is twice the previously reported average for low‐ and mid‐latitude trench regions. When scaled to the hadal region of the Aleutian Trench, this corresponds to a burial rate of 0.08 ± 0.03 Tg per year. Our findings underscore the distinctive nature of the Aleutian Trench regarding carbon transport and burial. Although significant spatial variability may occur at both inter‐ and intra‐trench scales, our study supports the importance of hadal environments as sinks for BC. Plain Language Summary: Black carbon (BC) is recognized as a slow‐cycling component of organic carbon that can be transported from terrestrial ecosystems to the deep ocean. Recent research suggests that the hadal zone, the deepest region of the ocean characterized by depths exceeding 6,000 m, functions as a significant sink for BC; however, data from high‐latitude trenches remain insufficient. In this study, we employed multiple methodologies to examine sedimentary BC in the Aleutian Trench, the northernmost hadal trench located between 46° and 58°N. Our results indicate that BC concentrations varied from 0.08% to 0.27%, averaging 30 ± 6% of the total organic carbon content. Carbon isotope analysis demonstrates that the primary source of BC is fossil fuel combustion, which accounts for 72%–78% of the total BC. The total burial flux of BC in the Aleutian Trench is estimated to be approximately 80,000 tons. On a per unit area (m2) basis, the annual accumulation rate of BC in the Aleutian Trench is 0.9 ± 0.1 g, which is 30 times greater than the global ocean average. These findings underscore the potential significance of hadal environments as important BC sinks. Key Points: Black carbon (BC)/total organic carbon ratio in the Aleutian Trench is significantly higher than that observed in low‐to mid‐latitude trenchesδ¹³CBC and B5CA/B6CA indicate variability in sources and degradation of BC from northern slope, through hadal, and to southern slopeThe BC accumulation rate in the Aleutian Trench is 0.91 g m⁻² yr⁻¹, corresponding to a burial flux of 80,000 tons per year [ABSTRACT FROM AUTHOR]
ISSN:21698953
DOI:10.1029/2026JG009789