The hadal zone is an important and heterogeneous sink of black carbon in the ocean

Xi Zhang,Zicheng Wang,Frank Wenzhöfer,Ronnie N Glud,Meixun Zhao,Min Luo,Kazumasa Oguri,Xuchen Wang,Jiasong Fang,Yasong Wang,Yin Fang,Xinxin Li,Yunping Xu,Liping Xu,Siddhartha Mitra,Ashley A Rowden,Wenjie Xiao

doi:10.1038/s43247-022-00351-7

Abstract

Black carbon is ubiquitous in the marine environment. However, whether it accumulates in the deepest ocean region, the hadal zone, is unknown. Here we measure the concentration and carbon isotopes (δ13C and Δ14C) of black carbon and total organic carbon in sediments from six hadal trenches. Black carbon constituted 10% of trench total organic carbon, and its δ13C and Δ14C were more negative than those of total organic carbon, suggesting that the black carbon was predominantly derived from terrestrial C3 plants and fossil fuels. The contribution of fossil carbon to the black carbon pool was spatially heterogeneous, which could be related to differences in the distance to landmass, land cover and socioeconomic development. Globally, we estimate a black carbon burial rate of 1.0 ± 0.5 Tg yr−1 in the hadal zone, which is seven-fold higher than the global ocean average per unit area. We propose that the hadal zone is an important, but overlooked, sink of black carbon in the ocean.

Highlights

Black carbon is ubiquitous in the marine environment
The content, δ13C and Δ14C of Black carbon (BC) and total organic carbon (TOC) in trench surface sediments are summarized in Supplementary Table 2
A weak but still significant correlation was observed between the BC and TOC contents (r = 0.43, p < 0.05; Fig. 2a)

Summary

Introduction

Black carbon is ubiquitous in the marine environment Whether it accumulates in the deepest ocean region, the hadal zone, is unknown. Trench (MT) and found that it is cycled and aged on the same time scales as bulk dissolved organic carbon (OC) in the ocean This finding, is not consistent with the prevailing view that the BC was thought to be a refractory pool of carbon with much old 14C ages (~20,000 yr BP)[10,14]. Recent studies have suggested that elevated OC accumulation rates[17,18], benthic abundance and biomass[19,20], and microbial activities[21,22,23] are prevalent in some hadal trenches. Given a close relationship between BC and TOC contents in marine sediments[7], we hypothesize that large amount of BC has been accumulated in the hadal zone

Methods

Results

Conclusion