Variable aging and storage of dissolved black carbon in the ocean

• 成果类型: Article
• 署名作者: Coppola, Alysha I.; Druffel, Ellen R. M.; Broek, Taylor A.; Haghipour, Negar; Eglinton, Timothy I.; Mccarthy, Matthew; Walker, Brett D.
• 署名单位: Swiss Federal Institutes of Technology Domain; ETH Zurich; University of California System; University of California Irvine; Woods Hole Oceanographic Institution; Swiss Federal Institutes of Technology Domain; ETH Zurich; University of California System; University of California Santa Cruz; University of Ottawa
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-13056
• DOI: 10.1073/pnas.2305030121
• 发表日期: 2024-03-26
• 关键词: organic-carbon; pyrogenic carbon; aromatic condensation; isotopic composition; molecular-weight; matter; pacific; radiocarbon; STABILITY; fire

摘要

During wildfires and fossil fuel combustion, biomass is converted to black carbon (BC) via incomplete combustion. BC enters the ocean by rivers and atmospheric deposition contributing to the marine dissolved organic carbon (DOC) pool. The fate of BC is considered to reside in the marine DOC pool, where the oldest BC C-14 ages have been measured (>20,000 C-14 y), implying long-term storage. DOC is the largest exchangeable pool of organic carbon in the oceans, yet most DOC (>80%) remains molecularly uncharacterized. Here, we report C-14 measurements on size-fractionated dissolved BC (DBC) obtained using benzene polycarboxylic acids as molecular tracers to constrain the sources and cycling of DBC and its contributions to refractory DOC (RDOC) in a site in the North Pacific Ocean. Our results reveal that the cycling of DBC is more dynamic and heterogeneous than previously believed though it does not comprise a single, uniformly old C-14 age. Instead, both semilabile and refractory DBC components are distributed among size fractions of DOC. We report that DBC cycles within DOC as a component of RDOC, exhibiting turnover in the ocean on millennia timescales. DBC within the low-molecular-weight DOC pool is large, environmentally persistent and constitutes the size fraction that is responsible for long-term DBC storage. We speculate that sea surface processes, including bacterial remineralization (via the coupling of photooxidation of surface DBC and bacterial co-metabolism), sorption onto sinking particles and surface photochemical oxidation, modify DBC composition and turnover, ultimately controlling the fate of DBC and RDOC in the ocean.