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Abstract The Thomas Fire ignited on December 4, 2017 and burned for over one month. As the Thomas Fire burned, Santa Ana winds carried a thick plume of smoke and ash over the Santa Barbara Channel. We sought to determine whether the deposition of Thomas Fire ash to the Santa Barbara Channel had a measurable effect on the concentration and stable carbon isotopic composition (δ13C) of dissolved black carbon (DBC) in coastal waters. DBC is the condensed aromatic fraction of thermally altered organic carbon quantified using the benzenepolycarboxylic acid (BPCA) method. DBC δ13C signatures were determined via BPCA‐specific stable carbon isotopic analysis. Surface water DBC concentrations beneath the smoke plume were up to 13% higher than other sampling stations. Via controlled leaching experiments, we found that Thomas Fire ash released a considerable amount of DBC in seawater (1.4 g‐DBC per kg of ash organic carbon), which was further enhanced by photodissolution. By combining in situ and experimental data, we constructed an isotopic mixing model to estimate inputs of ash‐derived DBC to marine surface waters. Although we were able to detect slight elevations in DBC concentrations beneath the smoke plume, the ash‐derived contributions were too small to meaningfully shift the δ13C signature, which resulted in an observed mismatch between modeled and measured DBC δ13C values. Few studies have investigated the immediate impacts of wildfire on coastal biogeochemistry. Therefore, our work provides an important foundation for understanding atmospheric contributions of fire‐derived DBC to coastal margins.
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Isotopic composition of oceanic dissolved black carbon reveals non-riverine source
Abstract A portion of the charcoal and soot produced during combustion processes on land (e.g., wildfire, burning of fossil fuels) enters aquatic systems as dissolved black carbon (DBC). In terms of mass flux, rivers are the main identified source of DBC to the oceans. Since DBC is believed to be representative of the refractory carbon pool, constraining sources of marine DBC is key to understanding the long-term persistence of carbon in our global oceans. Here, we use compound-specific stable carbon isotopes (δ13C) to reveal that DBC in the oceans is ~6‰ enriched in13C compared to DBC exported by major rivers. This isotopic discrepancy indicates most riverine DBC is sequestered and/or rapidly degraded before it reaches the open ocean. Thus, we suggest that oceanic DBC does not predominantly originate from rivers and instead may be derived from another source with an isotopic signature similar to that of marine phytoplankton.
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- Award ID(s):
- 1756812
- PAR ID:
- 10153857
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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