Extensive remineralization of peatland‐derived dissolved organic carbon and ocean acidification in the Sunda Shelf Sea, Southeast Asia

Zhou, Yongli; Evans, Christopher D. ORCID: https://orcid.org/0000-0002-7052-354X; Chen, Yuan; Chang, Kristy Y.W.; Martin, Patrick. 2021 Extensive remineralization of peatland‐derived dissolved organic carbon and ocean acidification in the Sunda Shelf Sea, Southeast Asia. Journal of Geophysical Research: Oceans, 126 (6), e2021JC017292. 23, pp. 10.1029/2021JC017292

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Abstract/Summary

Southeast Asia is a hotspot of riverine export of terrigenous organic carbon to the ocean, accounting for ∼10% of the global land-to-ocean riverine flux of terrigenous dissolved organic carbon (tDOC). While anthropogenic disturbance is thought to have increased the tDOC loss from peatlands in Southeast Asia, the fate of this tDOC in the marine environment and the potential impacts of its remineralization on coastal ecosystems remain poorly understood. We collected a multi-year biogeochemical time series in the central Sunda Shelf (Singapore Strait), where the seasonal reversal of ocean currents delivers water masses from the South China Sea first before (during Northeast Monsoon) and then after (during Southwest Monsoon) they have mixed with run-off from peatlands on Sumatra. The concentration and stable isotope composition of DOC, and colored dissolved organic matter spectra, reveal a large input of tDOC to our site during Southwest Monsoon. Using isotope mass balance calculations, we show that 60%–70% of the original tDOC input is remineralized in the coastal waters of the Sunda Shelf, causing seasonal acidification. The persistent CO2 oversaturation drives a CO2 efflux of 2.4–4.9 mol m−2 yr−1 from the Singapore Strait, suggesting that a large proportion of the remineralized peatland tDOC is ultimately emitted to the atmosphere. However, incubation experiments show that the remaining 30%–40% tDOC exhibits surprisingly low lability to microbial and photochemical degradation, suggesting that up to 20%–30% of peatland tDOC might be relatively refractory and exported to the open ocean.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1029/2021JC017292
UKCEH and CEH Sections/Science Areas:	Soils and Land Use (Science Area 2017-)
ISSN:	2169-9275
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	terrigenous organic carbon, remineralization, acidification, Sunda Shelf Sea, tropical peatlands
NORA Subject Terms:	Ecology and Environment
Date made live:	26 Jul 2021 09:40 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/530788

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