Suspended particles are hotspots of microbial remineralization in the ocean's twilight zone

Hemsley, V.; Füssel, J.; Duret, M.T.; Rayne, R.R.; Iversen, M.H.; Henson, S.A. ORCID: https://orcid.org/0000-0002-3875-6802; Sanders, R. ORCID: https://orcid.org/0000-0002-6884-7131; Lam, P.; Trimmer, M.. 2023 Suspended particles are hotspots of microbial remineralization in the ocean's twilight zone. Deep Sea Research Part II: Topical Studies in Oceanography, 212, 105339. https://doi.org/10.1016/j.dsr2.2023.105339

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Official URL: http://dx.doi.org/10.1016/j.dsr2.2023.105339

Abstract/Summary

The sinking of photosynthetically produced organic carbon from the ocean surface to its interior is a significant term in the global carbon cycle. Most sinking organic carbon is, however, remineralized in the mesopelagic zone (∼100 m–1000 m), thereby exerting control over ocean-atmosphere carbon dioxide (CO2) partitioning and hence global climate. Sinking particles are considered hotspots of microbial respiration in the dark ocean. However, our observations in the contrasting Scotia Sea and the Benguela Current show that >90% of microbial remineralisation is associated with suspended, rather than sinking, organic matter, resulting in rapid turnover of the suspended carbon pool and demonstrating its central role in mesopelagic carbon cycling. A non-steady-state model indicates that temporally variable particle fluxes, particle injection pumps and local chemoautotrophy are necessary to help balance the observed mesopelagic respiration. Temperature and oxygen exert control over microbial respiration, particularly for the suspended fraction, further demonstrating the susceptibility of microbial remineralisation to the ongoing decline in oxygen at mid-ocean depths. These observations suggest a partial decoupling of carbon cycling between non-sinking and fast-sinking organic matter, challenging our understanding of how oceanic biological processes regulate climate.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1016/j.dsr2.2023.105339
ISSN:	09670645
Additional Keywords:	Carbon cycling, Microbial respiration, Suspended particles, Dissolved organic matter, Chemoautotrophic
Date made live:	31 Oct 2023 14:29 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/536194

Item Type:

Publication - Article

Digital Object Identifier (DOI):

https://doi.org/10.1016/j.dsr2.2023.105339

ISSN:

09670645

Additional Keywords:

Carbon cycling, Microbial respiration, Suspended particles, Dissolved organic matter, Chemoautotrophic

Date made live:

31 Oct 2023 14:29 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/536194