Variable carbon isotope fractionation of photosynthetic communities over depth in an open-ocean euphotic zone.

Autor: Henderson LC; Department of Ocean Sciences, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami, Miami, FL 33149., Wittmers F; Faculty of Mathematics and Natural Sciences, Christian-Albrecht University of Kiel, Kiel SH 24118, Germany., Carlson CA; Department of Ecology, Evolution, and Marine Biology/Marine Science Institute, University of California, Santa Barbara, CA 93106., Worden AZ; Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA 02543., Close HG; Department of Ocean Sciences, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami, Miami, FL 33149.
Jazyk: angličtina
Zdroj: Proceedings of the National Academy of Sciences of the United States of America [Proc Natl Acad Sci U S A] 2024 Mar 05; Vol. 121 (10), pp. e2304613121. Date of Electronic Publication: 2024 Feb 26.
DOI: 10.1073/pnas.2304613121
Abstrakt: Marine particulate organic carbon (POC) contributes to carbon export, food webs, and sediments, but uncertainties remain in its origins. Globally, variations in stable carbon isotope ratios (δ 13 C values) of POC between the upper and lower euphotic zones (LEZ) indicate either varying aspects of photosynthetic communities or degradative alteration of POC. During summertime in the subtropical north Atlantic Ocean, we find that δ 13 C values of the photosynthetic product phytol decreased by 6.3‰ and photosynthetic carbon isotope fractionation (ε p ) increased by 5.6‰ between the surface and the LEZ-variation as large as that found in the geologic record during major carbon cycle perturbations, but here reflecting vertical variation in δ 13 C values of photosynthetic communities. We find that simultaneous variations in light intensity and phytoplankton community composition over depth may be important factors not fully accounted for in common models of photosynthetic carbon isotope fractionation. Using additional isotopic and cell count data, we estimate that photosynthetic and non-photosynthetic material (heterotrophs or detritus) contribute relatively constant proportions of POC throughout the euphotic zone but are isotopically more distinct in the LEZ. As a result, the large vertical differences in ε p result in significant, but smaller, differences in the δ 13 C values of total POC across the same depths (2.7‰). Vertical structuring of photosynthetic communities and export potential from the LEZ may vary across current and past ocean ecosystems; thus, LEZ photosynthesis may influence the exported and/or sedimentary δ 13 C values of both phytol and total organic carbon and affect interpretations of ε p over geologic time.
Competing Interests: Competing interests statement:The authors declare no competing interest.
Databáze: MEDLINE
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