Publication Date:
2022-10-26
Description:
Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research- Biogeosciences 125(2), (2020): e2019JG005276, doi:10.1029/2019JG005276.
Description:
A chemoautotrophy maximum is present in many anoxic basins at the sulfidic layer's upper boundary, but the factors controlling this feature are poorly understood. In 13 of 31 cruises to the Cariaco Basin, particulate organic carbon (POC) was enriched in 13C (δ13CPOC as high as −16‰) within the oxic/sulfidic transition compared to photic zone values (−23 to −26‰). During “heavy” cruises, fluxes of O2 and [NO3− + NO2−] to the oxic/sulfidic interface were significantly lower than during “light” cruises. Cruises with isotopically heavy POC were more common between 2013 and 2015 when suspended particles below the photic zone tended to be nitrogen rich compared to later cruises. Within the chemoautotrophic layer, nitrogen‐rich particles (molar ratio C/N〈 10) were more likely to be 13C‐enriched than nitrogen‐poor particles, implying that these inventories were dominated by living cells and fresh detritus rather than laterally transported or extensively decomposed detritus. During heavy cruises, 13C enrichments persisted to 1,300 m, providing the first evidence of downward transport of chemoautotrophically produced POC. Dissolved inorganic carbon assimilation during heavy cruises (n = 3) was faster and occurred deeper than during light cruises (n = 2). Metagenomics data from the chemoautotrophic layer during two cruises support prevalence of microorganisms carrying RuBisCO form II genes, which encode a carbon fixation enzyme that discriminates less against heavy isotopes than most other carbon fixation enzymes, and metatranscriptomics data indicate that higher expression of form II RuBisCO genes during the heavy cruises at depths where essential reactants coexist are responsible for the isotopically heavier POC.
Description:
We thank the captain and crew of the B/O Hermano Gines and the staff of Estación de Investigaciones Marinas, Fundación de la Salle de Ciencias Naturales, Margarita Island, Venezuela, for their field and laboratory assistance. We are also indebted to the many students, colleagues, and technicians who have participated in this project, in particular, L. Medina Faull for contour plots, E. Tappa (USC) for POC and δ13CPOC data measured in Robert Thunell's lab, and K. Fanning and K. Buck and W. Abbott (USF) for nutrient data. Digna‐Rueda‐Roa, Laura Lorenzoni, and Matt Biddle assisted greatly in getting the data into a format suitable for submission to the BCO‐DMO database. We are also grateful to two anonymous reviewers for their insightful comments. This research was supported by grants from NSF (OCE‐1259110 awarded to M. I. S. and G. T. T.; OCE‐1258991 to R. C. T.; OCE‐0326268, OCE‐0963028, OCE‐1259043, and OCE‐1649626 to F. M. K.; and OCE‐1336082 and OCE‐1335436 awarded to V. P. E. and G. T. T., respectively), from Venezuela's FONACIT (2000001702 and 2011000353 to Y. A.), and a WHOI subaward A101259 to M. G. P. Biological and Chemical Oceanography Data Management Office Metadata landing page for the Cariaco Time series Niskin bottle data is/https://www.bco‐dmo.org/dataset/3093. For the data from our biogeochemistry cruises the BCO‐DMO Metadata landing page is https://ww.bco‐dmo.org/dataset/3120 and for the Time series CTD data is https://www.bco‐dmo.org/dataset/3092. δ13CDIC data are presented in Table S1. Metagenome and metatranscriptome data are available from SRA (accession number PRJNA544741). δ13CPOC data are available at https://doi.org/10.6084/m9.figshare.8214470.v1.
Description:
2020-07-30
Keywords:
Cariaco Basin
;
Chemoautotrophy
;
Metagenomics
;
Carbon isotopes
Repository Name:
Woods Hole Open Access Server
Type:
Article
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