Geochemistry of an endorheic thalassohaline ecosystem: the Dziani Dzaha crater lake (Mayotte Archipelago, Indian Ocean)

Sarazin, Gérard; Jézéquel, Didier; Leboulanger, Christophe; Fouilland, Éric; Floc’h, Emilie Le; Bouvy, Marc; Gérard, Emmanuelle; Agogué, Hélène; Bernard, Cécile; Hugoni, Mylène; Grossi, Vincent; Troussellier, Marc; Ader, Magali

doi:10.5802/crgeos.43

Cited by 9 publications

(50 citation statements)

References 23 publications

(37 reference statements)

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“…The Dziani Dzaha water column has a combination of physical, chemical and biological features that are atypical for a modern lacustrine system, which have been previously recently documented and are summarized here. Its waters probably originated from seawater and are now characterized by high salinity (i.e., ranging from 34 to 71 psu), strong alkalinity (i.e., ranging from 0.1 to 0.2 M), elevated pH value (i.e., comprised between 9 and 9.5), and very high primary productivity (i.e., 8 gC m −2 day −1 (Leboulanger et al, 2017;Sarazin et al, 2020). The lake ecosystem is dominated by microorganisms with a dense and perennial bloom of two photosynthetic species [i.e., Picocystis salinarum (Chlorophyta) and Arthrospira fusiformis (Cyanobacteria), Bernard et al, 2019].…”

Section: Study Sitementioning

confidence: 99%

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Nitrogen Isotope Discrepancy Between Primary Producers and Sediments in an Anoxic and Alkaline Lake

et al. 2021

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Nitrogen isotope compositions (δ15N) in sedimentary rocks are extensively used to investigate the biogeochemical nitrogen cycle through geological times. This use relies on the observation that, in modern continental platforms and anoxic basins, surface sediments faithfully record the δ15N of primary producers, assuming that it was similar in the past. Over Earth’s history, however, surface environments experienced profound changes, including the transition of ammonium-dominated to nitrate-dominated waters and the transition from exclusively microbial ecosystems to ecosystems including multicellularity, which make modern environments significantly different compared to earlier ones, potentially invalidating the fundamental assumption that surface sediments faithfully record the δ15N of primary producers. In order to improve our understanding of the nitrogen isotopic information contained in the early Earth’s sedimentary rock record, we investigate here the nitrogen isotope systematics in a microbial, nitrate free and ammonium-rich modern system, the Dziani Dzaha Lake. In this modern system, the δ15N of the reduced dissolved inorganic nitrogen (i.e., NH4+ and NH3) in the water column is close to ∼7‰ . δ15N of suspended particulate matter (SPM) show a similar average value in surface waters (i.e., where SPM is massively composed of active primary producers), but increases up to 14‰ in the deeper part of the water column during periods when it is enriched in dissolved reduced species (i.e., CH4, H2S/HS− and NH4+/NH3). Surface sediments δ15N, with values comprised between 10 and 14 ‰, seem to preferentially record these positive isotopic signatures, rather than those of active primary producers. We propose here that the observed isotopic pattern is mainly linked to the assimilation of ammonium strongly enriched in 15N by isotope exchange with ammonia under basic conditions. Although ammonium assimilation seems here to be responsible for a significant isotopic enrichment due to the basic conditions, in neutral anoxic environments inhabited by similar microbial ecosystems, this process may also significantly impact the δ15N of primary producers towards more negative values. This would have strong implications for our interpretation of the Precambrian sedimentary record as this finding challenges one the fundamental hypotheses underlying the use of sedimentary δ15N in paleo-oceanographic reconstructions, i.e. that surface sediments faithfully record the δ15N of active primary producers in the photic zone.

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Section: Study Sitementioning

confidence: 99%

“…The water column is permanently anoxic below ca. 1.5 m depth, with the anoxic water being periodically euxinic (i.e., presence of H 2 S and HS − ) (e.g., Sarazin et al, 2020). The SO 4 2− content is relatively low compared to seawater (<3 mM, Sarazin et al, 2020).…”

Section: Study Sitementioning

confidence: 99%

Nitrogen Isotope Discrepancy Between Primary Producers and Sediments in an Anoxic and Alkaline Lake

et al. 2021

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“…2B) and CH4 concentrations approaching saturation (ca. 1.7 mM; Sarazin et al, 2020). During the dry season, sulfides were present in much lower concentrations (H2S/HS -<0.16 mM) in the anoxic waters, except below the deep permanent halocline where H2S/HSconcentrations were higher (>2.8 mM) than those measured between 2 and 14 m depth in the presence of the seasonal halocline.…”

Section: Geochemistry Of the Water Column At The Time Of Samplingmentioning

confidence: 80%

“…6C), along with a sharp decrease in cyanobacterial biomass (Figs. 3; 6A) and CH4 and NH3 production (Sarazin et al, 2020).…”

Section: Chemocline-dependent Microbial Community Compositionmentioning

confidence: 97%

“…Although the number of sequences related to Methanocalculus did not increase systematically in the euxinic waters of Lake Dziani Dzaha (Fig. S2B), where CH4 concentration approaches saturation (Sarazin et al, 2020), the presence of this genus along the water column suggests a major biogeochemical role, especially in CH4 production and, possibly, in acetate oxidation through syntrophic associations with Synthrophomonadaceae (Figs. 6;7;Timmers et al, 2018).…”

Section: Chemocline-dependent Microbial Community Compositionmentioning

confidence: 99%

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Influence of aphotic haloclines and euxinia on organic biomarkers and microbial communities in a thalassohaline and alkaline volcanic crater lake

et al. 2021

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Studies on microbial communities, and their associated organic biomarkers, that are found thriving in the aphotic euxinic waters in modern stratified ecosystems are scarce compared to those undertaken in euxinic photic zones. The Dziani Dzaha (Mayotte, Indian Ocean) is a tropical, saline, alkaline crater lake that has recently been presented as a modern analogue of Proterozoic Oceans due to its thalassohaline classification (having water of marine origin) and specific biogeochemical characteristics. Continuous intense photosynthetic production and microbial mineralization keeps most of the water column permanently aphotic and anoxic preventing the development of an euxinic (sulfidic and anoxic) photic zone despite a high sulfide/sulfate ratio and the presence of permanent or seasonal haloclines. In this study, the molecular composition of the organic matter in Lake Dziani Dzaha was investigated and compared to the microbial diversity evaluated through 16S rRNA gene amplicon sequencing, over two contrasting seasons (rainy vs. dry) that influence water column stratification. Depth profiles of organic biomarker concentrations (chlorophyll-a and lipid biomarkers) and bacterial and archaeal OTU abundances appeared to be strongly dependent on the presence of aphotic haloclines and euxinia.OTU abundances revealed the importance of specific haloalkaliphilic bacterial and archaeal assemblages in phytoplanktonic biomass recycling and the biogeochemical functioning of the lake, suggesting new haloalkaline non-phototrophic anaerobic microbial precursors for some of the lipid biomarkers. Uncultured Firmicutes from the family Syntrophomonadaceae (Clostridiales), and Bacteroidetes from the ML635J-40 aquatic group, emerged as abundant chemotrophic bacterial members in the anoxic or euxinic waters, and were probably responsible for the production of short-chain n-alkenes, wax esters, diplopterol and tetrahymanol. Halocline-dependent euxinia also had a strong impact on the archaeal community which was dominated by Woesearchaeota in the sulfide-free waters. In the euxinic waters, methanogenic Euryarchaeota from the Methanomicrobia, Thermoplasmata and WSA2 classes dominated and were likely at the origin of common hydrocarbon biomarkers of methanogens (phytane, pentamethyleicosenes, and partially hydrogenated squalene).

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Early stages of Type I-S kerogen formation revealed by Rock-Eval® 7S analysis of sediment from a modern halo-alkaline lake (Dziani Dzaha, Mayotte)

Baudin,

Jovovic,

Adam

et al. 2024

Organic Geochemistry

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Geochemistry of an endorheic thalassohaline ecosystem: the Dziani Dzaha crater lake (Mayotte Archipelago, Indian Ocean)

Cited by 9 publications

References 23 publications

Nitrogen Isotope Discrepancy Between Primary Producers and Sediments in an Anoxic and Alkaline Lake

Nitrogen Isotope Discrepancy Between Primary Producers and Sediments in an Anoxic and Alkaline Lake

Influence of aphotic haloclines and euxinia on organic biomarkers and microbial communities in a thalassohaline and alkaline volcanic crater lake

Early stages of Type I-S kerogen formation revealed by Rock-Eval® 7S analysis of sediment from a modern halo-alkaline lake (Dziani Dzaha, Mayotte)

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