Biological and physical modification of carbonate system parameters along the salinity gradient in shallow hypersaline solar salterns in Trapani, Italy

Isaji, Yuta; Kawahata, Hodaka; Kuroda, Junichiro; Yoshimura, Toshihiro; Ogawa, Nanako O.; Suzuki, Atsushi; Shibuya, Takazo; Jiménez-Espejo, Francisco Jose; Lugli, Stefano; Santulli, Andrea; Manzi, Vinicio; Roveri, Marco; Ohkouchi, Naohiko

doi:10.1016/j.gca.2017.04.013

Cited by 14 publications

(21 citation statements)

References 72 publications

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“…The analytical procedure used for the purification of chloropigments followed that described previously 23 . In brief, the surface deposits of the microbial mats (CU-1, -6, -7, and -8), and the yellowish transparent, green, and pink layers of the gypsum crusts (SS-1 and CH-1) were each freeze-dried and ground to powder.…”

Section: Methodsmentioning

confidence: 99%

“…All microbial mats and gypsum crusts investigated had similar distributions of chloropigments, which are mostly derived from benthic rather than planktic phototrophs 23 . We determined δ 15 N values for the chloropigments derived from the main phototrophs inhabiting each layer of the microbial mats: chlorophyll a from cyanobacteria, which generally dominate the yellow and green layers, and bacteriochlorophyll a from the purple sulfur bacteria living in the pink layers 24 .…”

Section: Distributions and δ15n Signatures Of Nitrogenous Compoundsmentioning

confidence: 97%

“…

Figure 2Variations in the concentrations and δ 15 N values of nitrate and ammonium in the Trapani solar salterns. ( A ) Concentrations of surface-brine nitrate (blue circles) and ammonium (red squares) along the salinity gradient in the samples collected in 2015, ( B ) surface-brine nitrate and ammonium concentrations normalized to the degree of evaporation (DE Mg ), ( C ) δ 15 N of the surface-brine ammonium, and ( D ) pH 23 . ( E ) Cross plot of δ 15 N and [NH 4 + ]/DE Mg of the surface-brine ammonium.…”

Section: Distributions and δ15n Signatures Of Nitrogenous Compoundsmentioning

confidence: 99%

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Efficient recycling of nutrients in modern and past hypersaline environments

Isaji

Kawahata

Ogawa

et al. 2019

Sci Rep

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The biogeochemistry of hypersaline environments is strongly influenced by changes in biological processes and physicochemical parameters. Although massive evaporation events have occurred repeatedly throughout Earth history, their biogeochemical cycles and global impact remain poorly understood. Here, we provide the first nitrogen isotopic data for nutrients and chloropigments from modern shallow hypersaline environments (solar salterns, Trapani, Italy) and apply the obtained insights to δ 15 N signatures of the Messinian salinity crisis (MSC) in the late Miocene. Concentrations and δ 15 N of chlorophyll a , bacteriochlorophyll a , nitrate, and ammonium in benthic microbial mats indicate that inhibition of nitrification suppresses denitrification and anammox, resulting in efficient ammonium recycling within the mats and high primary productivity. We also suggest that the release of 15 N-depleted NH 3(gas) with increasing salinity enriches ammonium 15 N in surface brine (≈34.0‰). Such elevated δ 15 N is also recorded in geoporphyrins isolated from sediments of the MSC peak (≈20‰), reflecting ammonium supply sufficient for sustaining phototrophic primary production. We propose that efficient nutrient supply combined with frequent bottom-water anoxia and capping of organic-rich sediments by evaporites of the Mediterranean MSC could have contributed to atmospheric CO 2 reduction during the late Miocene.

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Section: Methodsmentioning

confidence: 99%

Section: Distributions and δ15n Signatures Of Nitrogenous Compoundsmentioning

confidence: 97%

“…

Section: Distributions and δ15n Signatures Of Nitrogenous Compoundsmentioning

confidence: 99%

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Efficient recycling of nutrients in modern and past hypersaline environments

Isaji

Kawahata

Ogawa

et al. 2019

Sci Rep

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“…Relatively high δ 13 C of chlorophyll c-producing algae in part explains the 13 C-enrichment in TOC of the PLG shales compared to other stratified basins (e.g., van Breugel et al, 2005). In addition, considering that other MSC deposits also exhibit elevated δ 13 C TOC (Schouten et al, 2001;Yoshimura et al, 2016), a physicochemical process specific to hypersaline condition, such as the degassing of 13 C-depleted CO 2 (aq) from the brine induced by a decrease in gas solubility during evaporation (Stiller et al, 1985;Isaji et al, 2017), may also have contributed to δ 13 C TOC increase. It is noteworthy that, compared to other modern and ancient stratified basins, the δ 13 C values of the CO 2 at the chemocline during the deposition of PLG 4 shale are less depleted in 13 C with respect to CO 2 (atm) (van Breugel et al, 2005).…”

Section: Primary Producers and Nitrogen Cycle During The Deposition Omentioning

confidence: 99%

Diazotrophy Drives Primary Production in the Organic-Rich Shales Deposited Under a Stratified Environment During the Messinian Salinity Crisis (Vena del Gesso, Italy)

et al. 2019

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Density stratification between freshwater and brine is periodically formed during massive evaporation events, which often associates deposition of organic-rich sediments. Here, we investigated phototrophic communities and nitrogen cycle during the deposition of two organic-rich shale beds of gypsum-shale alternation, representing the initial stage of the Messinian salinity crisis (Vena del Gesso, Northern Apennines, Italy). The structural distributions and the carbon and nitrogen isotopic compositions of geoporphyrins show a common pattern in the two shales, indicating the predominance of a particular phototrophic community under freshwater-brine stratified conditions. The ∼6 difference in δ 13 C of total organic carbon between PLG 4 and 5 shales was associated with similar shift in δ 13 C of the porphyrins derived from chlorophyll c, suggesting that the eukaryotic algae producing chlorophyll c were the major constituent of the phototrophic community. Importantly, these porphyrins show δ 15 N values (−7.6-−4.7 ) indicative of N 2 -fixation. We suggest that nitrate-depletion in the photic zone induced the predominance of diazotrophic cyanobacteria, which supplied new nitrogen for the chlorophyll c-producing eukaryotic algae. The large difference in the δ 13 C values of porphyrins and total organic carbon between PLG 4 and 5 shales are interpreted to reflect the depth of the chemocline, which fluctuates in response to changes in the regional evaporation-precipitation balance. Such variation in the chemocline depth may have dynamically changed the mode of the nitrogen cycle (i.e., nitrificationdenitrification-N 2 -fixation coupling vs. phototrophic assimilation of ammonium) in the density-stratified marginal basins during the Messinian salinity crisis.

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“…Moreover, the transitions in the state and compositions of the microbial communities may in turn strongly affect the chemical characteristic of the evaporating brine. For example, biological activity strongly influences the CO 2 exchange between the brine and the atmosphere (Lazar et al 1992;Isaji et al 2017), and organic matter concentrated in the brine reduces the evaporation rate and the degree of evaporation that the brine can reach (Shalev et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Biomarker records and mineral compositions of the Messinian halite and K–Mg salts from Sicily

Isaji

Yoshimura

Kuroda

et al. 2019

Prog Earth Planet Sci

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The evaporites of the Realmonte salt mine (Sicily, Italy) are important archives recording the most extreme conditions of the Messinian Salinity Crisis (MSC). However, geochemical approach on these evaporitic sequences is scarce and little is known on the response of the biological community to drastically elevating salinity. In the present work, we investigated the depositional environments and the biological community of the shale-anhydrite-halite triplets and the K-Mg salt layer deposited during the peak of the MSC. Both hopanes and steranes are detected in the shale-anhydrite-halite triplets, suggesting the presence of eukaryotes and bacteria throughout their deposition. The K-Mg salt layer is composed of primary halites, diagenetic leonite, and primary and/or secondary kainite, which are interpreted to have precipitated from density-stratified water column with the halite-precipitating brine at the surface and the brineprecipitating K-Mg salts at the bottom. The presence of hopanes and a trace amount of steranes implicates that eukaryotes and bacteria were able to survive in the surface halite-precipitating brine even during the most extreme condition of the MSC.

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Biological and physical modification of carbonate system parameters along the salinity gradient in shallow hypersaline solar salterns in Trapani, Italy

Cited by 14 publications

References 72 publications

Efficient recycling of nutrients in modern and past hypersaline environments

Efficient recycling of nutrients in modern and past hypersaline environments

Diazotrophy Drives Primary Production in the Organic-Rich Shales Deposited Under a Stratified Environment During the Messinian Salinity Crisis (Vena del Gesso, Italy)

Biomarker records and mineral compositions of the Messinian halite and K–Mg salts from Sicily

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