Anaerobic microbial activity affects earliest diagenetic pathways of bivalve shells

Abstract

The earliest diagenetic post‐mortem exposure of biogenic carbonates at the sea floor and in the uppermost sediment column results in the colonization of hard‐part surfaces by bacterial communities. Some of the metabolic redox processes related to these communities have the potential to alter carbonate shell properties, and hence affect earliest diagenetic pathways with significant consequences for archive data. During a three‐month in vitro study, shell subsamples of the ocean quahog Arctica islandica (Linnaeus, 1767) were incubated in natural anoxic sediment slurries and bacterial culture medium of the heterotrophic Shewanella sediminisHAW‐EB3. Bulk analyses of the liquid media from the Shewanella sediminis incubation revealed an over ten‐fold increase in total alkalinity, dissolved inorganic carbon and ΩAragonite, and the alteration of the Mg/Ca, Mg/Sr and Sr/Ca ratios relative to control incubations without cultures. Ion ratios were most affected in the incubation with anoxic sediment, depicting a 25% decrease in Mg/Ca relative to the control. Shell sample surfaces that were exposed to both incubations displayed visible surface dissolution features, and an 8 wt% loss in calcium content. No such alteration features were detected in control shells. Apparently, alteration of shell carbonate properties was induced by microbially driven decomposition of shell intercrystalline organic constituents and subsequent opening of pathways for pore fluid–crystal exchange. This study illustrates the potential influence of benthic bacterial metabolism on biogenic carbonate archives during the initial stages of diagenetic alteration within a relatively short experimental duration of only three months. These results suggest that foremost the biological effect of bacterial cation adsorption on divalent cation ratios has the potential to complicate proxy interpretation. Results shown here highlight the necessity to consider bacterial metabolic activities in marine sediments for the interpretation of palaeo‐environmental proxies from shell carbonate archives.

Microbial activity affects sulphur in biogenic aragonite

“…4: Shell incubated in anoxic sediment slurry. Strontium maps of 1, 3 and 4 were previously published by Lange et al (2018). Sulphur and strontium map of the non‐incubated shell was previously published by Fichtner et al (2018).…”

“…For the first incubation experiment, the S. sediminis bacterial culture was grown in an anoxic DSMZ (Deutsche Sammlung von Mikroorganismen und Zellkulturen) medium 514 (for medium composition see Lange et al, 2018). 10 ml of this fluid was added to 900 ml of the sterile seawater with an additional 100 mg/l Fe (III) citrate, 1,000 mg/l yeast, and 200 µl resazurin as a redox/oxygen indicator.…”

“…The samples were subsequently dried at 40°C. A detailed description of the microbial incubation experiments used in this study was previously reported by Lange et al (2018).…”

“…One of the many processes that affect this proxy data is microbial colonisation of skeletal hardparts and related metabolisms, a factor rarely addressed in previous work (cf. Glover & Kidwell, 1993; Lange et al, 2018; Sejrup & Haugen, 1994). These studies demonstrated that microbial activity has the potential to alter the elemental composition of these archives, and thus, can also affect any conclusions drawn regarding ambient seawater conditions.…”

Coupling Relationship between Multistage Fluid Activity and Reservoir Abnormally High-Porosity Zones in the Songtao–Baodao Region, Qiongdongnan Basin

“…The contribution of dissolution to an abnormally highporosity zone lies in the dissolution of unstable minerals and the formation of additional secondary pores [9]. The geological factors controlling the AHPZ development are closely associated with the types and activities of diagenetic fluids [10].…”