Resolving the fate of trace metals during microbial remineralization of phytoplankton biomass in precursor banded iron formation sediments
Bibliographic record
Abstract
Abstract Banded Iron Formations (BIFs) have long been considered a sedimentary record of seawater trace metal composition during the Precambrian. However, recent work has suggested that the trace metal composition of BIFs was derived from phytoplankton biomass, not seawater. In this model, phytoplankton biomass settles from the photic zone to the seafloor sediments, where it is then oxidized by heterotrophic microbes, such as dissimilatory Fe(III) reducing (DIR) bacteria, for energy generation. Remineralization of this biomass released the trace metals associated with organic molecules from phytoplankton ( i . e ., in metalloproteins), allowing these metals to be captured by Fe (oxyhydr)oxides and preserved in BIFs. While there is compelling evidence that the phytoplankton biomass served as a trace metal shuttle to precursor BIF sediments, it is unclear whether the degradation of biomass by DIR bacteria would liberate the biogenic trace metals as the model proposes. This work tests this hypothesis by using anoxic incubations of a model DIR bacterium ( Shewanella oneidensis MR-1) with phytoplankton biomass as energy and carbon sources and ferrihydrite, a poorly crystalline Fe(III) oxyhydroxide (Fe(OH) 3 ), as electron acceptor. Our results show that while S. oneidensis MR-1 can consume some of the carbon substrates found in phytoplankton biomass, there is no evidence that S. oneidensis MR-1 degraded metalloproteins which would have liberated trace metals. In the context of the Precambrian, these data imply that other heterotrophic bacteria, such as fermenters, may have had a larger role in the liberation of trace metals from dead biomass during early BIF development. Highlights Phytoplankton are the proposed source of trace metals to banded iron formations Iron reducers are hypothesized to release metals from phytoplankton biomass Experiments show that iron reducers do not liberate metals when degrading biomass Other microbial heterotrophs must have liberated the biogenic trace metals
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".