Investigating variability in marine mollusk \ncarbonates using infrared spectroscopy and \nradiocarbon analysis
Bibliographic record
Abstract
Marine bivalve mollusks are complex hierarchical calcium carbonate (CaCO₃) materials \nthat are frequently used in archaeological studies and in chronologies that are \nused to study marine environment and climate change. Radiocarbon (¹⁴C) analysis \nof these materials is central to most of these studies. I study the variability of ¹⁴C \nsignatures within marine bivalve mollusk shells from British Columbia, Canada by \nconsidering both the raw, uncalibrated fraction of modern carbon measurements and \nthe calibrated age ranges. I use infrared (IR) spectroscopy as a method to screen for \ndiagenesis - contamination or alteration of the original shell CaCO₃ - prior to radiocarbon \nanalysis, and as a method to investigate the natural variability in the composition \nand structure of the shell CaCO₃. Using IR spectroscopy, I show that in three archaeological \nsamples of the butter clam (Saxidomus gigantea) from Sechelt, British \nColumbia, only one shell contained contaminating calcite. However, analysis of the \nrelative IR peak intensities showed a consistent difference between the inner nacreous \naragonite layer and the outer crossed lamellar aragonite layer for all three shells. This \nconsistent difference is likely correlated with that natural variability in aragonite microstructures. \nThree other archaeological shell samples from Deep Bay and Comox, \nBritish Columbia, were analyzed for ¹⁴C at three different locations within each of the \nshells. One sample displayed a variation in fraction of modern carbon within the shell \nwhile the others did not. I highlight that ¹⁴C measurements are meaningless without \nan understanding of date calibration and the choices that must be made when calibrating \nmarine and mixed marine-terrestrial samples. My results are a starting point \nfor developing best practices for ¹⁴C dating marine shell samples and for more focused \nstudies on the links between crystallinity, diagenesis, and ¹⁴C.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.003 | 0.006 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.003 |
| 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 teacher head, 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".