Revisiting Late Quaternary chronostratigraphy of the Arctic Ocean using the 230Th excess method
Bibliographic record
Abstract
The Late Quaternary chronostratigraphic framework of the Arctic Ocean remains contentious, hindering our understanding of Arctic paleoceanographic conditions and their influence on global climate change. Recent advances in microbiostratigraphy and amino acid racemization (AAR) dating challenge the high-sedimentation rate central Arctic scenario proposed nearly two decades ago. To address this issue, U-Th analyses were performed on a Lomonosov Ridge sediment core, ICE04, whose chronostratigraphy had previously been established using AMS14C dating, lithological and mineralogical correlations, and the identification of a paleomagnetic excursion.The Th-230 excess (230Thxs) distribution and decay downcore suggest a revised age framework. Specifically, the previously identified marine isotope stage (MIS) 3 layer can be re-assigned to MIS 3 to 6, while the MIS 4/4-5d layer extends back to MIS 7. Additionally, the 234U/238U ratio record indicates active late diagenetic processes likely driven by organic carbon decomposition. These findings highlight several key points: 1) younger organic carbon may dissolve and reprecipitate downcore due to late diagenetic processes, limiting the reliability of 14C ages derived from bulk organic carbon; 2) lithological correlations used to construct Late Quaternary chronostratigraphy can introduce significant uncertainties and may be biased by the misinterpretation of other methods, such as 14C dating; 3) dolomite peaks are recommended as reliable markers for the site-to-site correlations as they are linked to the meltwater discharge from the NW margin of the Laurentide Ice Sheet; and 4) the 1-meter-thick interval exhibiting a negative geomagnetic polarity, previously attributed to the Matuyama Chron (~780 ka) or the Laschamp (~41 ka) and Mono Lake (~35 ka) excursions, is dated to MIS 4-5d using the 230Thxs method. The revised age addresses the complexity of paleomagnetic behavior in the Arctic and underscores the need for further investigation to resolve these discrepancies.Using the 230Thxs method, we estimate a late Quaternary mean sedimentation rate of 4 cm/ka. These findings align with the sediment-starved deep Arctic scenario proposed prior to the 2000s, further indicating that an effort must be conducted to account for all the available data.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.003 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".