230Th-excess inventory and distribution in a southern Mendeleev Ridge core (Arctic Ocean): linkage with late Quaternary sedimentological and paleogeographical changes
Bibliographic record
Abstract
In addition to 14C-data, sedimentary excesses in 230Th (230Thxs) in central Arctic Ocean cored sequences yielded critical time constrains and sedimentation rates estimates, at least, at sites characterized by very low sedimentation rates (<< 1cm/ka). Closer to the Russian margin, where higher accumulation rates are recorded based on 14C-ages, the setting of a reliable stratigraphy based on 230Thxs reveals more challenging, as illustrated here, based on the analysis of a gravity core raised from the southern Mendeleev Ridge (core ARC7-E25; -179.4°E, 79.0°N; 1200 m water depth; 320 cm long). Subsamples were collected at a 4 to 8 cm interval. Measurements included: AMS 14C in foraminifera, grain size, bulk Xray mineralogy, clay mineralogy, geochemistry (Corg, Cinorg,13Corg, 238U, 234U, 230Th, 226Ra, 210Pb). Data indicate that some sediment were lost at core top. Nevertheless, 14C and 230Thxs data allow estimating a mean sedimentation rate of about 6 to 7 mm/ka during the last two climatic cycles. A comparison of the 230Thxs inventory and distribution pattern with those from other cores allows identifying important parameters involved in the cycling of the water column-produced 230Th in this basin and its sporadic sedimentary accumulation, in particular linkages with sea-ice production over shelves, thus sea-levels, sea-ice rafting routes, grain-size and mineralogy, potential winnowing of fine fractions, role of brines and relative duration of intervals with reduced or nil sedimentation preceding 230Thxs-accumulation intervals.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 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 | 0.000 |
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".