Oceanic Density Fronts Steering Bottom-Current Induced Sedimentation Deduced from a 50 ka Contourite-Drift Record and Numerical Modeling (off NW Spain)
Bibliographic record
Abstract
Abstract How the various bottom-near hydrographic and sedimentary processes control the formation of contourite drifts, i.e. of bottom-current related confined deep-sea depocenters, usually remains widely speculative. This study uses a transect of six sediment cores and a sediment echosounder profile across a whole contourite system off NW Spain to address the sediment dynamics responsible for the depositional pattern. This “mounded patch”-type contourite drift (18 km long, 20 km wide) with a 150-m deep channel (moat) has formed around an 800-m high structural obstacle. Deposition on the contourite drift in the past was characterized by alternating calm and high-energy bottom-flow conditions. Calm conditions (Last Glacial period: 27–17 cal ka BP; late Holocene times: Process-based numerical modeling demonstrates that pulse-like oceanic density fronts traveling within the transition zone of two water masses (Labrador Sea Water, Mediterranean Outflow Water) provide a powerful mechanism for contouritic deposition, rather than the core of a water mass itself. These gravity-driven density fronts lead to local re-suspension of sands stored inside the drift's moat and to subsequent upward transport towards the drift's crest. Here, the oceanic density fronts produce additional km-scale eddies. These migrating eddies provide an efficient mechanism for further widespread sediment re-distribution. In comparison with paleoceanographic reconstructions, a downward migration or expansion of the Mediterranean Outflow Water by about 300 m led most probably to such temporary contouritic sand deposition. We finally propose a conceptual model to explain how seafloor obstacles redirect and perturbate bottom currents. This model proposes not only a sharp contact between two water masses but also the transition zone between those as an important high-energy regime, offering oceanic density fronts a travel medium. These fronts are strong enough to distribute fine sands across highly pronounced seabed topography. On the respective time scale, the moat itself seems to act as the main source for those sands, making a remote source and a long-distance sediment transport unnecessary.
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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 | 0.001 | 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 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".