Reflection seismic indicators for submarine permafrost and gas hydrate distributions on the Canadian Arctic Beaufort Shelf
Bibliographic record
Abstract
Since the last glaciation the Canadian Arctic Beaufort Shelf is subjected to marine transgression. From subaerial mean annual temperatures during terrestrial exposure of ≤ -20°C, thermal conditions changed up to present submarine bottom water temperatures near -1°C. While conditions during the Pliocene favoured extensive formation of permafrost and gas hydrates, present occurrences are exposed to degradation due to the warmer climate. Today, submerged offshore permafrost is still responding to this thermal change. Ongoing degradation creates the potential of methane release of previously trapped biogenic gas within the relic permafrost and from gas hydrate dissociation. The mobilisation of methane and its possible release to the atmosphere plays a significant role in climate change. Yet, both the extent of permafrost and underlying gas hydrates is still poorly known. Here, we present seismic indicators for offshore permafrost and gas hydrates in 2D multichannel reflection seismic data acquired in the Canadian Beaufort Sea. Seismic lines that run from the shallow shelf towards deeper water show layer-crossing reflections that become gradually shallower towards the north-west into deeper water. These reflections show an amplitude-varying characteristic and are phase-reversed. We first use shot gathers from a synthetic model based on the field seismic acquisition characteristics and borehole geophysical data to verify our general ability to detect permafrost-and gas hydrate-related reflections. The synthetic data were processed using the same data processing applied to the field data and reveal clear top and base of permafrost and gas hydrate reflections. With this encouraging result, we can exclude any potentially misleading processing artefacts in the field seismic data. We interpret the amplitude-varying, phase-reversed and layer-crossing reflections seen in the field data as seismic indicators for the base of permafrost and base of gas hydrates. In contrast to the synthetic data, top of permafrost and top of gas hydrates are not clearly identified in the field data. However, additional seismic indicators support the interpretation of the presence of permafrost including attenuation of acoustic penetration and velocity pull-up effects at presumably horizontal strata. Furthermore, strong amplitude variations beneath the current base of gas hydrates and bright spots indicate trapped free gas accumulations from possible previously dissociated gas hydrates.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".