Inference of viscosity jump at 670 km depth and lower mantle viscosity structure from GIA observations
Bibliographic record
Abstract
A viscosity model with an exponential profile described by temperature (T) and pressure (P) distributions and constant activation energy (|$E_{{\rm{um}}}^{\rm{*}}$| for the upper mantle and |$E_{{\rm{lm}}}^*$| for the lower mantle) and volume (|$V_{{\rm{um}}}^{\rm{*}}$| and |$V_{{\rm{lm}}}^*$|) is employed in inferring the viscosity structure of the Earth's mantle from observations of glacial isostatic adjustment (GIA). We first construct standard viscosity models with an average upper-mantle viscosity (|${\bar{\eta }_{{\rm{um}}}}$|) of 2 × 1020 Pa s, a typical value for the oceanic upper-mantle viscosity, satisfying the observationally derived three GIA-related observables, GIA-induced rate of change of the degree-two zonal harmonic of the geopotential, |${\skew5\dot{J}_2}$|, and differential relative sea level (RSL) changes for the Last Glacial Maximum sea levels at Barbados and Bonaparte Gulf in Australia and for RSL changes at 6 kyr BP for Karumba and Halifax Bay in Australia. Standard viscosity models inferred from three GIA-related observables are characterized by a viscosity of ∼1023 Pa s in the deep mantle for an assumed viscosity at 670 km depth, ηlm(670), of (1 − 50) × 1021 Pa s. Postglacial RSL changes at Southport, Bermuda and Everglades in the intermediate region of the North American ice sheet, largely dependent on its gross melting history, have a crucial potential for inference of a viscosity jump at 670 km depth. The analyses of these RSL changes based on the viscosity models with |${\bar{\eta }_{{\rm{um}}}}$| ≥ 2 × 1020 Pa s and lower-mantle viscosity structures for the standard models yield permissible |${\bar{\eta }_{{\rm{um}}}}$| and ηlm (670) values, although there is a trade-off between the viscosity and ice history models. Our preferred |${\bar{\eta }_{{\rm{um}}}}$| and ηlm (670) values are ∼(7 − 9) × 1020 and ∼1022 Pa s, respectively, and the |${\bar{\eta }_{{\rm{um}}}}$| is higher than that for the typical value of oceanic upper mantle, which may reflect a moderate laterally heterogeneous upper-mantle viscosity. The mantle viscosity structure adopted in this study depends on temperature distribution and activation energy and volume, and it is difficult to discuss the impact of each quantity on the inferred lower-mantle viscosity model. We conclude that models of smooth depth variation in the lower-mantle viscosity following |$\eta ( z )\ \propto {\rm{\ exp}}[ {( {E_{{\rm{lm}}}^* + P( z )V_{{\rm{lm}}}^*} )/{\rm{R}}T( z )} ]$| with constant |$E_{{\rm{lm}}}^*$| and |$V_{{\rm{lm}}}^*$| are consistent with the GIA observations.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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 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".