A millennial multi-proxy reconstruction of summer PDSI for Southern South America
Bibliographic record
Abstract
Abstract. We present the first highly resolved millennial reconstruction of the summer (DJF) Palmer Drought Severity Index (PDSI) for the Southern Hemisphere. Our multi-proxy reconstruction focuses on Southern South-America (SSA, south of 20° S) and is based on a novel spectral analogue method that aims at reconstructing the low frequencies of PDSI series independently from higher frequencies. The analysis of past regimes and long-term fluctuations in the PDSI reveals considerable geographical and temporal variations over the last millennia in SSA. Hence, recent changes, although some were very significant, were rarely exceptional over the last thousand years. However, from the point of view of extremes, recent PDSI values associated to extreme droughts (e.g. in the Andes) or wet spells (e.g. in the Pampas) were unequalled over the last thousand years. A major feature of our reconstruction is that it highlights that low frequency water availability fluctuations in Patagonia were generally in antiphase with those found on the rest of the sub-continent. We show that such antiphases within SSA's hydroclimate could be attributed the Antarctic Oscillation (AAO). The AAO was an important climatic driver during the calibration period (1930–1993) in SSA, and possibly over the last millennia as well. ENSO and PDO signals are also embedded, to a lesser extent, within the PDSI series, but the influence of these forcings has considerably varied through time and space over the last thousand years. Our results therefore highlight the complexity of water-availability fluctuations in SSA and their important dependence on external ocean-atmospheric forcings.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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) | 0.002 | 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".