A comparison of Holocene temperature reconstructions from vegetation proxies and brGDGTs in northern Fennoscandia
Bibliographic record
Abstract
Studies on Holocene climate conditions commonly show discrepancies between different proxy-based reconstructions, calling for in-depth analysis of both the proxies and the derived climate reconstructions. Here, we conducted multi-proxy Holocene warm-season temperature reconstructions for a sedimentary record from Lake Tippakuru in northeastern Finland, using pollen, plant macrofossils, and the novel branched glycerol dialkyl glycerol tetraethers (brGDGTs) as climate proxies. In addition, we prepared a regional climate reconstruction by integrating pollen-based reconstructions from nearby sites. Mainly, we evaluated the potential of using brGDGTs as a climate proxy and compared the reconstructed climate shifts with those reconstructed from classical vegetation-based proxies (pollen and plant macrofossils). We see significant discrepancies between the three proxies, most notably during the early Holocene where plant macrofossils and brGDGTs indicate warm conditions while the pollen-based reconstructions are equivocal and strongly depend on the quantitative reconstruction method used. Additionally, the brGDGT records indicate an abrupt cooling at ca. 5.8 cal ka BP which is not seen in the classical proxies at the study site, but only in neighbouring localities. The results highlight the need for modern-day studies on seasonal variability and bacterial sources of brGDGTs to disentangle non-thermal biases and evaluate seasonal imprints in temperature reconstructions. In general, our results imply that not only the choice of climate proxies but also the methodological choices in the proxy-based quantitative reconstructions affect the climatic interpretation, especially during the early Holocene transitional period. We highlight the need for both multi-proxy and multi-method approaches in paleoclimate studies, as well as the need to expand the knowledge of brGDGT responses to climatic and other environmental variables. • Inconsistent early Holocene warm-season temperature conditions across proxies. • Mid-Holocene proxy-based temperature anomalies between +1 °C and +1.5 °C. • Proxies indicate long-term late Holocene cooling, but no short-term fluctuations.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".