Melt in the Greenland EastGRIP ice core reveals Holocene warming events
Bibliographic record
Abstract
Abstract. We present a record of melt events obtained from the EastGRIP ice core, in central north eastern Greenland, covering the largest part of the Holocene. The data were acquired visually using an optical dark-field line scanner. We detect and describe bubble free layers and -lenses throughout the ice above the bubble-clathrate transition, located at 1100 m in the EastGRIP ice core, corresponding to an age of 9720 years b2k. We distinguish between melt layers (bubble free layers continuous over the width of the core), melt lenses (discontinuous), crusts (thin and sharp bubble free layers) and attribute three levels of confidence to each of these, depending on how clearly they are identified. Our record of melt events shows a large, distinct peak around 1014 years b2k (986 CE) and a broad peak around 7000 years b2k corresponding to the Holocene Climatic Optimum. We analyze melt layer thicknesses and correct for ice thinning, we account for missing layers due to core breaks, and ignore layers thinner than 1.5 mm. We define the brittle zone in the EastGRIP ice core from 650 m to 950 m depth, where we count on average more than three core breaks per meter. In total we can identify approximately 831 mm of melt (corrected for thinning) over the past 10,000 years. We compare our melt layer record to the GISP2 and Renland melt layer records. Our climatic interpretation matches well with the Little Ice Age, the Medieval and Roman Warm Periods, the Holocene Climatic Optimum, and the 8.2 kyr event. We also compare the most recent 2500 years to a tree ring composite and find an overlap between melt events and tree ring anomalies indicating warm summers. We open the discussion for sloping bubble free layers (tilt angle off horizontal > 10°) being the effect of rheology and not climate. We also discuss our melt layers in connection to a coffee experiment (coffee as a colored substitute for melt infiltration into the snow pack) and the real time observations of the 2012 CE rain event at NEEM. We find that the melt event from 986 CE is most likely a large rain event, similar to 2012 CE, and that these two events are unprecedented throughout the Holocene. Furthermore, we suggest that the warm summer of 986 CE, with the exceptional melt event, was the trigger for the first Viking voyages to sail from Iceland to Greenland.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| 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) | 0.001 | 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".