Preprints
https://doi.org/10.5194/cp-2021-89
https://doi.org/10.5194/cp-2021-89

  16 Jul 2021

16 Jul 2021

Review status: this preprint is currently under review for the journal CP.

Melt in the Greenland EastGRIP ice core reveals Holocene warming events

Julien Westhoff1, Giulia Sinnl1, Anders Svensson1, Johannes Freitag2, Helle Astrid Kjær1, Paul Vallelonga1, Bo Vinther1, Sepp Kipfstuhl2, Dorthe Dahl-Jensen1,3, and Ilka Weikusat2,4 Julien Westhoff et al.
  • 1Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
  • 2Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
  • 3Centre for Earth Observation Science, University of Manitoba, Canada
  • 4Department of Geosciences, Eberhard Karls University Tübingen, Germany

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.

Julien Westhoff et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2021-89', Anonymous Referee #1, 01 Aug 2021
  • RC2: 'Comment on cp-2021-89', Anonymous Referee #2, 18 Oct 2021

Julien Westhoff et al.

Julien Westhoff et al.

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Short summary
We present a melt event record from an ice core from central Greenland, which covers the past 10,000 years. Our record displays warm summer events, which can be used for climatic interpretations. To further enhance our understanding of melt events, we compare our data to a snow pit study from the warm summer of 2012 CE and to a simple melt/rain experiment. We compare our data to anomalies of tree ring width and a historical event, the first sailing of Vikings to Greenland in 986 CE.