Preprints
https://doi.org/10.5194/cp-2024-26
https://doi.org/10.5194/cp-2024-26
18 Apr 2024
 | 18 Apr 2024
Status: this preprint is currently under review for the journal CP.

High-resolution Holocene record from Torfdalsvatn, north Iceland, reveals natural and anthropogenic impacts on terrestrial and aquatic environments

David J. Harning, Christopher R. Florian, Áslaug Geirsdóttir, Thor Thordarson, Gifford H. Miller, Yarrow Axford, and Sædís Ólafsdóttir

Abstract. Open questions remain around the Holocene variability of climate in Iceland, including the relative impacts of natural and anthropogenic factors on Late Holocene vegetation change and soil erosion. The lacustrine sediment record from Torfdalsvatn, north Iceland, is the longest known in Iceland (≤12000 cal a BP) and along with its high sedimentation rate, provides an opportunity to develop high-resolution quantitative records that address these challenges. In this study, we use two sediment cores from Torfdalsvatn to construct a high-resolution age model derived from marker tephra layers, paleomagnetic secular variation, and radiocarbon. We then apply this robust age constraint to support a complete tephrochronology (>2200 grains analyzed in 33 tephra horizons) and sub-centennial geochemical (MS, TOC, C/N, δ13C, and BSi) and algal pigment records. Along with previously published proxy records from the same lake, these records demonstrate generally stable terrestrial and aquatic conditions during the Early and Middle Holocene, except for punctuated disturbances linked to major tephra fall events. During the Late Holocene, there is strong evidence for naturally driven algal productivity decline beginning around 1800 cal a BP. These changes closely follow regional Late Holocene cooling driven by decreases in Northern Hemisphere summer insolation and the expansion of sea-ice laden Polar Water around Iceland. Then at 880 cal a BP, ~200 years after the presumed time of human settlement, a second shift in the record begins and is characterized by a strong uptick in landscape instability and possibly soil erosion. Collectively, the Torfdalsvatn record highlights the resilience of low-elevation, low-relief catchments to the pre-settlement soil erosion in Iceland, despite a steadily cooling background climate. The precisely dated, high-resolution tephra and paleoenvironmental record from this site can serve as a regional template for north Iceland.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
David J. Harning, Christopher R. Florian, Áslaug Geirsdóttir, Thor Thordarson, Gifford H. Miller, Yarrow Axford, and Sædís Ólafsdóttir

Status: open (until 16 Jun 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on cp-2024-26', David Lowe, 22 Apr 2024 reply
    • CC2: 'Reply on CC1', Thorvaldur Thordarson, 22 Apr 2024 reply
  • RC1: 'Comment on cp-2024-26', Anonymous Referee #1, 25 May 2024 reply
David J. Harning, Christopher R. Florian, Áslaug Geirsdóttir, Thor Thordarson, Gifford H. Miller, Yarrow Axford, and Sædís Ólafsdóttir
David J. Harning, Christopher R. Florian, Áslaug Geirsdóttir, Thor Thordarson, Gifford H. Miller, Yarrow Axford, and Sædís Ólafsdóttir

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Short summary
Questions remain about the past climate in Iceland, including the relative impacts of natural and human factors on vegetation change and soil erosion. We present a sub-centennial scale record of landscape and algal productivity from a lake in north Iceland. Along with high-resolution age constraint that covers the last ~12000 years, our record provides an environmental template for the region and novel insight into the sensitivity of the Icelandic ecosystem to natural and human impacts.