Preprints
https://doi.org/10.5194/cp-2023-74
https://doi.org/10.5194/cp-2023-74
27 Oct 2023
 | 27 Oct 2023
Status: a revised version of this preprint was accepted for the journal CP and is expected to appear here in due course.

A Holocene history of climate, fire, landscape evolution, and human activity in Northeast Iceland

Nicolò Ardenghi, David John Harning, Jonathan Henrik Raberg, Brooke René Holman, Thorvaldur Thordarson, Áslaug Geirsdóttir, Gifford H. Miller, and Julio Sepúlveda

Abstract. Paleoclimate reconstructions across Iceland provide a template for past changes in climate across the northern North Atlantic, a crucial region due to its position relative to the global northward heat transport system and its vulnerability to climate change. The roles of orbitally driven summer cooling, volcanism, and human impact as triggers of local environmental changes in the Holocene of Iceland, remain debated. While there are indications that human impact may have reduced environmental resilience during Late Holocene summer cooling, it is still difficult to resolve to what extent human and natural factors affected Iceland’s Late Holocene landscape instability. Here, we present a continuous Holocene fire record of northeastern Iceland from proxies archived in Stóra Viðarvatn sediment. We use pyrogenic polycyclic aromatic hydrocarbons (pyroPAHs) to trace shifts in fire regimes, paired with continuous biomarker and bulk geochemical records of soil erosion, lake productivity, and human presence. The molecular composition of pyroPAHs and a wind pattern reconstruction indicate a naturally driven fire signal that is mostly regional. Generally low fire frequency during most of the Holocene significantly increased at 3 ka and again after 1.5 ka BP, before known human settlement in Iceland. We propose that shifts in vegetation type caused by cooling summers over the past 3 kyr, in addition to changes in atmospheric circulation, such as shifts in North Atlantic Oscillation (NAO) regime, led to increased aridity and biomass flammability. Our results show no evidence of faecal biomarkers associated with human activity during or after human colonisation in the 9th century CE. Instead, faecal biomarkers follow the pattern described by erosional proxies, pointing toward a negligible human presence and/or a diluted signal in the lake’s catchment. However, low post-colonisation levels of pyroPAHs, in contrast to an increasing flux of erosional bulk proxies, suggest that farming and animal husbandry may have suppressed fire frequency by reducing the spread and flammability of fire-prone vegetation (e.g., heathlands).

Overall, our results describe a fire frequency heavily influenced by long term changes in climate through the Holocene. They also suggest that human colonisation had contrasting effects on the local environment by lowering its resilience to soil erosion while increasing its resilience to fire.

Nicolò Ardenghi, David John Harning, Jonathan Henrik Raberg, Brooke René Holman, Thorvaldur Thordarson, Áslaug Geirsdóttir, Gifford H. Miller, and Julio Sepúlveda

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-74', Anonymous Referee #1, 24 Nov 2023
    • AC1: 'Reply on RC1', Nicolò Ardenghi, 16 Feb 2024
    • AC2: 'Literature cited in the first reply', Nicolò Ardenghi, 16 Feb 2024
  • RC2: 'Comment on cp-2023-74', Anonymous Referee #2, 22 Jan 2024
    • AC3: 'Reply on RC2', Nicolò Ardenghi, 16 Feb 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-74', Anonymous Referee #1, 24 Nov 2023
    • AC1: 'Reply on RC1', Nicolò Ardenghi, 16 Feb 2024
    • AC2: 'Literature cited in the first reply', Nicolò Ardenghi, 16 Feb 2024
  • RC2: 'Comment on cp-2023-74', Anonymous Referee #2, 22 Jan 2024
    • AC3: 'Reply on RC2', Nicolò Ardenghi, 16 Feb 2024
Nicolò Ardenghi, David John Harning, Jonathan Henrik Raberg, Brooke René Holman, Thorvaldur Thordarson, Áslaug Geirsdóttir, Gifford H. Miller, and Julio Sepúlveda
Nicolò Ardenghi, David John Harning, Jonathan Henrik Raberg, Brooke René Holman, Thorvaldur Thordarson, Áslaug Geirsdóttir, Gifford H. Miller, and Julio Sepúlveda

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Short summary
Analysing a sediment record from Stóra Viðarvatn (NE Iceland), we reveal how natural factors and human activities influenced environmental changes (erosion, wildfires) over the last 11,000 years. We found increased fire activity around 3,000 and 1,500 years ago, predating human settlement, likely driven by natural factors like precipitation shifts. Declining summer temperatures increased erosion vulnerability, exacerbated by farming and animal husbandry, which in turn may have reduced wildfires.