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The Vedde Ash, originating from the Katla central volcano, Iceland, and taken to be dispersed across the North Atlantic and Europe at ~ 12 ka BP, is widely used as a geochronological marker. However, distal tephra layers with compositions like the Vedde Ash but of younger ages question the reliability of Vedde-like tephra layers as robust age control. Vedde-like tephra layers are rare in Icelandic sedimentary sequences and, where present, lack firm age control. Providing well-constrained local records of Early Holocene Katla layers is therefore critical to assess uncertainties related to the use of the Vedde Ash. Here we report three visible and stratigraphically separated Early Holocene Katla tephra layers from Torfdalsvatn, a lake in north Iceland, each with chemistry similar to the Vedde Ash. Using high-resolution 14C chronologies, we provide ages (± 1σ) for these tephra layers of 11,315 ± 180, 11,295 ± 195, and 11,170 ± 195 cal a BP. These observations reinforce that multiple explosive eruptions of Katla occurred over a 1000-year interval in the Early Holocene and challenge the precision of some paleoclimate records using the Vedde Ash as a geochronometer where age control is equivocal. This may lead to a re-evaluation of age models for some Early Holocene North Atlantic records.
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High-resolution Holocene record from Torfdalsvatn, north Iceland, reveals natural and anthropogenic impacts on terrestrial and aquatic environments
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.
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- Award ID(s):
- 1836981
- PAR ID:
- 10554358
- Publisher / Repository:
- Climate of the Past
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Posted Content:
- https://doi.org/10.5194/cp-2024-26
