Scottish early Holocene vegetation dynamics based on pollen and tephra records from Inverlair and Loch Etteridge, Inverness-shire

Abstract

This paper presents the results of an investigation of early Holocene cryptotephra layers recovered from sediments in two kettle-hole basins at Inverlair (Glen Spean) and Loch Etteridge (Glen Fernisdale). Electron probe micro-analysis (EPMA) of shards from two cryptotephra layers revealed that the uppermost layer in both sequences has a composition similar to the An Druim tephra, first reported from a site in Northern Scotland. We present evidence that distinguishes the An Druim from the chemically very similar early Holocene Ashik tephra. The lowermost layer at Inverlair matches the composition of the Askja-S tephra found in the Faroe Islands, Ireland, Sweden, Germany and Switzerland. This is the first published record of the Askja-S tephra from mainland Scotland. As at other sites, the Askja-S seems to mark a short-lived climatic deterioration, most likely the Pre-Boreal Oscillation: at Inverlair it occurs just above an oscillation represented by a reduction in LOI values and in the abundance of Betula pollen, and by a peak in Juniperus pollen. The lowermost layer at Loch Etteridge has a Katla-type chemistry and extends through the upper part of the Loch Lomond (Younger Dryas/GS-1) Stadial to the Stadial/Holocene transition; it may represent a composite layer which merges the Vedde and Abernethy tephras. One of the key conclusions is that the glacial-melt deposits in the vicinity of Inverlair (kames and kame terraces) were ice-free by c. 10.83 ka (the age of the Askja-S), providing a limiting age on the disappearance of LLR ice in Glen Spean.

Stratigraphy of a Lateglacial lake basin sediment sequence at Turret Bank, upper Glen Roy, Lochaber: implications for the age of the Turret Fan

“…An early Holocene age for the pollen sequence is supported by the identification of the Askja-S Tephra, dated to ~10.83 ka (Bronk Ramsey et al, 2015). This is consistent with the data reported from the nearby site of Inverlair (Kelly et al, 2017), where the Askja-S Tephra has also been identified: in both sequences this tephra layer coincides with the end of the prominent Juniperus phase ( Figure 6). It is speculated that TBL-328, the most prominent tephra peak below the Askja-S, could represent the Abernethy Tephra.…”

“…Figure 4 reveals an orderly sequence from the base of pollen spectra dominated successively by Salix-Rumex, Empetrum, Juniperus, Betula and Corylus, a sequence that is typical of early Holocene deposits in Scotland (e.g. Lowe andWalker, 1979, 1986;Lowe, 1981, 1982;Dawson et al, 1987;Benn et al, 1992), including sites within and adjacent to Glen Roy (Lowe and Cairns, 1991;Kelly et al, 2017). The pollen sequence is in general comparable to that published by Lowe and Cairns (1991) except in two important respects: (i) there are no contaminant pollen (Betula, Alnus, Corylus) in the lower part of the profile (zone TBpaz-1), which is dominated by herbaceous taxa; and (ii) Juniperus is much more clearly represented as a distinct peak (zone TBpaz-3) that succeeds the Empetrum phase (zone TBpaz-2/3); this resembles more clearly the pattern shown in other Scottish early Holocene records.…”

“…Norway (Pilcher et al, 2005), Ireland (Turney et al, 2006), the Faroe Islands (Lind and Wastegård, 2011), Germany (Lane et al, 2012a) and Switzerland (Lane et al, 2011), and more recently at a site in the Spean valley, only ~13 km due south of the Turret Bank site (Kelly et al, 2017). The current best-estimate age for the Askja-S Tephra, with a 2σ error range, is 10,944-10,716 cal BP (Bronk Ramsey et al, 2015).…”

“…The current best-estimate age for the Askja-S Tephra, with a 2σ error range, is 10,944-10,716 cal BP (Bronk Ramsey et al, 2015). Table 4 with the chemical envelopes for close-matching Lateglacial and early Holocene tephras: (A) total Davies et al, 2003;Pilcher et al, 2005;Turney et al, 2006;Lind and Wastegård 2011;Lane et al, 2013;Wulf et al, 2016;Kelly et al, 2017;Timms et al, 2016;Abernethy Tephra -Matthews et al, 2011;MacLeod et al 2015;Vedde Ash -Matthews et al, 2011;Lane et al, 2012b;MacLeod et al, 2015;Timms et al, 2016. (Lane et al, 2012b), the Abernethy Tephra, which is not well dated yet, but is consistently found close to the Stadial-Holocene lithostratigraphic boundary (MacLeod et al, 2015) and the Suðuroy Tephra; the last-named can be discounted as a possible correlative for TBL-316 or TBL-328, since it post-dates the Askja-S Tephra (Wastegård, 2002;Housley et al, 2012).…”

Traces of volcanic ash from the Mediterranean, Iceland and North America in a Holocene record from south Wales, UK

“…For instance, in the British Isles, cryptotephra records are predominantly from localities in Scotland, northern England and Ireland (e.g. Pilcher and Hall, 1992;Turney et al, 2006;Matthews et al, 2011;Kelly et al, 2017;Timms et al, 2018). Questions have often been raised about whether sites in Wales and southern England are beyond the limits of the dominant ash plumes from Iceland, or whether this pattern is a reflection of the intensity of tephra searches in other regions.…”