Revisiting the Borrobol Tephra

Self Cite

Contiguous sampling of ice spanning key intervals of the deglaciation from the Greenland ice cores of NGRIP, GRIP and NEEM has revealed three new silicic cryptotephra deposits that are geochemically similar to the well‐known Borrobol Tephra (BT). The BT is complex and confounded by the younger closely timed and compositionally similar Penifiler Tephra (PT). Two of the deposits found in the ice are in Greenland Interstadial 1e (GI‐1e) and an older deposit is found in Greenland Stadial 2.1 (GS‐2.1). Until now, the BT was confined to GI‐1‐equivalent lacustrine sequences in the British Isles, Sweden and Germany, and our discovery in Greenland ice extends its distribution and geochemical composition. However, the two cryptotephras that fall within GI‐1e ice cannot be separated on the basis of geochemistry and are dated to 14358 ± 177 a b2k and 14252 ± 173 a b2k, just 106 ± 3 years apart. The older deposit is consistent with BT age estimates derived from Scottish sites, while the younger deposit overlaps with both BT and PT age estimates. We suggest that either the BT in Northern European terrestrial sequences represents an amalgamation of tephra from both of the GI‐1e events identified in the ice‐cores or that it relates to just one of the ice‐core events. A firm correlation cannot be established at present due to their strong geochemical similarities. The older tephra horizon, found within all three ice‐cores and dated to 17326 ± 319 a b2k, can be correlated to a known layer within marine sediment cores from the North Iceland Shelf (ca. 17179‐16754 cal a BP). Despite showing similarities to the BT, this deposit can be distinguished on the basis of lower CaO and TiO2 and is a valuable new tie‐point that could eventually be used in high‐resolution marine records to compare the climate signals from the ocean and atmosphere.

“…Sweden: (25) Hässeldala port (Davies et al ., , ; Lind et al ., ). (26) Skallahult (Davies et al ., ; Lind et al ., ). Denmark: (27) Østerskov (Larsen, 2014 cited in Lind et al ., ).…”

Section: Introductionmentioning

confidence: 97%

“…(26) Skallahult (Davies et al ., ; Lind et al ., ). Denmark: (27) Østerskov (Larsen, 2014 cited in Lind et al ., ). Germany: (28) Lake Hämelsee (Jones et al ., ).…”

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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First identification and characterization of Borrobol‐type tephra in the Greenland ice cores: new deposits and improved age estimates

Cook

Davies

Guðmundsdóttir

et al. 2018

Self Cite

“…On the North Iceland shelf, Gudmundsdóttir et al () identified a ‘Borrobol‐like' tephra in MD99‐2272 and attached an age to it of 14.5 cal ka BP; this identification was used in the Xiao et al () paper. The similarity coefficient (Sarna‐Wojcicki et al ., ) between the B997‐338 tephras and the geochemistry of the type Borrobol (Lind et al ., ) suggests the closest match with the geochemistry at 90 cm. If correct, this supports the larger Δ R age estimates.…”

Section: Discussionmentioning

confidence: 99%

Sea ice, ice‐rafting, and ocean climate across Denmark Strait during rapid deglaciation (∼16–12 cal ka BP) of the Iceland and East Greenland shelves

Andrews

Cabedo‐Sanz²,

Jennings

et al. 2017

A suite of cores from the North-West Iceland and East Greenland shelves sampled fossiliferous or unfossiliferous basal glacial diamictons. Radiocarbon dates above the diamictons are similar on both shelves, but the value of the ocean reservoir correction, DR, is unknown. Deglaciation occurred either $16 or 14 cal ka BP depending on the choice of DR. The ice sheets were behind the present coastline by 12.2 cal ka BP. We examine seven cores that record the glacial/deglacial transition and present new data on the sea-ice biomarkers IP 25 and C 25:2 from four of the cores plus data on ice-rafted debris counts, grain-size spectra, d 18O on the near-surface planktonic foraminifera Neogloboquadrina pachyderma (s), foraminifera assemblages, and quartz percentage. IP 25 concentrations are markedly higher for the East Greenland sites, while they are frequently below the limit of quantification off Iceland, observations that parallel the wt% quartz in the sediments. The

“…Their equivalent rhyolitic glass composition is referred to collectively as ‘Borrobol‐type’, after its first detection in early Interstadial sediments at the Borrobol type‐site in northern Scotland (Turney et al , ). They occur singly or together in a number of terrestrial sequences in northern Europe (summarised by Lind et al , , and references therein). The recent detection of Borrobol‐type cryptotephras in early Interstadial Greenland ice (Cook et al , ) marks a possible further correlation with one or more of these layers in this valuable high‐precision record.…”

Section: Introductionmentioning

confidence: 99%

Glacier Peak and mid‐Lateglacial Katla cryptotephras in Scotland: potential new intercontinental and marine‐terrestrial correlations

Pyne-O’Donnell

Jensen

2019

Using contiguous high resolution sampling methods, we report the detection of a Glacier Peak volcanic ash from North America in Lateglacial Interstadial lake sediments in western Scotland. It occurs in close proximity to the Icelandic Borrobol and Penifiler tephras, but is distinguishable by its rhyolitic major‐element composition that is consistent with the earliest set G layer, one of a number of mid‐Interstadial Glacier Peak eruptions dated between 13.71 and 13.41 cal ka bp. Another cryptotephra layer present in these same Interstadial sediments has a rhyolitic composition consistent with the Icelandic Katla source. However, it is in a stratigraphic position below the widespread mid‐Lateglacial Stadial Vedde Ash from Katla, which is also present in these cores. The Katla layer is stratigraphically well defined, suggesting primary airfall, and is compositionally similar to a mid‐Interstadial rhyolitic tephra reported from a North Atlantic marine sequence south of Iceland dated to ~13.6 ka. The detection of Glacier Peak G in the European tephrostratigraphy will permit direct high‐precision correlation of mid‐Interstadial palaeoenvironments between North American and European terrestrial sequences. Any correlation between the new Katla layer and similar marine layers remains provisional, though if verified would permit similar correlation between North Atlantic marine and European terrestrial records.