TY - JOUR

T1 - An astronomically calibrated 40Ar/39Ar age for the North Atlantic Z2 Ash

T2 - Implications for the Greenland ice core timescale

AU - Groen, Mirek

AU - Storey, Michael

N1 - Publisher Copyright: © 2022 The Authors

PY - 2022

Y1 - 2022

N2 - Timescales based on counted annual ice layers underpin the interpretation of late Quaternary rapid climatic oscillations recorded in the Greenland ice cores and their correlation to tropical and Antarctic climate archives. An inherent problem in the annual counted ice layer dating method is the large accumulated age uncertainties for the older part of the Greenland ice core timescale due to so called uncertain annual ice layers. Annual ice layers become thinner with depth due to increased compaction. Thus, the occurrence of uncertain annual layers becomes more frequent, such that by a depth of ∼2150 m (43 ka) in the NGRIP ice core the accumulated uncertainty on the age is > 2%. Radio-isotopic age determination of interbedded volcanic ash layers can provide independent verification of the Greenland counted annual ice layer ages along with the possibility of improved precision for the older part of this important timescale. Here we report an astronomically calibrated Ar40/Ar39 age of 56.14 ± 0.44 ka (2σ) for the widespread North Atlantic Z2 ash forming Icelandic Thórsmörk peralkaline rhyolitic eruption. The Z2 ash is found at a depth of 2359.45 m in the NGRIP ice core and has an annual layer counted age of 55.38 ± 2.37 ka (2σ, b2k). Our radio-isotopic age for the Z2 eruption is > 5 times more precise than the one based on counted annual ice layers and when referenced relative to b2k indicates that the oldest part of the GICC05 timescale is systematically too young by approximately 740 years. We use our Z2 eruption age to calculate refined astronomically calibrated ages for Greenland Interstadials (GI) 11 to 17 which results in reducing the age uncertainties on the majority of these events from the millennial to the centennial level. Our refined ages for GI 11–17 generally show good agreement with the NALPS U–Th stalagmite record that covers this same interval and together these high-precision radio-isotopic timescales provide firmer constraints for testing for synchronicity, or leads and lags between different geographical parts of the late Pleistocene climate system.

AB - Timescales based on counted annual ice layers underpin the interpretation of late Quaternary rapid climatic oscillations recorded in the Greenland ice cores and their correlation to tropical and Antarctic climate archives. An inherent problem in the annual counted ice layer dating method is the large accumulated age uncertainties for the older part of the Greenland ice core timescale due to so called uncertain annual ice layers. Annual ice layers become thinner with depth due to increased compaction. Thus, the occurrence of uncertain annual layers becomes more frequent, such that by a depth of ∼2150 m (43 ka) in the NGRIP ice core the accumulated uncertainty on the age is > 2%. Radio-isotopic age determination of interbedded volcanic ash layers can provide independent verification of the Greenland counted annual ice layer ages along with the possibility of improved precision for the older part of this important timescale. Here we report an astronomically calibrated Ar40/Ar39 age of 56.14 ± 0.44 ka (2σ) for the widespread North Atlantic Z2 ash forming Icelandic Thórsmörk peralkaline rhyolitic eruption. The Z2 ash is found at a depth of 2359.45 m in the NGRIP ice core and has an annual layer counted age of 55.38 ± 2.37 ka (2σ, b2k). Our radio-isotopic age for the Z2 eruption is > 5 times more precise than the one based on counted annual ice layers and when referenced relative to b2k indicates that the oldest part of the GICC05 timescale is systematically too young by approximately 740 years. We use our Z2 eruption age to calculate refined astronomically calibrated ages for Greenland Interstadials (GI) 11 to 17 which results in reducing the age uncertainties on the majority of these events from the millennial to the centennial level. Our refined ages for GI 11–17 generally show good agreement with the NALPS U–Th stalagmite record that covers this same interval and together these high-precision radio-isotopic timescales provide firmer constraints for testing for synchronicity, or leads and lags between different geographical parts of the late Pleistocene climate system.

KW - Ar/Ar dating

KW - GICC05

KW - Iceland volcanism

KW - NAAZ II

KW - NGRIP

KW - Thórsmörk ignimbrite

KW - Z2 ash

U2 - 10.1016/j.quascirev.2022.107526

DO - 10.1016/j.quascirev.2022.107526

M3 - Journal article

AN - SCOPUS:85138442251

VL - 293

JO - Quaternary Science Reviews

JF - Quaternary Science Reviews

SN - 0277-3791

M1 - 107526

ER -