Preboreal oscillation
The preboreal oscillation (PBO) was a short cooling period within the preboreal stage of the Holocene epoch.
Definition
[edit | edit source]Based on evidence from pollen, early Holocene cooling periods have been discovered already from the 1960s on. Locally, they were referred to as ‘Friesland Oscillation’ (Denmark [1]), ‘Youngest Dryas’ (Germany [2]), ‘Rammelbeek Phase’ (Netherlands [3]), and ‘Piottino Oscillation’ (Switzerland [4]). The term "preboreal oscillation" was derived from attempts to synchronize these events.[5][6]
Dating
[edit | edit source]The Greenland ice cores record a distinct decline in stable oxygen isotope data dated to 11 650–11 270 ice layer a BP (11 700–11 320 b2k) with the coldest part between 11 470 and 11 350 ice layer a BP (11 520–11 400 b2k) labelled as the ‘11.4 ka event’.[7]
In lake sedimentary records, the exact timing and duration of the PBO remain uncertain because of dating uncertainties due to two early Holocene radiocarbon plateau and unclear proxy evidence. [8][9] Two ash layers derived from volcanic eruptions are frequently used as time markers for the PBO: the Askja-S and Hässeldalen tephras shortly before and after the event. [10] The ages of these layers were constrained to 11.228 ± 226 cal a BP and 11.380 ± 216 cal a BP, framing the cold event to a maximum duration of 152 +11/-8 years by varve counting. [11]
References
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[[Category:Quaternary]]