High resolution, continous, carbon monoxide records from Greenland ice cores

We present high-resolution measurements of CO mixing ratios from ice cores drilled at five different sites on the Greenland ice sheet. An optical-feedback cavity-enhanced absorption spectrometer (OF-CEAS) was coupled with continuous melter systems and operated during four analytical campaigns conducted between 2013 and 2019 at the Desert Research Institute (DRI, USA) and the Institut des Géoscience de l'Environnement (IGE, France). The CFA-based CO measurements exhibit excellent external precision (ranging from 3.3 to 6.6 ppbv, 1 sigma) and achieve consistently low blanks (ranging from 4.1 +/- 1.2 to 12.6 +/- 4.4 ppbv), enabling paleoatmospheric interpretations. Consistent baseline CO records from four Greenlandic sites (PLACE, D4, NGRIP, and NEEM) are combined to produce a multisite average ice core reconstruction of past atmospheric CO for the Northern Hemisphere high latitudes, covering the period from 1700 to 1957 CE. Such a reconstruction should be taken as an upper bound of past atmospheric CO abundance.