In-situ atmospheric measurements of CO2 polyisotopologues at Weybourne Atmospheric Observatory in the United Kingdom

The δ¹⁸O signature of atmospheric CO₂ can be used as a tracer for estimating gross primary production (GPP), however, this method requires having detailed knowledge of δ¹⁸O signatures of numerous water reservoirs and isotopic fractionation associated with transfer processes, which are highly variable due to the complexity of the hydrological cycle. Simultaneous measurements of δ¹⁸O-CO₂ and δ¹⁷O-CO₂ can simplify this requirement, since variations in δ¹⁷O are, for most processes, strongly correlated with variations in δ¹⁸O. Thus, it is possible to combine measurements of δ¹⁸O-CO₂ and δ¹⁷O-CO₂ into a tracer that removes the mass-dependent fractionations related to the hydrological cycle, known as the ‘triple oxygen isotope excess’ (Δ¹⁷O). Variability in Δ¹⁷O only depends weakly on the oxygen isotope signatures of soil and leaf water and should therefore in principle be a more direct tracer for GPP than variations in δ¹⁸O alone.

We present a 2.5-year record (2021-2024) of atmospheric δ¹³C-CO₂, δ¹⁸O-CO₂, δ¹⁷O-CO_2, Δ¹⁷O, and CO₂ mole fraction measurements at Weybourne Atmospheric Observatory on the north Norfolk coast in the UK (52º 57’ N, 1º 07’ E). Measurements are made in-situ every 4 minutes using a tuneable infrared laser direct adsorption spectroscopy (TILDAS) dual-laser analyser from Aerodyne Research Inc. We present observed atmospheric variability in Δ¹⁷O on seasonal, diurnal, and synoptic timescales, and report the measurement system short-term repeatability and reproducibility.