Long-term observations of δ13C-CO2, δ18O-CO2, δ17O-CO2 and “excess” 17O-CO2 by Quantum Cascade Dual-Laser Absorption Spectrometry in whole air flask samples from Lutjewad station, the Netherlands

We present long-term results of δ¹³C-CO₂, δ¹⁸O-CO₂, δ¹⁷O-CO₂ and “excess” ¹⁷O-CO₂ or Δ¹⁷O-CO₂ measurements in whole air flask samples collected at Lutjewad monitoring station in the Netherlands using an Aerodyne Quantum Cascade Dual-Laser Spectrometer system (QCDLAS). The station is located at the Dutch Wadden sea coast (6.353°E, 53.404°N) in a rural environment. The flask samples have been collected at 60 m altitude at a bi-weekly rate, spanning from July 2016 until the end of 2020. The location of Lutjewad station allows to measure clean marine background air from the north-northwest (~15% of the time) in contrast to continental air from a prevalent south-westerly direction (~50% of the time). Our observations include the summers of 2018 and 2019 which saw exceptionally hot and dry conditions in large parts of Europe, including the Netherlands.

The Δ¹⁷O-CO₂ anomaly is defined as the deviation from normal mass dependent fractionation reflected in CO₂ equilibrated with water, occurring over water bodies, but mainly in plant leaves. Atmospheric Δ¹⁷O-CO₂ has been used as a parameter to study gross primary production (GPP), notably as a function of water availability. Here, the determination of Δ¹⁷O-CO₂ is derived from the direct measurement of δ¹⁷O-CO₂ next to δ¹⁸O-CO₂ (Δ¹⁷O = ln(δ¹⁷O +1)-0.5229×ln(δ¹⁸O +1)). Using the summer 2018 and 2019 results we investigate the potential of using the Δ¹⁷O-CO₂ signal derived from QCDLAS measurements from Lutjewad as a tracer for suppressed plant assimilation due to water stress.