Fig. 1: Near-continuous nitrous oxide data across the Pacific basin.
From: On the natural spatio-temporal heterogeneity of South Pacific nitrous oxide
a Spatial map of 15-day back trajectories from the four Pacific monitoring stations analyzed in this study, overlain on dissolved oxygen concentrations at the 1026.5 kg m−3 density horizon, with the 10 and 20% saturation contours displayed (dashed blue lines). A random selection of ten trajectories each from Hawaii, Tasmania, and California-originating back-trajectories are shown in gray, and ten randomly selected Samoa back-trajectories in color. Squares represent the positions of the trajectories 15 days prior to arrival at the Samoa station. Only the Samoa station back-trajectories frequently intersect the boundaries of the oxygen minimum zones. b De-trended time series of atmospheric N2O concentrations measured at the Samoa station, split among austral summer (orange) and winter (purple) along with a mean annual oscillation (black). This seasonal cycle is driven largely by the southward shift of the intertropical convergence zone in January bringing the influence of higher northern hemisphere concentrations to the south. c De-seasonalized N2O concentrations (light gray dots, with monthly means represented by the dark gray line) compared with a 3-month forward shifted Niño 3.4 index (orange) and a running integrated Niño 3.4 index (green). All time series are shown normalized. The Niño index time series is flipped vertically to facilitate visual comparison with N2O, i.e., high N2O aligns with negative La Niña excursions. The N2O concentrations align well with both ENSO metrics, with p < 0.0001.
