Description: While being a major source for atmospheric CO2 the Peruvian upwelling region exhibits strong variability in surface fCO2 on short spatial and temporal scales. Understanding the physical processes driving the strong variability is of fundamental importance for constraining the effect of marine emissions from upwelling regions on the global CO2 budget. In this study, a frontal decay on length scales of (10km) was observed off the Peruvian coast following a pronounced decrease in downfrontal wind speed with a time lag of 9 hours. Simultaneously, the sea-to-air flux of CO2 on the inshore (cold) side of the front dropped from up to 80 to 10 mmol/m**2/day, while the offshore (warm) side of the front was constantly outgassing at a rate of 10-20 mmol/m**2/day. Based on repeated ship transects the decay of the front was observed to occur in two phases. The first phase was characterized by a development of coherent surface temperature anomalies which gained in amplitude over 6-9 hours. The second phase was characterized by a disappearance of the surface temperature front within 6 hours. Submesoscale mixed layer instabilities were present but seem too slow to completely remove the temperature gradient in this short time period. Dynamics such as a pressure driven gravity current appear to be a likely mechanism behind the evolution of the front.

Description: Continuous measurements of the climate-relevant trace gases carbon dioxide (CO2), nitrous oxide (N2O), and carbon monoxide (CO) in the surface ocean and overlying atmosphere were conducted during 9 SFB 754 cruises (see Table C14) spanning the North, South and equatorial Atlantic, as well as the South and equatorial Pacific. To this end, laser spectroscopy-based gas analyzers coupled to air-water equilibration chambers were used. For details of the analytical systems the reader is referred to the descriptions provided by Arévalo-Martínez et al. (2013) and Arévalo-Martínez et al. (2019). All trace gas measurements were quality-controlled to achieve the international standards for marine CO2 (Bender et al., 2002), N2O (Bange et al., 2019), and atmospheric CO (Zellweger et al., 2019; to date there is no accepted standard for seawater measurements). The final quality-controlled data is available through the Surface Ocean CO2 Atlas (SOCAT, https://www.socat.info/) and the Marine CH4-N2O database (MEMENTO, https://memento.geomar.de/) as well as on Pangaea

Description: The open ocean is a major source of nitrous oxide (N2O), an atmospheric trace gas attributable to global warming and ozone depletion. Intense sea-to-air N2O fluxes occur in major oceanic upwelling regions such as the eastern tropical South Pacific (ETSP). The ETSP is influenced by the El Niño–Southern Oscillation that leads to inter-annual variations in physical, chemical, and biological properties in the water column. In October 2015, a strong El Niño event was developing in the ETSP; we conduct field observations to investigate (1) the N2O production pathways and associated biogeochemical properties and (2) the effects of El Niño on water column N2O distributions and fluxes using data from previous non-El Niño years. Analysis of N2O natural abundance isotopomers suggested that nitrification and partial denitrification (nitrate and nitrite reduction to N2O) were occurring in the near-surface waters; indicating that both pathways contributed to N2O effluxes. Higher-than-normal sea surface temperatures were associated with a deepening of the oxycline and the oxygen minimum layer. Within the shelf region, surface N2O supersaturation was nearly an order of magnitude lower than that of non-El Niño years. Therefore, a significant reduction of N2O efflux (75 %–95 %) in the ETSP occurred during the 2015 El Niño. At both offshore and coastal stations, the N2O concentration profiles during El Niño showed moderate N2O concentration gradients, and the peak N2O concentrations occurred at deeper depths during El Niño years; this was likely the result of suppressed upwelling retaining N2O in subsurface waters. At multiple stations, water-column inventories of N2O within the top 1000 m were up to 160 % higher than those measured in non-El Niño years, indicating that subsurface N2O during El Niño could be a reservoir for intense N2O effluxes when normal upwelling is resumed after El Niño.