Nitric oxide (NO) in the Bohai and Yellow Seas

Abstract

<p><strong>Abstract.</strong> Nitric oxide (NO) is a short-lived compound of the marine nitrogen cycle; however, our knowledge about its oceanic distribution and pathways is rudimentary. Here we present the measurements of dissolved NO in the surface and bottom layers at 75 stations in the Bohai Sea (BS) and Yellow Sea (YS) in June 2011. Moreover, NO photoproduction rates were determined at 27 stations in both seas. The NO concentrations in the surface and bottom layers were highly variable and ranged from below the detection limit (i.e. 32 pmol L<sup>−1</sup>) to 616 pmol L<sup>−1</sup> in the surface layer and to 482 pmol L<sup>−1</sup> in the bottom layer. There was no significant difference between the mean NO concentrations in the surface (186 ± 108 pmol L<sup>−1</sup>) and bottom (174 ± 123 pmol L<sup>−1</sup>) layers. A decreasing trend of NO bottom layer concentrations salinity indicates a NO input by submarine groundwater discharge. NO in the surface layer was supersaturated at all stations during both day and night and therefore the BS and YS were a persistent source of NO to the atmosphere at the time of our measurements. The accumulation of NO during daytime was resulting from photochemical production and photoprodcution rates were correlated to illuminance. The persistent nighttime NO supersaturation pointed to a, so far unknown, NO dark production. NO sea-to-air flux densities were much lower than the NO photoproduction rates. Therefore, we conclude that the bulk of the NO produced in the mixed layer was rapidly consumed before its release to the atmosphere. Overall, the oceanic NO emissions to the atmosphere were negligible compared to anthropogenic NOx sources such as emissions from ships.</p>

Nitric oxide (NO) in the Bohai Sea and the Yellow Sea

“…Sampling for NO from both the surface (at 1 m) and the bottom layer (= 1 m above the ocean bottom) were performed at 75 sampling stations (including one 24 h anchor station: B65) shown in Fig. 1 and listed in Table 1 (Tian, 2019). Water samples were collected using 8 L Niskin bottles equipped with silicon O-rings and Teflon-coated springs and mounted on a Sea-Bird CTD (conductivity, temperature, depth) instrument (Sea-Bird Electronics, Inc., USA).…”

Photoproduction of nitric oxide in seawater

“…CC BY 4.0 License. coastal waters (Olasehinde et al, 2009;Tian et al, 2018) (Table 1). Our result is consistent with the RNO from the central equatorial Pacific Ocean (Zafiriou and McFarland, 1981) (Table 1).…”

“…for the details of the calculation see (Tian et al, 2018). Since onboard wind speeds were not available, we set the average wind speeds according to (Zhu et al, 2013) to 5 m s -1 for the stations S0301 to S0325, 235 to 8.5 m s -1 for stations S0701 to S0713, to 7 m s -1 for stations S0715 to S0725, and to 6 m s -1 for stations S0727 to S0735.…”