Abstract. Nitric oxide (NO) is a short-lived compound of the
marine nitrogen cycle; however, our knowledge about its oceanic distribution
and turnover 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
the 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 limit of
detection (i.e., 32 pmol L−1) to 616 pmol L−1 in the surface layer
and 482 pmol L−1 in the bottom layer. There was no significant
difference (p>0.05) between the mean NO concentrations in the
surface (186±108 pmol L−1) and bottom (174±123 pmol L−1) layers. A decreasing trend of NO in bottom-layer concentrations
with 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 average flux was about
4.5×10-16 mol cm−2 s−1 and the flux showed
significant positive relationship with the wind speed. The accumulation of
NO during daytime was a result of photochemical production, and
photoproduction rates were correlated to illuminance. The persistent
nighttime NO supersaturation pointed to an unidentified 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.
Long-term variations in biogenic elements of the Bohai Sea and the North Yellow Sea
