Evidence for the mutual effects of dimethylsulfoniopropionate and nitric oxide during the growth of marine microalgae

Evidence of nitrate-based nighttime atmospheric nucleation driven by marine microorganisms in the South Pacific

Our understanding of ocean-cloud interactions and their effect on climate lacks insight into a key pathway: do biogenic marine emissions form new particles in the open ocean atmosphere? Using measurements collected in ship-borne air-sea interface tanks deployed in the Southwestern Pacific Ocean, we identified new particle formation (NPF) during nighttime that was related to plankton community composition. We show that nitrate ions are the only species for which abundance could support NPF rates in our semicontrolled experiments. Nitrate ions also prevailed in the natural pristine marine atmosphere and were elevated under higher sub-10 nm particle concentrations. We hypothesize that these nucleation events were fueled by complex, short-term biogeochemical cycling involving the microbial loop. These findings suggest a new perspective with a previously unidentified role of nitrate of marine biogeochemical origin in aerosol nucleation.

Sources of nitric oxide during the outbreak of Ulva prolifera in coastal waters of the Yellow Sea off Qingdao

Nitric oxide (NO) has been identified as a key physiological modulator and signaling molecule in animals and plants. However, due to its high reactivity, our knowledge of its production and consumption pathways in the ocean remain limited. Laboratory experiments showed that Ulva prolifera can produce NO, producing as much as 0.44 ± 0.04 nmol h^-1 g^-1. During the growth period, U. prolifera released NO, but during the decay period NO was absorbed by U. prolifera and bacteria. Furthermore, field investigations examined NO concentrations in the coastal waters of the Yellow Sea off Qingdao, where the U. prolifera green tide occurred in summer 2018. The average concentrations of NO in the surface seawater were 70.2 ± 38.2 pmol L^-1 and 18.9 ± 10.3 pmol L^-1 in the late- and after-bloom periods, respectively. NO release by U. prolifera was the primary contributor to the high NO concentrations during the late-bloom period. The study area was a net source of NO to the atmosphere during the study period, with average NO sea-air fluxes from the Qingdao coastal waters being 1.5 × 10^-12 mol m^-2 s^-1 and 0.4 × 10^-12 mol m^-2 s^-1 in the late- and after-bloom periods, respectively. This study concluded that the coastal waters of the Yellow Sea off Qingdao contributed more NO to the atmosphere during the bloom of U. prolifera than afterward.

Changes in concentrations of biogenic sulfur compounds in coastal waters off Qingdao, China during an Ulva prolifera bloom

Distributions and variations of biogenic sulfur compounds including dimethylsulfide (DMS), dissolved and total dimethylsulfoniopropionate (DMSPd and DMSPt) and acrylic acid (AA) were investigated in coastal waters off Qingdao, China during the late-bloom and after-bloom periods of the Ulva prolifera bloom of 2015. DMSPd, DMS and AA concentrations after the bloom were significantly higher than during the late-bloom, but DMSPt concentrations in surface waters began to decrease. High concentrations of these compounds in the surface layer were associated with the bloom, with the exception of increased concentrations of DMSPt in the middle layer as decaying U. prolifera debris settled. The sea-to-air fluxes of DMS were estimated to be 18.08 and 24.24 μmol m^-2 d^-1 during the late-bloom and after-bloom, and about three times higher than the reported average fluxes of the Yellow Sea, which highlighted the impacts of U. prolifera blooms on DMS emissions.