| 02 Sep 2025
Sea spray promotes the sea-to-air transfer of dissolved organic carbon during phytoplankton bloom
Abstract. The formation of sea spray aerosols (SSA) is linked to wave-breaking events at the sea surface and is widely recognized as an important pathway for the transfer of marine substances to the atmosphere. Although climate change and sea eutrophication have led to the expansion and intensification of coastal phytoplankton blooms, systematic studies on the sea-to-air transfer of dissolved organic carbon (DOC) via SSA during phytoplankton blooms are still lacking, which hinders the understanding of SSA's atmospheric chemistry and climate impacts. In this study, we observed that the phytoplankton bloom can promote DOC enrichment in SSA by 10-fold to 30-fold and investigated the mechanism of DOC sea-to-air transfer using various characterization tools. First, DOC's dynamic accumulation during phytoplankton bloom can significantly impact the interfacial properties of seawater, influencing SSA formation and subsequent DOC transfer. Second, the sea-to-air transfer of DOC depends on its selective enrichment as well as the fractionation process at the air-water interface. Interestingly, the particulate property of operationally defined DOC still needs to be considered during SSA formation. Third, the sea-to-air transfer of DOC is influenced by the synergistic effects of phytoplankton production and heterotrophic microbial processing, rather than being solely dependent on chlorophyll-a concentration. Compared to previous studies, this work focuses on the sea-to-air interface, systematically and comprehensively elucidating the relationships between DOC's transfer mechanisms, biological activity, and SSA formation. This will further improve our understanding of the ocean-atmosphere carbon cycle and provide insights into its impact on global climate change.
A very interesting and important paper!Â
However, quoting Lines 190--2194, "Several studies have found that phytoplankton blooms can result in
the formation of mucus on the water surface, which is typically an excessive accumulation of extracellular polysaccharides
(Ternon et al., 2024; Medina-Pérez et al., 2021). In contract, this can increase the viscosity of SML and potentially enhance its
surface tension (Jenkinson and Sun, 2010). From day 1 to day 5, the rapid increase in the surface tension of SML samples
appears to be related to the rise in their saccharide concentration (see in Fig . 6a).".Â
As the authors say, mucus, secreted by organisms such as phytoplankton, consists of polymers can indeed increase viscosity of seawater. However, it tends to reduce surface tension below the value for "pure" (i.e. organics-free) seawater about 74 mN.m-1, not enhance (increase) it. As shown in the authors' Fig. 6d, the surface tension of SML water remained consistently less than that of subsurface water (SSW) by about 0.5 to 1 mN.m-1,consistent with enrichment in the SML. The much lower values at the beginning of the experiment remain enigmatic to me, unless they might have been caused by some tiny contaminant by a surfactant molecule such as detergent, often present on the surface of new apparatus. The subsequent increase could then have represented the incorporation of such a surfactant into other organic matter in the experiment, or its conversion or utilization by organisms present. I think this small issue does not affect the validity of the rest of the presentation.Â