Abstract Green tides, particularly the severe blooms of Ulva prolifera in the Yellow Sea since 2007, release significant amounts of organic carbon (OC); however, the fate of U. prolifera ‐derived OC is still unclear. This study traced U. prolifera ‐derived OC using its specific lipid biomarker (28‐isofucosterol) in suspended particles and surface sediments across three regions of the Southern Yellow Sea ( U. prolifera growth‐impact, settlement, and non‐outbreak regions) in May 2023. We also analyzed phytoplankton lipid biomarkers. Our findings revealed high concentrations of 28‐isofucosterol (up to 141.91 ng L −1 ) in the surface suspended particles within the non‐outbreak region, associated with floating U. prolifera observed, indicating the impact of newly grown U. prolifera on OC. In the bottom suspended particles, 28‐isofucosterol concentrations (62.74–83.65 ng L −1 ) were comparable across all regions, indicating integrated signals of remnants from previous years. 28‐isofucosterol thus remained detectable in suspended particles, showing its persistence and suitability as a tracer of U. prolifera deposition. Surface sediments, which reflect the inputs from multiple years, showed the highest contents of all lipid biomarkers in the settlement region. The proto‐burial efficiency of U. prolifera ‐derived OC (2%–4%) was quantified for the first time and was considerably lower than that of total phytoplankton lipid biomarkers (a proxy for phytoplankton‐derived OC) (13%–95%), emphasizing the transient nature of macroalgae‐derived OC inputs compared to the sustained input from phytoplankton. Our findings underscore the need for integrated approaches to better understand the ecological impacts and carbon cycling dynamics as bloom condition escalate.
Wang et al. (Sun,) studied this question.