Quantifying tidal zonation through pollen-microfacies coupling: A Holocene sea-level proxy from Hangzhou Bay, eastern China

Accelerating sea-level rise necessitates high-resolution paleoenvironmental proxies to refine future projections. Mid-Holocene analogs remain critical for coastal vulnerability assessments, yet microfacies-based reconstructions are constrained by limited diagnostic precision in sedimentary archives. Here, we address this gap through systematic analysis of modern vegetation zonation and pollen transport dynamics across tidal flat transects in South Hangzhou Bay, eastern China. Results demonstrate that pollen distributions encode quantifiable tidal elevation signals: (1) Allochthonous Pinus pollen dominates unvegetated lower intertidal zones and Spartina alterniflora-sparse middle flats, exhibiting an inverse relationship with elevation; (2) Autochthonous Chenopodiaceae and Taraxacum pollens show strong positive elevational dependencies, peaking in upper intertidal marshes and supratidal terrestrial interfaces; (3) Poaceae pollen lacks diagnostic value due to dual airborne/hydrodynamic transport pathways, producing homogenized distributions across tidal zones. We propose Pinus depletion trends and Chenopodiaceae enrichment thresholds as discrete elevational markers for reconstructing Holocene relative sea-level (RSL) index points. This work establishes pollen as a high-resolution proxy capable of resolving previously unrecognized tidal zonation patterns, thereby advancing the spatiotemporal precision of post-glacial RSL reconstructions in coastal systems.