STRONTIUM ISOTOPE RECORD OF SEASONAL SCALE VARIATIONS IN SEDIMENT SOURCES AND SEDIMENT TRAPPING IN LOW-ENERGY, SUBTIDAL AREAS OF THE LOWER HUDSON RIVER ESTUARY

Strontium isotope (⁸⁷Sr/⁸⁶Sr) profiles in two sediment cores collected from two low-energy, subtidal harbor slips in the lower Hudson River estuary exhibit patterns of variability that suggest different sources of sediment to these sites over time. Evidence from sediment Sr/Ca ratio, rare earth element (REE), Fe, Mn, total organic carbon (TOC), and CaCO₃ profiles at both sites suggests that the observed variability reflects differences in the relative input and trapping of fine-grained sediment from seaward sources vs. landward sources linked to seasonal-scale changes in freshwater flow. Trapped sediments are primarily derived from the same parent material but, during low (base) flow conditions, a higher fraction of mature material (resuspended sediment) from seaward sources deposits and accumulates. During high flow conditions, a larger fraction of immature, newly eroded basin materials are trapped. Results show that high-resolution, multi-geochemical tracer approaches using strontium isotope ratios can be used to distinguish sediment sources and constrain (quantify) seasonal scale variations in sediment trapping in dynamic estuarine environments. Low-energy, subtidal areas in estuaries serve as natural recorders of local, short-to-medium term sedimentary processes over seasonal-to-yearly time scales.