SEDIMENT TRANSPORT DYNAMICS IN THE SOUTHERN CALIFORNIA MARGIN: PRELIMINARY INSIGHTS

Coastal marine sediments from the Southern California margin provide valuable insights into past hydroclimate variability, yet marine-terrestrial interactions remain underexplored. Here, we present preliminary findings from a sediment core collected from the Southern California margin (~250 km offshore, at a water depth of 1690 meters) to characterize sediment transport dynamics during hydrological regime shifts. Using sedimentological and geochemical proxies - grain-size analysis, X-Ray fluorescence (XRF), and organic bulk analyses (e.g. δ¹³C and C/N ratios) - we identify three key intervals: (1) A dry phase (100–90 cm) marked by reduced sediment delivery, evidenced by decreased Fe/Ca ratios and increased δ¹³C values; (2) A wet phase (90–14.5 cm) characterized by enhanced sediment input, reflected in higher Fe/Ca ratios and consistent δ¹³C values (~-21‰); and (3) A recent dry phase (14.5–0 cm) showing lower Fe/Ca ratios, elevated δ¹³C, and higher C/N ratios, indicating reduced sediment transport to the study area.

The core is dominated by silt size-grains, suggesting a low-energy depositional environment. A notable increase in very coarse silt fractions (10.5–6.5 cm), coupled with elevated δ¹³C, Ti/Al, and Si/Al ratios, may indicate episodic high-energy events (e.g., flood pulses) and terrestrial input of C4 plant-derived organic matter. These findings reveal changes in sediment dynamics over time; however, further analyses, including age modeling, are needed to corroborate and refine these interpretations.