44-14 Investigating Geomorphic Controls on 210Pb and 137Cs-based Chronologies in Subaqueous Nearshore Sediments along the Connecticut Coast

Abstract:

Sedimentation rates along the dynamic coastal zone are rarely quantified, despite their extent and their importance in understanding coastal sediment dynamics and sea level rise. ²¹⁰Pb and ¹³⁷Cs chronometers are widely accepted tools for age-depth modeling, but chronologies are mostly developed for lakes and salt marshes. Most age models (CRS, CF:CS, Plum) assume constant or consistent sediment influx, an assumption the coastal nearshore zone frequently violates. 

In this study, we investigate ²¹⁰Pb and ¹³⁷Cs-based chronologies from 10 sediment cores spanning coastal Connecticut, with sites including a diverse range of geomorphic settings such as sheltered coves, tidal channels, and high-energy tidal inlets. These chronologies are compared to bulk Pb profiles, whose well-documented regional history serves as a proxy for industrial sediment preservation. Sites with consistent sediment preservation are modeled using the CRS method, which uses excess ²¹⁰Pb inventory to construct age-depth relationships, whereas sites with episodic records require alternative approaches. 

Sedimentation rates for continuously accumulating sites range from 0.15 to 0.2 cm yr⁻¹ while higher energy settings preserve episodic records that fall outside standard age model assumptions. Some sites preserve bulk Pb that may predate the 1920 marker, indicating earlier local industrial inputs that complicate its use as a single chronological marker. These chronologies provide a means of distinguishing pre- and post-1920 baselines for sedimentation rates, with implications for sediment budget and sea-level reconstruction studies. 

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