Anthropogenic structure emplacement and sediment transport at King Herod's harbour, Israel: ED-μXRF (Itrax) data and foraminifer Pararotalia calcariformata as proxies of coastal development over millennia

Abstract

The construction of harbours along high energy nearshore environments, which commonly include the emplacement of hard structures both as central features (e.g., piers, jetties) as well as protective measures (e.g., wave breakers, coastal armouring), can alter coastlines in a multitude of ways. These include reconfiguring the coast's morphology, introducing or redistributing exogenous and endogenous materials, and changing localized environmental substrate and structural conditions; and, as a result, impact the associated ecological communities. With growing coastal populations and associated coastal development, concerns over the long-term consequences of such projects are of global interest. Caesarea Maritima, a large-scale, artificially constructed ancient harbour built between 21 and 10 BCE, provides a rare opportunity to address these impacts and investigate its fingerprint on the landscape over 2000 years. To approach this, representative sediment samples were isolated and analyzed from two sediment cores (C1, C2), an excavated trench (W), and a sample of ancient harbour construction material (aeolianite sandstone and hydraulic concrete; COF). Geochemical (Itrax μXRF, magnetic susceptibility) and foraminifera analyses were conducted and results from both methods were statistically grouped into significantly similar clusters. Results demonstrated the increased presence of aeolianite-associated elemental contributions only after the construction of Caesarea as well as in particularly high concentrations following previously proposed tsunami events, during which shallower and deeper materials would have been transported and redeposited. The foraminifera data shows the appearance and eventual abundance dominance of Pararotalia calcariformata as an indicator of coastal hardening. Results suggest that they are an especially well-suited species to demonstrate changing environmental conditions existing today. In previous studies, this species was mistakenly presented as a recent Lessepsian arrival from the Red Sea, when in fact it has had a long history as an epiphyte living on hardgrounds in the Mediterranean and co-existencing with humans and their harbour-building habits. Specimens of P. calcariformata, therefore, are useful indicators for the timing of harbour construction at Caesarea and may be used as rapid and cost-effective biostratigraphic indicators on sandy nearshore coastline in future geoarchaeological studies. This has implications for future studies along the Israeli coast, including both paleoenvironmental and modern ecological assessments.