The taphonomy of historic shipwreck sites

Abstract

An understanding of the extent to which materials and energy are free to exchange across boundaries at shipwreck sites is fundamental to the archaeological interpretation of these unique resources. The limited previous work on the dynamics of shipwreck sites suggest that they can act as either near-closed systems (e.g. Mary Rose), or open systems at some state of dynamic/quasi- equilibrium with respect to their surroundings’ (e.g. Stirling Castle). Nonetheless, our understanding of the temporal evolution of shipwreck sites and thus, whether they are open or closed systems, is extremely limited. This thesis presents repeat (intra-annual; annual; and decadal) Multibeam Echosounder (MBES) surveys for five shipwreck sites (the largest published collection of shipwreck site MBES time-series to date) from a range of environments: the Richard Montgomery, tidally dominated (weakly asymmetrical); the Scylla, storm dominated; the Burgzand Noord site, tidally dominated (strongly asymmetrical); the Stirling Castle, dominated by large-scale geomorphological processes; and the Algerian, sheltered. By quantifying the temporal variability (through bed-level change plots) and the Metocean, geological and geomorphological conditions of these wreck sites, the impact of the differing marine environments on the wreck site’s taphonomic pathway was constrained. Through the collation of these MBES time-series the importance of being able to account for the uncertainty of the data when comparing two time steps was realised. To this end, a robust methodology for assessing the uncertainty of the MBES data was developed for the use with marine MBES data. The spatial patterns of scouring and deposition were accounted for through the application of the simple principles of scouring around bluff obstacles (cylinders, cuboids and piers etc.). Those sites which experienced a disturbance during the observation period (e.g. a storm event at the Scylla, sandbank migration at the Stirling Castle and the implementation of physical protection at the Burgzand Noord site) underwent a larger range of bed-level change and altered dramatically in their scour/deposition arrangement. Those sites at quasi-equilibrium (SS Richard Montgomery, Algerian and Scylla for the final time-step) underwent no perceivable net bed-level change over the observation period and had stable scour and deposition features. The comprehension of shipwreck site taphonomy gained through this thesis is fundamental to the efficacy of heritage management, allowing protective measures to be site-tailored and fills a large data- and knowledge-gap in the long term (multi-annual) evolution of scour around marine anthropogenic structures.

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ORCID for Justin Dix: orcid.org/0000-0003-2905-5403

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