Preliminary investigation of the local marine reservoir effect in Port Joli Harbour, Nova Scotia using archaeological M. arenaria shells

Abstract

Port Joli Harbour, situated on the southwest coast of the maritime province of Nova Scotia, Canada, has the highest density of shell midden deposits in Atlantic Canada. The terrestrial radiocarbon chronology points to continuous human occupation of the harbour from 1685 cal yr BP to 316 cal yr BP (2σ). Despite the abundance of the soft-shell clams Mya arenaria at shell midden sites throughout the harbour, they have not been incorporated into the chronology nor have they been used to study the local marine reservoir effect in the harbour. We report 12 new ¹⁴C measurements on archived Mya arenaria from the same depositional contexts as previously dated charcoal and terrestrial mammal bone samples from two shell middens in Port Joli Harbour. From these shell-charcoal and shell-bone pairs, we present preliminary calculations of local marine reservoir corrections (ΔR) for the harbour. The ΔR values are highly variable and are overall more positive than the pre-bomb values reported for the Scotian Shelf. The variability of these values highlights the challenges in calculating ΔR values from archived archaeological samples but also the opportunities to include high-resolution analysis of ΔR variations in discussions on human-environment interactions in coastal settings during the late Holocene. We suggest that the chondrophore may be more favourable for calculating first-order estimates of ΔR to be used in future archaeological calibrations, while high resolution analysis of the ventral margin region will be useful for climate reconstructions. We recommend that more ¹⁴C measurements from M. arenaria shells be obtained from either distinct features or rapidly deposited middens in Port Joli Harbour. A suite of temporally and geographically precise ΔR values for the harbour will not only allow for the study of middens that are at risk of coastal erosion and lack charcoal for ¹⁴C dating but will also allow for the reconstruction of past climate conditions and refine our understanding of late Holocene human-environment interactions in the North Atlantic.