Recent evolution of a paraglacial estuary under conditions of rapid sea-level rise: Chezzetcook Inlet, Nova Scotia

Abstract

The local response of estuaries to sea-level rise has received relatively little attention in the literature, despite the widespread use of estuarine deposits to establish marine/terrestrial index points for the interpretation of regional sea-level curves. Chezzetcook Inlet in Nova Scotia is experiencing a relatively rapid rise in sea-level (3.8 mm a −1 from 1920–70), resulting in widespread morphosedimentary adjustments. Sediment released from both soil erosion of the estuary catchment and from coastal erosion of drumlin cliffs is infilling the estuary. Sources and sinks of sediment vary throughout the estuary. Material released by wave action from glacial diamicts is partitioned into coarse gravels and boulders, sands and silts, each component playing a role in the development of the estuary. Coarse material accumulates in outer gravel barriers which provide protection for the deposition of sands and silts in the lower estuary. In turn, these deposits create platforms instrumental in allowing barrier migration. The development of lateral sand spits and flood tide deltas is especially rapid, and may be linked to sea-level changes. Textural analysis of vibracore sediments from both active and abandoned flood tide deltas, points to episodic sediment influx and remobilization over a period of 400–600 years, which may indicate breakdown phases in the outer barriers. On a slightly longer time scale palaeoecological investigations reveal the episodes of reduced influence of sea-level rise within the estuary, while mineral magnetic analysis indicates the extent of catchment sources to the pattern of infilling. Chezzetcook Inlet provides an example of estuarine response to sea-level forcing that may be compared to other estuaries both in North America and the United Kingdom. As a result, it is possible to propose a number of models in which the sensitivity of estuarine behaviour to sea-level change can be matched to the major controls on sedimentation.