Reconstructing abrupt, high-magnitude sea-level changes from near-field coastal environments

Abstract

Abrupt, high-magnitude sea-level changes pose a major challenge to society and have, in the past, been significant drivers of coastal change. Traditionally, sea-level reconstructions from near-field regions - those close to or strongly influenced by current or former ice masses - depict long-term, millennial-scale sea-level changes associated with low-amplitude ice-sheet histories. Types of abrupt sea-level change, including meltwater pulses, tsunamis and storms, are not well studied in near-field regions, but such areas have potential to provide a suitable context for recording and identifying evidence of abrupt sea-level change. For example, unusually high sedimentation rates due to the presence of glaciers might promote the development of high-resolution records, while a dominant glacio-isostatic adjustment signal might facilitate improved registration and identification of globally significant episodes of abrupt sea-level rise.

This thesis explores the efficacy of near-field regions in reconstructing abrupt sea-level change by using a combination of stratigraphic and dating methods at field sites in Scotland and Greenland. From southwest Scotland, a sub-centennially resolved, diatom-based sea-level reconstruction for the early Holocene constrains the timing and magnitude of three meltwater-induced sea-level accelerations in the c. 500 yrs prior to the 8.2 kyr BP event. Despite an inability of the 14C dating technique to confirm synchroneity of events, the three sea-level jumps overlap in age with other examples of abrupt change recorded in North Atlantic non-coastal and coastal archives, lending support to a three-event model of meltwater release from the Laurentide Ice Sheet as the driving mechanism responsible for the 8.2 kyr BP event.

In Greenland, nearshore and freshwater stratigraphic records contain evidence of landslide- and iceberg-induced tsunami events in the mid and late Holocene. Field sites in Vaigat (Disko Bugt, West Greenland) preserve evidence of five tsunami events in the past 1500-2000 years, which is comparable to tsunami recurrence intervals described from sites on large subduction zone margins. A coastal lake at Innaarsuit also provides the first reported sedimentary evidence of an iceberg-generated tsunami in the mid Holocene. The thesis concludes by reflecting on the opportunities and challenges in reconstructing abrupt sea-level change from near-field settings.