Evidence for Rapid Postglacial Sea-Level Changes off the Northern Ireland Coast

Marine geophysical surveys off the paraglacial coast of Northern Ireland show a range of geological evidence for changes in relative sea-level (RSL) during the late-glacial and early Holocene periods (c. 14-8 kyr BP). Geological evidence was interpreted from Chirp sub-bottom geophysical profiles, side-scan sonar data, and echo-sounded bathymetry. Evidence observed includes submerged notches and shore platforms, and tabular or wedge-like acoustic units which have variously sharp, graded, draped and unconformable contacts. Submerged notches and shore platforms, interpreted to represent sea-level stillstands, are present at -30 m, -24 m and -15 m OD. These are cut into, variously, acoustic units interpreted as subglacial and glaciomarine diamicts (tills), indicating a close relationship between glacial and marine sediment deposition and RSL stage. Separating these stillstand features spatially and stratigraphically are sandy and muddy sediment units which record periods of sediment infilling (reduction of accommodation space) under more slowly rising RSL. Interpretation of acoustic units using a systems tract approach identifies periods of sediment deposition associated with late-glacial (14-12 kyr BP) and early Holocene (10-8 kyr BP) transgressive RSL phases, which are separated by a deep RSL lowstand. Trangression between c. 11-9.5 kyr was up to 16 mm yr. The rapid changes in RSL, associated with changes in marine sedimentation patterns, are similar to those observed in the tropical coral (global eustatic) record, but those in Ireland have a different timing because of the interplay between glacio-isostatic and eustatic effects. The presence of short periods of eustatic RSL change along the Ireland coast - which are out of tempo with global eustatic patterns - may support evidence for varying strength of glacio-isostatic RSL rise over time, perhaps associated with reactivation of pre-existing regional faults.