Evidence for relative sea level changes during the middle and late Holocene is examined from two locations on the Atlantic coast of Harris, Outer Hebrides, Scotland, using morphological mapping and survey, stratigraphical, grain size and diatom analysis, and radiocarbon dating. The objective was to determine whether this location, peripheral to a glacio-isostatic uplift centre, would register fluctuations in the nearshore sea surface and whether local variations in ice loading might be detected in the altitudes of sea level index points. The earliest event identified is a marine flood, which occurred after 7982-8348
calibrated years (7370±8014C years) BP, when the sea crossed a threshold lying at -0.08m OD (-2.17m MHWS) before withdrawing. This could have been due to a storm or to the Holocene Storegga Slide tsunami. By 6407-6122 (5500±60) BP, relative sea levels had begun to fall from a sandflat surface with an indicated MHWS level of between 0.08 and - 1.96m (-2.01 to -4.05m). This fall reached between -0.30 and -2.35m (-2.39 to -4.44m) after 5841-5050 (4760±130) BP, but was succeeded by a relative sea level rise which reached between 0.54 and -1.57m (-1.55 to -3.66m) by 5450-4861 (4500±100) BP. This rise continued, possibly with an interruption, until a second sandflat surface was reached
between 2.34 and -0.26m (0.25 to -2.35m) between 2952-3375 (3000±80) and 1948-2325 (2130±70) BP, before present levels were reached. The regressive episode from the earliest sandflat is correlated with the abandonment of the Main Postglacial Shoreline. It is maintained that the fluctuations in relative sea level recorded can be correlated with similar events elsewhere on the periphery of the glacio-isostatic centre and may therefore reflect secular changes in nearshore sea surface levels. Despite published evidence from trim lines
of differential ice sheet loading across the area, no evidence of variations in uplift between the locations concerned could be found.
This paper was an oral presentation. The full abstract is available from the link given (page 19).
Presented at the Quaternary Research Association Annual Discussion Meeting: Sea-level Changes: the Science of a Changing World. Held 5-8 January 2010 at Durham University, UK. The conference website can be found at http://www.dur.ac.uk/geography/conferences/qra/
Jordan, J.T. , Smith, D.E. , Dawson, S. and Dawson, A.G. (2010) Holocene relative sea-level changes in Harris, Outer Hebrides, Scotland, UK. Journal of Quaternary Science, volume 25 (2): 115-134
- relative sea level