Late Glacial to Holocene relative sea-level change in Assynt, northwest Scotland, UK

Abstract

Relative sea-level change (RSL), from the Late Glacial through to the late Holocene, is reconstructed for the Assynt region, northwest Scotland, based on bio-and lithostratigraphical analysis. Four new radiocarbon-dated sea-level index points help constrain RSL change for the Late Glacial to the late Holocene. These new data, in addition to published material, capture the RSL fall during the Late Glacial and the rise and fall associated with the midHolocene highstand. Two of these index points constrain the Late Glacial RSL history in Assynt for the first time, reconstructing RSL falling from 2.47 ± 0.59 m OD to 0.15 ± 0.59 m OD at c. 14,000-15,000 cal yr BP. These new data test model predictions of glacial isostatic adjustment (GIA), particularly during the early deglacial period which is currently poorly constrained throughout the British Isles. Whilst the empirical data from the midto late-Holocene to present matches quite well with the recent GIA model output, there is a relatively poor fit between the timing of the Late Glacial RSL fall and early Holocene RSL rise. This mismatch, also evident elsewhere in northwest Scotland, may result from uncertainties associated with both the global and local ice components of GIA models. IntroductionThe United Kingdom has been the focus of sea-level research for a number of decades (e.g. Devoy, 1982;Tooley, 1982;Shennan et al., 2005;Shennan et al., 2006a). The British and Irish Ice Sheet (BIIS) provides a compact case study suitable for disentangling the relative contributions of eustasy, deformation of the ocean geoid, isostasy and local processes to regional records of post-Last Glacial Maximum (LGM) relative sea-level (RSL) change (Flemming, 1982;Shennan, 1989). The pattern of RSL change in Scotland is of particular interest as it is dominated by a complex spatial pattern of glacial isostatic adjustment (GIA) caused by the proximity of the centre of the LGM BIIS, and the peripheral effects of the Fennoscandian ice sheet (Peltier, 1998). As a consequence, post-LGM records of RSL change in Scotland have the potential to refine, both the ice-sheet history and Earth rheology components of GIA models. The Arisaig sea-level curve from western Scotland, which is currently the longest and most complete RSL archive for the British Isles (Shennan et al., 1996;Shennan et al., 2005), is a particularly important test of GIA models (e.g. Shennan et al., 2006a;Bradley et al., 2011). Many other locations, particularly those close to the centre of the LGM BIIS, currently have very limited records of past sea level, particularly covering the Late Glacial period, with spatially and temporally disparate sea-level index points. The aim of this paper is to develop new records of past sea level for the understudied Assynt region of northwest Scotland (Fig. 1), extending the current record, from Coigach (Shennan et al., 2000), beyond the mid-Holocene. Offshore geological records from northwest Scotland show that this region consisted of a series of LGM ice streams which channelled ice offsho...

Lateglacial and Holocene relative sea‐level changes and first evidence for the Storegga tsunami in Sutherland, Scotland

“…(). (B) Relative sea‐level observations from the mainland coast of northern Scotland including data from Loch Eriboll (this study), the Wick River Valley (Dawson and Smith, ) and Eddrachillis Bay (Hamilton et al ., ).…”

“…An equivalent higher‐than‐present Lateglacial RSL to that observed in Loch Eriboll is recorded at Eddrachillis Bay by Hamilton et al . (). Here the local marine limit is at ca.…”

“…In contrast, at Eddrachillis Bay, Hamilton et al . () interpret a single radiocarbon date from immediately below an abrupt ingression contact as evidence that RSL rose to above present by ca. 10 k cal a BP, supposedly re‐flooding the Loch Duart Marsh tidal basin.…”

Quaternary sea level change in Scotland

“…Since 1993, much research on Late Devensian and Holocene RSL change in Scotland has been concentrated on the W and NW mainland, where from the Arisaig area, Shennan et al (e.g., 1993, 1994, 1995a, b, 2005, 2006a) compiled the longest dated record of Late Devensian and Holocene RSL change in the UK (Figs 10D, 22(11)).

Figure 10Graphs of RSL (relative to the reference water level identified in the original papers) for isolation basin and coastal wetland sites at Assynt and Coigach (A), Loch Alsh and Loch Duich, Kintail (B), Kentra Moss (C), the Arisaig area (D) and Knapdale, Kintyre (E), based on data from Shennan et al (2000a, 2006b) and Hamilton et al (2015). Equivalent OD values and error margins are explained in the references quoted.

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“…7, sl. 19) were examined by Hamilton et al (2015), who found a Holocene highstand at below 2.4 7 e 0.59 m OD. They maintain that GIA models need to incorporate thicker ice in the NW sector of the BIIS to explain the values for RSL obtained for the timing of the Lateglacial fall and early Holocene RSL rise there.…”