A geomorphological reconstruction of the deglaciation of Loch Etive during the Loch Lomond Stadial

Abstract

The Loch Lomond Stadial (LLS) (12.9 – 11.7 ka BP) was the last climatic episode in which Scotland possessed a significant ice mass. Loch and Glen Etive represent one of the best-preserved glacial landsystems in western Scotland, having formed a conduit for ice draining from high on Rannoch Moor. Loch Etive is a glacially over-deepened trough 6 km north of Oban, now a sea loch 30 km long and up to 1.5 km wide, extending from the Firth of Lorn NE towards Rannoch Moor. It is a key site in which to understand the glacial processes that shaped the Western Highlands during the LLS, leading to full glacial retreat by 11.4 ka BP. Based on a comprehensive high-resolution multibeam bathymetric sonar survey, the morphology of the seabed was analysed using ArcGIS to create a series of detailed geomorphological maps. Morphological interpretations, backscatter and seismic reflection data from the loch were combined to reconstruct the deglaciation of Loch Etive. The presence of transverse ridges interpreted as recessional moraines and submarine eskers indicates a dynamic glacial retreat from the maximum seaward extent west of the present-day coastline. At its maximum extent, the glacier formed a proglacial delta generating large volumes of meltwater that flowed over the rock sill of the present-day Falls of Lora. The confluence of glacial ice masses, flowing from the Pass of Brander and tributary corrie glaciers, created a complex glaciofluvial environment in the outer basin of Loch Etive. This is reflected in the formation of a large submarine esker. In the inner loch basin, the presence of recessional moraines at intervals suggests a dynamic glacier, responding to seasonal temperature fluctuations, possibly subsequently retreating northeastwards c. 50 m annually as the LLS ended.

Where’s the Carbon: Exploring the Spatial Heterogeneity of Sedimentary Carbon in Mid-Latitude Fjords

“…Scottish and Irish fjords largely lack these data, a pattern observed in coastal systems globally. Other approaches to map the seabed and sediment type utilize multibeam and backscatter geophysical techniques (Serpetti et al, 2012;Lark et al, 2015;Audsley et al, 2016;Brown et al, 2019) where changes in acoustic responses are used to characterize seabed type. These methods provide an understanding of the spatial distribution of sediment types but have largely not been applied to fjord systems.…”

Progress in marine geoconservation in Scotland’s seas: assessment of key interests and their contribution to Marine Protected Area network planning

“…At a more local scale, the geomorphological and sedimentary archives of the west coast fjords of Scotland augment the terrestrial evidence for the later stages of deglaciation of the last British-Irish Ice Sheet and the subsequent re-expansion of glaciers in the north and west Highlands during the Loch Lomond (Younger Dryas) Stade McIntyre and Howe, 2010;McIntyre et al, 2011;Howe et al, 2015b;Audsley et al, 2016;Small et al, 2016). The fjord sediments also record palaeoenvironmental changes during the Holocene (Howe et al, 2002;Nørgaard-Pedersen et al, 2006;Baltzer et al, 2010;Cage and Austin, 2010;Cundill and Austin, 2010;Mokeddem et al, 2010) and form sinks for organic carbon from terrestrial sources (Burrows et al, 2014).…”

Surging glaciers in Scotland

“…Stagnation of this part of the Etive Glacier is also indicated by the submarine landform record. Within the area of kame terraces described above, is an area of 'irregular hummocky terrain', on the loch floor, consisting of complex networks of longitudinal and transverse mounds and ridges (Audsley et al, 2016;Figure 16A). These are similar to ridge networks formed by tidewater surge-type glaciers in Svalbard (Figure 7), raising the possibility that they may be crevasse-fill ridges.…”