Transect 1 – Shetland
T Bradwell, D Fabel, D Small, C Clark, R Chiverrell, M Burke, A Medialdea, M Saher, D Dove, S Morgan, C O’Cofiagh
Fieldwork and activities:
BackgroundThe interplay and separation of glaciologically distinct ice sheets is a rarely studied but crucially important phenomenon. Following dynamic separation, ice sheets can rapidly re-organize – as their geometries, internal structures and flow patterns adjust to new equilibria conditions – dramatically changing the way they behave. During the last glacial cycle, the British-Irish Ice Sheet (BIIS) extended into the northern North Sea Basin and during maxima coalesced with the much larger Fennoscandian Ice Sheet (FIS) to the east (Carr et al., 2006; Graham et al., 2007; Bradwell et al., 2008; Chiverrell and Thomas, 2010). Suites of Late Weichselian moraines on the continental shelf edge, west of Orkney and Shetland, relate to this maximum stage c. 25-30 ka BP (Fig. A).
At this time (LGM) the Norwegian Channel Ice Stream may not have operated, or fed into a larger ice stream to the west. Although the geometry and ice flow directions in this sector at LGM are still not firmly understood, there is now – since the advent of shelf-wide bathymetric data (Olex) – a much clearer understanding of the patterns and dynamics of the BIIS and FIS during retreat (Bradwell et al., 2008; Clark et al., 2011).
The clearly defined, but complex, glacial geology and geomorphology on the shelf east of Shetland display the unique footprint of a dynamically retreating ice sheet (Figs B, C). The retreat pattern describes the opening of a large corridor or deep embayment in the ice sheet margin, first reported by Bradwell et al (2008). This is believed to represent the initial separation or ‘unzipping’ of the BIIS from the larger FIS to the east. Detailed mapping shows how this corridor progressively widened, possibly as the result of marine processes playing a greater part in ice-sheet break up (Bradwell et al., 2008; Clark et al., 2011) (Fig. D). The rate and timing of this break-up is still unknown; however it was a major tipping point and probably resulted in widespread re-organization of the northern sector of the BIIS. This undoubtedly represents one of the key events within the decay of the last BIIS.
This transect will allow a detailed understanding of the rate and style of ice sheet separation, along with the internal and external forces driving this phenomenon. Straddling both the BIIS and FIS margins, this transect affords a unique examination of marine ice sheet break-up and re-organization in a climatically sensitive setting. These research questions could be ideally tested east of Shetland using a combination of existing offshore geophysical data (multibeam bathymetry, seismic profiling), coupled with limited onshore sampling (TCN) and more extensive offshore sampling of Quaternary sediments for dateable material (see Fig C).
TCN (Be-10 in quartz-bearing rocks)
- 6 key locations around the terrestrial periphery of east Shetland (including the eastern headlands of Unst, Fetlar, Whalsay and Out Skerries).
- Minimum of 3 samples (glacially deposited boulders) at each site.
C-14 (marine fauna)
- 18 marine cores (vibrocores) through glacial, glaciomarine and postglacial sediment (unlithified).
- 4 x AMS analysis of marine fauna (minimum) per core to determine age of seismo-stratigraphically resolved units of importance; constrain timing of ice sheet retreat (+readvances) along main NE-SW flow line and along N-S unzipping corridor.
OSL (terrestrial sands)
- Field sampling of glaciofluvial / glacio-lacustrine sediments for OSL analysis
- 2 sites in total; both on Unst (Shetland)