Transect 7 – Malin Sea

Transect Leader:

Sara Benetti (University of Ulster)

Personnel:

S Benetti, C O’Cofaigh, J Scourse, K Van Landeghem, T Bradwell, C Ballantyne, D Small, P Wilson

Fieldwork and activities:

  • August 2013 – 28 samples collected from Ross of Mull and Tiree

 

 

Figure 1

Background

The Donegal Barra Fan (DBF) is the largest sediment depocentre fed by the BIIS, covering an area of over 7000 km2 and represents the most southerly of the glacial prograding wedges of Northern Europe. Its 450 m thick sequence of glacial sediments was carried to the area by the draining action of BIIS during the Plio–Pleistocene (Armishaw et al., 1998; 2000). Scourse et al. (2009) have recently reviewed the IRD record from core MD95-2006 on the northern DBF. This record indicates major growth of the ice sheet in the north after 29 cal ka BP, with the DBIS reaching the shelf edge and generating turbidity currents on the fan at about 27 cal ka BP (Wilson and Austin, 2002). Presence of ice streaming in the Malin Sea area has been hypothesised based on terrestrial evidence and the occurrence of the Donegal-Barra (trough mouth) fan on the continental margin, but hardly any geophysical or sedimentological data exist on the offshore record of ice extent, character or timing of ice occupancy. The INSS data in Irish waters suggest the presence of a deepening at mid shelf (the Malin Deep) that recalls the structure of shelf troughs on other glaciated margins.

Existing datasets

  • Irish waters fully mapped by multibeam data and sub-bottom data show several seismic units that can be correlated to glacially-related units in UK waters (Fyfe et al., 1993; Dunlop et al., 2010).
  • Seafloor sediments mapped by BGS in UK waters.
  • Patchy multibeam data in UK waters (Fig. 2) and low quality Olex data across the area
  • (mapping by Clark et al., 2010)

Rationale

Figure 2

Figure 2

The Barra–Donegal Fan represents a major focus of glacial sediment (Knutz et al., 2001; Wilson et al., 2002), most probably fed by ice streams that periodically crossed the continental shelf, draining much of western Scotland and northwest Ireland. Deep water cores seem to indicate that this portion of the ice margin responded quickly to millennial climate oscillations and modelling of tidal regime over the last glaciation indicates that this Atlantic-facing portion of the BIIS margin was subject to the largest tides of the western margin of the BIIS. All evidence suggests that the DBIS was a particularly active outlet of the BIIS over a long period of time and likely affected by climatic and oceanographic changes.

Key factors to investigate:

  • Timing of retreat.
  • Continental shelf adverse slope.
  • Offshore evidence of ice streaming.
  • Character of ice retreat (lobate as north and south along western margin? Cf. Bradwell et
  • al, 2008; Ó Cofaigh et al, in press)

Sampling programme

Offshore

  • Geophysical acquisition: 1 week coverage to acquire multibeam and sub-bottom data in UK waters to map seafloor expression of last ice sheet advance and retreat on the shelf and select exact locations of key sites and other sites in UK waters.
  • Coring: (Min) Key transect of 10 marine cores across width of the shelf around the convergence of Scottish and Irish ice and 4 secondary sites on both sides of the key transect (in Irish waters sites can be selected without any additional ship time with INSS data).
  • 6 x AMS analysis of marine fauna (minimum) per core to determine age of glacial and glacially derived facies boundaries to constrain timing of ice sheet retreat along main transect and timing of retreat in opposite Scottish and Irish directions on two sides of central transect.
  • C-14 (marine fauna)

Onshore

  • 30 radiocarbon/20 cosmogenic/20 OSL