Large-scale submarine landslides, channel and gully systems on the southern Weddell Sea margin, Antarctica

Abstract

New multibeam bathymetric data from the southeastern Weddell Sea show significant differences in surface morphology of the outer continental shelf and slope between two adjacent cross-shelf troughs. These are the Filchner Trough and a smaller trough to the east we refer to as the 'Halley Trough'. Multibeam bathymetric data, acoustic sub-bottom profiler and seismic data show major differences in the incidence and morphologies of submarine gullies, channel systems, submarine slides and iceberg scours, and in sediment deposition.These large-scale differences suggest significant variation in slope and sedimentary processes and in the environmental setting between the two troughs, leading to much greater deposition at the mouth of the Filchner Trough. Bedforms, including a terminal moraine and scalloped embayments on the outer shelf of the Halley Trough provide insight into the relative timing and extent of past ice-sheet grounding and point to grounded ice near to the shelf edge during the Late Quaternary.The new data reveal two large-scale submarine slides on the upper slope of the eastern Crary Fan, a trough mouth fan offshore from the Filchner Trough. Both slides head at the shelf edge (~500 m water depth), with the largest slide measuring 20 km wide and with an incision depth of 60 m. Multibeam and seismic data show elongate slabs on the seafloor surface of the mid-slope. The lack of a discernible sedimentary cover suggests that they were generated after the Last Glacial Maximum (LGM). This is unusual because post-LGM submarine slides are very rare on the Antarctic continental margin, and to our knowledge, no other post-LGM slides have been documented on an Antarctic trough mouth fan. Because the slides occur on a part of the continental slope where the deposition of glacial debris was greatest, we speculate that weaker, unconsolidated sedimentary layers within the subsurface are important for slide initiation here.

The Weddell Gyre, Southern Ocean: Present Knowledge and Future Challenges

“…Several advances/retreats of the ice sheets in the southern Weddell Sea throughout the Quaternary are documented in seismic and acoustic data and in marine sediment cores from the continental margin (Anderson et al, ; Diekmann et al, ; Elverhøi, ; Gales et al, ; Gilbert et al, ; Grobe & Mackensen, ; Grobe et al, ; Hillenbrand et al, ; Kristoffersen et al, ; Kuhn & Weber, ; Larter et al, ; Mackensen et al, ; Melles & Kuhn, ; Michels et al, ; Ó Cofaigh et al, ; Pudsey et al, ; Shimmield et al, ; J.A. Smith et al, ; Weber et al, ), with sedimentary sequences from the southeastern Weddell Sea providing archives for decadal and perhaps annual resolution of ice dynamics because of the very high sedimentation rates (Sprenk et al, ; Weber et al, ).…”

“…Thus, these currents deposit sediments on the continental slope and rise but transport detritus even further down to the Weddell abyssal plain. The downslope transport processes are assumed to be much less active during interglacial times than during glacial periods (e.g., Gales et al, ; Lindeque et al, ) because of the “bulldozing” effect and subglacial till transport to the shelf break by advancing grounded ice with subsequent downslope redeposition during the latter times (e.g., Grobe & Mackensen, ). Sediment distribution is not spatially homogenous, with large fans extending hundreds of kilometers from the shelf break and sediment drifts forming depocenters on the rise (Gilbert et al, ; Huang et al, ; Kuhn & Weber, ; Kuvaas & Kristoffersen, ; Michels et al, ).…”

A geomorphological seabed classification for the Weddell Sea, Antarctica

“…Since the last ice sheet retread, icebergs continuously scour the shallower, outer parts of the shelf. This part of the shelf is structured in gullies and shows submarine landslides (Gales et al 2014). Channel-levee systems are found at the continental slope reaching out to the Weddell Sea abyssal plain (Kuhn and Weber 1993;Michels et al 2001Michels et al , 2002.…”

Source and progression of a submarine landslide and tsunami: The 1964 Great Alaska earthquake at Valdez

“…We note from the multibeam bathymetry that there are three channels that all emerge from this zone and coalesce into a 400 m wide primary channel downslope (Figures and ). Such linear slope “chutes” have been associated with submarine landslides in many other locations [e.g., Twichell et al ., ; Tappin , ; Migeon et al ., ; Jintasaeraneea et al ., ; Dalla Valle et al ., ; Gales et al ., ; Laberg et al ., ]. These are the primary pathways that landslide materials moved downslope on the Valdez delta front; we conclude this from interpreting the combination of multibeam bathymetry and subbottom seismic reflection profiling.…”