Description: Highlights • Glacial sediment-landform assemblages are documented from Disko Bay, West Greenland. • Jakobshavn Isbræ extended through the bay onto the continental shelf during the LGM. • Retreat was topographically controlled and changed from rapid to slow. • The depositional sedimentary environment was similar to East Greenland. • Glacimarine sedimentary processes depend on local controls rather than climate. Fast-flowing outlet glaciers currently drain the Greenland Ice Sheet (GIS), delivering ice, meltwater and debris to the fjords around Greenland. Although such glaciers strongly affect the ice sheet's mass balance, their glacimarine processes and associated products are still poorly understood. This study provides a detailed analysis of lithological and geophysical data from Disko Bay and the Vaigat Strait in central West Greenland. Disko Bay is strongly influenced by Jakobshavn Isbræ, Greenland's fastest-flowing glacier, which currently drains ∼7% of the ice sheet. Streamlined glacial landforms record the former flow of an expanded Jakobshavn Isbræ and adjacent GIS outlets through Disko Bay and the Vaigat Strait towards the continental shelf. Thirteen vibrocores contain a complex set of lithofacies including diamict, stratified mud, interbedded mud and sand, and bioturbated mud deposited by (1) suspension settling from meltwater plumes and the water column, (2) sediment gravity flows, and (3) iceberg rafting and ploughing. The importance of meltwater-related processes to glacimarine sedimentation in West Greenland fjords and bays is emphasised by the abundance of mud preserved in the cores. Radiocarbon dates constrain the position of the ice margin during deglaciation, and suggest that Jakobshavn Isbræ had retreated into central Disko Bay before 10.6 cal ka BP and to beyond Isfjeldsbanken by 7.6–7.1 cal ka BP. Sediment accumulation rates were up to 1.7 cm a−1 for ice-proximal glacimarine mud, and ∼0.007–0.05 cm a−1 for overlying distal sediments. In addition to elucidating the deglacial retreat history of Jakobshavn Isbræ, our findings show that the glacimarine sedimentary processes in West Greenland are similar to those in East Greenland, and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime.

Description: Non erosive margins are characterized by heavily sedimented trenches which obscure the morphological expression of the outer rise; a forebulge formed by the bending of the subducting oceanic lithosphere seaward of the trench. Depending on the flexural rigidity (D) of the oceanic lithosphere and the thickness of the trench sedimentary fill, sediment loading can affect the lithospheric downward deflection in the vicinity of the trench and hence the amount of sediment subducted. We used seismic and bathymetric data acquired off south central Chile, from which representative flexural rigidities are estimated and the downward deflection of the oceanic Nazca plate is studied. By flexural modeling we found that efficient sediment subduction preferentially occurs in weak oceanic lithosphere (low D), whereas wide accretionary prisms are usually formed in rigid oceanic lithosphere (high D). In addition, well developed forebulges in strong oceanic plates behaves as barrier to seaward transportation of turbidites, whereas the absence of a forebulge in weak oceanic plates facilitates seaward turbidite transportation for distances 〉200 km.

Description: In the Patagonian Andes erosion by temperate Pleistocene glaciers has produced a deeply incised fjord system in which glacial and non-glacial sedimentswere deposited since the Late Glacial glacier retreat. So far, fjord bathymetry and structures in the sediment infill were widely unexplored. Here we report the results of an investigation of morphology and sediment characteristics of a 250 km long fjord transect across the southernmost Andes (53°S), using multibeam and parametric echosounder data, and sediment cores. Subaquatic morphology reveals continuity of on-land tectonic lineaments mapped using field and remote sensing data. Our results indicate that glacial erosion and fjord orientation are strongly controlled by three major strike-slip fault zones. Furthermore, erosion is partly controlled by older and/or reactivated fracture zones as well as by differential resistance of the basement units to denudation. Basement morphology is regionally superimposed by Late Glacial and Holocene subaquatic moraines, which are associated to known glacier advances. The moraines preferentially occur on basement highs, which constrained the glacier flows. This suggests that the extent of glacier advances was also controlled by basement morphology. Subaquatic mass flows, fluid vent sites as well as distinct Late Glacial and Holocene sediment infills have furthermore modified fjord bathymetry. In the western fjord system close to the Strait of Magellan subaquatic terraces occur in 20 to 30 m water depth, providing an important tag for proglacial lake level during the Late Glacial.

Description: Following the devastating 2004 tsunami that hit the southwestern coast of Thailand, the need for detailed bathymetric data of the Andaman Sea outer shelf became evident in order to better predict tsunami wave propagation and coastal impact. Bathymetric data and subbottom profiler records covering the outer shelf and upper slope of the Thai exclusive economic zone (EEZ) were collected onboard Thai RV Chakratong Tongyai in 2006 and 2007. The data cover an area of approximately 3000 km2 between 500 and 1600 m water depth. The soundings allowed generating a final bathymetric grid with 50 m grid cell spacing. The outer shelf is rather smooth and slightly inclined southward, while the upper slope is strongly dissected by gullies. Several previously unknown features are identified including mud-domes, pockmarks, three large plateaus surrounded by moats, gas-charged sediment on subbottom profiler records, and only few indications for small submarine landslides on the upper slope. The largest of these possibly translational submarine landslides involved 2.2×107 m3 of sediment. This slide would have generated a tsunami wave of less than 0.12 m wave height. Considering the entire data, there is no evidence that landslides have been the source of tsunami waves in recent geological time. Highlights