What controls submarine channel development and the morphology of deltas entering deep-water fjords?

River deltas and associated turbidity current systems produce some of the largest and most rapid sediment accumulations on our planet. These systems bury globally significant volumes of organic carbon and determine the runout distance of potentially hazardous sediment flows and the shape of their deposits. Here we seek to understand the main factors that determine the morphology of turbidity current systems linked to deltas in fjords, and why some locations have well developed submarine channels whilst others do not. Deltas and associated turbidity current systems are analysed initially in five fjord systems from British Columbia in Canada, and then more widely. This provides the basis for a general classification of delta and turbidity current system types, where rivers enter relatively deep (>200 m) water. Fjord-delta area is found to be strongly bimodal. Avalanching of coarse-grained bedload delivered by steep mountainous rivers produces small Gilbert-type fan- deltas, whose steep gradient (11°-25°) approaches the sediment’s angle of repose. Bigger fjord-head deltas are associated with much larger and finer-grained rivers. These deltas have much lower gradients (1.5°-10°) that decrease offshore in a near exponential fashion. The lengths of turbidity current channels are highly variable, even in settings fed by rivers with similar discharges. This may be due to resetting of channel systems by delta-top channel avulsions or major offshore landslides, as well as the amount and rate of sediment supplied to the delta front by rivers

What controls submarine channel development and the morphology of deltas entering deep-water fjords?

River deltas and associated turbidity current systems produce some of the largest and most rapid sediment accumulations on our planet. These systems bury globally significant volumes of organic carbon and determine the runout distance of potentially hazardous sediment flows and the shape of their deposits. Here we seek to understand the main factors that determine the morphology of turbidity current systems linked to deltas in fjords, and why some locations have well developed submarine channels whilst others do not. Deltas and associated turbidity current systems are analysed initially in five fjord systems from British Columbia in Canada, and then more widely. This provides the basis for a general classification of delta and turbidity current system types, where rivers enter relatively deep (\u3e200 m) water. Fjord-delta area is found to be strongly bimodal. Avalanching of coarse-grained bedload delivered by steep mountainous rivers produces small Gilbert-type fan- deltas, whose steep gradient (11°-25°) approaches the sediment’s angle of repose. Bigger fjord-head deltas are associated with much larger and finer-grained rivers. These deltas have much lower gradients (1.5°-10°) that decrease offshore in a near exponential fashion. The lengths of turbidity current channels are highly variable, even in settings fed by rivers with similar discharges. This may be due to resetting of channel systems by delta-top channel avulsions or major offshore landslides, as well as the amount and rate of sediment supplied to the delta front by rivers

The newly discovered Odyssea Drift (Ross Sea): preliminary results

The Hillary Canyon is one of the main conduits for dense shelf water forming in the Ross Sea, over-flowing the shelf edge and transforming into the Antarctic Bottom Water (AABW). The main changes in past ocean circulation are recorded in the adjacent sediment drift. A wealth of data was acquired on the drift west of the Hillary Canyon during the 2017 OGS Explora expedition, which included the PNRA ODYSSEA and EUROFLEETS ANTSSS projects. The multi-disciplinary dataset acquired includes: single channel seismics, sub-bottom profiling, multibeam bathymetry, gravity and box cores, XBT launching, water sampling, CTD, L-ADCP, ADCP-VM, turbidity and florescence profiling. The sediment drift, which we named Odyssea Drift, is elongated in the NNE direction with dimensions of several tens of km. Prominent landslide scars and a giant landslide deposit, over 70 ms thick and spanning 200 km2, are visible on the drift. The sediment cores evidence well-developed cross beddings suggesting the effect of vigorous bottom currents. The oceanographic data show a ⇠200 m thick layer, near the bottom, with AABW characteristics (potential temperature < 0 C). The deeper layer displays also a strong velocity, mainly flowing along the isobaths. The energetic mixing between the along slope currents, mainly CDW, and the RSBW coming from the basin interior increase the turbidity of the bottom boundary layer. Our results will be merged with those obtained from the 2018 IODP drilling expedition 374 to develop a conceptual model of sediment deposition relating to marine-based ice sheet and oceanic processes along the Ross Sea continental margin occurring through the Neogene and Quaternary

Climate-controlled submarine landslides on the Antarctic continental margin

Antarctica’s continental margins pose an unknown submarine landslidegenerated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides

Climate-controlled submarine landslides on the Antarctic continental margin

Antarctica’s continental margins pose an unknown submarine landslide-generated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides

Climate-controlled submarine landslides on the Antarctic continental margin

Antarctica’s continental margins pose an unknown submarine landslide-generated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides

The International Bathymetric Chart of the Southern Ocean Version 2 (IBCSO v2)

The Southern Ocean surrounding Antarctica is a region that is key to a range of climatic and oceanographic processes with worldwide effects, and is characterised by high biological productivity and biodiversity. Since 2013, the International Bathymetric Chart of the Southern Ocean (IBCSO) has represented the most comprehensive compilation of bathymetry for the Southern Ocean south of 60°S. Recently, the IBCSO Project has combined its efforts with the Nippon Foundation – GEBCO Seabed 2030 Project supporting the goal of mapping the world’s oceans by 2030. New datasets initiated a second version of IBCSO (IBCSO v2). This version extends to 50°S (covering approximately 2.4 times the area of seafloor of the previous version) including the gateways of the Antarctic Circumpolar Current and the Antarctic circumpolar frontal systems. Due to increased (multibeam) data coverage, IBCSO v2 significantly improves the overall representation of the Southern Ocean seafloor and resolves many submarine landforms in more detail. This makes IBCSO v2 the most authoritative seafloor map of the area south of 50°S

Grain size determination of IODP Site 374-U1523

Cores U1523A, U1523B and U1523E were taken from the Iselin Bank, eastern Ross Sea, Antarctica (74°9.02′S, 176°47.70′W) in 828 m water depth during International Ocean Discovery Program Expedition 374. Grain size analysis of the 1 mm) was measured by dry sieving 1 cm³ subsamples using a nested stack at half-phi intervals (1.4 mm - 16 mm). Grain-size data is presented as the sand%, silt%, clay% and gravel%, sand%, mud% fractions according to the following grain-size intervals: very fine-coarse sand (1 mm - 62.5 μm), silt (62.5 - 4 μm) and clay (<4 μm). The volume mean grain-size diameter is also presented (D4,3)