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AbstractThe onshore central Corinth rift contains a syn‐rift succession >3 km thick deposited in 5–15 km‐wide tilt blocks, all now inactive, uplifted and deeply incised. This part of the rift records upward deepening from fluviatile to lake‐margin conditions and finally to sub‐lacustrine turbidite channel and lobe complexes, and deep‐water lacustrine conditions (Lake Corinth) were established over most of the rift by 3.6 Ma. This succession represents the first of two phases of rift development – Rift 1 from 5.0–3.6 to 2.2–1.8 Ma and Rift 2 from 2.2–1.8 Ma to present. Rift 1 developed as a 30 km‐wide zone of distributed normal faulting. The lake was fed by four major N‐ to NE‐flowing antecedent drainages along the southern rift flank. These sourced an axial fluvial system, Gilbert fan deltas and deep lacustrine turbidite channel and lobe complexes. The onset of Rift 2 and abandonment of Rift 1 involved a 30 km northward shift in the locus of rifting. In the west, giant Gilbert deltas built into a deepening lake depocentre in the hanging wall of the newly developing southern border fault system. Footwall and regional uplift progressively destroyed Lake Corinth in the central and eastern parts of the rift, producing a staircase of deltaic and, following drainage reversal, shallow marine terraces descending from >1000 m to present‐day sea level. The growth, linkage and death of normal faults during the two phases of rifting are interpreted to reflect self‐organization and strain localization along co‐linear border faults. In the west, interaction with the Patras rift occurred along the major Patras dextral strike‐slip fault. This led to enhanced migration of fault activity, uplift and incision of some early Rift 2 fan deltas, and opening of the Rion Straits at ca. 400–600 ka. The landscape and stratigraphic evolution of the rift was strongly influenced by regional palaeotopographic variations and local antecedent drainage, both inherited from the Hellenide fold and thrust belt.

AbstractVideo and image data are regularly used in the field of benthic ecology to document biodiversity. However, their use is subject to a number of challenges, principally the identification of taxa within the images without associated physical specimens. The challenge of applying traditional taxonomic keys to the identification of fauna from images has led to the development of personal, group, or institution level reference image catalogues of operational taxonomic units (OTUs) or morphospecies. Lack of standardisation among these reference catalogues has led to problems with observer bias and the inability to combine datasets across studies. In addition, lack of a common reference standard is stifling efforts in the application of artificial intelligence to taxon identification. Using the North Atlantic deep sea as a case study, we propose a database structure to facilitate standardisation of morphospecies image catalogues between research groups and support future use in multiple front-end applications. We also propose a framework for coordination of international efforts to develop reference guides for the identification of marine species from images. The proposed structure follows the Darwin Core standard to allow integration with existing databases. We suggest a management framework where high-level taxonomic groups are curated by a regional team, consisting of both end users and taxonomic experts. We identify a mechanism by which overall quality of data within a common reference guide could be raised over the next decade. Finally, we discuss the role of a common reference standard in advancing marine ecology and supporting sustainable use of this ecosystem.

Submarine canyons are known to force ocean mesoscale circulation and local hydrodynamics. Alternate up- and down-canyon near-bottom flows have been widely documented along the upper reaches, connecting the canyon heads with the contiguous outer shelves and vice versa. Nonetheless, we still miss clear evidence of bedform fields expressing these complex patterns. In this study, through a multi-scale analysis in both space and time, we document rare asymmetric bedforms, up to 880 m long and 10 m high, developing within a depth range of 168-220 m at the head of the Whittard Canyon (NE Atlantic). One field of well-developed sandwaves has an atypical up-slope asymmetry, with the steeper slope facing the shallower regions of the shelf, and contrasting with surrounding down-slope sandwaves facing the canyon. The bedforms are interpreted to represent both up-slope and down-slope bottom currents connecting the upper reaches of the canyon to the outer shelf on the southern Celtic Margin, in the Bay of Biscay. The sandwaves were surveyed with shipboard Multibeam bathymetry (5 m grid cell resolution), AUV sidescan sonar (0.15 m grid cell resolution) and ROV footage, and sampled with three ROV-mounted vibro-cores and two box-cores. Sidescan sonar mosaics groundtruthed by sediment samples and ROV footage show with unprecedented detail spectacular trains of fresh overprinting megaripples, previously undocumented sand peaks and bowl-shaped depressions on the crests of the tallest sandwaves. Differences in sedimentary settings and benthic habitats indicate that these features are currently active in particularly dynamic areas, allowing for very slow migration of sandwaves. Numerical modelling together with concurrent hydrographic observations suggest large-amplitude semi-diurnal internal tides, possibly transitioning to asymmetric internal bores, as the main mechanism maintaining the mapped up-slope sandwaves. This work highlights the importance of uncommon sediment dynamics in canyon head environments and adds insight to the traditional notions of gravity-driven processes, being dominant in these environments, envisaging implications for improving geo-hazard assessment of mobile substrates and quantification of offshore sediment and carbon fluxes Most of the data used in this work has been acquired in the JC125 cruise, funded by the ERC CODEMAP project (Complex Deep-sea Environments: Mapping habitat heterogeneity As Proxy for biodiversity) (Grant No. 258482, PI: Dr V.A.I. Huvenne). Additional data have been collected in the frame of the Natural Environment Research Council funded CLASS programme, Grant No. NE/R015953/1. With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI) 14 pages, 12 figures, supplementary material https://doi.org/10.1016/j.epsl.2020.116321

Pore fluid pressure is a key parameter for subaquatic slope stability and has been put forward to explain the development of many submarine landslides especially when occurring on very gentle slopes or in areas with high sedimentation rate. Due to the sparse availability of in situ pore pressure data a profound understanding and quantification of excess pore pressure development and its influence on subaquatic landslide processes is still missing. In this study we use glacigenic Lake Villarrica (Chile) as a model basin in which we document in situ excess pore pressure focused fluid escape features and subaquatic slope failures at relatively shallow subsurface depth (< 10 m). A subaquatic slope was characterized in great detail by a dense network of high resolution seismic reflection profiles multibeam bathymetry and sediment cores. In situ undrained shear strength and formation pore fluid pressures were documented using free fall piezocone penetrometer (CPTU) and subsequent pore pressure dissipation tests. We show four independent lines of evidence for overpressure of variable magnitude within the sedimentary slopes: i) pockmarks and other fluid escape features on seismic profiles and bathymetric maps ii) estimation of ambient in situ pore pressure via CPTU dissipation tests iii) underconsolidation and downward decrease in in situ undrained shear strength within units of uniform lithology and iv) hydrofractured glacio lacustrine sediments. Locally overpressure reaches about 80–90 of the hydrostatic vertical effective stress. We hypothesize that glacier proximal sediments are strongly underconsolidated and overpressured due to rapid deposition and/or subglacial meltwater pumping. Postglacial consolidation of a thick glacier proximal unit leads to the upward expulsion of excess pore water. A permeability barrier is formed by the overlying glacio lacustrine clays and fine silts focusing these migrating fluids to topographic highs. There very high overpressure ratios facilitate the development of hydro fractures repeated fluid escape and pockmarks on the lake bottom. Overpressure may decrease slope stability in Lake Villarrica in different manners: by focused fluid escape weakening sediments by generating underconsolidated sequences of low undrained shear strength and by facilitating static failure. Based on high quality in situ data this study confirms that high overpressure ratios in shallow sediments may be a typical feature at formerly glaciated marine and lacustrine environments and highlights the major role of pore fluid overpressure for preconditioning subaquatic slopes to failure.