Quaternary ice sheet limits on the continental shelf west of Ireland

Recent investigations have shown that the continental shelf west of Ireland contains sedimentary landforms recording occupation by grounded, lobate ice sheet margins that extended from Ireland during at least the last glacial cycle. This paper reviews some of the offshore evidence of past glacial events available from high-resolution bathymetry, 2D/3D seismic datasets (Fig. 1), and shallow sediment cores providing information on the sedimentology, rheology and age of glacigenic stratigraphic units. The available data suggest that the continental shelf has been repeatedly occupied by tidewater ice margins characterised by ice streaming, possibly since the mid-Pleistocene transition. The offshore record provides as yet incomplete information on the extent and timing of glaciation from multiple centres of dispersal in Ireland. The dynamics of former ice sheets in Ireland, downwind of the climatically important central North Atlantic region, makes them of wider interest in the study of partially marine based ice sheet-ocean interactions in rapidly changing environments

A stratigraphic investigation of the Celtic Sea megaridges based on seismic and core data from the Irish-UK sectors

The Celtic Sea contains the world's largest continental shelf sediment ridges. These megaridges were initially interpreted as tidal features formed during post-glacial marine transgression, but glacigenic sediments have been recovered from their flanks. We examine the stratigraphy of the megaridges using new decimetric-resolution geophysical data correlated to sediment cores to test hypothetical tidal vs glacial modes of formation. The megaridges comprise three main units, 1) a superficial fining-upward drape that extends across the shelf above an unconformity. Underlying this drape is 2), the Melville Formation (MFm) which comprises the upper bulk of the megaridges, sometimes displaying dipping internal acoustic reflections and consisting of medium to coarse sand and shell fragments; characteristics consistent with either a tidal or glacifluvial origin. The MFm unconformably overlies 3), the Upper Little Sole Formation (ULSFm), previously interpreted to be of late Pliocene to early Pleistocene age, but here shown to correlate to Late Pleistocene glacigenic sediments forming a precursor topography. The superficial drape is interpreted as a product of prolonged wave energy as tidal currents diminished during the final stages of post-glacial marine transgression. We argue that the stratigraphy constrains the age of the MFm to between 24.3 and 14 ka BP, based on published dates, coeval with deglaciation and a modelled period of megatidal conditions during post-glacial marine transgression. Stratigraphically and sedimentologically, the megaridges could represent preserved glacifluvial features, but we suggest that they comprise post-glacial tidal deposits (MFm) mantling a partially-eroded glacial topography (ULSFm). The observed stratigraphy suggests that ice extended to the continental shelf-edge

The ALBACORE oceanographic cruise: tectonic and sedimentary processes at distinct temporal and spatial scales in the Alboran Sea

European Geosciences Union (EGU) General Assembly, 23-27 May 2022, Vienna, AustriaThe Alboran Sea (Western Mediterranean) is a relatively small ocean basin connected with the Atlantic that provides a rich archive of tectonic and sedimentary processes at distinct temporal and spatial scales during the Quaternary. Since the collisional boundary of the Eurasia-Nubia plates crosses the Alboran Sea, this basin is also the locus of active geohazards: the constant seismic activity, concentrated mostly along the Al Idrissi strike-slip fault system and submarine landslides, that can cause tsunami hazards affecting the entire Alboran coasts and damages to submarine cables and infrastructures. Previous understanding of the Alboran Sea has been based on seafloor and subsurface geophysical data of differing resolution and scale, combined with very short sediment coring and IODP and industrial boreholes. In order to obtain new constrains on the geology of the Alboran Sea, the ALBACORE cruise was held in October and November 2021 onboard the R/V Pourquoi Pas? In addition to sites in the northern Alboran Sea targeting contourites, several sites in the southern Alboran Sea were selected as key study areas: the Al-Idrissi active fault zone, the Al-Hoceima shelf, the Xauen/Tofiño and the Francesc Pages banks. The scientific work of the ALBACORE campaign included the acquisition of Calypso cores (up to 28m long), sampling of consolidated strata with Cnexoville, in situ geotechnical measurements (Penfeld) with a seabed cone penetration test device (up to 50m long), heat flow measurements (up to 6m long), swath bathymetric imaging of the seafloor and water column, and sub-bottom profiling. The total length of sediments recovered reached 734m. Results from the ALBACORE cruise address the following scientific objectives: - To understand better the causal relationships between the present-day morpho-structural pattern and date Quaternary tectonic pulse and associated sedimentary systems - To determine the Late Pleistocene-Holocene stratigraphic pattern and the paleo-oceanographic implications of contourites. - To explore the chronological evolution of cold-water coral mounds and their paleoceanographic and palaeoclimatic signature since the Middle Pleistocene. - To investigate the causal factors of slope instability processes and evaluate the geological hazard associated with tectonic pulses and fluid seepage. - To determine the recent high-resolution sequence stratigraphy of the Al-Hoceima shelf in order to decode the late Pleistocene and Holocene sea-level changes at millennial scalePeer reviewe

Growth and retreat of the last British–Irish Ice Sheet, 31 000 to 15 000 years ago: the BRITICE-CHRONO reconstruction

The BRITICE-CHRONO consortium of researchers undertook a dating programme to constrain the timing of advance, maximum extent and retreat of the British–Irish Ice Sheet between 31 000 and 15 000 years before present. The dating campaign across Ireland and Britain and their continental shelves, and across the North Sea included 1500 days of field investigation yielding 18 000 km of marine geophysical data, 377 cores of sea floor sediments, and geomorphological and stratigraphical information at 121 sites on land; generating 690 new geochronometric ages. These findings are reported in 28 publications including synthesis into eight transect reconstructions. Here we build ice sheet-wide reconstructions consistent with these findings and using retreat patterns and dates for the inter-transect areas. Two reconstructions are presented, a wholly empirical version and a version that combines modelling with the new empirical evidence. Palaeoglaciological maps of ice extent, thickness, velocity, and flow geometry at thousand-year timesteps are presented. The maximum ice volume of 1.8 m sea level equivalent occurred at 23 ka. A larger extent than previously defined is found and widespread advance of ice to the continental shelf break is confirmed during the last glacial. Asynchrony occurred in the timing of maximum extent and onset of retreat, ranging from 30 to 22 ka. The tipping point of deglaciation at 22 ka was triggered by ice stream retreat and saddle collapses. Analysis of retreat rates leads us to accept our hypothesis that the marine-influenced sectors collapsed rapidly. First order controls on ice-sheet demise were glacio-isostatic loading triggering retreat of marine sectors, aided by glaciological instabilities and then climate warming finished off the smaller, terrestrial ice sheet. Overprinted on this signal were second order controls arising from variations in trough topographies and with sector-scale ice geometric readjustments arising from dispositions in the geography of the landscape. These second order controls produced a stepped deglaciation. The retreat of the British–Irish Ice Sheet is now the world’s most well-constrained and a valuable data-rich environment for improving ice-sheet modelling.publishedVersio

Chercher de la glace au fond de l’océan au large de l’Amazone

National audienc

Brazilian participation in International Programs for Scientific Drilling & Discovery of the Continents and Oceans (ICDP/IODP) : opportunities for BR-EU research collaboration

International audienceDrilling is a technology developed for the exploration of natural resources (water, hydrocarbons, minerals), which can also be used to address scientific questions regarding the Earth’s past, present and future. Scientific drilling initiatives are supported by the International Continental Drilling Program (ICDP) and the International Ocean Discovery Program (IODP). These international programs invite the submission of proposals that address scientific and societal challenges within thematic areas of climate change, the deep biosphere and natural hazards, as well as geodynamics and resources. Researchers from several Brazilian institutions are currently involved in ICDP and IODP projects that will lead to drilling campaigns from 2019. The largest is the Trans-Amazon Drilling Project, which aims to obtain transformative information on the development of the Amazon fluvial system and its biosphere in relation to the uplift of the Andes. The project involves an onshore to offshore transect of up to six sites, from the Andean foreland to the Atlantic margin, a distance corresponding to 10% of the Earth’s circumference. Onshore sites will be acquired during an ICDP project from 2019-2021, while sites on the Amazon deep-sea fan will be acquired in 2020 by the IODP vessel Joides Resolution. The South Atlantic campaign of the latter will involve at least one other IODP site on the Brazilian margin. These projects will generate datasets that imply inter-disciplinary collaborations among regional to global networks of researchers and students. They thus provide natural opportunities to further develop Brazilian-European research initiatives, through the Marie Skłodowska-Curie Actions and other mechanisms

Geomorphology of the continental shelf west of Ireland

International audienceThe continental shelf region West of Ireland contains a rich geomorphic and sedimentary record of glacially-influenced marine processes, including ice sheet extension from Ireland into the Atlantic during the last cold period (Late Midlandian glaciation in Ireland).  Intricate sets of curvilinear ridges of varying form and scale across the outer shelf have been recently associated with grounded glacial ice withdrawal from maximum limits.  The region lies at the southern limit of the glaciation of the Atlantic margin of northwest Europe, and thus occupies an important position in palaeoglaciological reconstructions.  Studies of seabed morphology west of Ireland have been greatly enhanced by exhaustive multibeam bathymetric coverage of the Irish National Seabed Survey, associated sediment sampling and high-resolution shallow seismic profiles; in places, these have been complemented by the use of industry 3D seismic data cubes to visualise the internal structure and geomorphology of glacigenic ridges and large-scale sediment aprons. This paper presents observations from combined sediment ground truthing, high-resolution geophysical and bathymetric data, focusing on the Porcupine Bank, Saddle and Inner shelf areas of the Western Irish Shelf, in order to examine available models of shelf glaciation