Site U1564

Proceedings of the International Ocean Discovery Program. Expedition reports · 2025-01-17

International audience

Variations in Ventilation and Deep-Water Export in the Scotia Sea during Glacial-Interglacial Cycles

2025-01-01

Onset of strong Iceland-Scotland overflow water 3.6 million years ago

Nature Communications · 2025-05-09 · 4 citations

North Atlantic Deep Water (NADW), the return flow component of the Atlantic Meridional Overturning Circulation (AMOC), is a major inter-hemispheric ocean water mass with strong climate effects but the evolution of its source components on million-year timescales is poorly known. Today, two major NADW components that flow southward over volcanic ridges to the east and west of Iceland are associated with distinct contourite drift systems that are forming off the coast of Greenland and on the eastern flank of the Reykjanes (mid-Atlantic) Ridge. Here we provide direct records of the early history of this drift sedimentation based on cores collected during International Ocean Discovery Programme (IODP) Expeditions 395C and 395. We find rapid acceleration of drift deposition linked to the eastern component of NADW, known as Iceland-Scotland Overflow Water at 3.6 million years ago (Ma). In contrast, the Denmark Strait Overflow Water feeding the western Eirik Drift has been persistent since the Late Miocene. These observations constrain the long-term evolution of the two NADW components, revealing their contrasting independent histories and allowing their links with climatic events such as Northern Hemisphere cooling at 3.6 Ma, to be assessed.

Site U1554

Proceedings of the International Ocean Discovery Program. Expedition reports · 2025-01-17 · 1 citations

International audience

Expedition 395 methods

Proceedings of the International Ocean Discovery Program. Expedition reports · 2025-01-17 · 7 citations

graphic correlation.While using the HLAPC, the same criteria is applied in terms of refusal as for the APC system.The XCB system is typically used when the APC/HLAPC system has difficulty penetrating the formation and/or damages the core liner or core.The XCB system can also be either used to initiate holes where the seafloor is not suitable for APC coring or interchanged with the APC/HLAPC when dictated by changing formation conditions.For example, the XCB system was deployed during Expedition 395 to better recover the sediment/basement interface.The XCB system has a small cutting shoe that extends below the large APC/XCB bit (Figure F3).The smaller bit can cut a semi-indurated core with less torque and fluid circulation than the main bit, optimizing recovery.The XCB cutting shoe extends ~30.5 cm ahead of the main bit in soft sediment but retracts into the main bit when hard formations are encountered.It cuts cores with a nominal diameter of 5.87 cm (2.31 inches), slightly less than the 6.6 cm diameter of APC cores.XCB cores are often broken (i.e., torqued) into biscuits, which are disc-shaped pieces a few to several centimeters long with remolded sediment (including some drilling slurry) interlayering the discs and packing the space between the discs and the core liner.This type of drilling disturbance may give the impression that the XCB cores have the same diameter (6.6 cm) as the APC cores.The bottom-hole assembly (BHA) used for APC and XCB coring during Expeditions 384 and 395C was composed of an 11 7 16 inch (~29.05cm) bit, a bit sub, a seal bore drill collar, a landing saver sub, a modified top sub, a modified head sub, a variable number of 8 inch control length drill collars, a tapered drill collar, two stands of 5 inch transition drill pipe, and a crossover sub to the drill pipe that extended to the surface.The same BHA was used during Expedition 395 except for the drill bit, which was a 9 inch polycrystalline diamond compact bit.The RCB system is designed to recover firm to hard sediments and basement rocks.The BHA, including the bit and outer core barrel, is rotated with the drill string while bearings allow the inner core barrel to remain stationary (Figure F4). Figure F3.XCB system used during Expedition 395 (see Graber et al., 2002).Coring soft sediment Coring hard sediment Outer barrel Latch Coil spring Landing

The Maud Belt (East Antarctica) as an accretionary orogen in Rodinia: Isotopic composition, evolution and spatial variation

Gondwana Research · 2025-06-24

Site U1563

Proceedings of the International Ocean Discovery Program. Expedition reports · 2025-01-17

International audience

Spatiotemporal development of diverse magmatic plumbing in long-lived distributed volcanic fields

Bulletin of Volcanology · 2025-08-18 · 2 citations

Site U1562

Proceedings of the International Ocean Discovery Program. Expedition reports · 2025-01-17

International audience

Shifting Antarctic Circumpolar Current south of Africa over the past 1.9 million years

Science Advances · 2025-01-01 · 7 citations

The Antarctic Circumpolar Current (ACC) dominates the transfer of heat, salt, and tracers around the Southern Ocean (SO), driving the upwelling of carbon-rich deep waters around Antarctica. Paleoclimate reconstructions reveal marked variability in SO circulation; however, few records exist coupling quantitative reconstructions of ACC flow with tracers of SO upwelling spanning multiple Pleistocene glacial cycles. Here, we reconstruct near-bottom flow speed variability in the SO south of Africa, revealing systematic glacial-interglacial variations in the strength and/or proximity of ACC jets. These are superimposed by warmer-than-present “super-interglacials,” whereby extreme slowdown in the midlatitude ACC (41°S) is opposed by faster flow at higher latitudes (>54°S), implying poleward strengthening of the ACC. Coupled with reconstructions of the subsurface-deep stable carbon isotope gradient, we show that the reorganization of ACC coincides with the upwelling of isotopically light deep waters around Antarctica, likely contributing to the interglacial rise in atmospheric carbon dioxide (CO 2 ) levels.