Description: Inclination, declination, and relative palaeointensity calculated as a composite (WINPSV-12K) of four sediment cores (+54-03/57PC, +54-03/64PC, +54-03/67PC, +54-03/68PC) from Windermere, UK, spanning the Holocene. The inclination and declination are reliable, but the RPI is not reliable and should not be used in publications. It is made available for those who wish to plot it anyway. For each variable we have included the calculated values and the 5% and 95% confidence envelope limits. Values are calaculated for every 50 year timestep.

Description: A Kongsberg EM122 onboard RRS James Cook during IODP Expedition 357 (Früh-Green et al., 2018; doi:10.1016/j.lithos.2018.09.012) was used to acquire the bathymetry data. Data were cleaned and processed using MB System and then gridded at ~20 m in x and y in NETCDF grd grid format (.grd) in geographic coordinates (latitude/longitude).

Description: 3.9.2. haiku captures scientific exploration and discovery as it took place in remote locales, far from the public eye. It invites audiences of all ages to engage with cores from the privileged point-of-view of researchers who were the first to see, smell and touch material from deep under the ocean floor; who, after watching the cores be split open, spent hours analyzing each centimeter. Their poems, and especially their readings of them, reveal not only the cores but also the scientists as they experience anticipation, frustration, awe, excitement and wonder. It turns out that haiku is an especially relevant way to package stories from cores of mud and rock from the Cretaceous period, which was the focus of IODP Expedition 392 to the Agulhas Plateau. An ancient poetic form consisting of 17 syllables in three lines (5-7-5), haiku compactly and powerfully captures moments of time . . . moments that, on the surface, may appear unremarkable—a frog jumping. Moments that resonate with the deep truths that emerge from paying close attention to the natural world. When introduced to the concept of 3.9.2 haiku, more than one brilliant researcher balked: “I’m no good at this. . . I can’t write poetry.” During several writing workshops conducted during the expedition, scientists began to recognize haiku as the linguistic equivalent to cores they were studying. They delighted that a dozen (or fewer) precisely packaged words could align so closely with the cores precisely drilled from the Agulhas Plateau. Each individual haiku is a gem. Strung together, they are a trove of impressions that span millennia.

Description: Serpentinized and metasomatized peridotites intruded by gabbros and dolerites have been drilled on the southern wall of the Atlantis Massif (Mid-Atlantic Ridge, 30°N) during International Ocean Discovery Program (IODP) Expedition 357. They occur in seven holes from five sites making up an east-west trending, spreading-parallel profile that crosscuts this exhumed detachment footwall. Here we have taken advantage of this sampling to study heterogeneities of alteration at scales less than a kilometer. We combine textural and mineralogical observations made on 77 samples with in situ major and trace element analyses in primary and serpentine minerals to provide a conceptual model for the development of alteration heterogeneities at the Atlantis Massif. Textural sequences and mineralogical assemblages reveal a transition between an initial pervasive phase of serpentinization and subsequent serpentinization and metasomatism focused along localized pathways preferentially used by hydrothermal fluids. We propose that these localized pathways are interconnected and form 100 m- to 1 km-sized cells in the detachment footwall. This change in fluid pathway distribution is accompanied by variable trace element enrichments in the serpentine textures: deep, syn-serpentinization fluid-peridotite interactions are considered the source of Cu, Zn, As, and Sb enrichments, whereas U and Sr enrichments are interpreted as markers of later, shallower fluid-serpentinized peridotite interaction. Alteration of gabbros and dolerites emplaced in the peridotite at different lithospheric levels leads to the development of amphibole, chlorite and, or, talc-bearing textures as well as enrichments in LREE, Nb, Y, Th, Ta in the serpentine textures of the surrounding peridotites. Combining these observations, we propose a model that places the drill holes in a conceptual frame involving mafic intrusions in the peridotites and heterogeneities during progressive alteration and emplacement on the seafloor.

Description: Highlights • Seabed rock drills and real-time fluid monitoring for first time in ocean drilling • First time recovery of continuous sequences along oceanic detachment fault zone • Highly heterogeneous rock type and alteration in shallow detachment fault zone • High methane and hydrogen concentrations in Atlantis Massif shallow basement • Oceanic serpentinites potentially provide important niches for microbial life Abstract IODP Expedition 357 used two seabed drills to core 17 shallow holes at 9 sites across Atlantis Massif ocean core complex (Mid-Atlantic Ridge 30°N). The goals of this expedition were to investigate serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. More than 57 m of core were recovered, with borehole penetration ranging from 1.3 to 16.4 meters below seafloor, and core recovery as high as 75% of total penetration in one borehole. The cores show highly heterogeneous rock types and alteration associated with changes in bulk rock chemistry that reflect multiple phases of magmatism, fluid-rock interaction and mass transfer within the detachment fault zone. Recovered ultramafic rocks are dominated by pervasively serpentinized harzburgite with intervals of serpentinized dunite and minor pyroxenite veins; gabbroic rocks occur as melt impregnations and veins. Dolerite intrusions and basaltic rocks represent the latest magmatic activity. The proportion of mafic rocks is volumetrically less than the amount of mafic rocks recovered previously by drilling the central dome of Atlantis Massif at IODP Site U1309. This suggests a different mode of melt accumulation in the mantle peridotites at the ridge-transform intersection and/or a tectonic transposition of rock types within a complex detachment fault zone. The cores revealed a high degree of serpentinization and metasomatic alteration dominated by talc-amphibole-chlorite overprinting. Metasomatism is most prevalent at contacts between ultramafic and mafic domains (gabbroic and/or doleritic intrusions) and points to channeled fluid flow and silica mobility during exhumation along the detachment fault. The presence of the mafic lenses within the serpentinites and their alteration to mechanically weak talc, serpentine and chlorite may also be critical in the development of the detachment fault zone and may aid in continued unroofing of the upper mantle peridotite/gabbro sequences. New technologies were also developed for the seabed drills to enable biogeochemical and microbiological characterization of the environment. An in situ sensor package and water sampling system recorded real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential (Eh), and temperature and during drilling and sampled bottom water after drilling. Systematic excursions in these parameters together with elevated hydrogen and methane concentrations in post-drilling fluids provide evidence for active serpentinization at all sites. In addition, chemical tracers were delivered into the drilling fluids for contamination testing, and a borehole plug system was successfully deployed at some sites for future fluid sampling. A major achievement of IODP Expedition 357 was to obtain microbiological samples along a west–east profile, which will provide a better understanding of how microbial communities evolve as ultramafic and mafic rocks are altered and emplaced on the seafloor. Strict sampling handling protocols allowed for very low limits of microbial cell detection, and our results show that the Atlantis Massif subsurface contains a relatively low density of microbial life.