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Heat flow across oceanic transform faults (TFs) and fracture zones (FZs) has rarely been studied in detail, despite these features representing distinct thermal boundaries within the oceanic lithosphere. Here, we present heat flow measurements across the St Paul fracture zone (SPFZ) in the equatorial Atlantic Ocean, from 48 Ma crust in the south to 71 Ma in the north. To the north of the FZ we find a basal heat flow of 63 mWm−2, and to the south a basal heat flow of 79 mWm−2, both in agreement with plate cooling models. However, within the SPFZ we find a heat flow of 83 mWm−2, greater than the values of the adjacent crust and 10–15 mWm−2 higher than predicted from conductive cooling models, suggesting that the thermal structure of the FZ has been modified. Evidence from seismic and sub‐bottom profiler data indicate recent active deformation within the SPFZ, potentially driven by lithospheric flexure across the FZ or temporal changes in TF configuration. We propose that this deformation may enable fluid circulation and heat advection within the basement, creating the seafloor heat flow anomaly within the FZ. These findings suggest that FZs may remain important zones predisposed to host deformation and fluid flow in the oceanic lithosphere, despite not being active plate boundaries., Key Points: A high heat flow anomaly of 10–15 mWm−2 is observed in the St Paul fracture zone compared to the adjacent oceanic crust. The heat flow anomaly is likely due to tectonically driven fluid flow but thermal rejuvenation at the transform fault could also contribute. Fracture zones may act as high permeability pathways for fluid flow, and form and evolve differently to standard oceanic lithosphere., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, FP7 Ideas: European Research Council http://dx.doi.org/10.13039/100011199, https://doi.pangaea.de/10.1594/PANGAEA.950419, https://doi.pangaea.de/10.1594/PANGAEA.950420

Marine heat flow data provide fundamental insights into thermal processes and advective heat transport occurring near and below the seafloor. Processes that influence and are influenced by heat transport within seafloor sediments and basement rocks include: the thermal evolution of the oceanic crust and lithosphere; the geodynamics of plate boundaries and mantle convection; fluid circulation and associated impacts on water-rock interactions, seismicity, tectonics, and magmatism;occurrence and stability of gas hydrates; maturation of hydrocarbons at passive margins. Understanding these processes involves the quantification of energy and fluid fluxes, requiring knowledge of the thermal state deduced from observations that include heat flux, sub-bottom temperature, and thermo-physical sediment properties.Our main objective is the presentation of methods, instrumentation, and recent and on-going projects to demonstrate the wide-range field of application. The Faculty of Geosciences and MARUM (University of Bremen) have a longstanding record of high-quality research in the field of marine heat flow studies. We present exemplary case studies from our field of expertise relating to subduction zones (seismogenic zones), gas hydrates, hydrothermal processes (Layer 2A, fault zones, fracture zones), and ridge related processes. Further on, economical projects like assessment and monitoring of thermal impact of buried off-shore power cables from wind farms on the environment come into focus., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The research cruise to the Eastern Mediterranean (GPF-18-2-40) originally planned on RV METEOR was relocated to RV SONNE (Fig. 1.2) due to the reduced number of scientists as part of the corona pandemic. The main objective of the Bremen Ocean Cluster expedition (DFG, EXC2077) was to investigate the interactions between the seabed and ocean water in Greek waters, whereby the plate tectonic constellation of a broad collision zone represents a special tectonic drive. A secondary goal was the sampling of the Sartori mud volcano, which is being processed in Italian waters as part of a separate DFG project and for which the GPF granted an additional permit for ship time (GPF 20-1_054). The expedition began on 12 October in Emden/Germany and ended on 01 December 2020, in Emden. Investigations on mud volcanoes were carried out divided into 3 working areas (Fig. 1.1, the Sartori mud volcano in the Calabrian arc, the so-called Cobblestone Area, the Olimpi mud volcano field including the United Nation Ridge). With the MARUM AUV SEAL (Fig. 1.3) 11 dives were successfully carried out to create high-resolution detailed maps of certain seafloor structures. A total of 38 gravity cores (Fig. 1.4), 30 multicorers (Fig. 1.5) and 4 minicorers were used for sampling sediments and 6 CTD stations for sampling methane in the water column. Furthermore, 10 profiles were carried out with the heat flow lance and 5 observation profiles with the on-board OFOS. In four different provinces, 16 mud volcanoes were examined, 10 of which are characterized by pore waters that show a distinct freshening, while three mud volcanoes, Napoli, Heraklion and Gelendzhik, are characterized by very high salt concentrations. The salt accumulations in these structures are derived from the Messinian salt deposits in the subbed, from which salty brines arise through subrosion, which interact in various ways with the mud volcanoes. The study areas were selected based on preliminary surveys and morphological structures and increased backscatter patterns from multibeam mapping carried out over 3580 nautical miles in Italian and Greek waters. 326

METEOR-Berichte

Report of the research cruise no. MSM69 of the German research vessel Maria S. Merian into the aquatorial Atlantic, conducting seismic refraction and wide-angle measurements., MARIA S. MERIAN-Berichte

Focused research on the Pine Island and Thwaites glaciers, which drain the West Antarctic Ice Shelf (WAIS) into the Amundsen Sea Embayment (ASE), revealed strong signs of instability in recent decades that result from variety of reasons, such as inflow of warmer ocean currents and reverse bedrock topogra- phy, and has been established as the Marine Ice Sheet Instability hypothesis. Geothermal heat flux (GHF) is a poorly constrained parameter in Antarctica and suspected to affect basal conditions of ice sheets, i.e., basal melting and subglacial hydrology. Thermomechanical models demonstrate the influential boundary condition of geothermal heat flux for (paleo) ice sheet stability. Due to a complex tectonic and magmatic history of West Antarctica, the region is suspected to exhibit strong heterogeneous geothermal heat flux variations. We present an approach to investigate ranges of realistic heat fluxes in the ASE by different methods, discuss direct observations, and 3-D numerical models that incorporate boundary conditions derived from various geophysical studies, including our new Depth to the Bottom of the Magnetic Source (DBMS) estimates. Our in situ temperature measurements at 26 sites in the ASE more than triples the number of direct GHF observations in West Antarctica. We demonstrate by our numerical 3-D models that GHF spatially varies from 68 up to 110 mW m-2.

North Pond is an isolated small sediment pond (6 km by 15 km) located on the western flank of the Mid-Atlantic Ridge (23��N) which offers the opportunity to study microbial communities and their activities in deeply-buried sediments and the underlying basement. North Pond has been previously studied by a series of DSDP and ODP drill holes and seafloor observatories. However the existing site survey data are not sufficient for the approved North Pond IODP drilling expedition, scheduled to take place in FY 2011. Therefore a site survey cruise on the German RV Maria S. Merian (MSM 11/1) took place from February 17 - March 12, 2009 (Fort-de- France, Martinique to Dakar, Senegal) with the goal to map in detail the sediment-basement interface and increase the heat flow measurement coverage. Due to an accident on board the scheduled working days on site were reduced from 14 to 6 days. Therefore a number of detailed investigations especially in the southern part of the basin had to be abandoned. A set of geophysical survey data was obtained comprising 14 lines (about 240 km) of multibeam data in combination with single channel seismics and sediment echosounding, 61 successful heat flow measurements, and recovery of 68 m of core. The survey confirms the existing results based on two seismic profiles from 1989 but the new data show the sedimentbasement interface in much more more detail. New heat flow measurements complement the existing heat flow coverage of Langseth et al. (1992) and confirm the hydrothermal circulation pattern with inflow of cold seawater at the southern rim of the basin and upflow of warm water at the north/north-western boundary. The new detailed geophysical data set will allow to position the proposed drillholes and constrain hydrogeological modelling of the circulation in the upper crust., MARIA S. MERIAN-Berichte

Berichte aus dem Zentrum f��r Meeres- und Klimaforschung / Z

Berichte zur Polarforschung = Reports on Polar Research