Marine sediment archives provide invaluable records of continental erosion and dynamics, important for understanding both crustal deformation and climatic processes. Yet these archives are influenced by autogenic and allogenic processes. Rigorous interpretation of these records therefore requires unravelling of these various intertwined factors, and a good understanding of source-to-sink.

The Bengal Fan is the largest marine sedimentary fan in the world. It, and its smaller “sister” the Indus Fan, as well as the Nicobar Fan, archive the erosional history of the Himalayas, the largest mountain belt in the world. Various IODP, and previously DSDP expeditions have cored the fans, and the material extensively studied to elucidate the history of the fans’ hinterland tectonics, source to sink dispersal patterns, and climatic variations through time, with an emphasis on the response to the Asian monsoons. Yet unravelling the competing influences on the sediment archives in this tectonically active region is challenging.

In this talk I will provide an overview on the use of isotopic provenance studies to discuss aspects of the progress made in using the archives to determine Himalayan tectonics, as well as in deconvolving autogenic versus allogenic influences and in our understanding of source-to-sink.

Ocean sediments are considered to contain microbial biomass that equals the stock of organic matter on all the continents combined. Knowledge on the spatiotemporal distribution and abundance of microbial life in marine subsurface sediments, however, is still sparse. A region particularly understudied in this respect is the Antarctic continental margin, in which the deep biosphere is largely terra incognita. A 794 m-long sediment sequence (Site U1532), recovered during IODP Expedition 379: “Amundsen Sea West Antarctic Ice Sheet History” provides the unique opportunity to study the composition and abundance of the deep biosphere in polar regions of the Southern Hemisphere. Porewater profiles of sulfate and methane concentrations indicate that the sulfate-methane transition zone (SMTZ) is located at a depth of ~660 mbsf, making it one of the deepest SMTZ ever encountered. Stable carbon isotope measurements attest to the biological origin of the methane and provide direct evidence for an active deep-dwelling microbial community. Cell abundances decline with depth by three orders of magnitudes but increase again within the SMTZ. Complementary biomarker analysis indicates that this change in cell abundances is associated with a shift in the microbial community to predominantly methanogens throughout the SMTZ. Our data thus provides first insights into the microbial diversity and abundance of the deep biosphere in the yet largely unstudied marine subsurface sediments surrounding Antarctica. Combining our results with previous data of cell abundances in marine sediments suggests that current projections of microbial biomass appears to be overestimated and need to be downsized.

Permanent carbonate mineralisation in basalt is a promising solution for Carbon Capture and Storage of anthropogenic greenhouse gases without the risk of leakage. While this process is known to occur at relatively low temperatures below 100°C, new research on Large Igneous Provinces (LIPs) and young rift basins suggests that much of the thermogenic gases mobilised during contact metamorphism can remain trapped and mineralised in the sills that mobilised them. This discovery is the result of two distinct drilling investigations on land (KARIN) and at sea (IODP Exp 385). It shows that basalts may not only trigger the sudden release of thermogenic gas, but also represent an important carbon sink. The two examples of carbonate trapping in sills presented here are from the Karoo and Guaymas basins. Results indicate that a large fraction of epimagmatic fluids charged with thermogenic gas systematically penetrated inside the sills during cooling. Our numerical solutions suggest that in both cases the higher permeability of the sill acquired during cooling and crystallisation compared to that of its host, ultimately dictates the fate of the thermogenic gas that accumulates in the igneous body. On this basis, we conclude on the role of basalts in the Earth’s carbon cycle from a geological and anthropogenic perspective.

Continuous limnic archives may record millions of years of climatic and environmental change at their locality. Typically, such archives reflect environmental conditions in the lakes’ catchments, but also the imprint of large-scale atmospheric systems e.g. related to insolation and/or global ice-sheet dynamics. These parameters may vary considerably in space and time, and our understanding on patterns across continents that relate to this forcing is still incomplete. Comparing sedimentation rates from limnic archives covering fundamental changes in the Earth’s system like the Mid-Pleistocene transition (change from 41kyr to 100kyr cycle world) has potential to shed light into spatial differences in Earth’s climate response, if applied carefully.

To better understand the sedimentation history of lakes, and especially their reaction to climate transitions, we compare sedimentation rates from lakes. In a second step, we systematically align several records to facilitate best comparability. We focus on limnic records that have been investigated during ICDP projects, and specifically assess the influence of the Mid-Pleistocene transition and the Mid-Brunhes transition on sedimentation rates.

The ICDP-Project BASE investigated Archean Surface Environments by coring the ca. 3220 Ma Moodies Group of the Barberton Greenstone Belt, South Africa, Oct. 2021 – August 2022. This unit represents some of the oldest shallow-water and terrestrial siliciclastic strata worldwide; it contains fossil microbial life. Because the BGB had repeatedly seen intensive gold exploration and features several active gold mines along its northern margin, the eight BASE drill sites, largely located within the 2018 declared Barberton-Makhonjwa Mountains WHS, had to counter initial suspicion that they masked a gold exploration project, largely controlled by foreign interests. We obtained goodwill, interest, and permits from the local population and from local, regional, and national government, respectively, and ensured safe and incident-free drilling operations by designing and executing a multi-faceted approach: Prior to project start, we contributed regularly to local and regional newspapers, had the planning workshop extensively covered by media, and cultivated contacts with stakeholders and local property owners. The Education/Outreach/Publication program employed a Barbertonian geologist full time to work with traditional government, radio stations, TV, schools, and institutions of higher learning. We set aside half of our core processing space in downtown Barberton as an exhibition area, trained all staff as tour guides, maintained an open-door policy, and encouraged visitors to observe us as we processed core. Delegations, school classes, and associations could inform themselves first-hand on the core retrieval process on field trips to drill sites. After operations, BASE added a room to the local museum dedicated to WHS geoscience research.