As an integral part of Earth’s climate system, the Antarctic Ice Sheet (AIS) impacts global sea level and interacts with Southern Ocean climate on a variety of timescales. A lack of long and continuous records of AIS variability on orbital timescales, however, has challenged our understanding of the complex interplay between the AIS, ocean, atmosphere, and biogeochemical cycles and its contribution to the evolution of Plio-Pleistocene climate. Here we sediment records from Iceberg Alley Site U1537 (IODP Expedition 382) from the Antarctic Zone of the Southern Ocean in combination with climate and ice-sheet model simulations to show that key components started to synchronize with orbitally-paced global climate change since ~1.5 million years ago (Ma), 0.3 Ma before the Mid-Pleistocene Transition (MPT) started. Since ~1.5 Ma, productivity (upwelling) and dust proxies of Site U1537 covaried on orbital time. From ~1.5–~0.9 Ma, Southern Hemisphere sea-ice increase was accompanied by a similar long-term decrease in sea-surface temperature. During that period, Antarctic ice volume also increased. Since ~0.9 Ma, all climate components show increased synchronization with global climate on orbital time scales. Since the Mid-Brunhes event (~0.45 Ma), all components of the Antarctic climate and ice-sheet system were locked into an orbital rhythm with high-amplitude, glacial-to interglacial variability. The weak response to orbital forcing prior to 1.5 Ma indicates sensitivity thresholds for the Southern Ocean and the AIS. Specifically, the sea-ice increase and sea-surface temperature decrease in combination with AIS growth increasingly regulated the carbon cycle across the MPT.

For much of the Meso- and Cenozoic epochs, the high latitudes were significantly warmer than at present and especially the Cretaceous world has been generally considered a time of strong greenhouse climate and therefore presumed to be ice-free. Accordingly, the first large permanent ice sheets of the past 100 m.y. originated in the earliest Oligocene (ca. 33.7 Ma), with small ephemeral ones perhaps present during the late Eocene. This broad view of a warm and stable Cretaceous climate has been challenged in recent decades by the publication of a considerable amount of new data suggesting more variability in climate. In this study, we aim to test for potential glaciation episodes in the latest Cretaceous by generating the first ever high-resolution δ¹⁸O_sw record for the late Maastrichtian from Ocean Drilling Program (ODP) Sites 1209 and 1210 (Leg 198, Shatsky Rise, western Pacific Ocean). Our results reveal evidence for a dynamic late Maastrichtian ice sheet waning and waxing on the Antarctic continent. Interglacial periods suggest ice sheets covering 0–19% of the modern Antarctic volume, whereas glacial ice sheets reached 55–80% of the present-day Antarctic ice volume, causing glacioeustatic relative sea-level falls of up to 50 m. Additionally, an ice-free Antarctic continent is further been inferred for the warm climate of the Mid-Maastrichtian Event. These findings indicate that fairly large ice sheets could grow and decay equally rapidly under the climatic conditions of the latest Cretaceous and that the Cretaceous was far from being ice free.

Drilled rocks from the Chicxulub impact crater are pervasively affected by decimeter-scale brittle shear faults. Measurements of the orientations and slip senses of 602 shear faults in shocked granitoid target rocks resulted in a unique fault-slip data set of unprecedented detail. The shear faults most likely represent a late stage of cratering, during which the crater grew horizontally. Based on numerical models, deformation during this stage is characterized by concentric and vertical extension and uniform radial shortening. Extracting principal strain axis directions from the inversion of brittle shear faults allowed us to test to what extent the observed brittle deformation corresponds to the deformation regime predicted by numerical models. As the fault-slip data were measured on drill core segments in horizontal position, the data had to be rotated back with regard to the in-situ positions of the segments prior to inversion. Results of the inversion show that the principal directions of observed brittle strain adhere to numerically predicted directions in the vicinity of a most prominent deformation zone at a depth between 1220 and 1316 m below the sea floor. By contrast, elsewhere above this deformation zone, principal strain orientations seem rather non-uniform. It remains to be determined to what extent the variation of strain axis orientations with depth may be systematic or abrupt across possible structural or lithological discontinuities. At any rate, the local orientation of the principal strains is more variable than predicted for the apparently simple strain regime during late-stage crater growth predicted by numerical models.

The active strike slip North Anatolian Fault poses significant seismic hazard in Turkey. One of its parts - the Main Marmara Fault - extends across the northern Sea of Marmara close to the metropolitan area of Istanbul, where a potentially hazardous earthquake 7 is overdue according to paleoseismic statistics. At the same time the Main Marmara Fault exhibits a segmentation along‐strike with creeping and locked parts, the understanding of which is still a challenge. To address this challenge the GONAF observatory was initiated by ICDP and enabled continuous research in the recent years. We present results obtained in the frame of the DFG-ICDP priority program that include a new 3D lithospheric‐scale model of the Sea of Marmara that combines gravity modelling and seismic tomography analysis with thermal and rheological modelling. Using forward and inverse gravity modelling with free‐air gravity data and available constraints of geological units we derived the intra‐crustal density structure. Shear‐wave velocity tomography models provided insights into the temperature and density configuration of the uppermost mantle, and the geometry of the 1330°C isotherm. We find crustal density variations with a lower‐density crust over the western and creeping part of the Main Marmara Fault, and a denser crust below the Istanbul Zone where the Main Marmara Fault is supposed to be locked. We analysed the combined effects of the density structure and of the thermal field on the rheological configuration and discuss which implications this configuration may have for the deformation of the Main Marmara Fault.

The Agulhas Plateau is an oceanic plateau located in the gateway between the South Atlantic and Indian Oceans. It is thought to have formed during the late Cretaceous together with the Maud Rise (MR) and Northeast Georgia Rise (NEGR) as a joint plateau. Igneous rocks, cored from the volcanic basement of Agulhas during IODP Expedition 392 (Uenzelmann-Neben et al., 2023, IODP Proceedings 392), include tholeiitic sills and pillow lavas. ⁴⁰Ar/³⁹Ar ages range from 78.61 ± 0.68 to 87.36 ± 0.19 Ma. Lavas from the Agulhas sites were also analyzed for Sr-Nd-Pb-Hf isotopic composition together with newly sampled legacy core samples from MR (ODP Leg 113) and NEGR (ODP Leg 114). The Agulhas rocks are less enriched compared to the adjacent and slightly older Mozambique Ridge lavas, which trend towards an “enriched mantle” composition (Jacques et al., 2019, Chem. Geol. 507). Instead, the Agulhas lavas show systematically lower initial ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios for a given ²⁰⁶Pb/²⁰⁴Pb and thus plot closer to the Northern Hemisphere Reference Line while forming a trend towards the Bouvet hotspot composition. In contrast, analyzed MR and NEGR lavas have a more enriched isotopic composition similar to Mozambique Ridge. In the light of these results and applying new plate tectonic reconstructions, we discuss if Agulhas shared a common magma source with MR and NEGR or whether the latter two plateaus formed as part of the earlier Mozambique event, which would result in a revised geodynamic history of oceanic plateau formation in the southern African marine gateway.

The Amundsen Sea Embayment of West Antarctica is today the site of pronounced glacial retreat and mass loss. Very little information is available on how the area looked like before the onset of large-scale continental glaciation, and on which morphologic boundary conditions finally led to the onset of glaciation. Here we report data from the first drilling campaign on the Amundsen Sea continental shelf, using the MeBo drilling system. We obtained coarse-grained sediments deposited during the Eocene, shortly before major ice sheet buildup. Our findings reveal the Eocene as a transition period from >40 million years of relative tectonic quiescence toward reactivation of the West Antarctic Rift System, coinciding with incipient volcanism, rise of the Transantarctic Mountains, and renewed sedimentation under temperate climate conditions. The recovered sediments were deposited in a coastal-estuarine swamp environment at the outlet of a >1500-km-long transcontinental river system, draining from the rising Transantarctic Mountains into the Amundsen Sea. Much of West Antarctica hence lied above sea level, but low topographic relief combined with low elevation inhibited widespread ice sheet formation.