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The latitudinal migration of the Southern Ocean hydrographic fronts has been suggested to influence oceanographic conditions within the Indian-Atlantic Ocean gateway by restricting the amount of warm, saline water from the Indo-Pacific, transported by Agulhas Current, feeding into the South Atlantic via the Agulhas leakage. The Agulhas Current is an integral part of the global thermohaline circulation system as it acts as potential modulator of the Atlantic Meridional Overturning Circulation, which drives changes in regional and global climate, over at least the last 1.4 million years. However, the dynamics of this frontal system and associated changes in surface ocean biogeochemistry have not been explored beyond this time period due to absence of long continuous records spanning the Pliocene. Using International Ocean Discovery Program Site U1475 located on the southwestern flank of the Agulhas Plateau (41°25.61′S; 25°15.64′E; 2669 m water depth), we present high-resolution palaeoclimate records spanning the early to mid-Pliocene (~2.8 to ~5 Ma), from assemblage composition and morphometry of coccoliths, combined with oxygen and carbon stable isotopes from the bulk coccolith fraction. Our new Pliocene reconstructions offer evidence of the changing position of the subtropical front in the Southern Indian Ocean, driving variations in surface ocean conditions (e.g., nutrients, temperature, stratification), and thus biological productivity. We also explore expressions of coccolith δ13C vital effects from size-separated coccolith fractions together with planktic foraminifer carbon and oxygen stable isotopes from co-registered samples, that have been linked to cell size, growth rate, and calcification degree, providing empirical correlation with aqueous and atmospheric CO2 concentrations.

Glacio-eustatic cycles lead to changes in sedimentation on all types of continental margins. There is, however, a paucity of sedimentation rate data over eustatic sea-level cycles in active subduction zones. During International Ocean Discovery Program Expedition 375, coring of the upper ∼110 m of the northern Hikurangi Trough Site U1520 recovered a turbidite-dominated succession deposited during the last ∼45 kyrs (Marine Isotope Stages (MIS) 1–3). We present an age model integrating radiocarbon dates, tephrochronology, and δ18O stratigraphy, to evaluate the bed recurrence interval (RI) and sediment accumulation rate (SAR). Our analyses indicate mean bed RI varies from ∼322 yrs in MIS1, ∼49 yrs in MIS2, and ∼231 yrs in MIS3. Large (6-fold) and abrupt variations in SAR are recorded across MIS transitions, with rates of up to ∼10 m/kyr occurring during the Last Glacial Maximum (LGM), and

Prior to ~1 million years ago (Ma), variations in global ice volume were dominated by changes in obliquity; however, the role of precession remains unresolved. Using a record of North Atlantic ice rafting spanning the past 1.7 million years, we find that the onset of ice rafting within a given glacial cycle (reflecting ice sheet expansion) consistently occurred during times of decreasing obliquity whereas mass ice wasting (ablation) events were consistently tied to minima in precession. Furthermore, our results suggest that the ubiquitous association between precession-driven mass wasting events and glacial termination is a distinct feature of the mid to late Pleistocene. Before then (increasing), obliquity alone was sufficient to end a glacial cycle, before losing its dominant grip on deglaciation with the southward extension of Northern Hemisphere ice sheets since ~1 Ma.

The Hikurangi Subduction Margin (HSM) of New Zealand is well-known for its variable seismic behaviour along strike, and across the Pacific-Australian subduction interface. Pacific-Australian plate motion is accommodated by a combination of slow slip and normal seismic events. The mechanics of slow slip earthquakes and their relationship to normal earthquakes are not well constrained, and so they represent a challenge to the development of hazard models for this region of New Zealand.Variability in a number of aspects of the stress state along the HSM may play a role in controlling the observed spatially variable seismic behaviour. Here we present preliminary analysis of stress orientation information from borehole image logs acquired from oil and gas exploration wells, and scientific wells drilled as part IODP Expedition 372. Orientations of borehole breakouts (BOs) and drilling-induced tensile fractures (DITFs) from these image logs are used to determine orientations of the minimum and maximum horizontal stress directions respectively within the upper 3 km of the over-riding Australian Plate (hanging wall of the HSM subduction interface). Our analysis reveals that present day maximum horizontal compressive stress orientation (SHmax) within the subduction hangingwall varies along the HSM strike, from NE-SW (oblique to Pacific-Australian plate motion, parallel to HSM strike) in the northern HSM, to NW-SE (oblique to Pacific-Australian plate motion and HSM strike) in the southern HSM. Some deviation from this trend can be observed in both regions. At the frontal thrust in the northern HSM, SHmax is oriented N-S, and in the southern HSM one well shows a shallow E-W oriented SHmax. The borehole image log SHmax orientations in the northern HSM are consistent with SHmax orientations derived from shallow focal mechanism inversion. In contrast, borehole image logs SHmax orientations in the south of HSM are oblique to focal mechanisms derived shallow SHmax orientations. Borehole SHmax orientations are compatible with the maximum horizontal contraction strain rate direction determined from campaign GPS surface velocities, though in the southern HSM multiple directions are determined from this technique. The difference in stress orientations along the HSM is consistent with the variation in seismic behaviour linked to changes in coupling at the subduction interface. Interestingly, it is the southern HSM, where the subduction interface is considered strongly coupled, that stress field orientations are not consistent with depth and show variability. In the northern HSM, where the subduction interface is considered to be weakly coupled, stress orientations appear broadly consistent with depth.