High-resolution seafloor mapping provides insights into the dynamics of past ice-sheets/ice-shelves on high-latitude continental margins. Geological/geophysical studies in the Arctic Ocean suggest widespread Pleistocene ice grounding on the Chukchi–East Siberian continental margin. However, flow directions, timing, and behavior of these ice masses are not yet clear due to insufficient data. We present a combined seismostratigraphic and morphobathymetric analysis of the Chukchi Rise off the northwestern Chukchi margin using the densely acquired sub-bottom profiler (SBP) and multibeam echosounder (MBES) data. Comparison with deeper airgun seismic records shows that the SBP data cover most of the glaciogenic stratigraphy possibly spanning ca. 0.5–1 Ma. Based on the stratigraphic distribution and geometry of acoustically transparent glaciogenic diamictons, the lateral and vertical extent of southern-sourced grounded ice became smaller over time. The older deposits are abundant as debris lobes on the slope contributing to a large trough mouth fan, whereas younger till wedges are found at shallower depths. MBES data show two sets of mega-scale lineations indicating at least two fast ice-streaming events of different ages. Contour-parallel recessional morainic ridges mark a stepwise retreat of the grounded ice margin, likely controlled by rising sea levels during deglaciation(s). The different inferred directions of ice advances and retreats reflect complex geomorphic settings on the borderland. The overall picture shows that the Chukchi Rise was an area of intense interaction(s) of different ice-sheets/ice-shelves. In addition to glaciogenic deposits, we identify a number of related or preceding seabed features including mounds, gullies/channels, and sediment waves.

The Australian-Antarctic Ridge (AAR) is the intermediate spreading system located between the Southeast Indian Ridge and Macquarie Triple Junction of the Australian-Antarctic-Pacific plates. KR1 is the easternmost and longest AAR segment and exhibits unique axial morphology and various volcanic structures. Within it, we identified three linearly aligned volcanic seamount chains positioned parallel to the seafloor spreading direction. We found that the seamount chains had formed asymmetrically and had developed through near-ridge volcanism at some distance away from the KR1 axis. Based on high-resolution bathymetric data, we identified the spatial distribution, morphology, and summit types of the isolated volcanic structures composing the seamount chains. The magnetic constraints on the age of the identified seamounts indicate that most had a formation time of less than ~600 kyrs, which primarily occurred during four distinct volcanic pulses from 0.3-0.8 Ma, 0.9-1.1 Ma, 1.6-2.1 Ma, and 2.2-2.7 Ma (or two major distinct pulses from 0.3-1.1 Ma and 1.6-2.7 Ma). When inconsistency existed between the observed and modeled ages of volcanic structures, volcanos were found to have a temporal gap of 200-650 kyrs between their formation and that of the underlying seafloor. Such volcanos are thought to have developed due to off-axis volcanism at a distance of 7-20 km. Considering the scale of off-axis volcanism and thickening lithosphere of such areas of ~20 km away from the axis of the intermediate spreading ridge, we propose that the seamounts originated from a deep plume source beneath the oceanic lithosphere.