Submarine volcanism interacted with icesheets in the western Ross Sea, Antarctica

The western part of the Ross Sea embayment of Antarctica is a showcase of the interaction among Earth systems at various time and spatial scales marked by volcanic and magmatic emergences.  We present a comprehensive investigation on the distribution and the vicinity of volcanic constructs within the western Ross Sea seafloor, which likely interacted with multiple advances and retreats of continental icesheets over time, using data acquired during the NBP25-01 Expedition(February-April 2025) on RVIB Nathaniel B. Palmer. Our study area is delimited by Ross Ice Shelf and Ross Island on the south and the Pacific to the north and is bordered by Transantarctic Mountains to the west and the Victoria Land Basin to the east with Terror Rift, currently an active magmatic rift under thick sediments, in between. Our expedition provides a refined view of the seafloor composed of widespread underwater volcanism within the Terror Rift Volcanic Field (TRVF) that include several polygenetic volcanic edifices, some of which appear to be highly eroded by ice sheets. Numerous monogenic volcanic cones were also identified, including a remarkable morphological type of flat-topped seamounts that are found throughout the western Ross Sea. They were mapped, sampled, and imaged, all of which provide evidence of varying amounts of erosion, that we suggest is caused by their interaction with grounded or pinned icesheets/shelves in past, including possible interaction during eruption of submarine volcanoes (i.e. glaciovolcanism). To better understand the lithosphere evolution with widespread volcanism that comprise the TRVF, including within the modern rift itself, we also present new heat flow measurements made during the NBP2501 Expedition via a violin-bow type heat flow probe. We conducted a total of 28 heat flow measurements along and across Terror Rift, from the Drygalski Ice Tongue to offshore Ross Island, which is twice the number of measurements taken by previous expeditions in total. The measured heat flow is ~30 and ~5 mW/m² higher than that of previously modeled in the northern and southern part of the basin, respectively. Conductive thermal modeling of volcanism along faults cannot fully explain the heat flow pattern of 90-110 mW/m² across the Terror Rift. Whereas hydrothermal cooling can effectively extract heat from young volcanism, as evidenced by imagery of and recovery of thermally altered materials, fluid circulation alone cannot simulate the heat flow pattern. The seafloor may experience a near-pure conductive heating condition during the Last Glacial Maximum as been suggested by our seafloor morphology characterization above. However,the high heat flow (at average of 100 mW/m²) would melt the base of thick ice at a rate of ~1 mm/yr, creating a nearly equivalent condition as in an open ocean setting. We therefore suggest the observed heat flow pattern is overwhelmingly reflecting a broader tectonic process, likely associated with a steeper geotherm through the lithosphere while minimizing the “icy blanket” effect in the Ross Sea, implying a shallower lithosphere-asthenosphere boundary at 45-55 km below seafloor across the Terror rift. These findings are critical to models for lithospheric rigidity and isostatic response to glacial cyclicity.