Evidence for a large-magnitude Holocene eruption of Mount Rittmann (Antarctica): A volcanological reconstruction using the marine tephra record

In Antarctica, the near-source exposures of volcanic eruption deposits are often limited as they are notwell preserved in the dynamic glacial environment, thus making volcanological reconstructions ofexplosive eruptions extremely challenging. Fortunately, pyroclastic deposits from explosive eruptions arepreserved in Southern Ocean sediments surrounding Antarctica, and the tephrostratigraphy of thesesequences offers crucial volcanological information including the timing and tempo of past eruptions,their magnitude, and eruption dynamics. Here we report the results of a tephrostratigraphy and tephrochronology study focused on four sediment cores recovered from the Wood Bay area in the westernRoss Sea, Antarctica. In all these sedimentary sequences, we found a well-stratified primary tephra ofconsiderable thickness, up to 80 cm, hereafter named the Aviator Tephra (AVT). According to the characteristics of the tephra deposit and its distribution, the AVT was associated with an eruption ofconsiderable intensity, potentially representing one of the largest Holocene eruptions recorded inAntarctica. Based on the major and trace element geochemistry and the mineral assemblage of thetephra, Mount Rittmann was identified as the source of the AVT. A Holocene age of ~11 ka was determined by radiocarbon dating organic material within the sediments and 40Ar-39Ar dating of alkalifeldspar crystals included in the tephra. Eruption dynamics were initially dominated by hydromagmatic magma fragmentation conditions producing a sustained, relatively wet and ash-rich eruptivecloud. The eruption then evolved into a highly energetic, relatively dry magmatic Plinian eruption. Thelast phase was characterized by renewed efficient magma-water interaction and/or collapse of theeruptive column producing pyroclastic density currents and associated co-ignimbritic plumes. The distaltephra deposits might be linked to the widespread lag breccia layer previously identified on the rim ofthe Mount Rittmann caldera which share the same geochemical composition. Diatoms found in thesediments surrounding the AVT and the primary characteristics of the tephra indicate that the Wood Bayarea was open sea at the time of the eruption, which is much earlier than previously thought. AVT is alsoan excellent tephrostratigraphic marker for the Wood Bay area, in the Ross Sea, and a useful marker forfuture synchronization of continental ice and marine archives in the region.