Cryptotephra layers in marine sequences of the Ross Sea, Antarctica: implications and potential applications

Marine sediments of Antarctica contain tephra, fragmented material produced by explosive eruptions of Antarctic volcanoes and widely dispersed by wind. Tephra are preserved especially when sequences suffer small disturbance and sedimentation rates are high. If fingerprinted, dated and linked to a volcanic source, tephra become timesynchronous markers for independent correlations between geological archives. Tephra are also significant for volcanological reconstructions to derive the type, magnitude, age and recurrence of eruptions. Tephra record can be significantly extended by examining successions for the presence of cryptotephra (nonvisible tephra). These are essential to increase the number of eruptions recognizable of any magnitude and in distal occurrences. We present the preliminary results of the tephrochronology study of marine sediments sampled in the Ross Sea (Antarctica) in the framework CHIMERA (CryptotepHra In Marine sEquences of the Ross Sea, Antarctica) and GRETA projects (CoolinG oveR thE VicToria LAnd: resolving the Ross Sea response to continental climate change during the last two millennia), funded by Italian Programma Nazionale delle Ricerche in Antartide (PNRA). We studied (i) TR1702, Anta9813, Anta9114 and Anta99Cj03 sediment cores recovered from the Joides Basin, (ii) Abio38c2 core from the Pennel Through and (iii) TR1708 and HLF1602 cores from the Edisto Inlet. These three sedimentary basins, which are located in the western Ross Sea, have different distances from the major active volcanoes of the Northern Victoria Land. Using magnetic susceptibility coupled to XRF and lithostratigraphic investigations, we detected several cryptotephra layers. These were further characterized by a detailed description of tephra texture, mineral assemblage, and single shards major and trace element geochemistry. The age of cryptotephra layers is based on accelerator mass spectrometry (AMS) radiocarbon dates performed either on acidinsoluble organic matter. Results indicate that some of the studied cryptotephra originate from historical eruptions of Mount Rittmann and Mount Melbourne volcanoes and allow the definition of new tephra markers for the synchronization and correlation of different sedimentary records. Furthermore, some of the studied cores record the rapid, synchronous increase in the abundance of volcaniclastic particles as detrital material in marine sediments possibly linked to ice shelf breakup processes.