In Antarctica, the near-source exposures of volcanic eruption deposits are often limited as they are not well preserved in the dynamic glacial environment, thus making volcanological reconstructions of explosive eruptions extremely challenging. Fortunately, pyroclastic deposits from explosive eruptions are preserved in Southern Ocean sediments surrounding Antarctica, and the tephrostratigraphy of these sequences 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 western Ross Sea, Antarctica. In all these sedimentary sequences, we found a well-stratified primary tephra of considerable 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 of considerable intensity, potentially representing one of the largest Holocene eruptions recorded in Antarctica. Based on the major and trace element geochemistry and the mineral assemblage of the tephra, 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 40 Ar-39 Ar dating of alkali-feldspar crystals included in the tephra. Eruption dynamics were initially dominated by hydromagmatic magma fragmentation conditions producing a sustained, relatively wet and ash-rich eruptive cloud. The eruption then evolved into a highly energetic, relatively dry magmatic Plinian eruption. The last phase was characterized by renewed efficient magma-water interaction and/or collapse of the eruptive column producing pyroclastic density currents and associated co-ignimbritic plumes. The distal tephra deposits might be linked to the widespread lag breccia layer previously identified on the rim of the Mount Rittmann caldera which share the same geochemical composition. Diatoms found in the sediments surrounding the AVT and the primary characteristics of the tephra indicate that the Wood Bay area was open sea at the time of the eruption, which is much earlier than previously thought. AVT is also an excellent tephrostratigraphic marker for the Wood Bay area, in the Ross Sea, and a useful marker for future synchronization of continental ice and marine archives in the region.
Abstract. During the Late Pleistocene–Holocene, the Ross Sea Ice Shelf exhibited
strong spatial variability in relation to the atmospheric and oceanographic
climatic variations. Despite being thoroughly investigated, the timing of
the ice sheet retreat from the outer continental shelf since the Last
Glacial Maximum (LGM) still remains controversial, mainly due to a lack of
sediment cores with a robust chronostratigraphy. For this reason, the recent
recovery of sediments containing a continuous occurrence of calcareous
foraminifera provides the important opportunity to create a reliable age
model and document the early deglacial phase in particular. Here we present
a multiproxy study from a sediment core collected at the Hallett Ridge (1800 m of depth), where significant occurrences of calcareous planktonic and benthic
foraminifera allow us to document the first evidence of the deglaciation
after the LGM at about 20.2 ka. Our results suggest that the
co-occurrence of large Neogloboquadrina pachyderma tests and abundant juvenile forms reflects the
beginning of open-water conditions and coverage of seasonal sea ice. Our
multiproxy approach based on diatoms, silicoflagellates, carbon and oxygen
stable isotopes on N. pachyderma, sediment texture, and geochemistry indicates that
abrupt warming occurred at approximately 17.8 ka, followed by a period of
increasing biological productivity. During the Holocene, the exclusive
dominance of agglutinated benthic foraminifera suggests that dissolution was
the main controlling factor on calcareous test accumulation and preservation.
Diatoms and silicoflagellates show that ocean conditions were variable
during the middle Holocene and the beginning of the Neoglacial period at
around 4 ka. In the Neoglacial, an increase in sand content testifies to
a strengthening of bottom-water currents, supported by an increase in the
abundance of the tycopelagic fossil diatom Paralia sulcata transported from the coastal
regions, while an increase in ice-rafted debris suggests more glacial
transport by icebergs.
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