Geology of the Wilkes land sub-basin and stability of the East Antarctic Ice Sheet: Insights from rock magnetism at IODP Site U1361

Abstract

IODP Expedition 318 drilled Site U1361 on the continental rise offshore of Adelie Land and the Wilkes sub-glacial basin. The objective was to reconstruct the stability of the East Antarctic Ice Sheet (EAIS) during Neogene warm periods, such as the late Miocene and the early Pliocene. The sedimentary record tells a complex story of compaction, and erosion (thus hiatuses). Teasing out the paleoenvironmental implications is essential for understanding the evolution of the EAIS. Anisotropy of magnetic susceptibility (AMS) is sensitive to differential compaction and other rock magnetic parameters like isothermal remanence and anhysteretic remanence are very sensitive to changes in the terrestrial source region. In general, highly anisotropic layers correspond with laminated clay-rich units, while more isotropic layers are bioturbated and have less clay. Layers enriched in diatoms are associated with the latter, which also have higher Ba/Al ratios consistent with higher productivity. Higher anisotropy layers have lower porosity and moisture contents and have fine grained magnetic mineralogy dominated by maghemite, the more oxidized form of iron oxide, while the lower anisotropy layers have magnetic mineralogies dominated by magnetite. The different magnetic mineralogies support the suggestion based on isotopic signatures by Cook et al. (2013) of different source regions during low productivity (cooler) and high productivity (warmer) times. These two facies were tied to the coastal outcrops of the Lower Paleozoic granitic terranes and the Ferrar Large Igneous Province in the more inland Wilkes Subglacial Basin respectively. Here we present evidence for a third geological unit, one eroded at the boundaries between the high and low clay zone with a "hard" (mostly hematite) dominated magnetic mineralogy. This unit likely outcrops in the Wilkes subglacial basin and could be hydrothermally altered Beacon sandstone similar to that detected by Craw and Findlay (1984) in Taylor Valley or the equivalent to the Elatina Formation in the Adelaide Geosyncline in Southern Australia (Schmidt and Williams, 2013). Correlation of the "hard" events with global oxygen isotope stacks of Zachos et al. (2001) and Lisiecki and Raymo (2005) To whom it may concern:Please find enclosed our revised manuscript entitled, "Geology of the Wilkes Land Sub-basin and Stability of the East Antarctic Ice Sheet: Insights from rock magnetism at IODP Site U1361" for consideration for publication in Earth and Planetary Science Letters. We have read the reviews carefully and responded as appropriate. Thank you for your consideration of our revised manuscript.Sincerely, Lisa TauxeCover LetterResponse to Reviews for "Geology of the Wilkes Land Sub-basin and Stability of the East Antarctic Ice Sheet: Insights from rock magnetism at IODP Site U1361", by Tauxe et al. Editor:Alternatively, you may submit the data to a publicly accessible database or repository such as PANGEA and indicate in the paper where the data can be accessed. If you decide to u...

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Polar Frontal Migration in the Warm Late Pliocene: Diatom Evidence From the Wilkes Land Margin, East Antarctica

“…The Wilkes Subglacial Basin houses the largest single ice drainage in East Antarctica (Mengel & Levermann, ) and is therefore a critical player in the stability of the EAIS. Aeromagnetic surveys have determined that the basin lies along two deep troughs that sit downslope of the current grounding line (Ferraccioli et al, ; Jordan et al, ; Tauxe et al, ). Ice thins rapidly when it interacts with warm ocean water via submarine troughs (Pritchard et al, ), and the marine ice sheet instability hypothesis further suggests that ice occupying the Wilkes Subglacial Basin is highly susceptible to runaway retreat (Schoof, ) due to the reverse slope of the bed.…”

10Be/9Be Ratios Reflect Antarctic Ice Sheet Freshwater Discharge During Pliocene Warming

“…Downcore Be isotopes compared to Cook et al () 𝛆Nd, 87 Sr/ 86 Sr, and opal weight percentage (opal % wt ) data and Tauxe et al's () Ba/Al data. Ba/Al: thin black line shows entire record, black dots indicate measurements at our corresponding sampling depths.…”

“…See Table for Be isotope measurements and Figure for a presentation of all isotope measurements alongside important geochemical proxies for biologic productivity and EAIS fluctuation in the Wilkes Land region, including εNd, 87 Sr/ 86 Sr, opal % wt (Cook et al, ), and scanning X‐ray fluorescence‐derived Ba/Al (Tauxe et al, ).…”