WAIS-ting Away Again in East Antarctica: Sirius-ly Searching for that Lost Shaker of Diatoms

Abstract:

Evidence of West-Antarctic-style Pliocene deglaciation of the East Antarctic Wilkes and Aurora marine basins is accumulating in the published literature. The far-field sea-level record seems to require an East Antarctic contribution, enhanced geophysical surveys show deep and wide channels that deglaciate under appropriate forcing in at least some models, and Pliocene ice-rafted debris pulses of appropriate age and source region indicate ice-shelf loss that would have caused loss of at least some grounded ice. Modeled rates of East Antarctic ice-sheet shrinkage are generally slower than peak possible West Antarctic behavior, but the ~14 m of Pliocene sea-level rise from East Antarctica in our modeling is large compared to West Antarctic sources.

In an effort led by RPS with modeling by RMD and DP, we argue that the Pliocene diatoms of the Sirius Group tillites in the Transantarctic Mountains, the subject of a decade-long debate between “stabilists” and “dynamicists”, record the Pliocene deglaciation of the marine basins, and thus further confirm large East Antarctic response to moderate forcing. An extensive literature has established that the Sirius tills are local deposits that predate the Pliocene, with wind-blown Pliocene diatoms mixed into the upper layers. The modern eolian flux contains few marine diatoms compared to non-marine; thus, the marine-diatom-dominated Sirius deposits imply a distinct source that is not available today. In our recently published modeling, the deglaciation of the East Antarctic basins in response to warm Pliocene conditions is followed by marine incursion that by analogy with modern conditions would have been highly productive of diatoms, and delayed isostatic uplift then raises large areas of the resulting marine sediments above sea level. New modeling indicates that diatoms lifted in storms from these marine sediments would have been directly and rapidly transported to the Sirius sites, where the warmer Pliocene conditions would have favored cryoturbation, allowing integration of eolian diatoms into the porous till surface. The new modeling results permit a successful synthesis and integration of opposing viewpoints in the Sirius debate, and has possible implications for sea levels in a world warmed above Pliocene levels by human forcing.