Vegetation prior to and during onset of East Antarctic glaciation: High resolution palynological insights from Sabrina Coast, East Antarctica

The Aurora Subglacial Basin (ASB) contains an estimated 3.5 m of global sea level equivalent ice and is primarily drained by the Totten Glacier system, which terminates at the Sabrina Coast, East Antarctica. Thinning and retreating of the Totten Glacier indicates that this region is highly susceptible to oceanographic and atmospheric changes. A paleoclimate perspective on these changes will improve understanding of East Antarctic Ice Sheet (EAIS) dynamics in this sensitive system. Gulick et al. (2017) used seismic and sediment core data to document a dynamic early evolution of the EAIS in the ASB, suggesting that this large ice sheet may not be as stable as previously thought. Here we present new high-resolution palynological data from NBP 14-02 jumbo piston cores (JPC) JPC-54 and JPC-55, which enable reconstruction of regional vegetation and environments during EAIS development. The newly described Sabrina Flora is dominated by angiosperms, with Gambierina (G.) rudata and G. edwardsii complexes, often exceeding 50% of the assemblage. Diverse Proteaceae, Battenipollis sectilis, Forcipites sp., Nothofagidites spp., fern and conifer palynomorphs are also notable in the assemblage. Because of pristine preservation and the frequent occurrence of Gambierina spp. clusters, the majority of the Sabrina Flora assemblage is interpreted as being penecontemporaneous with sedimentation. Preliminary biostratigraphic results indicate JPC-54 and JPC-55 as latest Paleocene to early-mid Eocene sediments with likely contributions from reworked mid-Cretaceous marine deposits (Smith et al., 2018). Biomarker evidence of plant wax n-alkanoic acid yields average ẟ¹³C₃₀ values of -30.2±0.5‰ (JPC 54 only) consistent with open canopy woodland or shrubby tundra. ẟD₃₀ values were stable across JPC 54 and 55 with a mean -215±4.5‰. A fractionation of ~-100‰ indicates ẟD_precip of -128‰, slightly more positive than coastal snow in the same region today, suggesting sourcing of plant biomarkers from close to the coast. Integration of biomarker and palynological results is ongoing but the abundance of Gambierina, Battenipollis and Proteaceae could be consistent with a drier, more open type of coastal vegetation rather than the closed rainforest vegetation often envisaged for Paleocene-Eocene Antarctica.