Snapshots of pre-glacial paleoenvironmental conditions along the Sabrina Coast, East Antarctica: New palynological and biomarker evidence

Abstract

The Aurora Subglacial Basin (ASB) catchment contains 3–5 m of sea-level equivalent ice volume that drains to the Sabrina Coast, East Antarctica via the Totten Glacier system. Observed thinning and retreat of Totten Glacier indicate regional sensitivity to oceanographic and atmospheric warming. Paleoclimate studies of climatically sensitive catchments are required to understand the evolution of the East Antarctic Ice Sheet (EAIS) and its outlet glacier systems. Recent seismic and sediment studies from the Sabrina Coast document the evolution of the EAIS in the ASB catchment, suggesting that the region has long been sensitive to climatic changes. This study presents new palynological and biomarker data from Sabrina Coast continental shelf sediments. Detailed palynological records were obtained from four short jumbo piston cores (JPC; NBP14-02 JPC-30, -31, -54 and -55), enabling reconstructions of regional vegetation and environments prior to and during Cenozoic EAIS development. The Sabrina Flora is dominated by angiosperms, with Gambierina spp. often exceeding 40% of the assemblage, and diverse Proteaceae, Battenipollis spp., Forcipites spp., Nothofagidites spp., fern, and conifer palynomorphs indicative of an open shrubby ecosystem. Excellent preservation and frequent occurrence of Gambierina spp. clusters suggest that a majority of the Sabrina Flora assemblage is penecontemporaneous with sedimentation; however, some uncertainties remain whether this sedimentation occurred in the Late Cretaceous or the Paleogene. Despite that uncertainty, high abundances of Gambierina spp. and Battenipollis spp., in combination with relatively low (<10%) Nothofagidites spp. abundances indicate that the Sabrina Flora is unique in Antarctica. Evaluation of biomarkers finds evidence for penecontemporaneous and reworked components. The penecontemporaneous C₃₀ n-alkanoic acids have δ¹³C values of −30.2 ± 0.5‰, consistent with δ¹³C values in an open canopy woodland or shrubby open vegetation. Their hydrogen isotope (δD) values of −215 ± 4.5‰, indicate precipitation isotopic composition (δD_precip) of −130‰, similar to coastal snow in the same region today. Together, Sabrina Flora palynomorph and plant wax data suggest a drier, more open coastal vegetation in the Aurora Basin of East Antarctica rather than the closed rainforest vegetation often described from other parts of Antarctica for the Cretaceous to Paleogene. To directly compare records from the circum-Antarctic, additional long sedimentary records with improved biostratigraphic constraints are required. Such records will enable identification of regional climate gradients or micro-climates, and allow assessment of the environmental conditions and mechanisms driving observed differences.