Sediment flux through the McMurdo Ice Shelf in Windless Bight, Antarctica

Abstract

A 19.8 m long firn core from the McMurdo Ice Shelf was analysed for dust concentration in order to calculate the contribution of aeolian sediment to sub-ice shelf sedimentation. The topmost 16 m of our record is dated using annual δ 18O layer counting which indicates the record is ~ 35 years in length. We estimate an average annual accumulation rate of 0.80 g m − 2 year of aeolian sediment onto the ice shelf surface at the core site. Comparison with nearby weather station data shows that the strongest 1% storms (winds > 35 m s − 1 ) originate exclusively from the south and a general correlation between storminess and measured aeolian sediment fallout rate at the core site is apparent. We use a simple ice flow model to calculate basal melt rates and hence dust flux through the ice shelf. The annual flux of sediment released from the base of the ice shelf to the sea floor is 2.2 g m − 2 year, which equates to a linear sedimentation rate of 0.22 cm ky − 1 , assuming a sea floor sediment density of 1.6 g cm − 3 . This rate can only account for 3–6% of the fine-grained post-glacial sediment that has accumulated there, highlighting the importance of the proximity of the calving (or grounding) lines for the supply of fine-grained sediment to the sub-ice shelf cavity.