Aeolian sediment flux from sea ice into Southern McMurdo Sound, Antarctica

Abstract

Aeolian sediment accumulates on the surface of annual sea ice in Southern McMurdo Sound (SMS). It is sourced from ice-free areas around the sound and is released from the sea ice during annual melting and sinks to the sea floor. However, the volume, composition and contribution to overall sedimentation in the region have not previously been quantified. Here, we present the results of a systematic, quantitative field study of aeolian sediment on the surface of sea ice in SMS carried out during the drilling of the ANDRILL 2-2A drillhole during the austral summer of 2007. Our results reveal a surprisingly large volume of aeolian sediment (between 7.8 and 24.0 tonnes of aeolian sediment per km 2) forming an elongate lobe extending north from the McMurdo Ice Shelf onto the sea ice surface. Detailed particle size analysis reveals distinctive fine sand and silt modes that progressively fine down wind, suggesting that the sediment is transported under two distinct wind transport processes. XRF grain composition analysis indicates that the material is predominantly volcanic and is sourced primarily from a large area of loose debris on the surface of the McMurdo Ice shelf. Comparison with modern sediment recovered from the sea floor shows a remarkable similarity in grain size distributions and suggests that the sea floor is dominated by aeolian sediment that has settled through the water column. Our calculations indicate that this process produces a sea floor sedimentation rate of up to 1.53 cm/ky in the local area. This new dataset quantifies the aeolian sediment flux in SMS and highlights the contribution of aeolian deposition to the modern sedimentary record in SMS. Furthermore, it draws attention to the recently demonstrated link between iron-bearing aeolian sediment release from sea ice and the triggering of phytoplankton blooms each spring.