Sedimentology and numerical modelling of aeolian sediment dispersal, McMurdo Sound, southwest Ross Sea, Antarctica

<p>Large volumes of aeolian sand and dust are deflated from unconsolidated till deposits, and supraglacial debris surrounding McMurdo Sound, Antarctica. This material is transported offshore with windblown snow onto extensive winter-formed sea ice in the southwest Ross Sea, and is subsequently released into the water-column during summer sea ice breakup. Aeolian sediment samples were collected from a ~600 km² area of sea ice in western McMurdo Sound to determine the magnitude of deposition and identify sediment sources. A new 2-dimensional numerical aeolian sediment transport model (NaMASTE) tuned specifically for the McMurdo Sound area, was used to explore the ability of the local wind system to move sediment from source areas to sea ice and to determine the pattern and extent of aeolian sediment dispersal to the southwest Ross Sea. Debris deposits on the McMurdo Ice Shelf debris bands are the most dominant sediment source for the area. Unconsolidated deposits between Cape Bernacchi and Spike Cape, and the Taylor Valley mouth are significant secondary deposits. Mass accumulation rates varied between 0.15 g m⁻² y⁻¹ and 54.6 g m⁻² y⁻¹, equating to a background aeolian sediment accumulation rate, excluding extremely high values, of 1.14 ± 0.59 g m⁻² y⁻¹ for the McMurdo Sound coastal sea ice zone. This is 3–5 orders of magnitude more than global background dust fallout for the Ross Sea. Modal grain size is very-fine sand to coarse silt. Notably, much of this material is distributed in localised, high sand content plumes that are oriented downwind from source, with finer deposits found outside these zones. An average seafloor linear sedimentation rate of 0.2 cm ky⁻¹ is calculated for McMurdo Sound, which is minor compared to biogenic sedimentation for the region. This equates to ~0.7 Gg y⁻¹ aeolian sediment entering McMurdo Sound during sea ice melt. Application of NaMASTE successfully simulated the general aeolian sediment distribution pattern. Testing of model variables suggests that aeolian material is mainly transported during strong (>20 m s⁻¹) wind events. Modelling also suggests aeolian material from McMurdo Sound can be transported north to the Drygalski Ice Tongue, ~250 km from source, but only in very trace quantities.</p>

Sedimentology and numerical modelling of aeolian sediment dispersal, McMurdo Sound, southwest Ross Sea, Antarctica

<p>Large volumes of aeolian sand and dust are deflated from unconsolidated till deposits, and supraglacial debris surrounding McMurdo Sound, Antarctica. This material is transported offshore with windblown snow onto extensive winter-formed sea ice in the southwest Ross Sea, and is subsequently released into the water-column during summer sea ice breakup. Aeolian sediment samples were collected from a ~600 km² area of sea ice in western McMurdo Sound to determine the magnitude of deposition and identify sediment sources. A new 2-dimensional numerical aeolian sediment transport model (NaMASTE) tuned specifically for the McMurdo Sound area, was used to explore the ability of the local wind system to move sediment from source areas to sea ice and to determine the pattern and extent of aeolian sediment dispersal to the southwest Ross Sea. Debris deposits on the McMurdo Ice Shelf debris bands are the most dominant sediment source for the area. Unconsolidated deposits between Cape Bernacchi and Spike Cape, and the Taylor Valley mouth are significant secondary deposits. Mass accumulation rates varied between 0.15 g m⁻² y⁻¹ and 54.6 g m⁻² y⁻¹, equating to a background aeolian sediment accumulation rate, excluding extremely high values, of 1.14 ± 0.59 g m⁻² y⁻¹ for the McMurdo Sound coastal sea ice zone. This is 3–5 orders of magnitude more than global background dust fallout for the Ross Sea. Modal grain size is very-fine sand to coarse silt. Notably, much of this material is distributed in localised, high sand content plumes that are oriented downwind from source, with finer deposits found outside these zones. An average seafloor linear sedimentation rate of 0.2 cm ky⁻¹ is calculated for McMurdo Sound, which is minor compared to biogenic sedimentation for the region. This equates to ~0.7 Gg y⁻¹ aeolian sediment entering McMurdo Sound during sea ice melt. Application of NaMASTE successfully simulated the general aeolian sediment distribution pattern. Testing of model variables suggests that aeolian material is mainly transported during strong (>20 m s⁻¹) wind events. Modelling also suggests aeolian material from McMurdo Sound can be transported north to the Drygalski Ice Tongue, ~250 km from source, but only in very trace quantities.</p>

Influence of Sand Trapping Fences on Dune Toe Growth and Its Relation with Potential Aeolian Sediment Transport

This study provides insights into dune toe growth around and between individual brushwood lines of sand trapping fences at the dune toe of coastal dunes using digital elevation models obtained from repeated unmanned aerial vehicle surveys. Prevailing boundary conditions, especially sediment supply, as well as the porosity and arrangement of the installed sand trapping fences significantly influence the effectiveness of different configurations of sand trapping fences. The dune toe growth is significant immediately after constructing a new sand trapping fence and decreases over time. According to the results presented in this study, for sand trapping fences that have been in place longer, the protruding branch height and the porosity of the remaining branches play a minor role in trapping sand. Sand trapping fences with lower permeability favour localized coastal dune toe growth directly at their brushwood lines, whereas fences with higher porosity allow for more sediment deposition further downwind. The trend in dune toe changes can be roughly predicted by integrating potential sediment transport rates calculated with hourly meteorological data.