Grain-size, morphometry and sediment transport in an Antarctic stream located close to the Spanish Antarctic Base ‘Juan Carlos I’ (Livingston Island, South Shetland Archipelago).

In this work, we present preliminary data on grain size, morphometry, and sediment transport for the lower sector of a stream located in the South Bay of the Hurd Peninsula (Livingston Island, South Shetland Archipelago). This stream flows close to the Spanish Antarctic Base ‘Juan Carlos I’ (BJCI) and has a length of roughly 300 m, representing a small proglacial channel draining the front of the Hurd Glacier. 
To characterize channel morphometry, we based on high-resolution topographic measures collected in the field with a dGPS (Trimble-R8S) and a 4-cm resolution photogrammetric DEM, built using aerial images taken with a drone. These data, together with field observations, allowed us to define three different sectors along the longitudinal profile of the studied stream. The most upstream sector flows through a raised beach, where the channel shows a typical braided morphology with a gentle slope (0.6º). The channel evolves downstream into a steeper (average slope 4º) and straight single-thread channel, which is incised through a series of successive raised beachs. The channel finally ends and flows into a small coastal lagoon, where it deposits its load and generates a fan-shaped sediment lobe. The lagoon is formed by the damming effect of the upper bar of the modern cobble beach.
We also sampled for grain-size characterization in four different sections: 1) a braided reach, located in the upstream sector of the channel: we observed there a highly heterometric and matrix-supported deposit, likely suggesting the influence of debris and/or hyperconcentrated flows; 2) a single-thread reach, incised into the beach terraces located in the middle sector of the channel: there, we documented a coarse, paved and clast-supported deposit that we interpreted as a basal lag; 3) the upper sector of the fan-shape lobe deposit in the coastal lagoon: we observe a coarse, but heterometric grain-size distribution typical of bedload transport; and 4) the lower sector of the fan-shape deposit: we reported a sand-rich grain-size distribution, typical of fluvial sediment transport. The observed downstream trends in grain size suggests a change in the rheology of the flow during the dominant channel-forming floods from hyperconcentrated to stream flows.
Moreover, we have launched a monitoring study of sediment transport processes in this stream. To do so, we seeded 50 PIT-tagged stones (tracers) for RFID tracking along two different cross-sections located in the single-threaded, middle sector of the studied channel. The tagged cobbles were collected from the riverbed, drilled and sealed with resin, after inserting PIT-tags into them. All these tasks were carried out at the BJCI facilities during the 2018-19 Antarctic campaign, and we are planning to return there in the 2022-23 campaign in order to track and document the tracer displacements.