|Fjord sedimentary signature of an advancing glacier: Final Report: Brilliant Marine Research Idea 2019|
Piret, L. (2020). Fjord sedimentary signature of an advancing glacier: Final Report: Brilliant Marine Research Idea 2019. Ghent University: Gent. 5 pp.
Proglacial sediments hold accurate, continuous, and high-resolution records of past glacier dynamics. In this study, we examine the sediments of Eyre Fjord (Fig. 1; 49°S), which is fed by the only glacier that is currently advancing in Chilean Patagonia (Pio XI), to gain a better understanding of how the advance of a surging glacier is recorded in marine sediments. An existing bathymetric map demonstrates that the fjord reaches depths between 400 and 600 m below sea level (1). Pio XI Glacier has experienced a net advance of >10 km since 1945 and its unique behaviour has been studied extensively by glaciologists (e.g., 2, 3). It has had several surging phases that last 2-3 years and occur every ~14 years. To achieve our goal, CTD casts were acquired along a 50-km long proximal-to-distal longitudinal transect and along three transverse transects in order to better understand the sediment pathways. Nine sediment cores were collected along a longitudinal transect from the glacier’s front outwards (Fig. 1). The sediment cores were X-ray CT scanned, scanned on a Geotek Multi Sensor Core Logger (MSCL) for sediment physical properties and analyzed with an Itrax XRF core scanner to obtain downcore elemental profiles. Gamma spectrometric analysis was used to assess the sedimentation rates in the fjord. From the CTD profiles we conclude that the main form of sediment transfer through the fjord during summer is by means of turbidity currents that form subaqueous, 20–100 m thick, sediment plumes. The sedimentation rates in the fjord exceed 2.5 cm/a. All the sediment cores consist mainly of fine glacial mud, sometimes intercalated with cm-scale thick sandy layers. Distally (>35 km away from the glacial front), the sediments are moderately bioturbated by bristle worms and XRF data (Br counts, ratio of incoherent-to-coherent X-ray scattering) indicates the highest level of marine organic matter in the fjord. The sediment cores in the proximal part (<35 km away from the glacier front) are well laminated. The XRF, CT and MSCL data all indicate the presence of sandy layers in the upper part of the sediment records. These show that the glacier has experienced enhanced hydrological activity, which could be linked to a new surging phase of the glacier.