Chasing Patagonian sediment

After travelling more than 13,000 kilometers over the Atlantic and across the Andes, our team from Ghent University has yet again arrived in Coyhaique for another year of chasing Patagonian mud. Coyhaique constitutes the capital of the Aysén region in Chile. This region is home to the largest temperate icefields of the Southern Hemisphere, being the Northern and Southern Patagonian Icefields (map). In case you were wondering, yes, Antarctica is still there, however, this is an ‘icecap’. A difference that is very dear to our colleagues cryologists. These icefields, together with Calluqueo glacier located on Monte San Lorenzo, will be the main focus of our research activities.

Map showing the towns where we will stay (orange) and the areas we will study (yellow).

The two main objectives of this year’s expedition consist of (1) retrieving and redeploying two moorings with sediment traps for the Paleo-GLOFs, HYDROPROX and GLADYS projects and (2) installing a sediment trap and acquiring CTD-profiles in Calluqueo lake for the GLADYS project, to better comprehend how glacial meltwater and sediment is transported and deposited in young proglacial lakes. This year’s team consists of Prof. Sébastien Bertrand and his youngest PhD student, Matthias Troch.

Figure 2: Matthias carefully weighing scrap metal from El Rey del Fierro for the mooring anchors.

The first step of this fieldtrip is the retrieval of two sediment traps deployed in Baker and Steffen fjords exactly one year ago. If all went well over the austral winter, these traps have again collected a year worth of sediment originating from the Baker and Huemules rivers, respectively. The Steffen trap will provide us an indication on how much sediment accumulates in Steffen fjord over one year, which is of invaluable importance for Loïc Piret, who is currently finishing a paper on the interaction between fjord sediments, proglacial lake size and retreating glaciers. The three years of sediment collected in Baker fjord at a 15 day resolution will enable our dear post-doc and senior scientist Benjamin Amann to differentiate seasonal variations in sedimentological tracers of glacial meltwater and rainfall. The original purpose of this sediment trap was to catch sediment transported by a Baker river GLOF to help Elke Vandekerkhove interpret the GLOF records from sediment cores obtained in Baker fjord three years ago (‘Better than manjar!’). Unfortunately for us, these GLOFS ended 3 months before the first deployment of the trap in 2017! Consequently, we decided to redeploy the sequential sediment trap in Steffen fjord, where GLOFs are becoming increasingly important. According to locals, at least one occurs every year in January-February. This year´s GLOF has yet to come …

Figure 3: Driving south along the Carretera Austral with the occasional road works causing “traffic jams”.

The second objective will bring us to the largest glacier, for now, of the Monte San Lorenzo icefield. Here, the receding Calluqueo glacier recently created proglacial ‘Calluqueo lake’. We will investigate how glacier meltwater enters and flows through this lake by taking CTD casts along proximal-distal and transversal transects. In addition, we will deploy a continuous sediment trap in the middle and deepest part of this lake to catch glacial sediment over a period of one year (2020-2021). Inevitably, this trap forces us to come back to this fierce landscape next year. The obtained CTD data and collected sediment will contribute to the GLADYS project which aims to understand how glacier recession is recorded in lake sediments. To serve this purpose, short sediment cores were previously taken from Calluqueo lake (‘Los dos Geolocos meet another Rey’).

Figure 4: Lucho and Matthias moving our equipment to the COPAS Sur-Austral lab in Tortel

Before leaving Coyhaique, we needed to collect dead weight for the mooring anchors. And nothing is better to serve this purpose than scrap metal from El Rey del Fierro. Stories tell this rusty king is on the verge of becoming dead weight himself and passing his iron treasure to the next generation. However, stories are often exaggerations of reality. Indeed, El Rey walks a bit crooked and can barely open both eyes, but he still jumps casually over his metal piles and provides us with his best pieces (Fig. 2). As for now, El Rey del Fierro is alive and kicking! Younger than ever, he says.

After driving 500 km south, with occasional traffic jams (Fig. 3), and navigating across the Baker river delta, we reached our temporary Chilean home in Caleta Tortel. As we are preparing our upcoming fjord ventures from the COPAS Sur-Austral lab (Fig. 4), we carefully follow local weather fluctuations to aim for the right moment to recover our sediment traps… we certainly don’t want to end up like the Invencible (Fig. 5).

Figure 5: The unfortunate Invencible stranded on the Baker river delta.

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