# Recent ice-contact delta formation in front of Pio XI glacier controls sedimentary processes in Eyre Fjord, Patagonia

Loic Piret, Sebastien Bertrand, Carlos Moffat, Peter Feldens, Svenja

Papenmeier, Helge Arz

► To cite this version:

Loic Piret, Sebastien Bertrand, Carlos Moffat, Peter Feldens, Svenja Papenmeier, et al. Recent ice-contact delta formation in front of Pio XI glacier controls sedimentary processes in Eyre Fjord, Patagonia. Earth Surface Processes and Landforms, 2024, pp.1-15. 10.1002/esp.6012. hal-04799627

HAL Id: hal-04799627

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Submitted on 23 Nov 2024

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# Recent ice-contact delta formation in front of Pio XI glacier controls sedimentary processes in Eyre Fjord, Patagonia

Loic Piret<fnref n="1" />,<fnref n="2" />

Sebastien Bertrand<fnref n="1" />,<fnref n="3" /> ID

Carlos Moffat<fnref n="4" />

Peter Feldens<fnref n="5" />

Svenja Papenmeier<fnref n="5" />

Helge Arz<fnref n="5" /> ID

**Correspondence**

Loic Piret, Renard Centre of Marine Geology, Department of Geology, Ghent University, Ghent, Belgium.

Email: lpiret@sas.upenn.edu

**Funding information**

Fonds Wetenschappelijk Onderzoek, Grant/Award Numbers: 1512318N, G0D7916N; Vlaams Instituut voor de Zee, Grant/Award Number: BMRI; Agencia Nacional de Investigación y Desarrollo, Grant/Award Number: FB210021; Bundesministerium für Bildung und Forschung, Grant/Award Number: 03G0296A; Belgian American Educational Foundation, Grant/Award Number: PDF2023

**Abstract**

Pio XI Glacier (49°S) is the largest and one of the very few advancing glaciers in Patagonia. Satellite data indicate that the main glacier terminus transitioned from calving to land-based around 2010, effectively resulting in the formation of an ice-contact delta at the head of Eyre Fjord. Here, we investigate how this ice-contact delta formation affected sediment transport processes in Eyre Fjord. Sediment cores and seismic profiles collected along the fjord provide evidence for a relatively abrupt increase in the number and magnitude of turbidity currents, coeval with the formation of the ice-contact delta. This observation is supported by modern summer hydrographic observations and bathymetric data. We posit that the ice-contact delta formation resulted in sediment input being concentrated at specific subaerial locations across the fjord head, which favoured the development of plume-triggered turbidity currents. This suggests that a sudden increase in turbidite thickness in fjord sediment records could represent ice-contact delta development at fjord heads.

**KEYWORDS**

fjord, grounding-line fan, ice-contact delta, satellite imagery, sediment record, turbidity current

## 1 | INTRODUCTION

The Southern Patagonian Icefield (SPI) is the largest temperate ice mass in the Southern Hemisphere and covers the southernmost Andes between 48°S and 52°S. The glaciers of the SPI have predominantly been retreating since the last neoglacial maximum (Little Ice Age chronozone), with the notable exceptions of a few glaciers such as Pio XI (Chile) and Perito Moreno (Argentina), which continued to advance (Minowa et al., 2015; Rivera, 2018). Pio XI Glacier, the largest glacier in South America, experienced an advance of over 10 km since 1945 (Rivera, 2018; Rivera et al., 1997b). Several reasons have been proposed to explain this anomalous behaviour, including increased precipitation (Rivera et al., 1997b), the influence of sediments on

glacier stability (Hata & Sugiyama, 2021; Warren et al., 1997), surging (Rivera et al., 1997a; Wilson et al., 2016) and a large accumulation area compared to its thin terminus (Carrivick et al., 2024).

Continued high sediment accumulation at the largest of Pio XI Glacier's two termini caused sediment mounds to emerge above sea level at the head of Eyre Fjord at least in 1992 (Warren & Rivera, 1994) and from 2010 onwards (Hata & Sugiyama, 2021; Rivera, 2018). These sediment mounds progressively isolated the glacier from Eyre Fjord, which led to decreased submarine melting and calving (Hata & Sugiyama, 2021). The sediment mounds contributed to ice thickening and ice surface uplift near the terminus (Abdel Jaber et al., 2019; Hata & Sugiyama, 2021; Wilson et al., 2016), and an overall decrease in ice velocity (Hata & Sugiyama, 2021; Mouginot &

This is an open access article under the terms of the [Creative Commons Attribution License](https://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2024 The Author(s). *Earth Surface Processes and Landforms* published by John Wiley & Sons Ltd.

<footnote n="1">¹Renard Centre of Marine Geology, Department of Geology, Ghent University, Ghent, Belgium</footnote>

<footnote n="2">²Penn BiCycles lab, Department of Earth and Environmental Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA</footnote>

<footnote n="3">³GEOPS, Paris-Saclay University, Orsay, France</footnote>

<footnote n="4">⁴School of Marine Science and Policy, University of Delaware, Newark, Delaware, USA</footnote>

<footnote n="5">⁵Marine Geology, Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Rostock, Germany</footnote>
Rignot, 2015; Wilson et al., 2016). The sediment mounds thus influence ice dynamics and may also modify sediment and meltwater delivery mechanisms to the fjord (Brinkerhoff et al., 2017).

Indeed, fjord sedimentation processes are largely controlled by the mechanism supplying sediments, either directly from the glacier or via rivers. In river-fed fjords, sediments typically form a delta where coarse sediments are deposited, while fine-grained sediments flow in a buoyant plume atop the saline oceanic water (Syvitski & Shaw, 1995). Conversely, fjords fed by marine-terminating glaciers predominantly receive sediments directly through subglacial conduits, with coarse sediments deposited near the glacier terminus in grounding-line fans (Powell, 1990) and fine-grained sediments rise in a buoyant plume before being transported oceanward (Hogan et al., 2020). In both types of fjords, fine-grained sediments in the buoyant plume can be transported over long distances (> 10 km) and eventually settle due to decreasing velocity, increased salinity and flocculation (Syvitski, 1991).

In addition to sediment transport in the plume, river-fed fjords also frequently feature turbidity currents with long runout lengths (Bailey et al., 2023; Bianchi et al., 2020; Hizzett et al., 2018). They can be generated through delta slope collapse, hyperpycnal plunging of a river plume or settling of a sediment plume (Hage et al., 2019; Hizzett et al., 2018) and can have an important influence on downstream sediment distribution (Vandekerkhove et al., 2020a) and seafloor morphology (Gales et al., 2019). Although less common in fjords with marine-terminating glaciers (Syvitski, 1989), active turbidity channels have been observed in Greenlandic and Alaskan fjords with marine-terminating glaciers (Batchelor et al., 2018; Pope et al., 2019). Pope et al. (2019) identified several criteria that increase the chances of turbidity currents to occur in fjords with marine-terminating glaciers: large glacier catchment areas (> 100 km²), high ice flux, high meltwater and sedimentation regimes, uninterrupted oceanward slope gradients and stable ice fronts with moraines, grounding-line fans or grounding-zone wedges.

Here, we investigate how the recent transition of Eyre Fjord from a tidewater-glacier fjord to a river-fed fjord influenced the dominant sedimentation processes in the fjord. To do so, we first reconstruct the evolution of the grounding line-fan into an ice-contact delta at the front of Pio XI Glacier using satellite images over the past four decades. We then analyse bathymetric data, seismic profiles, sediment cores and hydrographic observations from Eyre Fjord to decipher the evolution of sedimentation processes in this proglacial environment. Since fjord sediments are regularly used as high-resolution archives of glacier dynamics (e.g., Bertrand et al., 2012, 2017; Bianchi et al., 2020; Howe et al., 2010; Troch et al., 2022), it is important to fully understand how the formation of an ice-contact delta affects fjord sedimentation processes in order to correctly interpret proglacial fjord sediment records.

## 2 | SETTING

Pio XI Glacier is the largest (~1,300 km²) glacier in South America. It has a maximum altitude of 3,470 m and is located on the western side of the SPI (De Angelis, 2014). It is an advancing temperate glacier that overlies the Eastern Andean Metamorphic Complex (Gómez et al., 2019) and receives high amounts of precipitation year-round (4,100 mm yr⁻¹; Boisier et al., 2018).

The glacier surged for three years around 1981 and again between 1997 and 2000, with quiescent interphases of ~14 years (Wilson et al., 2016). Ice velocities during surging phases peak above 15 m d⁻¹ whilst during quiescent phases they are generally below 4 m d⁻¹ (Wilson et al., 2016). Although glacier surges often cause ice thinning in the upper regions of glaciers and thickening near their fronts, Pio XI Glacier has gradually thickened over its entire length since at least 1975 (Abdel Jaber et al., 2019; Foresta et al., 2018; Malz et al., 2018; Minowa et al., 2019; Wilson et al., 2016). Pio XI Glacier is among the most rapidly thickening glaciers in the world, with thickening rates of ~20 m a⁻¹ near the southern terminus between 2000 and 2018 (Hata & Sugiyama, 2021). Below 400 m elevation, Pio XI Glacier bifurcates into two distributaries, the smallest one flowing north into Greve Lake and the largest outlet flowing south into Eyre Fjord (Figure 1A).

Eyre Fjord (49°20'S, 74°05'W) is a ~ 40 km long, N-S oriented fjord in western Patagonia, with a typical width of 4–6 km and a maximum depth of ~600 m (Dowdeswell & Vasquez, 2013; Figure 1a). Swath bathymetry acquired in 2006 reveals a predominantly smooth sea floor, which is attributed to draping by fine-grained material (Dowdeswell & Vasquez, 2013). Numerous along-fjord streamlined ridges produced by past glacier activity protrude through the fine-grained sediment drape (Figure 1a). Falcon Fjord merges with Eyre Fjord 35 km downstream of Eyre Fjord's head. Falcon Fjord is ~400 m deep and exhibits a marked shallowing to ~100 m near its connection with Eyre Fjord (Figure 1a). Both fjords connect to the Pacific Ocean via the Wide Channel.

## 3 | METHODS

### 3.1 | Remote sensing

The geomorphological changes occurring at the tongue of the southern terminus of Pio XI Glacier between February 1976 and January 2023 were studied by analysing 94 Landsat (2, 5, 7, 8 and 9) and 28 Sentinel-2 scenes with a particular focus on the evolution of the crevasses and the appearance and growth of the sediment mounds (Table S1). All images were accessed via the SentinelHub Earth Observation browser. A total of 132 scenes from Landsat 5, 7 and 8, and Sentinel 2 were used to obtain ice front fluctuations between January 1986 and January 2023 (Table S1). The ice fronts were manually delineated on each image using Google Earth Engine Digitisation Tool (GEEDiT) v2 (Lea, 2018). The results were processed using the centreline method in Margin Change Quantification Tool (MaQiT) v1.03 (Lea, 2018).

### 3.2 | Oceanography

A total of 27 CTD casts were taken during a cruise aboard the R/V Sur-Austral in the summer (February) 2019 in Eyre Fjord and one in Falcon Fjord at stations with bottom depths ranging from 57 to 578 m (Figure 1a). We used the resulting hydrographic profiles to identify the water masses and assess the modern sedimentation processes in the fjord. CTD casts were taken along one 47 km long longitudinal transect from the fjord head to its towards Wide Channel,
<figure><img src="image_2.png" /><figcaption>**FIGURE 1** Location of Pio XI Glacier, Eyre Fjord and Falcon Fjord in Chilean Patagonia. (a) Overview map of Eyre Fjord consisting of a false colour composite Landsat-8 image with the evolution of Pio XI Glacier's front and indications of CTD casts, seismic profile, photo position (Figure 3) and sediment core locations on the bathymetric map of Dowdeswell & Vasquez (2013). (b) Evolution of Pio XI Glacier's ice front along the centreline with indication of the average advance rates between 1999 and 2011 and 2011–2022.</figcaption></figure>

as well as along three transverse transects (2.4–3.7 km long) at distances of 2, 25.7 and 38 km from the fjord head (Figure 1a). Pressure (depth), temperature, conductivity (salinity) and turbidity were measured with an RBR Maestro operated at a vertical speed of 0.7 m s⁻¹ with an acquisition rate of 6 Hz. Four water samples were taken with a Niskin bottle at various depths to calibrate the turbidity values. The water samples were stored in 10 L LDPE containers and filtered through 47 mm GF/F filters to obtain suspended sediment concentrations (SSC). Ocean Data View was used to grid and visualize the CTD data in transects along and across the fjord (Schlitzer, 2015).

## 3.3 | Sediment cores

A total of five sediment cores were retrieved in Eyre Fjord (Figure 1a): four during an R/V Sur Austral cruise in 2019 and one during a R/V Sonne cruise in 2023. The four R/V Sur Austral sediment cores were taken along a 35.6 km long longitudinal transect in water depths varying between 82 and 585 m (cores labelled FC19). They were collected with a gravity corer equipped with a 1.5 m long transparent liner and weights of 5–25 kg. Their length varies between 33 and 146.6 cm. The sediment-water interface was clearly sampled in all FC19 cores except for FC19-02 and FC19-03, for which overpenetration is

suspected. Furthermore, gravity core SO296-68-1 GC was collected at 544 m water depth in Eyre Fjord during the SO296 cruise onboard the R/V Sonne. This core is 6.36 m long but was originally longer since an additional ~4 m (at least) of overlying fluid sediment was lost during sectioning. Coring was attempted at additional sites during both cruises but the presence of fluid mud prevented the collection of intact sediment cores.

The internal structures of the FC19 cores were visualized using X-ray computed tomography (CT) scanning performed on a Siemens SOMATOM Definition Flash (Ghent University Hospital) operated at a voltage of 120 kV and a 1 s rotation time. The reconstructed CT volumes were visualized in VGStudio 2.0 and have a resolution of 0.6 mm downcore (in the vertical or z direction) and 0.2 mm acrosscore (in the horizontal x and y directions). A dual threshold of 1,500 to 1,625 HU was applied to the CT volumes of each FC19 sediment core to identify isolated sand and gravel grains to infer the presence of ice-rafted debris. The SO269-68-1 GC core has not been subjected to x-ray CT analysis but digital x-ray images were taken. The cores were subsequently split lengthwise and described immediately after opening with a focus on lithology, colour and sedimentary structures. All cores were scanned on an ITRAX X-ray fluorescence (XRF) core scanner to obtain inorganic geochemical data at a resolution of 2 mm (FC19 cores) or 0.5 mm (SO296 core). The FC19 cores were scanned
at Stockholm University, where the ITRAX was equipped with a molybdenum (Mo) tube operated at 30 kV and 50 mA with an exposure time of 25 s. The SO296-68-1 GC core was scanned at the Leibniz Institute for Baltic Sea Research, where the ITRAX was equipped with a chromium (Cr) tube and operated at 30 kV and 55 mA, with an exposure time of 15 seconds.

The southernmost FC19 core (FC19-07) and the SO296-68-1 GC core were sub-sampled for grain-size analysis. Two-mm thick samples were taken every 1 cm in core FC19-07, and every 10 cm in core SO296-68-1 GC. The samples were suspended in 10 ml of DI water and organic matter, carbonates and biogenic silica were subsequently removed with 2 ml H₂O₂ (35%), 1 ml HCl (10%) and 1 ml NaOH (2 N), respectively. Flocculation of the particles was prevented by adding 1 ml of 2% sodium hexametaphosphate ([NaPO₃]₆) prior to the measurement and through the continuous use of ultrasounds during the measurement. A Malvern Mastersizer 3,000 combined with a HydroMV dispersion unit operating at 2400 rpm was used to measure the grain-size distributions in triplicate for 12 seconds. Gradistat v9.1 (Blott & Pye, 2001) was used to process the resulting data and calculate the geometric mean grain size. The mean grain size of all the FC19 sediment cores was predicted based on the inorganic geochemical data obtained at a resolution of 2 mm following Liu et al. (2019). The prediction model was developed for core FC19-07 using nine elements (Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr) and subsequently applied to the other FC19 cores. Likewise, the mean grain size of sediment core SO296-68-1 GC was predicted every 0.5 mm with the same elements, but with a separate prediction model due to distinct XRF data acquisition parameters.

Gamma spectrometric analysis was performed on the most distal FC19 sediment core (FC19-07) and on SO296-68-1 GC to estimate sedimentation rates. The activity of radionuclides ¹³⁷Cs and ²¹⁰Pb was measured for approximately 24 h in HPGe detectors on seven freeze-dried samples of FC19-07 taken every 22 cm, and on 13 freeze-dried samples of SO296-68-1 GC taken every 10-90 cm.

## 3.4 | Geophysical data

A seismic profile of the sedimentary infill in the southernmost deep basin of Eyre Fjord was acquired during the SO296 scientific cruise in February 2023 (Figure 1a). The 11.3 km long profile was acquired with a hull-mounted Teledyne Atlas PARASOUND P70 system. The system uses two slightly different primary frequencies (18-20 kHz and 22-24 kHz) to generate two secondary frequencies. The data shown in this study was recorded with a resulting low frequency of 4 kHz. The aperture angle was 4.5° and the resulting footprint size was 7% of the water depth. All native PS3 data were converted to SEG-Y format using the ps32sgy software package (Hanno Keil, University of Bremen). Processing (including binning to 3 times the mean distance between individual shots) and display of the profile was performed using a custom Python script. Depth was calculated using a constant sound velocity of 1,500 m s⁻¹. The contrast of the seismic line was enhanced by applying a gamma function included in Scikit-Image (Van der Walt et al., 2014).

Sediment core SO296-68-1 GC was projected onto the seismic profile by correlating sedimentological changes observed in the core with acoustic variations identified in the seismic data, considering a

sound velocity of 1,500 m s⁻¹. The 2006 multibeam echosounder (MBES) data of Dowdeswell & Vasquez (2013) was smoothed and projected on the 2023 seismic profile following the same TWT-to-depth conversion. The depth of the bedrock on the 2006 MBES data matches the bedrock reflectors on the seismic profile, confirming that the projected 2006 seafloor has been projected correctly. Additional multibeam lines were acquired with a Kongsberg EM 122 and Kongsberg EM 710 MBES during the 2023 R/V Sonne cruise to investigate the presence of submarine channels.

# 4 | RESULTS

## 4.1 | Glacier evolution, proglacial geomorphology and structural glaciology

The southern terminus of Pio XI Glacier has experienced significant fluctuations in its position over the past few decades. Pio XI Glacier's southern terminus advanced 2.8 km between December 1984 and January 2023 (Figure 1b). Between December 1984 and July 1999, the glacier advanced 1.8 km after which the ice front retreated drastically by 1.3 km in only 3 months due to intense calving (Table S1). Later, from October 1999 to December 2011, the glacier advanced at an average rate of 0.15 km yr⁻¹. The average rate of glacier advance slowed down to 0.05 km yr⁻¹ between December 2011 and January 2023 (Figure 1b).

The southern terminus of Pio XI Glacier underwent considerable geomorphological and glaciological changes since 1976 (Figure 2; Video S1). Before 2010, the southern terminus was heavily fractured with transverse crevasses and was calving, leading to frequent icebergs at the head of the fjord (Figure 2a). By 2010–2013, small (< 0.03 km²) subaerial sediment mounds emerged at the foot of the glacier terminus (Figure 2b). These mounds grew in area and coalesced over time to form an ice-contact delta (Figure 3). In parallel, the glacier tongue became less heavily fractured, the crevasse pattern changed to splaying crevasses and icebergs were not present at the head of the fjord (Video S1). By 2019, a 200–500 m wide ice-contact delta spanned the full width of the fjord (~5 km; Figures 2c and 3), and it continued to grow until January 2023. By January 2023, a partial collapse of the ice-contact delta occurred (Figure 2d). The western side of the glacier tongue became fractured with transverse crevasses and icebergs were present at the head of the fjord.

## 4.2 | Fjord oceanography

Temperature and salinity in the fjord water column in February 2019 ranged from 5 to 11°C and from 10 to 33.4 (practical salinity units - dimensionless), respectively (Figure 4). The observed hydrographic structure appears influenced by waters of four distinct origins. The deep fjord (i.e., below 20–40 m) is occupied by relatively salty (30–33.4) and warm (~9°C) water. It corresponds to modified Subantarctic water (mSAAW), which enters Eyre Fjord via intermediate fjords from the south (Palma & Silva, 2004; Sievers & Silva, 2008), as has been observed in other proglacial fjords in this region (Moffat et al., 2018).

The surface layer is characterized by two distinct sets of properties. In the top 5 m near the fjord head, and across the entire width of
**FIGURE 2** Evolution of the calving front and ice-contact delta at the southern terminus of Pio XI Glacier at the head of Eyre Fjord. The images represent the situations at the southern terminus of Pio XI glacier before (a), during (b), after (c) the development of the ice-contact delta, and after (d) its partial collapse. Note the appearance and growth of sediment mounds at the front of the glacier and the crevasse style change from longitudinal to splaying. The full evolution from 1976 to 2023, based on 122 satellite images (Table S1), is available as a video in Supplementary Material.

<figure><img src="image_3.png" /></figure>

**FIGURE 3** Photo of the southern terminus of Pio XI Glacier taken on 16 October 2016 (photo credit: Jeff Mauritzen). Note the sediment mounds and sediment plumes at the head of Eyre Fjord.

<figure><img src="image_4.png" /></figure>

the fjord, we found relatively fresh (10–15) and cold (~5°C) water consistent with meltwater originating from Pio XI Glacier (Pio XI melt-water; PMW; Figure 4a,e). A remnant of this water is also observed in a section 25.7 km downstream from the fjord head (Figure 4b), but only on the eastern side, likely due to the influence of earth's rotation on this buoyant outflow. Elsewhere in the fjord, the surface layer is dominated by water with salinities of 20–27.5 and the highest measured temperatures (up to 11°C; Heated Estuarine Water – HEW; Figure 4). This layer thickened away from the head of the fjord,

reaching 26 m at the CTD station farthest from the fjord head (47 km). This surface water is common in this region and is likely the result of the mixing of several sources: precipitation, meltwater, inflow from rivers, with additional modification from heat exchange with the atmosphere (Palma & Silva, 2004; Pickard, 1973).

A final source of hydrographic variability is found near and downstream from the junction between Eyre and Falcon Fjords and within Falcon Fjord (Figure 4). Cold (~6°C) water with salinities of 27–30 was found wedged between the deep mSAAW and the
<figure><img src="image_5.png" /></figure>

**FIGURE 4** Gridded temperature (colour) and salinity (white isolines) transects through the top 100 m of the water column in Eyre and Falcon fjords taken in February 2019. Intersections of transects are indicated at the bottom of the cross-sections with white triangles. Note that part of the D - D' transect overlaps with E - E'. Transect D-D' is partly blank due to a lack of data in the western part of Falcon Fjord. Waters of different origins are indicated with black dotted lines. PMW: Pio XI meltwater; FFBW: brackish water originating from Falcon Fjord; mSAAW: modified Subantarctic water; HEW: heated estuarine water. The diamonds indicate the location of the CTD casts.

surface warm water described above. It is most prominent in Falcon Fjord (Figure 4d), extending ~8 km northwards from the intersection with Eyre Fjord, and continuing oceanward through Eyre Fjord although it appears to become thinner as it is presumably mixed downstream. This kind of cold, subsurface water has been observed near marine-terminating glaciers in this region and is generated as meltwater subducts under lighter ambient water or never reaches the surface after it is generated by ice melting at depth (e.g., Moffat et al., 2018; Pickard, 1973). Here, it is likely associated with meltwater from the glaciers draining in Falcon Fjord (HPS10, HPS12, HPS13 and HPS15).

SSCs in Eyre Fjord in February varied between 0 and 230 mg l⁻¹ but were presumably even higher as the turbidity sensor saturated (Figure 5). SSC was highest at the fjord head throughout the entire water column (Figure 5a). Farther down the fjord, suspended sediments are present near the water surface in a 5 m thick plume that extends 13 km throughout the fjord with SSC values reaching 28 mg l⁻¹ (Figure 5e). However, much higher SSC values were observed near the bottom 50–100 m of the water column with SSC values likely exceeding the 230 mg l⁻¹ sensor saturation value. The mid-fjord transverse transect (Figure 5b) shows that the sediments are concentrated towards the east of the fjord near the seafloor, although sediments are also present at the western side of the fjord in this transect albeit in lower concentrations. The volume of water near

the seafloor with high SSC values is thickest in the deepest part of the fjord where it is > 100 m thick (Figure 5e). The high SSCs do not persist oceanward of this deep basin, from which they are separated by a ~ 110 m sill (Figure 5c). SSCs measured in Falcon Fjord are very low to negligible (Figure 5d).

4.3 | Sediment cores

All sediment cores consist of predominantly blueish-grey mud intercalated with mm to cm-scale brownish-grey sandy laminae. The measured mean grain size of core FC19-07 varies between 5.5 and 73.3 µm, and that of core SO296-68-1 GC ranges from 5.5 to 61.3 µm (Figure 6). The mean grain-size predictions match the measured values remarkably well (FC19-07: r = 0.95, p < 0.00001, n = 132; SO296-68-1 GC: r = 0.93, p < 0.00001, n = 63). The predicted mean grain size of all FC19 cores varies between 4.8 and 85 µm and generally covaries with radiodensity (Figure 6). The most proximal core, FC19-02, contains fine-grained (7–17 µm) sediments in the top 20 cm and bottom 53 cm, and even finer background sediments (6–8 µm) in the middle part of the core, where three coarse-grained layers (up to 55 µm) are intercalated (Figure 6). Core FC19-03 holds the finest sediments with a mean grain size generally between 6 and 9 µm and a few thin (< 1 cm) coarse-grained (< 30 µm)
<figure><img src="image_6.png" /><figcaption>**FIGURE 5** Gridded suspended sediment concentration transects through the water column in Eyre and Falcon fjords taken in February 2019. Intersections of transects are indicated with white triangles at the bottom of the cross-sections. Note that part of the D – D' transect overlaps with E – E'.</figcaption></figure>

layers (Figure 6). The coarsest sediments sampled in Eyre Fjord are present in core FC19-06. They reach mean grain size values of 65–85 µm and are embedded in fine-grained (7–10 µm) background sediments (Figure 6).

The most comprehensive sediment records are contained in the most distal cores (FC19-07 and SO296-68-1 GC; Figure 6). Lithological Units were identified in these sediment cores based on lithological descriptions, grain-size patterns (both cores) and radiodensity variations (FC19-07 only). Due to unclear correlations between these sediment cores, the lithological units are numbered using Roman numerals for FC19-07 (and the other FC19 cores) and numbers for SO269-68-1 GC. Unit 1 in SO296-68-1 GC (637–407 cm) consists of fine-grained mud (8.1 ± 5.0 µm) with intercalations of coarser-grained layers that are relatively thin (up to 19 cm; Figure 6). These intercalated layers are graded (i.e. their grain size decreases from the base to the top) and are interpreted as turbidites. Unit 2 in SO296-68-1 GC (407–108 cm) differs from the lower unit due to the presence of much thicker (up to 65 cm) turbidites (Figure 6). Unit 3 is composed of relatively coarse (53–29 µm) and fining-upward sediments and represents only the bottom part of a more than 5 m thick unit consisting of predominantly fine-grained uncompacted to fluid mud that could not be recovered during core sectioning (Figure 6). Comparatively, Unit I at the bottom of FC19-07 (133–70 cm) consists of homogenous mud (7.8 ± 3.6 µm) without sandy intercalations, although the bottom of the sediment unit

in this core contains coarser sediments (up to 22 µm). Unit II in core FC19-07 (70–0 cm) is composed of fine background sediments (6.9 ± 0.8 µm) with intercalations of 15 mm to 8 cm-thick fining-upward sandy layers with mean grain sizes up to 73.3 µm (Figure 6). The mean grain size at the base of the turbidites in Unit II (up to 73.3 µm) is much higher than the mean grain size at the base of the turbidites in Unit 2 (core SO296-68-1 GC) which varies between 15 and 29 µm (Figure 6). Core-to-core correlations of the FC19 cores could not be made with high confidence but they suggest that all the proximal FC19 cores correspond to the upper unit (Unit II) of core FC19-07.

CT images of the FC19 cores indicate that the cores are internally laminated with the two most proximal cores (FC19-02 and FC19-03) holding the finest laminations. Ice-rafted debris (IRD), recognized as single coarse grains in a fine-grained matrix, was identified in the top 20 cm of the most proximal core (FC19-02) but was virtually absent throughout the other sediment cores, or too fine (< 0.5 mm) to be identified on the CT images.

The concentrations of short-lived radionuclides in cores FC19-07 and SO296-68-1 GC were either below the detection limit ($^{137}$Cs) or too low to accurately establish a core chronology (unsupported $^{210}$Pb, Figures S1 and S2). Similar observations were made in other proglacial fjords with high accumulation rates (1–70 cm yr$^{-1}$), indicating that the glacimarine particles settle too quickly to adsorb significant $^{210}$Pb (Jaeger & Nittrouer, 1999). High accumulation rates are likely also
<figure><img src="image_7.png" /><figcaption>FIGURE 6 Itrax X-ray radiograph of sediment core SO296-68-1 GC and central X-ray CT slice of the four FC19 sediment cores with measured mean grain size (black dots) and predicted mean grain size (red curves). All sediment cores are represented using the same vertical scale. The year of the core collection is indicated next to the core label. Lithological units based on lithological descriptions, grain-size patterns and radiointensity values are indicated. The blue bars represent coarse layers (high radiodensity) and clear undisturbed fining-up patterns are indicated with white arrows.</figcaption></figure>
responsible for the lack of a ¹³⁷Cs peak, either due to negligible scav-
enging of ¹³⁷Cs dissolved in seawater onto the particles or due to the
bottom of the sediment cores being younger than 1964. Therefore,
the radionuclide measurements cannot be used to generate core chro-
nologies but they suggest the presence of high to very high accumula-
tion rates (> 1 cm yr⁻¹).

4.4 | Geophysical data

The seismic profile through the western half of the southernmost basin
of Eyre Fjord, where sediment cores FC19-07 and SO296-68-1 GC
were taken, shows that the fjord sedimentary infill contains two dis-
tinct seismic facies (Figure 7). Seismic Unit A, the lowest unit, consists
of quasi-continuously stratified acoustic facies with parallel reflectors
and a few thin acoustically transparent layers. The unit has a draping
geometry, meaning that it covers the underlying topography with a
constant thickness (Figure 7). Seismic Unit B comprises the top acous-
tic facies of the sedimentary infill and is acoustically mostly transpar-
ent. It is sub-divided into seismic Unit B1, which is chaotic and visible
in the entire basin, and seismic Unit B2, which does not display
any internal chaotic reflectors and only occurs in the deepest,

i.e., southern, part of the basin. The internal reflectors that are present
in seismic Unit B1 are discontinuous and non-parallel to each other or
the seafloor reflector. The lowermost reflectors of this unit cut through
the uppermost reflectors of the underlying unit, meaning that seismic
Unit B1 has an erosive contact with the underlying Unit A (Figure 7).
Its thickness varies between 17 m in the southern part of the profile
and ~7 m in the northern part of the profile (Figure 7). Seismic Unit B2
is located above the seafloor reflector and its upper limit corresponds
to a lutocline, i.e. a strong density gradient at 534 m depth in the water
column. It is acoustically entirely transparent (i.e. without any internal
chaotic reflectors) and has a constant thickness of 25 m. This unit most
likely represents fluid mud (Ross & Mehta, 1989).

Projecting the 2006 multibeam data from Dowdeswell & Vasquez (2013) on the 2023 seismic profile (Figure 7) indicates that the limit between seismic Units A and B is younger than 2006. The latter also suggests that recent sedimentation rates are higher in the deepest part of the basin, compared to where the sediment cores are located (Figure 7). None of the MBES data (2006 and 2023) show the presence of submarine channels but the failure of the 2023 MBES survey to detect a solid seafloor in the southern part of the deep basin where a lutocline was identified on the seismic profile further confirms the presence of fluid mud (Figure 7).

<figure><img src="image_8.png" /></figure>

**FIGURE 7** Seismic profile of the southern basin of Eyre Fjord. The location of the profile is shown in Figure 1 and in the inset. The seafloor depth from the 2006 multibeam bathymetrical survey (Dowdeswell & Vasquez, 2013) is shown as a red dotted line. Core locations are indicated with arrows. Note that coring site FC19-07 is projected onto the profile since it is 200 m to the east of it. Panel b. shows the uninterpreted profile.
## 4.5 | Core-to-seismics correlation

The presence of a clear lithological transition at 108 cm in sediment core SO296-68-1 GC (between lithological Units 3-2) allows its projection on the seismic profile, where it corresponds to the abrupt transition between seismic units A (parallel reflectors) and B1 (transparent unit) (Figure 7). This projection indicates that lithological Unit 3 represents the base of a recent and uncompacted ~9 m thick turbidite (Figures 6 and 7), which likely represents a significant event that occurred recently between the two sampling campaigns. Seismic Unit B2, which represents fluid mud above Seismic Unit B1 in the southern part of the deep basin is likely concomitant, suggesting that Seismic Unit B represents a large magnitude event and that the finest sediment that it transported has yet to fully settle (Figure 7).

# 5 | DISCUSSION

## 5.1 | Ice-contact delta formation

The evolution of the grounding-line fan into an ice-contact delta, i.e., sediment mounds progressively accumulating at the southern terminus of Pio XI Glacier until reaching the surface (Figure 3), has caused profound impacts on the glacier dynamics upstream and sediment transport processes in the fjord downstream (Figure 2).

First, the formation of the ice-contact delta is likely responsible for the deceleration in the advance of Pio XI Glacier from 2011 onwards (Figure 1b) as the fjord-wide sediment mounds formed a pinning point which promoted ice-margin stability (Cowan et al., 2020; Hunter et al., 1996). This is supported by the crevasse pattern transitioning from transverse to splaying crevasses (Figure 2), which reflects a change in the stress regime from longitudinal extension to compression (Colgan et al., 2016; Van der Veen, 1999). The stress regime likely changed as a result of backstress from the sediment mound building up in front of the glacier terminus leading to increased ice-margin stability (Benn et al., 2007). By January 2023, however, the ice-contact delta partially collapsed on the western side of the fjord head leading to extensional stresses on that side of Pio XI Glacier, as evidenced by the newly-formed transverse crevasses (Figure 2d). Analogous glacier-moraine stress regimes and the related emergence of terminal moraines above sea level are not uncommon in tidewater environments. In Alaska, for example, historical advances of Taku and Hubbard glaciers also resulted in the formation of subaerial ice-contact deltas and frontal moraines at sea-level, which in turn decreased ice flow velocity and slowed down the glaciers advance (Motyka & Truffer, 2007; Post & Motyka, 1995). At Hubbard Glacier, the largest temperate tidewater glacier in the world, submarine proglacial sediments were pushed above seawater during a strong spring advance, leading to a decrease in ice flow velocity (Motyka & Truffer, 2007).

Second, the ice-contact delta has limited ice mass loss through calving, as evidenced by a decrease in the amount of icebergs in the fjord (Figure 2b,c). This is similar to observations made in front of Johns Hopkins Glacier (Alaska), where the growth and emergence of an end moraine also resulted in a decline in iceberg concentrations (Kaluzienski et al., 2023).

Third, as the grounding-line fan evolved into an ice-contact delta, the meltwater delivery to the fjord shifted from the bottom of the water column to the top, which likely altered how meltwater and sediments were dispersed throughout the fjord (Brinkerhoff et al., 2017).

## 5.2 | Chronology

Although radionuclides do not allow constructing sediment core chronologies, sedimentation rates can be estimated by comparing the depths of the 2006 MBES reflector to the 2023 seismic profile. In the northern part of the deep basin, near coring site SO296-68-1 GC, the estimated average sedimentation rate of unit A (i.e., without the 2023 turbidite) between 2006 and 2023 is ~25 cm yr⁻¹. Further north in the same basin, the sedimentation rate reaches ~50 cm yr⁻¹ but decreases again near coring site FC19-07, where the sediment packages pinch out. Such high sediment accumulation rates are in line with those found in temperate fjords fed by marine-terminating glaciers in Alaska (Jaeger & Nittrouer, 1999; Powell & Molnia, 1989) and elsewhere in Patagonia (Boldt, 2014). Based on this average accumulation rate, the bottom of sediment core SO296-68-1 GC reaches year 2002, and the transition from lithological Units 1 to 2 corresponds to 2011. Sediment core FC19-07, on the other hand, represents roughly years 2014–2019.

## 5.3 | Sedimentation processes in Eyre Fjord

Eyre Fjord receives sediments predominantly from Pio XI Glacier, as indicated by the high turbidity throughout the water column at the fjord head (Figure 5a). Interestingly, there is virtually no sediment input from Falcon Fjord, likely because sediments either already settle out of a buoyant plume or are trapped up-fjord where the fjord is deeper (Figure 5d).

### 5.3.1 | Recent change in sediment transport processes

Core SO296-68-1 GC is the longest sedimentological record in Eyre Fjord (Figure 6). The oldest lithological unit (Unit 1), deposited before ~2011, is dominated by fine-grained sediments representing settling from the plume intercalated with relatively thin turbidites (Figure 6). Lithological Unit 2, on the other hand, holds much thicker turbidites suggesting that stronger turbidity currents started reaching the deep basin of Eyre Fjord after ~2011 (Figure 6). This trend is further supported by the uncompacted Unit 3, which most likely represents a turbidite linked to the January 2023 partial collapse of the ice contact delta at the head of Eyre Fjord (Figure 2d). Although direct correlations between the two sediment cores in the deep basin cannot be made with high confidence, a similar trend is observed in sediment core FC19-07. The lower lithological unit (Unit I) holds almost exclusively fine-grained sediments, with the exception of the very base of the core (Figure 6). Conversely, the younger lithological Unit II in core FC19-07 contains several coarse-grained turbidites, representing multiple vigorous turbidity currents reaching the deep basin of the fjord. The latter also suggests that Unit II in FC19-07 is coeval with
(part of) Unit 2 in SO296-68-1, although the turbidites and lithological Unit II in general are ~80% thinner at site FC19-07 than at site SO296-68-1. This likely reflects the location of site FC19-07 at the southern end of the basin where the sediment packages may be condensed (Figure 7).

The modern occurrence of strong and frequent turbidity currents originating at the fjord head is supported by the other FC19 cores and direct observations made during both campaigns, which occurred in late summer when meltwater production is the highest. Evidence includes (a) the presence of turbidites in all FC19 cores, independently of location (Figure 6), (b) high turbidity in the bottom 50-100 m of the water column in 2019 (Figure 5), (c) fluid mud in the deep basin in 2023 (Unit B2; Figure 7) and (d) the presence of uncompacted sediment at several locations in 2019 and 2023, as demonstrated by failed coring attempts. Although no chronology can be established for these cores, it is likely that their full sediment records are contained within Unit II as sedimentation rates are usually higher near the fjord head (e.g., Cowan et al., 1999; Piret et al., 2021).

Together, the seismic profile and the sediment cores suggest that a change from plume-dominated to turbidity-dominated sedimentation occurred in 2010-2015. This shift in the dominant fjord sedimentological processes is not coeval with a surging phase of Pio XI Glacier (Wilson et al., 2016), nor with any strong climatological change over the watershed (Hata & Sugiyama, 2021). However, it appears coeval with the transition from a grounding-line fan to an ice-contact delta at the fjord head (from 2010 onwards). The formation of the ice-contact delta at the glacier terminus is therefore considered to drive the changes in the dominant sedimentological processes in the fjord (Figure 8).

<figure><img src="image_9.png" /><figcaption>**FIGURE 8** Evolution of a proglacial fjord head from a grounding-line fan to an ice-contact delta and its influence on the sedimentation processes in the fjord.</figcaption></figure>

Before the ice-contact delta formation, meltwater and sediments entered the fjord at the bottom of the water column from a subglacial conduit of Pio XI Glacier, which was prior to 2010 still marine-terminating (Figure 8a). As the coarse fraction (coarser than medium sand) was deposited near the terminus in a grounding-line fan (cf. Powell, 1981, 1990; Trusel et al., 2010), the fine silt and clays were transported in an overflow plume through Eyre Fjord. Therefore, prior to the formation of the ice-contact delta, sediments were dispersed distally through the fjord mostly by means of near-surface buoyant plumes from which sediments settled out (Figure 8a). The general lack of large-scale turbidity currents in Eyre Fjord during the deposition of lithological Units 1 and I is in agreement with observations from other fjords with relatively small grounding-line fans where gravity flows remained confined to the proximal area (Kehrl et al., 2011).

As the aggradation of the grounding line fan progressed, sediments entered the fjord at the top of the water column (Figure 8b). Ultimately, sediments were transported to the fjord via short subaerial rivers on the ice-contact delta which concentrated sediment input at specific fjord head locations. Such a setting allows for the formation of large-scale turbidity currents as observed in lithological Unit 2 and II of cores SO296-68-1 GC and FC19-07 respectively, as well as in the other FC19 sediment cores (Figure 6). Turbidity currents inferred to have formed at the head of Eyre Fjord could indeed reach the sites of FC19-07 and SO296-68-1 GC, which are located 26-35 km from the fjord head, as there is a possible pathway with a continuous oceanward seafloor slope (Figure 1a). However, only the uppermost sediments of the turbidity currents can reach site SO296-68-1 GC since it is located slightly higher (~30 m) than the deepest part of the southern basin of Eyre Fjord and because there is a ridge north of this coring site (Figure 1). This latter is possibly also reflected in the grain size of the bases of the turbidites which are coarser in the lower-lying FC19-07 core than in SO296-68-1 GC (Figure 6).

### 5.3.2 | Turbidity current dynamics in Eyre Fjord

Several triggering mechanisms could be responsible for the turbidity currents in Eyre Fjord: hyperpycnal plunging at the river mouth, delta slope collapse or settling from a sediment plume near the river mouth (Hage et al., 2019; Hizzett et al., 2018). A partial collapse of the growing delta or grounding-line fan is the most likely trigger for the infrequent turbidity currents that occurred prior to ~2011, i.e. before the full development of the ice-contact delta, as the growth of the ice-contact delta by sediment accumulation and pressure exerted by the advance of the southern terminus of Pio XI glacier could have led to local oversteepening favouring the triggering of turbidity currents (Clare et al., 2016). However, these turbidity currents were likely relatively weak since lithological Unit 1 in core SO296-68-1 GC only holds thin turbidites and lithological Unit I in core FC19-07 lacks turbidites altogether. The turbidity currents that occurred from 2010 to 2015 onwards likely had a different triggering mechanism since they are recorded as thicker and coarser turbidites in lithological Unit 2 of core SO296-68-1 GC and are present in lithological Unit I of core FC19-07. The direct plunging of meltwater entering the fjord is a possible triggering mechanism since the meltwater of Pio XI Glacier contains high suspended sediment loads (Hizzett et al., 2018). However, given the
> 30 km runout length of these turbidity currents, the most likely mechanism is the settling of a cold surficial sediment plume, near the river mouth (Hage et al., 2019; Parsons et al., 2001; Vandekerkhove et al., 2020a). Such plume-triggered turbidity currents are known to maintain turbulence longer than other turbidity currents as they are more dilute and thus run out farther down the fjord (Hizzett et al., 2018). Although such long runout turbidity currents are generally favoured by the presence of submarine channels, no channel was observed on the 2006 and 2023 MBES data, suggesting that these long runout turbidity currents started occurring recently. Lastly, the coarse sediments in Unit 3 of core SO269-68-1 GC likely represent the 2023 partial collapse of the ice-contact delta (Figure 2d).

The dynamics of turbidity currents formed at the head of Eyre Fjord are influenced by open fjord currents and the complex fjord bathymetry. For instance, part of the sediment that remains in suspension near the bottom of the fjord after the turbidity current wanes is likely carried back north (towards the fjord head) with the mSAAW and advected to the western side of the fjord, where coring site SO296-68-1 GC is located, possibly due to the Coriolis effect (Figure 5b). At the head of the fjord, grain size variations in the most proximal core (FC19-02) suggest that the main outlet of meltwater and sediments from the delta switched between the eastern and western sides of the fjord. Such switches can be accompanied by the release of icebergs as evidenced by the presence of IRD in the top of core FC19-02 (Figure 6). Furthermore, protruding ridges on the seafloor can either (1) shelter coring sites from turbidity currents, leading to finer sediments at those sites (e.g. FC19-03), or (2) concentrate turbidity currents leading to coarser turbidites (e.g. FC19-06; Figures 5b and 6). Together, this suggests that the circulation of meltwater and sediment within Eyre Fjord can be complex.

## 5.4 | Impact of ice-contact delta formation on fjord sedimentation

The increase in the number and magnitude of turbidity events with long runout lengths in Eyre Fjord appears to be driven by the presence of an ice-contact delta. Recent literature suggests that the presence of turbidity currents in proglacial fjords with marine-terminating glaciers is dependent on a series of conditions: a large catchment area, high ice and meltwater flux, a presence of a grounding-line fan and an uninterrupted oceanward sloping seafloor (Pope et al., 2019). Although all these conditions were already met in the Pio XI Glacier - Eyre Fjord system prior to 2011, the largest turbidites only started occurring in 2010-2015. The apparent synchronicity between the onset of large turbidites and the grounding-line fan turning into an ice-contact delta suggests that the two processes are related. Although large turbidity currents prior to 2010-2015 could have followed a different pathway, away from coring sites FC19-07 and SO296-68-1 GC, this explanation is not supported by the seismic data. Therefore, we suggest that the presence of a subaerial delta provides an environment more prone to the occurrence of large turbidity currents with long runout lengths. We posit that this is because sediments entering the fjord are concentrated by the rivers on a subaerial ice-contact delta so that the sediment concentration threshold to trigger turbidity currents is surpassed. In other words, turbidity currents are more likely to occur and to be more vigorous when a subaerial

ice-contact delta has formed. Indeed, turbidity currents occur frequently in other glacier-fed fjords with a delta at the head in Patagonia (Vandekerkhove et al., 2020a), Canada (Bailey et al., 2023; Normandeau et al., 2019) and Greenland (Storms et al., 2012).

The increase in magnitude of turbidity currents associated with the transformation of a grounding-line fan into an ice-contact delta also has implications for the use of fjord sediment records as paleoenvironmental archives. Fjord sediment records are often interpreted in terms of glacier dynamics, which are in turn used to reconstruct glacier evolution (Bertrand et al., 2012; Bianchi et al., 2020; Howe et al., 2010). Sediment grain-size has for instance been inferred to represent the distance from the coring site to the ice front (Bertrand et al., 2012) or has been related to the vigour of meltwater discharge (Bertrand et al., 2017; Cowan et al., 1999; Piret et al., 2021; Troch et al., 2023). More specifically, turbidites in fjord sediment records have been associated with, amongst others, precipitation-related floods, glacial lake outburst floods, rain-on-snow events and seismic activity (Liu et al., 2021; Piret et al., 2018; St-Onge et al., 2004; Vandekerkhove et al., 2020a; Vandekerkhove et al., 2020b; Wils et al., 2018). Here, we show that sediment grain-size in proximal fjord sediment records, and specifically turbidites, may also reflect the geomorphological evolution of the fjord head and that grain-size variations do not necessarily represent changes in ice-front position or climate, at least on short (decadal to centennial) timescales.

# 6 | CONCLUSIONS

An ice-contact delta appeared at the southern terminus of Pio XI Glacier during the last decade through the aggradation of sediments on the grounding-line fan. This geomorphic feature exerted backstress on the glacier, which slowed down the advance of the Pio XI Glacier and shifted the meltwater and sediment delivery from the bottom to the top of the water column. Sediment cores from Eyre Fjord suggest a concomitant shift in the dominant fjord sedimentation process. Prior to the formation of the ice-contact delta, sediments were mostly deposited by settling out from a buoyant plume and only weak turbidity currents occurred. When the grounding-line fan grew sufficiently large and later on developed into an ice-contact delta (i.e., sediments at the grounding line accumulated above the sea surface), turbidity currents became more frequent and intense and increasingly reached the distal part of Eyre Fjord. The latter were most likely triggered by the settling of a surficial plume. Although a buoyant sediment-laden plume was still present when the ice-contact delta had developed, it had a lower role in supplying sediments to the distal part of the fjord. The increase in the number and magnitude of turbidity currents in 2010-2015 is attributed to the formation of the ice-contact delta, as this concentrates the sediments above the threshold for plume-triggered turbidity currents with long runout lengths to occur. Furthermore, a relatively large partial collapse of the ice-contact delta at the head of Eyre Fjord in 2023 led to a thick distal turbidite. Our results therefore show that a significant change in a proglacial sediment record may reflect a relatively small-scale change at the fjord head. The increase in thickness and grain size of turbidites in fjord sediment records could therefore indicate the development of an ice-contact delta at the fjord head provided that such an interpretation can be supported by possible turbidity current pathways.
## AUTHOR CONTRIBUTIONS

(a) Conceptualization by LP, SB, CM; (b) funding acquisition by LP, SB, CM, HA; (c) methodology by LP, SB, CM, PF, SP, HA; (d) investigation by LP, SB, CM, PF, SP, HA; (e) resources (provision of data etc) by LP, SB, CM, HA; (f) software by LP, PF; (g) supervision by SB; (h) writing – initial draft by LP; and (i) writing – reviewing and editing by LP, SB, CM, PF, SP, HA.

## ACKNOWLEDGEMENTS

This study was financed by FWO research grant 1512318N "GLADYS" and FWO research project G0D7916N "PaleoGLOFs" to S. B and by a VLIZ BMRI research grant to L.P. C.M. received support from the COPAS Coastal (ANID FB210021) program and H.W.A., P.F. and S.P. were partly funded by the BMBF research grant 03G0296A. LP was supported by a Fellowship of the Belgian American Educational Foundation. We are grateful to the captains and crews of the R/V Sur Austral and R/V Sonne for the successful cruises. Benjamin Amann is thanked for his help in collecting the FC19 sediment cores and CTD casts. Anita Abarzua (Universidad Austral de Chile) is thanked for providing the gravity corer. Romina San Martin (University of Concepción, Chile) and the staff of CIEP (Centro de Investigación en Ecosistemas de la Patagonia, Coyhaique, Chile) helped with the field logistics. Malin Kylander (Stockholm University, Sweden) and Olivier Evrard (LSCE, France) are acknowledged for their help in running the sediment cores on the ITRAX core scanner and for conducting the radionuclide measurements on the Sonne sediment core, respectively. We are grateful to the Hydrographic and Oceanographic Service of the Chilean Navy (SHOA) for providing the 2006 bathymetric data. Lastly, we acknowledge the insightful comments and constructive suggestions provided by the two anonymous reviewers, which have significantly improved the clarity of this manuscript.

## CONFLICT OF INTEREST STATEMENT

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## DATA AVAILABILITY STATEMENT

The data used for the research described in this article are permanently available on Zenodo under DOI 10.5281/zenodo.13823805.

## ORCID

Sebastien Bertrand https://orcid.org/0000-0003-0374-4040

Helge Arz https://orcid.org/0000-0002-1997-1718

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## SUPPORTING INFORMATION

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**How to cite this article:** Piret, L., Bertrand, S., Moffat, C., Feldens, P., Papenmeier, S. & Arz, H. (2024) Recent ice-contact delta formation in front of Pio XI glacier controls sedimentary processes in Eyre Fjord, Patagonia. *Earth Surface Processes and Landforms*, 1–15. Available from: https://doi.org/10.1002/esp.6012