Sediment provenance in the Baker-Martínez fjord system (Chile, 48°s) indicated by magnetic susceptibility and inorganic geochemistry

Fjord sediments are increasingly used as high-resolution archives of climate and environmental change, including variations in glacier mass balance and terrestrial hydrology. To accurately interpret such sediment records, it is crucial to comprehend sediment transport processes and determine sediment provenance. With this in mind, our main objective is to identify cost-effective parameters that can be used to reconstruct relative variations in the origin of sediments deposited in the Baker-Martínez fjord system, which is located between the Northern (NPI) and Southern (SPI) Patagonian Icefields. We focus on estimating the proportions of sediment derived from each icefield, taking advantage of the clearly distinct lithologies that underlie NPI (Patagonian Batholith) and SPI (Eastern Andean Metamorphic Complex) glaciers. The magnetic susceptibility and inorganic geochemistry of 21 surface sediment samples collected along the fjord system and that of suspended sediment samples from the four main rivers that discharge at its heads were investigated. Results indicate that sediments derived from the NPI are characterized by higher magnetic susceptibility and log(Ti/Al) values than those from the SPI, reflecting the mafic nature of the batholith. In fjords that receive contributions from both the NPI and SPI, magnetic susceptibility and log(Ti/Al) primarily reflect sediment provenance. In fjords receiving sediment from only one icefield, however, these parameters are positively correlated with grain size and reflect the progressive settling of particles from the surficial plume. Our results suggest that magnetic susceptibility and log(Ti/Al) can be used to reconstruct sediment provenance within the Baker-Martínez fjord system, but that only log(Ti/Al) can provide quantitative estimates of the proportions of sediment derived from each icefield. Ultimately, applying these provenance indicators to long sediment cores from the Baker-Martínez fjord system could allow reconstructing relative variations in sediment input from each icefield, which may in turn be interpreted as changes in river discharge and/or glacier mass balance

Sediment provenance indicated by magnetic susceptibility and inorganic geochemistry in the Baker-Martínez fjord system (Chile, 48°S)

Patagonian fjord sediments are increasingly used as high-resolution archives of past climate and environmental change, including variations in glacier mass balance, flood frequency, and seismic activity. To accurately interpret these proxy records, it is crucial to comprehend modern day sedimentation processes and determine the provenance of the sediments. With this in mind, the main objective of this study is to identify parameters that can be used to reconstruct sediment provenance in the fjords of Chilean Patagonia. We focus on the Baker-Martínez fjord system, which is located between the Northern and Southern Patagonian Icefields and seems particularly sensitive to climate change. This fjord system connects the terrestrial ecosystems of Patagonia with the SE Pacific Ocean, and most of its sediment originates from glacier-fed rivers draining either the Patagonian Batholith (PB; Baker and Huemules rivers) to the north, or the Eastern Andes Metamorphic Complex (EAMC; Bravo and Pascua rivers) to the south. Eighteen surface sediment samples from across the Baker-Martínez fjord system and 44 suspended sediment samples from two sequential (Baker fjord) and one continuous (Steffen fjord) sediment trap were investigated. In addition, we analyzed suspended sediment samples collected at the mouths of the four main rivers that drain the PB and EAMC to define end-members. We focus on mass-specific magnetic susceptibility (MS) and inorganic geochemistry, which seem to be particularly promising in this fjord system dominated by lithogenic sediments (97–85 wt%). Our results indicate that sediments derived from the PB are characterized by high MS, Ti/Al, and Fe/Al values, reflecting the granodioritic nature of the batholith (rich in pyroxene and amphibole). In contrast, sediments from the southern EAMC-derived rivers have significantly lower MS, Ti/Al, and Fe/Al values. The sediment trap results reveal MS values that increase with increasing Baker river discharge, either during the summer melt season, or during high precipitation events (rain-on-snow) in winter. Likewise, the MS, Ti/Al and Fe/Al values of the fjord surface sediments are also directly related to sediment provenance. In fjords fed by only one river (e.g., Martínez channel), however, the MS is significantly correlated with mean grain size (r = 0.90; p < 0.01) and with the proportion of lithogenic particles (r = 0.73; p < 0.05). The latter observation means that future research is needed to correct the MS and geochemical data for grain-size before using them as quantitative provenance indicators. This study suggests that, after grain-size correction, MS and inorganic geochemistry (Ti/Al and Fe/Al) can be used to reconstruct sediment provenance within the Baker-Martínez fjord system. Ultimately, applying these provenance indicators to long sediment cores from the same fjord system will allow us to reconstruct variations in the behavior of outlet glaciers from both icefields independently

Geochemical and sedimentological analysis of the 12.2 m long, radiocarbon-dated JPC42 sediment core from Wide Channel (50°S; Chile).

We performed geochemical and sedimentological analyses on a 12.2 m long, radiocarbon-dated sediment core collected from Wide Channel (50°S; Chile) to reconstruct fluctuations of the marine-terminating HPS19, Penguin and Europa glaciers, located along the western side of the Southern Patagonian Icefield. The JPC42 sediment core was collected with a Jumbo Piston corer onboard the RV/IB Nathaniel B. Palmer in July 2005. An additional 1.5 m long Kasten core (KC41) was retrieved to sample the sediment-water interface. Both cores were scanned on an ITRAX XRF core scanner at WHOI in August 2008 and then sampled in 2 cm thick slices (ca. 10 cm3) every 10 cm at the Marine and Geology Repository of Oregon State University in February 2021. Samples were freeze-dried at Ghent University, and all discrete analyses were performed at a 10 cm interval, except for CaCO3 in the lower 5.9 m of the core, which was analyzed at a 20 cm interval

Geochemical and sedimentological analysis of sediment core JPC42 from Wide Channel, Chile

Organic geochemical and sedimentological data analyzed at a 10 to 20 cm interval on the JPC42 and KC41 cores including total organic carbon content, stable carbon isotopes, marine organic carbon content, calcium carbonate, grain-size mode, and ice-rafted debris (particles >150 µm)

Predicted mean grain size of the JPC42 sediment core from Wide Channel (Chile), calculated following Liu et al. (2019)

Mean grain size predicted at a 2 mm resolution using the XRF intensities of Fe, K, Ti, Rb, Zr and Mn following Liu et al. (2019, doi:10.1029/2018GC008154). A set of 112 samples was used to calibrate the prediction model

Mean ages calculated by the bayesian age-depth model of sediment core JPC42 from Wide Channel, Chile

Age-depth model of the JPC42 sediment core. The core chronology is based on the radiocarbon ages published in Caniupán et al. (2014). All radiocarbon ages were re-calibrated using the SHCal20 calibration curve (Hogg et al., 2020) and a marine reservoir age of 780 yr (Caniupán et al., 2014). The age-depth model and sedimentation rates were calculated using the BACON 2.5.5 software (Blaauw and Christen, 2011) in R (R Core Team, 2020), taking into account the instantaneous deposition of the four turbidites at 1089 – 1049, 551 – 516, 383 – 364, and 171 – 158 cm.. The table contains the mean age of the sediment every 1 mm

XRF core scanner geochemistry, PC1 scores and detrended PC1 scores of sediment core JPC42 from Wide Channel, Chile

Inorganic geochemical data of the JPC42 and KC41 cores obtained by ITRAX XRF core scanning (Cox Analytical Instruments) at the Woods Hole Oceanographic Institution, PC1 scores, and detrended PC1 scores, at a resolution of 2 mm. The XRF scanner was operated with 20 s scan times using a Mo X- Ray tube set to 30 kV and 45 mA. Elemental variations are expressed in terms of centered log-ratios (clr) to avoid dilution effects and to overcome the closed-sum effect and non-negative nature of compositional data (Weltje et al., 2015). The table contains both the raw (cps; counts per second) and processed clr (dimensionless) data. Principal Component Analysis (PCA) was conducted with XLSTAT v2016 and used to examine the covariance within the XRF core scanner data. Intervals with positive PC1 scores are interpreted as periods with higher-than-average terrestrial sediment supply, and vice versa

Postglacial fluctuations of western outlet glaciers of the Southern Patagonian Icefield reconstructed from fjord sediments (Chile, 50°S)

International audiencePostglacial fluctuations of Southern Patagonian Icefield (SPI) glaciers are well constrained on the leeward side of the Andes, but they remain mostly unknown on the windward side of the icefield, where most glaciers are marine-terminating. Here, we reconstruct the postglacial fluctuations of the HPS19, Penguin, and Europa glaciers along the hyperhumid western side of the SPI using a multi-proxy sedimentological and geochemical analysis of a 12.2 m long sediment core from Wide Channel (50°S). Results show that the glaciers retreated into Penguin and Europa fjords by 11.2 cal kyr BP and that they were relatively stable and marine-terminating between 11.2 and 5.8 cal kyr BP. Thereafter, they fluctuated rapidly, with four marked episodes of glacier shrinkage at 5.8–4.8, 3.9–2.4, 1.0–0.2 cal kyr BP, and during the 20th century. Although the HPS19, Penguin, and Europa glaciers were calving into Penguin and Europa fjords during most of the Holocene, our data suggest that they retreated to land-based positions between 5.8 and 4.8 cal kyr BP. The comparison of our sediment record with geological archives from both sides of the Patagonian icefields (46°–56°S) suggests synchronous glacier variability on multi-centennial timescales during the Neoglacial period, which is particularly clear after 2.5 cal kyr BP. We conclude that western SPI outlet glaciers remained relatively stable during the first half of the Holocene but fluctuated considerably during the Neoglacial period, and that they retreated to locations further inland than today during the first retreat of the Neoglacial period between 5.8 and 4.8 cal kyr B