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Two-thirds of all glaciers worldwide are projected to disappear by 2100 CE. Large uncertainties however remain in maritime settings, where some glaciers have recently gained mass in response to increased snowfall. One of these regions is southern Patagonia, where increased precipitation since the 1980s seems to have attenuated glacier retreat. Whether this exceptional behavior will continue in a warmer future is unclear. Here, we use a numerical ice-flow model constrained by paleoglaciological data to simulate how climate variability influenced the evolution of three maritime outlet glaciers of the Southern Patagonian Icefield during the last 6000 years. Our experiments suggest that precipitation drove 67% of the centennial-scale fluctuations in the volume of the modeled glaciers. When applied to the temperature projected by 2100 CE, our simulations show that precipitation needs to increase by 10–50% to maintain present-day glacier volumes, depending on the climate scenario (SSP1-2.6 to SSP5-8.5). This implies that if greenhouse-gas emission cuts fail, these glaciers will enter a warmer regime unseen over the last 6000 years, where precipitation cannot offset glacier mass loss. Conversely, if emissions are curtailed, increased precipitation could halt mass loss of some of Patagonia's largest glaciers, and potentially of other maritime glaciers worldwide. [ABSTRACT FROM AUTHOR]

Proglacial lakes are effective sediment traps but their impact on the reliability of downstream sediment records to reconstruct glacier variability remains unclear. Here, we investigate the sedimentary signature of the recent recession of Steffen Glacier (Chilean Patagonia, 47°S) in downstream fjord sediments, with a focus on identifying the trapping (decreased downstream sediment yield) and filtering (removal of coarse particles) effectiveness of a growing intermediate proglacial lake. Four sediment cores were collected along a 14 km longitudinal transect in Steffen Fjord and the sediment physical and chemical properties were compared with aerial imagery at high temporal resolution. The caesium‐137 (137Cs) chronology of the most distal core and sediment trap data suggest that sediment accumulation in the fjord remained relatively stable through time, despite the accelerating glacier recession and the growth of Steffen proglacial lake. This is in contrast with many studies that indicate a decrease in sediment yield during proglacial lake expansion. It implies that the increase in sediment export due to accelerating meltwater production may be balanced by the sediment trapping effect of the growing proglacial lake. The fjord sediments show a slight fining upward accompanied by a marked decrease in flood‐induced grain‐size peaks, most likely due to the increasing filtering and dampening effect of the expanding proglacial lake. Our findings show that the filtering effect of the proglacial lake reached a threshold in 1985, when the lake attained an area of 2.02 km2. The additional 5 km of glacier recession during the following 32 years did not have any significant impact on downstream sedimentation. This study confirms that proglacial lakes act as sediment traps but it indicates that (1) the trapping effect can be outpaced by accelerating glacier recession and (2) the filtering effect becomes stable once the lake attains a certain critical size. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Glaciated environments have been highlighted as important sources of bioavailable nutrients, with inputs of glacial meltwater potentially influencing productivity in downstream ecosystems. However, it is currently unclear how riverine nutrient concentrations vary across a spectrum of glacial cover, making it challenging to accurately predict how terrestrial fluxes will change with continued glacial retreat. Using 40 rivers in Chilean Patagonia as a unique natural laboratory, we investigate how glacial cover affects riverine Si and Fe concentrations, and infer how exports of these bioessential nutrients may change in the future. Dissolved Si (as silicic acid) and soluble Fe (<0.02 μm) concentrations were relatively low in glacier‐fed rivers, whereas concentrations of colloidal‐nanoparticulate (0.02–0.45 μm) Si and Fe increased significantly as a function of glacial cover. These colloidal‐nanoparticulate phases were predominately composed of aluminosilicates and Fe‐oxyhydroxides, highlighting the need for size‐fractionated analyses and further research to quantify the lability of colloidal‐nanoparticulate species. We also demonstrate the importance of reactive particulate (>0.45 μm) phases of both Si and Fe, which are not typically accounted for in terrestrial nutrient budgets but can dominate riverine exports. Dissolved Si and soluble Fe yield estimates showed no trend with glacial cover, suggesting no significant change in total exports with continued glacial retreat. However, yields of colloidal‐nanoparticulate and reactive sediment‐bound Si and Fe were an order of magnitude greater in highly glaciated catchments and showed significant positive correlations with glacial cover. As such, regional‐scale exports of these phases are likely to decrease as glacial cover disappears across Chilean Patagonia, with potential implications for downstream ecosystems. Key Points: Si and Fe concentrations from 40 rivers in Chilean Patagonia reveal the impact of glacial cover on terrestrial nutrient cyclingColloidal and reactive particulate phases of Si and Fe are elevated in glacier‐fed rivers and dominate export budgetsRiverine exports of Si and Fe are likely to significantly change with continued glacial retreat, which may impact productivity in downstream ecosystems [ABSTRACT FROM AUTHOR]

Most outlet glaciers of the Cordillera Darwin Icefield (CDI; Patagonia, 54°S) are currently transitioning from calving to land-based conditions. Whether this situation is unique to the modern climate or also occurred during the Holocene is entirely unknown. Here, we investigate the Holocene fluctuations of outlet glaciers from the northern flank of the CDI using a multi-proxy sedimentological and geochemical analysis of a 13.5 m long sediment core from Almirantazgo fjord. Our results demonstrate that sedimentation in Almirantazgo fjord started prior to 14,300 cal yr BP, with glacier-proximal deposits occurring until 13,500 cal yr BP. After 12,300 cal yr BP, most glaciers had retreated to land-locked locations and by 9800 cal yr BP, Almirantazgo fjord was a predominantly marine fjord environment with oceanographic conditions resembling the present-day setting. Our sediment record shows that during the first part of the Holocene, CDI glaciers were almost entirely land-based, with a possible re-advance at 7300–5700 cal yr BP. This is in clear contrast with the Neoglaciation, during which CDI glaciers rapidly re-advanced and shrank back several times, mostly in phase with the eastern outlet glaciers of the Southern Patagonian Icefield (SPI). Two significant meltwater events, indicative of rapid glacier retreat, were identified at 3250–2700 and 2000–1200 cal yr BP, based on an increase in grain-size mode and related inorganic geochemical parameters. This interpretation is additionally supported by concomitant decreases in organic carbon of marine origin and in Cl counts (salinity), reflecting higher terrestrial input to the fjord and freshening of the fjord waters. Overall, our record suggests that CDI outlet glaciers advanced in phase with eastern SPI glaciers during the Neoglaciation, and retreated far enough into their valleys twice to form large outwash plains. Our results also highlight the potential of fjord sediments to reconstruct glacier variability at high resolution on multi-millennial timescales. [ABSTRACT FROM AUTHOR]

Postglacial 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 BP. • SPI outlet glaciers retreated into Penguin and Europa fjords by 11.2 cal kyr BP. • Glaciers were relatively stable between 11.2 and 5.8 cal kyr BP. • High glacier variability during the last 5.8 kyr. • Glacier shrinkage occurred at 5.8–4.8, 3.9–2.4, 1.0–0.2 cal kyr BP, and during the 20th century. • Glaciers on both sides of the Patagonian Andes fluctuated synchronously on multi-centennial timescales during the last 5.8 kyr. [ABSTRACT FROM AUTHOR]

Basal ages obtained from proglacial lake sediments are often used to constrain deglaciation histories, based on the assumption that fine-grained stratigraphic records start forming immediately after glacier retreat. Here, we test this assumption by studying the onset of sedimentation in Calluqueo Lake, Chilean Patagonia, which progressively deglaciated between the 1940s and the end of the 20th century. Although the glacier-proximal basin has been ice-free for at least three decades, it does not yet contain a fine-grained stratigraphic record, despite the modern sedimentation rate of ∼3 cm yr−1. By comparison, the distal basin contains a fine-grained stratigraphic record starting in 1997 ± 2 CE, i.e., 20–50 years after it was deglaciated. Based on these results, we show that several decades are required for ∼1 m of fine-grained sediments to accumulate between the coarse till material and sufficiently smoothen the uneven lake floor to start forming a fine-grained stratigraphic record. Although the exact timing depends on lake floor morphology and sediment accumulation rates, our results suggest that proglacial lake sediment records lack the first decades of sedimentation. This delay is mostly negligible when using radiocarbon ages from basal sediments to date glacier retreat since it falls within the range of radiocarbon uncertainties, though its importance increases throughout the Holocene. It is however significant for chronologies entirely based on varve-counting. Therefore, our results support the use of basal ages to establish deglaciation chronologies but they call for attention when using them to reconstruct Holocene ice retreat, especially with varve chronologies. • First evidence of a delay between deglaciation and fine-grained stratigraphic record. • The fine-grained stratigraphic record starts 20–50 years after deglaciation. • Basal ages lag deglaciation by several decades. [ABSTRACT FROM AUTHOR]

Gualas Glacier is an outlet glacier of the Northern Patagonian Icefield, one of the largest temperate ice bodies on Earth. Golfo Elefantes, the depositional basin of Gualas Glacier, has a sedimentary record that spans, with some hiatuses, at least the last ~11.3±3.0 ka. During this period the gulf remained free of ice, as suggested by the absence of proximal glacimarine sediment and till in the sedimentary section. This implies that the arcuate terminal moraines that occur along the edges of Golfo Elefantes were formed during the waning stages of the local glacial maxima (Late Pleistocene) or the early Holocene. Between ~11.3±3.0 ka and ~4.2±0.3–1.4 ka, the basin received low sediment input consisting of fine-grained sediments in the form of low concentration density currents that filled bathymetric lows. Sediment discharge increased several times in the late Holocene (~<1.4 ka) and started with the accumulation of ~ 0.5 km3 of sandy sediments in a relatively short time span (~670 yr). This high discharge of sandy sediments is interpreted as being the result of glacial reworking of sediments stored in Gualas Glacier proglacial lake and thus implies that the glacier advanced at ~1.4–0.8 ka. The overall increase in sediment discharge in the late Holocene indicates a sharp increase in centennial timescale precipitation, which in turn suggests an increase in the intensity of the westerly winds in the area. Two recent periods of interannual sedimentation variability were identified at ~ad 1160–1460 and ~ad 1680–1890 and correlate with documented regional glacier advances. [ABSTRACT FROM PUBLISHER]

Our understanding of glacial isostatic rebound across Patagonia is highly limited, despite its importance to constrain past ice volume estimates and better comprehend relative sea-level variations. With this in mind, our research objective is to reconstruct the magnitude and rate of Late Glacial and Holocene glacial isostatic adjustment near the center of the former Patagonian Ice Sheet. We focus on Larenas Bay (48°S; 1.26 km2), which is connected to Baker Channel through a shallow (7.4 m) and narrow (ca. 150 m across) inlet, and hence has the potential to record periods of basin isolation and marine ingression. The paleoenvironmental evolution of the bay was investigated through a sedimentological analysis of a 9.2 m long radiocarbon-dated sediment core covering the last 16.8 kyr. Salinity indicators, including diatom paleoecology, alkenone concentrations and CaCO 3 content, were used to reconstruct the bay's connectivity to the fjord. Results indicate that Larenas Bay was a marine environment before 16.5 cal kyr BP and after 9.1 cal kyr BP, but that it was disconnected from Baker Channel in-between. We infer that the postglacial rebound started before 16.5 cal kyr BP and that it outpaced global sea-level rise until slightly before 9.1 cal kyr BP. During the Late Glacial and early Holocene, the center of the former Patagonian Ice Sheet experienced an absolute uplift of ca. 96 m, at an average rate of 1.3 cm/yr. During the remainder of the Holocene, glacial isostatic adjustment continued (ca. 20 m), but at a slower average pace of 0.2 cm/yr. Comparisons between multi-millennial variations in the salinity indicators and existing records of global sea-level rise suggest that the glacial isostatic adjustment rate also fluctuated within these time intervals, likely in response to glacier dynamics. More specifically, most of the glacial isostatic adjustment registered between 16.5 – 9.1 cal kyr BP seems to have occurred before meltwater pulse 1A (14.5 – 14.0 kyr BP). Likewise, it appears that the highest glacial isostatic rebound rates of the last 9.1 kyr occurred during the late Holocene, most likely in response to glacier recession from their Neoglacial maxima. This implies a relatively rapid response of the local solid earth to ice unloading, which agrees with independent modelling studies investigating contemporary uplift. We conclude that the center of the former Patagonian Ice Sheet experienced a glacial isostatic adjustment of ca. 116 m over the last 16.5 kyr, and that >80% occurred during the Late Glacial and early Holocene. • 116 m uplift near the center of the former Patagonian Ice Sheet during the last 16.5 kyr. • At least 80% of the uplift occurred during the Late Glacial and early Holocene. • The average uplift rate was 1.3 cm/yr between 16.5 – 9.1 cal kyr BP. • The average uplift rate was 0.2 cm/yr during the last 9.1 kyr. [ABSTRACT FROM AUTHOR]

The ability to trace and quantify sediment provenance in northwestern Patagonia is increasingly needed to properly understand modern sediment erosion and transport processes in this rapidly changing environment, and to accurately interpret sediment records from adjacent basins in terms of climate and environmental change. Nonetheless, no study so far has systematically evaluated the effectiveness of different tracers to reconstruct sediment provenance in this region. To fill this gap, we assess the effectiveness of commonly-used provenance indicators, including bulk mineralogy, major and rare earth element (REE) geochemistry, and Sr and Nd isotopes, to reconstruct sediment provenance in northwestern Patagonia. First, the ability of these tracers to discriminate between the main sources of sediment in the region is investigated, mostly using data compiled from the literature. Then, the potential of these tracers for provenance reconstruction is assessed by comparing the composition of sediments from six major Chilean rivers between 44 and 48°S to lithological proportions in their respective watersheds. The results suggest that mineralogy, major element geochemistry, and REE geochemistry can be used as qualitative tracers of sediment provenance. However, the compositional overlap between the sources and the relatively large variability within them prevent quantitative reconstructions. By comparison, 87Sr/86Sr and εNd allow to clearly differentiate between the sources, most likely due to significant age differences between the main lithologies, and to estimate the relative contribution of each source. End-member mixing results based on Sr and Nd isotopes show that the relative source contributions are in general agreement with the lithological proportions in the river watersheds. Differences between estimated contributions and lithological proportions in the watersheds are interpreted as the result of the high regional precipitation gradient and unequal glacier distribution, which lead to variable erosion rates across the study area. Our results demonstrate the suitability of 87Sr/86Sr and εNd for quantitative provenance reconstruction in northwestern Patagonia. They constitute a strong basis for the interpretation of sediment archives from the Patagonian fjords and from the eastern South Pacific, and they should be particularly useful to quantitatively investigate modern and past earth-surface processes. [ABSTRACT FROM AUTHOR]

One of the most important factors controlling fjord primary production in southernmost Patagonia is the variability in the thermohaline structure of the water column. In the present-day environment, thermal stratification is mostly related to freshwater input and in particular, the seasonal melting of glaciers. Here we assess whether this relation between fjord productivity and freshwater input holds true for the Holocene, using a sediment record from the central basin of the Strait of Magellan (core MD07-3132, 53°44.17′S; 70°19.03′W, 301 m). Our approach relies on a proxy-based reconstruction of fjord sea surface temperature (alkenone SST), paleosalinity, freshwater input, and paleoproductivity. The results indicate that, during the early Holocene, the accumulation rate (AR) of marine organic carbon was low (< 20 kg m − 2 kyr − 1 ), most likely due to high freshwater contribution resulting in low salinity and low SSTs. After 8.5 kyr BP and during the mid and late Holocene all the productivity proxies increase. The AR's of marine organic carbon (~ 30 kg m − 2 kyr − 1 ), biogenic CaCO 3 (~ 60 kg m − 2 kyr − 1 ) and biogenic opal (425 kg m − 2 kyr − 1 ) reached the highest values during the last millennium. This increase was probably driven by the marine transgression where marine macronutrient-rich waters entered into the central basin, while lowered precipitation and decreased meltwater input contributed to increase the basin's SSTs and salinity. The late Holocene rise in productivity was interrupted by a low salinity phase between 3.2 and 2.2 kyr BP, during which productivity returned to early Holocene conditions in response to increased input of glacial clays, as suggested by high values of K/Si ratio (~ 1.2). Our results indicate that meltwater contribution from glaciers plays a crucial role in controlling fjord productivity on seasonal to millennial timescales. [ABSTRACT FROM AUTHOR]