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The quantity and characteristics of sediment deposited in lakes are affected by climate to varying extents. As sediment is deposited, it provides a record of past climatic or environmental conditions. However, determining a direct relationship between specific climatic variables and measurable sediment properties, for instance between temperature and sediment optical reflectance, is complex. In this study, we investigate the suitability of sediment reflectance, recorded as sediment pixel intensity (PxI), as a paleoclimate proxy at a large ice-contact lake in southern Patagonia, Lago Argentino. We also evaluate whether sediment PxI can be used to investigate the present-day climatic drivers of sedimentation across Lago Argentino. First, we show that sediment PxIs relate to underlying sediment composition, and are significantly correlated with XRF-derived major element composition. Secondly, we find that PxIs correlate with both austral summer temperatures and wind speeds, but not with precipitation. PxI timeseries reach thep<0.1 correlation significance threshold for use as a paleo-wind proxy in as many as 6 cores and a paleo-temperature proxy in up to 4 cores. However, high spatial variability and the non-unique relationship between PxI and both temperature and wind speed challenges the necessary assumption of stationarity at Lago Argentino. While not suitable as a paleoclimatic proxy, correlations between PxI and instrumental climate data do chronicle current climatic controls on sediment deposition at Lago Argentino: high summer temperatures enhance settling of coarse, optically dark grains across the lake basin by promoting ice melt and lake stratification, while high wind speeds reduce the settling of fine, optically bright grains in the ice-proximal regions by transporting sediment-rich waters away from the glacier fronts. The assumptions required for quantitative paleoclimatic reconstruction must be carefully evaluated in complex lacustrine environments, but records unsuitable for use as proxies might nevertheless yield valuable information about the drivers of modern sedimentary transport and deposition.

 

Climatic variability across a large fraction of the Southern Hemisphere is controlled by the Southern Annular Mode and associated latitudinal shifts in the Southern Westerly Wind belt. In Patagonia, these changes control the large-scale temperature and precipitation trends – and resulting glacier surface mass balance. Our understanding of recent changes in this climatic oscillation is, however, limited by the number of paleo-environmental records in the mid to high-latitude Southern Hemisphere. Here, we first use a synthetic proxy record to demonstrate that periodicity may be preserved in a wider range of records than can be used for quantitative paleoclimatic reconstructions. We then analyze a 5000-year-long sedimentation record derived from Lago Argentino, a 1500 km2 ice-contact lake in Southern Patagonia. We extract a mass accumulation rate and greyscale pixel intensity record from 28 cores across all of Lago Argentino's main depositional environments. We align the mass accumulation rate and pixel intensity records to a common time axis through multivariate dynamic-time-warping, and investigate their spectral properties using the multi-taper Lomb Scargle periodogram. We find statistically significant spectral peaks at 200 ± 20, 150 ± 16, and 85 ± 9 years in two thirds of mass accumulation rate and one third of the pixel intensity records. These periodicities reveal the centennial periodicity of the Southern Annular Mode, which is the key climatic driver of sedimentation at Lago Argentino. 

Annual resolution sediment layers, known as varves, can provide continuous and high-resolution chronologies of sedimentary sequences. In addition, varve counting is not burdened with the high laboratory costs of geochronological analyses. Despite a more than 100-year history of use, many existing varve counting techniques are time consuming and difficult to reproduce. We present countMYvarves, a varve counting toolbox which uses sliding-window autocorrelation to count the number of repeated patterns in core scans or outcrop photos. The toolbox is used to build an annually-resolved record of sedimentation rates, which are depth-integrated to provide ages. We validate the model with repeated manual counts of a high sedimentation rate lake with biogenic varves (Herd Lake, USA) and a low sedimentation rate glacial lake (Lago Argentino, Argentina). In both cases, countMYvarves is consistent with manual counts and provides additional sedimentation rate data. The toolbox performs multiple simultaneous varve counts, enabling uncertainty to be quantified and propagated into the resulting age-depth model. The toolbox also includes modules to automatically exclude non-varved portions of sediment and interpolate over missing or disrupted sediment. CountMYvarves is open source, runs through a graphical user interface, and is available online for download for use on Windows, macOS or Linux at https://doi.org/10.5281/zenodo.4031811 . 

We present two hypotheses regarding the evolution of Holocene climate in the Northern Rocky Mountains that stem from a previously unpublished environmental magnetic record from Jones Lake, Montana. First, we link two distinct intervals of fining magnetic grain size (documented by an increasing ratio of anhysteretic to isothermal remanent magnetization) to the authigenic production of magnetic minerals in Jones Lake bottom waters. We propose that authigenesis in Jones Lake is limited by rates of groundwater recharge and ultimately regional hydroclimate. Second, at ~8.3 ka, magnetic grain size increases sharply, accompanied by a drop in concentration of magnetic minerals, suggesting a rapid termination of magnetic mineral authigenesis that is coeval with widespread effects of the 8.2 ka event in the North Atlantic. This association suggests a hydroclimatic response to the 8.2 ka event in the Northern Rockies that to our knowledge is not well documented. These preliminary hypotheses present compelling new ideas that we hope will both highlight the sensitivity of magnetic properties to record climate variability and attract more work by future research into aridity, hydrochemical response, and climate dynamics in the Northern Rockies. 

Since 2002, the National Center for Earth-Surface dynamics has collaborated with the Fond du Lac Band of Lake Superior Chippewa, the Fond du Lac Tribal and Community College, the University of Minnesota, and other partner institutions to develop programs aimed at supporting Native American participation in science, technology, engineering, and mathematics (STEM) fields, and especially in the Earth and Environmental Sciences. These include the gidakiimanaaniwigamig math and science camps for students in kindergarten through 12th grade, the Research Experience for Undergraduates on Sustainable Land and Water Resources, which takes place on two native reservations, and support for new majors at tribal colleges. All of these programs have a common focus on collaboration with communities, place-based education, community-inspired research projects, a focus on traditional culture and language, and resource management on reservations. Strong partnerships between university, tribal college, and Native American reservation were a foundation for success, but took time and effort to develop. This paper explores steps towards effective partnerships that support student success in STEM via environmental education. 

Proglacial lakes, whose numbers have been growing around the world, may drive accelerated glacier retreat and provide valuable records of past glacier and climatic changes. Despite their importance, few studies have investigated the sedimentary properties and processes acting within large proglacial lakes. Lago Argentino (LArg) is a 1,500 km²ice‐contact lake on the eastern flank of the Southern Patagonian Icefield. Here, we describe the results from a detailed analysis of 47 sediment cores obtained throughout this lake basin, supplemented with remotely sensed data. We show that: (a) LArg exhibits a seasonal variation in sediment properties (varves); (b) varve formation results from three distinct processes, driven by seasonal changes in glacial sediment input, seasonal changes in fluvial sediment input, and seasonal variations in lake mixing; and (c) distance from glacier calving fronts provides the first‐order control on sediment grain size and accumulation rate. Our findings highlight the exceptional preservation of annual laminations within proglacial lakes, their potential for reconstructing past glacier changes, and their relevance for forecasting future glacier–lake interactions.