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Aspect influences critical zone (CZ) function, particularly in mountainous terrain where it is an ecosystem-defining geographical feature. Distinct insolation across aspects is linked to differences in water availability and flows, land cover and vegetation productivity, soil thickness and rooting depths, frost cracking, weathering rates, and solute concentrations. Relatively few studies have explored any changing influence of aspect on vegetation productivity, which governs soil water storage and runoff. We probe the hypothesis that the productivity benefit of growing on aspects with greater radiation inputs in mountain systems has been declining over the past few decades as warming has accelerated. We quantify how forest productivity varies with aspect from 1985 to 2021 across the world’s mountain ranges using a monthly-averaged, satellite-derived measure of greenness (NDVI). Globally, most montane forests exhibited increasing greenness over time. Mountainous forests ~15° to ~40° latitude N or S of the equator exhibited behavior consistent with our hypothesis by increasingly favoring shadier aspects, particularly during growing seasons when rainfall and soil moisture can be limiting to productivity. In contrast, closer to the poles where climates are coolest and aspect has an even greater influence on annual solar radiation, the benefit of a sun-facing aspect appears to be increasing across all seasons, consistent with poleward forest community migration hypotheses. We also demonstrate greater increases over time in montane forest greenness on east-facing slopes compared to west-facing slopes; north of ~40° latitude this pattern appears less robust. These observations reveal that it is increasingly disadvantageous for montane forests growing on sunnier, hotter aspects at relatively low latitudes during the hottest times of the year. Given known linkages between ecosystem productivity and CZ functions like water storage, provision, and flows, soil development, solute production, and regolith thickness, these analyses cast light on yet-underappreciated consequences of a rapidly warming climate on Earth’s montane forests and their capacity to shape CZ processes. 

While microplastics (MPs) are globally prevalent in marine environments, extending to the Arctic and sub-Arctic regions, the extent and distribution of MPs in terrestrial waters, drinking water sources, and recreational water in these areas remain unknown. This field study establishes a baseline for MPs in surface water sources, including lakes, rivers, and creeks, as well as in snow across three geo-locations (i.e., Far North, Interior, and Southcentral) in Alaska. Results (mean ± SE) show that the highest MP counts exist in snow (681 ± 45 L−1), followed by lakes (361 ± 76 L−1), creeks (377 ± 88 L−1), and rivers (359 ± 106 L−1). The smallest MPs (i.e., 90.6 ± 4 μm) also happened to have occurred in snow, followed by their larger sizes in lakes (203.9 ± 65 μm), creeks (382.8 ± 136.5 μm), and rivers (455.4 ± 212 μm). The physical morphology of MPs varies widely. MP fragments are predominant (i.e., nearly 62–74%) in these sites, while MP fibers (nearly 13–21%), pellets (nearly 13–18%), and films (<6%) also exist in appreciable quantities. Geolocation-wise, the Far North, where MPs were collected from off-road locations, shows the highest MP counts (695 ± 58 L−1), compared to Interior (473 ± 64 L−1) and Southcentral (447 ± 62 L−1) Alaska. Results also indicate that the occurrence of MPs in the source waters and snow decreases with increasing distance from the nearest coastlines and towns or communities. These baseline observations of MPs in terrestrial waters and precipitation across Alaska indicate MP pollution even in less-explored environments. This can be seen as a cause for concern with regard to MP exposure and risks in the region and beyond.