Black carbon footprint of human presence in Antarctica

Light-absorbing impurities like dust and soot reduce snow albedo, increasing solar energy absorption and accelerating melting. Black carbon (BC), primarily from combustion, can travel long distances. While present in remote regions like the Arctic, North America, and the Andes, Antarctic BC concentrations are typically much lower (below 1 ng/g). This low background is attributed to limited meridional transport, suggesting local sources dominate. Ice-free areas contribute to dust deposition, while research stations and other human activities are known to elevate BC levels locally. Human presence in Antarctica has significantly increased in recent decades, with 76 research stations accommodating approximately 5,500 people in summer and around 74,000 tourists visiting in the 2019-2020 season. This study investigates the large-scale BC footprint of research and tourism, focusing on the heavily impacted Antarctic Peninsula and associated archipelagos, examining BC concentrations in snow samples from 28 sites spanning a 2000km transect across the peninsula and Ellsworth Mountains.

Previous research has established the presence of BC in Antarctic snow and ice cores, though at concentrations significantly lower than in other regions. Studies have shown that background BC levels in Antarctica are generally below 1 ng/g, an order of magnitude less than in Arctic snow. While long-range transport from Southern Hemisphere sources and episodic events like wildfires in South America and Australia contribute, back-trajectory analyses suggest a minor role for long-range transport. Local sources, particularly ice-free areas and research stations, are considered more important. Prior research has documented elevated BC concentrations near stations like Palmer Station and McMurdo, highlighting the local impact of human activities. This study builds upon these findings by conducting a broader survey across a larger transect and quantifying the impact of both research and tourism.

This large-scale survey measured BC in 155 snow samples collected from 28 sites over four summer seasons (2016-2020). The transect spanned from King George Island (62°S) to Union Glacier Camp (79°S). The Meltwater Filtration (MF) Technique was employed, vacuum-filtering meltwater and analyzing filters spectrophotometrically to determine BC concentration (ng/g) and the Ångström exponent (characterizing light absorption properties of impurities). Sampling sites were located hundreds of meters to several kilometers from apparent BC sources. On the Antarctic Peninsula, sampling expeditions mirrored typical tourist routes. A 2.6-meter deep snowpit at Union Glacier enabled investigation of year-to-year changes in BC deposition. The presence of snow algae was noted and accounted for in data analysis. Data on human presence in the region were obtained from the Council of Managers of National Antarctic Programs (COMNAP), the Antarctic Treaty Secretariat (ATS), and the International Association of Antarctica Tour Operators (IAATO). Albedo reduction estimates utilized the parameterization by Dang et al. (2015), considering cloud fraction, snow grain size, and BC concentration to estimate radiative forcing and resulting snowmelt. Back-trajectory analysis was employed using the HYSPLIT model to assess the role of long-range transport. Statistical analyses included ANOVA and Tukey's HSD tests.

BC concentrations in snow samples were significantly higher than background levels near research stations and tourist landing sites. The median BC concentration was approximately 3 ng/g, comparable to Greenland but well below other remote regions. A latitudinal trend was observed, with higher concentrations in the north (3-7 ng/g) and decreasing southward (1-2 ng/g). The highest levels (around 8 ng/g) were found near Esperanza Base (Argentina). The Ångström exponent indicated contributions from both BC and non-BC components (dust), with a greater influence of dust on the Antarctic Peninsula. Even at Union Glacier, a deep-field site, BC concentrations (1-3 ng/g) were above background, likely due to local airplane activity. Analysis of the snowpit revealed decreasing BC concentrations from 2013-2014, coinciding with the opening of the Union Glacier Camp. Snow algae presence influenced light absorption at visible wavelengths, but not significantly at wavelengths above 700nm. BC concentrations near research stations and tourist sites exceeded background levels and were not primarily attributable to intercontinental transport or large wildfire events. Albedo reduction estimates ranged from 0.001 to 0.004, corresponding to a positive local forcing of 0.25-1.00 W/m². Estimated snowmelt due to this forcing ranged from 5 to 23 kg/m² (5-23 mm water equivalent) per summer. The BC footprint of research stations on King George Island was estimated to cause 0.4 ± 0.2 Mt of additional snowmelt annually, and that of tourism on the Antarctic Peninsula and associated archipelagos to 4.4 ± 2.3 Mt. This translates to about 0.6 ± 0.3 kt of snowmelt per bed at research stations, and 83 ± 43 tons of snowmelt per tourist. Back-trajectory analysis indicated that most of the BC measured originated from local sources.

The study demonstrates significant BC deposition from human activities (research and tourism) in Antarctica's most visited region. While concentrations are lower than other remote regions, they are considerably above background levels. The associated radiative forcing significantly impacts snowmelt, accelerating snowpack shrinkage. The BC footprint varies geographically but is substantial: dozens to hundreds of tons of additional snowmelt per tourist and considerably more for researchers. The increasing construction of research facilities and the growth in tourism necessitate mitigation strategies. While some advancements have been made with cleaner fuel and alternative power sources, more is needed to limit future impacts.

This study quantifies the substantial impact of BC emissions from research and tourism on Antarctic snowmelt. Elevated BC concentrations, particularly near human infrastructure, accelerate melting. Mitigation strategies including sustainable tourism practices and the adoption of renewable energy sources in research stations are urgently needed. Future research could focus on refining BC source apportionment techniques, improving snowmelt modeling, and investigating the long-term ecological and climatological consequences of BC deposition in Antarctica.

Spatial and temporal sampling limitations might affect the generalizability of snowmelt estimates. The study focuses on the heavily impacted Antarctic Peninsula region, so findings might not be fully representative of the entire continent. Uncertainty in snow grain size and cloud fraction affects albedo reduction estimates. The analysis of snow algae's influence on light absorption is based on a limited number of samples.