Abstract: Mid-latitude atmospheric elemental mercury (Hg) emissions undergo extensive oxidation to reactive Hg (RM) compounds during Arctic polar sunrise, resulting in enhanced atmospheric deposition that impacts Arctic marine wildlife and humans. It has been difficult to estimate RM dry deposition, because RM concentrations, compounds, and their deposition velocities are ill-defined. Here, we investigate RM concentrations sampled with membrane-based methods and find these to exceed denuder-based RM detection by 5 times at the Zeppelin Observatory on Svalbard (March 26–July 24, 2019). Measured dry deposition of gaseous oxidized Hg was about half of the modeled RM deposition, demonstrating that particulate-bound Hg was an important component of dry deposition. Using thermal membrane desorption, RM chemistry was found to be dominated by Hg–Cl/Br (51%) and Hg–N (45%) compounds. Back-trajectory analysis indicated that Hg–Br/Cl compounds were predominantly advected from within the marine boundary layer (sea ice exposure), while Hg–N originated from the free troposphere. Weekly average RM compound-specific dry deposition velocities ranged from 0.12 to 0.49 cm s–1, with a net RM dry deposition of 1.9 μg m–2 (1.5–2.5 μg m–2; 95% confidence interval) that exceeds the mean annual Hg wet deposition flux in Svalbard. Overall, we find that springtime atmospheric RM deposition has been underestimated in the Arctic marine environment.

Abstract: Migratory marine species cross political borders and enter the high seas, where the lack of an effective global management framework for biodiversity leaves them vulnerable to threats. Here, we combine 10,108 tracks from 5775 individual birds at 87 sites with data on breeding population sizes to estimate the relative year-round importance of national jurisdictions and high seas areas for 39 species of albatrosses and large petrels. Populations from every country made extensive use of the high seas, indicating the stake each country has in the management of biodiversity in international waters. We quantified the links among national populations of these threatened seabirds and the regional fisheries management organizations (RFMOs) which regulate fishing in the high seas. This work makes explicit the relative responsibilities that each country and RFMO has for the management of shared biodiversity, providing invaluable information for the conservation and management of migratory species in the marine realm.

Abstract: Change in body size can be driven by social (density) and non-social (environmental and spatial variation) factors. In expanding metapopulations, spatial sorting by means of dispersal on the expansion front can further drive the evolution of body size. However, human intervention can dramatically affect these founder effects. Using long-term monitoring of the colonization of the remote Kerguelen islands by brown trout, a facultative anadromous salmonid, we analyse body size variation in 32 naturally founded and 10 human-introduced populations over 57 years. In naturally founded populations, we find that spatial sorting promotes slow positive changes in body size on the expansion front, then that body size decreases as populations get older and local density increases. This pattern is, however, completely different in human-introduced populations, where body size remains constant or even increases as populations get older. The present findings confirm that changes in body size can be affected by metapopulation expansion, but that human influence, even in very remote environments, can fully alter this process.

Abstract: Abstract. Atmospheric Information Embedded In Ice-core Nitrate Is Disturbed By Post-depositional Processing. Here We Used A Layered Snow Photochemical Column Model To Explicitly Investigate The Effects Of Post-depositional Processing On Snow Nitrate And Its Isotopes (δ15n And Δ17o) At Summit, Greenland, Where Post-depositional Processing Was Thought To Be Minimal Due To The High Snow Accumulation Rate. We Found Significant Redistribution Of Nitrate In The Upper Snowpack Through Photolysis, And Up To 21 % Of Nitrate Was Lost And/or Redistributed After Deposition. The Model Indicates Post-depositional Processing Can Reproduce Much Of The Observed δ15n Seasonality, While Seasonal Variations In δ15n Of Primary Nitrate Are Needed To Reconcile The Timing Of The Lowest Seasonal δ15n. In Contrast, Post-depositional Processing Can Only Induce Less Than 2.1 ‰ Seasonal Δ17o Change, Much Smaller Than The Observation (9 ‰) That Is Ultimately Determined By Seasonal Differences In Nitrate Formation Pathway. Despite Significant Redistribution Of Snow Nitrate In The Photic Zone And The Associated Effects On δ15n Seasonality, The Net Annual Effect Of Post-depositional Processing Is Relatively Small, Suggesting Preservation Of Atmospheric Signals At The Annual Scale Under The Present Summit Conditions. But At Longer Timescales When Large Changes In Snow Accumulation Rate Occur This Post-depositional Processing Could Become A Major Driver Of The δ15n Variability In Ice-core Nitrate.

Abstract: Three forms of killer whales (Orcinus orca) occur around the subantarctic islands of the southern Indian Ocean (42-53°S; 34-74°E). The form encountered in both inshore and offshore waters, described as generalist in its feeding preferences (seals, whales, penguins and fish as prey) and known to depredate toothfish from longliners has been opportunistically photo-identified around the Crozet archipelago since the 1960s. Together with photo-identification data collected in the Prince Edward/Marion EEZ, Kerguelen EEZ and international waters, this report provides up to date information on the abundance and distribution of the Crozet killer whales. In total, 124,313 photographs taken during 2,109 encounters since 1964 were analysed, allowing for 299 individuals to be identified. Most encounters with available data were from the Crozet EEZ (1,432 from longliners, 602 from Île de la Possession) and occurred after 2003 when photo-identification was implemented in the fishery observer program. Among the 188 individuals recorded in the Crozet EEZ since 2003, 22 (12%) were also photographed in the Kerguelen EEZ, 13 (7%) in the Prince Edward/Marion EEZ and 13 (7%) in adjacent international waters. The frequently encountered subset of the Crozet killer whale population was composed of 23 social units (maternal groups), 19 of which included individuals alive in 2020. These social units ranged in size from 1 to 11 individuals with a mean (± SD) of 4 ± 3 per unit. As of June 2020 when the latest photographs included in the study were taken, abundance of this subset was 89-94 individuals. However, detailed analysis of data collected between 2005 and 2020 shows that the number of confirmed deaths (n = 51) exceeds the number of recorded births (n = 46), resulting in a 5% decrease of the population size over this period. These deaths were distributed across the population with the majority occurring in the most common sex and age classes – adult females and juveniles. Factors contributing to mortalities are unclear, but may include lethal interactions with illegal fisheries. When paired with the fact that the Crozet killer whales already underwent a severe mortality episode in the 1990s, these findings raise strong concerns about the future of the population and stress the necessity of conservation actions while maintaining an intensive monitoring effort.