Application of very high resolution remote sensing data in studies of Antarctic penguins and greenhouse gases: A review

Abstract

Antarctic penguins are "bio-indicators" of environmental change in the Southern Ocean. The abundance of nutrients such as carbon (C) and nitrogen (N) in their excreta promotes the emission of greenhouse gases (GHGs), which makes penguin colonies an important source of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions. Since the 15th Chinese Antarctica research expedition, studies have been conducted via field observations and laboratory incubation experiments to determine the soil nutrient content in typical penguin colonies, and GHG production and emissions in these regions. These studies have indicated that the deposition of large amounts of penguin guano strongly influences the physical and chemical properties of soils in the Antarctic and creates favorable conditions for the production of CH4 and N2O in the soils and their subsequent emission. These studies have also shown that penguin activity significantly promotes CH4 and N2O emissions when compared with sites such as tundra ecosystems where penguins are absent. However, due to the lack of penguin population data, the total GHG emissions from penguin colonies at the regional and even circum-Antarctic scale have not been estimated. With the development of remote sensing technology, penguin colonies and their population changes have been identified by satellite images since the 1980s. In recent years, with the application of very high resolution (VHR) satellite images and aerial photographs, the identification of penguin populations at the regional scale has gradually been established. Based on previous research, this study comprehensively analyzed GHG emissions from penguins via field observations and laboratory incubation experiments, and introduced a method to estimate GHG emissions from penguin colonies via parameters such as guano deposition rates, CH4 and N2O emission factors, and penguin populations. This study also summarized the satellite data-based population estimations of five Antarctic penguin species: Adélie (Pygoscelis adéliae), Chinstrap (Pygoscelis Antarctica), Gentoo (Pygoscelis papua), emperor (Aptenodytes forsteri), and Macaroni (Eudyptes chrysolophus). Taking Adélie penguin as an example, Antarctic penguin colonies were investigated by considering the relationship between penguin guano areas and the number of breeding pairs, which determined a global total Adélie penguin population of 3.79 million breeding pairs. Some studies have shown that Adélie penguin populations have been declining rapidly on the islands of the northern Antarctic Peninsula, but have been increasing in the southern Antarctic Peninsula and the Ross Sea regions. The factors driving penguin populations were studied in terms of the physical and biological changes in the penguins' environment, including changes in sea-ice conditions (concentration, extent, and thickness), air temperature, wind speed, and sea surface temperature, all of which are likely to limit the abundance of Adélie penguins. Competition for food resources such as Antarctic krill (Euphausia superba) and continuous changes in the abundance of these resources also impacts on the number and density of Adélie penguins. Some of the factors that influence penguin population changes were discussed, including environmental factors (sea surface temperature, sea ice area, and Chlorophyll a concentration), human activities (the tourism and fishing industries), and other factors (food sources, volcanic eruptions, and iceberg calving). VHR remote sensing data-based estimations of penguin populations and GHG emissions will become a research focus in the field of polar ecology, and synthesizes the disciplines of remote sensing, biology, soil science, ecology, and geography.