Climate Change and Ecosystems: Impacts and Ecosystem-based Adaptation Case Study from the Antarctic and Southern Ocean Contributing authors: Tina Tin, David Ainley, James Barnes, Scott Hajost 1. Introduction This case study focuses on the Antarctic continent and the Southern Ocean. This region is governed under the Antarctic Treaty System (ATS). The Antarctic Treaty Area is defined as the area of land and sea south of 60 degrees latitude south. The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR), also part of the ATS, has a boundary that extends further north to the Antarctic Convergence which goes as far as 48 degrees south at certain latitudes. Terrestrial ecosystem (excerpt from Convey et al, in prep): Whatever definition of ‘biodiversity’ is adopted, Antarctic terrestrial biodiversity is low. At the level of species diversity, ‘richness’ is low, while at higher taxonomic levels many groups are missing. In terms of ecosystem functions or services, many are poorly or not represented (Convey, 2007b), and those that are present possess low levels of redundancy (i.e. other taxa performing similar functions). The terrestrial fauna is made up of invertebrates, predominantly microarthropods with only two ‘higher’ insect species present (Block, 1984), and plant communities are largely cryptogamic (mosses, liverworts, lichens) (Ochyra et al., 2009; Øvstedal & Smith, 2001), with only two higher plants present on the Antarctic continent. A greater, though still limited, diversity of higher plants and invertebrates is present on the sub-Antarctic islands (Convey, 2007a), although native terrestrial vertebrates are still absent on most islands (the exceptions being a single species of insectivorous passerine bird, two ducks and two sheathbills, each restricted to a single or at most two islands. Importantly, baseline survey data and up-to-date taxonomic treatments for most groups of biota remain very patchy, with existing published information heavily skewed to the areas of activity and scientific interest of certain national operators or individual specialists, both on the continent itself and the surrounding sub-Antarctic islands (e.g., Chown & Convey, 2007; Peat et al., 2007; Convey in press). The microbiota are the least known overall, and some recent studies suggest intriguingly they may be considerably more diverse than previously thought (e.g. Cowan et al., 2002; Pearce et al., 2009). Some of the simplest terrestrial ecosystems on the planet are found in this region (e.g., Convey & McInnes, 2005; Hogg et al., 2006). Marine ecosystem: In accord with a temperature-related gradient, biodiversity of the Southern Ocean is relatively low but biomass is huge. This overall pattern is related to the cold, nutrient-rich waters that circulate around the Antarctic continent as part of the largest ocean current on Earth, the Antarctic Circumpolar Current (ACC). Waters south of the Southern Boundary of the ACC are especially productive owing to extensive upwelling of nutrient-rich water, particularly along the continental margin, despite the fact that much of these waters are in darkness for a major portion of the year owing to the seasonal day- night cycle and the extensive sea ice that covers them during winter-spring. On the other hand, waters south of the SBACC are in continual sunlight for several months per year. Waters south of the Antarctic Polar Front (APF, Antarctic Convergence), accordingly, are the destination for numerous whales and seabirds, which forage here during summer but calf in warm waters or breed on islands of the subAntarctic or temperate latitudes. Populations no where else in the World Ocean can compare with their numbers in the Southern Ocean. A unique assemblage, as well, of seals, including the most abundant species in the world, frequent the pack ice region; the bird fauna associated with the pack ice is unique as well. The fish fauna is dominated by one unique family, the Nototheniidae, which diverged from the cosmopolitan fish fauna when Gonwanaland disintegrated and which radiated to fill dozens of ‘vacant’ niches. Finally, owing to the vary deep shelves of the Antarctic, due to the isostatic depression of the land from the mass of the ice sheet, the richest benthic fauna is spatial constrained to a limit of shallow water, in turn regularly perturbed by ice berg scour. The invertebrate fauna of mid-waters is dominated by several copepod and euphausiids species, including Antarctic krill, which assumes the role of the anchovy or sardine in temperate, upwelling-rich waters. In some southern areas, pteropods are especially abundant. Due to the cold waters, and the boundary formed by the APF, other than the many upper trophic-level species that migrate to forage during summer, the much of the Southern Ocean marine fauna is constrained to this region. 2. Vulnerability analysis In 2009, the Scientific Committee on Antarctic Research (SCAR) produced the review, Antarctic Climate Change and the Environment (ACCE), which summarizes current knowledge on the state of Antarctica’s climate and its relationship to the global climate system. To date, it is the most comprehensive document on the subject – more detailed and expansive than the Polar Regions chapter in the IPCC Assessment Reports – and can be used as a vulnerability analysis. 2.1 Overview The ACCE report concluded that (Turner et al. 2009): • FOR THE LAST 30 YEARS EFFECTS OF THE OZONE HOLE HAS WORKED IN OPPOSITION TO POTENTIAL EFFECTS OF ‘GLOBAL WARMING’, resulting in little change in surface temperature across the bulk of the continent. In addition, the cooling of the stratosphere (due to the ozone hole) and the warming of mid-latitudes has resulted in the acceleration of the circumpolar winds. That in turn has caused alteration of the placement of the polar jet. The main result of the latter is intense warming in the southwest Atlantic sector, where the jet dips much farther south than formerly, and especially warming of the western/windward side of the Antarctic Peninsula. This warming is several times higher than the average rate of global warming, making the Antarctic Peninsula one of the regions of the world that is warming most rapidly. The vast majority of the Antarctic, however, remains relatively unchanged. • THE SOUTHERN OCEAN IS WARMING – THE ECOSYSTEM WILL CHANGE. Antarctic Circumpolar Deep Water have warmed slightly due to warming in the mid-latitudes where these waters are formed; Antarctic Surface Water, except in the SW Atlantic region, has not warmed much due to its cooling during the Antarctic winter. The cold waters are problematic as atmospheric CO2 concentrations rise; cold waters dissolve more of the CO2, with progressive ocean acidification a result. Ecological key species (such as planktonic snails (pteropods) and benthic invertebrates) are expected to be disproportionately and negatively affected. Climate envelope models indicate that if waters continue to rise in temperature, the ranges of many Antarctic species will significantly decrease, as the continent itself represents a boundary to southern expansion of habitat. Increased seawater temperature may open the door to the immigration of a variety of "alien" species that are superior to local species in competition and replace the original Antarctic inhabitants; the arrival of crabs would severely impact the current benthic ecosystem. • NET SEA ICE EXTENT HAS CHANGED LITTLE AROUND THE ANTARCTIC OVER THE LAST 30 YEARS AS A RESULT OF THE OZONE HOLE AND MID-LATITUDE WARMING. While sea ice extent across the Arctic Ocean has decreased markedly over recent decades, around the Antarctic it has increased by perhaps 10% since 1980. The little change is the result of significant growth in extent in the Ross Sea region to counter the large decrease in the Bellingshausen Sea region (west of the Antarctic Peninsula). These changes are due to acceleration of circumpolar winds and alteration of the polar jet, with effects on local atmospheric circulation. Due to the loss of sea ice west of the Peninsula, changes in algal growth are seen along with a shift from large to smaller species. As a consequence, stocks of krill (the shrimp-like key species in the food web in that region) have declined significantly. The distribution of Adélie penguins has changed with many populations on the northern Antarctic Peninsula disappearing due to a reduced period of sea-ice, whilst in the Ross Sea and East Antarctica populations are generally stable or increasing. The consequences of historical harvesting reduce our ability to understand the impacts of climate change particularly on fish, seals and whales. It is highly possible that some whale species may not continue recovery from whaling if the krill population remains at a low level or decreases further. • THERE HAS BEEN RAPID EXPANSION OF PLANT COMMUNITIES ACROSS THE ANTARCTIC PENINSULA. Along with higher temperatures, the Antarctic Peninsula has experience a marked switch from snowfall to rain during the summer, and a retreat of ice fields. These linked changes have led to rapid expansion of plant communities and the colonisation of newly available land by plants and animals. c. In regions on land where there is greater availability of liquid water and higher temperatures, plant, animal and microbial communities will expand. Humans have inadvertently introduced alien organisms, including grasses, flies and bacteria. • ASSUMING A DOUBLING OF GREENHOUSE GAS CONCENTRATIONS OVER THE NEXT CENTURY, ANTARCTICA IS EXPECTED TO WARM BY AROUND 3º C. Sea ice extent around the continent is predicted to decrease by a third. 2.2 Specifics Marine Ecosystem: Between now and 2100 all components closely related to the sea ice will show significant changes in their ecological performance in response to changes in sea ice extent. A recent modeling study indicates that significant sea ice change will continue to show greater and greater effects well before 2100, i.e. when Earth’s atmosphere reaches 2C above industrial levels, projected to occur following current trends during 2025-2052 (Ainley et al., 2010).