comment The scientifc response to Antarctic ice-shelf loss Biological communities beneath Antarctic ice shelves remain a mystery, hampering assessment of ecosystem development after ice-shelf collapse. Here we highlight major gaps in understanding of the patterns and processes in these areas, and suggest efective ways to study the ecological impacts of ice-shelf loss under climate change. Jeroen Ingels, Richard B. Aronson and Craig R. Smith
he calving of A-68, a 5,800-km2, shelf edges and be entrained in currents for diverse shelf fauna15,16. Shifts in species trillion-tonne iceberg in July 2017 delivery to sub-ice-shelf organisms. Fossil distributions and altered phenologies may Tfrom the Larsen C Ice Shelf was one evidence reveals a sub-ice-shelf benthic lead to trophic mismatches17. Ice-shelf of more than ten significant ice-shelf-loss gradient with distance from open waters in retreat and the environmental changes that events in the past few decades resulting response to the intensity of food advection. follow such an event are thus expected to from accelerated warming around the Sessile suspension-feeders that need weaken synchronization between food Antarctic Peninsula. Ice shelves are thick, abundant particles falling through the water availability and food requirements across floating platforms of ice ranging from <100 column were found close to the edge of the various temporal and spatial scales, affecting to>1,500 m in thickness, and are formed ice shelf (where marine inflow is high) and predator–prey relationships and ultimately where glaciers or ice sheets flow on to the deposit-feeders and grazers that can feed ecosystem structure and function. ocean. Observations over the past 60 years on limited benthic food sources were found To fully comprehend the ecosystem shifts, indicate that the many ice shelves around further away from the shelf edge (where more frequent rapid-response research Antarctica are rapidly thinning, retreating food advection is lower)10. efforts are required. Such prompt responses and collapsing1–4. Rising atmospheric and The sparsity of sub-ice-shelf studies from are now feasible (conditions permitting) oceanic temperatures, which cause shelf boreholes stands in contrast to the number — as demonstrated by the mobilization thinning and melt, act with wind forcing of studies that have addressed physical and of researchers led by the British Antarctic and upwelling to increase ice-shelf retreat ecological questions about the aftermath Survey to the Larsen C area in January– and facilitate crevasse formation and of ice-shelf collapse. New areas of open February 2018, just five months after the propagation, ultimately leading to calving water provide increased access, permitting A-68 calving event18. However, because of events. These processes can take years, but studies with far greater spatial and temporal heavy sea ice the mission was redirected once thresholds are passed disintegration coverage. further north to the Prince Gustav Channel, can occur within weeks5. Antarctic ice Ice-shelf disintegration opens new which had been blocked by shelf ice until shelves are important because they create habitats in the form of polynyas and sea-ice 1995. South Korean scientists funded by a buttressing effect, preventing more rapid zones, which in general support rich and the Korean Polar Research Institute, in discharge and melting of the grounded abundant life, and productive food webs11 collaboration with investigators funded ice sheets and glaciers that would increase (Fig. 1). Ecosystem responses can be rapid, by the US National Science Foundation, global sea levels6. with high phytoplankton production and attempted to reach the Larsen C region in Ice shelves fringe 75% of the Antarctic biomass in newly opened areas less than April 2018, but were also thwarted by thick coastline and cover over 1.5 million km2 a year after collapse12. Ice-shelf collapse sea ice. The Alfred Wegener Institute and of seafloor, or about 30% of Antarctica’s has a significant impact on the biological the international consortium of the Weddell continental shelf. This enormous sub-ice- pump through changes in gas exchange, Sea Expedition 2019 are heading there next shelf area has been largely inaccessible to biogeochemical cycling and energy transfer, austral summer. the scientific community. The limitations potentially leading to increased carbon Many cross-disciplinary questions inherent to sampling from small (and sequestration in benthic sinks13. Such covering a broad range of spatial and expensive) boreholes through hundreds changes result in cascading effects on food- temporal scales remain to be answered. of metres of ice mean that only a few web dynamics and altered community Science–policy discussions at the studies have caught limited glimpses of life composition14. International Marine Ecosystem Assessment beneath ice shelves. These studies support At least five years elapsed after the Larsen for the Southern Ocean (MEASO) an advective-food hypothesis of energy A and Larsen B ice-shelf collapses before Conference in Hobart, Tasmania, in April supply from ice-free areas to the benthic scientists were able to study the resultant 2018 highlighted the need for investment communities living under the shelves. ecosystem developments; studies indicated in scientific infrastructure and research to Crustaceans, fish, microbial assemblages and extensive changes in marine ecosystems collect long-term observations with enough benthic suspension-feeders have been found within this short period. Different statistical power to draw robust conclusions. 12–450 km from open water7–9. Assemblages ecosystem components responded over Predictions of how the Southern Ocean under the ice shelves generally resemble different timescales, reflecting mobility and its ecosystems will respond to, and the communities found in the oligotrophic and colonization potential. In general, the interact with, Antarctica’s ice-shelf and ice- deep sea, which receive a sparse rain of food pelagic system seemed to respond rapidly to sheet dynamics (as well as how the changes particles (Fig. 1). This similarity implies that the ice-shelf collapse, whereas the benthos will affect Earth’s broader climate system) food sources for biotas under the ice shelves showed more gradual succession from an are needed. Future research programmes must arrive from distances away from the impoverished oligotrophic system to a more should work towards illuminating the
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Ice flow
Glaciers and ice sheet Ice shelf Phytoplankton bloom
Seabirds Krill Pinnipeds Fish Whales Basal melt High-salinity shelf water Melt plume Advective foodflow Grounding zone Mesopelagic Carbon fauna Advective POC flux food flow Sub-ice-shelf benthos Seeps Subglacial outflow
Continental shelf
Circumpolar Carbon Deep Water
Open-water benthos
Ice flow
Glaciers and ice sheet Ice-shelf collapse Calving front Phytoplankton bloom
Seabirds Krill Pinnipeds Fish Whales Basal melt Melt plume POC flux Advective foodflow Low-salinity meltwater Grounding zone Carbon Carbon Mesopelagic fauna
Sub-ice-shelf benthos Subglacial outflow Iceberg scouring
Carbon Continental shelf Circumpolar Deep Water
Open-water benthos
Fig. 1 | Ecosystem properties and processes shown with their responses to ice-shelf collapse. Top, Pre-collapse. Bottom, Post-collapse. Shifts in the spatial and temporal ranges of pelagic and benthic organisms, populations and communities post-collapse lead to changes in trophic dynamics and distribution ranges, altering ecosystem properties, processes and functions of sub-ice shelf areas. Thin black arrows between biota associated with krill indicate trophic interactions. The colour gradient of the particulate organic carbon (POC) flux indicates the change from fresh to more degraded/refractory material. Thicker arrows indicate higher fluxes. Figure adapted from ref. 5, AGU. linkages between Antarctica’s cryosphere dynamics, biogeochemical processes, the technologies that are needed for a and its ecosystems in a comprehensive, food web structure and population and comprehensive understanding of ice-shelf collaborative and interdisciplinary fashion, community dynamics19. collapse and ecosystem consequences. while acknowledging the importance Advances in marine technology will The Southern Ocean Observing System of long-term studies and assessments be key to achieving these aims. Reaching (SOOS), an international initiative that in concert with research conducted on and documenting pristine sub-ice-shelf facilitates the collection and delivery of shorter timescales. Such programmes ecosystems before dramatic change occurs observations across different platforms, could also provide a scientific network that will require an international scientific provides a framework for such international allows rapid, collaborative responses to infrastructure collaboratively utilized to collaborations. For example, the SOOS- abrupt events, including ice-shelf loss. The cover large spatial scales with high temporal endorsed Network for the Collection resulting studies should aim to document resolution. Oceanic and through-the- of Knowledge on Melt of Antarctic Ice ecosystem responses at all levels of biological ice moorings with equipment capable of Shelves (NECKLACE) project aims to organization — from the genome to shallow-to-deep sampling, weather- and measure ice-shelf melt across the entire continental scales — and the mechanistic climate-recording systems, and automated Antarctic through collaborative developed linkages among climate, cryosphere underwater vehicles are but a few of instruments, illustrating the potential role
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of SOOS in studying responses to ice-shelf in the Larsen C region was the first to Biology, Florida Institute of Technology, Melbourne, collapse. benefit from designation as a ‘special area FL, USA. 3Department of Oceanography, University In recent years, and especially for for scientific study in newly exposed marine of Hawaii at Manoa, Honolulu, HI, USA. the Larsen C collapse, scientists have areas following the collapse or retreat of *e-mail: [email protected] been making increased efforts to share ice shelves across the Antarctic Peninsula knowledge, identify important research region’ under CCAMLR’s conservation Published: xx xx xxxx priorities and knowledge gaps, and measures, providing a time window for https://doi.org/10.1038/s41558-018-0290-y outline strategic plans to advance our investigating ecosystem responses without understanding of the continent-wide confounding effects from fishing activities. References implications of climatic warming. 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Research on ice-shelf collapse and be achieved through internationally ecosystem responses can be used to coordinated, multidisciplinary research inform Antarctic conservation and that includes long-term measurements Acknowledgements management policies through SCAR and and the integrated analysis of physical, This Comment benefited from discussions at the ‘Antarctic the Commission for the Conservation biological and biogeochemical processes. Ecosystem Research Following Ice Shelf Collapse and of Antarctic Marine Living Resources Such projections will be of great value to Iceberg Calving Events’ workshop held in November 2017 at the Florida State University Coastal and Marine (CCAMLR), also embedded in the ATS. policymakers as rapid environmental Laboratory. The workshop and the creation of this product Science–policy interfacing is high on change continues, both in Antarctica were funded by the National Science Foundation’s Office of the agenda for the region, most recently and around the globe. ❐ Polar Programs through collaborative grants to all authors. illustrated by the aim of MEASO 2018 We gratefully acknowledge the contributions of the 38 to spear-head a quantitative ecosystem Jeroen Ingels1*, Richard B. Aronson2 and Antarctic scientists who participated in the workshop. Craig R. Smith3 This is contribution number 201 from the Institute for assessment that enables managers to reach Global Ecology at the Florida Institute of Technology, and 1 consensus in adapting their management Coastal and Marine Laboratory, Florida State contribution number 10419 from the School of Ocean and strategies. The newly exposed marine area University, St Teresa, FL, USA. 2Program in Marine Earth Sciences, University of Hawaii at Manoa.
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