Description: The Central and South Atlantic represents a vast ocean area and is home to a diverse range of ecosystems and species. Nevertheless, and similar to the rest of the global south, the area is comparatively understudied yet exposed to increasing levels of multisectoral pressures. To counteract this, the level of scientific exploration in the Central and South Atlantic has increased in recent years and will likely continue to do so within the context of the United Nations (UN) Decade of Ocean Science for Sustainable Development. Here, we compile the literature to investigate the distribution of previous scientific exploration of offshore (30 m+) ecosystems in the Central and South Atlantic, both within and beyond national jurisdiction, allowing us to synthesise overall patterns of biodiversity. Furthermore, through the lens of sustainable management, we have reviewed the existing anthropogenic activities and associated management measures relevant to the region. Through this exercise, we have identified key knowledge gaps and undersampled regions that represent priority areas for future research and commented on how these may be best incorporated into, or enhanced through, future management measures such as those in discussion at the UN Biodiversity Beyond National Jurisdiction negotiations. This review represents a comprehensive summary for scientists and managers alike looking to understand the key topographical, biological, and legislative features of the Central and South Atlantic.

Description: As marine-ice around Antarctica retracts, a vast ‘blue carbon’ sink, in the form of living biomass, is emerging. Properly protected and promoted Antarctic blue carbon will form the world’s largest natural negative feedback on climate change. However, fulfilling this promise may be challenging, given the uniqueness of the region and the legal systems that govern it. In this interdisciplinary study, we explain: the global significance of Antarctic blue carbon to international carbon mitigation efforts; the urgent need for international legal protections for areas where it is emerging; and the hurdles that need to be overcome to realize those goals. In order to progress conservation efforts past political blockages we recommend the development of an inter-instrument governance framework that quantifies the sequestration value of Antarctic blue carbon for attribution to states’ climate mitigation commitments under the 2015 Paris Agreement. Key policy insights Blue-carbon emergence around Antarctica’s coastlines will potentially store up to 160,000,000 tonnes of carbon annually. Blue-carbon will emerge in areas of rich biomass that will make it vulnerable to harvesting and other human activities; it is essential to incentivise conserving, rather than commercial exploitation of newly ice-free areas of the Southern Ocean. Antarctic blue carbon is a practical and prime candidate to build a cooperative, inter-instrument, non-market mitigation around; this should be considered at the ‘blue COP’ UN Climate change discussions in Spain. Allowing Antarctic fishing states to account for the carbon storage value of blue carbon zones through a non-market approach under the Paris Agreement could provide a vital incentive to their protection under the Antarctic Treaty System. The Scientific Committee on Antarctic Research would be the ideal body to facilitate the necessary connections between the relevant climate and Antarctic governance regimes.

Description: Carbon capture and storage by southern polar benthos is potentially the largest negative feedback on climate change. Most feedbacks on global climate change are positive; they exacerbate physical change. The few known strong negative feedbacks, those which reduce physical change, are polar, and include i) broadening existing sinks with sea-ice losses over polar continental shelves, ii) subarctic vegetation growth increases and iii) formation of new sinks where ice shelves collapse. To date, carbon sequestration gains have been recorded around the Antarctic coastal shallows where they are likely to be offset by fjordic losses associated with sedimentation, and open coast losses through increased iceberg scouring. These feedbacks are complicated by additional positive forcing associated with greater heat absorption from albedo change. In contrast there is no albedo change (negligible sea ice losses) over sub-Antarctic shelves, where rising sea temperatures are likely to increase carbon storage by animals. The continental shelves along polar continent margins and archipelagos are wide, deep and rich in life. Most species known from polar waters live on these shallower shelf regions and it has been observed that they play an increasingly important role in the carbon cycle. Carbon is transported through the system by being fixed in photosynthesis by algae, which are eaten by benthic invertebrates, and then buried when the animal dies. We aim to measure how much carbon is held per unit area of the seabed per year and how this varies in time and space. Teasing apart biological processes in these important geographic regions is vital to our understanding of global carbon capture. One of the biggest sources of error in this regard is understanding the extent to which these feedbacks are effects of climate forcing on sub-Antarctic and Arctic shelf benthos performance. This type of carbon sequestration, termed blue carbon (associated with natural processes), is likely to increase, so long as sea ice and ice shelf losses continue to be sustained. Our research project, titled Antarctic Seabed Carbon Capture Change (ASCCC) has participated in the Antarctic Circumnavigation Expedition (ACE) in 2016 and 2017 to address the question ‘How will regional warming influence how much carbon is captured and stored by life on the seabed around Antarctica and the sub-Antarctic?’, from which we plan to estimate increased benthic carbon stored across the southern polar region due to recent ice shelf losses, sea ice losses and temperature increases.

Description: Continental shelves around Antarctica are a globally important carbon sink, due to both oceanographic CO2 absorption and biological fixation and trophic cascading. Most carbon passing through the foodweb is pelagic and is recycled through microbial loops. However significant masses are accumulated and immobilized (within calcareous skeletons of benthos), accounting for sequestration potential of 106 tonnes per year. Burial potential is enhanced by being largely untrawled by human harvesting and too deep for iceberg scouring. Yet these are also true for subAntarctic island shelves where there are considerable phytoplankton blooms, little or no sea ice and warmer sea temperatures (enabling faster meal processing time by benthos) – yet their potential as a carbon sink has been largely ignored. We report on the Antarctic Seabed Carbon Capture Change (ASCCC) project which sampled most of the high southern latitude continental shelves during the 2016/17 Antarctic Circumnavigation Expedition (ACE). Video and photo- equipped trawls collected imagery and benthos samples allowing us to estimate changes in intra and inter-shelf variability in benthos density and biomass. Growth models constructed from age structure of sampled species with growth check lines (e.g. bryozoans, bivalves, brachiopods etc) enable annual carbon accumulation to be estimated. Preliminary data and analyses suggest that continental shelves of 40-55°S may be globally significant, both in terms of absolute carbon storage but also in trying to reduce error in climate models. See www.asccc.co.uk

Description: In the Southern Ocean, that is areas south of the Polar Front, long-term oceanographic cooling, geographic separation, development of isolating current and wind systems, tectonic drift and fluctuation of ice sheets amongst others have resulted in a highly endemic benthic fauna, which is generally adapted to the long-lasting, relatively stable environmental conditions. The Southern Ocean benthic ecosystem has been subject to minimal direct anthropogenic impact (compared to elsewhere) and thus presents unique opportunities to study biodiversity and its responses to environmental change. Since the beginning of the century, research under the Census of Marine Life and International Polar Year initiatives, as well as Scientific Committee of Antarctic Research biology programmes, have considerably advanced our understanding of the Southern Ocean benthos. In this paper, we evaluate recent progress in Southern Ocean benthic research and identify priorities for future research. Intense efforts to sample and describe the benthic fauna, coupled with coordination of information in global databases, have greatly enhanced understanding of the biodiversity and biogeography of the region. Some habitats, such as chemosynthetic systems, have been sampled for the first time, while application of new technologies and methods are yielding new insights into ecosystem structure and function. These advances have also highlighted important research gaps, notably the likely consequences of climate change. In a time of potentially pivotal environmental change, one of the greatest challenges is to balance conservation with increasing demands on the Southern Ocean’s natural resources and services. In this context, the characterization of Southern Ocean biodiversity is an urgent priority requiring timely and accurate species identifications, application of standardized sampling and reporting procedures, as well as cooperation between disciplines and nations.

Description: Precautionary conservation and cooperative global governance are needed to protect Antarctic blue carbon: the world's largest increasing natural form of carbon storage with high sequestration potential. As patterns of ice loss around Antarctica become more uniform, there is an underlying increase in carbon capture-to-storage-to-sequestration on the seafloor. The amount of carbon captured per unit area is increasing and the area available to blue carbon is also increasing. Carbon sequestration could further increase under moderate (+1°C) ocean warming, contrary to decreasing global blue carbon stocks elsewhere. For example, in warmer waters, mangroves and seagrasses are in decline and benthic organisms are close to their physiological limits, so a 1°C increase in water temperature could push them above their thermal tolerance (e.g. bleaching of coral reefs). In contrast, on the basis of past change and current research, we expect that Antarctic blue carbon could increase by orders of magnitude. The Antarctic seafloor is biophysically unique and the site of carbon sequestration, the benthos, faces less anthropogenic disturbance than any other ocean continental shelf environment. This isolation imparts both vulnerability to change, and an avenue to conserve one of the world's last biodiversity refuges. In economic terms, the value of Antarctic blue carbon is estimated at between £0.65 and £1.76 billion (~2.27 billion USD) for sequestered carbon in the benthos around the continental shelf. To balance biodiversity protection against society's economic objectives, this paper builds on a proposal incentivising protection by building a ‘non-market framework’ via the 2015 Paris Agreement to the United Nations Framework Convention on Climate Change. This could be connected and coordinated through the Antarctic Treaty System to promote and motivate member states to value Antarctic blue carbon and maintain scientific integrity and conservation for the positive societal values ingrained in the Antarctic Treaty System.