The Great Black-backed Gull Larus marinus is a generalist species that inhabits temperate and arctic coasts of the north Atlantic Ocean. In recent years, there has been growing concern about population declines at local and regional scales; however, there has been no attempt to robustly assess Great Black-backed Gull population trends across its global range. We obtained the most recent population counts across the species’ range and analysed population trends at a global, continental, and national scale over the most recent three-generation period (1985–2021) following IUCN Red List criteria. We found that, globally, the species has declined by 43%–48% over this period (1.2–1.3% per annum, respectively), from an estimated 291,000 breeding pairs to 152,000–165,000 breeding pairs under two different scenarios. North American populations declined more steeply than European ones (68% and 28%, respectively). We recommend that Great Black-backed Gull should be uplisted from ‘Least Concern’ to ‘Vulnerable’ on the IUCN Red List of Threatened Species under criterion A2 (an estimated reduction in population size >30% over three generations).

The Antarctic Roadmap Challenges (ARC) project identified critical requirements to deliver high priority Antarctic research in the 21st century. The ARC project addressed the challenges of enabling technologies, facilitating access, providing logistics and infrastructure, and capitalizing on international co-operation. Technological requirements include: i) innovative automated in situ observing systems, sensors and interoperable platforms (including power demands), ii) realistic and holistic numerical models, iii) enhanced remote sensing and sensors, iv) expanded sample collection and retrieval technologies, and v) greater cyber-infrastructure to process ‘big data’ collection, transmission and analyses while promoting data accessibility. These technologies must be widely available, performance and reliability must be improved and technologies used elsewhere must be applied to the Antarctic. Considerable Antarctic research is field-based, making access to vital geographical targets essential. Future research will require continent- and ocean-wide environmentally responsible access to coastal and interior Antarctica and the Southern Ocean. Year-round access is indispensable. The cost of future Antarctic science is great but there are opportunities for all to participate commensurate with national resources, expertise and interests. The scope of future Antarctic research will necessitate enhanced and inventive interdisciplinary and international collaborations. The full promise of Antarctic science will only be realized if nations act together.

Antarctic and Southern Ocean science is vital to understanding natural variability, the processes that govern global change and the role of humans in the Earth and climate system. The potential for new knowledge to be gained from future Antarctic science is substantial. Therefore, the international Antarctic community came together to ‘scan the horizon’ to identify the highest priority scientific questions that researchers should aspire to answer in the next two decades and beyond. Wide consultation was a fundamental principle for the development of a collective, international view of the most important future directions in Antarctic science. From the many possibilities, the horizon scan identified 80 key scientific questions through structured debate, discussion, revision and voting. Questions were clustered into seven topics: i) Antarctic atmosphere and global connections, ii) Southern Ocean and sea ice in a warming world, iii) ice sheet and sea level, iv) the dynamic Earth, v) life on the precipice, vi) near-Earth space and beyond, and vii) human presence in Antarctica. Answering the questions identified by the horizon scan will require innovative experimental designs, novel applications of technology, invention of next-generation field and laboratory approaches, and expanded observing systems and networks. Unbiased, non-contaminating procedures will be required to retrieve the requisite air, biota, sediment, rock, ice and water samples. Sustained year-round access to Antarctica and the Southern Ocean will be essential to increase winter-time measurements. Improved models are needed that represent Antarctica and the Southern Ocean in the Earth System, and provide predictions at spatial and temporal resolutions useful for decision making. A co-ordinated portfolio of cross-disciplinary science, based on new models of international collaboration, will be essential as no scientist, programme or nation can realize these aspirations alone.

Francis & Hewett (1993) identified two 10 Mpc-scale regions of the high-redshift universe that were seemingly very overdense in neutral hydrogen. Subsequent observations showed that at least one of these gas-rich regions enveloped a cluster of galaxies at redshift 2 ·38. We present improved observations of the three background QSOs with sightlines passing within a few Mpc of this cluster of galaxies. All three QSOs show strong neutral hydrogen absorption at the cluster redshift, suggesting that this cluster (and perhaps all high-redshift clusters) may be surrounded by a ~5 Mpc-scale region containing ~10 12 Mʘ of neutral gas. We show that if most high-redshift clusters are surrounded by such regions, the gas must be in the form of many small (<1 kpc), dense (> 0·03 cm ˗3 ) clouds, each of mass <10 6 Mʘ . These clouds are themselves probably gathered into >20 kpc-sized clumps, which may be galaxy halos or protogalaxies. If this gas exists, it will be partially photoionised by the UV background. We predict the diffuse Lyα flux from this photoionisation, and place observational limits on its intensity.