Abstract: Antarctic Bottom Water (AABW) production supplies the deep limb of the global overturning circulation and ventilates the deep ocean. While the Weddell and Ross Seas are recognized as key sites for AABW production, additional sources have been discovered in coastal polynya regions around East Antarctica, most recently at Vincennes Bay. Vincennes Bay, despite encompassing two distinct polynya regions, is considered the weakest source, producing Dense Shelf Water (DSW) only just dense enough to contribute to the lighter density classes of AABW found offshore. Here we provide the first detailed oceanographic observations of the continental shelf in Vincennes Bay (104-111°E), using CTD data from instrumented elephant seals spanning from February to November of 2012. We find that Vincennes Bay has East Antarctica’s warmest recorded intrusions of modified Circumpolar Deep Water (mCDW) and that warm mCDW drives basal melt under Vanderford and Underwood ice shelves. Our study also provides the first direct observational evidence for the inflow of meltwater to this region, which increases stratification and hinders DSW formation, and thus AABW production. The Vincennes Bay glaciers, together with the Totten Glacier, drain part of the Aurora Basin, which holds up to 7 m of sea level rise equivalent. Our results highlight the vulnerability of the East Antarctic Ice Sheet to intrusions of mCDW.

Abstract: Assessing the effects of climate and interspecific relationships on communities is challenging because of the complex interplay between species population dynamics, their interactions, and the need to integrate information across several biological levels (individuals, populations, communities). Usually used to quantify single-species demography, integrated population models (IPMs) have recently been extended to communities. These models allow fitting multispecies matrix models to data from multiple sources while simultaneously accounting for uncertainty in each data source. We used multispecies IPMs accommodating climatic variables to quantify the relative contribution of climate vs. interspecific interactions on demographic parameters, such as survival and breeding success, in the dynamics of a predator–prey system. We considered a stage-structured predator–prey system combining 22 yr of capture–recapture data and population counts of two seabirds, the Brown Skua (Catharacta lönnbergi) and its main prey the Blue Petrel (Halobaena caerulea), both breeding on the Kerguelen Islands in the Southern Ocean. Our results showed that climate and predator–prey interactions drive the demography of skuas and petrels in different ways. The breeding success of skuas appeared to be largely driven by the number of petrels and to a lesser extent by intraspecific density dependence. In contrast, there was no evidence of predation effects on the demographic parameters of petrels, which were affected by oceanographic factors. We conclude that bottom-up mechanisms are the main drivers of this skua–petrel system.

Abstract: Benthic life in the Southern Ocean (SO) features unique life history traits and species assemblages, but the origin and evolution of many of these taxonomic groups is still unclear. Sea stars (Asteroidea) are a diversified and abundant component of benthic ecosystems in the SO, in which they can play key ecological roles. Former studies suggest that the diversity of the entire class is still poorly known and underestimated, hampering the assessment of the origin and evolution of the class in the SO. In the present study, we analyse spatial patterns of SO sea star diversity using an occurrence database of ~14,000 entries. The biogeographic analysis is coupled with the exploration of an extensive molecular phylogeny based on over 4,400 specimen sequences to inform, support and/or question the observed diversity patterns. We show that the current taxonomy of SO asteroids needs revision and that their diversity has generally been overlooked and misinterpreted. Molecular results highlight the recent diversification of most studied taxa, at genus and species levels, which supports an evolutionary scenario referring to successive invasion and exchange events between the SO and adjacent regions, and clade diversification during periods of rapid environmental changes driven by the succession of glacial cycles. Our work advocates for employing, and endorsing the use of extensive genetic barcode libraries for biodiversity studies.

Abstract: Bird migration is commonly defined as a seasonal movement between breeding and non-breeding grounds. It generally involves relatively straight and directed large-scale movements, with a latitudinal change, and specific daily activity patterns comprising less or no foraging and more traveling time. Our main objective was to describe how this general definition applies to seabirds. We investigated migration characteristics of 6 pelagic seabird species (little auk Alle alle, Atlantic puffin Fratercula arctica, common guillemot Uria aalge, Brünnich’s guillemot U. lomvia, black-legged kittiwake Rissa tridactyla and northern fulmars Fulmarus glacialis). We analysed an extensive geolocator positional and saltwater immersion dataset from 29 colonies in the North-East Atlantic and across several years (2008-2019). We used a novel method to identify active migration periods based on segmentation of time series of track characteristics (latitude, longitude, net-squared displacement). Additionally, we used the saltwater immersion data of geolocators to infer bird activity. We found that the 6 species had, on average, 3 to 4 migration periods and 2 to 3 distinct stationary areas during the non-breeding season. On average, seabirds spent the winter at lower latitudes than their breeding colonies and followed specific migration routes rather than non-directionally dispersing from their colonies. Differences in daily activity patterns were small between migratory and stationary periods, suggesting that all species continued to forage and rest while migrating, engaging in a ‘fly-and-forage’ migratory strategy. We thereby demonstrate the importance of habitats visited during seabird migrations as those that are not just flown over, but which may be important for re-fuelling.

Abstract: Breeding at the right time is essential for animals living in seasonal environments to ensure that energy requirements for reproduction, especially the nutritional needs for rearing offspring, coincide with peak food availability. Climate change is likely to cause modifications in the timing of maximum food availability, and organisms living in polar environments where the breeding period is heavily contracted may be particularly affected. Here we used a 26-year dataset to study the phenological response of a pagophilic species, the Snow Petrel (Pagodroma nivea), to climate change and its demographic impact. First, we investigated the trends and relationships between climate variables and hatching dates measured in three neighboring colonies. In a second step, we examined the impact of the hatching date and environmental covariates on the fledging probability. Our results showed that sea ice, a climate-related variable, showed a positive temporal trend. We found that hatching date was delayed when sea ice concentration was greater and local weather conditions were worse (i.e., increase in the number of windy days or the number of snow days). Hatching date had a negative effect on fledging probability, and fledging probability showed a bell-shaped temporal trend. We suggest that Snow Petrels can delay breeding phenology in response to environmental conditions. However, this plasticity may be limited as fledging success decreased with delayed hatching, potentially making the Snow Petrel vulnerable to a mismatch between resource availability and nutritional needs.• Timing of reproduction is essential for wild animals to ensure that reproductive requirements, including nutritional requirements for rearing offspring, coincide with peak food availability.• Climate change can affect the timing of food availability, and organisms living in polar environments, where the timing of reproduction is highly contracted, may be particularly affected. We analyzed whether a sea ice dependent species, the Snow Petrel (Pagodroma nivea), would breed earlier or later in response to climate change, as measured by changes in sea ice and weather conditions. Then, we looked at the impact that a shift in reproduction might have on breeding success.• Our results showed that hatching date was delayed when sea ice increased and local weather conditions worsened. Secondly, we showed that the shift in hatching date had a negative effect on breeding success.• Snow Petrels adjusted the onset of reproduction in response to environmental changes. However, this adjustment had limits since late reproduction likely leads to a mismatch between the availability of resources and nutritional needs, and thus to a decrease the breeding success.