Abstract:

Abstract. The EPICA Dome C (EDC) ice core provides the longest continuous climatic record covering the last 800 000 years (800 kyrs). Obtaining homogeneous high resolution measurements and accounting for diffusion provide a unique opportunity to study the evolution of decadal to millennial variability within the past glacial and interglacial periods. We present here a compilation of high resolution (11 cm) water isotopic records with 27 000 ?¹⁸O measurements and 7 920 ?D measurements (covering respectively 94 % and 27 % of the whole EDC record), including published and new measurements (2 900 for both ?¹⁸O and ?D) over the last 800 kyrs on the EDC ice core. We show that overlapping measurement series performed over multiple depth ranges over the past 20 years, using different analytical methods and in different laboratories, are consistent within analytical uncertainty, and therefore can be combined to provide a homogeneous data set. A frequency decomposition of the most complete ?¹⁸O record and a simple assessment of the possible influence of diffusion on the measured profile shows that the variability during glacial periods at multi-decadal to multi-centennial timescale is higher than variability of the interglacial periods. This analysis shows as well that during interglacial periods characterized by a temperature optimum at its beginning, the multi-centennial variability is the strongest over this temperature optimum.

Abstract: The sea-ice zone constitutes the breeding and foraging habitat of large populations of ice-based species, pointing at its far-reaching ecological importance. Given its sensitivity to global warming, there is an urgent need for determining how predators use their environment, to understand and predict their response to climate variability. New perspectives are offered by miniature animal-borne sensors: in 2019, 3 sonar tags were deployed on lactating female Weddell seals for 7 days in Terre Adélie to study 3D animal movement and fine-scale predator-prey interactions. Lactating females demonstrated central-place foraging strategy, with restricted foraging area (3-6 km) and mostly benthic dives (97% of dives, visualising the seafloor on echograms). Their foraging effort was constrained by the presence of their pup: females spent most of their time hauling out (77% of overall recordings). The time spent underwater was mostly dedicated to diving (>5m) (1.36 on 7days, 854 dives recorded), as opposed to shallower under ice activities (<5m) (0.3 days). A total of 331 prey capture attempts (PrCA) were recorded, using tri-axial acceleration data, of which 125 prey (4.7 ± 1.5 cm on average) were identified by the sonar on 78 dives (4.24 ± 3.99 PrCA/dive). All PCA occur on the seafloor, at shallower depth than usual Weddell seal records (88 ± 30 m). Lactation is therefore a period of physiological stress, with foraging limited by pup compared with other parts of the life cycle. Using functional principal component analysis and model-based clustering on high resolution dive data, we found that PrCAs occur mostly in 2 of the 5 dive shape clusters. Foraging dives are characterised by W or V shape and high sinuosity, at the scale of the dive (W shapes) or during the ascent phase (V shapes). During the approach phase, seals constantly scan the area by regularly moving their head left to right, suggesting opportunistic behaviour. Shallow phase behaviour was studied using video recordings (2h recorded per seal). Seals spent most of their time interacting with their pup (33%) and
hauling-out (42%). Most mother-pup interactions were on sea-ice (71%), as opposed to underwater (29%). The results suggest lactating females’ energy budget changes, with lactation being a period of physiological stress. This period of feeding pressure might put them at higher risk regarding adaptation to environmental variability.

Abstract: Cephalopods are an important component of Southern Ocean food webs, but aspects of their trophic ecology remain unresolved. Here, we used archived squid (order Teuthida) beaks, collected from stomach contents of predators at Macquarie and Kerguelen Islands, to investigate the trophic structure within an assemblage of pelagic squids (Alluroteuthis antarcticus, Filippovia knipovitchi, Gonatus antarcticus, Histioteuthis eltaninae, Martialia hyadesi and Brachioteuthis linkovskyi). We combined bulk nitrogen stable isotopes (?15Nbulk) with compound-specific isotope analysis of amino acids (CSIA-AA) to estimate the trophic position (TP) of species and to assess isotopic relationships with body size at the species, community, and ocean basin levels. We observed significantly higher mean ?15Nbulk values for species at the Kerguelen Islands compared to conspecifics at Macquarie Island. This result was explained by regional variability in ?15N values of phenylalanine (?15NPhe), suggesting that predator species were accessing different isotopic baselines at each region. This may highlight the different foraging strategies of both species. The overlap in species TP estimates from CSIA-AA (TPCSIA) between the 2 communities (Macquarie Island TPCSIA min: 2.3, max: 5.3; Kerguelen Islands TPCSIA min: 2.7, max: 5.3) indicated a similar trophic structure at both locations. We note unrealistically low TPCSIA for some species, which we attribute to uncertainty of trophic discrimination factors. TP estimates suggested that squid encompass 3 trophic levels from mid-trophic levels to higher predators. We did not find strong or consistent relationships between TP and body size at either the species- or community-level. One of the largest squid species, M. hyadesi, occupied the lowest TP in both communities. These new insights into the trophic structure of the Southern Ocean squid community have important implications for the future representation of pelagic squids in ecosystem models.